Ephrin B2/EphB4 pathway in hepatic stellate cells stimulates Erk-dependent VEGF production and sinusoidal endothelial cell recruitment.

Publication Type:

Journal Article

Source:

American journal of physiology. Gastrointestinal and liver physiology, Volume 298, Issue 6, p.G908-15 (2010)

Keywords:

Animalsdigestive disease, digestive deseases Cells, Cultureddigestive disease, digestive deseases Endothelial Cellsdigestive disease, digestive deseases Ephrin-B2digestive disease, digestive deseases Extracellular Signal-Regulated MAP Kinasesdigestive disease, digestive deseases Gene Expression Regulationdigestive disease, digestive deseases Hepatic Stellate Cellsdigestive disease, digestive deseases Humansdigestive disease, digestive deseases Phosphorylationdigestive disease, digestive deseases Promoter Regions, Geneticdigestive disease, digestive deseases Ratsdigestive disease, digestive deseases Receptor, EphB4digestive disease, digestive deseases RNA, Messengerdigestive disease, digestive deseases Signal Transductiondigestive disease, digestive deseases Vascular Endothelial Growth Factor A

Abstract:

Chemotaxis signals between hepatic stellate cells (HSC) and sinusoidal endothelial cells (SEC) maintain hepatic vascular homeostasis and integrity and also regulate changes in sinusoidal structure in response to liver injury. Our prior studies have demonstrated that the bidirectional chemotactic signaling molecules EphrinB2 and EphB4 are expressed in HSC. The aim of our present study was to explore whether and how the EphrinB2/EphB4 system in HSC could promote SEC recruitment, which is essential for sinusoidal structure and remodeling. Stimulation of human HSC (hHSC) with chimeric agonists (2 microg/ml) of either EphrinB2 or EphB4 (EphrinB2 Fc or EphB4 Fc, respectively) significantly increased VEGF mRNA levels in hHSC as assessed by quantitative PCR, with respective small interfering RNAs for EphrinB2 and EphB4 inhibiting this increase (P < 0.05, n = 3). EphrinB2 agonist-induced increase in VEGF mRNA levels in hHSC was associated with increased phosphorylation of Erk and was significantly blocked by U0126 (20 microM), an inhibitor of MEK, which is a kinase upstream from Erk (P < 0.05, n = 3). The EphB4 agonist also significantly increased human VEGF promoter activity (P < 0.05, n = 3) as assessed by promoter reporter luciferase assay in transfected LX2-HSC. This was associated with upregulation of the vasculoprotective transcription factor, Kruppel-like factor 2 (KLF2). In Boyden chamber assays, conditioned media from hHSC stimulated with agonists of EphrinB2 or EphB4 increased SEC chemotaxis in a VEGF-dependent manner, compared with control groups that included basal media with agonists of EphrinB2, EphB4, or HSC-conditioned media from HSC in absence of agonist stimulation (P < 0.05, n = 3). EphB4 expression was detected in situ within liver sinusoidal vessels of rats after carbon tetrachloride-induced liver injury. In summary, activation of the EphrinB2/EphB4 signaling pathway in HSC promotes chemotaxis of SEC through a pathway that involves Erk, KLF2, and VEGF. These studies identify EphrinB2 or EphB4 as a key intermediary that links HSC signal transduction pathways with angiogenesis and sinusoidal remodeling.