Engineered Exosomes Deliver miR-370 Inhibitor to Regulate DNAJB1 and Synergize With miR-25 in Improving SCA3 Mice Behavior and Neuropathology.

Spinocerebellar ataxia type 3 (SCA3), the most common inherited ataxia, lacks effective therapies. Current microRNA (miRNA) approaches directly targeting ataxin-3 (ATXN3) mRNA risk reducing essential wild-type ATXN3, a key regulator of proteostasis and various signaling pathways. Consequently, developing neuron-targeted, noninvasive miRNA delivery strategies that employ alternative mechanisms is critical for SCA3. In this study, we engineered rabies virus glycoprotein (RVG)-modified exosomes to deliver miR-370 inhibitors to the brains of SCA3 mice, thereby upregulating the molecular chaperone DnaJ homolog subfamily B member 1 (DNAJB1) to promote clearance of mutant ATXN3. Systemic administration of RVG-exosomes carrying miR-370 inhibitors led to increased DNAJB1 expression, reduced mutant ATXN3 aggregation, improved neuronal survival, and restored motor coordination in SCA3 mice. Furthermore, combining miR-370 inhibitors with miR-25-a miRNA that directly targets ATXN3 mRNA-synergistically enhanced the reduction of pathogenic ATXN3 and provided greater neuroprotection compared to either therapy alone. These findings support the use of RVG-exosome-mediated miR-370 inhibition as a noninvasive strategy to improve proteostasis in SCA3 and demonstrate its potential in combination with ATXN3 mRNA-targeting miRNAs, offering a promising therapeutic paradigm for SCA3 and similar neurodegenerative disorders.