S100A8/A9 drives persistent transcriptional alterations of epigenetic enzymes underlying trained immunity in experimental myocardial infarction
A Manea, M L Vlad, R G Mares, S A Manea, M B Preda, L F Dudu, M R Fueriu, M Simionescu, A SchiopuAbstract
Background
Trained immunity (TRIM), a complex epigenetic-based immunological process leading to transcriptional and functional reprogramming of innate immune cells, mediates the amplification of inflammatory response in myocardial infarction (MI). TRIM is broadly characterized by increased propensity of innate immune cells to abruptly produce high level of pro-inflammatory cytokines in response to a subsequent exposure of the cells to a wide spectrum of cardiovascular risk factors, long after the initial ischemic myocardial injury. Histone methylation regulates TRIM-associated genes. The expression pattern of archetypal histone methyltransferases leading to the imprinting of specific histone marks across specific genomic regulatory elements remain poorly understood.
Purpose
We hypothesized that alarmin S100A8/A9 secreted by neutrophils during the acute phase of MI could induce gene expression alterations of specific TRIM-related histone methyltransferases.
Methods
Permanent ligation of the left coronary artery (LCA) was employed to establish MI condition in female C57BL/6J mice. Sham-operated and MI mice were randomly assigned into experimental groups to receive 30 mg/kg ABR-238901, a selective S100A8/A9 inhibitor, or its vehicle for three consecutive days. MI condition was confirmed by echocardiographic assessment of cardiac parameters. Mice were sacrificed at 3 and 21 days after LCA ligation, to harvest the left ventricle (LV) and the bone marrow. Leukocytes (CD45+ cells) were isolated from the bone marrow of mice using a CD45 positive selection kit. CD45+ cells were analyzed by flow cytometry. LV tissue samples and CD45+ cells were subjected to strand specific mRNA sequencing and real-time PCR analysis.
Results
Whole transcriptome data analysis and real-time PCR assays revealed significant gene expression up-regulation of key histone methyltransferases underlying TRIM, namely, SET7, MLL1, and KMT5A in both ischemic LV and CD45+ cells, in the acute inflammatory phase of MI. A similar mRNA expression pattern was determined for DOT1L, a unique histone methyltransferase typically associated with active and sustained gene transcription, in the absence of a specific histone demethylase counterpart. Persistent increases in SET7, MLL1, and KMT5A mRNA levels were determined in bone marrow-derived CD45+ cells of MI mice at 21 days post-MI. S100A8/A9 blockade mitigated the gene expression up-regulation of selected histone methyltransferases in ischemic LV and CD45+ cells in acute and reparatory phase post-MI.
Conclusion
Alarmin S100A8/A9 contributes to persistent gene expression up-regulation of key epigenetic enzymes underlying TRIM in MI. Identifying molecular triggers, mediators, and specific epigenetic mechanisms of TRIM could lead to the development of effective supportive therapeutic interventions to reduce the incidence of long-term complications post-MI, such as accelerated atherosclerosis, recurrent MI, and heart failure.