Hypoxia interferes with connective tissue growth factor (CTGF) gene expression in human proximal tubular cell lines.
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% O(2)) 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-1alpha knockdown by siRNA. Furthermore, exposure to hypoxia reduced CTGF synthesis in response to TGF-beta. A negative correlation between HIF-1alpha accumulation and CTGF synthesis was also observed in renal cell carcinoma cells (RCC4 and RCC10). Reexpression of von Hippel-Lindau protein reduced HIF-1alpha and increased CTGF synthesis.


CONCLUSIONS
We provide evidence that hypoxia inhibits CTGF synthesis in human proximal tubular epithelial cells, involving HIF-1alpha. Under hypoxic conditions, induction of CTGF by TGF-beta was repressed. The reduced synthesis of the profibrotic factor CTGF may contribute to a potential protective effect of hypoxic preconditioning in acute renal injury.
Kroening
Sven
S
Department of Nephrology and Hypertension, Medical Clinic 4, University Hospital of Erlangen-Nuremberg, 91054 Erlangen, Germany.
Neubauer
Emily
E
Wessel
Julia
J
Wiesener
Michael
M
Goppelt-Struebe
Margarete
M
D000600:Amino Acids, Dicarboxylic / Q000494:pharmacology; D002292:Carcinoma, Renal Cell / Q000378:metabolism; D015687:Cell Hypoxia; D002478:Cells, Cultured; D055513:Connective Tissue Growth Factor / Q000235:genetics*; D004847:Epithelial Cells / Q000378:metabolism; D005786:Gene Expression Regulation; D006801:Humans; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000502:physiology; D007680:Kidney Neoplasms / Q000378:metabolism; D007687:Kidney Tubules, Proximal / Q000166:cytology / Q000378:metabolism*; D011401:Promoter Regions, Genetic; D053773:Transforming Growth Factor beta1 / Q000502:physiology; D051794:Von Hippel-Lindau Tumor Suppressor Protein / Q000502:physiology
D000600:Amino Acids, Dicarboxylic; C497442:HIF1A protein, human; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D053773:Transforming Growth Factor beta1; D055513:Connective Tissue Growth Factor; D051794:Von Hippel-Lindau Tumor Suppressor Protein; C497446:VHL protein, human; C040947:oxalylglycine