The Use of Cocultured Mesenchymal Stem Cells with Tendon-Derived Stem Cells as a Better Cell Source for Tendon Repair

The current status of various preclinical therapeutic approaches for tendon repair

Tendons are fibroblastic structures that link muscle and bone. There are two kinds of tendon injuries, including acute and chronic. Each form of injury or deterioration can result in significant pain and loss of tendon function. The recovery of tendon damage is a complex and time-consuming recovery process. Depending on the anatomical location of the tendon tissue, the clinical outcomes are not the same. The healing of the wound process is divided into three stages that overlap: inflammation, proliferation, and tissue remodeling. Furthermore, the curing tendon has a high re-tear rate. Faced with the challenges, tendon injury management is still a clinical issue that must be resolved as soon as possible. Several newer directions and breakthroughs in tendon recovery have emerged in recent years. This article describes tendon injury and summarizes recent advances in tendon recovery, along with stem cell therapy, gene therapy, Platelet-rich plasma remedy, growth factors, drug treatment, and tissue engineering. Despite the recent fast-growing research in tendon recovery treatment, still, none of them translated to the clinical setting. This review provides a detailed overview of tendon injuries and potential preclinical approaches for treating tendon injuries.

Role of tendon-derived stem cells in tendon and ligament repair: focus on tissue engineer

This review offered a comprehensive analysis of tendon and ligament injuries, emphasizing the crucial role of tendon-derived stem cells (TDSCs) in tissue engineering as a potential solution for these challenging medical conditions. Tendon and ligament injuries, prevalent among athletes, the elderly, and laborers, often result in long-term disability and reduced quality of life due to the poor intrinsic healing capacity of these avascular structures. The formation of biomechanically inferior scar tissue and a high rate of reinjury underscore the need for innovative approaches to enhance and guide the regenerative process. This review delved into the complexities of tendon and ligament structure and function, types of injuries and their impacts, and the limitations of the natural repair process. It particularly focused on the role of TDSCs within the context of tissue engineering. TDSCs, with their ability to differentiate into tenocytes, are explored in various applications, including biocompatible scaffolds for cell tracking, co-culture systems to optimize tendon-bone healing, and graft healing techniques. The review also addressed the challenges of immunoreactivity post-transplantation, the importance of pre-treating TDSCs, and the potential of hydrogels and decellularized matrices in supporting tendon regeneration. It concluded by highlighting the essential roles of mechanical and molecular stimuli in TDSC differentiation and the current challenges in the field, paving the way for future research directions.

Achilles Tendinopathy Pathogenesis and Management: A Narrative Review

The Achilles tendon is the thickest and strongest tendon of the human body, and it is frequently injured during sports activity. The incidence of Achilles tendon pathologies has increased over recent decades, especially in the last few years, because of increased sports participation among the general population and due to the diffusion of competitive sports at a high level. Tendinopathies are common in athletes and in middle-aged overweight patients. The term "tendinopathy" refers to a condition characterised clinically by pain and swelling, with functional limitations of tendon and nearby structures, and consequently to chronic failure of healing response process. Tendinopathies can produce marked morbidity, and at present, scientifically validated management modalities are limited. Despite the constantly increasing interest and number of studies about Achilles tendinopathy (AT), there is still not a consensual point of view on which is the best treatment, and its management is still controversial. AT can be treated conservatively primarily, with acceptable results and clinical outcomes. When this approach fails, surgery should be considered. Several surgical procedures have been described for both conditions with a relatively high rate of success with few complications and the decision for treatment in patients with AT should be tailored on patient's needs and level of activity. The aim of this article is to give insights about the pathogenesis and most used and recent treatment options for AT.

Simvastatin promotes rat Achilles tendon-bone interface healing by promoting osteogenesis and chondrogenic differentiation of stem cells

To investigate the effect and mechanism of simvastatin on cell components of tendon-bone healing interface. The tendon-bone healing model was established by inserting the end of the Achilles tendon into the tibial tunnel on 24 rats, and simvastatin was used locally at the tendon-bone interface. Healing was evaluated at 8 weeks by mechanical testing, micro-CT, and qualitative histology including H&E, Toluidine blue, and immunohistochemical staining. In vitro, bone marrow stromal cells (BMSCs) and tendon-derived mesenchymal stem cells (TDSCs) underwent osteogenic and chondrogenic differentiation respectively by plate co-culture. An analysis was performed on days 7 and 14 of cell differentiation. Biomechanical testing demonstrated a significant increase in maximum stiffness in the simvastatin-treated group. Micro-CT analysis showed that the bone tunnels in the simvastatin group were smaller in diameter and had higher bone density. H&E and Toluidine blue staining demonstrated that tendon-bone healing was significantly greater with better tissue arrangement and more extracellular matrix in the simvastatin-treated group than that in the control group, and immunohistochemical staining showed the expression of VEGF in simvastatin group was significantly higher. Histological staining and RT-PCR confirmed that simvastatin could promote the differentiation of co-cultured BMSCs and TDSCs into osteoblasts and chondroblasts, respectively. The effect of promoting osteogenic differentiation was more tremendous at 14 days, while its effect on promoting chondroblast differentiation was more evident on the 7th day of differentiation. In conclusion, local administration of simvastatin can promote the tendon-bone healing by enhancing neovascularization, chondrogenesis, and osteogenesis in different stages of the tendon-bone healing process.

Optimizing repair of tendon ruptures and chronic tendinopathies: Integrating the use of biomarkers with biological interventions to improve patient outcomes and clinical trial design

Tendons are dense connective tissues of the musculoskeletal system that link bones with muscles to foster mobility. They have complex structures and exist in varying biomechanical, metabolic and biological environments. In addition, tendon composition and mechanical properties can change over the lifespan as an individual ages. Many tendons function in high stress conditions with a low vascular and neuronal supply, conditions often leading to development of chronic tendinopathies, and in some cases, overt rupture of the tissues. Given their essential nature for human mobility and navigation through the environment, the effective repair and regeneration of different tendons after injury or damage is critical for quality of life, and for elite athletes, the return to sport participation at a high level. However, for mainly unknown reasons, the outcomes following injury are not always successful and lead to functional compromise and risk for re-injury. Thus, there is a need to identify those patients who are at risk for developing tendon problems, as well those at risk for poor outcomes after injury and to design interventions to improve outcomes after injury or rupture to specific tendons. This review will discuss recent advances in the identification of biomarkers prognostic for successful and less successful outcomes after tendon injury, and the mechanistic implications of such biomarkers, as well as the potential for specific biologic interventions to enhance outcomes to improve both quality of life and a return to participation in sports. In addition, the implication of these biomarkers for clinical trial design is discussed, as is the issue of whether such biomarkers for successful healing of one tendon can be extended to all tendons or are valid only for tendons in specific biomechanical and biological environments. As maintaining an active lifestyle is critical for health, the successful implementation of these advances will benefit the large number of individuals at risk.

Stem cells in tendon regeneration and factors governing tenogenesis

Tendons are connective tissue structures of paramount importance to the human ability of locomotion. Tendinopathy and tendon rupture can be resistant to treatment and often recurs, thus resulting in a significant health problem with a relevant social impact worldwide. Unfortunately, existing treatment approaches are suboptimal. A better understanding of the basic biology of tendons may provide a better way to solve these problems and promote tendon regeneration. Stem cells, either obtained from tendons or non-tendon sources, such as bone marrow (BMSCs), adipose tissue (AMSCs), as well as embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs), have received increasing attention toward enhancing tendon healing. There are many studies showing that stem cells can contribute to improving tendon healing. Hence, in this review, the current knowledge of BMSCs, AMSCs, TSPCs, ESCs and iPSCs for tendon regeneration, as well as the advantages and limitations among them, has been highlighted. Moreover, the transcriptional and bioactive factors governing tendon healing processes have been discussed.

Comparison of Tendon Development Versus Tendon Healing and Regeneration

Tendon is a vital connective tissue in human skeletal muscle system, and tendon injury is very common and intractable in clinic. Tendon development and repair are two closely related but still not fully understood processes. Tendon development involves multiple germ layer, as well as the regulation of diversity transcription factors (Scx et al.), proteins (Tnmd et al.) and signaling pathways (TGFβ et al.). The nature process of tendon repair is roughly divided in three stages, which are dominated by various cells and cell factors. This review will describe the whole process of tendon development and compare it with the process of tendon repair, focusing on the understanding and recent advances in the regulation of tendon development and repair. The study and comparison of tendon development and repair process can thus provide references and guidelines for treatment of tendon injuries.

ADSC-Based Cell Therapies for Musculoskeletal Disorders: A Review of Recent Clinical Trials

Recently published clinical trials involving the use of adipose-derived stem cells (ADSCs) indicated that approximately one-third of the studies were conducted on musculoskeletal disorders (MSD). MSD refers to a wide range of degenerative conditions of joints, bones, and muscles, and these conditions are the most common causes of chronic disability worldwide, being a major burden to the society. Conventional treatment modalities for MSD are not sufficient to correct the underlying structural abnormalities. Hence, ADSC-based cell therapies are being tested as a form of alternative, yet more effective, therapies in the management of MSDs. Therefore, in this review, MSDs subjected to the ADSC-based therapy were further categorized as arthritis, craniomaxillofacial defects, tendon/ligament related disorders, and spine disorders, and their brief characterization as well as the corresponding conventional therapeutic approaches with possible mechanisms with which ADSCs produce regenerative effects in disease-specific microenvironments were discussed to provide an overview of under which circumstances and on what bases the ADSC-based cell therapy was implemented. Providing an overview of the current status of ADSC-based cell therapy on MSDs can help to develop better and optimized strategies of ADSC-based therapeutics for MSDs as well as help to find novel clinical applications of ADSCs in the near future.

Basic Research on Tendon Repair: Strategies, Evaluation, and Development

Tendon is a fibro-elastic structure that links muscle and bone. Tendon injury can be divided into two types, chronic and acute. Each type of injury or degeneration can cause substantial pain and the loss of tendon function. The natural healing process of tendon injury is complex. According to the anatomical position of tendon tissue, the clinical results are different. The wound healing process includes three overlapping stages: wound healing, proliferation and tissue remodeling. Besides, the healing tendon also faces a high re-tear rate. Faced with the above difficulties, management of tendon injuries remains a clinical problem and needs to be solved urgently. In recent years, there are many new directions and advances in tendon healing. This review introduces tendon injury and sums up the development of tendon healing in recent years, including gene therapy, stem cell therapy, Platelet-rich plasma (PRP) therapy, growth factor and drug therapy and tissue engineering. Although most of these therapies have not yet developed to mature clinical application stage, with the repeated verification by researchers and continuous optimization of curative effect, that day will not be too far away.

Sox11 Modified Tendon-Derived Stem Cells Promote the Repair of Osteonecrosis of Femoral Head

Osteonecrosis of the femoral head (ONFH) is a leading cause of mobility impairment which may lead to a total hip replacement. Recent studies have found tendon derived stem cells (TDSCs) might be an ideal cell source for musculoskeletal tissue regeneration. And our previous study has shown Sox11 could promote osteogenesis of bone marrow-derived MSCs. However, the effect of TDSCs or Sox11 over-expressing TDSCs (TDSCs-Sox11) on bone regeneration in ONFH has not been investigated. In the present study, TDSCs were infected with AAV carrying Sox11 or empty vector. We showed that Sox11 could promote the proliferation and osteogenic differentiation of TDSCs, as well as angiogenesis in vitro. The western blot analysis showed that Sox11 could activate the PI3K/Akt signaling pathway to promote osteogenesis of TDSCs. Finally, using a rabbit model of hormone-induced ONFH, our result demonstrated that local administration of TDSCs or TDSCs overexpressing Sox11 could accelerate bone regeneration in necrotic femoral heads, and TDSCs overexpressing Sox11 showed better effects. TDSCs over-expressing Sox11 might be a promising cell source for stem cell therapy to promote bone regeneration, such as ONFH, fracture, bone defect, and so on.

Mechanotransduction of stem cells for tendon repair

Tendon is a mechanosensitive tissue that transmits force from muscle to bone. Physiological loading contributes to maintaining the homeostasis and adaptation of tendon, but aberrant loading may lead to injury or failed repair. It is shown that stem cells respond to mechanical loading and play an essential role in both acute and chronic injuries, as well as in tendon repair. In the process of mechanotransduction, mechanical loading is detected by mechanosensors that regulate cell differentiation and proliferation via several signaling pathways. In order to better understand the stem-cell response to mechanical stimulation and the potential mechanism of the tendon repair process, in this review, we summarize the source and role of endogenous and exogenous stem cells active in tendon repair, describe the mechanical response of stem cells, and finally, highlight the mechanotransduction process and underlying signaling pathways.

In Vitro Innovation of Tendon Tissue Engineering Strategies

Tendinopathy is the term used to refer to tendon disorders. Spontaneous adult tendon healing results in scar tissue formation and fibrosis with suboptimal biomechanical properties, often resulting in poor and painful mobility. The biomechanical properties of the tissue are negatively affected. Adult tendons have a limited natural healing capacity, and often respond poorly to current treatments that frequently are focused on exercise, drug delivery, and surgical procedures. Therefore, it is of great importance to identify key molecular and cellular processes involved in the progression of tendinopathies to develop effective therapeutic strategies and drive the tissue toward regeneration. To treat tendon diseases and support tendon regeneration, cell-based therapy as well as tissue engineering approaches are considered options, though none can yet be considered conclusive in their reproduction of a safe and successful long-term solution for full microarchitecture and biomechanical tissue recovery. In vitro differentiation techniques are not yet fully validated. This review aims to compare different available tendon in vitro differentiation strategies to clarify the state of art regarding the differentiation process.

A microfluidics-derived growth factor gradient in a scaffold regulates stem cell activities for tendon-to-bone interface healing

Treatment of tendon-to-bone interface injury has long been challenging in sports medicine. The major obstacle lies with the complicated three-layer structure of the tissue that consists of a bone region with osteocytes, a tendon region with tenocytes and a transitional region with chondrocytes. Conventional tissue engineering approaches using simply biomaterial scaffolds, stem cells and combinations of them had limited abilities to reconstruct the gradient structure with normal biomechanical properties. We herein aim to construct a three-layer structure with bone marrow-derived stem cells and tendon stem cells cultured in a decellularized tendon scaffold, through application of a gradient of biological cues in the longitudinal direction of the scaffold that guides the stem cells to differentiate and remodel the extracellular matrix in response to different medium concentrations in different regions. A microfluidic chip, on which a tree-like flow pattern was implemented, was adopted to create the concentration gradient in a dichotomous manner. We screened for an optimized seeding ratio between the two stem cell types before incubation of the scaffold in the medium concentration gradient and surgical implantation. Histology and immunohistochemistry assessments, both qualitatively and semi-quantitatively, showed that the microfluidic system provided desired guidance to the seeded stem cells that the healing at 8-week post-implantation presented a similar structure to that of a normal tendon-to-bone interface, which was outstanding compared to treatments without gradient guidance, stem cells or scaffolds where chaotic and fibrotic structures were obtained. This strategy offers a potentially translational tissue engineering approach for better outcomes in tendon-to-bone healing.

Bone marrow mesenchymal stem cell-derived exosomes promote tendon regeneration by facilitating the proliferation and migration of endogenous tendon stem/progenitor cells

Mesenchymal stem cells (MSCs)-derived exosomes are being increasingly focused as the new biological pro-regenerative therapeutic agents for various types of tissue injury. Here, we explored the potential of a novel exosome-based therapeutic application combined with a local fibrin delivery strategy for tendon repair. After discovering that bone marrow mesenchymal stem cells-derived exosomes (BMSCs-exos) promoted the proliferation, migration and tenogenic differentiation of tendon stem/progenitor cells (TSPCs) in vitro, we embedded BMSCs-exos in fibrin and injected it into the defect area of rat patellar tendon, and the results showed that the exosomes could be controlled-released from the fibrin, retained within the defect area, and internalized by TSPCs. BMSCs-exos embedded in fibrin significantly improved the histological scores, enhanced the expression of mohawk, tenomodulin, and type I collagen, as well as the mechanical properties of neotendon, and also promoted the proliferation of local TSPCs in vivo. Overall, we demonstrated the beneficial role of BMSCs-exos in tendon regeneration, and that fibrin-exosomes delivery system represents a successful local treatment strategy of exosomes. This study brings prospects in the potential application of exosomes in novel therapies for tendon injury. STATEMENT OF SIGNIFICANCE: Mesenchymal stem cells have been identified as a preferred approach in tissue regeneration. In this study, we reported bone marrow mesenchymal stem cells (BMSCs) promote the proliferation and migration of tendon stem/progenitor cells (TSPCs) via the paracrine signaling effect of the nanoscale exosomes. We also demonstrated that the application of BMSCs-derived exosomes might be a promising approach to activate the regenerative potential of endogenous TSPCs in tendon injured region, and fibrin-exosomes delivery system represents a successful local treatment strategy of exosomes.

Electrospun thymosin Beta-4 loaded PLGA/PLA nanofiber/ microfiber hybrid yarns for tendon tissue engineering application

Microfiber yarns (MY) have been widely employed to construct tendon tissue grafts. However, suboptimal ultrastructure and inappropriate environments for cell interactions limit their clinical application. Herein, we designed a modified electrospinning device to coat poly(lactic-co-glycolic acid) PLGA nanofibers onto polylactic acid (PLA) MY to generate PLGA/PLA hybrid yarns (HY), which had a well-aligned nanofibrous structure, resembling the ultrastructure of native tendon tissues and showed enhanced failure load compared to PLA MY. PLGA/PLA HY significantly improved the growth, proliferation, and tendon-specific gene expressions of human adipose derived mesenchymal stem cells (HADMSC) compared to PLA MY. Moreover, thymosin beta-4 (Tβ4) loaded PLGA/PLA HY presented a sustained drug release manner for 28 days and showed an additive effect on promoting HADMSC migration, proliferation, and tenogenic differentiation. Collectively, the combination of Tβ4 with the nano-topography of PLGA/PLA HY might be an efficient strategy to promote tenogenesis of adult stem cells for tendon tissue engineering.

Co-cultured Bone-marrow Derived and Tendon Stem Cells: Novel Seed Cells for Bone Regeneration

Tendon-bone healing after injury is an unsolved problem. Several types of stem cells are used as seed cells. However, the optimal co-culture ratio of different types of cells suitable for tissue engineering as well as the stimulator for facilitating the differentiation of stem cells in tendon-bone healing is unclear. In this study, the proliferation of both bone marrow-derived stem cells (BMSCs) and tendon stem cells (TSCs) was increased at a 1:1 co-cultured ratio, and proliferation was suppressed by Tenascin C (TNC). TNC treatment can promote osteogenesis or chondrogenesis of both BMSCs and TSCs under a 1:1 co-cultured ratio. In addition, the expression level of Rho-associated kinase (ROCK) increased in the process of TNC-induced osteogenesis and decreased in the process of TNC-induced chondrogenesis. Furthermore, the level of insulin-like growth factor 1 receptor (IGF-1R) and mitogen-activated protein kinase (MEK) was upregulated during the osteogenesis and chondrogenesis of both BMSCs and TSCs after TNC treatment. Although our study was conducted in rats with no direct evaluation of the resulting cells for tendon-bone healing and regeneration, we show that the proliferation of BMSCs and TSCs was enhanced under a 1:1 co-cultured ratio. TNC has a significant impact on the proliferation and differentiation of co-cultured BMSCs and TSCs. IGF-IR, ROCK, and MEK may become involved in the process after TNC treatment.

Enhancement of tenogenic differentiation of rat tendon-derived stem cells by biglycan

Biglycan (BGN) has been identified as one of the critical components of the tendon-derived stem cells (TDSCs) niche and may be related to tendon formation. However, so far, no study has demonstrated whether the soluble BGN could induce the tenogenic differentiation of TDSCs in vitro. The aim of this study was to investigate the effect of BGN on the tenogenic differentiation of TDSCs. The proliferation and tenogenic differentiation of TDSCs exposed to different concentrations of BGN (0, 50, 100, and 500 ng/ml) were determined by the live/dead cell staining assay, CCK-8 assay, quantitative real-time polymerase chain reaction (qRT-PCR), and western blot analysis. The BGN signaling pathway of TDSCs (with and without 50 ng/ml of BGN) was determined by western blot analysis and qRT-PCR analysis. At a concentration of 50 ng/ml, BGN increased the expression of the tenogenic markers THBS-4 and TNMD at both the messenger RNA (mRNA) and protein levels. Meanwhile, 50 ng/ml of BGN inhibited the expression of the chondrogenic and osteogenic markers SOX9, ACN, and RUNX2 at both the mRNA and protein levels. Moreover, BGN (50 ng/ml) affected the expression of the components of the extracellular matrix of TDSCs. Additionally, BGN activated the Smad1/5/8 pathway as indicated by an increase in phosphorylation and demonstrated by inhibition experiments. Upregulation in the gene expression of BMP-associated receptors (BMPRII, ActR-IIa, and BMPR-Ib) and Smad pathway components (Smad4 and 8) was observed. Taken together, BGN regulates tenogenic differentiation of TDSCs via BMP7/Smad1/5/8 pathway and this regulation may provide a basic insight into treating tendon injury.

Mesenchymal Stem Cells Empowering Tendon Regenerative Therapies

Tendon tissues have limited healing capacity. The incidence of tendon injuries and the unsatisfactory functional outcomes of tendon repair are driving the search for alternative therapeutic approaches envisioning tendon regeneration. Cellular therapies aim at delivering adequate, regeneration-competent cell types to the injured tendon and toward ultimately promoting its reconstruction and recovery of functionality. Mesenchymal stem cells (MSCs) either obtained from tendons or from non-tendon sources, like bone marrow (BM-MSCs) or adipose tissue (ASCs), have been receiving increasing attention over the years toward enhancing tendon healing. Evidences from in vitro and in vivo studies suggest MSCs can contribute to accelerate and improve the quality of tendon healing. Nonetheless, the exact mechanisms underlying these repair events are yet to be fully elucidated. This review provides an overview of the main challenges in the field of cell-based regenerative therapies, discussing the role of MSCs in boosting tendon regeneration, particularly through their capacity to enhance the tenogenic properties of tendon resident cells.

Crosstalk between adipose stem cells and tendon cells reveals a temporal regulation of tenogenesis by matrix deposition and remodeling

Tendon injuries constitute an unmet clinical challenge owing to the limited intrinsic regenerative ability of this tissue. Cell-based therapies aim at improving tendon healing through the delicate orchestration of tissue rebuilding and regain of function. Hence, human adipose-derived stem cells (hASCs) have been proposed as a promising cell source for boosting tendon regeneration. In this work, we investigated the influence of hASCs on native human tendon-derived cells (hTDCs) through the establishment of a direct contact co-culture system. Results demonstrated that direct interactions between these cell types resulted in controlled proliferation and spontaneous cell elongation. ECM-related genes, particularly COL1A1 and TNC, and genes involved in ECM remodeling, such as MMP1, MMP2, MMP3, and TIMP1, were expressed in co-culture in a temporally regulated manner. In addition, deposition of collagen type I was accelerated in co-culture systems and favored over the production of collagen type III, resulting in an enhanced COL1/COL3 ratio as soon as 7 days. In conclusion, hASCs seem to be good candidates in modulating the behavior of native tendon cells, particularly through a balanced process of ECM synthesis and degradation.

Tendon explant cultures to study the communication between adipose stem cells and native tendon niche

Poor clinical outcomes of tendon repair, together with limited regenerative capacity of the tissue, have triggered the search for alternative regenerative medicine strategies. Human adipose-derived stem cells (hASCs) are being investigated as a promising cell source in contributing for tendon repopulation and reconstruction. However, the mechanisms involved in a potential beneficial effect in tendon regeneration are still to be uncovered. To gain further insights on the bi-directional crosstalk occurring between stem cells and the native tendon niche, it was used an indirect (trans-well) system for co-culturing human tendon explants and hASCs. The maintenance of tissue architecture was studied up to 14 days by histological techniques. The secretion of MMPs was evaluated at day 3. The behavior of hASCs was assessed regarding cell elongation and extracellular matrix (ECM) production. The paracrine communication enhanced collagenolytic activity of MMPs in co-cultures at day 3, in comparison to hASCs alone or tendon explants alone, suggesting that ECM remodeling is triggered early in culture. Moreover, hASCs were spontaneously more elongated in co-cultures and the deposition of collagen type III and tenascin-C by hASCs in co-culture was observed at a lower extent after 7 days, in comparison to hASCs alone, being lately recovered at day 14. Overall, explant co-cultures established herein may constitute a tool for replicating the first steps in tendon healing and help uncovering the bi-directional communication occurring between hASCs and the native tendon niche.

Effect of Tumor Necrosis Factor Alpha Dose and Exposure Time on Tumor Necrosis Factor-Induced Gene-6 Activation by Neonatal and Adult Mesenchymal Stromal Cells

Tumor necrosis factor alpha (TNF-α) induced protein 6 is a major anti-inflammatory mediator released by activated mesenchymal stromal cells (MSCs). Neonatal MSCs are considered more metabolically active than cells derived from adult tissues, and potentially less heterogeneous. We hypothesized that a TNF-α-activated neonatal MSC population [human umbilical cord perivascular cells (HUCPVCs)] would show an enhanced level of TSG-6 activation compared with adult bone marrow MSCs (BMMSCs). Thus, we stimulated HUCPVCs, and both human BMMSCs (hBMMSCs) and mouse BMMSCs (mBMMSCs) with 1, 10, 50, and 100 ng/mL of recombinant TNF-α over various exposure times. Supernatant, and total RNA, of the cells were collected for measurement of both TSG-6 RNA expression, and secreted TSG-6 protein. To compare gene levels, quantification was done by normalizing the expression levels of TSG-6 to the geometric mean of the three most stable reference genes, out of a cohort of 30 tested genes, using the Pfaffl method. We found that HUCPVCs exhibited both an enhanced and more rapid response to low dose (1 ng/mL) TNF-α exposure resulting in ∼11.5-fold increase in TSG-6 expression within the first 30 min. In contrast, hBMMSCs showed 2-fold increase by 1 h that increased to 9.5-fold with a higher (50 ng/mL) TNF-α exposure for the same time. mBMMSCs showed a two-fold increase after 24 h that was independent of TNF-α concentration. Thus, although TSG-6 expression level varied among donors, both hMSC populations exhibited enhanced TSG-6 upregulation, upon TNF-α stimulation, compared with mBMMSCs. In conclusion, HUCPVCs showed higher sensitivity, and a prompter response to TNF-α stimulation compared with hBMMSCs. Thus, neonatal MSCs may be a stronger candidate population than those derived from adult bone marrow to treat inflammatory diseases.

Proanthocyanidins Attenuation of H2O2-Induced Oxidative Damage in Tendon-Derived Stem Cells via Upregulating Nrf-2 Signaling Pathway

Proanthocyanidins (PCs) have shown inhibition of oxidative damage by improving Nrf-2 expression in many tissues. However, the cytoprotective effects of PCs on H₂O₂-induced tendon damage have not been verified. The current study was aimed at assessing the cytoprotection of PCs on the oxidative cellular toxicity of tendon-derived stem cells (TDSCs) induced by H₂O₂. The TDSCs were isolated from patellar tendons of Sprague Dawley (SD) rats, and the cells after third passage were used for subsequent experiments. The isolated cells were identified by flow cytometry assay and multidifferentiation potential assay. Cell Counting Kit-8 assay was performed to examine cell viability. Real-Time PCR and Western Blot were employed to, respectively, assess the mRNA and protein expressions of Nrf-2, GCLM, NQO-1, and HO-1. PCs significantly improved the cell viability of TDSCs. Furthermore, H₂O₂ upregulated Nrf-2, GCLM, NQO-1, and HO-1 without significant difference, while the proteins expressions were increased with significant difference in PCs group and PCs + H₂O₂ cotreated group. All the findings indicated that PCs could protect against the oxidative damage induced by H₂O₂ in TDSCs, and the cytoprotective effects might be due to the ability of PCs to activate the expressions of GCLM, HO-1, and NQO-1 via upregulating Nrf-2 signaling pathway.

Co-culture of Human Dental Pulp Stem Cells and Endothelial Cells Using Porous Biopolymer Microcarriers: A Feasibility Study for Bone Tissue Engineering

Delivery of stem cells with osteogenesis while enabling angiogenesis is important for vascularized bone tissue engineering. Here a three-dimensional (3D) co-culture system of dental pulp stem cells (DPSCs) and endothelial cells (ECs) was designed using porous microcarriers, and the feasibility of applying to bone tissue engineering was investigated in vitro. Highly porous spherical microcarriers made of degradable biopolymers were prepared with sizes of hundreds of micrometers. The microcarriers loaded with DPSCs were co-cultured with ECs embedded in a hydrogel of type I collagen. An optimal co-culture medium that preserves the viability of ECs while stimulating the osteogenic differentiation of DPSCs was found to be a 10:1 of osteogenic medium:endothelial medium. The co-cultured constructs of DPSCs/ECs showed significantly higher level of alkaline phosphatase activity than the mono-cultured cells. Moreover, the expressions of genes related with osteogenesis and angiogenesis were significantly up-regulated by the co-cultures with respect to the mono-cultures. Results imply the interplay between ECs and DPSCs through the designed 3D co-culture models. The microcarrier-enabled co-cultured cell system is considered to be useful as an alternative tool for future vascularized bone tissue engineering.

The potential of using semitendinosus tendon as autograft in rabbit meniscus reconstruction

Since transplantation of meniscal allograft or artificial menisci is limited by graft sources and a series of adverse events, substitution for meniscus reconstruction still needs to be explored. Natural biomaterials, which can provide a unique 3-D microenvironment, remain a promising alternative for tissue engineering. Among them, autograft is a preferred option for its safety and excellent biocompatibility. In this study, we utilized semitendinosus tendon autograft in meniscus reconstruction to investigate its fibrochondrogenic metaplasticity potential and chondroprotective effect. Tendon-derived stem cells (TDSCs) and synovial-derived mesenchymal stem cells (SMSCs), two most important stem cell sources in our strategy, exhibited excellent viability, distribution, proliferation and fibrochondrogenic differentiation ability in decellularized semitendinosus tendon (DST) scaffolds in vitro. Histologic evaluation of the tendon grafts in vivo suggested endogenous stem cells differentiated into fibrochondrocytes, synthesized proteoglycan, type II collagen and radial type I collagen at 12 weeks and 24 weeks post-surgery. As for elastic modulus and hardness of the grafts, there were no significant differences between native meniscus and regenerated meniscus at 24 weeks. The protection of condylar cartilage from degeneration was significantly better in the reconstruction group comparing to control group. Overall, semitendinosus tendon autograft seems to be a promising substitution in meniscus reconstruction.

Advances of stem cell based-therapeutic approaches for tendon repair

Tendon injuries are significant clinical problems. Current treatments often result in incomplete repair or healing, which may lead to reduced function and rupture. Stem cell-based therapy is a promising intervention for tendon repair. In this article, we attempt to provide a brief overview on the recent progress in the field, current understanding of the underlying mechanisms of the approach, and the potential of stem cell-based therapies beyond cell implantation. We conclude the review by sharing our viewpoints on the challenges, opportunities, and future directions of this approach. The translational potential of this article: This paper reviews recent progress on stem cell-based therapeutic approaches for tendon repair, which highlights its translational potential and challenges.

Current concepts on tenogenic differentiation and clinical applications

Tendon is a tissue that transmits force from muscle to bone. Chronic or acute tendon injuries are very common, and are always accompanied by pain and a limited range of motion in patients. In clinical settings, management of tendon injuries still remains a big challenge. Cell therapies, such as the application of stem cells for tenogenic differentiation, were suggested to be an ideal strategy for clinical translation. However, there is still a lack of specific methods for tenogenic differentiation due to the limited understanding of tendon biology currently. This review focuses on the summary of current published strategies for tenogenic differentiation, such as the application of growth factors, mechanical stimulation, biomaterials, coculture, or induced pluripotent stem cells. Current clinical applications of stem cells for treatment of tendon injuries and their limitations have also been discussed in this review.