title: Defective paracrine signalling by TGFbeta in yolk sac vasculature of endoglin mutant mice: a paradigm for hereditary haemorrhagic telangiectasia.
abstract: Hereditary haemorrhagic telangiectasia (HHT) is an autosomal dominant disorder in humans that is characterised by multisystemic vascular dyplasia and recurrent haemorrhage. Germline mutations in one of two different genes, endoglin or ALK1 can cause HHT. Both are members of the transforming growth factor (TGF) beta receptor family of proteins, and are expressed primarily on the surface of endothelial cells (ECs). Mice that lack endoglin or activin receptor like kinase (ALK) 1 die at mid-gestation as a result of defects in the yolk sac vasculature. Here, we have analyzed TGFbeta signalling in yolk sacs from endoglin knockout mice and from mice with endothelial-specific deletion of the TGFbeta type II receptor (TbetaRII) or ALK5. We show that TGFbeta/ALK5 signalling from endothelial cells to adjacent mesothelial cells is defective in these mice, as evidenced by reduced phosphorylation of Smad2. This results in the failure of vascular smooth muscle cells to differentiate and associate with endothelial cells so that blood vessels remain fragile and become dilated. Phosphorylation of Smad2 and differentiation of smooth muscle can be rescued by culture of the yolk sac with exogenous TGFbeta1. Our data show that disruption of TGFbeta signalling in vascular endothelial cells results in reduced availability of TGFbeta1 protein to promote recruitment and differentiation of smooth muscle cells, and provide a possible explanation for weak vessel walls associated with HHT.
authors.affiliation: Hubrecht Laboratory, Netherlands Institute for Developmental Biology, Uppsalalaan 8, 3584CT Utrecht, The Netherlands.
authors.forename: Rita L C
authors.initials: RL
authors.lastname: Carvalho
authors.forename: Leon
authors.initials: L
authors.lastname: Jonker
authors.forename: Marie-José
authors.initials: MJ
authors.lastname: Goumans
authors.forename: Jonas
authors.initials: J
authors.lastname: Larsson
authors.forename: Peter
authors.initials: P
authors.lastname: Bouwman
authors.forename: Stefan
authors.initials: S
authors.lastname: Karlsson
authors.forename: Peter Ten
authors.initials: PT
authors.lastname: Dijke
authors.forename: Helen M
authors.initials: HM
authors.lastname: Arthur
authors.forename: Christine L
authors.initials: CL
authors.lastname: Mummery
mesh_terms: D030201:Activin Receptors, Type I / Q000235:genetics / Q000378:metabolism; D030301:Activin Receptors, Type II; D000818:Animals; D002454:Cell Differentiation / Q000502:physiology*; D004268:DNA-Binding Proteins / Q000378:metabolism; D042783:Endothelial Cells / Q000378:metabolism / Q000473:pathology; D051379:Mice; D018345:Mice, Knockout; D032389:Myocytes, Smooth Muscle / Q000378:metabolism / Q000473:pathology; D019899:Paracrine Communication / Q000502:physiology*; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases; D000077293:Receptor, Transforming Growth Factor-beta Type I; D000077294:Receptor, Transforming Growth Factor-beta Type II; D018125:Receptors, Transforming Growth Factor beta / Q000235:genetics / Q000378:metabolism; D051899:Smad2 Protein; D013683:Telangiectasia, Hereditary Hemorrhagic / Q000235:genetics / Q000378:metabolism*; D015534:Trans-Activators / Q000378:metabolism; D016212:Transforming Growth Factor beta / Q000235:genetics / Q000378:metabolism*; D015017:Yolk Sac / Q000378:metabolism* / Q000473:pathology
chemical_list: D004268:DNA-Binding Proteins; D018125:Receptors, Transforming Growth Factor beta; D051899:Smad2 Protein; C497783:Smad2 protein, mouse; D015534:Trans-Activators; D016212:Transforming Growth Factor beta; D017346:Protein Serine-Threonine Kinases; D030201:Activin Receptors, Type I; D030301:Activin Receptors, Type II; C498931:Acvrl1 protein, mouse; D000077293:Receptor, Transforming Growth Factor-beta Type I; D000077294:Receptor, Transforming Growth Factor-beta Type II; C000625841:TGFBR1 protein, human; C000625842:Tgfbr1 protein, mouse