Vascular endothelial growth factor stimulates osteoblastic differentiation of cultured human periosteal-derived cells expressing vascular endothelial growth factor receptors

Periosteum Containing Implicit Stem Cells: A Progressive Source of Inspiration for Bone Tissue Regeneration

The periosteum is known as the thin connective tissue covering most bone surfaces. Its extrusive bone regeneration capacity was confirmed from the very first century-old studies. Recently, pluripotent stem cells in the periosteum with unique physiological properties were unveiled. Existing in dynamic contexts and regulated by complex molecular networks, periosteal stem cells emerge as having strong capabilities of proliferation and multipotential differentiation. Through continuous exploration of studies, we are now starting to acquire more insight into the great potential of the periosteum in bone formation and repair in situ or ectopically. It is undeniable that the periosteum is developing further into a more promising strategy to be harnessed in bone tissue regeneration. Here, we summarized the development and structure of the periosteum, cell markers, and the biological features of periosteal stem cells. Then, we reviewed their pivotal role in bone repair and the underlying molecular regulation. The understanding of periosteum-related cellular and molecular content will help enhance future research efforts and application transformation of the periosteum.

PAP Polypeptide Promotes Osteogenesis in Jaw Bone Defect Repair by Inhibiting Inflammatory Reactions

Jaw defects are common in oral and maxillofacial diseases and require surgical repair in extreme cases. Given the limitations in availability and efficacy of autologous bone grafts or allografts, great effort has been made in finding suitable, biocompatible, and effective artificial bone materials. Considering the key role of inflammation in bone resorption, we sought to identify a polypeptide with anti-inflammatory and bone-promoting effects. Rat bone marrow-derived mesenchymal cells (BMSCs) were treated with lipopolysaccharide (LPS) to induce an inflammatory environment, and 1,538 differentially abundant polypeptides were identified using mass spectrometry. Based on mass spectrometry signal intensity, multiple of difference, and structural stability, PAP was screened out as the polypeptide with the lowest abundance in the inflammatory condition. PAP showed no cytotoxicity to BMSCs with increasing concentrations. PAP (10 μM) also increased alkaline phosphatase activity and mRNA expression of Ocn, Bmp2, and Runx2 in a concentration-dependent manner, which confirmed that it can promote osteogenic induction of rat BMSCs. Moreover, PAP reduced LPS-induced expression of inflammatory cytokines (TNF-α, IL-1β, IL-6) and reactive oxygen species and inhibited polarization of RAW 264.7 macrophages to the inflammatory type. Finally, a skull defect mouse model was established, and mice were injected with LPS and/or PAP. Micro-CT, histological analysis, and immunohistochemical staining showed that PAP significantly reduced the number of LPS-induced bone resorption pits and maintained bone integrity. Overall, the polypeptide PAP screened using LPS stimulation of BMSCs is not cytotoxic and can inhibit the inflammatory reaction process to promote osteogenesis. This study thus provides a basis for development of PAP as a new osteogenic material in the repair of jaw defects.

Mesenchymal stem cells overexpressing BMP-9 by CRISPR-Cas9 present high in vitro osteogenic potential and enhance in vivo bone formation

Cell therapy is a valuable strategy for the replacement of bone grafts and repair bone defects, and mesenchymal stem cells (MSCs) are the most frequently used cells. This study was designed to genetically edit MSCs to overexpress bone morphogenetic protein 9 (BMP-9) using Clustered Regularly Interspaced Short Palindromic Repeats/associated nuclease Cas9 (CRISPR-Cas9) technique to generate iMSCs-VPRBMP-9+, followed by in vitro evaluation of osteogenic potential and in vivo enhancement of bone formation in rat calvaria defects. Overexpression of BMP-9 was confirmed by its gene expression and protein expression, as well as its targets Hey-1, Bmpr1a, and Bmpr1b, Dlx-5, and Runx2 and  protein expression of SMAD1/5/8 and pSMAD1/5/8. iMSCs-VPRBMP-9+ displayed significant changes in the expression of a panel of genes involved in TGF-β/BMP signaling pathway. As expected, overexpression of BMP-9 increased the osteogenic potential of MSCs indicated by increased gene expression of osteoblastic markers Runx2, Sp7, Alp, and Oc, higher ALP activity, and matrix mineralization. Rat calvarial bone defects treated with injection of iMSCs-VPRBMP-9+ exhibited increased bone formation and bone mineral density when compared with iMSCs-VPR- and phosphate buffered saline (PBS)-injected defects. This is the first study to confirm that CRISPR-edited MSCs overexpressing BMP-9 effectively enhance bone formation, providing novel options for exploring the capability of genetically edited cells to repair bone defects.

Periosteal Tissue Engineering: Current Developments and Perspectives

Periosteum, a highly vascularized bilayer connective tissue membrane plays an indispensable role in the repair and regeneration of bone defects. It is involved in blood supply and delivery of progenitor cells and bioactive molecules in the defect area. However, sources of natural periosteum are limited, therefore, there is a need to develop tissue-engineered periosteum (TEP) mimicking the composition, structure, and function of natural periosteum. This review explores TEP construction strategies from the following perspectives: i) different materials for constructing TEP scaffolds; ii) mechanical properties and surface topography in TEP; iii) cell-based strategies for TEP construction; and iv) TEP combined with growth factors. In addition, current challenges and future perspectives for development of TEP are discussed.

Vascular Endothelial Growth Factor: A Translational View in Oral Non-Communicable Diseases

Vascular endothelial growth factors (VEGFs) are vital regulators of angiogenesis that are expressed in response to soluble mediators, such as cytokines and growth factors. Their physiologic functions include blood vessel formation, regulation of vascular permeability, stem cell and monocyte/macrophage recruitment and maintenance of bone homeostasis and repair. In addition, angiogenesis plays a pivotal role in chronic pathologic conditions, such as tumorigenesis, inflammatory immune diseases and bone loss. According to their prevalence, morbidity and mortality, inflammatory diseases affecting periodontal tissues and oral cancer are relevant non-communicable diseases. Whereas oral squamous cell carcinoma (OSCC) is considered one of the most common cancers worldwide, destructive inflammatory periodontal diseases, on the other hand, are amongst the most prevalent chronic inflammatory conditions affecting humans and also represent the main cause of tooth loss in adults. In the recent years, while knowledge regarding the role of VEGF signaling in common oral diseases is expanding, new potential translational applications emerge. In the present narrative review we aim to explore the role of VEGF signaling in oral cancer and destructive periodontal inflammatory diseases, with emphasis in its translational applications as potential biomarkers and therapeutic targets.

Time Dependency of Non-Thermal Oxygen Plasma and Ultraviolet Irradiation on Cellular Attachment and mRNA Expression of Growth Factors in Osteoblasts on Titanium and Zirconia Surfaces

Ultraviolet (UV) light and non-thermal plasma (NTP) are promising chair-side surface treatment methods to overcome the time-dependent aging of dental implant surfaces. After showing the efficiency of UV light and NTP treatment in restoring the biological activity of titanium and zirconia surfaces in vitro, the objective of this study was to define appropriate processing times for clinical use. Titanium and zirconia disks were treated by UV light and non-thermal oxygen plasma with increasing duration. Non-treated disks were set as controls. Murine osteoblast-like cells (MC3T3-E1) were seeded onto the treated or non-treated disks. After 2 and 24 h of incubation, the viability of cells on surfaces was assessed using an MTS assay. mRNA expression of vascular endothelial growth factor (VEGF) and hepatocyte growth factor (HGF) were assessed using real-time reverse transcription polymerase chain reaction analysis. Cellular morphology and attachment were observed using confocal microscopy. The viability of MC3T3-E1 was significantly increased in 12 min UV-light treated and 1 min oxygen NTP treated groups. VEGF relative expression reached the highest levels on 12 min UV-light and 1 min NTP treated surfaces of both disks. The highest levels of HGF relative expression were reached on 12 min UV light treated zirconia surfaces. However, cells on 12 and 16 min UV-light and NTP treated surfaces of both materials had a more widely spread cytoskeleton compared to control groups. Twelve min UV-light and one min non-thermal oxygen plasma treatment on titanium and zirconia may be the favored times in terms of increasing the viability, mRNA expression of growth factors and cellular attachment in MC3T3-E1 cells.

The in vitro effect of VEGF receptor inhibition on primary alveolar osteoblast nodule formation

BACKGROUND

Vascular endothelial growth factor (VEGF) is a master regulator and is required for the effective coupling of angiogenesis and osteogenesis supporting both skeletal development and postnatal bone repair. A direct role for VEGF in intramembranous-derived osteoblast growth and differentiation is not clear. We investigated the expression of primary alveolar osteoblast VEGF receptors and the subsequent effects on mineralization and nodule formation in vitro following VEGFR inhibition.

METHODS

Primary human alveolar osteoblasts (HAOBs) were cultured in the presence of VEGF receptor inhibitors, exogenous VEGF or the bisphosphonate, zoledronic acid. VEGF, VEGFR1 and VEGFR2 mRNA expression and nodule formation following 21 days of culture. VEGFR1 protein expression was examined using immunofluorescence after 48 h.

RESULTS

The HAOBs expressed high levels of VEGF and VEGFR1 protein but VEGFR2 was not detected. The VEGFR1/2 inhibitors, ZM306416 and KRN633, lead to a dose-dependent decrease in mineralization. Treatment with zoledronic acid showed no difference in HAOB VEGF receptor expression.

CONCLUSION

VEGF/VEGFR1 pathway appears to be important for intramembranous-derived osteoblast differentiation and maturation in vitro.

Ginkgolide B enhances the differentiation of preosteoblastic MC3T3-E1 cells through VEGF: Involvement of the p38 MAPK signaling pathway

Ginkgolide B (GB) is one of the ginkgolides isolated from the leaves of the Ginkgo biloba tree. Our previous study indicated that GB promotes the proliferation, migration and adhesion of endothelial progenitor cells, and the induction of angiogenesis through vascular endothelial factor (VEGF). In the present study, the effects of GB on the differentiation of MC3T3‑E1 cells and the signaling pathway involved were investigated in vitro. The MC3T3‑E1 cell viability activities were assessed using an MTS assay. Measurements of alkaline phosphatase activity and Alizarin Red staining were used to identify osteoblastic differentiation of the MC3T3‑E1 cells. The mRNA and secretion levels of VEGF were detected using reverse transcription‑quantitative polymerase chain reaction (RT‑qPCR) analysis and enzyme-linked immunosorbent assays, respectively. The protein expression levels of phosphorylation‑associated markers were detected using western blot analysis and associated gene expression was determined using RT‑qPCR analysis. It was found that GB significantly promoted alkaline phosphatase activity and osteoblastic mineralization in the MC3T3‑E1 cells. In addition, the mRNA expression and secretion levels of VEGF in the MC3T3‑E1 cells were significantly increased in MC3T3‑E1 cells treated with GB. SB203580, a specific inhibitor of p38 mitogen‑activated protein (MAP) kinase, markedly suppressed the GB‑induced p38 kinase phosphorylation and GB‑induced synthesis of VEGF. PD98059, an inhibitor of the upstream kinase, which activates p44/p42 MAP kinase, had minimal effect on the GB‑induced phosphorylation of p44/p42 MAP kinase or the GB‑induced synthesis of VEGF. Taken together, these results indicated that GB promoted osteoblastic differentiation of the MC3T3‑E1 cells through VEGF, and that the p38, but not the p44/p42 MAP kinase signaling pathway, was involved in the GB‑induced synthesis of VEGF.

VEGFR-2 reduces while combined VEGFR-2 and -3 signaling increases inflammation in apical periodontitis

BACKGROUND

In apical periodontitis, oral pathogens provoke an inflammatory response in the apical area that induces bone resorptive lesions. In inflammation, angio- and lymphangiogenesis take place. Vascular endothelial growth factors (VEGFs) and their receptors (VEGFRs) are key players in these processes and are expressed in immune cells and endothelial cells in the lesions.

OBJECTIVE

We aimed at testing the role of VEGFR-2 and -3 in periapical lesion development and investigated their role in lymphangiogenesis in the draining lymph nodes.

DESIGN

We induced lesions by pulp exposure in the lower first molars of C57BL/6 mice. The mice received IgG injections or blocking antibodies against VEGFR-2 (anti-R2), VEGFR-3 (anti-R3), or combined VEGFR-2 and -3, starting on day 0 until day 10 or 21 post-exposure.

RESULTS

Lesions developed faster in the anti-R2 and anti-R3 group than in the control and anti-R2/R3 groups. In the anti-R2 group, a strong inflammatory response was found expressed as increased number of neutrophils and osteoclasts. A decreased level of pro-inflammatory cytokines was found in the anti-R2/R3 group. Lymphangiogenesis in the draining lymph nodes was inhibited after blocking of VEGFR-2 and/or -3, while the largest lymph node size was seen after anti-R2 treatment.

CONCLUSIONS

We demonstrate an anti-inflammatory effect of VEGFR-2 signaling in periapical lesions which seems to involve neutrophil regulation and is independent of angiogenesis. Combined signaling of VEGFR-2 and -3 has a pro-inflammatory effect. Lymph node lymphangiogenesis is promoted through activation of VEGFR-2 and/or VEGFR-3.

Effect of low-energy extracorporeal shock wave on vascular regeneration after spinal cord injury and the recovery of motor function

BACKGROUND

Latest studies show that low-energy extracorporeal shock wave therapy (ESWT) can upregulate levels of vascular endothelial growth factor (VEGF). VEGF can ease nervous tissue harm after spinal cord injury (SCI). This study aims to explore whether low-energy ESWT can promote expression of VEGF, protect nervous tissue after SCI, and improve motor function.

METHODS

Ninety adult female rats were divided into the following groups: Group A (simple laminectomy), Group B (laminectomy and low-energy ESWT), Group C (spinal cord injury), and Group D (spinal cord injury and low-energy ESWT). Impinger was used to cause thoracic spinal cord injury. Low-energy ESWT was applied as treatment after injury three times a week, for 3 weeks. After SCI, the Basso, Beattie, and Bresnahan (BBB) scale was used to evaluate motor function over a period of 42 days at different time points. Hematoxylin and eosin (HE) staining was used to evaluate nerve tissue injury. Neuronal nuclear antigen (NeuN) staining was also used to evaluate loss of neurons. Polymerase chain reaction was used to detect messenger RNA (mRNA) expression of VEGF and its receptor fms-like tyrosine kinase 1 (Flt-1). Immunostaining was used to evaluate VEGF protein expression level in myeloid tissue.

RESULTS

BBB scores of Groups A and B showed no significant result related to dyskinesia. HE and NeuN staining indicated that only using low-energy ESWT could not cause damage of nervous tissue in Group B. Recovery of motor function at 7, 35, and 42 days after SCI in Group D was better than that in Group C (P<0.05). Compared with Group C, number of NeuN-positive cells at 42 days after SCI increased significantly (P<0.05). The mRNA levels of VEGF and Flt-1 and VEGF expression at 7 days after SCI in Group D were significantly higher than those in Group C (P<0.05).

CONCLUSION

Low-energy ESWT promotes expression of VEGF, decreases secondary damage of nerve tissue, and improves recovery of motor function. It can be regarded as one mode of clinical routine adjunctive therapy for spinal injury.

Paraneoplastic syndromes in rheumatology

For patients that present with musculoskeletal symptoms, diagnostic procedures carried out by physicians and rheumatologists are primarily aimed at confirming or excluding the occurrence of primary rheumatic diseases. Another important trigger for musculoskeletal disease, however, is the presence of a tumour. Careful clinical investigation and knowledge of the gestalt of musculoskeletal syndromes related to respective tumour entities is of utmost importance for the diagnosis of paraneoplastic rheumatic diseases such as hypertrophic osteoarthropathy, paraneoplastic polyarthritis, RS3PE syndrome, palmar fasciitis and polyarthritis, cancer-associated myositis and tumour-induced osteomalacia. This places great responsibility on rheumatologists in diagnosing malignancies and referring the patient for effective treatment. The selective influence of tumours on musculoskeletal tissue is surprising and indicates that tumours alter tissues such as the periosteum, synovial membrane, subcutaneous connective tissue, fascia, muscles and bones by specific molecular processes. Some of the underlying mechanisms have been unravelled, providing valuable information on the physiologic and pathophysiologic roles of mediators such as vascular endothelial growth factor and fibroblast growth factor 23.

A histological comparison of the repair tissue formed when using either Chondrogide(®) or periosteum during autologous chondrocyte implantation

OBJECTIVE

In this study, we compare the clinical and histological outcome between periosteum and Chondrogide(®) during autologous chondrocyte implantation (ACI).

METHOD

This study consisted of 88 patients having received ACI in the knee; 33 treated with Chondrogide(®) (ACI-C) and 55 with periosteum (ACI-P). Post-operative biopsies were taken at a mean of 16.6 ± 8 months (range 7-37 months) and 19 ± 18.4 months (range 4-114) for ACI-C and ACI-P respectively. Histological assessment was performed using the ICRS II and OsScore scoring systems. The immunolocalisation of elastin and collagen types I and II was analysed using specific antibodies. Lysholm scores, a measure of knee function, were obtained pre- and post-operatively at the time of biopsy and annually thereafter.

RESULTS

Compared with ACI-P, the repair tissue formed from patients treated with ACI-C demonstrated a significantly higher score for cellular morphology (ICRS II score), significantly better surface morphology from medial femoral condyle treated defects (ICRS II score) and a significantly higher proportion of hyaline cartilage formation (OsScore). Elastin fibres were present in both ACI-C and ACI-P samples, although their presence was very variable in quantity, distribution, orientation, thickness and length. Patients treated with ACI-C demonstrated significantly more collagen type II immunolocalisation compared with ACI-P. Both groups exhibited a significant increase in Lysholm score post-ACI.

CONCLUSIONS

This study demonstrates a significantly better quality of repair tissue formed with ACI-C compared with ACI-P. Hence Chondrogide(®) is perhaps a better alternative to periosteum during ACI.

Establishment and characterization of the Masquelet induced membrane technique in a rat femur critical-sized defect model

The Masquelet induced membrane technique for reconstructing large diaphyseal defects has been shown to be a promising clinical treatment, yet relatively little is known about the cellular, histological and biochemical make-up of these membranes and how they produce this positive clinical outcome. We compared cellular make-up, histological changes and growth factor expression in membranes induced around femur bone defects and in subcutaneous pockets at 2, 4 and 6 weeks after induction, and to the periosteum. We found that membranes formed around bone defects were similar to those formed in subcutaneous pockets; however, both were significantly different from periosteum with regard to structural characteristics, location of blood vessels and overall thickness. Membranes induced at the femur defect (at 2 weeks) and in periosteum contain mesenchymal stem cells (MSCs; STRO-1⁺ ) which were not found in membranes induced subcutaneously. BMP-2, TGFβ and VEGF were significantly elevated in membranes induced around femur defects in comparison to subcutaneously induced membranes, whereas SDF-1 was not detectable in membranes induced at either site. We found that osteogenic and neovascular activity had mostly subsided by 6 weeks in membranes formed at both sites. It was conclude that cellular composition and growth factor content in induced membranes depends on the location where the membrane is induced and differs from periosteum. Osteogenic and neovascular activity in the membranes is maximal between 2 and 4 weeks and subsides after 6. Based on this, better and quicker bone healing might be achieved if the PMMA cement were replaced with a bone graft earlier in the Masquelet technique. Copyright © 2013 John Wiley & Sons, Ltd.

JNK signaling plays an important role in the effects of TNF-α and IL-1β on in vitro osteoblastic differentiation of cultured human periosteal-derived cells

The purpose of this study was to examine the effects of TNF-α and IL-1β on in vitro osteoblastic differentiation of cultured human periosteal-derived cells. To examine the effects of TNF-α and IL-1β on in vitro osteoblastic differentiation of cultured human periosteal-derived cells, the cells cultured in the osteogenic induction medium were treated with 0.1-10 ng/ml TNF-α and 0.01-1 ng/ml IL-1β. TNF-α and IL-1β enhanced the alkaline phosphatase (ALP) activity and alizarin red S staining in cultured human periosteal-derived cells. However, these cytokines did not stimulate the Runt-related transcription factor (Runx) 2 activity and osteocalcin secretion. The ALP activity was decreased in the periosteal-derived cells pretreated with mitogen activated protein kinase (MAPK) inhibitors and then treated with TNF-α or IL-1β. Among the periosteal-derived cells pretreated with MAPK inhibitors, the ALP activity was markedly decreased in the cells pretreated with SP 600125, the specific inhibitor of C-Jun N-terminal kinase (JNK). The periosteal-derived cells treated with TNF-α and IL-1β showed an increase in extracellular signal-regulated kinase (ERK) and JNK phosphorylation. Among the ERK and JNK phosphorylation, JNK phosphorylation was strongly observed in the cells. These results suggest that TNF-α and IL-1β increased the in vitro osteoblastic differentiation of cultured human periosteal-derived cells by enhancing the ALP activity and mineralization process, but not by Runx2 activation. The functional role of TNF-α and IL-1β in increasing the ALP activity and mineralization of periosteal-derived cells primarily depends on the JNK signaling among the MAPK pathways.

Localization and signaling patterns of vascular endothelial growth factors and receptors in human periapical lesions

INTRODUCTION

Vascular endothelial growth factors (VEGFs) and their receptors (VEGFRs) are key players in vasculogenesis and are also involved in pathologic conditions with bone destruction. Vasculogenesis is critical for disease progression, and bone resorption is a hallmark of apical periodontitis. However, the localization of VEGFs and VEGFRs and their gene signaling pathways in human apical periodontitis have not been thoroughly investigated. The aim of this study was to localize VEGFs and VEGFRs and analyze their gene expression as well as signaling pathways in human periapical lesions.

METHODS

Tissue was collected after endodontic surgery from patients diagnosed with chronic apical periodontitis. Periodontal ligament samples from extracted healthy wisdom teeth was also collected and used as control tissue. In lesion cryosections, VEGFs/VEGFRs were identified by immunohistochemistry/double immunofluorescence by using specific antibodies. A human VEGF signaling polymerase chain reaction array system was used for gene expression analysis comparing lesions with periodontal ligament samples.

RESULTS

The histologic evaluation revealed heterogeneous morphology of the periapical lesions with various degrees of inflammatory infiltrates. In the lesions, all investigated factors and receptors were identified in blood vessels and various immune cells. No lymphatic vessels were detected. Gene expression analysis revealed up-regulation of VEGF-A and VEGFR-3, although not significant. Phosphatidylinositol-3-kinases, protein kinase C, mitogen-activated protein kinases, and phospholipases, all known to be involved in VEGF-mediated angiogenic activity, were significantly up-regulated.

CONCLUSIONS

The cellular and vascular expressions of VEGFs and VEGFRs in chronic apical periodontitis, along with significant alterations of genes mediating VEGF-induced angiogenic responses, suggest ongoing vascular remodeling in established chronic periapical lesions.

Activation of proliferation and differentiation of dental follicle stem cells (DFSCs) by heat stress

OBJECTIVES

Adult stem cells (ASCs) remain in a slowly cycling/quiescent state under normal physiological conditions, but they can be awakened from this by certain factors, such as injury signals. Previously, our group has shown that dental follicle stem cells (DFSCs) appear to proliferate more rapidly than their non-stem cell counterparts at elevated temperatures. The study described here has aimed to (i) elucidate optimal temperature in which to culture DFSCs, (ii) determine whether elevated temperatures could enhance differentiation capability of DFSCs and (iii) characterize stem cell and osteogenic marker expression of DFSCs at elevated temperatures.

MATERIALS AND METHODS

DFSCs obtained from rat first molars were cultured at 37 (control), 38, 39, 40 and 41 ºC. Cell proliferation was evaluated by Alamar blue reduction assay and mean numbers of viable dissociated cells. Osteogenic differentiation was evaluated after 7 or 14 days osteogenic induction. Expression of selected marker genes was also assessed during proliferation and differentiation of the cells.

RESULTS

Increased cell proliferation was seen at heat-stress temperatures of 38º, 39º and 40 ºC. DFSCs revealed maximal osteogenesis when cultured at 39 and 40 ºC. Moreover, some stem cell and osteogensis-associated markers had elevated expression in heat-stress conditions.

CONCLUSIONS

Under determined heat-stress conditions, DFSCs increased their proliferation, osteogenic differentiation and expression of some marker genes. Thus, it is likely that elevated temperature could serve as a factor to activate adult stem cells.

Human periosteum-derived stem cells for tissue engineering applications: the role of VEGF

Mesenchymal stem cells (MSCs) are promising tools for studying the mechanisms of development and for the regeneration of injured tissues. Correct selection of the MSCs source is crucial in order to obtain a more efficient treatment and, in this respect Periosteum-Derived Cells (PDPCs) may represent an interesting alternative to bone marrow MSCs for osteochondral tissue regeneration. In the present study we have isolated and characterized a MSCs population from the periosteum of human adult donors. PDPCs were expanded under specific culture conditions that prevent fibroblast contamination and support the maintenance of their undifferentiated phenotype. We show, for the first time, that PDPCs expresses VEGF receptor (Flt1 and KDR/Flk1) proteins and that they were similar to bone marrow Multipotent Adult Progenitor Cells (MAPCs). Since the latter are able to differentiate into endothelial cells, we tested the possible PDPCs commitment toward an endothelial phenotype in view of bone tissue engineering approaches that takes into account not only bone formation but also vascularization. PDPCs were treated with two different VEGF concentrations for 7 and 15 days and, alternatively, with the supernatant of human primary osteoblasts. Differently from MAPCs our PDPCs were unable to differentiate into endothelial cells after their in vitro VEGF treatment. On the contrary, growth factor stimulation induces PDPCs differentiation toward osteoblasts. We concluded that in PDPCs the presence of VEGF receptors is related to different cross-talk between osteogenesis and angiogenesis that could involve in situ PDPCs recruitment.

Concise review: the periosteum: tapping into a reservoir of clinically useful progenitor cells

Elucidation of the periosteum and its regenerative potential has become a hot topic in orthopedics. Yet few review articles address the unique features of periosteum-derived cells, particularly in light of translational therapies and engineering solutions inspired by the periosteum's remarkable regenerative capacity. This review strives to define periosteum-derived cells in light of cumulative research in the field; in addition, it addresses clinical translation of current insights, hurdles to advancement, and open questions in the field. First, we examine the periosteal niche and its inhabitant cells and the key characteristics of these cells in the context of mesenchymal stem cells and their relevance for clinical translation. We compare periosteum-derived cells with those derived from the marrow niche in in vivo studies, addressing commonalities as well as features unique to periosteum cells that make them potentially ideal candidates for clinical application. Thereafter, we review the differentiation and tissue-building properties of periosteum cells in vitro, evaluating their efficacy in comparison with marrow-derived cells. Finally, we address a new concept of banking periosteum and periosteum-derived cells as a novel alternative to currently available autogenic umbilical blood and perinatal tissue sources of stem cells for today's population of aging adults who were "born too early" to bank their own perinatal tissues. Elucidating similarities and differences inherent to multipotent cells from distinct tissue niches and their differentiation and tissue regeneration capacities will facilitate the use of such cells and their translation to regenerative medicine.

Administration of growth factors for bone regeneration

Growth factors (GFs) such as BMPs, FGFs, VEGFs and IGFs have significant impacts on osteoblast behavior, and thus have been widely utilized for bone tissue regeneration. Recently, securing biological stability for a sustainable and controllable release to the target tissue has been a challenge to practical applications. This challenge has been addressed to some degree with the development of appropriate carrier materials and delivery systems. This review highlights the importance and roles of those GFs, as well as their proper administration for targeting bone regeneration. Additionally, the in vitro and in vivo performance of those GFs with or without the use of carrier systems in the repair and regeneration of bone tissue is systematically addressed. Moreover, some recent advances in the utility of the GFs, such as using fusion technology, are also reviewed.