Angiogenic sprouting into neural tissue requires Gpr124, an orphan G protein-coupled receptor

Abstract

The vasculature of the CNS is structurally and functionally distinct from that of other organ systems and is particularly prone to developmental abnormalities and hemorrhage. Although other embryonic tissues undergo primary vascularization, the developing nervous system is unique in that it is secondarily vascularized by sprouting angiogenesis from a surrounding perineural plexus. This sprouting angiogenesis requires the TGF-β and Wnt pathways because ablation of these pathways results in aberrant sprouting and hemorrhage. We have genetically deleted Gpr124, a member of the large family of long N-terminal group B G protein-coupled receptors, few members of which have identified ligands or well-defined biologic functions in mammals. We show that, in the developing CNS, Gpr124 is specifically expressed in the vasculature and is absolutely required for proper angiogenic sprouting into the developing neural tube. Embryos lacking Gpr124 exhibit vascular defects characterized by delayed vascular penetration, formation of pathological glomeruloid tufts within the CNS, and hemorrhage. In addition, they display defects in palate and lung development, two processes in which TGF-β and/or Wnt pathways also play important roles. We also show that TGF-β stimulates Gpr124 expression, and ablation of Gpr124 results in perturbed TGF-β pathway activation, suggesting roles for Gpr124 in modulating TGF-β signaling. These results represent a unique function attributed to a long N-terminal group B-type G protein-coupled receptor in a mammalian system. tumor endothelial marker 5 | orphan receptor | adhesion | forebrain

Wnt proteins synergize to activate β-catenin signaling

“…GPR124 is likely to be important in vasculature outside of the brain, as it was also identified as tumor endothelial marker 5 (TEM5), a transcript enriched in the vasculature of human colorectal cancer and murine tumors (Carson-Walter et al, 2001) and which is itself upregulated by TGF-β (Anderson et al, 2011) and Rac signaling (Vallon et al, 2010). Whether activated GPR124 couples to a G-protein, or whether it signals to the nucleus via other mechanisms is not currently known.…”

Excessive vascular sprouting underlies cerebral hemorrhage in mice lacking αVβ8-TGFβ signaling in the brain

“…In addition to Itgav and Itgb8, brain hemorrhage during embryonic development is observed in other mutant mice, including Gpr124 (Anderson et al, 2011;Cullen et al, 2011;Kuhnert et al, 2010), Nrp1 (Gerhardt et al, 2004;Gu et al, 2003;Kawasaki et al, 1999), Wnt7a/ b-Bcat (Daneman et al, 2009;Liebner et al, 2008;Stenman et al, 2008), Tgfb1/3 (Mu et al, 2008), Tgfbr2 (Nguyen et al, 2011;Robson et al, 2010), Alk5 (Nguyen et al, 2011), Smad4 , Smad2/Smad3 (Itoh et al, 2012) and S1pr1 (Gaengel et al, 2012). Prior work either did not address the cause of hemorrhage (Nrp1, Tgfb1/3, Smad2/Smad3, S1pr1) or attributed it to a dysfunctional BBB [Gpr124 (Anderson et al, 2011), Bcat (Liebner et al, 2008), Smad4 , Itgb8 (Mobley et al, 2009), Itgav-Tgfbr2-Alk5 (Nguyen et al, 2011)]. However, BBB dysfunction was generally tested by tracer injection after initiation of hemorrhage and thus did not determine whether BBB dysfunction precedes hemorrhage.…”

Defective adgra2 (gpr124) splicing and function in zebrafish ouchless mutants

“…In addition, Adgra2 and Reck function as essential regulators of brain vascular development by promoting Wnt/ β-catenin signaling in cerebrovascular endothelial cells (ECs) (Posokhova et al, 2015;Ulrich et al, 2016;Vanhollebeke et al, 2015;Zhou and Nathans, 2014). While the pivotal role of these proteins in cerebrovascular development is established both in the zebrafish and the mouse model (Anderson et al, 2011;Cullen et al, 2011;de Almeida et al, 2015;Kuhnert et al, 2010;Noda et al, 2016;Posokhova et al, 2015;Ulrich et al, 2016;Vanhollebeke et al, 2015;Zhou and Nathans, 2014), the molecular mechanisms underlying their activation and signal transduction remain to be determined. Given the phenotypic similarities, we therefore set out to test whether adgra2 and ouchless ( presumably sorbs3) co-operate during the process of DRG neurogenesis and brain vascularization.…”