Hepatocyte-Specific Deletion of Heme Oxygenase-1 Disrupts Redox Homeostasis in Basal and Oxidative Environments

Hepatocyte-Specific Deletion of Heme Oxygenase-1 Disrupts Redox Homeostasis in Basal and Oxidative Environments

TAKASHI MAMIYA,¹ FUMIKI KATSUOKA,² AKI HIRAYAMA,³ OSAMU NAKAJIMA,¹ AKIRA KOBAYASHI,¹ JONATHAN M. MAHER,² HIROFUMI MATSUI,¹ ICHINOSUKE HYODO,¹ MASAYUKI YAMAMOTO^1,2 AND TOMONORI HOSOYA¹

¹Graduate School of Comprehensive Human Sciences and Center for Tsukuba Advanced Research Alliance, Exploratory Research for Advanced Technology-Japan Science and Technology Corporation, Tsukuba, Japan
²Department of Medical Biochemistry, Tohoku University Graduate School of Medicine, Sendai, Japan
³Center for Integrative Medicine, Tsukuba University of Technology, Tsukuba, Japan

Heme oxygenase-1 (HO-1) is the rate-limiting enzyme of heme catabolism and has been assumed to be important in cellular response against oxidative stress through modification of the pro-oxidant heme into less toxic catabolites that behave as antioxidants. However, the precise mechanisms involved and the physiological significance of such activity remain to be clarified. To elucidate roles HO-1 plays in vivo, hepatocyte-specific conditional knockout (CKO) mice of HO-1 gene were generated by site-specific recombination using albumin-promoter-driven Cre-loxP system. In livers of HO-1 CKO mice HO-1 protein level decreased to approximately 30% of control mouse livers. The HO-1 CKO mice are viable, exhibit normal growth curves over six months, and show no histological and serological abnormalities. We found that several cytoprotective genes, such as NAD(P)H dehydrogenase quinone 1 and glutathione S-transferase P1, showed markedly elevated expression, suggesting the increase of oxidative stress in HO-1 CKO mice even under quiescent conditions. In vivo electron paramagnetic resonance studies demonstrated that signal decay times of nitroxyl radicals were significantly longer in livers of HO-1 CKO mice than that of control mice, indicating that radical scavenging activity was significantly compromised in the mutant liver. HO-1 CKO mice were susceptible to carbon tetrachloride hepatotoxicity. These results provide the first in vivo evidence that HO-1 acts to protect cells against the oxidative stress in both basal conditions and upon chemical insult.

keywords —— heme oxygenase-1; oxidative stress; reactive oxygen species; in vivo EPR; carbon tetrachloride.

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Tohoku J. Exp. Med., 2008, 216, 331-339

Correspondence: Masayuki Yamamoto, Department of Medical Biochemistry, Tohoku University Graduate School of Medicine, 2-1 Seiryo-cho, Aoba-ku, Sendai 980-8575, Japan.

e-mail: masi@mail.tains.tohoku.ac.jp