Comparison of TGF-beta/BMP pathways signaled by demineralized bone powder and BMP-2 in human dermal fibroblasts

Recombinant human bone morphogenetic protein-2 inhibits gastric cancer cell proliferation by inactivating Wnt signaling pathway via c-Myc with aurora kinases

The detailed molecular mechanisms and safety issues of recombinant human bone morphogenetic protein-2 (rhBMP-2) usage in bone graft substitution remain poorly understood. To investigate the molecular mechanisms underlying the function of rhBMP-2 in gastric cancer cells, we used microarrays to determine the gene expression patterns related to the effects of rhBMP-2. Based on a gene ontology analysis, several genes were upregulated during the regulation of the cell cycle and BMP signaling pathway. MYC was found to be significantly decreased along with its downstream target genes, the aurora kinases (AURKs), by rhBMP-2 in the network analysis. We further confirmed this finding with western blot data that rhBMP-2 inhibited c-Myc, AURKs, and β-catenin in SNU484 and SNU638 cells. An AURK inhibitor significantly decreased c-Myc expression in gastric cancer cells. Combination treatment with rhBMP-2 and AURK inhibitor resulted in significantly decreased c-Myc expression compared with gastric cancer cells treated with an rhBMP-2 or AURK inhibitor, respectively. Similar effects for decreased c-Myc expression were observed when we silenced β-catenin in gastric cancer cells. These results indicate that rhBMP-2 attenuated the growth of gastric cancer cells via the inactivation of β-catenin via c-Myc and AURKs. Therefore, our findings suggest that rhBMP-2 could be safely used with patients who undergo gastric or gastroesophageal cancer surgery.

A Selective Cell Population from Dermis Strengthens Bone Regeneration

Finding appropriate seed cells for bone tissue engineering remains a significant challenge. Considering that skin is the largest organ, we hypothesized that human bone morphogenetic protein receptor type IB (BmprIB)+ dermal cells could have enhanced osteogenic capacity in the healing of critical-sized calvarial defects in an immunodeficient mouse model. In this study, immunohistochemical staining revealed that BmprIB was expressed throughout reticular dermal cells; the positive expression rate of BmprIB was 3.5% ± 0.4% in freshly separated dermal cells, by flow cytometry. Furthermore, in vitro osteogenic capacity of BmprIB+ cells was confirmed by osteogenic-related staining and marker gene expression compared with unsorted dermal cells. In vivo osteogenic capacity was demonstrated by implantation of human BmprIB+ cell/coral constructs in the treatment of 4-mm diameter calvarial defects in an immunodeficient mouse model compared with implantation of unsorted cell/coral constructs and coral scaffold alone. These results indicate that the selective cell population BmprIB from human dermis is a promising osteogenic progenitor cell that can be a large-quantity and high-quality cell source for bone tissue engineering and regeneration. Stem Cells Translational Medicine 2017;6:306-315.

Wnt pathway regulation by demineralized bone is approximated by both BMP-2 and TGF-β1 signaling

Allogeneic demineralized bone is used extensively as a clinical graft material because it has osteo/chondroinductive and osteoconductive properties. Demineralized bone powder (DBP) induces chondrogenic differentiation of human dermal fibroblasts (hDFs) in three-dimensional collagen cultures, but the initiating mechanisms have not been fully characterized nor has it been shown that bone morphogenetic proteins (BMPs) recapitulate DBP's effects on target cells. Among the many signaling pathways regulated in hDFs by DBP prior to in vitro chondrogenesis, there are changes in Wnts and their receptors that may contribute to DBP actions. This study tests the hypothesis that DBP modulation of Wnt signaling entails both BMP and TGF-β pathways. We compared the effects of DBP, TGF-β1, or BMP-2 on Wnt signaling components in hDFs by Wnt signaling macroarray, RT-PCR, in situ hybridization, and Western immunoblot analyses. Many effects of DBP on Wnt signaling components were not shared by BMP-2, and likewise DBP effects on Wnt genes and β-catenin only partially required the TGF-β pathway, as shown by selective inhibition of TGF-β/activin receptor-like kinase. The analyses revealed that 64% (16/25) of the Wnt signaling components regulated by DBP were regulated similarly by the sum of effects by BMP-2 and by TGF-β1. In conclusion, signaling mechanisms of inductive DBP in human dermal fibroblasts involve the modulation of multiple Wnt signals through both BMP and TGF-β pathways.

Clinical characteristics influence in vitro action of 1,25-dihydroxyvitamin D(3) in human marrow stromal cells

Vitamin D is important for bone health, with low vitamin D levels being associated with skeletal fragility and fractures. Among its other biological activities, 1,25-dihydroxyvitamin D (1,25(OH)(2) D), stimulates the in vitro differentiation of human marrow stromal cells (hMSCs) to osteoblasts, which can be monitored by increases in alkaline phosphatase enzyme activity or osteocalcin gene expression. In this study, we tested the hypotheses that age and clinical attributes of subjects influence in vitro responsiveness of hMSCs to 1,25(OH)(2) D(3) . In a cohort of subjects whose hMSCs were isolated from bone marrow discarded during hip replacement surgery for osteoarthritis, there were significant inverse correlations with age for bone mineral density, renal function, body mass index, fat mass index, and lean mass index (n = 36-53). There were significant correlations with serum 25(OH)D for serum parathyroid hormone (PTH), body mass index, fat mass index, and lean mass index (n = 47-50). In vivo-in vitro correlation analyses indicated that there were significantly greater in vitro effects of 1,25(OH)(2) D(3) to stimulate osteoblast differentiation in hMSCs obtained from subjects who were younger than 65 years of age, or who had serum 25(OH)D ≤ 20 ng/mL, elevated serum PTH, or better renal function, assessed by estimated glomerular filtration rate. The greater in vitro stimulation of osteoblast differentiation by 1,25(OH)(2) D(3) in hMSCs from vitamin D-deficient subjects suggests that vitamin D replenishment may lead to more vigorous bone formation in subjects at risk.

Dermal fibroblast-mediated BMP2 therapy to accelerate bone healing in an equine osteotomy model

This study evaluated healing of equine metacarpal/metatarsal osteotomies in response to percutaneous injection of autologous dermal fibroblasts (DFbs) genetically engineered to secrete bone morphogenetic protein-2 (BMP2) or demonstrate green fluorescent protein (GFP) gene expression administered 14 days after surgery. Radiographic assessment of bone formation indicated greater and earlier healing of bone defects treated with DFb with BMP2 gene augmentation. Quantitative computed tomography and biomechanical testing revealed greater mineralized callus and torsional strength of DFb-BMP2-treated bone defects. On the histologic evaluation, the bone defects with DFb-BMP2 implantation had greater formation of mature cartilage and bone nodules within the osteotomy gap and greater mineralization activity on osteotomy edges. Autologous DFbs were successfully isolated in high numbers by a skin biopsy, rapidly expanded without fastidious culture techniques, permissive to adenoviral vectors, and efficient at in vitro BMP2 protein production and BMP2-induced osteogenic differentiation. This study demonstrated an efficacy and feasibility of DFb-mediated BMP2 therapy to accelerate the healing of osteotomies. Skin cell-mediated BMP2 therapy may be considered as a potential treatment for various types of fractures and bone defects.

Analysis of gene expression in PTHrP-/- mammary buds supports a role for BMP signaling and MMP2 in the initiation of ductal morphogenesis

Parathyroid hormone-related protein (PTHrP) acts on the mammary mesenchyme and is required for proper embryonic mammary development. In order to understand PTHrP's effects on mesenchymal cells, we profiled gene expression in WT and PTHrP(-/-) mammary buds, and in WT and K14-PTHrP ventral skin at E15.5. By cross-referencing the differences in gene expression between these groups, we identified 35 genes potentially regulated by PTHrP in the mammary mesenchyme, including 6 genes known to be involved in BMP signaling. One of these genes was MMP2. We demonstrated that PTHrP and BMP4 regulate MMP2 gene expression and MMP2 activity in mesenchymal cells. Using mammary bud cultures, we demonstrated that MMP2 acts downstream of PTHrP to stimulate ductal outgrowth. Future studies on the functional role of other genes on this list should expand our knowledge of how PTHrP signaling triggers the onset of ductal outgrowth from the embryonic mammary buds.

BMP signaling induces cell-type-specific changes in gene expression programs of human keratinocytes and fibroblasts

BMP signaling has a crucial role in skin development and homeostasis, whereas molecular mechanisms underlying its involvement in regulating gene expression programs in keratinocytes and fibroblasts remain largely unknown. We show here that several BMP ligands, all BMP receptors, and BMP-associated Smad1/5/8 are expressed in human primary epidermal keratinocytes and dermal fibroblasts. Treatment of both cell types by BMP-4 resulted in the activation of the BMP-Smad, but not BMP-MAPK pathways. Global microarray analysis revealed that BMP-4 treatment induces distinct and cell type-specific changes in gene expression programs in keratinocytes and fibroblasts, which are far more complex than the effects of BMPs on cell proliferation/differentiation described earlier. Furthermore, our data suggest that the potential modulation of cell adhesion, extracellular matrix remodeling, motility, metabolism, signaling, and transcription by BMP-4 in keratinocytes and fibroblasts is likely to be achieved by the distinct and cell-type-specific sets of molecules. Thus, these data provide an important basis for delineating mechanisms that underlie the distinct effects of the BMP pathway on different cell populations in the skin, and will be helpful in further establishing molecular signaling networks regulating skin homeostasis in health and disease.

Bone morphogenetic protein-2 activity is regulated by secreted phosphoprotein-24 kd, an extracellular pseudoreceptor, the gene for which maps to a region of the human genome important for bone quality

The material properties of bone are the sum of the complex and interrelated anabolic and catabolic processes that modulate formation and turnover. The 2q33-37 region of the human genome contains quantitative trait loci important in determining the broadband ultrasound attenuation (an index of trabecular microarchitecture, bone elasticity, and susceptibility to fracture) of the calcaneus, but no genes of significance to bone metabolism have been identified in this domain. Secreted phosphoprotein-24 kd (SPP24 or SPP2) is a novel and relatively poorly characterized growth hormone-regulated gene that maps to 2q37. The purpose of this review is to summarize the status of research related to spp24 and how it regulates bone morphogenetic protein (BMP) bioactivity in bone. SPP24 codes for an extracellular matrix protein that contains a high-affinity BMP-2-binding transforming growth factor-beta receptor II homology 1 loop similar to those identified in fetuin and the receptor itself. SPP24 is transcribed primarily in the liver and bone. High levels of spp24 (a hydroxyapatite-binding protein) are found in bone, and small amounts are found in fetuin-mineral complexes. Full-length secretory spp24 inhibits ectopic bone formation, and overexpression of spp24 reduces murine bone mass and density. Spp24 is extremely labile to proteolysis, a process that regulates its bioactivity in vivo. For example, an 18.5-kd degradation product of spp24, designated spp18.5, is pro-osteogenic. A synthetic cyclized Cys(1)-to-Cys(19) disulfide-bonded peptide (BMP binding peptide) corresponding to the transforming growth factor-beta receptor II homology 1 domain of spp24 and spp18.5 binds BMP-2 and increases the rate and magnitude of BMP-2-mediated ectopic bone formation. Thus, the mechanism of action of spp18.5 and spp24 may be to regulate the local bioavailability of BMP cytokines. SPP24 is regulated by growth hormone and 3 major families of transcription factors (nuclear factor of activated T cells, CCAAT/enhancer-binding protein, Cut/Cux/CCAAT displacement protein) that regulate mesenchymal cell proliferation, embryonic patterning, and terminal differentiation. The gene contains at least 2 single nucleotide polymorphisms. Given its mechanism of action and sequence variability, SPP24 may be an interesting candidate for future studies of the genetic regulation of bone mass, particularly during periods of BMP-mediated endochondral bone growth, development, and fracture healing.

The role of tissue engineering in articular cartilage repair and regeneration

Articular cartilage repair and regeneration continue to be largely intractable because of the poor regenerative properties of this tissue. The field of articular cartilage tissue engineering, which aims to repair, regenerate, and/or improve injured or diseased articular cartilage functionality, has evoked intense interest and holds great potential for improving articular cartilage therapy. This review provides an overall description of the current state of and progress in articular cartilage repair and regeneration. Traditional therapies and related problems are introduced. More importantly, a variety of promising cell sources, biocompatible tissue engineered scaffolds, scaffoldless techniques, growth factors, and mechanical stimuli used in current articular cartilage tissue engineering are reviewed. Finally, the technical and regulatory challenges of articular cartilage tissue engineering and possible future directions are also discussed.

Dexamethasone modulates BMP-2 effects on mesenchymal stem cells in vitro

Dexamethasone/ascorbic acid/glycerolphosphate (DAG) and bone morphogenic protein (BMP)-2 are potent agents in cell proliferation and differentiation pathways. This study investigates the in vitro interactions between dexamethasone and BMP-2 for an osteoblastic differentiation of mesenchymal stem cells (MSCs). Bone marrow-derived human MSCs were cultured with DAG (group A), BMP-2 + DAG (group B), and DAG + BMP-2 combined with a porous collagen I/III scaffold (group C). RT-PCR, ELISA, immuncytochemical stainings and flow cytometry analysis served to evaluate the osteogenic-promoting potency of each of the above conditions in terms of cell morphology/viability, antigen presentation, and gene expression. DAG induced collagen I secretion from MSCs, which was further increased by the combination of DAG + BMP-2. In comparison, the collagen scaffold and the control samples showed no significant influence on collagen I secretion of MSCs. DAG stimulation of MSCs led also to a steady but not significant increase of BMP-2 level. A DAG and more, a DAG + BMP-2, stimulation increased the number of mesenchymal cells (CD105+/CD73+). All samples showed mRNA of ALP, osteopontin, Runx2, Twist 1 and 2, Notch-1/2, osteonectin, osteocalcin, BSP, and collagen-A1 after 28 days of in vitro culture. Culture media of all samples showed a decrease in Ca(2+) and PO(4) (2-) concentration, whereas a collagen-I-peak only occurred at day 28 in DAG- and DAG + BMP-2-stimulated bone marrow cells. In conclusion, BMP-2 enhances DAG-induced osteogenic differentiation in mesenchymal bone marrow cells. Both agents interact in various ways and can modify osteoblastic bone formation.

Collagen scaffolds for tissue engineering

There are two major approaches to tissue engineering for regeneration of tissues and organs. One involves cell-free materials and/or factors and one involves delivering cells to contribute to the regeneraion process. Of the many scaffold materials being investigated, collagen type I, with selective removal of its telopeptides, has been shown to have many advantageous features for both of these approaches. Highly porous collagen lattice sponges have been used to support in vitro growth of many types of tissues. Use of bioreactors to control in vitro perfusion of medium and to apply hydrostatic fluid pressure has been shown to enhance histogenesis in collagen scaffolds. Collagen sponges have also been developed to contain differentiating-inducing materials like demineralized bone to stimulate differentiation of cartilage tissue both in vitro and in vivo.

Single nucleotide polymorphisms in bone turnover-related genes in Koreans: ethnic differences in linkage disequilibrium and haplotype

Background

Osteoporosis is defined as the loss of bone mineral density that leads to bone fragility with aging. Population-based case-control studies have identified polymorphisms in many candidate genes that have been associated with bone mass maintenance or osteoporotic fracture. To investigate single nucleotide polymorphisms (SNPs) that are associated with osteoporosis, we examined the genetic variation among Koreans by analyzing 81 genes according to their function in bone formation and resorption during bone remodeling.

Methods

We resequenced all the exons, splice junctions and promoter regions of candidate osteoporosis genes using 24 unrelated Korean individuals. Using the common SNPs from our study and the HapMap database, a statistical analysis of deviation in heterozygosity depicted.

Results

We identified 942 variants, including 888 SNPs, 43 insertion/deletion polymorphisms, and 11 microsatellite markers. Of the SNPs, 557 (63%) had been previously identified and 331 (37%) were newly discovered in the Korean population. When compared SNPs in the Korean population with those in HapMap database, 1% (or less) of SNPs in the Japanese and Chinese subpopulations and 20% of those in Caucasian and African subpopulations were significantly differentiated from the Hardy-Weinberg expectations. In addition, an analysis of the genetic diversity showed that there were no significant differences among Korean, Han Chinese and Japanese populations, but African and Caucasian populations were significantly differentiated in selected genes. Nevertheless, in the detailed analysis of genetic properties, the LD and Haplotype block patterns among the five sub-populations were substantially different from one another.

Conclusion

Through the resequencing of 81 osteoporosis candidate genes, 118 unknown SNPs with a minor allele frequency (MAF) > 0.05 were discovered in the Korean population. In addition, using the common SNPs between our study and HapMap, an analysis of genetic diversity and deviation in heterozygosity was performed and the polymorphisms of the above genes among the five populations were substantially differentiated from one another. Further studies of osteoporosis could utilize the polymorphisms identified in our data since they may have important implications for the selection of highly informative SNPs for future association studies.

Disruption of the insulin-like growth factor type 1 receptor in osteoblasts enhances insulin signaling and action

Defective bone formation is common in patients with diabetes, suggesting that insulin normally exerts anabolic actions in bone. However, because insulin can cross-activate the insulin-like growth factor type 1 receptor (IGF-1R), which also functions in bone, it has been difficult to establish the direct (IGF-1-independent) actions of insulin in osteoblasts. To overcome this problem, we examined insulin signaling and action in primary osteoblasts engineered for conditional disruption of the IGF-1 receptor (DeltaIGF-1R). Calvarial osteoblasts from mice carrying floxed IGF-1R alleles were infected with adenoviral vectors expressing the Cre recombinase (Ad-Cre) or green fluorescent protein (Ad-GFP) as control. Disruption of IGF-1R mRNA (>90%) eliminated IGF-1R without affecting insulin receptor (IR) mRNA and protein expression and eliminated IGF-1R/IR hybrids. In DeltaIGF-1R osteoblasts, insulin signaling was markedly increased as evidenced by increased phosphorylation of insulin receptor substrate 1/2 and enhanced ERK/Akt activation. Microarray analysis of RNA samples from insulin-treated, DeltaIGF-1R osteoblasts revealed striking changes in several genes known to be downstream of ERK including Glut-1 and c-fos. Treatment of osteoblasts with insulin induced Glut-1 mRNA, increased 2-[1,2-(3)H]-deoxy-d-glucose uptake, and enhanced proliferation. Moreover, insulin treatment rescued the defective differentiation and mineralization of DeltaIGF-1R osteoblasts, suggesting that IR signaling can compensate, at least in part, for loss of IGF-1R signaling. We conclude that insulin exerts direct anabolic actions in osteoblasts by activation of its cognate receptor and that the strength of insulin-generated signals is tempered through interactions with the IGF-1R.

Identification of cis and trans-acting transcriptional regulators in chondroinduced fibroblasts from the pre-phenotypic gene expression profile

Cell differentiation is regulated via expression of successive sets of genes. In an in vitro model of chondrocyte differentiation, human dermal fibroblasts (hDFs) cultured in collagen sponges are induced to express cartilage matrix genes after 7 days' culture with demineralized bone powder (DBP). A shift in expression of many other genes occurs within 3 days, before chondroblast phenotypic genes are detectable. In this study, the pre-chondrogenic gene expression profile was used as a starting point to derive information on transcriptional regulation of chondrocyte differentiation induced by DBP. Putative cis regulatory elements were identified by comparing promoter regions from three genes that are highly upregulated in chondroinduced hDFs (BIGH3, COL1A2, and FN1) [Zhou, S., Glowacki, J., Yates, K.E, 2004. Comparison of TGF-beta/BMP pathways signaled by demineralized bone powder and BMP-2 in human dermal fibroblasts. J. Bone Min. Res. 19, 1732-1741] and whose products are known to interact in the matrix [Kim, J.E., et al., 2002. Molecular properties of wild-type and mutant betaIG-H3 proteins. Investig. Ophthalmol. Vis. Sci. 43, 656-661]. The effect of DBP on nuclear protein binding to cis elements was measured with an array-based assay. Nuclear extracts from hDFs cultured in DBP/collagen sponges for 3 days showed increased binding to several cis elements belonging to the families that were identified by promoter analysis. Of note, those elements represented targets of both signal-activated and developmentally regulated transcription factors. Direct measurement of mRNAs showed increased gene expression of both types of transcription factors in chondroinduced hDFs, including NFKB2 (290% of control), RELA (160%), and GATA2 (190%). Moreover, DBP increased gene expression of chondrogenic transcription factors SOX9 (160% of control) and RUNX2 (180%). Immunoblot analysis showed that DBP increased both expression (200% of control) and phosphorylation (300%) of the Creb protein, a transcription factor that is downstream of several signal transduction pathways. Inhibition of protein kinase A, protein kinase C, or MAP kinase in hDFs cultured in DBP/collagen sponges reduced induction of BIGH3 to approximately 50% of control. These results suggest that both signal-activated and developmentally controlled transcriptional mechanisms contribute to chondroinduction of hDFs by DBP.

Low oxygen tension enhances chondroinduction by demineralized bone matrix in human dermal fibroblasts in vitro

Endochondral bone formation is induced by demineralized bone powder (DBP) when DBP is implanted subcutaneously in rodents. Previously, we developed an in vitro model of this process, wherein human dermal fibroblasts (hDFs) differentiate to chondrocytes when cultured in a three-dimensional porous collagen sponge containing DBP. In other studies, medium perfusion was beneficial in maintaining phenotype and viability of many cell types in plain porous collagen sponges, including fibroblasts, bone marrow stromal cells, osteoblasts, and epidermal cells. In contrast, medium perfusion inhibited chondrogenesis by articular chondrocytes; reduction of oxygen tension to 5%, however, restored chondrogenesis. These observations are consistent with the fact that in vivo cartilage is avascular and relatively hypoxic compared with other vascularized tissues. In this study, we tested the hypothesis that low oxygen tension (hypoxia, 5% oxygen) would enhance induced chondrogenesis in hDFs cultured with DBP. As expected, hypoxia upregulated hypoxia-inducible factor-1alpha in hDFs in all conditions (i.e. +/- perfusion, +/- DBP). Hypoxia increased accumulation of cartilage-specific matrix chondroitin 4-sulfate in hDFs, but only in the presence of DBP (165%, compared to normoxia, p < 0.05). Hypoxia did not appear to have detrimental effects on cell viability and proliferation. In sum, hypoxia enhanced cartilage matrix accumulation by hDFs cultured with DBP. These defined conditions can optimize the use of dermal fibroblasts for cartilage tissue engineering.

In vitro engineering of cartilage: effects of serum substitutes, TGF-beta, and IL-1alpha

OBJECTIVES

Cartilage is avascular and relatively homogeneous, making it an attractive tissue for in vitro histogenesis and surgical use in patients. We developed novel platform technologies in order to define the requirements for optimal in vitro chondrogenesis by isolated cells. In this series of studies, we tested alternatives to fetal bovine serum (FBS) and the effects of growth factors on formation of cartilage in 3D porous collagen sponges.

DESIGN

We used porous collagen sponges to assess the effects of serum substitutes and exogenous TGF-beta1 and IL-1alpha on chondrocytes (bovine articular chondrocytes, bACs) and on chondroinduced human dermal fibroblasts (hDFs). We determined the effects of low concentrations of FBS and two serum substitutes, Nutridoma and ITS(+3), on cellularity and matrix production. After culture for intervals, sponges were harvested for histological and biochemical measurement of cartilage-specific chondroitin 4-sulfate proteoglycan (C 4-S PG).

RESULTS

Cultured bACs showed equivalent growth in Nutridoma (1%) and 10% FBS. Both TGF-beta1 and IL-1alpha significantly stimulated accumulation of C 4-S PG by bACs in 3D porous collagen sponges. Many endogenous growth factors were upregulated in hDFs cultured with chondroinductive DBP. Addition of TGF-beta1 and IL-1alpha for 11 days significantly stimulated accumulation of C 4-S PG by hDFs cultured in DMEM with 1% Nutridoma.

CONCLUSION

Porous collagen sponges are supportive of chondrogenesis and of chondroinduction by DBP. Optimization of serum-free culture conditions, including growth factors, matrix components, and mechanical stimuli will expedite translation to wider clinical applications. Use of autogenous dermal fibroblasts pre-cultured with DBP and induced to chondrocytes offers an alternative to autogenous chondrocytes.

Demineralized bone promotes chondrocyte or osteoblast differentiation of human marrow stromal cells cultured in collagen sponges

Demineralized bone implants have been used for many types of craniomaxillofacial, orthopedic, periodontal, and hand reconstruction procedures. In previous studies, we showed that demineralized bone powder (DBP) induces chondrogenesis of human dermal fibroblasts in a DBP/collagen sponge system that optimized interactions between particles of DBP and target cells in cell culture. In this study, we test the hypothesis that DBP promotes chondrogenesis or osteogenesis of human marrow stromal cells (hMSCs) in 3-D collagen sponge culture, depending upon the culture conditions. We first confirmed that hMSCs have chondrogenic potential when treated with TGF-beta, either in 2-D monolayer cultures or in 3-D porous collagen sponges. Second, we found that DBP markedly enhanced chondrogenesis in hMSCs in 3-D sponges, as assessed by metachromasia and expression of chondrocyte-specific genes AGGRECAN, COL II, and COL X. Human dermal fibroblasts (hDFs) were used to define mechanisms of chondroinduction because unlike hMSCs they have no inherent chondrogenic potential. In situ hybridization revealed that hDFs vicinal to DBPs express chondrocyte-specific genes AGGRECAN or COL II. Macroarray analysis showed that DBP activates TGF-beta/BMP signaling pathway genes in hDFs. Finally, DBP induced hMSCs to express the osteoblast phenotype when cultured with osteogenic supplements. These studies show how culture conditions can influence the differentiation pathway that human marrow stromal cells follow when stimulated by DBP. These results support the potential to engineer cartilage or bone in vitro by using human bone marrow stromal cells and DBP/collagen scaffolds.

NFAT and Osterix cooperatively regulate bone formation

Immunosuppressants are crucial in the prevention of detrimental immune reactions associated with allogenic organ transplantation, but they often cause adverse effects in a number of biological systems, including the skeletal system. Calcineurin inhibitors FK506 and cyclosporin A inhibit nuclear factor of activated T cells (NFAT) activity and induce strong immunosuppression. Among NFAT proteins, NFATc1 is crucial for the differentiation of bone-resorbing osteoclasts. Here we show FK506 administration induces the reduction of bone mass despite a blockade of osteoclast differentiation. This reduction is caused by severe impairment of bone formation, suggesting that NFAT transcription factors also have an important role in the transcriptional program of osteoblasts. In fact, bone formation is inhibited in Nfatc1- and Nfatc2-deficient cells as well as in FK506-treated osteoblasts. Overexpression of NFATc1 stimulates Osterix-dependent activation of the Col1a1 (encoding type I collagen) promoter, but not Runx2-dependent activation of the Bglap1 (encoding osteocalcin) promoter. NFAT and Osterix form a complex that binds to DNA, and this interaction is important for the transcriptional activity of Osterix. Thus, NFAT and Osterix cooperatively control osteoblastic bone formation. These results may provide important insight into the management of post-transplantation osteoporosis as well as a new strategy for promoting bone regeneration in osteopenic disease.

Wnt Influence on Chondrocyte Differentiation and Cartilage Function

The Wnt signaling network regulates chondrocyte differentiation, proliferation, and maturation during embryonic limb development. In this review, we summarize studies of Wnt signaling during the chondrocyte life cycle in avian and mammalian systems, both before and after birth. Recent reports that implicate abnormal Wnt signaling as a contributing factor to pathogenic joint conditions are also discussed. In addition, we show new data that suggests Wnt signaling is active in adult cartilage. Overall, it appears that the Wnt network has dual roles in cartilage, as has been described in other tissues: it is an important regulator of chondrocyte development, but deregulated signaling is detrimental to mature tissues and may lead to disease.

Hypoxia inhibition of adipocytogenesis in human bone marrow stromal cells requires transforming growth factor-beta/Smad3 signaling

Although hypoxia and transforming growth factor-beta (TGF-beta) inhibit differentiation of adipocytes from preadipocytes and bone marrow-derived cells in several species, the relationship between hypoxia and TGF-beta signaling in adipocytogenesis is unknown. In this study, we evaluated the mechanisms of inhibition of adipocyte differentiation by hypoxia and TGF-beta in human and murine marrow stromal cells (MSCs) and the role of TGF-beta/Smad signaling in the inhibition of adipocytogenesis by hypoxia. Both hypoxia-mimetic deferoxamine mesylate (DFO) and TGF-beta1 inhibited adipocyte differentiation (1.0% versus the control at 15 microm DFO and 1.4% versus the control at 1 ng/ml TGF-beta1) and adipocyte gene expression (peroxisome proliferator-activated receptor-gamma2 and lipoprotein lipase) in human MSCs after 21 days of treatment. Hypoxia (2% O(2)) and DFO (but not TGF-beta1) increased hypoxia-inducible factor-1alpha as shown by Western blotting. Macroarrays and Western and Northern blot analyses showed that hypoxia activated the TGF-beta/Smad signaling pathway and that both hypoxia and TGF-beta1 modulated adipocyte differentiation pathways such as the insulin-, peroxisome proliferator-activated receptor-gamma-, phosphatidylinositol 3-kinase-, and MAPK-associated signaling pathways. Studies with mouse marrow stromal cell lines derived from Smad3(+/+) or Smad3(-/-) mice revealed that the TGF-beta type I receptor (ALK-5) and its intracellular signaling molecule Smad3 were necessary for the inhibition of adipocyte differentiation by both TGF-beta and hypoxia-mimetic DFO. Thus, the TGF-beta/Smad signaling pathway is required for hypoxia-mediated inhibition of adipocyte differentiation in MSCs.

Combinatorial gene therapy for bone regeneration: Cooperative interactions between adenovirus vectors expressing bone morphogenetic proteins 2, 4, and 7

Bone morphogenetic proteins (BMPs) have demonstrated effectiveness as bone regeneration agents whether delivered as recombinant proteins or via gene therapy. Current gene therapy approaches use vectors expressing single BMPs. In contrast, multiple BMPs are coordinately expressed during bone development and fracture healing. Furthermore, BMPs likely exist in vivo as heterodimeric molecules having enhanced biological activity. In the present study, we test the hypothesis that gene therapy-based bone regeneration can be enhanced by expressing combinations of BMPs. For in vitro studies, mesenchymal cell lines were transduced with individual adenoviruses containing BMP2, 4, or 7 cDNA under control of a CMV promoter (AdBMP2, 4, 7) or virus combinations. Significantly, combined transduction with AdBMP2 plus AdBMP7 or AdBMP4 plus AdBMP7 resulted in a synergistic stimulation of osteoblast differentiation. This synergy is best explained by formation of BMP2/7 and 4/7 heterodimers. To test in vivo biological activity, fibroblasts were transduced with specific virus combinations and implanted into C57BL6 mice. Consistent with in vitro results, strong synergy was observed using combined AdBMP2/BMP7 treatment, which induced twofold to threefold more bone than would be predicted based on the activity of individual AdBMPs. These studies show that dramatic enhancement of osteogenesis can be achieved using gene therapy to express specific combinations of interacting regenerative molecules.