TNFR1 Expressing Exosomes are Critical Mediators of Pathological Immune Activation in the Spleen post-Myocardial Infarction

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Project Summary Immune activation is a hallmark of myocardial infarction (MI) and dictate infarct healing and left ventricular (LV) remodeling. It is established, both in preclinical and clinical studies, that immediately after infarction immune cells from the spleen and the bone-marrow (BM) egress into the systemic circulation and traffic to the ischemic hearts. This suggests that the damage signals from the injured hearts are communicated to the lymphoid and the hematopoietic tissues to initiate cardiac-specific immune responses. However, the mechanisms by which these signals are transferred to the immune-rich niches such as the spleen are not known. Recent studies have shown that exosomes, membranous vesicles of 30-100 nm size, are potent intercellular communication vehicles that can shuttle mRNA, miRNA, and proteins to the distant tissues for physiological and pathological immune activation. It is also known that circulating exosomal levels increase during myocyte damage and contain sarcomeric, cytosolic and mitochondrial proteins in their cargo. Despite this understanding, it is not known if exosomes also serve as the antigenic vehicles to carry damage- associated protein signals from the ischemic myocardium to the spleen for subsequent immune activation. Indeed, our preliminary results clearly show that intravenous administration of exosomes released by the ischemic hearts (as compared to sham) into the naïve mice induce i) systolic dysfunction (increased end- diastolic and end-systolic volumes and decreased ejection fraction), ii) gene expression of damage associated signals (S100A8, S100A9 and eotaxin) in the left-ventricles, iii) splenic remodeling, and iv) infiltration of innate and adaptive immune cells in the myocardium. Moreover, MI exosomes expressed tumor necrosis factor receptor-1 (TNFR1; and not TNFR2) on their membranes, a classical pro-inflammatory signaling molecule that have been shown to correlate with HF severity and cardiac dysfunction clinically. Importantly, intravenous injection of exosomes isolated from 1d MI TNFR1-/- mice failed to induce cardiac dysfunction in naïve mice suggesting a potent, and previously unknown, role of exosomal TNFR1 in mediating immune activation post-MI and cardiac dysfunction. Therefore, this led us to hypothesize that exosomes carry cardiac antigens to mediate splenic immune cell activation during MI, are critical for immune cell mediated pathological LV remodeling, and these effects are dependent upon the exosomal TNFR1 expression. Importantly, these are key cellular targets for immunomodulation. We will test this hypothesis by i) determining the pathophysiological role of the spleen in mediating exosomal processing post-MI, ii) defining the source and role of vesicular TNFR1 in exosome mediated cardiac dysfunction, and iii) determining the role of exosomal TNFR1 in mediating immunogenic signaling.