title: Toll-like receptor 4 increases intestinal permeability through up-regulation of membrane PKC activity in alcoholic steatohepatitis.
abstract: Intestinal hyperpermeability is a causal factor for the development of alcoholic endotoxemia and steatohepatitis. However, the mechanisms governing this link remain unknown. The purpose of this study was to determine whether toll-like receptor 4 (TLR4) is involved in ethanol's deleterious effects on the intestinal barrier. Caco-2 cells were incubated in vitro with 1-10% ethanol. The results indicated that ethanol had a dose-dependent effect in increasing TLR4 expression and intercellular permeability. Then the effects of TLR4 on protein kinase C (PKC) and the intercellular junction protein occludin were assessed with and without pretreatment with a TLR4 inhibitor. The results indicated that TLR4 increased nonspecific PKC activity and reduced the expression of phosphorylated occludin in the membrane, which increased intercellular permeability. These effects were prevented by pretreatment with TLR4 mAb. Wild-type C57BL/6 mice were fed an ethanol or isocaloric liquid diet for 6 weeks. Hepatitis was diagnosed by the presence of an associated elevated blood endotoxin level. Chronic ethanol treatment significantly elevated blood endotoxin levels, intestinal permeability, and the expression of TLR4 in the ileum and colon. Moreover, ethanol exposure reduced the distribution of phosphorylated occludin in the intestinal epithelium because of PKC activation. In conclusion, chronic ethanol exposure induces a high response of TLR4 to lipopolysaccharide (LPS), and TLR4 increases intestinal permeability through down-regulation of phosphorylated occludin expression in the intestinal epithelial barrier, accompanied by membrane PKC hyperactivity.
authors.affiliation: Department of Gastroenterology, Beijing Tiantan Hospital, Capital Medical University, 6 Tiantan Xili, Dongcheng District, Beijing 100050, PR China.
authors.forename: Xin
authors.initials: X
authors.lastname: Li
authors.forename: Chen
authors.initials: C
authors.lastname: Wang
authors.forename: Jiao
authors.initials: J
authors.lastname: Nie
authors.forename: Dong
authors.initials: D
authors.lastname: Lv
authors.forename: Tianyi
authors.initials: T
authors.lastname: Wang
authors.forename: Youqing
authors.initials: Y
authors.lastname: Xu
mesh_terms: D000818:Animals; D018938:Caco-2 Cells; D005235:Fatty Liver, Alcoholic / Q000378:metabolism; D006801:Humans; D007413:Intestinal Mucosa / Q000378:metabolism; D051379:Mice; D053594:Myeloid Differentiation Factor 88 / Q000096:biosynthesis; D062793:Occludin / Q000378:metabolism; D010539:Permeability / Q000187:drug effects; D011493:Protein Kinase C / Q000378:metabolism*; D051197:Toll-Like Receptor 4 / Q000096:biosynthesis / Q000502:physiology*; D015854:Up-Regulation
chemical_list: C507780:Myd88 protein, mouse; D053594:Myeloid Differentiation Factor 88; D062793:Occludin; C495345:TLR4 protein, human; C493487:Tlr4 protein, mouse; D051197:Toll-Like Receptor 4; D011493:Protein Kinase C
keywords: Alcoholic steatohepatitis; Intestinal permeability; Occludin; Protein kinase C; Toll-like receptor 4