Coculture of Vascular Endothelial Cells and Adipose-Derived Stem Cells as a Source for Bone Engineering

Adipose derived stem cells - Sources, differentiation capacity and a new target for reconstructive and regenerative medicine

Adipose-derived stem cells (ADSCs) are mesenchymal stem cells (MSCs) derived from adipose tissue with mesenchymal lineage differentiation potential and remarkable potential in regenerative medicine. ADSCs are easily sourced from adipose tissue, share regenerative characteristics akin to other MSCs. Their convenient adherence to plastic culture flasks, coupled with their capacity for in vitro expansion and multi-lineage differentiation, underscores their promise as a robust tool for tissue repair and enhancement. The accessibility of human adipose tissue and the development of minimally invasive isolation protocols have further propelled the autologous use of ADSCs, fueling excitement in both organ repair and regenerative medicine. Consequently, research in ADSCsis experiencing rapid growth. A detailed overview of the current landscape of ADSCs isolation and differentiation capacity including the latest advancements in ADSCs usage, encompassing ongoing clinical investigations are important considerations to understand their potential to shape the landscape of regenerative medicine.

Cell-based mechanisms and strategies of co-culture system both in vivo and vitro for bone tissue engineering

The lack of a functional vascular supply has been identified as a major challenge limiting the clinical introduction of stem cell-based bone tissue engineering (BTE) for the repair of large-volume bone defects (LVBD). Various approaches have been explored to improve the vascular supply in tissue-engineered constructs, and the development of strategies that could effectively induce the establishment of a functional vascular supply has become a major goal of BTE research. One of the state-of-the-art methods is to incorporate both angiogenic and osteogenic cells in co-culture systems. This review clarifies the key concepts involved, summarises the cell types and models used to date, and systematically evaluates their performance. We also discuss the cell-to-cell communication between these two cell types and the strategies explored in BTE constructs with angiogenic and osteogenic cells to optimise their functions. In addition, we outline unresolved issues and remaining obstacles that need to be overcome for further development in this field and eventual successful repair of LVBD.

Effects of Tissue-engineered Bone by Coculture of Adipose-derived Stem Cells and Vascular Endothelial Cells on Host Immune Status

AIM

The study aimed to explore the effects of tissue-engineered bone constructed with partially deproteinized biologic bone (PDPBB) and coculture of adipose-derived stem cells (ADSCs) and vascular endothelial cells (VECs) on host immune status, providing a very useful clue for the future development of bone engineering.

METHODS

Tissue-engineered bones constructed by PDPBB and ADSCs, VECs or coculture of them were implanted into the muscle bag of bilateral femurs of Sprague-Dawley rats. Partially deproteinized biologic bone alone and blank control were also implanted. After transplantation, the proliferation of implanted seed cells in tissue-engineered bones was labeled by bromodeoxyuridine staining. Moreover, the changes of T-lymphocyte subpopulations, including CD3 + CD4+ and CD3 + CD8+ in peripheral blood were then detected using flow cytometry to analyze the immune rejection of tissue-engineered bone implantation based on peripheral blood CD4/CD8 ratios.

RESULTS

After transplantation, the proliferation of implanted seed cells was observed in tissue-engineered bones of different groups. At different time points after transplantation, the CD4+/CD8+ ratio in peripheral blood of PDPBB + ADSCs, PDPBB + coculture, and blank control groups did not exhibit significant change. Although the CD4+/CD8+ ratio in peripheral blood of PDPBB + VECs group was significantly higher than other group at 1 week after transplantation, that of PDPBB + VECs and PDPBB + coculture group was significantly decreased at 8 week after transplantation compared with that of blank control group.

CONCLUSIONS

Our results indicated that there was no significant immune rejection after transplantation of tissue-engineered bone constructed with PDPBB and coculture of ADSCs and VECs as seed cells.

Effect of a subset of adipose-derived stem cells isolated with liposome magnetic beads to promote cartilage repair

This study aimed to investigate the ability of CD146⁺ subset of ADSCs to repair cartilage defects. In this study, we prepared CD146⁺ liposome magnetic beads (CD146⁺LMB) to isolate CD146⁺ADSCs. The cells were induced for chondrogenic differentiation and verified by cartilage‐specific mRNA and protein expression. Then a mouse model of cartilage defect was constructed and treated by filling the induced cartilage cells into the damaged joint, to evaluate the function of such cells in the cartilage microenvironment. Our results demonstrated that the CD146⁺LMBs we prepared were uniform, small and highly stable, and cell experiments showed that the CD146⁺LMB has low cytotoxicity to the ADSCs. ADSCs isolated with CD146⁺LMB were all CD146⁺, CD105⁺, CD166⁺ and CD73⁺. After chondrogenic induction, the cells showed significantly increased expression of cartilage markers Sox9, collagen Ⅱ and aggrecan at protein level and significantly increased Sox9, collagen Ⅱ and aggrecan at mRNA level, and the protein expression and mRNA expression of CD146⁺ADSCs group were higher than those of ADSCs group. The CD146⁺ADSCs group showed superior tissue repair ability than the ADSCs group and blank control group in the animal experiment, as judged by gross observation, histological observation and histological scoring. The above results proved that CD146⁺LMB can successfully isolate the CD146⁺ADSCs, and after chondrogenic induction, these cells successfully promoted repair of articular cartilage defects, which may be a new direction of tissue engineering.

Construction of tissue engineering bone with the co‑culture system of ADSCs and VECs on partially deproteinized biologic bone in vitro: A preliminary study

Scaffold‑based bone tissue engineering has therapeutic potential in the regeneration of osseous defects. The present study aimed to explore the adhesion and cell viability of a co‑culture system composed of vascular endothelial cells PI‑/Annexin V+ represents early apoptotic cells, and PI+/Annexin V+ represents late apoptotic cells (VECs) and adipose‑derived stem cells (ADSCs) on partially deproteinized biologic bone (PDPBB) in vitro, and determine the optimum time period for maximum cell viability that could possibly be used for standardizing the scaffold transplant into the in vivo system. VECs and ADSCs were isolated from pregnant Sprague‑Dawley rats and confirmed by immunostaining with von Willebrand factor and CD90, respectively. PDPBB was prepared using standardized protocols involving coating partially deproteinized bone with fibronectin. PDPBB was incubated in a mono‑culture with VECs or ADSCs, or in a co‑culture with both of these cells at a ratio of 1:1. An MTT assay was used to assess the adhesion and cell viability of VECs and ADSCs on PDPBB in the three different cultures. Scanning electron microscopy was used to observe the adhesion, cell viability and morphology of the different types of cells on PDPBB. It was observed that the absorbance of each group increased gradually and peaked on the 10th day; the highest absorbance was found for the co‑cultured cells group. The difference of cell viability between each cell group was statistically significant. On the 10th day, in the co‑cultured cells group, several cells adhered on the PDPBB material and a nest‑like distribution morphology was observed. Therefore, the adhesion and cell viability of the co‑cultured cells was higher compared with the mono‑cultures of VECs or ADSCs. As cell viability was highest on the 10th day, this could be the optimal length of time for incubation and therefore could be used for in vivo experiments.

Bone tissue engineering using adipose-derived stem cells and endothelial cells: Effects of the cell ratio

The microvascular endothelial network is essential for bone formation and regeneration. In this context, endothelial cells not only support vascularization but also influence bone physiology via cell contact-dependent mechanisms. In order to improve vascularization and osteogenesis in tissue engineering applications, several strategies have been developed. One promising approach is the coapplication of endothelial and adipose derived stem cells (ADSCs). In this study, we aimed at investigating the best ratio of human umbilical vein endothelial cells (HUVECs) and osteogenic differentiated ADSCs with regard to proliferation, apoptosis, osteogenesis and angiogenesis. For this purpose, cocultures of ADSCs and HUVECs with ratios of 25%:75%, 50%:50% and 75%:25% were performed. We were able to prove that cocultivation supports proliferation whereas apoptosis was unidirectional decreased in cocultured HUVECs mediated by a p-BAD-dependent mechanism. Moreover, coculturing ADSCs and HUVECs stimulated matrix mineralization and the activity of alkaline phosphatase (ALP). Increased gene expression of the proangiogenic markers eNOS, Flt, Ang2 and MMP3 as well as sprouting phenomena in matrigel assays proved the angiogenic potential of the coculture. In summary, coculturing ADSCs and HUVECs stimulates proliferation, cell survival, osteogenesis and angiogenesis particularly in the 50%:50% coculture.

[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.

Skeletogenic Capacity of Human Perivascular Stem Cells Obtained Via Magnetic-Activated Cell Sorting

Human perivascular stem/stromal cells (PSC) are a multipotent mesenchymal progenitor cell population defined by their perivascular residence. PSC are increasingly studied for their application in skeletal regenerative medicine. PSC from subcutaneous white adipose tissue are most commonly isolated via fluorescence-activated cell sorting (FACS), and defined as a bipartite population of CD146⁺CD34^-CD31^-CD45^- pericytes and CD34⁺CD146^-CD31^-CD45^- adventitial cells. FACS poses several challenges for clinical translation, including requirements for facilities, equipment, and personnel. The purpose of this study is to identify if magnetic-activated cell sorting (MACS) is a feasible method to derive PSC, and to determine if MACS-derived PSC are comparable to our previous experience with FACS-derived PSC. In brief, CD146⁺ pericytes and CD34⁺ adventitial cells were enriched from human lipoaspirate using a multistep column approach. Next, cell identity and purity were analyzed by flow cytometry. In vitro multilineage differentiation studies were performed with MACS-defined PSC subsets. Finally, in vivo application was performed in nonhealing calvarial bone defects in Scid mice. Results showed that human CD146⁺ pericytes and CD34⁺ adventitial cells may be enriched by MACS, with defined purity, anticipated cell surface marker expression, and capacity for multilineage differentiation. In vivo, MACS-derived PSC induce ossification of bone defects. These data document the feasibility of a MACS approach for the enrichment and application of PSC in the field of tissue engineering and regenerative medicine. Impact Statement Our findings suggest that perivascular stem/stromal cells, and in particular adventitial cells, may be isolated by magnetic-activated cell sorting and applied as an uncultured autologous stem cell therapy in a same-day setting for bone defect repair.

Cultured cell-derived extracellular matrices to enhance the osteogenic differentiation and angiogenic properties of human mesenchymal stem/stromal cells

Cell-derived extracellular matrix (ECM) consists of a complex assembly of fibrillary proteins, matrix macromolecules, and associated growth factors that mimic the composition and organization of native ECM micro-environment. Therefore, cultured cell-derived ECM has been used as a scaffold for tissue engineering settings to create a biomimetic micro-environment, providing physical, chemical, and mechanical cues to cells, and support cell adhesion, proliferation, migration, and differentiation. Here, we present a new strategy to produce different combinations of decellularized cultured cell-derived ECM (dECM) obtained from different cultured cell types, namely, mesenchymal stem/stromal cells (MSCs) and human umbilical vein endothelial cells (HUVECs), as well as the coculture of MSC:HUVEC and investigate the effects of its various compositions on cell metabolic activity, osteogenic differentiation, and angiogenic properties of human bone marrow (BM)-derived MSCs, vital features for adult bone tissue regeneration and repair. Our findings demonstrate that dECM presented higher cell metabolic activity compared with tissue culture polystyrene. More importantly, we show that MSC:HUVEC ECM enhanced the osteogenic and angiogenic potential of BM MSCs, as assessed by in vitro assays. Interestingly, MSC:HUVEC (1:3) ECM demonstrated the best angiogenic response of MSCs in the conditions tested. To the best of our knowledge, this is the first study that demonstrates that dECM derived from a coculture of MSC:HUVEC impacts the osteogenic and angiogenic capabilities of BM MSCs, suggesting the potential use of MSC:HUVEC ECM as a therapeutic product to improve clinical outcomes in bone regeneration.

Co-culture cell-derived extracellular matrix loaded electrospun microfibrous scaffolds for bone tissue engineering

Cell-derived extracellular matrix (ECM) has been employed as scaffolds for tissue engineering, creating a biomimetic microenvironment that provides physical, chemical and mechanical cues for cells and supports cell adhesion, proliferation, migration and differentiation by mimicking their in vivo microenvironment. Despite the enhanced bioactivity of cell-derived ECM, its application as a scaffold to regenerate hard tissues such as bone is still hampered by its insufficient mechanical properties. The combination of cell-derived ECM with synthetic biomaterials might result in an effective strategy to enhance scaffold mechanical properties and structural support. Electrospinning has been used in bone tissue engineering to fabricate fibrous and porous scaffolds, mimicking the hierarchical organized fibrillar structure and architecture found in the ECM. Although the structure of the scaffold might be similar to ECM architecture, most of these electrospun scaffolds have failed to achieve functionality due to a lack of bioactivity and osteoinductive factors. In this study, we developed bioactive cell-derived ECM electrospun polycaprolactone (PCL) scaffolds produced from ECM derived from human mesenchymal stem/stromal cells (MSC), human umbilical vein endothelial cells (HUVEC) and their combination based on the hypothesis that the cell-derived ECM incorporated into the PCL fibers would enhance the biofunctionality of the scaffold. The aims of this study were to fabricate and characterize cell-derived ECM electrospun PCL scaffolds and assess their ability to enhance osteogenic differentiation of MSCs, envisaging bone tissue engineering applications. Our findings demonstrate that all cell-derived ECM electrospun scaffolds promoted significant cell proliferation compared to PCL alone, while presenting similar physical/mechanical properties. Additionally, MSC:HUVEC-ECM electrospun scaffolds significantly enhanced osteogenic differentiation of MSCs as verified by increased ALP activity and osteogenic gene expression levels. To our knowledge, these results describe the first study suggesting that MSC:HUVEC-ECM might be developed as a biomimetic electrospun scaffold for bone tissue engineering applications.

Emerging Strategies for Stem Cell Lineage Commitment in Tissue Engineering and Regenerative Medicine

Stem cells have transformed the fields of tissue engineering and regenerative medicine, and their potential to further advance these fields cannot be overstated. The stem cell niche is a dynamic microenvironment that determines cell fate during development and tissue repair following an injury. Classically, stem cells were studied in isolation of their microenvironment; however, contemporary research has produced a myriad of evidence that shows the importance of multiple aspects of the stem cell niche in regulating their processes. In the context of tissue engineering and regenerative medicine studies, the niche is an artificial environment provided by culture conditions. In vitro culture conditions may involve coculturing with other cell types, developing specific biomaterials, and applying relevant forces to promote the desired lineage commitment. Considerable advance has been made over the past few years toward directed stem cell differentiation; however, the unspecific differentiation of stem cells yielding a mixed population of cells has been a challenge. In this review, we provide a systematic review of the emerging strategies used for lineage commitment within the context of tissue engineering and regenerative medicine. These strategies include scaffold pore-size and pore-shape gradients, stress relaxation, sonic and electromagnetic effects, and magnetic forces. Finally, we provide insights and perspectives into future directions focusing on signaling pathways activated during lineage commitment using external stimuli.

Letter to the Editor

BACKGROUND

Neuroendocrine tumors (NETs) are uncommon type of cancers, also known as APUD (amine precursor uptake decarboxylation) tumors, which are becoming increasingly prevalent. Alkaline phosphatase (ALP) is a poor prognosis factor in a number of hepatic diseases. However, its distribution and prognostic value in primary hepatic neuroendocrine tumors (PHNETs) are still not clear. In this study, our aim is to investigate the correlations between ALP and clinicopathological features and prognostic factors of PHNETs.

METHODS

The clinical data of 22 patients with PHNETs were retrospectively reviewed to investigate whether ALP affects the prognosis of PHNETs.

RESULTS

In this study, ALP is correlated to γ-glutamyl transpeptidase (GGT; p = 0.002) and the tumor location in the liver (p = 0.007), and increased levels of ALP had poor effects on overall survival (p = 0.006) and progression-free survival (p = 0.022).

CONCLUSION

ALP was identified as an independent prognostic factor for overall survival of PHNETs.

Conditioned Medium from Human Umbilical Vein Endothelial Cells Promotes Proliferation, Migration, Invasion and Angiogenesis of Adipose Derived Stem Cells

Preeclampsia (PE) is a pregnancy-specific hypertensive complication, closely related to endothelial dysfunction. Adipose derived stem cells (ADSCs) have the capacity to differentiate into endothelial cells for vascular repair. Therefore, we hypothesized that induced endothelial differentiation of ADSCs might hold great potential for the treatment of PE. In this study, the primary ADSCs and human umbilical vein endothelial cells (HUVECs) were isolated by the collagenase digestion method. The supernatant of HUVECs was collected from the first generation of cells. Then, ADSCs were divided into two groups: ADSCs alone group and induced ADSCs (iADSCs) group. In iADSCs group, ADSCs were induced by HUVECs conditioned medium and ADSCs special culture medium at a ratio of 1:1 over a two-week period. In order to identify the endothelial characteristics of iADSCs, CD31 and CD34 were examined by flow cytometry. The proliferation, migration, invasion and angiogenesis assays were employed to compare the bioactivity of iADSCs and ADSCs. Furthermore, The levels of angiogenic related factors including vascular endothelial growth factor (VEGF) and placenta growth factor (P1GF) were detected by RT-PCR and Western blotting. Results showed conditioned medium from HUVECs promoted ADSCs proliferation, migration, invasion and angiogenesis. In addition, the levels of VEGF and P1GF were significantly enhanced in iADSCs group. This study uncovered the iADSCs application potential in the therapy and intervention of PE.

Intra-articular Xenotransplantation of Adipose-Derived Stromal Cells to Treat Osteoarthritis in a Goat Model

Adipose-derived stromal cells (ASCs) have been investigated as a cell source for tissue regeneration. The purpose of this study was first to confirm if medial meniscectomy induces osteoarthritis (OA) in goats within a relative short period of time, and more importantly, to investigate if systemic treatment with immunosuppressive drugs is necessary in intra-articular ASC xenotransplantation for successful regeneration of articular cartilage and prevention of joint inflammation. Eight Korean native black goats 1-2 years of age underwent medial meniscectomy. To evaluate the gross and histological appearance of articular cartilage, knee joints were re-exposed by a medial parapatellar incision at 8 weeks. After macroscopic scoring of gross appearance, cartilage biopsy specimens 6 mm in diameter were obtained from the femoral condyle in four goats. The goats were injected with single intra-articular dose of 7×106 human ASCs (hASCs) 7 days after the second arthrotomy. Four animals were treated with daily injections of cyclosporin A 10 mg/kg for 7 days, followed by a reduced dose of 5 mg/kg for another 7 days, while other 4 animals did not receive immunosuppressive therapy. All animals were sacrificed for analysis 8 weeks after injection of hASCs. OA was successfully induced 8 weeks after medial meniscectomy. Eight weeks after injection of hASCs, various signs of articular cartilage regeneration were observed. There were no significant macroscopic and histological differences between goats treated with cyclosporine and untreated goats. Interleukin-1ß and tumor necrosis factor-α level from synovial fluid did not differ between cyclosporine-treated and untreated goats. The results indicate that immunosuppressive therapy did not influence the result of ASC xenotransplantation to treat OA.

PHBV/bioglass composite scaffolds with co-cultures of endothelial cells and bone marrow stromal cells improve vascularization and osteogenesis for bone tissue engineering

PHBV + 10% BG composite scaffolds stimulated osteogenic differentiation and angiogenic differentiation of co-cultures of HBMSCs and HUVECs by enhancing paracrine effects between the two types of cells.

Endochondral Priming: A Developmental Engineering Strategy for Bone Tissue Regeneration

Tissue engineering and regenerative medicine have significant potential to treat bone pathologies by exploiting the capacity for bone progenitors to grow and produce tissue constituents under specific biochemical and physical conditions. However, conventional tissue engineering approaches, which combine stem cells with biomaterial scaffolds, are limited as the constructs often degrade, due to a lack of vascularization, and lack the mechanical integrity to fulfill load bearing functions, and as such are not yet widely used for clinical treatment of large bone defects. Recent studies have proposed that in vitro tissue engineering approaches should strive to simulate in vivo bone developmental processes and, thereby, imitate natural factors governing cell differentiation and matrix production, following the paradigm recently defined as "developmental engineering." Although developmental engineering strategies have been recently developed that mimic specific aspects of the endochondral ossification bone formation process, these findings are not widely understood. Moreover, a critical comparison of these approaches to standard biomaterial-based bone tissue engineering has not yet been undertaken. For that reason, this article presents noteworthy experimental findings from researchers focusing on developing an endochondral-based developmental engineering strategy for bone tissue regeneration. These studies have established that in vitro approaches, which mimic certain aspects of the endochondral ossification process, namely the formation of the cartilage template and the vascularization of the cartilage template, can promote mineralization and vascularization to a certain extent both in vitro and in vivo. Finally, this article outlines specific experimental challenges that must be overcome to further exploit the biology of endochondral ossification and provide a tissue engineering construct for clinical treatment of large bone/nonunion defects and obviate the need for bone tissue graft.

Osteogenic Differentiation of Mesenchymal Stem Cells by Mimicking the Cellular Niche of the Endochondral Template

In vitro bone regeneration strategies that prime mesenchymal stem cells (MSCs) with chondrogenic factors, to mimic aspects of the endochondral ossification process, have been shown to promote mineralization and vascularization by MSCs both in vitro and when implanted in vivo. However, these approaches required the use of osteogenic supplements, namely dexamethasone, ascorbic acid, and β-glycerophosphate, none of which are endogenous mediators of bone formation in vivo. Rather MSCs, endothelial progenitor cells, and chondrocytes all reside in proximity within the cartilage template and might paracrineally regulate osteogenic differentiation. Thus, this study tests the hypothesis that an in vitro bone regeneration approach that mimics the cellular niche existing during endochondral ossification, through coculture of MSCs, endothelial cells, and chondrocytes, will obviate the need for extraneous osteogenic supplements and provide an alternative strategy to elicit osteogenic differentiation of MSCs and mineral production. The specific objectives of this study were to (1) mimic the cellular niche existing during endochondral ossification and (2) investigate whether osteogenic differentiation could be induced without the use of any external growth factors. To test the hypothesis, we evaluated the mineralization and vessel formation potential of (a) a novel methodology involving both chondrogenic priming and the coculture of human umbilical vein endothelial cells (HUVECs) and MSCs compared with (b) chondrogenic priming of MSCs alone, (c) addition of HUVECs to chondrogenically primed MSC aggregates, (d-f) the same experimental groups cultured in the presence of osteogenic supplements and (g) a noncoculture group cultured in the presence of osteogenic growth factors alone. Biochemical (DNA, alkaline phosphatase [ALP], calcium, CD31⁺, vascular endothelial growth factor [VEGF]), histological (alcian blue, alizarin red), and immunohistological (CD31⁺) analyses were conducted to investigate osteogenic differentiation and vascularization at various time points (1, 2, and 3 weeks). The coculture methodology enhanced both osteogenesis and vasculogenesis compared with osteogenic differentiation alone, whereas osteogenic supplements inhibited the osteogenesis and vascularization (ALP, calcium, and VEGF) induced through coculture alone. Taken together, these results suggest that chondrogenic and vascular priming can obviate the need for osteogenic supplements to induce osteogenesis of human MSCs in vitro, while allowing for the formation of rudimentary vessels.

Influence of different calcium phosphate ceramics on growth and differentiation of cells in osteoblast-endothelial co-cultures

Strategies for improvement of angiogenesis and vasculogenesis using different cells and materials are paramount aims in the field of bone tissue engineering. Thereby, the interaction between different cell types and scaffold materials is crucial for growth, differentiation, and long-term outcomes of tissue-engineered constructs. In this study, we evaluated the interaction of osteoblasts and endothelial cells in three-dimensional tissue-engineered constructs using beta tricalciumphosphate (β-TCP, [ß-Ca₃ (PO₄ )₂ ]) and calcium-deficient hydroxyapatite (CDHA, [Ca₉ (PO₄ )₅ (HPO₄ )OH]) ceramics as scaffolds. We focused on initial cell organization, cell proliferation, and differential expression of osteoblastic and endothelial markers employing monocultures and co-cultures of endothelial cells of two different origins [human umbilical vein endothelial cells (HUVECs) and outgrowth endothelial cells (OECs)] with primary human osteoblasts (hOBs). Despite different chemical and physical characteristics of CDHA and β-TCP ceramics, similar patterns in cell growth, differentiation, and gene expression were detected in tissue-engineered constructs consisting of hOB, HUVEC, and HUVEC/hOB-co-cultures. Under dynamic cell culture conditions we found proliferation of these cells with stable endothelial and osteoblastic differentiation patterns. Both material types are highly biocompatible with these cells providing a promising perspective for the future research. In this study, both materials did not support growth and differentiation of OEC. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 1950-1962, 2017.

Application of buccal fat pad-derived stem cells in combination with autogenous iliac bone graft in the treatment of maxillomandibular atrophy: a preliminary human study

Stem cell therapy for the treatment of bone defects is an alternative or adjunct to autologous bone grafting. This study assessed the efficacy of buccal fat pad-derived stem cells (BFPSCs) with iliac bone block grafting for the treatment of extensive human alveolar ridge defects. Eight patients with extensive jaw atrophy were selected for this study. The jaws were reconstructed with non-vascularized anterior iliac crest bone blocks. Gaps between the blocks were filled with freeze-dried bone granules and covered with a collagen membrane. In the test group (n=4), these granules were seeded with BFPSCs. Cone beam computed tomography scans were used to assess the amount of new bone formed at six sites in each patient. Trephine biopsies of 2-mm were also taken from the graft site during implant placement for histomorphometric analysis. The mean bone width change at the graft site was greater in the test group than in the control group (3.94±1.62mm vs. 3.01±0.89mm). New bone formation was 65.32% in the test group versus 49.21% in the control group. The application of BFPSCs in conjunction with iliac bone block grafts may increase the amount of new bone formation and decrease secondary bone resorption in extensively atrophic jaws.

Biomimetic gelatin methacrylamide hydrogel scaffolds for bone tissue engineering

The biomimetic GelMA scaffolds which have highly porous, interconnected macropores, and rough surface could promote ADSC to differentiate into osteoblasts and bone formation.

The use of total human bone marrow fraction in a direct three-dimensional expansion approach for bone tissue engineering applications: focus on angiogenesis and osteogenesis

Current approaches in bone tissue engineering have shown limited success, mostly owing to insufficient vascularization of the construct. A common approach consists of co-culture of endothelial cells and osteoblastic cells. This strategy uses cells from different sources and differentiation states, thus increasing the complexity upstream of a clinical application. The source of reparative cells is paramount for the success of bone tissue engineering applications. In this context, stem cells obtained from human bone marrow hold much promise. Here, we analyzed the potential of human whole bone marrow cells directly expanded in a three-dimensional (3D) polymer matrix and focused on the further characterization of this heterogeneous population and on their ability to promote angiogenesis and osteogenesis, both in vitro and in vivo, in a subcutaneous model. Cellular aggregates were formed within 24 h and over the 12-day culture period expressed endothelial and bone-specific markers and a specific junctional protein. Ectopic implantation of the tissue-engineered constructs revealed osteoid tissue and vessel formation both at the periphery and within the implant. This work sheds light on the potential clinical use of human whole bone marrow for bone regeneration strategies, focusing on a simplified approach to develop a direct 3D culture without two-dimensional isolation or expansion.

Evaluation of the cellular origins of heterotopic ossification

Heterotopic ossification (HO), acquired or hereditary, is featured by the formation of bone outside of the normal skeleton. Typical acquired HO is a common, debilitating condition associated with traumatic events. Cardiovascular calcification, an atypical form of acquired HO, is prevalent and associated with high rates of cardiovascular mortality. Hereditary HO syndromes, such as fibrodysplasia ossificans progressiva and progressive osseous heteroplasia, are rare, progressive, life-threatening disorders. The cellular origins of HO remain elusive. Some bona fide contributing cell populations have been found through genetic lineage tracing and other experiments in vivo, and various other candidate populations have been proposed. Nevertheless, because of the difficulties in establishing cellular phenotypes in vivo and other confounding factors, the true identities of these populations are still uncertain. This review critically evaluates the accumulating data in the field. The major focus is on the candidate populations that may give rise to osteochondrogenic lineage cells directly, not the populations that may contribute to HO indirectly. This issue is important not solely because of the clinical implications, but also because it highlights the basic biological processes that govern bone formation.

A glycosaminoglycan based, modular tissue scaffold system for rapid assembly of perfusable, high cell density, engineered tissues

The limited ability to vascularize and perfuse thick, cell-laden tissue constructs has hindered efforts to engineer complex tissues and organs, including liver, heart and kidney. The emerging field of modular tissue engineering aims to address this limitation by fabricating constructs from the bottom up, with the objective of recreating native tissue architecture and promoting extensive vascularization. In this paper, we report the elements of a simple yet efficient method for fabricating vascularized tissue constructs by fusing biodegradable microcapsules with tunable interior environments. Parenchymal cells of various types, (i.e. trophoblasts, vascular smooth muscle cells, hepatocytes) were suspended in glycosaminoglycan (GAG) solutions (4%/1.5% chondroitin sulfate/carboxymethyl cellulose, or 1.5 wt% hyaluronan) and encapsulated by forming chitosan-GAG polyelectrolyte complex membranes around droplets of the cell suspension. The interior capsule environment could be further tuned by blending collagen with or suspending microcarriers in the GAG solution These capsule modules were seeded externally with vascular endothelial cells (VEC), and subsequently fused into tissue constructs possessing VEC-lined, inter-capsule channels. The microcapsules supported high density growth achieving clinically significant cell densities. Fusion of the endothelialized, capsules generated three dimensional constructs with an embedded network of interconnected channels that enabled long-term perfusion culture of the construct. A prototype, engineered liver tissue, formed by fusion of hepatocyte-containing capsules exhibited urea synthesis rates and albumin synthesis rates comparable to standard collagen sandwich hepatocyte cultures. The capsule based, modular approach described here has the potential to allow rapid assembly of tissue constructs with clinically significant cell densities, uniform cell distribution, and endothelialized, perfusable channels.

In vitro and in vivo angiogenic capacity of BM-MSCs/HUVECs and AT-MSCs/HUVECs cocultures

The aim of this study was to comparatively evaluate the angiogenic capacity of cocultures using either human bone marrow- or human adipose tissue-derived mesenchymal stem cells (MSCs) (BM- or AT-MSCs) with human umbilical vein endothelial cells (HUVECs) both in vitro and in vivo at early time points (i.e. days 3 and 7). In vitro, cells were either monocultured (i.e. BM-MSCs, AT-MSCs or HUVECs) or cocultured (i.e. BM-MSCs/HUVECs and AT-MSCs/HUVECs) on Thermanox® (2-dimensional, 2D) or in collagen gels (3-dimensional, 3D). For the in vivo experiment, cells (cocultures) were embedded in collagen gels and implanted subcutaneously in nude mice. For both in vitro and in vivo experiments, samples were collected on days 3 and 7 and histologically processed for hematoxylin-eosin and platelet endothelial cell adhesion molecule (PECAM-1; CD31) staining. For in vivo samples, quantitative parameters for evaluating angiogenesis included CD31-positive staining percentage, total vessel-like structure (VLS) area percentage, VLS density, and average VLS area (i.e. the size of per VLS). In vitro results showed the formation of VLS in both cocultures, while none of the monocultures showed VLS formation, irrespective of 2D or 3D culture condition. Although VLS formation occurred after in vivo implantation, no significant difference in angiogenic capacity was observed between the two cocultures, either on day 3 or on day 7. Further, VLS density decreased and anastomosis of the new human vessels with the murine host vasculature occurred over time. In conclusion, this study demonstrated that AT-MSCs/HUVECs and BM-MSCs/HUVECs have equal angiogenic capacity both in vitro and in vivo, and that vessels from donor origin can anastomose with the host vasculature within seven days of implantation.

Cell interactions between human progenitor-derived endothelial cells and human mesenchymal stem cells in a three-dimensional macroporous polysaccharide-based scaffold promote osteogenesis

Several studies have reported the benefits of mesenchymal stem cells (MSCs) for bone tissue engineering. However, vascularization remains one of the main obstacles that must be overcome to reconstruct large bone defects. In vitro prevascularization of the three-dimensional (3-D) constructs using co-cultures of human progenitor-derived endothelial cells (PDECs) with human bone marrow mesenchymal stem cells (HBMSCs) appeared as a potential strategy. However, the crosstalk between the two lineages has been studied in two-dimensional (2-D), but remains unknown in 3-D. The aim of this study is to investigate the cell interactions between PDECs and HBMSCs in a porous matrix composed of polysaccharides. This biodegradable scaffold promotes cell interactions by inducing multicellular aggregates composed of HBMSCs surrounded by PDECs. Cell aggregation contributes to the formation of junctional proteins composed of Connexin43 (Cx43) and VE-cadherin, and an activation of osteoblastic differentiation of HBMSCs stimulated by the presence of PDECs. Inhibition of Cx43 by mimetic peptide 43GAP27 induced a decrease in mRNA levels of Cx43 and all the bone-specific markers. Finally, subcutaneous implantations for 3 and 8 weeks in NOG mice revealed an increase in osteoid formation with the tissue-engineered constructs seeded with HBMSCs/PDECs compared with those loaded with HBMSCs alone. Taking together, these results demonstrate that this 3-D microenvironment favored cell communication, osteogenesis and bone formation.

One-stage focal cartilage defect treatment with bone marrow mononuclear cells and chondrocytes leads to better macroscopic cartilage regeneration compared to microfracture in goats

OBJECTIVE

The combination of chondrocytes and mononuclear fraction (MNF) cells might solve the expansion induced dedifferentiation problem of reimplanted cells in autologous chondrocytes implantation as sufficient cells would be available for direct, one-stage, implantation. Earlier in vitro work already showed a positive stimulation of cartilage specific matrix production when chondrocytes and MNF cells were combined. Therefore, this study aimed to evaluate cartilage regeneration using a one-stage procedure combining MNF cells and primary chondrocytes for the treatment of focal cartilage lesions in goats compared to microfracture treatment.

DESIGN

Freshly created focal cartilage defects were treated with either a combination of chondrocytes and MNF cells embedded in fibrin glue or microfracture treatment. After 6 months follow-up local regeneration as well as the general joint cartilage health were evaluated using validated scores and biochemical assays.

RESULTS

Macroscopic (P = 0.015) scores for the cartilage surface at the treated defect were, after 6 months, significantly higher for the chondrocyteMNF treatment compared to microfracture-treated defects, but microscopic scores were not (P = 0.067). The articulating cartilage showed more (P = 0.005) degeneration following microfracture treatment compared to chondrocyteMNF treatment. Biochemical glycosaminoglycans (GAG) evaluation did not reveal differences between the treatments. Both treatments had resulted in a slight to moderate cartilage degeneration at other locations in the joint.

CONCLUSION

In conclusion, treatment of focal articular cartilage lesions in goats using a combination of MNF cells from bone marrow and unexpanded chondrocytes leads to better macroscopic regeneration compared to microfracture, however needs further fine-tuning to decrease the negative influence on other joint compartments.

Adipose tissue-derived mesenchymal stem cells as monocultures or cocultures with human umbilical vein endothelial cells: performance in vitro and in rat cranial defects

The aim of this study was to compare the osteogenic capacity between human adipose tissue-derived mesenchymal stem cells (AT-MSCs) and their cocultures with human umbilical vein endothelial cells (HUVECs) in vitro and their biological performance in vivo. First, the optimal cell ratio in cocultures for osteogenic differentiation was determined by seeding AT-MSCs and HUVECs in ratios varying from 100:0 to 0:100 on tissue culture plates. Afterward, AT-MSCs and AT-MSCs/HUVECs (50:50) were seeded on porous titanium fiber mesh scaffolds (Ti) for both in vitro and in vivo osteogenic evaluation. For in vitro evaluation, cell osteogenic differentiation was assessed by alkaline phosphatase (ALP) activity and calcium assay. For in vivo evaluation, the scaffolds were implanted bilaterally into rat cranial defects (5 mm diameter) and bone formation was assessed histologically and histomorphometrically after 8 weeks. The ratio of 50:50 was chosen in the cocultures because this coculture condition retained similar amount of calcium deposition while using the least amount of AT-MSCs. Moreover, AT-MSCs showed higher osteogenic differentiation in comparison to AT-MSCs/HUVECs on Ti in vitro. Furthermore, superior bone formation was observed in AT-MSCs compared to AT-MSCs/HUVECs in rat cranial defects. In conclusion, AT-MSCs showed significantly higher osteogenic potential compared to AT-MSCs/HUVECs both in vitro and in vivo.