BLOC1S1 depletion via splice-switching oligonucleotides improves mitochondrial respiration and rescues ALS phenotypes

Amyotrophic lateral sclerosis (ALS) is a rapidly progressing and debilitating neurodegenerative disease, yet the mechanisms underlying disease onset and progression remain poorly understood, particularly in sporadic ALS. Emerging evidence suggests that mitochondrial dysfunction and metabolic dysregulation are central to ALS pathophysiology. A key feature of ALS motor neurons (MNs) is hyper-acetylation of mitochondrial proteins, which disrupt mitochondrial respiration and energy homeostasis. In this study, we identify BLOC1S1 (also known as GCN5L1) as a novel regulator of mitochondrial acetylation in ALS. We demonstrate that BLOC1S1 is significantly upregulated in ALS patient-derived MNs, postmortem motor cortices, and spinal cords of ALS mouse models. Functional studies in induced pluripotent stem cell-derived MNs reveal that BLOC1S1 depletion rescues key disease phenotypes. Therefore, we develop an efficacious splice-switching antisense oligonucleotide that induces nonsense-mediated decay of BLOC1S1 transcripts as a potential therapeutic candidate. Besides mitigating ALS-relevant cellular deficits in MN cultures from diverse genetic backgrounds, it was validated to extend disease-free and overall survival that is associated with improved rotarod performance in an ALS mouse model. These findings establish BLOC1S1 as a critical modifier of disease progression in ALS and highlight its potential as a novel therapeutic target.