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) Heart sections were stained with Masson’s trichrome to locate collagen (blue, fibrous collagen), which revealed extensive fibrosis of the left ventricle of HO-1(CM)–/– mice, mainly after hyperoxia (Scale bar = 50 μm). (B) The graph shows quantitation of fibrosis by densitometry. (C) Analysis of Col1A1 mRNA levels in the two strains of mice before and after hyperoxia. (D). Western blots of TGF-β and CCN5 proteins expression in heart lysates prepared before and after hyperoxia. The graph shows TGF-β and CCN5 protein quantification by densitometry relative to coomassie loading control (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.).