Endothelial cell modulation of bone marrow stromal cell osteogenic potential

Enhanced osteo-angiogenic coupling by a bioactive cell-free fat extract (CEFFE) delivered through electrospun fibers

Regeneration of functional bone tissue relies heavily on achieving adequate vascularization in engineered bone constructs following implantation. This process requires the close integration of osteogenesis and angiogenesis. Cell-free fat extract (CEFFE or FE), a recently emerging acellular fat extract containing abundant growth factors, holds significant potential for regulating osteo-angiogenic coupling and promoting regeneration of vascularized bone tissue. However, its specific role in modulating the coupling between angiogenesis and osteogenesis remains unclear. Our previous research demonstrated that FE-decorated electrospun fibers of polycaprolactone/gelatin (named FE-PDA@PCL/GT) exhibited pro-vasculogenic capabilities both in vitro and in vivo (D. Li, Q. Li, T. Xu, X. Guo, H. Tang, W. Wang, W. Zhang and Y. Zhang, Pro-vasculogenic fibers by PDA-mediated surface functionalization using cell-free fat extract (CEFFE), Biomacromolecules 2024, 25, 1550-1562). Herein, we firstly demonstrated that the FE-PDA@PCL/GT fibers also significantly stimulated osteogenesis in a mouse calvaria osteoblast-like cell line MC3T3-E1 cells, as evidenced by the increased production of alkaline phosphatase (ALP), mineral deposits, and collagen I, as well as the upregulated expression of osteogenic marker genes in the osteoblasts. Using a transwell co-culture system, we further demonstrated that the release of FE from the FE-PDA@PCL/GT fibers not only promoted osteogenesis and angiogenesis but also markedly enhanced the paracrine functions and reciprocal communications between endothelial cells and osteoblasts. This dynamic interaction played a key role in the observed enhancement of osteo-angiogenic coupling. With the confirmed pro-osteogenic and pro-angiogenic properties of FE-PDA@PCL/GT, it is envisaged that these newly engineered bioactive fibers can be used to develop highly biomimicking bone constructs. These constructs are designed to promote native-like cell-scaffold and cell-cell interactions, which are essential for the effective regeneration of defected bone tissue with adequate vasculature.

Bone Tissue Engineering: From Biomaterials to Clinical Trials

Bone tissue engineering is a promising field that aims to rebuild the bone tissue using biomaterials, cells, and signaling molecules. Materials like natural and synthetic polymers, inorganic materials, and composite materials are used to create scaffolds that mimic the hierarchical microstructure of bone. Stem cells, particularly mesenchymal stem cells (MSCs), play a crucial role in bone tissue engineering by promoting tissue regeneration and modulating the immune response. Growth factors like bone morphogenetic proteins (BMPs), vascular endothelial growth factor (VEGF), and platelet-derived growth factor (PDGF) are utilized to accelerate bone regeneration. Clinical applications include treating nonunion and mal-union fractures, osteonecrosis, orthopedic surgery, dental applications, and spinal cord injuries. Recent advances in the field include nanotechnology, 3D printing, bioprinting techniques, gene editing technologies, and microfluidic devices for drug testing. However, challenges remain, such as standardization of protocols, large-scale biomaterial production, personalized medicine approaches, cost-effectiveness, and regulatory issues. Current clinical trials are investigating the safety and efficacy of various bone tissue engineering approaches, with the potential to modernize patient care by providing more adequate treatments for bone defects and injuries.

Endothelial cell-derived exosomes trigger a positive feedback loop in osteogenesis-angiogenesis coupling via up-regulating zinc finger and BTB domain containing 16 in bone marrow mesenchymal stem cell

The close spatial and temporal connection between osteogenesis and angiogenesis around type H vasculature is referred as "osteogenesis-angiogenesis coupling", which is one of the basic mechanisms of osteogenesis. Endothelial cells (ECs), bone marrow mesenchymal stem cells (BMSCs), and their specific lineage constitute important cluster that participate in the regulation of osteogenesis and angiogenesis in bone microenvironment. However, the regulatory mechanism of osteogenesis-angiogenesis coupling under the condition of bone healing has not been unveiled. In this study, we demonstrated that the exosome derived from ECs (EC-exo) is an initiator of type H blood vessels formation, and EC-exo acts as a mediator in orchestrating osteogenesis-angiogenesis coupling by enhancing BMSC osteogenic differentiation and EC angiogenesis both in monolayer and stereoscopic co-culture system of primary human cells. The transcriptome array indicated that zinc finger and BTB domain containing 16 (ZBTB16) is a key gene in EC-exo-mediated osteogenesis, and ZBTB16 is indispensable in EC-exo-initiated osteogenesis-angiogenesis coupling. Mechanistically, EC-exo up-regulated the expression of ZBTB16 in BMSCs, thereby promoting osteoprogenitor phenotype transformation; the osteoprogenitors further promote ECs which constitute type H vessel (H-ECs) generation by activating HIF-1α pathway; and the H-ECs conversely promotes osteogenic differentiation of BMSCs. The crosstalk between BMSCs and ECs triggered by EC-exo constitutes a positive feedback loop that enhances osteogenesis-angiogenesis coupling. This study demonstrates that EC-exo can become an effective therapeutic tool to promote bone regeneration and repair.

Efforts to promote osteogenesis-angiogenesis coupling for bone tissue engineering

Repair of bone defects exceeding a critical size has been always a big challenge in clinical practice. Tissue engineering has exhibited great potential to effectively repair the defects with less adverse effect than traditional bone grafts, during which how to induce vascularized bone formation has been recognized as a critical issue. Therefore, recently many studies have been launched to attempt to promote osteogenesis-angiogenesis coupling. This review summarized comprehensively and explored in depth current efforts to ameliorate the coupling of osteogenesis and angiogenesis from four aspects, namely the optimization of scaffold components, modification of scaffold structures, loading strategies for bioactive substances, and employment tricks for appropriate cells. Especially, the advantages and the possible reasons for every strategy, as well as the challenges, were elaborated. Furthermore, some promising research directions were proposed based on an in-depth analysis of the current research. This paper will hopefully spark new ideas and approaches for more efficiently boosting new vascularized bone formations.

The Role of Vasculature and Angiogenic Strategies in Bone Regeneration

Bone regeneration is a complex process that involves various growth factors, cell types, and extracellular matrix components. A crucial aspect of this process is the formation of a vascular network, which provides essential nutrients and oxygen and promotes osteogenesis by interacting with bone tissue. This review provides a comprehensive discussion of the critical role of vasculature in bone regeneration and the applications of angiogenic strategies, from conventional to cutting-edge methodologies. Recent research has shifted towards innovative bone tissue engineering strategies that integrate vascularized bone complexes, recognizing the significant role of vasculature in bone regeneration. The article begins by examining the role of angiogenesis in bone regeneration. It then introduces various in vitro and in vivo applications that have achieved accelerated bone regeneration through angiogenesis to highlight recent advances in bone tissue engineering. This review also identifies remaining challenges and outlines future directions for research in vascularized bone regeneration.

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.

Regulation of endothelial cells on the osteogenic ability of bone marrow mesenchymal stem cells in peri-implantitis

OBJECTIVES

The relationship between bone resorption and angiogenesis in peri-implantitis remains to be studied. We constructed a Beagle dog model of peri-implantitis, and extracted bone marrow mesenchymal stem cells (BMSCs) and endothelial cells (ECs) for culture. The osteogenic ability of BMSCs in the presence of ECs was investigated through an in vitro osteogenic induction model, and its mechanism was initially explored.

SUBJECTS AND METHODS

The peri-implantitis model was verified by ligation, bone loss was observed by micro-CT, and cytokines were detected by ELISA. The isolated BMSCs and ECs were cultured to detect the expression of angiogenesis, osteogenesis-related proteins, and NF-κB signaling pathway-related proteins.

RESULTS

8 weeks after surgery, the peri-implant gums were swollen, and micro-CT showed bone resorption. Compared with the control group, IL-1β, TNF-α, ANGII and VEGF were markedly increased in the peri-implantitis group. In vitro studies found that the osteogenic differentiation ability of BMSCs co-cultured with IECs was decreased, and the expression of NF-κB signaling pathway-related cytokines was increased.

CONCLUSION

Endothelial cells inhibit the osteogenic differentiation of bone marrow mesenchymal stem cells through NF-κB signaling in the environment of peri-implantitis, which may become a new target for the treatment of peri-implantitis.

Towards a New Concept of Regenerative Endodontics Based on Mesenchymal Stem Cell-Derived Secretomes Products

The teeth, made up of hard and soft tissues, represent complex functioning structures of the oral cavity, which are frequently affected by processes that cause structural damage that can lead to their loss. Currently, replacement therapy such as endodontics or implants, restore structural defects but do not perform any biological function, such as restoring blood and nerve supplies. In the search for alternatives to regenerate the dental pulp, two alternative regenerative endodontic procedures (REP) have been proposed: (I) cell-free REP (based in revascularization and homing induction to remaining dental pulp stem cells (DPSC) and even stem cells from apical papilla (SCAP) and (II) cell-based REP (with exogenous cell transplantation). Regarding the last topic, we show several limitations with these procedures and therefore, we propose a novel regenerative approach in order to revitalize the pulp and thus restore homeostatic functions to the dentin-pulp complex. Due to their multifactorial biological effects, the use of mesenchymal stem cells (MSC)-derived secretome from non-dental sources could be considered as inducers of DPSC and SCAP to completely regenerate the dental pulp. In partial pulp damage, appropriate stimulate DPSC by MSC-derived secretome could contribute to formation and also to restore the vasculature and nerves of the dental pulp.

Bioengineered Hierarchical Bonelike Compartmentalized Microconstructs Using Nanogrooved Microdiscs

Fabrication of vascularized large-scale constructs for regenerative medicine remains elusive since most strategies rely solely on cell self-organization or overly control cell positioning, failing to address nutrient diffusion limitations. We propose a modular and hierarchical tissue-engineering strategy to produce bonelike tissues carrying signals to promote prevascularization. In these 3D systems, disc-shaped microcarriers featuring nanogrooved topographical cues guide cell behavior by harnessing mechanotransduction mechanisms. A sequential seeding strategy of adipose-derived stromal cells and endothelial cells is implemented within compartmentalized, liquefied-core macrocapsules in a self-organizing and dynamic system. Importantly, our system autonomously promotes osteogenesis and construct's mineralization while promoting a favorable environment for prevascular-like endothelial organization. Given its modular and self-organizing nature, our strategy may be applied for the fabrication of larger constructs with a highly controlled starting point to be used for local regeneration upon implantation or as drug-screening platforms.

Gelatin methacryloyl-alginate core-shell microcapsules as efficient delivery platforms for prevascularized microtissues in endodontic regeneration

Combined injectable cell-laden microspheres and angiogenesis approaches are promising for functional vascularized endodontic regeneration. However, advanced microsphere designs and production techniques that benefit practical applications are rarely developed. Herein, gelatin methacryloyl (GelMA)-alginate core-shell microcapsules were fabricated to co-encapsulate human dental pulp stem cells (hDPSCs) and human umbilical vein endothelial cells (HUVECs) based on a coaxial electrostatic microdroplet technique. This technique enables high-throughput production, convenient collection, and minimal material waste. The average diameter of core-shell microcapsules was ∼359 µm, and that of GelMA cores was ∼278 µm. There were higher proliferation rates for hDPSCs and HUVECs co-encapsulated in the GelMA cores than for hDPSCs or HUVECs monoculture group. HUVECs assembled to form 3D capillary-like networks in co-culture microcapsules. Moreover, HUVECs promoted the osteo/odontogenic differentiation of hDPSCs in microcapsules. After 14 days of cultivation, prevascularized microtissues formed in microcapsules that contained abundant deposited extracellular matrix (ECM); no microcapsule aggregation occurred. In vivo studies confirmed that better microvessel formation and pulp-like tissue regeneration occurred in the co-culture group than in hDPSCs group. Thus, an effective platform for prevascularization microtissue preparation was proposed and showed great promise in endodontic regeneration and tissue engineering applications. STATEMENT OF SIGNIFICANCE: Cell-laden microspheres combined with the proangiogenesis approach are promising in endodontic regeneration. We proposed GelMA-alginate core-shell microcapsules generated via the coaxial electrostatic microdroplet (CEM) method, which utilizes a double-lumen needle to allow for core-shell structures to form. The microcapsules were used for co-culturing hDPSCs and HUVECs to harvest large amounts of prevascularized microtissues, which further showed improved vascularization and pulp-like tissue regeneration in vivo. This CEM method and the microcapsule system have advantages of high-throughput generation, convenient collection, and avoid aggregation during long-term culturing. We proposed a high-effective platform for mass production of prevascularized microtissues, which exhibit great promise in the clinical transformation of endodontic regeneration and other applications in regenerative medicine.

Concentrated Growth Factors Promote hBMSCs Osteogenic Differentiation in a Co-Culture System With HUVECs

Osteogenesis is a complex physiologic process that occurs during bone regeneration. This process requires several growth factors that act on bone marrow-derived mesenchymal stem cells (BMSCs). Concentrated growth factor (CGF) is a new-generation platelet-rich derivative that is an appealing autologous material for application in tissue repair and bone regenerative medicine because it contains a variety of fibrin and growth factors. In this study, the effects of CGF on the proliferation and osteogenic differentiation of hBMSCs and human umbilical vein endothelial cells (HUVECs) were explored with in vitro cell co-culture experiments. HBMSCs and HUVECs were directly co-cultured at the ratio of 1:2 under different concentrations (0, 2, 5, 10, 20%) of CGF for 7 days. Alkaline phosphatase (ALP) staining and quantitative reverse transcription polymerase chain reaction were used to detect the effects of CGF on the expression of osteogenic genes (ALP, osteocalcin [OCN], type I collagen [COL-1], Runt-related transcription factor 2 [RUNX2]) and connexin 43 (CX43). RNA sequencing was used to explore potential regulated genes and signaling pathways that affect the osteogenesis of co-cultured hBMSCs exposed to CGF. The results showed higher expressions of ALP, COL-1, RUNX2, OCN, and CX43 in the direct co-culture group containing 10% CGF compared to the direct co-culture group without CGF and the indirect co-culture group. In summary, 10% CGF can significantly promote osteogenesis in hBMSCs directly co-cultured with HUVECs. Intercellular communication between the direct co-culture of hBMSCs and HUVECs through CX43 may be one of the main regulatory mechanisms.

Cell encapsulation in alginate-based microgels using droplet microfluidics; a review on gelation methods and applications

Cell encapsulation within the microspheres using a semi-permeable polymer allows the two-way transfer of molecules such as oxygen, nutrients, and growth factors. The main advantages of cell encapsulation technology include controlling the problems involved in transplanting rejection in tissue engineering applications and reducing the long-term need for immunosuppressive drugs following organ transplantation to eliminate the side effects. Cell-laden microgels can also be used in 3D cell cultures, wound healing, and cancerous clusters for drug testing. Since cell encapsulation is used for different purposes, several techniques have been developed to encapsulate cells. Droplet-based microfluidics is one of the most valuable techniques in cell encapsulating. This study aimed to review the geometries and the mechanisms proposed in microfluidic systems to precisely control cell-laden microgels production with different biopolymers. We also focused on alginate gelation techniques due to their essential role in cell encapsulation applications. Finally, some applications of these microgels and researches will be explored.

Tissue Engineered Neurovascularization Strategies for Craniofacial Tissue Regeneration

Craniofacial tissue injuries, diseases, and defects, including those within bone, dental, and periodontal tissues and salivary glands, impact an estimated 1 billion patients globally. Craniofacial tissue dysfunction significantly reduces quality of life, and successful repair of damaged tissues remains a significant challenge. Blood vessels and nerves are colocalized within craniofacial tissues and act synergistically during tissue regeneration. Therefore, the success of craniofacial regenerative approaches is predicated on successful recruitment, regeneration, or integration of both vascularization and innervation. Tissue engineering strategies have been widely used to encourage vascularization and, more recently, to improve innervation through host tissue recruitment or prevascularization/innervation of engineered tissues. However, current scaffold designs and cell or growth factor delivery approaches often fail to synergistically coordinate both vascularization and innervation to orchestrate successful tissue regeneration. Additionally, tissue engineering approaches are typically investigated separately for vascularization and innervation. Since both tissues act in concert to improve craniofacial tissue regeneration outcomes, a revised approach for development of engineered materials is required. This review aims to provide an overview of neurovascularization in craniofacial tissues and strategies to target either process thus far. Finally, key design principles are described for engineering approaches that will support both vascularization and innervation for successful craniofacial tissue regeneration.

Bone Regeneration and Angiogenesis by Co-transplantation of Angiotensin II-Pretreated Mesenchymal Stem Cells and Endothelial Cells in Early Steroid-Induced Osteonecrosis of the Femoral Head

Mesenchymal stem cells (MSCs) have been shown to exert a positive impact on osteonecrosis of the femoral head (ONFH) in preclinical experiments and clinical trials. After the femoral head suffers avascular necrosis, the transplanted MSCs undergo a great deal of stress-induced apoptosis and senescence in this microenvironment. So, survival and differentiation of MSCs in osteonecrotic areas are especially important in ONFH. Although MSCs and endothelial cells (ECs) co-culture enhancing proliferation and osteogenic differentiation of MSCs and form more mature vasculature in vivo, it remains unknown whether the co-culture cells are able to repair ONFH. In this study, we explored the roles and mechanisms of co-transplantation of angiotensin II (Ang II)-MSCs and ECs in repairing early ONFH. In vitro, when MSCs and ECs were co-cultured in a ratio of 5:1, both types of cells managed to proliferate and induce both osteogenesis and angiogenesis. Then, we established a rabbit model of steroid-induced ONFH and co-transplantation of Ang II-MSCs and ECs through the tunnel of core decompression. Four weeks later, histological and Western blot analyses revealed that ONFH treated with Ang II-MSCs and ECs may promote ossification and revascularization by increasing the expression of collagen type I, runt-related transcription factor 2, osteocalcin, and vascular endothelial growth factor in the femoral head. Our data suggest that co-transplantation of Ang II-MSCs and ECs was able to rescue the early steroid-induced ONFH via promoting osteogenesis and angiogenesis, which may be regarded as a novel therapy for the treatment of ONFH in a clinical setting.

Gene expression profiling on effect of aspirin on osteogenic differentiation of periodontal ligament stem cells

Periodontal ligament (PDL) contains a unique population of mesenchymal stem cells (MSCs), also known as PDL stem cells (PDLSCs). The regenerative properties of PDLSCs hold great potential for its use in stem cells based therapy, particularly for periodontal or bone regeneration. The present study investigated the global gene expression profile in PDLSCs during osteogenic differentiation. MSCs from PDL were isolated from normal permanent human teeth (n = 3). Microarray analysis was used to study the effects of ASA (200, 500, and 1000 μM) on the gene expression profiles in PDLSCs during osteogenic differentiation. Microarray study revealed that ASA was able to modulate PDLSCs gene expression profile. At 200 µM, 315 genes were dysregulated genes (DE), involving 151 upregulated and 164 downregulated genes. At 500 µM, 794 genes were DE, involving of 364 upregulated and 430 downregulated genes. At 1000 µM, the number of DE genes increased to 2035, of which 735 were upregulated and 1300 were downregulated. Bioinformatics analyses of the gene expression data revealed that the majority of DE genes (for 500 and 1000 µM ASA treatment) are involved in osteogenic differentiation. The gene network analysis was carried out using Ingenuity Pathway Analysis (IPA) software, and this revealed that the number of gene groups involved in cell adhesion and extracellular matrix components were increased. This study indicated that ASA could enhance PDLSCs functions and provide evidence for the potential use of ASA with PDLSCs for regenerative dentistry applications, particularly in the areas of periodontal health and regeneration. Periodontal ligament stem cells (PDLSCs) Aspirin (ASA) Microarray Osteogenic.

Periosteal Tissue Engineering: Current Developments and Perspectives

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

Cross-Talk Between Mesenchymal Stromal Cells (MSCs) and Endothelial Progenitor Cells (EPCs) in Bone Regeneration

Bone regeneration is a complex, well-orchestrated process based on the interactions between osteogenesis and angiogenesis, observed in both physiological and pathological situations. However, specific conditions (e.g., bone regeneration in large quantity, immunocompromised regenerative process) require additional support. Tissue engineering offers novel strategies. Bone regeneration requires a cell source, a matrix, growth factors and mechanical stimulation. Regenerative cells, endowed with proliferation and differentiation capacities, aim to recover, maintain, and improve bone functions. Vascularization is mandatory for bone formation, skeletal development, and different osseointegration processes. The latter delivers nutrients, growth factors, oxygen, minerals, etc. The development of mesenchymal stromal cells (MSCs) and endothelial progenitor cells (EPCs) cocultures has shown synergy between the two cell populations. The phenomena of osteogenesis and angiogenesis are intimately intertwined. Thus, cells of the endothelial line indirectly foster osteogenesis, and conversely, MSCs promote angiogenesis through different interaction mechanisms. In addition, various studies have highlighted the importance of the microenvironment via the release of extracellular vesicles (EVs). These EVs stimulate bone regeneration and angiogenesis. In this review, we describe (1) the phenomenon of bone regeneration by different sources of MSCs. We assess (2) the input of EPCs in coculture in bone regeneration and describe their contribution to the osteogenic potential of MSCs. We discuss (3) the interaction mechanisms between MSCs and EPCs in the context of osteogenesis: direct or indirect contact, production of growth factors, and the importance of the microenvironment via the release of EVs.

Mesenchymal stem cells in the treatment of osteonecrosis of the jaw

Medication-related osteonecrosis of the jaw (MRONJ) has recently associated to the increase in antiresorptive and anti-angiogenic drugs prescriptions in the treatment of oncologic and osteoporotic patients. The physiopathogenesis of MRONJ remains unclear and available treatments are unsatisfactory. Newer pharmacological treatments have shown good results, but are not curative and could have major side effects. At the same time as pharmacological treatments, mesenchymal stem cells (MSCs) have emerged as a promising therapeutic modality for tissue regeneration and repair. MSCs are multipotential non-hematopoietic progenitor cells capable to differentiating into multiple lineages of the mesenchyme. Bone marrow MSCs can differentiate into osteogenic cells and display immunological properties and secrete paracrine anti-inflammatory factors in damaged tissues. The immunomodulatory, reparative, and anti-inflammatory properties of bone marrow MSCs have been tested in a variety of animal models of MRONJ and applied in specific clinical settings. The aim of this review is to discuss critically the immunogenicity and immunomodulatory properties of MSCs, both in vitro and in vivo, the possible underlying mechanisms of their effects, and their potential clinical use as modulators of immune responses in MRONJ, and to identify clinical safety and recommendations for future research.

Potential Osteoinductive Effects of Hydroxyapatite Nanoparticles on Mesenchymal Stem Cells by Endothelial Cell Interaction

Nano-hydroxyapatite (nano-HA) has attracted substantial attention in the field of regenerative medicine. Endothelial cell (EC)-mesenchymal stem cell (MSC) interactions are necessary for bone reconstruction, but the manner in which nano-HA interacts in this process remains unknown. Herein, we investigated the cytotoxicity and osteoinductive effects of HA nanoparticles (HANPs) on MSCs using an indirect co-culture model mediated by ECs and highlighted the underlying mechanisms. It was found that at a subcytotoxic dose, HANPs increased the viability and expression of osteoblast genes, as well as mineralized nodules and alkaline phosphatase production of MSCs. These phenomena relied on HIF-1α secreted by ECs, which triggered the ERK1/2 signaling cascade. In addition, a two-stage cell-lineage mathematical model was established to quantitatively analyze the impact of HIF-1α on the osteogenic differentiation of MSCs. It demonstrated that HIF-1α exerted a dose-dependent stimulatory effect on the osteogenic differentiation rate of MSCs up to 1500 pg/mL, which was in agreement with the above results. Our data implied that cooperative interactions between HANPs, ECs, and MSCs likely serve to stimulate bone regeneration. Furthermore, the two-stage cell-lineage model is helpful in vitro system for assessing the potential influence of effector molecules in bone tissue engineering.

Endothelial progenitor cells promote osteogenic differentiation in co-cultured with mesenchymal stem cells via the MAPK-dependent pathway

BACKGROUND

The role of bone tissue engineering is to regenerate tissue using biomaterials and stem cell-based approaches. Combination of two or more cell types is one of the strategies to promote bone formation. Endothelial progenitor cells (EPCs) may enhance the osteogenic properties of mesenchymal stem cells (MSCs) and promote bone healing; this study aimed to investigate the possible mechanisms of EPCs on promoting osteogenic differentiation of MSCs.

METHODS

MSCs and EPCs were isolated and co-cultured in Transwell chambers, the effects of EPCs on the regulation of MSC biological properties were investigated. Real-time PCR array, and western blotting were performed to explore possible signaling pathways involved in osteogenesis. The expression of osteogenesis markers and calcium nodule formation was quantified by qRT-PCR, western blotting, and Alizarin Red staining.

RESULTS

Results showed that MSCs exhibited greater alkaline phosphatase (ALP) activity and increased calcium mineral deposition significantly when co-cultured with EPCs. The mitogen-activated protein kinase (MAPK) signaling pathway was involved in this process. p38 gene expression and p38 protein phosphorylation levels showed significant upregulation in co-cultured MSCs. Silencing expression of p38 in co-cultured MSCs reduced osteogenic gene expression, protein synthesis, ALP activity, and calcium nodule formation.

CONCLUSIONS

These data suggest paracrine signaling from EPCs influences the biological function and promotes MSCs osteogenic differentiation. Activation of the p38MAPK pathway may be the key to enhancing MSCs osteogenic differentiation via indirect interactions with EPCs.

Aspiration-assisted bioprinting of co-cultured osteogenic spheroids for bone tissue engineering

Conventional top-down approaches in tissue engineering involving cell seeding on scaffolds have been widely used in bone engineering applications. However, scaffold-based bone tissue constructs have had limited clinical translation due to constrains in supporting scaffolds, minimal flexibility in tuning scaffold degradation, and low achievable cell seeding density as compared with native bone tissue. Here, we demonstrate a pragmatic and scalable bottom-up method, inspired from embryonic developmental biology, to build three-dimensional (3D) scaffold-free constructs using spheroids as building blocks. Human umbilical vein endothelial cells (HUVECs) were introduced to human mesenchymal stem cells (hMSCs) (hMSC/HUVEC) and spheroids were fabricated by an aggregate culture system. Bone tissue was generated by induction of osteogenic differentiation in hMSC/HUVEC spheroids for 10 days, with enhanced osteogenic differentiation and cell viability in the core of the spheroids compared to hMSC-only spheroids. Aspiration-assisted bioprinting (AAB) is a new bioprinting technique which allows precise positioning of spheroids (11% with respect to the spheroid diameter) by employing aspiration to lift individual spheroids and bioprint them onto a hydrogel. AAB facilitated bioprinting of scaffold-free bone tissue constructs using the pre-differentiated hMSC/HUVEC spheroids. These constructs demonstrated negligible changes in their shape for two days after bioprinting owing to the reduced proliferative potential of differentiated stem cells. Bioprinted bone tissues showed interconnectivity with actin-filament formation and high expression of osteogenic and endothelial-specific gene factors. This study thus presents a viable approach for 3D bioprinting of complex-shaped geometries using spheroids as building blocks, which can be used for various applications including but not limited to, tissue engineering, organ-on-a-chip and microfluidic devices, drug screening and, disease modeling.

3D co-culture model of endothelial colony-forming cells (ECFCs) reverses late passage adipose-derived stem cell senescence for wound healing

Background

Extensive passage of adipose-derived stem cells (ASCs) in vitro leads to loss of function. Endothelial colony-forming cells (ECFCs) can be isolated from adult peripheral blood. A 3D co-culture system may rescue in vitro ASC senescence.

Methods

A 3D co-culture model was successfully established using hyaluronic acid (HA) gel and a 10:1 ratio of late-passage ASCs and ECFCs. Cell density and culture conditions were optimized. Stem cell phenotype was characterized by flow cytometry. ELISA was used to measure the trophic effect of angiogenic growth factors and compare the effects of these factors between the 3-D co-culture and single-cell culture. Therapeutic potential of ASC/ECFC 3-D co-cultures was evaluated in a mouse chronic injury model.

Results

Following incubation in a HA substrate 3D co-culture system, ASC morphology, phenotype, secretory profile, and differentiation capacity were restored. The ASC/ECFC co-culture increased the secretion of cytokines, such as hepatocyte growth factor, compared with single-cell 3D culture or monolayer culture. Mice radiation-ulcer wounds treated with ASC/ECFC 3-D co-cultures (spheroids) showed epithelialization and improved healing compared with wounds treated with ASCs or ECFCs alone. Further, transplanted ASC/ECFC spheroids exhibited superior angiogenic potential due to the ability of the ASCs to transdifferentiate into pericytes.

Conclusion

3D co-culture of ECFCs and ASCs in vitro restored native ASC properties by reversing cellular senescence and loss of trophic function. Transplant of ASC/ECFC 3D spheroids in vivo demonstrated pro-angiogenic capacity with improved therapeutic potential.

Optimization of culture duration of bone marrow cells before transplantation with a β-tricalcium phosphate/recombinant collagen peptide hybrid scaffold

INTRODUCTION

Currently, various kinds of materials are used for the treatment of bone defects. In general, these materials have a problem of formativeness. The three -dimensional (3D) printing technique has been introduced to fabricate artificial bone with arbitrary shapes, but poor bone replacement is still problematic.Our group has created a β⁻tricalcium phosphate (β⁻TCP) scaffold by applying 3D printing technology. This scaffold has an arbitrary shape and an internal structure suitable for cell loading, growth, and colonization. The scaffold was coated with a recombinant collagen peptide (RCP) to promote bone replacement.As indicated by several studies, cells loaded to scaffolds promote bone regeneration, especially when they are induced osteoblastic differentiation before transplantation. In this study, culture duration for bone marrow cells was optimized before being loaded to this new scaffold material.

METHOD

Bone marrow cells isolated from C57BL/6J mice were subjected to osteogenic culture for 4, 7, and 14 days. The differentiation status of the cells was examined by alkaline phosphatase staining, alizarin red staining, and real-time RT-PCR for differentiation markers. In addition, the flow of changes in the abundance of endothelial cells and monocytes was analyzed by flow cytometry according to the culture period of bone marrow cells.Next, cells at days 4, 7, and 14 of culture were placed on a β-TCP/RCP scaffold and implanted subcutaneously into the back of C57BL/6J mice. Grafts were harvested and evaluated histologically 8 weeks later. Finally, Cells cultured for 7 days were also transplanted subperiosteally in the skull of the mouse with scaffolds.

RESULT

Alkaline phosphatase staining was most prominent at 7 days, and alizarin red staining was positive at 14 days. Real-time RT-PCR revealed that Runx2 and Alp peaked at 7 days, while expression of Col1a1 and Bglap was highest at 14 days. Flow cytometry indicated that endothelial cells increased from day 0 to day 7, while monocytes increased continuously from day 0 to day 14. When transplanted into mice, the scaffold with cells cultured for 7 days exhibited the most prominent osteogenesis. The scaffold, which was transplanted subperiosteally in the skull, retained its shape and was replaced with regenerated bone over a large area of the field of view.

CONCLUSION

Osteoblasts before full maturation are most efficient for bone regeneration, and the pre-culture period suitable for cells to be loaded onto a β-TCP/RCP hybrid scaffold is approximately 7 days.This β-TCP/RCP hybrid scaffolds will also be useful for bone augmentation.

Advanced gelatin-based vascularization bioinks for extrusion-based bioprinting of vascularized bone equivalents

Bone tissue is highly vascularized. The crosstalk of vascular and osteogenic cells is not only responsible for the formation of the strongly divergent tissue types but also for their physiological maintenance and repair. Extrusion-based bioprinting presents a promising fabrication method for bone replacement. It allows for the production of large-volume constructs, which can be tailored to individual tissue defect geometries. In this study, we used the all-gelatin-based toolbox of methacryl-modified gelatin (GM), non-modified gelatin (G) and acetylated GM (GMA) to tailor both the properties of the bioink towards improved printability, and the properties of the crosslinked hydrogel towards enhanced support of vascular network formation by simple blending. The vasculogenic behavior of human dermal microvascular endothelial cells (HDMECs) and human adipose-derived stem cells (ASCs) was evaluated in the different hydrogel formulations for 14 days. Co-culture constructs including a vascular component and an osteogenic component (i.e. a bone bioink based on GM, hydroxyapatite and ASCs) were fabricated via extrusion-based bioprinting. Bioprinted co-culture constructs exhibited functional tissue-specific cells whose interplay positively affected the formation and maintenance of vascular-like structures. The setup further enabled the deposition of bone matrix associated proteins like collagen type I, fibronectin and alkaline phosphatase within the 30-day culture.

Osteoinductive Material to Fine-Tune Paracrine Crosstalk of Mesenchymal Stem Cells With Endothelial Cells and Osteoblasts

While stem cell/biomaterial studies provide solid evidences that biomaterial intrinsic cues deeply affect cell fate, current strategies tend to neglect their effects on mesenchymal stem cells (MSCs) secretory activities and resulting cell-crosstalks. The present study aims to investigate the impact of bone-mimetic material (B-MM), with intrinsic osteoinductive property, on MSCs mediator secretions; and to explore underlying effects on cells involved in bone regeneration. Human MSCs were cultured, on B-MM, made from inorganic calcium phosphate supplemented with chitosan and hyaluronic acid biopolymers. Collected MSCs culture media were assessed for mediators release quantification and used further to stimulate endothelial cells (ECs) and alveolar bone derived osteoblasts (OBs). Without osteogenic supplements, MSCs committed into bone lineage forming thus 3D bone-like nodules after 21 days. Despite a weak percentage of cell commitment, our data elucidate new aspects of osteoinductive material effect on MSCs functions through the regulation of the secretion of mediators involved in bone regeneration and subsequently the MSCs/ECs indirect crosstalk with osteogenesis-boosting effect. Using MSCs culture media, we demonstrate a large potential of osteoinductive materials and MSCs in bone regenerative medicine. Such strategies could help to address some insights in cell-free therapies using MSCs derived media.

Extracellular vesicles in bone and tooth: A state-of-art paradigm in skeletal regeneration

Bone and tooth, fundamental parts of the craniofacial skeleton, are anatomically and developmentally interconnected structures. Notably, pathological processes in these tissues underwent together and progressed in multilevels. Extracellular vesicles (EVs) are cell-released small organelles and transfer proteins and genetic information into cells and tissues. Although EVs have been identified in bone and tooth, particularly EVs have been identified in the bone formation and resorption, the concrete roles of EVs in bone and tooth development and diseases remain elusive. As such, we review the recent progress of EVs in bone and tooth to highlight the novel findings of EVs in cellular communication, tissue homeostasis, and interventions. This will enhance our comprehension on the skeletal biology and shed new light on the modulation of skeletal disorders and the potential of genetic treatment.

Tissue Constructs with Human Adipose-Derived Mesenchymal Stem Cells to Treat Bone Defects in Rats

The use of porous scaffolds created by additive manufacturing is considered a viable approach for the regeneration of critical-size bone defects. This paper investigates the xenotransplantation of polycaprolactone (PCL) tissue constructs seeded with differentiated and undifferentiated human adipose-derived mesenchymal stem cells (hADSCs) to treat calvarial critical-sized defect in Wistar rats. PCL scaffolds without cells were also considered. In vitro and in vivo biological evaluations were performed to assess the feasibility of these different approaches. In the case of cell seeded scaffolds, it was possible to observe the presence of hADSCs in the rat tissue contributing directly (osteoblasts) and indirectly (stimulation by paracrine factors) to tissue formation, organization and mineralization. The presence of bone morphogenetic protein-2 (BMP-2) in the rat tissue treated with cell-seeded PCL scaffolds suggests that the paracrine factors of undifferentiated hADSC cells could stimulate BMP-2 production by surrounding cells, leading to osteogenesis. Moreover, BMP-2 acts synergistically with growth factors to induce angiogenesis, leading to higher numbers of blood vessels in the groups containing undifferentiated and differentiated hADSCs.

Isogenic-induced endothelial cells enhance osteogenic differentiation of mesenchymal stem cells on silk fibroin scaffold

Aim: We investigated the role of induced endothelial cells (iECs) in mesenchymal stem cells (MSCs)/iECs co-culture and assessed their osteogenic ability on silk fibroin nanofiber scaffolds. Methods: The osteogenic differentiation was assessed by the ALP assay, calcium assay and gene expression studies. Results: The osteogenic differentiation of the iECs co-cultures was found to be higher than the MSCs group and proximal to endothelial cells (ECs) co-cultures. Furthermore, the usage of isogenic iECs for co-culture increased the osteogenic and endothelial gene expression. Conclusion: These findings suggest that iECs mimic endothelial cells when co-cultured with MSCs and that one MSCs source can be used to give rise to both MSCs and iECs. The isogenic MSCs/iECs co-culture provides a new option for bone tissue engineering applications.

Boosting mesenchymal stem cells regenerative activities on biopolymers-calcium phosphate functionalized collagen membrane

The regeneration of bone-soft tissue interface, using functional membranes, remains challenging and can be promoted by improving mesenchymal stem cells (MSCs) paracrine function. Herein, a collagen membrane, used as guided bone regeneration membrane, was functionalized by calcium phosphate, chitosan and hyaluronic acid hybrid coating by simultaneous spray of interacting species process. Composed of brushite, octacalcium phosphate and hydroxyapatite, the hybrid coating increased the membrane stiffness by 50%. After 7 days of MSCs culture on the hybrid coated polymeric membrane, biological studies were marked by a lack of osteoblastic commitment. However, MSCs showed an enhanced proliferation along with the secretion of cytokines and growth factors that could block bone resorption and favour endothelial cell recruitment without exacerbating polynuclear neutrophils infiltration. These data shed light on the great potential of inorganic/organic coated collagen membranes as an alternative bioactive factor-like platform to improve MSCs regenerative capacity, in particular to support bone tissue vascularization and to modulate inflammatory infiltrates.

Bioceramic akermanite enhanced vascularization and osteogenic differentiation of human induced pluripotent stem cells in 3D scaffolds in vitro and vivo

A growing number of studies suggest that the modulation of cell differentiation by biomaterials is critical for tissue engineering. In previous work, we demonstrated that human induced pluripotent stem cells (iPSCs) are remarkably promising seed cells for bone tissue engineering. In addition, we found that the ionic products of akermanite (Aker) are potential inducers of osteogenic differentiation of iPSCs. Furthermore, composite scaffolds containing polymer and bioceramics have more interesting properties compared to pure bioceramic scaffolds for bone tissue engineering. The characteristic of model biomaterials in bone tissue engineering is their ability to control the osteogenic differentiation of stem cells and simultaneously induce the angiogenesis of endothelia cells. Thus, this study aimed at investigating the effects of poly(lactic-co-glycolic acid)/Aker (PLGA-Aker) composite scaffolds on angiogenic and osteogenic differentiation of human iPSCs in order to optimize the scaffold compositions. The results from Alizarin Red S staining, qRT-PCR analysis of osteogenic genes (BMP2, RUNX2, ALP, COL1 and OCN) and angiogenic genes (VEGF and CD31) demonstrated that PLGA/Aker composite scaffolds containing 10% Aker exhibited the highest stimulatory effects on the osteogenic and angiogenic differentiation of human iPSCs among all scaffolds. After the scaffolds were implanted in nu/nu mice subcutaneous pockets and calvarial defects, H&E staining, BSP immunostaining, qRT-PCR analysis and micro-CT analysis (BMD, BV/TV) indicated that PLGA + 10% Aker scaffolds enhanced the vascularization and osteogenic differentiation of human iPSCs and stimulated the repair of bone defects. Taken together, our work indicated that combining scaffolds containing silicate bioceramic Aker and human iPSCs is a promising approach for the enhancement of bone regeneration.

Bioceramics akermanite enhanced vascularization and osteogenic differentiation of human iPSCs in 3D scaffolds in vitro and vivo.

The Influence of Physicochemical Properties of Biomimetic Hydroxyapatite on the In Vitro Behavior of Endothelial Progenitor Cells and Their Interaction with Mesenchymal Stem Cells

Calcium phosphate (CaP) substrates are successfully used as bone grafts due to their osteogenic properties. However, the influence of the physicochemical features of CaPs in angiogenesis is frequently neglected despite it being a crucial process for bone regeneration. The present work focuses on analyzing the effects of textural parameters of biomimetic calcium deficient hydroxyapatite (CDHA) and sintered beta-tricalcium phosphate (β-TCP), such as specific surface area, surface roughness, and microstructure, on the behavior of rat endothelial progenitor cells (rEPCs) and their crosstalk with rat mesenchymal stem cells (rMSCs). The higher reactivity of CDHA results in low proliferation rates in monocultured and cocultured systems. This effect is especially pronounced for rMSCs alone, and for CDHA with a fine microstructure. In terms of angiogenic and osteogenic gene expressions, the upregulation of particular genes is especially enhanced for needle-like CDHA compared to plate-like CDHA and β-TCP, suggesting the importance not only of the chemistry of the substrate, but also of its textural features. Moreover, the coculture of rEPCs and rMSCs on needle-like CDHA results in early upregulation of osteogenic modulator, i.e., protein deglycase 1 might be a possible cause of overexpression of osteogenic-related genes on the same substrate.

Efficiency of coculture with angiogenic cells or physiological BMP-2 administration on improving osteogenic differentiation and bone formation of MSCs

Cell-based bone regeneration with mesenchymal stem cells (MSCs) represents the current challenge toward repair of bone defects and fractures. The supposed hurdles for satisfactory performance of cell-based constructs include inadequate vascularization and osteogenic signals. Considering the reported beneficial role of angiogenic cells in promoting vascularization and osteogenic differentiation and the osteogenic potential of bone morphogenetic protein 2 (BMP-2), we here evaluated the efficiency of coculture with angiogenic cells or a physiological dose of BMP-2 on improving osteogenic differentiation of MSCs and bone formation in vivo. In three dimensional (3D) collagen hydrogels in vitro, cocultured human umbilical vein endothelial cells (HUVECs) in a 1:1 ratio or with a physiological dose of BMP-2 (2 ng/μL) promoted the osteogenic potential of MSCs evidenced by enhanced alkaline phosphatase activity and gene expression of osteogenic markers. Notably, HUVECs evoked similar osteogenic stimulation as BMP-2, albeit in a delayed manner. When their bone formation capacity was further evaluated in a mouse subcutaneous implantation model, MSCs with BMP-2 demonstrated the highest efficiency with reproducible bone formation. In contrast, MSCs cocultured with HUVECs constructs displayed substantial blood vessel-like structures with fibrous tissue rather than ectopic bone as MSC monoculture controls. Our findings confirm the priority of generating cell-based bone constructs with physiological BMP-2 administration and indicate the potential of using angiogenic cells to develop vascularized constructs. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 107A: 643-653, 2019.

A Fluidic Culture Platform for Spatially Patterned Cell Growth, Differentiation, and Cocultures

Stem cell cultures within perfusion bioreactors, while efficient in obtaining cell numbers, often lack the similarity to native tissues and consequently cell phenotype. We develop a three-dimensional (3D)-printed fluidic chamber for dynamic stem cell culture, with emphasis on control over flow and substrate curvature in a 3D environment, two physiologic features of native tissues. The chamber geometry, consisting of an array of vertical cylindrical pillars, facilitates actin-mediated localization of human mesenchymal stem cells (hMSCs) within ∼200 μm distance from the pillars, enabling spatial patterning of hMSCs and endothelial cells in cocultures and subsequent modulation of calcium signaling between these two essential cell types in the bone marrow microenvironment. Flow-enhanced osteogenic differentiation of hMSCs in growth media imposes spatial variations of alkaline phosphatase expression, which positively correlates with local shear stress. Proliferation of hMSCs is maintained within the chamber, exceeding the cell expansion in conventional static culture. The capability to manipulate cell spatial patterning, differentiation, and 3D tissue formation through geometry and flow demonstrates the culture chamber's relevant chemomechanical cues in stem cell microenvironments, thus providing an easy-to-implement tool to study interactions among substrate curvature, shear stress, and intracellular actin machinery in the tissue-engineered construct.

Decellularized Cortical Bone Scaffold Promotes Organized Neovascularization In Vivo

IMPACT STATEMENT

Bone loss and skeletal deficiencies due to musculoskeletal diseases, traumatic injury, abnormal development, and cancer are major problems worldwide, frequently requiring surgical intervention. There has been a shift in paradigm to utilize tissue engineering applications. This novel bone technology has the potential to promote bone regeneration for large bone defects without the addition of growth factors and offers a unique architecture for cell attachment, proliferation, and differentiation. This scaffold serves as a tailored therapeutic for bone injuries and defects, leading to an increased quality of life by decreasing the risk of reoccurring surgeries and complications.

EXPRESS: Gremlin1 blocks vascular endothelial growth factor signalling in the pulmonary microvascular endothelium

The bone morphogenetic protein (BMP) antagonist gremlin 1 plays a central role in the pathogenesis of hypoxic pulmonary hypertension (HPH). Recently, non-canonical functions of gremlin 1 have been identified, including specific binding to the vascular endothelial growth factor receptor-2 (VEGFR2). We tested the hypothesis that gremlin 1 modulates VEGFR2 signaling in the pulmonary microvascular endothelium.

We examined the effect of gremlin 1 haploinsufficiency on the expression of VEGF responsive genes and proteins in the hypoxic (10% O2) murine lung in vivo. Using human microvascular endothelial cells in vitro we examined the effect of gremlin 1 on VEGF signaling.

Gremlin 1 haploinsufficiency (Grem1+/–) attenuated the hypoxia-induced increase in gremlin 1 observed in the wild-type mouse lung. Reduced gremlin 1 expression in hypoxic Grem1+/– mice restored VEGFR2 expression and endothelial nitric oxide synthase (eNOS) expression and activity to normoxic values. Recombinant monomeric gremlin 1 inhibited VEGFA-induced VEGFR2 activation, downstream signaling, and VEGF-induced increases in Bcl-2, cell number, and the anti-apoptotic effect of VEGFA in vitro.

These results show that the monomeric form of gremlin 1 acts as an antagonist of VEGFR2 activation in the pulmonary microvascular endothelium. Given the previous demonstration that inhibition of VEGFR2 causes marked worsening of HPH, our results suggest that increased gremlin 1 in the hypoxic lung, in addition to blocking BMP receptor type-2 (BMPR2) signaling, contributes importantly to the development of PH by a non-canonical VEGFR2 blocking activity.

Synergistic effects of dual growth factor delivery from composite hydrogels incorporating 2-N,6-O-sulphated chitosan on bone regeneration

A promising strategy to accelerate bone generation is to deliver a combination of certain growth factors to the integration site via a controlled spatial and temporal delivery mode. Here, a composite hydrogel incorporating poly(lactide-co-glycolide) (PLGA) microspheres was accordingly prepared to load and deliver the osteogenic rhBMP-2 and angiogenic rhVEGF₁₆₅ in the required manner. In addition, 2-N,6-O-sulphated chitosan (26SCS), which is a synergetic factor of growth factors, was incorporated in the composite hydrogel as well. The system showed a similar release behaviour of the two growth factors regardless of 26SCS inclusion. RhBMP-2 loaded in PLGA microspheres showed a sustained release over a period of 2 weeks, whereas rhVEGF₁₆₅ loaded in hydrogel eluted almost completely from the hydrogel over the first 16 days. Both growth factors retained their efficacy, as quantified with relevant in vitro assays. Moreover, an enhanced cell response was achieved upon the delivery of dual growth factors, compared to that obtained with a single factor. Furthermore, in the presence of 26SCS, the system revealed significantly upregulated alkaline phosphatase activity, human umbilical vein endothelial cell proliferation, sprouting, nitric oxide secretion, and angiogenic gene expression. This study highlighted that the composite hydrogel incorporated with 26SCS appears to constitute a promising approach to deliver multiple growth factors. From our findings, we could also conclude that rhBMP-2 can promote angiogenesis and that the mechanism is worthy of further study in subsequent research.

Silk Biomaterials-Mediated miRNA Functionalized Orthopedic Devices

Silk-based bioresorbable medical devices, such as screws, plates, and rods, have been under investigation due to their promising properties for orthopedic repairs. Options to functionalize these new devices for enhanced control of bone regeneration would also exploit the compatible processing methods used to generate the devices. MicroRNAs are important regulators of bone maintenance and formation, and miRNA-based therapeutics have the potential to aid bone repair, utilizing a transient therapeutic approach with local bioactivity. We hypothesized that silk-based orthopedic devices could be used for the local delivery of miRNAs, using anti-sense miR-214 (AS-miR-214), to inhibit endogenous expression of osteoinductive antagonist and thereby supporting the upregulation of osteoinductive target molecules activating transcription factor 4 (ATF4) and Osterix (Osx). AS-miR-214 silk devices, prepared using surface coating, demonstrated continuous release of miRNA inhibitors up to 7 days in vitro. Additionally, human mesenchymal stem cells seeded on AS-miR-214 silk films expressed higher levels of osteogenic genes ATF4, Osx, Runx2, and Osteocalcin. Interestingly, these cells exhibited lower cell viability and DNA content over 21 days. Conversely, the cells demonstrated significantly higher levels of alkaline phosphatase expression and calcium deposition compared with cells seeded on silk films with nontargeting miRNA controls. The study demonstrated that the silk-based orthopedic devices, in conjunction with bioactive miRNA-based therapeutics, may serve as a novel system for localized bone tissue engineering, enhancing osteogenesis at the implant interface while avoiding detrimental systematic side effects.

Tension-loaded bone marrow stromal cells potentiate the paracrine osteogenic signaling of co-cultured vascular endothelial cells

Co-culture of bone marrow stromal cells (BMSCs) and vascular endothelial cells (VECs) is a promising strategy for better osteogenesis and pre-vascularization in bone tissue engineering. Recent reports have shown that mechanical stretching further promotes osteogenesis in BMSC/VEC co-culture systems, but the underlying mechanism of this process remains unclear. In this study, noncontact co-cultures of rat primary BMSCs and VECs were employed to interrogate paracrine cell-to-cell communications in response to tension. Exposure of VECs to 6% tension for 48 h elicited neither ALP activity nor mRNA expression of OCN and OPN in BMSCs incubated in a shared culture medium. Instead, BMSCs subjected to tension induced robust VEGF release, and its conditioned medium enhanced the proliferation and tubular formation of VECs with a concurrent increase in BMP-2 and IGF-1 production. Conditioned medium from activated VECs in turn promoted expression of osteogenic genes in BMSCs, followed by an increase in matrix mineralization. The addition of VEGF-R inhibitor Tivozanib to these systems abrogated the tension-induced paracrine effects on VECs and subsequently impaired BMSC osteogenesis. These results clearly demonstrate that the response of BMSCs to tension potentiates paracrine osteogenic signaling from VECs; this positive feedback loop is initiated by VEGF release.

Cell-secreted extracellular matrix, independent of cell source, promotes the osteogenic differentiation of human stromal vascular fraction

Lipoaspirates contain a readily accessible heterogeneous cell source for use in bone regeneration collectively referred to as the stromal vascular fraction (SVF). However, the osteogenic potential of SVF is inferior to other progenitor cell populations, thereby requiring alternative strategies to potentiate its effective use in cell-based therapies of bone repair. Cell-secreted extracellular matrix (ECM) is a promising substrate to guide cell phenotype or for use in biomaterial design, yet the instructional capacity of ECMs produced by various cell types is unknown. To determine whether the bioactivity of cell-secreted ECM was dependent on cell source, we assessed the osteogenic response of human SVF on ECMs secreted by bone marrow-derived mesenchymal stem cells (MSCs), adipose stromal cells (ASCs), and human dermal fibroblasts (HDFs). Tissue culture plastic (TCP), type I collagen, and ECM induced expression of integrin subunits α₂, α₅, and β₁ in SVF, yet seeding efficiency was only improved on MSC-derived ECM. Regardless of ECM source, SVF deposited over 8- and 1.3-fold more calcium compared to TCP and collagen-coated controls, respectively. Flow cytometry confirmed that SVF cultured on ECM retained CD31 and CD34 positive cell populations better than TCP. After depleting accessory cells, ASCs deposited significantly less calcium compared to donor-matched SVF. This function was partially restored in the presence of MSC-derived ECM when donor-matched endothelial cells (ECs) were added in an ASC/EC co-culture, confirming a role for ECs in osteogenic differentiation. These findings support the use of cell-derived ECM as a means to promote cell retention and osteogenic differentiation of SVF.

Endothelial cells and endothelin‑1 promote the odontogenic differentiation of dental pulp stem cells

It has been established that dental pulp stem cells (DPSCs) serve an important role in the restoration and regeneration of dental tissues. DPSCs are present in blood vessels and also exist in the vessel microenvironment in vivo and have a close association with endothelial cells (ECs). The present study aimed to evaluate the influence of ECs and their secretory product endothelin-1 (ET-1) on the differentiation of DPSCs. In the present study, cells were divided into four groups: i) a DPSC-only control group; ii) a DPSC with ET-1 administration group; iii) a DPSC and human umbilical vein endothelial cell (HUVEC) direct co-culture group; and iv) a DPSC and HUVEC indirect co-culture group using a Transwell system. Reverse transcription-quantitative polymerase chain reaction was used to detect the expression of the odontoblastic differentiation-associated genes, including dentin sialoprotein (DSP) and dentin matrix acidic phosphoprotein 1 (DMP-1) at days 4, 7, 14 and 21. Alizarin Red S staining, immunofluorescence and western blot analyses were also conducted to assess the differentiation of the DPSCs in each group. The highest expression levels of odontoblastic differentiation-associated genes were observed on day 7 and in the two co-culture groups were increased compared with the DPSC-only and DPSC + ET-1 culture groups at all four time points. However, expression levels in the DPSC + ET-1 group were not downregulated as notably as in the co-culture groups on days 14 and 21. The Transwell group exhibited the greatest ability for odontoblastic differentiation compared with the other groups according to staining with Alizarin Red S, immunofluorescence and western blot analysis results. According to the results of the present study, the culture solution with HUVECs affected the differentiation of DPSCs. In addition, ET-1 may promote the odontoblastic differentiation of DPSCs.

Engineering in-vitro stem cell-based vascularized bone models for drug screening and predictive toxicology

The production of veritable in-vitro models of bone tissue is essential to understand the biology of bone and its surrounding environment, to analyze the pathogenesis of bone diseases (e.g., osteoporosis, osteoarthritis, osteomyelitis, etc.), to develop effective therapeutic drug screening, and to test potential therapeutic strategies. Dysregulated interactions between vasculature and bone cells are often related to the aforementioned pathologies, underscoring the need for a bone model that contains engineered vasculature. Due to ethical restraints and limited prediction power of animal models, human stem cell-based tissue engineering has gained increasing relevance as a candidate approach to overcome the limitations of animals and to serve as preclinical models for drug testing. Since bone is a highly vascularized tissue, the concomitant development of vasculature and mineralized matrix requires a synergistic interaction between osteogenic and endothelial precursors. A number of experimental approaches have been used to achieve this goal, such as the combination of angiogenic factors and three-dimensional scaffolds, prevascularization strategies, and coculture systems. In this review, we present an overview of the current models and approaches to generate in-vitro stem cell-based vascularized bone, with emphasis on the main challenges of vasculature engineering. These challenges are related to the choice of biomaterials, scaffold fabrication techniques, and cells, as well as the type of culturing conditions required, and specifically the application of dynamic culture systems using bioreactors.