Mitochondria-targeted heme oxygenase-1 induces oxidative stress and mitochondrial dysfunction in macrophages, kidney fibroblasts and in chronic alcohol hepatotoxicity

Seema Bansal,Gopa Biswas,Narayan G Avadhani

doi:10.1016/j.redox.2013.07.004

Seema Bansal, Gopa Biswas + Show 1 more

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https://doi.org/10.1016/j.redox.2013.07.004

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Journal: Redox Biology	Publication Date: Jul 23, 2013
Citations: 144	License type: cc-by

Affiliation: University of Pennsylvania

Abstract

The inducible form of Heme Oxygenase-1 (HO-1), a major endoplasmic reticulum (ER) associated heme protein, is known to play important roles in protection against oxidative and chemical stress by degrading free heme released from degradation of heme proteins. In this study we show that induced expression of HO-1 by subjecting macrophage RAW-264.7 cells to chemical or physiological hypoxia resulted in significant translocation of HO-1 protein to mitochondria. Transient transfection of COS-7 cells with cloned cDNA also resulted in mitochondrial translocation of HO-1. Deletion of N-terminal ER targeting domain increased mitochondrial translocation under the transient transfection conditions. Mitochondrial localization of both intact HO-1 and N-terminal truncated HO-1 caused loss of heme aa-3 and cytochrome c oxidase (CcO) activity in COS-7 cells. The truncated protein, which localizes to mitochondria at higher levels, induced substantially steeper loss of CcO activity and reduced heme aa3 content. Furthermore, cells expressing mitochondria targeted HO-1 also induced higher ROS production. Consistent with dysfunctional state of mitochondria induced by HO-1, the mitochondrial recruitment of autophagy markers LC-3 and Drp-1 was also increased in these cells. Chronic ethanol feeding in rats also caused an increase in mitochondrial HO-1 and decrease in CcO activity. These results show that as opposed to the protective effect of the ER associated HO-1, mitochondria targeted HO-1 under normoxic conditions induces mitochondrial dysfunction.

Highlights

Heme oxygenases (HO) represent a family of evolutionarily conserved endoplasmic reticulum (ER) enzymes that have been described as fonts of multiple messengers [1]
Exposure of cells to hypoxia led to a 2–4 fold induction of Heme Oxygenase-1 (HO-1) in mitochondria as well as in the microsomes; the mitochondrial HO-1 peaked at 12 h while the microsomal HO1 levels remained high until 24 h of hypoxia (Fig. 1C and D)
Mitochondrial localization of HO-1 was first reported by Srivastava and Pandey in Mastomys Coucha during malaria infection [56], and subsequently reported by several other groups [32,34]

Summary

Introduction

Heme oxygenases (HO) represent a family of evolutionarily conserved endoplasmic reticulum (ER) enzymes that have been described as fonts of multiple messengers [1]. HO's are widely considered as the central components of mammalian stress response and defense against oxidative stress [2,3,4,5]. Three different isoforms of HO have been described in mammalian systems including the inducible HO-1; constitutive HO-2; and a newly identified HO-3, which is not catalytically active [6,7]. Its function remains obscure, HO-3 may be involved in heme binding. Out of the three isoforms, the inducible HO-1 is highly concentrated in tissues that are heavily involved in the catabolism of heme proteins [9]. The enzyme requires NADPH–cytochrome–P450-reductase (NPR) as the donor of electrons for substrate metabolism by HO-1[10,11,12]

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