The role of insulin-like growth factor binding protein-3 during oval-cell mediated liver regeneration

Insulin-like growth factor binding protein (IGFBP)-3 is one of six characterized binding proteins to insulin-like growth factor (IGF)-I and II, and is primarily produced by the liver. IGFBP-3 has been shown to play a role in cell proliferation and differentiation in a variety of different cell and tissue types, including several different types of cancer. Recently, IGFBP-3 has been identified as a potent chemoattractant for hematopoietic stem cells and endothelial progenitor cells both in vitro and in vivo. Since hematopoietic stem cells share many common characteristics and cell markers with the hepatic stem cell population known as "oval cells" and because IGFBP-3 is primarily produced in the liver, we hypothesized that IGFBP-3 may act as a chemoattractant for the oval cells during this specific type of liver regeneration. Additionally, IGFBP-3 production has been linked to the TGF-beta superfamily, a pathway known to be induced during oval cell proliferation.;In this study, we set out to determine whether IGFBP-3 plays a role in the proliferation, migration and/or differentiation of the oval cell population during this specific type of liver regeneration. Through the use of the 2AAF/PHx liver regeneration model in the rat, we found that IGFBP-3 is elevated in liver and serum of animals during peak days of oval cell activation. Furthermore, in vitro assays found that WB-344 cells, a liver stem cell line similar to oval cells, were induced to migrate in the presence of IGFBP-3. When expression of IGFBP-3 was knocked down during oval cell activation in vivo through the use of IGFBP-3 siRNA, we found oval cell proliferation to be highly upregulated compared to control animals and observed the appearance of numerous atypical ductular structures, which were OV-6 and Ki67 positive. Finally, quantitative real-time PCR analysis of IGFBP-3 siRNA treated livers found that expression of TGF-beta family members, including TGF-betaRII and Smads 2, 3, and 4 were significantly downregulated compared to untreated liver. Therefore, we determined that IGFBP-3 may function as a potent chemoattractant of oval cells during specific types of liver regeneration and may be involved in regulating oval cell proliferation and differentiation in vivo via the TGF-beta pathway. (Full text of this dissertation may be available via the University of Florida Libraries web site. Please check http://www.uflib.ufl.edu/etd.html)...