MC3T3-E1 osteoprogenitor cells systemically migrate to a bone defect and enhance bone healing

The Osteogenic Peptide P-15 for Bone Regeneration: A Narrative Review of the Evidence for a Mechanism of Action

Bone regeneration is a complex multicellular process involving the recruitment and attachment of osteoprogenitors and their subsequent differentiation into osteoblasts that deposit extracellular matrixes. There is a growing demand for synthetic bone graft materials that can be used to augment these processes to enhance the healing of bone defects resulting from trauma, disease or surgery. P-15 is a small synthetic peptide that is identical in sequence to the cell-binding domain of type I collagen and has been extensively demonstrated in vitro and in vivo to enhance the adhesion, differentiation and proliferation of stem cells involved in bone formation. These events can be categorized into three phases: attachment, activation and amplification. This narrative review summarizes the large body of preclinical research on P-15 in terms of these phases to describe the mechanism of action by which P-15 improves bone formation. Knowledge of this mechanism of action will help to inform the use of P-15 in clinical practice as well as the development of methods of delivering P-15 that optimize clinical outcomes.

Differentiation of osteoblasts: the links between essential transcription factors

Osteoblasts, cells derived from mesenchymal stem cells (MSCs) in the bone marrow, are cells responsible for bone formation and remodeling. The differentiation of osteoblasts from MSCs is triggered by the expression of specific genes, which are subsequently controlled by pro-osteogenic pathways. Mature osteoblasts then differentiate into osteocytes and are embedded in the bone matrix. Dysregulation of osteoblast function can cause inadequate bone formation, which leads to the development of bone disease. Various key molecules are involved in the regulation of osteoblastogenesis, which are transcription factors. Previous studies have heavily examined the role of factors that control gene expression during osteoblastogenesis, both in vitro and in vivo. However, the systematic relationship of these transcription factors remains unknown. The involvement of ncRNAs in this mechanism, particularly miRNAs, lncRNAs, and circRNAs, has been shown to influence transcriptional factor activity in the regulation of osteoblast differentiation. Here, we discuss nine essential transcription factors involved in osteoblast differentiation, including Runx2, Osx, Dlx5, β-catenin, ATF4, Ihh, Satb2, and Shn3. In addition, we summarize the role of ncRNAs and their relationship to these essential transcription factors in order to improve our understanding of the transcriptional regulation of osteoblast differentiation. Adequate exploration and understanding of the molecular mechanisms of osteoblastogenesis can be a critical strategy in the development of therapies for bone-related diseases.Communicated by Ramaswamy H. Sarma.

Bone Marrow Stromal Cells Sorted by Semiconducting Polymer Nanodots for Bone Repair

The use of bone marrow stromal cells (BMSCs) for bone defect repair has shown great promise due to their differentiation potential. However, isolating the BMSCs from various cell types within the bone marrow remains challenging. To tackle this issue, we utilized semiconducting polymer dots (Pdots) as markers to select the BMSCs within a specific time frame. The therapeutic efficacy of the obtained Pdot-labeled BMSCs was assessed in a bone defect model. Initially, we evaluated the binding capacity of the Pdots with four different types of cells present in the bone marrow including BMSCs, osteoblasts, macrophages, and vascular endothelial cells, in vitro. Notably, BMSCs showed the most rapid uptake of the Pdots, being labeled within only one h of coculture, while other cells took four h to become labeled. Moreover, by colocalizing the Pdots with Prrx1, Sca-1, OSX, F480, and CD105 in the bone marrow cells of monocortical tibial defect (MTD) mice in vivo, we determined the proportions of BMSCs, macrophages, and vascular endothelial cells among all labeled cells from 1 to 8 h after the Pdots injection. It was found that BMSCs have the highest proportion (92%) among all labeled cells extracted after 1 h of Pdots injection. The therapeutic efficacy of the obtained Pdots-labeled BMSCs (1 h) was assessed in a bone defect model. Results showed that the new bone accrual was significantly increased in the treatment of Pdots-labeled BMSCs compared to the bone marrow cell-treated group. Our study revealed that BMSCs screened by the Pdots could improve bone defect repair, suggesting a promising application of the Pdots in bone healing.

Therapeutic effects of MSCs, genetically modified MSCs, and NFĸB-inhibitor on chronic inflammatory osteolysis in aged mice

The number of total joint replacements is increasing, especially in elderly patients, and so too are implant-related complications such as prosthesis loosening. Wear particles from the prosthesis induce a chronic inflammatory reaction and subsequent osteolysis, leading to the need for revision surgery. This study investigated the therapeutic effect of NF-ĸB decoy oligodeoxynucleotides (ODN), mesenchymal stem cells (MSCs), and genetically-modified NF-ĸB sensing interleukin-4 over-secreting MSCs (IL4-MSCs) on chronic inflammation in aged mice. The model was generated by continuous infusion of contaminated polyethylene particles into the intramedullary space of the distal femur of aged mice (15-17 months old) for 6 weeks. Local delivery of ODN showed increased bone mineral density (BMD), decreased osteoclast-like cells, increased alkaline phosphatase (ALP)-positive area, and increased M2/M1 macrophage ratio. Local injection of MSCs and IL4-MSCs significantly decreased osteoclast-like cells and increased the M2/M1 ratio, with a greater trend for IL4-MSCs than MSCs. MSCs significantly increased ALP-positive area and BMD values compared with the control. The IL4-MSCs demonstrated higher values for both ALP-positive area and BMD. These findings demonstrated the therapeutic effects of ODN, MSCs, and IL4-MSCs on chronic inflammatory osteolysis in aged mice. The two MSC-based therapies were more effective than ODN in increasing the M2/M1 macrophage ratio, reducing bone resorption, and increasing bone formation. Specifically, MSCs were more effective in increasing bone formation, and IL4-MSCs were more effective in mitigating inflammation. This study suggests potential therapeutic strategies for treating wear particle-associated inflammatory osteolysis after arthroplasty in the elderly.

Physiological Mineralization during In Vitro Osteogenesis in a Biomimetic Spheroid Culture Model

Bone health-targeting drug development strategies still largely rely on inferior 2D in vitro screenings. We aimed at developing a scaffold-free progenitor cell-based 3D biomineralization model for more physiological high-throughput screenings. MC3T3-E1 pre-osteoblasts were cultured in α-MEM with 10% FCS, at 37 °C and 5% CO₂ for up to 28 days, in non-adherent V-shaped plates to form uniformly sized 3D spheroids. Osteogenic differentiation was induced by 10 mM β-glycerophosphate and 50 µg/mL ascorbic acid. Mineralization stages were assessed through studying expression of marker genes, alkaline phosphatase activity, and calcium deposition by histochemistry. Mineralization quality was evaluated by Fourier transformed infrared (FTIR) and scanning electron microscopic (SEM) analyses and quantified by micro-CT analyses. Expression profiles of selected early- and late-stage osteoblast differentiation markers indicated a well-developed 3D biomineralization process with strongly upregulated Col1a1, Bglap and Alpl mRNA levels and type I collagen- and osteocalcin-positive immunohistochemistry (IHC). A dynamic biomineralization process with increasing mineral densities was observed during the second half of the culture period. SEM–Energy-Dispersive X-ray analyses (EDX) and FTIR ultimately confirmed a native bone-like hydroxyapatite mineral deposition ex vivo. We thus established a robust and versatile biomimetic, and high-throughput compatible, cost-efficient spheroid culture model with a native bone-like mineralization for improved pharmacological ex vivo screenings.

Mesenchymal Stem Cells and NF-κB Sensing Interleukin-4 Over-Expressing Mesenchymal Stem Cells Are Equally Effective in Mitigating Particle-Associated Chronic Inflammatory Bone Loss in Mice

Wear particles from total joint arthroplasties (TJAs) induce chronic inflammation, macrophage infiltration and lead to bone loss by promoting bone destruction and inhibiting bone formation. Inhibition of particle-associated chronic inflammation and the associated bone loss is critical to the success and survivorship of TJAs. The purpose of this study is to test the hypothesis that polyethylene particle induced chronic inflammatory bone loss could be suppressed by local injection of NF-κB sensing Interleukin-4 (IL-4) over-expressing MSCs using the murine continuous polyethylene particle infusion model. The animal model was generated with continuous infusion of polyethylene particles into the intramedullary space of the femur for 6 weeks. Cells were locally injected into the intramedullary space 3 weeks after the primary surgery. Femurs were collected 6 weeks after the primary surgery. Micro-computational tomography (μCT), histochemical and immunohistochemical analyses were performed. Particle-infusion resulted in a prolonged pro-inflammatory M1 macrophage dominated phenotype and a decrease of the anti-inflammatory M2 macrophage phenotype, an increase in TRAP positive osteoclasts, and lower alkaline phosphatase staining area and bone mineral density, indicating chronic particle-associated inflammatory bone loss. Local injection of MSCs or NF-κB sensing IL-4 over-expressing MSCs reversed the particle-associated chronic inflammatory bone loss and facilitated bone healing. These results demonstrated that local inflammatory bone loss can be effectively modulated via MSC-based treatments, which could be an efficacious therapeutic strategy for periprosthetic osteolysis.

Model-based data analysis of tissue growth in thin 3D printed scaffolds

Tissue growth in three-dimensional (3D) printed scaffolds enables exploration and control of cell behaviour in more biologically realistic geometries than that allowed by traditional 2D cell culture. Cell proliferation and migration in these experiments have yet to be explicitly characterised, limiting the ability of experimentalists to determine the effects of various experimental conditions, such as scaffold geometry, on cell behaviour. We consider tissue growth by osteoblastic cells in melt electro-written scaffolds that comprise thin square pores with sizes that were deliberately increased between experiments. We collect highly detailed temporal measurements of the average cell density, tissue coverage, and tissue geometry. To quantify tissue growth in terms of the underlying cell proliferation and migration processes, we introduce and calibrate a mechanistic mathematical model based on the Porous-Fisher reaction-diffusion equation. Parameter estimates and uncertainty quantification through profile likelihood analysis reveal consistency in the rate of cell proliferation and steady-state cell density between pore sizes. This analysis also serves as an important model verification tool: while the use of reaction-diffusion models in biology is widespread, the appropriateness of these models to describe tissue growth in 3D scaffolds has yet to be explored. We find that the Porous-Fisher model is able to capture features relating to the cell density and tissue coverage, but is not able to capture geometric features relating to the circularity of the tissue interface. Our analysis identifies two distinct stages of tissue growth, suggests several areas for model refinement, and provides guidance for future experimental work that explores tissue growth in 3D printed scaffolds.

Effects of topographical guidance cues on osteoblast cell migration

Cell migration is a fundamental process that is crucial for many biological functions in the body such as immune responses and tissue regeneration. Dysregulation of this process is associated with cancer metastasis. In this study, polydimethylsiloxane platforms with various topographical features were engineered to explore the influence of guiding patterns on MC3T3-E1 osteoblast cell migration. Focusing on the guiding effects of grating patterns, variations such as etch depth, pattern discontinuity, and bending angles were investigated. In all experiments, MC3T3-E1 cells on patterned surfaces demonstrated a higher migration speed and alignment when compared to flat surfaces. The study revealed that an increase in etch depth from 150 nm to 4.5 μm enhanced cell alignment and elongation along the grating patterns. In the presence of discontinuous elements, cell migration speed was accelerated when compared to gratings of the same etch depth. These results indicated that cell directionality preference was influenced by a high level of pattern discontinuity. On patterns with bends, cells were more inclined to reverse on 45° bends, with 69% of cells reversing at least once, compared to 54% on 135° bends. These results are attributed to cell morphology and motility mechanisms that are associated with surface topography, where actin filament structures such as filopodia and lamellipodia are essential in sensing the surrounding environment and controlling cell displacement. Knowledge of geometric guidance cues could provide a better understanding on how cell migration is influenced by extracellular matrix topography in vivo.

Attenuated regenerative properties in human periodontal ligament-derived stem cells of older donor ages with shorter telomere length and lower SSEA4 expression

Periodontal ligament (PDL) stem cell properties are critical in the periodontal tissue regeneration for periodontitis. Previously, we have demonstrated that cigarette smoking attenuates PDL-derived stem cell (PDLSC) regenerative properties. Here, we report the findings on the regenerative properties of human PDLSCs with different donor ages and the underlying mechanisms. Human PDLSCs from 18 independent donors were divided into different age groups (≤ 20, 20-40, and > 40 years old). The proliferation of PDLSCs with donor age of ≤ 20 years old was significantly higher than that of the 20-40- and > 40-years-old groups, whereas the migration of PDLSCs with donor age of ≤ 20 and 20-40 years old was significantly higher than that of the > 40-years-old group. Moreover, the mesodermal lineage differentiation capabilities of PDLSCs were also higher in the donor age group of ≤ 20 years old than the donor age of > 40 years old. In addition, shorter telomere length and lower expression of SSEA4 were found in PDLSCs with donor age of > 40 years old, compared with those with donor age of ≤ 20-years-old group. Besides, PDLSCs with donor age of 20-40 and > 40 years old had higher IL6 and CXCL8 gene expressions. In summary, results from this study revealed the attenuated proliferation, migration, and mesodermal lineage differentiation properties in human PDLSCs with older donor ages. Donor age of PDLSCs should be considered as the selection criteria for the periodontal tissue regeneration treatment.

Functional and cell surface characteristics of periodontal ligament cells (PDLCs) on RGD-synthetic polypeptide conjugate coatings

BACKGROUND AND OBJECTIVE

Periodontal ligament cells (PDLCs) are an important source for periodontal tissue healing and regeneration. Proper cell adhesion is a key for survival of anchorage-dependent cells and also initiates further intracellular signals for essential cellular functions. We aimed to test 3 different synthetic conjugates with integrin-binding RGD sequence (SAK-c[RGDfC], AK-c[RGDfC], and SAK-opn on the adhesion of human PDLCs and subsequent events including proliferation, migration, behavior of cell surface molecules, and osteogenic differentiation.

MATERIALS AND METHODS

Synthetic peptides were synthesized by solid-phase technique and attached to branched chain polymeric polypeptides via thioether linkage. Simple adsorption method was used to coat tissue culture plastic or electric arrays. PDLCs were isolated from 24 surgically extracted human third molars. Cell adhesion and proliferation were measured with real-time impedimetric xCELLigence SP system. Cell migration assay was performed with Ibidi^® Culture inserts. Cell surface antigens were detected using flow cytometry analysis. Osteogenic differentiation was assessed with alkaline phosphatase (ALP) assay and Alizarin Red S staining, and real-time qPCR was performed to analyze the osteoblast-related gene expression. Osteogenic differentiation and adipogenic differentiation of PDLCs were monitored by real-time Electrical Cell-Substrate Impedance Spectroscopy (ECIS).

RESULTS

Primary outcome of this study relies on that all three synthetic RGD peptides improved PDLC adhesion (P < .05). When animal serum is absent in culture medium, SAK-c[RGDfC] and AK-c[RGDfC] elevated cell adhesion (P < .05). Cell migration was enhanced by SAK-c[RGDfC] and AK-c[RGDfC] (P < .05). After 1-week treatment, all synthetic peptides elevated CD105 (1.7- to 2.2-fold) and CD146 (1.3- to 1.5-fold) markers and caused different integrin patterns. ALP activity (1.4-fold) and ARS (1.8- and 2.0-fold) were increased by SAK-c[RGDfC] and AK-c[RGDfC] in absence of osteogenic supplements, and all the peptides supported the mineralization under osteogenic condition (P < .05). RT-qPCR revealed the upregulation of bone sialoprotein (5.0- to 7.8-fold), osteocalcin (2.3- to 2.7-fold), and ALP (1.9- to 2.3-fold) gene expression in osteogenesis-induced PDLCs. ECIS monitoring showed that higher impedance was generated by the osteogenic induction compared with the adipogenic or the non-induced (P < .05).

CONCLUSIONS

Our study demonstrates that SAK-c[RGDfC] and AK-c[RGDfC] improved adhesion and migration of PDLCs and supported osteogenic differentiation of PDLCs. These cyclic RGD peptides proved to be applicable biocompatible material in regenerative medicine.

Effects of different oxygen concentrations on the proliferation, survival, migration, and osteogenic differentiation of MC3T3-E1 cells

In physiological and pathological environments, the concentration of oxygen around osteoblasts varies widely. No studies have systematically evaluated the effects of different oxygen concentrations on the proliferation, survival, migration, and osteogenic differentiation of osteoblasts. In this study, we cultured the osteoblast precursor cell line MC3T3-E1 in small individual chambers with oxygen concentrations of 1%, 3%, 6%, 9%, and 21%. Cell proliferation was evaluated by the proliferation index test and EdU staining. To test cell survival, a live/dead assay was performed. A tablet scratch assay was performed to detect the migratory ability of the cells. Bone nodule formation experiments and immunofluorescence and Western blotting analyses of osteogenic-related proteins were performed to assess the osteogenic differentiation of the cells. We found that the proliferation and osteogenic differentiation ability of MC3T3-E1 cells in different oxygen concentrations were both approximately bell-shaped curves and that the optimal oxygen concentrations were approximately 6% and 9%, respectively. The live/dead assay showed that the survival of MC3T3-E1 cells in different oxygen concentrations was affected by the amount of serum. The tablet scratch experiment showed that there was greater cell migration with oxygen concentrations of 1%, 3%, and 21% than with oxygen concentrations of 6% and 9%. Our results have significant reference value for the intervention of the pathological processes involving osteoblasts, such as fracture, osteoporosis, and some vascular diseases. These results also have an important guiding role for the new scientific idea that osteoblasts can function as treatment cells to repair bone defects.

Tracking Cell Transplants in Femoral Osteonecrosis with Magnetic Resonance Imaging: A Proof-of-Concept Study in Patients

PURPOSE

Osteonecrosis is a devastating complication of high-dose corticosteroid therapy in patients with cancer. Core decompression for prevention of bone collapse has been recently combined with the delivery of autologous concentrated bone marrow aspirates. The purpose of our study was to develop an imaging test for the detection of transplanted bone marrow cells in osteonecrosis lesions.

EXPERIMENTAL DESIGN

In a prospective proof-of-concept clinical trial (NCT02893293), we performed serial MRI studies of nine hip joints of 7 patients with osteonecrosis before and after core decompression. Twenty-four to 48 hours prior to the surgery, we injected ferumoxytol nanoparticles intravenously to label cells in normal bone marrow with iron oxides. During the surgery, iron-labeled bone marrow cells were aspirated from the iliac crest, concentrated, and then injected into the decompression track. Following surgery, patients received follow-up MRI up to 6 months after bone marrow cell transplantation.

RESULTS

Iron-labeled cells could be detected in the access canal by a dark (negative) signal on T2-weighted MR images. T2* relaxation times of iron-labeled cell transplants were significantly lower compared with unlabeled cell transplants of control patients who were not injected with ferumoxytol (P = 0.02). Clinical outcomes of patients who received ferumoxytol-labeled or unlabeled cell transplants were not significantly different (P = 1), suggesting that the added ferumoxytol administration did not negatively affect bone repair.

CONCLUSIONS

This immediately clinically applicable imaging test could become a powerful new tool to monitor the effect of therapeutic cells on bone repair outcomes after corticosteroid-induced osteonecrosis.

Strontium-Substituted Bioceramics Particles: A New Way to Modulate MCP-1 and Gro-α Production by Human Primary Osteoblastic Cells

Background: To avoid morbidity and limited availability associated with autografts, synthetic calcium phosphate (CaP) ceramics were extensively developed and used as bone filling materials. Controlling their induced-inflammatory response nevertheless remained a major concern. Strontium-containing CaP ceramics were recently demonstrated for impacting cytokines’ secretion pattern of human primary monocytes. The present study focuses on the ability of strontium-containing CaP to control the human primary bone cell production of two major inflammatory and pro-osteoclastogenic mediators, namely MCP-1 and Gro-α, in response to ceramics particles. Methods: This in vitro study was performed using human primary osteoblasts in which their response to ceramics was evaluated by PCR arrays, antibody arrays were used for screening and real-time PCR and ELISA for more focused analyses. Results: Study of mRNA and protein expression highlights that human primary bone cells are able to produce these inflammatory mediators and reveal that the adjunction of CaP in the culture medium leads to their enhanced production. Importantly, the current work determines the down-regulating effect of strontium-substituted CaP on MCP-1 and Gro-α production. Conclusion: Our findings point out a new capability of strontium to modulate human primary bone cells’ communication with the immune system.

Investigation of angiogenesis in bioactive 3-dimensional poly(d,l-lactide-co-glycolide)/nano-hydroxyapatite scaffolds by in vivo multiphoton microscopy in murine calvarial critical bone defect

Reconstruction of critical size bone defects remains a major clinical challenge because of poor bone regeneration, which is usually due to poor angiogenesis during repair. Satisfactory vascularization is a prerequisite for the survival of grafts and the integration of new tissue with existing tissue. In this work, we investigated angiogenesis in 3D scaffolds by in vivo multiphoton microscopy during bone formation in a murine calvarial critical bone defect model and evaluated bone regeneration 8weeks post-implantation. The continuous release of bioactive lentiviral vectors (LV-pdgfb) from the scaffolds could be detected for 5days in vitro. In vivo, the released LV-pdgfb transfected adjacent cells and expressed PDGF-BB, facilitating angiogenesis and enhancing bone regeneration. The expression of both pdgfb and the angiogenesis-related genes vWF and VEGFR2 was significantly increased in the pdgfb gene-carrying scaffold (PHp) group. In addition, microCT scanning and histomorphology results proved that there was more new bone ingrowth in the PHp group than in the PLGA/nHA (PH) and control groups. MicroCT parameters, including BMD, BV/TV, Tb.Sp, and Tb.N indicated that there was significantly more new bone formation in the PHp group than in the other groups. With regard to neovascularization, 8weeks post-implantation, blood vessel areas (BVAs) were 9428±944μm(2), 4090±680.3μm(2), and none in the PHp, PH, and control groups, respectively. At each time point, BVAs in the PHp scaffolds were significantly higher than in the PH scaffolds. To our knowledge, this is the first use of multiphoton microscopy in bone tissue-engineering to investigate angiogenesis in scaffolds in vivo. This method represents a valuable tool for investigating neovascularization in bone scaffolds to determine if a certain scaffold is beneficial to neovascularization. We also proved that delivery of the pdgfb gene alone can improve both angiogenesis and bone regeneration Acronyms.

STATEMENT OF SIGNIFICANCE

Reconstruction of critical size bone defects remains a major clinical challenge because of poor bone regeneration, which is usually due to poor angiogenesis during repair. Satisfactory vascularization is a prerequisite for the survival of grafts and the integration of new tissue with existing tissue. In this work, we investigated angiogenesis in 3D scaffolds by in vivo multiphoton microscopy during bone formation in a murine calvarial critical bone defect model and evaluated bone regeneration 8weeks post-implantation. To verify that pdgfb-expressing vectors carried by the scaffolds can promote angiogenesis in 3D-printed scaffolds in vivo, we monitored angiogenesis within the implants by multiphoton microscopy. To our knowledge, this is the first study to dynamically investigate angiogenesis in bone tissue engineering scaffolds in vivo.

Restoration of miR-1305 relieves the inhibitory effect of nicotine on periodontal ligament-derived stem cell proliferation, migration, and osteogenic differentiation

BACKGROUND

Nicotine hinders the regenerative potentials of human periodontal ligament-derived stem cells (PDLSCs) and delays the healing process of periodontal diseases, but the underlying mechanism remains unclear. miR-1305 upregulation and its potential target RUNX2 downregulation exist in the PDLSCs exposed to nicotine. In this study, we aimed to investigate whether nicotine inhibits PDLSC proliferation, migration, and osteogenic differentiation by increasing miR-1305 level and decreasing RUNX2 level.

METHODS

Quantitative real-time PCR (qRT-PCR) and Western blot assays were performed to detect the expression levels of miR-1305 and RUNX2 in the PDLSCs exposed to nicotine, respectively. PDLSCs with miR-1305 overexpression, low expression, or RUNX2 overexpression were constructed by lipofectin transfection. MTT, migration, and Western blot assays were applied to assess the effect of miR-1305 on PDLSC proliferation, migration, and osteogenic differentiation, respectively. Target prediction and luciferase reporter assays were performed to investigate the targets of miR-1305.

RESULTS

Nicotine promoted miR-1305 expression and inhibited RUNX2 expression in PDLSCs. Cell proliferation, migration, and differentiation detection showed that nicotine suppressed proliferation, migration, and osteogenic differentiation of PDLSCs, and restoration of miR-1305 relieved the inhibitory effect of nicotine on PDLSCs. Moreover, we identified and validated that RUNX2 was a direct target of miR-1305, and upregulation of RUNX2 had similar effects with the downregulation of miR-1305 on relieving the inhibitory effect of nicotine on PDLSCs.

CONCLUSION

Nicotine suppresses proliferation, migration, and osteogenic differentiation of PDLSCs, and restoration of miR-1305 relieves the inhibitory effect of nicotine on PDLSCs depending on its target RUNX2.

Cigarette smoking hinders human periodontal ligament-derived stem cell proliferation, migration and differentiation potentials

Cigarette smoking contributes to the development of destructive periodontal diseases and delays its healing process. Our previous study demonstrated that nicotine, a major constituent in the cigarette smoke, inhibits the regenerative potentials of human periodontal ligament-derived stem cells (PDLSC) through microRNA (miRNA) regulation. In this study, we hypothesized that the delayed healing in cigarette smokers is caused by the afflicted regenerative potential of smoker PDLSC. We cultured PDLSC from teeth extracted from smokers and non-smokers. In smoker PDLSC, we found significantly reduced proliferation rate and retarded migration capabilities. Moreover, alkaline phosphatase activity, calcium deposition and acidic polysaccharide staining were reduced after BMP2-induced differentiation. In contrast, more lipid deposition was observed in adipogenic-induced smoker PDLSC. Furthermore, two nicotine-related miRNAs, hsa-miR-1305 (22.08 folds, p = 0.040) and hsa-miR-18b (15.56 folds, p = 0.018), were significantly upregulated in smoker PDLSC, suggesting these miRNAs might play an important role in the deteriorative effects on stem cells by cigarette smoke. Results of this study provide further evidences that cigarette smoking affects the regenerative potentials of human adult stem cells.

Chronic inflammation in biomaterial-induced periprosthetic osteolysis: NF-κB as a therapeutic target

Biomaterial-induced tissue responses in patients with total joint replacement are associated with the generation of wear particles, which may lead to chronic inflammation and local bone destruction (periprosthetic osteolysis). Inflammatory reactions associated with wear particles are mediated by several important signaling pathways, the most important of which involves the transcription factor NF-κB. NF-κB activation is essential for macrophage recruitment and maturation, as well as the production of pro-inflammatory cytokines and chemokines such as TNF-α, IL-1β, IL-6 and MCP1. In addition, NF-κB activation contributes to osteoclast differentiation and maturation via RANK/RANKL signaling, which increases bone destruction and reduces bone formation. Targeting individual downstream cytokines directly (such as TNF-α or IL-1β) may not effectively prevent wear particle induced osteolysis. A more logical upstream therapeutic approach may be provided by direct modulation of the core IκB/IKKα/β/NF-κB signaling pathway in the local environment. However, the timing, dose and strategy for administration should be considered. Suppression of chronic inflammation via inhibition of NF-κB activity in patients with malfunctioning joint replacements may be an effective strategy to mitigate wear particle induced periprosthetic osteolysis.

Cell-based approaches to the engineering of vascularized bone tissue

This review summarizes recent efforts to create vascularized bone tissue in vitro and in vivo through the use of cell-based therapy approaches. The treatment of large and recalcitrant bone wounds is a serious clinical problem, and in the United States approximately 10% of all fractures are complicated by delayed union or non-union. Treatment approaches with the use of growth factor and gene delivery have shown some promise, but results are variable and clinical complications have arisen. Cell-based therapies offer the potential to recapitulate key components of the bone-healing cascade, which involves concomitant regeneration of vasculature and new bone tissue. For this reason, osteogenic and vasculogenic cell types have been combined in co-cultures to capitalize on the function of each cell type and to promote heterotypic interactions. Experiments in both two-dimensional and three-dimensional systems have provided insight into the mechanisms by which osteogenic and vasculogenic cells interact to form vascularized bone, and these approaches have been translated to ectopic and orthotopic models in small-animal studies. The knowledge generated by these studies will inform and facilitate the next generation of pre-clinical studies, which are needed to move cell-based orthopaedic repair strategies into the clinic. The science and application of cytotherapy for repair of large and ischemic bone defects is developing rapidly and promises to provide new treatment methods for these challenging clinical problems.

Molecular imaging: an innovative force in musculoskeletal radiology

OBJECTIVE

A review of the innovative role molecular imaging plays in musculoskeletal radiology is provided. Musculoskeletal molecular imaging is under development in four key areas: imaging the activity of osteoblasts and osteoclasts, imaging of molecular and cellular biomarkers of arthritic joint destruction, cellular imaging of osteomyelitis, and imaging generators of musculoskeletal pain.

CONCLUSION

Together, these applications suggest that next-generation musculoskeletal radiology will facilitate quantitative visualization of molecular and cellular biomarkers, an advancement that appeared futuristic just a decade ago.

Bactericidal property and biocompatibility of gentamicin-loaded mesoporous carbonated hydroxyapatite microspheres

Implant-associated infection is a serious problem in orthopaedic surgery. One of the most effective ways is to introduce a controlled antibiotics delivery system into the bone filling materials, achieving sustained release of antibiotics in the local sites of bone defects. In the present work, mesoporous carbonated hydroxyapatite microspheres (MCHMs) loaded with gentamicin have been fabricated according to the following stages: (i) the preparation of the MCHMs by hydrothermal method using calcium carbonate microspheres as sacrificial templates, and (ii) loading gentamicin into the MCHMs. The MCHMs exhibit the 3D hierarchical nanostructures constructed by nanoplates as building blocks with mesopores and macropores, which make them have the higher drug loading efficiency of 70-75% than the conventional hydroxyapatite particles (HAPs) of 20-25%. The gentamicin-loaded MCHMs display the sustained drug release property, and the controlled release of gentamicin can minimize significantly bacterial adhesion and prevent biofilm formation against S. epidermidis. The biocompatibility tests by using human bone marrow stromal cells (hBMSCs) as cell models indicate that the gentamicin-loaded MCHMs have as excellent biocompatibility as the HAPs, and the dose of the released gentamicin from the MCHMs has no toxic effects on the hBMSCs. Hence, the gentamicin-loaded MCHMs can be served as a simple, non-toxic and controlled drug delivery system to treat bone infections.

Cell-based therapies for regenerating bone

Cellular therapies to replenish bone lost due to acquired conditions such as trauma, infection, tumor, periprosthetic osteolysis and other etiologies have become widespread. Traditional, open, surgical bone grafting techniques have given way to newer cellular therapies that are potentially less invasive and have a lower complication rate and faster recovery time. These new technologies include bone marrow harvesting with concentration of osteoprogenitor cells with/without cell culture, scaffolds which are both osteoconductive and osteoinductive, attempts to facilitate mesenchymal stem cell and osteoprogenitor cell homing both locally and systemically, genetic engineering of specialized stem cells, and the use of potentially immune-privileged fetal and other types of stem cells. Some of these techniques have already been introduced into the orthopaedic clinic, whereas others are still in the pre-clinical testing phase. Given the limited supply of autologous graft, these new techniques will have a dramatic impact on bone regeneration in the future.

Effects of sclerostin antibody on healing of a non-critical size femoral bone defect

Sclerostin is a glycoprotein secreted by osteocytes and inhibits osteoblastogenesis via inhibition of Wnt signaling. We hypothesized that sclerostin antibody (Scl-AbIII) would accelerate the healing of a murine femoral non-critical size bone defect model. A unilateral and unicortical 0.8 mm-sized drill hole was made in the proximal femoral shaft of adult female nude mice. One group of mice received subcutaneous injections of Scl-AbIII and a second group received vehicle only. Reporter MC3T3 osteoprogenitor cells were injected via the tail vein 3 days after surgery to monitor systemic trafficking of exogenous osteoprogenitors. Bioluminescence imaging (BLI), microcomputed tomography (microCT), micropositron emission tomography (microPET) and histological analysis were used to compare the bone healing responses to Scl-AbIII treatment. Bone mineral density (BMD) significantly increased at the defect site after week 1, and was significantly higher in the treatment compared with the control group at all time points. This finding was also confirmed on histological analysis by increased deposition of new woven bone. MicroPET scanning showed a trend for greater activity in the control group at day 21 compared with the Scl-AbIII group, indicating early bone maturation following treatment with Scl-AbIII. Whereas the BLI signals derived from the injected osteoprogenitor cells showed no differences between vehicle and Scl-AbIII treated groups, systemic migration of MC3T3 cells to the bone defect was clearly identified in both groups using immunohistochemistry. Systemic administration of Scl-AbIII resulted in earlier healing and maturation of a non-critical size bone defect. These findings underscore the potential use of Scl-AbIII for treatment of complicated fractures, non-unions, and other clinical scenarios.

Applications of exogenous mesenchymal stem cells and low intensity pulsed ultrasound enhance fracture healing in rat model

The present study aimed to investigate the effects of combined treatment of exogenous mesenchymal stem cells (MSCs) and low intensity pulsed ultrasound (LIPUS) on fracture healing by comparing LIPUS-MSC, MSC and control (CTL) groups. Radiography and quantitative callus width/area demonstrated that the MSC-LIPUS group had the best healing, MSC group the second and CTL group the poorest with significant differences among each at different time points. Micro-CT data supported that MSC-LIPUS had the highest bone volume/tissue volume. Histomorphometry showed a significantly faster remodeling in late phase in MSC-LIPUS and MSC groups. These indicated that the combined treatment of MSCs and LIPUS was beneficial to fracture healing. Regenerative power and homing ability of MSCs were shown by promotion in fracture healing and locally found green fluorescent protein (GFP)-labeled MSCs at fracture calluses. This evidence reflects that co-treatment of MSCs and LIPUS may be developed as an intervention for delayed union or nonunion.

Nicotine alters MicroRNA expression and hinders human adult stem cell regenerative potential

Adult stem cells are critical for the healing process in regenerative medicine. However, cigarette smoking inhibits stem cell recruitment to tissues and delays the wound-healing process. This study investigated the effect of nicotine, a major constituent in the cigarette smoke, on the regenerative potentials of human mesenchymal stem cells (MSC) and periodontal ligament-derived stem cells (PDLSC). The cell proliferation of 1.0 μM nicotine-treated MSC and PDLSC was significantly reduced when compared to the untreated control. Moreover, nicotine also retarded the locomotion of these adult stem cells. Furthermore, their osteogenic differentiation capabilities were reduced in the presence of nicotine as evidenced by gene expression (RUNX2, ALPL, BGLAP, COL1A1, and COL1A2), calcium deposition, and alkaline phosphatase activity analyses. In addition, the microRNA (miRNA) profile of nicotine-treated PDLSC was altered; suggesting miRNAs might play an important role in the nicotine effects on stem cells. This study provided the possible mechanistic explanations on stem cell-associated healing delay in cigarette smoking.