Balanced Regulation of Proliferation, Growth, Differentiation, and Degradation in Skeletal Cells

CREB3L1/OASIS: cell cycle regulator and tumor suppressor

Cell cycle checkpoints detect DNA errors, eventually arresting the cell cycle to promote DNA repair. Failure of such cell cycle arrest causes aberrant cell proliferation, promoting the pathogenesis of multiple diseases, including cancer. Endoplasmic reticulum (ER) stress transducers activate the unfolded protein response, which not only deals with unfolded proteins in ER lumen but also orchestrates diverse physiological phenomena such as cell differentiation and lipid metabolism. Among ER stress transducers, cyclic AMP-responsive element-binding protein 3-like protein 1 (CREB3L1) [also known as old astrocyte specifically induced substance (OASIS)] is an ER-resident transmembrane transcription factor. This molecule is cleaved by regulated intramembrane proteolysis, followed by activation as a transcription factor. OASIS is preferentially expressed in specific cells, including astrocytes and osteoblasts, to regulate their differentiation. In accordance with its name, OASIS was originally identified as being upregulated in long-term-cultured astrocytes undergoing cell cycle arrest because of replicative stress. In the context of cell cycle regulation, previously unknown physiological roles of OASIS have been discovered. OASIS is activated as a transcription factor in response to DNA damage to induce p21-mediated cell cycle arrest. Although p21 is directly induced by the master regulator of the cell cycle, p53, no crosstalk occurs between p21 induction by OASIS or p53. Here, we summarize previously unknown cell cycle regulation by ER-resident transcription factor OASIS, particularly focusing on commonalities and differences in cell cycle arrest between OASIS and p53. This review also mentions tumorigenesis caused by OASIS dysfunctions, and OASIS's potential as a tumor suppressor and therapeutic target.

p53-independent tumor suppression by cell-cycle arrest via CREB/ATF transcription factor OASIS

CREB/ATF transcription factor OASIS/CREB3L1 is upregulated in long-term-cultured astrocytes undergoing cell-cycle arrest due to loss of DNA integrity by repeated replication. However, the roles of OASIS in the cell cycle remain unexplored. We find that OASIS arrests the cell cycle at G₂/M phase after DNA damage via direct induction of p21. Cell-cycle arrest by OASIS is dominant in astrocytes and osteoblasts, but not in fibroblasts, which are dependent on p53. In a brain injury model, Oasis^-/- reactive astrocytes surrounding the lesion core show sustained growth and inhibition of cell-cycle arrest, resulting in prolonged gliosis. We find that some glioma patients exhibit low expression of OASIS due to high methylation of its promoter. Specific removal of this hypermethylation in glioblastomas transplanted into nude mice by epigenomic engineering suppresses the tumorigenesis. These findings suggest OASIS as a critical cell-cycle inhibitor with potential to act as a tumor suppressor.

Geopolymer Materials for Bone Tissue Applications: Recent Advances and Future Perspectives

With progress in the bone tissue engineering (BTE) field, there is an important need to develop innovative biomaterials to improve the bone healing process using reproducible, affordable, and low-environmental-impact alternative synthetic strategies. This review thoroughly examines geopolymers' state-of-the-art and current applications and their future perspectives for bone tissue applications. This paper aims to analyse the potential of geopolymer materials in biomedical applications by reviewing the recent literature. Moreover, the characteristics of materials traditionally used as bioscaffolds are also compared, critically analysing the strengths and weaknesses of their use. The concerns that prevented the widespread use of alkali-activated materials as biomaterials (such as their toxicity and limited osteoconductivity) and the potentialities of geopolymers as ceramic biomaterials have also been considered. In particular, the possibility of targeting their mechanical properties and morphologies through their chemical compositions to meet specific and relevant requirements, such as biocompatibility and controlled porosity, is described. A statistical analysis of the published scientific literature is presented. Data on "geopolymers for biomedical applications" were extracted from the Scopus database. This paper focuses on possible strategies necessary to overcome the barriers that have limited their application in biomedicine. Specifically, innovative hybrid geopolymer-based formulations (alkali-activated mixtures for additive manufacturing) and their composites that optimise the porous morphology of bioscaffolds while minimising their toxicity for BTE are discussed.

Dexamethasone promotes mesenchymal stem cell apoptosis and inhibits osteogenesis by disrupting mitochondrial dynamics

Long‐term or heavy use of glucocorticoids can cause severe necrosis of the femoral head, but the underlying mechanisms are still unclear. Recent studies have found that mitochondrial dynamics play an important role in femoral head necrosis. Here, we investigated the effect of dexamethasone on the mitochondrial function of mesenchymal stem cells. We observed that high concentrations of dexamethasone (10⁻⁶ mol·L⁻¹) decreased cell activity, promoted apoptosis, elevated levels of reactive oxygen species and disrupted mitochondrial dynamics. Furthermore, dexamethasone (10⁻⁶ mol·L⁻¹) inhibited osteogenesis of stem cells and promoted adipogenesis. These findings may facilitate greater understanding of the adverse effects of dexamethasone on the femoral head.

Hematological Malignancy-Derived Small Extracellular Vesicles and Tumor Microenvironment: The Art of Turning Foes into Friends

Small extracellular vesicles (small EVs) are commonly released by all cells, and are found in all body fluids. They are implicated in cell to cell short- and long-distance communication through the transfer of genetic material and proteins, as well as interactions between target cell membrane receptors and ligands anchored on small EV membrane. Beyond their canonical functions in healthy tissues, small EVs are strategically used by tumors to communicate with the cellular microenvironment and to establish a proper niche which would ultimately allow cancer cell proliferation, escape from the immune surveillance, and metastasis formation. In this review, we highlight the effects of hematological malignancy-derived small EVs on immune and stromal cells in the tumor microenvironment.

3D Printing and Electrospinning of Composite Hydrogels for Cartilage and Bone Tissue Engineering

Injuries of bone and cartilage constitute important health issues costing the National Health Service billions of pounds annually, in the UK only. Moreover, these damages can become cause of disability and loss of function for the patients with associated social costs and diminished quality of life. The biomechanical properties of these two tissues are massively different from each other and they are not uniform within the same tissue due to the specific anatomic location and function. In this perspective, tissue engineering (TE) has emerged as a promising approach to address the complexities associated with bone and cartilage regeneration. Tissue engineering aims at developing temporary three-dimensional multicomponent constructs to promote the natural healing process. Biomaterials, such as hydrogels, are currently extensively studied for their ability to reproduce both the ideal 3D extracellular environment for tissue growth and to have adequate mechanical properties for load bearing. This review will focus on the use of two manufacturing techniques, namely electrospinning and 3D printing, that present promise in the fabrication of complex composite gels for cartilage and bone tissue engineering applications.

Differential effects of amnion and chorion membrane extracts on osteoblast-like cells due to the different growth factor composition of the extracts

Human amniotic membrane extracts contain numerous growth factors and bioactive substances. However, osteogenic effects of amnion and chorion membrane extracts (AME and CME, respectively) on osteoblasts are unclear. In this study, we explored the ability of AME and CME to promote the osteogenic differentiation of osteoblast-like MG-63 cells. MG-63 cells were cultured in osteogenic induction medium (OIM) with or without exogenous AME and CME. CME enhanced the osteogenic differentiation of MG-63 cells compared with AME, as indicated by increased mineralization; alkaline phosphatase activity; and mRNA expression of osteogenic marker genes encoding integrin-binding sialoprotein (IBSP), RUNX2, OSTERIX, and osteocalcin (OCN). Interestingly, AME and CME contained different combinations of osteogenesis-related growth factors, including basic fibroblast growth factor (bFGF), transforming growth factor beta-1 (TGFβ-1), and epidermal growth factor (EGF), which differentially regulated the osteogenic differentiation of MG-63 cells. bFGF and TGFβ-1 present in CME positively regulated the osteogenic differentiation of MG-63 cells, whereas EGF present in AME negatively regulated the differentiation of MG-63 cells. Moreover, exogenous treatment of EGF antagonized CME-induced mineralization of extracellular matrix on MG-63 cells. We compared the osteogenic efficacy of CME with that of BMP2, bFGF, and TGFβ-1 alone or their combinations. We observed that CME greatly enhanced osteogenesis by providing a conductive environment for the differentiation of MG-63 cells. Together, our results indicated that human AME and CME exerted differential effects on osteogenesis because of the presence of different compositions of growth factors. In addition, our results highlighted a new possible strategy of using CME as a biocompatible therapeutic material for bone regeneration.

Dried Plum Ingestion Increases the Osteoblastogenic Capacity of Human Serum

In cell culture studies, dried plum (Prunus domestica L.) polyphenols increased osteoblast alkaline phosphatase (ALP) activity, mineralized nodule formation, and the expression of the bone marker genes runt-related transcription factor 2 (RUNX2) and osterix. The purpose of this study was to determine whether human serum collected 1 and 2 h after dried plum ingestion influenced osteoblast cell activity and gene expression. Five healthy women ingested 100 g of dried plum, and serum samples were collected at baseline (before dried plum ingestion) and 1 and 2 h postingestion of dried plum. MC3T3-E1 osteoblast cells were treated (2% of medium) with these serum samples for 3 or 9 days. Intracellular and extracellular ALP activities were significantly increased after 3 or 9 days of treatment with serum both postingestion time points, with no effect seen in baseline samples. Also, serum obtained 1 and 2 h postingestion significantly increased the mRNA expression of bone markers RUNX2 and connexin43 (CX43) after both 3 and 9 days of incubation periods. Finally, serum obtained 1 and 2 h postingestion increased the mRNA expression of β-catenin after 9 days of incubation. We conclude that osteoblast activity and function are increased by dried plum ingestion, which may, in part, explain its beneficial effects on bone health.

Scaffolds for Bone Tissue Engineering: State of the art and new perspectives

This review is intended to give a state of the art description of scaffold-based strategies utilized in Bone Tissue Engineering. Numerous scaffolds have been tested in the orthopedic field with the aim of improving cell viability, attachment, proliferation and homing, osteogenic differentiation, vascularization, host integration and load bearing. The main traits that characterize a scaffold suitable for bone regeneration concerning its biological requirements, structural features, composition, and types of fabrication are described in detail. Attention is then focused on conventional and Rapid Prototyping scaffold manufacturing techniques. Conventional manufacturing approaches are subtractive methods where parts of the material are removed from an initial block to achieve the desired shape. Rapid Prototyping techniques, introduced to overcome standard techniques limitations, are additive fabrication processes that manufacture the final three-dimensional object via deposition of overlying layers. An important improvement is the possibility to create custom-made products by means of computer assisted technologies, starting from patient's medical images. As a conclusion, it is highlighted that, despite its encouraging results, the clinical approach of Bone Tissue Engineering has not taken place on a large scale yet, due to the need of more in depth studies, its high manufacturing costs and the difficulty to obtain regulatory approval. PUBMED search terms utilized to write this review were: "Bone Tissue Engineering", "regenerative medicine", "bioactive scaffolds", "biomimetic scaffolds", "3D printing", "3D bioprinting", "vascularization" and "dentistry".

The Proteasome Inhibitor Carfilzomib Suppresses Parathyroid Hormone-induced Osteoclastogenesis through a RANKL-mediated Signaling Pathway

Parathyroid hormone (PTH) induces osteoclast formation and activity by increasing the ratio of RANKL/OPG in osteoblasts. The proteasome inhibitor carfilzomib (CFZ) has been used as an effective therapy for multiple myeloma via the inhibition of pathologic bone destruction. However, the effect of combination of PTH and CFZ on osteoclastogenesis is unknown. We now report that CFZ inhibits PTH-induced RANKL expression and secretion without affecting PTH inhibition of OPG expression, and it does so by blocking HDAC4 proteasomal degradation in osteoblasts. Furthermore, we used different types of culture systems, including co-culture, indirect co-culture, and transactivation, to assess the effect of CFZ on PTH action to induce osteoclastogenesis. Our results demonstrated that CFZ blocks PTH-induced osteoclast formation and bone resorption by its additional effect to inhibit RANKL-mediated IκB degradation and NF-κB activation in osteoclasts. This study showed for the first time that CFZ targets both osteoblasts and osteoclasts to suppress PTH-induced osteoclast differentiation and bone resorption. These findings warrant further investigation of this novel combination in animal models of osteoporosis and in patients.

Proliferation assays (BrdU and EdU) on skeletal tissue sections

Assessing cell proliferation in situ is an important phenotyping component of skeletal tissues from development to adult stages and disease. Various methods exist including immunostaining for proteins and protein modifications associated with specific steps of the cell cycle, but the gold standard is to quantify the percentage of DNA-synthesizing cells. The thymidine analog 5-bromo-2'-deoxyuridine (BrdU) has been widely used in the last decades for this purpose, with the inconvenience that its detection is lengthy and requires harsh treatment of tissue sections to give access of anti-BrdU antibody to nucleosides in genomic DNA. In 2008, Salic and Mitchison developed a new method and proved it to be quicker, simpler, and highly sensitive in non-skeletal tissues. This method relies on incorporation of 5-ethynyl-2'-deoxyuridine (EdU) into de novo DNA. This other thymidine analog is readily detected by click chemistry, i.e., covalent cross-linking of its ethynyl group with a fluorescent azide, a molecule small enough to diffuse freely through native tissues and DNA. Here, we describe and compare the BrdU and EdU approaches in skeletal tissues and conclude that in these tissues too EdU provides an easy and very sensitive alternative to BrdU.

Parathyroid hormone and parathyroid hormone type-1 receptor accelerate myocyte differentiation

The ZHTc6-MyoD embryonic stem cell line expresses the myogenic transcriptional factor MyoD under the control of a tetracycline-inducible promoter. Following induction, most of the ZHTc6-MyoD cells differentiate to myotubes. However, a small fraction does not differentiate, instead forming colonies that retain the potential for myocyte differentiation. In our current study, we found that parathyroid hormone type 1 receptor (PTH1R) expression in colony-forming cells at 13 days after differentiation was higher than that in the undifferentiated ZHTc6-MyoD cells. We also found that PTH1R expression was required for myocyte differentiation, and that parathyroid hormone accelerated the differentiation. Our analysis of human and mouse skeletal muscle tissues showed that most cells expressing PTH1R also expressed Pax7 and CD34, which are biomarkers of satellite cells. Furthermore, we found that parathyroid hormone treatment significantly improved muscle weakness in dystrophin-deficient mdx mice. This is the first report indicating that PTH1R and PTH accelerate myocyte differentiation.

Tumor necrosis factor-α enhances the transcription of Smad ubiquitination regulatory factor 1 in an activating protein-1- and Runx2-dependent manner

Smad ubiquitination regulatory factor 1 (Smurf1) is an E3 ubiquitin ligase that negatively regulates osteoblast differentiation. Although tumor necrosis factor-α (TNF-α) has been shown to increase Smurf1 expression, the details of the regulatory mechanisms remain unclear. Here, we investigated the molecular mechanism by which TNF-α stimulates Smurf1 expression in C2C12 and primary cultured mouse calvarial cells. TNF-α treatment rapidly induced the activation of NF-κB and MAPKs. Smurf1 induction by TNF-α was blocked by the inhibition of JNK or ERK, while the inhibition of NF-κB and p38 MAPK had no effect on Smurf1 induction. TNF-α treatment or c-Jun overexpression enhanced the activity of a luciferase reporter that contained a 2.7 kb mouse Smurf1 promoter sequence. Site-directed mutagenesis of the Smurf1 reporter and chromatin immunoprecipitation analysis demonstrated that the activating protein-1 (AP-1) binding motif at -922 bp on the mouse Smurf1 promoter mediated TNF-α/JNK/AP-1-stimulated Smurf1 transcription. Interestingly, Smurf1 expression was not observed in Runx2-null mouse calvarial cells. When Runx2 was ectopically expressed in these cells, the basal and TNF-α-induced expression of Smurf1 was restored. Overexpression of Runx2 transactivated the Smurf1 promoter in a dose-dependent manner. Reporter and chromatin immunoprecipitation assays demonstrated that the Runx2-binding motif at -202 bp functioned in Runx2-mediated Smurf1 expression. ERK activation by TNF-α treatment or constitutively active MEK1 overexpression increased Smurf1 expression in a Runx2-dependent manner. These results suggest that the JNK/AP-1 and ERK/Runx2 signaling pathways mediate TNF-α-dependent Smurf1 transcription.

Salvianolic acid B prevents bone loss in prednisone-treated rats through stimulation of osteogenesis and bone marrow angiogenesis

Glucocorticoid (GC) induced osteoporosis (GIO) is caused by the long-term use of GC for treatment of autoimmune and inflammatory diseases. The GC related disruption of bone marrow microcirculation and increased adipogenesis contribute to GIO development. However, neither currently available anti-osteoporosis agent is completely addressed to microcirculation and bone marrow adipogenesis. Salvianolic acid B (Sal B) is a polyphenolic compound from a Chinese herbal medicine, Salvia miltiorrhiza Bunge. The aim of this study was to determine the effects of Sal B on osteoblast bone formation, angiogenesis and adipogenesis-associated GIO by performing marrow adipogenesis and microcirculation dilation and bone histomorphometry analyses. (1) In vivo study: Bone loss in GC treated rats was confirmed by significantly decreased BMD, bone strength, cancellous bone mass and architecture, osteoblast distribution, bone formation, marrow microvessel density and diameter along with down-regulation of marrow BMPs expression and increased adipogenesis. Daily treatment with Sal B (40 mg/kg/d) for 12 weeks in GC male rats prevented GC-induced cancellous bone loss and increased adipogenesis while increasing cancellous bone formation rate with improved local microcirculation by capillary dilation. Treatment with Sal B at a higher dose (80 mg/kg/d) not only prevented GC-induced osteopenia, but also increased cancellous bone mass and thickness, associated with increase of marrow BMPs expression, inhibited adipogenesis and further increased microvessel diameters. (2) In vitro study: In concentration from 10⁻⁶ mol/L to 10⁻⁷ mol/L, Sal B stimulated bone marrow stromal cell (MSC) differentiation to osteoblast and increased osteoblast activities, decreased GC associated adipogenic differentiation by down-regulation of PPARγ mRNA expression, increased Runx2 mRNA expression without osteoblast inducement, and, furthermore, Sal B decreased Dickkopf-1 and increased β-catenin mRNA expression with or without adipocyte inducement in MSC. We conclude that Sal B prevented bone loss in GC-treated rats through stimulation of osteogenesis, bone marrow angiogenesis and inhibition of adipogenesis.

Expression of IGF-1R in Colorectal Polyps and its Role in Colorectal Carcinogenesis

Insulin-like Growth Factor Receptor 1 (IGF-1R) may play a role in the neoplastic progression of colorectal cancer because it is related to both cellular proliferation and differentiation. The aim of this study was to further elucidate the role of IGF-1R in colorectal carcinogenesis by evaluating IGF-1R expression in different types of precancerous colorectal polyps and comparing its expression to normal mucosa and colorectal carcinoma. A total of 47 colorectal polyps and their respective adjacent normal mucosa were collected from 32 patients. In addition, 20 colorectal adenocarcinoma tissues were obtained from patients undergoing colorectal resection, and 12 normal non-malignant colorectal mucosal tissues collected from outpatients served as the control group. The pit patterns of polyps were classified by the Kudo classification scheme through magnifying chromoendoscopy. Immunohistochemistry and quantitative real-time RT-PCR were utilized for expression analysis of IGF-1R in colorectal mucosa, polyps, and adenocarcinoma tissue. The results of immunohistochemistry showed no significant differences in IGF-1R expression in inflammatory polyps compared with their surrounding normal mucosa by the Mann-Whitney U test (p = 0.251); however, tubular adenoma and villous adenoma tissues exhibited significantly higher levels of IGF-1R expression (p = 0.000). The results of real-time RT-PCR showed that IGF-1R was transcribed at a high level in colorectal adenomatous polyps and adenocarcinoma compared with their respective paired normal mucosa. Spearman's rank correlation two-variable analysis was used to demonstrate a significant correlation between the expression of IGF-1R and neoplastic progression from normal mucosa to adenomatous polyps and finally to colorectal cancer (r = 0.574, p = 0.000). This study suggests that the expression of IGF-1R correlates with the degree of carcinogenesis. In addition, these results demonstrated that there is a significant correlation between the level of IGF-1R expression and pit patterns of polyps (r = 0.432, p = 0.002). Thus, IGF-1R might be a factor in the morphological change of colorectal mucosal crypts, and it may play an important role in the growth and malignant transformation of precancerous polyps. These results suggest that IGF-1R can be considered a biomarker for the stage and risk of carcinogenesis during neoplastic initiation and progression along the colorectal normal mucosa-polyp-cancer sequence. Inhibitors of IGF-1R are not only a promising targeted anticancer strategy, but also a possible option for the chemoprevention of colorectal cancer.

Retinoic acid-induced Smad3 expression is required for the induction of osteoblastogenesis of mesenchymal stem cells

Mesenchymal stem cells are pluripotent precursor cells that can differentiate into osteoblasts, adipocytes, chondrocytes and myocytes. Despite their important therapeutic potential little is known about the transcriptional cascades that govern lineage decisions in these cells. Treatment of C3H10T1/2 mouse mesenchymal stem cells with retinoic acid (RA) inhibits adipogenesis and enhances osteoblastogenesis. In particular, RA treatment stimulates the expression of the osteoblast master regulator, runt-related transcription factor 2 (Runx2), whose expression is necessary for the formation of bone. We have shown previously in mesenchymal stem cells that RA acts to stimulate osteoblastogenesis by interfering with the actions of the bzip transcription factor CCAAT/Enhancer Binding Protein beta (C/EBPβ), where it binds to a negative regulatory element within the Runx2 promoter and inhibits its expression. Herein we show that Smad3, whose expression is stimulated by RA, relays the effects of RA on differentiation by initiating the displacement of C/EBPβ from the Runx2 promoter. In addition to stimulating Smad3 expression, RA also stimulated the nuclear localization of this factor, such that in the absence of RA, ectopic Smad3 was unable to drive osteoblastogenesis. While not sufficient to promote osteoblastogenesis, knockdown of Smad3 using a specific shRNA prevented the RA-mediated stimulation of differentiation and displacement of C/EBPβ from the Runx2 P1 promoter. Taken together, these data indicate that Smad3 is an important mediator of RA activity during mesenchymal stem cell differentiation and is necessary for the stimulation of osteoblastogenesis.

Elevation of PTH and PTHrp induced by excessive fluoride in rats on a calcium-deficient diet

Study on the role of parathyroid hormone (PTH) and parathyroid hormone-related peptide (PTHrp) in the process of skeletal fluorosis, involved especially in calcium deficiency, is rare. We evaluated the level of serum PTH and mRNA expression of PTHrp in femur when rats were exposed to excessive fluoride with low-calcium diet. Wistar rats (n = 60) was divided into four groups, a control group, fluoride group, low-calcium group, and low-calcium fluoride group. The fluoride groups were treated with fluoride by drinking tap water containing 100 mg F-/L. The low-calcium diet contained 0.05% calcium. Serum was collected in the first, fourth, eighth, and 12th of phase for the detemination of PTH and Ca(2+). RNA extraction from femora was used to analyze the mRNA express of PTHrp, osteopontin (OPN), and osteocalcin (OCN) after 12 weeks of fluoride dosing. Results showed that serum PTH increased gradually with the extension of fluoride exposure, but Ca2+ decreased, both of which embodied a time-dependent relationship. Cotreatment of excessive fluoride with low-calcium diet largely stimulated the secretion of PTH. The low dietary calcium markedly increased mRNA expression of PTHrp in animals with fluoride treatment. Expression of OPN and OCN significantly increased in the rats treated with excessive fluoride and low-calcium diet. We demonstrated that fluoride by itself affected the body's calcium metabolism and stimulate the secretion of PTH. PTH may play an important role in anabolic effect of excessive fluoride on bone turnover of skeletal fluorosis and calcium deficiency exacerbated the action of PTH and PTHrp on the characteristic bone lesion of fluorosis.

Porcine bone marrow stromal cell differentiation on heparin-adsorbed poly(e-caprolactone)-tricalcium phosphate-collagen scaffolds

We evaluate the potential of heparin as a substrate component for the fabrication of bone tissue engineering constructs using poly(e-caprolactone)-tricalcium phosphate-collagen type I (PCL-TCP-Col) three-dimensional (3-D) scaffolds. First we explored the ability of porcine bone marrow precursor cells (MPCs) to differentiate down both the adipogenic and osteogenic pathways within 2-D culture systems, with positive results confirmed by Oil-Red-O and Alizarin Red staining, respectively. Secondly, we examined the influence of heparin on the interaction and behaviour of MPCs when seeded onto PCL-TCP-Col 3-D scaffolds, followed by their induction into the osteogenic lineage. Our 3-D findings suggest that cell metabolism and proliferation increased between days 1 and 14, with deposition of extracellular matrix also observed up to 28 days. However, no noticeable difference could be detected in the extent of osteogenesis for PCL-TCP-Col scaffolds groups with the addition of heparin compared to identical control scaffolds without the addition of heparin.

Developments in the scientific understanding of osteoporosis

During the past 10 years we have experienced very significant developments in our understanding of bone biology, and this has improved our abilities to both diagnose and treat patients with osteoporosis. This review covers some of the significant discoveries in bone biology that have led to a better understanding of osteoporosis, including a few of the discoveries that have been translated into new therapies to treat patients with osteoporosis and the structural deterioration of patients with inflammatory arthritis.

Glucocorticoid excess in mice results in early activation of osteoclastogenesis and adipogenesis and prolonged suppression of osteogenesis: a longitudinal study of gene expression in bone tissue from glucocorticoid-treated mice

OBJECTIVE

Glucocorticoid (GC) excess induces alterations in bone metabolism that weaken bone structure and increase fracture risk. The aim of this study was to identify genes associated with bone metabolism in GC-treated mice, by performing a microarray analysis.

METHODS

Long bones from mice exposed to GC excess were collected after 0, 7, 28, and 56 days of treatment, to measure bone microarchitecture and extract RNA for microarray analyses.

RESULTS

Bone loss in this animal model was confirmed by changes in bone turnover markers as well as bone architecture, as measured by microfocal computed tomography. GC excess induced an early up-regulation of genes involved in osteoclast activation, function, and adipogenesis, which peaked on day 7. The expression of genes associated with osteoclast cytoskeletal reorganization and genes associated with matrix degradation peaked on day 28. On day 28 and day 56, the expression of genes associated with osteoblast activation and maturation was decreased from baseline, while the expression of Wnt antagonists was increased. In addition, the expression of genes expressed in osteocytes associated with bone mineralization was significantly higher at the later time points, day 28 and day 56. Reverse transcription-polymerase chain reaction confirmed the results of microarray analysis in selected genes.

CONCLUSION

GC excess is associated with early activation of genes associated with osteoclastogenesis and adipogenesis and a later suppression of genes associated with osteogenesis and mineralization. Novel interventions with agents that modulate either Wnt signaling or mineralization may be effective in GC-induced osteoporosis.