Bone marrow stromal cells contribute to bone formation following infusion into femoral cavities of a mouse model of osteogenesis imperfecta

Emerging Landscape of Osteogenesis Imperfecta Pathogenesis and Therapeutic Approaches

Osteogenesis imperfecta (OI) is an uncommon genetic disorder characterized by shortness of stature, hearing loss, poor bone mass, recurrent fractures, and skeletal abnormalities. Pathogenic variations have been found in over 20 distinct genes that are involved in the pathophysiology of OI, contributing to the disorder's clinical and genetic variability. Although medications, surgical procedures, and other interventions can partially alleviate certain symptoms, there is still no known cure for OI. In this Review, we provide a comprehensive overview of genetic pathogenesis, existing treatment modalities, and new developments in biotechnologies such as gene editing, stem cell reprogramming, functional differentiation, and transplantation for potential future OI therapy.

FRZB affects Staphylococcus aureus‑induced osteomyelitis in human bone marrow derived stem cells by regulating the Wnt/β‑catenin signaling pathway

Osteomyelitis is an infectious disease of bone tissue caused by bacterial infection, which can infect through hematogenous, traumatic or secondary ways and then lead to acute or chronic bone injury and relative clinical symptoms, bringing physical injury and economic burden to patients. Frizzled related protein (FRZB) participates in the regulation of various diseases (osteoarthritis, cardiovascular diseases and types of cancer) by regulating cell proliferation, motility, differentiation and inflammation, while its function in osteomyelitis remains to be elucidated. The present study aimed to uncover the role and underlying mechanism of FRZB mediation in Staphylococcus aureus (S. aureus)-induced osteomyelitis. Human bone marrow derived stem cells (hBMSCs) were treated with S. aureus to imitate an inflammatory osteomyelitis micro-environment in vitro, then mRNA and protein expression were severally assessed by RT-PCR and western blotting. The activity, apoptosis and differentiation of the cells were characterized via CCK-8, caspase-3 activity and Alizarin red sulfate/alkaline phosphatase staining, respectively. Expression levels of FRZB were upregulated in S. aureus-infected hBMSCs. Over-expression of FRZB significantly reduced hBMSC cell viability and differentiation while promoting cell apoptosis with or without S. aureus infection. However, FRZB knockdown reversed these effects. Once Wnt was impeded, the effect of FRZB downregulation was impeded to a great extent. Taken together, FRZB participated to regulate the osteomyelitis by activating the Wnt/β-catenin signaling pathway.

An Update on Animal Models of Osteogenesis Imperfecta

Osteogenesis imperfecta (OI) is a heterogeneous disorder characterized by bone fragility, multiple fractures, bone deformity, and short stature. In recent years, the application of next generation sequencing has triggered the discovery of many new genetic causes for OI. Until now, more than 25 genetic causes of OI and closely related disorders have been identified. However, the mechanisms of many genes on skeletal fragility in OI are not entirely clear. Animal models of OI could help to understand the cellular, signaling, and metabolic mechanisms contributing to the disease, and how targeting these pathways can provide therapeutic targets. To date, a lot of animal models, mainly mice and zebrafish, have been described with defects in 19 OI-associated genes. In this review, we summarize the known genetic causes and animal models that recapitulate OI with a main focus on engineered mouse and zebrafish models. Additionally, we briefly discuss domestic animals with naturally occurring OI phenotypes. Knowledge of the specific molecular basis of OI will advance clinical diagnosis and potentially stimulate targeted therapeutic approaches.

Clock-modified mesenchymal stromal cells therapy rescues molecular circadian oscillation and age-related bone loss via miR142-3p/Bmal1/YAP signaling axis

Age-related bone loss and disease strongly affect the quality of life of the elderly population. Cellular circadian rhythms have been reported to regulate bone aging, and micro RNAs (miRNAs) play crucial posttranscriptional regulatory roles in the peripheral clock network. Proliferation capability, osteogenic lineage commitment, senescence-associated secreted phenotype (SASP) and circadian oscillation of clock genes under osteogenic condition were assessed in bone marrow mesenchymal stromal cells (BMSCs) from young adult and aged adult mice. miRNAs targeting the core clock gene brain and muscle arntl-like protein 1 (Bmal1) were screened and verified in young and old BMSCs with RT-qPCR and Western Blot analysis. ChIP-seq and RNA-seq datasets were mined to define the downstream mechanism and gain- and loss-of-function genetic experiments were performed to confirm the hypothesis. To compare the therapeutic effect of these clock-engineered BMSCs, SASP and osteogenic capability of Bmal1-overexpressing and miR-142-3p-inhibited BMSCs were investigated in vitro and transplanted into bone defects and femur cavities of aged mice. Aged BMSCs displayed an abolished circadian rhythm, impaired self-renewal capability and decreased osteoblast differentiation. miR-142-3p was elevated with aging, which downregulated Bmal1 and diminished the osteogenic potential of BMSCs. In addition, Bmal1 inhibited YAP expression to promote BMSCs osteogenesis, which was independent from the activation of Hippo signaling pathway. Overexpression of Bmal1 or inhibition of miR-142-3p rescued the molecular temporal rhythm and osteoblast differentiation ex vivo. Cell-based circadian therapy showed improved bone formation and higher turnover levels in vivo. This study demonstrates that transcriptional and post-transcriptional level clock-modified BMSCs rescued circadian oscillation and age-related bone loss via miR-142-3p/Bmal1/YAP signaling axis. These data provide promising clinical prospects of circadian-mediated stromal cell-based therapy and bone tissue regeneration.

A systematic review and meta-analysis on the efficacy of stem cell therapy on bone brittleness in mouse models of osteogenesis imperfecta

There is no cure for osteogenesis imperfecta (OI), and current treatments can only partially correct the bone phenotype. Stem cell therapy holds potential to improve bone quality and quantity in OI. Here, we conduct a systematic review and meta-analysis of published studies to investigate the efficacy of stem cell therapy to rescue bone brittleness in mouse models of OI. Identified studies included bone marrow, mesenchymal stem cells, and human fetal stem cells. Effect size of fracture incidence, maximum load, stiffness, cortical thickness, bone volume fraction, and raw engraftment rates were pooled in a random-effects meta-analysis. Cell type, cell number, injection route, mouse age, irradiation, anatomical bone, and follow up time were considered as moderators. It was not possible to investigate further parameters due to the lack of standards of investigation between the studies. Despite the use of oim mice in the majority of the investigations considered and the lack of sham mice as control, this study demonstrates the promising potential of stem cell therapy to reduce fractures in OI. Although their low engraftment, cell therapy in mouse models of OI had a beneficial effect on maximum load, but not on stiffness, cortical thickness and bone volume. These parameters all depend on bone geometry and do not inform on its material properties. Being bone fractures the primary symptom of OI, there is a critical need to measure the fracture toughness of OI bone treated with stem cells to assess the actual efficacy of the treatment to rescue OI bone brittleness.

Hematopoietic stem cell-derived functional osteoblasts exhibit therapeutic efficacy in a murine model of osteogenesis imperfecta

Currently, there is no cure for osteogenesis imperfecta (OI)-a debilitating pediatric skeletal dysplasia. Herein we show that hematopoietic stem cell (HSC) therapy holds promise in treating OI. Using single-cell HSC transplantation in lethally irradiated oim/oim mice, we demonstrate significant improvements in bone morphometric, mechanics, and turnover parameters. Importantly, we highlight that HSCs cause these improvements due to their unique property of differentiating into osteoblasts/osteocytes, depositing normal collagen-an attribute thus far assigned only to mesenchymal stem/stromal cells. To confirm HSC plasticity, lineage tracing was done by transplanting oim/oim with HSCs from two specific transgenic mice-VavR, in which all hematopoietic cells are GFP+ and pOBCol2.3GFP, where GFP is expressed only in osteoblasts/osteocytes. In both models, transplanted oim/oim mice demonstrated GFP+ HSC-derived osteoblasts/osteocytes in bones. These studies unequivocally establish that HSCs differentiate into osteoblasts/osteocytes, and HSC transplantation can provide a new translational approach for OI.

Erythropoietin (EPO) as a Key Regulator of Erythropoiesis, Bone Remodeling and Endothelial Transdifferentiation of Multipotent Mesenchymal Stem Cells (MSCs): Implications in Regenerative Medicine

Human erythropoietin (EPO) is an N-linked glycoprotein consisting of 166 aa that is produced in the kidney during the adult life and acts both as a peptide hormone and hematopoietic growth factor (HGF), stimulating bone marrow erythropoiesis. EPO production is activated by hypoxia and is regulated via an oxygen-sensitive feedback loop. EPO acts via its homodimeric erythropoietin receptor (EPO-R) that increases cell survival and drives the terminal erythroid maturation of progenitors BFU-Es and CFU-Es to billions of mature RBCs. This pathway involves the activation of multiple erythroid transcription factors, such as GATA1, FOG1, TAL-1, EKLF and BCL11A, and leads to the overexpression of genes encoding enzymes involved in heme biosynthesis and the production of hemoglobin. The detection of a heterodimeric complex of EPO-R (consisting of one EPO-R chain and the CSF2RB β-chain, CD131) in several tissues (brain, heart, skeletal muscle) explains the EPO pleotropic action as a protection factor for several cells, including the multipotent MSCs as well as cells modulating the innate and adaptive immunity arms. EPO induces the osteogenic and endothelial transdifferentiation of the multipotent MSCs via the activation of EPO-R signaling pathways, leading to bone remodeling, induction of angiogenesis and secretion of a large number of trophic factors (secretome). These diversely unique properties of EPO, taken together with its clinical use to treat anemias associated with chronic renal failure and other blood disorders, make it a valuable biologic agent in regenerative medicine for the treatment/cure of tissue de-regeneration disorders.

Engraftment of skeletal progenitor cells by bone-directed transplantation improves osteogenesis imperfecta murine bone phenotype

Osteogenesis imperfecta (OI) is a genetic disorder most commonly caused by mutations associated with type I collagen, resulting in a defective collagen bone matrix. Current treatments for OI focus on pharmaceutical strategies to increase the amount of defective bone matrix, but do not address the underlying collagen defect. Introducing healthy donor stem cells that differentiate into osteoblasts producing normal collagen in OI patients has the potential to increase bone mass and correct the mutant collagen matrix. In this study, donor bone marrow stromal cells (BMSCs, also known as bone marrow mesenchymal stem cells) expressing both αSMACreERT2/Ai9 progenitor reporter and osteoblast reporter Col2.3GFP were locally transplanted into the femur of OI murine (OIM) mice. One month post-transplantation, 18% of the endosteal surface was lined by donor Col2.3GFP expressing osteoblasts indicating robust engraftment. Long-term engraftment in the marrow was observed 3 and 6 months post-transplantation. The presence of Col1a2-expressing donor cell-derived cortical bone matrix was detected in transplanted OIM femurs. Local transplantation of BMSCs increased cortical thickness (+12%), the polar moment of inertia (+14%), bone strength (+30%), and stiffness (+30%) 3 months post-transplantation. Engrafted cells expressed progenitor markers CD51 and Sca-1 up to 3 months post-transplantation. Most importantly, 3 months post-transplantation donor cells maintained the ability to differentiate into Col2.3GFP+ osteoblasts in vitro, and in vivo following secondary transplantation into OIM animals. Locally transplanted BMSCs can improve cortical structure and strength, and persist as continued source of osteoblast progenitors in the OIM mouse for at least 6 months.

Prenatal stem cell therapy for inherited diseases: Past, present, and future treatment strategies

Imagine the profits in quality of life that can be made by treating inherited diseases early in life, maybe even before birth! Immense cost savings can also be made by treating diseases promptly. Hence, prenatal stem cell therapy holds great promise for developing new and early‐stage treatment strategies for several diseases. Successful prenatal stem cell therapy would represent a major step forward in the management of patients with hematological, metabolic, or immunological disorders. However, treatment before birth has several limitations, including ethical issues. In this review, we summarize the past, the present, and the future of prenatal stem cell therapy, which includes an overview of different stem cell types, preclinical studies, and clinical attempts treating various diseases. We also discuss the current challenges and future strategies for prenatal stem cell therapy and also new approaches, which may lead to advancement in the management of patients with severe incurable diseases.

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.

Geraniin promotes osteogenic differentiation of bone marrow mesenchymal stem cells (BMSCs) via activating β-catenin: a comparative study between BMSCs from normal and osteoporotic rats

Abnormal osteogenic differentiation of bone marrow mesenchymal stem cells (BMSCs) has been correlated with the pathogenesis of osteoporosis. Geraniin, a polyphenolic compound isolated from Phyllanthus amarus, is effective in preventing osteoporosis, but the mechanisms of action of geraniin and the impact of osteoporotic condition on drug action are not known. In this study we compared the proliferation and osteoblastic differentiation potential of BMSCs from normal rats with that from osteoporotic rats, and examined the responses of both BMSCs to geraniin in parallel. BMSCs of rats subjected to ovariectomy or sham operation were isolated and treated with geraniin. Cell proliferation was measured by CCK-8 assay. Osteoblastic differentiation was quantified by Alizarin Red S staining and alkaline phosphatase assay. Nuclear translocation of β-catenin was monitored by immunofluorescent staining. Expression of β-catenin was determined by Western blot and quantitative real-time polymerase chain reaction. Results showed that the proliferation and osteoblast formation of osteoporotic BMSCs decreased in comparison to that of normal BMSCs. Geraniin enhanced proliferation and osteoblastic differentiation of both BMSCs, but the responses of osteoporotic BMSCs to geraniin were less than those of normal BMSCs. Expression and nuclear accumulation of β-catenin in osteoporotic BMSCs were found to be diminished. Geraniin increased nuclear translocation and expression of β-catenin in both BMSCs. This study associated the osteogenic effect of geraniin to activation of Wnt/β-catenin signaling, and provided rationale for pharmacological investigation of geraniin in osteoporosis prevention and treatment.

Evidence for Lgr6 as a Novel Marker of Osteoblastic Progenitors in Mice

Bone marrow-derived mesenchymal stem cells are an important source of osteoblasts critical for both bone homeostasis and repair. The ability to isolate, or specifically target, mesenchymal stem cells committed to the osteogenic lineage is necessary for orthopedic translational therapy efforts; however the precise molecular signature of these cells remains elusive. Previously, we identified a population of osteoprogenitor cells expressing the Wnt signaling agonist Lgr6, which contributes to the development and regeneration of the mouse digit tip bone. In our present study we build upon this data and investigate the expression of Lgr6 more broadly in the skeleton. We find that Lgr6, and closely related Lgr4, are expressed in mouse primary calvarial cells, bone marrow cells, and bone marrow-derived mesenchymal stem cells. In addition, our data demonstrates that Lgr4 expression is modestly increased throughout the differentiation and mineralization of mesenchymal stem cells. In contrast, we find Lgr6 expression to be strikingly increased upon osteogenic induction and subsequently decreased upon differentiation and mineralization. These findings provide evidence for Lgr6 as a novel marker of osteoprogenitor cells in bone marrow, which could prove useful for isolation of this population toward future research and clinical applications.

Restoration of bone defects using modified heterogeneous deproteinized bone seeded with bone marrow mesenchymal stem cells

The aim of the present study was to investigate the effect of modified heterogeneous deproteinized bone combined with bone marrow mesenchymal stem cells (BMSCs) in the restoration of a validated bone defect model. BMSCs were identified by flow cytometry and multilineage differentiation assay. The structural features of the modified heterogeneous deproteinized bone scaffold and biocompatibility between BMSCs and the scaffold were confirmed by scanning electron microscope (SEM) detection. The cytotoxicity of the modified heterogeneous deproteinized bone scaffolds were detected by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenytetrazolium bromide (MTT) assay. SEM detection proved that modified heterogeneous deproteinized bone scaffold had no negative impact on the proliferation of BMSCs. MTT assay results demonstrated that the scaffold had no apparent cytotoxicity. Biomechanical detection showed that the stiffness and ultimate loading of tibias in the scaffold + BMSCs group were significantly higher than those of the scaffold alone group (P < 0.05) and the control group (P < 0.01). Histological analyses confirmed that the greatest quantity of new bone was generated in the scaffold + BMSCs group, when compared with all other groups, at 8 weeks' post-operation. The bone mineral density (BMD) in the scaffold + BMSC group was significantly higher than that of the scaffold alone group (P < 0.05) and the control group (P < 0.01). Fluorometric analyses confirmed the presence of BMSCs at high concentration within the bone defect areas in the scaffold + BMSCs group at 4 weeks after transplantation. These findings suggest that the modified heterogeneous deproteinized bone scaffold seeded with BMSCs can effectively enhance the restoration of bone defects.

Bone resorptive activity of human peripheral blood mononuclear cells after fusion with polyethylene glycol

The bone remodeling process occurs through bone formation by osteoblasts and bone resorption by osteoclasts, a process involving the contribution of endocrine and nervous systems. The mechanisms associated to differentiation and proliferation of osteoclasts and osteoblasts are considered a potential therapeutic target for treating some erosive bone diseases. The aim of the present study is to explore the feasibility of generating active osteoclast-like cells from peripheral blood mononuclear cells (PBMCs) following polyethylene glycol (PEG)-induced fusion. PEG-fused PBMCs showed TRAP⁺-multinucleated cells and bone resorption activity, and were also positive for osteoclast markers such as carbonic anhydrase II, calcitonin receptor, vacuolar ATPase, and cathepsin K, when examined by reverse transcription-polymerase chain reaction, immunochemistry and Western blotting. TRAP expression and bone resorptive activity were higher in whole PEG-fused PBMCs than in separated T lymphocytes, B lymphocytes or monocytes. Both TRAP expression and bone resorptive activity were also higher in osteogenesis imperfecta patients compared to PEG-fused PBMCs from healthy individuals. PEG-induced fusion was more efficient in inducing TRAP and bone resorptive activities than macrophage colony-stimulating factor or dexamethasone treatment. Bone resorptive activity of PEG-fused PMBCs was inhibited by bisphosphonates. Evidence is provided that the use of PEG-based cell fusion is a straightforward and amenable method for studying human osteoclast differentiation and testing new therapeutic strategies.

Calcium-phosphate ceramics and polysaccharide-based hydrogel scaffolds combined with mesenchymal stem cell differently support bone repair in rats

Research in bone tissue engineering is focused on the development of alternatives to autologous bone grafts for bone reconstruction. Although multiple stem cell-based products and biomaterials are currently being investigated, comparative studies are rarely achieved to evaluate the most appropriate approach in this context. Here, we aimed to compare different clinically relevant bone tissue engineering methods and evaluated the kinetic repair and the bone healing efficiency supported by mesenchymal stem cells and two different biomaterials, a new hydrogel scaffold and a commercial hydroxyapatite/tricalcium phosphate ceramic, alone or in combination.Syngeneic mesenchymal stem cells (5 × 10⁵) and macroporous biphasic calcium phosphate ceramic granules (Calciresorb C35^®, Ceraver) or porous pullulan/dextran-based hydrogel scaffold were implanted alone or combined in a drilled-hole bone defect in rats. Using quantitative microtomography measurements and qualitative histological examinations, their osteogenic properties were evaluated 7, 30, and 90 days after implantation. Three months after surgery, only minimal repair was evidenced in control rats while newly mineralized bone was massively observed in animals treated with either hydrogels (bone volume/tissue volume = 20%) or ceramics (bone volume/tissue volume = 26%). Repair mechanism and resorption kinetics were strikingly different: rapidly-resorbed hydrogels induced a dense bone mineralization from the edges of the defect while ceramics triggered newly woven bone formation in close contact with the ceramic surface that remained unresorbed. Delivery of mesenchymal stem cells in combination with these biomaterials enhanced both bone healing (>20%) and neovascularization after 1 month, mainly in hydrogel.Osteogenic and angiogenic properties combined with rapid resorption make hydrogels a promising alternative to ceramics for bone repair by cell therapy.

Overview of retinal differentiation potential of mesenchymal stem cells: A promising approach for retinal cell therapy

Retinal disease caused by retinal cell apoptosis leads to irreversible vision loss. Stem cell investigation efforts have been made to solve and cure retinal disorders. There are several sources of stem cells which have been used in these experiments. Numerous studies demonstrated that transplanted stem cells can migrate into and integrate in different layers of retina. Among these, mesenchymal stem cells (MSCs) were considered a promising source for cell therapy. Here, we review the literature assessing the potential of MSCs to differentiate into retinal cells in vivo and in vitro as well as their clinical application. However, more investigation is required to define the protocols that optimize stem cell differentiation and their functional integration in the retina.

Mechanical Loading Attenuates Radiation-Induced Bone Loss in Bone Marrow Transplanted Mice

Exposure of bone to ionizing radiation, as occurs during radiotherapy for some localized malignancies and blood or bone marrow cancers, as well as during space travel, incites dose-dependent bone morbidity and increased fracture risk. Rapid trabecular and endosteal bone loss reflects acutely increased osteoclastic resorption as well as decreased bone formation due to depletion of osteoprogenitors. Because of this dysregulation of bone turnover, bone’s capacity to respond to a mechanical loading stimulus in the aftermath of irradiation is unknown. We employed a mouse model of total body irradiation and bone marrow transplantation simulating treatment of hematologic cancers, hypothesizing that compression loading would attenuate bone loss. Furthermore, we hypothesized that loading would upregulate donor cell presence in loaded tibias due to increased engraftment and proliferation. We lethally irradiated 16 female C57Bl/6J mice at age 16 wks with 10.75 Gy, then IV-injected 20 million GFP(+) total bone marrow cells. That same day, we initiated 3 wks compression loading (1200 cycles 5x/wk, 10 N) in the right tibia of 10 of these mice while 6 mice were irradiated, non-mechanically-loaded controls. As anticipated, before-and-after microCT scans demonstrated loss of trabecular bone (-48.2% Tb.BV/TV) and cortical thickness (-8.3%) at 3 wks following irradiation. However, loaded bones lost 31% less Tb.BV/TV and 8% less cortical thickness (both p<0.001). Loaded bones also had significant increases in trabecular thickness and tissue mineral densities from baseline. Mechanical loading did not affect donor cell engraftment. Importantly, these results demonstrate that both cortical and trabecular bone exposed to high-dose therapeutic radiation remain capable of an anabolic response to mechanical loading. These findings inform our management of bone health in cases of radiation exposure.

Animal models of osteogenesis imperfecta: applications in clinical research

Osteogenesis imperfecta (OI), commonly known as brittle bone disease, is a genetic disease characterized by extreme bone fragility and consequent skeletal deformities. This connective tissue disorder is caused by mutations in the quality and quantity of the collagen that in turn affect the overall mechanical integrity of the bone, increasing its vulnerability to fracture. Animal models of the disease have played a critical role in the understanding of the pathology and causes of OI and in the investigation of a broad range of clinical therapies for the disease. Currently, at least 20 animal models have been officially recognized to represent the phenotype and biochemistry of the 17 different types of OI in humans. These include mice, dogs, and fish. Here, we describe each of the animal models and the type of OI they represent, and present their application in clinical research for treatments of OI, such as drug therapies (ie, bisphosphonates and sclerostin) and mechanical (ie, vibrational) loading. In the future, different dosages and lengths of treatment need to be further investigated on different animal models of OI using potentially promising treatments, such as cellular and chaperone therapies. A combination of therapies may also offer a viable treatment regime to improve bone quality and reduce fragility in animals before being introduced into clinical trials for OI patients.

Bone repair with skeletal stem cells: rationale, progress to date and clinical application

Bone marrow (BM) contains stem cells for both hematopoietic and nonhematopoietic lineages. Hematopoietic stem cells enable hematopoiesis to occur in a controlled manner in order to accurately compensate for the loss of short- as well as long-lived mature blood cells. The physiological role of nonhematopoietic BM stem cells, often referred to as multipotential stromal cells or skeletal stem cells (SSCs), is less understood. According to an authoritative current opinion, the main function of SSCs is to give rise to cartilage, bone, marrow fat and hematopoiesis-supportive stroma, in a specific sequence during embryonic and postnatal development. This review outlines recent advances in the understanding of origins and homeostatic functions of SSCs in vivo and highlights current and future SSC-based treatments for skeletal and joint disorders.

Osteoblast Lineage Cells Play an Essential Role in Periodontal Bone Loss Through Activation of Nuclear Factor-Kappa B

Bacterial pathogens stimulate periodontitis, the most common osteolytic disease in humans and the most common cause of tooth loss in adults. Previous studies identified leukocytes and their products as key factors in this process. We demonstrate for the first time that osteoblast lineage cells play a critical role in periodontal disease. Oral infection stimulated nuclear localization of NF-κB in osteoblasts and osteocytes in the periodontium of wild type but not transgenic mice that expressed a lineage specific dominant negative mutant of IKK (IKK-DN) in osteoblast lineage cells. Wild-type mice were also susceptible to bacteria induced periodontal bone loss but transgenic mice were not. The lack of bone loss in the experimental group was linked to reduced RANKL expression by osteoblast lineage cells that led to diminished osteoclast mediated bone resorption and greater coupled new bone formation. The results demonstrate that osteoblast lineage cells are key contributors to periodontal bone loss through an NF-κB mediated mechanism.

Intrauterine Bone Marrow Transplantation in Osteogenesis Imperfecta Mice Yields Donor Osteoclasts and Osteomacs but Not Osteoblasts

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The goal of osteogenesis imperfecta (OI) cell therapy is osteoblast replacement

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In utero transplantation (IUT) of bone marrow was conducted in OI mice

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Donor-derived osteoblasts were absent following bone marrow IUT

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Donor-derived hematopoietic cells included osteoclasts and osteal macrophages

Engraftability of Murine Bone Marrow-Derived Multipotent Mesenchymal Stem Cell Subpopulations in the Tissues of Developing Mice following Systemic Transplantation

INTRODUCTION

Cell therapies for generalized musculoskeletal diseases would require distribution of cells to all the skeletal tissues; however, there are controversies regarding the transplantability of multipotent mesenchymal stems cells (MSCs). We generated single-cell subpopulations of MSCs from murine bone marrow and assessed them for differences in trafficking through the circulatory system and engraftment in bone and other tissues.

MATERIALS AND METHODS

Seven single-cell clonal subpopulations were generated by serial dilution of GFP-marked MSCs isolated from bone marrow. The subpopulations were examined for putative MSC surface marker expression, in vitro differentiation toward osteogenic and adipogenic lineages, migration and engraftment in different tissues following intravenous delivery in normal, sublethally irradiated neonatal mice.

RESULTS

The surface marker expression profile revealed notable differences among clonal cells, specifically CD44 and CD105. All the cell subpopulations differentiated toward osteogenic and adipogenic lineages, with some committed to only one or the other. Two clones enriched in CXCR4 expression were highly efficient in migrating and engrafting in skeletal tissue including bone; this confirmed the role of this chemokine in cell migration. Donor cells retrieved from various tissues displayed different morphologies and potential differentiation into tissue cell type of engraftment, suggesting modification by the tissues in which the donor cells engrafted.

CONCLUSION

We have reported that, within bone marrow, there are heterogeneous subpopulations of MSCs that may differ in their ability to migrate in the circulatory system and engraft in different tissues.

Ex Vivo Expanded Allogeneic Mesenchymal Stem Cells with Bone Marrow Transplantation Improved Osteogenesis in Infants with Severe Hypophosphatasia

Patients with severe hypophosphatasia (HPP) develop osteogenic impairment with extremely low alkaline phosphatase (ALP) activity, resulting in a fatal course during infancy. Mesenchymal stem cells (MSCs) differentiate into various mesenchymal lineages, including bone and cartilage. The efficacy of allogeneic hematopoietic stem cell transplantation for congenital skeletal and storage disorders is limited, and therefore we focused on MSCs for the treatment of HPP. To determine the effect of MSCs on osteogenesis, we performed multiple infusions of ex vivo expanded allogeneic MSCs for two patients with severe HPP who had undergone bone marrow transplantation (BMT) from asymptomatic relatives harboring the heterozygous mutation. There were improvements in not only bone mineralization but also muscle mass, respiratory function, and mental development, resulting in the patients being alive at the age of 3. After the infusion of MSCs, chimerism analysis of the mesenchymal cell fraction isolated from bone marrow in the patients demonstrated that donor-derived DNA sequences existed. Adverse events of BMT were tolerated, whereas those of MSC infusion did not occur. However, restoration of ALP activity was limited, and normal bony architecture could not be achieved. Our data suggest that multiple MSC infusions, following BMT, were effective and brought about clinical benefits for patients with lethal HPP. Allogeneic MSC-based therapy would be useful for patients with other congenital bone diseases and tissue disorders if the curative strategy to restore clinically normal features, including bony architecture, can be established.

Autologous implantation of BMP2-expressing dermal fibroblasts to improve bone mineral density and architecture in rabbit long bones

Cell-mediated gene therapy may treat bone fragility disorders. Dermal fibroblasts (DFb) may be an alternative cell source to stem cells for orthopedic gene therapy because of their rapid cell yield and excellent plasticity with bone morphogenetic protein-2 (BMP2) gene transduction. Autologous DFb or BMP2-expressing autologous DFb were administered in twelve rabbits by two delivery routes; a transcortical intra-medullar infusion into tibiae and delayed intra-osseous injection into femoral drill defects. Both delivery methods of DFb-BMP2 resulted in a successful cell engraftment, increased bone volume, bone mineral density, improved trabecular bone microarchitecture, greater bone defect filling, external callus formation, and trabecular surface area, compared to non-transduced DFb or no cells. Cell engraftment within trabecular bone and bone marrow tissue was most efficiently achieved by intra-osseous injection of DFb-BMP2. Our results suggested that BMP2-expressing autologous DFb have enhanced efficiency of engraftment in target bones resulting in a measurable biologic response by the bone of improved bone mineral density and bone microarchitecture. These results support that autologous implantation of DFb-BMP2 warrants further study on animal models of bone fragility disorders, such as osteogenesis imperfecta and osteoporosis to potentially enhance bone quality, particularly along with other gene modification of these diseases.

Presentation of a novel model of chitosan- polyethylene oxide-nanohydroxyapatite nanofibers together with bone marrow stromal cells to repair and improve minor bone defects

OBJECTIVES

Various methods for repairing bone defects are presented. Cell therapy is one of these methods. Bone marrow stromal cells (BMSCs) seem to be suitable for this purpose. On the other hand, lots of biomaterials are used to improve and repair the defect in the body, so in this study we tried to produce a similar structure to the bone by the chitosan and hydroxyapatite.

MATERIALS AND METHODS

In this study, the solution of chitosan-nanohydroxyapatite-polyethylene oxide (PEO) Nanofibers was produced by electrospinning method, and then the BMSCs were cultured on this solution. A piece of chitosan-nanohydroxyapatite Nanofibers with BMSCs was placed in a hole with the diameter of 1 mm at the distal epiphysis of the rat femur. Then the biomechanical and radiographic studies were performed.

RESULTS

Biomechanical testing results showed that bone strength was significantly higher in the Nanofiber/BMSCs group in comparison with control group. Also the bone strength in nanofiber/BMSCs group was significant, but in nanofiber group was nearly significant. Radiographic studies also showed that the average amount of callus formation (radio opacity) in nanofiber and control group was not significantly different. The callus formation in nanofiber/BMSCs group was increased compared to the control group, and it was not significant in the nanofiber group.

CONCLUSION

Since chitosan-nanohydroxyapatite nanofibers with BMSCs increases the rate of bone repair, the obtained cell-nanoscaffold shell can be used in tissue engineering and cell therapy, especially for bone defects.

Effect of heterologous bone marrow mononuclear cell transplantation on midpalatal expansion in rats

The aim of this study was to explore whether bone marrow mononuclear cell (BMMC) transplantation is able to accelerate the bone remodeling induced by midpalatal expansion in rats. A total of 48 male Sprague-Dawley rats (mean weight, 208.36±7.32 g) were divided into control and midpalatal expansion with or without BMMC transplantation groups. Histological and morphological changes were observed in each group. The osteogenic activities and differential potentials of the transplanted BMMCs labeled with bromodeoxyuridine in the midpalatal bone tissue were assessed by osteocalcin expression. The receptor activator of nuclear factor κB ligand (RANKL)/osteoprotegerin (OPG) ratio was determined by reverse transcription-quantitative polymerase chain reaction (RT-qPCR) to reflect the equilibrium between bone resorption and formation. The results demonstrated that the width of the maxillary dental arch increased distinctly within 2 weeks of midpalatal expansion with BMMC transplantation. The morphology of the midpalatal suture in this group changed significantly; the cartilage was completely replaced by fibrous-like tissue expressing osteocalcin. The palatal bone was reorganized from a cancellous form into a mature compact structure after an additional 2-week relapse period. Immunostaining results indicated that the heterologous transplanted BMMCs survived and differentiated into osteoblasts during the remodeling induced by midpalatal expansion. The RANKL/OPG expression ratio significantly decreased after 2 weeks of midpalatal expansion with BMMC transplantation due to the inhibition of RANKL expression. Heterologous BMMC transplantation appears to accelerate the midpalatal bone remodeling induced by expansion of the rats through increasing the number of osteoprogenitor cells and regulating the RANKL-OPG signaling pathway.

Pigment epithelium-derived factor enhances differentiation and mineral deposition of human mesenchymal stem cells

Pigment epithelium-derived factor (PEDF) is a potent antiangiogenic factor found in a wide variety of tissues. Recent findings indicated that lack of PEDF leads to osteogenesis imperfecta type VI whose hallmark is a defect in mineralization. We investigated the effects of PEDF on human mesenchymal stem cells (hMSCs) and signaling pathways through which PEDF displays its activities in hMSCs. hMSCs incubated in a medium supplemented with PEDF induced expression of osteoblastic-related genes. In addition, PEDF induced alkaline phosphatase (ALP) activity in MSCs at 14 days of incubation in maintenance medium; hMSCs incubated in osteogenic medium in presence of PEDF expressed 19% more ALP activity (35.655 ± 1.827 U/mg protein, p = .041 than cells incubated in the same medium without PEDF supplementation (29.956 ± 2.100 U/μg protein). hMSCs incubated in osteogenic medium in presence of PEDF deposited 50% more mineral (2.108 ± 0.306 OD/ml per well per 1 × 10(4) cells per square centimeter, p = .017) than MSCs incubated in absence of the protein (1.398 ± 0.098 OD/ml per well per 1 × 10(4) cells per square centimeter) as determined by Alizarin Red quantitation. Reduction in PEDF expression in MSCs by siRNA led to decreased ALP activity (33.552 ± 2.009 U/ng protein of knockdown group vs. 39.269 ± 3.533 U/ng protein of scrambled siRNA group, p = .039) and significant reduction in mineral deposition (0.654 ± 0.050 OD/ml per well per 1 × 10(4) cells per square centimeter of knockdown group vs. 1.152 ± 0.132 OD/ml per well per 1 × 10(4) cells per square centimeter of wild-type group, p = .010). Decreased ALP activity and mineral deposition were restored by supplementation with exogenous PEDF protein. PEDF activated ERK and AKT signaling pathways in MSCs to induce expression of osteoblastic-related genes. These data suggest that PEDF is involved in MSCs osteoblastic differentiation.

Local transplantation is an effective method for cell delivery in the osteogenesis imperfecta murine model

PURPOSE

Osteogenesis imperfecta is a serious genetic disorder that results from improper type I collagen production. We aimed to evaluate whether bone marrow stromal cells (BMSC) delivered locally into femurs were able to engraft, differentiate into osteoblasts, and contribute to formation of normal bone matrix in the osteogenesis imperfect murine (oim) model.

METHODS

Donor BMSCs from bone-specific reporter mice (Col2.3GFP) were expanded in vitro and transplanted into the femoral intramedullary cavity of oim mice. Engraftment was evaluated after four weeks.

RESULTS

We detected differentiation of donor BMSCs into Col2.3GFP+ osteoblasts and osteocytes in cortical and trabecular bone of transplanted oim femurs. New bone formation was detected by deposition of dynamic label in the proximity to the Col2.3GFP+ osteoblasts, and new bone showed more organized collagen structure and expression of type I α2 collagen. Col2.3GFP cells were not found in the contralateral femur indicating that transplanted osteogenic cells did not disseminate by circulation. No osteogenic engraftment was observed following intravenous transplantation of BMSCs. BMSC cultures derived from transplanted femurs showed numerous Col2.3GFP+ colonies, indicating the presence of donor progenitor cells. Secondary transplantation of cells recovered from recipient femurs and expanded in vitro also showed Col2.3GFP+ osteoblasts and osteocytes confirming the persistence of donor stem/progenitor cells.

CONCLUSION

We show that BMSCs delivered locally in oim femurs are able to engraft, differentiate into osteoblasts and osteocytes and maintain their progenitor potential in vivo. This suggests that local delivery is a promising approach for introduction of autologous MSC in which mutations have been corrected.

Bone formation in rabbit's leg muscle after autologous transplantation of bone marrow-derived mesenchymal stem cells expressing human bone morphogenic protein-2

BACKGROUND

To test whether autologous transplantation of bone marrow-derived mesenchymal stem cells (BM-MSCs) expressing human bone morphogenic protein-2 (hBMP-2) can produce bone in rabbit leg muscles.

MATERIALS AND METHODS

MSCs were isolated from BM of the iliac crest of rabbits and then infected with lentiviral vectors (LVs) bearing hBMP-2 and green fluorescent protein under the control of the cytomegalovirus (immediate early promoter). Differentiation of transduced MSCs to osteoblasts in vitro was evaluated with an alkaline phosphatase activity assay and immuohistochemistry against osteoblast specific markers. MSCs expressing hBMP-2 were placed in an absorbable gelatin sponge, which was then transplanted into the gastrocnemius of rabbits from which MSCs were isolated. Bone formation was examined by X-ray and histological analysis.

RESULTS

LVs efficiently mediated hBMP-2 gene expression in rabbit BM-MSCs. Ectopic expression of hBMP in these MSCs induced osteoblastic differentiation in vitro. Bone was formed after the MSCs expressing hBMP-2 were transplanted into rabbit muscles.

CONCLUSION

Ectopic expression of hBMP-2 in rabbit MSCs induces them to differentiate into osteoblasts in vitro and to form a bone in vivo.

Effect of Intra-Medullar and Intra-Venous Infusions of Mesenchymal Stem Cells on Cell Engraftment by In-Vivo Cell Tracking and Osteoinductivity in Rabbit Long Bones: A Pilot Study

OBJECTIVE

Stem cell therapy can be an efficacious treatment option for bone fragility disorders (eg, osteogenesis imperfecta, disuse osteopenia, and osteoporosis), and successful cell therapy application may be dependent on optimal cell engraftment in target bones. The objective of this study was to compare the efficiency of intra-medullar and intra-venous delivery of mesenchymal stem cells (MSC) to improve cell engraftment rate, bone mineral density, and micro-architecture.

METHODS

By using six healthy juvenile New Zealand White rabbits, MSC were isolated from cancellous bone harvests and confirmed to have osteogenic capacity by inducing ectopic bone formation. The MSC were cultured, transduced by foamy viral vectors with marker genes for in vivo cell tracking, and expanded. All rabbits had one randomly selected limb receive intra-medullar infusion of 3×10⁷ to 1×10⁸ autologous MSC in the distal femur or the distal femur and proximal tibia. Two of six rabbits also received an intra-venous MSC infusion. At 28 days, MSC bone engraftment was assessed by PCR and the bone density and microstructure assessed by computed tomography and histomorphometry.

RESULTS

The intra-medullar-infused MSC were detected in epiphysis or diaphysis of the distal femurs and/or proximal tibiae. Infused MSC comprised 0.01 to 0.3% of all cells in the bone tissues. The intra-venous-infused MSC were not detected in any location. Neither intra-medullar nor intra-venous MSC infusion altered bone volume, bone mineral density, or cortical bone porosity/thickness. Systemic biodistribution of intra-medullar-infused MSC was not evident.

CONCLUSIONS

Our results indicated that intra-medullar infusion can be an effective cell delivery route for stem cell therapy potentially for orthopedic disorders, in preference to systemic administration. Further research is warranted to demonstrate an efficacy of intra-medullar MSC infusion on bone density and micro-architecture using animal models of bone disorders.

Cells derived from murine induced pluripotent stem cells (iPSC) by treatment with members of TGF-beta family give rise to osteoblasts differentiation and form bone in vivo

Background

Induced pluripotent stem cells (iPSC) are generated by reprogramming somatic cells into embryonic like state (ESC) using defined factors. There is great interest in these cells because of their potential for application in regenerative medicine.

Results

iPSC reprogrammed from murine tail tip fibroblasts were exposed to retinoic acid alone (RA) or in combination with TGF-β1 and 3, basic fibroblast growth factor (bFGF) or bone morphogenetic protein 2 (BMP-2). The resulting cells expressed selected putative mesenchymal stem cells (MSCs) markers; differentiated toward osteoblasts and adipocytic cell lineages in vitro at varying degrees. TGF-beta1 and 3 derived-cells possessed higher potential to give rise to osteoblasts than bFGF or BMP-2 derived-cells while BMP-2 derived cells exhibited a higher potential to differentiate toward adipocytic lineage. TGF-β1 in combination with RA derived-cells seeded onto HA/TCP ceramics and implanted in mice deposited typical bone. Immunofluorescence staining for bone specific proteins in cell seeded scaffolds tissue sections confirmed differentiation of the cells into osteoblasts in vivo.

Conclusions

The results demonstrate that TGF-beta family of proteins could potentially be used to generate murine iPSC derived-cells with potential for osteoblasts differentiation and bone formation in vivo and thus for application in musculoskeletal tissue repair and regeneration.

Implantation of osteogenic differentiated donor mesenchymal stem cells causes recruitment of host cells

The interaction between host and donor cells is believed to play an important role in osteogenesis. However, it is still unclear how donor osteogenic cells behave and interact with host cells in vivo. The purpose of this study was to track the interactions between transplanted osteogenic cells and host cells during osteogenesis. In vitro migration assay was carried out to investigate the ability of osteogenic differentiated human mesenchymal stem cells (O-hMSCs) to recruit MSCs. At the in vivo level, O-hMSCs were implanted subcutaneously or into skull defects in severe combined immunodeficient (SCID) mice. New bone formation was observed by micro-CT and histological procedures. In situ hybridization (ISH) against human Alu sequences was performed to distinguish donor osteogenic cells from host cells. In vitro migration assay revealed an increased migration potential of MSCs by co-culturing with O-hMSCs. In agreement with the results of in vitro studies, ISH against human Alu sequences showed that host mouse MSCs migrated in large numbers into the transplantation site in response to O-hMSCs. Interestingly, host cells recruited by O-hMSCs were the major cell populations in newly formed bone tissues, indicating that O-hMSCs can trigger and initiate osteogenesis when transplanted in orthotopic sites. The observations from this study demonstrated that in vitro induced O-hMSCs were able to attract host MSCs in vivo and were involved in osteogenesis together with host cells, which may be of importance for bone tissue-engineering applications.

Gene delivery to bone

Gene delivery to bone is useful both as an experimental tool and as a potential therapeutic strategy. Among its advantages over protein delivery are the potential for directed, sustained and regulated expression of authentically processed, nascent proteins. Although no clinical trials have been initiated, there is a substantial pre-clinical literature documenting the successful transfer of genes to bone, and their intraosseous expression. Recombinant vectors derived from adenovirus, retrovirus and lentivirus, as well as non-viral vectors, have been used for this purpose. Both ex vivo and in vivo strategies, including gene-activated matrices, have been explored. Ex vivo delivery has often employed mesenchymal stem cells (MSCs), partly because of their ability to differentiate into osteoblasts. MSCs also have the potential to home to bone after systemic administration, which could serve as a useful way to deliver transgenes in a disseminated fashion for the treatment of diseases affecting the whole skeleton, such as osteoporosis or osteogenesis imperfecta. Local delivery of osteogenic transgenes, particularly those encoding bone morphogenetic proteins, has shown great promise in a number of applications where it is necessary to regenerate bone. These include healing large segmental defects in long bones and the cranium, as well as spinal fusion and treating avascular necrosis.

Differentiating multipotent mesenchymal stromal cells generate factors that exert paracrine activities on exogenous MSCs: Implications for paracrine activities in bone regeneration

The mechanisms by which multipotent mesenchymal stromal cells (MSCs) contribute to tissue repair following transplantation into host tissues remains poorly understood. Current concepts suggest that, in addition to differentiation into cells of the host tissues, MSCs also generate trophic factors that modulate host tissue microenvironment to aid in the repair process. In this communication, we assessed whether factors secreted by MSCs undergoing osteogenic differentiation induce expression of osteoblast markers in exogenous MSCs as well as their migration. Murine MSCs were cultured in osteogenic medium, and at different time points, medium conditioned by the cells was collected and assessed for its effects on differentiation and migration of exogenous MSCs. In addition, we determined whether MSCs infused into mice femurs expressed genes encoding for factors predicted to play a role in paracrine activities. The results showed that MSCs maintained in osteogenic medium, secreted factors at specific time points that induced alkaline phosphatase activity (ALP) in exogenous MSCs as well as their migration. MSCs infused into mice femurs and retrieved at different days expressed genes that encoded predicted factors that play a role in cell differentiation and migration. Neutralizing antibodies to bone morphogenetic protein-2 (BMP-2) led to the decrease in ALP activity by exogenous MSCs. These data demonstrated that, as MSCs differentiate toward osteogenic lineage, they secrete factors that induce recruitment and differentiation of endogenous progenitors. These data reveal mechanisms by which donor MSCs may contribute to the bone reparative process and provide a platform for designing approaches for stem cell therapies of musculoskeletal disorders.

Recent progress in osteogenesis imperfecta

Osteogenesis imperfecta (OI), a rare clinical disease with abnormal type I collagen, is inherited or caused by mutation. A classification of OI into four types was proposed in 1979 and has been used up until four new types were added recently. A tough clinical challenge, OI causes abnormal blood coagulation and cardiovascular structure, airways obstruction, and delayed wound healing. The authors of the current article have reviewed recent progress in OI worldwide, including the mechanisms, classification, detection, clinical difficulties, and treatment.

Mesenchymal stem cells in tissue growth and repair

It has been established in the recent several decades that stem cells play a crucial role in tissue renewal and regeneration. Mesenchymal stem cells (MSCs) are part of the most important population of adult stem cells. These cells have hereby been identified for the very first time and subsequently isolated from bone marrow stroma. Bone marrow-derived MSCs have been believed to play the role of a source of cells for the renewal and repair of connective tissues, including bone, cartilage and adipose tissues. Cells similar to bone marrow-derived MSCs have now been identified in all postnatal tissues. Data on the distribution and function of MSCsin vivocollected using novel approaches pertaining to the identification of MSCsin situ, to their isolation from tissues, and finally to the determination of their biological properties have enabled successful revision of the role of MSCs in various organs and tissues. This review summarizes our own, as well as others', data concerning the role of MSCs in the regulation processes of tissue repair and regeneration. In our opinion, MSCs provide the connection between the blood-vascular, immune, endocrine, and nervous systems and tissue-specific stem cells in the body.

The elusive nature and function of mesenchymal stem cells

Mesenchymal stem cells (MSCs) are a diverse subset of multipotent precursors present in the stromal fraction of many adult tissues and have drawn intense interest from translational and basic investigators. MSCs have been operationally defined by their ability to differentiate into osteoblasts, adipocytes and chondrocytes after in vitro expansion. Nevertheless, their identity in vivo, heterogeneity, anatomical localization and functional roles in adult tissue homeostasis have remained enigmatic and are only just starting to be uncovered.