Triptolide inhibits extracellular matrix protein synthesis by suppressing the Smad2 but not the MAPK pathway in TGF-beta1-stimulated NRK-49F cells.
BACKGROUND
Triptolide has been used for treating various autoimmune diseases. However, it remains unclear whether triptolide exerts effects on extracellular matrix (ECM) synthesis, which plays an important role in renal fibrosis.


METHODS
NRK-49F cells stimulated with TGF-β1 were incubated with triptolide in various concentrations. ECM proteins, including collagen type III and fibronectin, were detected using the reverse transcription real-time PCR and ELISA methods. MAPK and Smad2/3 phosphorylation were measured with western blot. P38 and ERK 1/2 pathways were inhibited with the specific inhibitors, SB203580 and PD98059. The Smad2 signal was blocked with the siRNA method.


RESULTS
Triptolide inhibited ECM synthesis in TGF-β1-stimulated NRK-49F cells in a concentration-dependent manner. Triptolide enhanced TGF-β1-induced activation of the p38, ERK 1/2 signals, whereas it inhibited Smad2 activation. There was no crosstalk between the p38, ERK 1/2 and Smad2 pathways in NRK-49F cells. Inhibition of either the p38 or ERK 1/2 signals reduced ECM synthesis. Triptolide downregulated synthesis of fibronectin and collagen type III in TGF-β1-stimulated cells treated with SB203580 and/or PD98059. SB203580 and/or PD98059 significantly repressed synthesis of fibronectin and collagen type III in TGF-β1-stimulated cells treated with triptolide. Smad2 inhibition by siRNA significantly reduced ECM synthesis. However, ECM synthesis in NRK-49F cells transfected with Smad2 siRNA and treated by triptolide was increased compared with Smad2 siRNA-transfected cells.


CONCLUSIONS
The effect of triptolide to suppress ECM synthesis by inhibiting Smad2 activation may surpass its stimulating effect on ECM synthesis by activation of p38 and ERK 1/2, leading to a total inhibition of ECM synthesis in TGF-β1-stimulated NRK-49F cells.
Zhu
Bin
B
Department of Nephrology, Hangzhou Hospital of Traditional Chinese Medicine, Hangzhou Guangxing Hospital, Zhejiang Chinese Medical University, Hangzhou, Zhejiang Province, China. zhubing@hotmail.com
Wang
Yong-jun
YJ
Zhu
Cai-feng
CF
Lin
Yi
Y
Zhu
Xiao-ling
XL
Wei
Sheng
S
Lu
Ying
Y
Cheng
Xiao-xia
XX
D000818:Animals; D000894:Anti-Inflammatory Agents, Non-Steroidal / Q000494:pharmacology*; D002460:Cell Line; D004224:Diterpenes / Q000494:pharmacology*; D004852:Epoxy Compounds / Q000494:pharmacology; D016326:Extracellular Matrix Proteins / Q000096:biosynthesis*; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D007668:Kidney / Q000187:drug effects* / Q000378:metabolism; D020935:MAP Kinase Signaling System / Q000187:drug effects*; D010616:Phenanthrenes / Q000494:pharmacology*; D010766:Phosphorylation; D051381:Rats; D051899:Smad2 Protein / Q000037:antagonists & inhibitors*; D053773:Transforming Growth Factor beta1 / Q000494:pharmacology*; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism
D000894:Anti-Inflammatory Agents, Non-Steroidal; D004224:Diterpenes; D004852:Epoxy Compounds; D016326:Extracellular Matrix Proteins; D010616:Phenanthrenes; D051899:Smad2 Protein; D053773:Transforming Growth Factor beta1; C001899:triptolide; D048049:Extracellular Signal-Regulated MAP Kinases; D048051:p38 Mitogen-Activated Protein Kinases