Critical role of monocyte chemoattractant protein-1/CC chemokine ligand 2 in the pathogenesis of ischemic cardiomyopathy.

BACKGROUND: Cardiac interstitial fibrosis plays an important role in the pathogenesis of ischemic cardiomyopathy, contributing to systolic and diastolic dysfunction. We have recently developed a mouse model of fibrotic noninfarctive cardiomyopathy due to brief repetitive myocardial ischemia and reperfusion. In this model, fibrotic changes are preceded by marked and selective induction of the CC chemokine monocyte chemoattractant protein-1 (MCP-1). We hypothesized that MCP-1 may mediate fibrotic remodeling through recruitment of mononuclear cells and direct effects on fibroblasts. METHODS AND RESULTS: Wild-type (WT) and MCP-1-null mice underwent daily 15-minute coronary occlusions followed by reperfusion. Additional WT animals received intraperitoneal injections of a neutralizing anti-MCP-1 antibody after the end of each ischemic episode. Hearts were examined echocardiographically and processed for histological and RNA studies. WT mice undergoing repetitive brief myocardial ischemia and reperfusion protocols exhibited macrophage infiltration after 3 to 5 days and marked interstitial fibrosis in the ischemic area after 7 days, accompanied by ventricular dysfunction. MCP-1-null mice had markedly diminished interstitial fibrosis, lower macrophage infiltration, and attenuated ventricular dysfunction compared with WT animals. MCP-1 neutralization also inhibited interstitial fibrosis, decreasing left ventricular dysfunction and regional hypocontractility. Cardiac myofibroblasts isolated from WT but not from MCP-1-null animals undergoing repetitive myocardial ischemia and reperfusion demonstrated enhanced proliferative capacity. However, MCP-1 stimulation did not induce cardiac myofibroblast proliferation and did not alter expression of fibrosis-associated genes. CONCLUSIONS: Defective MCP-1 signaling inhibits the development of ischemic fibrotic cardiomyopathy in mice. The profibrotic actions of MCP-1 are associated with decreased macrophage recruitment and may not involve direct effects on cardiac fibroblasts.

Mast cell tryptase may modulate endothelial cell phenotype in healing myocardial infarcts.

Mast cells and macrophages infiltrate healing myocardial infarcts and may play an important role in regulating fibrous tissue deposition and extracellular matrix remodelling. This study examined the time-course of macrophage and mast cell accumulation in healing infarcts and studied the histological characteristics and protease expression profile of mast cells in a canine model of experimental infarction. Although macrophages were more numerous than mast cells in infarct granulation tissue, macrophage density decreased during maturation of the scar, whereas mast cell numbers remained persistently elevated. During the inflammatory phase of infarction, newly recruited leucocytes infiltrated the injured myocardium and appeared to be clustered in close proximity to degranulating cardiac mast cells. During the proliferative phase of healing, mast cells had decreased granular content and were localized close to infarct neovessels. In contrast, macrophages showed no selective localization. Mast cells in healing canine infarcts were alcian blue/safranin-positive cells that expressed both tryptase and chymase. In order to explain the pro-inflammatory and angiogenic actions of tryptase--the major secretory protein of mast cells--its effects on endothelial chemokine expression were examined. Chemokines are chemotactic cytokines that play an important role in leucocyte trafficking and angiogenesis and are highly induced in infarcts. Tryptase, a proteinase-activated receptor (PAR)-2 agonist, induced endothelial expression of the angiogenic chemokines CCL2/MCP-1 and CXCL8/IL-8, but not the angiostatic chemokine CXCL10/IP-10. Endothelial PAR-2 stimulation with the agonist peptide SLIGKV induced a similar chemokine expression profile. Mast cell tryptase may exert its angiogenic effects in part through selective stimulation of angiogenic chemokines.