(F1223) DECREASED A-TO-I RNA EDITING AND HYPEREXCITABILITY ASSOCIATED WITH ENHANCED CHOLESTEROL BIOSYNTHESIS IN LOWER MOTOR NEURONS OF PATIENTS WITH AMYOTROPHIC LATERAL SCLEROSIS
Undergraduate Student Keio University, Tokyo, Japan
Abstract: Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease characterized by the degeneration and loss of motor neurons (MNs). Genome- and epigenome-wide association studies identify genetic predisposition to enhanced cholesterol biosynthesis as a risk factor for ALS. We previously reported that lower MNs derived from induced pluripotent stem cells (iPSC-LMNs) of patients with ALS exhibit upregulated expression of cholesterol biosynthesis enzymes relative to controls, and that this upregulation correlates with ALS-like phenotypes such as reduced neurite length. However, the mechanistic link between enhanced cholesterol biosynthesis in MNs and neurodegeneration in ALS remains incompletely understood. Here, we demonstrate that increased cholesterol biosynthesis in MNs is associated with reduced adenosine-to-inosine (A-to-I) RNA editing activity, as well as hyperexcitability. Under normal conditions, GRIA2, a subunit of the AMPA receptor, undergoes A-to-I RNA editing at the pre-mRNA level, thereby conferring calcium ion impermeability. In contrast, the unedited form remains permeable to calcium ions and contributes to excitotoxic damage. To accurately quantify A-to-I editing activity in iPSC-LMNs, we first confirmed that the A-to-I editing index, which is calculated based on editing activity for Alu sequences, correlates with the A-to-I editing ratio in GRIA2 (R=0.4513, P< 0.001). In iPSC-LMNs, overexpression of SREBF2, a key regulator of cholesterol biosynthesis, decreased the A-to-I RNA editing index and induced hyperexcitability, as measured by microelectrode array (P < 0.001). Conversely, siRNA-mediated knockdown of either SREBF2 or HMGCR (the rate-limiting enzyme in cholesterol biosynthesis), as well as treatment with ropinirole hydrochloride (which suppresses the expression of cholesterol biosynthesis enzymes in MNs), increased the A-to-I RNA editing index (P < 0.004) and mitigated hyperexcitability (P < 0.001). These findings suggest that upregulated cholesterol biosynthesis in MNs may promote calcium ion-mediated excitotoxicity through reduced GRIA2 A-to-I RNA editing, potentially representing a crucial pathogenic mechanism in ALS. They further imply that inhibiting cholesterol biosynthesis in MNs could serve as a promising therapeutic strategy for ALS.
Funding Source: This study was supported by grants from the Japan Society for the Promotion of Science (JSPS) and the Japan Society for the Promotion of Science (AMED).
