Abnormal expression of RNA polymerase II-associated proteins in muscle of patients with myofibrillar myopathies

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Abstract

Aims:

Myofibrillar myopathies (MFMs) are a group of inherited or sporadic neuromuscular disorders characterized morphologically by foci of myofibril dissolution, disintegration of the Z-disk and insoluble protein aggregates within the muscle fibres. The sequential events leading to muscle fibre damage remains largely unknown.

Methods and results:

We investigated the expression and the cellular localization of RNA polymerase II (RNAPII)-associated proteins (RPAPs) in muscle biopsies from patients with genetically proven and sporadic MFMs. Our data demonstrated that RPAP2, and to a lesser extent GPN1/RPAP4, are accumulated focally in the cytoplasm of MFM muscle fibres in which they co-localize with POLR2A/RPB1, the largest subunit of RNAPII, and correspond to αB-cystallin deposits in distribution and staining intensity. No abnormal staining for RPAP2 has been observed in muscle of patients with central cores, minicores and neurogenic target fibres.

Conclusions:

Together, these findings could provide new insights into the molecular pathogenesis of MFMs and suggest that RPAP2 immunostaining can be a useful diagnostic tool to depict protein aggregates in MFMs.

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