Background

AUTHOR=Ito Masatoshi , Fujii Natsuko , Kohara Saori , Tanaka Masayuki , Takao Masaki , Mihara Ban , Saito Yuko , Mizuma Atsushi , Nakayama Taira , Netsu Shizuka , Suzuki Naoto , Kakita Akiyoshi , Nagata Eiichiro TITLE=Elevation of inositol pyrophosphate IP7 in the mammalian spinal cord of amyotrophic lateral sclerosis JOURNAL=Frontiers in Neurology VOLUME=14 YEAR=2024 URL=https://www.frontiersin.org/journals/neurology/articles/10.3389/fneur.2023.1334004 DOI=10.3389/fneur.2023.1334004 ISSN=1664-2295 ABSTRACT=Background

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disorder associated with progressive impairment of spinal motor neurons. Continuous research endeavor is underway to fully understand the molecular mechanisms associating with this disorder. Although several studies have implied the involvement of inositol pyrophosphate IP₇ in ALS, there is no direct experimental evidence proving this notion. In this study, we analyzed inositol pyrophosphate IP₇ and its precursor IP₆ in the mouse and human ALS biological samples to directly assess whether IP₇ level and/or its metabolism are altered in ALS disease state.

Methods

We used a liquid chromatography-mass spectrometry (LC-MS) protocol originally-designed for mammalian IP₆ and IP₇ analysis. We measured the abundance of these molecules in the central nervous system (CNS) of ALS mouse model SOD1(G93A) transgenic (TG) mice as well as postmortem spinal cord of ALS patients. Cerebrospinal fluid (CSF) and peripheral blood mononuclear cells (PBMCs) from ALS patients were also analyzed to assess if IP₇ status in these biofluids is associated with ALS disease state.

Results

SOD1(G93A) TG mice showed significant increase of IP₇ level in the spinal cord compared with control mice at the late stage of disease progression, while its level in cerebrum and cerebellum remains constant. We also observed significantly elevated IP₇ level and its product-to-precursor ratio (IP₇/IP₆) in the postmortem spinal cord of ALS patients, suggesting enhanced enzymatic activity of IP₇-synthesizing kinases in the human ALS spinal cord. In contrast, human CSF did not contain detectable level of IP₆ and IP₇, and neither the IP₇ level nor the IP₇/IP₆ ratio in human PBMCs differentiated ALS patients from age-matched healthy individuals.

Conclusion

By directly analyzing IP₇ in the CNS of ALS mice and humans, the findings of this study provide direct evidence that IP₇ level and/or the enzymatic activity of IP₇-generating kinases IP6Ks are elevated in ALS spinal cord. On the other hand, this study also showed that IP₇ is not suitable for biofluid-based ALS diagnosis. Further investigation is required to elucidate a role of IP₇ in ALS pathology and utilize IP₇ metabolism on the diagnostic application of ALS.