Matrix metalloproteinase-7 in platelet-activated macrophages accounts for cardiac remodeling in uremic mice

Heart failure is the leading cause of mortality in patients with end-stage renal disease, and progressive cardiac remodeling is the key pathological basis of heart failure. However, the mechanism by which uremia-induced cardiac remodeling occurs is not well understood. Here, we showed that platelets were significantly activated in 5/6 nephrectomy-operated mice, and cardiac remodeling in the uremic mice was significantly improved when platelets were effectively depleted. A cardiac fibrosis-related gene expression profile revealed that Mmp7, encoding matrix metalloproteinase-7 (MMP-7), exhibited the greatest degree of downregulation in the hearts of uremic mice with platelets depleted. Using fluorescence-activated cell sorting, we discovered that MMP-7 was mainly expressed in M1 and M4 cardiac macrophages, although it was also extensively expressed in heart tissues. For the upstream therapeutic target, neutralization of platelet factor 4 (PF4) with monoclonal antibody not only significantly suppressed M4 macrophages in vivo, but also notably prevented collagen destruction in heart tissues. For the downstream therapeutic target, the pharmacological inhibition of MMP-7 with selective inhibitor failed to notably affect the platelet status, but significantly reduced heart collagen destruction in mice, a further indication that MMP-7 is a crucial downstream molecular target of platelet activation. In vitro, platelets interacted with macrophages and drove them to upregulate MMP-7 expression via free molecules, especially PF4. Taken together, the data suggest that MMP-7 is a key downstream target of platelet activation during uremia. Thus, MMP-7 is a likely and novel therapeutic target for intervention of cardiac remodeling during uremia.