Antisense oligonucleotides reverse SPTLC1-related hereditary sensory neuropathy in a mouse model

Hereditary sensory neuropathy type IA (HSN1A) is a rare neurodegenerative condition caused by dominant mutations in the Serine Palmitoyl Transferase Long Chain base subunit 1 (SPTLC1) gene. There is no treatment available. Allele-specific silencing by antisense oligonucleotides (ASOs) to preferentially silence the mutant transcripts has shown therapeutic promise for dominant gain-of-function genetic disorders. In this study, we validated an allele-specific ASO therapy to selectively silence mutant SPTLC1 (p.S331F) in a disease mouse model carrying a heterozygous p.S331F mutation (S331F mice). Gapmer ASOs, targeting the S331F variant in either 2'-O-methyl (2'-OMe), locked nucleic acid (LNA) or 2'-O-methoxy ethyl (MOE) chemistries, were first studied in cultured mouse skin fibroblasts. The candidate ASOs in LNA or MOE were further evaluated in vivo. Single subcutaneous injection of ASOs into neonatal or adult S331F mice achieved over 90% mutant transcript silencing in liver and dorsal root ganglia (DRG). Weekly subcutaneous injections of LNA-ASOs, either unconjugated or conjugated with N-acetylgalactosamine (GalNAc), into S331F mice showed GalNAc-LNA-ASOs to be more efficient than unconjugated LNA-ASOs at reducing mutant transcripts in liver, DRG and sciatic nerve, without affecting wild-type transcripts. GalNAc-LNA-ASOs also resulted in significantly reduced blood levels of 1-deoxysphingoid bases (1-deoxySL), neurotoxic metabolites used as biomarkers in HSN1A patients. Transcriptomic studies in DRG demonstrated mitochondrial pathway involvement in the pathological changes observed in S331F mice. Quantitative RT-PCR confirmed the differentially expressed genes between S331F and wild-type mice. Furthermore, these aberrantly expressed genes in S331F mice were reversed by GalNAc-LNA-ASO treatment. Our data provide necessary in vivo evidence as proof of concept for ASO-mediated mutant-allele-specific silencing as a therapeutic approach for SPTLC1-related HSN1.