Hepatic stellate cells (HSCs) play key roles in hepatic fibrosis. One of the most striking alterations in activated HSCs is loss of cytoplasmic lipid droplets. However, the association of lipid storage with the activation of HSCs remains unclear. CCAAT/enhancer-binding proteins family (C/EBPs), especially C/EBP-alpha, controls differentiation of adipocytes. We suggested that C/EBP-alpha gene may be involved in HSCs activation. The present results showed that the expression levels of C/EBP-alpha and QEBP-alpha genes declined in activated HSCs. Over-expression of C/EBP-alpha gene in activated HSCs: (1) inhibited HSCs proliferation, extracellular matrix-producing, alpha-smooth muscle actin gene expression, and induced rebound of cytoplasmic lipid droplets; (2) reduced retinoic acid receptor-beta, C/EBP-delta and -beta gene expressions, but increased the active form C/EBP-beta PSer(105), and induced retinoid X receptor-alpha gene expression; and (3) did not affect the protein level of p161NK4a, p21Cip1/WAF1 or p27Kip1. In conclusions, C/EBP-alpha gene is involved in in vitro activation of rat HSCs. (C) 2004 Elsevier Inc. All rights reserved.