Rationale: The mechanistic target of rapamycin complex-1 (mTORC1) controls metabolism and protein homeostasis, and is activated following ischemic reperfusion (IR) injury and with preconditioning (IPC). However, studies vary as to whether this activation is beneficial or detrimental, and its influence on metabolism after IR is little studied. A limitation of prior investigations is the use of broad gain/loss of mTORC1 function, most applied prior to ischemic stress.  This can now be circumvented by regulating one serine (S1365) on tuberous sclerosis complex (TSC2) to achieve bi-directional mTORC1 modulation but only upon co-stimulation.

Objective: We tested the hypothesis that reduced TSC2 S1365 phosphorylation protects the myocardium against IR and IPC by amplifying mTORC1 activity to favor glycolytic metabolism.

Methods & Results: Mice with either S1365A (TSC2^SA; phospho-null) or S1365E (TSC2^SE; phosphomimetic) knock-in mutations were studied in vivo and ex vivo.  In response to IR, hearts from TSC2^SA mice displayed amplified mTORC1 activity and improved heart function as compared to WT or TSC2^SE hearts.  The magnitude of protection matched IPC. Reduced S1365 phosphorylation was also required for IPC, as TSC2^SE hearts gained no benefit and failed to activate mTORC1 with IPC. IR metabolism was altered in TSC2^SA, with greater extracellular acidification and lactate, and reduced long-chain acyl-carnitine levels during ischemia. Changing cardiac perfusion from glucose only to fatty acid (palmitate) + reduced glucose eliminated IR protection in TSC2^SA, converting it to a marked detriment.  By contrast, the IR response in WT and TSC2^SE hearts was unaffected by the change in perfusate. 

Conclusions: Thus, TSC2-S1365 phosphorylation status regulates myocardial substrate utilization, and its decline activates mTORC1 biasing metabolism from fatty acid oxidation to glycolysis to confer potent protection against IR.  This pathway is also engaged and reduced phosphorylation required for effective IPC.