(A and B) Apoptotic RBCs were labeled with CFDA-SE and cocultured with mKO BMDMs (±1 μM mtT) for 3 hours. Representative histograms of total CFDA-SE⁺ cell counts (A) and quantitation of phagocytic macrophages (B) (n = 5/group). **P < 0.01, by 2-tailed Student’s t test. (C–H) mRNA levels in mKO BMDMs after mtT (1 μM) or vehicle treatment and coculturing with or without apoptotic RBCs for 8 hours. All values are presented as the fold change relative to untreated control BMDMs. Dashed lines indicate mRNA levels in the control BMDMs cocultured with apoptotic RBCs. Data are shown as the mean ± SEM. All experiments were repeated in BMDMs from 4–5 mice per group. *P < 0.05, **P < 0.01, and ****P < 0.0001, by 2-way ANOVA. (I) Survival rates of mKO mice with or without administration of mito-TEMPO (10 mg/kg day) out to post-MI day 7. *P < 0.05, by Gehan–Breslow–Wilcoxon test. (J) Cardiac rupture rate during the first 7 days after MI. (K) Representative immunofluorescence images of cardiac myofibroblast proliferation at post-MI day 3. Proliferating myofibroblasts were identified (white arrows) as PDGFRα⁺ (green) and EdU⁺ (pink). Nuclei are stained with Hoechst (blue). Scale bar: 25 μm. (L) Quantitation of PDGFRα⁺ and EdU⁺ cells as a percentage of total PDGFRα⁺ cells in the infarcted region (n = 4–5/group). Dots represent biological replicates, and data represent the mean ± SEM. (M) Immunofluorescence images of fibronectin in infarcted heart tissue at post-MI day 7. Scale bars: 25 μm. (N) Quantitative morphometry of immunostaining, in which the relative abundance of the stained area was calculated by averaging the results from multiple independent images of heart sections (n = 4/group). (O) Representative immunofluorescence images of α-SMA in the infarcted heart section at post-MI day 7: fibronectin (red), α-SMA (green), and Hoechst (blue). Scale bars: 50 μm. (P) Quantification of α-SMA⁺ levels in heart tissue at post-MI day 7 (n = 4/group). Dots represent biological replicates, and data represent the mean ± SEM.