Stem cell-conditioned medium accelerates distraction osteogenesis through multiple regenerative mechanisms

Mesenchymal stem cell secretome for regenerative medicine: Where do we stand?

BACKGROUND

Mesenchymal stem cell (MSC)-based therapies have yielded beneficial effects in a broad range of preclinical models and clinical trials for human diseases. In the context of MSC transplantation, it is widely recognized that the main mechanism for the regenerative potential of MSCs is not their differentiation, with in vivo data revealing transient and low engraftment rates. Instead, MSCs therapeutic effects are mainly attributed to its secretome, i.e., paracrine factors secreted by these cells, further offering a more attractive and innovative approach due to the effectiveness and safety of a cell-free product.

AIM OF REVIEW

In this review, we will discuss the potential benefits of MSC-derived secretome in regenerative medicine with particular focus on respiratory, hepatic, and neurological diseases. Both free and vesicular factors of MSC secretome will be detailed. We will also address novel potential strategies capable of improving their healing potential, namely by delivering important regenerative molecules according to specific diseases and tissue needs, as well as non-clinical and clinical studies that allow us to dissect their mechanisms of action.

KEY SCIENTIFIC CONCEPTS OF REVIEW

MSC-derived secretome includes both soluble and non-soluble factors, organized in extracellular vesicles (EVs). Importantly, besides depending on the cell origin, the characteristics and therapeutic potential of MSC secretome is deeply influenced by external stimuli, highlighting the possibility of optimizing their characteristics through preconditioning approaches. Nevertheless, the clarity around their mechanisms of action remains ambiguous, whereas the need for standardized procedures for the successful translation of those products to the clinics urges.

The potent paracrine effect of umbilical cord mesenchymal stem cells mediates mitochondrial quality control to restore chemotherapy-induced damage in ovarian granulosa cells

The basic principle of chemotherapy is to attack cells with fast growth, and cancer cells are targeted by anticancer drugs because they have a faster growth rate than normal cells. High doses of anticancer drugs may cause an irreversible decline in reproductive capacity, and novel approaches for fertility preservation and/or restoration after anticancer treatment are urgently needed. Here, we provide important insights into the recovery of human reproductive cells damaged by chemotherapy. We performed a detailed screening of the cytokines of various human mesenchymal stem cells (hMSCs) to select superior MSCs. Also, we analyzed the Ovarian granulosa cell (OGC)-)-specific functions for restoring function, apoptosis, and mitochondrial functions to confirm the recovery mechanism in damaged OGCs. As a result, we demonstrated that conditioned media (CM) of Umbilical cord mesenchymal stem cells (UC-MSCs) could restore the functions of damaged OGCs primarily through antiapoptotic and antioxidant effects. Furthermore, CM changed the phenotype of damaged OGCs to an energetic status by restoring mitochondrial function and enhanced the mitochondrial metabolic activity decreased by chemotherapy. Finally, we demonstrated that the restoration of mitochondrial function in damaged OGCs was mediated through mitochondrial autophagy (mitophagy). Our findings offer new insights into the potential of stem cell-based therapy for fertility preservation and/or restoration in female cancer patients.

Stem cells derived from human exfoliated deciduous teeth-based media in a rat root resorption model

OBJECTIVE

Root resorption may occur during orthodontic treatment. Herein, we investigated the effect of a culture supernatant of stem cells derived from human exfoliated deciduous teeth on root resorption.

DESIGN

Twelve 8-week-old male Sprague-Dawley rats were used, and their maxillary first molars were pulled with excessive orthodontic force to induce root resorption. On days 1 and 7 after traction initiation, stem cells derived from human exfoliated deciduous teeth and alpha minimum essential medium (control group) were administered. After 14 days, the maxillary bone was evaluated for tooth movement. The expression of osteoprotegerin, receptor activator of nuclear factor κB ligand, tumor necrosis factor α, interleukin 1β, interleukin 6, and interleukin 17 was evaluated on the compression side and tension side.

RESULTS

No significant difference in tooth movement was observed between the two groups. Root resorption decreased in the group administered the culture supernatant compared with in the control. Immunohistochemical staining revealed increased osteoprotegerin expression and decreased receptor activators for nuclear factor κB ligand, tumor necrosis factor α, interleukin 1β, interleukin 6, and interleukin 17 on the compression side and tension side.

CONCLUSIONS

Administration of stem cells derived from human exfoliated deciduous teeth affected the expression of osteoprotegerin, receptor activator of nuclear factor κB ligand, tumor necrosis factor α, interleukin 1β, interleukin 6 and interleukin 17; hence, these stem cells may inhibit root resorption by regulating their expression.

The Lower in Vivo Osteogenicity of Adipose Tissue-Derived Stem Cells Correlates with a Higher Innate Immune Response

Adipose tissue-derived mesenchymal stem cells (ATSCs) have been used as an alternative to bone marrow-derived mesenchymal stem cells (BMSCs) for bone tissue engineering applications. The ability of ATSCs to promote new bone formation remains lower than that of BMSCs. This study aimed to investigate the mechanisms underlying osteogenicity differences between human ATSCs and BMSCs in ceramic constructs, focusing on the effects of inflammation on this process. In contrast to ATSC-containing constructs, which did not induce bone formation in an ectopic mouse model, BMSC constructs consistently did so. Gene expression analysis revealed that human BMSCs, concomitantly with host murine progenitors, differentiated into the osteogenic lineage early post-implantation. In contrast, ATSCs differentiated later, when few implanted viable cells remained post-implantation, while the host murine cells did not differentiate. Comparison of the inflammatory profile in the cell constructs indicated concomitant upregulation of some human and murine inflammatory genes in the ATSC-constructs compared to the BMSC-constructs during the first-week post-implantation. The high level of chemokine production by the ATSCs was confirmed at the gene and protein levels before implantation. The immune cell recruitment within the constructs was then explored post-implantation. Higher numbers of TRAP-/ MRC1 (CD206) + multinucleated giant cells, NOS2 + M1, and ARG1 + M2 macrophages were present in the ATSC constructs than in the BMSC constructs. These results proved that ATSCs are a transient source of inflammatory cytokines promoting a transient immune response post-implantation; this milieu correlates with impaired osteogenic differentiation of both the implanted ATSCs and the host osteoprogenitor cells.

Immunity-and-matrix-regulatory cells enhance cartilage regeneration for meniscus injuries: a phase I dose-escalation trial

Immunity-and-matrix-regulatory cells (IMRCs) derived from human embryonic stem cells have unique abilities in modulating immunity and regulating the extracellular matrix, which could be mass-produced with stable biological properties. Despite resemblance to mesenchymal stem cells (MSCs) in terms of self-renew and tri-lineage differentiation, the ability of IMRCs to repair the meniscus and the underlying mechanism remains undetermined. Here, we showed that IMRCs demonstrated stronger immunomodulatory and pro-regenerative potential than umbilical cord MSCs when stimulated by synovial fluid from patients with meniscus injury. Following injection into the knees of rabbits with meniscal injury, IMRCs enhanced endogenous fibrocartilage regeneration. In the dose-escalating phase I clinical trial (NCT03839238) with eighteen patients recruited, we found that intra-articular IMRCs injection in patients was safe over 12 months post-grafting. Furthermore, the effective results of magnetic resonance imaging (MRI) of meniscus repair and knee functional scores suggested that 5 × 107 cells are optimal for meniscus injury treatment. In summary, we present the first report of a phase I clinical trial using IMRCs to treat meniscus injury. Our results demonstrated that intra-articular injection of IMRCs is a safe and effective therapy by providing a permissive niche for cartilage regeneration.

The role of toll-like receptors in orchestrating osteogenic differentiation of mesenchymal stromal cells and osteoimmunology

Osteoimmunology is a concept involving molecular and cellular crosstalk between the skeletal and immune systems. Toll-like receptors (TLRs) are widely expressed both on mesenchymal stromal cells (MSCs), the hematopoietic cells, and immune cells in the osteogenic microenvironment for bone development or repair. TLRs can sense both exogenous pathogen-associated molecular patterns (PAMPs) derived from microorganisms, and damage-associated molecular patterns (DAMPs) derived from normal cells subjected to injury, inflammation, or cell apoptosis under physiological or pathological conditions. Emerging studies reported that TLR signaling plays an important role in bone remodeling by directly impacting MSC osteogenic differentiation or osteoimmunology. However, how to regulate TLR signaling is critical and remains to be elucidated to promote the osteogenic differentiation of MSCs and new bone formation for bone tissue repair. This review outlines distinct TLR variants on MSCs from various tissues, detailing the impact of TLR pathway activation or inhibition on MSC osteogenic differentiation. It also elucidates TLR pathways' interplay with osteoclasts, immune cells, and extracellular vesicles (EVs) derived from MSCs. Furthermore, we explore biomaterial-based activation to guide MSCs' osteogenic differentiation. Therefore, understanding TLRs' role in this context has significant implications for advancing bone regeneration and repair strategies.

Bone marrow mesenchymal stem cells' osteogenic potential: superiority or non-superiority to other sources of mesenchymal stem cells?

Skeletal problems are an increasing issue due to the increase in the global aging population. Different statistics reports show that today, the global population is aging that results in skeletal problems, increased health system costs, and even higher mortality associated with skeletal problems. Common treatments such as surgery and bone grafts are not always effective and in some cases, they can even cause secondary problems such as infections or improper repair. Cell therapy is a method that can be utilized along with common treatments independently. Mesenchymal stem cells (MSCs) are a very important and efficient source in terms of different diseases, especially bone problems. These cells are present in different tissues such as bone marrow, adipose tissue, umbilical cord, placenta, dental pulp, peripheral blood, amniotic fluid and others. Among the types of MSCs, bone marrow mesenchymal stem cells (BMMSCs) are the most widely used source of these cells, which have appeared to be very effective and promising in terms of skeletal diseases, especially compared to the other sources of MSCs. This study focuses on the specific potential and content of BMMSCs from which the specific capacity of these cells originates, and compares their osteogenic potential with other types of MSCs, and also the future directions in the application of BMMSCs as a source for cell therapy.

Progress in Regenerative Medicine: Exploring Autologous Platelet Concentrates and Their Clinical Applications

The goal of regenerative medicine is to achieve tissue regeneration. In the past, commonly used techniques included autologous or allogeneic transplantation and stem cell therapy, which have limitations, such as a lack of donor sites in the case of autologous transplantation and the invasiveness of stem cell harvesting. In recent years, research has, therefore, focused on new and less invasive strategies to achieve tissue regeneration. A step forward in this direction has been made with the development of autologous platelet concentrates (APCs), which are derived from the patient's own blood. They can be classified into three generations: platelet-rich plasma (PRP), platelet-rich fibrin (PRF), and concentrated growth factors (CGFs). These APCs have different structural characteristics, depending on the distinctive preparation method, and contain platelets, leukocytes, and multiple growth factors, including those most involved in regenerative processes. The purpose of this review is to clarify the most used techniques in the field of regenerative medicine in recent years, comparing the different types of APCs and analyzing the preparation protocols, the composition of the growth factors, the level of characterization achieved, and their clinical applications to date.

Fortifying angiogenic efficacy of conditioned media using phototoxic-free blue light for wound healing

We used a blue organic light-emitting diode (bOLED) to increase the paracrine factors secreted from human adipose-derived stem cells (hADSCs) for producing conditioned medium (CM). Our results showed that while the bOLED irradiation promotes a mild-dose reactive oxygen generation that enhances the angiogenic paracrine secretion of hADSCs, it does not induce phototoxicity. The bOLED enhances paracrine factors via a cell-signaling mechanism involving hypoxia-inducible factor 1 alpha. This study demonstrated that the CM resulting from bOLED treatment shows improved therapeutic effects on mouse wound-healing models. This method contributes to overcoming the barriers to stem-cell therapies, including the toxicity and low yields from other methods such as nanoparticles, synthetic polymers, and even cell-derived vesicles.

Hopes and opportunities of stem cells from human exfoliated deciduous teeth (SHED) in cartilage tissue regeneration

Cartilage lesions are common conditions, affecting elderly and non-athletic populations. Despite recent advances, cartilage regeneration remains a major challenge today. The absence of an inflammatory response following damage and the inability of stem cells to penetrate into the healing site due to the absence of blood and lymph vessels are assumed to hinder joint repair. Stem cell-based regeneration and tissue engineering have opened new horizons for treatment. With advances in biological sciences, especially stem cell research, the function of various growth factors in the regulation of cell proliferation and differentiation has been established. Mesenchymal stem cells (MSCs) isolated from different tissues have been shown to increase into therapeutically relevant cell numbers and differentiate into mature chondrocytes. As MSCs can differentiate and become engrafted inside the host, they are considered suitable candidates for cartilage regeneration. Stem cells from human exfoliated deciduous teeth (SHED) provide a novel and non-invasive source of MSCs. Due to their simple isolation, chondrogenic differentiation potential, and minimal immunogenicity, they can be an interesting option for cartilage regeneration. Recent studies have reported that SHED-derived secretome contains biomolecules and compounds that efficiently promote regeneration in damaged tissues, including cartilage. Overall, this review highlighted the advances and challenges of cartilage regeneration using stem cell-based therapies by focusing on SHED.

The potential therapeutic role of extracellular vesicles in critical-size bone defects: Spring of cell-free regenerative medicine is coming

In recent years, the incidence of critical-size bone defects has significantly increased. Critical-size bone defects seriously affect patients' motor functions and quality of life and increase the need for additional clinical treatments. Bone tissue engineering (BTE) has made great progress in repairing critical-size bone defects. As one of the main components of bone tissue engineering, stem cell-based therapy is considered a potential effective strategy to regenerate bone tissues. However, there are some disadvantages including phenotypic changes, immune rejection, potential tumorigenicity, low homing efficiency and cell survival rate that restrict its wider clinical applications. Evidence has shown that the positive biological effects of stem cells on tissue repair are largely mediated through paracrine action by nanostructured extracellular vesicles (EVs), which may overcome the limitations of traditional stem cell-based treatments. In addition to stem cell-derived extracellular vesicles, the potential therapeutic roles of nonstem cell-derived extracellular vesicles in critical-size bone defect repair have also attracted attention from scholars in recent years. Currently, the development of extracellular vesicles-mediated cell-free regenerative medicine is still in the preliminary stage, and the specific mechanisms remain elusive. Herein, the authors first review the research progress and possible mechanisms of extracellular vesicles combined with bone tissue engineering scaffolds to promote bone regeneration via bioactive molecules. Engineering modified extracellular vesicles is an emerging component of bone tissue engineering and its main progression and clinical applications will be discussed. Finally, future perspectives and challenges of developing extracellular vesicle-based regenerative medicine will be given. This review may provide a theoretical basis for the future development of extracellular vesicle-based biomedicine and provide clinical references for promoting the repair of critical-size bone defects.

Applications of regenerative techniques in adult orthodontics

Management of the growing adult orthodontic patient population must contend with challenges particular to orthodontic treatment in adults. These include a limited rate of tooth movement, increased incidence of periodontal complications, higher risk of iatrogenic root resorption and pulp devitalisation, resorbed edentulous ridges, and lack of growth potential. The field of regenerative dentistry has evolved numerous methods of manipulating cellular and molecular processes to rebuild functional oral and dental tissues, and research continues to advance our understanding of stem cells, signalling factors that stimulate repair and extracellular scaffold interactions for the purposes of tissue engineering. We discuss recent findings in the literature to synthesise our understanding of current and prospective approaches based on biological repair that have the potential to improve orthodontic treatment outcomes in adult patients. Methods such as mesenchymal stem cell transplantation, biomimetic scaffold manipulation, and growth factor control may be employed to overcome the challenges described above, thereby reducing adverse sequelae and improving orthodontic treatment outcomes in adult patients. The overarching goal of such research is to eventually translate these regenerative techniques into clinical practice, and establish a new gold standard of safe, effective, autologous therapies.

Autogenous dentin combined with mesenchymal stromal cells as an alternative alveolar bone graft: an in vivo study

OBJECTIVE

Considering the chemical and structural properties of dentin, this study was aimed at evaluating the effect of dentin matrix alone or combined with mesenchymal stromal cells (MSC) on postextraction alveolar bone regeneration.

MATERIAL AND METHODS

Wistar rats were subjected to tooth extraction with osteotomy and allocated into groups according to the graft inserted: (1) Gelita-Spon^®, (2) Bio-Oss^®, (3) Dentin, (4) MSC, (5) Dentin/MSC, and (6) Control. Maxillae were analyzed by means of hematoxylin and eosin (H&E) staining, immunohistochemical (IHC) analysis, microcomputed tomography (micro-CT), and scanning electron microscopy (SEM). Serum levels of calcium and phosphorus were quantified.

RESULTS

The Bio-Oss group showed less bone than Gelita-Spon and Dentin/MSC; no other significant differences were seen in H&E analysis. The Bio-Oss group showed higher expression of collagen type I compared to the Dentin and Dentin/MSC groups and also higher osteocalcin expression than the Dentin/MSC group. There was a tendency of higher expression of osteopontin in the MSC, Dentin, and Dentin/MSC groups and higher VEGF in the MSC group. On micro-CT analysis, the Bio-Oss and the Dentin/MSC groups exhibited greater bone volume than the Control. Serum calcium and phosphorus levels did not significantly differ between the groups. SEM analysis depicted particles of Bio-Oss and dentin in the respective groups, as well as significant cellularity in the MSC group.

CONCLUSION

Autogenous nondemineralized dentin is an alternative for alveolar bone grafting, which can be improved by combination with MSC.

CLINICAL RELEVANCE

This work provides support for the clinical applicability of dentin graft alone or combined with MSC.

Engineering exosomes for bone defect repair

Currently, bone defect repair is still an intractable clinical problem. Numerous treatments have been performed, but their clinical results are unsatisfactory. As a key element of cell-free therapy, exosome is becoming a promising tool of bone regeneration in recent decades, because of its promoting osteogenesis and osteogenic differentiation function in vivo and in vitro. However, low yield, weak activity, inefficient targeting ability, and unpredictable side effects of natural exosomes have limited the clinical application. To overcome the weakness, various approaches have been applied to produce engineering exosomes by regulating their production and function at present. In this review, we will focus on the engineering exosomes for bone defect repair. By summarizing the exosomal cargos affecting osteogenesis, the strategies of engineering exosomes and properties of exosome-integrated biomaterials, this work will provide novel insights into exploring advanced engineering exosome-based cell-free therapy for bone defect repair.

Hsp20 Promotes Endothelial Progenitor Cell Angiogenesis via Activation of PI3K/Akt Signaling Pathway under Hypoxia

BACKGROUND

Mandibular distraction osteogenesis (MDO) is a kind of endogenous tissue engineering technology that lengthens the jaw and opens airway so that a patient can breathe safely and comfortably on his or her own. Endothelial progenitor cells (EPCs) are crucial for MDO-related angiogenesis. Moreover, emerging evidence suggests that heat shock protein 20 (Hsp20) modulates angiogenesis under hypoxic conditions. However, the specific role of Hsp20 in EPCs, in the context of MDO, is not yet known. The aim of this study was to explore the expression of Hsp20 during MDO and the effects of Hsp20 on EPCs under hypoxia.

METHODS

Mandibular distraction osteogenesis and mandibular bone defect (MBD) canine model were established. The expression of CD34, CD133, HIF-1α, and Hsp20 in callus was detected by immunofluorescence on day 14 after surgery. Canine bone marrow EPCs were cultured, with or without optimal cobalt chloride (CoCl2) concentration. Hypoxic effects, caused by CoCl2, were evaluated by means of the cell cycle, cell apoptosis, transwell cell migration, and tube formation assays. The Hsp20/KDR/PI3K/Akt expression levels were evaluated via immunofluorescence, RT-qPCR, and western blot. Next, EPCs were incorporated with either Hsp20-overexpression or Hsp20-siRNA lentivirus. The resulting effects were evaluated as described above.

RESULTS

CD34, CD133, HIF-1α, and Hsp20 were displayed more positive in the callus of MDO compared with MBD. In addition, hypoxic conditions, generated by 0.1 mM CoCl2, in canine EPCs, accelerated cell proliferation, migration, tube formation, and Hsp20 expression. Hsp20 overexpression in EPCs significantly stimulated cell proliferation, migration, and tube formation, whereas Hsp20 inhibition produced the opposite effect. Additionally, the molecular mechanism was partly dependent on the KDR/PI3K/Akt pathway.

CONCLUSION

In summary, herein, we present a novel mechanism of Hsp20-mediated regulation of canine EPCs via Akt activation in a hypoxic microenvironment.

Effects of Human Deciduous Dental Pulp-Derived Mesenchymal Stem Cell-Derived Conditioned Medium on the Metabolism of HUVECs, Osteoblasts, and BMSCs

In this study, we assessed the effects of human deciduous dental pulp-derived mesenchymal stem cell-derived conditioned medium (SHED-CM) on the properties of various cell types. The effects of vascular endothelial growth factor (VEGF) in SHED-CM on the luminal architecture, proliferative ability, and angiogenic potential of human umbilical vein endothelial cells (HUVECs) were determined. We also investigated the effects of SHED-CM on the proliferation of human-bone-marrow mesenchymal stem cells (hBMSCs) and mouse calvarial osteoblastic cells (MC3T3-E1) as well as the expression of ALP, OCN, and RUNX2. The protein levels of ALP were examined using Western blot analysis. VEGF blockade in SHED-CM suppressed the proliferative ability and angiogenic potential of HUVECs, indicating that VEGF in SHED-CM contributes to angiogenesis. The culturing of hBMSCs and MC3T3-E1 cells with SHED-CM accelerated cell growth and enhanced mRNA expression of bone differentiation markers. The addition of SHED-CM enhanced ALP protein expression in hBMSCs and MT3T3-E1 cells compared with that of the 0% FBS group. Furthermore, SHED-CM promoted the metabolism of HUVECs, MC3T3-E1 cells, and hBMSCs. These findings indicate the potential benefits of SHED-CM in bone tissue regeneration.

Extracellular vesicles derived from GMSCs stimulated with TNF-α and IFN-α promote M2 macrophage polarization via enhanced CD73 and CD5L expression

Immunoregulatory properties of mesenchymal stem cell (MSC)-derived extracellular vesicles (EVs) are promising. Gingival tissue-derived MSCs (GMSCs) have unique immunoregulatory capacity and secrete large amounts of EVs. Recent findings suggest that priming MSCs with inflammatory stimuli is an effective strategy for cell-free therapy. However, the precise mechanism by which the contents of EVs are customized has not been fully elucidated. Here, we show that EVs derived from GMSCs primed with a combination of two pro-inflammatory cytokines, tumor necrosis factor-α (TNF-α) and interferon-α (IFN-α), synergistically promote anti-inflammatory M2 macrophage polarization by increasing the expression of cluster of differentiation 73 (CD73) and CD5 molecule-like (CD5L). Expression of CD73 by TNF-α/IFN-α stimulation was transcriptionally upregulated by the activation of mammalian target of rapamycin signaling and nuclear translocation of hypoxia-inducible factor 1α in GMSCs. TNF-α/IFN-α treatment also significantly increased the expression of CD5L mRNA via the transcription factor DNA-binding protein inhibitor ID3 and liver X receptor. Interestingly, exosomal CD5L is a prerequisite for the synergistic effect of EVs-mediated M2 macrophage polarization. These results indicate that combined pre-licensing with TNF-α and IFN-α in GMSCs is ideal for enhancing the anti-inflammatory function of EVs, which contributes to the establishment of a therapeutic tool.

Mesenchymal Stem Cell-Derived Extracellular Vesicles for Bone Defect Repair

The repair of critical bone defects is a hotspot of orthopedic research. With the development of bone tissue engineering (BTE), there is increasing evidence showing that the combined application of extracellular vesicles (EVs) derived from mesenchymal stem cells (MSCs) (MSC-EVs), especially exosomes, with hydrogels, scaffolds, and other bioactive materials has made great progress, exhibiting a good potential for bone regeneration. Recent studies have found that miRNAs, proteins, and other cargo loaded in EVs are key factors in promoting osteogenesis and angiogenesis. In BTE, the expression profile of the intrinsic cargo of EVs can be changed by modifying the gene expression of MSCs to obtain EVs with enhanced osteogenic activity and ultimately enhance the osteoinductive ability of bone graft materials. However, the current research on MSC-EVs for repairing bone defects is still in its infancy, and the underlying mechanism remains unclear. Therefore, in this review, the effect of bioactive materials such as hydrogels and scaffolds combined with MSC-EVs in repairing bone defects is summarized, and the mechanism of MSC-EVs promoting bone defect repair by delivering active molecules such as internal miRNAs is further elucidated, which provides a theoretical basis and reference for the clinical application of MSC-EVs in repairing bone defects.

In vivo and in silico monitoring bone regeneration during distraction osteogenesis of the mouse femur

BACKGROUND AND OBJECTIVE

Distraction osteogenesis (DO) is a mechanobiological process of producing new bone by gradual and controlled distraction of the surgically separated bone segments. Mice have been increasingly used to study the role of relevant biological factors in regulating bone regeneration during DO. However, there remains a lack of in silico DO models and related mechano-regulatory tissue differentiation algorithms for mouse bone. This study sought to establish an in silico model based on in vivo experimental data to simulate the bone regeneration process during DO of the mouse femur.

METHODS

In vivo micro-CT, including time-lapse morphometry was performed to monitor the bone regeneration in the distraction gap. A 2D axisymmetric finite element model, with a geometry originating from the experimental data, was created. Bone regeneration was simulated with a fuzzy logic-based two-stage (distraction and consolidation) mechano-regulatory tissue differentiation algorithm, which was adjusted from that used for fracture healing based on our in vivo experimental data. The predictive potential of the model was further tested with varied distraction frequencies and distraction rates.

RESULTS

The computational simulations showed similar bone regeneration patterns to those observed in the micro-CT data from the experiment throughout the DO process. This consisted of rapid bone formation during the first 10 days of the consolidation phase, followed by callus reshaping via bone remodeling. In addition, the computational model predicted a faster and more robust bone healing response as the model's distraction frequency was increased, whereas higher or lower distraction rates were not conducive to healing.

CONCLUSIONS

This in silico model could be used to investigate basic mechanobiological mechanisms involved in bone regeneration or to optimize DO strategies for potential clinical applications.

Strontium doped mesoporous silica nanoparticles accelerate osteogenesis and angiogenesis in distraction osteogenesis by activation of Wnt pathway

Distraction osteogenesis (DO) is a powerful method to reconstruct segmented bone defects in the extremities. However, the main shortcoming of DO is the time-consuming consolidation period. To shorten the consolidation process, two biocompatible inorganic ions, strontium and silicone, were applied to design a biocompatible material to enhance bone mineralization ability during DO. In the present study, we integrated strontium into a one-pot synthesis of mesoporous silica nanoparticles to obtain strontium-doped mesoporous silica nanoparticles characterized by a homogeneous spherical morphology and uniform ion-releasing dynamics. This dual-ion releasing osteogenic and angiogenic drug delivery system was investigated to accelerate mineralization in DO. Osteogenesis was promoted by activation of the Wnt/β-catenin pathway, while bone resorption was inhibited by reduction of the osteoclastogenic factor RANKL/OPG. In addition, angiogenesis may have been enhanced indirectly by secretion of vascular endothelial growth factor (VEGF) from bone marrow stem cells. Therefore, strontium-doped mesoporous silica nanoparticles could be a potential biomaterial candidate for accelerating consolidation during DO.

Bone resorption improvement by conditioned medium of stem cells from human exfoliated deciduous teeth in ovariectomized mice

Stem cells from human exfoliated deciduous teeth (SHED) are mesenchymal stem cells with multipotent differentiation potential present in the dental pulp tissue of the deciduous teeth. SHED produce secretions that have immunomodulatory and regenerative functions. In the present study, we investigated the effects of SHED-conditioned medium (SHED-CM) on osteopenia induced by the ovariectomy (OVX) phenotype and its corresponding immunological changes. Eleven-week-old female C3H/HeJ mice were subjected to OVX. SHED-CM was administered intraperitoneally in these mice for 4 weeks starting immediately after OVX. SHED-CM improved bone mass after OVX and elevated the polarization of M2 macrophages in the peritoneal cavity. SHED-CM also suppressed an OVX-induced increase in interferon-γ (INF-γ) and interleukin-17 (IL-17) concentrations in the peripheral blood. Inhibition of M2 macrophage polarization with neutralizing antibodies did not reduce the concentration of IFN-γ and IL-17 in peripheral blood, which were increased by OVX, and did not alleviate osteopenia induced by the OVX phenotype. Mechanistically, these findings suggest that SHED-CM alleviates bone resorption by suppressing the activation of IFN-γ and IL-17 cells by polarizing M2 macrophages. In conclusion, our data indicate that SHED-CM contains active secretions that may have promising efficacy to ameliorate OVX-induced osteopenia. We suggest that SHED-CM has the potential to be used as a novel therapeutic agent to inhibit osteoporosis.

Immunomodulatory effects and mechanisms of distraction osteogenesis

Distraction osteogenesis (DO) is widely used for bone tissue engineering technology. Immune regulations play important roles in the process of DO like other bone regeneration mechanisms. Compared with others, the immune regulation processes of DO have their distinct features. In this review, we summarized the immune-related events including changes in and effects of immune cells, immune-related cytokines, and signaling pathways at different periods in the process of DO. We aim to elucidated our understanding and unknowns about the immunomodulatory role of DO. The goal of this is to use the known knowledge to further modify existing methods of DO, and to develop novel DO strategies in our unknown areas through more detailed studies of the work we have done.

Advances in mesenchymal stem cell conditioned medium-mediated periodontal tissue regeneration

Periodontitis is a chronic inflammatory disease that leads to the destruction of both soft and hard periodontal tissues. Complete periodontal regeneration in clinics using the currently available treatment approaches is still a challenge. Mesenchymal stem cells (MSCs) have shown promising potential to regenerate periodontal tissue in various preclinical and clinical studies. The poor survival rate of MSCs during in vivo transplantation and host immunogenic reaction towards MSCs are the main drawbacks of direct use of MSCs in periodontal tissue regeneration. Autologous MSCs have limited sources and possess patient morbidity during harvesting. Direct use of allogenic MSCs could induce host immune reaction. Therefore, the MSC-based indirect treatment approach could be beneficial for periodontal regeneration in clinics. MSC culture conditioned medium (CM) contains secretomes that had shown immunomodulatory and tissue regenerative potential in pre-clinical and clinical studies. MSC-CM contains a cocktail of growth factors, cytokines, chemokines, enzymes, and exosomes, extracellular vesicles, etc. MSC-CM-based indirect treatment has the potential to eliminate the drawbacks of direct use of MSCs for periodontal tissue regeneration. MSC-CM holds the tremendous potential of bench-to-bed translation in periodontal regeneration applications. This review focuses on the accumulating evidence indicating the therapeutic potential of the MSC-CM in periodontal regeneration-related pre-clinical and clinical studies. Recent advances on MSC-CM-based periodontal regeneration, existing challenges, and prospects are well summarized as guidance to improve the effectiveness of MSC-CM on periodontal regeneration in clinics.

The role of micro-vibration parameters in inflammatory responses of macrophages cultured on biphasic calcium phosphate ceramics and the resultant influence on osteogenic differentiation of mesenchymal stem cells

Although in vitro studies have shown that biomaterials and mechanical stimuli can mediate inflammatory responses or regulate osteogenesis of MSCs, the underlying behaviour of the inflammatory response of macrophages on biomaterials mediated by mechanical stimuli, which regulates osteogenesis, is relatively unknown. Thus, it is imperative to explore the role of bionic mechanical stimulation in the biomaterial-mediated inflammatory response of macrophages. In this study, we used osteoinductive biphasic calcium phosphate (BCP) ceramics as the model biomaterial and chose micro-vibration stimulation (MVs) with three variable parameters (frequency, magnitude, and time). Based on orthogonal experiments, nine combinations of MVs parameters were generated, and their effects on the BCP-mediated macrophage inflammatory response were investigated. MVs significantly affected the gene expression and cytokine secretion of macrophages grown on BCP ceramics and further influenced the behaviour of bone marrow mesenchymal stem cells (BMMSCs) in a paracrine manner. Moreover, frequency seemed to be the most dominant factor (compared with magnitude and time) in regulating the inflammatory response of macrophages. The optimal combination of MVs parameters (frequency 10 Hz, magnitude 0.45 g, and time 60 min) could induce a healing-associated M2 phenotype, as evidenced by the downregulated pro-inflammatory gene (Il-1β, and Tnf-α) expression, the upregulated anti-inflammatory gene (Il10) expression, and the inhibited pro-inflammatory cytokine (Il-1β and Tnf-α) secretion of macrophages grown on BCP ceramics, and its conditioned medium (CM) could further promote osteogenic differentiation of BMMSCs. These findings provide valuable insights into the mechanical stimulus-mediated macrophage inflammatory response and osteogenesis in the presence of osteoinductive BCP ceramics and allow accurate evaluation of the biological performance of biomaterials in vitro, in order to optimize bone substitute materials to achieve the desired clinical performance.

Effect of mesenchymal stem cells with platelet-rich plasma carriers on bone formation after rapid maxillary expansion: An Animal Study

OBJECTIVE

To evaluate the effect of bone mesenchymal stem cells (BMSCs) with or without platelet-rich plasma (PRP) carriers on sutural new bone formation after rapid palatal expansion (RPE).

SETTINGS AND SAMPLE POPULATION

Sixty male Wistar rats were used in this study.

MATERIAL AND METHODS

All samples were subjected to 50cN of palatal expansion force for 7 days followed by 3 weeks of the retention period. The experimental groups received a single-dose injection of the specified solution at the time of retainer placement (BMSCs, PRP, BMSCs+PRP, normal saline). BMSCs used in this study were marked with the green fluorescent protein (GFP). New bone formation (NBF) in the sutural area was evaluated by µCT and occlusal radiography. In addition, semi-quantitative analyses were performed on histology images to analyse the quality of sutural bone, connective tissue and vascularization. Immunohistochemistry analyses were conducted for osteocalcin and collagen type I proteins.

RESULTS

After the 21-day retention period, limited GFP marked cells were detected around the sutural area. Samples treated with BMSCs + PRP had the highest NBF and showed higher expression of collagen type I and osteocalcin.

CONCLUSION

Injecting BMSCs + PRP may increase sutural bone density significantly. However, injecting BMSCs or PRP carriers alone did not affect sutural bone density.

Assessment of the Bone Healing Process Mediated by Periosteum-Derived Mesenchymal Stem Cells' Secretome and a Xenogenic Bioceramic-An In Vivo Study in the Rabbit Critical Size Calvarial Defect Model

The mesenchymal stem cell (MSC) secretome has been considered an innovative therapeutic biological approach, able to modulate cellular crosstalk and functionality for enhanced tissue repair and regeneration. This study aims to evaluate the functionality of the secretome isolated from periosteum-derived MSCs, from either basal or osteogenic-induced conditions, in the healing of a critical size calvarial bone defect in the rabbit model. A bioceramic xenograft was used as the vehicle for secretome delivery, and the biological response to the established biocomposite system was assessed by clinical, histological, histomorphometric, and microtomographic analysis. A comparative analysis revealed that the osteogenic-induced secretome presented an increased diversity of proteins, with emphasis on those related to osteogenesis. Microtomographic and histological morphometric analysis revealed that bioceramic xenografts implanted with secretomes enhanced the new bone formation process, with the osteogenic-induced secretome inducing the highest bone tissue formation. The application of the MSC secretome, particularly from osteogenic-induced populations, may be regarded as an effective therapeutic approach to enhance bone tissue healing and regeneration.

Therapeutic mesenchymal stromal stem cells: Isolation, characterization and role in equine regenerative medicine and metabolic disorders

Mesenchymal stromal cells (MSC) have become a popular treatment modality in equine orthopaedics. Regenerative therapies are especially interesting for pathologies like complicated tendinopathies of the distal limb, osteoarthritis, osteochondritis dissecans (OCD) and more recently metabolic disorders. Main sources for MSC harvesting in the horse are bone marrow, adipose tissue and umbilical cord blood. While the acquisition of umbilical cord blood is fairly easy and non-invasive, extraction of bone marrow and adipose tissue requires more invasive techniques. Characterization of the stem cells as a result of any isolation method, is also a crucial step for the confirmation of the cells' stemness properties; thus, three main characteristics must be fulfilled by these cells, namely: adherence, expression of a series of well-defined differentiation clusters as well as pluripotency. EVs, resulting from the paracrine action of MSCs, also play a key role in the therapeutic mechanisms mediated by stem cells; MSC-EVs are thus largely implicated in the regulation of proliferation, maturation, polarization and migration of various target cells. Evidence that EVs alone represent a complex network 0involving different soluble factors and could then reflect biophysical characteristics of parent cells has fuelled the importance of developing highly specific techniques for their isolation and analysis. All these aspects related to the functional and technical understanding of MSCs will be discussed and summarized in this review.

Local administration of allogeneic or autologous bone marrow-derived mesenchymal stromal cells enhances bone formation similarly in distraction osteogenesis

BACKGROUND AIMS

Distraction osteogenesis (DO) is a surgical technique to promote bone regeneration that requires a long time for bone healing. Bone marrow-derived mesenchymal stromal cells (MSCs) have been applied to accelerate bone formation in DO. Allogeneic MSCs are attractive, as they could be ready to use in clinics. Whether allogeneic MSCs would have an effect similar to autologous MSCs with regard to promoting bone formation in DO is still unknown. This study compares the effect of autologous MSCs versus allogeneic MSCs on bone formation in a rat DO model.

METHODS

Rat bone marrow-derived MSCs were isolated, characterized and expanded in vitro. Adult rats were subjected to right tibia transverse osteotomy. On the third day of distraction, each rat received one injection of phosphate-buffered saline (PBS), autologous MSCs or allogeneic MSCs at the distraction site. Tibiae were harvested after 28 days of consolidation for micro-computed tomography examination, mechanical test and histological analysis.

RESULTS

Results showed that treatment with both allogeneic and autologous MSCs promoted bone formation, with significantly higher bone mass, mechanical properties and mineral apposition rate as well as expression of angiogenic and bone formation markers at the regeneration sites compared with the PBS-treated group. No statistical difference in bone formation was found between the allogeneic and autologous MSC treatment groups.

CONCLUSIONS

This study indicates that allogeneic and autologous MSCs have a similar effect on promoting bone consolidation in DO. MSCs from an allogeneic source could be used off-the-shelf with DO to achieve early bone healing.

Extracellular vesicles in bone and periodontal regeneration: current and potential therapeutic applications

Oral mesenchymal stem cells (MSCs) and their secretomes are considered important factors in the field of medical tissue engineering and cell free biotherapy due to their ease of access, differentiation potential, and successful therapeutic outcomes. Extracellular vesicles (EVs) and the conditioned medium (CM) from MSCs are gaining more attraction as an alternative to cell-based therapies due to the less ethical issues involved, and their easier acquisition, preservation, long term storage, sterilization, and packaging. Bone and periodontal regenerative ability of EVs and CM have been the focus of some recent studies. In this review, we looked through currently available literature regarding MSCs' EVs or conditioned medium and their general characteristics, function, and regenerative potentials. We will also review the novel applications in regenerating bone and periodontal defects.

Mesenchymal stem cells secretome: The cornerstone of cell-free regenerative medicine

Mesenchymal stem cells (MSCs) are the most frequently used stem cells in clinical trials due to their easy isolation from various adult tissues, their ability of homing to injury sites and their potential to differentiate into multiple cell types. However, the realization that the beneficial effect of MSCs relies mainly on their paracrine action, rather than on their engraftment in the recipient tissue and subsequent differentiation, has opened the way to cell-free therapeutic strategies in regenerative medicine. All the soluble factors and vesicles secreted by MSCs are commonly known as secretome. MSCs secretome has a key role in cell-to-cell communication and has been proven to be an active mediator of immune-modulation and regeneration both in vitro and in vivo. Moreover, the use of secretome has key advantages over cell-based therapies, such as a lower immunogenicity and easy production, handling and storage. Importantly, MSCs can be modulated to alter their secretome composition to better suit specific therapeutic goals, thus, opening a large number of possibilities. Altogether these advantages now place MSCs secretome at the center of an important number of investigations in different clinical contexts, enabling rapid scientific progress in this field.

Conditioned Medium from Canine Amniotic Membrane-Derived Mesenchymal Stem Cells Improved Dog Sperm Post-Thaw Quality-Related Parameters

Simple Summary

Mesenchymal stem cells and their derivatives are used in clinical studies for their anti-apoptotic, anti-oxidant, immunomodulatory, and regenerative properties. Their use in reproductive medicine is increasing as they have been proved to be beneficial for infertility treatment. Mesenchymal stem cells can secrete factors that influence biological processes in target tissues or cells; these factors are either directly secreted by the cells or mediated through their derivatives. Although the amniotic membrane is easy to obtain and is a good source of stem cells, clinical trials using amniotic membrane-derived mesenchymal stem cells are still uncommon, especially in reproductive medicine or artificial reproductive technologies. The objective of the present study was to demonstrate the effects of conditioned medium prepared from amniotic membrane-derived stem cells on dog sperm cryopreservation. Our results showed that 10% of the conditioned medium enhanced the quality-related parameters of frozen–thawed sperm cells because of the presence of antioxidants and growth factors in the medium, which probably protected spermatozoa during the freeze–thaw process. These results suggest that conditioned media prepared from amniotic membrane-derived mesenchymal stem cells might have clinical applications in assisted reproductive technologies.

Abstract

This study investigated the effects of conditioned medium (CM) from canine amniotic membrane-derived MSCs (cAMSCs) on dog sperm cryopreservation. For this purpose, flow cytometry analysis was performed to characterize cAMSCs. The CM prepared from cAMSCs was subjected to proteomic analysis for the identification of proteins present in the medium. Sperm samples were treated with freezing medium supplemented with 0%, 5%, 10%, and 15% of the CM, and kinetic parameters were evaluated after 4–6 h of chilling at 4 °C to select the best concentration before proceeding to cryopreservation. Quality-related parameters of frozen–thawed sperm were investigated, including motility; kinetic parameters; viability; integrity of the plasma membrane, chromatin, and acrosome; and mitochondrial activity. The results showed that 10% of the CM significantly enhanced motility, viability, mitochondrial activity, and membrane integrity (p < 0.05); however, the analysis of chromatin and acrosome integrity showed no significant differences between the treatment and control groups. Therefore, we concluded that the addition of 10% CM derived from cAMSC in the freezing medium protected dog sperm during the cryopreservation process.

Protective effects of stem cells from human exfoliated deciduous teeth derived conditioned medium on osteoarthritic chondrocytes

Treatment of osteoarthritis (OA) is still a major clinical challenge due to the limited inherent healing capacity of cartilage. Recent studies utilising stem cells suggest that the therapeutic benefits of these cells are mediated through the paracrine mechanism of bioactive molecules. The present study evaluates the regenerative effect of stem cells from human exfoliated deciduous teeth (SHED) conditioned medium (CM) on OA chondrocytes. The CM was collected after the SHED were cultured in serum-free medium (SFM) for 48 or 72 h and the cells were characterised by the expression of MSC and pluripotency markers. Chondrocytes were stimulated with interleukin-1β and treated with the CM. Subsequently, the expression of aggrecan, collagen type 2 (COL 2), matrix metalloproteinase-13 (MMP-13), nuclear factor-kB (NF-kB) and the level of inflammatory and anti-inflammatory markers were evaluated. SHED expressed mesenchymal stromal cell surface proteins but were negative for haematopoietic markers. SHED also showed protein expression of NANOG, OCT4 and SOX2 with differential subcellular localisation. Treatment of OA chondrocytes with CM enhanced anti-inflammation compared to control cells treated with SFM. Furthermore, the expression of MMP-13 and NF-kB was significantly downregulated in stimulated chondrocytes incubated in CM. The study also revealed that CM increased the expression of aggrecan and COL 2 in OA chondrocytes compared to SFM control. Both CM regenerate extracellular matrix proteins and mitigate increased MMP-13 expression through inhibition of NF-kB in OA chondrocytes due to the presence of bioactive molecules. The study underscores the potential of CM for OA treatment.

Conditioned media from mesenchymal stromal cells and periodontal ligament fibroblasts under cyclic stretch stimulation promote bone healing in mouse calvarial defects

BACKGROUND AIMS

When cells are exposed to stresses such as mechanical stimuli, they release growth factors and adapt to the surrounding environment H ere, we demonstrated that mechanical stimulation during culture affects the production of osteogenic and angiogenic factors.

METHODS

Human bone marrow derived mesenchymal stromal cells (hMSCs) and human periodontal ligament fibroblasts (HPLFs ) were cultured under cyclic stretch stimulation for 24 h. Collected of the cells and conditioned media (CM), the gene and protein expression levels of osteogenic and angiogenic factors were evaluated. CM was also evaluated for angiogenic activity and calc ification ability. In in vivo study, CM was administered to a mouse calvarial defect model and histologically and radiologically evaluated.

RESULTS

Quantitative real time polymerase chain reaction results showed that the expression of bone morphogenetic pro tein 2, 4 (BMP 2, 4), vascular endothelial growth factor A (VEGF A), and platelet derived growth factor AA (PDGF AA) was upregulated in the cyclic stretch stimulation group in comparison with the non stretch group in each cell type. Enzyme linked immunosor bent assay results revealed that the expression of BMP 2,4, VEGF A was upregulated in the cyclic stretch group in comparison with the non stretch group in each cell type. Only HPLFs showed significant difference in PDGF AA expression between the cyclic str etch and the non stretch group. Tube formation assay and Alizarin Red S staining results showed that angiogenic activity and calcification ability of CM was upregulated in the cyclic stretch stimulation group in comparison with the non stretch group in eac h cell type. CM was administered to the mouse calvarial defect model. Histological and radiological examination showed that the bone healing was promoted by CM from the cyclic stretch culture group. Immunohistological staining revealed that CM from cyclic stretch group have greater angiogenic effect than CM from the non stretch group.

CONCLUSIONS

These results indicate that osteogenesis was promoted by CM obtained under cyclic stretch stimulation through the increase of angiogenesis in the mouse calvarial defect model.

[Bone segment transport for defects of the tibia : Technique with unilateral fixator and plate]

BACKGROUND

Various options are available for treatment of bone defects of the tibia. Bone segment transport is carried out relatively rarely because the surgical technique is not easy and there is a learning curve.

OBJECTIVE

This article gives an overview of the history, indications, planning and surgical technique of bone segment transport of the tibia.

MATERIAL AND METHODS

A technique using unilateral external fixation in combination with a locking plate osteosynthesis is described.

RESULTS

The technique and results are explained exemplified by a case report and in particular pitfalls during surgery and the aftercare concept are outlined.

CONCLUSION

Bone segment transport of the tibia using an external fixator and a locking plate is a reliable and practicable technique for treatment of bone defects of the tibia.

Effect of cAMP Signaling Regulation in Osteogenic Differentiation of Adipose-Derived Mesenchymal Stem Cells

The successful implementation of adipose-derived mesenchymal stem cells (ADSCs) in bone regeneration depends on efficient osteogenic differentiation. However, a literature survey and our own experience demonstrated that current differentiation methods are not effective enough. Since the differentiation of mesenchymal stem cells (MSCs) into osteoblasts and adipocytes can be regulated by cyclic adenosine monophosphate (cAMP) signaling, we investigated the effects of cAMP activator, forskolin, and inhibitor, SQ 22,536, on the early and late osteogenic differentiation of ADSCs cultured in spheroids or in a monolayer. Intracellular cAMP concentration, protein kinase A (PKA) activity, and inhibitor of DNA binding 2 (ID2) expression examination confirmed cAMP up- and downregulation. cAMP upregulation inhibited the cell cycle and protected ADSCs from osteogenic medium (OM)-induced apoptosis. Surprisingly, the upregulation of cAMP level at the early stages of osteogenic differentiation downregulated the expression of osteogenic markers RUNX2, Osterix, and IBSP, which was more significant in spheroids, and it is used for the more efficient commitment of ADSCs into preosteoblasts, according to the previously reported protocol. However, cAMP upregulation in a culture of ADSCs in spheroids resulted in significantly increased osteocalcin production and mineralization. Thus, undifferentiated and predifferentiated ADSCs respond differently to cAMP pathway stimulation in terms of osteogenesis, which might explain the ambiguous results from the literature.

Effectiveness of mesenchymal stem cell-conditioned medium in bone regeneration in animal and human models: a systematic review and meta-analysis

Background

Given the limitations of current therapies for the reconstruction of bone defects, regenerative medicine has arisen as a new therapeutic strategy along with mesenchymal stem cells (MSCs), which, because of their osteogenic potential and immunomodulatory properties, have emerged as a promising alternative for the treatment of bone injuries. In vivo studies have demonstrated that MSCs have a positive effect on regeneration due to their secretion of cytokines and growth factors that, when collected in conditioned medium (MSC-CM) and applied to an injured tissue, can modulate and promote the formation of new tissue.

Objective

To evaluate the effectiveness of application of conditioned medium derived from mesenchymal stem cells in bone regeneration in animal and human models.

Methods

We conducted a systematic review with a comprehensive search through February of 2018 using several electronic databases (MEDLINE, EMBASE, SCOPUS, CENTRAL (Ovid), and LILACS), and we also used the “snowballing technique”. Articles that met the inclusion criteria were selected through abstract review and subsequent assessment of the full text. We assessed the risk of bias with the SYRCLE and Cochrane tools, and three meta-analyses were performed.

Results

We included 21 articles, 19 of which used animal models and 2 of which used human models. In animal models, the application of MSC-CM significantly increased the regeneration of bone defects in comparison with control groups. Human studies reported early mineralization in regenerated bones, and no bone resorption, inflammation, nor local or systemic alterations were observed in any case. The meta-analysis showed an overall favorable effect of the application of MSC-CM.

Conclusions

The application of MSC-CM to bone defects has a positive and favorable effect on the repair and regeneration of bone tissue, particularly in animal models. It is necessary to perform additional studies to support the application of MSC-CM in clinical practice.

Replicative senescence in MSCWJ-1 human umbilical cord mesenchymal stem cells is marked by characteristic changes in motility, cytoskeletal organization, and RhoA localization

Here, we document changes in cell motility and organization of the contractile apparatus of human umbilical cord Wharton's jelly mesenchymal stem cells (MSCWJ-1) in the process of replicative senescence. Colocalization dynamics of F-actin and actin-binding proteins (myosin-9, α-actinin-4, RhoA) were examined in the MSCWJ-1 cell line. The results show that nuclear-cytoplasmic redistribution of RhoA occurs during replicative senescence, with maximal RhoA/nucleus colocalization evident at passage 15. At that time point, decreases in colocalization, namely myosin-9/F-actin and α-actinin-4/F-actin, were seen and myosin-9 was found in cytosolic extracts in the assembly-incompetent form. Using an automated intravital confocal cytometry system and quantitative analysis of MSCWJ-1 movements, we found that changes in cytoskeletal organization correlate with cell motility characteristics over a time period from passages 9 to 38. The factors examined (cytoskeleton structure, cell motility) indicate that the process by which cells transition to replicative senescence is best represented as three stages. The first stage lasts from cell culture isolation to passage 15 and is characterized by: accumulation of actin-binding proteins in assembly-incompetent forms; nuclear RhoA accumulation; and an increase in movement tortuosity. The second stage extends from passages 15 to 28 and is characterized by: an increase in the structural integrity of the actin cytoskeleton; exit of RhoA and alpha-actinin-4 from the nucleus; and a decrease in path tortuosity. The third stage extends from passage 28 to 38 and is marked by: a plateau in actin cytoskeleton structural integrity; significant decreases in nuclear RhoA levels; and decreases in cell speed.

Administration of allogeneic mesenchymal stem cells in lengthening phase accelerates early bone consolidation in rat distraction osteogenesis model

BACKGROUND

Distraction osteogenesis (DO) is a surgical technique to promote bone regeneration which may require long duration for bone consolidation. Bone marrow-derived mesenchymal stem cells (MSCs) have been applied to accelerate bone formation in DO. However, the optimal time point for cell therapy in DO remains unknown. This study sought to determine the optimal time point of cell administration to achieve early bone consolidation in DO. We hypothesized that the ratio of circulating MSCs to peripheral mononuclear cells and the level of cytokines in serum might be indicators for cell administration in DO.

METHODS

Unilateral tibial osteotomy with an external fixator was performed in adult Sprague Dawley rats. Three days after osteotomy, the tibia was lengthened at 0.5 mm/12 h for 5 days. At first, 5 rats were used to analyze the blood components at 6 different time points (3 days before lengthening, on the day lengthening began, or 3, 6, 10, or 14 days after lengthening began) by sorting circulating MSCs and measuring serum levels of stromal cell-derived factor 1 (SDF-1) and interleukin 1β. Then, 40 rats were used for cell therapy study. A single dose of 5 × 10⁵ allogeneic MSCs was locally injected at the lengthening site on day 3, 6, or 10 after lengthening began, or 3 doses of MSCs were injected at the three time points. Sequential X-ray radiographs were taken weekly. Endpoint examinations included micro-computed tomography analysis, mechanical testing, histomorphometry, and histology.

RESULTS

The number of circulating MSCs and serum level of SDF-1 were significantly increased during lengthening, and then decreased afterwards. Single injection of MSCs during lengthening phase (on day 3, but not day 6 or 10) significantly increased bone volume fraction, mechanical maximum loading, and bone mineralization of the regenerate. Triple injections of MSCs at three time points also significantly increased bone volume and maximum loading of the regenerates.

CONCLUSION

This study demonstrated that bone consolidation could be accelerated by a single injection of MSCs during lengthening when the ratio of peripheral MSCs to mononuclear cells and the serum SDF-1 presented at peak levels concurrently, suggesting that day 3 after lengthening began may be the optimal time point for cell therapy to promote early bone consolidation.

Inflammatory macrophages facilitate mechanical stress-induced osteogenesis

Mechanical stress has been recognized as a key inducer of bone regeneration in bone damage, which is experimentally mimicked by distraction osteogenesis (DO), a bone-regenerative process induced by post-osteotomy distraction of the surrounding vascularized bone segments, and realized by new bone formation within the distraction gap. The mechanisms that underlie the DO-induced bone regeneration remain poorly understood and a role of macrophages in the process has been inadequately studied. Here, in a mouse model of DO, we showed significant increase in macrophages in the regeneration area. Moreover, in a loss-of-function approach by depleting inflammatory macrophages, the bone regeneration was compromised by assessment of histology and molecular biology. Thus, our study demonstrates the necessary participation of inflammatory macrophages in the process of DO-induced bone regeneration, and suggests that targeting inflammatory macrophages may help to improve clinical bone repair.

Extracellular Vesicles from Mesenchymal Stem Cells as Novel Treatments for Musculoskeletal Diseases

Mesenchymal stem/stromal cells (MSCs) represent a promising therapy for musculoskeletal diseases. There is compelling evidence indicating that MSC effects are mainly mediated by paracrine mechanisms and in particular by the secretion of extracellular vesicles (EVs). Many studies have thus suggested that EVs may be an alternative to cell therapy with MSCs in tissue repair. In this review, we summarize the current understanding of MSC EVs actions in preclinical studies of (1) immune regulation and rheumatoid arthritis, (2) bone repair and bone diseases, (3) cartilage repair and osteoarthritis, (4) intervertebral disk degeneration and (5) skeletal muscle and tendon repair. We also discuss the mechanisms underlying these actions and the perspectives of MSC EVs-based strategies for future treatments of musculoskeletal disorders.

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.

Bovine pericardium membrane, gingival stem cells, and ascorbic acid: a novel team in regenerative medicine

Recently, the development and the application of 3D scaffold able to promote stem cell differentiation represented an essential field of interest in regenerative medicine. In particular, functionalized scaffolds improve bone tissue formation and promote bone defects repair. This research aims to evaluate the role of ascorbic acid (AS) supplementation in an in vitro model, in which a novel 3D-scaffold, bovine pericardium collagen membrane called BioRipar (BioR) was functionalized with human Gingival Mesenchymal Stem Cells (hGMSCs). As extensively reported in the literature, AS is an essential antioxidant molecule involved in the extracellular matrix secretion and in the osteogenic induction. Specifically, hGMSCs were seeded on BioR and treated with 60 and 90 μg/mL of AS in order to assess their growth behavior, the expression of bone specific markers involved in osteogenesis (runt-related transcription factor 2, RUNX2; collagen1A1, COL1A1; osteopontin, OPN; bone morphogenetic protein2/4, BMP2/4), and de novo deposition of calcium. The expression of COL1A1, RUNX2, BMP2/4 and OPN was evaluated by RT-PCR, Western blotting and immunocytochemistry, and proved to be upregulated. Our results demonstrate that after three weeks of treatment AS at 60 and 90 μg/mL operates as an osteogenic inductor in hGMSCs. These data indicate that the AS supplementation produces an enhancement of osteogenic phenotype commitment in an in vitro environment. For this reason, AS could represent a valid support for basic and translational research in tissue engineering and regenerative medicine.

Stem Cells for Bone Regeneration: Current State and Future Directions

Mesenchymal stem cells (MSCs) are capable of differentiating into osteoblasts, chondrocytes, and adipocytes, each of which is important for musculoskeletal tissue regeneration and repair. Reconstruction and healing of bony defects remains a major clinical challenge. Even as surgical practices advance, some severe cases of bone loss do not yield optimal recovery results. New techniques involving implantation of stem cells and tissue-engineered scaffolds are being developed to help improve bone and cartilage repair. The invasiveness and low yield of harvesting MSCs from the bone marrow (BMSCs) has led to the investigation of alternatives, including adipose-derived mesenchymal stem cells (ASCs). A review of the literature yielded several studies concerning the use of BMSCs and ASCs for the treatment of bone defects in both in vitro and in vivo models. Although both ASCs and BMSCs have demonstrated bone regenerative capabilities, BMSCs have outperformed ASCs in vitro. Despite these in vitro study findings, in vivo study results remain variable. Analysis of the literature seems to conclude there is no significant difference between bone regeneration using ASCs or BMSCs in vivo. Improved study design and standardization may enhance the application of these studies to patient care in the clinical setting.

Regeneration of large bone defects using mesoporous silica coated magnetic nanoparticles during distraction osteogenesis

Distraction osteogenesis (DO) represents an effective but undesirably lengthy treatment for large bone defects. Both magnetic nanoparticles and silicon have been shown to induce osteogenic differentiation of mesenchymal stem cells (MSCs), the key participant in bone regeneration. We herein synthesized mesoporous silica coated magnetic (Fe₃O₄) nanoparticles (M-MSNs) and evaluated its potential for acceleration of bone regeneration in a rat DO model. The M-MSNs exhibited good biocompatibility and remarkable capability in promoting the osteogenic differentiation of MSCs via the canonical Wnt/β-catenin pathway in vitro. More importantly, local injection of M-MSNs dramatically accelerated bone regeneration in a rat DO model according to the results of X-ray imaging, micro-CT, mechanical testing, histological examination, and immunochemical analysis. This study demonstrates the notable potential of M-MSNs in promoting bone regeneration during DO by enhancing the osteogenic differentiation of MSCs, paving the way for clinical translation of M-MSNs in DO to repair large bone defects.

Microfiber-Reinforced Composite Hydrogels Loaded with Rat Adipose-Derived Stem Cells and BMP-2 for the Treatment of Medication-Related Osteonecrosis of the Jaw in a Rat Model

Severe adverse reactions of bisphosphonates and anti-resorptive or anti-angiogenic medications, termed medication-related osteonecrosis of the jaw (MRONJ), have been reported. MRONJ are difficult to completely cure and could cause great pain to patients. Recent studies have shown that mesenchymal stem cell (MSC) therapies are effective for treating MRONJ, but the method of intravenous injection is unstable and increases the risk of producing tumors. In the present study, low-acyl gellan gum (LAGG) hydrogels were modified with hemicellulose polysaccharide microfibers (PMs) to improve the performance of supporting three-dimensional (3D) cell growth. LAGG-PM composite hydrogels were found to be nontoxic to rat adipose-derived stem cells (rADSCs) in vitro. The hydrogels also promoted the secretion of angiogenic factors, induced osteoclastogenesis by conditioned medium, and supported osteogenic marker expression after the addition of human bone morphogenetic protein-2 (BMP-2). Due to its injectability, the LAGG-PM composite hydrogel incorporated with rADSCs and BMP-2 could be applied into the MRONJ lesion site, which promoted mucosal recovery, bone tissue reconstruction, and osteoclastogenesis. This study confirms the potential applications of LAGG-PM composite hydrogels as 3D cell culture platforms and delivery vehicles for the treatment of MRONJ in a rat model.

Immune Modulation by Transplanted Calcium Phosphate Biomaterials and Human Mesenchymal Stromal Cells in Bone Regeneration

A wide variety of biomaterials have been developed as both stabilizing structures for the injured bone and inducers of bone neoformation. They differ in chemical composition, shape, porosity, and mechanical properties. The most extensively employed and studied subset of bioceramics are calcium phosphate materials (CaPs). These materials, when transplanted alongside mesenchymal stem cells (MSCs), lead to ectopic (intramuscular and subcutaneous) and orthotopic bone formation in preclinical studies, and effective fracture healing in clinical trials. Human MSC transplantation in pre-clinical and clinical trials reveals very low engraftment in spite of successful clinical outcomes and their therapeutic actions are thought to be primarily through paracrine mechanisms. The beneficial role of transplanted MSC could rely on their strong immunomodulatory effect since, even without long-term engraftment, they have the ability to alter both the innate and adaptive immune response which is critical to facilitate new bone formation. This study presents the current knowledge of the immune response to the implantation of CaP biomaterials alone or in combination with MSC. In particular the central role of monocyte-derived cells, both macrophages and osteoclasts, in MSC-CaP mediated bone formation is emphasized. Biomaterial properties, such as macroporosity and surface microstructure, dictate the host response, and the ultimate bone healing cascade. Understanding intercellular communications throughout the inflammation, its resolution and the bone regeneration phase, is crucial to improve the current therapeutic strategies or develop new approaches.

The effect of adipose-derived stem cells on enthesis healing after repair of acute and chronic massive rotator cuff tears in rats

BACKGROUND

Chronic massive rotator cuff tears heal poorly and often retear. This study investigated the effect of adipose-derived stem cells (ADSCs) and transforming growth factor-β3 (TGF-β3) delivered in 1 of 2 hydrogels (fibrin or gelatin methacrylate [GelMA]) on enthesis healing after repair of acute or chronic massive rotator cuff tears in rats.

METHODS

Adult male Lewis rats underwent bilateral transection of the supraspinatus and infraspinatus tendons with intramuscular injection of botulinum toxin A (n = 48 rats). After 8 weeks, animals received 1 of 8 interventions (n = 12 shoulders/group): (1) no repair, (2) repair only, or repair augmented with (3) fibrin, (4) GelMA, (5) fibrin + ADSCs, (6) GelMA + ADSCs, (7) fibrin + ADSCs + TGF-β3, or (8) GelMA + ADSCs + TGF-β3. An equal number of animals underwent acute tendon transection and immediate application of 1 of 8 interventions. Enthesis healing was evaluated 4 weeks after the repair by microcomputed tomography, histology, and mechanical testing.

RESULTS

Increased bone loss and reduced structural properties were seen in chronic compared with acute tears. Bone mineral density of the proximal humerus was higher in repairs of chronic tears augmented with fibrin + ADSCs and GelMA + ADSCs than in unrepaired chronic tears. Similar improvement was not seen in acute tears. No intervention enhanced histologic appearance or structural properties in acute or chronic tears.

CONCLUSIONS

Surgical repair augmented with ADSCs may provide more benefit in chronic tears compared with acute tears, although there was no added benefit to supplementing ADSCs with TGF-β3.

Conditioned media derived from mesenchymal stem cell cultures: The next generation for regenerative medicine

Recent studies suggest that the main driving force behind the therapeutic activity observed in mesenchymal stem cells (MSCs) are the paracrine factors secreted by these cells. These biomolecules also trigger antiapoptotic events to prevent further degeneration of the diseased organ through paracrine signalling mechanisms. In comparison with the normal physiological conditions, an increased paracrine gradient is observed within the peripheral system of diseased organs that enhances the migration of tissue-specific MSCs towards the site of infection or injury to promote healing. Thus, upon administration of conditioned media derived from mesenchymal stem cell cultures (MSC-CM) could contribute in maintaining the increased paracrine factor gradient between the diseased organ and the stem cell niche in order to speed up the process of recovery. Based on the principle of the paracrine signalling mechanism, MSC-CM, also referred as the secretome of the MSCs, is a rich source of the paracrine factors and are being studied extensively for a wide range of regenerative therapies such as myocardial infarction, stroke, bone regeneration, hair growth, and wound healing. This article highlights the current technological applications and advances of MSC-CM with the aim to appraise its future potential as a regenerative therapeutic agent.