Inflammation and ECM (extracellular matrix) remodelling play important roles in LV (left ventricular) remodelling following acute MI (myocardial infarction). Previous studies show elevated plasma MMP (matrix metalloproteinase) levels in patients with acute MI, but their sources are not clear. The recruitment of mononuclear cells into the infarcted myocardium is critical for inflammatory responses, but their exact roles in LV remodelling have not been fully investigated, as it is difficult to isolate and study the function of regional inflammatory cells. To address these questions, we isolated PBMCs (peripheral blood mononuclear cells) from blood samples of patients with acute MI or stable angina, or healthy controls (n=14, 8 and 12 respectively). PBMCs were cultured for 24 h and the MMP9 level in the culture medium was measured by gelatin zymography, and MMP9 gene expression was measured by real-time PCR. Two superarrays (ECM and adhesion molecules, and common cytokines; 84 genes included in each array) were employed to screen gene expression profiles by PBMCs in five patients with acute MI and five controls. We found that MMP9 expression by PBMCs at both the mRNA and protein levels was increased 2-fold (both P<0.05) in patients with acute MI compared with the two control groups. Notably, MMP2 was not expressed by PBMCs. Superarray screening revealed that PBMCs not only expressed MMPs, TIMPs (tissue inhibitors of metalloproteinases) and matrix proteins, but also served as an important source of cell adhesion molecules, inflammatory cytokines and growth factors. A total of 42 genes were differentially expressed in patients with acute MI compared with controls. Expression of selected genes was confirmed by real-time PCR. In conclusion, PBMCs constitute a key cellular source for elevated plasma MMP9, but not for MMP2. PBMCs also contribute to systemic and regional inflammation and matrix remodelling in acute MI.

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