Potential implications of cell therapy for osteogenesis imperfecta

New Perspectives of Therapies in Osteogenesis Imperfecta-A Literature Review

(1) Background: Osteogenesis imperfecta (OI) is a rare skeletal dysplasia characterized as a heterogeneous disorder group with well-defined phenotypic and genetic features that share uncommon bone fragility. The current treatment options, medical and orthopedic, are limited and not efficient enough to improve the low bone density, bone fragility, growth, and mobility of the affected individuals, creating the need for alternative therapeutic agents. (2) Methods: We searched the medical database to find papers regarding treatments for OI other than conventional ones. We included 45 publications. (3) Results: In reviewing the literature, eight new potential therapies for OI were identified, proving promising results in cells and animal models or in human practice, but further research is still needed. Bone marrow transplantation is a promising therapy in mice, adults, and children, decreasing the fracture rate with a beneficial effect on structural bone proprieties. Anti-RANKL antibodies generated controversial results related to the therapy schedule, from no change in the fracture rate to improvement in the bone mineral density resorption markers and bone formation, but with adverse effects related to hypercalcemia. Sclerostin inhibitors in murine models demonstrated an increase in the bone formation rate and trabecular cortical bone mass, and a few human studies showed an increase in biomarkers and BMD and the downregulation of resorption markers. Recombinant human parathormone and TGF-β generated good results in human studies by increasing BMD, depending on the type of OI. Gene therapy, 4-phenylbutiric acid, and inhibition of eIF2α phosphatase enzymes have only been studied in cell cultures and animal models, with promising results. (4) Conclusions: This paper focuses on eight potential therapies for OI, but there is not yet enough data for a new, generally accepted treatment. Most of them showed promising results, but further research is needed, especially in the pediatric field.

Gene-repaired iPS cells as novel approach for patient with osteogenesis imperfecta

Introduction: The benefits of patient's specific cell/gene therapy have been reported in relation to numerous genetic related disorders including osteogenesis imperfecta (OI). In osteogenesis imperfecta particularly also a drug therapy based on the administration of bisphosphonates partially helped to ease the symptoms. Methods: In this controlled trial, fibroblasts derived from patient diagnosed with OI type II have been successfully reprogrammed into induced Pluripotent Stem cells (iPSCs) using Yamanaka factors. Those cells were subjected to repair mutations found in the COL1A1 gene using homologous recombination (HR) approach facilitated with star polymer (STAR) as a carrier of the genetic material. Results: Delivery of the correct linear DNA fragment to the osteogenesis imperfecta patient's cells resulted in the repair of the DNA mutation with an 84% success rate. IPSCs showed 87% viability after STAR treatment and 82% with its polyplex. Discussion: The use of novel polymer Poly[N,N-Dimethylaminoethyl Methacrylate-co-Hydroxyl-Bearing Oligo(Ethylene Glycol) Methacrylate] Arms (P(DMAEMA-co-OEGMA-OH) with star-like structure has been shown as an efficient tool for nucleic acids delivery into cells (Funded by National Science Centre, Contract No. UMO-2020/37/N/NZ2/01125).

Current Overview of Osteogenesis Imperfecta

Osteogenesis imperfecta (OI), or brittle bone disease, is a heterogeneous disorder characterised by bone fragility, multiple fractures, bone deformity, and short stature. OI is a heterogeneous disorder primarily caused by mutations in the genes involved in the production of type 1 collagen. Severe OI is perinatally lethal, while mild OI can sometimes not be recognised until adulthood. Severe or lethal OI can usually be diagnosed using antenatal ultrasound and confirmed by various imaging modalities and genetic testing. The combination of imaging parameters obtained by ultrasound, computed tomography (CT), and magnetic resource imaging (MRI) can not only detect OI accurately but also predict lethality before birth. Moreover, genetic testing, either noninvasive or invasive, can further confirm the diagnosis prenatally. Early and precise diagnoses provide parents with more time to decide on reproductive options. The currently available postnatal treatments for OI are not curative, and individuals with severe OI suffer multiple fractures and bone deformities throughout their lives. In utero mesenchymal stem cell transplantation has been drawing attention as a promising therapy for severe OI, and a clinical trial to assess the safety and efficacy of cell therapy is currently ongoing. In the future, early diagnosis followed by in utero stem cell transplantation should be adopted as a new therapeutic option for severe OI.

The effect of adrenocorticotropic hormone on alpha-2-macroglobulin in osteoblasts derived from human mesenchymal stem cells

Nowadays, alpha-2-macroglobulin (A2M) gene has allocated escalating interest among several genes involved in the pathogenesis of avascular necrosis of the femoral head (ANFH). This molecule could interact with several osteogenic-related proteins. It was reported that adrenocorticotropic hormone (ACTH) affects bones through its receptor located on osteoblasts, suggesting it as a potential target in ANFH treatment. In this study, the effect of ACTH on A2M expression was investigated in osteoblasts as well as during the differentiation of human mesenchymal stem cells (MSCs) into osteoblasts. In this study, MSCs derived from bone marrow were isolated and purified using Ficoll gradient and several passaging. MSCs were characterized by induction with osteogenic and adipogenic medium followed by Oil Red O, Alizarin Red and alkaline phosphatase staining. Besides, MSCs were exposed to various concentrations of ACTH to evaluate the cell variability by MTT assay. MSCs and differentiated osteoblasts were treated with 10^-8 molar ACTH for 16 and 26 days, respectively. Then, the total RNA was extracted and A2M expression was quantified by real-time qPCR. The protein expression levels of osteoblast markers including alkaline phosphatase (ALPL) and bone gamma-carboxyglutamate protein (BGLAP) were also measured. The results showed that A2M expression in cells treated with ACTH was up-regulated significantly compared to the control group. Similarly, the expression of osteoblast gene markers including ALPL and BGLAP was significantly increased. ACTH, as an osteoblastic differentiation enhancer, up-regulates A2M, which promotes osteoblastic differentiation probably through TGF-β induction.

Enhancement of Mesenchymal Stem Cell-Driven Bone Regeneration by Resveratrol-Mediated SOX2 Regulation

Mesenchymal stem cells (MSCs) are an attractive cell source for regenerative medicine. However, MSCs age rapidly during long-term ex vivo culture and lose their therapeutic potential before they reach effective cell doses (ECD) for cell therapy. Thus, a prerequisite for effective MSC therapy is the development of cell culture methods to preserve the therapeutic potential during long-term ex vivo cultivation. Resveratrol (RSV) has been highlighted as a therapeutic candidate for bone disease. Although RSV treatment has beneficial effects on bone-forming cells, in vivo studies are lacking. The current study showed that long-term (6 weeks from primary culture date)-cultured MSCs with RSV induction retained their proliferative and differentiation potential despite reaching ECD. The mechanism of RSV action depends entirely on the SIRT1-SOX2 axis in MSC culture. In a rat calvarial defect model, RSV induction significantly improved bone regeneration after MSC transplantation. This study demonstrated an example of efficient MSC therapy for treating bone defects by providing a new strategy using the plant polyphenol RSV.

Distribution pattern following systemic mesenchymal stem cell injection depends on the age of the recipient and neuronal health

Background

Mesenchymal stem cells (MSCs) show therapeutic efficacy in many different age-related degenerative diseases, including Alzheimer’s disease. Very little is currently known about whether or not aging impacts the transplantation efficiency of MSCs.

Methods

In this study, we investigated the distribution of intravenously transplanted syngeneic MSCs derived from young and aged mice into young, aged, and transgenic APP/PS1 Alzheimer’s disease mice. MSCs from male donors were transplanted into female mice and their distribution pattern was monitored by PCR using Y-chromosome specific probes. Biodistribution of transplanted MSCs in the brains of APP/PS1 mice was additionally confirmed by immunofluorescence and confocal microscopy.

Results

Four weeks after transplantation into young mice, young MSCs were found in the lung, axillary lymph nodes, blood, kidney, bone marrow, spleen, liver, heart, and brain cortex. In contrast, young MSCs that were transplanted into aged mice were only found in the brain cortex. In both young and aged mouse recipients, transplantation of aged MSCs showed biodistribution only in the blood and spleen. Although young transplanted MSCs only showed neuronal distribution in the brain cortex in young mice, they exhibited a wide neuronal distribution pattern in the brains of APP/PS1 mice and were found in the cortex, cerebellum, hippocampus, olfactory bulb, and brainstem. The immunofluorescent signal of both transplanted MSCs and resident microglia was robust in the brains of APP/PS1 mice. Monocyte chemoattractant-1 levels were lowest in the brain cortex of young mice and were significantly increased in APP/PS1 mice. Within the hippocampus, monocyte chemoattractant-1 levels were significantly higher in aged mice compared with younger and APP/PS1 mice.

Conclusions

We demonstrate in vivo that MSC biodistribution post transplantation is detrimentally affected by aging and neuronal health. Aging of both the recipient and the donor MSCs used attenuates transplantation efficiency. Clinically, our data would suggest that aged MSCs should not be used for transplantation and that transplantation of MSCs into aged patients will be less efficacious.

Electronic supplementary material

The online version of this article (doi:10.1186/s13287-017-0533-2) contains supplementary material, which is available to authorized users.

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.

Comparison of Differentiation of Induced Pluripotent Stem Cells and Bone-Marrow Mesenchymal Stem Cells to Osteoblast: Osteogenesis versus Pluripotency

BACKGROUND

Derivation of induced pluripotent stem cells (iPSCs) from various adult somatic cells through over-expression of pluripotent genes could allow for the unlimited autologous supply in regenerative medicine. On the other hand the generation of various progenitors from bone-marrow mesenchymal stem cells (MSCs) is justly well established.

OBJECTIVE

In this study we compared the expression level of pluripotent genes oct4, c-myc, sox-2, nanog, klf4 and lin28 in iPSCs and MSCs derived from bone marrow. Also the potential of osteogenesis of iPSCs and bone-marrow MSCs were compared.

METHODS

We analyzed the expression level of oct4, sox-2, c-myc, klf4, nanog and lin28 genes in human MSCs derived from iPSCs and MSCs by cell culture and real-time PCR. Also the expression level of osteocalcin and osteopontin in both groups were evaluated.

RESULTS

We found that the expression of osteogenic markers in differentiated iPSCs to osteoblast were higher than bone-marrow MSCs. While the levels of pluripotency genes oct4, c-myc and klf4 in iPSCs were significantly (p<0.05) higher than bone-marrow MSCs, MSCs showed higher expression of sox-2, nanog and lin28 compared with iPSCs (p=NS).

CONCLUSION

It seems that the higher expression of osteopontin and osteocalcin in MSCs compared to iPSCs may be due to other factors (besides pluripotency) required for differentiation of stem cells to osteoblast.

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.

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.

Severe osteogenesis imperfecta Type-III and its challenging treatment in newborn and preschool children. A systematic review

Osteogenesis imperfecta (OI) is a group of genetic disorders, of which Type III is the most severe among survivors. The disease is characterised in particular by bone fragility, decreased bone mass and increased incidence of fractures. Other usual findings are muscle hypotonia, joint hypermobility and short stature. Fractures and weak bones may consequently cause limb and spinal deformity and chronic physical disability. Bisphosphonates have revolutionised the treatment of newborn children with severe OI type III. Surgery is still needed in most patients due to high frequency of the fractures. In this systematic review we describe the present state-of-art in treating the most severe type of OI in newborn and preschool children with their bone fractures.

Lower Oncogenic Potential of Human Mesenchymal Stem Cells Derived from Cord Blood Compared to Induced Pluripotent Stem Cells

BACKGROUND

In regenerative medicine, use of each of the mesenchymal stem cells derived from bone marrow, cord blood, and adipose tissue, has several cons and pros. Mesenchymal stem cells derived from cord blood have been considered the best source for precursor transplantation. Direct reprogramming of a somatic cell into induced pluripotent stem cells by over-expression of 6 transcription factors Oct4, Sox2, Klf4, lin28, Nanog, and c-Myc has great potential for regenerative medicine, eliminating the ethical issues of embryonic stem cells and the rejection problems of using non-autologous cells.

OBJECTIVE

To compare reprogramming and pluripotent markers OCT4, Sox-2, c-Myc, Klf4, Nanog, and lin28 in mesenchymal stem cells derived from cord blood and induced pluripotent stem cells.

METHODS

We analyzed the expression level of OCT4, Sox-2, c-Myc, Klf4, Nanog and lin28 genes in human mesenchymal stem cells derived from cord blood and induced pluripotent stem cells by cell culture and RT-PCR.

RESULTS

The expression level of pluripotent genes OCT4 and Sox-2, Nanog and lin28 in mesenchymal stem cells derived from cord blood were significantly higher than those in induced pluripotent stem cells. In contrast to OCT-4A and Sox-2, Nanog and lin28, the expression level of oncogenic factors c-Myc and Klf4 were significantly higher in induced pluripotent stem cells than in mesenchymal stem cells derived from cord blood.

CONCLUSION

It could be concluded that mesenchymal stem cells derived from human cord blood have lower oncogenic potential compared to induced pluripotent stem cells.

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.

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.

Toll-like receptor 3 and suppressor of cytokine signaling proteins regulate CXCR4 and CXCR7 expression in bone marrow-derived human multipotent stromal cells

Background

The use of bone marrow-derived human multipotent stromal cells (hMSC) in cell-based therapies has dramatically increased in recent years, as researchers have exploited the ability of these cells to migrate to sites of tissue injury, inflammation, and tumors. Our group established that hMSC respond to “danger” signals – by-products of damaged, infected or inflamed tissues – via activation of Toll-like receptors (TLRs). However, little is known regarding downstream signaling mediated by TLRs in hMSC.

Methodology/Principal Findings

We demonstrate that TLR3 stimulation activates a Janus kinase (JAK) 2/signal transducer and activator of transcription (STAT) 1 pathway, and increases expression of suppressor of cytokine signaling (SOCS) 1 and SOCS3 in hMSC. Our studies suggest that each of these SOCS plays a distinct role in negatively regulating TLR3 and JAK/STAT signaling. TLR3-mediated interferon regulatory factor 1 (IRF1) expression was inhibited by SOCS3 overexpression in hMSC while SOCS1 overexpression reduced STAT1 activation. Furthermore, our study is the first to demonstrate that when TLR3 is activated in hMSC, expression of CXCR4 and CXCR7 is downregulated. SOCS3 overexpression inhibited internalization of both CXCR4 and CXCR7 following TLR3 stimulation. In contrast, SOCS1 overexpression only inhibited CXCR7 internalization.

Conclusion/Significance

These results demonstrate that SOCS1 and SOCS3 each play a functionally distinct role in modulating TLR3, JAK/STAT, and CXCR4/CXCR7 signaling in hMSC and shed further light on the way hMSC respond to danger signals.

The stem cell niche should be a key issue for cell therapy in regenerative medicine

Recent advances in stem cell research have highlighted the role played by such cells and their environment (the stem cell niche) in tissue renewal and homeostasis. The control and regulation of stem cells and their niche are remaining challenges for cell therapy and regenerative medicine on several tissues and organs. These advances are important for both, the basic knowledge of stem cell regulation, and their practical translational applications into clinical medicine. This article is primarily concerned with the mesenchymal stem cells (MSCs) and it reviews the current aspects of their own niche. We discuss on the need for a deeper understanding of the identity of this cell type and its microenvironment in order to improve the effectiveness of any cell therapy for regenerative medicine. Ex vivo reproduction of the conditions of the natural stem cell niche, when necessary, would provide success to tissue engineering. The first challenge of regenerative medicine is to find cells able to replace and/or repair the lost function of tissues and organs by disease or aging and the trophic and immunomodulatory effects recently found for MSCs open up for new opportunities. If MSCs are pericytes, as it has been proposed, perhaps it may explain the ubiquity of these cells and their possible role in miscellaneous repairs throughout the body opening for new chances for extensive tissue repair.

The collagen family

Collagens are the most abundant proteins in mammals. The collagen family comprises 28 members that contain at least one triple-helical domain. Collagens are deposited in the extracellular matrix where most of them form supramolecular assemblies. Four collagens are type II membrane proteins that also exist in a soluble form released from the cell surface by shedding. Collagens play structural roles and contribute to mechanical properties, organization, and shape of tissues. They interact with cells via several receptor families and regulate their proliferation, migration, and differentiation. Some collagens have a restricted tissue distribution and hence specific biological functions.

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

Currently, there are conflicting data in literature regarding contribution of bone marrow stromal cells (BMSCs) to bone formation when the cells are systemically delivered in recipient animals. To understand if BMSCs contribute to bone cell phenotype and bone formation in osteogenesis imperfecta bones (OI), MSCs marked with GFP were directly infused into the femurs of a mouse model of OI (oim). The contribution of the cells to the cell phenotype and bone formation was assessed by histology, immunohistochemistry and biomechanical loading of recipient bones. Two weeks following infusion of BMSCs, histological examination of the recipient femurs demonstrated presence of new bone when compared to femurs injected with saline which showed little or no bone formation. The new bone contained few donor cells as demonstrated by GFP fluorescence. At 6 weeks following cell injection, new bone was still detectable in the recipient femurs but was enhanced by injection of the cells suspended in pepsin solubilized type I collagen. Immunofluorescence and immunohistochemical staining showed that donor GFP positive cells in the new bone were localized with osteocalcin expressing cells suggesting that the cells differentiated into osteoblasts in vivo. Biomechanical loading to failure in three point bending, revealed that, femurs infused with BMSCs in PBS or in soluble type I collagen were biomechanically stronger than those injected with PBS or type I collagen alone. Taken together, the results indicate that transplanted cells differentiated into osteoblasts in vivo and contributed to bone formation in vivo; we also speculate that donor cells induced differentiation or recruitment of endogenous cells to initiate reparative process at early stages following transplantation.

Derivation of murine induced pluripotent stem cells (iPS) and assessment of their differentiation toward osteogenic lineage

Induced pluripotent stem cells (iPSCs) have generated hope and excitement because of the potential they possess for generating patient-specific embryonic-like stem cells (ESCs). Although many hurdles remain to be solved before the cells can be applied clinically; studies directed toward understanding factors that control differentiation of the cells toward various cell lineages are prerequisites for their future application. In the present study, we generated murine iPSC and assessed their differentiation toward osteogenic lineage. Murine tail tip fibroblasts were reprogrammed into embryonic-like state by transduction with defined factors (Oct3/4, Sox2, c-Myc, and klf4) carried in a retroviral vector. The reprogrammed cells expressed ESC markers, gave rise to three germ layers as demonstrated by teratoma formation and immunofluorescence staining. These data confirmed that the reprogrammed cells exhibited ESC-like state. Treatment of iPSCs-derived embryoid bodies (EBs) with transforming growth factor beta 1 (TGF-beta1) in the presence of retinoic acid enhanced generation of MSC-like cells. The MSCs-like cells expressed putative makers associated with MSCs; the cells deposited calcium in vitro when cultured in osteogenic medium. Interestingly MSCs-like cells generated from iPSC directed EBs by treatment with retinoic acid and TGF-beta1 deposited more calcium in vitro than cells derived without TGF-beta1 treatment. Taken together, the data demonstrate that iPSC give rise to MSCs-like state and that the cells have potential to differentiate toward osteoblasts. In addition, brief treatment of iPSC-derived EBs with TGF-beta1 may be an approach for directing iPSC toward MSC-like state.