Protein aggregation in inclusion body myositis, a sporadic form among protein aggregate myopathies, and in myofibrillar myopathies--a comparative study.
Protein aggregation has been identified in muscle fibres and, thus, in certain neuromuscular disorders. There are certain similarities between IBM and DRM: midlife or late-onset clinical symptoms, apparently of both sporadic and genetic background, morphologically autophagocytosis by vacuole formation, which is frequent in IBM though rare in DRM, and presence of tubulofilamentous aggregates, which is almost regular in IBM but scantily found in DRM as beta-amyloid components have been identified as accruing proteins, both in IBM and DRM. Previous studies pointed to the hypothesis that clear morphological borders between the two types of diseases--hereditary inclusion body myopathies/myositis and desmin-related myopathies may not exist. Therefore, we analysed and morphologically characterised the spectrum of proteins accumulating in both types of disorders in order to compare them and more clearly define similarities and dissimilarities between these two different groups of protein aggregate myopathies. Previous studies showed that there is an overlap among some of the proteins accruing in these diseases, but there might also be differences in that a large number of proteins found aggregated in desmin-related myopathies had not yet been described in IBM. The aim of describing the comparative protein profiles is to give more insights into the mechanism of protein aggregation within muscle fibres. We studied diagnostic muscle biopsies from 10 sIMB patients and 6 MM patients with histological, histochemical, enzyme histochemical, ultrastructural and immunohistochemical techniques using a large number of antibodies. We noticed a partial overlap of protein expression in the two cohorts of patients for sarcomeric, chaperone and mostly for cytoskeletal proteins. In both of the cohorts, the nuclear proteins were absent in the cytoplasmic bodies. A different pattern of immunolabelling was noted for trans-sarcolemmal proteins, constantly enhanced in the inclusion bodies in MM, but never found in IBM, except for delta-sarcoglycan, dysferlin and caveolin. The partial overlap among some of the proteins accruing in these diseases raise the hypothesis that clear nosological borders between s-IBM and MM may not always exist. There are also dissimilarities in the pattern of protein aggregation, suggesting that other additional factors are involved in the pathogenesis.