Correlating Protein Aggregate Structure with Cellular Function in Differentiated Muscle Cells: Discriminating Pathogenic from Non-Pathogenic Forms

Ageing has a major adverse impact on maintaining cellular proteostasis and age-related dysregulation leads to an increase in protein aggregation. Equivalently, the accumulation of aggregated proteins accelerates proteostasis impairment. Accumulation of protein aggregates and impaired proteostasis are hallmarks of ageing-associated neuromuscular disorders and tissue degeneration is predominantly in post-mitotic muscle and neuronal cells. A short alanine expansion mutation in the Poly(A) binding protein nuclear 1 (PABPN1) causes Oculopharyngeal muscular dystrophy (OPMD), a rare age-associated protein aggregation myopathy. PABPN1 is a vital RNA-binding protein but OPMD pathology is limited to skeletal muscles connected to nuclear aggregates. In contrast to the mutant PABPN1, the wild-type PABPN1 forms age-associated non-pathogenic aggregates. We generated an inducible muscle cell models for mutant and wild-type PABPN1 protein aggregation. By combining four different, but complementary, imaging modalities, covering micro- to nanoscale resolutions, we were able to characterise differences in structure and dynamics between pathogenic and non-pathogenic PABPN1 aggregates in differentiated muscle cells. These data allowed us to correlate the structure of aggregates to cellular function, providing important insights into how aggregates lead to cell dysfunction in post-mitotic cells. ### Competing Interest Statement The authors have declared no competing interest.