Structural Features of Pathogenic Aggregates Correlate with Cell Pathology in Differentiated Cells

The accumulation of intracellular protein aggregates is a hallmark of aging. In hereditary adult-onset neuromuscular diseases (NMDs), these aggregates are not only characteristic but also pathogenic, marking age-related neuromuscular disorders. The transition from age-associated non-pathogenic aggregates to disease-driving pathogenic aggregates remains poorly understood. Poly(A) binding protein nuclear 1 (PABPN1) forms non-pathogenic nuclear aggregates in post-mitotic aged cells. However, a short trinucleotide expansion in PABPN1 leads to muscle dysfunction in Oculopharyngeal Muscular Dystrophy (OPMD), where insoluble nuclear aggregates in skeletal muscle become a defining disease feature. Combining an array of advanced imaging modalities, we examined the morphological differences between nuclear aggregates formed by non-pathogenic and pathogenic PABPN1 variants. Through micro- to nanoscale analyses, we identified key structural differences in the aggregation propensity of these variants in both differentiated and undifferentiated muscle cells and linked these differences to mRNA cellular dysfunctions. Our findings provide new insights into the structural distinctions between pathogenic and non-pathogenic aggregates and their implications for cellular dysfunction in neuromuscular diseases.