Effects of S-adenosyl-L-methionine on collagen expression in activated hepatic stellate cells.

摘要

Liver fibrosis is defined as the excessive accumulation of extracellular matrix (ECM) components, which can disrupt the normal liver microcirculation and lead to injury. Unresolved, hepatic fibrosis can progress to cirrhosis, an end-state liver disease. Hepatic stellate cells (HSCs) are the chief mediator of fibrosis in the liver. Normal HSCs are quiescent, store vitamin A, and regulate sinusoidal blood flow. Upon a noxious stimulus, HSCs transdifferentiate into a myofibroblast-like cell, proliferate, migrate to the site of injury, and secrete ECM components, in particular type I collagen. The antioxidant S-adenosyl-L-methionine (SAMe) was evaluated as a therapeutic agent for the modulation of type I collagen in activated HSCs. Treatment with SAMe resulted in a 91% reduction in type I collagen secretion, however there was no significant change in intracellular collagen protein or mRNA expression. SAMe also increased NF-kappaB activity, a redox-sensitive transcription factor. Blocking NF-kappaB with a dominant-negative form of IkappaBalpha abolished SAMe-mediated type I collagen inhibition in Rat-1 fibroblasts. Examination of post-transcriptional fate of procollagen mRNAs revealed polyubiquitination of intracellular type I collagen following administration of SAMe. The endoplasmic reticulum (ER) proteins Grp78 and protein disulfide isomerase (PDI) were also significantly decreased by SAMe following 24 hours of treatment. These findings may represent a novel mechanism for modulating type I collagen expression in activated HSCs. We also report the development of a "two-hit" model of hepatic fibrosis, utilizing the Lieber-DeCarli liquid ethanol diet with concomitant injections of 0.5 mg/kg LPS semi-weekly. After 8 weeks of ethanol and LPS, animals developed significant perivenular and perisinusoidal fibrosis. Treatment with 10 mg/kg of SAMe daily abolished ethanol and LPS-induced fibrosis with a decrease in oxidative stress, and expression of TGF-beta and the downstream signaling molecule Smad3. SAMe also attenuated established hepatic fibrosis in a BDL model. These findings suggest SAMe is effective as both a preventative and curative treatment for hepatic fibrosis, and our "two-hit" model of ethanol feeding with LPS administration is appropriate for investigating liver fibrosis.