Protective role of PASH-1 in CGG repeat-driven RNA and protein toxicity in FXTAS
Fragile X-associated tremor/ataxia syndrome (FXTAS) is a neurodegenerative disorder caused by CGG repeat expansions (55–200 repeats) in the FMR1 gene. FXTAS pathogenesis arises from expanded-repeat mRNA, either directly through protein sequestration or indirectly through aberrant translation of a toxic polyglycine-containing peptide (FMRpolyG). Using a Caenorhabditis elegans model, we generated single-copy insertions of the human FMR1 5' UTR containing 0, 16, or 99 CGG repeats under a pan-neuronal promoter. Worms expressing 99 CGG repeats showed impaired motility, altered neuronal morphology, and disrupted miRNA homeostasis. Co-expression of PASH-1, the C. elegans ortholog of DGCR8, a miRNA-processing protein sequestered in FXTAS, mitigated both RNA- and peptide-mediated toxicity, restoring locomotion, neuronal structure, and miRNA regulation balance. Elimination of FMRpolyG alone reduced motor impairment by approximately 50%, indicating that RNA and protein toxicity contribute additively to pathogenesis. Furthermore, glial-specific expression of 99 CGG repeats did not impair motility but significantly disrupted olfactory behavior by altering adjacent neuronal cilia, revealing a non-cell-autonomous mechanism. These findings establish the protective role of PASH-1 against CGG-induced neurotoxicity and underscore the utility of C. elegans as a model for dissecting FXTAS mechanisms and exploring therapeutic strategies.