Neuromuscular Dysfunction and Charcot-Marie-Tooth Disease Reversal in Mfn2 T105M Knock-In Rats

Charcot-Marie-Tooth (CMT) disease type 2A is a rare heritable disorder caused by pathogenic variants of mitofusin (MFN) 2 that suppress mitochondrial fusion and motility in peripheral nerves, culminating in denervation myoatrophy. The rarity of this condition and the limited choice of animal models preclude pre-clinical evaluation of many tests that could be translated to human trials. Here, we introduced the CMT2A pathogenic variant MFN2 T105M into the rat genome for phenotype characterization and evaluation of disease response to a third-generation mitofusin activator, 8015-P2. CMT2A rats exhibited peripheral motor and sensory neuron dysfunction. Functional, histological, neuroelectrophysiological and magnetic resonance imaging testing readily distinguished between wild-type (WT) and mutant rats via axonopathy and myoatrophy. Compound 8015-P2 reversed CMT2A-linked neuromuscular degeneration in a dose- and time-dependent manner; at 10 mg/kg/d, normalization occurred at 4 weeks. The minimal effective 8015-P2 dose was 2 mg/kg/day. Rapidity of phenotype reversal and primary muscle abnormalities are consistent with extra-neuronal effects of the causal MFN2 DNA variant. These data demonstrate unprecedented utility of the Mfn2 T105M rat as a model of CMT2A, expand the menu of clinically applicable tests that may have use in future human trials, and establish a strong foundation for exploration of extra-neuronal consequences of pathogenic mitofusin variants in non-mouse models.