A mouse model of CHCHD10 p.R15L familial ALS presents mild, age-related motor neuron degeneration without protein instability or mitochondrial dysfunction.

Mutations in the mitochondrial protein CHCHD10 (D10) cause a spectrum of hereditary neurodegenerative disorders. Among these, the p.R15L variant is linked to a slowly progressive, late-onset familial form of amyotrophic lateral sclerosis (ALS) with unclear pathogenic mechanisms. To better understand this, we investigated a knock-in (KI) mouse model carrying the p.R15L mutation in the endogenous protein. Unlike previously described mutant D10 KI models, p.R15L KI mice exhibited normal D10 protein levels, with no evidence of large protein aggregates. Mitochondrial respiration and hydrogen peroxide emission in mitochondria isolated from muscle and brain were unaltered. Similarly, fibroblasts from human p.R15L carriers exhibited normal D10 levels and unchanged oxidative phosphorylation function. Histochemical analyses of p.R15L KI muscle revealed mild increases in mitochondrial enzymatic activity in a subset of muscle fibers and muscle transcriptomics showed elevated expression of PGC-1α, suggesting enhanced mitochondrial biogenesis. p.R15L KI mice developed subtle, late-onset phenotypes, including reduced body weight and motor activity and increased anxiety-like behavior. Importantly, in aged mice electrophysiological studies demonstrated decreased amplitude of the compound muscle action potential, commensurate with a moderate loss of spinal cord motor neurons and elevated serum neurofilament light levels, indicative of neurodegeneration. Together, these results indicate that the p.R15L mutation produces a mild, late-onset motor neuron phenotype in mice, partially recapitulating the human disease, without mitochondrial functional or morphological alterations. The findings indicate that p.R15L D10 selectively impairs mouse motor neurons through a gain-of-function mechanism, providing a genetically accurate yet mild in vivo model of familial ALS.