Dataset Information

BMP-Smad Signaling Regulates Postnatal Crown Dentinogenesis in Mouse Molar.

ABSTRACT: Dentinogenesis, a formation of dentin by odontoblasts, is an essential process during tooth development. Bone morphogenetic proteins (BMPs) are one of the most crucial growth factors that contribute to dentin formation. However, it is still unclear how BMP signaling pathways regulate postnatal crown and root dentinogenesis. BMPs transduce signals through canonical Smad and non-Smad signaling pathways including p38 and ERK signaling pathways. To investigate the roles of Smad and non-Smad signaling pathways in dentinogenesis, we conditionally deleted Bmpr1a, which encodes the type 1A receptor for BMPs, to remove both Smad and non-Smad pathways in Osterix-expressing cells. We also expressed a constitutively activated form of Bmpr1a (caBmpr1a) to increase Smad1/5/9 signaling activity without altered non-Smad activity in odontoblasts. To understand the function of BMP signaling during postnatal dentin formation, Cre activity was induced at the day of birth. Our results showed that loss of BmpR1A in odontoblasts resulted in impaired dentin formation and short molar roots at postnatal day 21. Bmpr1a cKO mice displayed a reduction of dentin matrix production compared to controls associated with increased cell proliferation and reduced Osx and Dspp expression. In contrast, caBmpr1a mutant mice that show increased Smad1/5/9 signaling activity resulted in no overt tooth phenotype. To further dissect the functions of each signaling activity, we generated Bmpr1a cKO mice also expressing caBmpr1a to restore only Smad1/5/9 signaling activity. Restoring Smad activity in the compound mutant mice rescued impaired crown dentin formation in the Bmpr1a cKO mice; however, impaired root dentin formation and short roots were not changed. These results suggest that BMP-Smad signaling in odontoblasts is responsible for crown dentin formation, while non-Smad signaling may play a major role in root dentin formation and elongation. © 2019 The Authors. JBMR Plus published by Wiley Periodicals, Inc. on behalf of American Society for Bone and Mineral Research. © 2019 The Authors. JBMR Plus published by Wiley Periodicals, Inc. on behalf of American Society for Bone and Mineral Research.

SUBMITTER: Omi M

PROVIDER: S-EPMC7017888 | biostudies-literature | 2020 Feb

REPOSITORIES: biostudies-literature

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BMP-Smad Signaling Regulates Postnatal Crown Dentinogenesis in Mouse Molar.

Omi Maiko M Kulkarni Anshul K AK Raichur Anagha A Fox Mason M Uptergrove Amber A Zhang Honghao H Mishina Yuji Y

JBMR plus 20191114 2

Dentinogenesis, a formation of dentin by odontoblasts, is an essential process during tooth development. Bone morphogenetic proteins (BMPs) are one of the most crucial growth factors that contribute to dentin formation. However, it is still unclear how BMP signaling pathways regulate postnatal crown and root dentinogenesis. BMPs transduce signals through canonical Smad and non-Smad signaling pathways including p38 and ERK signaling pathways. To investigate the roles of Smad and non-Smad signalin ...[more]

PMID: 32149267

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Project description:Bone morphogenetic proteins (BMPs) are important mediators of osteoclast differentiation. Although accumulating evidence has implicated BMPs in osteoblastogenesis, the mechanisms by which BMPs regulate osteoclastogenesis remain unclear. Activin A receptor type 1 (ACVR1) is a BMP type 1 receptor essential for skeletal development. Here, we observed that BMP-7, which preferentially binds to ACVR1, promotes osteoclast differentiation, suggesting ACVR1 is involved in osteoclastogenesis. To investigate this further, we isolated osteoclasts from either Acvr1-floxed mice or mice with constitutively-activated Acvr1 (caAcvr1) carrying tamoxifen-inducible Cre driven by a ubiquitin promotor and induced Cre activity in culture. Osteoclasts from the Acvr1-floxed mice had reduced osteoclast numbers and demineralization activity, whereas those from the caAcvr1-mutant mice formed large osteoclasts and demineralized pits, suggesting that BMP signaling through ACVR1 regulates osteoclast fusion and activity. It is reported that BMP-2 binds to BMPR1A, another BMP type 1 receptor, whereas BMP-7 binds to ACVR1 to activate SMAD1/5/9 signaling. Here, Bmpr1a-disrupted osteoclasts displayed reduced phospho-SMAD1/5/9 (pSMAD1/5/9) levels when induced by BMP-2, whereas no impacts on pSMAD1/5/9 were observed when induced by BMP-7. In contract, Acvr1-disrupted osteoclasts displayed reduced pSMAD1/5/9 levels when induced either by BMP-2 or BMP-7, suggesting that ACVR1 is the major receptor for transducing BMP-7 signals in osteoclasts. Indeed, LDN-193189 and LDN-212854, which specifically block SMAD1/5/9 phosphorylation, inhibited osteoclastogenesis of caAcvr1-mutant cells. Moreover, increased BMP signaling promoted nuclear translocation of nuclear factor-activated T-cells 1 (NFATc1), which was inhibited by LDN treatments. Taken together, ACVR1-mediated BMP-SMAD signaling activates NFATc1, a regulatory protein crucial for receptor activator of NF-?B ligand (RANKL)-induced osteoclastogenesis.

Project description:Mechanical loading contributes to bone development, growth, and metabolism. However, the mechanisms underlying long bone mineralization via changes in loading during the growth period are unclear. The aim of the present study was to investigate the regulatory mechanisms underlying endochondral ossification and endosteal mineralization by developing an ex vivo organ culture model with cyclic axial mechanical loads. The metacarpal bones of 3-week-old C57BL/6 mice were exposed to mechanical loading (0, 7.8, and 78 mN) for 1 h/day for 4 days. Histomorphometry revealed that axial mechanical loading regulated the thickness of the calcified zone in the growth plate and endosteal mineralization in the diaphysis in a load-dependent manner. Mechanical loading also resulted in load-dependent upregulation of endochondral ossification and bone mineralization-related genes, including bone morphogenetic protein 2 (Bmp2). Recombinant human BMP-2 administration caused similar changes in tissue structures. Conversely, inhibition of the BMP-Smad pathway diminished the stimulatory effects of mechanical loading and BMP-2 administration, suggesting that the effects of mechanical loading may be exerted through activation of the BMP-Smad pathway with the results of gene ontology and pathway analyses. Mechanical loading increased alkaline phosphatase activity and decreased carbonic anhydrase IX (Car9) mRNA expression, resulting in a significant pH increase in the culture supernatant. We hypothesize that, through activation of the BMP-Smad pathway, mechanical loading downregulates Car9, which may alkalize the local milieu, thereby inducing bone formation and long bone mineralization. Our results showed that cyclic axial mechanical loading increased endochondral ossification and endosteal mineralization in developing mouse long bones, which may have resulted from changes in the pH, ALP activity, and Pi/PPi of the extracellular environment. These findings advance our understanding of the regulation of mineralization mechanisms by mechanical loading mediated through activation of the BMP-Smad pathway.

Dataset Information

BMP-Smad Signaling Regulates Postnatal Crown Dentinogenesis in Mouse Molar.

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BMP-Smad Signaling Regulates Postnatal Crown Dentinogenesis in Mouse Molar.

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