NDT Advance Access published online on June 23, 2009
Nephrology Dialysis Transplantation, doi:10.1093/ndt/gfp305
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Hypoxia interferes with connective tissue growth factor (CTGF) gene expression in human proximal tubular cell lines
Department of Nephrology and Hypertension, Medical Clinic 4, University Hospital of Erlangen-Nuremberg, 91054 Erlangen, Germany
Correspondence and offprint requests to: Margarete Goppelt-Struebe; E-mail: margarete.goppelt-struebe{at}uk-erlangen.de
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Abstract |
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Background. Hypoxia plays an important role in kidney injury. By the stabilization of the transcription factor HIF-1, hypoxia affects gene expression also in tubular epithelial cells. Increased expression of connective tissue growth factor (CTGF) is observed in different kidney diseases and is associated with deteriorating renal function. Therefore, we hypothesized that the expression of CTGF might be modulated under hypoxic conditions.
Methods. The human proximal tubular epithelial cell lines HK-2 and HKC-8 were treated with reduced oxygen tension (1% O2) or the hypoxia mimetic dimethyloxalyl glycine (DMOG). CTGF was analysed by Western blotting, real-time RT-PCR and luciferase gene expression assays.
Results. Exposure of HK-2 or HKC-8 cells to hypoxia or treatment with DMOG for up to 24 h reduced cellular as well as secreted CTGF protein synthesis. Downregulation was also detectable at the mRNA level and was confirmed by reporter gene assays. Hypoxic repression of CTGF synthesis was dependent on HIF-1, as shown by HIF-1
knockdown by siRNA. Furthermore, exposure to hypoxia reduced CTGF synthesis in response to TGF-β. A negative correlation between HIF-1 accumulation and CTGF synthesis was also observed in renal cell carcinoma cells (RCC4 and RCC10). Reexpression of von Hippel-Lindau protein reduced HIF-1 and increased CTGF synthesis.
Conclusions. We provide evidence that hypoxia inhibits CTGF synthesis in human proximal tubular epithelial cells, involving HIF-1. Under hypoxic conditions, induction of CTGF by TGF-β was repressed. The reduced synthesis of the profibrotic factor CTGF may contribute to a potential protective effect of hypoxic preconditioning in acute renal injury.
Keywords: connective tissue growth factor; human proximal tubular epithelial cells; hypoxia inducible factor; hypoxia
* The first two authors contributed equally to this study.
Received for publication: 28. 4.09
Accepted in revised form: 29. 5.09