Synemin, an intermediate filament expressed in skeletal, cardiac and smooth muscle, is associated with the protein kinase A (PKA) through its tail domain, acting as an A-kinase-anchoring protein (AKAP) that regulates the spatial and temporal targeting of PKA activity. Previously we found that mechanical overload of skeletal muscle induces fiber hypertrophy in synemin-knockout mice. Moreover, two missense mutations near the AKAP domain have been identified in human patients with dilated cardiomyopathy.

Our aim is to investigate the impact of synemin in cardiac hypertrophy by a combination of in vivo and in vitro models.

Functional, morphological and molecular analyzes were carried on cardiomyocyte-specific synemin-knockout mice (SynHKO) after 14 days of isoproterenol administration (30mg/kg/day) by Alzet mini-pumps. Moreover, we investigated the response of human SYNM-KO induced pluripotent stem cells (iPSC) – derived cardiomyocytes to stimulation with isoproterenol (10nM) or forskolin (10μM), both activators of PKA.

After isoproterenol administration, SynHKO mice exhibited increased heart weight (+14%) and cardiac cell width (+26%), significant fibrosis, and left ventricular dysfunction compared to controls. Then, we generated human SYNM-KO iPSC lines using CRISPR/Cas9 system. They are able to differentiate into beating cardiomyocytes with desmin and cardiac troponin expression. The human SYNM-KO cardiomyocytes, stimulated for 7 days with isoproterenol, exhibit an increase of their area (+52%). No noticeable effect was observed in the control group (Fig. 1). Measurements of the calcium flux and contraction kinetic 20minutes after forskolin stimulations indicated that SYNM-KO cardiac cells reached calcium and contraction peaks faster with a 24% increase of calcium decay time and beat interval compared to control cells. Finally, a variation in the phosphorylation profile of PKA targets was observed in these cardiomyocytes stimulated by forskolin.

These findings suggest a crucial role of synemin in cardiac remodelling and the loss of synemin-PKA coupling could trigger these alterations.