AUTHOR=Tang Nana , Yang Yang , Xie Yifei , Yang Guohui , Wang Qin , Li Chang , Liu Zeyi , Huang Jian-an 

TITLE=CD274 (PD-L1) negatively regulates M1 macrophage polarization in ALI/ARDS

JOURNAL=Frontiers in Immunology

VOLUME=15

YEAR=2024

URL=https://www.frontiersin.org/journals/immunology/articles/10.3389/fimmu.2024.1344805

DOI=10.3389/fimmu.2024.1344805

ISSN=1664-3224

ABSTRACT=<sec><title>Background</title><p>Acute lung injury (ALI)/severe acute respiratory distress syndrome (ARDS) is a serious clinical syndrome characterized by a high mortality rate. The pathophysiological mechanisms underlying ALI/ARDS remain incompletely understood. Considering the crucial role of immune infiltration and macrophage polarization in the pathogenesis of ALI/ARDS, this study aims to identify key genes associated with both ALI/ARDS and M1 macrophage polarization, employing a combination of bioinformatics and experimental approaches. The findings could potentially reveal novel biomarkers for the diagnosis and management of ALI/ARDS.</p></sec><sec><title>Methods</title><p>Gene expression profiles relevant to ALI were retrieved from the GEO database to identify co-upregulated differentially expressed genes (DEGs). GO and KEGG analyses facilitated functional annotation and pathway elucidation. PPI networks were constructed to identify hub genes, and differences in immune cell infiltration were subsequently examined. The expression of hub genes in M1 versus M2 macrophages was evaluated using macrophage polarization datasets. The diagnostic utility of <italic>CD274</italic> (PD-L1) for ARDS was assessed by receiver operating characteristic (ROC) analysis in a validation dataset. Experimental confirmation was conducted using two LPS-induced M1 macrophage models and an ALI mouse model. The role of <italic>CD274</italic> (PD-L1) in M1 macrophage polarization and associated proinflammatory cytokine production was further investigated by siRNA-mediated silencing.</p></sec><sec><title>Results</title><p>A total of 99 co-upregulated DEGs were identified in two ALI-linked datasets. Enrichment analysis revealed that these DEGs were mainly involved in immune-inflammatory pathways. The following top 10 hub genes were identified from the PPI network: <italic>IL-6</italic>, <italic>IL-1β</italic>, <italic>CXCL10</italic>, <italic>CD274</italic>, <italic>CCL2</italic>, <italic>TLR2</italic>, <italic>CXCL1</italic>, <italic>CCL3</italic>, <italic>IFIT1</italic>, and <italic>IFIT3</italic>. Immune infiltration analysis revealed a significantly increased abundance of M1 and M2 macrophages in lung tissue from the ALI group compared to the control group. Subsequent analysis confirmed that <italic>CD274</italic> (PD-L1), a key immunological checkpoint molecule, was highly expressed within M1 macrophages. ROC analysis validated <italic>CD274</italic> (PD-L1) as a promising biomarker for the diagnosis of ARDS. Both <italic>in vitro</italic> and <italic>in vivo</italic> experiments supported the bioinformatics analysis and confirmed that the JAK-STAT3 pathway promotes <italic>CD274</italic> (PD-L1) expression on M1 macrophages. Importantly, knockdown of <italic>CD274</italic> (PD-L1) expression potentiated M1 macrophage polarization and enhanced proinflammatory cytokines production.</p></sec><sec><title>Conclusion</title><p>This study demonstrates a significant correlation between <italic>CD274</italic> (PD-L1) and M1 macrophages in ALI/ARDS. <italic>CD274</italic> (PD-L1) functions as a negative regulator of M1 polarization and the secretion of proinflammatory cytokines in macrophages. These findings suggest potential new targets for the diagnosis and treatment of ALI/ARDS.</p></sec>