Mitochondrial quality-control dysregulation in conditional HO-1^-/- mice.

Abstract

The heme oxygenase-1 (<i>Hmox1</i>; HO-1) pathway was tested for defense of mitochondrial quality control in cardiomyocyte-specific <i>Hmox1</i> 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 <i>Pink1</i>- and <i>Park2</i>-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 <i>Hmox1</i> 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.