Comparative study assessing effects of sonic hedgehog and VEGF in a human co-culture model for bone vascularisation strategies

Functional Approaches in Promoting Vascularization and Angiogenesis in Bone Critical-Sized Defects via Delivery of Cells, Growth Factors, Drugs, and Particles

Critical-sized bone defects, or CSDs, are defined as bone defects that cannot be regenerated by themselves and require surgical intervention via employing specific biomaterials and a certain regenerative strategy. Although a variety of approaches can be used to treat CSDs, poor angiogenesis and vascularization remain an obstacle in these methods. The complex biological healing of bone defects depends directly on the function of blood flow to provide sufficient oxygen and nutrients and the removal of waste products from the defect site. The absence of vascularization can lead to non-union and delayed-union defect development. To overcome this challenge, angiogenic agents can be delivered to the site of injury to stimulate vessel formation. This review begins by introducing the treatment methods for CSDs. The importance of vascularization in CSDs is subsequently highlighted. Delivering angiogenesis agents, including relevant growth factors, cells, drugs, particles, cell secretion substances, their combination, and co-delivery to CSDs are fully explored. Moreover, the effects of such agents on new bone formation, followed by vessel formation in defect areas, are evaluated.

Toll-like Receptor 4, Osteoblasts and Leukemogenesis; the Lesson from Acute Myeloid Leukemia

Toll-like receptor 4 (TLR4) is a pattern-recognizing receptor that can bind exogenous and endogenous ligands. It is expressed by acute myeloid leukemia (AML) cells, several bone marrow stromal cells, and nonleukemic cells involved in inflammation. TLR4 can bind a wide range of endogenous ligands that are present in the bone marrow microenvironment. Furthermore, the TLR4-expressing nonleukemic bone marrow cells include various mesenchymal cells, endothelial cells, differentiated myeloid cells, and inflammatory/immunocompetent cells. Osteoblasts are important stem cell supporting cells localized to the stem cell niches, and they support the proliferation and survival of primary AML cells. These supporting effects are mediated by the bidirectional crosstalk between AML cells and supportive osteoblasts through the local cytokine network. Finally, TLR4 is also important for the defense against complicating infections in neutropenic patients, and it seems to be involved in the regulation of inflammatory and immunological reactions in patients treated with allogeneic stem cell transplantation. Thus, TLR4 has direct effects on primary AML cells, and it has indirect effects on the leukemic cells through modulation of their supporting neighboring bone marrow stromal cells (i.e., modulation of stem cell niches, regulation of angiogenesis). Furthermore, in allotransplant recipients TLR4 can modulate inflammatory and potentially antileukemic immune reactivity. The use of TLR4 targeting as an antileukemic treatment will therefore depend both on the biology of the AML cells, the biological context of the AML cells, aging effects reflected both in the AML and the stromal cells and the additional antileukemic treatment combined with HSP90 inhibition.

Bone Microvasculature: Stimulus for Tissue Function and Regeneration

Bone is a highly vascularized organ, providing structural support to the body, and its development, regeneration, and remodeling depend on the microvascular homeostasis. Loss or impairment of vascular function can develop diseases, such as large bone defects, avascular necrosis, osteoporosis, osteoarthritis, and osteopetrosis. In this review, we summarize how vasculature controls bone development and homeostasis in normal and disease cases. A better understanding of this process will facilitate the development of novel disease treatments that promote bone regeneration and remodeling. Specifically, approaches based on tissue engineering components, such as stem cells and growth factors, have demonstrated the capacity to induce bone microvasculature regeneration and mineralization. This knowledge will have relevant clinical implications for the treatment of bone disorders by developing novel pharmaceutical approaches and bone grafts. Finally, the tissue engineering approaches incorporating vascular components may widely be applied to treat other organ diseases by enhancing their regeneration capacity. Impact statement Bone vasculature is imperative in the process of bone development, regeneration, and remodeling. Alterations or disruption of the bone vasculature leads to loss of bone homeostasis and the development of bone diseases. In this study, we review the role of vasculature on bone diseases and how vascular tissue engineering strategies, with a detailed emphasis on the role of stem cells and growth factors, will contribute to bone therapeutics.

Polymorphisms in GP6, PEAR1A, MRVI1, PIK3CG, JMJD1C, and SHH Genes in Patients with Unstable Angina

INTRODUCTION

Coronary artery disease (CAD) is a significant public health problem because it is one of the major causes of death worldwide. Several studies have investigated the associations between CAD and polymorphisms in genes connected with platelet aggregation and the risk of venous thromboembolism.

AIM

In this study, we examined the associations between polymorphisms in GP6 (rs1671152), PEAR1A (rs12566888), MRVI1 (rs7940646), PIK3CG (rs342286), JMJD1C (rs10761741), SHH (rs2363910), and CAD in the form of unstable angina as well as selected clinical and biochemical parameters. The study enrolled 246 patients with diagnosed unstable angina and 189 healthy controls.

RESULTS

There were no significant differences in the distribution of the studied polymorphisms between the patients with unstable angina and the controls. In patients with the GP6 rs1671152 GG genotype, we observed increased BMI values and an increased frequency of type 2 diabetes diagnosis.

CONCLUSIONS

The results of this study suggest a lack of association between GP6 (rs1671152), PEAR1A (rs12566888), MRVI1 (rs7940646), PIK3CG (rs342286), JMJD1C (rs10761741), SHH (rs2363910), and unstable angina. The results indicate an association between GP6 (rs1671152) and type 2 diabetes.

Role of Hedgehog Signaling in Vasculature Development, Differentiation, and Maintenance

The role of Hedgehog (Hh) signaling in vascular biology has first been highlighted in embryos by Pepicelli et al. in 1998 and Rowitch et al. in 1999. Since then, the proangiogenic role of the Hh ligands has been confirmed in adults, especially under pathologic conditions. More recently, the Hh signaling has been proposed to improve vascular integrity especially at the blood–brain barrier (BBB). However, molecular and cellular mechanisms underlying the role of the Hh signaling in vascular biology remain poorly understood and conflicting results have been reported. As a matter of fact, in several settings, it is currently not clear whether Hh ligands promote vessel integrity and quiescence or destabilize vessels to promote angiogenesis. The present review relates the current knowledge regarding the role of the Hh signaling in vasculature development, maturation and maintenance, discusses the underlying proposed mechanisms and highlights controversial data which may serve as a guideline for future research. Most importantly, fully understanding such mechanisms is critical for the development of safe and efficient therapies to target the Hh signaling in both cancer and cardiovascular/cerebrovascular diseases.

Dl-3-N-butylphthalide promotes angiogenesis and upregulates sonic hedgehog expression after cerebral ischemia in rats

INTRODUCTION

Dl-3-N-butylphthalide (NBP), a small molecule drug used clinically in the acute phase of ischemic stroke, has been shown to improve functional recovery and promote angiogenesis and collateral vessel circulation after experimental cerebral ischemia. However, the underlying molecular mechanism is unknown.

AIMS

To explore the potential molecular mechanism of angiogenesis induced by NBP after cerebral ischemia.

RESULTS

NBP treatment attenuated body weight loss, reduced brain infarct volume, and improved neurobehavioral outcomes during focal ischemia compared to the control rats (P < 0.05). NBP increased the number of CD31⁺ microvessels, the number of CD31⁺ /BrdU⁺ proliferating endothelial cells, and the functional vascular density (P < 0.05). Further study demonstrated that NBP also promoted the expression of vascular endothelial growth factor and angiopoietin-1 (P < 0.05), which was accompanied by upregulated sonic hedgehog expression in astrocytes in vivo and in vitro.

CONCLUSION

NBP treatment promoted the expression of vascular endothelial growth factor and angiopoietin-1, induced angiogenesis, and improved neurobehavioral recovery. These effects were associated with increased sonic hedgehog expression after NBP treatment. Our results broadened the clinical application of NBP to include the later phase of ischemia.

Platelet-rich fibrin-based matrices to improve angiogenesis in an in vitro co-culture model for bone tissue engineering

In the context of prevascularization strategies for tissue‐engineering purposes, co‐culture systems consisting of outgrowth endothelial cells (OECs) and primary osteoblasts (pOBs) have been established as a promising in vitro tool to study regeneration mechanisms and to identify factors that might positively influence repair processes such as wound healing or angiogenesis. The development of autologous injectable platelet‐rich fibrin (PRF), which can be generated from peripheral blood in a minimal invasive procedure, fulfils several requirements for clinically applicable cell‐based tissue‐engineering strategies. During this study, the established co‐culture system of OECs and pOBs was mixed with injectable PRF and was cultivated in vitro for 24 h or 7 days. The aim of this study was to analyse whether PRF might have a positive effect on wound healing processes and angiogenic activation of OECs in the co‐culture with regard to proinflammatory factors, adhesion molecules and proangiogenic growth factor expression. Histological cell detection revealed the formation of lumina and microvessel‐like structures in the PRF/co‐culture complexes after 7 days of complex cultivation. Interestingly, the angiogenic activation of OECs was accompanied by an upregulation of wound healing‐associated factors, as well as by a higher expression of the proangiogenic factor vascular endothelial growth factor, which was evaluated both on the mRNA level as well as on the protein level. Thus, PRF might positively influence wound healing processes, in particular angiogenesis, in the in vitro co‐culture, making autologous PRF‐based matrices a beneficial therapeutic tool for tissue‐engineering purposes by simply profiting from the PRF, which contains blood plasma, platelets and leukocytes.

Crude Fucoidan Extracts Impair Angiogenesis in Models Relevant for Bone Regeneration and Osteosarcoma via Reduction of VEGF and SDF-1

The marine origin polysaccharide fucoidan combines multiple biological activities. As demonstrated by various studies in vitro and in vivo, fucoidans show anti-viral, anti-tumor, anti-oxidant, anti-inflammatory and anti-coagulant properties, although the detailed molecular action remains to be elucidated. The aim of the present study is to assess the impact of crude fucoidan extracts, on the formation of vascular structures in co-culture models relevant for bone vascularization during bone repair and for vascularization processes in osteosarcoma. The co-cultures consisted of bone marrow derived mesenchymal stem cells, respectively the osteosarcoma cell line MG63, and human blood derived outgrowth endothelial cells (OEC). The concentration dependent effects on the metabolic activity on endothelial cells and osteoblast cells were first assessed using monocultures of OEC, MSC and MG63 suggesting a concentration of 100 µg/mL as a suitable concentration for further experiments. In co-cultures fucoidan significantly reduced angiogenesis in MSC/OEC but also in MG63/OEC co-cultures suggesting a potential application of fucoidan to lower the vascularization in bone tumors such as osteosarcoma. This was associated with a decrease in VEGF (vascular endothelial growth factor) and SDF-1 (stromal derived factor-1) on the protein level, both related to the control of angiogenesis and furthermore discussed as crucial factors in osteosarcoma progression and metastasis. In terms of bone formation, fucoidan slightly lowered on the calcification process in MSC monocultures and MSC/OEC co-cultures. In summary, these data suggest the suitability of lower fucoidan doses to limit angiogenesis for instance in osteosarcoma.

Co-Seeding Human Endothelial Cells with Human-Induced Pluripotent Stem Cell-Derived Mesenchymal Stem Cells on Calcium Phosphate Scaffold Enhances Osteogenesis and Vascularization in Rats

A major challenge in repairing large bone defects with tissue-engineered constructs is the poor vascularization in the defect. The lack of vascular networks leads to insufficient oxygen and nutrients supply, which compromises the survival of seeded cells. To achieve favorable regenerative effects, prevascularization of tissue-engineered constructs by co-culturing of endothelial cells and bone cells is a promising strategy. The aim of this study was to investigate the effects of human-induced pluripotent stem cell-derived mesenchymal stem cells (hiPSC-MSCs) co-cultured with human umbilical vein endothelial cells (HUVECs) for prevascularization of calcium phosphate cement (CPC) scaffold on bone regeneration in vivo for the first time. HUVECs co-cultured with hiPSC-MSCs formed microcapillary-like structures in vitro. HUVECs promoted mineralization of hiPSC-MSCs on CPC scaffolds. Four groups were tested in a cranial bone defect model in nude rats: (1) CPC scaffold alone (CPC control); (2) HUVEC-seeded CPC (CPC-HUVEC); (3) hiPSC-MSC-seeded CPC (CPC-hiPSC-MSC); and (4) HUVECs co-cultured with hiPSC-MSCs on CPC scaffolds (co-culture group). After 12 weeks, the co-culture group achieved the greatest new bone area percentage of 46.38% ± 3.8% among all groups (p < 0.05), which was more than four folds of the 10.61% ± 1.43% of CPC control. In conclusion, HUVECs co-cultured with hiPSC-MSCs substantially promoted bone regeneration. The novel construct of HUVECs co-cultured with hiPSC-MSCs delivered via CPC scaffolds is promising to enhance bone and vascular regeneration in orthopedic applications.

Biologically active and biomimetic dual gelatin scaffolds for tissue engineering

We have designed, developed and optimized Genipin cross-linked 3D gelatin scaffolds that were biologically active and biomimetic, show a dual activity both for growth factor and cell delivery. Type B gelatin powder was dissolved in DI water. 100mg of genipin was dissolved in 10ml of DI water. Three genipin concentrations were prepared: 0.1%, 0.2% and 0.3% (w/v). Solutions were mixed at 40°C and under stirring and then left crosslinking for 72h. Scaffolds were obtained by punching 8 mm-cylinders into ethanol 70% solution for 10min and then freeze-drying. Scaffolds were biologically, biomechanically and morphologically evaluated. Cell adhesion and morphology of D1-Mesenchymal stem cells (MSCs) and L-929 fibroblast was studied. Vascular endothelial grwoth factor (VEGF) and Sonic hedgehog (SHH) were used as model proteins. Swelling ratio increased and younǵs module decreased along with the concentration of genipin. All scaffolds were biocompatible according to the toxicity test. MSC and L-929 cell adhesion improved in 0.2% of genipin, obtaining better results with MSCs. VEGF and SHH were released from the gels. This preliminary study suggest that the biologically active and dual gelatin scaffolds may be used for tissue engineering approaches like bone regeneration.

Role of myeloid early endothelial progenitor cells in bone formation and osteoclast differentiation in tissue construct based on hydroxyapatite poly(ester-urethane) scaffolds

Engineering of a vascularized bone construct is a highly challenging task which needs to take into account the impact of different components on the bone regeneration process. Bone repair influencing factors in such constructs range from the material properties and scaffold design, to the interaction of different cell types contributing to bone formation and remodeling or neovascularization, respectively. In this context, early endothelial progenitor cells (EPC), mononuclear cells isolated from the peripheral blood, express the endothelial marker CD31 but also a series of myeloid markers and have been shown to support the formation of vessel-like structures. These cells are also characterized by a highly adaptable phenotype influenced by other cells creating an instructive niche. The present study was designed to investigate the impact of EPC on bone formation or remodeling using a co-culture system of outgrowth endothelial cells, mature endothelial cells isolated from the peripheral blood cell cultures, and mesenchymal stem cells grown on hydroxyapatite poly(ester-urethane) scaffolds. The formation of vessel-like structures in these constructs was shown by CLSM and immunohistochemistry and further evaluated by real time RT-PCR. Osteogenic differentiation in these constructs was investigated by von Kossa, Alizarin Red, and real time PCR. Data indicated that osteogenic differentiation occurred within the constructs after 14 days of culture but without a direct influence by EPC in this process. Finally, although we observed a series of osteoclast related makers in the constructs when EPC were included, no indications for an increased osteoclast-like activity, which might lead to increased bone resorption, were observed. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:1922-1932, 2016.

Increased expression of the sonic hedgehog and vascular endothelial growth factor with co-localization in varicocele veins

Objectives

Varicocele is characterized by dilatation and tortuosity of the internal spermatic vein. Sonic hedgehog plays an important role in angiogenesis and vascular remodeling under hypoxic stress. We studied the relationship and distribution of SHH and vascular endothelial growth factor in internal spermatic vein in patients diagnosed with varicocele.

Methods

Specimens of 1 cm were taken from the internal spermatic vein during left varicocele repair (N = 20). The control samples of ISV were obtained from eight male patients who underwent left inguinal herniorrhaphy. We analyzed the sonic hedgehog and vascular endothelial growth factor expression and distribution by immunoblotting, immunohistochemistry, immunofluorescent staining, and confocal laser scanning microscopy. The data were analyzed using the Student’s t test.

Results

Immunoblotting showed higher expression of sonic hedgehog and vascular endothelial growth factor proteins in varicocele veins than in the control group ( P < 0.05) which located over muscle layer and endothelium was demonstrated by immunohistochemical staining. Both proteins with co-localization in the muscle layer and especially distributed in endothelium of varicocele veins were revealed under confocal microscopy.

Conclusions

These findings showed the upexpression of sonic hedgehog and vascular endothelial growth factor with co-localization in varicocele veins which imply that the reducing hypoxia or using sonic hedgehog antagonists may be helpful for this vascular disease.

Tissue engineering strategies for promoting vascularized bone regeneration

This review focuses on current tissue engineering strategies for promoting vascularized bone regeneration. We review the role of angiogenic growth factors in promoting vascularized bone regeneration and discuss the different therapeutic strategies for controlled/sustained growth factor delivery. Next, we address the therapeutic uses of stem cells in vascularized bone regeneration. Specifically, this review addresses the concept of co-culture using osteogenic and vasculogenic stem cells, and how adipose derived stem cells compare to bone marrow derived mesenchymal stem cells in the promotion of angiogenesis. We conclude this review with a discussion of a novel approach to bone regeneration through a cartilage intermediate, and discuss why it has the potential to be more effective than traditional bone grafting methods.

Hedgehog signaling mediates woven bone formation and vascularization during stress fracture healing

Hedgehog (Hh) signaling is critical in developmental osteogenesis, and recent studies suggest it may also play a role in regulating osteogenic gene expression in the post-natal setting. However, there is a void of studies directly assessing the effect of Hh inhibition on post-natal osteogenesis. This study utilized a cyclic loading-induced ulnar stress fracture model to evaluate the hypothesis that Hh signaling contributes to osteogenesis and angiogenesis during stress fracture healing. Immediately prior to loading, adult rats were given GDC-0449 (Vismodegib - a selective Hh pathway inhibitor; 50mg/kg orally twice daily), or vehicle. Hh signaling was upregulated in response to stress fracture at 3 days (Ptch1, Gli1 expression), and was markedly inhibited by GDC-0449 at 1 day and 3 days in the loaded and non-loaded ulnae. GDC-0449 did not affect Hh ligand expression (Shh, Ihh, Dhh) at 1 day, but decreased Shh expression by 37% at 3 days. GDC-0449 decreased woven bone volume (-37%) and mineral density (-17%) at 7 days. Dynamic histomorphometry revealed that the 7 day callus was composed predominantly of woven bone in both groups. The observed reduction in woven bone occurred concomitantly with decreased expression of Alpl and Ibsp, but was not associated with differences in early cellular proliferation (as determined by callus PCNA staining at 3 days), osteoblastic differentiation (Osx expression at 1 day and 3 days), chondrogenic gene expression (Acan, Sox9, and Col2α1 expression at 1 day and 3 days), or bone resorption metrics (callus TRAP staining at 3 days, Rankl and Opg expression at 1 day and 3 days). To evaluate angiogenesis, vWF immunohistochemistry showed that GDC-0449 reduced fracture callus blood vessel density by 55% at 3 days, which was associated with increased Hif1α gene expression (+30%). Dynamic histomorphometric analysis demonstrated that GDC-0449 also inhibited lamellar bone formation. Lamellar bone analysis of the loaded limb (directly adjacent to the woven bone callus) showed that GDC-0449 significantly decreased mineral apposition rate (MAR) and bone formation rate (BFR/BS) (-17% and -20%, respectively). Lamellar BFR/BS in the non-loaded ulna was also significantly decreased (-37%), indicating that Hh signaling was required for normal bone modeling. In conclusion, Hh signaling plays an important role in post-natal osteogenesis in the setting of stress fracture healing, mediating its effects directly through regulation of bone formation and angiogenesis.

Improving vascularization of engineered bone through the generation of pro-angiogenic effects in co-culture systems

One of the major problems with bone tissue engineering is the development of a rapid vascularization after implantation to supply the growing osteoblast cells with the nutrients to grow and survive as well as to remove waste products. It has been demonstrated that capillary-like structures produced in vitro will anastomose rapidly after implantation and become functioning blood vessels. For this reason, in recent years many studies have examined a variety of human osteoblast and endothelial cell co-culture systems in order to distribute osteoblasts on all parts of the bone scaffold and at the same time provide conditions for the endothelial cells to migrate to form a network of capillary-like structures throughout the osteoblast-colonized scaffold. The movement and proliferation of endothelial cells to form capillary-like structures is known as angiogenesis and is dependent on a variety of pro-angiogenic factors. This review summarizes human 2- and 3-D co-culture models to date, the types and origins of cells used in the co-cultures and the proangiogenic factors that have been identified in the co-culture models.

TLR4 stimulation by LPS enhances angiogenesis in a co-culture system consisting of primary human osteoblasts and outgrowth endothelial cells

The development of new approaches leading to fast and successful vascularization of tissue-engineered constructs is one of the most intensively studied subjects in tissue engineering and regenerative medicine. Recently, TLR4 activation and LPS stimulation of endothelial cells have been reported to promote angiogenesis in a variety of settings. In this study, we demonstrate that TLR4 activation by Ultrapure LPS Escherichia coli 0111:B4 (LPS-EB) significantly enhances microvessel formation in a co-culture system consisting of outgrowth endothelial cells (OECs) and primary human osteoblasts (pOBs). The precise modes of TLR4 action on the process of angiogenesis have also been investigated in this study. Using quantitative fluorescence microscopy in monocultures of OECs and pOBs, it was found that TLR4 activation through LPS-EB upregulates the expression level of TLR4/MYD88 and enhances both angiogenesis and osteogenesis. Furthermore, ELISA and qRT-PCR have shown that the level of two adhesion molecules (ICAM-1 and E-selectin), two cytokines (IL-6 and IL-8) and two growth factors (VEGF and PDGF-BB) related to angiogenesis increase significantly after LPS-EB treatment. This increased understanding of the role of TLR4 in angiogenesis could be of value in various settings related to tissue repair and tissue engineering. Moreover, since LPS and TLR4 agonists improve angiogenesis and osteogenesis, TLR4 agonists (endogenous or synthetic) could be used for angiogenesis intervention in vivo and therefore could be tested for their potential clinical applications in promoting angiogenesis in bone tissue engineering. Copyright © 2015 John Wiley & Sons, Ltd.

Hedgehog and Resident Vascular Stem Cell Fate

The Hedgehog pathway is a pivotal morphogenic driver during embryonic development and a key regulator of adult stem cell self-renewal. The discovery of resident multipotent vascular stem cells and adventitial progenitors within the vessel wall has transformed our understanding of the origin of medial and neointimal vascular smooth muscle cells (SMCs) during vessel repair in response to injury, lesion formation, and overall disease progression. This review highlights the importance of components of the Hh and Notch signalling pathways within the medial and adventitial regions of adult vessels, their recapitulation following vascular injury and disease progression, and their putative role in the maintenance and differentiation of resident vascular stem cells to vascular lineages from discrete niches within the vessel wall.

Investigating the effect of hypoxic culture on the endothelial differentiation of human amniotic fluid-derived stem cells

Amniotic fluid-derived stem cells (AFSCs) are a unique stem cell source that may have great potential for use in tissue engineering (TE) due to their pluripotentiality. AFSCs have previously shown angiogenic potential and may present an alternative cell source for endothelial-like cells that could be used in range of applications, including the pre-vascularisation of TE constructs and the treatment of ischaemic diseases. This study investigated the ability of these cells to differentiate down an endothelial lineage with the aim of producing an endothelial-like cell suitable for use in pre-vascularisation. As hypoxia and the associated HIF-1 pathway have been implicated in the induction of angiogenesis in a number of biological processes, it was hypothesised that culture in hypoxic conditions could enhance the endothelial differentiation of AFSCs. The cells were cultured in endothelial cell media supplemented with 50 ng mL(-1) of VEGF, maintained in normoxia, intermittent hypoxia or continuous hypoxia and assessed for markers of endothelial differentiation at day 7 and 14. The results demonstrated that AFSCs subjected to these culture conditions display an endothelial gene expression profile and adopted functional endothelial cell characteristics indicative of early endothelial differentiation. Culture in continuous hypoxia enhanced endothelial gene expression but did not enhance functional endothelial cell characteristics. Overall, AFSCs subjected to endothelial stimuli demonstrated a less mature endothelial gene expression profile and phenotype when compared with HUVECs, the endothelial cell control. However, this study is the first time that the positive effect of an extended period of continuous hypoxic culture on endothelial differentiation in AFSCs has been demonstrated.

Is sonic Hedgehog involved in human fracture healing? --a prospective study on local and systemic concentrations of SHH

INTRODUCTION

Sonic Hedgehog (SHH) is a new signalling pathway in bone repair. Evidence exist that SHH pathway plays a significant role in vasculogenesis and limb development during embryogenesis. Some in vitro and animal studies has already proven its potential for bone regeneration. However, no data on the role of SHH in the human fracture healing have been published so far.

METHODS

Seventy-five patients with long bone fractures were included into the study and divided in 2 groups. First group contained 69 patients with normal fracture healing. Four patients with impaired fracture healing formed the second group. 34 volunteers donated blood samples as control. Serum samples were collected over a period of 1 year following a standardized time schedule. In addition, SHH levels were measured in fracture haematoma and serum of 16 patients with bone fractures.

RESULTS

Fracture haematoma and patients serum both contained lower SHH concentrations compared to control serum. The comparison between the patients' serum SHH level and the control serum revealed lower levels for the patients at all measurement time points. Significantly lower concentrations were observed at weeks 1 and 2 after fracture. SHH levels were slightly decreased in patients with impaired fracture healing without statistical significance.

CONCLUSION

This is the first study to report local and systemic concentration of SHH in human fracture healing and SHH serum levels in healthy adults. A significant reduction of the SHH levels during the inflammatory phase of fracture healing was found. SHH concentrations in fracture haematoma and serum were lower than the concentration in control serum for the rest of the healing period. Our findings indicate that there is no relevant involvement of SHH in human fracture healing. Fracture repair process seem to reduce the SHH level in human. Further studies are definitely needed to clarify the underlying mechanisms.

Heparin-chitosan nanoparticle functionalization of porous poly(ethylene glycol) hydrogels for localized lentivirus delivery of angiogenic factors

Hydrogels have been extensively used for regenerative medicine strategies given their tailorable mechanical and chemical properties. Gene delivery represents a promising strategy by which to enhance the bioactivity of the hydrogels, though the efficiency and localization of gene transfer have been challenging. Here, we functionalized porous poly(ethylene glycol) hydrogels with heparin-chitosan nanoparticles to retain the vectors locally and enhance lentivirus delivery while minimizing changes to hydrogel architecture and mechanical properties. The immobilization of nanoparticles, as compared to homogeneous heparin and/or chitosan, is essential to lentivirus immobilization and retention of activity. Using this gene-delivering platform, we over-expressed the angiogenic factors sonic hedgehog (Shh) and vascular endothelial growth factor (Vegf) to promote blood vessel recruitment to the implant site. Shh enhanced endothelial recruitment and blood vessel formation around the hydrogel compared to both Vegf-delivering and control hydrogels. The nanoparticle-modified porous hydrogels for delivering gene therapy vectors can provide a platform for numerous regenerative medicine applications.

Biomaterials in co-culture systems: towards optimizing tissue integration and cell signaling within scaffolds

Most natural tissues consist of multi-cellular systems made up of two or more cell types. However, some of these tissues may not regenerate themselves following tissue injury or disease without some form of intervention, such as from the use of tissue engineered constructs. Recent studies have increasingly used co-cultures in tissue engineering applications as these systems better model the natural tissues, both physically and biologically. This review aims to identify the challenges of using co-culture systems and to highlight different approaches with respect to the use of biomaterials in the use of such systems. The application of co-culture systems to stimulate a desired biological response and examples of studies within particular tissue engineering disciplines are summarized. A description of different analytical co-culture systems is also discussed and the role of biomaterials in the future of co-culture research are elaborated on. Understanding the complex cell-cell and cell-biomaterial interactions involved in co-culture systems will ultimately lead the field towards biomaterial concepts and designs with specific biochemical, electrical, and mechanical characteristics that are tailored towards the needs of distinct co-culture systems.

In vitro 3D angiogenesis assay in egg white matrix: comparison to Matrigel, compatibility to various species, and suitability for drug testing

In vitro angiogenesis assays are commonly used to assess pro- or anti-angiogenic drug properties. Extracellular matrix (ECM) substitutes such as Matrigel and collagen gel became very popular in in vitro 3D angiogenesis assays as they enable tubule formation by endothelial cells from culture or aortic rings. However, these assays are usually used with a single cell type, lacking the complex cellular interactions occurring during angiogenesis. Here, we report a novel angiogenesis assay using egg white as ECM substitute. We found that, similar to Matrigel, egg white elicited prevascular network formation by endothelial and/or smooth muscle cell coculture. This matrix was suitable for various cells from human, mouse, and rat origin. It is compatible with aortic ring assay and also enables vascular and tumor cell coculture. Through simple labeling (DAPI, Hoechst 33258), cell location and resulting prevascular network formation can easily be quantified. Cell transfection with green fluorescent protein improved whole cell visualization and 3D structure characterization. Finally, egg-based assay dedicated to angiogenesis studies represents a reliable and cost-effective way to produce and analyze data regarding drug effects on vascular cells.

Sonic hedgehog mediates a novel pathway of PDGF-BB-dependent vessel maturation

Recruitment of mural cells (MCs), namely pericytes and smooth muscle cells (SMCs), is essential to improve the maturation of newly formed vessels. Sonic hedgehog (Shh) has been suggested to promote the formation of larger and more muscularized vessels, but the underlying mechanisms of this process have not yet been elucidated. We first identified Shh as a target of platelet-derived growth factor BB (PDGF-BB) and found that SMCs respond to Shh by upregulating extracellular signal-regulated kinase 1/2 and Akt phosphorylation. We next showed that PDGF-BB-induced SMC migration was reduced after inhibition of Shh or its signaling pathway. Moreover, we found that PDGF-BB-induced SMC migration involves Shh-mediated motility. In vivo, in the mouse model of corneal angiogenesis, Shh is expressed by MCs of newly formed blood vessels. PDGF-BB inhibition reduced Shh expression, demonstrating that Shh is a target of PDGF-BB, confirming in vitro experiments. Finally, we found that in vivo inhibition of either PDGF-BB or Shh signaling reduces NG2(+) MC recruitment into neovessels and subsequently reduces neovessel life span. Our findings demonstrate, for the first time, that Shh is involved in PDGF-BB-induced SMC migration and recruitment of MCs into neovessels and elucidate the molecular signaling pathway involved in this process.

Mild heat stress enhances angiogenesis in a co-culture system consisting of primary human osteoblasts and outgrowth endothelial cells

The repair and regeneration of large bone defects, including the formation of functional vasculature, represents a highly challenging task for tissue engineering and regenerative medicine. Recent studies have shown that vascularization and ossification can be stimulated by mild heat stress (MHS), which would offer the option to enhance the bone regeneration process by relatively simple means. However, the mechanisms of MHS-enhanced angiogenesis and osteogenesis, as well as potential risks for the treated cells are unclear. We have investigated the direct effect of MHS on angiogenesis and osteogenesis in a co-culture system of human outgrowth endothelial cells (OECs) and primary osteoblasts (pOBs), and assessed cytotoxic effects, as well as the levels of various heat shock proteins (HSPs) synthesized under these conditions. Enhanced formation of microvessel-like structures was observed in co-cultures exposed to MHS (41°C, 1 h), twice per week, over a time period of 7-14 days. As shown by real-time polymerase chain reaction (PCR), the expression of vascular endothelial growth factor (VEGF), angiopoietin-1 (Ang-1), angiopoietin-2 (Ang-2), and tumor necrosis factor-alpha was up-regulated in MHS-treated co-cultures 24 h post-treatment. At the protein level, significantly elevated VEGF and Ang-1 concentrations were observed in MHS-treated co-cultures and pOB mono-cultures compared with controls, indicating paracrine effects associated with MHS-induced angiogenesis. MHS-stimulated co-cultures and OEC mono-cultures released higher levels of Ang-2 than untreated cultures. On the other hand MHS treatment of co-cultures did not result in a clear effect regarding osteogenesis. Nevertheless, real-time PCR demonstrated that MHS increased the expression of mitogen-activated protein kinase, interleukin-6, and bone morphogenetic protein 2, known as HSP-related molecules in angiogenic and osteogenic regulation pathways. In agreement with these observations, the expression of some selected HSPs also increased at both the mRNA and protein levels in MHS-treated co-cultures.

Comparison of different strategies for in vivo seeding of prevascularized scaffolds

Scaffolds seeded with multipotent precursor cells were hypothesized to heal critically sized bone defects. However, the success of this concept was limited by low cell survival after transplantation due to a lack of nutrients and oxygen. In vivo prevascularization of scaffolds before cell seeding may improve cell survival, yet the best seeding technique and time point of cell application remain elusive. Thus, the aim of this study was to compare different strategies. Demineralized bone matrix scaffolds were implanted around the saphenous arteriovenous (AV) bundle in nude mice. In vivo seeding was performed 0, 5, or 21 days after implantation using enhanced green fluorescent protein (eGFP)-expressing mesenchymal stem cells (MSCs). Cells were applied either by injection or the repetitive dripping technique. In vitro seeded and subcutaneously implanted scaffolds served as controls. Fourteen days after cell application, the fluorescence intensity of transplanted cells and the extent of newly formed vessels were quantified. We found that the AV flow through model as well as cell application increased vessel formation. In vitro seeding resulted in significantly higher cell numbers than in vivo seeding. With increasing time of prevascularization, the number of cells declined dramatically. In vivo seeding by cell injection was superior to the repetitive dripping protocol. On subcutaneously implanted scaffolds, significantly, more cells were found than on axially perfused scaffolds. We conclude that in vitro seeding is more efficient compared to the two novel in vivo seeding techniques of prevascularized scaffolds. With increasing time of prevascularization, the seeding efficiency for the in vivo methods further decreases, presumably due to the ingrowth of connective tissue. Even though, the presence of MSCs and the longer period of prevascularization enhances vessel formation, this conceivable advantage is limited supposedly by the inferior seeding efficiency.

Immune and inflammatory pathways are involved in inherent bone marrow ossification

BACKGROUND

Bone marrow plays a key role in bone formation and healing. Although a subset of marrow explants ossifies in vitro without excipient osteoinductive factors, some explants do not undergo ossification. The disparity of outcome suggests a significant heterogeneity in marrow tissue in terms of its capacity to undergo osteogenesis.

QUESTIONS/PURPOSES

We sought to identify: (1) proteins and signaling pathways associated with osteogenesis by contrasting the proteomes of ossified and poorly ossified marrow explants; and (2) temporal changes in proteome and signaling pathways of marrow ossification in the early and late phases of bone formation.

METHODS

Explants of marrow were cultured. Media conditioned by ossified (n = 4) and poorly ossified (n = 4) subsets were collected and proteins unique to each group were identified by proteomic analysis. Proteomic data were processed to assess proteins specific to the early phase (Days 1-14) and late phase (Days 15-28) of the culture period. Pathways involved in bone marrow ossification were identified through bioinformatics.

RESULTS

Twenty-eight proteins were unique to ossified samples and eight were unique to poorly ossified ones. Twelve proteins were expressed during the early phase and 15 proteins were specific to the late phase. Several identified pathways corroborated those reported for bone formation in the literature. Immune and inflammatory pathways were specific to ossified samples.

CONCLUSIONS

The marrow explant model indicates the inflammatory and immune pathways to be an integral part of the osteogenesis process.

Perivascular-like cells contribute to the stability of the vascular network of osteogenic tissue formed from cell sheet-based constructs

In recent years several studies have been supporting the existence of a close relationship in terms of function and progeny between Mesenchymal Stem Cells (MSCs) and Pericytes. This concept has opened new perspectives for the application of MSCs in Tissue Engineering (TE), with special interest for the pre-vascularization of cell dense constructs. In this work, cell sheet technology was used to create a scaffold-free construct composed of osteogenic, endothelial and perivascular-like (CD146⁺) cells for improved in vivo vessel formation, maturation and stability. The CD146 pericyte-associated phenotype was induced from human bone marrow mesenchymal stem cells (hBMSCs) by the supplementation of standard culture medium with TGF-β1. Co-cultured cell sheets were obtained by culturing perivascular-like (CD146⁺) cells and human umbilical vein endothelial cells (HUVECs) on an hBMSCs monolayer maintained in osteogenic medium for 7 days. The perivascular-like (CD146⁺) cells and the HUVECs migrated and organized over the collagen-rich osteogenic cell sheet, suggesting the existence of cross-talk involving the co-cultured cell types. Furthermore the presence of that particular ECM produced by the osteoblastic cells was shown to be the key regulator for the singular observed organization. The osteogenic and angiogenic character of the proposed constructs was assessed in vivo. Immunohistochemistry analysis of the explants revealed the integration of HUVECs with the host vasculature as well as the osteogenic potential of the created construct, by the expression of osteocalcin. Additionally, the analysis of the diameter of human CD146 positive blood vessels showed a higher mean vessel diameter for the co-cultured cell sheet condition, reinforcing the advantage of the proposed model regarding blood vessels maturation and stability and for the in vitro pre-vascularization of TE constructs.

Extracellular matrix deposition and scaffold biodegradation in an in vitro three-dimensional model of bone by X-ray computed microtomography

The development of an in vitro model of bone and the optimization of tools for determining the biological processes occurring during bone repair remains a major goal in the field of bone tissue engineering. Recently, a model based on a three-dimensional co-culture of osteoblasts and osteoclast precursors in Skelite(TM) scaffolds was developed. Although induction of osteoblast and osteoclast differentiation was observed, a complete evaluation of bone deposition and biodegradation processes was missing due to technical limitations. In the current study, both X-ray computed microtomography and histological analysis were used to monitor these two key biological processes in the same in vitro model. Either osteoblasts or a combination of osteoblasts and osteoclasts were seeded on Skelite(TM) scaffolds. Scaffold biodegradation and increased bone deposition together with a more organized extracellular matrix were observed in the co-cultures, highlighting the role of osteoclasts in the determination and regulation of bone deposition. Results confirmed the potential and relevance of co-culturing osteoblasts and osteoclasts to resemble native tissue. The combination of X-ray computed microtomography and histology presented in this study could be useful in future studies for the validation and development of new in vitro culture systems for bone tissue engineering.

Sonic Hedgehog-mediated synergistic effects guiding angiogenesis and osteogenesis

Sonic hedgehog (Shh) is a morphogen controlling the skeletal and vascular development in the embryo but is also reactivated during adult repair processes. Thus, this molecule holds great therapeutic potential for biotechnological and biomedical approaches aiming to enhance tissue regeneration or to replace damaged tissues. According to present knowledge, Shh signaling controls the expression of several families of growth factors involved in neovascularization and vessel maturation and acts upstream of the most prominent angiogenic growth factor, vascular endothelial growth factor. In this context, a very interesting feature of Shh is that it controls both angiogenic activity and vessel stabilization by mural cells. In parallel, Shh seems to have a direct effect on endothelial cell tube formation and seems to trigger the differentiation process of mesenchymal stem cells toward the osteogenic lineage. In this chapter, we will therefore shortly summarize the multifaceted potential of Shh for bone repair and vascularization according to the current literature. In addition, we will show how coculture models based on outgrowth endothelial cells and primary osteoblasts can be used to reveal some of the relevant mechanisms by which Shh drives and connects bone regeneration and vascularization.

Paracrine effects influenced by cell culture medium and consequences on microvessel-like structures in cocultures of mesenchymal stem cells and outgrowth endothelial cells

Mesenchymal stem cells (MSC) from bone marrow and outgrowth endothelial cells (OEC) from peripheral blood are considered as attractive cell types for applications in regenerative medicine aiming to build up complex vascularized tissue-engineered constructs. MSC provide several advantages such as the potential to differentiate to osteoblasts and to support the neovascularization process by release of proangiogenic factors. On the other hand, the neovascularization process can be actively supported by OEC forming perfused vascular structures after co-implantation with other cell types. In this study the formation of angiogenic structures in vitro was investigated in cocultures of MSC and OEC, cultured either in the medium for osteogenic differentiation of MSC (ODM) or in the medium for OEC cultivation endothelial cell growth medium-2 (EGM2 Bullet Kit). After 2 weeks, cocultures in EGM2 formed more microvessel-like structures compared to cocultures in ODM as demonstrated by immunofluorescence staining for the endothelial marker CD31. Increased expression of CD31 and CD146 in quantitative real-time polymerase chain reaction as well as a higher percentage of CD31- and CD146-positive cells in flow cytometry indicated a beneficial influence of EGM2 on endothelial cell growth and function. In addition, the improved formation of vascular structures in EGM2 correlates with higher levels of the proangiogenic factor vascular endothelial growth factor and platelet-derived growth factor in the supernatant of cocultures as well as in monocultures of MSC when cultivated in EGM-2. Nevertheless, ODM was more suitable for the differentiation of MSC to osteoblastic lineages in the cocultures, whereas EGM2 favored factors involved in vessel stabilization by pericytes. In conclusion, this study highlights the importance of medium components for cell interaction triggering the formation of angiogenic structures.