REVIEW article

Front. Mol. Biosci., 26 April 2022

Sec. Molecular Recognition

Volume 9 - 2022 | https://doi.org/10.3389/fmolb.2022.864039

Peroxisome Proliferator–Activated Receptor-α: A Pivotal Regulator of the Gastrointestinal Tract

  • 1. Department of Oral Medicine, School of Basic Medical Sciences, Capital Medical University, Beijing, China

  • 2. Eight Program of Clinical Medicine, Peking University Health Science Center, Beijing, China

  • 3. Department of Physiology and Pathophysiology, School of Basic Medical Sciences, Capital Medical University, Beijing, China

  • 4. Clinical Medicine of “5+3” Program, School of Basic Medical Sciences, Capital Medical University, Beijing, China

  • 5. Department of Biomedical Informatics, Faculty of Biomedical Engineering, Capital Medical University, Beijing, China

  • 6. Department of Dermatology, Tongren Hospital, Capital Medical University, Beijing, China

Abstract

Peroxisome proliferator–activated receptor (PPAR)-α is a ligand-activated transcription factor distributed in various tissues and cells. It regulates lipid metabolism and plays vital roles in the pathology of the cardiovascular system. However, its roles in the gastrointestinal tract (GIT) are relatively less known. In this review, after summarizing the expression profile of PPAR-α in the GIT, we analyzed its functions in the GIT, including physiological control of the lipid metabolism and pathologic mediation in the progress of inflammation. The mechanism of this regulation could be achieved via interactions with gut microbes and further impact the maintenance of body circadian rhythms and the secretion of nitric oxide. These are also targets of PPAR-α and are well-described in this review. In addition, we also highlighted the potential use of PPAR-α in treating GIT diseases and the inadequacy of clinical trials in this field.

Highlights

In this review, after briefly introducing the characteristics of the PPAR family in the liver and cardiovascular system, we highlighted the specialties of PPAR-α and summarized its role in the gastrointestinal tract. It is responsible for the regulation of nutrient uptake and mediation of the inflammatory process. Moreover, studies also reported its participation in the maintenance of gastrointestinal circadian rhythms or circadian clock and satiety. These may provide novel and therapeutic targets for the treatment of gastrointestinal and systemic diseases.

Introduction

Since the discovery and cloning by Issemann et al. in 1990, peroxisome proliferator–activated receptors (PPARs) have received increasing attention for their multiple functions (Issemann and Green, 1990). Three subtype proteins found within the family are known as PPAR-α, PPAR-γ, and PPAR-β/δ, regulating the lipid metabolism and inflammation state (Dreyer et al., 1992; Bordet et al., 2006). They share common functions in metabolism and inflammatory regulation but are distinct from one another in both the distribution patterns and target molecules (Braissant et al., 1995). The common structure of the ligand-binding domain (LBD) in the shape of the letter Y laid the basis for the similarity and differences among this protein family (Mandard et al., 2004). The first arm containing hydrophilic amino acid residues is responsible for ligand binding and exists in all three subtypes, while the remaining two parts consisting of far fewer amino acid hydrophilic residues account for the specialties among them. PPAR-α is a transcription factor belonging to the nuclear receptor superfamily and could be activated by fibrates, eicosanoids, and fatty acids (Forman et al., 1997). However, contrary to steroid hormone receptors acting as homodimers, transcriptional regulation by PPARs requires heterodimerization with the retinoid X receptor (RXR; NR2B) in the same receptor superfamily (Mandard et al., 2004).

PPARs are ligand-activated transcription factors originally known to be activated by hepatocarcinogens and lead to peroxisome proliferation (Desvergne and Wahli, 1999). They are detected in a wide range of tissues, including endothelial and muscular cells and macrophages (Mφs) and monocytes. This endows them with a wide range of roles, including immune functions all over the body and regulations of a specific organ (Mandard et al., 2004). The well-recognized roles in alleviating heart dysfunction and hypertension in the cardiovascular system have been well-characterized (Goikoetxea et al., 2004; Usuda and Kanda, 2014), and their abilities to regulate fatty acid transportation and oxidation in the liver have been well-illustrated, further unveiling its association with various kinds of liver injuries (Botta et al., 2018; Kong et al., 2021). These could lead to some systematic diseases including diabetes and result in pathological dysfunctions in multiple organs (R. Moschen et al., 2012). In the meantime, studies have verified their roles in peripheral and neural inflammation (Piomelli, 2013). However, although much effort has been put into investigating its roles in the cardiovascular system, investigations on its roles in the gastrointestinal tract were relatively less. Recent analysis has certificated the distribution and activation of PPAR-α in the GIT with a higher level in the more differentiated cells near the lumen compared to those residing in the crypts (Mansén et al., 1996). Furthermore, studies also confirm the expression of PPAR-α in enterocytes along the small intestine with the highest levels in the duodenum and the jejunum. A higher level of PPAR-α is also found in villus tips than in crypts (Bünger et al., 2007). This expression pattern is similar to that of several other genes involved in dietary fat absorption, including microsomal triglyceride transfer protein (Mttp), diacylglycerol acyltransferase 1 (Dgat1), fatty acid translocase (Cd36), and fatty acid transport protein 4 (Fatp4), and lay the foundation for their wide interactions (Suzuki et al., 2009).

In this review, the roles of PPAR-α in the development of inflammation and regulation of metabolism are depicted and show its broad regulatory effects in the GIT and the whole body. Meanwhile, as agonists and antagonists are commonly used as drugs for the cardiovascular system (CVS), we evaluated the possibilities of their use in treating GIT diseases.

A Pivotal Regulator of Metabolism

As mentioned earlier, PPAR-α is involved in regulating the expression of various genes in lipid metabolism. However, despite the well-depicted regulation of genes associated with lipid metabolism in the liver, the regulation of genes by PPAR-α in the intestine is relatively less described (Steineger et al., 1994). In fact, in addition to the similarity in expression modes, Affymetrix arrays and quantitative RT-PCR analysis have demonstrated a PPAR-α–dependent upregulation of eight genes concerning transporters and phase I/II metabolism during fasting (the details of these genes are shown in Table 1) (van den Bosch et al., 2007). Several other studies also corroborated the increase of PPAR-α in mice and the downregulation of genes related to lipid metabolism (Escher et al., 2001; Shimakura et al., 2006).

TABLE 1

AbbreviationFull nameLocalizationReference
Cypt4a10Cytochrome P450, family 4, subfamily a, polypeptide 10MicrosomeWu et al. (2020)
Abca1ATP-binding cassette, sub-family A (ABC1), member 1Nucleoplasm and vesiclesSasaki et al. (2019)
Smct1 (Slc5a8)Solute carrier family 5 (iodide transporter), member 8ApicalSivaprakasam et al. (2017)
Sert (Slc6a4)Solute carrier family 6 (neurotransmitter transporter, serotonin), member 4BasolateralMastinu et al. (2012)
Dtd (Slc26a2)Solute carrier family 26 (sulfate transporter), member 2ApicalHaila et al. (2001)
Slc25a36Solute carrier family 25, member 36MitochondriaLee et al. (2018)
Chst4Carbohydrate (chondroitin 6/keratan) sulfotransferase 4Intracellular membraneYu et al. (2018)
Mgst1Microsomal glutathione S-transferase 1Intracellular membraneCui et al. (2010)

Metabolic genes regulated by PPAR-α.

Intestinal fatty acid–binding proteins (IFABPs) are important for regulating the uptake and transportation of the long-chain fatty acids (LCFAs) and significant biomarkers of gastrointestinal diseases (Holehouse et al., 1998; Kokesova et al., 2019). Detected more in proximal than in distal small intestine (Poirier et al., 1996), the IFABP expression in the rat jejunum showed significant enhancement during the postnatal development, concomitant with the increased mRNA level of PPAR in situ. Electrophoretic mobility shift assays revealed the existence of the PPAR-α-9-cis-retinoic acid receptor (RXRα), a heterodimer whose binding activities could be enhanced by an additional PPAR-α agonist WY-14643 (Mochizuki et al., 2001). Although this is inconsistent with some previous findings that the levels of PPAR-α and IFABPs show contrary variations under some treatment (Poirier et al., 1997), the regulation of metabolism by PPAR-α via gene transcription might be undeniable as more investigations utilizing different types of the PPAR-α agonist witnessed a concomitant increase of the IFABP level with PPAR-α (Mallordy et al., 1995).

Meanwhile, studies comparing the expression mode of genes between obesity-resistant A/J and obesity-prone C57BL/6J mice show a prominent upregulation of genes regulating lipid metabolism. However, this increase is restricted in the small intestine with no significant change in other organs such as the liver and white adipose tissue. Experiments in mouse Caco-2/TC7 cells and in human jejunal biopsies show that PPAR-α activation using WY-14643 increases the expression of ATP-binding cassette transporter A1 (ABCA1) (Knight et al., 2003). However, when WY-1463 was replaced by fibrates, the levels of both ABCA1 and protein-1c gene (SREBP-1c) increased. This is concomitant with the increase in the expression of genes modifying cholesterol trafficking and the decreased capacity of cholesterol esterification. Meanwhile, other findings show that the usage of fenofibrate, a selective PPAR-α agonist, and elafibranor (GFT505), a selective PPAR-α/δ agonist, did not remain the same in different experiments (Colin et al., 2013). Similar experiments further verified that this modulation could also be applied to the expression of genes regulating lipid metabolism (Kondo et al., 2006). For example, intraperitoneal (IP) administration of pirinixic acid (Wy-14643), a selective and highly potent PPAR-α agonist, stimulates fatty acid oxidation (FAO) and ketogenesis in the intestine This is concomitant with a significant increase in the expression of cytochrome P450 1A1(CPT 1A1) in the jejunum and duodenum and of HMG-CoAS2 in the jejunum (Stavinoha et al., 2004; Sérée et al., 2004). However, in this experiment neither CPT 1A nor HMG-CoAS2 expression was increased in the liver, suggesting a pivotal role the intestine plays in this regulation (Karimian Azari et al., 2013). Other genes in this type of regulation include fatty acid translocase (FAT)/cluster of differentiation 36 (CD36), fatty acid transport protein (FATP), NPC1L1, Acox1, Fabp1 (Hutch et al., 2020), and mitochondrial aspartate aminotransferase (mAspAT) (refer to Table 2 for more detailed information) (Uchida et al., 2011; Roberts, 1989; Valasek et al., 2007). Contrarily, Pan et al. found a PPAR-α independent way of OEA to increase the secretion of triacylglycerols, ApoB, and MTP in differentiated Caco-2 cells and primary enterocytes (Pan et al., 2018). Consistently, Mariana et al. also found no pertinence between the component of nutrient transporters and the level of PPAR-α (Losacco et al., 2018). Also, in many experiments, the level alteration in the intestine differs from that in the liver and the range of targeted genes varied with different kinds of agonists, indicating a complex mechanism waiting for investigation (Motojima et al., 1998). The use of PPAR-α agonists, both natural and synthetic, is an effective and widely accepted method to examine its functions (as shown in Table 2) (Lefebvre et al., 2006). Further analysis of these molecules, including oleoylethanolamide (OEA), palmitoylethanolamine (PEA), and WY-14643, provides the foundation for the understanding of the broad variety of PPAR-α functions.

TABLE 2

AbbreviationFull nameFunctionsReference
FATPFatty acid transport proteinTransport fatty acidsOchiai et al. (2019)
FAT/CD36Fatty acid translocaseFatty acid translocaseHaidari et al. (2021)
NPC1L1NPC1-like intracellular cholesterol transporter 1Membrane transportationLong et al. (2021)
Acox1Acyl-CoA oxidase 1Rate-limiting enzyme of the peroxisomal beta-oxidation pathway acyl-CoA oxidase 1Vluggens et al. (2010)
Fabp1Fatty acid–binding protein 1Transport long-chain fatty acids through cell membranes and mediate intracellular transport as a chaperoneValizadeh et al. (2021)
mAspATMitochondrial aspartate aminotransferaseMitochondrial aspartate aminotransferaseOchiai et al. (2019)

Genes regulating fat metabolism by PPAR-α.

TABLE 3

ClassificationNameSourceUsageLimitationsReferences
Natural and multi-functional acidsOleoylethanolamideOleic acid-derivedDiabetesMechanisms not fully clearLaleh et al. (2019)
PalmitoylethanolamineNaturally occurring lipid that falls under the fatty acid amide groupNeuroinflammationMulti-functions and lack of clinical dataSkaper et al. (2015)
Mimetic acidWY-14643A versatile fatty acid mimeticCancer and inflammationNot so typical as a PPAR agonistPollinger and Merk (2017)
Novel PPARα-selective agonists9-hydroxy-10(E),12(E)-octadecadienoic acidKoji extractDecreases plasma triglyceride and glucose levels and body weight gainSelectivity unclearYoshizaki et al. (2014)
Novel PPARα/γ dual agonistsLDT477Treatment of metabolic and inflammatory diseasesIn vivo effects remain unknownMaltarollo et al. (2018)

Representative agonists of PPAR-α.

All these findings show novel roles of PPAR-α in the intestine compared to those in the liver and are worth more investigations for full elucidation (Refer to Figure 1 for visual understanding).

FIGURE 1

Oleoylethanolamide, a Widely Accepted Endogenous Peroxisome Proliferator–Activated Receptor-α Agonist Used in Investigations

Oleoylethanolamide (OEA) is a kind of endogenous PPAR-α agonist with high affinity and plays an important role in the treatment of obesity and atherosclerosis. It is a structural analog of the endocannabinoid anandamide, an endogenous free fatty acid known for its role in regulating lipid metabolism (Rodríguez de Fonseca et al., 2001). It could be derived from digestion products by intestinal microbes and could be secreted endogenously by enterocytes (Obici et al., 2002). Meanwhile, it is also synthesized by astrocytes and neurons and could serve as a significant neurotransmitter regulating satiety (Cani et al., 2004). Most of these functions are mediated by PPAR-α, making it a potential target toward diabetes and giving it increasing significance considering the relationship with cardiovascular and neuron dysfunctions mentioned earlier (Koethe et al., 2009). It is also reported to bear a higher affinity compared with the other two agonists (Lo Verme et al., 2005; Brown et al., 2017). Moreover, the use of OEA supplements has been approved by the FDA for the treatment of obesity and shows prospective effects (Brown et al., 2018a). This is contrary to some previous studies revealing the side effects of OEA, indicating the requirement for more detailed studies (Nielsen et al., 2004; Brown et al., 2018b). These regulations in general help with the maintenance of a proper level of PPAR-α in the intestine and the homeostasis under its regulation.

Apart from the roles in regulating metabolite-associated gene expressions, OEA is also found to lower body weight and relieve hyperlipidemia in obese rats via the regulation of NO synthesis (Fu et al., 2003). Further analysis showed that it could also regulate satiety through a paracrine PPAR-α–mediated mechanism involving the recruitment of afferent sensory fibers (DiPatrizio and Piomelli, 2015). OEA produced by small-intestinal enterocytes during dietary fat digestion activates PPAR-α to trigger an afferent signal that causes satiety (Igarashi et al., 2017). Using a rat model of Roux-en-Y gastric bypass (RYGB), Hankir et al. found that marked reductions in fat appetite are due to enhanced gut lipid sensing through PPAR-α, which is in turn transmitted to the central nervous system (CNS) by sensory vagal afferents, culminating in increased dorsal striatal D1R signaling (Hankir et al., 2017). However, using multiple dopamine D2/D3 receptor agonists and celiac superior mesenteric ganglionectomy (CGX) or subdiaphragmatic vagal deafferentation (SDA), Shahana et al. showed that IP OEA’s anorectic effect may be secondary to impaired locomotion rather than physiological satiety and that vagal afferents do not mediate exogenous OEA’s anorectic effects. They also suggested a role for spinal afferents in addition to an alternative, non-neuronal signaling route (Fedele et al., 2018). Taken together, these findings raised the possibilities for the treatment of eating disorders by OEA and other PPAR-α–related products (Bünger et al., 2007).

Important Regulators of Inflammation

Intestinal bowel diseases (IBD), including mainly Crohn’s disease and ulcerative colitis, are relapsing and chronic GIT disorders becoming increasingly prevalent all over the world (Windsor and Kaplan, 2019). Despite the poor understanding of its pathogenesis, tissue examinations of various patients show different levels of mucosa injuries concomitant with the courses of diseases (Ahmad et al., 2017). These findings suggest the dysregulation of epithelial cell functions resulting from stimulations both directly from the lumen contents and cytokines secreted by lymphocytes and Mφ. As is known that metabolites could serve as mediators of IBD, it is reasonable to understand the underlying indirect role PPAR family proteins plays in the process of IBD (Roediger and Nance, 1986). Meanwhile, transcriptomic and proteomic profiling of human colon biopsy specimens showed the downregulation of PPAR signaling pathways in IBD (Jin et al., 2019). Studies also found disruption of the protective roles of PPAR-α agonists in PPAR-α-KO mice, indicating the pivotal functions it may have in the course of GIT diseases (Capasso et al., 2014). Also, the level of PPAR-α is decreased in a resection model of short bowel syndrome and is consistent with its level alteration in high malignant human tissue mucosa (Wang et al., 2007). Using human HCA7 cells, Jackson et al. further convinced the activation of PPRE-tk-luc, a PPRE-driven reporter gene, by PPAR-α using the transfection method (Jackson et al., 2003). In the dextran sodium sulfate (DSS)–induced mouse ulcerative colitis model, Manoharan et al. found that PPAR-α regulates the expression of IL-22 and antimicrobial peptides RegIIIb, RegIIIg, and calprotectin (Manoharan et al., 2016). IL-22 is an important member of the IL-10 cytokine family and has bidirectional functions for both anti-inflammation and pro-inflammation (Wei et al., 2020). However, the detailed mechanism by which PPAR-α activated NKp46+ ILC3 cells, the major producers of IL-22 under homeostatic conditions in the gut, still remains to be elucidated. Studies also corroborated that PPAR-α played defensive roles in the progression of IBD and CAC mainly via the stimulation of antimicrobial peptides RegIIIb and RegIIIg (Zheng et al., 2008; Killig et al., 2014) In interleukin 10 knockout (IL-10−/−) colitis mice, treatment with fenofibrate repressed interferon-gamma and IL-17 expression in isolated T cells. Considering the activation of PPAR-α by fenofibrate, this protection could be attributed to PPAR-α and put into clinical uses (Lee et al., 2007). Increased levels of Th17 and Th1 cells in this model may also account for injuries in the GIT as the secretion of IL-17 by Th17 is a core step in the progression of GIT disorders (Yang et al., 2017). An increasing number of other pro-inflammatory factors including IL-1b, IL-6, and TNF-α could be possible reasons for this enhancement in Th17 and Th1 cells. Concomitant with this, DNBS-treated PPAR-α–knockout (PPAR-αKO) mice experienced severer colon injuries accompanied with upregulation of ICAM-1 (Cuzzocrea et al., 2004). The levels of TNF-α and interleukin-1β (IL-1β) were also increased, resulting in antibody-mediated membrane dysfunctions (Stack et al., 1997). The decreased level of ICAM-1 and other adhesion molecules including VCAM-1 and P-selectin reduces the infiltration of neutrophils and ROS formation and thus aggravates the intestinal inflammation (Cuzzocrea et al., 2001). Apart from the anti-inflammatory roles of PPAR-α on DNBS-induced colitis, the functions of PPAR-α could also be enhanced by glucocorticoids (GCs). Other studies also show a less degree of colitis in WT mice compared to that in PPAR-αKO mice with an inhibition of p65 phosphorylation, which is an important regulator of the NF-κB pathway (Riccardi et al., 2009). Similarly, in human enterocytes (Caco-2), Shinsuke et al. also found the involvement of NF-κB after OEA injection (Otagiri et al., 2020). Also, in the splanchnic artery occlusion (SAO) shock model, administration of PEA 5 min before reperfusion significantly reduced the inflammatory parameters, including IL-1β and TNF-α. These effects were at least partly dependent on PPAR-α as the decrease of inflammatory markers was less significant in PPAR-α−/− mice than that in WT ones (Di Paola et al., 2012). In conclusion, all these studies provide novel insights into the roles of PPAR-α in mediating GIT inflammation and provide a potential target for pharmaceutical synthesis.

As an analogy of OEA, palmitoylethanolamide, a well-recognized PPAR-α agonist, could also exert an antiproliferative effect and downregulate VEGF signaling in Caco-2 through selective and PPAR-α-dependent inhibition of the Akt/mTOR pathway (Sarnelli et al., 2016). Several studies have corroborated the effect of palmitoylethanolamide in attenuating the GIT injuries using different models of both humans and mice (Borrelli et al., 2015). Mustafa et al. demonstrated its roles in modulating intestinal permeability in a PPAR-α–dependent method using the antagonist GW6471 (Karwad et al., 2017). In the intestine, PEA treatment also improves all macroscopic signs of UC and decreases the expression of the pro-inflammatory biomarkers, including PGE2, IL-1β, and TNFα. Further analysis shows that this effect is mediated mainly by selective targeting of the S100B/TLR4 axis on ECG and downstream inhibition of NF-кB-dependent inflammation (Esposito et al., 2014). Using mice with chronic intestinal inflammation induced by croton oil, Raffaele et al. found significantly decreased levels of PEA in inflammatory mice which could probably contribute to the exaggerated transition (Capasso et al., 2001). However, Cluny et al. showed no difference in gut mobility between PPAR-αKO and WT mice, indicating a PPAR-α–independent pathway in remaining elucidation (Cluny et al., 2009).

Apart from the roles as a significant mediator in IBD, PPAR-α can also regulate the progress of GIT cancer. Studies have found gastric gavage of the PPAR-α ligand bezafibrate inhibited the DSS-induced colitis by and lowered trefoil factor-2 content in colonic mucosa (Tanaka et al., 2001). It also inhibits the formation of aberrant crypt foci (ACF), which is recognized as a precursor lesion in colorectal cancer (Shivapurkar et al., 1997). Further investigations show increased expressions of cyclooxygenase-2 (COX-2), an important mediator in the development of colonic carcinoma in the human colorectal epithelial cell line HT-29 (Prescott and White, 1996; Ma et al., 2018). This could be explained by previous findings that show COX-2–mediated regulation is one of the important downstream pathways induced by TFF2 and enhanced the COX-2 expression via PPAR ligands in some human colorectal epithelial cells (Ikawa et al., 2001; Meade et al., 1999).

Mediation Between Metabolism and Inflammation

Acknowledged as the “second brain” in the human body, gut microbiota play essential roles in the gastrointestinal tract that is regarded as the largest digestive as well as immune organ (Ridaura and Belkaid, 2015). Based on our aforementioned analysis, PPAR-α exerts a significant influence on the components of gastrointestinal microbes and the host physical health condition via the regulation of gene transcription (Rooks and Garrett, 2016; Ashrafian et al., 2019; Hasan et al., 2019). Lactobacillus species are significant protectors of the GIT, and the reduction of their number is an important characterization in many GIT diseases (Tan et al., 2020). This regulation is partly mediated via the PPAR-α as sub-chronic OEA administration to mice fed with a normal chow pellet diet changes the fecal microbiota profile and shifts the Firmicutes: Bacteroidetes ratio in favor of Bacteroidetes (in particular Bacteroides genus). It also decreases the number of Firmicutes (Lactobacillus) and reduces the intestinal cytokine expression by immune cells isolated from Peyer’s patches. (Di Paola et al., 2018; Cai et al., 2020; Kersten et al., 1999), Meanwhile, the introduction of probiotic Lactobacillus plantarum into simian immunodeficiency virus (SIV)–inflamed intestinal lumen resulted in a higher level of PPAR-α concomitant with a recovered expression of PPAR-α–targeted genes (Crakes et al., 2019). Studies also found that mice fed with high-fat chow and supplemented with the probiotic bacteria Lactobacillus paracasei ssp. paracasei F19 (F19) exhibit significantly less body fat. This is also accompanied by a higher level of angiopoietin-like 4 (ANGPTL4), a circulating lipoprotein lipase (LPL) inhibitor regulated by PPAR-α and shows the protective roles of it (Aronsson et al., 2010). These findings corroborated the roles of PPAR-α with Lactobacillus and provided novel prospects for future studies. Apart from the roles in modulating GIT functions, the effect of this interaction could also alter the physiological and pathological conditions of other organs via metabolites transporting in blood as experiments found that exposure to high-fat diets and food deprivation enhances PPAR-α-dependent signaling in the liver and intestine. Lactobacillus plantarum FRT10 could also alleviate the high-fat diet-induced obesity in mice via regulating the PPAR-α signal pathway (Duparc et al., 2017).

Apart from the roles in regulating metabolism and inflammation, respectively, interactions between PPAR-α and gut microbiota also help with the maintenance of the circadian rhythms. This could be confirmed by its disruption under microbiota depletion and result in activation of the c-Jun expression, leading to the dysregulation of a serious set of genes related to inflammation (Mukherji et al., 2013).

Nitric oxide (NO) is one of the major biomarkers of GIT inflammation mainly synthesized by the inducible nitric oxide synthase (iNOS) enzyme in serum and affected tissues. It can exacerbate GIT inflammation and is elevated in times of colitis (Kamalian et al., 2020). Meanwhile, it also has close interplays with microbial components and liver metabolism (Yaguchi and Yaguchi, 2019). Studies using leukotriene B4, a PPAR-α agonist, have found naturally occurring PPAR agonists can inhibit the iNOS enzyme pathway. They further proposed the possibility of this modulation by the stress protein heme oxygenase 1, although the exact mechanisms wait for more investigations (Colville-Nash et al., 1998). Concomitantly, Fu et al. provided evidence for this correlation in OEA which was also recognized as a potential regulation of satiety (Fu et al., 2003; Sihag and Jones, 2018) (Refer to Figure 2 for vivid understanding).

FIGURE 2

Circadian Rhythm Regulation in the Gastrointestinal Tract and its Interplays With Peroxisome Proliferator–Activated Receptor-α

Studies have found that circadian rhythms or circadian clock regulation is achieved via the expression of key genes and downstream pathways, as shown in Table 4. These genes take control of a broad range of physiological activities and share close interactions. One typical role of PPAR-α in this process lies in its activation of the clock gene via RORα and subsequent influence on the expression of E4BP4. However, as far as we are concerned, the current analysis focused on the roles of PPAR-α in the CVS, and more investigations focusing on its roles in GIT are recommended. Refer to Figure 3 for photographic illustration.

TABLE 4

AbbreviationFull nameFunctionsReferences
TLR1-5,9Toll-like receptor 1-5,9Sense pathogen-associated molecular patternsLim and Staudt (2013)
NOD2Nucleotide-binding oligomerization domain 2 (NOD2)Senses bacterial peptidoglycan (PGN)–conserved motifs in cytosolOkamura-Oho (2004)
RORERetinoic acid-related orphan receptor response elementsRegulating the expression of genes, including BMAL1 and CLOCKOkamura-Oho (2004)
c-Junc-JunBinds to the enhancer heptamer motif and increased steroidogenic gene expression upon cAMP signaling pathway stimulationZhang et al. (2019)
RevErbReverbTranscriptional repressor coordinating circadian rhythms or circadian clock rhythm and metabolic pathways in a heme-dependent mannerPrabhat et al. (2020)
RORαRetinoid-related orphan receptor alpha (RORalpha)Ligand-activated transcription factor involved in numerous biological processesLiu et al. (2007)
BmalBrain and muscle ARNT-like1Transcriptional activator which forms a core component of the circadian rhythms or circadian clockTognini et al. (2017)
ClockCircadian rhythms or circadian clock locomotor output cycles kaputTranscriptional activator which forms a core component of the circadian rhythms or circadian clockVoigt et al. (2016)
DBP1Dibutyl phthalateTranscriptional activator recognizes and binds to the sequence 5′-RTTAYGTAAY-3′Yu et al. (2019)
E4BP4E4 promoter-binding protein 4 (E4BP4)A transcriptional regulator that recognizes and binds to the sequence 5′-[GA]TTA[CT]GTAA[CT]-3′Agarwal et al. (2018)
Cyp11a1Cytochrome P450, family 11, subfamily A, polypeptide 1Encoding a critical enzyme for steroid biosynthesisShih et al. (2008)

Relative molecules involved in circadian rhythm regulation.

FIGURE 3

Pharmacological Perspective of Peroxisome Proliferator–Activated Receptor-α

Numerous investigations have been put into the analysis of PPAR-α due to its wide distribution and multiple functions in a variety of tissues and cells (Berger and Moller, 2002). Long-chain fatty acids and their derivatives proved to be the main sources of natural PPAR-α agonists, while synthetic ones also play important roles in these studies (Kliewer et al., 1997). Although some agonists of PPAR-α have been used for treating different diseases, many of them are still in the experimental stage (Feng et al., 2016). Most clinical trials focused on their usage in metabolic diseases, especially those symptoms in the liver, while others concerning the gastrointestinal tract are relatively less (Petrosino et al., 2010). Also, considering the difference of distribution in humans and mice, more clinical trials are required in order to fully elucidate the mechanisms. Moreover, many exogenous nutrients and endogenous metabolites serve as ligands for PPAR-α while their functions and related dosage vary a lot. This increases the difficulty in developing clinical uses and requires further elucidation (O'Sullivan, 2016). However, we considered it worth the time and effort due to its potential usage in treating GIT diseases and decreasing the number of IBD patients all over the world.

Conclusion

PPAR-α has been recognized as an important regulator in the cardiovascular system and lipid metabolism. In addition, it also exerts substantial impacts on the GIT functions both physiologically and pathologically. Other than the well-known abilities to regulate lipid metabolism, PPAR-α mediates the process of inflammation via the regulation of cytokine secretion and activation of inflammatory pathways. Furthermore, the target genes of PPAR-α include those controlling gut circadian rhythms and the synthesis of NO, which could form an integrated regulatory network of GI functions. Meanwhile, many endogenous and exogenous food metabolites serve as agonists of PPAR-α, and their use in the treatment of GIT diseases is expected to shed light for a bright future.

Statements

Author contributions

Y-XG and J-DX wrote the manuscript; B-YW, Y-XG, and HG designed the illustrations; C-WH, YW, and LG helped analyze the literature; J-DX revised the manuscript. All authors read and approved the final manuscript.

Funding

The research in the authors’ laboratory was supported by the National Natural Science Foundation of China (Grant Nos. 82174056 and 81673671).

Acknowledgments

We appreciate Dr. Tao Xin from the Department of Applied Linguistics, School of Medical Humanities, Capital Medical University, for excellent language expression assistance.

Conflict of interest

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Publisher’s note

All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.

Glossary

  • ABCA1

    ATP-binding cassette transporter A1

    ATP-binding cassette, sub-family A, member 1

  • ABCA1

    ATP-binding cassette transporter A1

    ATP-binding cassette, sub-family A, member 1

  • ACF

    aberrant crypt foci

  • ANGPTL4, a circulating lipoprotein lipase

    angiopoietin-like 4

  • Cd36

    fatty acid translocase

  • CD36

    cluster of differentiation 36

  • CGX

    celiac superior mesenteric ganglionectomy

  • Chst4

    carbohydrate (chondroitin 6/keratan) sulfotransferase 4

  • CNS

    central nervous system

  • COX-2

    cyclooxygenase-2

  • CPT 1A1

    cytochrome P450 1A1

  • CVS

    cardiovascular system

  • Cypt4a10

    cytochrome P450, family 4, subfamily a, polypeptide 10

  • Dgat1

    diacylglycerol acyltransferase 1

  • DSS

    dextran sodium sulfate

  • Dtd Slc26a2

    solute carrier family 26 (sulfate transporter), member 2

  • ERS

    endoplasmic reticulum stress

  • F19

    paracasei ssp paracasei F19

  • FAT

    fatty acid translocase

  • FATP

    fatty acid transport protein

  • Fatp4

    fatty acid transport protein 4

  • GCs

    glucocorticoids

  • GFT505

    elafibranor

  • GIT

    gastrointestinal tract

  • IBD

    intestinal bowel diseases

  • IFABPs

    intestinal fatty acid–binding proteins

  • IL-1b

    interleukin-1b

  • iNOS

    inducible nitric oxide synthase

  • IP

    intraperitoneal

  • LBD

    ligand-binding domain

  • LCFAs

    long-chain fatty acids

  • mAspAT

    mitochondrial aspartate aminotransferase

  • Mgst1

    microsomal glutathione S-transferase 1

  • Mttp

    microsomal triglyceride transfer protein

  • macrophages

  • NO

    nitric oxide

  • OEA

    oleoylethanolamide

  • PEA

    palmitoylethanolamine

  • PPAR

    peroxisome proliferator–activated receptor

  • PPAR-αKO

    PPAR-α-knockout mice

  • RXR; NR2B

    retinoid X receptor

  • RYGB

    Roux-en-Y gastric bypass

  • SAO

    splanchnic artery occlusion

  • SDA

    subdiaphragmatic vagal deafferentation

  • Sert Slc6a4

    solute carrier family 6 (neurotransmitter transporter, serotonin), member 4

  • SIV

    simian immunodeficiency virus

  • Slc25a36

    solute carrier family 25, member 36

  • Smct1 Slc5a8

    solute carrier family 5 (iodide transporter), member 8

  • TNF-a

    tumor necrosis factor-alpha

  • Wy-14643

    pirinixic acid

References

  • 1

    AgarwalN.MishraI.RaniS.KumarV. (2018). Temporal Expression of Clock Genes in central and Peripheral Tissues of Spotted Munia under Varying Light Conditions: Evidence for Circadian Regulation of Daily Physiology in a Non-photoperiodic Circannual Songbird Species. Chronobiology Int.35, 617632. 10.1080/07420528.2017.1422742

  • 2

    AhmadR.SorrellM. F.BatraS. K.DhawanP.SinghA. B. (2017). Gut Permeability and Mucosal Inflammation: Bad, Good or Context Dependent. Mucosal Immunol.10, 307317. 10.1038/mi.2016.128

  • 3

    AronssonL.HuangY.PariniP.Korach-AndréM.HåkanssonJ.GustafssonJ. Å.et al (2010). Decreased Fat Storage by Lactobacillus Paracasei Is Associated with Increased Levels of Angiopoietin-like 4 Protein (ANGPTL4). PLoS One5. 10.1371/journal.pone.0013087

  • 4

    AshrafianF.ShahriaryA.BehrouziA.MoradiH. R.Keshavarz Azizi RaftarS.LariA.et al (2019). Akkermansia Muciniphila-Derived Extracellular Vesicles as a Mucosal Delivery Vector for Amelioration of Obesity in Mice. Front. Microbiol.10, 2155. 10.3389/fmicb.2019.02155

  • 5

    BergerJ.MollerD. E. (2002). The Mechanisms of Action of PPARs. Annu. Rev. Med.53, 409444. 10.1146/annurev.med.53.082901.104018

  • 6

    BordetR.OukT.PetraultO.GeléP.GautierS.LapraisM.et al (2006). PPAR: a New Pharmacological Target for Neuroprotection in Stroke and Neurodegenerative Diseases. Biochem. Soc. Trans.34, 13411346. 10.1042/bst0341341

  • 7

    BorrelliF.RomanoB.PetrosinoS.PaganoE.CapassoR.CoppolaD.et al (2015). Palmitoylethanolamide, a Naturally Occurring Lipid, Is an Orally Effective Intestinal Anti-inflammatory Agent. Br. J. Pharmacol.172, 142158. 10.1111/bph.12907

  • 8

    BottaM.AudanoM.SahebkarA.SirtoriC. R.MitroN.RuscicaM. (2018). PPAR Agonists and Metabolic Syndrome: An Established Role?Int. J. Mol. Sci.19. 10.3390/ijms19041197

  • 9

    BraissantO.FoufelleF.ScottoC.DauçaM.WahliW. (1995). Differential Expression of Peroxisome ProliferatorActivated Receptors (PPARs): Tissue Distribution of PPAR-A, B, and -y in the Adult Rat. Endocrinology137, 354366. 10.1210/endo.137.1.8536636

  • 10

    BrownJ. D.Karimian AzariE.AyalaJ. E. (2017). Oleoylethanolamide: A Fat Ally in the Fight against Obesity. Physiol. Behav.176, 5058. 10.1016/j.physbeh.2017.02.034

  • 11

    BrownJ. D.McAnallyD.AyalaJ. E.BurmeisterM. A.MorfaC.SmithL.et al (2018). Oleoylethanolamide Modulates Glucagon-like Peptide-1 Receptor Agonist Signaling and Enhances Exendin-4-Mediated Weight Loss in Obese Mice. Am. J. Physiology-Regulatory, Integr. Comp. Physiol.315, R595R608. 10.1152/ajpregu.00459.2017

  • 12

    BrownM. A.MageeL. A.KennyL. C.KarumanchiS. A.McCarthyF. P.SaitoS.et al (2018). Hypertensive Disorders of Pregnancy. Hypertension72, 2443. 10.1161/hypertensionaha.117.10803

  • 13

    BüngerM.van den BoschH. M.van der MeijdeJ.KerstenS.HooiveldG. J. E. J.MüllerM. (2007). Genome-wide Analysis of PPARα Activation in Murine Small Intestine. Physiol. Genomics30, 192204. 10.1152/physiolgenomics.00198.2006

  • 14

    CaiH.WenZ.LiX.MengK.YangP. (2020). Lactobacillus Plantarum FRT10 Alleviated High-Fat Diet-Induced Obesity in Mice through Regulating the PPARα Signal Pathway and Gut Microbiota. Appl. Microbiol. Biotechnol.104, 59595972. 10.1007/s00253-020-10620-0

  • 15

    CaniP. D.MontoyaM. L.NeyrinckA. M.DelzenneN. M.LambertD. M. (2004). Potential Modulation of Plasma Ghrelin and Glucagon-like Peptide-1 by Anorexigenic Cannabinoid Compounds, SR141716A (Rimonabant) and Oleoylethanolamide. Br. J. Nutr.92, 757761. 10.1079/bjn20041256

  • 16

    CapassoR.IzzoA. A.FezzaF.PintoA.CapassoF.MascoloN.et al (2001). Inhibitory Effect of Palmitoylethanolamide on Gastrointestinal Motility in Mice. Br. J. Pharmacol.134, 945950. 10.1038/sj.bjp.0704339

  • 17

    CapassoR.OrlandoP.PaganoE.AvetaT.BuonoL.BorrelliF.et al (2014). Palmitoylethanolamide Normalizes Intestinal Motility in a Model of post-inflammatory Accelerated Transit: Involvement of CB1receptors and TRPV1 Channels. Br. J. Pharmacol.171, 40264037. 10.1111/bph.12759

  • 18

    ClunyN. L.KeenanC. M.LutzB.PiomelliD.Sharkeyk. a. (2009). The Identification of Peroxisome Proliferator-Activated Receptor Alpha-independent Effects of Oleoylethanolamide on Intestinal Transit in Mice. Neurogastroenterology Motil. : official J. Eur. Gastrointest. Motil. Soc.21, 420429. 10.1111/j.1365-2982.2008.01248.x

  • 19

    ColinS.BriandO.ToucheV.WoutersK.BaronM.PattouF.et al (2013). Activation of Intestinal Peroxisome Proliferator-Activated Receptor- Increases High-Density Lipoprotein Production. Eur. Heart J.34, 25662574. 10.1093/eurheartj/ehs227

  • 20

    Colville-NashP. R.QureshiS. S.WillisD.WilloughbyD. A. (1998). Inhibition of Inducible Nitric Oxide Synthase by Peroxisome Proliferator-Activated Receptor Agonists: Correlation with Induction of Heme Oxygenase 1. J. Immunol.161, 978984.

  • 21

    CrakesK. R.Santos RochaC.GrishinaI.HiraoL. A.NapoliE.GaulkeC. A.et al (2019). Pparα-Targeted Mitochondrial Bioenergetics Mediate Repair of Intestinal Barriers at the Host-Microbe Intersection during SIV Infection. Proc. Natl. Acad. Sci. U.S.A.116, 2481924829. 10.1073/pnas.1908977116

  • 22

    CuiJ. Y.ChoudhuriS.KnightT. R.KlaassenC. D. (2010). Genetic and Epigenetic Regulation and Expression Signatures of Glutathione S-Transferases in Developing Mouse Liver. Toxicol. Sci. : official J. Soc. Toxicol.116, 3243. 10.1093/toxsci/kfq115

  • 23

    CuzzocreaS.Di PaolaR.MazzonE.GenoveseT.MuiàC.CentorrinoT.et al (2004). Role of Endogenous and Exogenous Ligands for the Peroxisome Proliferators Activated Receptors Alpha (PPAR-α) in the Development of Inflammatory Bowel Disease in Mice. Lab. Invest.84, 16431654. 10.1038/labinvest.3700185

  • 24

    CuzzocreaS.MazzonE.DugoL.CaputiA. P.RileyD. P.SalveminiD. (2001). Protective Effects of M40403, a Superoxide Dismutase Mimetic, in a Rodent Model of Colitis. Eur. J. Pharmacol.432, 7989. 10.1016/s0014-2999(01)01427-3

  • 25

    DesvergneB.WahliW. (1999). Peroxisome Proliferator-Activated Receptors: Nuclear Control of Metabolism. Endocr. Rev.20 (5), 649688. 10.1210/edrv.20.5.0380

  • 26

    Di PaolaM.BonechiE.ProvensiG.CostaA.ClarkeG.BalleriniC.et al (2018). Oleoylethanolamide Treatment Affects Gut Microbiota Composition and the Expression of Intestinal Cytokines in Peyer's Patches of Mice. Sci. Rep.8, 14881. 10.1038/s41598-018-32925-x

  • 27

    Di PaolaR.ImpellizzeriD.TorreA.MazzonE.CappellaniA.FaggioC.et al (2012). Effects of Palmitoylethanolamide on Intestinal Injury and Inflammation Caused by Ischemia-Reperfusion in Mice. J. Leukoc. Biol.91, 911920. 10.1189/jlb.0911485

  • 28

    DiPatrizioN. V.PiomelliD. (2015). Intestinal Lipid-Derived Signals that Sense Dietary Fat. J. Clin. Invest.125, 891898. 10.1172/jci76302

  • 29

    DreyerC.KreyG.KellerH.GivelF.HelftenbeinG.WahliW. (1992). Control of the Peroxisomal β-oxidation Pathway by a Novel Family of Nuclear Hormone Receptors. Cell68, 879887. 10.1016/0092-8674(92)90031-7

  • 30

    DuparcT.PlovierH.MarrachelliV. G.Van HulM.EssaghirA.StåhlmanM.et al (2017). Hepatocyte MyD88 Affects Bile Acids, Gut Microbiota and Metabolome Contributing to Regulate Glucose and Lipid Metabolism. Gut66, 620632. 10.1136/gutjnl-2015-310904

  • 31

    EscherP.BraissantO.Basu-ModakS.MichalikL.WahliW.DesvergneB. (2001). Rat PPARs: Quantitative Analysis in Adult Rat Tissues and Regulation in Fasting and Refeeding. Endocrinology142, 41954202. 10.1210/endo.142.10.8458

  • 32

    EspositoG.CapocciaE.TurcoF.PalumboI.LuJ.SteardoA.et al (2014). Palmitoylethanolamide Improves colon Inflammation through an Enteric Glia/toll like Receptor 4-dependent PPAR-α Activation. Gut63, 13001312. 10.1136/gutjnl-2013-305005

  • 33

    FedeleS.ArnoldM.KriegerJ. P.WolfstädterB.MeyerU.LanghansW.et al (2018). Oleoylethanolamide-induced Anorexia in Rats Is Associated with Locomotor Impairment. Physiol. Rep.6. 10.14814/phy2.13517

  • 34

    FengX.GaoX.JiaY.ZhangH.XuY.WangG. (2016). PPAR-α Agonist Fenofibrate Decreased RANTES Levels in Type 2 Diabetes Patients with Hypertriglyceridemia. Med. Sci. Monit.22, 743751. 10.12659/msm.897307

  • 35

    FormanB. M.ChenJ.EvansR. M. (1997). Hypolipidemic Drugs, Polyunsaturated Fatty Acids, and Eicosanoids Are Ligands for Peroxisome Proliferator-Activated Receptors Alpha and delta. Proc. Natl. Acad. Sci. U S A.94, 43124317. 10.1073/pnas.94.9.4312

  • 36

    FuJ.GaetaniS.OveisiF.Lo VermeJ.SerranoA.Rodríguez de FonsecaF.et al (2003). Oleylethanolamide Regulates Feeding and Body Weight through Activation of the Nuclear Receptor PPAR-α. Nature425, 9093. 10.1038/nature01921

  • 37

    GoikoetxeaM. J.BeaumontJ.DíezJ. (2004). Peroxisome Proliferator-Activated Receptor Alpha and Hypertensive Heart Disease. Drugs64 (Suppl. 2), 918. 10.2165/00003495-200464002-00003

  • 38

    HaidariS.TröltzschM.KnöselT.LiokatisP.KasintsovaA.EberlM.et al (2021). Fatty Acid Receptor CD36 Functions as a Surrogate Parameter for Lymph Node Metastasis in Oral Squamous Cell Carcinoma. Cancers (Basel)13. 10.3390/cancers13164125

  • 39

    HailaS.HästbackaJ.BöhlingT.Karjalainen–LindsbergM.-L.KereJ.Saarialho–KereU. (2001). SLC26A2 (Diastrophic Dysplasia Sulfate Transporter) Is Expressed in Developing and Mature Cartilage but Also in Other Tissues and Cell Types. J. Histochem. Cytochem.49, 973982. 10.1177/002215540104900805

  • 40

    HankirM. K.SeyfriedF.HintschichC. A.DiepT.-A.KlebergK.KranzM.et al (2017). Gastric Bypass Surgery Recruits a Gut PPAR-α-Striatal D1R Pathway to Reduce Fat Appetite in Obese Rats. Cel Metab.25, 335344. 10.1016/j.cmet.2016.12.006

  • 41

    HasanA. U.RahmanA.KoboriH. (2019). Interactions between Host PPARs and Gut Microbiota in Health and Disease. Int. J. Mol. Sci.20. 10.3390/ijms20020387

  • 42

    HolehouseE. L.LiuM.-L.AponteG. W. (1998). Oleic Acid Distribution in Small Intestinal Epithelial Cells Expressing Intestinal-Fatty Acid Binding Protein. Biochim. Biophys. Acta (Bba) - Lipids Lipid Metab.1390, 5264. 10.1016/s0005-2760(97)00176-8

  • 43

    HutchC. R.TrakimasD. R.RoelofsK.PresslerJ.SorrellJ.CotaD.et al (2020). Oea Signaling Pathways and the Metabolic Benefits of Vertical Sleeve Gastrectomy. Ann. Surg.271, 509518. 10.1097/sla.0000000000003093

  • 44

    IgarashiM.NarayanaswamiV.KimonisV.GalassettiP. M.OveisiF.JungK.-M.et al (2017). Dysfunctional Oleoylethanolamide Signaling in a Mouse Model of Prader-Willi Syndrome. Pharmacol. Res.117, 7581. 10.1016/j.phrs.2016.12.024

  • 45

    IkawaH.KamedaH.KamitaniH.BaekS. J.NixonJ. B.HsiL. C.et al (2001). Effect of PPAR Activators on Cytokine-Stimulated Cyclooxygenase-2 Expression in Human Colorectal Carcinoma Cells. Exp. Cel Res.267, 7380. 10.1006/excr.2001.5233

  • 46

    IssemannI.GreenS. (1990). Activation of a Member of the Steroid Hormone Receptor Superfamily by Peroxisome Proliferators. Nature347, 645. 10.1038/347645a0

  • 47

    JacksonL.WahliW.MichalikL.WatsonS. A.MorrisT.AndertonK.et al (2003). Potential Role for Peroxisome Proliferator Activated Receptor (PPAR) in Preventing colon Cancer. Gut52, 13171322. 10.1136/gut.52.9.1317

  • 48

    JinL.LiL.HuC.Paez-CortezJ.BiY.MacorittoM.et al (2019). Integrative Analysis of Transcriptomic and Proteomic Profiling in Inflammatory Bowel Disease Colon Biopsies. Inflamm. Bowel Dis.25, 19061918. 10.1093/ibd/izz111

  • 49

    KamalianA.AslM. S.DolatshahiM.AfshariK.ShamshiriS.RoudsariN. M.et al (2020). Interventions of Natural and Synthetic Agents in Inflammatory Bowel Disease, Modulation of Nitric Oxide Pathways. World J. Gastroenterol.26, 33653400. 10.3748/wjg.v26.i24.3365

  • 50

    Karimian AzariE.LeitnerC.JaggiT.LanghansW.MansouriA. (2013). Possible Role of Intestinal Fatty Acid Oxidation in the Eating-Inhibitory Effect of the PPAR-α Agonist Wy-14643 in High-Fat Diet Fed Rats. PLoS One8, e74869. 10.1371/journal.pone.0074869

  • 51

    KarwadM. A.MacphersonT.WangB.TheophilidouE.SarmadS.BarrettD. A.et al (2017). Oleoylethanolamine and Palmitoylethanolamine Modulate Intestinal Permeability In Vitro via TRPV1 and PPARα. FASEB j.31, 469481. 10.1096/fj.201500132

  • 52

    KerstenS.SeydouxJ.PetersJ. M.GonzalezF. J.DesvergneB.WahliW. (1999). Peroxisome Proliferator-Activated Receptor α Mediates the Adaptive Response to Fasting. J. Clin. Invest.103, 14891498. 10.1172/jci6223

  • 53

    KilligM.GlatzerT.RomagnaniC. (2014). Recognition Strategies of Group 3 Innate Lymphoid Cells. Front. Immunol.5, 142. 10.3389/fimmu.2014.00142

  • 54

    KliewerS. A.SundsethS. S.JonesS. A.BrownP. J.WiselyG. B.KobleC. S.et al (1997). Fatty Acids and Eicosanoids Regulate Gene Expression through Direct Interactions with Peroxisome Proliferator-Activated Receptors α and γ. Proc. Natl. Acad. Sci. U.S.A.94, 43184323. 10.1073/pnas.94.9.4318

  • 55

    KnightB. L.PatelD. D.HumphreysS. M.WigginsD.GibbonsG. F. (2003). Inhibition of Cholesterol Absorption Associated with a PPARα-dependent Increase in ABC Binding Cassette Transporter A1 in Mice. J. lipid Res.44, 20492058. 10.1194/jlr.m300042-jlr200

  • 56

    KoetheD.SchreiberD.GiuffridaA.MaussC.FaulhaberJ.HeydenreichB.et al (2009). Sleep Deprivation Increases Oleoylethanolamide in Human Cerebrospinal Fluid. J. Neural Transm. (Vienna)116, 301305. 10.1007/s00702-008-0169-6

  • 57

    KokesovaA.CoufalS.FrybovaB.KverkaM.RyglM. (2019). The Intestinal Fatty Acid-Binding Protein as a Marker for Intestinal Damage in Gastroschisis. PLoS One14, e0210797. 10.1371/journal.pone.0210797

  • 58

    KondoH.MinegishiY.KomineY.MoriT.MatsumotoI.AbeK.et al (2006). Differential Regulation of Intestinal Lipid Metabolism-Related Genes in Obesity-Resistant A/J vs. Obesity-Prone C57BL/6J Mice. Am. J. Physiology-Endocrinology Metab.291, E1092E1099. 10.1152/ajpendo.00583.2005

  • 59

    KongL.ChenJ.JiX.QinQ.YangH.LiuD.et al (2021). Alcoholic Fatty Liver Disease Inhibited the Co-expression of Fmo5 and PPARα to Activate the NF-Κb Signaling Pathway, Thereby Reducing Liver Injury via Inducing Gut Microbiota Disturbance. J. Exp. Clin. Cancer Res.40, 18. 10.1186/s13046-020-01782-w

  • 60

    LalehP.YaserK.AlirezaO. (2019). Oleoylethanolamide: A Novel Pharmaceutical Agent in the Management of Obesity‐an Updated Review. J. Cell Physiol.234, 78937902. 10.1002/jcp.27913

  • 61

    LeeH. J.JungH.ChoH.LeeK.HwangK. T. (2018). Black Raspberry Seed Oil Improves Lipid Metabolism by Inhibiting Lipogenesis and Promoting Fatty-Acid Oxidation in High-Fat Diet-Induced Obese Mice and Db/db Mice. Lipids53, 491504. 10.1002/lipd.12050

  • 62

    LeeJ. W.BajwaP. J.CarsonM. J.JeskeD. R.CongY.ElsonC. O.et al (2007). Fenofibrate Represses Interleukin-17 and Interferon-γ Expression and Improves Colitis in Interleukin-10-Deficient Mice. Gastroenterology133, 108123. 10.1053/j.gastro.2007.03.113

  • 63

    LefebvreP.ChinettiG.FruchartJ. C.StaelsB. (2006). Sorting Out the Roles of PPAR in Energy Metabolism and Vascular Homeostasis. J. Clin. Invest.116, 571580. 10.1172/jci27989

  • 64

    LimK.-H.StaudtL. M. (2013). Toll-like Receptor Signaling. Cold Spring Harbor Perspect. Biol.5, a011247. 10.1101/cshperspect.a011247

  • 65

    LiuC.LiS.LiuT.BorjiginJ.LinJ. D. (2007). Transcriptional Coactivator PGC-1α Integrates the Mammalian Clock and Energy Metabolism. Nature447, 477481. 10.1038/nature05767

  • 66

    Lo VermeJ.FuJ.AstaritaG.La RanaG.RussoR.CalignanoA.et al (2005). The Nuclear Receptor Peroxisome Proliferator-Activated Receptor-α Mediates the Anti-inflammatory Actions of Palmitoylethanolamide. Mol. Pharmacol.67, 1519. 10.1124/mol.104.006353

  • 67

    LongT.LiuY.QinY.DeBose-BoydR. A.LiX. (2021). Structures of Dimeric Human NPC1L1 Provide Insight into Mechanisms for Cholesterol Absorption. Sci. Adv.7, 3997. 10.1126/sciadv.abh3997

  • 68

    LosaccoM. C.de AlmeidaC. F. T.HijoA. H. T.Bargi-SouzaP.GamaP.NunesM. T.et al (2018). High-fat Diet Affects Gut Nutrients Transporters in Hypo and Hyperthyroid Mice by PPAR-A Independent Mechanism. Life Sci.202, 3543. 10.1016/j.lfs.2018.03.053

  • 69

    MaS.LeiY.ZhangL.WangJ. (2018). Research on the Inhibiting Effect of Tanshinone IIA on colon Cancer Cell Growth via COX-2-Wnt/β-Catenin Signaling Pathway. J. BUON23, 13371342.

  • 70

    MallordyA.PoirierH.BesnardP.NiotI.CarlierH. (1995). Evidence for Transcriptional Induction of the Liver Fatty-Acid-Binding-Protein Gene by Bezafibrate in the Small Intestine. Eur. J. Biochem.227, 801807. 10.1111/j.1432-1033.1995.tb20204.x

  • 71

    MaltarolloV. G.KronenbergerT.WindshugelB.WrengerC.TrossiniG. H. G.HonorioK. M. (2018). Advances and Challenges in Drug Design of PPARδ Ligands. Curr. Drug. Targets.19, 144154. 10.2174/1389450118666170414113159

  • 72

    MandardS.MüllerM.KerstenS. (2004). Peroxisome Proliferator-Activated Receptor a Target Genes. Cell Mol. Life Sci. (Cmls)61, 393416. 10.1007/s00018-003-3216-3

  • 73

    ManoharanI.SuryawanshiA.HongY.RanganathanP.ShanmugamA.AhmadS.et al (2016). Homeostatic PPARα Signaling Limits Inflammatory Responses to Commensal Microbiota in the Intestine. J.I.196, 47394749. 10.4049/jimmunol.1501489

  • 74

    MansénA.Guardiola-DiazH.RafterJ.BrantingC.GustafssonJ.-Å. (1996). Expression of the Peroxisome Proliferator-Activated Receptor (PPAR) in the Mouse Colonic Mucosa. Biochem. biophysical Res. Commun.222, 844851. 10.1006/bbrc.1996.0832

  • 75

    MastinuA.PiraM.PaniL.PinnaG. A.LazzariP. (2012). NESS038C6, a Novel Selective CB1 Antagonist Agent with Anti-obesity Activity and Improved Molecular Profile. Behav. Brain Res.234, 192204. 10.1016/j.bbr.2012.06.033

  • 76

    MeadeE. A.McIntyreT. M.ZimmermanG. A.PrescottS. M. (1999). Peroxisome Proliferators Enhance Cyclooxygenase-2 Expression in Epithelial Cells. J. Biol. Chem.274, 83288334. 10.1074/jbc.274.12.8328

  • 77

    MochizukiK.SurugaK.YagiE.TakaseS.GodaT. (2001). The Expression of PPAR-Associated Genes Is Modulated through Postnatal Development of PPAR Subtypes in the Small Intestine. Biochim. Biophys. Acta (Bba) - Mol. Cel Biol. Lipids1531, 6876. 10.1016/s0167-4889(01)00071-4

  • 78

    MotojimaK.PassillyP.PetersJ. M.GonzalezF. J.LatruffeN. (1998). Expression of Putative Fatty Acid Transporter Genes Are Regulated by Peroxisome Proliferator-Activated Receptor α and γ Activators in a Tissue- and Inducer-specific Manner. J. Biol. Chem.273, 1671016714. 10.1074/jbc.273.27.16710

  • 79

    MukherjiA.KobiitaA.YeT.ChambonP. (2013). Homeostasis in Intestinal Epithelium Is Orchestrated by the Circadian Clock and Microbiota Cues Transduced by TLRs. Cell153, 812827. 10.1016/j.cell.2013.04.020

  • 80

    NielsenM. J.PetersenG.AstrupA.HansenH. S. (2004). Food Intake Is Inhibited by Oral Oleoylethanolamide. J. lipid Res.45, 10271029. 10.1194/jlr.c300008-jlr200

  • 81

    O'SullivanS. E. (2016). An Update on PPAR Activation by Cannabinoids. Br. J. Pharmacol.173, 18991910. 10.1111/bph.13497

  • 82

    ObiciS.FengZ.MorganK.SteinD.KarkaniasG.RossettiL. (2002). Central Administration of Oleic Acid Inhibits Glucose Production and Food Intake. Diabetes51, 271275. 10.2337/diabetes.51.2.271

  • 83

    OchiaiY.UchidaY.TachikawaM.CouraudP. O.TerasakiT. (2019). Amyloid Beta25‐35impairs Docosahexaenoic Acid Efflux by Down‐regulating Fatty Acid Transport Protein 1 (FATP1/SLC27A1) Protein Expression in Human Brain Capillary Endothelial Cells. J. Neurochem.150, 385401. 10.1111/jnc.14722

  • 84

    Okamura-OhoY. (2004). Perturbation Due to Environmental Stress. Tanpakushitsu Kakusan Koso49, 28502854.

  • 85

    OtagiriS.OhnishiS.OharaM.FuQ.YamamotoK.YamamotoK.et al (2020). Oleoylethanolamide Ameliorates Dextran Sulfate Sodium-Induced Colitis in Rats. Front. Pharmacol.11, 1277. 10.3389/fphar.2020.01277

  • 86

    PanX.SchwartzG. J.HussainM. M. (2018). Oleoylethanolamide Differentially Regulates Glycerolipid Synthesis and Lipoprotein Secretion in Intestine and Liver. J. lipid Res.59, 23492359. 10.1194/jlr.m089250

  • 87

    PetrosinoS.IuvoneT.Di MarzoV. (2010). N-palmitoyl-ethanolamine: Biochemistry and New Therapeutic Opportunities. Biochimie92, 724727. 10.1016/j.biochi.2010.01.006

  • 88

    PiomelliD. (2013). A Fatty Gut Feeling. Trends Endocrinol. Metab.24, 332341. 10.1016/j.tem.2013.03.001

  • 89

    PoirierH.NiotI.DegraceP.MonnotM. C.BernardA.BesnardP. (1997). Fatty Acid Regulation of Fatty Acid-Binding Protein Expression in the Small Intestine. Am. J. Physiol.273, G289. 10.1152/ajpgi.1997.273.2.G289

  • 90

    PoirierH.DegraceP.NiotI.BernardA.BesnardP. (1996). Localization and Regulation of the Putative Membrane Fatty-Acid Transporter (FAT) in the Small Intestine. Comparison with Fatty Acid-Binding Proteins (FABP). Eur. J. Biochem.238, 368373. 10.1111/j.1432-1033.1996.0368z.x

  • 91

    PollingerJ.MerkD. (2017). Therapeutic Applications of the Versatile Fatty Acid Mimetic WY14643. Expert Opin. Ther. patents27, 517525. 10.1080/13543776.2017.1272578

  • 92

    PrabhatA.MalikI.JhaN. A.BhardwajS. K.KumarV. (2020). Developmental Effects of Constant Light on Circadian Behaviour and Gene Expressions in Zebra Finches: Insights into Mechanisms of Metabolic Adaptation to Aperiodic Environment in Diurnal Animals. J. Photochem. Photobiol. B: Biol.211, 111995. 10.1016/j.jphotobiol.2020.111995

  • 93

    PrescottS. M.WhiteR. L. (1996). Self-Promotion? Intimate Connections between APC and Prostaglandin H Synthase-2. Cell87, 783786. 10.1016/s0092-8674(00)81983-2

  • 94

    RiccardiL.MazzonE.BruscoliS.EspositoE.CrisafulliC.Di PaolaR.et al (2009). Peroxisome Proliferator-Activated Receptor-Alpha Modulates the Anti-inflammatory Effect of Glucocorticoids in a Model of Inflammatory Bowel Disease in Mice. Shock (Augusta, Ga.)31, 308316. 10.1097/shk.0b013e31818339e7

  • 95

    RidauraV.BelkaidY. (2015). Gut Microbiota: the Link to Your Second Brain. Cell161, 193194. 10.1016/j.cell.2015.03.033

  • 96

    R. MoschenA.WieserV.TilgH. (2012). Adiponectin: Key Player in the Adipose Tissue-Liver Crosstalk. Curr. Med. Chem.19, 54675473. 10.2174/092986712803833254

  • 97

    RobertsW. C. (1989). Safety of Fenofibrate – US and Worldwide Experience. Cardiology76, 169179. 10.1159/000174488

  • 98

    Rodríguez de FonsecaF.NavarroM.GómezR.EscuredoL.NavaF.FuJ.et al (2001). An Anorexic Lipid Mediator Regulated by Feeding. Nature414, 209212. 10.1038/35102582

  • 99

    RoedigerW. E.NanceS. (1986). Metabolic Induction of Experimental Ulcerative Colitis by Inhibition of Fatty Acid Oxidation. Br. J. Exp. Pathol.67, 773782.

  • 100

    RooksM. G.GarrettW. S. (2016). Gut Microbiota, Metabolites and Host Immunity. Nat. Rev. Immunol.16, 341352. 10.1038/nri.2016.42

  • 101

    SarnelliG.GigliS.CapocciaE.IuvoneT.CirilloC.SeguellaL.et al (2016). Palmitoylethanolamide Exerts Antiproliferative Effect and Downregulates VEGF Signaling in Caco-2 Human Colon Carcinoma Cell Line through a Selective PPAR-α-dependent Inhibition of Akt/mTOR Pathway. Phytother. Res.30, 963970. 10.1002/ptr.5601

  • 102

    SasakiY.Raza-IqbalS.TanakaT.MurakamiK.AnaiM.OsawaT.et al (2019). Gene Expression Profiles Induced by a Novel Selective Peroxisome Proliferator-Activated Receptor α Modulator (SPPARMα) Pemafibrate. Int. J. Mol. Sci.20. 10.3390/ijms20225682

  • 103

    SéréeE.VillardP.-H.PascussiJ.-M.PineauT.MaurelP.NguyenQ. B.et al (2004). Evidence for a New Human CYP1A1 Regulation Pathway Involving PPAR-α and 2 PPRE Sites. Gastroenterology127, 14361445. 10.1053/j.gastro.2004.08.023

  • 104

    ShihM.-C.HsuN.-C.HuangC.-C.WuT.-S.LaiP.-Y.ChungB.-c. (2008). Mutation of MouseCyp11a1Promoter Caused Tissue-specific Reduction of Gene Expression and Blunted Stress Response without Affecting Reproduction. Mol. Endocrinol.22, 915923. 10.1210/me.2007-0222

  • 105

    ShimakuraJ.TeradaT.SaitoH.KatsuraT.InuiK.-i. (2006). Induction of Intestinal Peptide Transporter 1 Expression during Fasting Is Mediated via Peroxisome Proliferator-Activated Receptor α. Am. J. Physiol. Gastrointest. Liver Physiol.291, G851G856. 10.1152/ajpgi.00171.2006

  • 106

    ShivapurkarN.HuangL.RuggeriB.SwalskyP. A.BakkerA.FinkelsteinS.et al (1997). K-ras and P53 Mutations in Aberrant Crypt Foci and Colonic Tumors from colon Cancer Patients. Cancer Lett.115, 3946. 10.1016/s0304-3835(97)04709-5

  • 107

    SihagJ.JonesP. J. H. (2018). Oleoylethanolamide: The Role of a Bioactive Lipid Amide in Modulating Eating Behaviour. Obes. Rev.19, 178197. 10.1111/obr.12630

  • 108

    SivaprakasamS.BhutiaY. D.YangS.GanapathyV. (2017). Short‐Chain Fatty Acid Transporters: Role in Colonic Homeostasis. Compr. Physiol.8, 299314. 10.1002/cphy.c170014

  • 109

    SkaperS. D.FacciL.BarbieratoM.ZussoM.BruschettaG.ImpellizzeriD.et al (2015). N-palmitoylethanolamine and Neuroinflammation: a Novel Therapeutic Strategy of Resolution. Mol. Neurobiol.52, 10341042. 10.1007/s12035-015-9253-8

  • 110

    StackW.MannS.RoyA.HeathP.SopwithM.FreemanJ.et al (1997). Randomised Controlled Trial of CDP571 Antibody to Tumour Necrosis Factor-α in Crohn's Disease. The Lancet349, 521524. 10.1016/s0140-6736(97)80083-9

  • 111

    StavinohaM. A.RaySpellicyJ. W.EssopM. F.GraveleauC.AbelE. D.Hart-SailorsM. L.et al (2004). Evidence for Mitochondrial Thioesterase 1 as a Peroxisome Proliferator-Activated Receptor-α-Regulated Gene in Cardiac and Skeletal Muscle. Am. J. Physiology-Endocrinology Metab.287, E888E895. 10.1152/ajpendo.00190.2004

  • 112

    SteinegerH. H.SorensenH. N.TugwoodJ. D.SkredeS.SpydevoldO.GautvikK. M. (1994). Dexamethasone and Insulin Demonstrate Marked and Opposite Regulation of the Steady-State mRNA Level of the Peroxisomal Proliferator-Activated Receptor (PPAR) in Hepatic Cells. Hormonal Modulation of Fatty-Acid-Induced Transcription. Eur. J. Biochem.225, 967974. 10.1111/j.1432-1033.1994.0967b.x

  • 113

    SuzukiT.MochizukiK.GodaT. (2009). Localized Expression of Genes Related to Carbohydrate and Lipid Absorption along the Crypt-Villus axis of Rat Jejunum. Biochim. Biophys. Acta (Bba) - Gen. Subjects1790, 16241635. 10.1016/j.bbagen.2009.08.004

  • 114

    TanB.TangH.XuY.ChenM. J.WangM. Z.QianJ. M. (2020). Protective Effect and Mechanism of Lactobacillus Rhamnosus on Immune Checkpoint Inhibitors Related Colitis in Mice. Zhonghua yi xue za zhi100, 33323337. 10.3760/cma.j.cn112137-20200520-01598

  • 115

    TanakaT.KohnoH.YoshitaniS.TakashimaS.OkumuraA.MurakamiA.et al (2001). Ligands for Peroxisome Proliferator-Activated Receptors and Chemically Induced Colitis and Formation of Aberrant Crypt Foci in Rats. Cancer Res.61, 24242428.

  • 116

    TogniniP.MurakamiM.LiuY.Eckel-MahanK. L.NewmanJ. C.VerdinE.et al (2017). Distinct Circadian Signatures in Liver and Gut Clocks Revealed by Ketogenic Diet. Cel Metab.26, 523538. e5. 10.1016/j.cmet.2017.08.015

  • 117

    UchidaA.SlipchenkoM. N.ChengJ.-X.BuhmanK. K. (2011). Fenofibrate, a Peroxisome Proliferator-Activated Receptor α Agonist, Alters Triglyceride Metabolism in Enterocytes of Mice. Biochim. Biophys. Acta (Bba) - Mol. Cel Biol. Lipids1811, 170176. 10.1016/j.bbalip.2010.12.011

  • 118

    UsudaD.KandaT. (2014). Peroxisome Proliferator-Activated Receptors for Hypertension. World J. Cardiol.6, 744754. 10.4330/wjc.v6.i8.744

  • 119

    ValasekM. A.ClarkeS. L.RepaJ. J. (2007). Fenofibrate Reduces Intestinal Cholesterol Absorption via PPARα-dependent Modulation of NPC1L1 Expression in Mouse. J. lipid Res.48, 27252735. 10.1194/jlr.m700345-jlr200

  • 120

    ValizadehM.AghasizadehM.NematiM.HashemiM.Aghaee-BakhtiariS. H.Zare-FeyzabadiR.et al (2021). The Association between a Fatty Acid Binding Protein 1 (FABP1) Gene Polymorphism and Serum Lipid Abnormalities in the MASHAD Cohort Study. Prostaglandins, Leukot. Essent. Fatty Acids172, 102324. 10.1016/j.plefa.2021.102324

  • 121

    van den BoschH. M.BüngerM.de GrootP. J.van der MeijdeJ.HooiveldG. J.MüllerM. (2007). Gene Expression of Transporters and Phase I/II Metabolic Enzymes in Murine Small Intestine during Fasting. BMC genomics8, 267. 10.1186/1471-2164-8-267

  • 122

    VluggensA.AndreolettiP.ViswakarmaN.JiaY.MatsumotoK.KulikW.et al (2010). Functional Significance of the Two ACOX1 Isoforms and Their Crosstalks with PPARα and RXRα. Lab. Invest.90, 696708. 10.1038/labinvest.2010.46

  • 123

    VoigtR. M.ForsythC. B.GreenS. J.EngenP. A.KeshavarzianA. (2016). Circadian Rhythm and the Gut Microbiome. Int. Rev. Neurobiol.131, 193205. 10.1016/bs.irn.2016.07.002

  • 124

    WangL.TangY.RubinD. C.LevinM. S. (2007). Chronically Administered Retinoic Acid Has Trophic Effects in the Rat Small Intestine and Promotes Adaptation in a Resection Model of Short Bowel Syndrome. Am. J. Physiology-Gastrointestinal Liver Physiol.292, G1559G1569. 10.1152/ajpgi.00567.2006

  • 125

    WeiH.-X.WangB.LiB. (2020). IL-10 and IL-22 in Mucosal Immunity: Driving Protection and Pathology. Front. Immunol.11, 1315. 10.3389/fimmu.2020.01315

  • 126

    WindsorJ. W.KaplanG. G. (2019). Evolving Epidemiology of IBD. Curr. Gastroenterol. Rep.21, 40. 10.1007/s11894-019-0705-6

  • 127

    WuJ.LiY.YuJ.GanZ.WeiW.WangC.et al (2020). Resveratrol Attenuates High-Fat Diet Induced Hepatic Lipid Homeostasis Disorder and Decreases m6A RNA Methylation. Front. Pharmacol.11, 568006. 10.3389/fphar.2020.568006

  • 128

    YaguchiJ.YaguchiS. (2019). Evolution of Nitric Oxide Regulation of Gut Function. Proc. Natl. Acad. Sci. U.S.A.116, 56075612. 10.1073/pnas.1816973116

  • 129

    YangF.WangD.LiY.SangL.ZhuJ.WangJ.et al (2017). Th1/Th2 Balance and Th17/Treg-Mediated Immunity in Relation to Murine Resistance to Dextran Sulfate-Induced Colitis. J. Immunol. Res.2017, 7047201. 10.1155/2017/7047201

  • 130

    YoshizakiY.KawasakiC.ChengK.-C.UshikaiM.AmitaniH.AsakawaA.et al (2014). Ricekojireduced Body Weight Gain, Fat Accumulation, and Blood Glucose Level in High-Fat Diet-Induced Obese Mice. PeerJ2, e540. 10.7717/peerj.540

  • 131

    YuF.ZhangT.ZhouC.XuH.GuoL.ChenM.et al (2019). The Circadian Clock Gene Bmal1 Controls Intestinal Exporter MRP2 and Drug Disposition. Theranostics9, 27542767. 10.7150/thno.33395

  • 132

    YuS.-Y.HsiaoC.-T.IzawaM.YusaA.IshidaH.NakamuraS.et al (2018). Distinct Substrate Specificities of Human GlcNAc-6-Sulfotransferases Revealed by Mass Spectrometry-Based Sulfoglycomic Analysis. J. Biol. Chem.293, 1516315177. 10.1074/jbc.ra118.001937

  • 133

    ZhangZ.YiP.TuC.ZhanJ.JiangL.ZhangF. (2019). Curcumin Inhibits ERK/c-Jun Expressions and Phosphorylation against Endometrial Carcinoma. Biomed. Res. Int.2019, 8912961. 10.1155/2019/8912961

  • 134

    ZhengY.ValdezP. A.DanilenkoD. M.HuY.SaS. M.GongQ.et al (2008). Interleukin-22 Mediates Early Host Defense against Attaching and Effacing Bacterial Pathogens. Nat. Med.14, 282289. 10.1038/nm1720

Summary

Keywords

peroxisome proliferator–activated receptor (PPAR)-α, gastrointestinal diseases, metabolism, transcription, disorder

Citation

Guo Y-X, Wang B-Y, Gao H, Hua R-X, Gao L, He C-W, Wang Y and Xu J-D (2022) Peroxisome Proliferator–Activated Receptor-α: A Pivotal Regulator of the Gastrointestinal Tract. Front. Mol. Biosci. 9:864039. doi: 10.3389/fmolb.2022.864039

Received

28 January 2022

Accepted

14 March 2022

Published

26 April 2022

Volume

9 - 2022

Edited by

Emil Alexov, Clemson University, United States

Reviewed by

Kristina Brooke Martinez-Guryn, Midwestern University, United States

Roberta Imperatore, University of Sannio, Italy

Updates

Copyright

*Correspondence: Jing-Dong Xu,

†These authors have contributed equally to this work

This article was submitted to Molecular Recognition, a section of the journal Frontiers in Molecular Biosciences

Disclaimer

All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article or claim that may be made by its manufacturer is not guaranteed or endorsed by the publisher.

Outline

Figures

Cite article

Copy to clipboard


Export citation file


Share article

Article metrics