Gene therapy-mediated overexpression of wild-type MFN2 improves Charcot-Marie-Tooth disease type 2A

Charcot-Marie-Tooth disease type 2A (CMT2A) is the most common axonal CMT and is associated with an early onset and severe motor-dominant phenotype. CMT2A is mainly caused by dominant mutations in the MFN2 gene, encoding Mitofusin-2, a GTPase located in the outer membrane of the mitochondria and endoplasmic reticulum (ER). Mutations in MFN2 are known to affect mitochondrial dynamics. We previously demonstrated that the mutated MFN2Arg94Gln further disrupts contacts between the ER and the mitochondria, leading to progressive axonal degeneration. There is no effective therapeutic approach to slow or reverse the progression of CMT2A, and treatments currently under development primarily focus on restoring mitochondrial function. Here, we provide proof-of-concept that neuronal overexpression of wild-type MFN2 (MFN2WT) provides therapeutic benefit in transgenic CMT2A mice carrying the mutated MFN2Arg94Gln. Intrathecal delivery of an AAV9 vector expressing MFN2WT effectively targets motor and sensory neurons, restoring ER-mitochondria contacts and mitochondrial morphology, thereby preserving both neuromuscular junction integrity and motor function. Strikingly, therapeutic efficacy is also achieved following vector injection after the onset of symptoms, rescuing the molecular hallmarks of CMT2A pathology and reversing locomotor. Notably, AAV administration was well tolerated, with no evidence neither of hepatotoxicity nor dorsal root ganglion inflammation. These results establish that boosting MFN2s levels using gene therapy is a promising therapeutic avenue for CMT2A.