The role of mesenchymal stem cells in bone repair and regeneration

Integrating bioprinting, cell therapies and drug delivery towards in vivo regeneration of cartilage, bone and osteochondral tissue

The biological and biomechanical functions of cartilage, bone and osteochondral tissue are naturally orchestrated by a complex crosstalk between zonally dependent cells and extracellular matrix components. In fact, this crosstalk involves biomechanical signals and the release of biochemical cues that direct cell fate and regulate tissue morphogenesis and remodelling in vivo. Three-dimensional bioprinting introduced a paradigm shift in tissue engineering and regenerative medicine, since it allows to mimic native tissue anisotropy introducing compositional and architectural gradients. Moreover, the growing synergy between bioprinting and drug delivery may enable to replicate cell/extracellular matrix reciprocity and dynamics by the careful control of the spatial and temporal patterning of bioactive cues. Although significant advances have been made in this direction, unmet challenges and open research questions persist. These include, among others, the optimization of scaffold zonality and architectural features; the preservation of the bioactivity of loaded active molecules, as well as their spatio-temporal release; the in vitro scaffold maturation prior to implantation; the pros and cons of each animal model and the graft-defect mismatch; and the in vivo non-invasive monitoring of new tissue formation. This work critically reviews these aspects and reveals the state of the art of using three-dimensional bioprinting, and its synergy with drug delivery technologies, to pattern the distribution of cells and/or active molecules in cartilage, bone and osteochondral engineered tissues. Most notably, this work focuses on approaches, technologies and biomaterials that are currently under in vivo investigations, as these give important insights on scaffold performance at the implantation site and its interaction/integration with surrounding tissues.

Development of a Gene-Activated Scaffold Incorporating Multifunctional Cell-Penetrating Peptides for pSDF-1α Delivery for Enhanced Angiogenesis in Tissue Engineering Applications

Non-viral gene delivery has become a popular approach in tissue engineering, as it permits the transient delivery of a therapeutic gene, in order to stimulate tissue repair. However, the efficacy of non-viral delivery vectors remains an issue. Our lab has created gene-activated scaffolds by incorporating various non-viral delivery vectors, including the glycosaminoglycan-binding enhanced transduction (GET) peptide into collagen-based scaffolds with proven osteogenic potential. A modification to the GET peptide (FLR) by substitution of arginine residues with histidine (FLH) has been designed to enhance plasmid DNA (pDNA) delivery. In this study, we complexed pDNA with combinations of FLR and FLH peptides, termed GET* nanoparticles. We sought to enhance our gene-activated scaffold platform by incorporating GET* nanoparticles into collagen-nanohydroxyapatite scaffolds with proven osteogenic capacity. GET* N/P 8 was shown to be the most effective formulation for delivery to MSCs in 2D. Furthermore, GET* N/P 8 nanoparticles incorporated into collagen-nanohydroxyapatite (coll-nHA) scaffolds at a 1:1 ratio of collagen:nanohydroxyapatite was shown to be the optimal gene-activated scaffold. pDNA encoding stromal-derived factor 1α (pSDF-1α), an angiogenic chemokine which plays a role in BMP mediated differentiation of MSCs, was then delivered to MSCs using our optimised gene-activated scaffold platform, with the aim of significantly increasing angiogenesis as an important precursor to bone repair. The GET* N/P 8 coll-nHA scaffolds successfully delivered pSDF-1α to MSCs, resulting in a significant, sustained increase in SDF-1α protein production and an enhanced angiogenic effect, a key precursor in the early stages of bone repair.

Neuroinflammation in Primary Cultures of the Rat Spinal Dorsal Horn Is Attenuated in the Presence of Adipose Tissue-Derived Medicinal Signalling Cells (AdMSCs) in a Co-cultivation Model

Neuroinflammation within the superficial dorsal horn (SDH) of the spinal cord induces inflammatory pain with symptoms of hyperalgesia and allodynia. Glial activation and production of inflammatory mediators (e.g. cytokines) is associated with modulation of nociceptive signalling. In this context, medicinal signalling cells, e.g. obtained from adipose tissue (AdMSCs), gained attention due to their capacity to modulate the inflammatory response in several diseases, e.g. spinal cord injury. We applied the recently established mixed neuroglial primary cell culture of the rat SDH to investigate effects of AdMSCs on the inflammatory response of SDH cells. Following establishment of a co-cultivation system, we performed specific bioassays for tumour necrosis factor alpha (TNFα) and interleukin (IL)-6, RT-qPCR and immunocytochemistry to detect changes in cytokine production and glial activation upon inflammatory stimulation with lipopolysaccharide (LPS). LPS-induced expression and release of pro-inflammatory cytokines (TNFα, IL-6) by SDH cells was significantly attenuated in the presence of AdMSCs. Further evidence for anti-inflammatory capacities of AdMSCs derived from a blunted LPS-induced TNFα/IL-10 expression ratio and suppressed nuclear translocation of the inflammatory transcription factor nuclear factor kappa B (NFκB) in SDH microglial cells. Expression of IL-10, transforming growth factor beta (TGF-β) and TNFα-stimulated gene-6 (TSG-6) was detected in AdMSCs, which are putative candidates for anti-inflammatory capacities of these cells. We present a novel co-cultivation system of AdMSCs with neuroglial primary cultures of the SDH to investigate immunomodulatory effects of AdMSCs at a cellular level.

Guided Bone Regeneration with Ammoniomethacrylate-Based Barrier Membranes in a Radial Defect Model

Large bone defects pose an unsolved challenge for orthopedic surgeons. Our group has previously reported the construction of a barrier membrane made of ammoniomethacrylate copolymer USP (AMCA), which supports the adhesion, proliferation, and osteoblastic differentiation of human mesenchymal stem cells (hMSCs). In this study, we report the use of AMCA membranes to seclude critical segmental defect (~1.0 cm) created in the middle third of rabbit radius and test the efficiency of bone regeneration. Bone regeneration was assessed by radiography, biweekly for 8 weeks. The results were verified by histology and micro-CT at the end of the follow-up. The AMCA membranes were found superior to no treatment in terms of new bone formation in the defect, bone volume, callus surface area normalized to total volume, and the number of bone trabeculae, after eight weeks. Additional factors were then assessed, and these included the addition of simvastatin to the membrane, coating the membrane with human MSC, and a combination of those. The addition of simvastatin to the membranes demonstrated a stronger effect at a similar radiological follow-up. We conclude that AMCA barrier membranes per se and simvastatin delivered in a controlled manner improve bone regeneration outcome.

Allogeneic umbilical cord-derived mesenchymal stem cells for treating critical-sized bone defects: a translational study

INTRODUCTION

The current 'gold-standard' treatment of critical-sized bone defects (CSBDs) is autografts; however, they have drawbacks including lack of massive bone source donor site morbidity, incomplete remodeling, and the risk of infection. One potential treatment for treating CSBDs is bone marrow-derived mesenchymal stem cells (BM-MSCs). Previously, there were no studies regarding the use of human umbilical cord-mesenchymal stem cells (hUC-MSCs) for treating BDs. We aim to investigate the use of allogeneic hUC-MSCs for treating CSBDs.

METHOD

We included subjects who were diagnosed with non-union fracture with CSBDs who agreed to undergo hUC-MSCs implantation. All patients were given allogeneic hUC-MSCs. All MSCs were obtained and cultured using the multiple-harvest explant method. Subjects were evaluated functionally using the Lower Extremity Functional Scale (LEFS) and radiologically by volume defect reduction.

RESULT

A total of seven (3 male, 4 female) subjects were recruited for this study. The subjects age ranged from 14 to 62 years. All seven subjects had increased LEFS during the end of the follow-up period, indicating improved functional ability. The follow-up period ranged from 12 to 36 months. One subject had wound dehiscence and infection, and two subjects developed partial union.

CONCLUSION

Umbilical cord mesenchymal stem cells are a potential new treatment for CSBDs. Additional studies with larger samples and control groups are required to further investigate the safety and efficacy of umbilical cord-derived mesenchymal stem cells for treating CSBDs.

LncRNA HOTAIRM1 promotes osteogenesis by controlling JNK/AP-1 signalling-mediated RUNX2 expression

Mesenchymal stem cells (MSCs) have potential ability to differentiate into osteocytes in response to in vitro specific induction. However, the molecular basis underlying this biological process remains largely unclear. In this study, we identify lncRNA HOTAIRM1 as a critical regulator to promote osteogenesis of MSCs. Loss of HOTAIRM1 significantly inhibits the calcium deposition and alkaline phosphatase activity of MSCs. Mechanistically, we find that HOTAIRM1 positively modulates the activity of JNK and c-Jun, both of which are widely accepted as crucial regulators of osteogenic differentiation. More importantly, c-Jun is found to be functionally involved in the regulation of RUNX2 expression, a master transcription factor of osteogenesis. In detail, c-Jun can help recruit the acetyltransferase p300 to RUNX2 promoter, facilitating acetylation of histone 3 at K27 site, therefore epigenetically activating RUNX2 gene transcription. In summary, this study highlights the functional importance of HOTAIRM1 in regulation of osteogenesis, and we characterize HOTAIRM1 as a promising molecular target for bone tissue repair and regeneration.

Asymmetrical methyltransferase PRMT3 regulates human mesenchymal stem cell osteogenesis via miR-3648

Histone arginine methylation, which is catalyzed by protein arginine methyltransferases (PRMTs), plays a key regulatory role in various biological processes. Several PRMTs are involved in skeletal development; however, their role in the osteogenic differentiation of mesenchymal stem cells (MSCs) is not completely clear. In this study, we aimed to elucidate the function of PRMT3, a type-I PRMT that catalyzes the formation of ω-mono- or asymmetric dimethyl arginine, in MSCs osteogenesis. We found that PRMT3 promoted MSCs osteogenic commitment and bone remodeling. PRMT3 activated the expression of miR-3648 by enhancing histone H4 arginine 3 asymmetric dimethylation (H4R3me2a) levels at promoter region of the gene. Overexpression of miR-3648 rescued impaired osteogenesis in PRMT3-deficient cells. Moreover, administration of Prmt3 shRNA or a chemical inhibitor of PRMT3 (SGC707) caused an osteopenia phenotype in mice. These results indicate that PRMT3 is a potential therapeutic target for the treatment of bone regeneration and osteopenia disorders.

Application of a Bioactive/Bioresorbable Three-Dimensional Porous Uncalcined and Unsintered Hydroxyapatite/Poly-D/L-lactide Composite with Human Mesenchymal Stem Cells for Bone Regeneration in Maxillofacial Surgery: A Pilot Animal Study

A novel three-dimensional (3D) porous uncalcined and unsintered hydroxyapatite/poly-d/l-lactide (3D-HA/PDLLA) composite demonstrated superior biocompatibility, osteoconductivity, biodegradability, and plasticity, thereby enabling complex maxillofacial defect reconstruction. Mesenchymal stem cells (MSCs)-a type of adult stem cell-have a multipotent ability to differentiate into chondrocytes, adipocytes, and osteocytes. In a previous study, we found that CD90 (Thy-1, cluster of differentiation 90) and CD271 (low-affinity nerve growth factor receptor) double-positive cell populations from human bone marrow had high proliferative ability and differentiation capacity in vitro. In the present study, we investigated the utility of bone regeneration therapy using implantation of 3D-HA/PDLLA loaded with human MSCs (hMSCs) in mandibular critical defect rats. Microcomputed tomography (Micro-CT) indicated that implantation of a 3D-HA/PDLLA-hMSC composite scaffold improved the ability to achieve bone regeneration compared with 3D-HA/PDLLA alone. Compared to the sufficient blood supply in the mandibular defection superior side, a lack of blood supply in the inferior side caused delayed healing. The use of Villanueva Goldner staining (VG staining) revealed the gradual progression of the nucleated cells and new bone from the scaffold border into the central pores, indicating that 3D-HA/PDLLA loaded with hMSCs had good osteoconductivity and an adequate blood supply. These results further demonstrated that the 3D-HA/PDLLA-hMSC composite scaffold was an effective bone regenerative method for maxillofacial boney defect reconstruction.

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

PURPOSE

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

The effect of intra-articular injection of autologous bone marrow stem cells on pain and knee function in patients with osteoarthritis

AIM

Management of osteoarthritis (OA) is basically symptomatic. Recently, stem cells (SC) have been used in the search for an optimum treatment. We decided to conduct a controlled clinical trial to determine if a single intra-articular injection of in vivo stimulated bone marrow SC could lead to an improvement in pain management and quality of life in patients with knee OA.

METHOD

This was a prospective, open-label, phase I/II clinical trial to assess the safety and efficacy of a single intra-articular injection of autologous stimulated bone marrow stem cells (BM-SC) in patients with knee OA. Individuals of both genders older than 30 years with confirmed diagnosis of OA who signed informed consent were included in two groups: SC group received in vivo BM stimulation with subcutaneous administration of granulocyte colony stimulating factor (G-CSF). SC were obtained by BM aspiration and administered in a single intra-articular injection. The control group received exclusively oral acetaminophen. Visual analogue scale and Western Ontario and McMaster Universities Osteoarthritis Index scores were performed at 1 week, 1 month and 6 months in both groups. This trial was registered in ClinialTrials.gov NCT01485198.

RESULTS

A total of 61 patients were included. Socio-demographic characteristics, OA grades and initial scores were similar in both groups. The BM-SC group showed significant improvement in knee pain and quality of life during the 6-month follow-up.

CONCLUSION

The study demonstrates feasibility and supports efficacy of a completely ambulatory procedure in treatment of knee OA.

Periostin promotes ectopic osteogenesis of CTLA4-modified bone marrow mesenchymal stem cells

The improved ectopic osteogenesis of cytotoxic T-lymphocyte-associated antigen 4-Ig-modified bone marrow mesenchymal stem cells (MSCs-CTLA4) has been demonstrated but the mechanisms involved remain to be determined. The extracellular matrix (ECM) has recently been reported to play a vital role in bone formation and periostin (POSTN) has been suggested as a key member in constructing the ECM in bone tissue. We found that POSTN expression in the MSCs-CTLA4 group is significantly enhanced compared with that in the MSCs group, not only in tissue-engineered bone (TEB) with femur heterotopic transplantation in vivo but also under the immune activation condition in vitro. This ectopic osteogenesis effect is in accordance with POSTN expression. We also found that the soluble POSTN treatment up-regulates osteogenic marker expression in MSCs, including runt-related transcription factor 2, collagen 1, osteocalcin, osterix, and alkaline phosphatase and calcium nodule formation. These effects are diminished when the soluble POSTN is neutralized. Our results demonstrate that POSTN promotes the osteogenic differentiation of MSCs and that CTLA4 enhances the ectopic osteogenesis of MSCs-CTLA4-based TEB, potentially by maintaining POSTN expression in xenotransplantation.

Matrix Metalloproteinases in Bone Resorption, Remodeling, and Repair

Matrix metalloproteinases (MMPs) are the major protease family responsible for the cleavage of the matrisome (global composition of the extracellular matrix (ECM) proteome) and proteins unrelated to the ECM, generating bioactive molecules. These proteins drive ECM remodeling, in association with tissue-specific and cell-anchored inhibitors (TIMPs and RECK, respectively). In the bone, the ECM mediates cell adhesion, mechanotransduction, nucleation of mineralization, and the immobilization of growth factors to protect them from damage or degradation. Since the first description of an MMP in bone tissue, many other MMPs have been identified, as well as their inhibitors. Numerous functions have been assigned to these proteins, including osteoblast/osteocyte differentiation, bone formation, solubilization of the osteoid during bone resorption, osteoclast recruitment and migration, and as a coupling factor in bone remodeling under physiological conditions. In turn, a number of pathologies, associated with imbalanced bone remodeling, arise mainly from MMP overexpression and abnormalities of the ECM, leading to bone osteolysis or bone formation. In this review, we will discuss the functions of MMPs and their inhibitors in bone cells, during bone remodeling, pathological bone resorption (osteoporosis and bone metastasis), bone repair/regeneration, and emergent roles in bone bioengineering.

Bone Regenerative Medicine in Oral and Maxillofacial Region Using a Three-Dimensional Printer<sup/>

Bone grafts currently used for the treatment of large bone defect or asymmetry in oral and maxillofacial region include autologous, allogeneic, and artificial bones. Although artificial bone is free from the concerns of donor site morbidity, limitation of volume, disease transmission, and ethical issues, it lacks osteogenic and osteoinductive activities. In addition, molding of the artificial bone is an issue especially when it is used for the augmentation of bone as onlay grafts. To solve this problem, additive manufacturing techniques have been applied to fabricate bones which have outer shapes conformed to patients' bones. We developed a custom-made artificial bone called a computed tomography (CT)-bone. Efficacy of CT-bone was proven in a clinical research and clinical trial, showing good manipulability, stability, and patient satisfaction. However, low replacement rate of artificial bones by endogenous bones remain an unsolved issue. Loading of cells and growth factors will improve the bone replacement by inducing osteogenic and osteoinductive activities. In addition, the three-dimensional bioprinting technique will facilitate bone regeneration by placing cells and biological substances into appropriate sites.

Autologous osteoblast transplantation, an innovative method of bone defect treatment: role of a tissue and cell bank in the process

BACKGROUND

The idea of cell treatment of various diseases and medical conditions has become very popular. Some procedures are well established, as is autologous chondrocyte implantation, whereas others are still in the process of early development, laboratory experiments, and some clinical trials.

METHODS

This report is devoted to an example of an emerging cell treatment: bone augmentation with the use of autologous cells and its legal and technical background. Various requirements set by law must be met by tissue banks performing cell seeding of grafts. In Europe, the requirements are described in directives 2004/23/EC, 2006/17/EC, 2006/86/EC, and in the regulation 2007/1394/EC.

RESULTS

Revitalization of biostatic allografts gives new, promising tools for creation of functional parts of organs; brings the methodology used in tissue banks closer to tissue engineering; places the enterprise in the mainstream of advanced biotechnology; allows the full potential of tissue allografts; and opens a new, large area for clinical and laboratory research. Cell and tissue processing also have a financial impact on the treatment: it produces additional expenditures.

CONCLUSIONS

Clinical effectiveness will be the most decisive factor of whether this innovative treatment will be applied in a particular type of medical condition. From a tissue establishment perspective, the most important issue is to develop a procedure that ensures safety for the patient in graft quality terms.

EphB4 Promotes Osteogenesis of CTLA4-Modified Bone Marrow-Derived Mesenchymal Stem Cells Through Cross Talk with Wnt Pathway in Xenotransplantation

BACKGROUND

Cytotoxic T lymphocyte-associated antigen 4-Ig (CTLA4-Ig)-modified bone marrow-derived mesenchymal stem cells (MSCs-CTLA4) have excellent osteogenic function in xenografts, but their mechanism of action remains to be elucidated. As bidirectional signaling between erythropoietin-producing hepatocyte receptors B4 (EphB4) and ephrinB2 is vital for bone remodeling, this study aimed to fully characterize the role of MSCs-CTLA4 in promoting bone regeneration in xenotransplantation through EphB4/ephrinB2 and their cross talk with the Wnt/beta-catenin pathway.

METHODS

MSCs-CTLA4 were investigated for their osteogenic capacity through xenotransplantation in vivo. MSCs-CTLA4 were treated with ephrinB2-FC or FC under conditions of osteogenic induction and cultured with or without immune activation conditions established by phytohemagglutinin and peripheral blood mononuclear cells in vitro. Osteogenesis markers and the Wnt pathway-related molecules such as EphB4, runt-related transcription factor 2 (Runx2), collagen 1 (COL1), osteocalcin (OCN), alkaline phosphatase (ALP), calcium nodus, β-catenin, phospho-glycogen synthase kinase 3-beta (p-GSK-3β)-Ser9, and glycogen synthase kinase 3-beta (GSK-3β) were detected.

RESULTS

MSCs-CTLA4-based xenografts show better osteogenic capacity compared with MSC-based xenografts. EphB4 expression was reduced in MSCs compared with MSCs-CTLA4 under immune activation conditions. In ephrinB2-FC-treated cells, levels of osteogenesis markers were increased compared with FC-treated cells. The activity of GSK-3 was inhibited and the expression of β-catenin in MSCs was increased by ephrinB2-FC treatment.

CONCLUSIONS

CTLA4 modification maintains EphB4 expression in MSCs under immune activation conditions, and EphB4 cross talk with the Wnt pathway promotes osteogenic differentiation of MSCs-CTLA4.

Bone and cartilage regeneration with the use of umbilical cord mesenchymal stem cells

INTRODUCTION

The production of functional alternatives to bone autografts and the development new treatment strategies for cartilage defects are great challenges that could be addressed by the field of tissue engineering. Umbilical cord mesenchymal stem cells (MSCs) can be used to produce cost-effective, atraumatic and possibly autologous bone and cartilage grafts.

AREAS COVERED

MSCs can be isolated from umbilical cord Wharton's jelly, perivascular tissue and blood using various techniques. Those cells have been characterized and phenotypic similarities with bone marrow-derived MSCs (BM-MSCs) and embryonic stem cells have been found. Findings on their differentiation into the osteogenic and chondrogenic lineage differ between studies and are not as consistent as for BM-MSCs.

EXPERT OPINION

MSCs from umbilical cords have to be more extensively studied and the mechanisms underlying their differentiation have to be clarified. To date, they seem to be an attractive alternative to BM-MSCs. However, further research with suitable scaffolds and growth factors as well as with novel scaffold fabrication and culture technology should be conducted before they are introduced to clinical practice and replace BM-MSCs.

CTLA4 enhances the osteogenic differentiation of allogeneic human mesenchymal stem cells in a model of immune activation

Allogeneic mesenchymal stem cells (allo-MSCs) have recently garnered increasing interest for their broad clinical therapy applications. Despite this, many studies have shown that allo-MSCs are associated with a high rate of graft rejection unless immunosuppressive therapy is administered to control allo-immune responses. Cytotoxic T-lymphocyte-associated protein 4 (CTLA4) is a co-inhibitory molecule expressed on T cells that mediates the inhibition of T-cell function. Here, we investigated the osteogenic differentiation potency of allo-MSCs in an activated immune system that mimics the in vivo allo-MSC grafting microenvironment and explored the immunomodulatory role of the helper T cell receptor CTLA4 in this process. We found that MSC osteogenic differentiation was inhibited in the presence of the activated immune response and that overexpression of CTLA4 in allo-MSCs suppressed the immune response and promoted osteogenic differentiation. Our results support the application of CTLA4-overexpressing allo-MSCs in bone tissue engineering.