Abstract 12972: Trained Innate Immunity Through Toll-Like Receptor 4/Interferon Signaling Establishes Cardioprotection in a Stress-Induced Cardiomyopathy Model

Abstract

Introduction: Although extensively studied, the mechanisms responsible for the development of cardioprotection following preconditioning stimuli are not known. Our group showed that isoproterenol (ISO) mediated cardiac injury induces potent cardioprotection against a second ISO challenge for up to 5 weeks. The lack of an immune response after the second ISO dose and the durability of protection suggested that trained innate immunity might represent a novel mechanism for cardioprotection. Hypothesis: We hypothesized that ISO confers cardioprotection through trained immunity via Toll-like receptor 4 (TLR4) signaling that is activated by damage-associated molecular patterns released by ISO-induced cell necrosis. Methods: Wild-type C57BL/6J mice were intraperitoneally injected with TLR agonists or diluent (saline), and then 300 mg/kg ISO a week later. Mice were assessed before and after receiving ISO via serum cardiac troponin analysis, flow cytometry, and 2-D echocardiography. Results: The TLR4 agonist lipopolysaccharide (LPS), but not TLR1/2 or TLR3 agonists, induced cardioprotection as shown by decreased troponin I release (p<0.01), reduced cardiac neutrophil influx (p<0.05), and decreased left ventricle wall motion abnormalities (p<0.05) following ISO injury compared to saline treated controls . RNA sequencing identified interferon signaling as commonly upregulated (p<0.05) in mouse hearts a week after LPS or ISO pre-treatment. Blocking type I/II interferon receptors partially abolished LPS-induced cardioprotection, while pre-treatment with recombinant interferon β+γ conferred cardioprotection as shown by decreased troponin I release post-ISO (p<0.01). Given that β-glucan reverses the epigenetic tolerizing effects of LPS in immune cells, we treated mice with β-glucan following LPS pre-treatment and observed that the cardioprotection to ISO was abolished. Conclusions: Viewed together this study shows for the first time that TLR4/interferon signaling confers cardioprotection against ISO-induced injury. Our findings further suggest that this cardioprotective response may be secondary to TLR4 mediated epigenetic changes that dampen immune responses following tissue injury, consistent with trained innate immunity.