Abstract O-2: The Role of Post-translational Modifications in SERCA2a-related Cardiac Dysfunction

The cardiac sarcoplasmic reticulum calcium ATPase (SERCA2a) has become a validated target for the treatment of heart failure (HF). The relationship between reduced SERCA2a activity and decreases in protein expression in the setting of HF has been found to be non-linear and the toxic intracellular milieu in HF contributes to SERCA2a’s dysfunction. Post-translational modification (PTM) of SERCA2a has been recently described to as an important mechanism that can explain a reduction in SERCA2a activity in HF. Based on a comprehensive proteomic analysis, we found that the levels and activity of SERCA2a in cardiomyocytes are modulated in parallel with the levels of small ubiquitin-like modifier type 1 (SUMO-1). Moreover, our work has shown that SUMO-1 plays a critical role in protecting SERCA2a from pathological conditions (Kho et al, Nature, 2011). More recently, we demonstrated that SUMO-1 gene transfer and its combination with SERCA2a led to a reversal of HF in a porcine model of ischemic induced HF (Tilemann et al, Sci Transl Med, 2013). In our analysis of SERCA2a PTM in animal models of HF, we observed that SERCA2a is acetylated, and that this acetylation is more prominent in failing hearts. The acetylation of SERCA2a was validated by acetylation assays with acetyltransferase and HDAC inhibitors. We identified several lysine residues on SERCA2a for susceptible to acetylation. In addition, we found that Sirt1 enzyme deacetylates SERCA2a. Sirt1 down-regulation in HL-1 cells using small interfering RNA increased SERCA2a acetylation and thereby decreased its activity. Moreover, SERCA2a acetylation was increased when Sirt1 was depleted by recombinant adeno-associated virus carrying short hairpin RNA for Sirt1 in mice model, which reflected a decrease in intensity of interaction between Sirt1 and SERCA2a. Reduced acetylation was accompanied by an increase in SERCA2a SUMOylation in the heart. Decreased acetylation, combined with increased SUMOylation, of SERCA2a may contribute to the cardioprotective effects of Sirt1. Our results show that SERCA2a acetylation increases during HF and negatively impacts SERCA2a’s function, suggesting that the down-regulation of SERCA2a acetylation may afford a novel intervention in the setting of heart failure.