The neuropathy-causing GARS1ΔETAQ mutation drives pathology in subsets of motor and sensory neurons in mice

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.

DNM2 -Charcot-Marie-Tooth neuropathy stems from disrupted Schwann cell function and shows limited therapeutic reversibility

Dominant loss-of-function mutations in DNM2 cause Charcot-Marie-Tooth neuropathy characterized by sensory and motor deficits associated with myelin and/or axonal abnormalities and muscle atrophy. Increasing DNM2 activity from embryogenesis has been reported to ameliorate neuromuscular phenotypes in the Dnm2K562E/+ Charcot-Marie-Tooth mouse; however, this model displays predominantly muscle pathology and limited nerve involvement, precluding rigorous evaluation of neuropathic mechanisms and potential therapies. Here, we performed comprehensive behavioral, electrophysiological, histological and molecular analyses to characterize the Dnm2K562E/SC- mouse, which combines systemic heterozygosity for the common K562E mutation together with Schwann cell-specific deletion of wild-type Dnm2. This model faithfully reproduces key clinical and pathological features of DNM2-Charcot-Marie-Tooth, including motor deficits, reduced general force and coordination, and severe sensory and motor conduction deficits associated with axonal loss, demyelination, and inflammation. Mechanistically, we delineate a coherent pathological sequence that explains the profound functional deficits. In particular, a downregulation of the transcription factor EGR2, a master regulator of myelin gene expression, and of the myelin protein MPZ correlates with demyelination. To evaluate the therapeutic potential of DNM2 supplementation, post-symptomatic intrathecal delivery of AAV9-DNM2 driven by the Schwann cell-specific MPZ promoter was performed at 4 weeks. Although DNM2 expression increased in peripheral nerves (∼1.9-fold), no significant improvements were observed across behavioral, electrophysiological, structural, or molecular parameters. Together, these findings establish the Dnm2K562E/SC- mouse as a robust preclinical model, recapitulating key features of DNM2- Charcot-Marie-Tooth, and provides crucial insight into the biological and temporal constraints that must guide future therapeutic strategies for DNM2-Charcot-Marie-Tooth.

Peripheral neuropathy in a mouse model lacking GBA1 in Schwann cells.

Peripheral neuropathic symptoms have been reported in Gaucher disease (GD), a rare lysosomal storage disorder caused by mutations in β-glucocerebrosidase gene (GBA1), albeit poorly investigated only in clinical settings. To shed light on the involvement of peripheral myelination by Schwann cells (SCs) in GD, we generated a conditional knockout mouse line in which β-glucocerebrosidase is depleted in myelinating glia (Gba1f/f::cre). Adult Gba1f/f::cre peripheral nerves presented hypomyelination of large caliber axons and higher frequency of myelin infoldings, accompanied by evidence of repair-SC program activation, as indicated by the expression of p75ntr and cJun. The Gba1f/f::cre mice displayed reduced motor performance, associated with altered neuromuscular junction morphology and neuromuscular transmission. Given the well-established role of β-glucocerebrosidase in lysosomal function and autophagy, we also investigated whether its deficiency in SCs could affect nerve injury response. Despite the ability of conditional knockout mice to reach a full recovery, the initial steps of myelinophagy, a process required to eliminate myelin debris, thus prompting axon regeneration, were impaired in β-glucocerebrosidase deficient SCs in vivo. Consistently, when in vitro nerve degeneration was induced in presence of the β-glucocerebrosidase inhibitor conduritol B epoxide (CBE), a block in the autophagic flux was observed. Our data show that decreased degradation efficiency and/or accumulation of bioactive lipids in SCs lacking β-glucocerebrosidase sustain the activation of a repair-SC program, leading to myelin and axonal defects. These results indicate a novel role for GBA1 in guaranteeing SC lysosomal function as relevant for peripheral nerve homeostasis.

Establishing Sensory Neurons as Therapeutic Targets in Peripheral Neuropathy Driven by Polyglutamine Expanded Murine ATXN3.

OBJECTIVE Repeat expansion mutations underlie diverse neurogenetic disorders, many involving the peripheral nervous system. Despite peripheral neuropathy being the most common neurological disorder worldwide, its contribution to repeat expansion diseases remains poorly defined, and robust preclinical models are limited. We established a translational framework to study peripheral neuropathy in spinocerebellar ataxia type 3 (SCA3), a fatal multisystem disorder caused by a pathogenic CAG expansion in ATXN3. METHODS SCA3 Knock-In Atxn3Q300/Q6 (KI) and Atxn3-/- Knock-Out (KO) mice underwent sensorimotor nerve conduction and behavioral testing. Peripheral tissues were evaluated for SCA3-related pathology, and transcriptional changes in KI dorsal root ganglia (DRG) were assessed by bulk RNA sequencing. To test therapeutic relevance, we generated a conditional "OFF" SCA3 knock-in (cKI) mouse and crossed it with Avil-Cre to selectively silence mutant ATXN3 in sensory neurons. Peripheral phenotyping was repeated in Avil-Cre; cKI mice. RESULTS KI mice developed progressive sensorimotor deficits, peripheral histopathology, and RNA splicing dysregulation that parallel clinical features of SCA3. In contrast, KO mice showed normal peripheral nerve function, implicating toxic gain-of-function from mutant ATXN3 as the causative driver. Sensory neuron-specific silencing of mutant ATXN3 significantly ameliorated peripheral nerve abnormalities and DRG splicing dysregulation. INTERPRETATION These findings define a pathogenic role for repeat expansion-driven peripheral nerve degeneration in SCA3, identify sensory neurons as key therapeutic targets, and provide a preclinical platform for developing peripheral interventions in SCA3 and related repeat expansion disorders. ANN NEUROL 2026.

Axonopathy in Duchenne Muscular Dystrophy limits microdystrophin gene therapy efficacy

A mouse model of autosomal dominant spastic ataxia and myopathy caused by a mutation in Tuba4a.

Hereditary ataxias are a heterogeneous group of neurodegenerative disorders characterized by impaired balance and coordination, often due to cerebellar dysfunction. Despite advances in identifying genetic causes, animal models remain essential for dissecting underlying mechanisms and testing therapeutic strategies. Here we describe a mouse model of spastic ataxia and myopathy caused by a missense mutation in Tuba4a (n.A626C, p.Gln176Pro). In an ENU mutagenesis screen, a male C57BL/6 J mouse exhibiting muscle wasting and an intention tremor starting at approximately 4 weeks-of-age was identified. The male was bred by in vitro fertilization to BALB/cByJ oocyte donors. Genetic mapping determined dominant inheritance and localized the mutation to Chromosome 1. Genome sequencing revealed single nucleotide polymorphisms (SNPs) in serine threonine kinase 36 (Stk36Y1003N) and alpha-tubulin 4A (Tuba4aQ176P) in the mapping interval. These SNPs were CRISPR-engineered into C57BL/6 J mice, which confirmed the Tuba4aQ176P variant as the causative mutation. Mutant mice are normal at 3 weeks, except for decrement in muscle response following repetitive nerve stimulation. However, by 30 days these mice have overt ataxia, Purkinje neuron degeneration, and extensive skeletal muscle defects, which contribute to a decreased lifespan. Dominant TUBA4A mutations in humans are associated with spastic ataxia type 11 (SPAX11), congenital myopathy type 26 (CMYO26), and frontotemporal dementia/amyotrophic lateral sclerosis type 9 (FTDALS9). Our mice exhibit hallmark features of SPAX11 and CMYO26, but do not show motor neuron degeneration. This specificity makes this model a valuable tool for studying cell-type selective effects of TUBA4A mutations in neurodegeneration and myopathy.