G.P.57 Differential proteomic analysis of protein aggregates in desminopathy

Abstract Desminopathy is a subtype of myofibrillar myopathies (MFM) caused by mutations in DES, the gene encoding desmin. A histopathologic hallmark of the disease is a massive protein aggregation within skeletal muscle fibers. The aim of our study was to elucidate the composition of aggregates in MFM patients with different desmin mutations by using a label-free mass spectrometry approach. Aggregates and control tissue from muscle biopsies of MFM patients with four different mutations in DES were collected by laser microdissection and analyzed by a combination of mass-spectrometry and spectral index calculation. Proteins with a ratio >1.8 (sum of peptides identified in aggregates compared to intraindividual controls) were accepted as accumulated in aggregates. Results of selected proteins were validated by immunofluorescence studies. Mass spectrometric data were searched against an extended human protein database to detect desmin mutations at the protein level. Three hundred and seventeen different proteins were identified and 98 of them showed an accumulation in aggregates. Aggregate compositions were more heterogenous than in other MFM subtypes, depending on individual mutations, but desmin was on top of the list of abundant proteins in all cases except of one. Immunolocalization findings were consistent with proteomic data. Three out of four desmin mutations were identified at the protein level. Our proteomic approach enabled the identification of many novel components of pathologic protein aggregates within skeletal muscle fibers of desminopathy patients. This provides new insights in the pathogenesis of the disease. Differences in aggregate composition in patients with different desmin mutations indicate diverse pathomechanisms, consistent with data of previous functional studies.