Extracellular Vesicles Mediate Splenic Immune Activation and Trafficking to the Heart post-Myocardial Infarction

Immune activation against cardiac damage associated molecular patterns (DAMPs) and cardiac infiltration of innate and adaptive immune cells from hematopoietic tissues such as the bone marrow and the spleen is a hallmark of myocardial infarction (MI). However, the vehicles that carry DAMPs or the mechanisms that mediate this inter-tissue crosstalk are unknown. We hypothesize that DAMPs are carried in extracellular vesicles (EVs) that mediate immune activation in the extra-hematopoietic tissues post-MI. To test this, we treated male mice with an EV biogenesis inhibitor, GW4869, at a dose of 5 mg/kg (i.p., daily) or vehicle starting a day before MI. At 3 days post-MI, we harvested tissues and measured efflux of splenic innate and adaptive immune cells and their infiltration into the hearts using flow cytometry. Inhibition of EV biogenesis by GW4869 significantly inhibited splenic regression, as evident by increased tibia normalized spleen weight (3.73±0.21 mg vs 2.43±0.43 in vehicle; p=0.0179) when compared with vehicle treated 3d MI mice, and blunted efflux of CD45 + leukocytes. We also observed decreased cardiac levels of innate immune cells, such as CD11c + dendritic cells, CD11b + myeloid cells, Ly6G + neutrophils and Ly6C high monocytes, and adaptive immune cells, such as CD3 + T-cells, CD4 + helper T-cells (Th), and CD8 + cytotoxic T-cells in mice treated with GW4869 as compared to the vehicle treated MI mice indicating blunted immune cell recruitment. Significantly decreased levels of polarized CD4 + Th subsets expressing TNFα, IFNγ (Th1), IL-4 (Th2), FoxP3 (regulatory T-cells), or IL-17 (Th17) in the hearts upon treatment with GW4869 were also observed. These results were also supported by increased retention of innate and adaptive immune cells in the spleen, as evident by increased immune cell levels in GW4869 treated mice as compared to the vehicle. Our studies suggest that necrotic/apoptotic cardiomyocytes from infarcted hearts release EVs that carry signals, presumably DAMPs, required either for the activation or the egress of the immune cells from the spleen. Inhibition of EV biogenesis can be used to fine-tune immune responses post-MI to reduce inflammatory tissue-damage and promote healing post-ischemic injury. This work is supported by NIH grants HL153164 and HL167912. This abstract was presented at the American Physiology Summit 2025 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.