The role of complement C3 in the outcome of regional myocardial infarction

Abstract

Coronary heart disease leading to myocardial ischemia is a major cause of heart failure. A hallmark of heart failure is myocardial fibrosis. Using a murine model of myocardial ischemia/reperfusion injury (IRI), we showed that, following IRI, in mice genetically deficient in the central factor of complement system, C3, myocardial necrosis was reduced compared with WT mice. Four weeks after the ischemic period, the C3^-/- mice had significantly less cardiac fibrosis and better cardiac function than the WT controls. Overall, our results suggest that innate immune response through complement C3 plays an important role in necrotic cell death, which contributes to the cardiac fibrosis that underlies post-infarction heart failure.

Keywords: C4BP, C4 binding protein; Cardiac fibrosis. 1; Complement C3; DTBT, door-to-balloon time; FB, Factor B; FH, Factor F; FI, Factor I; IR, ischemia/reperfusion; IRI, ischemia/reperfusion injury; Ischemia/reperfusion injury (IRI); MBL, mannose binding lectin; Necrosis; TCC, terminal complement complex.

Fig. 1

Necrosis is decreased while apoptosis is increased in the hearts of C3^−/− mice after IR. (a) C3^−/− and WT mice (n = 6–8/group) were subjected to occlusion of the left anterior descending (LAD) artery for 1 h followed by reperfusion for 24 h. Next, propidium iodide (PI - enters cells through damaged cell membranes and binds DNA in necrotic cells) and blue fluorescent microspheres (BFM – present in un-occluded blood vessels) (the latter after re-occlusion of the LAD) were injected in vivo just prior to heart harvesting to delineate the infarcted area, and the area at risk (AAR) for necrosis (i.e., lacking BFM), respectively. After animal sacrifice, each ventricle was divided into four slices (top and bottom of each slice are adjacent). LPMI-positive necrotic tissue (bright red) was visualized immediately under a fluorescent microscope with a 2× objective lens. Non-ischemic tissue was defined by the blue fluorescence of BFM, the non-fluorescing tissue constituting ischemic tissue, the area at risk (AAR) for necrosis. The necrotic area was traced with dotted lines as an example. (b) The LPMI-positive necrotic area expressed as % of AAR. (c) C3^−/− mice had less cardiac fibrosis after IR. C3^−/− mice and control WT mice (n = 4 per group) underwent 1 h myocardial ischemia followed by reperfusion. 4 weeks after initial heart ischemia, mice were sacrificed and cardiac fibrosis in heart sections was assessed by the Masson Trichrome stain (VWR, PA). Blue arrows indicated the areas of positive staining for fibrosis. (d) Fibrotic areas were quantified and expressed as a percentage of the total area of heart sections. (e) C3^−/− mice had better LVEDD after IR. Cardiac functions were followed by echocardiography during the 4-week post-ischemia period. *indicates P < 0.05 between the C3^−/− and WT groups at 4 weeks' post-ischemia.