Osteoblast Gene Expression in Response to Bicc1 Knockdown
ABSTRACT: We recently identified Bicc1 as a regulator of osteoblast differentiation and bone mass. Bicc1 encodes an RNA-binding protein. Here, we have used siRNA to decrease Bicc1 expression in primary calvarial osteoblasts. Illlumina microarrays were then used to profile global gene expression changes. The experiment consisted of 16 total samples in 4 treatment groups (N=4 replicates per treatment). The treatment groups were osteoblasts treated with 1). control scrambled siRNA, 2) Bicc1_1 siRNA, 3) Bicc1_2 siRNA and 3) Bicc1_3 siRNA. Cells were isolated, transfected and 48 hours later RNA was isolated and hybridized to arrays.
Project description:To screen mRNAs specifically regulated by mTORC1, a global mRNA expression profile in calvarial osteoblasts (OBs) from mice with or without OB-specific Tsc1 knockout was developed using microarray. Wild type (WT) or OB-specific Tsc1 knockout (KO) mice were sacrificed, with calvarial osteoblasts harvested and subjected to total RNA extraction.
Project description:Wnt signaling is critical for normal skeletal development as well as whole-body metabolic function. In this study, we described a previously unrecognized function for Wnt-Lrp5 signaling in the osteoblast that allows bone to acquire the resources necessary to fuel bone formation. Mice lacking the Lrp5 co-receptor specifically in osteoblasts and osteocytes exhibit the expected reductions in postnatal bone mass and also develop peripheral adiposity with corresponding reductions in energy expenditure. Conversely, mice expressing a high-bone mass mutant Lrp5 allele are leaner with reduced plasma triglyceride and free fatty acid levels. In this context, Wnt-initiated signals downstream of Lrp5, but not Lrp6, regulate the expression of key enzymes required for fatty acid β-oxidation. These results suggest that Wnt-Lrp5 signaling regulates basic cellular activities beyond those associated with fate-specification and differentiation in bone and that the skeleton influences global energy homeostasis via mechanisms independent of osteocalcin and glucose metabolism Total RNA isolated from cultures of Lrp5-deficient osteoblasts differentiated for 7 days in vitro compared to control osteoblasts
Project description:We recently identified Bicc1 as a regulator of osteoblast differentiation and bone mass. Bicc1 encodes an RNA-binding protein. Here, we have used siRNA to decrease Bicc1 expression in primary calvarial osteoblasts. Illlumina microarrays were then used to profile global gene expression changes. Overall design: The experiment consisted of 16 total samples in 4 treatment groups (N=4 replicates per treatment). The treatment groups were osteoblasts treated with 1). control scrambled siRNA, 2) Bicc1_1 siRNA, 3) Bicc1_2 siRNA and 3) Bicc1_3 siRNA. Cells were isolated, transfected and 48 hours later RNA was isolated and hybridized to arrays.
Project description:The benefits of estrogens on bone health are well established; how estrogens signal to regulate bone formation and resorption is less well understood. We show here that 17?-estradiol (E2)-induced apoptosis of bone-resorbing osteoclasts is mediated by cleavage and solubilization of osteoblast-expressed Fas ligand (FasL). U2OS-ER? osteoblast-like cells expressing an EGFP-tagged FasL at the C-terminus showed decreased fluorescence after E2 treatment, indicative of a cleavage event. Treatment of U2OS-ER? cultures with a specific MMP3 inhibitor in the presence of E2 blocked FasL cleavage and showed an increase in the number of EGFP-FasL+ cells. siRNA experiments successfully knocked down MMP3 expression and restored full-length FasL to basal levels. E2 treatment of both human and murine primary osteoblasts showed upregulation of MMP3 mRNA expression, and calvarial organ cultures showed increased expression of MMP3 protein and colocalization with the osteoblast-specific RUNX2 after E2 treatment. In addition, osteoblast cell cultures derived from ER?KO mice showed decreased expression of MMP3 but not MMP7 and ADAM10, two known FasL proteases, demonstrating that ER? signaling regulates MMP3. Also, conditioned media of E2-treated calvarial osteoblasts showed an approximate sixfold increase in the concentration of soluble FasL, indicating extensive cleavage, and soluble FasL concentrations were reduced in the presence of a specific MMP3 inhibitor. Finally, to show the role of soluble FasL in osteoclast apoptosis, human osteoclasts were cocultured with MC3T3 osteoblasts. Both a specific MMP3 inhibitor and an MMP inhibitor cocktail preserved osteoclast differentiation and survival in the presence of E2 and demonstrate the necessity of MMP3 for E2-induced osteoclast apoptosis. These experiments further define the molecular mechanism of estrogen's bone-protective effects by inducing osteoclast apoptosis through upregulation of MMP3 and FasL cleavage.
Project description:Ossification defects leading to craniofacial dysmorphism or rhizomelia are typical phenotypes in patients and corresponding knockout mouse models with distinct peroxisomal disorders. Despite these obvious skeletal pathologies, to date no careful analysis exists on the distribution and function of peroxisomes in skeletal tissues and their alterations during ossification. Therefore, we analyzed the peroxisomal compartment in different cell types of mouse cartilage and bone as well as in primary cultures of calvarial osteoblasts. The peroxisome number and metabolism strongly increased in chondrocytes during endochondral ossification from the reserve to the hypertrophic zone, whereas in bone, metabolically active osteoblasts contained a higher numerical abundance of this organelle than osteocytes. The high abundance of peroxisomes in these skeletal cell types is reflected by high levels of Pex11β gene expression. During culture, calvarial pre-osteoblasts differentiated into secretory osteoblasts accompanied by peroxisome proliferation and increased levels of peroxisomal genes and proteins. Since many peroxisomal genes contain a PPAR-responsive element, we analyzed the gene expression of PPARɑ/ß/ɣ in calvarial osteoblasts and MC3T3-E1 cells, revealing higher levels for PPARß than for PPARɑ and PPARɣ. Treatment with different PPAR agonists and antagonists not only changed the peroxisomal compartment and associated gene expression, but also induced complex alterations of the gene expression patterns of the other PPAR family members. Studies in M3CT3-E1 cells showed that the PPARß agonist GW0742 activated the PPRE-mediated luciferase expression and up-regulated peroxisomal gene transcription (Pex11, Pex13, Pex14, Acox1 and Cat), whereas the PPARß antagonist GSK0660 led to repression of the PPRE and a decrease of the corresponding mRNA levels. In the same way, treatment of calvarial osteoblasts with GW0742 increased in peroxisome number and related gene expression and accelerated osteoblast differentiation. Taken together, our results suggest that PPARß regulates the numerical abundance and metabolic function of peroxisomes via Pex11ß in parallel to osteoblast differentiation.
Project description:Icariin, a prenylated flavonol glycoside isolated from the herb Epimedium, has been considered as a potential alternative therapy for osteoporosis. Previous research has shown that, unlike other flavonoids, icariin is unlikely to act via the estrogen receptor, but its exact mechanism of action is unknown. In this study, using rat calvarial osteoblast culture and rat bone growth models, we demonstrated that icariin promotes bone formation by activating the cAMP/protein kinase A (PKA)/cAMP response element-binding protein (CREB) pathway requiring functional primary cilia of osteoblasts. We found that icariin increases the peak bone mass attained by young rats and promotes the maturation and mineralization of rat calvarial osteoblasts. Icariin activated cAMP/PKA/CREB signaling of the osteoblasts by increasing intracellular cAMP levels and facilitating phosphorylation of both PKA and CREB. Blocking cAMP/PKA/CREB signaling with inhibitors of the cAMP-synthesizing adenylyl cyclase (AC) and PKA inhibitors significantly inhibited the osteogenic effect of icariin in the osteoblasts. Icariin-activated cAMP/PKA/CREB signaling was localized to primary cilia, as indicated by localization of soluble AC and phosphorylated PKA. Furthermore, blocking ciliogenesis via siRNA knockdown of a cilium assembly protein, IFT88, inhibited icariin-induced PKA and CREB phosphorylation and also abolished icariin's osteogenic effect. Finally, several of these outcomes were validated in icariin-treated rats. Together, these results provide new insights into icariin function and its mechanisms of action and strengthen existing ties between cAMP-mediated signaling and osteogenesis.
Project description:Calvarial bones arise from two embryonic tissues, namely, the neural crest and the mesoderm. In this study we have addressed the important question of whether disparate embryonic tissue origins impart variable osteogenic potential and regenerative capacity to calvarial bones, as well as what the underlying molecular mechanism(s). Thus, by performing in vitro and in vivo studies, we have investigated whether differences exist between neural crest-derived frontal and paraxial mesodermal-derived parietal bone. Of interest, our data indicate that calvarial bone osteoblasts of neural crest origin have superior potential for osteogenic differentiation. Furthermore, neural crest-derived frontal bone displays a superior capacity to undergo osseous healing compared with calvarial bone of paraxial mesoderm origin. Our study identified both in vitro and in vivo enhanced endogenous canonical Wnt signaling in frontal bone compared with parietal bone. In addition, we demonstrate that constitutive activation of canonical Wnt signaling in paraxial mesodermal-derived parietal osteoblasts mimics the osteogenic potential of frontal osteoblasts, whereas knockdown of canonical Wnt signaling dramatically impairs the greater osteogenic potential of neural crest-derived frontal osteoblasts. Moreover, fibroblast growth factor 2 (FGF-2) treatment induces phosphorylation of GSK-3beta and increases the nuclear levels of beta-catenin in osteoblasts, suggesting that enhanced activation of Wnt signaling might be mediated by FGF. Taken together, our data provide compelling evidence that indeed embryonic tissue origin makes a difference and that active canonical Wnt signaling plays a major role in contributing to the superior intrinsic osteogenic potential and tissue regeneration observed in neural crest-derived frontal bone.
Project description:Mechanical loading of bone is important for maintenance of bone mass and structural stability of the skeleton. When bone is mechanically loaded, movement of fluid within the spaces surrounding bone cells generates fluid shear stress (FSS) that stimulates osteoblasts, resulting in enhanced anabolic activity. The mechanisms by which osteoblasts convert the external stimulation of FSS into biochemical changes, a process known as mechanotransduction, remain poorly understood. Focal adhesions are prime candidates for transducing external stimuli. Focal adhesion kinase (FAK), a nonreceptor tyrosine kinase found in focal adhesions, may play a key role in mechanotransduction, although its function has not been directly examined in osteoblasts. We examined the role of FAK in osteoblast mechanotransduction using short interfering RNA (siRNA), overexpression of a dominant negative FAK, and FAK(-/-) osteoblasts to disrupt FAK function in calvarial osteoblasts. Osteoblasts were subjected to varying periods oscillatory fluid flow (OFF) from 5 min to 4 h, and several physiologically important readouts of mechanotransduction were analyzed including: extracellular signal-related kinase 1/2 phosphorylation, upregulation of c-fos, cyclooxygenase-2, and osteopontin, and release of prostaglandin E(2). Osteoblasts with disrupted FAK signaling exhibited severely impaired mechanical responses in all endpoints examined. These data indicate the importance of FAK for both short and long periods of FSS-induced mechanotransduction in osteoblasts.
Project description:Axin2-expressing calvarial suture stem cells can contribute to calvarial development, homeostatic maintenance, repair, and regeneration. We used microarray to examine the gene expression profiles of Axin2-expressing suture stem cells and Axin2-negative cells in suture mesenchyme. Three of Axin2+/GFP+ and three of Axin2-/GFP- cell samples were collected from mice carrying Axin2rtTA and TREH2BGFP transgenes. Each samples were isolated from 6-8 Axin2rtTA; TRE-H2BGFP mice and sorted by the GFP intensity.
Project description:Disseminated tumor cells (DTCs) undergo a dormant state in the distant metastatic site(s) before becoming overt metastatic diseases. In prostate cancer (PCa), bone metastasis can occur years after prostatectomy, suggesting that bone may provide dormancy-inducing factors. To search for these factors, we prepared conditioned media (CM) from calvariae. Using live-cell imaging, we found that Calvarial-CM treatment increased cellular quiescence in C4-2B4 PCa cells. Mass spectrometry analysis of Calvarial-CM identified 132 secreted factors. Western blot and ELISA analyses confirmed the presence of several factors, including DKK3, BMP1, neogenin and vasorin in the Calvarial-CM. qRT-PCR analysis of total calvariae versus isolated osteoblasts showed that DKK3, BMP1, vasorin and neogenin are mainly expressed by osteoblasts, while MIA, LECT1, NGAL and PEDF are expressed by other calvarial cells. Recombinant human DKK3, BMP1, vasorin, neogenin, MIA and NGAL treatment increased cellular quiescence in both C4-2b and C4-2B4 PCa cells. Mechanistically, DKK3, vasorin and neogenin, but not BMP1, increased dormancy through activating the p38MAPK signaling pathway. Consistently, DKK3, vasorin and neogenin failed to induce dormancy in cells expressing dominant-negative p38?MAPK while BMP1 remained active, suggesting that BMP1 uses an alternative dormancy signaling pathway. Thus, bone secretes multiple dormancy-inducing factors that employ distinct signaling pathways to induce DTC dormancy in bone.