Toll-like receptor 4 induces trained innate immune tolerance in the heart in a model of stress-induced cardiomyopathy

AIMS: Although the ability of the heart to adapt to environmental stress has been studied extensively, the molecular and cellular mechanisms responsible for cardioprotection are not yet fully understood. In this study, we sought to elucidate these mechanisms for cytoprotection using a model of stress-induced cardiomyopathy. METHODS AND RESULTS: We administered Toll-like receptor (TLR) agonists or diluent to wild-type mice and assessed for cardioprotection against injury from a high intraperitoneal dose of isoproterenol (ISO) administered 7 days later. Cardioprotective effects were analysed through serum cardiac troponin I levels, immune profiling via flow cytometry, echocardiography, and multiomic single-nuclei RNA/ATAC sequencing. Pretreatment with the TLR4 agonist lipopolysaccharide (LPS), but not TLR1/2 or TLR3 agonists, conferred cardioprotection, as demonstrated by reduced cardiac troponin I leakage, decreased inflammation, preserved cardiac structure and function, and improved survival. Remarkably, LPS-induced tolerance was reversed by β-glucan treatment. Multiomic analysis showed that LPS-tolerized hearts had greater chromatin accessibility and up-regulated gene expression vs. hearts treated with LPS and β-glucan (reverse-tolerized). LPS tolerance was associated with up-regulation of interferon response pathways across various cell types, including cardiac myocytes and stromal cells. Blocking both Type 1 and 2 interferon signalling eliminated LPS-induced tolerance against ISO, while pretreatment with recombinant Type 1 and 2 interferons conferred cardiac protection. Multiomic sequencing further revealed enhanced cytoprotective signalling in interferon-treated hearts. Analysis of cell-cell communication networks indicated increased autocrine signalling by cardiac myocytes, as well as greater paracrine signalling between stromal cells and myeloid cells, in LPS-tolerized vs. reverse-tolerized hearts. CONCLUSION: LPS pretreatment confers cardiac protection against ISO-induced injury through TLR4-mediated Type 1 and 2 interferon signalling, consistent with trained innate immune tolerance. The observation that LPS-induced protection in cardiac myocytes involves both cell-autonomous and non-cell-autonomous mechanisms underscores the complexity of innate immune tolerance in the heart, warranting further investigation into this cardioprotective phenotype.