Abstract Body: Introduction: Mitochondrial function is impaired in the failing heart but the mechanisms causing mitochondrial dysfunction are not fully understood. Our recent finding indicates failure to activate mitophagy in HFpEF hearts leads to poor mitochondrial quality control and dysfunction which contributes to the cardiac phenotype of HFpEF. The goal of this study is to investigate the role of lysosomal function in cardiac mitochondrial quality control in HFpEF.
Methods: HFpEF was induced by high-fat diet (HFD) and Nω-nitrol-arginine methyl ester (L-NAME) treatment for 10 weeks in male mice. Mitophagy activity was examined by mtKeima mice and the release of mitochondria to extracellular space was assessed by quantifying mitochondria-containing extracellular vesicles (mitoEV) isolated from cardiac tissue. Lysosomal abundance and function in HFpEF hearts were evaluated using LysoTracker for mass, LysoSensor for pH, and DQ-BSA for proteolytic function, respectively. Mitochondrial function was assessed by measuring oxygen consumption rate (OCR). Rab7, a key regulator in lysosomal maturation and function, was quantified and targeted by a pharmacological activator (ML-098) in HFpEF mice.
Results: Cardiomyocytes isolated from HFpEF mice (n=5) exhibited normal lysosomal abundance but a higher lysosomal pH (up by 22%, p=0.0016) and a decline in proteolytic capacity (down by 46%, p=0.021) relative to those from Chow mice (n=5). Rab7 expression in HFpEF hearts (n=4) was reduced by 53% (p=0.0031) compared to Chow hearts (n=4). Despite evidence of mitochondrial stress, mitophagy didn't increase while mitoEV release doubled (p=0.0171) in HFpEF hearts, suggesting that lysosomal dysfunction may be responsible for the impaired intracellular pathway for mitochondrial quality control and the upregulation of mitochondria release. In HFpEF mice treated with ML-098 (n=3) versus DMSO (n=3), lysosomal abundance remained unaltered, but lysosomal pH decreased by 72% (p=0.0016), proteolytic capacity enhanced by 65% (p=0.0001), and OCR elevated by 92% (p=0.0095). ML-098 also attenuated mitoEV release by 41% (p=0.0171) and ameliorated diastolic dysfunction (E/e' ratio down by 29%, p<0.0001).
Conclusion: Our results show that lysosomal dysfunction in HFpEF hearts triggers abnormal mitochondrial quality control which impairs mitochondrial function and increases the release of mitoEV. Lysosome targeted therapy protects myocardial function and mitigates cardiac phenotype of the disease.