Wnt/β-catenin signaling is critical for various cellular processes in multiple cell types,including osteoblast(OB)differentiation and function.Exactly how Wnt/β-catenin signaling is regulated in OBs remain elusive.A...Wnt/β-catenin signaling is critical for various cellular processes in multiple cell types,including osteoblast(OB)differentiation and function.Exactly how Wnt/β-catenin signaling is regulated in OBs remain elusive.ATP6AP2,an accessory subunit of V-ATPase,plays important roles in multiple cell types/organs and multiple signaling pathways.However,little is known whether and how ATP6AP2 in OBs regulates Wnt/β-catenin signaling and bone formation.Here we provide evidence for ATP6AP2 in the OB-lineage cells to promote OB-mediated bone formation and bone homeostasis selectively in the trabecular bone regions.Conditionally knocking out(CKO)ATP6AP2 in the OB-lineage cells(Atp6ap2^(Ocn-Cre))reduced trabecular,but not cortical,bone formation and bone mass.Proteomic and cellular biochemical studies revealed that LRP6 and N-cadherin were reduced in ATP6AP2-KO BMSCs and OBs,but not osteocytes.Additional in vitro and in vivo studies revealed impairedβ-catenin signaling in ATP6AP2-KO BMSCs and OBs,but not osteocytes,under both basal and Wnt stimulated conditions,although LRP5 was decreased in ATP6AP2-KO osteocytes,but not BMSCs.Further cell biological studies uncovered that osteoblastic ATP6AP2 is not required for Wnt3a suppression ofβ-catenin phosphorylation,but necessary for LRP6/β-catenin and N-cadherin/β-catenin protein complex distribution at the cell membrane,thus preventing their degradation.Expression of activeβ-catenin diminished the OB differentiation deficit in ATP6AP2-KO BMSCs.Taken together,these results support the view for ATP6AP2 as a critical regulator of both LRP6 and N-cadherin protein trafficking and stability,and thus regulatingβ-catenin levels,demonstrating an un-recognized function of osteoblastic ATP6AP2 in promoting Wnt/LRP6/β-catenin signaling and trabecular bone formation.展开更多
YAP（yes-associated protein） is a transcriptional factor that is negatively regulated by Hippo pathway, a conserved pathway for the development and size control of multiple organs. The exact function of YAP in bone h...YAP（yes-associated protein） is a transcriptional factor that is negatively regulated by Hippo pathway, a conserved pathway for the development and size control of multiple organs. The exact function of YAP in bone homeostasis remains controversial. Here we provide evidence for YAP＇s function in promoting osteogenesis, suppressing adipogenesis, and thus maintaining bone homeostasis.YAP is selectively expressed in osteoblast（OB）-lineage cells. Conditionally knocking out Yap in the OB lineage in mice reduces cell proliferation and OB differentiation and increases adipocyte formation, resulting in a trabecular bone loss. Mechanistically, YAP interacts with β-catenin and is necessary for maintenance of nuclear β-catenin level and Wnt/β-catenin signaling. Expression of β-catenin in YAP-deficient BMSCs（bone marrow stromal cells） diminishes the osteogenesis deficit. These results thus identify YAP-β-catenin as an important pathway for osteogenesis during adult bone remodeling and uncover a mechanism underlying YAP regulation of bone homeostasis.展开更多
Patients with Alzheimer’s disease(AD)often have lower bone mass than healthy individuals.However,the mechanisms underlying this change remain elusive.Previously,we found that Tg2576 mice,an AD animal model that ubiqu...Patients with Alzheimer’s disease(AD)often have lower bone mass than healthy individuals.However,the mechanisms underlying this change remain elusive.Previously,we found that Tg2576 mice,an AD animal model that ubiquitously expresses Swedish mutant amyloid precursor protein(APPswe),shows osteoporotic changes,reduced bone formation,and increased bone resorption.To understand how bone deficits develop in Tg2576 mice,we used a multiplex antibody array to screen for serum proteins that are altered in Tg2576 mice and identified hepcidin,a master regulator of iron homeostasis.We further investigated hepcidin’s function in bone homeostasis and found that hepcidin levels were increased not only in the serum but also in the liver,muscle,and osteoblast(OB)lineage cells in Tg2576 mice at both the mRNA and protein levels.We then generated mice selectively expressing hepcidin in hepatocytes or OB lineage cells,which showed trabecular bone loss and increased osteoclast(OC)-mediated bone resorption.Further cell studies suggested that hepcidin increased OC precursor proliferation and differentiation by downregulating ferroportin(FPN)expression and increasing intracellular iron levels.In OB lineage cells,APPswe enhanced hepcidin expression by inducing ER stress and increasing OC formation,in part through hepcidin.Together,these results suggest that increased hepcidin expression in hepatocytes and OB lineage cells in Tg2576 mice contributes to enhanced osteoclastogenesis and trabecular bone loss,identifying the hepcidin-FPN-iron axis as a potential therapeutic target to prevent AD-associated bone loss.展开更多
Neogenin is a transmembrane receptor critical for multiple cellular processes,including neurogenesis,astrogliogenesis,endochondral bone formation,and iron homeostasis.Here we present evidence that loss of neogenin con...Neogenin is a transmembrane receptor critical for multiple cellular processes,including neurogenesis,astrogliogenesis,endochondral bone formation,and iron homeostasis.Here we present evidence that loss of neogenin contributes to pathogenesis of persistent hyperplastic primary vitreous(PHPV)formation,a genetic disorder accounting for^5% of blindness in the USA.Selective loss of neogenin in neural crest cells(as observed in Wntl-Cre;Neofff mice),but not neural stem cells(as observed in GFAP-Cre and Nestin-Cre;Neo^f/f mice),resulted in a dysregulation of neural crest cell migration or delamination,exhibiting features of PHPV-like pathology(e.g.elevated retrolental mass),unclosed retinal fissure,and microphthalmia.These results demonstrate an unrecognized function of neogenin in preventing PHPV pathogenesis,implicating neogenin regulation of neural crest cell delamination/migration and retinal fissure formation as potential underlying mechanisms of PHPV.展开更多
基金supported in part by grants from the National Institutes of Health(AG045781,AG051510,and AG066526)(to WCX).
文摘Wnt/β-catenin signaling is critical for various cellular processes in multiple cell types,including osteoblast(OB)differentiation and function.Exactly how Wnt/β-catenin signaling is regulated in OBs remain elusive.ATP6AP2,an accessory subunit of V-ATPase,plays important roles in multiple cell types/organs and multiple signaling pathways.However,little is known whether and how ATP6AP2 in OBs regulates Wnt/β-catenin signaling and bone formation.Here we provide evidence for ATP6AP2 in the OB-lineage cells to promote OB-mediated bone formation and bone homeostasis selectively in the trabecular bone regions.Conditionally knocking out(CKO)ATP6AP2 in the OB-lineage cells(Atp6ap2^(Ocn-Cre))reduced trabecular,but not cortical,bone formation and bone mass.Proteomic and cellular biochemical studies revealed that LRP6 and N-cadherin were reduced in ATP6AP2-KO BMSCs and OBs,but not osteocytes.Additional in vitro and in vivo studies revealed impairedβ-catenin signaling in ATP6AP2-KO BMSCs and OBs,but not osteocytes,under both basal and Wnt stimulated conditions,although LRP5 was decreased in ATP6AP2-KO osteocytes,but not BMSCs.Further cell biological studies uncovered that osteoblastic ATP6AP2 is not required for Wnt3a suppression ofβ-catenin phosphorylation,but necessary for LRP6/β-catenin and N-cadherin/β-catenin protein complex distribution at the cell membrane,thus preventing their degradation.Expression of activeβ-catenin diminished the OB differentiation deficit in ATP6AP2-KO BMSCs.Taken together,these results support the view for ATP6AP2 as a critical regulator of both LRP6 and N-cadherin protein trafficking and stability,and thus regulatingβ-catenin levels,demonstrating an un-recognized function of osteoblastic ATP6AP2 in promoting Wnt/LRP6/β-catenin signaling and trabecular bone formation.
基金supported in part by grants from the National Institutes of Health(AG051773)and VA(BX000838)
文摘YAP（yes-associated protein） is a transcriptional factor that is negatively regulated by Hippo pathway, a conserved pathway for the development and size control of multiple organs. The exact function of YAP in bone homeostasis remains controversial. Here we provide evidence for YAP＇s function in promoting osteogenesis, suppressing adipogenesis, and thus maintaining bone homeostasis.YAP is selectively expressed in osteoblast（OB）-lineage cells. Conditionally knocking out Yap in the OB lineage in mice reduces cell proliferation and OB differentiation and increases adipocyte formation, resulting in a trabecular bone loss. Mechanistically, YAP interacts with β-catenin and is necessary for maintenance of nuclear β-catenin level and Wnt/β-catenin signaling. Expression of β-catenin in YAP-deficient BMSCs（bone marrow stromal cells） diminishes the osteogenesis deficit. These results thus identify YAP-β-catenin as an important pathway for osteogenesis during adult bone remodeling and uncover a mechanism underlying YAP regulation of bone homeostasis.
基金supported in part by grants from the National Institutes of Health(AG051773)the U.S.Department of Veterans Affairs(BX000838)by the Meisel family and InMotion in Cleveland,Ohio.
文摘Patients with Alzheimer’s disease(AD)often have lower bone mass than healthy individuals.However,the mechanisms underlying this change remain elusive.Previously,we found that Tg2576 mice,an AD animal model that ubiquitously expresses Swedish mutant amyloid precursor protein(APPswe),shows osteoporotic changes,reduced bone formation,and increased bone resorption.To understand how bone deficits develop in Tg2576 mice,we used a multiplex antibody array to screen for serum proteins that are altered in Tg2576 mice and identified hepcidin,a master regulator of iron homeostasis.We further investigated hepcidin’s function in bone homeostasis and found that hepcidin levels were increased not only in the serum but also in the liver,muscle,and osteoblast(OB)lineage cells in Tg2576 mice at both the mRNA and protein levels.We then generated mice selectively expressing hepcidin in hepatocytes or OB lineage cells,which showed trabecular bone loss and increased osteoclast(OC)-mediated bone resorption.Further cell studies suggested that hepcidin increased OC precursor proliferation and differentiation by downregulating ferroportin(FPN)expression and increasing intracellular iron levels.In OB lineage cells,APPswe enhanced hepcidin expression by inducing ER stress and increasing OC formation,in part through hepcidin.Together,these results suggest that increased hepcidin expression in hepatocytes and OB lineage cells in Tg2576 mice contributes to enhanced osteoclastogenesis and trabecular bone loss,identifying the hepcidin-FPN-iron axis as a potential therapeutic target to prevent AD-associated bone loss.
文摘Neogenin is a transmembrane receptor critical for multiple cellular processes,including neurogenesis,astrogliogenesis,endochondral bone formation,and iron homeostasis.Here we present evidence that loss of neogenin contributes to pathogenesis of persistent hyperplastic primary vitreous(PHPV)formation,a genetic disorder accounting for^5% of blindness in the USA.Selective loss of neogenin in neural crest cells(as observed in Wntl-Cre;Neofff mice),but not neural stem cells(as observed in GFAP-Cre and Nestin-Cre;Neo^f/f mice),resulted in a dysregulation of neural crest cell migration or delamination,exhibiting features of PHPV-like pathology(e.g.elevated retrolental mass),unclosed retinal fissure,and microphthalmia.These results demonstrate an unrecognized function of neogenin in preventing PHPV pathogenesis,implicating neogenin regulation of neural crest cell delamination/migration and retinal fissure formation as potential underlying mechanisms of PHPV.
