Project description:Osteoblasts are adherent cells. Under physiological conditions they attach to mineralized and non-mineralized osseous surfaces. However, how exactly osteoblasts respond to these different osseous surfaces is largely unknown. Our hypothesis was that the state of matrix mineralization provides a functional signal to osteoblasts. To assess the osteoblast response to mineralized compared to demineralized osseous surfaces, we assessed the transcriptom.
Project description:Long non-coding RNAs (lncRNAs) are master regulators of gene expression and have recently emerged as potential innovative therapeutic targets. The deregulation of lncRNA expression patterns has been associated with age-related and noncommunicable diseases, including osteoporosis and bone tumors. However, the specific role of lncRNAs in physiological or pathological conditions in the bone tissue still needs to be further clarified, for their exploitation as therapeutic tools. In the present study, we evaluate the potential of the lncRNA CASC2 as a regulator of osteogenic differentiation and mineralization. Results show that CASC2 expression is decreased during osteogenic differentiation of human bone marrow-derived Mesenchymal Stem/Stromal cells (MSCs). CASC2 knockdown using small interfering RNA (siCASC2) increases the expression of the late osteogenic marker Bone Sialoprotein (BSP), but does not impact ALP staining levels, or the expression of early osteogenic transcripts including RUNX2 and OPG. Although siCASC2 does not impact hMSC proliferation nor apoptosis, it promotes the mineralization of hMSC cultured under osteogenic-inducing conditions, as shown by the increase of calcium deposits. Mass spectrometry-based proteomic analysis revealed that 89 proteins are regulated by CASC2 at late osteogenic stages, including proteins associated with bone diseases or anthropometric and musculoskeletal traits. Specifically, the Cartilage Oligomeric Matrix Protein (COMP) is highly enhanced by CASC2 knockdown at late stages of osteogenic differentiation, at either transcriptional and protein level. Inhibition of COMP impairs osteoblasts mineralization as well as the expression of BSP levels. The results indicate that lncRNA CASC2 regulates late osteogenesis and mineralization in hMSC via COMP and BSP. In conclusion, this study suggests lncRNA CASC2 as a potential new therapeutic target in bone mineralization.
Project description:Bone mineral density (BMD) is a highly heritable predictor of osteoporotic fracture. Genome wide association studies (GWAS) have identified hundreds of loci influencing BMD, but few have been functionally analyzed. In this study, we show that SNPs within a BMD locus on Chromosome 14q32.32 alter splicing and expression of PAR-1a/MARK3, a conserved serine/threonine kinase known to regulate bioenergetics, cell division and polarity. Mice lacking Mark3 either globally or selectively in osteoblasts have increased bone mass at maturity. RNA profiling from Mark3 deficient osteoblasts suggested changes in the expression of components of the Notch signaling pathway. Mark3 deficient osteoblasts exhibited greater matrix mineralization compared with controls that was accompanied by reduced Jag1/Hes1 expression and diminished downstream JNK signaling. Overexpression of Jag1 in Mark3 deficient osteoblasts both in vitro and in vivo normalized mineralization capacity and bone mass, respectively. Together, these findings reveal a mechanism whereby genetically regulated alterations in Mark3 expression perturb cell signaling in osteoblasts to influence bone mass.
Project description:We used gene array analysis of cortical bone to identify Phex-dependent gene transcripts regulating Fgf23 production and mineralization in Hyp mice. We discovered that activation of Fgf receptor- and Wnt-pathways contribute to increased Ffg23 gene transcription in Hyp bone. We found evidence in Hyp bone for increased expression of Fgf1, Fgf7, and Egr2 in the Fgf-signaling pathway and decrements in Sost and Cpz and increments in Sfrp1 and 4 in the Wnt-signaling pathway. Moreover, activation of Fgf and Wnt-signaling stimulated, whereas Tgf β inhibited Fgf23 promoter activity in osteoblasts. We also observed reductions in Bmp1, a metalloproteinase that metabolizes the Fgf23 regulatory extracellular matrix protein Dmp1. These findings suggest that elevation of Fgf23 expression in osteocytes is regulated by interactions between cell surface expression of Phex, extracellular matrix proteins and paracrine effects of Fgf and Wnt. Alterations were also found in enzymes regulating the posttranslational processing and stability of Fgf23, including decrements in the glycosyltransferase Galnt3 and the proprotein convertase Pcsk5. In addition, we found that the Pcsk5 and the glycosyltransferase Galnt3 were decreased in Hyp bone, suggesting that reduced post-translational processing of FGF23 may also contribute to increased Fgf23 levels in Hyp mice. With regards to mineralization, we identified additional candidates to explain the intrinsic mineralization defect in Hyp osteoblasts, including increases in the mineralization inhibitors Mgp and Thbs4, as well as increases in local pH altering factors, carbonic anhydrase 12 (Car12) and 3 (Car3) and the sodium-dependent citrate transporter (Slc13a5). These studies demonstrate the complexity of gene expression alterations in bone that accompanies inactivating Phex mutations and identify novel pathways that may coordinate Fgf23 expression and mineralization of extracellular matrix in Hyp bone. We isolated total RNAs from long bones of both WT and Hyp mice at 12 days of age. Since the RNA yields from the long bones are very low, we combined 2 bone samples with same genotype (WT or Hyp) for one RNA extraction. We will compare the difference of the gene expressions between Hyp and WT. We will use 4 samples in each animal condition.
Project description:We used gene array analysis of cortical bone to identify Phex-dependent gene transcripts regulating Fgf23 production and mineralization in Hyp mice. We discovered that activation of Fgf receptor- and Wnt-pathways contribute to increased Ffg23 gene transcription in Hyp bone. We found evidence in Hyp bone for increased expression of Fgf1, Fgf7, and Egr2 in the Fgf-signaling pathway and decrements in Sost and Cpz and increments in Sfrp1 and 4 in the Wnt-signaling pathway. Moreover, activation of Fgf and Wnt-signaling stimulated, whereas Tgf β inhibited Fgf23 promoter activity in osteoblasts. We also observed reductions in Bmp1, a metalloproteinase that metabolizes the Fgf23 regulatory extracellular matrix protein Dmp1. These findings suggest that elevation of Fgf23 expression in osteocytes is regulated by interactions between cell surface expression of Phex, extracellular matrix proteins and paracrine effects of Fgf and Wnt. Alterations were also found in enzymes regulating the posttranslational processing and stability of Fgf23, including decrements in the glycosyltransferase Galnt3 and the proprotein convertase Pcsk5. In addition, we found that the Pcsk5 and the glycosyltransferase Galnt3 were decreased in Hyp bone, suggesting that reduced post-translational processing of FGF23 may also contribute to increased Fgf23 levels in Hyp mice. With regards to mineralization, we identified additional candidates to explain the intrinsic mineralization defect in Hyp osteoblasts, including increases in the mineralization inhibitors Mgp and Thbs4, as well as increases in local pH altering factors, carbonic anhydrase 12 (Car12) and 3 (Car3) and the sodium-dependent citrate transporter (Slc13a5). These studies demonstrate the complexity of gene expression alterations in bone that accompanies inactivating Phex mutations and identify novel pathways that may coordinate Fgf23 expression and mineralization of extracellular matrix in Hyp bone.
Project description:Rosiglitazone-targeted transcriptional networks as gene expression signature of physiological and pathological mineralization – a top-down approach to identify novel targets for bone and vascular health Clinical studies have recently revealed detrimental skeletal and vascular effects of the insulin sensitizer rosiglitazone. At the cellular level, we have shown earlier that rosiglitazone accelerates osteoblast differentiation from human mesenchymal stem cells (hMSC) at the expense of increased oxidative stress and apoptosis. In calcifying human vascular cells, rosiglitazone stimulates pathological mineralization, an effect that was diminished by the antioxidant resveratrol. In order to elucidate the transcriptional networks underlying the rosiglitazone-enhanced mineralization phenotype, we performed genome-wide transcriptional profiling of osteogenic hMSCs treated with rosiglitazone for short-term periods of 1 up to 48h during the first two days of culture time, a phase that we show is sufficient to mediate the stimulatory effect of rosiglitazone on mineralization. Microarray-based mRNA expression analysis revealed 190 probes that were differently expressed in at least one condition compared to vehicle-treated control. This rosiglitazone gene signature contained confirmed primary PPAR targets and was also endogenously regulated during osteogenic differentiation from hMSCs and osteoblast-like differentiation of vascular smooth muscle cells (VSMCs) into calcifying vascular cells (CVCs). Further comparative analysis revealed rosiglitazone targets that were commonly enriched in osteoblasts and CVCs or specifically enriched in either osteoblasts or CVCs. Finally, we compared the expression patterns of CVC-specific genes with patient expression data from carotid plaque versus intact adjacent tissue, and identified five rosiglitazone targets that were differentially regulated in CVCs and carotid plaque but not osteoblasts when compared to their respective non-mineralizing counterparts. These targets, i.e PDK4, SDC4, SPRY4, TCF4, and DACT1 may specifically control extracellular matrix mineralization in vascular cells and hence provide interesting candidates for further investigations to improve vascular health.
Project description:Osteoblasts are adherent cells, and under physiological conditions they attach to both mineralized and non-mineralized osseous surfaces. However, how exactly osteoblasts respond to these different osseous surfaces is largely unknown. Our hypothesis was that the state of matrix mineralization provides a functional signal to osteoblasts. To assess the osteoblast response to mineralized compared to demineralized osseous surfaces, we developed and validated a novel tissue surface model. We demonstrated that with the exception of the absence of mineral, the mineralized and demineralized surfaces were similar in molecular composition as determined, for example, by collagen content and maturity. Subsequently, we used the human osteoblastic cell line MG63 in combination with genome-wide gene set enrichment analysis (GSEA) to record and compare the gene expression signatures on mineralized and demineralized surfaces. Assessment of the 5 most significant gene sets showed on mineralized surfaces an enrichment exclusively of genes sets linked to protein synthesis, while on the demineralized surfaces 3 of the 5 enriched gene sets were associated with the matrix. Focusing on these three gene sets, we observed not only the expected structural components of the bone matrix, but also gene products, such as HMCN1 or NID2, that are likely to act as temporal migration guides. Together, these findings suggest that in osteoblasts mineralized and demineralized osseous surfaces favor intracellular protein production and matrix formation, respectively. Further, they demonstrate that the mineralization state of bone independently controls gene expression in osteoblastic cells.
Project description:That phosphate homeostasis is tightly linked to skeletal mineralization is probably best underscored by the fact that the phosphaturic hormone FGF23 is primarily expressed by terminally differentiated osteoblasts/osteocytes, and that increased circulating FGF23 levels are causative for different types of hypophosphatemic rickets. In contrast, FGF23-inactivation results in hyperphosphatemia, and unexpectedly this phenotype is associated with severe osteomalacia in Fgf23-deficient mice. In this context it is interesting that different types of bone cells have been shown to respond to extracellular phosphate, thereby raising the concept that phosphate can act as a signaling molecule. To identify phosphate-responsive genes in primary murine osteoblasts we performed genome-wide expression analysis with cells maintained in medium containing either 1 mM or 4 mM sodium phosphate for 6 hours. As confirmed by qRT-PCR, this analysis revealed that several known osteoblast differentiation markers (Bglap, Ibsp or Phex) were unaffected by raising extracellular phosphate levels. In contrast, we found that the expression of Enpp1 and Ank, two genes encoding inhibitors of matrix mineralization, was induced by extracellular phosphate, while the expression of Sost and Dkk1, two genes encoding inhibitors of bone formation, was negatively regulated. The ability of osteoblasts to respond to extracellular phosphate was dependent on their differentiation state, and shRNA-dependent repression of the phosphate transporter Slc20a1 in MC3T3-E1 cells partially abolished their molecular response to phosphate. Taken together, our results provide further evidence for a role of extracellular phosphate as a signaling molecule and raise the possibility that severe hyperphosphatemia can negatively affect skeletal mineralization.
Project description:Bone defects arising from fractures or disease represent a significant problem for surgeons to manage and are a substantial economic burden on the healthcare economy. Recent advances in the development of biomaterial substitutes provides an attractive alternative to the current “gold standard” autologous bone grafting. Despite on-going research, we are yet to identify cost effective biocompatible, osteo-inductive factors that stimulate controlled, accelerated bone regeneration.We have recently reported that enzymes with peroxidase activity possess previously unrecognised roles in extracellular matrix biosynthesis, angiogenesis and osteoclastogenesis, which are essential processes in bone remodelling and repair. Here, we report for the first time, that plant-derived soybean peroxidase (SBP) possesses pro-osteogenic ability by promoting collagen I biosynthesis and matrix mineralization of human osteoblasts in vitro. Mechanistically, SBP regulates osteogenic genes responsible for inflammation, extracellular matrix remodelling and ossification, which are necessary for normal bone healing. Furthermore, SBP was shown to have osteo-inductive properties, that when combined with commercially available biphasic calcium phosphate (BCP) granules can accelerate bone repair in a critical size long bone defect ovine model. Micro-CT analysis showed that SBP when combined with commercially available biphasic calcium phosphate (BCP) granules significantly increased bone formation within the defects as early as 4 weeks compared to BCP alone. Histomorphometric assessment demonstrated accelerated bone formation prominent at the defect margins and surrounding individual BCP granules, with evidence of intramembranous ossification. These results highlight the capacity of SBP to be an effective regulator of osteoblastic function and may be beneficial as a new and cost effective osteo-inductive agent to accelerate repair of large bone defects.
Project description:Analysis of GPM6B silenced osteogenic hMSC at gene expression level. Analysis is showing significant changes in genes involved in cytoskeleton organization and biogenesis. Immunocytochemistry confirms changed distribution of actin filaments and change in shape and in size of focal adhesions upon GPM6B silencing. Moreover, we demonstrated that production and release of ALP-positive matrix vesicles (MVs) was reduced. In conclusion, we identified GPM6B as a novel regulator of osteoblast differentiation and bone formation and thereby demonstrating the significance of cytoskeleton organization for MV production and eventual mineralization. Total RNA obtained from osteogenic hMSC, 7days after shRNAi lenti viral transductions with 3 different GPM6B silencing constructs (sh1, sh2, sh3) compared to 3 different controls (shC:non-silencing shRNA, tGFP: tGFP control vector and Mock: mock transduced cells)