Impact of synemin protein, an intermediate filament, in cardiac physiopathology

Abstract

Synemin is a protein belonging to the intermediate filament family involved in the cytoarchitecture of skeletal, cardiac and smooth muscle cells. Synemin copolymerizes with other intermediate filaments (desmin, vimentin) and interacts with sarcomeric and costameric proteins, acting as bridging protein. The tail domain of synemin ties the type II α regulatory (R) subunit of protein kinase A (PKA). Therefore, synemin is an A-kinase-anchoring protein (AKAP) that allows and modulates spatial and temporal targeting of its activity. We have previously found that mechanical overload of skeletal muscle induces greater hypertrophy of muscle fibres in synemin-knockout mice associated with an impairment of PKA signalling pathways. In humans, two missense mutations, located near the AKAP domain, have been recorded in patients with dilated cardiomyopathy. The aims are: (1) To analyze the role of synemin in cardiac hypertrophy; (2) To characterize the signalling pathways related to synemin in the hypertrophic response. Morphological (body and heart weights), cellular (immunostaining) and molecular (RT-qPCR, Western blot) analyzes were carried out on cardiomyocyte-specific synemin-knockout mice at 10, 30 and 60 days after tamoxifen injections. Then, we studied the response of the hypertrophic agent angiotensin II (Ang II) after 14 days delivered by Alzet osmotic mini-pumps in these mice. Our data show a decrease (> 50%) of synemin expression in heart of conditional knockout mice 10 days after tamoxifen injections. Thus, we observed an increase of stress gene expression (ANF, βMHC) and fibrotic markers (vimentin, coll3α1). Immunofluorescence of vimentin on heart sections reveals a strong increase of protein expression suggesting an activation of fibroblast proliferation. Chronic administration of Ang II does not show modification in gene expression profile between control and conditional synemin-knockout mice. At 30 and 60 days after tamoxifen injections, we observed the maintenance of mRNA synemin level indicating a compensatory expression of this protein by other cells in heart (fibroblasts, macrophages, endothelial and smooth cells). Our data indicate a crucial role of synemin as modulator in the physiopathological conditions. Moreover, the relevance of synemin-PKA coupling in cardiac hypertrophy will be characterized in the near future.