Role of inflammation in postoperative atrial fibrillation

PROJECT SUMMARY / ABSTRACT Postoperative atrial fibrillation (poAF) is a common complication of cardiothoracic surgery with an incidence between 10 and 50%, which typically peaks on day 2-3 following surgery. Moreover, poAF is associated with an 8-fold higher risk of recurrent AF (recAF) after hospitalization. While there is evidence that inflammatory mediators play a central role in the pathogenesis of poAF, there remains a fundamental gap in our understanding of the molecular drivers of this condition. Our pilot data reveal increased levels of infiltrating macrophages (Ms) and proinflammatory cytokines such as interleukin-6 (IL-6) and M migration inhibitory factor (MIF) in the pericardial fluid of patients who develop poAF vs those who remain in SR. Our preliminary studies reveal that the pericardial fluid from poAF patients alters gene expression in atrial cardiomyocytes (ACMs) and induces a profibrotic phenotype in cultured fibroblasts. Our lab has developed a novel mouse model of poAF that mimics key aspects of this condition in humans, including spontaneous episodes of AF around postoperative days (POD) 2-4. Single cell RNA sequencing (scRNAseq) of non-myocytes from mice with and without poAF after thoracotomy identified Ms as the most altered cell type in the atria of poAF mice. Bioinformatics analysis suggests that C-C chemokine receptor 2 (CCR2) is important for monocyte mobilization out of the bone marrow and recruitment of Ms into the damaged atria after surgery. Our data also suggest that the cytokine MIF plays a role in arresting Ms in the atria. Finally, our pilot data suggest that the inflammatory response during the early post-operative days accelerates atrial substrate development as pseudotime trajectory analysis of scRNAseq data revealed IL-6 and MIF among the top altered genes involved in M-atrial cardiofibroblast signaling. IL-6 was shown to upregulate miR-31, which in turn suppresses the expression of the calcitonin receptor (CTR), which we recently linked to profibrotic remodeling. Elevated levels of miR-31 suppress Calcr (CTR gene) expression, while selective disruption of miR-31-binding to Calcr mRNA in mice reduced fibrosis and AF burden. We hypothesize that infiltrating M release proinflammatory cytokines that promote triggered activity in ACMs leading to poAF, while M-mediated activation of ACFs promotes fibrosis and recAF. We will test this hypothesis in three major aims: Aim 1 will determine which factors released from the heart into pericardial fluid in poAF patients promote triggered activity in ACMs and a profibrotic phenotype in ACFs. Aim 2 will test which chemokine(s) and receptor(s) are necessary for poAF development a mouse model of poAF. Aim 3 will assess how M-induced suppression of calcitonin signaling within ACFs promotes fibrosis and recurrent AF after poAF. These studies are expected to reveal how altered infiltrating Ms contribute to proinflammatory and profibrotic remodeling and atrial arrhythmia development. In line with NHLBI’s mission to translate basic discoveries into clinical practice, our mechanistic studies into the interplay between inflammation and fibrotic remodeling may lead to new treatments for postoperative and recurrent AF.