From isolation to implantation: a concise review of mesenchymal stem cell therapy in bone fracture repair

Clinical management and innovation in fracture non-union

INTRODUCTION

With the introduction and continuous improvement in operative fracture fixation, even the most severe bone fractures can be treated with a high rate of successful healing. However, healing complications can occur and when healing fails over prolonged time, the outcome is termed a fracture non-union. Non-union is generally believed to develop due to inadequate fixation, underlying host-related factors, or infection. Despite the advancements in fracture fixation and infection management, there is still a clear need for earlier diagnosis, improved prediction of healing outcomes and innovation in the treatment of non-union.

AREAS COVERED

This review provides a detailed description of non-union from a clinical perspective, including the state of the art in diagnosis, treatment, and currently available biomaterials and orthobiologics.Subsequently, recent translational development from the biological, mechanical, and infection research fields are presented, including the latest in smart implants, osteoinductive materials, and in silico modeling.

EXPERT OPINION

The first challenge for future innovations is to refine and to identify new clinical factors for the proper definition, diagnosis, and treatment of non-union. However, integration of in vitro, in vivo, and in silico research will enable a comprehensive understanding of non-union causes and correlations, leading to the development of more effective treatments.

Accelerated Bone Healing via Electrical Stimulation

Piezoelectric effect produces an electrical signal when stress is applied to the bone. When the integrity of the bone is destroyed, the biopotential within the defect site is reduced and several physiological responses are initiated to facilitate healing. During the healing of the bone defect, the bioelectric potential returns to normal levels. Treatment of fractures that exceed innate regenerative capacity or exhibit delayed healing requires surgical intervention for bone reconstruction. For bone defects that cannot heal on their own, exogenous electric fields are used to assist in treatment. This paper reviews the effects of exogenous electrical stimulation on bone healing, including osteogenesis, angiogenesis, reduction in inflammation and effects on the peripheral nervous system. This paper also reviews novel electrical stimulation methods, such as small power supplies and nanogenerators, that have emerged in recent years. Finally, the challenges and future trends of using electrical stimulation therapy for accelerating bone healing are discussed.

Sustainably cultured coral scaffold supports human bone marrow mesenchymal stromal cell osteogenesis

The current gold standard grafting material is autologous bone due to its osteoinductive and osteoconductive properties. Autograft harvesting results in donors site morbidity. Coral scaffolds offer a natural autograft alternative, sharing the density and porosity of human bone. This study investigated the biocompatibility and osteogenic potential of a novel, sustainably grown Pocillopora scaffold with human bone marrow-derived mesenchymal stromal cells (MSCs). The coral-derived scaffold displays a highly textured topography, with concavities of uniform size and a high calcium carbonate content. Large scaffold samples exhibit compressive and diametral tensile strengths in the range of trabecular bone, with strengths likely increasing for smaller particulate samples. Following the in vitro seeding of MSCs adjacent to the scaffold, the MSCs remained viable, continued proliferating and metabolising, demonstrating biocompatibility. The seeded MSCs densely covered the coral scaffold with organized, aligned cultures with a fibroblastic morphology. In vivo coral scaffolds with MSCs supported earlier bone and blood vessel formation as compared to control constructs containing TCP-HA and MSCs. This work characterized a novel, sustainably grown coral scaffold that was biocompatible with MSCs and supports their in vivo osteogenic differentiation, advancing the current repertoire of biomaterials for bone grafting.

A Cartilaginous Construct with Bone Collar Exerts Bone-Regenerative Property Via Rapid Endochondral Ossification

Three-dimensional clumps of mesenchymal stem cells (MSCs)/extracellular matrix (ECM) complexes (C-MSCs) can be implanted into tissue defects with no artificial scaffolds. In addition, the cellular properties and characteristics of the ECM in C-MSCs can be regulated in vitro. Most bone formation in the developmental and healing process is due to endochondral ossification, which occurs after bone collar formation surrounding cartilage derived from MSCs. Thus, to develop a rapid and reliable bone-regenerative cell therapy, the present study aimed to generate cartilaginous tissue covered with a mineralized bone collar-like structure from human C-MSCs by combining chondrogenic and osteogenic induction. Human bone marrow-derived MSCs were cultured in xeno-free/serum-free (XF) growth medium. Confluent cells that formed cellular sheets were detached from the culture plate using a micropipette tip. The floating cellular sheet contracted to round clumps of cells (C-MSCs). C-MSCs were maintained in XF-chondro-inductive medium (CIM) and XF-osteo-inductive medium (OIM). The biological and bone-regenerative properties of the generated cellular constructs were assessed in vitro and in vivo. C-MSCs cultured in CIM/OIM formed cartilaginous tissue covered with a mineralized matrix layer, whereas CIM treatment alone induced cartilage with no mineralization. Transplantation of the cartilaginous tissue covered with a mineralized matrix induced more rapid bone reconstruction via endochondral ossification in the severe combined immunodeficiency mouse calvarial defect model than that of cartilage generated using only CIM. These results highlight the potential of C-MSC culture in combination with CIM/OIM to generate cartilage covered with a bone collar-like structure, which can be applied for novel bone-regenerative cell therapy.

Clumps of mesenchymal stem cells/extracellular matrix complexes directly reconstruct the functional periodontal tissue in a rat periodontal defect model

Periodontitis is an inflammatory disease characterized by tooth-supporting periodontal tissue destruction, including the cementum, periodontal ligament, and alveolar bone. To regenerate the damaged periodontal tissue, mesenchymal stem cells (MSCs) have attracted much scientific and medical attention. Recently, we generated clumps of MSCs/extracellular matrix (ECM) complexes (C-MSCs), which consist of cells and self-produced ECM. C-MSCs can be transplanted into lesion areas without artificial scaffold to induce tissue regeneration. To develop reliable scaffold-free periodontal tissue regenerative cell therapy by C-MSCs, this study investigated the periodontal tissue regenerative capacity of C-MSCs and the behavior of the transplanted cells. Rat bone marrow-derived MSCs were isolated from rat femur. Confluent cells were scratched using a micropipette tip and then torn off. The sheet was rolled to make a three-dimensional round clump of cells, C-MSCs. Then, ten C-MSCs were grafted into a rat periodontal fenestration defect model. To trace the grafted cells in the defect, PKH26-labeled cells were also employed. Micro-CT and histological analyses demonstrated that transplantation of C-MSCs induced successful periodontal tissue regeneration in the rat periodontal defect model. Interestingly, the majority of the cells in the reconstructed tissue, including cementum, periodontal ligaments, and alveolar bone, were PKH26 positive donor cells, suggesting the direct tissue formation by MSCs. This study demonstrates a promising scaffold-free MSCs transplantation strategy for periodontal disease using C-MSCs and offers the significance of multipotency of MSCs to induce successful periodontal tissue regeneration.

Priming with a Combination of FGF2 and HGF Restores the Impaired Osteogenic Differentiation of Adipose-Derived Stem Cells

Classical aging-associated diseases include osteoporosis, diabetes, hypertension, and arthritis. Osteoporosis causes the bone to become brittle, increasing fracture risk. Among the various treatments for fractures, stem cell transplantation is currently in the spotlight. Poor paracrine/differentiation capacity, owing to donor age or clinical history, limits efficacy. Lower levels of fibroblast growth factor 2 (FGF2) and hepatocyte growth factor (HGF) are involved in cell repopulation, angiogenesis, and bone formation in the elderly ADSCs (ADSC-E) than in the young ADSCs (ADSC-Y). Here, we study the effect of FGF2/HGF priming on the osteogenic potential of ADSC-E, determined by calcium deposition in vitro and ectopic bone formation in vivo. Age-induced FGF2/HGF deficiency was confirmed in ADSCs, and their supplementation enhanced the osteogenic differentiation ability of ADSC-E. Priming with FGF2/HGF caused an early shift of expression of osteogenic markers, including Runt-related transcription factor 2 (Runx-2), osterix, and alkaline phosphatase (ALP) during osteogenic differentiation. FGF2/HGF priming also created an environment favorable to osteogenesis by facilitating the secretion of bone morphogenetic protein 2 (BMP-2) and vascular endothelial growth factor (VEGF). Bone tissue of ADSC-E origin was observed in mice transplanted with FGF/HGF-primed ADSC-E. Collectively, FGF2/HGF priming could enhance the bone-forming capacity in ADSC-E. Therefore, growth factor-mediated cellular priming can enhance ADSC differentiation in bone diseases and thus contributes to the increased efficacy in vivo.

A Review Into the Insights of the Role of Endothelial Progenitor Cells on Bone Biology

In addition to its important transport functions, the skeletal system is involved in complex biological activities for the regulation of blood vessels. Endothelial progenitor cells (EPCs), as stem cells of endothelial cells (ECs), possess an effective proliferative capacity and a powerful angiogenic capacity prior to their differentiation. They demonstrate synergistic effects to promote bone regeneration and vascularization more effectively by co-culturing with multiple cells. EPCs demonstrate a significant therapeutic potential for the treatment of various bone diseases by secreting a combination of growth factors, regulating cellular functions, and promoting bone regeneration. In this review, we retrospect the definition and properties of EPCs, their interaction with mesenchymal stem cells, ECs, smooth muscle cells, and immune cells in bone regeneration, vascularization, and immunity, summarizing their mechanism of action and contribution to bone biology. Additionally, we generalized their role and potential mechanisms in the treatment of various bone diseases, possibly indicating their clinical application.

Xenotransplantation of cryopreserved human clumps of mesenchymal stem cells/extracellular matrix complexes pretreated with IFN-γ induces rat calvarial bone regeneration

Introduction

Three-dimensional (3D) clumps of mesenchymal stem cells (MSCs)/extracellular matrix (ECM) complexes, composed with cells and self-produced intact ECM, can be grafted into defect areas without artificial scaffold to induce successful bone regeneration. Moreover, C-MSCs pretreated with IFN-γ (C-MSCsγ) increased the immunomodulatory enzyme indoleamine 2,3-dioxygenase (IDO) expression and thereby inhibited T cell activity. Xenotransplantation of human C-MSCsγ suppressed host T cell immune rejection and induced bone regeneration in mice. Besides, we have also reported that C-MSCs retain the 3D structure and bone regenerative property even after cryopreservation. To develop the "off-the-shelf" cell preparation for bone regenerative therapy that is promptly provided when needed, we investigated whether C-MSCsγ can retain the immunosuppressive and osteogenic properties after cryopreservation.

Methods

Confluent human MSCs that had formed on the cellular sheet were scratched using a micropipette tip and then torn off. The sheet was rolled to make a round clump of cells. The round cell clumps were incubated with a growth medium for 3 days, and then C-MSCs were obtained. To generate C-MSCsγ, after 2 days' culture, C-MSCs were stimulated with 50 ng/ml of IFN-γ. Both C-MSCs and C-MSCsγ were cryopreserved for 2 days and then thawed to obtain Cryo-C-MSCs and Cryo-C-MSCsγ, respectively. The biological properties of those cell clumps were assessed in vitro. In addition, to test whether human Cryo-C-MSCsγ attenuates immune rejection to induce bone regeneration, a xenograft study using a rat calvarial defect was performed.

Results

Both IFN-γ pretreatment and cryopreservation process did not affect the 3D structure and cell viability in all human cell clumps. Interestingly, Cryo-C-MSCsγ showed significantly increased IDO mRNA expression equivalent to C-MSCsγ. More importantly, xenotransplantation of human C-MSCsγ and Cryo-C-MSCsγ induced rat calvarial bone regeneration by suppressing rat T cells infiltration and the grafted human cells reduction in the grafted area. Finally, there were no human donor cells in the newly formed bone, implying that the bone reconstruction by C-MSCsγ and Cryo-C-MSCsγ can be due to indirect host osteogenesis.

Conclusion

These findings implied that Cryo-C-MSCsγ can be a promising bone regenerative allograft therapy that can be certainly and promptly supplied on demand.

Effects of Systemic or Local Administration of Mesenchymal Stem Cells from Patients with Osteoporosis or Osteoarthritis on Femoral Fracture Healing in a Mouse Model

The purpose of this study was to analyze the regenerative capacity of mesenchymal stem cells (MSCs) in the treatment of fractures. MSCs extracted from patients with osteoporotic hip fractures or hip osteoarthritis undergoing hip replacement surgeries were cultured and injected into mice with femoral fracture. Two experimental models were established, one for the systemic administration of MSCs (n = 29) and another one for local administration (n = 30). Fracture consolidation was assessed by micro-CT and histology. The degree of radiological consolidation and corticalization was better with MSCs from osteoporosis than from osteoarthritis, being significant after systemic administration (p = 0.0302 consolidation; p = 0.0243 corticalization). The histological degree of consolidation was also better with MSCs from osteoporosis than from osteoarthritis. Differences in histological scores after systemic infusion were as follows: Allen, p = 0.0278; Huo, p = 0.3471; and Bone Bridge, p = 0.0935. After local administration at the fracture site, differences in histological scores were as follows: Allen, p = 0.0764; Huo, p = 0.0256; and Bone Bridge, p = 0.0012. As osteoporosis and control groups were similar, those differences depended on an inhibitory influence by MSCs from patients with osteoarthritis. In conclusion, we found an unexpected impairment of consolidation induced by MSCs from patients with osteoarthritis. However, MSCs from patients with osteoporosis compared favorably with cells from patients with osteoarthritis. In other words, based on this study and previous studies, MSCs from patients with osteoporosis do not appear to have worse bone-regenerating capabilities than MSCs from non-osteoporotic individuals of similar age.

Development of a Gene-Activated Scaffold Incorporating Multifunctional Cell-Penetrating Peptides for pSDF-1α Delivery for Enhanced Angiogenesis in Tissue Engineering Applications

Non-viral gene delivery has become a popular approach in tissue engineering, as it permits the transient delivery of a therapeutic gene, in order to stimulate tissue repair. However, the efficacy of non-viral delivery vectors remains an issue. Our lab has created gene-activated scaffolds by incorporating various non-viral delivery vectors, including the glycosaminoglycan-binding enhanced transduction (GET) peptide into collagen-based scaffolds with proven osteogenic potential. A modification to the GET peptide (FLR) by substitution of arginine residues with histidine (FLH) has been designed to enhance plasmid DNA (pDNA) delivery. In this study, we complexed pDNA with combinations of FLR and FLH peptides, termed GET* nanoparticles. We sought to enhance our gene-activated scaffold platform by incorporating GET* nanoparticles into collagen-nanohydroxyapatite scaffolds with proven osteogenic capacity. GET* N/P 8 was shown to be the most effective formulation for delivery to MSCs in 2D. Furthermore, GET* N/P 8 nanoparticles incorporated into collagen-nanohydroxyapatite (coll-nHA) scaffolds at a 1:1 ratio of collagen:nanohydroxyapatite was shown to be the optimal gene-activated scaffold. pDNA encoding stromal-derived factor 1α (pSDF-1α), an angiogenic chemokine which plays a role in BMP mediated differentiation of MSCs, was then delivered to MSCs using our optimised gene-activated scaffold platform, with the aim of significantly increasing angiogenesis as an important precursor to bone repair. The GET* N/P 8 coll-nHA scaffolds successfully delivered pSDF-1α to MSCs, resulting in a significant, sustained increase in SDF-1α protein production and an enhanced angiogenic effect, a key precursor in the early stages of bone repair.

Characteristics of Mesenchymal Stem Cells Are Independent of Bone Marrow Storage Temperatures

Mesenchymal stem cells play an important role in regenerative medicine due to their capability of self-renewal and multipotent differentiation. For research or clinical application, bone marrow aspirates are harvested during elective surgeries to isolate MSCs. If an immediate purification of the MSCs is not possible, the bone marrow must be stored. Therefore, the aim of this study was to investigate possible differences of stem cell characteristics regarding the self-renewal capability, the adipogenic, chondrogenic, and osteogenic differentiation, and the expression of surface antigens after different storage conditions of the bone marrow aspirates. Three groups were analysed: the first group was purified immediately after harvesting, the other two groups were processed after they were stored 18 to 24 hours at 22°C (room temperature) or at 4°C. Comparisons between the groups were performed using the Kruskal-Wallis test for nonparametric data. The final results showed no significant difference between the different storage conditions. Therefore, storage of bone marrow aspirates for 18 to 24 hours at room temperature or 4°C is possible without loss of stem cell characteristics.

Clumps of Mesenchymal Stem Cells/Extracellular Matrix Complexes Generated with Xeno-Free Chondro-Inductive Medium Induce Bone Regeneration via Endochondral Ossification

Three-dimensional clumps of mesenchymal stem cells (MSCs)/extracellular matrix (ECM) complexes (C-MSCs) can be transplanted into tissue defect site with no artificial scaffold. Importantly, most bone formation in the developing process or fracture healing proceeds via endochondral ossification. Accordingly, this present study investigated whether C-MSCs generated with chondro-inductive medium (CIM) can induce successful bone regeneration and assessed its healing process. Human bone marrow-derived MSCs were cultured with xeno-free/serum-free (XF) growth medium. To obtain C-MSCs, confluent cells that had formed on the cellular sheet were scratched using a micropipette tip and then torn off. The sheet was rolled to make a round clump of cells. The cell clumps, i.e., C-MSCs, were maintained in XF-CIM. C-MSCs generated with XF-CIM showed enlarged round cells, cartilage matrix, and hypertrophic chondrocytes genes elevation in vitro. Transplantation of C-MSCs generated with XF-CIM induced successful bone regeneration in the SCID mouse calvaria defect model. Immunofluorescence staining for human-specific vimentin demonstrated that donor human and host mouse cells cooperatively contributed the bone formation. Besides, the replacement of the cartilage matrix into bone was observed in the early period. These findings suggested that cartilaginous C-MSCs generated with XF-CIM can induce bone regeneration via endochondral ossification.

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.

Fibronectin in Fracture Healing: Biological Mechanisms and Regenerative Avenues

The importance of extracellular matrix (ECM) proteins in mediating bone fracture repair is evident, and fibronectin (FN) has emerged as a pivotal regulator of this process. FN is an evolutionarily conserved glycoprotein found in all tissues of the body, and functions in several stages of fracture healing. FN acts as a three-dimensional scaffold immediately following trauma, guiding the assembly of additional ECM components. Furthermore, FN regulates cellular behavior via integrin-binding and growth factor-binding domains, promoting downstream responses including cell recruitment, proliferation and differentiation. Due to its diverse functions, the development of FN-based strategies to promote fracture healing is under intense research. In this review, we discuss the recent advancements in utilizing FN-based biomaterials, showing promise in tissue engineering and regenerative medicine applications.

Apigenin promotes osteogenic differentiation of mesenchymal stem cells and accelerates bone fracture healing via activating Wnt/β-catenin signaling

Apigenin (API), a natural plant flavone, is abundantly found in common fruits and vegetables. As a bioactive flavonoid, API exhibits several activities including antiproliferation and anti-inflammation. A recent study showed that API could retard osteoporosis progress, indicating its role in the skeletal system. However, the detailed function and mechanism remain obscure. In the present study, API was found to promote osteogenic differentiation of mesenchymal stem cells (MSCs). And further investigation showed that API could enhance the expression of the critical transcription factor β-catenin and several downstream target genes of Wnt signaling, thus activated Wnt/β-catenin signaling. Using a rat femoral fracture model, API was found to improve new bone formation and accelerate fracture healing in vivo. In conclusion, our data demonstrated that API could promote osteogenesis in vitro and facilitate the fracture healing in vivo via activating Wnt/β-catenin signaling, indicating that API may be a promising therapeutic candidate for bone fracture repair.NEW & NOTEWORTHY1) API promoted osteogenic differentiation of human MSCs in vitro; 2) API facilitated bone formation and accelerated fracture healing in vivo; 3) API stimulated Wnt/β-catenin signaling during osteogenesis of human MSCs.

Cell Sources for Human In vitro Bone Models

PURPOSE OF REVIEW

One aim in bone tissue engineering is to develop human cell-based, 3D in vitro bone models to study bone physiology and pathology. Due to the heterogeneity of cells among patients, patient's own cells are needed to be obtained, ideally, from one single cell source. This review attempts to identify the appropriate cell sources for development of such models.

RECENT FINDINGS

Bone marrow and peripheral blood are considered as suitable sources for extraction of osteoblast/osteocyte and osteoclast progenitor cells. Recent studies on these cell sources have shown no significant differences between isolated progenitor cells. However, various parameters such as medium composition affect the cell's proliferation and differentiation potential which could make the peripheral blood-derived stem cells superior to the ones from bone marrow. Peripheral blood can be considered a suitable source for osteoblast/osteocyte and osteoclast progenitor cells, being less invasive for the patient. However, more investigations are needed focusing on extraction and differentiation of both cell types from the same donor sample of peripheral blood.

A Plastic β-Tricalcium Phosphate/Gelatine Scaffold Seeded with Allogeneic Adipose-Derived Stem Cells for Mending Rabbit Bone Defects

To investigate the feasibility of β-tricalcium phosphate (TCP)/gelatine scaffold combined with allogeneic adipose-derived stem cells (ASCs) to repair hole shape defect, third-passage ASCs were seeded onto composite scaffolds to prepare an ASC-β-TCP/gelatine tissue-engineered bone to pack into the rabbit cavernous bone defects of experimental groups. In animal models, the bone defect area was completely filled and difficult to recognize in the experimental group at 12 weeks post-surgery by gross observation and radiographic examination. The average bone mineral density value of them was higher than that of the control group. Because of the biocompatibility with allogenic ASCs and the osteoconductivity of β-TCP/gelatine scaffolds, β-TCP/gelatine is suitable as a plastic scaffold for the ASC-seeded tissue-engineered bone to repair cavernous defects.

[The association of stromal mesenchymal cells with the bone substitute for the treatment of non-union of long bones, an alternative to autologous spongy grafts: a case report]

Bone is the most transplanted human tissue. Surgical interventions for bone repair are necessary for various pathologies such as nonunion, osteoporosis or osteonecrosis. Although autologous bone grafts remain the benchmark for bone regeneration, they unfortunately have a number of disadvantages: the need for a second intervention and the limited amount of tissue removed. Synthetic bone substitutes overcome some of these drawbacks, but their osteoinductive properties do not make it possible to treat significant bone losses. Cellular therapies based on mesenchymal stromal stem cells (MSC) in combination with bone substitutes may be alternatives to autologous bone grafting. It is in this context that we report the case of a patient with congenital dysplasia treated for non-union of the femur. The association of mesenchymal stem cells with bone substitute allowed us to obtain consolidation after 6 months.

Intramedullary Nail Fixation with Autologous Bone Marrow Transplantation in an Incomplete Atypical Femoral Fracture Patient: Use of Bone Marrow Extracted from the Hollow Reamer

The present report describes an incomplete atypical femoral fracture (AFF) patient who underwent simultaneous autogenous bone transplantation to the resected fracture region during intramedullary nail fixation. A 73-year-old female with a history of multiple myeloma had been undergoing treatment with intravenous drip injections of Zoledronic Acid. She was introduced to our department due to the left lateral thigh pain, with no trauma incidence. An anteroposterior radiograph showed a transverse thin fracture line with localized periosteal and endosteal thickening, which is compatible with subtrochanteric incomplete AFF. A biochemical investigation revealed the existence of severely suppressed bone turnover. She underwent intramedullary nail fixation for fear of a complete fracture. After the fixation, the cortical bone at the fracture region was excised as a wedge-shaped block, and bone marrow extracted from the hollow reamer was simultaneously transplanted to the resected fracture region. Histological examination showed few bone formation features at the fracture line in the excised lateral cortical bone. At 7 months after surgery, radiographs demonstrated complete bone repair, and no clinical problems were observed two years postoperatively. To the best of our knowledge, this is the first report in which autogenous bone marrow transplantation, noninvasive to the iliac crest, was performed in an incomplete AFF patient. We believe that this low invasive procedure can be a useful technique for AFF treatment.

Impact of Type 2 Diabetes Mellitus on Human Bone Marrow Stromal Cell Number and Phenotypic Characteristics

Human bone marrow-derived mesenchymal stromal cells (MSCs) have been investigated in numerous disease settings involving impaired regeneration because of the crucial role they play in tissue maintenance and repair. Considering the number of comorbidities associated with type 2 diabetes mellitus (T2DM), the hypothesis that MSCs mediate these comorbidities via a reduction in their native maintenance and repair activities is an intriguing line of inquiry. Here, it is demonstrated that the number of bone marrow-derived MSCs in people with T2DM was reduced compared to that of age-matched control (AMC) donors and that this was due to a specific decrease in the number of MSCs with osteogenic capacity. There were no differences in MSC cell surface phenotype or in MSC expansion, differentiation, or angiogenic or migratory capacity from donors living with T2DM as compared to AMCs. These findings elucidate the basic biology of MSCs and their potential as mediators of diabetic comorbidities, especially osteopathies, and provide insight into donor choice for MSC-based clinical trials. This study suggests that any role of bone marrow MSCs as a mediator of T2DM comorbidity is likely due to a reduction in the osteoprogenitor population size and not due to a permanent alteration to the MSCs' capacity to maintain tissue homeostasis through expansion and differentiation.

Exosomal miRNA-128-3p from mesenchymal stem cells of aged rats regulates osteogenesis and bone fracture healing by targeting Smad5

Transplantation of mesenchymal stem cells (MSCs) has been considered an effective therapeutic treatment for a variety of diseases including bone fracture. However, there are associated complications along with MSCs transplantation. There is evidence to show that exosomes (Exos) derived from MSCs exert a similar paracrine function. In addition, repair capabilities of MSCs decline with age. Hence, this study aims to confirm whether the Exos protective function on osteogenic differentiation and fracture healing from aged MSCs was attenuated. This information was used in order to investigate the underlying mechanism. MSCs were successfully isolated and identified from young and aged rats, and Exos were then obtained. Aged-Exos exhibited significantly attenuated effects on MSCs osteogenic differentiation in vitro and facture healing in vivo. Using miRNA array analysis, it was shown that miR-128-3p was markedly upregulated in Aged-Exos. In vitro experiments confirmed that Smad5 is a direct downstream target of miR-128-3p, and was inhibited by overexpressed miR-128-3p. A series gain- and loss- function experiment indicated that miR-128-3P serves a suppressor role in the process of fracture healing. Furthermore, effects caused by miR-128-3P mimic/inhibitor were reversed by the application of Smad5/siSmad5. Taken together, these results suggest that the therapeutic effects of MSCs-derived Exos may vary according to differential expression of miRNAs. Exosomal miR-128-3P antagomir may act as a promising therapeutic strategy for bone fracture healing, especially for the elderly.

Strontium Promotes the Proliferation and Osteogenic Differentiation of Human Placental Decidual Basalis- and Bone Marrow-Derived MSCs in a Dose-Dependent Manner

The osteogenic potential of mesenchymal stromal cells (MSCs) varies among different tissue sources. Strontium enhances the osteogenic differentiation of bone marrow-derived MSCs (BM-MSCs), but whether it exerts similar effects on placental decidual basalis-derived MSCs (PDB-MSCs) remains unknown. Here, we compared the influence of strontium on the proliferation and osteogenic differentiation of human PDB- and BM-MSCs in vitro. We found that 1 mM and 10 mM strontium, but not 0.1 mM strontium, evidently promoted the proliferation of human PDB- and BM-MSCs. These doses of strontium showed a comparable alkaline phosphatase activity in both cell types, but their osteogenic gene expressions were promoted in a dose-dependent manner. Strontium at doses of 0.1 mM and 1 mM elevated several osteogenic gene expressions of PDB-MSCs, but not those of BM-MSCs at an early stage. Nevertheless, they failed to enhance the mineralization of either cell type. By contrast, 10 mM strontium facilitated the osteogenic gene expression as well as the mineralization of human PDB- and BM-MSCs. Collectively, this study demonstrated that human PDB- and BM-MSCs shared a great similarity in response to strontium, which promoted their proliferation and osteogenic differentiation in a dose-dependent manner.

Exosomes from conditioned media of bone marrow-derived mesenchymal stem cells promote bone regeneration by enhancing angiogenesis

Growth factors in serum-free conditioned media from human bone marrow-derived mesenchymal stem cells (MSC-CM) are known to be effective in bone regeneration. However, the secretomes in MSC-CM that act as active ingredients for bone regeneration, as well as their mechanisms, remains unclear. Exosomes, components of MSC-CM, provide the recipient cells with genetic information and enhance the recipient cellular paracrine stimulation, which contributes to tissue regeneration. We hypothesized that MSC-CM-derived exosomes (MSC-Exo) promoted bone regeneration, and that angiogenesis was a key step. Here, we prepared an MSC-Exo group, MSC-CM group, and Exo-antiVEGF group (MSC-Exo with angiogenesis inhibitor), and examined the osteogenic and angiogenic potential in MSCs. Furthermore, we used a rat model of calvaria bone defect and implanted each sample to evaluate bone formation weekly, until week 4 after treatment. Results showed that MSC-Exo enhanced cellular migration and osteogenic and angiogenic gene expression in MSCs compared to that in other groups. In vivo, early bone formation by MSC-Exo was also confirmed. Two weeks after implantation, the newly formed bone area was 31.5 ± 6.5% in the MSC-Exo group while those in the control and Exo-antiVEGF groups were 15.4 ± 4.4% and 8.7 ± 1.1%, respectively. Four weeks after implantation, differences in the area between the MSC-Exo group and the Exo-antiVEGF or control groups were further broadened. Histologically, notable accumulation of osteoblast-like cells and vascular endothelial cells was observed in the MSC-Exo group; however, fewer cells were found in the Exo-antiVEGF and control groups.

In conclusion, MSC-Exo promoted bone regeneration during early stages, as well as enhanced angiogenesis. Considering the tissue regeneration with transplanted cells and their secretomes, this study suggests that exosomes might play an important role, especially in angiogenesis.

Clumps of Mesenchymal Stem Cell/Extracellular Matrix Complexes Generated with Xeno-Free Conditions Facilitate Bone Regeneration via Direct and Indirect Osteogenesis

Three-dimensional clumps of mesenchymal stem cell (MSC)/extracellular matrix (ECM) complexes (C-MSCs) consist of cells and self-produced ECM. We demonstrated previously that C-MSCs can be transplanted into bone defect regions with no artificial scaffold to induce bone regeneration. To apply C-MSCs in a clinical setting as a reliable bone regenerative therapy, the present study aimed to generate C-MSCs in xeno-free/serum-free conditions that can exert successful bone regenerative properties and to monitor interactions between grafted cells and host cells during bone healing processes. Human bone marrow-derived MSCs were cultured in xeno-free/serum-free medium. To obtain C-MSCs, confluent cells that had formed on the cellular sheet were scratched using a micropipette tip and then torn off. The sheet was rolled to make a round clump of cells. Then, C-MSCs were transplanted into an immunodeficient mouse calvarial defect model. Transplantation of C-MSCs induced bone regeneration in a time-dependent manner. Immunofluorescence staining showed that both donor human cells and host mice cells contributed to bone reconstruction. Decellularized C-MSCs implantation failed to induce bone regeneration, even though the host mice cells can infiltrate into the defect area. These findings suggested that C-MSCs generated in xeno-free/serum-free conditions can induce bone regeneration via direct and indirect osteogenesis.

Challenges in Clinical Development of Mesenchymal Stromal/Stem Cells: Concise Review

Identified 50 years ago, mesenchymal stromal/stem cells (MSCs) immediately generated a substantial interest among the scientific community because of their differentiation plasticity and hematopoietic supportive function. Early investigations provided evidence of a relatively low engraftment rate and a transient benefit for challenging congenital and acquired diseases. The reasons for these poor therapeutic benefits forced the entire field to reconsider MSC mechanisms of action together with their ex vivo manipulation procedures. This phase resulted in advances in MSCs processing and the hypothesis that MSC‐tissue supportive functions may be prevailing their differentiation plasticity, broadening the spectrum of MSCs therapeutic potential far beyond their lineage‐restricted commitments. Consequently, an increasing number of studies have been conducted for a variety of clinical indications, revealing additional challenges and suggesting that MSCs are still lagging behind for a solid clinical translation. For this reason, our aim was to dissect the current challenges in the development of still promising cell types that, after more than half a century, still need to reach their maturity. stem cells translational medicine2019;8:1135–1148

TRAF4 positively regulates the osteogenic differentiation of mesenchymal stem cells by acting as an E3 ubiquitin ligase to degrade Smurf2

TNF receptor-associated factor 4 (TRAF4), a member of the TRAF family, plays an important role in the embryogenesis and development of the bone system. Mesenchymal stem cells (MSCs), which are the primary origin of osteoblasts in vivo, are key cells in bone development; however, whether TRAF4 modulates the osteogenic capacity of MSCs has never been explored. In this study, we demonstrated that TRAF4 positively regulates the osteogenic process of MSCs both in vitro and in vivo. In addition, we further demonstrated that TRAF4 modulates the osteogenic process of MSCs by acting as an E3 ubiquitin ligase to mediate the K48-linked ubiquitination of Smurf2 at the K119 site and cause degradation. Furthermore, TRAF4 was abnormally decreased in bone sections of ovariectomized rat and osteoporosis patients. Taken together, our findings suggest that TRAF4 positively regulates the osteogenic differentiation of MSCs by acting as an E3 ubiquitin ligase to degrade Smurf2. These results emphasize the critical role of TRAF4 in bone formation and could not only improve the clinical use of MSCs in tissue engineering but also clarify the pathogenesis of bone metabolism disorders.

Convergence of TGFβ and BMP signaling in regulating human bone marrow stromal cell differentiation

Targeting regulatory signaling pathways that control human bone marrow stromal (skeletal or mesenchymal) stem cell (hBMSC) differentiation and lineage fate determination is gaining momentum in the regenerative medicine field. Therefore, to identify the central regulatory mechanism of osteoblast differentiation of hBMSCs, the molecular phenotypes of two clonal hBMSC lines exhibiting opposite in vivo phenotypes, namely, bone forming (hBMSC^+bone) and non-bone forming (hBMSC^−Bone) cells, were studied. Global transcriptome analysis revealed significant downregulation of several TGFβ responsive genes, namely, TAGLN, TMP1, ACTA2, TGFβ2, SMAD6, SMAD9, BMP2, and BMP4 in hBMSC^−Bone cells and upregulation on SERPINB2 and NOG. Transcriptomic data was associated with marked reduction in SMAD2 protein phosphorylation, which thereby implies the inactivation of TGFβ and BMP signaling in those cells. Concordantly, activation of TGFβ signaling in hBMSC^−Bone cells using either recombinant TGFβ1 protein or knockdown of SERPINB2 TGFβ-responsive gene partially restored their osteoblastic differentiation potential. Similarly, the activation of BMP signaling using exogenous BMP4 or via siRNA-mediated knockdown of NOG partially restored the differentiation phenotype of hBMSC^−Bone cells. Concordantly, recombinant NOG impaired ex vivo osteoblastic differentiation of hBMSC^+Bone cells, which was associated with SERBINB2 upregulation. Our data suggests the existence of reciprocal relationship between TGFB and BMP signaling that regulates hBMSC lineage commitment and differentiation, whilst provide a plausible strategy for generating osteoblastic committed cells from hBMSCs for clinical applications.

MiR-148a regulates bone marrow mesenchymal stem cells-mediated fracture healing by targeting insulin-like growth factor 1

The purpose of this study was to investigate the underlying molecular mechanisms of fracture healing mediated by bone marrow mesenchymal stem cells. Differentially expressed microRNAs in acutely injured subjects and healthy volunteers were screened by microarray analysis. The dual luciferase reporter system was used to verify whether insulin-like growth factor 1 (IGF1) was the direct target gene regulated by miR-148a. The expression level of miR-148a and IGF1 after osteogenic differentiation was detected by quantitative real-time polymerase chain reaction. Western blot was used to determine the protein expression of bone markers, including IGF1, runt-related transcription factor 2 (Runx2), osteocalcin, and osteopontin in rat bone marrow-derived mesenchymal stem cells. Alkaline phosphatase and alizarin red staining was used to detect alkaline phosphatase activity and calcium deposition. An animal fracture model was used for in vivo experiments. MiR-148a was highly expressed in acutely injured subjects compared with healthy volunteers, and IGF1 was a target of miR-148a. Moreover, compared with the negative control group, IGF1 messenger RNA expression was significantly increased in the miR-148a antagomir group. During osteogenic differentiation, the expression of IGF1, Runx2, osteocalcin, and osteopontin was higher in the miR-148a antagomir group than other groups. In vivo experiments further confirmed that upregulation of IGF1 enhanced fracture healing efficiently by decreasing callus width and area and improving bone mineral density, maximum load, stiffness, and energy absorption. It was proved that IGF1 was the direct target gene of miR-148a, and the use of rat bone marrow-derived mesenchymal stem cells with low expression of miR-148a could improve fracture healing by upregulating IGF1.

Embryonic-Like Mineralized Extracellular Matrix/Stem Cell Microspheroids as a Bone Graft Substitute

Native bone extracellular matrix (ECM) secreted by mesenchymal precursors provides an optimal biological framework, comprising structural collagen proteins and a microenvironment niche, which supports cell attachment and differentiation, and bone growth. Inspired by nature, the embryonic-like mineralized ECM/stem cell microspheroids (MECS) are developed, in which self-assembly of the stem cell microspheroids (CS) and mineralization of the self-produced ECM occur simultaneously. The uniform-sized MECS exhibit a solid spherical appearance with stem cells embedded inside, recapitulating the early stage of intramembranous ossification. Compared with pure CS, MECS show enhanced Young's modulus, cell viability, intercellular communication, and osteogenic differentiation. Additionally, the capability of MECS is explored without the use of exogenous scaffolds to substitute and repair lost bone in rat critical-sized defects. It is found that the MECS can achieve excellent bone regeneration outcomes with 97.99 ± 2.28% of the defect area filled with new bony structures and blood vessels, while nearly half or one-third of the defect area is repaired by CS (52.79 ± 4.63%) or β-tricalcium phosphate (38.09 ± 7.79%), respectively. The study demonstrates that embryonic-like MECS is a novel effective bone graft substitute for bone tissue regeneration.

Imaging of a high concentration of iron labeled cells with positive contrast in a rat knee

PURPOSE

The sweep imaging with Fourier transformation (SWIFT) imaging technique has been shown to provide positive contrast from diluted cell suspensions labeled with super-paramagnetic iron oxide (SPIO) in a tissue, as an alternative to T2*-weighted imaging. Here we demonstrate a variation of the SWIFT technique that yields a hyperintense signal from a concentrated cell suspension. The proposed technique provides minimal background signal from host tissue and facilitates visualization of injected cells.

METHODS

The proton resonance frequency and linewidth were determined for SPIO solutions of different concentrations. The original SWIFT sequence was modified and a dual saturation Gaussian shape RF pulse with ~200 Hz bandwidth was incorporated into the acquisition protocol to suppress host tissue and fat signals. This modification of the original acquisition protocol permits the detection of a hyperintense signal from grafted cells with minimal background signal from the host tissue.

RESULTS

SPIO particles not only induce broadening of NMR line-width but also an initiate proton resonance frequency shift. This shift is linearly proportional to the concentration of the iron oxide particles and induced by the bulk magnetic susceptibility of SPIOs. The shift of the resonance frequency of iron labeled cells allowed us effectively suppress the host tissues with saturation RF pulse to improve MRI detection of grafted cells.

CONCLUSIONS

Iron oxide particles increase the resonance frequency of water proton signal. This shift permitted us to add the tissue/fat saturation RF pulse into the original SWIFT acquisition protocol and detect distinct hyperintense signals from grafted cells with minimal background signal from the host tissue.

A Micro-Ark for Cells: Highly Open Porous Polyhydroxyalkanoate Microspheres as Injectable Scaffolds for Tissue Regeneration

To avoid large open surgery using scaffold transplants, small-sized cell carriers are employed to repair complexly shaped tissue defects. However, most cell carriers show poor cell adherences and viability. Therefore, polyhydroxyalkanoate (PHA), a natural biopolymer, is used to prepare highly open porous microspheres (OPMs) of 300-360 µm in diameter, combining the advantages of microspheres and scaffolds to serve as injectable carriers harboring proliferating stem cells. In addition to the convenient injection to a defected tissue, and in contrast to poor performances of OPMs made of polylactides (PLA OPMs) and traditional less porous hollow microspheres (PHA HMs), PHA OPMs present suitable surface pores of 10-60 µm and interconnected passages with an average size of 8.8 µm, leading to a high in vitro cell adhesion of 93.4%, continuous proliferation for 10 d and improved differentiation of human bone marrow mesenchymal stem cells (hMSCs). PHA OPMs also support stronger osteoblast-regeneration compared with traditional PHA HMs, PLA OPMs, commercial hyaluronic acid hydrogels, and carrier-free hMSCs in an ectopic bone-formation mouse model. PHA OPMs protect cells against stresses during injection, allowing more living cells to proliferate and migrate to damaged tissues. They function like a micro-Noah's Ark to safely transport cells to a defect tissue.

Cryopreserved clumps of mesenchymal stem cell/extracellular matrix complexes retain osteogenic capacity and induce bone regeneration

BACKGROUND

Three-dimensional (3D) cultured clumps of mesenchymal stem cell (MSC)/extracellular matrix (ECM) complexes (C-MSCs) consist of cells and self-produced ECM. C-MSCs can regulate cellular functions in vitro and can be grafted into a defect site without an artificial scaffold to induce bone regeneration. Long-term cryopreservation of C-MSCs, which can enable them to serve as a ready-to-use cell preparation, may be helpful in developing beneficial cell therapy for bone regeneration. Therefore, the aim of this study was to investigate the effect of cryopreservation on C-MSCs.

METHODS

MSCs isolated from rat femurs were cultured in growth medium supplemented with ascorbic acid. To obtain C-MSCs, confluent cells that had formed on the cellular sheet were scratched using a micropipette tip and were then torn off. The sheet was rolled to make a round clumps of cells. The C-MSCs were cryopreserved in cryomedium including 10% dimethyl sulfoxide.

RESULTS

Cryopreserved C-MSCs retained their 3D structure and did not exhibit a decrease in cell viability. In addition, stem cell marker expression levels and the osteogenic differentiation properties of C-MSCs were not reduced by cryopreservation. However, C-MSCs pretreated with collagenase before cryopreservation showed a lower level of type I collagen and could not retain their 3D structure, and their rates of cell death increased during cryopreservation. Both C-MSC and cryopreserved C-MSC transplantation into rat calvarial defects induced successful bone regeneration.

CONCLUSION

These data indicate that cryopreservation does not reduce the biological properties of C-MSCs because of its abundant type I collagen. More specifically, cryopreserved C-MSCs could be applicable for novel bone regenerative therapies.

Advances in mesenchymal stromal cell therapy in the management of Crohn's disease

The aim of therapy in Crohn's disease (CD) is induction and maintenance of remission, promotion of mucosal healing and restoration of quality of life. Even the best treatment regimes, including combinations of biologics and immunomodulators lack durable efficacy and have well documented side effects. Accordingly, there is an unmet need for novel therapies. Mesenchymal stromal cells (MSCs) are a subset of non-hematopoietic stem cells that home to sites of inflammation where they exert potent immunomodulatory effects and contribute to tissue repair. Their utility is being explored in several inflammatory and immune mediated disorders including CD, where they have demonstrated favourable safety, feasibility and efficacy profiles. Areas covered: This review highlights current knowledge on MSC therapy and critically evaluates their safety, efficacy and potential mechanisms of action in CD. Expert commentary: Building on positive early phase clinical trials and a recent phase 3 trial in perianal CD, there is considerable optimism for the possibility of MSCs changing the treatment landscape in complicated CD. Although important questions remain unanswered, including the safety and durability of MSC therapy, optimal adjunctive therapies and their sourcing and manufacturing, it is anticipated that MSCs are likely to enter mainstream treatment algorithms in the near future.

Sports Injuries: Diagnosis, Prevention, Stem Cell Therapy, and Medical Sport Strategy

Sports injuries diagnosis, prevention, and treatment are the most important issues of sports medicine. Fortunately, sports injuries are often treated effectively, and people with damage recover and return to the sport in a satisfactory condition. Meanwhile, many sports injuries and complications can be prevented. In general, sports injuries include acute or chronic injuries. Given increasing in popularity, sports medicine doctors use stem cells to treat a wide variety of sports injuries, including damage to tendons, ligaments, muscles, and cartilage. Stem cell therapy to an injured area could be done through direct surgical application, stem-cell-bearing sutures, and injection. Stem cell therapy holds potential for repair and functional plasticity following sports injuries compared to traditional methods; however, the mechanism of stem cell therapy for sports injuries remains largely unknown. Medical imaging technologies provide the hope to ample the knowledge concerning basic stem cell biology in real time when transplanted into sport-induced damaged organs. Using stem cell treatment might restore continuity and regeneration and promote growth back the organ targets. Besides, using a noninvasive medical imaging method would have the long-time monitoring advantage to the stem cells transplanting individual. The multimodality imaging technique allows for studying acute pathological events following sports injuries; therefore, the use of imaging techniques in medicine permits the straight examination of dynamic regenerative events of specific stem cells following a sports injury in people.

Inferior In Vivo Osteogenesis and Superior Angiogenesis of Human Adipose‐Derived Stem Cells Compared with Bone Marrow‐Derived Stem Cells Cultured in Xeno‐Free Conditions

The possibility of using adipose tissue-derived stromal cells (ATSC) as alternatives to bone marrow-derived stromal cells (BMSC) for bone repair has garnered interest due to the accessibility, high cell yield, and rapid in vitro expansion of ATSC. For clinical relevance, their bone forming potential in comparison to BMSC must be proven. Distinct differences between ATSC and BMSC have been observed in vitro and comparison of osteogenic potential in vivo is not clear to date. The aim of the current study was to compare the osteogenesis of human xenofree-expanded ATSC and BMSC in vitro and in an ectopic nude mouse model of bone formation. Human MSC were implanted with biphasic calcium phosphate biomaterials in subcutis pockets for 8 weeks. Implant groups were: BMSC, ATSC, BMSC and ATSC mixed together in different ratios, as well as MSC primed with either osteogenic supplements (250 μM ascorbic acid, 10 mM β-glycerolphosphate, and 10 nM dexamethasone) or 50 ng/ml recombinant bone morphogenetic protein 4 prior to implantation. In vitro results show osteogenic gene expression and differentiation potentials of ATSC. Despite this, ATSC failed to form ectopic bone in vivo, in stark contrast to BMSC, although osteogenic priming did impart minor osteogenesis to ATSC. Neovascularization was enhanced by ATSC compared with BMSC; however, less ATSC engrafted into the implant compared with BMSC. Therefore, in the content of bone regeneration, the advantages of ATSC over BMSC including enhanced angiogenesis, may be negated by their lack of osteogenesis and prerequisite for osteogenic differentiation prior to transplantation. Stem Cells Translational Medicine 2017;6:2160-2172.

Nano-copper-bearing stainless steel promotes fracture healing by accelerating the callus evolution process

Treatment for fractures requires internal fixation devices, which are mainly produced from stainless steel or titanium alloy without biological functions. Therefore, we developed a novel nano-copper-bearing stainless steel with nano-sized copper-precipitation (317L-Cu SS). Based on previous studies, this work explores the effect of 317L-Cu SS on fracture healing; that is, proliferation, osteogenic differentiation, osteogenesis-related gene expression, and lysyl oxidase activity of human bone mesenchymal stem cells were detected in vitro. Sprague-Dawley rats were used to build an animal fracture model, and fracture healing and callus evolution were investigated by radiology (X-ray and micro-CT), histology (H&E, Masson, and safranin O/fast green staining), and histomorphometry. Further, the Cu2+ content and Runx2 level in the callus were determined, and local mechanical test of the fracture was performed to assess the healing quality. Our results revealed that 317L-Cu SS did not affect the proliferation of human bone mesenchymal stem cells, but promoted osteogenic differentiation and the expression of osteogenesis-related genes. In addition, 317L-Cu SS upregulated the lysyl oxidase activity. The X-ray and micro-CT results showed that the callus evolution efficiency and fracture healing speed were superior for 317L-Cu SS. Histological staining displayed large amounts of fibrous tissues at 3 weeks, and cartilage and new bone at 6 weeks. Further, histomorphometric analysis indicated that the callus possessed higher osteogenic efficiency at 6 weeks, and a high Cu2+ content and increased Runx2 expression were observed in the callus for 317L-Cu SS. Besides, the mechanical strength of the fracture site was much better than that of the control group. Overall, we conclude that 317L-Cu SS possesses the ability to increase Cu2+ content and promote osteogenesis in the callus, which could accelerate the callus evolution process and bone formation to provide faster and better fracture healing.

TGFβ3 recruits endogenous mesenchymal stem cells to initiate bone regeneration

Background

The recruitment of a sufficient number of endogenous mesenchymal stem cells (MSCs) is the first stage of in-situ tissue regeneration. Transforming growth factor beta-3 (TGFβ3) could recruit stem or progenitor cells and endothelial cells to participate in tissue regeneration. However, the mechanism of TGFβ3 recruiting MSCs toward bone regeneration has remained obscure.

Methods

We estimated the promigratory property of TGFβ3 on human bone marrow MSCs (hBMSCs) cocultured with the vascular cells (human umbilical artery smooth muscle cells or human umbilical vein endothelial cells) or not by Transwell assay. After the addition of the inhibitor (SB431542) or Smad3 siRNA, the levels of MCP1 and SDF1 in coculture medium were tested by ELISA kit, and then the migratory signaling pathway of hBMSCs induced by TGFβ3 was investigated by western blot analysis. In vivo, a 2-mm FVB/N mouse femur defect model was used to evaluate chemokine secretion, endogenous cell homing, and bone regeneration induced by scaffolds loading 1 μg TGFβ3 through qPCR, immunofluorescent staining, immunohistochemical analysis, and Micro-CT, compared to the vehicle group.

Results

TGFβ3 (25 ng/ml) directly showed a nearly 40% increase in migrated hBMSCs via the TGFβ signaling pathway, compared to the vehicle treatment. Then, in the coculture system of hBMSCs and vascular cells, TGFβ3 further upregulated nearly 3-fold MCP1 secretion from vascular cells in a Smad3-dependent manner, to indirectly enhance nearly more than 50% of migrated hBMSCs. In vivo, TGFβ3 delivery improved MCP1 expression by nearly 7.9-fold, recruited approximately 2.0-fold CD31⁺ vascular cells and 2.0-fold Sca-1⁺ PDGFR-α⁺ MSCs, and achieved 2.5-fold bone volume fraction (BV/TV) and 2.0-fold bone mineral density, relative to TGFβ3-free delivery.

Conclusions

TGFβ3, as a MSC homing molecule, recruited MSCs to initiate bone formation in the direct-dependent and indirect-dependent mechanisms. This may shed light on the improvement of MSC homing in bone regeneration.

MicroRNAs and Fracture Healing

MicroRNAs (miRNAs) are small molecules found to have major regulatory roles in many biological processes. This review aims to provide an overview of the recent advances in knowledge of the role of miRNAs in fracture healing and bone repair. A search of the published literature was performed (using the PubMed database) to include all relevant studies published in English. These studies were then reviewed and the results condensed into this review paper. MiRNAs have now been shown to have significant alterations in expression levels in bone tissue in the presence of fractures. This is thought to be related to the process of fracture healing through effects on osteoblasts and bone growth factors. These small molecules are also detectable in the circulation where their expression appears to be altered by the presence of fractures. Although further research is required in this area, miRNAs may present an opportunity for future clinical applications in fracture management.

SERPINB2 is a novel TGFβ-responsive lineage fate determinant of human bone marrow stromal cells

TGF-β1, a multifunctional regulator of cell growth and differentiation, is the most abundant bone matrix growth factor. During differentiation of human bone stromal cells (hBMSCs), which constitute bone marrow osteoblast (OS) and adipocyte (AD) progenitor cells, continuous TGF-β1 (10 ng/ml) treatment enhanced OS differentiation as evidenced by increased mineralised matrix production. Conversely, pulsed TGF-β1 administration during the commitment phase increased mature lipid-filled adipocyte numbers. Global gene expression analysis using DNA microarrays in hBMSCs treated with TGF-β1 identified 1587 up- and 1716 down-regulated genes in OS-induced, TGF-β1-treated compared to OS-induced hBMSCs (2.0 fold change (FC), p < 0.05). Gene ontology (GO) analysis revealed enrichment in ‘osteoblast differentiation’ and ‘skeletal system development-associated’ genes and up-regulation of several genes involved in ‘osteoblastic-differentiation related signalling pathways’. In AD-induced, TGF-β1-treated compared to AD-induced hBMSCs, we identified 323 up- and 369 down-regulated genes (2.0 FC, p < 0.05) associated with ‘fat cell differentiation’, ‘fatty acid derivative biosynthesis process’, ‘fatty acid derivative metabolic process’, and ‘inositol lipid-mediated’. Serpin peptidase inhibitor, clade B (ovalbumin), member 2 (SERPINB2) was down-regulated 3-fold in TGF-β1-treated hBMSCs. siRNA-mediated SERPINB2 inhibition enhanced OS and AD differentiation. Thus, TGF-β signalling is important for hBMSC OS and AD differentiation and SERPINB2 is a TGF-β-responsive gene that plays a negative regulatory role in hBMSC differentiation.

The Role of Three-Dimensional Scaffolds in Treating Long Bone Defects: Evidence from Preclinical and Clinical Literature-A Systematic Review

Long bone defects represent a clinical challenge. Bone tissue engineering (BTE) has been developed to overcome problems associated with conventional methods. The aim of this study was to assess the BTE strategies available in preclinical and clinical settings and the current evidence supporting this approach. A systematic literature screening was performed on PubMed database, searching for both preclinical (only on large animals) and clinical studies. The following string was used: "(Scaffold OR Implant) AND (Long bone defect OR segmental bone defect OR large bone defect OR bone loss defect)." The search retrieved a total of 1573 articles: 51 preclinical and 4 clinical studies were included. The great amount of preclinical papers published over the past few years showed promising findings in terms of radiological and histological evidence. Unfortunately, this in vivo situation is not reflected by a corresponding clinical impact, with few published papers, highly heterogeneous and with small patient populations. Several aspects should be further investigated to translate positive preclinical findings into clinical protocols: the identification of the best biomaterial, with both biological and biomechanical suitable properties, and the selection of the best choice between cells, GFs, or their combination through standardized models to be validated by randomized trials.

The CD45lowCD271high Cell Prevalence in Bone Marrow Samples May Provide a Useful Measurement of the Bone Marrow Quality for Cartilage and Bone Regenerative Therapy

BACKGROUND

Bone marrow aspirates and concentrates are increasingly being used for musculoskeletal regenerative therapies, providing bone and cartilage progenitors. However, the quality of these bone marrow samples remains imprecise within clinical settings. As there is a need for the development of these therapies, a method of counting CD45CD271 cells was optimized and tested as an indicator of bone marrow sample quality.

METHODS

Bone marrow aspirates were collected from 54 donors (28 male and 26 female; median age of 48 years). The reagent concentrations were optimized for fast staining, and an acoustic-focusing flow cytometer (Attune) was used to enable automated CD45CD271 cell counting in bone marrow aspirates, bone marrow concentrates, and samples loaded onto a collagen scaffold. The CD45CD271 cell counts were compared with those obtained using another flow-cytometry-based method (LSR II) and with connective tissue progenitor (CTP) counts quantified using a colony forming unit-fibroblast (CFU-F) assay.

RESULTS

The optimized method enabled the counting of CD45CD271 cells within only 15 minutes. The quantified cell counts (median, 1,520; range, 96 to 20,992 cells/mL of bone marrow) were positively correlated with the CTP counts (p < 0.0001; r = 0.7237). In agreement with CFU-F and LSR II-based assays, the CD45CD271 cell counts quantified using the Attune-based method decreased with age in the samples from female but not male donors (p = 0.0015 and p = 0.3877, respectively). A significant increase in CD45CD271 cell counts was detected following bone marrow concentration (mean, 5-fold; 95% confidence interval [CI], 3.6 to 7.2-fold). Additionally, the number of CD45CD271 cells attached to the collagen scaffold was positively correlated with the number of progenitor cells that survived on the scaffold after 2-week culture (p = 0.0348).

CONCLUSIONS

An assay for counting CD45CD271 cells may provide a useful measurement of bone marrow quality. While the specificity of this measurement of CD45CD271 cells remained low in our experimental conditions, CD45CD271 cell counts were positively and modestly correlated with the prevalence of CTPs.

CLINICAL RELEVANCE

A fast and automated assessment of bone marrow aspirate/concentrate quality using CD45CD271 cell counting may be a useful tool for improving the quality of regenerative therapy.

MSC/ECM Cellular Complexes Induce Periodontal Tissue Regeneration

Transplantation of mesenchymal stem cells (MSCs), which possess self-renewing properties and multipotency, into a periodontal defect is thought to be a useful option for periodontal tissue regeneration. However, developing more reliable and predictable implantation techniques is still needed. Recently, we generated clumps of an MSC/extracellular matrix (ECM) complex (C-MSC), which consisted of cells and self-produced ECM. C-MSCs can regulate their cellular functions in vitro and can be grafted into a defect site, without any artificial scaffold, to induce bone regeneration. Accordingly, this study aimed to evaluate the effect of C-MSC transplantation on periodontal tissue regeneration in beagle dogs. Seven beagle dogs were employed to generate a premolar class III furcation defect model. MSCs isolated from dog ilium were seeded at a density of 7.0 × 10⁴ cells/well into 24-well plates and cultured in growth medium supplemented with 50 µg/mL ascorbic acid for 4 d. To obtain C-MSCs, confluent cells were scratched using a micropipette tip and were then torn off as a cellular sheet. The sheet was rolled up to make round clumps of cells. C-MSCs were maintained in growth medium or osteoinductive medium (OIM) for 5 or 10 d. The biological properties of C-MSCs were evaluated in vitro, and their periodontal tissue regenerative activity was tested by using a dog class III furcation defect model. Immunofluorescence analysis revealed that type I collagen fabricated the form of C-MSCs. OIM markedly elevated calcium deposition in C-MSCs at day 10, suggesting its osteogenic differentiation capacity. Both C-MSCs and C-MSCs cultured with OIM transplantation without an artificial scaffold into the dog furcation defect induced periodontal tissue regeneration successfully compared with no graft, whereas osteogenic-differentiated C-MSCs led to rapid alveolar bone regeneration. These findings suggested that the use of C-MSCs refined by self-produced ECM may represent a novel predictable periodontal tissue regenerative therapy.

Xenotransplantation of interferon-gamma-pretreated clumps of a human mesenchymal stem cell/extracellular matrix complex induces mouse calvarial bone regeneration

Background

Three-dimensional cultured clumps of a mesenchymal stem cell (MSC)/extracellular matrix (ECM) complex (C-MSC) consists of cells and self-produced ECM. C-MSC can regulate the cellular function in vitro and induce successful bone regeneration using ECM as a cell scaffold. Potentiating the immunomodulatory capacity of C-MSCs, which can ameliorate the allo-specific immune response, may be helpful in developing beneficial “off-the-shelf” cell therapy for tissue regeneration. It is well reported that interferon (IFN)-γ stimulates the immunosuppressive properties of MSC via upregulation of the immunomodulatory enzyme IDO. Therefore, the aim of this study was to investigate the effect of IFN-γ on the immunomodulatory capacity of C-MSC in vitro and to test the bone regenerative activity of C-MSC or IFN-γ-pretreated C-MSC (C-MSCγ) xenografts in a mice calvarial defect model.

Methods

Human bone marrow-derived MSCs were seeded at a density of 2.0 × 10⁵ cells/well into 24-well plates and cultured with growth medium supplemented with 50 μg/mL L-ascorbic acid for 4 days. To obtain C-MSC, confluent cells that had formed on the cellular sheet were scratched using a micropipette tip and were then torn off. The cellular sheet was rolled to make a round clump of cells. C-MSC was stimulated with IFN-γ and IDO expression, immunosuppressive capacity, and immunophenotype were evaluated in vitro. Moreover, C-MSC or C-MSCγ was xenotransplanted into immunocompetent or immunodeficient mice calvarial defect models without artificial scaffold, respectively.

Results

IFN-γ stimulated IDO expression in C-MSC. C-MSCγ, but not C-MSC, attenuated CD3/CD28-induced T cell proliferation and its suppressive effect was reversed by an IDO inhibitor. C-MSCγ showed upregulation of HLA-DR expression, but its co-stimulatory molecule, CD86, was not detected. Xenotransplantation of C-MSCγ into immunocompetent mice calvarial defect induced bone regeneration, whereas C-MSC xenograft failed and induced T cell infiltration in the grafted area. On the other hand, both C-MSC and C-MSCγ xenotransplantation into immunodeficient mice caused bone regeneration.

Conclusions

Xenotransplantation of C-MSCγ, which exerts immunomodulatory properties via the upregulation of IDO activity in vitro, may attenuate xenoreactive host immune response, and thereby induce bone regeneration in mice. Accordingly, C-MSCγ may constitute a promising novel allograft cell therapy for bone regeneration.

Electronic supplementary material

The online version of this article (doi:10.1186/s13287-017-0550-1) contains supplementary material, which is available to authorized users.

Immunomodulatory oligonucleotide IMT504: Effects on mesenchymal stem cells as a first-in-class immunoprotective/immunoregenerative therapy

The immune responses of humans and animals to insults (i.e., infections, traumas, tumoral transformation and radiation) are based on an intricate network of cells and chemical messengers. Abnormally high inflammation immediately after insult or abnormally prolonged pro-inflammatory stimuli bringing about chronic inflammation can lead to life-threatening or severely debilitating diseases. Mesenchymal stem cell (MSC) transplant has proved to be an effective therapy in preclinical studies which evaluated a vast diversity of inflammatory conditions. MSCs lead to resolution of inflammation, preparation for regeneration and actual regeneration, and then ultimate return to normal baseline or homeostasis. However, in clinical trials of transplanted MSCs, the expectations of great medical benefit have not yet been fulfilled. As a practical alternative to MSC transplant, a synthetic drug with the capacity to boost endogenous MSC expansion and/or activation may also be effective. Regarding this, IMT504, the prototype of a major class of immunomodulatory oligonucleotides, induces in vivo expansion of MSCs, resulting in a marked improvement in preclinical models of neuropathic pain, osteoporosis, diabetes and sepsis. IMT504 is easily manufactured and has an excellent preclinical safety record. In the small number of patients studied thus far, IMT504 has been well-tolerated, even at very high dosage. Further clinical investigation is necessary to demonstrate the utility of IMT504 for resolution of inflammation and regeneration in a broad array of human diseases that would likely benefit from an immunoprotective/immunoregenerative therapy.

Positive contrast from cells labeled with iron oxide nanoparticles: Quantitation of imaging data

PURPOSE

Conventional T₂ -weighted MRI produces a hypointense signal from iron-labeled cells, which renders quantification unfeasible. We tested a SWeep Imaging with Fourier Transformation (SWIFT) MRI pulse sequence to generate a quantifiable hyperintense signal from iron-labeled cells.

METHODS

Mesenchymal stem cells (MSCs) were labeled with different concentrations of iron oxide particles and examined for cell viability, proliferation, and differentiation. The SWIFT sequence was optimized to detect and quantify the amount of iron in the muscle tissue after injection of iron oxide solution and iron-labeled MSCs.

RESULTS

The incubation of MSCs with iron oxide and low concentration of poly-L-lysine mixture resulted in an internalization of up to 22 pg of iron per cell with no adverse effect on MSCs. Phantom experiments showed a dependence of SWIFT signal intensity on the excitation flip angle. The hyperintense signal from iron-labeled cells or solutions was detected, and an amount of the iron oxide in the tissue was quantified with the variable flip angle method.

CONCLUSIONS

The SWIFT sequence can produce a quantifiable hyperintense MRI signal from iron-labeled cells. The graft of 18 x 10⁶ cells was detectable for 19 days after injection and the amount of iron was quantifiable. The proposed protocol simplifies the detection and provides a means to quantify cell numbers. Magn Reson Med 78:1900-1910, 2017. © 2017 International Society for Magnetic Resonance in Medicine.

The role of bone marrow aspirate cells in the management of atrophic mandibular fractures by mini-invasive surgical approach: Single-institution experience

PURPOSE

The treatment of fractures involves addressing the biology of fracture repair and the mechanical stability of fracture fixation. Traditionally it has included the addition of bone graft to enhance healing. New advances in the understanding of the cellular and molecular mechanisms of fracture repair have led to the use of growth factors to accelerate bone healing. This study aimed to assess the advantages of autologous stem cell use for atrophic mandibular fracture treatment in comparison to standard technique.

MATERIALS AND METHODS

A total of 35 patients (14 male and 21 female) were treated for fractures of atrophic mandibles between January 2011 and December 2014. Surgical technique provided mini-invasive open reduction with or without immediate homologous bone graft, while selected patients received autologous bone marrow aspirate cell grafts in addition to the standard treatment. Demographic data and details of treatment and outcomes were recorded.

RESULTS

Patients were categorized according to the use of autologous stem cells, leaving 17 patients treated with standard technique and autologous stem cells (Group A) and 18 treated with standard osteosynthesis only (Group B). Of the 35 patients, 26 had bilateral fractures; most patients had significant medical co-morbidities. Immediate bone graft was used in 37.1% of patients (7 in group A and 6 in group B). Complications occurred in 5 patients (14.3%). Two patients in group B (11.1%) showed non-union of the fracture. One patient in group A (5.8%) and one patient in group B (5.5%) showed wound dehiscence and were treated conservatively; one patient in group B had a local infection (5.5%), one out of 35 (2.8%), that was managed by prolonged antibiotic treatment.

CONCLUSIONS

Despite the advanced age and medical co-morbidities of the vast majority of patients, mini-invasive open approach with autologous bone graft ensures a fast and excellent recovery. Moreover, the management of atrophic mandibular fractures by bone marrow aspirate cells is a safe and useful procedure which has a lower complication rate when compared to standard technique.

miR-195 in human primary mesenchymal stromal/stem cells regulates proliferation, osteogenesis and paracrine effect on angiogenesis

Mesenchymal Stromal/Stem Cells (MSC) are currently being explored in diverse clinical applications, including regenerative therapies. Their contribution to regeneration of bone fractures is dependent on their capacity to proliferate, undergo osteogenesis and induce angiogenesis. This study aimed to uncover microRNAs capable of concomitantly regulate these mechanisms. Following microRNA array results, we identified miR-195 and miR-497 as downregulated in human primary MSC under osteogenic differentiation. Overexpression of miR-195 or miR-497 in human primary MSC leads to a decrease in osteogenic differentiation and proliferation rate. Conversely, inhibition of miR-195 increased alkaline phosphatase expression and activity and cells proliferation. Then, miR-195 was used to study MSC capacity to recruit blood vessels in vivo. We provide evidence that the paracrine effect of MSC on angiogenesis is diminishedwhen cells over-express miR-195. VEGF may partially mediate this effect, as its expression and secreted protein levels are reduced by miR-195, while increased by anti-miR-195, in human MSC. Luciferase reporter assays revealed a direct interaction between miR-195 and VEGF 3′-UTR in bone cancer cells. In conclusion, our results suggest that miR-195 regulates important mechanisms for bone regeneration, specifically MSC osteogenic differentiation, proliferation and control of angiogenesis; therefore, it is a potential target for clinical bone regenerative therapies.

Growth Factor Content in Human Sera Affects the Isolation of Mesangiogenic Progenitor Cells (MPCs) from Human Bone Marrow

Mesangiogenic Progenitor Cells (MPCs) are human bone marrow-derived multipotent cells, isolated in vitro under selective culture conditions and shown to retain both mesengenic and angiogenic potential. MPCs also co-isolated with multipotent stromal cells (MSCs) when bone marrow primary cultures were set up for clinical applications, using human serum (HS) in place of fetal bovine serum (FBS). MPC culture purity (over 95%) is strictly dependent on HS supplementation with significant batch-to-batch variability. In the present paper we screened different sources of commercially available pooled human AB type serum (PhABS) for their ability to promote MPC production under selective culture conditions. As the majority of "contaminating" cells in MPC cultures were represented by MSC-like cells, we hypothesized a role by differentiating agents present in the sera. Therefore, we tested a number of growth factors (hGF) and found that higher concentrations of FGF-2, EGF, PDGF-AB, and VEGF-A as well as lower concentration of IGF-1 give sub-optimal MPC recovery. Gene expression analysis of hGF receptors was also carried out both in MSCs and MPCs, suggesting that FGF-2, EGF, and PDGF-AB could act promoting MSC proliferation, while VEGF-A contribute to MSC-like cell contamination, triggering MPC differentiation. Here we demonstrated that managing hGF contents, together with applying specific receptors inhibitors (Erlotinib-HCl and Nintedanib), could significantly mitigate the batch-to-batch variability related to serum supplementation. These data represent a fundamental milestone in view of manufacturing MPC-based medicinal products.