Total body irradiation is permissive for mesenchymal stem cell-mediated new bone formation following local transplantation

Effects of acute- and long-term aerobic exercises at different intensities on bone in mice

INTRODUCTION

Exercise intensity determines the benefits of aerobic exercise. Our objectives were, in aerobic exercise at different intensities, to determine (1) changes in bone metabolism-related genes after acute exercise and (2) changes in bone mass, strength, remodeling, and bone formation-related proteins after long-term exercise.

MATERIALS AND METHODS

Total 36 male C57BL/6J mice were divided into a control group and exercise groups at 3 different intensities: low, moderate, or high group. Each exercise group was assigned to acute- or long-term exercise groups. Tibias after acute exercise were evaluated by real-time PCR analysis. Furthermore, hindlimbs of long-term exercise were assessed by micro-CT, biomechanical, histological, and immunohistochemical analyses.

RESULTS

Acute moderate-intensity exercise decreased RANKL level as bone resorption marker, whereas low- and high-intensity exercise did not alter it. Additionally, only long-term exercise at moderate intensity increased bone mass and strength. Moderate-intensity exercise promoted osteoblast activity and suppressed osteoclast activity. After low- and high-intensity exercise, osteoblast and osteoclast activity were unchanged. An increase in the number of β-catenin-positive cells and a decrease in sclerostin-positive cells were observed in the only moderate group.

CONCLUSION

These results showed that moderate-intensity exercise can inhibit bone resorption earlier, and long-term exercise can increase bone mass and strength through promoted bone formation via the Wnt/β-catenin activation. High-intensity exercise, traditionally considered better for bone, may fail to stimulate bone remodeling, leading to no change in bone mass and strength. Our findings suggest that moderate-intensity exercise, neither too low nor high, can maintain bone health.

Review of Osteoradionecrosis of the Jaw: Radiotherapy Modality, Technique, and Dose as Risk Factors

Radiotherapy (RT) or concurrent chemoradiotherapy (CCRT) is the cornerstone of organ-sparing or adjuvant therapy for nearly all head and neck cancers. Unfortunately, aggressive RT or CCRT can result in severe late toxicities, such as osteoradionecrosis of the jaws (ORNJ). The incidence of ORNJ is currently less than 5-6% due to advances in dental preventive care programs, RT planning systems, and RT techniques. Although numerous patient-, tumor-, and treatment-related factors may influence the incidence rates of ORNJ, RT modality (equipment), technique, and dose-volume-related factors are three of the most influential factors. This is mainly because different RT equipment and techniques have different levels of success at delivering the prescribed dose to the focal volume of the treatment while keeping the "organ at risk" safe. ORNJ risk is ultimately determined by mandibular dose, despite the RT technique and method being known predictors. Regardless of the photon delivery method, the radiobiological effects will be identical if the total dose, dose per fraction, and dose distribution within the tissue remain constant. Therefore, contemporary RT procedures mitigate this risk by reducing mandibular dosages rather than altering the ionizing radiation behavior in irradiated tissues. In light of the paucity of studies that have examined the impact of RT modality, technique, and dose-volume-related parameters, as well as their radiobiological bases, the present review aims to provide a comprehensive overview of the published literature on these specific issues to establish a common language among related disciplines and provide a more reliable comparison of research results.

Direct ionizing radiation and bystander effect in mouse mesenchymal stem cells

Purpose: This study aimed to evaluate the radiation-induced direct and bystander (BYS) responses of mesenchymal stem cells (MSCs) and to characterize these cells radiobiologically.Methods and materials: MSCs were irradiated (IR) and parameters related to DNA damage and cellular signaling were verified in a dose range from 0.5 to 15 Gy; also a transwell insert co-culture system was used to study medium-mediated BYS effects.Results: The main effects on directly IR cells were seen at doses higher than 6 Gy: induction of cell death, cell cycle arrest, upregulation of p21, and alteration of redox status. Irrespective of a specific dose, induction of micronuclei formation, H2AX phosphorylation, and decreased Akt expression also occurred. Thus, mTOR expression, cell senescence, nitric oxide generation, and calcium levels, in general were not significantly modulated by radiation. Data from the linear-quadratic model showed a high alpha/beta ratio, which is consistent with a more exponential survival curve. BYS effects from the unirradiated MSCs placed into companion wells with the directly IR cells, were not observed.Conclusions: The results can be interpreted as a positive outcome, meaning that the radiation damage is restricted to the directed IR MSCs not leading to off-target cell responses.

Expression of long noncoding RNA Xist is induced by glucocorticoids

Glucocorticoids (GCs) are potent anti-inflammatory and immunosuppressive agents. However, their clinical usage is limited by severe multisystemic side effects. Glucocorticoid induced osteoporosis results in significant morbidity and mortality but the cellular and molecular mechanisms underlying GC-induced bone loss are not clear. GC use results in decreased osteoblast differentiation with increased marrow adiposity through effects on bone marrow stem cells. GC effects are transduced through its receptor (GR). To identify novel GR regulated genes, we performed RNA sequencing (RNA-Seq) analysis comparing conditional GR knockout mouse made by crossing the floxed GR animal with the Col I promoter-Cre, versus normal floxed GR without Cre, and that testing was specific for Col I promoter active cells, such as bone marrow mesenchymal stem/osteoprogenitor cells (MSCs) and osteoblasts. Results showed 15 upregulated genes (3- to 10-fold) and 70 downregulated genes (-2.7- to -10-fold), with the long noncoding RNA X-inactive specific transcript (Xist) downregulated the most. The differential expression of genes measured by RNA-Seq was validated by qRT-PCR analysis of selected genes and the GC/GR signaling-dependent expression of Xist was further demonstrated by GC (dexamethasone) treatment of GR-deficient MSCs in vitro and by GC injection of C57BL/6 mice (wild-type males and females) in vivo. Our data revealed that the long noncoding RNA Xist is a GR regulated gene and its expression is induced by GC both in vitro and in vivo. To our knowledge, this is the first evidence showing that Xist is transcriptionally regulated by GC/GR signaling.

Sclerostin antibody increases trabecular bone and bone mechanical properties by increasing osteoblast activity damaged by whole-body irradiation in mice

Irradiation therapy causes bone deterioration and increased risk for skeletal-related events. Irradiation interferes with trabecular architecture through increased osteoclastic activity, decreased osteoblastic activity, and increased adipocyte expansion in the bone marrow (BM), which further compounds bone-related disease. Neutralizing antibodies to sclerostin (Scl-Ab) increase bone mass and strength by increasing bone formation and reducing bone resorption. We hypothesized that treatment with Scl-Ab would attenuate the adverse effects of irradiation by increasing bone volume and decreasing BM adipose tissue (BMAT), resulting in better quality bone. In this study, 12-week-old female C57BL/6J mice were exposed to 6 Gy whole-body irradiation or were non-irradiated, then administered Scl-Ab (25 mg/kg) or vehicle weekly for 5 weeks. Femoral μCT analysis confirmed that the overall effect of IR significantly decreased trabecular bone volume/total volume (Tb.BV/TV) (2-way ANOVA, p < 0.0001) with a -43.8% loss in Tb.BV/TV in the IR control group. Scl-Ab independently increased Tb.BV/TV by 3.07-fold in non-irradiated and 3.6-fold in irradiated mice (2-way ANOVA, p < 0.0001). Irradiation did not affect cortical parameters, although Scl-Ab increased cortical thickness and area significantly in both irradiated and non-irradiated mice (2-way ANOVA, p < 0.0001). Femoral mechanical testing confirmed Scl-Ab significantly increased bending rigidity and ultimate moment independently of irradiation (2-way ANOVA, p < 0.0001). Static and dynamic histomorphometry of the femoral metaphysis revealed osteoblast vigor, not number, was significantly increased in the irradiated mice treated with Scl-Ab. Systemic alterations were assessed through serum lipidomic analysis, which showed that Scl-Ab normalized lipid profiles in the irradiated group. This data supports the theory of sclerostin as a novel contributor to the regulation of osteoblast activity after irradiation. Overall, our data support the hypothesis that Scl-Ab ameliorates the deleterious effects of whole-body irradiation on bone and adipose tissue in a mouse model. Our findings suggest that future research into localized and systemic therapies after irradiation exposure is warranted.

CircRNA-016901 silencing attenuates irradiation-induced injury in bone mesenchymal stem cells via regulating the miR-1249-5p/HIPK2 axis

Currently, bone marrow transplantation remains the basic treatment for various hematological tumors and irradiation is one of the most important pretreatment methods. However, irradiation pretreatment may result in damage to bone mesenchymal stem cells (BMSCs). The present study aimed to investigate the effect of circular RNA-016901 (circ-016901) on the injury of irradiation-induced BMSCs and the underlying mechanism. The expression levels of circ-016901, microRNA-1249-5p (miR-1249-5p) and homeodomain interacting protein kinase 2 (HIPK2) in irradiation-induced mouse BMSCs at various irradiation doses were detected via reverse transcription-quantitative PCR (RT-qPCR). The effect of circ-016901 on cell proliferation was examined using Cell Counting Kit-8 assays following silencing or overexpression of circ-016901. Cell apoptosis was detected by flow cytometry and caspase-3/7 activity. The expression of autophagy-related markers, including Beclin-1 and LC3-II/I, was detected at the mRNA and protein levels by RT-qPCR and western blotting, respectively. Irradiation treatment upregulated the expression of circ-016901 and HIPK2 and downregulated miR-1249-5p expression. The expression levels of LC3-II/I and Beclin-1 in BMSCs were downregulated in a dose-dependent manner. Silencing of circ-016901 promoted proliferation of irradiation-induced BMSCs and attenuated irradiation-induced apoptosis. Moreover, silencing of circ-016901 elevated the expressions of LC3-II/I and Beclin-1 in irradiation-induced BMSCs. Similar results were obtained with miR-1249-5p overexpression and HIPK2 silencing. These results demonstrated that circ-016901 silencing attenuated injury in irradiation-induced mouse BMSCs by regulating the miR-1249-5p/HIPK2 axis, providing a novel target for future research on the mechanism of radiation resistance in BMSCs.

Scaffold-free human mesenchymal stem cell construct geometry regulates long bone regeneration

Biomimetic bone tissue engineering strategies partially recapitulate development. We recently showed functional restoration of femoral defects using scaffold-free human mesenchymal stem cell (hMSC) condensates featuring localized morphogen presentation with delayed in vivo mechanical loading. Possible effects of construct geometry on healing outcome remain unclear. Here, we hypothesized that localized presentation of transforming growth factor (TGF)-β1 and bone morphogenetic protein (BMP)-2 to engineered hMSC tubes mimicking femoral diaphyses induces endochondral ossification, and that TGF-β1 + BMP-2-presenting hMSC tubes enhance defect healing with delayed in vivo loading vs. loosely packed hMSC sheets. Localized morphogen presentation stimulated chondrogenic priming/endochondral differentiation in vitro. Subcutaneously, hMSC tubes formed cartilage templates that underwent bony remodeling. Orthotopically, hMSC tubes stimulated more robust endochondral defect healing vs. hMSC sheets. Tissue resembling normal growth plate was observed with negligible ectopic bone. This study demonstrates interactions between hMSC condensation geometry, morphogen bioavailability, and mechanical cues to recapitulate development for biomimetic bone tissue engineering.

Herberg et al. previously showed functional healing of femoral defects using scaffold-free human mesenchymal stem cell (hMSC) condensates with localized morphogen presentation. In this study, they report the importance of the tubular geometry of MSC condensates in long bone regeneration. Unlike loosely packed hMSC sheets, only hMSC tubes induced regenerate tissue partially resembling normal growth plate.

Modulation of p75NTR on Mesenchymal Stem Cells Increases Their Vascular Protection in Retinal Ischemia-Reperfusion Mouse Model

Mesenchymal stem cells (MSCs) are a promising therapy to improve vascular repair, yet their role in ischemic retinopathy is not fully understood. The aim of this study is to investigate the impact of modulating the neurotrophin receptor; p75NTR on the vascular protection of MSCs in an acute model of retinal ischemia/reperfusion (I/R). Wild type (WT) and p75NTR-/- mice were subjected to I/R injury by increasing intra-ocular pressure to 120 mmHg for 45 min, followed by perfusion. Murine GFP-labeled MSCs (100,000 cells/eye) were injected intravitreally 2 days post-I/R and vascular homing was assessed 1 week later. Acellular capillaries were counted using trypsin digest 10-days post-I/R. In vitro, MSC-p75NTR was modulated either genetically using siRNA or pharmacologically using the p75NTR modulator; LM11A-31, and conditioned media were co-cultured with human retinal endothelial cells (HREs) to examine the angiogenic response. Finally, visual function in mice undergoing retinal I/R and receiving LM11A-31 was assessed by visual-clue water-maze test. I/R significantly increased the number of acellular capillaries (3.2-Fold) in WT retinas, which was partially ameliorated in p75NTR-/- retinas. GFP-MSCs were successfully incorporated and engrafted into retinal vasculature 1 week post injection and normalized the number of acellular capillaries in p75NTR-/- retinas, yet ischemic WT retinas maintained a 2-Fold increase. Silencing p75NTR on GFP-MSCs coincided with a higher number of cells homing to the ischemic WT retinal vasculature and normalized the number of acellular capillaries when compared to ischemic WT retinas receiving scrambled-GFP-MSCs. In vitro, silencing p75NTR-MSCs enhanced their secretome, as evidenced by significant increases in SDF-1, VEGF and NGF release in MSCs conditioned medium; improved paracrine angiogenic response in HREs, where HREs showed enhanced migration (1.4-Fold) and tube formation (2-Fold) compared to controls. In parallel, modulating MSCs-p75NTR using LM11A-31 resulted in a similar improvement in MSCs secretome and the enhanced paracrine angiogenic potential of HREs. Further, intervention with LM11A-31 significantly mitigated the decline in visual acuity post retinal I/R injury. In conclusion, p75NTR modulation can potentiate the therapeutic potential of MSCs to harness vascular repair in ischemic retinopathy diseases.

Age-related increase of kynurenine enhances miR29b-1-5p to decrease both CXCL12 signaling and the epigenetic enzyme Hdac3 in bone marrow stromal cells

Mechanisms leading to age-related reductions in bone formation and subsequent osteoporosis are still incompletely understood. We recently demonstrated that kynurenine (KYN), a tryptophan metabolite, accumulates in serum of aged mice and induces bone loss. Here, we report on novel mechanisms underlying KYN's detrimental effect on bone aging. We show that KYN is increased with aging in murine bone marrow mesenchymal stem cells (BMSCs). KYN reduces bone formation via modulating levels of CXCL12 and its receptors as well as histone deacetylase 3 (Hdac3). BMSCs responded to KYN by significantly decreasing mRNA expression levels of CXCL12 and its cognate receptors, CXCR4 and ACKR3, as well as downregulating osteogenic gene RUNX2 expression, resulting in a significant inhibition in BMSCs osteogenic differentiation. KYN's effects on these targets occur by increasing regulatory miRNAs that target osteogenesis, specifically miR29b-1-5p. Thus, KYN significantly upregulated the anti-osteogenic miRNA miR29b-1-5p in BMSCs, mimicking the up-regulation of miR-29b-1-5p in human and murine BMSCs with age. Direct inhibition of miR29b-1-5p by antagomirs rescued CXCL12 protein levels downregulated by KYN, while a miR29b-1-5p mimic further decreased CXCL12 levels. KYN also significantly downregulated mRNA levels of Hdac3, a target of miR-29b-1-5p, as well as its cofactor NCoR1. KYN is a ligand for the aryl hydrocarbon receptor (AhR). We hypothesized that AhR mediates KYN's effects in BMSCs. Indeed, AhR inhibitors (CH-223191 and 3',4'-dimethoxyflavone [DMF]) partially rescued secreted CXCL12 protein levels in BMSCs treated with KYN. Importantly, we found that treatment with CXCL12, or transfection with an miR29b-1-5p antagomir, downregulated the AhR mRNA level, while transfection with miR29b-1-5p mimic significantly upregulated its level. Further, CXCL12 treatment downregulated IDO, an enzyme responsible for generating KYN. Our findings reveal novel molecular pathways involved in KYN's age-associated effects in the bone microenvironment that may be useful translational targets for treating osteoporosis.

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.

Therapeutic Irradiation: Consequences for Bone and Bone Marrow Adipose Tissue

Radiotherapy continues to be one of the most accepted medical treatments for cancer. Localized irradiation is the most common treatment for prostate, pancreatic, rectal, cervical and endometrial malignancies. Conventional localized fractions are total doses of 30-62Gy at 1.8-2Gy per fraction, with administration of ~60Gy often used for tumor ablation. However, even the lowest dose of localized irradiation exposure can result in adverse complications to adjacent organs, tissues, and vessels, which absorb a portion of the treatment. Skeletal complications are common amongst cancer patients undergoing these localized treatments. Irradiation exposure causes deterioration to the overall quantity and quality of bone by interfering with the trabecular architecture through increased osteoclast activity and decreased osteoblast activity. Irradiation-induced bone damage parallels adipocyte infiltration of the bone marrow (BM) resulting in compositional alterations of the microenvironment that may further affect bone quality and disease state. There may also be direct effects of irradiation on the BM adipocyte/pre-adipocyte, although in vitro findings do not always agree and cellular response is dependent on irradiation dosage. Hematopoietic cells also become apoptotic upon irradiation, which causes a range of skeletal effects. Bone loss leaves patients at a greater risk for osteopenia, osteoporosis, osteonecrosis, and skeletal fractures that drastically reduce quality of life. Osteoanabolic agents stimulate bone formation and reduce fracture risk in patients with low bone density; thus, osteoanabolic or anti-resorptive agents may be useful co-treatments with irradiation. This review discusses these topics and proposes further research directions using novel or combination therapies to enhance bone health during irradiation.

Whole-Body Vibration Mimics the Metabolic Effects of Exercise in Male Leptin Receptor-Deficient Mice

Whole-body vibration (WBV) has gained attention as a potential exercise mimetic, but direct comparisons with the metabolic effects of exercise are scarce. To determine whether WBV recapitulates the metabolic and osteogenic effects of physical activity, we exposed male wild-type (WT) and leptin receptor-deficient (db/db) mice to daily treadmill exercise (TE) or WBV for 3 months. Body weights were analyzed and compared with WT and db/db mice that remained sedentary. Glucose and insulin tolerance testing revealed comparable attenuation of hyperglycemia and insulin resistance in db/db mice following TE or WBV. Both interventions reduced body weight in db/db mice and normalized muscle fiber diameter. TE or WBV also attenuated adipocyte hypertrophy in visceral adipose tissue and reduced hepatic lipid content in db/db mice. Although the effects of leptin receptor deficiency on cortical bone structure were not eliminated by either intervention, exercise and WBV increased circulating levels of osteocalcin in db/db mice. In the context of increased serum osteocalcin, the modest effects of TE and WBV on bone geometry, mineralization, and biomechanics may reflect subtle increases in osteoblast activity in multiple areas of the skeleton. Taken together, these observations indicate that WBV recapitulates the effects of exercise on metabolism in type 2 diabetes.

Tracking and Quantification of Magnetically Labeled Stem Cells using Magnetic Resonance Imaging

Stem cell based therapies have critical impacts on treatments and cures of diseases such as neurodegenerative or cardiovascular disease. In vivo tracking of stem cells labeled with magnetic contrast agents is of particular interest and importance as it allows for monitoring of the cells' bio-distribution, viability, and physiological responses. Herein, recent advances are introduced in tracking and quantification of super-paramagnetic iron oxide (SPIO) nanoparticles-labeled cells with magnetic resonance imaging, a noninvasive approach that can longitudinally monitor transplanted cells. This is followed by recent translational research on human stem cells that are dual-labeled with green fluorescence protein (GFP) and SPIO nanoparticles, then transplanted and tracked in a chicken embryo model. Cell labeling efficiency, viability, and cell differentiation are also presented.

Mesenchymal stem cell expression of SDF-1β synergizes with BMP-2 to augment cell-mediated healing of critical-sized mouse calvarial defects

Bone has the potential for spontaneous healing. This process, however, often fails in patients with comorbidities. Tissue engineering combining functional cells, biomaterials and osteoinductive cues may provide alternative treatment strategies. We have recently demonstrated that stromal cell-derived factor-1β (SDF-1β) works in concert with bone morphogenetic protein-2 (BMP-2) to potentiate osteogenic differentiation of bone marrow-derived mesenchymal stem/stromal cells (BMSCs). Here, we test the hypothesis that SDF-1β overexpressed in Tet-Off-SDF-1β BMSCs, delivered on acellular dermal matrix (ADM), synergistically augments BMP-2-induced healing of critical-sized mouse calvarial defects. BMSC therapies alone showed limited bone healing, which was increased with co-delivery of BMP-2. This was further enhanced in Tet-Off-SDF-1β BMSCs + BMP-2. Only limited BMSC retention on ADM constructs was observed after 4 weeks in vivo, which was increased with BMP-2 co-delivery. In vitro cell proliferation studies showed that supplementing BMP-2 to Tet-Off BMSCs significantly increased the cell number during the first 24 h. Consequently, the increased cell numbers decreased the detectable BMP-2 levels in the medium, but increased cell-associated BMP-2. The data suggest that SDF-1β provides synergistic effects supporting BMP-2-induced, BMSC-mediated bone formation and appears suitable for optimization of bone augmentation in combination therapy protocols. Copyright © 2015 John Wiley & Sons, Ltd.

Caloric restriction and the adipokine leptin alter the SDF-1 signaling axis in bone marrow and in bone marrow derived mesenchymal stem cells

Growing evidence suggests that the chemokine stromal cell-derived factor-1 (SDF-1) is essential in regulating bone marrow (BM) derived mesenchymal stromal/stem cell (BMSC) survival, and differentiation to either a pro-osteogenic or pro-adipogenic fate. This study investigates the effects of caloric restriction (CR) and leptin on the SDF-1/CXCR4 axis in bone and BM tissues in the context of age-associated bone loss. For in vivo studies, we collected bone, BM cells and BM interstitial fluid from 12 and 20 month-old C57Bl6 mice fed ad-libitum (AL), and 20-month-old mice on long-term CR with, or without, intraperitoneal injection of leptin for 10 days (10 mg/kg). To mimic conditions of CR in vitro, 18 month murine BMSCs were treated with (1) control (Ctrl): normal proliferation medium, (2) nutrient restriction (NR): low glucose, low serum medium, or (3) NR + leptin: NR medium + 100 ng/ml leptin for 6-48 h. In BMSCs both protein and mRNA expression of SDF-1 and CXCR4 were increased by CR and CR + leptin. In contrast, the alternate SDF-1 receptor CXCR7 was decreased, suggesting a nutrient signaling mediated change in SDF-1 axis signaling in BMSCs. However, in bone SDF-1, CXCR4 and 7 gene expression increase with age and this is reversed with CR, while addition of leptin returns this to the "aged" level. Histologically bone formation was lower in the calorically restricted mice and BM adipogenesis increased, both effects were reversed with the 10 day leptin treatment. This suggests that in bone CR and leptin alter the nutrient signaling pathways in different ways to affect the local action of the osteogenic cytokine SDF-1. Studies focusing on the molecular interaction between nutrient signaling by CR, leptin and SDF-1 axis may help to address age-related musculoskeletal changes.

Mesenchymal stem cell expression of stromal cell-derived factor-1β augments bone formation in a model of local regenerative therapy

Bone has the potential for spontaneous healing. However, this process often fails in patients with co-morbidities requiring clinical intervention. Numerous studies have revealed that bone marrow-derived mesenchymal stem/stromal cells (BMSCs) hold great potential for regenerative therapies. Common problems include poor cell engraftment, which can be addressed by irradiation prior to transplantation. Increasing evidence suggests that stromal cell-derived factor-1 (SDF-1) is involved in bone formation. However, osteogenic contributions of the beta splice variant of SDF-1 (SDF-1β), which is highly expressed in bone, remain unclear. Using the tetracycline (Tet)-regulatory system we have shown that SDF-1β enhances BMSC osteogenic differentiation in vitro. Here we test the hypothesis that SDF-1β augments bone formation in vivo in a model of local BMSC transplantation following irradiation. We found that SDF-1β, expressed at high levels in Tet-Off-SDF-1β BMSCs, augments the cell-mediated therapeutic effects resulting in enhanced bone formation, as evidenced by ex vivo μCT and bone histomorphometry. The data demonstrate the specific contribution of SDF-1β to BMSC-mediated bone formation, and validate the feasibility of the Tet-Off technology to regulate SDF-1β expression in vivo. In conclusion, SDF-1β provides potent synergistic effects supporting BMSC-mediated bone formation and appears a suitable candidate for optimization of bone augmentation in translational protocols.