Hypoxia reduces the expression and anti-inflammatory effects of peroxisome proliferator-activated receptor-gamma in human proximal renal tubular cells.
BACKGROUND
Peroxisome proliferator-activated receptor (PPAR)-gamma may counteract tissue fibrosis via its anti-inflammatory actions, while hypoxia, a new pro-fibrotic factor, reportedly modifies PPAR-gamma expression. However, the effects of hypoxia on the expression and anti-inflammatory actions of PPAR-gamma have yet remained to be clarified in renal tubular cells.


METHODS
Confluent human proximal renal tubular epithelial cells (HPTECs) were exposed to hypoxia (1% O2) and/or TNF-alpha at 10 ng/ml for up to 48 h. The cells were incubated with PPAR-gamma agonists, 15d-PGJ2 or pioglitazone, for 30 min before stimulation. Precise amounts of PPAR-gamma and MCP-1 mRNA and protein were measured by TaqMan quantitative PCR and immunoblot or ELISA, respectively.


RESULTS
A cDNA array analysis identified PPAR-gamma as one of the hypoxia-affected genes in HPTECs. Hypoxia reduced mRNA levels of PPAR-gamma at 24 and 48 h and protein levels at 6 and 48 h. Knockout of hypoxia-inducible factor-1alpha (HIF-1alpha) with its dominant negative form did not block the hypoxia-induced reduction in PPAR-gamma expression. PPAR-gamma's activation with 15d-PGJ2 or pioglitazone reduced basal and TNF-alpha-stimulated MCP-1 expression at mRNA and protein levels at 24 h under normoxia. MCP-1 reduction rates at basal mRNA and protein levels were slightly but significantly lower during hypoxia than normoxia (9 vs 69% and 36 vs 42%, respectively, for 15d-PGJ2, and 0 vs 34% and 12 vs 21%, respectively, for pioglitazone). Finally, a specific inhibitor for PPAR-gamma, GW9662, weakened the MCP-1-decreasing effect of 15d-PGJ2 by about 30%, under basal conditions, while it abolished the effect of pioglitazone almost completely.


CONCLUSIONS
Hypoxia-induced loss of function of PPAR-gamma reduces anti-inflammatory effects of PPAR-gamma activation, possibly modulating inflammatory responses in the diseased kidney.
Li
Xuan
X
Division of Nephrology, Department of General Medicine, School of Medicine, Faculty of Medical Sciences, University of Fukui, 23 Matsuokashimoaizuki, Eiheiji-cho, Yoshida, Fukui 910-1193, Japan.
Kimura
Hideki
H
Hirota
Kiichi
K
Sugimoto
Hidehiro
H
Kimura
Noriyo
N
Takahashi
Naoki
N
Fujii
Hiroshi
H
Yoshida
Haruyoshi
H
D000975:Antioxidants / Q000494:pharmacology; D002478:Cells, Cultured; D018932:Chemokine CCL2 / Q000235:genetics / Q000378:metabolism; D003497:Cyclic N-Oxides / Q000494:pharmacology; D005786:Gene Expression Regulation / Q000187:drug effects; D006801:Humans; D007004:Hypoglycemic Agents / Q000494:pharmacology; D000860:Hypoxia / Q000378:metabolism*; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000235:genetics / Q000378:metabolism; D007674:Kidney Diseases / Q000378:metabolism* / Q000503:physiopathology; D007687:Kidney Tubules, Proximal / Q000166:cytology / Q000378:metabolism*; D020411:Oligonucleotide Array Sequence Analysis; D047495:PPAR gamma / Q000378:metabolism*; D000077205:Pioglitazone; D015230:Prostaglandin D2 / Q000031:analogs & derivatives / Q000494:pharmacology; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D013113:Spin Labels; D045162:Thiazolidinediones / Q000494:pharmacology; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology
C477819:15-deoxyprostaglandin J2; D000975:Antioxidants; C111835:CCL2 protein, human; D018932:Chemokine CCL2; D003497:Cyclic N-Oxides; C497442:HIF1A protein, human; D007004:Hypoglycemic Agents; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D047495:PPAR gamma; D012333:RNA, Messenger; D013113:Spin Labels; D045162:Thiazolidinediones; D014409:Tumor Necrosis Factor-alpha; D015230:Prostaglandin D2; C001803:tempol; D000077205:Pioglitazone