Metabolic reprogramming mediates macrophage polarization following myocardial infarction

Macrophages play critical roles in mediating inflammation and cardiac remodeling after myocardial infarction (MI). Metabolic transitioning between glycolysis and oxidative phosphorylation (OXPHOS) is associated with macrophage polarization to pro‐inflammatory (M1) and anti‐inflammatory (M2) phenotypes. M1 macrophages rely on glycolysis and M2 macrophages rely on OXPHOS. However, the role of metabolism in macrophage polarization after MI is unknown. Thus, we hypothesized that inhibiting glycolysis after MI would promote macrophage polarization to an anti‐inflammatory M2 phenotype and improve post‐MI outcomes. MI was induced in adult male C57BL/6J mice by permanent left anterior coronary artery ligation for 1, 3, and 7 days. To directly assess macrophage glycolysis and OXPHOS after MI, macrophages (CD11b+Ly6−) were isolated from the infarct region (n=3 for D1 and D3) or healthy control hearts (day 0 or D0; n=3) by immunomagnetic separation or flushed from the peritoneal cavity and subjected to Seahorse analysis to determine the extracellular acidification rate (ECAR) and the oxygen consumption rate (OCR). To assess the role of macrophage metabolism, a separate group of mice was administered dimethyl fumarate (DMF, 15mg/kg I.P.) or vehicle solution as a control, for the first 3 days after MI to inhibit macrophage glycolysis during the acute inflammatory response, and studied at day 7. DMF is a clinically approved anti‐inflammatory drug with immunometabolic properties. Left ventricular (LV) function was assessed by echocardiography. Infarct macrophage phenotypes were determined by flow cytometry. By Seahorse analysis, DMF inhibited glycolysis in vitro in peritoneal macrophages. The basal glycolytic ECAR was increased in macrophages at D1 (0.3±0.1 mPh/min D0 versus 4.2±1.0 mPh/min D1) and further increased at D3 (8.9±1.2 mPh/min D3). Maximal glycolytic capacity was similarly increased in D1 and D3 versus D0 (6.0±1.3 mPh/min D1 and 10.8±1.7 mPh/min D3 versus 0.4±0.5 mPh/min D0). No differences were observed in basal, maximal or spare capacity OCR, indicating that increased glycolysis alone mediates macrophage polarization after MI. Treatment with DMF improved the post‐MI survival rate after 7 days by 11%. Of the surviving mice (n=3 each group), no differences in the LV, RV, lung, or spleen mass were observed. By echocardiography, DMF did not affect LV diastolic or systolic volumes, ejection fraction, or anterior wall thinning, but prevented MI‐induced LV posterior wall thinning (0.73±0.14 mm DMF versus 0.42±0.09 mm vehicle). By flow cytometry, DMF increased the number of M2 macrophages (CD45+CD11b+Ly6G−CD206high) in the infarcted region (62±13% DMF versus 40±2% vehicle). In conclusion, macrophage metabolic reprogramming underlies polarization after MI, and targeting macrophage metabolism may improve post‐MI LV remodeling and survival.