Abstract Body: The ubiquitin-proteasome system is the main proteolytic pathway for quality control (PQC) and regulatory degradation of proteins in living cells. Systolic overload, as seen in hypertension and aortic stenosis, is a leading cause of heart failure (HF). Proteasome functional insufficiency is implicated in HF caused by systolic overload. Previous studies have established that Ser14-RPN6 phosphorylation (pS14-RPN6) mediates the activation of 26S proteasomes by protein kinase A. However, the pathophysiological significance of pS14-RPN6 in systolic overload remains to be established.
We hypothesize that pS14-RPN6 helps maintain proteostasis and protects the heart during systolic overload.
We observed a significant increase in myocardial pS14-RPN6 and ubiquitin conjugates in human HF of ischemic or non-ischemic etiologies (p=0.020, p=0.034) and similarly in wild type (WT) mice after 2 weeks of transverse aortic constriction (TAC) (p<0.0001, p=0.001).
To investigate the role of pS14-RPN6 in vivo, our lab created Rpn6^S14A (S14A) knock-in mice where Ser14-Rpn6 phosphorylation is blocked. Here we have compared the responses to TAC between WT and S14A mice.
We found that TAC-induced increases in myocardial proteasome peptidase activities were significantly attenuated, and accumulation of ubiquitin conjugates exacerbated in S14A mice (p<0.0001; p<0.0005). Serial echocardiography revealed that S14A mice displayed significantly greater left ventricular (LV) end-diastolic posterior wall thickness and LV mass to body weight ratios at 1- and 12-week post-TAC (p=0.024, 0.0003; p=0.005, 0.01), and lower ejection fraction at 12-week post-TAC than WT mice (p=0.035). S14A mice also showed greater heart weight to tibial length (TL) and ventricular weight to TL ratios at 1 and 12-week post-TAC (1-week, p=0.043, 0.039; 12-week, p=0.007, 0.006). Wheat germ agglutinin and picrosirius red staining indicated a greater cardiomyocyte cross-sectional area and cardiac fibrosis in 12-week post-TAC S14A mice vs. WT mice (p<0.0001; p=0.005).
These novel findings demonstrate compellingly that myocardial pS14-RPN6 helps maintain proteostasis, curtails cardiac hypertrophy and delays heart failure occurrence during systolic overload