Bone and Mineral Research Unit

Portland, United States

Bone and Mineral Research Unit

Portland, United States
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Wiren K.M.,Bone and Mineral Research Unit | Wiren K.M.,Oregon Health And Science University | Hashimoto J.G.,Bone and Mineral Research Unit | Hashimoto J.G.,Oregon Health And Science University | And 4 more authors.
Bone | Year: 2011

Although androgen is considered an anabolic hormone, the consequences of androgen receptor (AR) overexpression in skeletally-targeted AR-transgenic lines highlight the detrimental effect of enhanced androgen sensitivity on cortical bone quality. A compartment-specific anabolic response is observed only in male and not in female AR3.6-transgenic (tg) mice, with increased periosteal bone formation and calvarial thickening. To identify anabolic signaling cascades that have the potential to increase bone formation, qPCR array analysis was employed to define expression differences between AR3.6-tg and wild-type (WT) periosteal tissue. Notably, categories that were significantly different between the two genotypes included axonal guidance, CNS development and negative regulation of Wnt signaling with a node centered on stem cell pathways. Further, fine mapping of AR3.6-tg calvaria revealed that anabolic thickening in vivo is not uniform across the calvaria, occurring only in frontal and in not parietal bones. Multipotent fraction 1 progenitor populations from both genotypes were cultured separately as frontal bone neural crest stem-like cells (fNCSC) and parietal bone mesenchymal stem-like cells (pMSC). Both osteoblastic and adipogenic differentiation in these progenitor populations was influenced by embryonic lineage and by genotype. Adipogenesis was enhanced in WT fNCSC compared to pMSC, but transgenic cultures showed strong suppression of lipid accumulation only in fNCSC cells. Osteoblastogenesis was significantly increased in transgenic fNCSC cultures compared to WT, with elevated alkaline phosphatase (ALP) activity and induction of mineralization and nodule formation assessed by alizarin red and von Kossa staining. Osteocalcin (OC) and ALP mRNA levels were also increased in fNCSC cultures from AR3.6-tg vs. WT, but in pMSC cultures ALP mRNA levels, mineralization and nodule formation were decreased in AR3.6-tg cells. Expression differences identified by array in long bone periosteal tissue from AR3.6-tg vs. WT were recapitulated in the fNCSC samples while pMSC profiles reflected cortical expression. These observations reveal the opposing effects of androgen signaling on lineage commitment and osteoblast differentiation that is enhanced in cells derived from a neural crest origin but inhibited in cells derived from a mesodermal origin, consistent with in vivo compartment-specific responses to androgen. Combined, these results highlight the complex action of androgen in the body that is dependent on the embryonic lineage and developmental origin of the cell. Further, these data these data suggest that the periosteum surrounding long bone is derived from neural crest. © 2011.


Wiren K.M.,Bone and Mineral Research Unit | Wiren K.M.,Oregon Health And Science University | Semirale A.A.,Bone and Mineral Research Unit | Semirale A.A.,Oregon Health And Science University | And 4 more authors.
Bone | Year: 2010

Periosteal expansion is a recognized response to androgen exposure during bone development and in profoundly hypogonadal adults. However, androgen also suppresses endocortical bone formation, indicating that its effects on bone are dichotomous and envelope-specific. In fact, enhanced androgen signaling has been shown to have dramatic detrimental effects on whole bone biomechanical properties in two different transgenic models with skeletally targeted androgen receptor (AR) overexpression. As the mechanisms underlying this response are uncharacterized, we compared patterns of gene expression in periosteum-free cortical bone samples derived from AR-overexpressing transgenic male mice and their wild-type counterparts. We then assessed direct androgen effects in both wild-type and AR-overexpressing osteoblasts in primary culture. Among major signaling pathways associated with bone formation, focused quantitative RT-PCR (qPCR) array-based analysis of endocortical bone gene expression from wild-type vs. transgenic males identified the transforming growth factor-beta (TGF-Β) superfamily and bone morphogenetic protein (BMP) signaling as significantly altered by androgen in vivo. Bioinformatic analyses indicated proliferation, osteoblast differentiation and mineralization as major biological processes affected. Consistent with the in vivo array data and bioinformatic analyses, inhibition of differentiation observed with androgen exposure was reduced by exogenous BMP2 treatment of AR-overexpressing cultures to stimulate BMP signaling, confirming array pathway analysis. In addition, nonaromatizable dihydrotestosterone (DHT) inhibited osteoblast proliferation, differentiation and several indices of mineralization, including mineral accumulation and mineralized nodule formation in primary cultures from both wild-type and AR-transgenic mice. These findings identify a molecular mechanism based on altered BMP signaling that contributes to androgen inhibition of osteoblast differentiation and mineralization. Such detrimental effects of androgen on osteoblast function may underlie the generally disappointing results of androgen therapy. © 2009 Published by Elsevier Inc.


PubMed | Bone and Mineral Research Unit
Type: Journal Article | Journal: Bone | Year: 2011

Although androgen is considered an anabolic hormone, the consequences of androgen receptor (AR) overexpression in skeletally-targeted AR-transgenic lines highlight the detrimental effect of enhanced androgen sensitivity on cortical bone quality. A compartment-specific anabolic response is observed only in male and not in female AR3.6-transgenic (tg) mice, with increased periosteal bone formation and calvarial thickening. To identify anabolic signaling cascades that have the potential to increase bone formation, qPCR array analysis was employed to define expression differences between AR3.6-tg and wild-type (WT) periosteal tissue. Notably, categories that were significantly different between the two genotypes included axonal guidance, CNS development and negative regulation of Wnt signaling with a node centered on stem cell pathways. Further, fine mapping of AR3.6-tg calvaria revealed that anabolic thickening in vivo is not uniform across the calvaria, occurring only in frontal and in not parietal bones. Multipotent fraction 1 progenitor populations from both genotypes were cultured separately as frontal bone neural crest stem-like cells (fNCSC) and parietal bone mesenchymal stem-like cells (pMSC). Both osteoblastic and adipogenic differentiation in these progenitor populations was influenced by embryonic lineage and by genotype. Adipogenesis was enhanced in WT fNCSC compared to pMSC, but transgenic cultures showed strong suppression of lipid accumulation only in fNCSC cells. Osteoblastogenesis was significantly increased in transgenic fNCSC cultures compared to WT, with elevated alkaline phosphatase (ALP) activity and induction of mineralization and nodule formation assessed by alizarin red and von Kossa staining. Osteocalcin (OC) and ALP mRNA levels were also increased in fNCSC cultures from AR3.6-tg vs. WT, but in pMSC cultures ALP mRNA levels, mineralization and nodule formation were decreased in AR3.6-tg cells. Expression differences identified by array in long bone periosteal tissue from AR3.6-tg vs. WT were recapitulated in the fNCSC samples while pMSC profiles reflected cortical expression. These observations reveal the opposing effects of androgen signaling on lineage commitment and osteoblast differentiation that is enhanced in cells derived from a neural crest origin but inhibited in cells derived from a mesodermal origin, consistent with in vivo compartment-specific responses to androgen. Combined, these results highlight the complex action of androgen in the body that is dependent on the embryonic lineage and developmental origin of the cell. Further, these data these data suggest that the periosteum surrounding long bone is derived from neural crest.


PubMed | Bone and Mineral Research Unit
Type: Comparative Study | Journal: Bone | Year: 2010

Periosteal expansion is a recognized response to androgen exposure during bone development and in profoundly hypogonadal adults. However, androgen also suppresses endocortical bone formation, indicating that its effects on bone are dichotomous and envelope-specific. In fact, enhanced androgen signaling has been shown to have dramatic detrimental effects on whole bone biomechanical properties in two different transgenic models with skeletally targeted androgen receptor (AR) overexpression. As the mechanisms underlying this response are uncharacterized, we compared patterns of gene expression in periosteum-free cortical bone samples derived from AR-overexpressing transgenic male mice and their wild-type counterparts. We then assessed direct androgen effects in both wild-type and AR-overexpressing osteoblasts in primary culture. Among major signaling pathways associated with bone formation, focused quantitative RT-PCR (qPCR) array-based analysis of endocortical bone gene expression from wild-type vs. transgenic males identified the transforming growth factor-beta (TGF-beta) superfamily and bone morphogenetic protein (BMP) signaling as significantly altered by androgen in vivo. Bioinformatic analyses indicated proliferation, osteoblast differentiation and mineralization as major biological processes affected. Consistent with the in vivo array data and bioinformatic analyses, inhibition of differentiation observed with androgen exposure was reduced by exogenous BMP2 treatment of AR-overexpressing cultures to stimulate BMP signaling, confirming array pathway analysis. In addition, nonaromatizable dihydrotestosterone (DHT) inhibited osteoblast proliferation, differentiation and several indices of mineralization, including mineral accumulation and mineralized nodule formation in primary cultures from both wild-type and AR-transgenic mice. These findings identify a molecular mechanism based on altered BMP signaling that contributes to androgen inhibition of osteoblast differentiation and mineralization. Such detrimental effects of androgen on osteoblast function may underlie the generally disappointing results of androgen therapy.

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