Abstract Body: Introduction: Cardiometabolic heart failure with preserved ejection fraction (HFpEF) results in severe exercise intolerance. Dysregulated skeletal muscle metabolism and mitochondrial function are key drivers of exercise intolerance in cardiometabolic HFpEF. Mitochondrial hydrogen sulfide (H₂S) generated by 3-mercaptopyruvate sulfur transferase (3-MST) exerts potent bioenergetic properties. We have recently shown that H₂S bioavailability is significantly attenuated in HFpEF. The role of H2S in skeletal muscle metabolism and exercise tolerance in HFpEF is currently unknown.
Hypothesis: We tested the hypothesis that the loss of skeletal muscle H₂S results in metabolic dysfunction in skeletal muscle and contributes to exercise intolerance in cardiometabolic HFpEF.
Methods: Skeletal muscle (gastrocnemius) from L-NAME + High Fat diet (“two-hit”) treated, and chow-fed control male mice (n=10/group) were assessed for free H₂S and 3-MST enzymatic activity using GC-chemiluminescence detection. Additionally, muscles were processed for RNA sequencing. Next, male global 3-MST knockout (KO) mice (n=12) and controls (n=10) were subjected to “two-hit” HFpEF for 10 weeks, and exercise tolerance was evaluated. Skeletal muscle (soleus and gastroc) was subjected to high-resolution respirometry and substrate oxidation of radiolabeled isotope (¹⁴C) for leucine and palmitate.
Results: Skeletal muscle H₂S levels (0.73 ± 0.18 vs. 1.0 ± 0.24 nmol/g/tissue) and 3-MST activity (0.46 ± 0.01 vs 0.57 ± 0.01 µmol/g/tissue/min) were significantly (p < 0.05) reduced in “two-hit” HFpEF mice compared to control mice. At the transcriptome level, 3-MST was one of the top 50 differentially regulated genes (i.e., reduced expression) in “two-hit” mice (Adjusted p=0.01). Genetic deficiency of 3-MST KO mice exacerbated (p < 0.05) exercise intolerance as measured by treadmill running distance (53 ± 24 vs. 138 ± 104 meters) vs. “two-hit” HFpEF genotype controls. Mitochondrial Complex I (low ADP) respiration was reduced by 23% in 3-MST KO HFpEF mice (p < 0.05). Genetic deficiency of 3-MST also reduced skeletal muscle leucine oxidation (58 ± 19 vs 84 ± 8; p = 0.01) and dramatically increased incomplete palmitate oxidation by 2.5-fold (p < 0.001) without changing complete oxidation.
Conclusion: We demonstrate that skeletal muscle mitochondrial H₂S is a critical regulator of metabolic function and exercise capacity in cardiometabolic HFpEF.