Research Projects

Dominant mutations in 7+ tRNA synthetase (aaRS) genes cause Charcot-Marie-Tooth disease (CMT), a rare neuromuscular disorder characterized by progressive degeneration of motor and sensory nerves. In 2021, it was reported that CMT-associated mutations in glycyl tRNA synthetase (GARS, CMT type 2D) and tyrosyl tRNA synthetase (YARS, dominant intermediate CMT type C) sequester tRNAs, causing ribosomes to stall, activating the integrated stress response (ISR) via the sensor kinase, GCN2. Genetic KO or pharmacological inhibition of GCN2 in mice with pathogenic Gars mutations reverses ISR activation and the neuropathy phenotype. REF1, REF2, REF3

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Recent work shows that the transcription factor, ATF4, is the primary driver behind CMT-related phenotypes in a preclinical mouse model of CMT2D. Overexpression of ATF4 in motor neurons (ATF4-OE) is sufficient to produce a CMT-like phenotype in mice, while motor neuron-specific ATF4 knockout (ATF4-KO) in Gars/CMT2D mice ameliorates relevant neuromuscular deficits, such as grip strength and nerve conduction velocity (NCV), and almost completely reversed gene expression changes caused by the Gars mutation. The manuscript describing this work is being prepared for publication.

While we have identified an aaRS-CMT disease mechanism (tRNA sequestration, ISR activation) and successfully tested a drug targeting this mechanism (GCN2iB) in mice, it is not known if the ISR is activated in the human disease. Since it is not feasible to obtain quality postmortem tissue samples from patients with an uncommon subtype of a rare disease to validate our disease mechanism, we will use human induced pluripotent stem cells (hiPSCs) that have been genetically engineered to express CMT-associated aaRS mutations and differentiate them into motor neurons and skeletal muscle in compartmentalized dishes. This system will enhance translatability of our research by validating our hypothesized mechanism in a human neuromuscular system and being used for high throughput testing of therapeutic strategies.

A mouse line with ataxia and muscle wasting was derived from a mutagenesis screen for neuromuscular phenotypes. Genetic mapping and whole genome sequencing revealed segregating mutations in two genes: Stk36Y1003N and Tuba4aQ176P. CRISPR-engineering these variants into C57BL/6J mice confirmed Tuba4aQ176P as the causative mutation, while Stk36 mice were overtly normal. The phenotype of Tuba4aQ176P mice includes Purkinje neuron degeneration, skeletal muscle wasting, and decreased bone density. The manuscript describing these mice is in preparation to submit for publication.