Metabolic Reprogramming Mediates Macrophage Polarization After Myocardial Infarction

Background Macrophages play a critical role in left ventricular (LV) remodeling after myocardial infarction (MI), and limiting macrophage‐mediated inflammatory responses while enhancing reparative roles is a promising therapeutic strategy. Monocyte‐derived M1 macrophages mediate the early inflammatory response, while M2 macrophages mediate the later wound healing and scar formation phase. Metabolic reprogramming from glycolysis to mitochondrial oxidative phosphorylation mediates M1 to M2 polarization. We hypothesized that metabolic reprogramming occurs in macrophages over the course of post‐MI remodeling, and that blocking macrophage glycolysis attenuates post‐MI inflammation. Methods MI was induced in adult (16‐20 week old) male C57BL/6J mice by permanent ligation of the left coronary artery for 1, 3, or 7 days, and cardiac function was assessed by echocardiography. Macrophages were extracted from the LV infarct area by immunomagnetic sorting. Macrophage metabolic flux was assessed by Extracellular Flux Analysis (Seahorse); upon glucose administration, glycolysis was measured by extracellular acidification rate (ECAR) while glucose oxidation was measured by oxygen consumption (OCR). Leukocyte subtypes (neutrophils, monocytes, resident macrophages) were assessed by flow cytometry. Real‐time PCR was used to assess gene expression by relative mRNA levels. To specifically block macrophage glycolysis, LysMCre mice were crossed with mice floxed for Slc2a1, the major macrophage glucose transporter, to generate macrophage‐Slc2a1 null mice. Results MI led to LV contractile dysfunction (decreased ejection fraction; days 1, 3, and 7 versus day 0), thinning of the infarct wall (days 1, 3, and 7) and non‐infarct wall (day 7), and dilation (increased internal diameter at diastole and end‐diastolic volume; day 7). At day 1, increased neutrophils (Ly6G+) and monocytes (Ly6C hi ) were observed in the infarcted LV; at day 7, neutrophils and monocytes returned to baseline levels and the majority of macrophages were resident M2 subtype (Ly6C low versus day 1). Day 1 macrophages showed elevated glycolysis (ECAR versus day 0) and increased mRNA levels of the M1 marker Il1b (versus day 3 and 7); day 3 macrophages showed increased glycolysis (ECAR versus day 0) and decreased glucose oxidation (versus day 0); day 7 macrophages showed decreased glycolysis (ECAR versus day 1 and 3) and increased glucose oxidation (OCR versus day 1 and 3), and increased Slc2a1 mRNA, Krebs cycle genes ( Pdha1, Idh1/2, Sdha/b mRNA), pentose phosphate pathway genes ( G6pd2/x , Pgd , Rpia , Taldo1 mRNA), and Il10 (M2 marker) mRNA. In macrophage‐Slc2a1 null mice, macrophage glycolysis was decreased and glucose oxidation increased at day 3, and infarct levels of Il1b were decreased compared to floxed controls. Conclusions Our results indicate that time‐dependent macrophage metabolic reprogramming occurs over the MI remodeling process, and that blocking macrophage glycolysis may be a promising strategy for limiting post‐MI inflammation and adverse remodeling.