title: Sustained BMP signaling in osteoblasts stimulates bone formation by promoting angiogenesis and osteoblast differentiation.
abstract: Angiogenesis and bone formation are tightly coupled during the formation of the skeleton. Bone morphogenetic protein (BMP) signaling is required for both bone development and angiogenesis. We recently identified endosome-associated FYVE-domain protein (endofin) as a Smad anchor for BMP receptor activation. Endofin contains a protein-phosphatase pp1c binding domain, which negatively modulates BMP signals through dephosphorylation of the BMP type I receptor. A single point mutation of endofin (F872A) disrupts interaction between the catalytic subunit pp1c and sensitizes BMP signaling in vitro. To study the functional impact of this mutation in vivo, we targeted expression of an endofin (F872A) transgene to osteoblasts. Mice expressing this mutant transgene had increased levels of phosphorylated Smad1 in osteoblasts and showed increased bone formation. Trabecular bone volume was significantly increased in the transgenic mice compared with the wildtype littermates with corresponding increases in trabecular bone thickness and number. Interestingly, the transgenic mice also had a pronounced increase in the density of the bone vasculature measured using contrast-enhanced microCT imaging of Microfil-perfused bones. The vessel surface and volume were both increased in association with elevated levels of vascular endothelial growth factor (VEGF) in osteoblasts. Endothelial sprouting from the endofin (F872A) mutant embryonic metatarsals cultured ex vivo was increased compared with controls and was abolished by an addition of a VEGF neutralizing antibody. In conclusion, osteoblast targeted expression of a mutant endofin protein lacking the pp1c binding activity results in sustained signaling of the BMP type I receptor, which increases bone formation and skeletal angiogenesis.
authors.affiliation: Department of Pathology, University of Alabama at Birmingham, Birmingham, Alabama, USA.
authors.forename: Fengjie
authors.initials: F
authors.lastname: Zhang
authors.forename: Tao
authors.initials: T
authors.lastname: Qiu
authors.forename: Xiangwei
authors.initials: X
authors.lastname: Wu
authors.forename: Chao
authors.initials: C
authors.lastname: Wan
authors.forename: Weibin
authors.initials: W
authors.lastname: Shi
authors.forename: Ying
authors.initials: Y
authors.lastname: Wang
authors.forename: Jian-guo
authors.initials: JG
authors.lastname: Chen
authors.forename: Mei
authors.initials: M
authors.lastname: Wan
authors.forename: Thomas L
authors.initials: TL
authors.lastname: Clemens
authors.forename: Xu
authors.initials: X
authors.lastname: Cao
mesh_terms: D019943:Amino Acid Substitution; D000818:Animals; D052005:Bone Morphogenetic Protein Receptors, Type I / Q000235:genetics / Q000378:metabolism*; D019485:Bone Morphogenetic Proteins / Q000235:genetics / Q000378:metabolism; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D020134:Catalytic Domain / Q000502:physiology; D004622:Embryo, Mammalian / Q000166:cytology / Q000378:metabolism; D019204:GTP-Binding Proteins; D051379:Mice; D008822:Mice, Transgenic; D020125:Mutation, Missense; D018919:Neovascularization, Physiologic / Q000502:physiology*; D010012:Osteogenesis / Q000502:physiology*; D010766:Phosphorylation / Q000502:physiology; D054645:Protein Phosphatase 1 / Q000235:genetics / Q000378:metabolism; D017434:Protein Structure, Tertiary / Q000502:physiology; D015398:Signal Transduction / Q000502:physiology*; D051898:Smad1 Protein / Q000235:genetics / Q000378:metabolism; D019076:Transgenes / Q000235:genetics; D042461:Vascular Endothelial Growth Factor A / Q000235:genetics / Q000378:metabolism
chemical_list: D019485:Bone Morphogenetic Proteins; D002352:Carrier Proteins; C491124:SARA protein, mouse; D051898:Smad1 Protein; C497401:Smad1 protein, mouse; D042461:Vascular Endothelial Growth Factor A; C467480:vascular endothelial growth factor A, mouse; D052005:Bone Morphogenetic Protein Receptors, Type I; D054645:Protein Phosphatase 1; D019204:GTP-Binding Proteins