Dual interplay between desmin phosphorylation and dysregulated autophagy in heart failure

Abstract

Post-translational modifications (PTMs) of sarcomeric proteins could participate to left ventricular (LV) remodeling and contractile dysfunction leading in advanced heart failure (HF) with altered ejection fraction.Using an experimental rat model of HF (ligation of left coronary artery) and phosphoproteomic analysis, we highlighted an increase of phosphorylated desmin on serine residues in LV of 2 month-HF rats, dependent of PKCζ and GSK3β. We verified the desmin phosphorylation profile by Phos-Tag™ gel and observed that desmin is mainly expressed in insoluble fraction of LV of HF rats. Electron microscopy shows alteration of sarcomere in LV of HF rats due to desmin filaments desorganisation and immunofluorescence accumulation of desmin aggregates that could be toxic in cardiomyocytes. We then analyzed whether the autophagic pathways (macro-autophagy and chaperone-mediated autophagy (CMA)) may be involved in phosphorylated desmin clearance in our experimental model of HF. We found a decrease of macroautophagy processes (LC3II/LC3I, p62, beclin-1) throughout LV remodeling that may participate to hyperphosphorylated desmin accumulation. We identified that CMA is activated throughout the LV remodelling post-MI with increased CMA markers (Lamp-2a, hsc70, hsp90) in LV of HF rats suggesting that CMA may be involved in the clearance of aggregates of phosphorylated desmin. Bioinformatical analysis identified desmin as a new CMA substrate with 4 KFERQ motifs conserved in the aminoacid sequence of rat, mouse, bovine, pig, danio Rerio and human species. We then developed an in vitro model of CMA induction in neonate cardiomyocytes with geldanamycin. We observed increased levels of hsc70 and hsp90 and colocalization of desmin and Lamp2a that suggests desmin lysosomal sequestration by PLA technique. CMA activation did not induce changes in insoluble desmin but decreased levels of soluble desmin and phosphorylated soluble desmin. Conversely, preliminary data on inhibition of CMA with Lamp2a siRNA only induced increase of soluble desmin and phosphorylated soluble desmin. Our data suggest for the first time that CMA is able to clear monomeric phosphorylated soluble desmin but is not sufficient for intracellular clearance of phosphorylated desmin aggregates in the experimental model of ischemic HF. We could speculate that induction of early CMA activation in post-infarction might be a therapeutic approach to fight against desmin aggregates in order to maintain cardiomyocyte survival.