Abstract Body: Background: Splenic immune activation against cardiac damage associated molecular patterns (DAMPs) and their trafficking to the heart is a hallmark of myocardial infarction (MI). However, the vehicles that carry these injury signals are unknown.
Hypothesis: We hypothesize that extracellular vesicles (EVs) released by the ischemic heart carry injury signals and mediate splenic immune activation post-MI.
Approach: Mice were treated with an EV biogenesis inhibitor, GW4869 (5 mg/kg; i.p. daily), or vehicle starting a day before MI and continued for two days post-MI. At 3d and 8w post-MI trafficking of innate and adaptive immune cells from the spleen to the heart was measured. Survival, cardiac function, hypertrophy, fibrosis, and expression of inflammatory mediators was measured at 8w post-MI. EVs were isolated from MI (or sham) hearts using a langendorff system and adoptively transferred (AT) to naïve mice (180x10⁶ EVs, i.v, twice/day, 8 h apart for 2 days) to determine their pathological activity.
Results: EV biogenesis inhibitor (GW4869), as compared to vehicle, significantly increased the spleen weight and decreased efflux of splenic Ly6G⁺ neutrophils, Ly6c⁺ pro- and anti-inflammatory monocytes and CD11c⁺ dendritic cells, and CD4⁺, CD4⁺TNFα⁺, and CD4⁺IFNγ⁺ helper T-cell at 3d post-MI. A corresponding decrease in their trafficking to the infarcted hearts was also observed in GW4869 treated MI mice. Importantly, EV biogenesis inhibition early after MI, vs vehicle significantly improved cardiac function and decreased cellular hypertrophy, but not fibrosis, at 8w post-MI. AT of MI EVs (using Langendorff system), as compared to sham, resulted in increased cardiac levels of CCR2⁺MHC-II^hi infiltrating macrophages, CD11c⁺ DCs, and CD4⁺ and CD4⁺TNFα⁺ T-cells in naïve mice at 3d post-injection. Importantly, AT of MI EVs, as compared to sham, increased heart and LV weights, induced systolic dysfunction, cellular hypertrophy and fibrosis in naïve mice at 8w post-injection.
Conclusion: Our studies suggest that EVs carry injury-signals required for the trafficking of splenic immune cells to the heart post-MI. EV biogenesis inhibition can fine-tune immune responses to reduce inflammatory tissue-damage and promote healing post-MI.