TDP-43 proteinopathy alters the ribosome association of multiple mRNAs including the glypican Dally-like protein (Dlp)/GPC6

Amyotrophic lateral sclerosis (ALS) is a genetically heterogeneous neurodegenerative disease in which 97% of patients exhibit cytoplasmic aggregates containing the RNA binding protein TDP-43. Using a combination of RNA immunoprecipitations and tagged ribosome affinity purifications in Drosophila models of TDP-43 proteinopathy, we identified several TDP-43 dependent translational alterations including the glypican Dally like protein (Dlp), a wingless (wg/wnt) signaling component. Here we show that dlp mRNA is enriched in TDP-43 protein complexes and depleted from ribosomes in the context of TDP-43 proteinopathy. We also show that dlp mRNA is insolubilized and Dlp protein is significantly depleted from neuromuscular synapses while steady state transcript levels remain unchanged, consistent with mRNA sequestration and translation inhibition. Furthermore, we find that Dlp accumulates in cytoplasmic puncta in the Drosophila ventral cord, supporting the possibility of added axonal transport deficits, a well-established ALS phenotype. Notably, overexpression of dlp in Drosophila motor neurons is sufficient to mitigate TDP-43 dependent neurodegenerative phenotypes indicating that dlp is a physiologically relevant target of TDP-43. Finally, we show that similar to Dlp in the Drosophila ventral cord, the human ortholog GPC6 forms puncta-like structures in ALS patient spinal cords, further supporting a role for Dlp/GPC6 in TDP-43 induced neurodegeneration.