Impact Of Voluntary Wheel Running On ENOS And Muscle Microvasculature In A Model Of HFpEF

Heart failure with preserved ejection fraction (HFpEF) is a cardiometabolic syndrome characterized by exercise intolerance. Skeletal muscle hypoperfusion is cited as a mediator of exercise intolerance in HFpEF. Exercise is recommended for patients with HFpEF to improve exercise tolerance, however, the impact of exercise on skeletal muscle perfusion remains unclear. PURPOSE: To determine the impact of exercise on skeletal muscle capillarity and endothelial nitric oxide synthase (eNOS) in a “two-hit” murine model of HFpEF. METHODS: Eleven Male C57BL/6 N mice (9 weeks old) were treated with a high-fat diet and nitric oxide synthase inhibitor (L-NAME) for 10 weeks to induce HFpEF. After 5 weeks, the mice were randomly allocated to a sedentary condition (Sed, n = 5), or provided a wheel for voluntary exercise (Ex, n = 6). An additional five mice were allocated to sedentary normal chow control (C = 5). Immunohistochemistry and microscopy were conducted on liquid nitrogen cooled isopentane frozen quadriceps using antibodies for CD31, eNOS, Alexa Flour 488 and Alexa Flour 647. ANOVA and post hoc T-tests were used to detect group differences for eNOS (mean fluorescence), capillaries, muscle fiber count, and capillary-to-fiber ratio (C:F). RESULTS: ANOVA indicated differences between groups for eNOS (p = 0.0175). T-test showed eNOS mean fluorescence trending higher in Ex vs Sed mice (54.4 ± 8.7; 43.8 48 ± 12.8; p = 0.16). No differences were detected in Ex vs Sed mice for capillarity (216 ± 58.3; 216.6 ± 28.1; p = 0.98), muscle fiber count (95.1 ± 14.8; 93.5 ± 9.5; p = 0.83) or C:F (2.29 ± 0.5; 2.35 ± 0.3; p = 0.81). Differences were observed for C:F in C vs Sed (1.79 ± 0.30; 2.35 ± 0.36; p = 0.030) and capillarity (180.4 ± 25.9; 216.6 ± 28.1; p = 0.033). No differences were observed between C vs Sed for eNOS (34.7 ± 6.7; 43.8 48 ± 12.8; p = 0.10), muscle fiber count (102.3 ± 8.77; 93.5 ± 9.5; p = 0.16). CONCLUSIONS: Our results suggest a trend for an exercise-induced increased eNOS in skeletal muscle of mice with HFpEF, showing a positive benefit of voluntary wheel running on vascular function. Voluntary exercise did not lead to an increase in capillarization or C:F. Future, well-powered, studies are needed to elucidate the specific molecular pathways of exercise eNOS upregulation. P20GM135002, William Prescott (Pres) Foster