Project description:G protein coupled receptor (GPCR) signaling in osteoblasts (OBs) is an important regulator of bone formation. We previously described a mouse model expressing Rs1, an engineered constitutively active Gs-coupled GPCR, under the control of the 2.3 kb-Col I promoter. These mice showed a dramatic age-dependent increase in trabecular bone which were accompanied by an increase in OB lineage cells, especially immature OBs, indicated by an expansion of cells expressing Osterix and Runx2 in the whole femur. In this study, we further evaluated how Gs signaling in OBs affects intramembranous bone formation by examining calvariae of one-and nine-week-old Col1(2.3)/Rs1 mice. Rs1 calvariae displayed a dramatic increase in total volume and trabecular bone volume with partial loss of cortical structure. By immunohistochemistry, Osterix was detected in cells throughout the inter-trabecular space in Rs1 expressing mice while Osteocalcin was expressed predominantly in cells along bone surfaces. These findings resembled that previously seen in Rs1 femoral bones, suggesting the role of paracrine mediators secreted from OBs driven by 2.3 kb-Col I promoter could influence early OB commitment, differentiation, and/or proliferation. However, it is still unclear how G protein signaling in mature OBs leads to the observed alterations in bone mass. In this study, we investigated the cellular basis of the skeletal changes by assessing the effect of Rs1 expression in vivo on the transcriptome of mature OBs. We identified the complete set of Gs-GPCRs and other GPCRs that are expressed on OBs which may contribute to the observed skeletal phenotype. Candidate paracrine mediators of the effect of Gs signaling in OBs were determined. Genes affected by Rs1 signaling include those encoding proteins important for cell differentiation, cytokines and growth factors, angiogenesis, coagulation, and energy metabolism. Our results identify novel candidate mediators of the anabolic response to the skeleton to Gs signaling in mature OBs. We utilized a microarray approach to examine Rs1-induced alterations in the OB transcriptome. The approach used to identify an approximate snapshot of the OB transcriptome at the time of sacrifice by isolating the OB population that expresses Rs1 by GFP labeling, without the use of cell culture. We compared gene expression between control OBs and OBs-expressing Rs1 in triplicates.

Project description:Hutchinson-Gilford Progeria Syndrome (HGPS) is a premature aging disorder that affects tissues of mesenchymal origin. Most individuals with HGPS harbor a de novo c.1824C>T (p.G608G) mutation in the gene encoding lamin A (LMNA), which activates a cryptic splice donor site resulting in production of a toxic protein termed “progerin”. Clinical manifestations include growth deficiency, lipodystrophy, sclerotic dermis, cardiovascular defects and bone dysplasia. In this study we utilized the LmnaG609G knock-in (KI) mouse model of HGPS to further define mechanisms of bone loss associated with normal and premature aging disorders. Newborn skeletal staining of KI mice revealed altered rib cage shape and spinal curvature, and delayed calvarial mineralization with increased craniofacial and mandibular cartilage content. MicroCT analysis and mechanical testing of adult femurs indicated increased fragility associated with reduced cortical and trabecular bone mass, recapitulating the progressive bone deterioration that occurs in HGPS patients. We investigated underlying mechanisms of bone loss in KI mice at the cellular level in bone cell populations. Formation of wild-type and KI osteoclasts from bone marrow-derived precursors was inhibited in the presence of KI osteoblast-conditioned media in vitro, suggesting an extrinsic factor(s) responsible for the decreased number of TRAcP-positive osteoclasts observed on KI trabecular surfaces in vivo. Cultured KI osteoblasts exhibited abnormal differentiation characterized by reduced capacity to deposit and mineralize extracellular matrix and increased lipid accumulation compared to wild-type, providing a mechanism for the reduced mineral apposition and bone formation rates observed in vivo. Furthermore, quantitative analyses of KI transcripts confirmed upregulation of adipogenic genes both in vitro and in vivo. These data demonstrate that osteoblast phenotypic plasticity, rather than dysregulated bone remodelling, contributes to abnormal bone formation in HGPS mice.

Project description:G protein coupled receptor (GPCR) signaling in osteoblasts (OBs) is an important regulator of bone formation. We previously described a mouse model expressing Rs1, an engineered constitutively active Gs-coupled GPCR, under the control of the 2.3 kb-Col I promoter. These mice showed a dramatic age-dependent increase in trabecular bone which were accompanied by an increase in OB lineage cells, especially immature OBs, indicated by an expansion of cells expressing Osterix and Runx2 in the whole femur. In this study, we further evaluated how Gs signaling in OBs affects intramembranous bone formation by examining calvariae of one-and nine-week-old Col1(2.3)/Rs1 mice. Rs1 calvariae displayed a dramatic increase in total volume and trabecular bone volume with partial loss of cortical structure. By immunohistochemistry, Osterix was detected in cells throughout the inter-trabecular space in Rs1 expressing mice while Osteocalcin was expressed predominantly in cells along bone surfaces. These findings resembled that previously seen in Rs1 femoral bones, suggesting the role of paracrine mediators secreted from OBs driven by 2.3 kb-Col I promoter could influence early OB commitment, differentiation, and/or proliferation. However, it is still unclear how G protein signaling in mature OBs leads to the observed alterations in bone mass. In this study, we investigated the cellular basis of the skeletal changes by assessing the effect of Rs1 expression in vivo on the transcriptome of mature OBs. We identified the complete set of Gs-GPCRs and other GPCRs that are expressed on OBs which may contribute to the observed skeletal phenotype. Candidate paracrine mediators of the effect of Gs signaling in OBs were determined. Genes affected by Rs1 signaling include those encoding proteins important for cell differentiation, cytokines and growth factors, angiogenesis, coagulation, and energy metabolism. Our results identify novel candidate mediators of the anabolic response to the skeleton to Gs signaling in mature OBs.

Dataset Information

Premature aging in growth-plate and periosteum resident skeletal stem cells is responsible for bone loss

Similar Datasets

OmicsDI is part of the ELIXIR infrastructure