Novel truncating Desmin mutation Arg150Stop disrupts structural integrity and cellular homeostasis by formation of...

Desminopathies are a heterogeneous group of myofibrillar myopathies defined by the presence of desmin-positive aggregates that compromise cytoskeletal integrity in skeletal and cardiac muscle. Although desmin knockout models and several truncating mutations typically result in a functional null phenotype without inclusion body formation, the molecular consequences of specific stop-gain variants remain poorly understood. In this study, we investigated the pathogenic mechanism of a novel Desmin (DES) nonsense mutation, NM_001927.4:c.448 C > T; p.(Arg150Stop), previously identified in an Indian patient with congenital myopathy. This premature stop codon lies within the Linker 1 A domain and is predicted to generate a truncated protein lacking the C-terminal tail. To delineate its functional consequences, we used two complementary experimental approaches: transient overexpression of the Arg150Stop mutant in skeletal and cardiac myocytes, and a CRISPR/Cas9-engineered homozygous Arg150stop cardiomyocyte line (Des^tr-CRISPR). Both models consistently revealed the formation of persistent aggregate-like structures, in striking contrast to desmin knockout systems that do not generate inclusions. These aggregate-like structures disrupted actin filament organization, impaired filament bundling, and induced organelle mislocalization. Biochemical analysis indicated that the aggregates were resistant to proteasomal degradation, yet they were partially cleared by autophagy, underscoring a role for protein quality control pathways in modulating disease severity. Importantly, the Des^tr-CRISPR line demonstrated aggregate-driven pathology at endogenous levels, confirming that this mutation acts through a toxic gain-of-function mechanism rather than simple loss of desmin function. Our findings establish the Arg150Stop variant as a mechanistically distinct truncating mutation that generates aggregation-prone protein rather than a null state. By reproducing hallmark features of desminopathy in a physiologically relevant human cell models, this work not only broadens the known pathogenic spectrum of DES variants but also highlights aggregate formation as a central driver of cellular dysfunction and a promising therapeutic target in desminopathies.