Distinct Osteogenic Potentials of BMP-2 and FGF-2 in Extramedullary and Medullary Microenvironments

Delivery of A Jagged1-PEG-MAL hydrogel with Pediatric Human Bone Cells Regenerates Critically-Sized Craniofacial Bone Defects

Treatments for congenital and acquired craniofacial (CF) bone abnormalities are limited and expensive. Current reconstructive methods include surgical correction of injuries, short-term bone stabilization, and long-term use of bone grafting solutions, including implantation of (i) allografts which are prone to implant failure or infection, (ii) autografts which are limited in supply. Current bone regenerative approaches have consistently relied on BMP2 application with or without addition of stem cells. BMP2 treatment can lead to severe bony overgrowth or uncontrolled inflammation, which can accelerate further bone loss. Bone marrow-derived mesenchymal stem cell-based treatments, which do not have the side effects of BMP2, are not currently FDA approved, and are time and resource intensive. There is a critical need for novel bone regenerative therapies to treat CF bone loss that have minimal side effects, are easily available, and are affordable. In this study we investigated novel bone regenerative therapies downstream of JAGGED1 (JAG1). We previously demonstrated that JAG1 induces murine cranial neural crest (CNC) cells towards osteoblast commitment via a NOTCH non-canonical pathway involving JAK2-STAT5 (1) and that JAG1 delivery with CNC cells elicits bone regeneration in vivo. In this study, we hypothesize that delivery of JAG1 and induction of its downstream NOTCH non-canonical signaling in pediatric human osteoblasts constitute an effective bone regenerative treatment in an in vivo murine bone loss model of a critically-sized cranial defect. Using this CF defect model in vivo, we delivered JAG1 with pediatric human bone-derived osteoblast-like (HBO) cells to demonstrate the osteo-inductive properties of JAG1 in human cells and in vitro we utilized the HBO cells to identify the downstream non-canonical JAG1 signaling intermediates as effective bone regenerative treatments. In vitro, we identified an important mechanism by which JAG1 induces pediatric osteoblast commitment and bone formation involving the phosphorylation of p70 S6K. This discovery enables potential new treatment avenues involving the delivery of tethered JAG1 and the downstream activators of p70 S6K as powerful bone regenerative therapies in pediatric CF bone loss.

Osteoporosis: Emerging targets on the classical signaling pathways of bone formation

Osteoporosis is a multifaceted skeletal disorder characterized by reduced bone mass and structural deterioration, posing a significant public health challenge, particularly in the elderly population. Treatment strategies for osteoporosis primarily focus on inhibiting bone resorption and promoting bone formation. However, the effectiveness and limitations of current therapeutic approaches underscore the need for innovative methods. This review explores emerging molecular targets within crucial signaling pathways, including wingless/integrated (WNT), bone morphogenetic protein (BMP), hedgehog (HH), and Notch signaling pathway, to understand their roles in osteogenesis regulation. The identification of crosstalk targets between these pathways further enhances our comprehension of the intricate bone metabolism cycle. In summary, unraveling the molecular complexity of osteoporosis provides insights into potential therapeutic targets beyond conventional methods, offering a promising avenue for the development of new anabolic drugs.

Enhanced Bone Formation by Rapidly Formed Bony Wall over the Bone Defect Using Dual Growth Factors

BACKGROUND

In guided bone regeneration (GBR), there are various problems that occur in the bone defect after the wound healing period. This study aimed to investigate the enhancement of the osteogenic ability of the dual scaffold complex and identify the appropriate concentration of growth factors (GF) for new bone formation based on the novel GBR concept that is applying rapid bone forming GFs to the membrane outside of the bone defect.

METHODS

Four bone defects with a diameter of 8 mm were formed in the calvaria of New Zealand white rabbits each to perform GBR. Collagen membrane and biphasic calcium phosphate (BCP) were applied to the bone defects with the four different concetration of BMP-2 or FGF-2. After 2, 4, and 8 weeks of healing, histological, histomorphometric, and immunohistochemical analyses were conducted.

RESULTS

In the histological analysis, continuous forms of new bones were observed in the upper part of bone defect in the experimental groups, whereas no continuous forms were observed in the control group. In the histomorphometry, The group to which BMP-2 0.5 mg/ml and FGF-2 1.0 mg/ml was applied showed statistically significantly higher new bone formation. Also, the new bone formation according to the healing period was statistically significantly higher at 8 weeks than at 2, 4 weeks.

CONCLUSION

The novel GBR method in which BMP-2, newly proposed in this study, is applied to the membrane is effective for bone regeneration. In addition, the dual scaffold complex is quantitatively and qualitatively advantageous for bone regeneration and bone maintenance over time.

The Osteogenesis Mechanisms of Dental Alveolar Bone Socket Post Induction with Hydroxyapatite Bovine Tooth Graft: An Animal Experimental in Rattus norvegicus Strain Wistar

OBJECTIVES

 Surgical endodontics (hemisection) commonly involves the alveolar bone socket and the periradicular tissue. In today's era, optimizing the bone healing process is updated by using bone graft induction. This study explores the mechanisms of bone healing of the alveolar bone socket post-dental extraction of Wistar rats after administration of a bovine tooth graft (hydroxyapatite bovine tooth graft [HAp-BTG]).

MATERIALS AND METHODS

 Fifty Wistar rats were randomly selected into two groups, control and treatment, and into five subgroups on days 3, 7, 14, 21, and 28. The postextraction socket was filled with polyethylene glycol (PEG) as the control and PEG + HAp-BTG as the treatment group. On days 3, 7, 14, 21, and 28, Wistar rats were sacrificed, mandibles were taken, paraffin blocks were made, cut 4 µm thick, and made into glass preparations for microscopic examination. The variable analysis was performed by staining hematoxylin-eosin for osteoblasts (OBs) and osteoclasts (OCs) and immunohistochemistry for runt-related transcription factor 2 (RUNX2), osterix (OSX), osteocalcin (OCN), bone morphogenic protein (BMP) 2. We analyzed the expressed cell count per microscope field.

RESULTS

 In general, the number of cell expressions in the treatment group was significantly higher and faster, except for significantly lower OC. The high variables peak occurred on day 14 for RUNX2 and OCN, on day 7 for OSX, while OB significantly increased on day 21 and remained until day 28. The decrease of OC cells occurred on day 7 and remained low until 28 days. BMP2 was first dominantly induced by HAp-BTG, then the others.

CONCLUSION

 HAp-BTG can induce higher and faster bone healing biomarkers. BMP2 is the dominant first impacted. On the 28th day, it did not significantly express the suppression of OC by OB, which entered the bone formation and remodeling step.

Transcriptional regulation of FRZB in chondrocytes by Osterix and Msx2

INTRODUCTION

Osteoarthritis is a common joint disease that causes destruction of articular cartilage and severe inflammation surrounding knee and hip joints. However, to date, effective therapeutic reagents for osteoarthritis have not been developed because the underlying molecular mechanisms are complex. Recent genetic findings suggest that a Wnt antagonist, frizzled-related protein B (FRZB), is a potential therapeutic target for osteoarthritis. Therefore, this study aimed to examine the transcriptional regulation of FRZB in chondrocytes.

MATERIALS AND METHODS

Frzb/FRZB expression was assessed by RT-qPCR analyses in murine articular chondrocytes and SW1353 chondrocyte cell line. Overexpression and knockdown experiments were performed using adenovirus and lentivirus, respectively. Luciferase-reporter and chromatin immunoprecipitation assays were performed for determining transcriptional regulation. Protein-protein interaction was determined by co-immunoprecipitation analysis.

RESULTS

Frzb was highly expressed in cartilages, especially within articular chondrocytes. Interleukin-1α markedly reduced Frzb expression in articular chondrocytes in association with cartilage destruction and increases in ADAM metallopeptidase with thrombospondin type 1 motif (Adamts) 4 and Adamts5 expression. Bone morphogenetic protein 2 (BMP2) increased FRZB expression in SW1353 cells through Smad signaling. Osterix and msh homeobox 2 (Msx2), both of which function as downstream transcription factors of BMP2, induced FRZB expression and upregulated its promoter activity. Co-immunoprecipitation results showed a physical interaction between Osterix and Msx2. Knockdown of either Osterix or Msx2 inhibited BMP2-dependent FRZB expression. Chromatin immunoprecipitation indicated a direct association of Osterix and Msx2 with the FRZB gene promoter.

CONCLUSION

These results suggest that BMP2 regulates FRZB expression through Osterix and Msx2.

Application of BMP in Bone Tissue Engineering

At present, bone nonunion and delayed union are still difficult problems in orthopaedics. Since the discovery of bone morphogenetic protein (BMP), it has been widely used in various studies due to its powerful role in promoting osteogenesis and chondrogenesis. Current results show that BMPs can promote healing of bone defects and reduce the occurrence of complications. However, the mechanism of BMP in vivo still needs to be explored, and application of BMP alone to a bone defect site cannot achieve good therapeutic effects. It is particularly important to modify implants to carry BMP to achieve slow and sustained release effects by taking advantage of the nature of the implant. This review aims to explain the mechanism of BMP action in vivo, its biological function, and how BMP can be applied to orthopaedic implants to effectively stimulate bone healing in the long term. Notably, implantation of a system that allows sustained release of BMP can provide an effective method to treat bone nonunion and delayed bone healing in the clinic.

Heterotopic Ossification: Clinical Features, Basic Researches, and Mechanical Stimulations

Heterotopic ossification (HO) is defined as the occurrence of extraskeletal bone in soft tissue. Although this pathological osteogenesis process involves the participation of osteoblasts and osteoclasts during the formation of bone structures, it differs from normal physiological osteogenesis in many features. In this article, the primary characteristics of heterotopic ossification are reviewed from both clinical and basic research perspectives, with a special highlight on the influence of mechanics on heterotopic ossification, which serves an important role in the prophylaxis and treatment of HO.

Endogenous FGF-2 levels impact FGF-2/BMP-2 growth factor delivery dosing in aged murine calvarial bone defects

Bone repair in elderly mice has been shown to be improved or negatively impacted by supplementing the highly osteogenic bone morphogenetic protein-2 (BMP-2) with fibroblast growth factor-2 (FGF-2). To better predict the outcome of FGF-2 supplementation, we investigated whether endogenous levels of FGF-2 play a role in optimal dosing of FGF-2 for augmenting BMP-2 activity in elderly mice. In vivo calvarial bone defect studies in Fgf2 knockout mice with wildtype controls were conducted with the growth factors delivered in a highly localized manner from a biomimetic calcium phosphate/polyelectrolyte multilayer coating applied to a bone graft substitute. Endogenous FGF-2 levels were measured in old mice versus young and found to decrease with age. Optimal dosing for improving bone defect repair correlated with levels of endogenous FGF-2, with a larger dose of FGF-2 required to have a positive effect on bone healing in the Fgf2 knockout mice. The same dose in wildtype old mice, with higher levels of FGF-2, promoted chondrogenesis and increased osteoclast activity. The results suggest a personalized medicine approach, based on a knowledge of endogenous levels of FGF-2, should guide FGF-2 supplementation in order to avoid provoking excessive bone resorption and cartilage formation, both of which inhibited calvarial bone repair.

Serial administration of rhBMP-2 and alendronate enhances the differentiation of osteoblasts

AIM

The incorporation of growth factors is an effective strategy to accelerate bone induction. Bone morphogenetic protein-2 (BMP-2) promotes osteoblast differentiation and induces bone formation. Alendronate (ALN) is an osteoclast deactivation drug. We investigated the effect of serial administration of recombinant human BMP-2 (rhBMP-2) and ALN on osteoblast differentiation.

METHODS

The effect of serial administration of rhBMP-2 (0-150 ng/mL) and ALN (0-15 µmol/L) on the viability and differentiation of a clonal murine calvarial cell line, MC3T3-E1, was evaluated at various concentrations and for different periods. The Cell Counting Kit-8 assay was used to assess cell viability. The alkaline phosphatase activity was evaluated as an indicator of osteogenic differentiation. The expression levels of runt domain-containing transcription factor 2 (Runx2) and osteopontin (OPN) were analyzed by real-time polymerase chain reaction and western blotting. Statistical analyses were performed using Student's t test.

RESULTS

The serial treatment with rhBMP-2 and ALN increased the expression of the differentiation-related factors Runx2 and OPN, as well as the differentiation ability of osteoblasts compared with individual or simultaneous treatment. The osteoblasts treated with rhBMP-2 followed by ALN showed the highest differentiation. The degree of differentiation in the group treated with rhBMP-2 for 7 days followed by ALN for 3 days was increased by 1.5 times compared with that of the group treated with rhBMP-2 alone (P < .01).

CONCLUSION

These findings indicate that the serial administration of rhBMP-2 and ALN may exert osteogenic effects on osteoblastic cells via the upregulation of Runx2 and OPN.