Systemic AAV8-SIL1-TAT therapy improves motor function in a mouse model of Marinesco-Sjögren syndrome

: Marinesco-Sjögren Syndrome (MSS) is a rare genetic disorder characterized by cerebellar ataxia, congenital cataracts, and progressive myopathy. Approximately 60% of cases result from SIL1 gene mutations, causing endoplasmic reticulum stress and neuromuscular degeneration. We investigated AAV8-mediated SIL1 gene replacement combined with TAT peptide-mediated protein delivery in the woozy (Sil1wz) mouse model. Thirty-two female Sil1wz mice received either AAV8-SIL1-TAT vector (5 × 1012 genome copies) or saline intravenously at 4 weeks of age. The construct enabled liver-produced SIL1 protein uptake by peripheral tissues. Motor performance, cognitive behaviour, and molecular changes were monitored over 20 weeks. Treated mice showed significant motor improvement versus controls. Accelerating rotarod testing revealed delayed motor deficit onset by approximately 3 weeks, with significantly higher performance from weeks 10-14 (p < 0.001). Beam walking assessment showed reduced traversal time and contralateral falls from week 9 onwards. Western blotting and immunohistochemistry confirmed intracellular SIL1 localization in hepatocytes and muscle fibres, but not cerebellum. Quadriceps SIL1 delivery peaked at 2 weeks post-treatment, then gradually declined. Treatment normalized peIF2α and LC3 expression in quadriceps, indicating reduced ER stress and autophagy in skeletal muscle. This study provides proof-of-concept evidence for liver-based protein production combined with cell-penetrating peptides as a viable approach for treating peripheral manifestations of multisystemic disorders, while highlighting the need for alternative CNS delivery strategies for comprehensive therapeutic coverage in MSS.