Endotoxin-tolerance modulates the immune microenvironment of transplanted hearts through macrophage epigenetic and metabolic reprogramming

Background Heart transplantation is the golden therapeutic option that prolongs the life of numerous patients with terminal heart failure. Despite advances in pharmacologic immunosuppression, long-term morbidity and mortality of patients undergoing heart transplantation remain high. In this study, we seek to a more efficient immunosuppressive regimens in heart transplantation. Methods We combined endotoxin-tolerance with murine transplant models (C57BL/6J, CAG-Cre; R26-tdTomato, CCR2-/-, TLR4-/- mice), and evaluated serum cardiac troponin I levels, echocardiography, and survival analysis of allografts. We performed single-cell RNA sequencing to profile the transcriptional landscapes of allografts, as well as quantitative polymerase chain reaction, Western blotting, Elisa, IHC and whole-mount staining to characterize cellular composition and communication. We performed BMDM (bone marrow-derived macrophage) endotoxin-tolerance model in vitro. Following the instructions of the Agilent Seahorse XFe24 kit, the mitochondrial function was analyzed. By reconstituting irradiated C57BL/6J mice with whole bone marrow from CAG-Cre; R26-tdTomato mice (Endotoxin-tolerance or not), chimeras were generated. Subsequently, C57BL/6J mice received an infusion of endotoxin-educated or non-educated bone marrow before the heart transplantation. We systematically analyzed human cardiac allograft atlas of patients. Results Here, we showed that endotoxin exposure had a cardioprotective effect manifested as the better angiogenic ability and more intact myocardial architecture against acute immune rejection of cardiac allografts. This protective phenotype is marked by an enriched population of CD206+ M2 macrophages in endotoxin-treated allografts, which indicated a M1 to M2 transition. The immune tolerance initiated an epigenetic and metabolic shift within allografts. Epigenetically imprinted macrophages significantly mitigate myocardial rejection. Through the multi-omics integration of our established heart transplantation biobank of human and mouse, we decoded the landscapes governing this tolerance-driven heart protection. Conclusions Our study unveils a new strategy for mitigating rejection, diverging from conventional immunosuppressive paradigms that primarily antagonize T cell-mediated adaptive responses. Our findings offer a promising therapy for longevity of cardiac allografts without long-time use of immunosuppressants, offering a more durable alternative for clinical translation in patients with end-stage heart failure.Figure 1.Graphical Abstract.Figure 2.reparative macrophage polarization