Abstract Body: Introduction: Macrophages influence cardiac injury and repair following ischemia-reperfusion (I/R). MTOR complex 1 (mTORC1) signaling regulates macrophage function, but its role in cardiac remodeling after I/R remains unknown. Here, we tested whether constitutive activation of macrophage mTORC1 via myeloid-specific TSC2 deletion (Lys2^Cre x TSC2^flx/flx, MΦ^TSC2-/-) alters cardiac inflammation, immune cell dynamics, and ventricular recovery after I/R injury.
Methods/Results: MΦ^TSC2-/- exhibited basal mTORC1 activation (increased p-S6K1 and p-4E-BP1) and feedback inhibition of mTORC2 (decreased p-AKT at Ser473 and Thr308). MΦ^TSC2- macrophages also displayed M1-like polarization upon LPS stimulation (increased TNF-α, NOS2, and IL-1β) and impaired M2 polarization in response to IL-4 (decreased Arg1, Retnla, and IL-10); both reversed by rapamycin. Despite these phenotypes in vitro, MΦ^TSC2-/- mice were protected against I/R injury, with improved ejection fraction (17.24%, P=1.67e-010), less ventricular dilation, hypertrophy, lung edema, and fibrosis. Similar results were obtained in mice depleted of neutrophils by anti LY6G antibody, highlighting macrophage-based effects. Infiltration of inflammatory macrophages (CCR2+MHCIIhi), LY6C+ monocytes, neutrophils, and CD8+ cytotoxic T cells were reduced at 5 and 14 days post-I/R. The same protocol was repeated in mice receiving rapamycin before and after I/R, and cardioprotection, immune modulation, and fibrotic suppression were all absent despite MΦ^TSC2-/-, confirming mTORC1 dependence. Recent studies have identified glycoprotein nonmetastatic melanoma protein B (GPNMB) as upregulated MΦ after I/R and involved with cardioprotection. Other studies have found increased GPNMB associated with mTOR activation in tumors linked to tuberous sclerosis. GPNMB was constitutively greater in MΦ^TSC2-/- macrophages and hearts after I/R, and this was eliminated by rapamycin.
Conclusion: Constitutive macrophage-specific mTORC1 activation via TSC2 deletion paradoxically limits cardiac inflammation, attenuates fibrosis, and preserves cardiac function post-I/R, lowering infiltrating inflammatory MΦ and enhancing GPNMB. These findings reveal a novel cardioprotective mTORC1-GPNMB signaling axis in macrophages that could pave future therapeutics for ischemic heart disease.