The heme oxygenase-1 (Hmox1; HO-1) pathway was tested for defense of mitochondrial quality control in cardiomyocyte-specific Hmox1 KO mice (HO-1[CM]–/–) exposed to oxidative stress (100% O2). After 48 hours of exposure, these mice showed persistent cardiac inflammation and oxidative tissue damage that caused sarcomeric disruption, cardiomyocyte death, left ventricular dysfunction, and cardiomyopathy, while control hearts showed minimal damage. After hyperoxia, HO-1(CM)–/– hearts showed suppression of the Pgc-1α/nuclear respiratory factor-1 (NRF-1) axis, swelling, low electron density mitochondria by electron microscopy (EM), increased cell death, and extensive collagen deposition. The damage mechanism involves structurally deficient autophagy/mitophagy, impaired LC3II processing, and failure to upregulate Pink1- and Park2-mediated mitophagy. The mitophagy pathway was suppressed through loss of NRF-1 binding to proximal promoter sites on both genes. These results indicate that cardiac Hmox1 induction not only prevents heme toxicity, but also regulates the timing and registration of genetic programs for mitochondrial quality control that limit cell death, pathological remodeling, and cardiac fibrosis.
Hagir B. Suliman, Jeffrey E. Keenan, Claude A. Piantadosi
(A–D) Heart total protein from WT/Cre and HO-1(CM)–/– mice pre- and posthyperoxia were quantified for LC3II/I, p62, Atg4B, and Beclin1 protein expression. Coomassie staining was used as loading controls. The ratio of LC3-II/LC3-I was significantly decreased in the HO-1(CM)–/– mice at 8d after hyperoxia. In contrast, in the WT/Cre mice, LC3-I expression was increased, and its conversion to LC3-II was significantly enhanced in the hearts after hyperoxia (mean ± SEM; horizontal bars represent mean values. *P < 0.05 for pre- vs. posthyperoxia; †P < 0.05 for WT/Cre vs. HO-1(CM)–/–; n = 6 per group; 2-way ANOVA).