Expression of Toll-like receptor 4 in rat liver during the course of carbon tetrachloride-induced liver injury.
OBJECTIVE
It has recently been reported that Toll-like receptor 4 (TLR4) is involved in cellular responses to lipopolysaccharides (LPS) and early liver injury induced by LPS. The aim of the present study was to investigate the alterations of TLR4 gene expression in liver tissues and Kupffer cells during the course of carbon tetrachloride (CCl(4))-induced chronic liver injury and fibrosis and its role in liver injury.


METHODS
Rats were induced with liver injury and fibrosis by CCl(4) administered subcutaneously twice weekly for up to 8 weeks. The Kupffer cells were isolated by the combined collagenase-pronase perfusion method and incubated with varying doses of LPS. The mRNA expression of TLR4 in liver tissues and Kupffer cells was measured by reverse transcriptase polymerase chain reaction. The levels of tumor necrosis factor (TNF)-alpha in Kupffer cell culture supernatants were determined by enzyme-linked immunosorbent assay. The plasma levels of the endotoxin were determined by chromogenic substrate limulus amebocyte lysate assay. The association of the endotoxin receptor expression with plasma endotoxin levels was assessed.


RESULTS
CCl(4) administration elicited extensive changes in liver morphology, including steatosis, inflammation, necrosis, and fibrosis. Low levels of TLR4 mRNA were detected in normal rat liver tissues, but no expression was detected in the Kupffer cells. The expression of TLR4 mRNA in liver tissues and Kupffer cells was increased 2 weeks after CCl(4) administration, peaked at 4 and 6 weeks, and declined at 8 weeks. Basic TNF-alpha production of Kupffer cells isolated from CCl(4)-treated rats at 4 and 6 weeks was significantly higher than that of normal rats (P < 0.05). Upon LPS stimulation, production of TNF-alpha was markedly increased in Kupffer cells isolated from normal and 2-,4-, and 6-week CCl(4)-treated rats. Moreover, LPS-induced TNF-alpha production was dose-dependent. The plasma levels of the endotoxin were increased during the time of liver injury. There was a correlation between plasma endotoxin levels and TLR4 gene expression in the early and middle stage of liver injury.


CONCLUSIONS
The gene expression of TLR4 was upregulated during the course of CCl(4)-induced liver injury, which is associated with the degree of liver injury and Kupffer cell activation. The gut-derived endotoxin may be involved in the upregulation of TLR4 expression.
Hua
Jing
J
Division of Gastroenterology and Hepatology, Shanghai Institute of Digestive Disease, Renji Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai, China. hua-jing88@hotmail.com
Qiu
De Kai
DK
Li
Ji Qiang
JQ
Li
Eng Lin
EL
Chen
Xiao Yu
XY
Peng
Yan Sheng
YS
D000818:Animals; D002252:Carbon Tetrachloride Poisoning; D002478:Cells, Cultured; D007728:Kupffer Cells / Q000378:metabolism; D008106:Liver Cirrhosis, Experimental / Q000139:chemically induced / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D020133:Reverse Transcriptase Polymerase Chain Reaction; D051197:Toll-Like Receptor 4 / Q000378:metabolism*; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism
C495347:Tlr4 protein, rat; D051197:Toll-Like Receptor 4; D014409:Tumor Necrosis Factor-alpha