Protective effect of peroxisome proliferator-activated receptor-gamma agonists on activated renal proximal tubular epithelial cells in IgA nephropathy.
BACKGROUND
We have previously demonstrated a glomerulo-tubular 'crosstalk' operating in the pathogenesis of tubulointerstitial injury in IgA nephropathy (IgAN). The present study aims to explore any possible beneficial effect of a peroxisome proliferator-activated receptor-gamma (PPAR-gamma) agonist in alleviating the tubulointerstitial inflammation in IgAN.


METHODS
Human proximal tubular epithelial cells (PTEC) were pre-treated with increasing concentration of a PPAR-gamma agonist rosiglitazone or troglitazone (0-5 microM) followed by further incubation with the conditioned medium (IgA-HMC) collected from human mesangial cells (HMC) incubated with polymeric IgA isolated from IgAN patients. Gene expression of interleukin-6 (IL-6) and angiotensin II type 1 receptor (ATR1) was detected by reverse transcription-polymerase chain reaction (RT-PCR); protein expression of IL-6 and ATR1 was determined by ELISA and western blot, respectively. The mitogen-activated protein kinase extracellular signal-related kinase 1/2 (ERK1/2) activation was examined by western blot.


RESULTS
An IgA-HMC conditioned medium prepared from IgAN patients increased gene expression and protein synthesis of IL-6 and ATR1 in PTEC when compared with a conditioned medium prepared from healthy controls. The upregulated gene expression and protein synthesis of IL-6 and ATR1 in PTEC induced by the IgA-HMC conditioned medium were readily attenuated following pre-treatment with a PPAR-gamma agonist, thiazolidinedione (TZD). The ATR1-downregulating effect exerted by the PPAR-gamma agonist occurred through the inhibition of ERK1/2 activation. The PPAR-gamma antagonist, GW9662, significantly attenuated the inhibitory action of rosiglitazone on the increased synthesis of IL-6 and ATR1 protein.


CONCLUSIONS
Our current findings suggest that the PPAR-gamma agonist attenuates excessive inflammatory response in activated PTEC in IgAN through suppressing ATR1 expression. This ATR1-downregulating effect is likely through the inhibition of ERK1/2 activation and is found to be PPAR-gamma dependent. TZDs may possibly be new therapeutic additives to established treatment regime for renin-angiotensin system (RAS) blockade in IgAN.
Xiao
Jing
J
Department of Medicine, Queen Mary Hospital, University of Hong Kong, Hong Kong.
Leung
Joseph C K
JC
Chan
Loretta Y Y
LY
Guo
Hong
H
Lai
Kar Neng
KN
D002478:Cells, Cultured; D002839:Chromans / Q000627:therapeutic use*; D004847:Epithelial Cells / Q000187:drug effects* / Q000502:physiology*; D005260:Female; D005922:Glomerulonephritis, IGA / Q000150:complications*; D006801:Humans; D007249:Inflammation / Q000209:etiology* / Q000517:prevention & control*; D007687:Kidney Tubules, Proximal / Q000166:cytology*; D008297:Male; D047495:PPAR gamma / Q000819:agonists*; D000077154:Rosiglitazone; D045162:Thiazolidinediones / Q000627:therapeutic use*; D000077288:Troglitazone
D002839:Chromans; D047495:PPAR gamma; D045162:Thiazolidinediones; D000077154:Rosiglitazone; D000077288:Troglitazone