PKA-Mediated Proteasome Activation Protects Against Cardiac Remodeling and Heart Failure During Systolic Overload

Heart failure (HF) resulting from chronic systolic overload is associated with increased burden on proteostasis and impaired proteasome function. Phosphorylation of proteasome subunit RPN6/PSMD11 at Ser14 (pS14-RPN6) mediates the activation of 26S proteasomes by PKA, but its significance in common forms of heart disease remains obscure. Hence, we investigated the impact of genetic blockade of pS14-RPN6 on cardiac remodeling and HF during systolic overload, a common condition occurring in hypertension and aortic stenosis. We detected marked increases in ubiquitin conjugates, along with elevated levels of RPN6 and pS14-RPN6 proteins in myocardial tissues from human patients with nonischemic HF. Similarly, myocardial pS14-Rpn6 was increased in wild-type mice 2 and 4 weeks after transverse aortic constriction (TAC). Compared with wild-type littermates, mice with genetic blockade of pS14-Rpn6 resulting from germline knock-in of Rpn6^S14A (S14A mice) developed greater cardiac hypertrophy, fibrosis, left ventricular dysfunction, and lung congestion after TAC. Mechanistically, TAC induced comparable increases in 26S and 30S proteasomes at 2-week in both genotypes but, at 4-week post-TAC, the increases were remarkably attenuated in S14A mice. Meanwhile, TAC-induced increases in proteasome peptidase activities were significantly attenuated (2-week) or abolished (4-week) in S14A mice, accompanied by greater increases in total and K48-linked ubiquitin conjugates. Collectively, these findings demonstrate that pS14-RPN6 plays an essential role in upregulating myocardial proteasome activities and sustained upregulation of proteasome assembly, thereby assisting in maintaining proteostasis and protecting against maladaptive cardiac remodeling and HF during systolic overload.