The role of vascular actors in two dimensional dialogue of human bone marrow stromal cell and endothelial cell for inducing self-assembled network

Engineering Cell Microenvironment Using Nanopattern-Derived Multicellular Spheroids and Photo-Crosslinked Gelatin/Hyaluronan Hydrogels

Cell cultures of dispersed cells within hydrogels depict the interaction of the cell-extracellular matrix (ECM) in 3D, while the coculture of different cells within spheroids combines both the effects of cell-cell and cell-ECM interactions. In this study, the cell co-spheroids of human bone mesenchymal stem cells/human umbilical vein endothelial cells (HBMSC/HUVECs) are prepared with the assistance of a nanopattern, named colloidal self-assembled patterns (cSAPs), which is superior to low-adhesion surfaces. A phenol-modified gelatin/hyaluronan (Gel-Ph/HA-Ph) hydrogel is used to encapsulate the multicellular spheroids and the constructs are photo-crosslinked using blue light. The results show that Gel-Ph/HA-Ph hydrogels with a 5%-to-0.3% ratio have the best properties. Cells in HBMSC/HUVEC co-spheroids are more favorable for osteogenic differentiation (Runx2, ALP, Col1a1 and OPN) and vascular network formation (CD31+ cells) compared to HBMSC spheroids. In a subcutaneous nude mouse model, the HBMSC/HUVEC co-spheroids showed better performance than HBMSC spheroids in angiogenesis and the development of blood vessels. Overall, this study paves a new way for using nanopatterns, cell coculturing and hydrogel technology for the generation and application of multicellular spheroids.

Promoting osteointegration effect of Cu alloyed titanium (TiCu) in ovariectomized rats

Osteoporosis is a common skeletal disease making patients be prone to the osteoporotic fracture. However, the clinical implants made of titanium and its alloys with a poor osseointegration need a long time for healing and easily to loosening. Thus, a new class of Cu-alloyed titanium (TiCu) alloys with excellent mechanical properties and bio-functionalization has been developed. In this study, the osteoporosis modeled rats were used to study the osteointegration effect and underlying mechanism of TiCu. The results showed that after implantation for 4 weeks, TiCu alloy could promote the reconstruction of vascular network around the implant by up-regulating vascular endothelial growth factor expression. After 8 weeks, it could further promote the proliferation and differentiation of osteoblasts, mineralization and deposition of collagens, and then significantly increasing bone mineral density around the implant. In conclusion, TiCu alloy would enhance the fixation stability, accelerate the osteointegration, and thus reduce the risk of aseptic loosening during the long-term implantation in the osteoporosis environment. This study was the first to report the role and mechanism of a Cu-alloyed metal in promoting osteointegration in osteoporosis environment, which provides a new attractive support for the improvement of future clinical applications of Cu-alloyed antibacterial titanium alloys.

Enhanced osteogenesis and angiogenesis of calcium phosphate cement incorporated with zinc silicate by synergy effect of zinc and silicon ions

Calcium phosphate cement (CPC) with good injectability and osteoconductivity plays important roles in bone grafting application. Much attention has been paid to achieve multifunctionality through incorporating trace elements into CPC. Silicon and zinc can be used as additives to endow CPC with biological functions of osteogenesis, angiogenesis and anti-osteoclastogenesis. In this study, zinc and silicate ions were co-incorporated into CPC through mixing with submicron zinc silicate (Zn₂SiO₄, ZS) to obtain zinc silicate-modified CPCs (ZS/CPCs) with different contents. The results revealed that the addition of ZS increased the compressive strength, prolonged the setting time, and densified the structure of CPC. Low addition content of ZS facilitated the formation of surface apatite layer in the early mineralization stage. Incorporating ZS significantly induced osteogenesis of mouse bone marrow stromal cells (mBMSCs) and angiogenesis of human umbilical vein endothelial cells (HUVECs), and moreover, restricted osteoclastogenesis of Raw 264.7 in vitro. Silicate and zinc ions could be steadily released from ZS/CPCs into the culture medium. With the synergistic effect of silicate and zinc ions, ZS/CPCs provided an appropriate microenvironment for the immune cells to facilitate the osteogenesis of mBMSCs and angiogenesis of HUVECs further. Taken together, it can be concluded that incorporating ZS is an effective way to endow CPC with multifunctionality and better bone regeneration for bone defect repair.

Network analysis and the impact of Aflibercept on specific mediators of angiogenesis in HUVEC cells

Angiogenesis, inflammation and endothelial cells’ migration and proliferation exert fundamental roles in different diseases. However, more studies are needed to identify key proteins and pathways involved in these processes. Aflibercept has received the approval of the US Food and Drug Administration (FDA) for the treatment of wet AMD and colorectal cancer. Moreover, the effect of Aflibercept on VEGFR2 downstream signalling pathways has not been investigated yet. Here, we integrated text mining data, protein‐protein interaction networks and multi‐experiment microarray data to specify candidate genes that are involved in VEGFA/VEGFR2 signalling pathways. Network analysis of candidate genes determined the importance of the nominated genes via different centrality parameters. Thereupon, several genes—with the highest centrality indexes—were recruited to investigate the impact of Aflibercept on their expression pattern in HUVEC cells. Real‐time PCR was performed, and relative expression of the specific genes revealed that Aflibercept modulated angiogenic process by VEGF/PI3KA/AKT/mTOR axis, invasion by MMP14/MMP9 axis and inflammation‐related angiogenesis by IL‐6‐STAT3 axis. Data showed Aflibercept simultaneously affected these processes and determined the nominated axes that had been affected by the drug. Furthermore, integrating the results of Aflibercept on expression of candidate genes with the current network analysis suggested that resistance against the Aflibercept effect is a plausible process in HUVEC cells.

Role of ex vivo Expanded Mesenchymal Stromal Cells in Determining Hematopoietic Stem Cell Transplantation Outcome

Overall, the human organism requires the production of ∼1 trillion new blood cells per day. Such goal is achieved via hematopoiesis occurring within the bone marrow (BM) under the tight regulation of hematopoietic stem and progenitor cell (HSPC) homeostasis made by the BM microenvironment. The BM niche is defined by the close interactions of HSPCs and non-hematopoietic cells of different origin, which control the maintenance of HSPCs and orchestrate hematopoiesis in response to the body’s requirements. The activity of the BM niche is regulated by specific signaling pathways in physiological conditions and in case of stress, including the one induced by the HSPC transplantation (HSCT) procedures. HSCT is the curative option for several hematological and non-hematological diseases, despite being associated with early and late complications, mainly due to a low level of HSPC engraftment, impaired hematopoietic recovery, immune-mediated graft rejection, and graft-versus-host disease (GvHD) in case of allogenic transplant. Mesenchymal stromal cells (MSCs) are key elements of the BM niche, regulating HSPC homeostasis by direct contact and secreting several paracrine factors. In this review, we will explore the several mechanisms through which MSCs impact on the supportive activity of the BM niche and regulate HSPC homeostasis. We will further discuss how the growing understanding of such mechanisms have impacted, under a clinical point of view, on the transplantation field. In more recent years, these results have instructed the design of clinical trials to ameliorate the outcome of HSCT, especially in the allogenic setting, and when low doses of HSPCs were available for transplantation.

Studies on the changes of uPA system in a co-culture model of bone marrow stromal cells-leukemia cells

The core of the tumor microenvironment in the hematological system is formed by bone marrow stromal cells (BMSCs). In the present study, we explored the interaction between the urokinase plasminogen activator (uPA) system and the leukemia bone marrow microenvironment (BMM). We established BMSCs–HL60 and HS-5–K562 co-culture models in direct contact mode to simulate the BMM in leukemia. In BMSCs-HL60 co-culture model, the expression levels of uPA, uPA receptor (uPAR), plasminogen activator inhibitor 1 (PAI-1) and vascular endothelial growth factor (VEGF) in BMSCs were higher than those in mono-cultured BMSCs. Matrix metalloproteinase (MMP)-9 (MMP-9) was up-regulated in co-cultured HL60 cells. In HS-5–K562 co-culture model, only uPA, PAI-1, and VEGF-A were up-regulated in HS-5 cells. The levels of the uPA protein in the co-culture supernatant were significantly higher than that of mono-cultured BMSCs or HS-5 cells. Our findings demonstrate that the co-culture stimulates the production of uPA, uPAR, PAI-1, MMP-9, and VEGF-A by BMSCs. It could further explain how the uPA system in leukemia cells is involved in the growth, development, and prognosis of leukemia.

Laminin 221 fragment is suitable for the differentiation of human induced pluripotent stem cells into brain microvascular endothelial-like cells with robust barrier integrity

BACKGROUND

In vitro blood-brain barrier (BBB) models using human induced pluripotent stem (iPS) cell-derived brain microvascular endothelial-like cells (iBMELCs) have been developed to predict the BBB permeability of drug candidates. For the differentiation of iBMELCs, Matrigel, which is a gelatinous protein mixture, is often used as a coating substrate. However, the components of Matrigel can vary among lots, as it is obtained from mouse sarcoma cells with the use of special technics and also contains various basement membranes. Therefore, fully defined substrates as substitutes for Matrigel are needed for a stable supply of iBMELCs with less variation among lots.

METHODS

iBMELCs were differentiated from human iPS cells on several matrices. The barrier integrity of iBMELCs was evaluated based on transendothelial electrical resistance (TEER) values and permeability of fluorescein isothiocyanate-dextran 4 kDa (FD4) and Lucifer yellow (LY). Characterization of iBMELCs was conducted by RT-qPCR and immunofluorescence analysis. Functions of efflux transporters were defined by intracellular accumulation of the substrates in the wells of multiwell plates.

RESULTS

iBMELCs differentiated on laminin 221 fragment (LN221F-iBMELCs) had higher TEER values and lower permeability of LY and FD4 as compared with iBMELCs differentiated on Matrigel (Matrigel-iBMELCs). Besides, the gene and protein expression levels of brain microvascular endothelial cells (BMEC)-related markers were similar between LN221F-iBMELCs and Matrigel-iBMELCs. Moreover, both Matrigel- and LN221F-iBMELCs had functions of P-glycoprotein and breast cancer resistance protein, which are essential efflux transporters for barrier functions of the BBB.

CONCLUSION

The fully defined substrate LN221F presents as an optimal coating matrix for differentiation of iBMELCs. The LN221F-iBMELCs had more robust barrier function for a longer period than Matrigel-iBMELCs with characteristics of BMECs. This finding will contribute the establishment of an iBMELC supply system for pharmacokinetic and pathological models of the BBB.

3D printing of metal-organic framework nanosheets-structured scaffolds with tumor therapy and bone construction

After surgical resection for a bone tumor, the uncleared bone tumor cells can multiply and cause recurrence of the bone tumor. It is worthwhile to design a scaffold that kills the remaining bone tumor cells and repairs bone defects that were given rise to by surgical resection. Additionally, it is extremely important to consider the function of angiogenesis in the process of bone regeneration because the newly formed blood vessels can offer the nutrients for bone regeneration. In this work, a novel metal-organic framework Cu-TCPP nanosheets interface-structured β-tricalcium phosphate (TCP) (Cu-TCPP-TCP) scaffold was successfully prepared through integrating a 3D-printing technique with an in-situ growth method in a solvothermal system. Owing to the excellent photothermal effect of Cu-TCPP nanosheets, Cu-TCPP-TCP scaffolds that were illuminated by near-infrared (NIR) light demonstrated photothermal performance, which was well regulated through varying the contents of Cu-TCPP nanosheets, and the ambient humidity and power density of NIR light. When cultured with osteosarcoma cells, Cu-TCPP-TCP scaffolds killed a significant quantity of osteosarcoma cells through released heat energy after exposure to NIR light with power density 1.0 W cm^-2 and duration 10 min. Similarly, Cu-TCPP-TCP scaffolds ablated subcutaneous bone tumor tissues on the backs of naked mice and suppressed their growth because of the heat energy transformed from NIR light. I n-vitro studies found that Cu-TCPP-TCP scaffolds ably supported the attachments of both human bone marrow stromal cells (HBMSCs) and human umbilical vein endothelial cells (HUVECs), and significantly stimulated expressions of osteogenesis differentiation-related genes in HBMSCs and angiogenesis differentiation-related genes in HUVECs. After implanting Cu-TCPP-TCP scaffolds into the bone defects of rabbits, they effectively promoted bone regeneration. Thus, the integration of the bone-forming bioactivity of TCP scaffolds with the photothermal properties of Cu-TCPP nanosheets and angiogenesis activity of Cu ions makes Cu-TCPP-TCP scaffolds multifunctional, representing a new horizon to develop biomaterials for simultaneously curing bone tumors and repairing bone defects.

[Heterotopic osteogenesis study of tissue engineered bone by co-culture of vascular endothelial cells and adipose-derived stem cells]

OBJECTIVE

To investigate the heterotopic osteogenesis of tissue engineered bone using the co-culture system of vascular endothelial cells (VECs) and adipose-derived stem cells (ADSCs) as seed cells.

METHODS

The partially deproteinized biological bone (PDPBB) was prepared by fibronectin combined with partially deproteinized bone (PDPB). The ADSCs of 18-week-old Sprague Dawley (SD) rats and VECs of cord blood of full-term pregnant SD rats were isolated and cultured. Three kinds of tissue engineered bone were constructed in vitro: PDPBB+VECs (group A), PDPBB+ADSCs (group B), PDPBB+co-cultured cells (VECs∶ADSCs was 1∶1, group C), and PDPBB was used as control group (group D). Scanning electron microscopy was performed at 10 days after cell transplantation to observe cell adhesion on scaffolds. Forty-eight 18-week-old SD rats were randomly divided into groups A, B, C, and D, with 12 rats in each group. Four kinds of scaffolds, A, B, C, and D, were implanted into the femoral muscle bags of rats in corresponding groups. The animals were killed at 2, 4, 8, and 12 weeks after operation for gross observation, HE staining and Masson staining histological observation, and the amount of bone collagen was measured quantitatively by Masson staining section.

RESULTS

Scanning electron microscopy showed that the pores were interconnected in PDPB materials, and a large number of lamellar protein crystals on the surface of PDPBB modified by fibronection were loosely attached to the surface of the scaffold. After 10 days of co-culture PDPBB and cells, a large number of cells attached to PDPBB and piled up with each other to form cell clusters in group C. Polygonal cells and spindle cells were mixed and distributed, and some cells grew along bone trabeculae to form cell layers. Gross observation showed that the granulation tissue began to grow into the material pore at 2 weeks after operation. In group C, a large number of white cartilage-like substances were gradually produced on the surface of the material after 4 weeks, and the surface of the material was uneven. At 12 weeks, the amount of blood vessels on the surface of group A increased, and the material showed consolidation; there was a little white cartilage-like material on the surface of group B, but the pore size of the material did not decrease significantly; in group D, the pore size of the material did not decrease significantly. Histological observation showed that there was no significant difference in the amount of bone collagen between groups at 2 weeks after operation ( F=2.551, P=0.088); at 4, 8, and 12 weeks after operation, the amount of bone collagen in group C was significantly higher than that in other 3 groups, and that in group B was higher than that in group D ( P<0.05); there was no significant difference between group A and groups B, D ( P>0.05).

CONCLUSION

The ability of heterotopic osteogenesis of tissue engineered bone constructed by co-culture VECs and ADSCs was the strongest.

Human Umbilical Vein Endothelial Cells (HUVECs) Co-Culture with Osteogenic Cells: From Molecular Communication to Engineering Prevascularised Bone Grafts

The repair of bone defects caused by trauma, infection or tumor resection is a major clinical orthopedic challenge. The application of bone grafts in orthopedic procedures is associated with a problem of inadequate vascularization in the initial phase after implantation. Meanwhile, the survival of cells within the implanted graft and its integration with the host tissue is strongly dependent on nutrient and gaseous exchange, as well as waste product removal, which are effectuated by blood microcirculation. In the bone tissue, the vasculature also delivers the calcium and phosphate indispensable for the mineralization process. The critical role of vascularization for bone healing and function, led the researchers to the idea of generating a capillary-like network within the bone graft in vitro, which could allow increasing the cell survival and graft integration with a host tissue. New strategies for engineering pre-vascularized bone grafts, that apply the co-culture of endothelial and bone-forming cells, have recently gained interest. However, engineering of metabolically active graft, containing two types of cells requires deep understanding of the underlying mechanisms of interaction between these cells. The present review focuses on the best-characterized endothelial cells-human umbilical vein endothelial cells (HUVECs)-attempting to estimate whether the co-culture approach, using these cells, could bring us closer to development and possible clinical application of prevascularized bone grafts.

3D printed HUVECs/MSCs cocultures impact cellular interactions and angiogenesis depending on cell-cell distance

Vascularization is a crucial process during the growth and development of bone ¹, yet it remains one of the main challenges in the reconstruction of large bone defects. The use of in vitro coculture of human umbilical vein endothelial cells (HUVECs) and human mesenchymal stem cells (hMSCs) has been one of the most explored options. Both cell types secrete specific growth factors that are mutually beneficial, and studies suggested that cell-cell communication and paracrine secretion could be affected by a number of factors. However, little is known about the effect of cell patterning and the distance between cell populations on their crosstalk. In the present study, we showed that the separation and distance between ECs and MSCs populations affects angiogenesis by modulating cell-cell communication. HUVECs grown farther apart from MSCs (˃400 μm) presented characteristics of an early stage of angiogenesis (migration/proliferation). Results showed an increase in the up-regulation of VEGF, FGF-2, and ITGA3 (integrins) but a smaller fold change in the expression of VE-Cadherin and Ang-1. HUVECs were also still highly proliferative. On the contrary, HUVECs incubated closer (≤200 μm) to MSCs, showed signs of stabilization, mainly an increase in Ang-1 and VE-cadherin expression, as well as tighter monolayers. Conditioned media collected from HUVECs and MSCs grown ≤200 μm apart preferentially promoted tube formation, a later stage of angiogenesis, due in part to a significant increase in Ang-1 paracrine secretion. In addition, in groups in which fibers were printed farther apart (400 μm), cells produced EVs with a significantly increase cargo. Finally, in vivo experiment results showed an increase in blood vessels density and new bone thickness after 12 weeks of implantation in rat cranial defect, further suggesting the higher efficiency of indirect ECs/MSCs contact in prompting the release of paracrine signals that stimulate the angiogenesis of local tissues, and enhanced subsequent bone regeneration.

Micropatterning of endothelial cells to create a capillary-like network with defined architecture by laser-assisted bioprinting

Development of a microvasculature into tissue-engineered bone substitutes represents a current challenge. Seeding of endothelial cells in an appropriate environment can give rise to a capillary-like network to enhance prevascularization of bone substitutes. Advances in biofabrication techniques, such as bioprinting, could allow to precisely define a pattern of endothelial cells onto a biomaterial suitable for in vivo applications. The aim of this study was to produce a microvascular network following a defined pattern and preserve it while preparing the surface to print another layer of endothelial cells. We first optimise the bioink cell concentration and laser printing parameters and then develop a method to allow endothelial cells to survive between two collagen layers. Laser-assisted bioprinting (LAB) was used to pattern lines of tdTomato-labeled endothelial cells cocultured with mesenchymal stem cells seeded onto a collagen hydrogel. Formation of capillary-like structures was dependent on a sufficient local density of endothelial cells. Overlay of the pattern with collagen I hydrogel containing vascular endothelial growth factor (VEGF) allowed capillary-like structures formation and preservation of the printed pattern over time. Results indicate that laser-assisted bioprinting is a valuable technique to pre-organize endothelial cells into high cell density pattern in order to create a vascular network with defined architecture in tissue-engineered constructs based on collagen hydrogel.

Data driven mathematical modeling reveals the dynamic mechanism of MSC-induced neovascularization

Coculture of mesenchymal stem cells (MSCs) and vascular endothelial cells (ECs) in vitro leads to the formation of a capillary-like reticular structure by ECs, which has great potential as a better substitute for artificial blood vessels in terms of stability and functionality. To investigate the mechanisms of the early neovascularization induced by MSCs, we analyzed the kinematic features of the motion of ECs and concluded that the dynamic interaction between cells and the extracellular matrix would reveal the capillary-like structure formation. Based on this hypothesis, we proposed a mathematical model to simulate the vascular-like migration pattern of ECs in silico, which was confirmed by in vitro studies. These in vitro studies validated that the dynamic secretion and degradation of collagen I is the critical factor for capillary structure formation. The model proposed based on cell tracking, single cell sequencing, and mathematical simulation provides a better understanding of the neovascularization process induced by MSCs and a possible simple explanation guiding this important cellular behavior.-Yu, Y., Situ, Q., Jia, W., Li, J., Wu, Q., Lei, J. Data driven mathematical modeling reveals the dynamic mechanism of MSC-induced neovascularization.

Improved vasculogenesis and bone matrix formation through coculture of endothelial cells and stem cells in tissue-specific methacryloyl gelatin-based hydrogels

The coculture of osteogenic and angiogenic cells and the resulting paracrine signaling via soluble factors are supposed to be crucial for successfully engineering vascularized bone tissue equivalents. In this study, a coculture system combining primary human adipose-derived stem cells (hASCs) and primary human dermal microvascular endothelial cells (HDMECs) within two types of hydrogels based on methacryloyl-modified gelatin (GM) as three-dimensional scaffolds was examined for its support of tissue specific cell functions. HDMECs, together with hASCs as supporting cells, were encapsulated in soft GM gels and were indirectly cocultured with hASCs encapsulated in stiffer GM hydrogels additionally containing methacrylate-modified hyaluronic acid and hydroxyapatite particles. After 14 days, the hASC in the stiffer gels (constituting the "bone gels") expressed matrix proteins like collagen type I and fibronectin, as well as bone-specific proteins osteopontin and alkaline phosphatase. After 14 days of coculture with HDMEC-laden hydrogels, the viscoelastic properties of the bone gels were significantly higher compared with the gels in monoculture. Within the soft vascularization gels, the formed capillary-like networks were significantly longer after 14 days of coculture than the structures in the control gels. In addition, the stability as well as the complexity of the vascular networks was significantly increased by coculture. We discussed and concluded that osteogenic and angiogenic signals from the culture media as well as from cocultured cell types, and tissue-specific hydrogel composition all contribute to stimulate the interplay between osteogenesis and angiogenesis in vitro and are a basis for engineering vascularized bone.

Titanium-based implant comprising a porous microstructure assembled with nanoleaves and controllable silicon-ion release for enhanced osseointegration

Osseointegration is crucial for early fixation as well as for long-term implantation success, hence numerous efforts have been made to tune the surface topography or chemical composition of biomedical implants to improve osseointegration. In this work, various nanostructures, including nanoflocs, nanobundles, nanorods, and nanoleaves, were introduced to the surface of silicon (Si)-incorporated microporous structure to form Si-incorporated micro-nano hierarchical structures on titanium (Ti)-based implants. The osseointegration of the implants were systemically assessed in vivo and in vitro. The in vitro evaluations showed that the nanostructures promoted the protein adsorption, thus modulating the early cellular responses, including the attachment and spreading of osteoblasts and human endothelial cells (HUVECs), and subsequent cell proliferation and differentiation. Furthermore, compared with the single microporous structure, the nanostructures located over the microporous structure protected the Si ions from quick release and allowed the long-term sustained Si-ions release, which further contributed to the proliferation and differentiation of osteoblasts and vascular endothelial growth factor (VEGF) secretion as well as the tube formation of HUVECs. Collectively, the favorable nano-surface structures, especially the nanoleaves structure, and the constant Si-ion release together led to robust osteogenic and angiogenic activities. More importantly, in vivo micro-CT evaluation and histological observations further verified that the Si-incorporated micro-nano hierarchical implant with nanoleaves structure could efficiently promote new bone formation, thus indicating it was an attractive candidate as a next-generation bone-implant material.

The effect of gap junction-mediated transfer of miR-200b on osteogenesis and angiogenesis in a co-culture of MSCs and HUVECs

For successful engineering of pre-vascularized bone tissue in vitro, understanding the interactions between vasculogenic cells and bone-forming cells is a prerequisite. Mounting evidence indicates that microRNAs can serve as intercellular signals that allow cell-cell communication. Here, the role of the transfer of the microRNA miR-200b between vasculogenic and osteogenic cells was explored in a co-culture system. Rat bone-marrow derived mesenchymal stem cells (BMSCs) formed functional gap junctions composed of connexin 43 (Cx43, also known as GJA1) with human umbilical vein endothelial cells (HUVECs), through which miR-200b could transfer from BMSCs to HUVECs to regulate osteogenesis and angiogenesis. As a negative regulator, the decrease in miR-200b level in BMSCs derepressed the expression of VEGF-A, leading to increased osteogenic differentiation. Once inside HUVECs, miR-200b reduced the angiogenic potential of HUVECs through downregulation of ZEB2, ETS1, KDR and GATA2 Additionally, TGF-β was found to trigger the transfer of miR-200b to HUVECs. Upon adding the TGF-β inhibitor SB431542 or TGF-β-neutralizing antibody, the formation of capillary-like structures in co-culture could be partially rescued. These findings may be fundamental to the development of a cell-based bone regeneration strategy.

An injectable double-network hydrogel for the co-culture of vascular endothelial cells and bone marrow mesenchymal stem cells for simultaneously enhancing vascularization and osteogenesis

Utilization of a GC/Alg DN hydrogel for the co-culture of BM-MSCs with VECs to promote vascularization and osteogenesis simultaneously.

VEGF secreted by mesenchymal stem cells mediates the differentiation of endothelial progenitor cells into endothelial cells via paracrine mechanisms

Stem cell therapy is a promising treatment strategy for ischemic diseases. Mesenchymal stem cells (MSCs) and endothelial progenitor cells (EPCs) adhere to each other in the bone marrow cavity and in in vitro cultures. We have previously demonstrated that the adhesion between MSCs and EPCs is critical for MSC self-renewal and their multi-differentiation into osteoblasts and chondrocytes. In the present study, the influence of the indirect communication between EPCs and MSCs on the endothelial differentiation potential of EPCs was investigated, and the molecular mechanisms underlying MSC-mediated EPC differentiation were explored. The effects of vascular endothelial growth factor (VEGF), which is secreted by MSCs, on EPC differentiation via paracrine mechanisms were examined via co-culturing MSCs and EPCs. Reverse transcription-quantitative polymerase chain reaction and western blot analysis were used to detect the expression of genes and proteins of interest. The present results demonstrated that co-culturing EPCs with MSCs enhanced the expression of cluster of differentiation 31 and von Willebrand factor, which are specific markers of an endothelial phenotype, thus indicating that MSCs may influence the endothelial differentiation of EPCs in vitro. VEGF appeared to be critical to this process. These findings are important for the understanding of the biological interactions between MSCs and EPCs, and for the development of applications of stem cell-based therapy in the treatment of ischemic diseases.

Evidence based anti-osteoporosis effects of Periplaneta americana L on osteoblasts, osteoclasts, vascular endothelial cells and bone marrow derived mesenchymal stem cells

Background

Kangfuxin (KFX) is the ethanol extract of Periplaneta americana L, which has been widely used in the Traditional Chinese Medicine for the repair and regeneration of injured organ and tissues with long history. This study is to investigate the influence of KFX in the various cellular activities and evaluate the anti-osteoporosis potential of KFX.

Methods

The influence of the KFX in the cellular activities, including: 1) migration, osteocalcin secretion of osteoblasts; 2) apoptosis of osteoclasts; 3) migration and tube formation of human umbilical vein endothelial cell (HUVEC); and 4) proliferation, cell cycle regulation and migration of bone marrow mesenchymal stem cells (BMSCs), were investigated systematically.

Results

KFX was shown to significantly 1) Promote of the migration of osteoblasts, HUVEC, and BMSCs; 2) Increase the secretion of osteocalcin and mineralization of osteoblasts; 3) Accelerate the apoptosis of osteoclasts; 4) Stimulate the proliferation and regulate the cell cycle of BMSCs.

Conclusion

Taken together, these results provide the evidence for the osteogenesis, anti-osteoporosis and angiogenesis effects of KFX, with the mechanism of activating the bone formation through stimulating the osteoblasts and HUVECs, as well as inhibiting the bone absorption by inhibiting the osteoclasts activities. The KFX was definitely shown a promising bone turnover agent with great potential for anti-osteoporosis treatment.

In vitro degradation and surface bioactivity of iron-matrix composites containing silicate-based bioceramic

Iron-matrix composites with calcium silicate (CS) bioceramic as the reinforcing phase were fabricated through powder metallurgy processes. The microstructures, mechanical properties, apatite deposition and biodegradation behavior of the Fe-CS composites, as well as cell attachment and proliferation on their surfaces, were characterized. In the range of CS weight percentages selected in this study, the composites possessed compact structures and showed differently decreased bending strengths as compared with pure iron. Immersion tests in simulated body fluid (SBF) revealed substantially enhanced deposition of CaP on the surfaces of the composites as well as enhanced degradation rates as compared with pure iron. In addition, the composite containing 20% CS showed a superior ability to stimulate hBMSCs proliferation when compared to pure iron. Our results suggest that incorporating calcium silicate particles into iron could be an effective approach to developing iron-based biodegradable bone implants with improved biomedical performance.

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Fe-based biocomposites containing calcium silicate (CS) bioceramic possess enhanced degradation behavior and surface bioactivity.

Hierarchical bioceramic scaffolds with 3D-plotted macropores and mussel-inspired surface nanolayers for stimulating osteogenesis

The hierarchical structure of biomaterials plays an important role in the process of tissue reconstruction and regeneration. 3D-plotted scaffolds have been widely used for bone tissue engineering due to their controlled macropore structure and mechanical properties. However, the lack of micro- or nano-structures on the strut surface of 3D-plotted scaffolds, especially for bioceramic scaffolds, limits their biological activity. Inspired by the adhesive versatility of mussels and the active ion-chelating capacity of polydopamine, we set out to prepare a hierarchical bioceramic scaffold with controlled macropores and mussel-inspired surface nanolayers by combining the 3D-plotting technique with the polydopamine/apatite hybrid strategy in order to synergistically accelerate the osteogenesis and angiogenesis. β-Tricalcium phosphate (TCP) scaffolds were firstly 3D-plotted and then treated in dopamine-Tris/HCl and dopamine-SBF solutions to obtain TCP-DOPA-Tris and TCP-DOPA-SBF scaffolds, respectively. It was found that polydopamine/apatite hybrid nanolayers were formed on the surface of both TCP-DOPA-Tris and TCP-DOPA-SBF scaffolds and TCP-DOPA-SBF scaffolds induced apatite mineralization for the second time during the cell culture. As compared to TCP scaffolds, both TCP-DOPA-Tris and TCP-DOPA-SBF scaffolds significantly promoted the osteogenesis of bone marrow stromal cells (BMSCs) as well as the angiogenesis of human umbilical vein endothelial cells (HUVECs), and the TCP-DOPA-SBF group presented the highest in vitro osteogenic/angiogenic activity among the three groups. Furthermore, both TCP-DOPA-Tris and TCP-DOPA-SBF scaffolds significantly improved the formation of new bone in vivo as compared to TCP scaffolds without a nanostructured surface. Our results suggest that the utilization of a mussel-inspired Ca, P-chelated polydopamine nanolayer on 3D-plotted bioceramic scaffolds is a viable and effective strategy to construct a hierarchical structure for synergistically accelerating osteogenesis.

A synergistic approach to the design, fabrication and evaluation of 3D printed micro and nano featured scaffolds for vascularized bone tissue repair

3D bioprinting has begun to show great promise in advancing the development of functional tissue/organ replacements. However, to realize the true potential of 3D bioprinted tissues for clinical use requires the fabrication of an interconnected and effective vascular network. Solving this challenge is critical, as human tissue relies on an adequate network of blood vessels to transport oxygen, nutrients, other chemicals, biological factors and waste, in and out of the tissue. Here, we have successfully designed and printed a series of novel 3D bone scaffolds with both bone formation supporting structures and highly interconnected 3D microvascular mimicking channels, for efficient and enhanced osteogenic bone regeneration as well as vascular cell growth. Using a chemical functionalization process, we have conjugated our samples with nano hydroxyapatite (nHA), for the creation of novel micro and nano featured devices for vascularized bone growth. We evaluated our scaffolds with mechanical testing, hydrodynamic measurements and in vitro human mesenchymal stem cell (hMSC) adhesion (4 h), proliferation (1, 3 and 5 d) and osteogenic differentiation (1, 2 and 3 weeks). These tests confirmed bone-like physical properties and vascular-like flow profiles, as well as demonstrated enhanced hMSC adhesion, proliferation and osteogenic differentiation. Additional in vitro experiments with human umbilical vein endothelial cells also demonstrated improved vascular cell growth, migration and organization on micro-nano featured scaffolds.

Bioglass Activated Skin Tissue Engineering Constructs for Wound Healing

Wound healing is a complicated process, and fibroblast is a major cell type that participates in the process. Recent studies have shown that bioglass (BG) can stimulate fibroblasts to secrete a multitude of growth factors that are critical for wound healing. Therefore, we hypothesize that BG can stimulate fibroblasts to have a higher bioactivity by secreting more bioactive growth factors and proteins as compared to untreated fibroblasts, and we aim to construct a bioactive skin tissue engineering graft for wound healing by using BG activated fibroblast sheet. Thus, the effects of BG on fibroblast behaviors were studied, and the bioactive skin tissue engineering grafts containing BG activated fibroblasts were applied to repair the full skin lesions on nude mouse. Results showed that BG stimulated fibroblasts to express some critical growth factors and important proteins including vascular endothelial growth factor, basic fibroblast growth factor, epidermal growth factor, collagen I, and fibronectin. In vivo results revealed that fibroblasts in the bioactive skin tissue engineering grafts migrated into wound bed, and the migration ability of fibroblasts was stimulated by BG. In addition, the bioactive BG activated fibroblast skin tissue engineering grafts could largely increase the blood vessel formation, enhance the production of collagen I, and stimulate the differentiation of fibroblasts into myofibroblasts in the wound site, which would finally accelerate wound healing. This study demonstrates that the BG activated skin tissue engineering grafts contain more critical growth factors and extracellular matrix proteins that are beneficial for wound healing as compared to untreated fibroblast cell sheets.

The proangiogenic potential of a novel calcium releasing biomaterial: Impact on cell recruitment

In current bone tissue engineering strategies the achievement of sufficient angiogenesis during tissue regeneration is still a major limitation in order to attain full functionality. Several strategies have been described to tackle this problem, mainly by the use of angiogenic factors or endothelial progenitor cells. However, when facing a clinical scenario these approaches are inherently complex and present a high cost. As such, more cost effective alternatives are awaited. Here, we demonstrate the potential of electrospun poly(lactic acid) (PLA) fiber-based membranes, containing calcium phosphate ormoglass (CaP) particles, to elicit angiogenesis in vivo, in a subcutaneous model in mice. We show that the current approach elicited the local expression of angiogenic factors, associated to a chemotactic effect on macrophages, and sustained angiogenesis into the biomaterial. As both PLA and CaP are currently accepted for clinical application these off-the-shelf novel membranes have great potential for guided bone regeneration applications.

STATEMENT OF SIGNIFICANCE

In current bone tissue engineering approaches the achievement of sufficient angiogenesis, during tissue regeneration, is a major limitation in order to attain full tissue functionality. Recently, our group has found that calcium ions released by the degradation of calcium phosphate ormoglasses (CaP) are effective angiogenic promoters. Based on this, in this work we successfully produced hybrid fibrous mats with different contents of CaP nanoparticles and thus with different calcium ion release rates, using an ormoglass - poly(lactic acid) blend approach. We show that these matrices, upon implantation in a subcutaneous site, could elicit the local expression of angiogenic factors, associated to a chemotactic effect on macrophages, and sustained angiogenesis into the biomaterial, in a CaP dose dependent manner. This off-the-shelf cost effective approach presents great potential to translate to the clinics.

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.

CXCR2 modulates bone marrow vascular repair and haematopoietic recovery post-transplant

Murine models of bone marrow transplantation show that pre‐conditioning regimens affect the integrity of the bone marrow endothelium and that the repair of this vascular niche is an essential pre‐requisite for successful haematopoietic stem and progenitor cell engraftment. Little is known about the angiogenic pathways that play a role in the repair of the human bone marrow vascular niche. We therefore established an in vitro humanized model, composed of bone marrow stromal and endothelial cells and have identified several pro‐angiogenic factors, VEGFA, ANGPT1, CXCL8 and CXCL16, produced by the stromal component of this niche. We demonstrate for the first time that addition of CXCL8 or inhibition of its receptor, CXCR2, modulates blood vessel formation in our bone marrow endothelial niche model. Compared to wild type, Cxcr2^−/− mice displayed a reduction in bone marrow cellularity and delayed platelet and leucocyte recovery following myeloablation and bone marrow transplantation. The delay in bone marrow recovery correlated with impaired bone marrow vascular repair. Taken together, our data demonstrate that CXCR2 regulates bone marrow blood vessel repair/regeneration and haematopoietic recovery, and clinically may be a therapeutic target for improving bone marrow transplantation.

Superparamagnetic plasmonic nanoshells for improved imaging, separation and seeding of co-cultured cells

Multifunctional superparamagnetic nanoshells were applied for improved 2D and 3D two-photon luminescence imaging, separation and seeding of co-cultured cells.

Transcriptional profiling reveals crosstalk between mesenchymal stem cells and endothelial cells promoting prevascularization by reciprocal mechanisms

Mesenchymal stem cells (MSCs) show great promise in blood vessel restoration and vascularization enhancement in many therapeutic situations. Typically, the co-implantation of MSCs with vascular endothelial cells (ECs) is effective for the induction of functional vascularization in vivo, indicating its potential applications in regenerative medicine. The effects of MSCs-ECs-induced vascularization can be modeled in vitro, providing simplified models for understanding their underlying communication. In this article, a contact coculture model in vitro and an RNA-seq approach were employed to reveal the active crosstalk between MSCs and ECs within a short time period at both morphological and transcriptional levels. The RNA-seq results suggested that angiogenic genes were significantly induced upon coculture, and this prevascularization commitment might require the NF-κB signaling. NF-κB blocking and interleukin (IL) neutralization experiments demonstrated that MSCs potentially secreted IL factors including IL1β and IL6 to modulate NF-κB signaling and downstream chemokines during coculture. Conversely, RNA-seq results indicated that the MSCs were regulated by the coculture environment to a smooth muscle commitment within this short period, which largely induced myocardin, the myogenic co-transcriptional factor. These findings demonstrate the mutual molecular mechanism of MSCs-ECs-induced prevascularization commitment in a quick response.

Silicate bioceramics enhanced vascularization and osteogenesis through stimulating interactions between endothelia cells and bone marrow stromal cells

The facts that biomaterials affect the behavior of single type of cells have been widely accepted. However, the effects of biomaterials on cell-cell interactions have rarely been reported. Bone tissue engineering involves osteoblastic cells (OCs), endothelial cells (ECs) and the interactions between OCs and ECs. It has been reported that silicate biomaterials can stimulate osteogenic differentiation of OCs and vascularization of ECs. However, the effects of silicate biomaterials on the interactions between ECs and OCs during vascularization and osteogenesis have not been reported, which are critical for bone tissue regeneration in vivo. Therefore, this study aimed to investigate the effects of calcium silicate (CS) bioceramics on interactions between human umbilical vein endothelial cells (HUVECs) and human bone marrow stromal cells (HBMSCs) and on stimulation of vascularization and osteogenesis in vivo through combining co-cultures with CS containing scaffolds. Specifically, the effects of CS on the angiogenic growth factor VEGF, osteogenic growth factor BMP-2 and the cross-talks between VEGF and BMP-2 in the co-culture system were elucidated. Results showed that CS stimulated co-cultured HBMSCs (co-HBMSCs) to express VEGF and the VEGF activated its receptor KDR on co-cultured HUVECs (co-HUVECs), which was also up-regulated by CS. Then, BMP-2 and nitric oxide expression from the co-HUVECs were stimulated by CS and the former stimulated osteogenic differentiation of co-HBMSCs while the latter stimulated vascularization of co-HVUECs. Finally, the poly(lactic-co-glycolic acid)/CS composite scaffolds with the co-cultured HBMSCs and HUVECs significantly enhanced vascularization and osteogenic differentiation in vitro and in vivo, which indicates that it is a promising way to enhance bone regeneration by combining scaffolds containing silicate bioceramics and co-cultures of ECs and OCs.

Synergy effects of copper and silicon ions on stimulation of vascularization by copper-doped calcium silicate

Copper (Cu) has been reported to be able to stimulate vascularization/angiogenesis, which is critical for regeneration of vascularized tissue in tissue engineering. Silicate bioceramics have also been reported to have stimulatory effects on vascularization due to the silicon (Si) ions released from silicate biomaterials. Therefore, we hypothesize that a combination of Cu and Si ions may show synergy effects on vascularization. Therefore, a copper-doped calcium silicate bioceramic (Cu-CaSiO₃, Cu-CS) was designed and synthesized with the purpose to enhance the stimulatory effects of copper salts or pure silicate bioceramics on vascularization by combining the effects of Cu and Si ions. The cytocompatibility of Cu-CS was firstly assessed by testing the influence of Cu-CS ion extracts on proliferation of human umbilical vein endothelial cells (HUVECs). Thereafter, vascularization of HUVECs on ECMatrix™ gel or co-cultured with human dermal fibroblasts (HDFs) in Cu-CS extracts was evaluated and expression of angiogenic growth factors was analyzed. Results revealed that, as compared to CS extracts and media containing soluble CuSO₄, Cu-CS extracts possessed stronger stimulatory effects on upregulation of angiogenic growth factors, which finally resulted in better stimulatory effects on vascularization. During the vascularization process, paracrine effects dominated in the co-culture system. In addition, lower concentrations of Cu and Si ions released from Cu-CS than those released from pure CS or CuSO₄ were enough to stimulate vascularization, which indicated that there were synergy effects between Cu and Si ions during stimulation of vascularization by Cu-CS. Taken together, the designed Cu-CS may be suitable as a new biomaterial for regenerating blood vessels in tissue engineering.

In vitro assessment of three-dimensionally plotted nagelschmidtite bioceramic scaffolds with varied macropore morphologies

It is known that porous scaffolds play an important role in bone/periodontal tissue engineering. A new nagelschmidtite (NAGEL, Ca7Si2P2O16) ceramic has recently been prepared which shows excellent apatite mineralization ability and osteo-/cementostimulation properties in vitro. However, up to now porous NAGEL scaffolds have not been developed yet. There has been no systematic study of the effect of macropore morphology of bioceramic scaffolds on their physico-chemical and biological properties. The aim of this study was to prepare NAGEL scaffolds for bone tissue engineering applications. We applied a modified three-dimensional (3-D) plotting method to prepare highly controllable NAGEL scaffolds and investigated the effect of macropore morphology on the physico-chemical and biological properties. The results showed that the macropore size and morphology of 3-D plotted NAGEL scaffolds could be effectively controlled. Compared with β-tricalcium phosphate (β-TCP) scaffolds NAGEL scaffolds possess a significantly enhanced compressive strength, a higher modulus and better degradability. Nagel scaffolds with a square pore morphology presented a higher compressive strength, a higher modulus and greater weight loss rate than those with triangular and parallelogram pore morphologies. In addition, all of the NAGEL scaffolds with the three macropore morphologies supported the attachment and proliferation of MC3T3 cells. The proliferation of MC3T3 cells on NAGEL scaffolds with triangular and parallelogram structures was higher than that on β-TCP scaffolds with the same pore structure. Cells on all three groups of NAGEL scaffolds revealed higher alkaline phosphatase (ALP) activity compared with cells on β-TCP scaffolds, and among the three NAGEL scaffolds groups those with a parallelogram pore structure showed the highest ALP activity. Furthermore, the angiogenic cell experiments showed that the ionic products from NAGEL scaffolds promoted tube formation, expression of pro-angiogenic factors and their receptors on human umbilical vein endothelial (HUVECs) compared with β-TCP scaffolds, indicating that NAGEL scaffolds possessed improved angiogenesis capacity. Our results suggest that 3-D plotted NAGEL scaffolds are a promising bioactive material for bone tissue engineering by virtue of their highly controllable macropore structure, excellent mechanical strength, degradability and in vitro biological response to osteogenic/angiogenic cells.

Enhanced osteoporotic bone regeneration by strontium-substituted calcium silicate bioactive ceramics

The regeneration capacity of the osteoporotic bones is generally lower than that of the normal bones. Current methods of bone defect treatment for osteoporosis are not always satisfactory. Recent studies have shown that the silicate based biomaterials can stimulate osteogenesis and angiogenesis due to the silicon (Si) ions released from the materials, and enhance bone regeneration in vivo. Other studies showed that strontium (Sr) plays a distinct role on inhibiting bone resorption. Based on the hypothesis that the combination of Si and Sr may have synergetic effects on osteoporotic bone regeneration, the porous Sr-substituted calcium silicate (SrCS) ceramic scaffolds combining the functions of Sr and Si elements were developed with the goals to promote osteoporotic bone defect repair. The effects of the ionic extract from SrCS on osteogenic differentiation of bone marrow mesenchymal stem cells derived from ovariectomized rats (rBMSCs-OVX), angiogenic differentiation of human umbilical vein endothelial cells (HUVECs) were investigated. The in vitro results showed that Sr and Si ions released from SrCS enhanced cell viability, alkaline phosphatase (ALP) activity, and mRNA expression levels of osteoblast-related genes of rBMSCs-OVX and expression of vascular endothelial growth factor (VEGF) without addition of extra osteogenic and angiogenic reagents. The activation in extracellular signal-related kinases (ERK) and p38 signaling pathways were observed in rBMSCs-OVX cultured in the extract of SrCS, and these effects could be blocked by ERK inhibitor PD98059, and P38 inhibitor SB203580, respectively. Furthermore, the ionic extract of SrCS stimulated HUVECs proliferation, differentiation and angiogenesis process. The in vivo experiments revealed that SrCS dramatically stimulated bone regeneration and angiogenesis in a critical sized OVX calvarial defect model, and the enhanced bone regeneration might be attributed to the modulation of osteogenic differentiation of endogenous mesenchymal stem cells (MSCs) and the inhibition of osteoclastogenesis, accompanying with the promotion of the angiogenic activity of endothelial cells (ECs).

Bioactive silicate materials stimulate angiogenesis in fibroblast and endothelial cell co-culture system through paracrine effect

Angiogenesis is critical in tissue engineering, and bioceramic-induced angiogenesis has been reported. However, the role of other types of cells such as fibroblasts in this bioceramic-induced angiogenesis process has not been reported, and is closer to the in vivo situation of tissue regeneration. In this study, the paracrine effect of silicate bioceramic-induced angiogenesis in the presence of fibroblasts was confirmed by investigating the effects of calcium silicate (CS), one of the simplest silicate bioactive ceramics, on angiogenesis in co-cultures of human dermal fibroblasts (HDF) and human umbilical vein endothelial cells (HUVEC). Results showed that CS extracts stimulated the expression of vascular endothelial growth factor (VEGF) from co-cultured HDF and subsequently enhanced the expression of VEGF receptor 2 on co-cultured HUVEC (co-HUVEC). The endothelial nitric oxide synthase and nitric oxide production in co-HUVEC was then increased to finally initiate the proangiogenesis. During this process, the expression of vascular endothelial cadherin from co-HUVEC was up-regulated, and cadherin proteins were concentrated at the cell junctions to facilitate tube formation. Silicon ions are confirmed to play an important role during silicate bioceramic-inducing angiogenesis, and effective silicon ion concentrations (0.7-1.8μgml(-1)) are proposed.

Stimulation of proangiogenesis by calcium silicate bioactive ceramic

Angiogenesis is critical for bone tissue engineering. Stimulating proangiogenesis in an engineered bone construct using bioglass or bioceramic is now attracting much attention. However, the specific ion that plays important roles in the stimulation of proangiogenesis has not yet been elucidated. In this study, calcium silicate (CS), an osteogenic bioceramic containing only Ca and Si ions, significantly stimulated proangiogenesis of human umbilical vein endothelial cells (HUVECs). The determination of the ionic dissolution product indicates that Si ion concentrations of the CS extracts were significantly higher than that of the calcium phosphate ceramic extracts and control medium. However, the concentrations of Ca and P ions of both ceramic extracts and normal medium were at the same level. With the specific Si ion and its effective concentrations, CS extracts stimulated the proliferation of HUVECs, up-regulated the expression of vascular endothelial growth factor, basic fibroblast growth factor and their receptors, and finally stimulated the proangiogenesis. As the Si ion played an important role in osteogenesis stimulated by Si-containing bioceramics, confirmation of the Si ion's specific role and its effective ion concentrations in CS-induced angiogenesis may be extremely useful in designing osteogenic and angiogenic bioactive materials for bone tissue engineering.

Bone marrow-derived mesenchymal stem cells increase dopamine synthesis in the injured striatum

Previous studies showed that tyrosine hydroxylase or neurturin gene-modified cells transplanted into rats with Parkinson’s disease significantly improved behavior and increased striatal dopamine content. In the present study, we transplanted tyrosine hydroxylase and neurturin gene-modified bone marrow-derived mesenchymal stem cells into the damaged striatum of Parkinson’s disease model rats. Several weeks after cell transplantation, in addition to an improvement of motor function, tyrosine hydroxylase and neurturin proteins were up-regulated in the injured striatum, and importantly, levels of dopamine and its metabolite 3,4-dihydroxyphenylacetic acid increased significantly. Furthermore, the density of the D2 dopamine receptor in the postsynaptic membranes of dopaminergic neurons was decreased. These results indicate that transplantation of tyrosine hydroxylase and neurturin gene-modified bone marrow-derived mesenchymal stem cells increases dopamine synthesis and significantly improves the behavior of rats with Parkinson’s disease.

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.

Whatever their differentiation status, human progenitor derived - or mature - endothelial cells induce osteoblastic differentiation of bone marrow stromal cells

Association of the bone-forming osteoblasts (OBs) and vascular endothelial cells (ECs) into a biomaterial composite provides a live bone graft substitute that can repair the bone defect when implanted. An intimate functional relationship exists between these cell types. This communication is crucial to the coordinated cell behaviour necessary for bone development and remodelling. Previous studies have shown that direct co-culture of primary human osteoprogenitors (HOPs) with primary human umbilical vein endothelial cells (HUVECs) stimulates HOPs differentiation and induces tubular-like networks. The present work aims to test the use of human bone marrow stromal cells (HBMSCs) co-cultured with human endothelial progenitor cells in order to assess whether progenitor-derived ECs (PDECs) could support osteoblastic differentiation as mature ECs do. Indeed, data generated from the literature by different laboratories considering these co-culture systems appear difficult to compare. Monocultures of HUVECs, HOPs, HBMSCs (in a non-orientated lineage), PDECs (from cord blood) were used as controls and four combinations of co-cultures were undertaken: HBMSCs-PDECs, HBMSCs-HUVECs, HOPs-PDECs, HOPs-HUVECs with ECs (mature or progenitor) for 6 h to 7 days. At the end of the chosen co-culture time, intracellular alkaline phosphatase (ALP) activity was detected in HOPs and HBMSCs and quantified in cell extracts. Quantitative real-time polymerase chain reaction (qPCR) of ALP was performed over time and vascular endothelial growth factor (VEGF) was measured. After 21 days, calcium deposition was observed, comparing mono- and co-cultures. We confirm that ECs induce osteoblastic differentiation of mesenchymal stem cells in vitro. Moreover, HUVECs can be replaced by PDECs, the latter being of great interest in tissue engineering.

Reciprocal induction of human dermal microvascular endothelial cells and human mesenchymal stem cells: time-dependent profile in a co-culture system

OBJECTIVES

Angiogenesis is closely associated with osteogenesis where reciprocal interactions between endothelial and osteoblast cells play an important role in bone regeneration. For these reasons, the aim of this work was to develop a co-culture system to study in detail any time-dependent interactions between human mesenchymal stem cells (HMSC) and human dermal microvascular endothelial cells (HDMEC), co-cultured in a 2D system, for 35 days.

MATERIALS AND METHODS

HMSC and HDMEC were co-cultured at a ratio of 1:4, respectively. Single-cell cultures were used as controls. Cell viability/proliferation was assessed using MTT, DNA quantification and calcein-AM assays. Cell morphology was monitored using confocal microscopy, and real time PCR was performed. Alkaline phosphatase activity and histochemical staining were evaluated. Matrix mineralization assays were also performed.

RESULTS

Cells were able to grow in characteristic patterns maintaining their viability and phenotype expression throughout culture time, compared to HMSC and HDMEC monocultures. HMSC differentiation seemed to be enhanced in the co-culture conditions, since it was observed an over expression of osteogenesis-related genes, and of ALP activity. Furthermore, presence of calcium phosphate deposits was also confirmed.

CONCLUSIONS

This work reports in detail the interactions between HMSC and HDMEC in a long-term co-culture 2D system. Endothelial and mesenchymal stem cells cultured in the present co-culture conditions ensured proliferation and phenotype differentiation of cell types, osteogenesis stimulation and over-expression of angiogenesis-related genes, in the same culture system. It is believed that the present work can lead to significant developments for bone tissue regeneration and cell biology studies.