Abstract Body: Introduction: Heart failure with preserved ejection fraction (HFpEF) is a complex, multi-organ syndrome responsible for 50% of all heart failure cases, with limited therapies to improve cardiac function. Disrupted protein homeostasis (proteostasis) is a recognized contributor to cardiac disease. We recently found that a mouse model of cardiometabolic HFpEF induced by a high-fat diet and L-NAME (2-hit stress) is characterized by increased overall protein synthesis and impaired autophagy, indicating a disruption in proteostasis. This imbalance is accompanied by mTORC1 activation, a key regulatory pathway governing these processes. However, its causative role in HFpEF pathogenesis and its potential as therapeutic target remains unclear.
Hypothesis: Cardiac-specific mTORC1 suppression would restore cardiac proteostasis and prevent HFpEF development.
Methods and Results: We generated an inducible (MerCreMer) cardiac-specific (aMHC) heterozygous knockout of Raptor (MCM-Raptor het KO), an essential subunit of the mTORC1 complex. Tamoxifen was administered four weeks prior to initiating the 2-hit stress to suppress mTORC1 during the pathogenesis of HFpEF. After 15 weeks of 2-hit stress, control mice developed cardiac hypertrophy and diastolic dysfunction, whereas MCM-Raptor het KO mice were protected, maintaining baseline heart size and normal diastolic function. Control mice also demonstrated pulmonary fluid accumulation, which was absent in MCM-Raptor het KO mice. Deuterium oxide labeling experiments revealed a trending reduction in myofibrillar and mitochondrial protein synthesis in MCM-Raptor het KO mice compared to controls. MCM-Raptor het KO mice also had higher LC3 II/I ratios, indicating protection against HFpEF-related suppression of autophagy. To dissect the mechanisms underlying the mTORC1 activation in HFpEF pathogenesis, we performed phospho-proteomics on wild-type mice after 5 weeks of 2-hit stress. These early-stage HFpEF mice had reduced phosphorylation of Sestrin1, an established mTORC1 regulator, along with increased total LC3 protein abundance, suggesting altered autophagy.
Conclusion: mTORC1 hyperactivation drives anabolic activation and autophagy decline in HFpEF pathogenesis, supporting mTORC1 inhibition as a promising therapeutic approach to improve cardiac function.