TSC2 serine 1365 phosphorylation improves liver metabolism to rescue murine heart failure with preserved ejection fraction

Rationale: The role of mechanistic target of rapamycin complex-1 (mTORC1) in heart failure with preserved ejection fraction (HFpEF) is unknown. The tuberous sclerosis complex 2 (TSC2) is the main inhibitor of mTORC1 which mediates translation, autophagy and metabolism.

Objective: To detect the role of mTORC1 in murine HFpEF and its effect and heart and liver metabolism.

Methods: We use KI mice expressing a phospho-mimetic TSC2 (S1365E, TSC2^SE) to induce mTORC1 inhibition (in TSC2^SE) only when pathologically hyperactivated hereby circumventing common genetic or pharmaceutical broad mTORC1 inhibition side-effects. To induce HFpEF, we feed TSC2^WT and TSC2^SE  mice with high-fat diet (HFD) and/or N[w]-nitro-l-arginine methyl ester (L-NAME) via the drinking water for a total of 15 weeks, or cross them into a db/db background (genetic obesity). Metabolic cages are used to determine of CO₂ elimination (VCO2), and rate of O₂ consumption (VO2), treadmills to detect exercise capacity. We use lung weight to assess lung congestion. We measured glucose tolerance via intraperitoneal glucose injection and use magnetic resonance imaging for detection of body composition. We performed echocardiography to evaluate diastolic and systolic function.

Results: Only in the 2-hit combined HFD plus L-NAME HFpEF model, but not in HFD alone or in a db/db background, TSC2^SE mice have not only improved signs of HFpEF but also improved liver homeostasis: in TSC2^SE we see improved exercise capacity (running), improved VO₂ and VCO₂ and improved lung congestion as well as diastolic function. Additionally liver showed markedly reduced microsteatosis and improved liver weight characterized by improved glucose tolerance and less circulating cholesterols in TSC2^SE mice. Ribosomal (and total) RNA sequencing of liver tissue revealed improved hepatic metabolism and altered translatome likely through mTORC1 inhibition by TSC2 phosphorylation. Intriguingly, proteomics of HFpEF hearts reveals altered abundance of proteins usually secreted by the liver and not to be found in the heart suggesting a liver-heart cross-talk.

Conclusions: TSC2^SE mutant mice characterized by inhibited mTOR signaling are protected in a murine model of HFpEF likely through an altered liver metabolism and translatome.