Angiogenesis enhances the proliferation and function of cultured human fetal liver progenitor cells

Abstract

Objective To determine the role of angiogenesis in the expansion of human fetal liver progenitors (LPC) co-cultured with endothelial cells. Methods. Enriched LPCs were either cultured alone or were co-cultured with human umbilical vein endothelial cells (HUVEC) in three-dimensional fibrin gel (3D) or in monolayer (2D). LPC clusters were tracked in situ through the expression of fluorescent proteins driven by human hepatic-specific promoters albumin and alpha-fetoprotein. ELISA was used to measure albumin (Alb), alpha-fetoprotein (AFP), VEGF, HGF, endostatin and angiostatin levels. LPC proliferation was determined by BrdU labeling. Results When co-cultured with HUVEC, there was increased LPC proliferation and increased production of Alb and AFP. There were more LPC clusters, Alb-positive cells and increased Alb and AFP production when LPC were co-cultured with HUVEC undergoing angiogenesis (3D cultures) than that observed with LPC alone or with LPC co-cultured with HUVEC monolayers (no angiogenesis). In 3D LPC-HUVEC co-cultures, there was increased production of endogenous angiogenic factors VEGF and HGF. At late time points, there was increased production of anti-angiogenic factors endostatin and angiostatin in these 3D co-cultures. Inhibition of angiogenesis resulted in decreased production of Alb, AFP, endostatin and angiostatin in the LPC-HUVEC co-cultures. Conclusion The presence of angiogenesis enhances LPC proliferation and function in vitro. This process involves a balance between the endogenous production of pro- and anti-angiogenic factors.