Toll-like receptor-4 signaling and Kupffer cells play pivotal roles in the pathogenesis of non-alcoholic steatohepatitis.
OBJECTIVE
Studies in animal models and humans suggest a link between endotoxemia and non-alcoholic steatohepatitis. Since Kupffer cells are responsible for clearing endotoxin and are activated via endotoxin interaction with Toll-like receptor 4 (TLR-4), we examined the relationship between hepatic TLR-4 expression and Kupffer cell content during the genesis of steatohepatitis.


METHODS
Male C57BL/6, C3H/HouJ and TLR-4 mutant C3H/HeJ mice were fed control or methionine/choline-deficient diet (MCDD). In one group of C57BL/6 mice, Kupffer cells were depleted by weekly intraperitoneal injections of clodronate liposomes. After 3 weeks, serum ALT activity and portal endotoxin levels were measured. Real-time PCR was used to examine mRNA expression of TLR-4, TLR-2, CD14, MD-2, TGFbeta, TNFalpha, CD36, PPAR-alpha, liver fatty acid binding protein (L-FABP) and collagen alpha1.


RESULTS
We observed histological evidence typical of steatohepatitis, portal endotoxemia and enhanced TLR-4 expression in wild type mice fed MCDD. In contrast, injury and lipid accumulation markers were significantly lower in TLR-4 mutant mice. Destruction of Kupffer cells with clodronate liposomes blunted histological evidence of steatohepatitis and prevented increases in TLR-4 expression.


CONCLUSIONS
These findings demonstrate the importance of TLR-4 signaling and underscore a direct link between TLR-4 and Kupffer cells in the pathogenesis of steatohepatitis.
Rivera
Chantal A
CA
Department of Molecular and Cellular Physiology, Louisiana State University Health Sciences Center, Shreveport, LA 71130, USA. Crive1@lsuhsc.edu
Adegboyega
Patrick
P
van Rooijen
Nico
N
Tagalicud
Arlene
A
Allman
Monique
M
Wallace
Matthew
M
D000818:Animals; D002796:Choline Deficiency; D004002:Clodronic Acid / Q000494:pharmacology; D024042:Collagen Type I / Q000172:deficiency; D000090602:Collagen Type I, alpha 1 Chain; D004032:Diet; D019446:Endotoxemia / Q000150:complications* / Q000235:genetics; D005234:Fatty Liver / Q000209:etiology* / Q000473:pathology; D006520:Hepatitis, Animal / Q000209:etiology* / Q000473:pathology; D007728:Kupffer Cells / Q000187:drug effects / Q000502:physiology*; D008233:Lymphotoxin-alpha / Q000172:deficiency; D008715:Methionine / Q000172:deficiency; D051379:Mice; D008817:Mice, Mutant Strains; D047493:PPAR alpha / Q000378:metabolism; D015398:Signal Transduction; D051197:Toll-Like Receptor 4 / Q000235:genetics / Q000502:physiology*; D014280:Triglycerides / Q000032:analysis
D024042:Collagen Type I; D000090602:Collagen Type I, alpha 1 Chain; D008233:Lymphotoxin-alpha; D047493:PPAR alpha; D051197:Toll-Like Receptor 4; D014280:Triglycerides; D004002:Clodronic Acid; D008715:Methionine