Activation of Hypoxia-Inducible Factor by Cobalt Is Associated with the Attenuation of Tissue Injury and Apoptosis in Cyclosporine-Induced Nephropathy

Activation of Hypoxia-Inducible Factor by Cobalt Is Associated with the Attenuation of Tissue Injury and Apoptosis in Cyclosporine-Induced Nephropathy

SE WON OH,¹ JEONG MYUNG AHN,² YUN-MI LEE,¹ SEJOONG KIM,^1,3 HO JUN CHIN,^1,3 DONG-WAN CHAE^1,3 and KI YOUNG NA^1,3

¹Department of Internal Medicine, Seoul National University Bundang Hospital, Seongnam, Korea
²Department of Internal Medicine, Maryknoll Hospital, Busan, Korea
³Department of Internal Medicine, Seoul National University College of Medicine, Seoul, Korea

Hypoxia-inducible factor (HIF) is a transcription factor that regulates cellular hypoxic responses. Despite the therapeutic benefits of cyclosporine A (CsA) in organ transplantation, its clinical use is limited due to chronic nephropathy. We investigated whether HIF activation by cobalt could improve CsA-induced nephropathy, and investigated the related mechanism. In animal experiments, rats were kept on a 0.05% low-salt diet and administered CsA subcutaneously for 28 days (15 mg/kg/day). They also received cobalt (10 mg/kg/day) during the entire experimental period. The administration of cobalt significantly increased HIF-1α expression in the kidney. The increased expression of HIF-1α ameliorated CsA-induced afferent arteriolopathy and tubulointerstitial injury in the kidney. Cobalt significantly reduced the infiltration of macrophages/monocytes into the renal tubulointerstitium. In addition, HIF activation by cobalt reduced the number of CsA-induced apoptotic cells in the kidney. Subsequently, HK-2 human renal tubular epithelial cells were used for in vitro experiments. They were pre-treated with 150 μM of cobalt to activate HIF, and then exposed to 10 μM CsA. HIF activation by cobalt decreased the CsA-induced apoptosis in HK-2 cells, as judged by the decreases in the number of apoptotic cells, pro-apoptotic caspase-3 activity, and the expression level of cleaved caspase-3, together with the increase in the expression of anti-apoptotic bcl-2. Cobalt pretreatment also reduced the CsA-induced phosphorylation of NF-κB and the CsA-induced expression of vimentin and α-smooth muscle actin, suggesting the attenuation of inflammation and fibrosis. In conclusion, the activation of HIF by cobalt may ameliorate the CsA-induced nephropathy by inhibiting apoptosis, inflammation, and fibrosis.

keywords —— apoptosis; cyclosporine; fibrosis; hypoxia-inducible factor 1; inflammation

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Tohoku J. Exp. Med., 2012, 226, 197-206

Correspondence: Ki Young Na, M.D., Ph.D., Department of Internal Medicine, Seoul National University Bundang Hospital, Gumi-ro 166, Bundang-gu, Seongnam-si, Gyeonggi-do 463-707, Republic of Korea.

e-mail: kyna@snubh.org