Vitamin A inhibits pancreatic stellate cell activation: implications for treatment of pancreatic fibrosis.

BACKGROUND AND AIMS Activated pancreatic stellate cells (PSCs) are implicated in the production of alcohol induced pancreatic fibrosis. PSC activation is invariably associated with loss of cytoplasmic vitamin A (retinol) stores. Furthermore, retinol and ethanol are known to be metabolised by similar pathways. Our group and others have demonstrated that ethanol induced PSC activation is mediated by the mitogen activated protein kinase (MAPK) pathway but the specific role of retinol and its metabolites all-trans retinoic acid (ATRA) and 9-cis retinoic acid (9-RA) in PSC quiescence/activation, or its influence on ethanol induced PSC activation is not known. Therefore, the aims of this study were to (i) examine the effects of retinol, ATRA, and 9-RA on PSC activation; (ii) determine whether retinol, ATRA, and 9-RA influence MAPK signalling in PSCs; and (iii) assess the effect of retinol supplementation on PSCs activated by ethanol. METHODS Cultured rat PSCs were incubated with retinol, ATRA, or 9-RA for varying time periods and assessed for: (i) proliferation; (ii) expression of alpha smooth muscle actin (alpha-SMA), collagen I, fibronectin, and laminin; and (iii) activation of MAPKs (extracellular regulated kinases 1 and 2, p38 kinase, and c-Jun N terminal kinase). The effect of retinol on PSCs treated with ethanol was also examined by incubating cells with ethanol in the presence or absence of retinol for five days, followed by assessment of alpha-SMA, collagen I, fibronectin, and laminin expression. RESULTS Retinol, ATRA, and 9-RA significantly inhibited: (i) cell proliferation, (ii) expression of alpha-SMA, collagen I, fibronectin, and laminin, and (iii) activation of all three classes of MAPKs. Furthermore, retinol prevented ethanol induced PSC activation, as indicated by inhibition of the ethanol induced increase in alpha-SMA, collagen I, fibronectin, and laminin expression. CONCLUSIONS Retinol and its metabolites ATRA and 9-RA induce quiescence in culture activated PSCs associated with a significant decrease in the activation of all three classes of MAPKs in PSCs. Ethanol induced PSC activation is prevented by retinol supplementation.