Effects of dietary polyunsaturated fat on ethanol-induced Ito cell activation

Ito cells, vitamin A-storing perisinusoidal cells, are believed to undergo myofibroblastic transformation in liver fibrogenesis. Our previous studies have shown that a diet high in polyunsaturated fat was key for induction of experimental alcoholic liver fibrosis. To investigate the cellular basis for this fibrogenic effect of a high-fat diet, we analyzed the content of vitamin A and cellular retinol binding protein (CRBP), the steady-state mRNA levels of procollagen-alpha1(I), transforming growth factor-beta1 (TGF-beta1), interleukin-6 (IL-6), and smooth muscle alpha-actin (alpha-SM) in freshly isolated Ito cells from rats given isocaloric amounts of ethanol and a low- or high-fat diet. After 10 wk, the Ito cell content of retinyl palmitate was severely reduced in both the high- and low-fat diet-ethanol-fed animals to 13-17% of those measured in respective pair-fed controls. On the other hand, the content of CRBP was reduced in the high-fat-ethanol rats but not in the low-fat-ethanol group. The cells from the high-fat-ethanol but not low-fat ethanol rats showed an 18-fold increase in procollagen-alpha1(I) mRNA at 17 wk, which was accompanied by 2.8- and 2.3-fold enhancement of TGF-beta1 and alpha-SM transcripts. IL-6 mRNA was not detected in the cells from any groups. These results demonstrate 1) myofibroblastic activation of Ito cells is evident in rats given a high-fat diet and ethanol but not in the low-fat-ethanol animals; 2) vitamin A depletion of Ito cells is the early and general effect of chronic ethanol intake but does not necessarily predict subsequent myofibroblastic activation; 3) reduced CRBP level is more closely associated with the subsequent cellular activation seen under the high-fat-ethanol regimen; and 4) IL-6 is not expressed in vivo by Ito cells from either normal livers or livers with alcoholic liver fibrosis.