Liver fibrosis is induced by many environmental and genetic factors, and chronic ethanol abuse is one of the most common causes of fibrosis in the US. Hepatic lipocytes are generally accepted to be the major effector cells involved in fibrogenesis. Lipocyte activation seems to require hepatocyte (HC) injury and may involve recruitment or injury of other cell types. Careful investigations have shown that cytokines, growth factors and other un-defined factors can induce lipocyte activation. However, these peptides individually or together are insufficient by themselves to sustain all of the observed processes of lipocyte activation. Other pericytes, in non-hepatic organs, have been more extensively studied than hepatic lipocytes. These research efforts have demonstrated that EGF, PDGF, TGF-alpha, and bFGF induce expression and/or modify components of the Insulin-Like Growth factor (IGF) superfamily as a critical and essential part of cellular activation. A limited number of investigations have shown that cultured lipocytes have an functional IGF system in that activated lipocytes express IGF-IR, secrete IGF-I and IGFBPs, and can grow at increased rates with added IGF- I. This effect of IGF-I can be enhanced by addition of hepatocyte- conditioned media. The applicant's recent work substantially supports a role for IGF-I in lipocyte activation and resembles that of other pericytes. Lipocyte steady state IGF-IR mRNA is increased several fold in 7 day cultures relative to newly isolated lipocytes. Differential growth conditions (plastic vs. Matrigel) modulate abundance of two IGFBPs, identified as IGFBP2 and 4 by immunoblot. IGF-Ia to IGF-Ib mRNA abundance in 7th day cultured lipocytes resembles that of other mesenchymal cell types. In addition, the PI has used the chronic intra- gastric ethanol feeding rat model to demonstrate derangement of IGF-l and IGFBPs parallels ethanol-induced hepatic injury in vivo; and markedly increased IGFBP-1, -2, and -4 production by hepatocytes cultured from ethanol-fed animals relative to their paired controls. In total, these data underscore the critical need for further research in the hepatic IGF system. The investigations proposed here address specific issues related to induction of the lipocyte IGF system. first, the factors that induce lipocyte IGF-IR are unknown, and the proposed research will test selected conditions which induce IGF-IR in other cell lines (PDGF, IGFBPs, IGF-I). Secondly, ethanol or acetaldehyde may directly or indirectly (other hepatic cell response) modify the lipocyte IGF-I system, and this will be examined in lipocyte culture, co-culture or by addition of ethanol- treated hepatic cell- conditioned media. Thirdly, dependence of an intact IGF-l system on lipocyte activation will be tested with selective neutralization (antibody, antisense RNA). It is hypothesized that there must be a very tightly controlled IGF-I system in lipocytes: under normal conditions these cells are constantly exposed to a 15 fold higher concentration of IGF-I than any other extrahepatic cell type of mesenchymal origin. Disruption of control of this system by factors which induce lipocyte activation has several implications in understanding the-accelerated course of co-morbid liver diseases, as well as potential therapeutic interventions.
| Block, G D; Locker, J; Bowen, W C et al. (1996) Population expansion, clonal growth, and specific differentiation patterns in primary cultures of hepatocytes induced by HGF/SF, EGF and TGF alpha in a chemically defined (HGM) medium. J Cell Biol 132:1133-49 |
