Regulation of BMP-7 expression by retinoic acid and prostaglandin E(2)

Effects of NSAID use on bone healing: A meta-analysis of retrospective case–control and cohort studies within clinical settings

Introduction

This meta-analysis aims to determine whether non-steroidal anti-inflammatory drug (NSAID) use is significantly associated with adverse bone healing outcomes within clinical settings, including trauma and elective spine settings. It will also explore bone healing outcomes with the type, route, dosage and duration of NSAID exposure and aims to demonstrate the effects of various other confounding factors on bone healing outcomes.

Methods

Electronic databases including MedLine, Embase and Cochrane were searched from January 1975 to December 2017. A distinct analysis of observational long bone and spine studies in adult populations was performed, assessing the effects of NSAID exposure on bone healing. Studies from paediatric population and randomised trials also underwent separate assessment in the synthesis. Meta-analysis was conducted in compliance with QUORUM and PRISMA guidelines.

Results

Quantitative assessment of observational studies suggested a significant risk of bone healing complications with NSAID exposure across each clinical group: long bone (p = 0.0004) and spine (p = 0.02). Analysis of paediatric studies revealed a non-significant association of poor outcomes with NSAID use (p = 0.36), while assessment of randomised trials demonstrated a statistically significant risk of complications following NSAID administration (p = 0.04). Meta-regression further suggested smoking to be a substantial confounder associated with adverse bone healing outcomes (p < 0.00001).

Conclusion

Inclusion of only fair and moderate-quality retrospective cohort and case–control studies in the current synthesis limits the clinical application of its findings and therefore warrants the need for further research. Thus, attempts to conduct high-quality prospective cohort and randomised trials to study the effects of NSAID use on bone healing would be very helpful and will provide a basis for more extensive research in future.

In vitro bone-like nodules generated from patient-derived iPSCs recapitulate pathological bone phenotypes

The recapitulation of bone formation via the in vitro generation of bone-like nodules is frequently used to understand bone development. However, current bone-induction techniques are slow and difficult to reproduce. Here, we report the formation of bone-like nodules within ten days, via the use of retinoic acid (RA) to induce the osteogenic differentiation of human induced pluripotent stem cells (hiPSCs) into osteoblast-like and osteocyte-like cells that create human bone tissue when implanted in calvarial defects in mice. We also show that the induction of bone formation depends on cell signalling through the RA receptors RARα and RARβ, which simultaneously activate the BMP (bone morphogenetic protein) and Wnt signalling pathways. Moreover, by using patient-derived hiPSCs, the bone-like nodules recapitulated the osteogenesis-imperfecta phenotype, which was rescued via the correction of disease-causing mutations and partially by an mTOR (mechanistic target of rapamycin) inhibitor. The method of inducing bone nodules may serve as a fast and reproducible model for the study of the formation of both healthy and pathological bone.

Effects of Nonsteroidal Anti-Inflammatory Drugs at the Molecular Level

Nonsteroidal anti-inflammatory drugs (NSAIDs) are commonly used for their anti-inflammatory, analgesic, and antipyretic effects. NSAIDs generally work by blocking the production of prostaglandins (PGs) through the inhibition of two cyclooxygenase enzymes. PGs are key factors in many cellular processes, such as gastrointestinal cytoprotection, hemostasis and thrombosis, inflammation, renal hemodynamics, turnover of cartilage, and angiogenesis. Interest has grown in the various effects of NSAIDs during the last decade. Epidemiological studies have revealed the reduced risk of several cancer types and neurodegenerative diseases by prolonged use of NSAIDs. Recent advances in the understanding of the cellular and molecular mechanisms of NSAIDs will accelerate the processes of discovery and clinical implementation. This review summarizes the molecular mechanisms of NSAIDs on the body systems.

Effects of three-dimensional spheroid culture on equine mesenchymal stem cell plasticity

Mesenchymal stem cells (MSCs) are useful candidates for tissue engineering and cell therapy fields. We optimize culture conditions of equine adipose tissue-derived MSCs (eAD-MSCs) for treatment of horse fractures. To investigate enhancing properties of three-dimensional (3D) culture system in eAD-MSCs, we performed various sized spheroid formation and determined changes in gene expression levels to obtain different sized spheroid for cell therapy. eAD-MSCs were successfully isolated from horse tailhead. Using hanging drop method, spheroid formation was generated for three days. Quantitative real-time PCR was performed to analyze gene expression. As results, expression levels of pluripotent markers were increased depending on spheroid size and the production of PGE₂ was increased in spheroid formation compared to that in monolayer. Ki-67 showed a remarkable increase in the spheroid formed with 2.0 × 10⁵ cells/drop as compared to that in the monolayer. Expression levels of angiogenesis-inducing factors such as VEGF, IL-6, IL-8, and IL-18 were significantly increased in spheroid formation compared to those in the monolayer. Expression levels of bone morphogenesis-inducing factors such as Cox-2 and TGF-β1 were also significantly increased in spheroid formation compared to those in the monolayer. Expression levels of osteocyte-specific markers such as RUNX2, osteocalcin, and differentiation potential were also significantly increased in spheroid formation compared to those in the monolayer. Therefore, spheroid formation of eAD-MSCs through the hanging drop method can increases the expression of angiogenesis-inducing and bone morphogenesis-inducing factors under optimal culture conditions.

9-cis retinoic acid induces neurorepair in stroke brain

The purpose of this study was to examine the neurorestorative effect of delayed 9 cis retinoic acid (9cRA) treatment for stroke. Adult male rats received a 90-min right distal middle cerebral artery occlusion (dMCAo). Animals were separated into two groups with similar infarction sizes, based on magnetic resonance imaging on day 2 after dMCAo. 9cRA or vehicle was given via an intranasal route daily starting from day 3. Stroke rats receiving 9cRA post-treatment showed an increase in brain 9cRA levels and greater recovery in motor function. 9cRA enhanced the proliferation of bromodeoxyuridine (+) cells in the subventricular zone (SVZ) and lesioned cortex in the stroke brain. Using subventricular neurosphere and matrigel cultures, we demonstrated that proliferation and migration of SVZ neuroprogenitor cells were enhanced by 9cRA. Our data support a delayed and non-invasive drug therapy for stroke. Intranasal 9cRA can facilitate the functional recovery and endogenous repair in the ischemic brain.

Expression of Bone Morphogenetic Proteins in Stromal Cells from Human Bone Marrow Long-term Culture

Highly purified primitive hemopoietic stem cells express BMP receptors but do not synthesize bone morphogenetic proteins (BMPs). However, exogenously added BMPs regulate their proliferation, differentiation, and survival. To further explore the mechanism by which BMPs might be involved in hemopoietic differentiation, we tested whether stromal cells from long-term culture (LTC) of normal human bone marrow produce BMPs, BMP receptors, and SMAD signaling molecules. Stromal cells were immunohistochemically characterized by the presence of lyzozyme, CD 31, factor VIII, CD 68, S100, alkaline phosphatase, and vimentin. Gene expression was analyzed by RT-PCR and the presence of BMP protein was confirmed by immunohistochemistry (IHC). The supportive role of the stromal cell layer in hemopoiesis in vitro was confirmed by a colony assay of clonogenic progenitors. Bone marrow stromal cells express mRNA and protein for BMP-3, -4, and -7 but not for BMP-2, -5, and -6 from the first to the eighth week of culture. Furthermore, stromal cells express the BMP type I receptors, activin-like kinase-3 (ALK-3), ALK-6, and the downstream transducers SMAD-1, -4, and -5. Thus, human bone marrow stromal cells synthesize BMPs, which might exert their effects on hemopoietic stem cells in a paracrine manner through specific BMP receptors.

Prostaglandin F2α receptor (FP) signaling regulates Bmp signaling and promotes chondrocyte differentiation

Prostaglandins are a group of lipid signaling molecules involved in various physiological processes. In addition, prostaglandins have been implicated in the development and progression of diseases including cancer, cardiovascular disease, and arthritis. Prostaglandins exert their effects through the activation of specific G protein-coupled receptors (GPCRs). In this report, we examined the role of prostaglandin F2α receptor (FP) signaling as a regulator of chondrocyte differentiation. We found that FP expression was dramatically induced during the differentiation of chondrocytes and was up-regulated in cartilages. Forced expression of FP in ATDC5 chondrogenic cell line resulted in the increased expression of differentiation-related genes and increased synthesis of the extracellular matrix (ECM) regardless of the presence of insulin. Similarly, PGF2α treatment induced the expression of chondrogenic marker genes. In contrast, knockdown of endogenous FP expression suppressed the expression of chondrocyte marker genes and ECM synthesis. Organ culture of cartilage rudiments revealed that PGF2α induces chondrocyte hypertrophy. Additionally, FP overexpression increased the levels of Bmp-6, phospho-Smad1/5, and Bmpr1a, while knockdown of FP reduced expression of those genes. These results demonstrate that up-regulation of FP expression plays an important role in chondrocyte differentiation and modulates Bmp signaling.

Retinoic acid signalling regulates the development of tonotopically patterned hair cells in the chicken cochlea

Precise frequency discrimination is a hallmark of auditory function in birds and mammals and is required for distinguishing similar sounding words, like 'bat,' 'cat' and 'hat.' In the cochlea, tuning and spectral separation result from longitudinal differences in basilar membrane stiffness and numerous individual gradations in sensory hair cell phenotypes, but it is unknown what patterns the phenotypes. Here we used RNA-seq to compare transcriptomes from proximal, middle and distal regions of the embryonic chicken cochlea, and found opposing longitudinal gradients of expression for retinoic acid (RA)-synthesizing and degrading enzymes. In vitro experiments showed that RA is necessary and sufficient to induce the development of distal-like hair cell phenotypes and promotes expression of the actin-crosslinking proteins, Espin and Fscn2. These and other findings highlight a role for RA signalling in patterning the development of a longitudinal gradient of frequency-tuned hair cell phenotypes in the cochlea.

α(E)-catenin regulates BMP-7 expression and migration in renal epithelial cells

BACKGROUND

The aging kidney has a decreased ability to repair following injury. We have shown a loss in expression of α-catenin in the aging rat kidney and hypothesize that decreased α-catenin expression in tubular epithelial cells results in diminished repair capacity.

METHODS

In an effort to elucidate alterations due to the loss of α-catenin, we generated NRK-52E cell lines with stable knockdown of α(E)-catenin.

RESULTS

α(E)-catenin knockdown resulted in decreased wound repair due to alterations in cell migration. Analysis of gene expression in the α(E)-catenin knockdown cells demonstrated almost a complete loss of bone morphogenetic protein-7 (BMP-7) expression that was associated with decreased phospho-Smad1/5/8 staining. However, addition of exogenous BMP-7 increased phospho-Smad1/5/8, suggesting that the BMP-7 pathway remained intact in C2 cells. Given the potential role of BMP-7 in repair, we investigated its role in wound repair. Inhibition of BMP-7 decreased repair in non-targeted control cells; conversely, exogenous BMP-7 restored repair in α(E)-catenin knockdown cells to control levels.

CONCLUSIONS

Taken together, the data suggests that the loss of α(E)-catenin expression and subsequent downregulation of BMP-7 is a mechanism underlying the altered migration of tubular epithelial cells that contributes to the inability of the aging kidney to repair following injury.

NSAIDs and fracture healing

PURPOSE OF REVIEW

Published data raise concerns about the use of nonselective NSAIDs and selective cyclo-oxygenase (COX)-2 inhibitors as anti-inflammatory or analgesic drugs in patients after a recent fracture or who are undergoing (uncemented) arthroplasty or osteotomy. However, clinical reports on the effect of COX-2 inhibition on fracture healing in humans have been variable and inconclusive. This review gives an overview of the published data and an advice when to avoid NSAIDs.

RECENT FINDINGS

Prostaglandins play an important role as mediators of inflammation and COX are required for their production. Inflammation is an essential step in the fracture healing process in which prostaglandin production by COX-2 is involved. Data from animal studies suggest that NSAIDs, which inhibit COX-2, can impair fracture healing due to the inhibition of the endochondral ossification pathway. Animal data suggest that the effects of COX-2 inhibitors are dependent on the timing, duration, and dose, and that these effects are reversible.

SUMMARY

These animal data, together with the view of limited scientifically robust clinical evidence in humans, indicate that physicians consider only short-term administration of COX-2 inhibitors or other drugs in the pain management of patients who are in the phase of fracture or other bone defect healing. COX-2-inhibitors should be considered a potential risk factor for fracture healing, and therefore to be avoided in patients at risk for delayed fracture healing.

Cellular and molecular mechanisms of accelerated fracture healing by COX2 gene therapy: studies in a mouse model of multiple fractures

This study sought to determine the cellular and molecular mechanisms of cyclooxygenase-2 (COX2) gene therapy to accelerate fracture repair in a mouse multiple tibial fractures model. The lenti-COX2 (or lenti-gfp control vector) was injected into fractures on day 1 post-fracture. At days 3-7, the COX2 treatment increased Sdf1-, Cxcr4-, Nes-, and Podxl-expressing mesenchymal stem cells (MSCs) within fracture calluses, suggesting an enhanced MSC recruitment or expansion. The COX2-treated mice formed smaller cartilaginous calluses that had less cartilage tissues than control mice. The expression of Sox9 mRNA was 7-fold less in COX2-treated than in control calluses at day 14, implying that COX2 reduces chondrocytic differentiation of MSCs. The therapy also enhanced angiogenesis as reflected by increased immunostaining of CD31, vWF, and α-SMA over controls in the cartilaginous callus at day 14-21. At which time, the COX2 gene therapy promoted bony remodeling of the cartilaginous callus to bridge the fracture gap that was accompanied by 2-fold increase in osteoclasts along the surface of the woven bone and an onset of osteogenesis. Blocking angiogenesis with daily injection of endostatin from day 4 to day 10 into fracture sites blocked the COX2-mediated reduction of callus size that was associated with an increase in hypertrophic chondrocytes and concomitant reduction in osteoclasts. In conclusion, COX2 accelerates fracture healing in part through three biological actions: 1) increased recruitment/expansion of MSCs; 2) decreased cartilaginous callus formation; and 3) increased angiogenesis-dependent cartilage remodeling. These effects were associated with an earlier onset of bony bridging of the fracture gap.

Retinoic acid receptor-dependent, cell-autonomous, endogenous retinoic acid signaling and its target genes in mouse collecting duct cells

BACKGROUND

Vitamin A is necessary for kidney development and has also been linked to regulation of solute and water homeostasis and to protection against kidney stone disease, infection, inflammation, and scarring. Most functions of vitamin A are mediated by its main active form, all-trans retinoic acid (tRA), which binds retinoic acid receptors (RARs) to modulate gene expression. We and others have recently reported that renal tRA/RAR activity is confined to the ureteric bud (UB) and collecting duct (CD) cell lineage, suggesting that endogenous tRA/RARs primarily act through regulating gene expression in these cells in embryonic and adult kidney, respectively.

METHODOLOGY/PRINCIPAL FINDINGS

To explore target genes of endogenous tRA/RARs, we employed the mIMCD-3 mouse inner medullary CD cell line, which is a model of CD principal cells and exhibits constitutive tRA/RAR activity as CD principal cells do in vivo. Combining antagonism of RARs, inhibition of tRA synthesis, exposure to exogenous tRA, and gene expression profiling techniques, we have identified 125 genes as candidate targets and validated 20 genes that were highly regulated (Dhrs3, Sprr1a, and Ppbp were the top three). Endogenous tRA/RARs were more important in maintaining, rather than suppressing, constitutive gene expression. Although many identified genes were expressed in UBs and/or CDs, their exact functions in this cell lineage are still poorly defined. Nevertheless, gene ontology analysis suggests that these genes are involved in kidney development, renal functioning, and regulation of tRA signaling.

CONCLUSIONS/SIGNIFICANCE

A rigorous approach to defining target genes for endogenous tRA/RARs has been established. At the pan-genomic level, genes regulated by endogenous tRA/RARs in a CD cell line have been catalogued for the first time. Such a catalogue will guide further studies on molecular mediators of endogenous tRA/RARs during kidney development and in relation to renal defects associated with vitamin A deficiency.

Do nonsteroidal anti-inflammatory drugs affect bone healing? A critical analysis

Nonsteroidal anti-inflammatory drugs (NSAIDs) play an essential part in our approach to control pain in the posttraumatic setting. Over the last decades, several studies suggested that NSAIDs interfere with bone healing while others contradict these findings. Although their analgesic potency is well proven, clinicians remain puzzled over the potential safety issues. We have systematically reviewed the available literature, analyzing and presenting the available in vitro animal and clinical studies on this field. Our comprehensive review reveals the great diversity of the presented data in all groups of studies. Animal and in vitro studies present so conflicting data that even studies with identical parameters have opposing results. Basic science research defining the exact mechanism with which NSAIDs could interfere with bone cells and also the conduction of well-randomized prospective clinical trials are warranted. In the absence of robust clinical or scientific evidence, clinicians should treat NSAIDs as a risk factor for bone healing impairment, and their administration should be avoided in high-risk patients.

Y-box protein-1 is a transcriptional regulator of BMP7

Bone morphogenetic protein-7 (BMP7) is an endogenous antifibrogenic protein in the kidney which is down regulated in experimental chronic kidney diseases such as obstructive and diabetic nephropathy in parallel with progressively increasing TGFβ. In vitro studies were performed in Madin-Darby Canine Kidney (MDCK)-cells to identify transcriptional regulators of BMP7. Experiments with various BMP7 promoter fragments (465-4,267  bp) identify small proximal promoter segments that are transcriptionally activated by high glucose (3.2-fold) but down regulated by TGFβ (0.2-fold) compared to normal glucose. Protein binding to these DNA segments is increased by high glucose and decreased by TGFβ in a time-dependent, progressive manner. Analysis of BMP7 promoter-binding proteins with liquid chromatography/tandem mass spectrometry (LC/MS/MS) identifies seven unique, partially overlapping peptides, spanning 25% of the amino acid sequence of Y-box protein-1 (YB1). EMSA-Western blot combination experiments confirm that YB1 is a BMP7 promoter-binding protein. YB1 knock-down reduces transcriptional responses to high glucose and TGFβ by about one-half, respectively. In addition, high glucose induces but TGFβ reduces nuclear translocation of YB1 from the cytoplasm. These studies identify YB1 as a transcriptional activator of BMP7 and helps to explain the progressive decline in renal BMP7 in diabetic nephropathy and other kidney diseases.

NSAIDS inhibit in vitro MSC chondrogenesis but not osteogenesis: implications for mechanism of bone formation inhibition in man

The non-steroidal anti-inflammatory drugs (NSAIDs) are widely used for analgesia but may inhibit bone formation. We investigated whether the reported NSAID effect on bone is related to inhibition of bone marrow mesenchymal stem cell (MSC) proliferation and osteogenic and chondrogenic differentiation and evaluated both cyclooxygenase (COX)-1 and COX-2 specific drugs. The effects of seven COX-1 and COX-2 inhibitors on MSC proliferation and osteogenic and chondrogenic differentiation were tested using Vybrant, sodium 3'-[1-(phenylaminocarbonyl)- 3,4-tetrazolium]-bis (4-methoxy-6-nitro) benzene sulfonic acid hydrate (XTT), functional and quantitative assays of MSC differentiation. The MSC expression of COX-1 and COX-2 and prostaglandin E2 (PGE-2) levels were evaluated serially during lineage differentiation by quantitative PCR and ELISA. None of the NSAIDs at broad range of concentration (range 10(-3) to 100 μg/ml) significantly affected MSC proliferation. Surprisingly, MSC osteogenic differentiation inhibition was not evident. However, NSAIDs affected chondrogenic potential with a reduction in sulphated glycosaminoglycans (sGAG) content by 45% and 55% with diclofenac and ketorolac, respectively (P < 0.05 compared to controls). Parecoxib and meloxicam, more COX-2 specific reagents inhibited sGAG to a lesser degree, 22% and 27% respectively (P < 0.05 compared to controls). Cartilage pellet immunohistochemistry confirmed the above results. Pellet chondrogenesis was associated with increased COX-1 expression levels but not COX-2, and COX-1 specific drugs suppressed MSC PGE-2 more than COX-2 specific inhibitors. These findings suggest that NSAIDs may inhibit bone formation via blockage of MSC chondrogenic differentiation which is an important intermediate phase in normal endochondral bone formation.

A defect in Δ6 and Δ5 desaturases may be a factor in the initiation and progression of insulin resistance, the metabolic syndrome and ischemic heart disease in South Asians

The high incidence of insulin resistance and the metabolic syndrome in South Asians remains unexplained. I propose that a defect in the activity of Δ⁶ and Δ⁵ desaturases and consequent low plasma and tissue concentrations of polyunsaturated fatty acids such as γ-linolenic acid (GLA), dihomo-γ-linolenic acid (DGLA), arachidonic acid (AA), eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) and formation of their anti-inflammatory products prostaglandin E₁ (PGE₁), prostacyclin (PGI₂), PGI₃, lipoxins, resolvins, protectins, maresins and nitrolipids could be responsible for the high incidence of insulin resistance, the metabolic syndrome and ischemic heart disease (IHD) in South Asians. This proposal is supported by the observation that South Asian Indians have lower plasma and tissue concentrations of GLA, DGLA, AA, EPA and DHA, the precursors of PGE₁, PGI₂, PGI₃, lipoxins, resolvins, protectins, and nitrolipids, the endogenous molecules that prevent platelet aggregation, vasoconstriction, thrombus formation, leukocyte activation and possess anti-inflammatory action and thus, are capable of preventing the development of insulin resistance, atherosclerosis, hypertension, type 2 diabetes mellitus and premature ischemic heart disease. Genetic predisposition, high carbohydrate intake, lack of exercise, tobacco use and low birth weight due to maternal malnutrition suppress the activity of Δ⁶ and Δ⁵ desaturases that leads to low plasma and tissue concentrations of polyunsaturated fatty acids and their products. This implies that adequate provision of polyunsaturated fatty acids and co-factors needed for their metabolism, and efforts to enhance the formation of their beneficial metabolites PGE₁, PGI₂, PGI₃, lipoxins, resolvins, protectins, maresins and nitrolipids could form a novel approach in the prevention and management of these diseases in this high-risk population.

NSAID exposure and risk of nonunion: a meta-analysis of case-control and cohort studies

Nonsteroidal anti-inflammatory drugs (NSAIDs) are frequently used for postoperative pain control. However, concerns regarding the potential deleterious effects of NSAIDs on bone healing have compelled many physicians to avoid NSAIDs in patients with healing fractures, osteotomies, and fusions. We systematically reviewed and analyzed the best clinical evidence regarding the effects of NSAID exposure on bone healing. Medline, Embase, and Cochrane electronic databases were searched for prospective and retrospective clinical studies of fracture, osteotomy, and fusion studies of patients with NSAID exposure and nonunion as an outcome. Study quality was assessed using the Newcastle-Ottawa Scale. Data on study design, patient characteristics, and risk estimates were extracted. Pooled effect estimates were calculated. Subanalyses were performed by bone type and by NSAID dose, duration, and route of administration. In the initial analysis of 11 cohort and case-control studies, the pooled odds ratio for nonunion with NSAID exposure was 3.0 (95% confidence interval 1.6-5.6). A significant association between lower-quality studies and higher reported odds ratios for nonunion was observed. When only higher-quality studies were considered, seven spine fusion studies were analyzed, and no statistically significant association between NSAID exposure and nonunion was identified (odds ratio = 2.2, 95% confidence interval 0.8-6.3). There was no increased risk of nonunion with NSAID exposure when only the highest-quality studies were assessed. Randomized controlled trials assessing NSAID exposure in fracture, fusion, and osteotomy populations are warranted to confirm or refute the findings of this meta-analysis of observational studies.

Retinoic acid enhances osteogenesis in cranial suture-derived mesenchymal cells: potential mechanisms of retinoid-induced craniosynostosis

BACKGROUND

In utero retinoid exposure results in numerous craniofacial malformations, including craniosynostosis. Although many malformations associated with retinoic acid syndrome are associated with neural crest defects, the specific mechanisms of retinoid-induced craniosynostosis remain unclear. The authors used the culture of mouse cranial suture-derived mesenchymal cells to probe the potential cellular mechanisms of this teratogen to better elucidate mechanisms of retinoid-induced suture fusion.

METHODS

Genes associated with retinoid signaling were assayed in fusing (posterofrontal) and patent (sagittal, coronal) sutures by quantitative real-time polymerase chain reaction. Cultures of mouse suture-derived mesenchymal cells from the posterofrontal suture were established from 4-day-old mice. Cells were cultured with all-trans retinoic acid (1 and 5 muM). Proliferation, osteogenic differentiation, and specific gene expression were assessed.

RESULTS

Mouse sutures were found to express genes necessary for retinoic acid synthesis, binding, and signal transduction, demonstrated by quantitative real-time polymerase chain reaction (Raldh1, Raldh2, Raldh3, and Rbp4). These genes were not found to be differentially expressed in fusing as compared with patent cranial sutures in vivo. Addition of retinoic acid enhanced the osteogenic differentiation of suture-derived mesenchymal cells in vitro, including up-regulation of alkaline phosphatase activity and Runx2 expression. Contemporaneously, cellular proliferation was repressed, as shown by proliferative cell nuclear antigen expression. The pro-osteogenic effect of retinoic acid was accompanied by increased gene expression of several hedgehog and bone morphogenetic protein ligands.

CONCLUSIONS

Retinoic acid represses proliferation and enhances osteogenic differentiation of suture-derived mesenchymal cells. These in vitro data suggest that retinoid exposure may lead to premature cranial suture fusion by means of enhanced osteogenesis and hedgehog and bone morphogenetic protein signaling.

Regulation of embryonic kidney branching morphogenesis and glomerular development by KISS1 receptor (Gpr54) through NFAT2- and Sp1-mediated Bmp7 expression

G-protein-coupled receptor 54 (Gpr54, KISS1 receptor) plays critical roles in puberty regulation, tumor metastasis suppression, and vasoconstriction. Bone morphogenetic protein-7 (Bmp7) is required for kidney organogenesis. However, whether Gpr54 is involved in embryonic kidney development and how Bmp7 expression is regulated in the kidney are largely unknown. Here we report that Gpr54 deletion leads to kidney branching morphogenesis and glomerular development retardation in embryonic kidneys in vivo and in explanted kidneys in vitro. Gpr54 inactivation results in a high risk of low glomerular number in adult kidneys. Gpr54 is expressed in condensed mesenchyme at E12.5 and epithelial cells of proximal and distal tubules and collecting ducts at E17.5 and P0 mouse kidney. Deletion of Gpr54 decreases Bmp7 expression and Smad1 phosphorylation in the developing kidney. Using chromatin immunoprecipitation and luciferase assays, we demonstrate that Gpr54 regulates NFAT2- and Sp1-mediated Bmp7 transcription. Furthermore, we show that NFAT2 cooperates with Sp1 to promote Bmp7 transcription activation. Together, these data suggest that Gpr54 regulates Bmp7 expression through NFAT2 and Sp1 and plays an important role in embryonic kidney branching morphogenesis and glomerular development.

Acute phosphate restriction leads to impaired fracture healing and resistance to BMP-2

Hypophosphatemia leads to rickets and osteomalacia, the latter of which results in decreased biomechanical integrity of bones, accompanied by poor fracture healing. Impaired phosphate-dependent apoptosis of hypertrophic chondrocytes is the molecular basis for rickets. However, the underlying pathophysiology of impaired fracture healing has not been characterized previously. To address the role of phosphate in fracture repair, mice were placed on a phosphate-restricted diet 2 days prior to or 3 days after induction of a mid-diaphyseal femoral fracture to assess the effects of phosphate deficiency on the initial recruitment of mesenchymal stem cells and their subsequent differentiation. Histologic and micro-computed tomographic (microCT) analyses demonstrated that both phosphate restriction models dramatically impaired fracture healing primarily owing to a defect in differentiation along the chondrogenic lineage. Based on Sox9 and Sox5 mRNA levels, neither the initial recruitment of cells to the callus nor their lineage commitment was effected by hypophosphatemia. However, differentiation of these cells was impaired in association with impaired bone morphogenetic protein (BMP) signaling. In vivo ectopic bone-formation assays and in vitro investigations in ST2 stromal cells confirmed that phosphate restriction leads to BMP-2 resistance. Marrow ablation studies demonstrate that hypophosphatemia has different effects on injury-induced intramembranous bone formation compared with endochondral bone formation. Thus phosphate plays an important role in the skeleton that extends beyond mineralized matrix formation and growth plate maturation and is critical for endochondral bone repair.

Adiponectin stimulates osteoblast differentiation through induction of COX2 in mesenchymal progenitor cells

In bone marrow, osteoblasts and adipocytes are differentiated from mesenchymal progenitor cells and their differentiation is reciprocally regulated by largely unknown mechanisms. In this study, we investigated downstream signaling cascades of adiponectin, a member of the adipocytokine family, in the regulation of osteoblast differentiation. Adiponectin augmented expression of several osteogenic marker genes and increased osteoblast differentiation in mesenchymal progenitor cells. The expression of cyclooxygenase-2 (COX2) was potently increased by adiponectin, whereas inhibition of COX2 activity abolished the effect of adiponectin on osteogenesis. In addition, adiponectin rapidly stimulated p38 mitogen-activated protein kinase via the adiponectin receptor, AdipoR1, which resulted in c-Jun activation for COX2 expression. Adiponectin also stimulated BMP2 expression in a COX2-dependent manner. Moreover, Runx2, a key osteogenic transcription factor, contributed to the acceleration of osteogenesis in the presence of adiponectin. Collectively, the finding that adiponectin could promote osteogenesis through an intracellular signaling cascade in mesenchymal progenitor cells suggests that adiponectin would be a potential therapeutic target for bone-related diseases.

Marrow stromal cell-based cyclooxygenase 2 ex vivo gene-transfer strategy surprisingly lacks bone-regeneration effects and suppresses the bone-regeneration action of bone morphogenetic protein 4 in a mouse critical-sized calvarial defect model

This study evaluated whether the murine leukemia virus (MLV)-based cyclooxygenase-2 (Cox-2) ex vivo gene-transfer strategy promotes healing of calvarial defects and/or synergistically enhances bone morphogenetic protein (BMP) 4-mediated bone regeneration. Gelatin scaffolds impregnated with mouse marrow stromal cells (MSCs) transduced with MLV-expressing BMP4, Cox-2, or a control gene were implanted into mouse calvarial defects. Bone regeneration was assessed by X-ray, dual-energy X-ray absorptiometry, and histology. In vitro, Cox-2 or prostanglandin E(2) enhanced synergistically the osteoblastic differentiation action of BMP4 in mouse MSCs. In vivo, implantation of BMP4-expressing MSCs yielded massive bone regeneration in calvarial defects after 2 weeks, but the Cox-2 strategy surprisingly did not promote bone regeneration even after 4 weeks. Staining for alkaline phosphatase (ALP)-expressing osteoblasts was strong throughout the defect of animals receiving BMP2/4-expressing cells, but defects receiving Cox-2-expressing cells displayed weak ALP staining along the edge of original intact bone, indicating that the Cox-2 strategy lacked bone-regeneration effects. The Cox-2 strategy not only lacked bone-regeneration effects but also suppressed the BMP4-induced bone regeneration. In vitro coculture of Cox-2-expressing MSCs with BMP4-expressing MSCs in gelatin scaffolds reduced BMP4 mRNA transcript levels, suggesting that Cox-2 may promote BMP4 gene silencing in BMP4-expressing cells, which may play a role in the suppressive action of Cox-2 on BMP4-mediated bone formation. In summary, the Cox-2 ex vivo gene-transfer strategy not only lacks bone-regeneration effects but also suppresses the bone-regeneration action of BMP4 in healing of calvarial defects.

9-Cis-retinoic acid reduces ischemic brain injury in rodents via bone morphogenetic protein

Retinoic acid (RA), a biologically active derivative of vitamin A, has protective effects against damage caused by H(2)O(2) or oxygen-glucose deprivation in mesangial and PC12 cells. In cultured human osteosarcoma cells, RA enhances the expression of bone morphogenetic protein-7 (BMP7), a trophic factor that reduces ischemia- or neurotoxin-mediated neurodegeneration in vivo. The purpose of this study is to examine whether RA reduces ischemic brain injury through a BMP7 mechanism. We found that intracerebroventricular administration of 9-cis-retinoic acid (9cRA) enhanced BMP7 mRNA expression, detected by RT-PCR, in rat cerebral cortex at 24 hr after injection. Rats were also subjected to transient focal ischemia induced by ligation of the middle cerebral artery (MCA) at 1 day after 9cRA injection. Pretreatment with 9cRA increased locomotor activity and attenuated neurological deficits 2 days after MCA ligation. 9cRA also reduced cerebral infarction and TUNEL labeling. These protective responses were antagonized by the BMP antagonist noggin given 1 day after 9cRA injection. Taken together, our data suggest that 9cRA has protective effects against ischemia-induced injury, and these effects involve BMPs.

Global age-dependent differences in gene expression in response to calvarial injury

Children less than 2 years of age are capable of healing large calvarial defects, whereas adults have been found to lack this endogenous ability. In this study, we used microarray analysis to compare genomewide expression patterns during active regeneration after injury with calvaria in skeletally immature and mature mice. Parietal bone defects were created in 6-day-old (juvenile) and 60-day-old (adult) mice using a 4-mm trephine bit (n = 20 mice per age group). The calvarial disc was removed, leaving the underlying dura mater intact. Two weeks after injury, the region of regeneration with the underlying dura mater was harvested, and RNA was extracted for microarray analysis. The 25 most differentially upregulated genes in juvenile regenerates compared with adults were listed, as well as selected bone-related genes. In addition, QRT-PCR confirmation of specific genes was performed for validation. Juvenile regenerates expressed significantly greater amounts of BMP-2, -4, -7, as well as FGF-2 and its receptor FGFR-1. Various other growth factors were also noted to be upregulated, including IGF-2 and Ptn. This corresponded with the increased expression of markers for osteogenic differentiation of Sparc and Oc. Markers of osteoclast activity, Acp5, Ctsk, and Mmp2, were noted to be greater in juvenile regenerates compared with adults. The observation of Mmp14 upregulation, however, highlights the importance of balanced osteoclast-mediated bone resorption for ultimate healing. The 2 most differentially regulated genes, transthyretin (Ttr) and prostaglandin D2 synthase (Ptgds), highlight the potential role of retinoic acid signaling and the prostaglandin axis on skeletal regeneration. These findings underscore the multitude of biomolecular mechanisms at play, allowing juvenile calvaria to heal after injury. The identification of various growth factors and cytokines involved also suggests novel therapeutic strategies for tissue-engineering purposes.

Expression and regulation of the decoy bone morphogenetic protein receptor BAMBI in the developing avian face

Here, we examine the expression and regulation of the gene BAMBI, a kinase-deficient decoy receptor capable of interacting with type I bone morphogenetic protein (BMP) receptors in avian embryos. Initially, expression was limited to the endoderm during neurula and pharyngula stages. From embryonic day 3.5 (stage 20) and onward, BAMBI expression almost perfectly overlapped with known expression patterns for BMP4, particularly in the face and limbs. We performed bead implant experiments in the face to see which signals could be repressing or promoting expression of BAMBI. Our data point to retinoids and BMPs as being major positive regulators of BAMBI expression; however, fibroblast growth factor 2 acts to repress BAMBI. Furthermore, retinoic acid is likely to act directly on BAMBI as induction occurs in the presence of cycloheximide. The data suggested that BAMBI could be used to regulate Bmp signaling during tissue interactions that are an integral part of facial morphogenesis.

Retroviral-based gene therapy with cyclooxygenase-2 promotes the union of bony callus tissues and accelerates fracture healing in the rat

BACKGROUND

An in vivo gene therapy strategy was developed to accelerate bone fracture repair.

METHODS

Direct injection of a murine leukemia virus-based vector targeted transgene expression to the proliferating periosteal cells arising shortly after fracture. Cyclooxygenase-2 (Cox-2) was selected because the transgene for its prostaglandin products that promote angiogenesis, bone formation and bone resorption, are all required for fracture healing. The human (h) Cox-2 transgene was modified to remove AU-rich elements in the 3'-untranslated region and to improve protein translation.

RESULTS

In vitro studies revealed robust and sustained Cox-2 protein expression, prostaglandin E(2) and alkaline phosphatase production in rat bone marrow stromal cells and osteoblasts transgenic for the hCox-2 gene. In vivo studies in the rat femur fracture revealed that Cox-2 transgene expression produced bony union of the fracture by 21 days post-fracture, a time when cartilage persisted within the fracture tissues of control animals and approximately 1 week earlier than the healing normally observed in this model. None of the ectopic bone formation associated with bone morphogenetic protein gene therapy was observed.

CONCLUSIONS

This study represents the first demonstration that a single local application of a retroviral vector expressing a single osteoinductive transgene consistently accelerated fracture repair.

Prostate cancer induces bone metastasis through Wnt-induced bone morphogenetic protein-dependent and independent mechanisms

Prostate cancer (PCa) is frequently accompanied by osteosclerotic (i.e., excessive bone production) bone metastases. Although bone morphogenetic proteins (BMP) and Wnts are mediators of PCa-induced osteoblastic activity, the relation between them in PCa bone metastases is unknown. The goal of this study was to define this relationship. Wnt3a and Wnt5a administration or knockdown of DKK-1, a Wnt inhibitor, induced BMP-4 and 6 expression and promoter activation in PCa cells. DKK-1 blocked Wnt activation of the BMP promoters. Transfection of C4-2B cells with axin, an inhibitor of canonical Wnt signaling, blocked Wnt3a but not Wnt5a induction of the BMP promoters. In contrast, Jnk inhibitor I blocked Wnt5a but not Wnt3a induction of the BMP promoters. Wnt3a, Wnt5a, and conditioned medium (CM) from C4-2B or LuCaP23.1 cells induced osteoblast differentiation in vitro. The addition of DKK-1 and Noggin, a BMP inhibitor, to CM diminished PCa CM-induced osteoblast differentiation in a synergistic fashion. However, pretreatment of PCa cells with DKK-1 before collecting CM blocked osteoblast differentiation, whereas pretreatment with Noggin only partially reduced osteoblast differentiation, and pretreatment with both DKK-1 and Noggin had no greater effect than pretreatment with DKK-1 alone. Additionally, knockdown of BMP expression in C4-2B cells inhibited Wnt-induced osteoblastic activity. These results show that PCa promotes osteoblast differentiation through canonical and noncanonical Wnt signaling pathways that stimulate both BMP-dependent and BMP-independent osteoblast differentiation. These results show a clear link between Wnts and BMPs in PCa-induced osteoblast differentiation and provide novel targets, including the noncanonical Wnt pathway, for therapy of PCa.

Pharmacological agents and impairment of fracture healing: what is the evidence?

Bone healing is an extremely complex process which depends on the coordinated action of several cell lineages on a cascade of biological events, and has always been a major medical concern. The use of several drugs such as corticosteroids, chemotherapeutic agents, non-steroidal anti-inflammatory drugs (NSAIDs), antibiotics, anticoagulants and drugs which reduce osteoclastic activity have been shown to affect bone healing. This review article presents our current understanding on this topic, focusing on data illustrating the effect of these drugs on fracture healing and bone regeneration.

Materials in particulate form for tissue engineering. 2. Applications in bone

Materials in particulate form have been the subjects of intensive research in view of their use as drug delivery systems. While within this application there are still issues to be addressed, these systems are now being regarded as having a great potential for tissue engineering applications. Bone repair is a very demanding task, due to the specific characteristics of skeletal tissues, and the design of scaffolds for bone tissue engineering presents several difficulties. Materials in particulate form are now seen as a means of achieving higher control over parameters such as porosity, pore size, surface area and the mechanical properties of the scaffold. These materials also have the potential to incorporate biologically active molecules for release and to serve as carriers for cells. It is believed that the combination of these features would create a more efficient approach towards regeneration. This review focuses on the application of materials in particulate form for bone tissue engineering. A brief overview of bone biology and the healing process is also provided in order to place the application in its broader context. An original compilation of molecules with a documented role in bone tissue biology is listed, as they have the potential to be used in bone tissue engineering strategies. To sum up this review, examples of works addressing the above aspects are presented.

Inhibition of fracture healing

This paper reviews the current literature concerning the main clinical factors which can impair the healing of fractures and makes recommendations on avoiding or minimising these in order to optimise the outcome for patients. The clinical implications are described.

The effects of COX-1 and COX-2 inhibitors on prostaglandin synthesis and the formation of heterotopic bone in a rat model

INTRODUCTION

Traumatic heterotopic ossification (HO) is a common clinical condition associated with various orthopedic procedures that involve injury to soft tissues near bone. In this study, we tested the hypothesis that the prophylactic effects of NSAID's in the treatment of HO are mediated via inhibition of the COX-2 enzyme. Here we describe a rat model that simulates HO in the human that was used to test the above hypothesis.

MATERIALS AND METHODS

Heterotopic ossification was surgically induced in the quadriceps by injury to the muscle and femoral periosteum and transplantation of donor bone marrow cells containing osteoprogenitors into the site of injury. HO was imaged and quantified by micro-CT scanning of femurs removed from sacrificed animals at 6 weeks post-injury, three-dimensional computer reconstructions of the scanned bones and computer-assisted morphometric analysis. Prostaglandin E(2) (PGE(2)) synthesis was quantified using an enzyme immunoassay system. The effects of a nonselective COX inhibitor or specific inhibitors of COX-1 or COX-2 following oral administration on the content of ectopic bone and PGE(2) were also measured.

RESULTS

Micro-CT and histological analyses demonstrated that all of the femurs in operated limbs developed HO in the vastus lateralis muscle belly of the quadriceps close to the anterior femur. Only the COX-1,2 nonselective and COX-2 inhibitors significantly decreased HO formation (by about one-third in each case; P < 0.05). PGE(2) synthesis at the site of injury was increased 50- and 100-fold (to 25 ng/g tissue) within 1 and 7 days, respectively, post-injury with the levels declining to near baseline within 2 weeks of surgery. Both the COX-1,2 nonselective and COX-2 inhibitors significantly decreased PGE(2) levels to 25% of control HO levels within 24 h of the first administration, even at low dosages. The COX-1 inhibitor only produced the same effect after 1 week of administration.

CONCLUSION

These findings suggest that although inhibitors of COX-2 or COX-1 reduced PGE(2) synthesis, only the COX-2 enzyme plays a role in the mechanism of traumatic HO.

Effects of direct current electrical stimulation on gene expression of osteopromotive factors in a posterolateral spinal fusion model

STUDY DESIGN

An in vivo model was used to determine levels of mRNA expression in response to direct current (DC) electrical stimulation in a rabbit posterolateral fusion model.

OBJECTIVES

This study tested the possibility that DC stimulation at the surgery site would increase expression of genes related to bone formation relative to expression in autograft alone.

SUMMARY OF BACKGROUND DATA

DC electrical stimulation as an adjunct treatment in spinal surgery has shown increased fusion rates when compared with autograft alone, yet the biology of such treatment is not fully understood.

METHODS

Thirty New Zealand White rabbits were entered into the study. A posterolateral, intertransverse process fusion was performed bilaterally at L4-L5, with autogenous bone graft. An implantable DC stimulator was placed across the decorticated transverse processes before placement of autograft. Animals were killed at 3, 7, 14, 21, and 28 days. mRNA levels of BMP-2, 4, 6, 7, VEGF, FGF-2, TGF-beta, ALK-2, and ALK-3 were evaluated with real-time RT-PCR.

RESULTS

mRNA expression was significantly higher in the DC stimulated animals versus the control animals for several of the genes studied. In particular, levels of mRNA were elevated for BMP-2, BMP-6, and BMP-7.

CONCLUSIONS

This study shows for the first time that DC stimulation results in a sustained increase of multiple osteogenic genes, suggesting that the biologic mechanism for the DC-induced increase in the rate and extent of bone formation observed clinically may be mediated by the up-regulation of these osteoinductive factors.

Toxoplasma gondii prevents neuron degeneration by interferon-gamma-activated microglia in a mechanism involving inhibition of inducible nitric oxide synthase and transforming growth factor-beta1 production by infected microglia

Interferon (IFN)-gamma, the main cytokine responsible for immunological defense against Toxoplasma gondii, is essential in all infected tissues, including the central nervous system. However, IFN-gamma-activated microglia may cause tissue injury through production of toxic metabolites such as nitric oxide (NO), a potent inducer of central nervous system pathologies related to inflammatory neuronal disturbances. Despite potential NO toxicity, neurodegeneration is not commonly found during chronic T. gondii infection. In this study, we describe decreased NO production by IFN-gamma-activated microglial cells infected by T. gondii. This effect involved strong inhibition of iNOS expression in IFN-gamma-activated, infected microglia but not in uninfected neighboring cells. The inhibition of NO production and iNOS expression were parallel with recovery of neurite outgrowth when neurons were co-cultured with T. gondii-infected, IFN-gamma-activated microglia. In the presence of transforming growth factor (TGF)-beta1-neutralizing antibodies, the beneficial effect of the parasite on neurons was abrogated, and NO production reverted to levels similar to IFN-gamma-activated uninfected co-cultures. In addition, we observed Smad-2 nuclear translocation, a hallmark of TGF-beta1 downstream signaling, in infected microglial cultures, emphasizing an autocrine effect restricted to infected cells. Together, these data may explain a neuropreservation pattern observed during immunocompetent host infection that is dependent on T. gondii-triggered TGF-beta1 secretion by infected microglia.

Diverse biological effect and Smad signaling of bone morphogenetic protein 7 in prostate tumor cells

We found that bone morphogenetic protein (BMP) 7, a member of the BMP family, was strikingly up-regulated during the development of primary prostatic adenocarcinoma in the conditional Pten deletion mouse model. To determine the relevance of this finding to human prostate cancer, we examined the expression of BMPs and BMP receptors (BMPR) as well as the responsiveness to recombinant human BMP7 in a series of human prostate tumor cell lines. All prostatic cell lines tested expressed variable levels of BMP2, BMP4, and BMP7 and at least two of each type I and II BMPRs. In all cases, BMP7 induced Smad phosphorylation in a dose-dependent manner, with Smad5 activation clearly demonstrable. However, the biological responses to BMP7 were cell type specific. BPH-1, a cell line representing benign prostatic epithelial hyperplasia, was growth arrested at G1. In the bone metastasis-derived PC-3 prostate cancer cells, BMP7 induced epithelial-mesenchymal transdifferentiation with classic changes in morphology, motility, invasiveness, and molecular markers. Finally, BMP7 inhibited serum starvation-induced apoptosis in the LNCaP prostate cancer cell line and more remarkably in its bone metastatic variant C4-2B line. Each of the cell lines influenced by BMP7 was also responsive to BMP2 in a corresponding manner. The antiapoptotic activity of BMP7 in the LNCaP and C4-2B cell lines was not associated with a significant alteration in the levels of the proapoptotic protein Bax or the antiapoptotic proteins Bcl-2, Bcl-xl, and X-linked inhibitor of apoptosis. However, in C4-2B cells but not in LNCaP cells, a starvation-induced decrease in the level of survivin was counteracted by BMP7. Taken together, these findings suggest that BMPs are able to modulate the biological behavior of prostate tumor cells in diverse and cell type-specific manner and point to certain mechanisms by which these secreted signaling molecules may contribute to prostate cancer growth and metastasis.

Midkine and retinoic acid reduce cerebral infarction induced by middle cerebral artery ligation in rats

The present study investigates the neuroprotective effects of midkine (MK) and retinoic acid (RA) against ischemia in the CNS. Primary cortical neurons, derived from rat E15 embryos (DIV9), were treated with 9-cis-RA (9cRA), all-trans-RA (atRA) or vehicle. Using quantitative PCR, the level of MK mRNA was significantly increased at 4h after 9cRA application. The protective effect of RA and MK was also investigated in adult Sprague-Dawley rats. 9cRA, atRA, MK, or vehicle was injected into the lateral ventricle prior to a 60-min-MCA ligation. Pretreatment with 9cRA or MK attenuated cerebral infarction in stroke animals. Application of a similar dose of atRA did not reduce the size of infarction. In conclusion, our data suggest that 9cRA has neuroprotective effects against ischemia-related brain injury which may involve upregulation of midkine.

High-dose retinoic acid modulates rat calvarial osteoblast biology

Retinoic acid has been shown to adversely affect craniofacial development. Cleft palate and craniosynostosis are two examples of craniofacial defects associated with prenatal exposure to this agent. Although the effects of retinoic acid on cephalic neural crest-derived tissues have previously been studied, the specific effects of retinoic acid on the cellular biology of osteoblasts remain unclear. The purpose of this study was to analyze in detail the effects of pharmacologic doses of retinoic acid on the differentiation and proliferation of osteoblasts derived from an intramembranous source. Primary rat calvarial osteoblasts were established in culture and treated with 1 or 10 microM all-trans-retinoic acid. Retinoic acid treatment markedly increased expression of osteopontin up to 48 h after stimulation. Consistent with this early stage of differentiation, both mRNA and protein analysis of FGF receptor isoforms demonstrated a switch in predominance from fibroblast growth factor receptor 2 (fgfr2) to fgfr1. Analysis of PCNA protein confirmed inhibition of proliferation by retinoic acid. To determine whether these alterations in osteoblast biology would lead to increased differentiation, we examined short term [alkaline phosphatase (AP) activity] and long term (von Kossa staining) surrogates of bone formation in vitro. These assays confirmed that retinoic acid increased osteogenesis, with a 4-fold increase in bone nodule formation in cells treated with 10 microM retinoic acid after 28 days. Overall, our results demonstrated that pharmacologic doses of all-trans-retinoic acid decreased osteoblast proliferation and increased differentiation, suggesting that retinoic acid may effect craniofacial development by pathologically enhancing osteogenesis.

Expression of bone morphogenetic proteins in acute promyelocytic leukemia before and after combined all trans-retinoic acid and cytotoxic treatment

We investigated the dynamics of bone morphogenetic protein (BMP) and their receptor mRNA expression in relation to combined treatment with all trans-retinoic acid (ATRA) and chemotherapy in four patients with acute promyelocytic leukemia (APL). Reverse transcription-polymerase chain reaction (RT-PCR) analysis of the bone marrow cells at diagnosis showed strong expression of BMP-2, -4, and -7, and their receptors RIA, RIB, and RII, parallel to the expression of promyelocytic leukemia/retinoic acid receptor alpha (PML/RARalpha) fusion gene transcripts. Therapeutic clearance of the tumor molecular marker corresponded to the absence of BMP expression, suggesting the possible role of BMPs as markers of the minimal residual disease (MRD) in APL.

Signals from lateral plate mesoderm instruct endoderm toward a pancreatic fate

During embryonic development, organs arise along the gut tube as a series of buds in a stereotyped anterior-posterior (A-P) pattern. Using chick-quail chimeras and in vitro tissue recombination, we studied the interactions governing the induction and maintenance of endodermal organ identify focusing on the pancreas. Though several permissive signals in pancreatic development have been previously identified, here we provide evidence that lateral plate mesoderm sends instructive signals to the endoderm, signals that induce expression of the pancreatic genes Pdx1, p48, Nkx6.1, glucagon, and insulin. Moreover, this instructive signal directs cells to form ectopic insulin-positive islet-like clusters in endoderm that would otherwise form more rostral organs. Once generated, endocrine cells no longer require interaction with mesoderm, but nonendocrine cells continue to require permissive signals from the mesoderm. Stimulation of activin, BMP, or retinoic acid signaling is sufficient to induce Pdx1 expression in endoderm anterior to the pancreas. Lateral plate mesoderm appears to pattern the endoderm in a posterior-dominant fashion as first noted in the patterning of the neural tube at the same embryonic stage. These findings argue for a central role of the mesoderm in coordinating the A-P pattern of all three primary germ layers.

Bone morphogenetic protein and retinoic acid signaling cooperate to induce osteoblast differentiation of preadipocytes

Mesenchymal cells can differentiate into osteoblasts, adipocytes, myoblasts, or chondroblasts. Whether mesenchymal cells that have initiated differentiation along one lineage can transdifferentiate into another is largely unknown. Using 3T3-F442A preadipocytes, we explored whether extracellular signals could redirect their differentiation from adipocyte into osteoblast. 3T3-F442A cells expressed receptors and Smads required for bone morphogenetic protein (BMP) signaling. BMP-2 increased proliferation and induced the early osteoblast differentiation marker alkaline phosphatase, yet only mildly affected adipogenic differentiation. Retinoic acid inhibited adipose conversion and cooperated with BMP-2 to enhance proliferation, inhibit adipogenesis, and promote early osteoblastic differentiation. Expression of BMP-RII together with BMP-RIA or BMP-RIB suppressed adipogenesis of 3T3-F442A cells and promoted full osteoblastic differentiation in response to retinoic acid. Osteoblastic differentiation was characterized by induction of cbfa1, osteocalcin, and collagen I expression, and extracellular matrix calcification. These results indicate that 3T3-F442A preadipocytes can be converted into fully differentiated osteoblasts in response to extracellular signaling cues. Furthermore, BMP and retinoic acid signaling cooperate to stimulate cell proliferation, repress adipogenesis, and promote osteoblast differentiation. Finally, BMP-RIA and BMP-RIB induced osteoblast differentiation and repressed adipocytic differentiation to a similar extent.

Cyclooxygenase-2 regulates mesenchymal cell differentiation into the osteoblast lineage and is critically involved in bone repair

Preclinical and clinical studies suggest a possible role for cyclooxygenases in bone repair and create concerns about the use of nonsteroidal antiinflammatory drugs in patients with skeletal injury. We utilized wild-type, COX-1(-/-), and COX-2(-/-) mice to demonstrate that COX-2 plays an essential role in both endochondral and intramembranous bone formation during skeletal repair. The healing of stabilized tibia fractures was significantly delayed in COX-2(-/-) mice compared with COX-1(-/-) and wild-type controls. The histology was characterized by a persistence of undifferentiated mesenchyme and a marked reduction in osteoblastogenesis that resulted in a high incidence of fibrous nonunion in the COX-2(-/-) mice. Similarly, intramembranous bone formation on the calvaria was reduced 60% in COX-2(-/-) mice following in vivo injection of FGF-1 compared with either COX-1(-/-) or wild-type mice. To elucidate the mechanism involved in reduced bone formation, osteoblastogenesis was studied in bone marrow stromal cell cultures obtained from COX-2(-/-) and wild-type mice. Bone nodule formation was reduced 50% in COX-2(-/-) mice. The defect in osteogenesis was completely rescued by addition of prostaglandin E2 (PGE(2)) to the cultures. In the presence of bone morphogenetic protein (BMP-2), bone nodule formation was enhanced to a similar level above that observed with PGE(2) alone in both control and COX-2(-/-) cultures, indicating that BMPs complement COX-2 deficiency and are downstream of prostaglandins. Furthermore, we found that the defect in COX-2(-/-) cultures correlated with significantly reduced levels of cbfa1 and osterix, two genes necessary for bone formation. Addition of PGE(2) rescued this defect, while BMP-2 enhanced cbfa1 and osterix in both COX-2(-/-) and wild-type cultures. Finally, the effects of these agents were additive, indicating that COX-2 is involved in maximal induction of osteogenesis. These results provide a model whereby COX-2 regulates the induction of cbfa1 and osterix to mediate normal skeletal repair.