G Protein-Coupled Receptor 15 Expression Is Associated with Myocardial Infarction.

Beyond the influence of lifestyle-related risk factors for myocardial infarction (MI), the mechanisms of genetic predispositions for MI remain unclear. We sought to identify and characterize differentially expressed genes in early-onset MI in a translational approach. In an observational case−control study, transcriptomes from 112 early-onset MI individuals showed upregulated G protein-coupled receptor 15 (GPR15) expression in peripheral blood mononuclear cells compared to controls (fold change = 1.4, p = 1.87 × 10−7). GPR15 expression correlated with intima-media thickness (ß = 0.8498, p = 0.111), C-reactive protein (ß = 0.2238, p = 0.0052), ejection fraction (ß = −0.9991, p = 0.0281) and smoking (ß = 0.7259, p = 2.79 × 10−10). The relation between smoking and MI was diminished after the inclusion of GPR15 expression as mediator in mediation analysis (from 1.27 (p = 1.9 × 10−5) to 0.46 (p = 0.21)). The DNA methylation of two GPR15 sites was 1%/5% lower in early-onset MI individuals versus controls (p = 2.37 × 10−6/p = 0.0123), with site CpG3.98251219 significantly predicting risk for incident MI (hazard ratio = 0.992, p = 0.0177). The nucleotide polymorphism rs2230344 (C/T) within GPR15 was associated with early-onset MI (odds ratio = 3.61, p = 0.044). Experimental validation showed 6.3-fold increased Gpr15 expression in an ischemic mouse model (p < 0.05) and 4-fold increased Gpr15 expression in cardiomyocytes under ischemic stress (p < 0.001). After the induction of MI, Gpr15gfp/gfp mice showed lower survival (p = 0.042) and deregulated gene expression for response to hypoxia and signaling pathways. Using a translational approach, our data provide evidence that GPR15 is linked to cardiovascular diseases, mediating the adverse effects of smoking.

Cytokine-Mediated Alterations of Human Cardiac Fibroblast's Secretome.

Fibroblasts contribute to approximately 20% of the non-cardiomyocytic cells in the heart. They play important roles in the myocardial adaption to stretch, inflammation, and other pathophysiological conditions. Fibroblasts are a major source of extracellular matrix (ECM) proteins whose production is regulated by cytokines, such as TNF-α or TGF-ß. The resulting myocardial fibrosis is a hallmark of pathological remodeling in dilated cardiomyopathy (DCM). Therefore, in the present study, the secretome and corresponding transcriptome of human cardiac fibroblasts from patients with DCM was investigated under normal conditions and after TNF-α or TGF-ß stimulation. Secreted proteins were quantified via mass spectrometry and expression of genes coding for secreted proteins was analyzed via Affymetrix Transcriptome Profiling. Thus, we provide comprehensive proteome and transcriptome data on the human cardiac fibroblast's secretome. In the secretome of quiescent fibroblasts, 58% of the protein amount belonged to the ECM fraction. Interestingly, cytokines were responsible for 5% of the total protein amount in the secretome and up to 10% in the corresponding transcriptome. Furthermore, cytokine gene expression and secretion were upregulated upon TNF-α stimulation, while collagen secretion levels were elevated after TGF-ß treatment. These results suggest that myocardial fibroblasts contribute to pro-fibrotic and to inflammatory processes in response to extracellular stimuli.

Macrophage Migration Inhibitory Factor (MIF) Expression Increases during Myocardial Infarction and Supports Pro-Inflammatory Signaling in Cardiac Fibroblasts.

Macrophage migration inhibitory factor (MIF) is a pleiotropic cytokine known to play a major role in inflammatory diseases such as myocardial infarction (MI), where its expression increases. Cardio protective functions of MIF during ischemia have been reported. Recently, the structurally related MIF-2 was identified and similar effects are assumed. We wanted to further investigate the role of MIF and MIF-2 on inflammatory processes during MI. Therefore, we subjected mice to experimentally induced MI by coronary occlusion for one and five days. During the acute phase of MI, the gene expression of Mif was upregulated in the infarct zone, whereas Mif-2 was downregulated, suggesting a minor role of MIF-2. Simulating ischemic conditions or mechanical stress in vitro, we demonstrated that Mif expression was induced in resident cardiac cells. To investigate possible auto /paracrine effects, cardiomyocytes and cardiac fibroblasts were individually treated with recombinant murine MIF, which in turn induced Mif expression and the expression of pro-inflammatory genes in cardiac fibroblasts. Cardiomyocytes did not respond to recombinant MIF with pro-inflammatory gene expression. While MIF stimulation alone did not change the expression of pro-fibrotic genes in cardiac fibroblasts, ischemia reduced their expression. Mimicking the increased MIF levels during MI, we exposed cardiac fibroblasts to simulated ischemia in the presence of MIF, which led to further reduced expression of pro-fibrotic genes. The presented data show that MIF was expressed by resident cardiac cells during MI. In vitro, Mif expression was induced by different external stimuli in cardiomyocytes and cardiac fibroblasts. Addition of recombinant MIF protein increased the expression of pro-inflammatory genes in cardiac fibroblasts including Mif expression itself. Thereby, cardiac fibroblasts may amplify Mif expression during ischemia promoting cardiomyocyte survival.