BMP-2 differentially modulates FGF-2 isoform effects in osteoblasts from newborn transgenic mice

Developmental principles informing human pluripotent stem cell differentiation to cartilage and bone

Human pluripotent stem cells can differentiate into any cell type given appropriate signals and hence have been used to research early human development of many tissues and diseases. Here, we review the major biological factors that regulate cartilage and bone development through the three main routes of neural crest, lateral plate mesoderm and paraxial mesoderm. We examine how these routes have been used in differentiation protocols that replicate skeletal development using human pluripotent stem cells and how these methods have been refined and improved over time. Finally, we discuss how pluripotent stem cells can be employed to understand human skeletal genetic diseases with a developmental origin and phenotype, and how developmental protocols have been applied to gain a better understanding of these conditions.

Genetic Polymorphisms in FGFR2 Underlie Skeletal Malocclusion

Fibroblast growth factor receptor 2 ( FGFR2) in craniofacial bones mediates osteoprogenitor proliferation, differentiation, and apoptosis. The distortion of proper craniofacial bone growth may cause class II and class III skeletal malocclusion and result in compromised function and aesthetics. Here, we investigated the association between variations in FGFR2 and skeletal malocclusions. First, 895 subjects were included in a 2-stage case-control study with independent populations (stage 1: n = 138 class I, 111 class II, and 81 class III; stage 2: n = 279 class I, 187 class II, and 99 class III). Eight candidate single-nucleotide polymorphisms (SNPs) in FGFR2 were screened and validated. Five SNPs (rs2162540, rs2981578, rs1078806, rs11200014, and rs10736303) were found to be associated with skeletal malocclusions (all P < 0.05). That is, rs2162540 was significantly associated with skeletal class II malocclusion, while others were associated with skeletal class III malocclusion. Electrophoretic mobility shift assay and chromatin immunoprecipitation analysis showed that the common genotypes of rs2981578 and rs10736303 contained the binding sites of RUNX2 and SMAD4. Compared with the common genotypes, the minor genotypes at these 2 SNPs decreased the binding affinity and enhancer effect of RUNX2 and SMAD4, as well the levels of FGFR2 expression. In addition, FGFR2 expression contributed positively to osteogenic differentiation in vitro. Thus, we identified FGFR2 as a skeletal malocclusion risk gene, and FGFR2 polymorphisms regulated its transcriptional expression and then osteogenic differentiation.

Fibroblast growth factors in skeletal development

Fibroblast growth factors (FGFs) and their receptors (FGFRs) are expressed throughout all stages of skeletal development. In the limb bud and in cranial mesenchyme, FGF signaling is important for formation of mesenchymal condensations that give rise to bone. Once skeletal elements are initiated and patterned, FGFs regulate both endochondral and intramembranous ossification programs. In this chapter, we review functions of the FGF signaling pathway during these critical stages of skeletogenesis, and explore skeletal malformations in humans that are caused by mutations in FGF signaling molecules.

A Comparative Study Between the Effectiveness of 980 nm Photobiomodulation Delivered by Hand-Piece With Gaussian vs. Flat-Top Profiles on Osteoblasts Maturation

Photobiomodulation (PBM) is a clinically accepted tool in regenerative medicine and dentistry to improve tissue healing and repair and to restore the functional disability. The current in vitro study aimed to investigate the photobiomodulatory effects of 980 nm wavelength (the real energy at the target: ~0.9 W, ~0.9 W/cm², 60 s, ~55 J/cm² and a single energy ~55 J in CW) on MC3T3-E1 pre-osteoblast, delivered with flattop profile in comparison to the standard profile. The laser groupings and their associated energies were: Group 1 - once per week (total energy 110 J); Group 2 - three times per week (alternate day) (total energy 330 J); Group 3 - five times per week (total energy 550 J). The metabolic activity and the osteoblasts maturation were analyzed by alkaline phosphatase assay, alizarin red S histological staining, immunoblot and/or double immunolabeling analysis for Bcl2, Bax, Runx-2, Osx, Dlx5, osteocalcin, and collagen Type 1. Our data, for the first time, prove that laser irradiation of 980 nm wavelength with flat-top beam profile delivery system, compared to standard-Gaussian profile, has improved photobiomodulatory efficacy on pre-osteoblastic cells differentiation. Mechanistically, the irradiation enhances the pre-osteoblast differentiation through activation of Wnt signaling and activation of Smads 2/3-βcatenin pathway.

Fibroblast Growth Factor 2 and Its Receptors in Bone Biology and Disease

The fibroblast growth factor (FGF) regulatory axis is phylogenetically ancient, evolving into a large mammalian/human gene family of 22 ligands that bind to four receptor tyrosine kinases for a complex physiologic system controlling cell growth, differentiation, and metabolism. The tissue targets for the primary FGF function are mainly in cartilage and in bone for morphogenesis, mineralization, and metabolism. A multitude of complexities in the FGF ligand-receptor signaling pathways have made translation into therapies for FGF-related bone disorders such as osteomalacia, osteoarthritis, and osteoporosis difficult but not impossible.

TGF-β Family Signaling in Mesenchymal Differentiation

Mesenchymal stem cells (MSCs) can differentiate into several lineages during development and also contribute to tissue homeostasis and regeneration, although the requirements for both may be distinct. MSC lineage commitment and progression in differentiation are regulated by members of the transforming growth factor-β (TGF-β) family. This review focuses on the roles of TGF-β family signaling in mesenchymal lineage commitment and differentiation into osteoblasts, chondrocytes, myoblasts, adipocytes, and tenocytes. We summarize the reported findings of cell culture studies, animal models, and interactions with other signaling pathways and highlight how aberrations in TGF-β family signaling can drive human disease by affecting mesenchymal differentiation.

The Effects of Photobiomodulation of 808 nm Diode Laser Therapy at Higher Fluence on the in Vitro Osteogenic Differentiation of Bone Marrow Stromal Cells

The literature has supported the concept of mesenchymal stromal cells (MSCs) in bone regeneration as one of the most important applications in oro-maxillofacial reconstructions. However, the fate of the transplanted cells and their effects on the clinical outcome is still uncertain. Photobiomodulation (PBM) plays an important role in the acceleration of tissue regeneration and potential repair. The aim of this in vitro study is to evaluate the effectiveness of PBM with 808 nm diode laser therapy, using a flat-top hand-piece delivery system at a higher-fluence (64 J/cm²) irradiation (1 W, continuous-wave) on bone marrow stromal cells (BMSCs). The BMSCs of 3 old female Balb-c mice were analyzed. The cells were divided into two groups: irradiated group and control group. In the former the cells were irradiated every 24 h during 0 day (T0), 5 (T1), 10 (T2), and 15 (T3) days, whereas the control group was non-irradiated. The results have shown that the 64 J/cm² laser irradiation has increased the Runt-related transcription factor 2 (Runx2). Runx2 is the most important early marker of osteoblast differentiation. The higher-fluence suppressed the synthesis of adipogenic transcription factor (PPARγ), the pivotal transcription factor in adipogenic differentiation. Also, the osteogenic markers such as Osterix (Osx) and alkaline phosphatase (ALP) were upregulated with an increase in the matrix mineralization. Furthermore, western blotting data demonstrated that the laser therapy has induced a statistically valid increase in the synthesis of transforming growth factor β1 (TGF-β1) but had no effects on the tumor necrosis factor α (TNFα) production. The data has statistically validated the down-regulation of the important pro-inflammatory cytokines such as interleukin IL-6, and IL-17 after 808 nm PBM exposition. An increase in anti-inflammatory cytokines such as IL-1rα and IL-10 was observed. These in vitro studies provide for first time the initial proof that the PBM of the 808 nm diode laser therapy with flat-top hand-piece delivery system at a higher-fluence irradiation of 64 J/cm² (1 W/cm²) can modulate BMSCs differentiation in enhancing osteogenesis.

Bmp5 Regulates Neural Crest Cell Survival and Proliferation via Two Different Signaling Pathways

Neural crest progenitor cells, which give rise to many ectodermal and mesodermal derivatives, must maintain a delicate balance of apoptosis and proliferation for their final tissue contributions. Here we show that zebrafish bmp5 is expressed in neural crest progenitor cells and that it activates the Smad and Erk signaling pathways to regulate cell survival and proliferation, respectively. Loss-of-function analysis showed that Bmp5 was required for cell survival and this response is mediated by the Smad-Msxb signaling cascade. However, the Bmp5-Smad-Msxb signaling pathway had no effect on cell proliferation. In contrast, Bmp5 was sufficient to induce cell proliferation through the Mek-Erk-Id3 signaling cascade, whereas disruption of this signaling cascade had no effect on cell survival. Taken together, our results demonstrate an important regulatory mechanism for bone morphogenic protein-initiated signal transduction underlying the formation of neural crest progenitors. Stem Cells 2017;35:1003-1014.

Plasmid DNA-coding p62 as a bone effective anti-inflammatory/anabolic agent

We recently reported that a DNA plasmid coding p62-SQSTM1 acts as an effective anti tumor vaccine against both transplantable mouse tumors and canine spontaneous mammary neoplasms. Here we report the unexpected finding that intramuscular delivery of p62 DNA exerts a powerful anti-osteoporotic activity in a mouse model of inflammatory bone loss (i.e, ovariectomy) by combining bone-sparing and osteo-synthetic effects. Notably, the suppression of osteoporosis by p62DNA was associated with a sharp down-regulation of master inflammatory cytokines, and up-regulation of endogenous p62 protein by bone-marrow stromal cells. The present data provide a solid rational to apply p62 DNA vaccine as a safe, new therapeutic for treatment of inflammatory related bone loss diseases.

Fibroblast growth factor signaling in skeletal development and disease

Fibroblast growth factor (FGF) signaling pathways are essential regulators of vertebrate skeletal development. FGF signaling regulates development of the limb bud and formation of the mesenchymal condensation and has key roles in regulating chondrogenesis, osteogenesis, and bone and mineral homeostasis. This review updates our review on FGFs in skeletal development published in Genes & Development in 2002, examines progress made on understanding the functions of the FGF signaling pathway during critical stages of skeletogenesis, and explores the mechanisms by which mutations in FGF signaling molecules cause skeletal malformations in humans. Links between FGF signaling pathways and other interacting pathways that are critical for skeletal development and could be exploited to treat genetic diseases and repair bone are also explored.

microRNA-375 inhibits osteogenic differentiation by targeting runt-related transcription factor 2

microRNAs (miRNAs) are involved in the regulation of almost all physiological and pathological processes, including osteoblast proliferation and differentiation. miR-375 has been reported to be aberrantly expressed in various tumor types and to inhibit cell proliferation and invasion by targeting a number of key genes. However, the effects of miR-375 on osteogenic differentiation have not been investigated. Thus, the present study aimed to elucidate the function served by miR-375 in osteogenic differentiation. The expression levels of miR-375 were observed to decrease in a C2C12 cell model of osteogenic differentiation. Overexpression of miR-375 inhibited the activity of key osteoblast markers, including osteocalcin (OC), alkaline phosphatase (ALP) and collagen, type I, α 1 (COL1A1). By contrast, inhibition of miR-375 expression resulted in an increase in the osteogenic potential, as indicated by the enhanced expression levels of OC, ALP and COL1A1. In addition, a dual-luciferase reporter assay indicated that runt-related transcription factor 2 (RUNX2) was a target of miR-375. Western blot analysis revealed that the inhibition of miR-375 led to a significant increase in the protein expression levels of RUNX2. In addition, overexpression of RUNX2 was observed to attenuate the miR-375-mediated suppression of osteogenic differentiation. Therefore, the results demonstrated that miR-375 was able to inhibit osteogenic differentiation via the regulation of RUNX2 expression.

A nuclear odyssey: fibroblast growth factor-2 (FGF-2) as a regulator of nuclear homeostasis in the nervous system

Nuclear localization of classical growth factors is a well-known phenomenon but still remains a molecular and cellular conundrum. Fibroblast growth factor-2 (FGF-2) is an excellent example of a protein which functions as an extracellular molecule involved in canonical receptor tyrosine kinase signaling as well as displaying intracellular functions. Paracrine and nuclear functions are two important sides of the same protein. FGF-2 is expressed in isoforms with different molecular weights from one mRNA species. In rodents, all of these isoforms become imported to the nucleus. In this review, we discuss structural and functional aspects of FGF-2 isoforms in the nervous system. The nuclear odyssey of FGF-2 is reflected by nuclear dynamics, localization to nuclear bodies such as nucleoli, binding to chromatin and engagement in various protein interactions. Recently discovered molecular partnerships of the isoforms shed light on their nuclear functions, thereby greatly extending our knowledge of the multifaceted functions of FGF-2.

Dimerization capacities of FGF2 purified with or without heparin-affinity chromatography

Fibroblast growth factor-2 (FGF2) is a pleiotropic growth factor exhibiting a variety of biological activities. In this article, we studied the capacity of FGF2 purified with or without heparin affinity chromatography to self-associate. Analyzing the NMR HSQC spectra for different FGF2 concentrations, heparin-affinity purified FGF2 showed perturbations that indicate dimerization and are a higher-order oligomerization state. HSQC perturbation observed with different FGF2 concentrations revealed a heparin-binding site and two dimer interfaces. Thus, with increasing protein concentrations, FGF2 monomers make contacts with each other and form dimers or higher order oligomers. On the contrary, FGF2 purified with ion-exchange chromatography did not show similar perturbation indicating that self-association of FGF2 is eliminated if purification is done without heparin-affinity chromatography. The HSQC spectra of heparin-affinity purified FGF2 can be reproduced to some extent by adding heparin tetra-saccharide to ion exchange chromatography purified FGF2. Heparin-affinity purified FGF2 bound to acceptor and donor beads in a tagged form using His-tagged or GST-tagged proteins, also dimerized in the AlphaScreen™ assay. This assay was further validated using different experimental conditions and competitors. The assay constitutes an interesting tool to study dimerization of other FGF forms as well.

Synergistic induction of early stage of bone formation by combination of recombinant human bone morphogenetic protein-2 and epidermal growth factor

This study evaluates whether the combination of the rhBMP-2 and various types of growth factors including EGF, FGF, PDGF and VEGF increases osteoinductivity compared to the single use of rhBMP-2 through in vitro and in vivo study. Cultured human MSCs were treated with rhBMP-2 only or in combination with growth factors. For in vivo evaluation, rhBMP-2 only or with growth factors was implanted into the calvarial defect made on SD rats. Both EGF and PDGF significantly increased both ALP activity and expression level in hMSCs when treated in combination with rhBMP-2 at 3 and 7 days of differentiation and significantly raised the accumulation of the calcium at day 14. Furthermore, micro-CT scanning revealed that the EGF an FGF groups show significantly increased new bone surface ratio compared to the rhBMP-2 only group and, the EGF treatment significantly up regulated percent bone volume and trabecular number at two weeks after the surgery. VEGF treatment also significantly raised trabecular number and FGF treatment significantly increased the trabecular thickness. Histological examination revealed that the EGF combination group showed enhanced bone regeneration than the rhBMP-2 only group two weeks after the implantation. Even though the treatment of rhBMP-2 with PDGF and FGF failed to show enhanced osteogenesis in vitro and in vivo simultaneously, these results suggest that the positive effect of the combination of EGF and rhBMP-2 is expected to induce the bone formation earlier compared to the single use of rhBMP-2 in vitro and in vivo. © 2014 The Authors. Journal of Tissue Engineering and Regenerative Medicine published by John Wiley & Sons Ltd.

Identification of a growth factor mimicking the synergistic effect of fetal bovine serum on BMP-9 cell response

The bone morphogenetic proteins (BMPs) are potent osteogenic molecules that are used for bone repair in delivery systems and in regenerative medicine. We studied the responses of murine MC3T3-E1 preosteoblasts to doses of recombinant human (rh)BMP-9 with and without fetal bovine serum (FBS). rhBMP-2 was used as a control since it is currently approved by the Food and Drug Administration for bone application. We analyzed the major cell signaling pathways and the expression of osteogenic markers. Without FBS, BMP-9 had a similar effect on MC3T3-E1 preosteoblast differentiation in comparison to BMP-2. In contrast, FBS reduced the EC50 of BMP-9 fourfold to sixfold, as determined by osterix gene expression and alkaline phosphatase (ALP) activity, while it had no influence on EC50 of BMP-2. As suggested by MAPK inhibitor assays, FBS could induce an intracellular signaling environment that favors cell response to BMP-9 by inhibiting ERK1/2 activation and increasing p38 phosphorylation. Finally, IGF-2 (100 ng/mL) could mimic the effect of FBS on BMP-9 cell response in terms of MAPK signaling and ALP activity. Thus, the action of BMP-9 on preosteoblast differentiation can be greatly improved by IGF-2. This finding may well be critical for developing optimal growth factor delivery systems and bone tissue engineering strategies.

Fibroblast growth factor-2 isoform (low molecular weight/18 kDa) overexpression in preosteoblast cells promotes bone regeneration in critical size calvarial defects in male mice

Repair of bone defects remains a significant clinical problem. Bone morphogenetic protein 2 (BMP2) is US Food and Drug Administration-approved for fracture healing but is expensive and has associated morbidity. Studies have shown that targeted overexpression of the 18-kDa low-molecular-weight fibroblast growth factor 2 isoform (LMW) by the osteoblastic lineage of transgenic mice increased bone mass. This study tested the hypotheses that overexpression of LMW would directly enhance healing of a critical size calvarial bone defect in mice and that this overexpression would have a synergistic effect with low-dose administration of BMP2 on critical size calvarial bone defect healing. Bilateral calvarial defects were created in LMW transgenic male mice and control/vector transgenic (Vector) male mice and scaffold with or without BMP2 was placed into the defects. New bone formation was assessed by VIVA-computed tomography of live animals over a 27-week period. Radiographic and computed tomography analysis revealed that at all time points, healing of the defect was enhanced in LMW mice compared with that in Vector mice. Although the very low concentration of BMP2 did not heal the defect in Vector mice, it resulted in complete healing of the defect in LMW mice. Histomorphometric and gene analysis revealed that targeted overexpression of LMW in osteoblast precursors resulted in enhanced calvarial defect healing due to increased osteoblast activity and increased canonical Wnt signaling.

Fibroblast growth factor receptor 3 interacts with and activates TGFβ-activated kinase 1 tyrosine phosphorylation and NFκB signaling in multiple myeloma and bladder cancer

Cancer is a major public health problem worldwide. In the United States alone, 1 in 4 deaths is due to cancer and for 2013 a total of 1,660,290 new cancer cases and 580,350 cancer-related deaths are projected. Comprehensive profiling of multiple cancer genomes has revealed a highly complex genetic landscape in which a large number of altered genes, varying from tumor to tumor, impact core biological pathways and processes. This has implications for therapeutic targeting of signaling networks in the development of treatments for specific cancers. The NFκB transcription factor is constitutively active in a number of hematologic and solid tumors, and many signaling pathways implicated in cancer are likely connected to NFκB activation. A critical mediator of NFκB activity is TGFβ-activated kinase 1 (TAK1). Here, we identify TAK1 as a novel interacting protein and target of fibroblast growth factor receptor 3 (FGFR3) tyrosine kinase activity. We further demonstrate that activating mutations in FGFR3 associated with both multiple myeloma and bladder cancer can modulate expression of genes that regulate NFκB signaling, and promote both NFκB transcriptional activity and cell adhesion in a manner dependent on TAK1 expression in both cancer cell types. Our findings suggest TAK1 as a potential therapeutic target for FGFR3-associated cancers, and other malignancies in which TAK1 contributes to constitutive NFκB activation.

The dual face of parathyroid hormone and prostaglandins in the osteoimmune system

The microenvironment of bone marrow, an extraordinarily heterogeneous and dynamic system, is populated by bone and immune cells, and its functional dimension has been at the forefront of recent studies in the field of osteoimmunology. The interaction of both marrow niches supports self-renewal, differentiation, and homing of the hematopoietic stem cells and provides the essential regulatory molecules for osteoblast and osteoclast homeostasis. Impaired signaling within the niches results in a pathological tableau and enhances disease, including osteoporosis and arthritis, or the rejection of hematopoietic stem cell transplants. Discovering the anabolic players that control these mechanisms has become warranted. In this review, we focus on parathyroid hormone (PTH) and prostaglandins (PGs), potent molecular mediators, both of which carry out a multitude of functions, particularly in bone lining cells and T cells. These two regulators proved to be promising therapeutic agents when strictly clinical protocols on dose treatments were applied.

miR-145 suppresses osteogenic differentiation by targeting Sp7

Osteogenesis depends on a coordinated network of transcription factors including Sp7. Emerging evidence indicates that microRNAs (miRNAs) act as pivotal regulators in various biological processes including osteoblast proliferation and differentiation. Here, we investigated the effect of miR-145 on osteogenic differentiation. miR-145 was decreased during osteogenic differentiation, which could suppress the osteogenic differentiation of C2C12 and MC3T3-E1 cells confirmed by gain- and loss-of-function experiments. Moreover, bioinformatic analysis combined with luciferase reporter assay, and Western blot validated that miR-145 negatively regulated Sp7 expression. Inhibition of Sp7 showed similar effect with miR-145 on osteogenic differentiation, whereas overexpression of Sp7 attenuated this effect. Collectively, these data indicate that miR-145 is a novel regulator of Sp7, and it suppresses the osteogenic differentiation of C2C12 and MC3T3-E1 cells.