PTH Induces Systemically Administered Mesenchymal Stem Cells to Migrate to and Regenerate Spine Injuries. Mol Ther. 2016;24:318-330. [PMID: 26585691 DOI: 10.1038/mt.2015.211]

The Application of Mesenchymal Stem Cells in Future Vaccine Synthesis

Vaccines have significant potential in treating and/or preventing diseases, yet there remain challenges in developing effective vaccines against some diseases, such as AIDS and certain tumors. Mesenchymal stem cells (MSCs), a subset of cells with low immunogenicity, high proliferation potential, and an abundant source of extracellular vesicles (EVs), represent one of the novel and promising vaccine platforms. This review describes the unique features and potential mechanisms of MSCs as a novel vaccine platform. We also cover aspects such as the safety and stability of MSCs that warrant future in-depth studies.

Parathyroid hormone enhances the therapeutic effect of mesenchymal stem cells on temporomandibular joint osteoarthritis in rats

OBJECTIVES

Temporomandibular joint osteoarthritis (TMJOA) is a degenerative disease affecting the joint, which is characterized by injury to the articular cartilage, as well as changes in the synovial and subchondral bone. TMJOA has a high incidence rate, without any effective treatment. Despite the therapeutic potential of mesenchymal stem cells (MSCs) in various diseases, their efficacy in treating TMJOA is constrained by the local hypoxic conditions and elevated reactive oxygen species (ROS) environment within the damaged temporomandibular joint. In recent years, many studies have reported that parathyroid hormone (PTH) can effectively treat TMJOA, and has an important impact on MSC differentiation. Therefore, we hypothesized that PTH may influence the potential of MSCs, thereby improving their therapeutic effect on TMJOA.

METHODS

First, we isolated and cultured rat bone marrow MSCs, and evaluated their proliferation and differentiation after adding PTH. Next, the in vitro environment of hypoxia and high ROS was established by hypoxia condition and H2O2 treatment, and the resistance of PTH-treated MSCs to hypoxia and ROS was subsequently investigated. Finally, PTH-treated MSCs were used to treat TMJOA in a rat model to evaluate the efficacy of PTH.

RESULTS

PTH enhanced the proliferation ability of MSCs, promoted the osteogenic differentiation of MSCs, and improved the tolerance of MSCs to hypoxia and ROS. Finally, the therapeutic effect of PTH-treated MSCs on TMJOA was significantly improved.

CONCLUSION

PTH enhances the therapeutic effect of MSCs on TMJOA in rats.

iPSC-neural crest derived cells embedded in 3D printable bio-ink promote cranial bone defect repair

Cranial bone loss presents a major clinical challenge and new regenerative approaches to address craniofacial reconstruction are in great demand. Induced pluripotent stem cell (iPSC) differentiation is a powerful tool to generate mesenchymal stromal cells (MSCs). Prior research demonstrated the potential of bone marrow-derived MSCs (BM-MSCs) and iPSC-derived mesenchymal progenitor cells via the neural crest (NCC-MPCs) or mesodermal lineages (iMSCs) to be promising cell source for bone regeneration. Overexpression of human recombinant bone morphogenetic protein (BMP)6 efficiently stimulates bone formation. The study aimed to evaluate the potential of iPSC-derived cells via neural crest or mesoderm overexpressing BMP6 and embedded in 3D printable bio-ink to generate viable bone graft alternatives for cranial reconstruction. Cell viability, osteogenic potential of cells, and bio-ink (Ink-Bone or GelXa) combinations were investigated in vitro using bioluminescent imaging. The osteogenic potential of bio-ink-cell constructs were evaluated in osteogenic media or nucleofected with BMP6 using qRT-PCR and in vitro μCT. For in vivo testing, two 2 mm circular defects were created in the frontal and parietal bones of NOD/SCID mice and treated with Ink-Bone, Ink-Bone + BM-MSC-BMP6, Ink-Bone + iMSC-BMP6, Ink-Bone + iNCC-MPC-BMP6, or left untreated. For follow-up, µCT was performed at weeks 0, 4, and 8 weeks. At the time of sacrifice (week 8), histological and immunofluorescent analyses were performed. Both bio-inks supported cell survival and promoted osteogenic differentiation of iNCC-MPCs and BM-MSCs in vitro. At 4 weeks, cell viability of both BM-MSCs and iNCC-MPCs were increased in Ink-Bone compared to GelXA. The combination of Ink-Bone with iNCC-MPC-BMP6 resulted in an increased bone volume in the frontal bone compared to the other groups at 4 weeks post-surgery. At 8 weeks, both iNCC-MPC-BMP6 and iMSC-MSC-BMP6 resulted in an increased bone volume and partial bone bridging between the implant and host bone compared to the other groups. The results of this study show the potential of NCC-MPC-incorporated bio-ink to regenerate frontal cranial defects. Therefore, this bio-ink-cell combination should be further investigated for its therapeutic potential in large animal models with larger cranial defects, allowing for 3D printing of the cell-incorporated material.

Parathyroid Hormone 1 Receptor Signaling in Dental Mesenchymal Stem Cells: Basic and Clinical Implications

Parathyroid hormone (PTH) and parathyroid hormone-related protein (PTHrP) are two peptides that regulate mineral ion homeostasis, skeletal development, and bone turnover by activating parathyroid hormone 1 receptor (PTH1R). PTH1R signaling is of profound clinical interest for its potential to stimulate bone formation and regeneration. Recent pre-clinical animal studies and clinical trials have investigated the effects of PTH and PTHrP analogs in the orofacial region. Dental mesenchymal stem cells (MSCs) are targets of PTH1R signaling and have long been known as major factors in tissue repair and regeneration. Previous studies have begun to reveal important roles for PTH1R signaling in modulating the proliferation and differentiation of MSCs in the orofacial region. A better understanding of the molecular networks and underlying mechanisms for modulating MSCs in dental diseases will pave the way for the therapeutic applications of PTH and PTHrP in the future. Here we review recent studies involving dental MSCs, focusing on relationships with PTH1R. We also summarize recent basic and clinical observations of PTH and PTHrP treatment to help understand their use in MSCs-based dental and bone regeneration.

The role of intermittent PTH administration in conjunction with allogenic stem cell treatment to stimulate fracture healing

Aims

A growing number of fractures progress to delayed or nonunion, causing significant morbidity and socioeconomic impact. Localized delivery of stem cells and subcutaneous parathyroid hormone (PTH) has been shown individually to accelerate bony regeneration. This study aimed to combine the therapies with the aim of upregulating fracture healing.

Methods

A 1.5 mm femoral osteotomy (delayed union model) was created in 48 female juvenile Wistar rats, aged six to nine months, and stabilized using an external fixator. At day 0, animals were treated with intrafracture injections of 1 × 10⁶ cells/kg bone marrow mesenchymal stem cells (MSCs) suspended in fibrin, daily subcutaneous injections of high (100 μg/kg) or low (25 μg/kg) dose PTH 1-34, or a combination of PTH and MSCs. A group with an empty gap served as a control. Five weeks post-surgery, the femur was excised for radiological, histomorphometric, micro-CT, and mechanical analysis.

Results

Combination therapy treatment led to increased callus formation compared to controls. In the high-dose combination group there was significantly greater mineralized tissue volume and trabecular parameters compared to controls (p = 0.039). This translated to significantly improved stiffness (and ultimate load to failure (p = 0.049). The high-dose combination therapy group had the most significant improvement in mean modified Radiographic Union Score for Tibia fractures (RUST) compared to controls (13.8 (SD 1.3) vs 5.8 (SD 0.5)). All groups demonstrated significant increases in the radiological scores – RUST and Allen score – histologically compared to controls.

Conclusion

We demonstrate the beneficial effect of localized MSC injections on fracture healing combined with low- or high-dose teriparatide, with efficacy dependent on PTH dose.

Cite this article: Bone Joint Res 2021;10(10):659–667.

Parathyroid hormone and its related peptides in bone metabolism

Parathyroid hormone (PTH) is an 84-amino-acid peptide hormone that is secreted by the parathyroid gland. It has different administration modes in bone tissue through which it promotes bone formation (intermittent administration) and bone resorption (continuous administration) and has great potential for application in sbone defect repair. PTH regulates bone metabolism by binding to PTH1R. PTH plays an osteogenic role by acting directly on mesenchymal stem cells, cells with an osteoblastic lineage, osteocytes, and T cells. It also participates as an osteoclast by indirectly acting on osteoclast precursor cells and osteoclasts and directly acting on T cells. In these cells, PTH activates the Wnt signaling, cAMP/PKA, cAMP/PKC, and RANKL/RANK/OPG pathways and other signaling pathways. Although PTH(1-34), also known as teriparatide, has been used clinically, it still has some disadvantages. Developing improved PTH-related peptides is a potential solution to teriparatide's shortcomings. The action mechanism of these PTH-related peptides is not exactly the same as that of PTH. Thus, the mechanisms of PTH and PTH-related peptides in bone metabolism were reviewed in this paper.

Safety and efficacy of Wharton's jelly-derived mesenchymal stem cells with teriparatide for osteoporotic vertebral fractures: A phase I/IIa study

Osteoporotic vertebral compression fractures (OVCFs) are serious health problems. We conducted a randomized, open-label, phase I/IIa study to determine the feasibility, safety, and effectiveness of Wharton's jelly-derived mesenchymal stem cells (WJ-MSCs) and teriparatide (parathyroid hormone 1-34) in OVCFs. Twenty subjects with recent OVCFs were randomized to teriparatide (20 μg/day, daily subcutaneous injection for 6 months) treatment alone or combined treatment of WJ-MSCs (intramedullary [4 × 107 cells] injection and intravenous [2 × 108 cells] injection after 1 week) and teriparatide (20 μg/day, daily subcutaneous injection for 6 months). Fourteen subjects (teriparatide alone, n = 7; combined treatment, n = 7) completed follow-up assessment (visual analog scale [VAS], Oswestry Disability Index [ODI], Short Form-36 [SF-36], bone mineral density [BMD], bone turnover measured by osteocalcin and C-terminal telopeptide of type 1 collagen, dual-energy x-ray absorptiometry [DXA], computed tomography [CT]). Our results show that (a) combined treatment with WJ-MSCs and teriparatide is feasible and tolerable for the patients with OVCFs; (b) the mean VAS, ODI, and SF-36 scores significantly improved in the combined treatment group; (c) the level of bone turnover markers were not significantly different between the two groups; (d) BMD T-scores of spine and hip by DXA increased in both control and experimental groups without a statistical difference; and (e) baseline spine CT images and follow-up CT images at 6 and 12 months showed better microarchitecture in the combined treatment group. Our results indicate that combined treatment of WJ-MSCs and teriparatide is feasible and tolerable and has a clinical benefit for fracture healing by promoting bone architecture. Clinical trial registration: https://nedrug.mfds.go.kr/, MFDS: 201600282-30937.

Neural crest-derived mesenchymal progenitor cells enhance cranial allograft integration

Replacement of lost cranial bone (partly mesodermal and partly neural crest‐derived) is challenging and includes the use of nonviable allografts. To revitalize allografts, bone marrow‐derived mesenchymal stromal cells (mesoderm‐derived BM‐MSCs) have been used with limited success. We hypothesize that coating of allografts with induced neural crest cell‐mesenchymal progenitor cells (iNCC‐MPCs) improves implant‐to‐bone integration in mouse cranial defects. Human induced pluripotent stem cells were reprogramed from dermal fibroblasts, differentiated to iNCCs and then to iNCC‐MPCs. BM‐MSCs were used as reference. Cells were labeled with luciferase (Luc2) and characterized for MSC consensus markers expression, differentiation, and risk of cellular transformation. A calvarial defect was created in non‐obese diabetic/severe combined immunodeficiency (NOD/SCID) mice and allografts were implanted, with or without cell coating. Bioluminescence imaging (BLI), microcomputed tomography (μCT), histology, immunofluorescence, and biomechanical tests were performed. Characterization of iNCC‐MPC‐Luc2 vs BM‐MSC‐Luc2 showed no difference in MSC markers expression and differentiation in vitro. In vivo, BLI indicated survival of both cell types for at least 8 weeks. At week 8, μCT analysis showed enhanced structural parameters in the iNCC‐MPC‐Luc2 group and increased bone volume in the BM‐MSC‐Luc2 group compared to controls. Histology demonstrated improved integration of iNCC‐MPC‐Luc2 allografts compared to BM‐MSC‐Luc2 group and controls. Human osteocalcin and collagen type 1 were detected at the allograft‐host interphase in cell‐seeded groups. The iNCC‐MPC‐Luc2 group also demonstrated improved biomechanical properties compared to BM‐MSC‐Luc2 implants and cell‐free controls. Our results show an improved integration of iNCC‐MPC‐Luc2‐coated allografts compared to BM‐MSC‐Luc2 and controls, suggesting the use of iNCC‐MPCs as potential cell source for cranial bone repair.

Assessing the Resident Progenitor Cell Population and the Vascularity of the Adult Human Meniscus

PURPOSE

To identify, characterize, and compare the resident progenitor cell populations within the red-red, red-white, and white-white (WW) zones of freshly harvested human cadaver menisci and to characterize the vascularity of human menisci using immunofluorescence and 3-dimensional (3D) imaging.

METHODS

Fresh adult human menisci were harvested from healthy donors. Menisci were enzymatically digested, mononuclear cells isolated, and characterized using flow cytometry with antibodies against mesenchymal stem cell surface markers (CD105, CD90, CD44, and CD29). Cells were expanded in culture, characterized, and compared with bone marrow-derived mesenchymal stem cells. Trilineage differentiation potential of cultured cells was determined. Vasculature of menisci was mapped in 3D using a modified uDisco clearing and immunofluorescence against vascular markers CD31, lectin, and alpha smooth muscle actin.

RESULTS

There were no significant differences in the clonogenicity of isolated cells between the 3 zones. Flow cytometry showed presence of CD44⁺CD105⁺CD29⁺CD90⁺ cells in all 3 zones with high prevalence in the WW zone. Progenitors from all zones were found to be potent to differentiate to mesenchymal lineages. Larger vessels in the red-red zone of meniscus were observed spanning toward red-white, sprouting to smaller arterioles and venules. CD31⁺ cells were identified in all zones using the 3D imaging and co-localization of additional markers of vasculature (lectin and alpha smooth muscle actin) was observed.

CONCLUSIONS

The presence of resident mesenchymal progenitors was evident in all 3 meniscal zones of healthy adult donors without injury. In addition, our results demonstrate the presence of vascularization in the WW zone.

CLINICAL RELEVANCE

The existence of progenitors and presence of microvasculature in the WW zone of the meniscus suggests the potential for repair and biologic augmentation strategies in that zone of the meniscus in young healthy adults. Further research is necessary to fully define the functionality of the meniscal blood supply and its implications for repair.

Clinical Application of Bone Marrow Mesenchymal Stem/Stromal Cells to Repair Skeletal Tissue

There has been an escalation in reports over the last decade examining the efficacy of bone marrow derived mesenchymal stem/stromal cells (BMSC) in bone tissue engineering and regenerative medicine-based applications. The multipotent differentiation potential, myelosupportive capacity, anti-inflammatory and immune-modulatory properties of BMSC underpins their versatile nature as therapeutic agents. This review addresses the current limitations and challenges of exogenous autologous and allogeneic BMSC based regenerative skeletal therapies in combination with bioactive molecules, cellular derivatives, genetic manipulation, biocompatible hydrogels, solid and composite scaffolds. The review highlights the current approaches and recent developments in utilizing endogenous BMSC activation or exogenous BMSC for the repair of long bone and vertebrae fractures due to osteoporosis or trauma. Current advances employing BMSC based therapies for bone regeneration of craniofacial defects is also discussed. Moreover, this review discusses the latest developments utilizing BMSC therapies in the preclinical and clinical settings, including the treatment of bone related diseases such as Osteogenesis Imperfecta.

PTH(1‑34) activates the migration and adhesion of BMSCs through the rictor/mTORC2 pathway

The ability of intermittent parathyroid hormone (1-34) [PTH(1-34)] treatment to enhance bone-implant osseo-integration was recently demonstrated in vivo. However, the mechanisms through which PTH (1-34) regulates bone marrow-derived stromal cells (BMSCs) remain unclear. The present study thus aimed to investigate the effects of PTH(1-34) on the migration and adhesion of, and rictor/mammalian target of rapamycin complex 2 (mTORC2) signaling in BMSCs. In the present study, BMSCs were isolated from Sprague-Dawley rats treated with various concentrations of PTH(1-34) for different periods of time. PTH(1-34) treatment was performed with or without an mTORC1 inhibitor (20 nM rapamycin) and mTORC1/2 inhibitor (10 µM PP242). Cell migration was assessed by Transwell cell migration assays and wound healing assays. Cell adhesion and related mRNA expression were investigated through adhesion assays and reverse transcription-quantitative polymerase chain reaction (RT-qPCR), respectively. The protein expression of chemokine receptors (CXCR4 and CCR2) and adhesion factors [intercellular adhesion molecule 1 (ICAM-1), fibronectin and integrin β1] was examined by western blot analysis. The results revealed that various concentrations (1, 10, 20, 50 and 100 nM) of PTH(1-34) significantly increased the migration and adhesion of BMSCs, as well as the expression of CXCR4, CCR2, ICAM-1, fibronectin and integrin β1. In addition, the p-Akt and p-S6 levels were also upregulated by PTH(1-34). BMSCs subjected to mTORC1/2 signaling pathway inhibition or rictor silencing exhibited a markedly reduced PTH-induced migration and adhesion, while no such effect was observed for the BMSCs subjected to mTORC1 pathway inhibition or raptor silencing. These results indicate that PTH(1-34) promotes BMSC migration and adhesion through rictor/mTORC2 signaling in vitro. Taken together, the results of the present study reveal an important mechanism for the therapeutic effects of PTH(1-34) on bone-implant osseointegration and suggest a potential treatment strategy based on the effect of PTH(1-34) on BMSCs.

Injectable Hydrogels as Three-Dimensional Network Reservoirs for Osteoporosis Treatment

Despite tremendous progresses made in the field of tissue engineering over the past several decades, it remains a significant challenge for the treatment of osteoporosis (OP) due to the lack of appropriate carriers to improve the bioavailability of therapeutic agents and the unavailability of artificial bone matrix with desired properties for the replacement of damaged bone regions. Encouragingly, the development of injectable hydrogels for the treatment of OP has attracted increasing attention in recent years because they can serve either as a reservoir for various therapeutic species or as a perfect filler for bone injuries with irregular shapes. However, the relationship between the complicated pathological mechanism of OP and the properties of diverse polymeric materials lacks elucidation, which clearly hampers the clinical application of injectable hydrogels for the efficient treatment of OP. To clarify this relationship, this article summarized both localized and systematic treatment of OP using an injectable hydrogel-based strategy. Specifically, the pathogenesis of OP and the limitations of current treatment approaches were first analyzed. We further focused on the use of hydrogels loaded with various therapeutic substances following a classification standard of the encapsulated cargoes for OP treatment with an emphasis on the application and precautions of each category. A concluding remark on existing challenges and future directions of this rapidly developing research area was finally made. Impact statement Effective osteoporosis (OP) treatment remains a significant challenge due substantially to the unavailability of appropriate drug carriers and artificial matrices with desired properties to promote bone repair and replace damaged regions. For this purpose, this review focused on the development of diverse injectable hydrogel systems for the delivery of various therapeutic agents, including drugs, stem cells, and nucleic acids, for effective increase in bone mass and favorable osteogenesis. The summarized important guidelines are believed to promote clinical development and translation of hydrogels for the efficient treatment of OP and OP-related bone damages toward improved life quality of millions of patients.

A Translational Porcine Model for Human Cell-Based Therapies in the Treatment of Posttraumatic Osteoarthritis After Anterior Cruciate Ligament Injury

BACKGROUND

There is a high incidence of posttraumatic osteoarthritis (PTOA) after anterior cruciate ligament (ACL) injury, and these injuries represent an enormous health care economic burden. In an effort to address this unmet clinical need, there has been increasing interest in cell-based therapies.

PURPOSE

To establish a translational large animal model of PTOA and demonstrate the feasibility of intra-articular human cell-based interventions.

STUDY DESIGN

Descriptive laboratory study.

METHODS

Nine Yucatan mini-pigs underwent unilateral ACL transection and were monitored for up to 12 weeks after injury. Interleukin 1 beta (IL-1β) levels and collagen breakdown were evaluated longitudinally using enzyme-linked immunosorbent assays of synovial fluid, serum, and urine. Animals were euthanized at 4 weeks (n = 3) or 12 weeks (n = 3) after injury, and injured and uninjured limbs underwent magnetic resonance imaging (MRI) and histologic analysis. At 2 days after ACL injury, an additional 3 animals received an intra-articular injection of 10⁷ human bone marrow-derived mesenchymal stem cells (hBM-MSCs) combined with a fibrin carrier. These cells were labeled with the luciferase reporter gene (hBM-MSCs-Luc) as well as fluorescent markers and intracellular iron nanoparticles. These animals were euthanized on day 0 (n = 1) or day 14 (n = 2) after injection. hBM-MSC-Luc viability and localization were assessed using ex vivo bioluminescence imaging, fluorescence imaging, and MRI.

RESULTS

PTOA was detected as early as 4 weeks after injury. At 12 weeks after injury, osteoarthritis could be detected grossly as well as on histologic analysis. Synovial fluid analysis showed elevation of IL-1β shortly after ACL injury, with subsequent resolution by 2 weeks after injury. Collagen type II protein fragments were elevated in the synovial fluid and serum after injury. hBM-MSCs-Luc were detected immediately after injection and at 2 weeks after injection using fluorescence imaging, MRI, and bioluminescence imaging.

CONCLUSION

This study demonstrates the feasibility of reproducing the chondral changes, intra-articular cytokine alterations, and body fluid biomarker findings consistent with PTOA after ACL injury in a large animal model. Furthermore, we have demonstrated the ability of hBM-MSCs to survive and express transgene within the knee joint of porcine hosts without immunosuppression for at least 2 weeks.

CLINICAL RELEVANCE

This model holds great potential to significantly contribute to investigations focused on the development of cell-based therapies for human ACL injury-associated PTOA in the future (see Appendix Figure A1, available online).

Mechanisms of action of neuropeptide Y on stem cells and its potential applications in orthopaedic disorders

Musculoskeletal disorders are the leading causes of disability and result in reduced quality of life. The neuro-osteogenic network is one of the most promising fields in orthopaedic research. Neuropeptide Y (NPY) system has been reported to be involved in the regulations of bone metabolism and homeostasis, which also provide feedback to the central NPY system via NPY receptors. Currently, potential roles of peripheral NPY in bone metabolism remain unclear. Growing evidence suggests that NPY can regulate biological actions of bone marrow mesenchymal stem cells, hematopoietic stem cells, endothelial cells, and chondrocytes via a local autocrine or paracrine manner by different NPY receptors. The regulative activities of NPY may be achieved through the plasticity of NPY receptors, and interactions among the targeted cells as well. In general, NPY can influence proliferation, apoptosis, differentiation, migration, mobilization, and cytokine secretion of different types of cells, and play crucial roles in the development of bone delayed/non-union, osteoporosis, and osteoarthritis. Further basic research should clarify detailed mechanisms of action of NPY on stem cells, and clinical investigations are also necessary to comprehensively evaluate potential applications of NPY and its receptor-targeted drugs in management of musculoskeletal disorders.

Teriparatide (recombinant parathyroid hormone 1-34) enhances bone allograft integration in a clinically relevant pig model of segmental mandibulectomy

Massive craniofacial bone loss poses a clinical challenge to maxillofacial surgeons. Structural bone allografts are readily available at tissue banks but are rarely used due to a high failure rate. Previous studies showed that intermittent administration of recombinant parathyroid hormone (rPTH) enhanced integration of allografts in a murine model of calvarial bone defect. To evaluate its translational potential, the hypothesis that rPTH would enhance healing of a mandibular allograft in a clinically relevant large animal model of mandibulectomy was tested. Porcine bone allografts were implanted into a 5-cm-long continuous mandible bone defect in six adult Yucatan minipigs, which were randomized to daily intramuscular injections of rPTH (1.75 μg/kg) and placebo (n = 3). Blood tests were performed on Day 56 preoperation, Day 0 and on Day 56 postoperation. Eight weeks after the surgery, bone healing was analyzed using high-resolution X-ray imaging (Faxitron and micro computed tomography [CT]) and three-point bending biomechanical testing. The results showed a significant 2.6-fold rPTH-induced increase in bone formation (p = 0.02). Biomechanically, the yield failure properties of the healed mandibles were significantly higher in the rPTH group (yield load: p < 0.05; energy to yield: p < 0.01), and the post-yield displacement and energy were higher in the placebo group (p < 0.05), suggesting increased mineralized integration of the allograft in the rPTH group. In contrast to similar rPTH therapy studies in dogs, no signs of hypercalcemia, hyperphosphatemia, or inflammation were detected. Taken together, we provide initial evidence that rPTH treatment enhances mandibular allograft healing in a clinically relevant large animal model.

Mesenchymal stem cells modifications for enhanced bone targeting and bone regeneration

In pathological bone conditions (e.g., osteoporotic fractures or critical size bone defects), increasing the pool of osteoblast progenitor cells is a promising therapeutic approach to facilitate bone healing. Since mesenchymal stem cells (MSCs) give rise to the osteogenic lineage, a number of clinical trials investigated the potential of MSCs transplantation for bone regeneration. However, the engraftment of transplanted cells is often hindered by insufficient oxygen and nutrients supply and the tendency of MSCs to home to different sites of the body. In this review, we discuss various approaches of MSCs transplantation for bone regeneration including scaffold and hydrogel constructs, genetic modifications and surface engineering of the cell membrane aimed to improve homing and increase cell viability, proliferation and differentiation.

Mesenchymal Stromal Cell-Based Bone Regeneration Therapies: From Cell Transplantation and Tissue Engineering to Therapeutic Secretomes and Extracellular Vesicles

Effective regeneration of bone defects often presents significant challenges, particularly in patients with decreased tissue regeneration capacity due to extensive trauma, disease, and/or advanced age. A number of studies have focused on enhancing bone regeneration by applying mesenchymal stromal cells (MSCs) or MSC-based bone tissue engineering strategies. However, translation of these approaches from basic research findings to clinical use has been hampered by the limited understanding of MSC therapeutic actions and complexities, as well as costs related to the manufacturing, regulatory approval, and clinical use of living cells and engineered tissues. More recently, a shift from the view of MSCs directly contributing to tissue regeneration toward appreciating MSCs as "cell factories" that secrete a variety of bioactive molecules and extracellular vesicles with trophic and immunomodulatory activities has steered research into new MSC-based, "cell-free" therapeutic modalities. The current review recapitulates recent developments, challenges, and future perspectives of these various MSC-based bone tissue engineering and regeneration strategies.

Human iPSCs can be differentiated into notochordal cells that reduce intervertebral disc degeneration in a porcine model

Introduction: As many as 80% of the adult population experience back pain at some point in their lifetimes. Previous studies have indicated a link between back pain and intervertebral disc (IVD) degeneration. Despite decades of research, there is an urgent need for robust stem cell therapy targeting underlying causes rather than symptoms. It has been proposed that notochordal cells (NCs) appear to be the ideal cell type to regenerate the IVD: these cells disappear in humans as they mature, are replaced by nucleus pulposus (NP) cells, and their disappearance correlates with the initiation of degeneration of the disc. Human NCs are in short supply, thus here aimed for generation of notochordal-like cells from induced pluripotent cells (iPSCs).

Methods: Human iPSCs were generated from normal dermal fibroblasts by transfecting plasmids encoding for six factors: OCT4, SOX2, KLF4, L-MYC, LIN28, and p53 shRNA. Then the iPSCs were treated with GSK3i to induce differentiation towards Primitive Streak Mesoderm (PSM). The differentiation was confirmed by qRT-PCR and immunofluorescence. PSM cells were transfected with Brachyury (Br)-encoding plasmid and the cells were encapsulated in Tetronic-tetraacrylate-fibrinogen (TF) hydrogel that mimics the NP environment (G'=1kPa), cultured in hypoxic conditions (2% O2) and with specifically defined growth media. The cells were also tested in vivo in a large animal model. IVD degeneration was induced after an annular puncture in pigs, 4 weeks later the cells were injected and IVDs were analyzed at 12 weeks after the injury using MRI, gene expression analysis and histology.

Results: After short-term exposure of iPSCs to GSK3i there was a significant change in cell morphology, Primitive Streak Mesoderm (PSM) markers (Brachyury, MIXL1, FOXF1) were upregulated and markers of pluripotency (Nanog, Oct4, Sox2) were downregulated, both compared to the control group. PSM cells nucleofected with Br (PSM-Br) cultured in TF hydrogels retained the NC phenotype consistently for up to 8 weeks, as seen in the gene expression analysis. PSM-Br cells were co-cultured with bone marrow (BM)-derived mesenchymal stem cells (MSCs) which, with time, expressed the NC markers in higher levels, however the levels of expression in BM-MSCs alone did not change. Higher expression of NC and NP marker genes in human BM-MSCs was found to be induced by iNC-condition media (iNC-CM) than porcine NC-CM. The annular puncture induced IVD degeneration as early as 2 weeks after the procedure. The injected iNCs were detected in the degenerated discs after 8 weeks in vivo. The iNC-treated discs were found protected from degeneration. This was evident in histological analysis and changes in the pH levels, indicative of degeneration state of the discs, observed using qCEST MRI. Immunofluorescence stains show that their phenotype was consistent with the in vitro study, namely they still expressed the notochordal markers Keratin 18, Keratin 19, Noto and Brachyury.

Conclusion: In the present study, we report a stepwise differentiation method to generate notochordal cells from human iPSCs. These cells not only demonstrate a sustainable notochordal cell phenotype in vitro and in vivo, but also show the functionality of notochordal cells and have protective effect in case of induced disc degeneration and prevent the change in the pH level of the injected IVDs. The mechanism of this effect could be suggested via the paracrine effect on resident cells, as it was shown in the in vitro studies with MSCs.

Bone-chip system to monitor osteogenic differentiation using optical imaging

Human organoids and organ-on-chip systems to predict human responses to new therapies and for the understanding of disease mechanisms are being more commonly used in translational research. We have developed a bone-chip system to study osteogenic differentiation in vitro, coupled with optical imaging approach which provides the opportunity of monitoring cell survival, proliferation and differentiation in vitro without the need to terminate the culture. We used the mesenchymal stem cell (MSC) line over-expressing bone morphogenetic protein-2 (BMP-2), under Tet-Off system, and luciferase reporter gene under constitutive promoter. Cells were seeded on chips and supplemented with osteogenic medium. Flow of media was started 24 h later, while static cultures were performed using media reservoirs. Cells grown on the bone-chips under constant flow of media showed enhanced survival/proliferation, comparing to the cells grown in static conditions; luciferase reporter gene expression and activity, reflecting the cell survival and proliferation, was quantified using bioluminescence imaging and a significant advantage to the flow system was observed. In addition, the flow had positive effect on osteogenic differentiation, when compared with static cultures. Quantitative fluorescent imaging, performed using the osteogenic extra-cellular matrix-targeted probes, showed higher osteogenic differentiation of the cells under the flow conditions. Gene expression analysis of osteogenic markers confirmed the osteogenic differentiation of the MSC-BMP2 cells. Immunofluorescent staining performed against the Osteocalcin, Col1, and BSP markers illustrated robust osteogenic differentiation in the flow culture and lessened differentiation in the static culture. To sum, the bone-chip allows monitoring cell survival, proliferation, and osteogenic differentiation using optical imaging.

Extracellular vesicles from human umbilical cord blood ameliorate bone loss in senile osteoporotic mice

OBJECTIVE

Senile osteoporosis is one of the most common age-related diseases worldwide. Accumulating evidences have indicated that young blood can reverse age-related impairments. Extracellular vesicles (EVs) exert therapeutic effects in a variety of diseases by delivering bioactive molecules such as microRNAs (miRNAs). The aim of the study is to evaluate the therapeutic potential of EVs from human umbilical cord blood plasma (UCB-EVs) on senile osteoporosis and to preliminarily clarify the underlying mechanism.

METHODS

UCB-EVs were injected into the tail vein of aged (16 months old) male C57BL/6 mice. Microcomputed tomography was performed to evaluate bone mass and microarchitecture of mice. The osteogenic and osteoclastic activities were determined by quantitative real-time PCR (qRT-PCR), histological examination and western blot analysis. In vitro, qRT-PCR assay was undertaken to explore the enrichment levels of a number of miRNAs that have positive effects in reducing bone loss. The efficacy of UCB-EVs on osteoblastic differentiation of bone marrow mesenchymal stromal cells (BMSCs) and osteoclastogenesis of RAW264.7 cells were assessed by cytochemical staining. Gene and protein expression changes were detected by qRT-PCR and western blotting respectively. Meanwhile, the roles of the selected miRNA in the regulatory effects of UCB-EVs on BMSCs and RAW264.7 cells were evaluated by using specific miRNA inhibitor.

RESULTS

The intravenous injection of UCB-EVs for two months attenuated bone loss in old mice, as defined by increased trabecular and cortical bone mass, enhanced osteoblast formation and reduced osteoclast formation compared to the control mice. In vitro, UCB-EVs could promote the osteogenic differentiation of BMSCs and inhibit the osteoclastogenesis of RAW264.7 cells. Moreover, it was confirmed that miR-3960 was highly enriched in UCB-EVs and miR-3960 inhibitor reversed the stimulatory effect of UCB-EVs on osteoblastic differentiation of BMSCs.

CONCLUSION

Our findings indicate that UCB-EVs ameliorate age-related bone loss by stimulating bone formation and inhibiting bone resorption, and miR-3960 mediated the osteogenic effect of UCB-EVs on BMSCs. Thus, UCB-EVs may represent a promising agent for prevention of senile osteoporosis.

Allogenic Stem Cells in Spinal Fusion: A Systematic Review

STUDY DESIGN

Systematic review.

OBJECTIVES

To review, critically appraise, and synthesize evidence on the use of allogenic stem cell products for spine fusion compared with other bone graft materials.

METHODS

Systematic searches of PubMed/MEDLINE, through October 31, 2018 and of EMBASE and ClinicalTrials.gov through April 13, 2018 were conducted for literature comparing allogenic stem cell sources for fusion in the lumbar or cervical spine with other fusion methods. In the absence of comparative studies, case series of ≥10 patients were considered.

RESULTS

From 382 potentially relevant citations identified, 6 publications on lumbar fusion and 5 on cervical fusion met the inclusion criteria. For lumbar arthrodesis, mean Oswestry Disability Index (ODI), visual analogue scale (VAS) pain score, and fusion rates were similar for anterior lumbar interbody fusion (ALIF) using allogenic multipotent adult progenitor cells (Map3) versus recombinant human bone morphogenetic protein-2 (rhBMP-2) in the one comparative lumbar study (90% vs 92%). Across case series of allogenic stem cell products, function and pain were improved relative to baseline and fusion occurred in ≥90% of patients at ≥12 months. For cervical arthrodesis across case series, stem cell products improved function and pain compared with baseline at various time frames. In a retrospective cohort study fusion rates were not statistically different for Osteocel compared with Vertigraft allograft (88% vs 95%). Fusion rates varied across time frames and intervention products in case series.

CONCLUSIONS

The overall quality (strength) of evidence of effectiveness and safety of allogenic stem cells products for lumbar and cervical arthrodesis was very low, meaning that we have very little confidence that the effects seen are reflective of the true effects.

The Emerging Role of Mesenchymal Stem Cells in Vascular Calcification

Vascular calcification (VC), characterized by hydroxyapatite crystal depositing in the vessel wall, is a common pathological condition shared by many chronic diseases and an independent risk factor for cardiovascular events. Recently, VC is regarded as an active, dynamic cell-mediated process, during which calcifying cell transition is critical. Mesenchymal stem cells (MSCs), with a multidirectional differentiation ability and great potential for clinical application, play a duplex role in the VC process. MSCs facilitate VC mainly through osteogenic transformation and apoptosis. Meanwhile, several studies have reported the protective role of MSCs. Anti-inflammation, blockade of the BMP2 signal, downregulation of the Wnt signal, and antiapoptosis through paracrine signaling are possible mechanisms. This review displays the evidence both on the facilitating role and on the protective role of MSCs, then discusses the key factors determining this divergence.

Nonviral ultrasound-mediated gene delivery in small and large animal models

Ultrasound-mediated gene delivery (sonoporation) is a minimally invasive, nonviral and clinically translatable method of gene therapy. This method offers a favorable safety profile over that of viral vectors and is less invasive as compared with other physical gene delivery approaches (e.g., electroporation). We have previously used sonoporation to overexpress transgenes in different skeletal tissues in order to induce tissue regeneration. Here, we provide a protocol that could easily be adapted to address various other targets of tissue regeneration or additional applications, such as cancer and neurodegenerative diseases. This protocol describes how to prepare, conduct and optimize ultrasound-mediated gene delivery in both a murine and a porcine animal model. The protocol includes the preparation of a microbubble-DNA mix and in vivo sonoporation under ultrasound imaging. Ultrasound-mediated gene delivery can be accomplished within 10 min. After DNA delivery, animals can be followed to monitor gene expression, protein secretion and other transgene-specific outcomes, including tissue regeneration. This procedure can be accomplished by a competent graduate student or technician with prior experience in ultrasound imaging or in performing in vivo procedures.

Effects of Intermittent Parathyroid Hormone 1-34 Administration on Circulating Mesenchymal Stem Cells in Postmenopausal Osteoporotic Women

BACKGROUND Intermittent parathyroid hormone (PTH) 1-34 administration stimulates osteogenesis and increases bone marrow mesenchymal stem cell (MSC) density; however, its effect on the circulating MSCs is unknown. This study aimed to examine the effect of intermittent PTH 1-34 administration on circulating MSCs in the peripheral blood of postmenopausal osteoporotic women. MATERIAL AND METHODS Fifty-four postmenopausal osteoporotic women at high risk of fracture were enrolled and administered either teriparatide (PTH 1-34) or alendronate for 12 months. Whole blood samples were obtained at baseline, 1, 3, 6, and 12 months after initiation of treatment. Flow cytometry analyses were performed to identify circulating MSCs (CD73+, CD90+, CD105+, CD34-, and CD45-). Serum markers of bone formation, bone resorption, as well as bone mineral density (BMD) were serially measured. Circulating MSCs were isolated from peripheral blood of teriparatide treated women and cultured in osteogenic medium to examine their osteogenic differentiation potential. RESULTS Teriparatide treatment increased circulating MSCs to 141±96% (P<0.001) by month 1, persisting until month 12; this increase was positively associated with increases in bone formation and bone resorption biomarkers (at month 6) and spine BMD (at month 12). Furthermore, intermittent PTH 1-34 administration promoted in vitro osteogenic differentiation of circulating MSCs, evident from increased alkaline phosphatase (ALP) activity, ALP-expressing cell density, calcium deposition, and Runx-2, OSX, COL 1a1, and osteocalcin mRNA upregulation. CONCLUSIONS Intermittent PTH 1-34 administration increased circulating MSC density in women with postmenopausal osteoporosis and enhanced in vitro osteogenic differentiation potential of these cells.

Parathyroid hormone for bone regeneration

Delayed healing and/or non-union occur in approximately 5-10% of the fractures that occur annually in the United States. Segmental bone loss increases the probability of non-union. Though grafting can be an effective treatment for segmental bone loss, autografting is limited for large defects since a limited amount of bone is available for harvest. Parathyroid hormone (PTH) is a key regulator of calcium homeostasis in the body and plays an important role in bone metabolism. Presently PTH is FDA approved for use as an anabolic treatment for osteoporosis. The anabolic effect PTH has on bone has led to research on its use for bone regeneration applications. Numerous studies in animal models have indicated enhanced fracture healing as a result of once daily injections of PTH. Similarly, in a human case study, non-union persisted despite treatment attempts with internal fixation, external fixation, and autograft in combination with BMP-7, until off label use of PTH1-84 was utilized. Use of a biomaterial scaffold to locally deliver PTH to a defect site has also been shown to improve bone formation and healing around dental implants in dogs and drill defects in sheep. Thus, PTH may be used to promote bone regeneration and provide an alternative to autograft and BMP for the treatment of large segmental defects and non-unions. This review briefly summarizes the unmet clinical need for improved bone regeneration techniques and how PTH may help fill that void by both systemically and locally delivered PTH for bone regeneration applications. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:2586-2594, 2018.

CXCR4 Has the Potential to Enhance Bone Formation in Osteopenic Rats

Osteoporosis is characterized by reduced bone mass and aberrant bone microarchitecture, thus increasing susceptibility to fracture due to reduced strength and quality. The aims of this study were to investigate the role of CXCR4 transfected on stem cell homing and osteogenic characteristics in osteopenic rats, particularly elucidating the effect on cell migration.

METHODS

Mesenchymal stem cells (MSCs) were harvested from young, and ovariectomized animals and transfected with CXCR4; these cells were administered intravenously in ovariectomized rats. Micro CT and mechanical testing were completed after 12 weeks.

RESULTS

Rats injected with young CXCR4 transfected cells had significantly higher bone mineral density (BMD) compared to placebo injected rats (p < 0.05). Rats injected with ovariectomized CXCR4 transfected cells had higher BMD compared to those injected with saline or nontransfected cells (p < 0.04). L4 vertebral stiffness was significantly higher in rats treated with young CXCR4 transfected cells compared to all other groups (p < 0.05).

CONCLUSION

CXCR4 genetically modified cells from young and ovariectomized sources improve some aspects of bone formation in the ovariectomized model of osteoporosis and, thus, may play a role in patient treatment regimens.

Mesenchymal Stem Cell Migration during Bone Formation and Bone Diseases Therapy

During bone modeling, remodeling, and bone fracture repair, mesenchymal stem cells (MSCs) differentiate into chondrocyte or osteoblast to comply bone formation and regeneration. As multipotent stem cells, MSCs were used to treat bone diseases during the past several decades. However, most of these implications just focused on promoting MSC differentiation. Furthermore, cell migration is also a key issue for bone formation and bone diseases treatment. Abnormal MSC migration could cause different kinds of bone diseases, including osteoporosis. Additionally, for bone disease treatment, the migration of endogenous or exogenous MSCs to bone injury sites is required. Recently, researchers have paid more and more attention to two critical points. One is how to apply MSC migration to bone disease therapy. The other is how to enhance MSC migration to improve the therapeutic efficacy of bone diseases. Some considerable outcomes showed that enhancing MSC migration might be a novel trick for reversing bone loss and other bone diseases, such as osteoporosis, fracture, and osteoarthritis (OA). Although plenty of challenges need to be conquered, application of endogenous and exogenous MSC migration and developing different strategies to improve therapeutic efficacy through enhancing MSC migration to target tissue might be the trend in the future for bone disease treatment.

Recent Advances and Future of Gene Therapy for Bone Regeneration

PURPOSE OF REVIEW

The purpose of this review is to discuss the recent advances in gene therapy as a treatment for bone regeneration. While most fractures heal spontaneously, patients who present with fracture nonunion suffer from prolonged pain, disability, and often require additional operations to regain musculoskeletal function.

RECENT FINDINGS

In the last few years, BMP gene delivery by means of electroporation and sonoporation resulted in repair of nonunion bone defects in mice, rats, and minipigs. Ex vivo transfection of porcine mesenchymal stem cells (MSCs) resulted in bone regeneration following implantation in vertebral defects of minipigs. Sustained release of VEGF gene from a collagen-hydroxyapatite scaffold to the mandible of a human patient was shown to be safe and osteoinductive. In conclusion, gene therapy methods for bone regeneration are systematically becoming more efficient and show proof-of-concept in clinically relevant animal models. Yet, on the pathway to clinical use, more investigation is needed to determine the safety aspects of the various techniques in terms of biodistribution, toxicity, and tumorigenicity.

Ultrasound-Mediated Gene Delivery Enhances Tendon Allograft Integration in Mini-Pig Ligament Reconstruction

Ligament injuries occur frequently, substantially hindering routine daily activities and sports participation in patients. Surgical reconstruction using autogenous or allogeneic tissues is the gold standard treatment for ligament injuries. Although surgeons routinely perform ligament reconstructions, the integrity of these reconstructions largely depends on adequate biological healing of the interface between the ligament graft and the bone. We hypothesized that localized ultrasound-mediated, microbubble-enhanced therapeutic gene delivery to endogenous stem cells would lead to significantly improved ligament graft integration. To test this hypothesis, an anterior cruciate ligament reconstruction procedure was performed in Yucatan mini-pigs. A collagen scaffold was implanted in the reconstruction sites to facilitate recruitment of endogenous mesenchymal stem cells. Ultrasound-mediated reporter gene delivery successfully transfected 40% of cells recruited to the reconstruction sites. When BMP-6 encoding DNA was delivered, BMP-6 expression in the reconstruction sites was significantly enhanced. Micro-computed tomography and biomechanical analyses showed that ultrasound-mediated BMP-6 gene delivery led to significantly enhanced osteointegration in all animals 8 weeks after surgery. Collectively, these findings demonstrate that ultrasound-mediated gene delivery to endogenous mesenchymal progenitor cells can effectively improve ligament reconstruction in large animals, thereby addressing a major unmet orthopedic need and offering new possibilities for translation to the clinical setting.

In situ bone tissue engineering via ultrasound-mediated gene delivery to endogenous progenitor cells in mini-pigs

More than 2 million bone-grafting procedures are performed each year using autografts or allografts. However, both options carry disadvantages, and there remains a clear medical need for the development of new therapies for massive bone loss and fracture nonunions. We hypothesized that localized ultrasound-mediated, microbubble-enhanced therapeutic gene delivery to endogenous stem cells would induce efficient bone regeneration and fracture repair. To test this hypothesis, we surgically created a critical-sized bone fracture in the tibiae of Yucatán mini-pigs, a clinically relevant large animal model. A collagen scaffold was implanted in the fracture to facilitate recruitment of endogenous mesenchymal stem/progenitor cells (MSCs) into the fracture site. Two weeks later, transcutaneous ultrasound-mediated reporter gene delivery successfully transfected 40% of cells at the fracture site, and flow cytometry showed that 80% of the transfected cells expressed MSC markers. Human bone morphogenetic protein-6 (BMP-6) plasmid DNA was delivered using ultrasound in the same animal model, leading to transient expression and secretion of BMP-6 localized to the fracture area. Micro-computed tomography and biomechanical analyses showed that ultrasound-mediated BMP-6 gene delivery led to complete radiographic and functional fracture healing in all animals 6 weeks after treatment, whereas nonunion was evident in control animals. Collectively, these findings demonstrate that ultrasound-mediated gene delivery to endogenous mesenchymal progenitor cells can effectively treat nonhealing bone fractures in large animals, thereby addressing a major orthopedic unmet need and offering new possibilities for clinical translation.

Semiautomated Longitudinal Microcomputed Tomography-based Quantitative Structural Analysis of a Nude Rat Osteoporosis-related Vertebral Fracture Model

Osteoporosis-related vertebral compression fractures (OVCFs) are a common and clinically unmet need with increasing prevalence as the world population ages. Animal OVCF models are essential to the preclinical development of translational tissue engineering strategies. While a number of models currently exist, this protocol describes an optimized method for inducing multiple highly reproducible vertebral defects in a single nude rat. A novel longitudinal semiautomated microcomputed tomography (µCT)-based quantitative structural analysis of the vertebral defects is also detailed. Briefly, rats were imaged at multiple time points post-op. The day 1 scan was reoriented to a standard position, and a standard volume of interest was defined. Subsequent µCT scans of each rat were automatically registered to the day 1 scan so the same volume of interest was then analyzed to assess for new bone formation. This versatile approach can be adapted to a variety of other models where longitudinal imaging-based analysis could benefit from precise 3D semiautomated alignment. Taken together, this protocol describes a readily quantifiable and easily reproducible system for osteoporosis and bone research. The suggested protocol takes 4 months to induce osteoporosis in nude ovariectomized rats and between 2.7 and 4 h to generate, image, and analyze two vertebral defects, depending on tissue size and equipment.

Teriparatide Treatment Improves Bone Defect Healing Via Anabolic Effects on New Bone Formation and Non-Anabolic Effects on Inhibition of Mast Cells in a Murine Cranial Window Model

Investigations of teriparatide (recombinant parathyroid hormone [rPTH]) as a potential treatment for critical defects have demonstrated the predicted anabolic effects on bone formation, and significant non-anabolic effects on healing via undefined mechanisms. Specifically, studies in murine models of structural allograft healing demonstrated that rPTH treatment increased angiogenesis (vessels <30 μm), and decreased arteriogenesis (>30 μm) and mast cell numbers, which lead to decreased fibrosis and accelerated healing. To better understand these non-anabolic effects, we interrogated osteogenesis, vasculogenesis, and mast cell accumulation in mice randomized to placebo (saline), rPTH (20 μg/kg/2 days), or the mast cell inhibitor sodium cromolyn (SC) (24 μg/kg/ 2days), via longitudinal micro-computed tomography (μCT) and multiphoton laser scanning microscopy (MPLSM), in a critical calvaria defect model. μCT demonstrated that SC significantly increased defect window closure and new bone volume versus placebo (p < 0.05), although these effects were not as great as rPTH. Interestingly, both rPTH and SC have similar inhibitory effects on arteriogenesis versus placebo (p < 0.05) without affecting total vascular volume. MPLSM time-course studies in untreated mice revealed that large numbers of mast cells were detected 1 day postoperation (43 ± 17), peaked at 6 days (76 ± 6), and were still present in the critical defect at the end of the experiment on day 30 (20 ± 12). In contrast, angiogenesis was not observed until day 4, and functional vessels were first observed on 6 days, demonstrating that mast cell accumulation precedes vasculogenesis. To confirm a direct role of mast cells on osteogenesis and vasculogenesis, we demonstrated that specific diphtheria toxin-α deletion in Mcpt5-Cre-iDTR mice results in similar affects as SC treatment in WT mice. Collectively, these findings demonstrate that mast cells inhibit bone defect healing by stimulating arteriogenesis associated with fibrotic scaring, and that an efficacious non-anabolic effect of rPTH therapy on bone repair is suppression of arteriogenesis and fibrosis secondary to mast cell inhibition. © 2017 American Society for Bone and Mineral Research.

Systemic administration of mesenchymal stem cells combined with parathyroid hormone therapy synergistically regenerates multiple rib fractures

Background

A devastating condition that leads to trauma-related morbidity, multiple rib fractures, remain a serious unmet clinical need. Systemic administration of mesenchymal stem cells (MSCs) has been shown to regenerate various tissues. We hypothesized that parathyroid hormone (PTH) therapy would enhance MSC homing and differentiation, ultimately leading to bone formation that would bridge rib fractures.

Methods

The combination of human MSCs (hMSCs) and a clinically relevant PTH dose was studied using immunosuppressed rats. Segmental defects were created in animals’ fifth and sixth ribs. The rats were divided into four groups: a negative control group, in which animals received vehicle alone; the PTH-only group, in which animals received daily subcutaneous injections of 4 μg/kg teriparatide, a pharmaceutical derivative of PTH; the hMSC-only group, in which each animal received five injections of 2 × 10⁶ hMSCs; and the hMSC + PTH group, in which animals received both treatments. Longitudinal in vivo monitoring of bone formation was performed biweekly using micro-computed tomography (μCT), followed by histological analysis.

Results

Fluorescently-dyed hMSCs were counted using confocal microscopy imaging of histological samples harvested 8 weeks after surgery. PTH significantly augmented the number of hMSCs that homed to the fracture site. Immunofluorescence of osteogenic markers, osteocalcin and bone sialoprotein, showed that PTH induced cell differentiation in both exogenously administered cells and resident cells. μCT scans revealed a significant increase in bone volume only in the hMSC + PTH group, beginning by the 4^th week after surgery. Eight weeks after surgery, 35% of ribs in the hMSC + PTH group had complete bone bridging, whereas there was complete bridging in only 6.25% of ribs (one rib) in the PTH-only group and in none of the ribs in the other groups. Based on the μCT scans, biomechanical analysis using the micro-finite element method demonstrated that the healed ribs were stiffer than intact ribs in torsion, compression, and bending simulations, as expected when examining bone callus composed of woven bone.

Conclusions

Administration of both hMSCs and PTH worked synergistically in rib fracture healing, suggesting this approach may pave the way to treat multiple rib fractures as well as additional fractures in various anatomical sites.

Electronic supplementary material

The online version of this article (doi:10.1186/s13287-017-0502-9) contains supplementary material, which is available to authorized users.

Mesenchymal stromal/stem cells in drug therapy: New perspective

Mesenchymal stromal/stem cells (MSC) have emerged as a class of cells suitable for cellular delivery of nanoparticles, drugs and micro-RNA cargo for targeted treatments such as tumor and other protective mechanisms. The special properties of MSC underscore the current use for various clinical applications. Examples of applications include but are not limited to regenerative medicine, immune disorders and anti-cancer therapies. In recent years, there has been intense research in modifying MSC to achieve targeted and efficient clinical outcomes. This review discusses effects of MSC in an inflammatory microenvironment and then explains how these properties could be important to the overall application of MSC in cell therapy. The article also advises caution in the application of these cells because of their role in tumorigenesis. The review stresses the use of MSC as vehicles for drug delivery and discusses the accompanying challenges, based on the influence of the microenvironment on MSC.

Improved Mobilization of Exogenous Mesenchymal Stem Cells to Bone for Fracture Healing and Sex Difference

Mesenchymal stem cell (MSC) transplantation has been tested in animal and clinical fracture studies. We have developed a bone-seeking compound, LLP2A-Alendronate (LLP2A-Ale) that augments MSC homing to bone. The purpose of this study was to determine whether treatment with LLP2A-Ale or a combination of LLP2A-Ale and MSCs would accelerate bone healing in a mouse closed fracture model and if the effects are sex dependent. A right mid-femur fracture was induced in two-month-old osterix-mCherry (Osx-mCherry) male and female reporter mice. The mice were subsequently treated with placebo, LLP2A-Ale (500 μg/kg, IV), MSCs derived from wild-type female Osx-mCherry adipose tissue (ADSC, 3 x 10⁵ , IV) or ADSC + LLP2A-Ale. In phosphate buffered saline-treated mice, females had higher systemic and surface-based bone formation than males. However, male mice formed a larger callus and had higher volumetric bone mineral density and bone strength than females. LLP2A-Ale treatment increased exogenous MSC homing to the fracture gaps, enhanced incorporation of these cells into callus formation, and stimulated endochondral bone formation. Additionally, higher engraftment of exogenous MSCs in fracture gaps seemed to contribute to overall fracture healing and improved bone strength. These effects were sex-independent. There was a sex-difference in the rate of fracture healing. ADSC and LLP2A-Ale combination treatment was superior to on callus formation, which was independent of sex. Increased mobilization of exogenous MSCs to fracture sites accelerated endochondral bone formation and enhanced bone tissue regeneration. Stem Cells 2016;34:2587-2600.