Aging induces declines in proteasome proteolytic efficiency but not abundance in myocardium of FVB/N and C57BL/6J mice

Background and Objectives: Proteasomes formed by a 20S proteasome capped by the 19S regulatory particle at one (26S) or both ends (30S) are responsible for the proteolytic step of the ubiquitin-proteasome system-mediated targeted degradation of most cellular proteins. Proteasome dysfunction is associated with a wide range of age-related diseases, including cardiac diseases. However, age-related changes in myocardial proteasome abundance, activity, and catalytic efficiency, as well as their sex-dependence are understudied. This study was conducted to systematically characterize changes in cardiac proteasome abundance and function across the lifespan of two commonly used mouse strains. Hypothesis: We hypothesized that aging reduces the abundance and/or catalytic efficiency of myocardial proteasomes. Methods: Crude protein extracts from ventricular myocardium of male (n=4, 4, 3) and female (n=4, 5, 3) FVB/N mice, and male (n=4, 4, 5) and female (n=5, 4, 4) C57BL/6J mice at 4-, 12-, and 24-month of age were subjected to native gel electrophoresis. In-gel chymotrypsin-like activity assays followed by Western blot analyses for the β5 subunit (Psmb5) of the 20S proteasome and Rpt2 of the 19S cap were performed, which allows quantification of the abundance and activities of 30S and 26S proteasomes and the abundance of 20S proteasomes in the same gel. Two-way (age, sex) ANOVA followed by Tukey’s post hoc tests were adopted for statistical comparisons. Results: Age-related but sex-independent increases in 20S and 30S abundance were detected in both FVB/N (p=0.002, 0.046) and C57BL/6J (p=0.002, 0.010) mice. In FVB/N mice, the 30S activity exhibited age- and sex-dependent variations (p=0.012, 0.027), but abundance-corrected 30S activity showed an age-dependent decline (p=0.005) without sex difference (p=0.162); 26S abundance was unaffected by age (p=0.587), but its activity showed an age-dependent decline (p=0.001), resulting in age-dependent decreases in abundance-corrected 26S activities (p=0.059). In C57BL/6J mice, 30S activity exhibited sex-dependent variation (p=0.007) without significant impact from age (p=0.341), but abundance-corrected 30S activity showed age dependence (p=0.0387) with no sex difference (p=0.8832); 26S abundance and activity were not affected by age (p=0.123, 0.189) but abundance-corrected 26S activity displayed age-dependent declines (p=0.015). No sex differences were observed in any 26S parameters in FVB/N or C57BL/6J mice. Conclusions: Aging increases myocardial proteasome abundance in FVB/N and C57BL/6J mice, but this is accompanied by a reduced catalytic efficiency in both sexes. It will be important to test whether this occurs in other organs and elucidate the mechanism underlying this age-related decline. Funding Sources: NIH grants R01AG072510, R01HL072166, and R01HL153614 (to X. Wang). 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.