IL-10-STAT3-Galectin-3 Axis is Essential for Osteopontin-Producing Reparative Macrophage Polarization After Myocardial Infarction [Original Research Article]

Background—Both osteopontin (OPN) and galectin-3 have been implicated in phagocytic clearance of dead cells and reparative fibrosis during wound healing. CD206+ macrophages are involved in tissue repair through phagocytosis and fibrosis after myocardial infarction (MI). However, the relationship among OPN, galectin-3 and macrophage polarization in the context of MI remains unclear.Methods—The time course of Spp1 (encoding OPN) expression in the heart after MI showed a strong activation of Spp1 on day 3 after MI. To identify where in the body and in which cell’s the transcriptional activity of Spp1 increased after MI, we analyzed EGFP-Spp1 knock-in (KI) reporter mice on day 3 after MI. Results—The transcriptional activity of Spp1 increased only in CD206+ macrophages in the infarct myocardium and most of CD206+ macrophages have strong transcriptional activation of Spp1 after MI. The temporal expression pattern of Lgal3 (encoding galectin-3) in cardiac macrophages after MI was similar to that of Spp1, and OPN is almost exclusively produced by galectin-3hiCD206+ macrophages. Although both IL-4 and IL-10 were reported to promote CD206+ macrophages-mediated cardiac repair after MI, IL-10-, but not IL-4-, stimulated CD11b+ Ly6G− cells could differentiate into OPN-producing galectin-3hiCD206+ macrophages and showed enhanced phagocytic ability. Inhibition of STAT3 tyrosine phosphorylation suppressed IL-10-induced expression of intracellular galectin-3 and transcriptional activation of Spp1. Knockdown of galectin-3 suppressed their ability to differentiate into OPN-producing cells, but not STAT3 activation. The tyrosine phosphorylation of STAT3 and the appearance rate of galectin-3hiCD206+ cells on cardiac CD11b+Ly6G− cells in Spp1-KO mice were the same as those in WT mice. Spp1 KO mice showed vulnerable to developing post-MI LV chamber dilatation and the TUNEL-positive cells in the infarcted myocardium after MI remained higher in number in Spp1-KO mice than in WT mice. Conclusions—OPN is almost exclusively produced by galectin-3hiCD206+ macrophages, which specifically appear in the infarct myocardium after MI. IL-10-STAT3-galactin-3 axis is essential for OPN-producing reparative macrophage polarization after myocardial infarction and these macrophages contribute to tissue repair by promoting fibrosis and clearance of apoptotic cells. These results suggest that galectin-3 may contribute to reparative fibrosis in the infarct myocardium by controlling OPN levels.