Relationship Between Coronary Atheroma, Epicardial Adipose Tissue Inflammation, and Adipocyte Differentiation Across the Human Myocardial Bridge

Abstract

Background Inflammation in epicardial adipose tissue (EAT) may contribute to coronary atherosclerosis. Myocardial bridge is a congenital anomaly in which the left anterior descending coronary artery takes a “tunneled” course under a bridge of myocardium: while atherosclerosis develops in the proximal left anterior descending coronary artery, the bridged portion is spared, highlighting the possibility that geographic separation from inflamed EAT is protective. We tested the hypothesis that inflammation in EAT was related to atherosclerosis by comparing EAT from proximal and bridge depots in individuals with myocardial bridge and varying degrees of atherosclerotic plaque. Methods and Results Maximal plaque burden was quantified by intravascular ultrasound, and inflammation was quantified by pericoronary EAT signal attenuation (pericoronary adipose tissue attenuation) from cardiac computed tomography scans. EAT overlying the proximal left anterior descending coronary artery and myocardial bridge was harvested for measurement of mRNA and microRNA (miRNA) using custom chips by Nanostring; inflammatory cytokines were measured in tissue culture supernatants. Pericoronary adipose tissue attenuation was increased, indicating inflammation, in proximal versus bridge EAT, in proportion to atherosclerotic plaque. Individuals with moderate‐high versus low plaque burden exhibited greater expression of inflammation and hypoxia genes, and lower expression of adipogenesis genes. Comparison of gene expression in proximal versus bridge depots revealed differences only in participants with moderate‐high plaque: inflammation was higher in proximal and adipogenesis lower in bridge EAT. Secreted inflammatory cytokines tended to be higher in proximal EAT. Hypoxia‐inducible factor 1a was highly associated with inflammatory gene expression. Seven miRNAs were differentially expressed by depot: 3192‐5P, 518D‐3P, and 532‐5P were upregulated in proximal EAT, whereas miR 630, 575, 16‐5P, and 320E were upregulated in bridge EAT. miR 630 correlated directly with plaque burden and inversely with adipogenesis genes. miR 3192‐5P, 518D‐3P, and 532‐5P correlated inversely with hypoxia/oxidative stress, peroxisome proliferator‐activated receptor gamma coactivator 1‐alpha (PCG1a), adipogenesis, and angiogenesis genes. Conclusions Inflammation is specifically elevated in EAT overlying atherosclerotic plaque, suggesting that EAT inflammation is caused by atherogenic molecular signals, including hypoxia‐inducible factor 1a and/or miRNAs in an “inside‐to‐out” relationship. Adipogenesis was suppressed in the bridge EAT, but only in the presence of atherosclerotic plaque, supporting cross talk between the vasculature and EAT. miR 630 in EAT, expressed differentially according to burden of atherosclerotic plaque, and 3 other miRNAs appear to inhibit key genes related to adipogenesis, angiogenesis, hypoxia/oxidative stress, and thermogenesis in EAT, highlighting a role for miRNA in mediating cross talk between the coronary vasculature and EAT.

Epicardial Adipose Tissue as an Independent Cardiometabolic Risk Factor for Coronary Artery Disease

“…Since then, several studies have identified genes encoding other inflammatory adipokines, such as resistin and chemerin [36,52]. Due to the lack of anatomic intervening barrier, inflammatory cytokines expressed by EAT affect coronary arteries through paracrine and vasocrine pathways [53]. Lately, it has been shown that elevated abnormal EAT proteasome leads to thicker EAT layer, more intense chronic inflammation and therefore more severe CAD [15,44,54].…”

“…Epicardial adipose tissue has also been gaining interest regarding oxidative stress [53]. Recently, it has been proposed that epicardial fat in humans suffering from CAD presents higher concentration of reactive oxygen species (ROS) [58].…”

Epicardial Adipose Tissue in Patients with Coronary Artery Disease: A Meta-Analysis

“…Epicardial adipose tissue (EAT) is a type of visceral adipose tissue surrounding the myocardium and visceral layer of the pericardium [ 7 , 8 ]. In distinct conditions, EAT can secrete pro- and anti-inflammatory factors (e.g., TNF-α, IL-6, adiponectin, and leptin) through paracrine or endocrine [ 9 , 10 , 11 ]. Evidence shows that EAT is involved in the local regulation of myocardial and coronary function by modulating lipid metabolism and energy homeostasis [ 12 ].…”

Weight Loss and Fat Metabolism during Multi-Day High-Altitude Sojourns: A Hypothesis Based on Adipocyte Signaling

“…The time, duration and dose factors of this mechanism and its implications for an adapted nutrition for altitude sojourns in the human metabolism are not completely understood [19]. Research at a cellular level on isolated human adipocytes in their reaction to hypoxia most often concentrates on HIF-mediated inflammatory signaling in a long-term hypoxic state in regard to obesity, cancer or cardiovascular diseases [20][21][22][23]. However, there is some research on isolated human adipocytes, which could give hints for a time dose-response-curve of leptin and GLUT1 up-and downregulation mediated by levels of HIF 1 α in hypoxia and its effects on appetite of high fat saturated nutrients at high altitude [24].…”