PKA-mediated activation of 26S proteasomes protects against post-MI cardiac remodeling

Heart failure (HF) is primarily driven by ischemic heart disease (IHD), including myocardial infarction (MI). Phosphorylation of RPN6 at Ser14 (pS14-RPN6) by the cAMP-dependent kinase (PKA) enhances proteasomes, but its pathophysiological importance in IHD remains unclear. This study tests the hypothesis that proteasome activation via pS14-RPN6 protects against myocardial ischemic injury and post-MI cardiac remodeling and HF. Genetic blockade of the activation of 26S proteasomes by PKA in Rpn6S14A/S14A knock-in (S14A) mice was previously validated. MI was surgically induced in wild-type (WT) and S14A mice. Myocardial pS14-Rpn6 and ubiquitinated protein levels were measured by western blots. Serial echocardiography was performed before and after (every two weeks for 12 weeks) surgery. Post-MI survival was compared between genotypes during acute and chronic phases. Left ventricular (LV) cavity volume was measured at terminal experiments. Following acute MI, pS14-Rpn6 was significantly increased in WT mice (3.58±0.56-fold vs. sham, p< 0.05). Compared to WT MI, S14A MI showed higher levels of total ubiquitinated (1.20±0.13 vs. 1.57±0.25-fold, p< 0.05) and K48-linked ubiquitinated proteins (1.31±0.14 vs. 1.53±0.21-fold, p< 0.05), indicating impaired proteasome function. In chronic post-MI hearts, S14A MI exhibited persistently higher total ubiquitinated (1.29±0.04 vs. 1.64±0.07-fold, p< 0.05) and K48-linked ubiquitinated proteins (1.32±0.07 vs. 1.64±0.11-fold, p< 0.05) versus WT MI, confirming sustained proteasome dysfunction. From 4 to 12 weeks post-MI, echocardiography revealed a progressive decline in systolic function in S14A mice compared with WT mice, as reflected by greater reductions in ejection fraction (EF) and fractional shortening (FS), and more progressive chamber dilatation in S14A MI vs. WT MI. At 12-week endpoint, S14A MI mice showed more decreases in EF (18.34±1.61% vs. 11.49±1.30%, p< 0.0001) and FS (8.40±1.19% vs. 5.22±0.59%, p< 0.0001), along with more increases in LV end-diastolic volume (152.0±25.06 vs. 214.0±34.31, p< 0.0001), and LV mass to body weight ratio (5.82±0.85 vs. 7.64±1.04, p< 0.0001). LV cavity volume was significantly larger in S14A MI hearts compared with WT MI at 12 weeks (46.60±1.60 vs. 55.60±2.42, p< 0.01). Acute post-MI survival did not differ between genotypes, but chronic survival was reduced in S14A MI mice (p< 0.05). These findings demonstrate that pS14-RPN6 is essential for myocardial proteostasis and protects against post-MI cardiac remodeling, indicating proteasome activation by PKA as a key cardioprotective mechanism and potential therapeutic strategy for IHD. Funding: This study is supported by NIH R01 grants (R01 HL072166-18, R01 HL153614-05, R01 AG072510-02). 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.