Protective role of PASH-1 in CGG repeat-driven RNA and protein toxicity in FXTAS.

Fragile X-associated tremor/ataxia syndrome (FXTAS) is caused by CGG repeat expansions in FMR1, leading to RNA toxicity and toxic FMRpolyG peptide from abnormal translation. 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 a miRNA-processing DGCR8 sequestered in FXTAS, mitigated both RNA- and peptide-mediated toxicity, restoring locomotion, neuronal structure, and miRNA regulation balance. Removing FMRpolyG improved movement by ∼50%, suggesting RNA toxicity is the primary pathogenesis. Glial 99 CGG expression altered nearby neuronal cilia, disrupting olfaction without affecting movement, revealing non-cell-autonomous toxicity. These findings establish the protective role of PASH-1 against CGG-induced neurotoxicity and underscore C. elegans as a model for dissecting FXTAS mechanisms and exploring therapeutic strategies.