The fate of systemically administrated allogeneic mesenchymal stem cells in mouse femoral fracture healing

The Effect of Exercise on Mesenchymal Stem Cells and their Application in Obesity Treatment

Mesenchymal stem cells (MSCs) have demonstrated considerable potential in tissue repair and the treatment of immune-related diseases, but there are problems with homing efficiency during MSCs transplantation. Exercise, as an intervention, has been shown to have an important impact on the properties of MSCs. This review summarizes the effects of exercise on the properties (including proliferation, apoptosis, differentiation, and homing) of bone marrow-derived MSCs and adipose-derived MSCs. Studies indicated that exercise enhances bone marrow-derived MSCs proliferation, osteogenic differentiation, and homing while reducing adipogenic differentiation. For adipose-derived MSCs, exercise enhances proliferation and reduces adipogenic differentiation. In addition, studies have investigated the therapeutic effects of combined therapy of MSCs transplantation with exercise on diseases of the bone, cardiac, and nervous systems. The combined therapy improves tissue repair by increasing the homing of transplanted MSCs and cytokine secretion (such as neurotrophin 4). Furthermore, MSCs transplantation also has potential for the treatment of obesity. Although the effect is not significant in weight loss, MSCs transplantation shows effects in controlling blood glucose, improving dyslipidemia, reducing inflammation, and improving liver disease. Finally, the potential role of combined MSCs transplantation and exercise therapy in addressing obesity is discussed.

Bone Organoids: Recent Advances and Future Challenges

Bone defects stemming from tumorous growths, traumatic events, and diverse conditions present a profound conundrum in clinical practice and research. While bone has the inherent ability to regenerate, substantial bone anomalies require bone regeneration techniques. Bone organoids represent a new concept in this field, involving the 3D self-assembly of bone-associated stem cells guided in vitro with or without extracellular matrix material, resulting in a tissue that mimics the structural, functional, and genetic properties of native bone tissue. Within the scientific panorama, bone organoids ascend to an esteemed status, securing significant experimental endorsement. Through a synthesis of current literature and pioneering studies, this review offers a comprehensive survey of the bone organoid paradigm, delves into the quintessential architecture and ontogeny of bone, and highlights the latest progress in bone organoid fabrication. Further, existing challenges and prospective directions for future research are identified, advocating for interdisciplinary collaboration to fully harness the potential of this burgeoning domain. Conclusively, as bone organoid technology continues to mature, its implications for both clinical and research landscapes are poised to be profound.

Enhancing Immunomodulatory Function of Mesenchymal Stromal Cells by Hydrogel Encapsulation

Mesenchymal stromal cells (MSCs) showcase remarkable immunoregulatory capabilities in vitro, positioning them as promising candidates for cellular therapeutics. However, the process of administering MSCs and the dynamic in vivo environment may impact the cell-cell and cell-matrix interactions of MSCs, consequently influencing their survival, engraftment, and their immunomodulatory efficacy. Addressing these concerns, hydrogel encapsulation emerges as a promising solution to enhance the therapeutic effectiveness of MSCs in vivo. Hydrogel, a highly flexible crosslinked hydrophilic polymer with a substantial water content, serves as a versatile platform for MSC encapsulation. Demonstrating improved engraftment and heightened immunomodulatory functions in vivo, MSCs encapsulated by hydrogel are at the forefront of advancing therapeutic outcomes. This review delves into current advancements in the field, with a focus on tuning various hydrogel parameters to elucidate mechanistic insights and elevate functional outcomes. Explored parameters encompass hydrogel composition, involving monomer type, functional modification, and co-encapsulation, along with biomechanical and physical properties like stiffness, viscoelasticity, topology, and porosity. The impact of these parameters on MSC behaviors and immunomodulatory functions is examined. Additionally, we discuss potential future research directions, aiming to kindle sustained interest in the exploration of hydrogel-encapsulated MSCs in the realm of immunomodulation.

Allogeneic Mesenchymal Stem Cells After In Vivo Transplantation: A Review

Autologous mesenchymal stem cells (MSCs) are ideal for tissue regeneration because of their ability to circumvent host rejection, but their procurement and processing present logistical and time-sensitive challenges. Allogeneic MSCs provide an alternative cell-based therapy capable of positively affecting all human organ systems, and can be readily available. Extensive research has been conducted in the treatment of autoimmune, degenerative, and inflammatory diseases with such stem cells, and has demonstrated predominantly safe outcomes with minimal complications. Nevertheless, continued clinical trials are necessary to ascertain optimal harvest and transplant techniques.

Review on the protective activity of osthole against the pathogenesis of osteoporosis

Osteoporosis (OP), characterized by continuous bone loss and increased fracture risk, has posed a challenge to patients and society. Long-term administration of current pharmacological agents may cause severe side effects. Traditional medicines, acting as alternative agents, show promise in treating OP. Osthole, a natural coumarin derivative separated from Cnidium monnieri (L.) Cusson and Angelica pubescens Maxim. f., exhibits protective effects against the pathological development of OP. Osthole increases osteoblast-related bone formation and decreases osteoclast-related bone resorption, suppressing OP-related fragility fracture. In addition, the metabolites of osthole may exhibit pharmacological effectiveness against OP development. Mechanically, osthole promotes osteogenic differentiation by activating the Wnt/β-catenin and BMP-2/Smad1/5/8 signaling pathways and suppresses RANKL-induced osteoclastogenesis and osteoclast activity. Thus, osthole may become a promising agent to protect against OP development. However, more studies should be performed due to, at least in part, the uncertainty of drug targets. Further pharmacological investigation of osthole in OP treatment might lead to the development of potential drug candidates.

Biological mechanisms and applied prospects of mesenchymal stem cells in premature ovarian failure

Premature ovarian failure (POF), also known as primary ovarian insufficiency (POI), refers to the loss of ovarian function in women after puberty and before the age of 40 characterized by high serum gonadotropins and low estrogen, irregular menstruation, amenorrhea, and decreased fertility. However, the specific pathogenesis of POF is unexplained, and there is no effective therapy for its damaged ovarian tissue structure and reduced reserve function. Mesenchymal stem cells (MSCs), with multidirectional differentiation potential and self-renewal ability, as well as the cytokines and exosomes they secrete, have been studied and tested to play an active therapeutic role in a variety of degenerative pathologies, and MSCs are the most widely used stem cells in regenerative medicine. MSCs can reverse POI and enhance ovarian reserve function through differentiation into granulosa cells (GCs), immune regulation, secretion of cytokines and other nutritional factors, reduction of GCs apoptosis, and promotion of GCs regeneration. Many studies have proved that MSCs may have a restorative effect on the structure and fertility of injured ovarian tissues and turn to be a useful clinical approach to the treatment of patients with POF in recent years. We intend to use MSCs-based therapy to completely reverse POI in the future.

Untargeted Metabolomics Reveal the Protective Effect of Bone Marrow Mesenchymal Stem Cell Transplantation Against Ovariectomy-Induced Osteoporosis in Mice

Bone marrow mesenchymal stem cell transplantation (BMSCT) is a potential treatment for osteoporosis, capable of contributing to bone tissue repair. BMSCT has demonstrated osteoinductive effects and the ability to regulate microenvironmental metabolism; however, its role and mechanisms in bone loss due to reduced estrogen levels remain unclear. In this study, the effect of BMSCT on ovariectomy (OVX)-induced osteoporosis in mice was assessed, and liquid chromatography–mass spectrometry (LC-MS) metabolomic studies of bone tissue were conducted to identify potential metabolic molecular markers. The results revealed that BMSCT reduces OVX-induced bone loss in mice while improving the mechanical properties of mouse femurs and increasing the expression of osteogenic markers in peripheral blood. In a metabolomic study, 18 metabolites were screened as potential biomarkers of the anti-osteoporotic effect of BMSCT. These metabolites are mainly involved in arachidonic acid metabolism, taurine and hypotaurine metabolism, and pentose and glucuronate interconversions. Collectively, these results illustrate the correlation between metabolites and the underlying mechanisms of osteoporosis development and are important for understanding the role and mechanisms of exogenous bone marrow mesenchymal stem cells (BMSCs) in osteoporosis management. This study lays the foundation for research on BMSCs as a treatment strategy for osteoporosis.

Evaluation of the effects of preconditioned human stem cells plus a scaffold and photobiomodulation administration on stereological parameters and gene expression levels in a critical size bone defect in rats

We assessed the impact of photobiomodulation (PBM) plus adipose-derived stem cells (ASCs) during the anabolic and catabolic stages of bone healing in a rat model of a critical size femoral defect (CSFD) that was filled with a decellularized bone matrix (DBM). Stereological analysis and gene expression levels of bone morphogenetic protein 4 (BMP4), Runt-related transcription factor 2 (RUNX2), and stromal cell-derived factor 1 (SDF1) were determined. There were six groups of rats. Group 1 was the untreated control or DBM. Study groups 2-6 were treated as follows: ASC (ASC transplanted into DBM, then implanted in the CSFD); PBM (CSFD treated with PBM); irradiated ASC (iASC) (ASCs preconditioned with PBM, then transplanted into DBM, and implanted in the CSFD); ASC + PBM (ASCs transplanted into DBM, then implanted in the CSFD, followed by PBM administration); and iASC + PBM (the same as iASC, except CSFDs were exposed to PBM). At the anabolic step, all treatment groups had significantly increased trabecular bone volume (TBV) (24.22%) and osteoblasts (83.2%) compared to the control group (all, p = .000). However, TBV in group iASC + PBM groups were superior to the other groups (97.48% for osteoblast and 58.8% for trabecular bone volume) (all, p = .000). The numbers of osteocytes in ASC (78.2%) and iASC + PBM (30%) groups were remarkably higher compared to group control (both, p = .000). There were significantly higher SDF (1.5-fold), RUNX2 (1.3-fold), and BMP4 (1.9-fold) mRNA levels in the iASC + PBM group compared to the control and some of the treatment groups. At the catabolic step of bone healing, TBV increased significantly in PBM (30.77%), ASC + PBM (32.27%), and iASC + PBM (35.93%) groups compared to the control group (all, p = .000). There were significantly more osteoblasts and osteocytes in ASC (71.7%, 62.02%) (p = .002, p = .000); PBM (82.54%, 156%), iASC (179%, 23%), and ASC + PBM (108%, 110%) (all, p = .000), and iASC + PBM (79%, 100.6%) (p = .001, p = .000) groups compared to control group. ASC preconditioned with PBM in vitro plus PBM in vivo significantly increased stereological parameters and SDF1, RUNX2, and BMP4 mRNA expressions during bone healing in a CSFD model in rats.

Extracellular vesicles-encapsulated microRNA-29b-3p from bone marrow-derived mesenchymal stem cells promotes fracture healing via modulation of the PTEN/PI3K/AKT axis

Bone marrow-derived mesenchymal stem cells (BM-MSCs) are well-established as vital regulators of fracture healing, whereas angiogenesis is one of the critical processes during the course of bone healing. Accordingly, the current study sought to determine the functions of microRNA (miR)-29b-3p from BM-MSCs-derived extracellular vesicles (EVs) on the angiogenesis of fracture healing via the PTEN/PI3K/AKT axis. Firstly, BM-MSCs-EVs were extracted and identified. The lentiviral protocol was adopted to construct miR-29b-3p^KD-BMSCs or miR-negative control-BMSCs, which were then co-cultured with human umbilical vein endothelial cells (HUVECs) in vitro to determine the roles of EVs-encapsulated miR-29b-3p on the proliferation, migration, and angiogenesis of HUVECs in vitro with the help of a CCK-8 assay, scratch test, and tube formation assay. Subsequent database prediction, luciferase activity assay, RT-qPCR, and Western blot assay findings identified the downstream target gene of miR-29b-3p, PTEN, and a signaling pathway, PI3K/AKT. Furthermore, the application of si-PTEN attenuated the effects induced by miR-29b-3p^KD-EVs. Finally, a mouse model of femoral fracture was established with a locally instilled injection of equal volumes of BM-MSCs-EVs and miR-29b-3p^KD-BM-MSCs-EVs. Notably, the mice treated with BMSC-EVs presented with enhanced neovascularization at the fracture site, in addition to increased bone volume (BV), BV/tissue volume, and mean bone mineral density; whereas miR-29b-3p^KD-BMSCs-EVs-treated mice exhibited decreased vessel density with poor fracture healing capacity. Collectively, our findings elicited that BM-MSCs-EVs carrying miR-29b-3p were endocytosed by HUVECs, which consequently suppressed the PTEN expression and activated the PI3K/AKT pathway, thereby promoting HUVEC proliferation, migration, and angiogenesis, and ultimately facilitating fracture healing.

Preclinical and Clinical Amelioration of Bone Fractures with Mesenchymal Stromal Cells: a Systematic Review and Meta-Analysis

Even though reunion of bone fracture confronts clinicians, mesenchymal stromal cells (MSCs) are investigated to be curative in bone fracture. This study aimed to explore the application potential of MSCs for healing bone fractures. By inputting search terms and retrieving studies published up to March 2021, multiple databases, including PubMed, EMBASE, Web of Science, and Cochrane Library, were searched to identify eligible studies. The mean difference (MD) and 95% confidence interval (95% CI) were calculated to analyze the main results in the meta-analysis. Data analysis was performed using Engauge Digitizer 10.8 and R Software. Of the 31 articles, 26 were preclinical studies (n = 913), and 5 were clinical trials (n = 335). Preclinically, MSCs therapy significantly augmented the progress of bone regeneration [(bone volume over tissue volume (MD7.35, p < 0.01)], despite some non-significant effects (on the callus index, bone strength, work to failure, and stiffness). Clinically, the MSC group had a significantly reduced incidence of poor recovery (odds ratio (OR) 0.30, p < 0.01); however, a significant decrease in healing time was not observed in the MSC group (MD 2.47, p = 0.26). In summary, our data suggest that patients with bone fractures benefited from MSC administration and that MSCs are a potentially useful agent for bone regeneration. Despite these satisfactory outcomes, larger randomised clinical trials (RCTs) are necessary to confirm these findings.

The therapeutic potential of mesenchymal stem cells in treating osteoporosis

Osteoporosis (OP), a common systemic metabolic bone disease, is characterized by low bone mass, increasing bone fragility and a high risk of fracture. At present, the clinical treatment of OP mainly involves anti-bone resorption drugs and anabolic agents for bone, but their long-term use can cause serious side effects. The development of stem cell therapy and regenerative medicine has provided a new approach to the clinical treatment of various diseases, even with a hope for cure. Recently, the therapeutic advantages of the therapy have been shown for a variety of orthopedic diseases. However, these stem cell-based researches are currently limited to animal models; the uncertainty regarding the post-transplantation fate of stem cells and their safety in recipients has largely restricted the development of human clinical trials. Nevertheless, the feasibility of mesenchymal stem cells to treat osteoporotic mice has drawn a growing amount of intriguing attention from clinicians to its potential of applying the stem cell-based therapy as a new therapeutic approach to OP in the future clinic. In the current review, therefore, we explored the potential use of mesenchymal stem cells in human OP treatment.

Systemic therapy of MSCs in bone regeneration: a systematic review and meta-analysis

Objectives

Over the past decades, many studies focused on mesenchymal stem cells (MSCs) therapy for bone regeneration. Due to the efficiency of topical application has been widely dicussed and systemic application was also a feasible way for new bone formation, the aim of this study was to systematically review systemic therapy of MSCs for bone regeneration in pre-clinical studies.

Methods

The article search was conducted in PubMed and Embase databases. Original research articles that assessed potential effect of systemic application of MSCs for bone regeneration in vivo were selected and evaluated in this review, according to eligibility criteria. The efficacy of MSC systemic treatment was analyzed by random effects meta-analysis, and the outcomes were expressed in standard mean difference (SMD) and its 95% confidence interval. Subgroup analyses were conducted on animal species and gender, MSCs types, frequency and time of injection, and bone diseases.

Results

Twenty-three articles were selected in this review, of which 21 were included in meta-analysis. The results showed that systemic therapy increased bone mineral density (SMD 3.02 [1.84, 4.20]), bone volume to tissue volume ratio (2.10 [1.16, 3.03]), and the percentage of new bone area (7.03 [2.10, 11.96]). Bone loss caused by systemic disease tended to produce a better response to systemic treatment (p=0.05 in BMD, p=0.03 in BV/TV).

Conclusion

This study concluded that systemic therapy of MSCs promotes bone regeneration in preclinical experiments. These results provided important information for the systemic application of MSCs as a potential application of bone formation in further animal experiments.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-021-02456-w.

Optimization of oxidative stress for mesenchymal stromal/stem cell engraftment, function and longevity

Mesenchymal stromal/stem cells (MSCs) are multipotent cells that possess great potential as a cellular therapeutic based on their ability to differentiate to different lineages and to modulate immune responses. However, their potential is limited by their low tissue abundance, and thus the need for robust ex vivo expansion prior to their application. This creates its own issues, namely replicative senescence, which could lead to reduced MSC functionality and negatively impact their engraftment. Ex vivo expansion and MSC aging are associated with greater oxidative stress. Therefore, there is great need to identify strategies to reduce oxidative stress in MSCs. This review summarizes the achievements made to date in addressing oxidative stress in MSCs and speculates about interesting avenues of future investigation to solve this critical problem.

Shear-Resistant, Biological Tethering of Nanostimulators for Enhanced Therapeutic Cell Paracrine Factor Secretion

Mesenchymal stromal cells (MSCs) secreting multiple growth factors and immunomodulatory cytokines are promising for regenerative medicine. To further enhance their secretory activity, efforts have emerged to tether nanosized carriers of secretory stimuli, named nanostimulators, to the MSC surface by forming nonchemical bonds. Despite some successes, there is a great need to improve the retention of nanostimulators during transport through a syringe needle, where high shear stress exerted on the cell surface separates them. To this end, we hypothesize that poly(lactic-co-glycolic acid)-block-hyaluronic acid (PLGA-HA) conjugated with integrin-binding RGD peptides, denoted PLGA-HA-RGD, can form nanostimulators that remain on the cell surface stably during the injection. The resulting HA-CD44 and RGD-integrin bonds would synergistically increase the adhesion strength of nanostimulators. Interestingly, nanostimulators prepared with PLGA-HA-RGD show 3- to 6-fold higher retention than those made with PLGA-HA. Therefore, the PLGA-HA-RGD nanostimulators induced MSCs to secrete 1.5-fold higher vascular endothelial growth factors and a 1.2-fold higher tissue inhibitor of matrix metalloproteinase-1 as compared to PLGA-HA nanostimulators. Consequently, MSCs tethered with PLGA-HA-RGD nanostimulators served to stimulate endothelial cell activities to form a blood vessel-like endothelial lumen with increased length and number of junctions. The nanostimulator design strategy would also be broadly applicable to regulate, protect, and home a broad array of therapeutic or immune cells by tethering carriers with bioactive molecules of interest.

Advances in mesenchymal stem cell transplantation for the treatment of osteoporosis

Osteoporosis is a systemic metabolic bone disease with characteristics of bone loss and microstructural degeneration. The personal and societal costs of osteoporosis are increasing year by year as the ageing of population, posing challenges to public health care. Homing disorders, impaired capability of osteogenic differentiation, senescence of mesenchymal stem cells (MSCs), an imbalanced microenvironment, and disordered immunoregulation play important roles during the pathogenesis of osteoporosis. The MSC transplantation promises to increase osteoblast differentiation and block osteoclast activation, and to rebalance bone formation and resorption. Preclinical investigations on MSC transplantation in the osteoporosis treatment provide evidences of enhancing osteogenic differentiation, increasing bone mineral density, and halting the deterioration of osteoporosis. Meanwhile, the latest techniques, such as gene modification, targeted modification and co-transplantation, are promising approaches to enhance the therapeutic effect and efficacy of MSCs. In addition, clinical trials of MSC therapy to treat osteoporosis are underway, which will fill the gap of clinical data. Although MSCs tend to be effective to treat osteoporosis, the urgent issues of safety, transplant efficiency and standardization of the manufacturing process have to be settled. Moreover, a comprehensive evaluation of clinical trials, including safety and efficacy, is still needed as an important basis for clinical translation.

New insights on the reparative cells in bone regeneration and repair

Bone possesses a remarkable repair capacity to regenerate completely without scar tissue formation. This unique characteristic, expressed during bone development, maintenance and injury (fracture) healing, is performed by the reparative cells including skeletal stem cells (SSCs) and their descendants. However, the identity and functional roles of SSCs remain controversial due to technological difficulties and the heterogeneity and plasticity of SSCs. Moreover, for many years, there has been a biased view that bone marrow is the main cell source for bone repair. Together, these limitations have greatly hampered our understanding of these important cell populations and their potential applications in the treatment of fractures and skeletal diseases. Here, we reanalyse and summarize current understanding of the reparative cells in bone regeneration and repair and outline recent progress in this area, with a particular emphasis on the temporal and spatial process of fracture healing, the sources of reparative cells, an updated definition of SSCs, and markers of skeletal stem/progenitor cells contributing to the repair of craniofacial and long bones, as well as the debate between SSCs and pericytes. Finally, we also discuss the existing problems, emerging novel technologies and future research directions in this field.

Administration of Human Non-Diabetic Mesenchymal Stromal Cells to a Murine Model of Diabetic Fracture Repair: A Pilot Study

Individuals living with type 1 diabetes mellitus may experience an increased risk of long bone fracture. These fractures are often slow to heal, resulting in delayed reunion or non-union. It is reasonable to theorize that the underlying cause of these diabetes-associated osteopathies is faulty repair dynamics as a result of compromised bone marrow progenitor cell function. Here it was hypothesized that the administration of non-diabetic, human adult bone marrow-derived mesenchymal stromal cells (MSCs) would enhance diabetic fracture healing. Human MSCs were locally introduced to femur fractures in streptozotocin-induced diabetic mice, and the quality of de novo bone was assessed eight weeks later. Biodistribution analysis demonstrated that the cells remained in situ for three days following administration. Bone bridging was evident in all animals. However, a large reparative callus was retained, indicating non-union. µCT analysis elucidated comparable callus dimensions, bone mineral density, bone volume/total volume, and volume of mature bone in all groups that received cells as compared to the saline-treated controls. Four-point bending evaluation of flexural strength, flexural modulus, and total energy to re-fracture did not indicate a statistically significant change as a result of cellular administration. An ex vivo lymphocytic proliferation recall assay indicated that the xenogeneic administration of human cells did not result in an immune response by the murine recipient. Due to this dataset, the administration of non-diabetic bone marrow-derived MSCs did not support fracture healing in this pilot study.

Comparison of skeletal and soft tissue pericytes identifies CXCR4+ bone forming mural cells in human tissues

Human osteogenic progenitors are not precisely defined, being primarily studied as heterogeneous multipotent cell populations and termed mesenchymal stem cells (MSCs). Notably, select human pericytes can develop into bone-forming osteoblasts. Here, we sought to define the differentiation potential of CD146⁺ human pericytes from skeletal and soft tissue sources, with the underlying goal of defining cell surface markers that typify an osteoblastogenic pericyte. CD146⁺CD31^-CD45^- pericytes were derived by fluorescence-activated cell sorting from human periosteum, adipose, or dermal tissue. Periosteal CD146⁺CD31^-CD45^- cells retained canonical features of pericytes/MSC. Periosteal pericytes demonstrated a striking tendency to undergo osteoblastogenesis in vitro and skeletogenesis in vivo, while soft tissue pericytes did not readily. Transcriptome analysis revealed higher CXCR4 signaling among periosteal pericytes in comparison to their soft tissue counterparts, and CXCR4 chemical inhibition abrogated ectopic ossification by periosteal pericytes. Conversely, enrichment of CXCR4⁺ pericytes or stromal cells identified an osteoblastic/non-adipocytic precursor cell. In sum, human skeletal and soft tissue pericytes differ in their basal abilities to form bone. Diversity exists in soft tissue pericytes, however, and CXCR4⁺ pericytes represent an osteoblastogenic, non-adipocytic cell precursor. Indeed, enrichment for CXCR4-expressing stromal cells is a potential new tactic for skeletal tissue engineering.

GARP is a key molecule for mesenchymal stromal cell responses to TGF-β and fundamental to control mitochondrial ROS levels

Multipotent mesenchymal stromal cells (MSCs) have emerged as a promising cell therapy in regenerative medicine and for autoimmune/inflammatory diseases. However, a main hurdle for MSCs-based therapies is the loss of their proliferative potential in vitro. Here we report that glycoprotein A repetitions predominant (GARP) is required for the proliferation and survival of adipose-derived MSCs (ASCs) via its regulation of transforming growth factor-β (TGF-β) activation. Silencing of GARP in human ASCs increased their activation of TGF-β which augmented the levels of mitochondrial reactive oxygen species (mtROS), resulting in DNA damage, a block in proliferation and apoptosis. Inhibition of TGF-β signaling reduced the levels of mtROS and DNA damage and restored the ability of GARP-/low ASCs to proliferate. In contrast, overexpression of GARP in ASCs increased their proliferative capacity and rendered them more resistant to etoposide-induced DNA damage and apoptosis, in a TGF-β-dependent manner. In summary, our data show that the presence or absence of GARP on ASCs gives rise to distinct TGF-β responses with diametrically opposing effects on ASC proliferation and survival.

mi R -15a/15b Cluster Modulates Survival of Mesenchymal Stem Cells to Improve Its Therapeutic Efficacy of Myocardial Infarction

Background

The poor viability of transplanted mesenchymal stem cells (MSCs) hampers their therapeutic efficacy for ischemic heart disease. MicroRNAs are involved in regulation of MSC survival and function. The present study was designed to investigate the molecular effects of miR‐15a/15b on MSC survival, focusing on the role of vascular endothelial growth factor receptor 2.

Methods and Results

We first harvested donor luc(Luciferase)‐MSCs (5×10⁵) isolated from the luciferase transgenic mice with FVB background. Luc‐MSCs were transfected with miR‐15a/15b mimics or inhibitors and cultured under oxygen glucose deprivation condition for 12 hours to mimics the harsh microenvironment in infarcted heart; they were subjected to MTT (3‐(4,5‐dimethyl‐2‐thiazolyl)‐2,5‐diphenyl‐2‐H‐tetrazolium bromide?Thiazolyl Blue Tetrazolium Bromide) assay, bioluminescence imaging, quantitative reverse transcription–polymerase chain reaction, transferase‐mediated deoxyuridine triphosphate–digoxigenin nick‐end labeling assay, and flow cytometry. Furthermore, the levels of vascular endothelial growth factor receptor 2, protein kinase B, p(Phosphorylate)‐protein kinase B, Bcl‐2, Bax, and caspase‐3 proteins were available by Western blotting assay. In vivo, acute myocardial infarction was induced in 24 mice by coronary ligation, with subsequent receipt of Luc‐MSCs, Luc‐MSCs+miR‐15a/15b inhibitors, or PBS treatment. The therapeutic procedure and treatment effects were tracked and assessed using bioluminescence imaging and echocardiographic measurement. Next, ex vivo imaging and immunohistochemistry were conducted to verify the distribution of MSCs. We demonstrated that miR‐15a/15b targeted vascular endothelial growth factor receptor 2 to modulate MSC survival, possibly via phosphatidylinositol 3‐kinase/protein kinase B signaling pathway, which was proved by bioluminescence imaging, immunohistochemistry analysis, and echocardiographic measurement.

Conclusions

Luc‐MSCs could be followed dynamically in vitro and in vivo by bioluminescence imaging, and the role of miR‐15a/b could be inferred from the loss of signals from luc‐MSCs. This finding may have practical clinical implications in miR‐15a/15b–modified MSC transplantation in treating myocardial infarction.

Lgr5-overexpressing mesenchymal stem cells augment fracture healing through regulation of Wnt/ERK signaling pathways and mitochondrial dynamics

Fracture remains one of the most common traumatic conditions in orthopedic surgery. The use of mesenchymal stem cells (MSCs) to augment fracture repair is promising. Leucine-rich repeat-containing GPCR 5 (Lgr5), a transmembrane protein, has been identified as a novel adult stem cell marker in various organs and tissues. However, the roles of Lgr5 in MSCs are not fully understood. In this study, we investigated cellular functions of Lgr5 in MSCs and its potential implications in treating fracture. Lgr5-overexpressing MSCs (MSC^Lgr5) were established in murine SV40 promoter-driven luciferase reporter MSC line through virus transfection. Results of real-time quantitative PCR and Western blot analysis confirmed the increased expression of Lgr5 in MSC^Lgr5. MSC^Lgr5 exhibited increased osteogenic capacity, which may result from elevated expression of β-catenin and phosphorylated ERK1/2 within the nuclear region of cells. In contrast, inhibition of Lgr5 expression decreased the osteogenic differentiation ability of MSCs, accompanied with increased mitochondrial fragmentation and reduced expression of β-catenin. Local transplantation of MSC^Lgr5 at fracture sites accelerated fracture healing via enhanced osteogenesis and angiogenesis. MSC^Lgr5 stimulated the tube formation capacity of HUVECs in a Matrigel coculture system in vitro significantly. Taken together, results suggest that Lgr5 is implicated in the cellular processes of osteogenic differentiation of MSCs through regulation of Wnt and ERK signaling pathways and mitochondrial dynamics in fusion and fission. Inhibition of Lgr5 expression induced increased mitochondrial fragmentation and suppression of osteogenesis. MSC^Lgr5 exhibited enhanced therapeutic efficacy for fracture healing, which may serve as a superior cell source for bone tissue repair.-Lin, W., Xu, L., Pan, Q., Lin, S., Feng, L., Wang, B., Chen, S., Li, Y., Wang, H., Li, Y., Wang, Y., Lee, W. Y. W., Sun, D., Li, G. Lgr5-overexpressing mesenchymal stem cells augment fracture healing through regulation of Wnt/ERK signaling pathways and mitochondrial dynamics.

MiR-539-5p negatively regulates migration of rMSCs induced by Bushen Huoxue decoction through targeting Wnt5a

Bone fractures are very common, and above 5% of the fractures are impaired, leading to nonunions and severe disablilities. The traditional Chinese medicine Bushen Huoxue decoction (BHD) has been used to treat fracture in China. Our previous report has found that BHD promotes migration of rat mesenchymal stem cells (rMSCs) by activating Wnt5a signaling pathway. However, whether and how miRNAs are involved in modulating rMSCs migration induced by BHD has not been explored. In the present study, miRNA microarray analysis and further validation by real-time quantitative RT-PCR revealed that miR-539-5p was down-regulated in BHD-induced rMSCs. Transfection of miR-539-5p mimics suppressed rMSCs migration while the miR-539-5p inhibitor promoted rMSCs migration. Our results suggested that miR-539-5p was a negative regulator of migration of rMSCs induced by BHD. Target prediction analysis tools and Dual-luciferase reporter gene assay identified Wnt5a as a direct target of miR-539-5p. MiR-539-5p inhibited the expression of the Wnt5a and its downstream signaling molecules including JNK, PKC and CaMKII, which played a critical role in regulating migration of rMSCs. Taken together, our results demonstrate that miR-539-5p negatively regulates migration of rMSCs induced by BHD through targeting Wnt5a. These findings provide evidence that miR-539-5p should be considered as an important candidate target for the development of preventive or therapeutic approaches against bone nonunions.

A mouse model for the study of transplanted bone marrow mesenchymal stem cell survival and proliferation in lumbar spinal fusion

PURPOSE

Bone marrow aspirate has been successfully used alongside a variety of grafting materials to clinically augment spinal fusion. However, little is known about the fate of these transplanted cells. Herein, we develop a novel murine model for the in vivo monitoring of implanted bone marrow cells (BMCs) following spinal fusion.

METHODS

A clinical-grade scaffold was implanted into immune-intact mice undergoing spinal fusion with or without freshly isolated BMCs from either transgenic mice which constitutively express the firefly luciferase gene or syngeneic controls. The in vivo survival, distribution and proliferation of these luciferase-expressing cells was monitored via bioluminescence imaging over a period of 8 weeks and confirmed via immunohistochemistry. MicroCT imaging was performed 8 weeks to assess fusion.

RESULTS

Bioluminescence imaging indicated transplanted cell survival and proliferation over the first 2 weeks, followed by a decrease in cell numbers, with transplanted cell survival still evident at the end of the study. New bone formation and increased fusion mass volume were observed in mice implanted with cell-seeded scaffolds.

CONCLUSIONS

By enabling the tracking of transplanted bone marrow-derived cells during spinal fusion in vivo, this mouse model will be integral to developing a deeper understanding of the biological processes underlying spinal fusion in future studies. These slides can be retrieved under Electronic Supplementary Material.

Effect of cell therapy with allogeneic osteoblasts on bone repair of rat calvaria defects

BACKGROUND AIMS

Regenerative medicine strategies based on cell therapy are considered a promising approach to repair bone defects. The aims of this study were to evaluate the effect of subculturing on the osteogenic potential of osteoblasts derived from newborn rat calvaria and the effect of these osteoblasts on bone repair of rat calvaria defects.

METHODS

Cells were obtained from 50 newborn rat calvaria, and primary osteoblasts (OB) were compared with first passage (OB-P1) in terms of osteogenic potential by assaying cell proliferation, alkaline phosphatase (ALP) activity, extracellular matrix mineralization and gene expression of the osteoblastic markers RUNX2, ALP, osteocalcin and bone sialoprotein. Then, 5-mm calvaria defects were created in 24 Wistar rats, and after 2 weeks, they were locally injected with 50 µL of phosphate-buffered saline containing either 5 × 10⁶ osteoblasts (OB-P1, n = 12) or no cells (control, n = 12). Four weeks post-injection, the bone formation was evaluated by micro-computed tomography and histological analyses. Data were compared by analysis of variance, followed by the Student-Newman-Keuls's test or Student's t-test (P ≤ 0.05).

RESULTS

OB-P1 showed high proliferation and ALP activity, and despite the reduced gene expression of osteoblastic markers and extracellular matrix mineralization compared with OB, they displayed osteogenic potential, being a good choice for injection into calvaria defects. The micro-tomographic and histological data showed that defects treated with OB-P1 presented higher bone formation compared with control defects.

DISCUSSION

Our results indicate that cells derived from newborn rat calvaria retain osteoblastic characteristics after subculturing and that these osteoblasts stimulate bone repair in a rat calvaria defect model.

MicroRNA-218 Promotes Osteogenic Differentiation of Mesenchymal Stem Cells and Accelerates Bone Fracture Healing

As a regulator of osteogenesis, microRNA-218 (miR-218) is reported to promote osteogenesis of mesenchymal stem cells (MSCs). However, the in vivo osteogenic effect of miR-218 remains elusive. In this study, miR-218 was confirmed to promote osteogenic differentiation of MSCs by stimulating the alkaline phosphatase activity, calcium nodule formation, and osteogenic marker gene expression. For in vivo study, the miR-218-overexpressing BMSCs were locally administrated into the fracture sites in a femur fracture mouse model. Based on the X-rays, micro-computed tomography, mechanical testing, histology, and immunohistochemistry examinations, miR-218 overexpression improved new bone formation and accelerated fracture healing. These findings suggest that miR-218 may be a promising therapeutic target for bone repair in future clinical applications.

Transplantation of bone-marrow-derived mesenchymal stem cells into a murine model of immune thrombocytopenia

: Several reports have demonstrated T regulatory cells may play an important role in the pathophysiology of immune thrombocytopenia (ITP). As the immunomodulator, bone-marrow-derived mesenchymal stem cells (MSCs) (BM-MSCs) regulate T regulatory cells and show therapeutic effects on autoimmune diseases. However, it is not clear how BM-MSCs affect ITP. In this study, we explored the specific effects of BM-MSCs on ITP in mice. Using a murine model of ITP, mice were randomly divided into three groups: normal control group, ITP control group and ITP and BM-MSCs group. Platelet (PLT) levels were monitored by an automatic blood cell counter, and T regulatory cells were analyzed by flow cytometry. Compared with the untreated ITP mice, the PLT level of the ITP mice was significantly increased after BM-MSCs treatment. In the BM-MSCs group, T regulatory cells were significantly decreased. These findings demonstrate that bone-marrow-derived MSCs are effective in improving PLT levels and reducing the T regulatory cells mediating proinflammatory response in ITP mice.

Allogeneic transplantation of mobilized dental pulp stem cells with the mismatched dog leukocyte antigen type is safe and efficacious for total pulp regeneration

Background

We recently demonstrated that autologous transplantation of mobilized dental pulp stem cells (MDPSCs) was a safe and efficacious potential therapy for total pulp regeneration in a clinical study. The autologous MDPSCs, however, have some limitations to overcome, such as limited availability of discarded teeth from older patients. In the present study, we investigated whether MDPSCs can be used for allogeneic applications to expand their therapeutic use.

Methods

Analysis of dog leukocyte antigen (DLA) was performed using polymerase chain reaction from blood. Canine allogeneic MDPSCs with the matched and mismatched DLA were transplanted with granulocyte-colony stimulating factor in collagen into pulpectomized teeth respectively (n = 7, each). Results were evaluated by hematoxylin and eosin staining, Masson trichrome staining, PGP9.5 immunostaining, and BS-1 lectin immunostaining performed 12 weeks after transplantation. The MDPSCs of the same DLA used in the first transplantation were further transplanted into another pulpectomized tooth and evaluated 12 weeks after transplantation.

Results

There was no evidence of toxicity or adverse events of the allogeneic transplantation of the MDPSCs with the mismatched DLA. No adverse event of dual transplantation of the MDPSCs with the matched and mismatched DLA was observed. Regenerated pulp tissues including neovascularization and neuronal extension were quantitatively and qualitatively similar at 12 weeks in both matched and mismatched DLA transplants. Regenerated pulp tissue was similarly observed in the dual transplantation as in the single transplantation of MDPSCs both with the matched and mismatched DLA.

Conclusions

Dual allogeneic transplantation of MDPSCs with the mismatched DLA is a safe and efficacious method for total pulp regeneration.

Electronic supplementary material

The online version of this article (10.1186/s13287-018-0855-8) contains supplementary material, which is available to authorized users.

pIL6-TRAIL-engineered umbilical cord mesenchymal/stromal stem cells are highly cytotoxic for myeloma cells both in vitro and in vivo

Background

Mesenchymal/stromal stem cells (MSCs) are favorably regarded in anti-cancer cytotherapies for their spontaneous chemotaxis toward inflammatory and tumor environments associated with an intrinsic cytotoxicity against tumor cells. Placenta-derived or TRAIL-engineered adipose MSCs have been shown to exert anti-tumor activity in both in-vitro and in-vivo models of multiple myeloma (MM) while TRAIL-transduced umbilical cord (UC)-MSCs appear efficient inducers of apoptosis in a few solid tumors. However, apoptosis is not selective for cancer cells since specific TRAIL receptors are also expressed by a number of normal cells. To overcome this drawback, we propose to transduce UC-MSCs with a bicistronic vector including the TRAIL sequence under the control of IL-6 promoter (pIL6) whose transcriptional activation is promoted by the MM milieu.

Methods

UC-MSCs were transduced with a bicistronic retroviral vector (pMIGR1) encoding for green fluorescent protein (GFP) and modified to include the pIL6 sequence upstream of the full-length human TRAIL cDNA. TRAIL expression after stimulation with U-266 cell conditioned medium, or IL-1α/IL-1β, was evaluated by flow cytometry, confocal microscopy, real-time PCR, western blot analysis, and ELISA. Apoptosis in MM cells was assayed by Annexin V staining and by caspase-8 activation. The cytotoxic effect of pIL6-TRAIL⁺-GFP⁺-UC-MSCs on MM growth was evaluated in SCID mice by bioluminescence and ex vivo by caspase-3 activation and X-ray imaging. Statistical analyses were performed by Student’s t test, ANOVA, and logrank test for survival curves.

Results

pIL6-TRAIL⁺-GFP⁺-UC-MSCs significantly expressed TRAIL after stimulation by either conditioned medium or by IL-1α/IL-1β, and induced apoptosis in U-266 cells. Moreover, when systemically injected in SCID mice intratibially xenografted with U-266, those cells underwent within MM tibia lesions and significantly reduced the tumor burden by specific induction of apoptosis in MM cells as revealed by caspase-3 activation.

Conclusions

Our tumor microenvironment-sensitive model of anti-MM cytotherapy is regulated by the axis pIL6/IL-1α/IL-1β and appears suitable for further preclinical investigation not only in myeloma bone disease in which UC-MSCs would even participate to bone healing as described, but also in other osteotropic tumors whose milieu is enriched of cytokines triggering the pIL6.

Sequential and sustained release of SDF-1 and BMP-2 from silk fibroin-nanohydroxyapatite scaffold for the enhancement of bone regeneration

In this study, a cell-free bone tissue engineering system based on a silk fibroin (SF)/nano-hydroxyapatite (nHAp) scaffold was developed, in which two bioactive molecules, stromal cell derived factor-1 (SDF-1) and bone morphogenetic protein-2 (BMP-2), were embedded and released in a sequential and controlled manner to facilitate cell recruitment and bone formation, respectively. BMP-2 was initially loaded into SF microspheres, and these BMP-2 containing microspheres were subsequently encapsulated into the SF/nHAp scaffolds, which were successively functionalized with SDF-1 via physical adsorption. The results indicated rapid initial release of SDF-1 during the first few days, followed by slow and sustained release of BMP-2 for as long as three weeks. The composite scaffold significantly promoted the recruitment of bone marrow mesenchymal stem cells (BMSCs) and osteogenic differentiation of them in vitro. Further, the in vivo studies using D-Luciferin-labeled BMSCs indicated that implantation of this composite scaffold markedly promoted the recruitment of BMSCs to the implanted sites. Enhanced bone regeneration was identified at 12 weeks' post-implantation. Taken together, our findings suggested that the sequential and sustained release of SDF-1 and BMP-2 from the SF/nHAp scaffolds resulted in a synergistic effect on bone regeneration. Such a composite system, therefore, shows promising potential for cell-free bone tissue engineering applications.

Mesenchymal Stem Cells Derived from Human Bone Marrow and Adipose Tissue Maintain Their Immunosuppressive Properties After Chondrogenic Differentiation: Role of HLA-G

Mesenchymal stem cells (MSC) have emerged as alternative sources of stem cells for regenerative medicine because of their multipotency and strong immune-regulatory properties. Also, human leukocyte antigen G (HLA-G) is an important mediator of MSC-mediated immunomodulation. However, it is unclear whether MSC retain their immune-privileged potential after differentiation. As promising candidates for cartilage tissue engineering, the immunogenic and immunomodulatory properties of chondro-differentiated MSC (chondro-MSC) require in-depth exploration. In the present study, we used the alginate/hyaluronic acid (Alg/HA) hydrogel scaffold and induced both bone marrow- and adipose tissue-derived MSC into chondrocytes in three-dimensional condition. Then, MSC before and after chondrocyte differentiation were treated or not with interferon γ and tumor necrosis factor α mimicking inflammatory conditions and were compared side by side using flow cytometry, mixed lymphocyte reaction, and immunostaining assays. Results showed that chondro-MSC were hypoimmunogenic and could exert immunosuppression on HLA-mismatched peripheral blood mononuclear cells as well as undifferentiated MSC did. This alloproliferation inhibition mediated by MSC or chondro-MSC was dose dependent. Meanwhile, chondro-MSC exerted inhibition on natural killer cell-mediated cytolysis. Also, we showed that HLA-G expression was upregulated in chondro-MSC under hypoxia context and could be boosted in allogenic settings. Besides, the Alg/HA hydrogel scaffold was hypoimmunogenic and its addition for supporting MSC chondrocyte differentiation did not modify the immune properties of MSC. Finally, considering their chondro-regenerative potential and their retained immunosuppressive capacity, MSC constitute promising allogenic sources of stem cells for cartilage repair.

Mesenchymal Stem Cells after Polytrauma: Actor and Target

Mesenchymal stem cells (MSCs) are multipotent cells that are considered indispensable in regeneration processes after tissue trauma. MSCs are recruited to damaged areas via several chemoattractant pathways where they function as “actors” in the healing process by the secretion of manifold pro- and anti-inflammatory, antimicrobial, pro- and anticoagulatory, and trophic/angiogenic factors, but also by proliferation and differentiation into the required cells. On the other hand, MSCs represent “targets” during the pathophysiological conditions after severe trauma, when excessively generated inflammatory mediators, complement activation factors, and damage- and pathogen-associated molecular patterns challenge MSCs and alter their functionality. This in turn leads to complement opsonization, lysis, clearance by macrophages, and reduced migratory and regenerative abilities which culminate in impaired tissue repair. We summarize relevant cellular and signaling mechanisms and provide an up-to-date overview about promising future therapeutic MSC strategies in the context of severe tissue trauma.

The Placenta as an Organ and a Source of Stem Cells and Extracellular Matrix: A Review

The placenta is a temporal, dynamic and diverse organ with important immunological features that facilitate embryonic and fetal development and survival, notwithstanding the fact that several aspects of its formation and function closely resemble tumor progression. Placentation in mammals is commonly used to characterize the evolution of species, including insights into human evolution. Although most placentas are discarded after birth, they are a high-yield source for the isolation of stem/progenitor cells and are rich in extracellular matrix (ECM), representing an important resource for regenerative medicine purposes. Interactions among cells, ECM and bioactive molecules regulate tissue and organ generation and comprise the foundation of tissue engineering. In the present article, differences among several mammalian species regarding the placental types and classifications, phenotypes and potency of placenta-derived stem/progenitor cells, placental ECM components and current placental ECM applications were reviewed to highlight their potential clinical and biomedical relevance.