Elevation of inositol pyrophosphate IP 7 in the mammalian spinal cord of amyotrophic lateral sclerosis

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 IP in ALS, there is no direct experimental evidence proving this notion. In this study, we analyzed inositol pyrophosphate IP and its precursor IP in the mouse and human ALS biological samples to directly assess whether IP level and/or its metabolism are altered in ALS disease state. We used a liquid chromatography-mass spectrometry (LC-MS) protocol originally-designed for mammalian IP and IP analysis. We measured the abundance of these molecules in the central nervous system (CNS) of ALS mouse model (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 IP status in these biofluids is associated with ALS disease state. (G93A) TG mice showed significant increase of IP 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 IP level and its product-to-precursor ratio (IP /IP ) in the postmortem spinal cord of ALS patients, suggesting enhanced enzymatic activity of IP -synthesizing kinases in the human ALS spinal cord. In contrast, human CSF did not contain detectable level of IP and IP , and neither the IP level nor the IP /IP ratio in human PBMCs differentiated ALS patients from age-matched healthy individuals. By directly analyzing IP in the CNS of ALS mice and humans, the findings of this study provide direct evidence that IP level and/or the enzymatic activity of IP -generating kinases IP6Ks are elevated in ALS spinal cord. On the other hand, this study also showed that IP is not suitable for biofluid-based ALS diagnosis. Further investigation is required to elucidate a role of IP in ALS pathology and utilize IP metabolism on the diagnostic application of ALS.