von Hippel-Lindau protein regulates transition from the fetal to the adult circulatory system in retina

Abstract

SUMMARYIn early neonates, the fetal circulatory system undergoes dramatic transition to the adult circulatory system. Normally, embryonic connecting vessels, such as the ductus arteriosus and the foramen ovale, close and regress. In the neonatal retina, hyaloid vessels maintaining blood flow in the embryonic retina regress, and retinal vessels take over to form the adult-type circulatory system. This process is regulated by a programmed cell death switch mediated by macrophages via Wnt and angiopoietin 2 pathways. In this study, we seek other mechanisms that regulate this process, and focus on the dramatic change in oxygen environment at the point of birth. The von Hippel-Lindau tumor suppressor protein (pVHL) is a substrate recognition component of an E3-ubiquitin ligase that rapidly destabilizes hypoxia-inducible factor as (HIF-as) under normoxic, but not hypoxic, conditions. To examine the role of oxygen-sensing mechanisms in retinal circulatory system transition, we generated retina-specific conditional-knockout mice for VHL (Vhl a-CreKO mice). These mice exhibit arrested transition from the fetal to the adult circulatory system, persistence of hyaloid vessels and poorly formed retinal vessels. These defects are suppressed by intraocular injection of FLT1-Fc protein [a vascular endothelial growth factor (VEGF) receptor-1 (FLT1)/Fc chimeric protein that can bind VEGF and inhibit its activity], or by inactivating the HIF-1a gene. Our results suggest that not only macrophages but also tissue oxygen-sensing mechanisms regulate the transition from the fetal to the adult circulatory system in the retina.

Apoptosis regulates endothelial cell number and capillary vessel diameter but not vessel regression during retinal angiogenesis

“…In these cases, the presence of persistent hyaloids has been attributed to defects in the retinal vasculature, probably through increased retina hypoxia and a subsequent increase in VEGFA expression (Xu et al, 2004). Increased VEGFA levels or perturbation of VEGFA isoform expression are associated with persistent hyaloid vessels (Kurihara et al, 2010;Rao et al, 2013;Stalmans et al, 2002). In some cases, however, it has been suggested that persistent hyaloid vessels are causal for accompanying retinal vascular defects (Kurihara et al, 2010).…”

A role for endothelial cells in promoting the maturation of astrocytes through the apelin/APJ system in mice

“…Enucleated eyes were fixed in 4% paraformaldehyde. Antibodies for staining were anti-PECAM1 (BD Biosciences, 1:100; or Chemicon International, 1:100), anti-GFAP (Sigma-Aldrich, 1:100), anti-PDGFR (eBioscience, 1:100), anti-desmin (DAKO, 1:100), anti-PAX2 (Covance, 1:100), anti-KI67 (DAKO, 1:100), anti-neurofilament (American Research Products, 1:100), anti-type IV collagen (Cosmo Bio, 1:100), anti-HIF1 (1:100) (Kurihara et al, 2010), anti-apelin (1:100) (Kidoya et al, 2008) and anti-APJ (1:100) (Kidoya et al, 2008). The secondary antibodies used were Alexa Fluor 488/546/647-conjugated IgGs (Invitrogen,1:200) or FITC/Cy5-conjugated IgGs (Jackson ImmunoResearch Laboratories, 1:200).…”

Developmental regression of hyaloid vasculature is triggered by neurons

“…Retinal neurons are also suggested to act on hyaloid vasculature (Xu et al, 2004;Kurihara et al, 2010), in part by secreting VEGF (Rao et al, 2013). Therefore, we generated mice lacking Vegfa in retinal neurons using Pax6α-Cre or Chx10-Cre.…”