Egr-1 is involved in the inhibitory effect of leptin on PPARgamma expression in hepatic stellate cell in vitro.
OBJECTIVE
Hepatic stellate cell (HSC) activation is a key step in the hepatic fibrogenic process. Increasing evidence demonstrates the pro-fibrogenic action of leptin in rodent liver. Peroxisome proliferator-activated receptor-gamma (PPARgamma) is a potential molecular target for inhibition of HSC activation. Our previous study suggested that leptin markedly down-regulated PPARgamma gene expression in HSCs. The aim of this study is to explore the molecular mechanisms underlying the inhibitory effect of leptin on PPARgamma expression in rat HSCs in vitro.


METHODS
The effects of leptin on the expression and trans-activation activity of early growth response-1 (Egr-1) are examined by using real-time PCR, Western blotting analysis, transient transfection, and electrophoretic mobility shift assay. The role of Egr-1 in PPARgamma gene expression is demonstrated by co-transfection approach, Western blotting analysis and real-time PCR.


RESULTS
We document that leptin increases Egr-1 expression at protein and mRNA levels, and significantly stimulates Egr-1 trans-activation activity. Moreover, leptin induces the expression and activity of Egr-1 through activation of extracellular signal-regulated kinase (ERK) or phosphatidylinositol 3-kinase/AKT signaling (PI-3K/AKT) pathway. Further investigation reveals that Egr-1 exerts a clear inhibitory effect on the promoter activity and expression of PPARgamma gene and demonstrates that Egr-1 increases the expression of HSC activation markers and promotes HSC growth. Taken together, these findings suggest that Egr-1 is involved in the inhibitory effect of leptin on PPARgamma expression in rat HSCs in vitro.


CONCLUSIONS
Our results provide novel insights into the mechanisms of leptin-induced inhibition of PPARgamma expression in HSCs in vitro.
Zhou
Yajun
Y
Department of Biochemistry and Molecular Biology, Medical College, Nantong University, Qixiu Road 19, Nantong, 226001, Jiangsu, China. zhouyajun64@yahoo.com
Jia
Xin
X
Zhou
Mingming
M
Liu
Jie
J
D000818:Animals; D015153:Blotting, Western; D018929:Cell Culture Techniques; D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D051766:Early Growth Response Protein 1 / Q000096:biosynthesis / Q000502:physiology*; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D015870:Gene Expression / Q000187:drug effects*; D055166:Hepatic Stellate Cells / Q000187:drug effects* / Q000201:enzymology / Q000378:metabolism; D020738:Leptin / Q000494:pharmacology*; D008297:Male; D047495:PPAR gamma / Q000037:antagonists & inhibitors* / Q000235:genetics; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010957:Plasmids; D011401:Promoter Regions, Genetic; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014162:Transfection; D015854:Up-Regulation
D051766:Early Growth Response Protein 1; C486110:Egr1 protein, rat; D020738:Leptin; D047495:PPAR gamma; D019869:Phosphatidylinositol 3-Kinases; D051057:Proto-Oncogene Proteins c-akt; D048049:Extracellular Signal-Regulated MAP Kinases