Elevation of inositol pyrophosphate IP7 in the mammalian spinal cord of amyotrophic lateral sclerosis

Masatoshi Ito; Natsuko Fujii; Saori Kohara; Masayuki Tanaka; Masaki Takao; Ban Mihara; Yuko Saito; Atsushi Mizuma; Taira Nakayama; Shizuka Netsu; Naoto Suzuki; Akiyoshi Kakita; Eiichiro Nagata

doi:10.3389/fneur.2023.1334004

Elevation of inositol pyrophosphate IP₇ in the mammalian spinal cord of amyotrophic lateral sclerosis

Front Neurol. 2024 Jan 11:14:1334004. doi: 10.3389/fneur.2023.1334004. eCollection 2023.

Authors

Masatoshi Ito^{1

2}, Natsuko Fujii¹, Saori Kohara¹, Masayuki Tanaka³, Masaki Takao^{4

5}, Ban Mihara⁵, Yuko Saito⁶, Atsushi Mizuma¹, Taira Nakayama¹, Shizuka Netsu¹, Naoto Suzuki¹, Akiyoshi Kakita⁷, Eiichiro Nagata¹

Affiliations

¹ Department of Neurology, Tokai University School of Medicine, Isehara, Japan.
² Department of Legal Medicine, St. Marianna University School of Medicine, Kawasaki, Japan.
³ Support Center for Medical Research and Education, Tokai University, Isehara, Japan.
⁴ Department of Clinical Laboratory, National Center of Neurology and Psychiatry, National Center Hospital, Tokyo, Japan.
⁵ Department of Neurology, Mihara Memorial Hospital, Isesaki, Japan.
⁶ Department of Neuropathology, Tokyo Metropolitan Geriatric Hospital and Institute of Gerontology, Tokyo, Japan.
⁷ Department of Pathology, Brain Research Institute, Niigata University, Niigata, Japan.

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.

Keywords: amyotrophic lateral sclerosis; diphosphoinositol pentakisphosphate; inositol hexakisphosphate; inositol pyrophosphate; liquid chromatography-tandem mass spectrometry.

Grants and funding

The author(s) declare financial support was received for the research, authorship, and/or publication of this article. This work was partly supported by grants-in-aid numbers JP19K07851 and JP22K07379 for scientific research from Japan Society for the Promotion of Science (to EN), Japan Agency for Medical Research and Development under Grant Number JP21wm0425019 (to MTak and AK) and JP23jm0210097 (to AK), intramural funds from the National Center of Neurology and Psychiatry (to MTak), and the Collaborative Research Project of the Brain Research Institute of Niigata University (to AK).