Loss of pS14-Rpn6 in S14A mice accelerated maladaptive remodeling and systolic dysfunction after transverse aortic constriction compared to wild-type mice (p<0.01 for reduced ejection fraction).
Does pS14-RPN6 protect the heart from maladaptive remodeling and maintain proteostasis during systolic overload?
Loss of pS14-Rpn6 disrupts proteostasis and accelerates maladaptive remodeling and heart failure during systolic overload, suggesting its upregulation is a compensatory protective mechanism.
Objective: Heart failure (HF) resulting from chronic systolic overload is characterized by increased proteotoxic stress (IPTS) and impaired ubiquitin proteasome system (UPS) function. The UPS is the main pathway for intracellular proteolysis. Recent evidence challenges the notion that substrate ubiquitination is the only rate-limiting step in UPS-mediated degradation and shows that proteasomal substrate cleavage can also be rate-limiting. Phosphorylation of the 19S proteasome (Psm) subunit RPN6 at Ser14 (pS14-RPN6) is the primary mechanism for PKA to activate the 26S Psm and can attenuate cardiac proteinopathy. However, its role in systolic overload remains unknown; so, this study was conducted to fill this gap. Hypothesis: We hypothesize that pS14-RPN6 is essential for maintaining proteostasis and protects the heart under systolic overload. Methods: Wild type (WT) and Rnp6S14A knock-in (S14A) mice underwent transverse aortic constriction (TAC), and cardiac remodeling was assessed by echocardiography, gravimetry, histology, and biochemical analyses. Proteostasis was examined by quantifying myocardial pS14-Rpn6, Psm abundance and peptidase activity, and total and K48-linked ubiquitin (Ub) conjugates. Human left-ventricular (LV) tissues from non-ischemic HF (NI-HF) patients and non-failing donors were also analyzed. Results: NI-HF myocardium showed increases in total RPN6 (p=0.021), pS14-RPN6 (p=0.019), total Ub-conjugates (p=0.004) and K48-linked Ub-conjugates (p=0.008), indicating IPTS with likely compensatory upregulation of pS14-RPN6 in human HF. Myocardial pS14-Rpn6 increased in WT mice 2 and 4 weeks after TAC (p< 0.005). Although showing no baseline difference, S14A mice displayed greater hypertrophy 1 week after TAC, with increased heart weight, LV wall thickness and LV mass (all p< 0.001) and greater expression of Nppa and Nppb (p=0.038, 0.036). Chronically, TAC induced more severe remodeling, including greater cardiomyocyte profile area, heart and ventricular weight to tibial length ratios, and cardiac fibrosis (all p< 0.001) and more severe systolic dysfunction evidenced by reduced ejection fraction and stroke volume (all p< 0.01), and increased lung congestion indicated by higher lung weight to tibia length ratio (p=0.023) in S14A mice compared to WT mice. Mechanistically, TAC-induced robust increases in myocardial 26S and 30S Psm abundance and activities (all p< 0.05) in WT mice but the TAC-induced Psm activation was significantly blunted, although the changes in abundance were less affected, by S14A, which resulted in greater increases in total and K48-linked Ub-conjugates at 2 and 4 weeks after TAC (p< 0.001). These findings demonstrate that loss of pS14-Rpn6 disrupts proteostasis, accelerates maladaptive remodeling, and HF in systolic overload. Conclusion: pS14-RPN6 is required for efficient Psm-mediated clearance of unwanted proteins during systolic overload and upregulation of pS14-RPN6 is likely a compensatory response during HF, suggesting increasing pS14-RPN6 as a potential therapeutic strategy. Acknowledgement: This study is in part supported by NIH R01HL072166, R01HL153614, and RF1AG072510. This abstract was presented at the American Physiology Summit 2026 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.
Ahammed et al. (2026) studied Heart failure and systolic overload. Rnp6S14A knock-in (S14A) vs. Wild type (WT) mice was evaluated on Cardiac remodeling, proteostasis, and systolic function after transverse aortic constriction. Loss of pS14-Rpn6 in S14A mice accelerated maladaptive remodeling and systolic dysfunction after transverse aortic constriction compared to wild-type mice (p<0.01 for reduced ejection fraction).