Characterization of mesenchymal stem cells derived from the equine synovial fluid and membrane

The potential role of synovial cells in the progression and treatment of osteoarthritis

Osteoarthritis (OA), the commonest arthritis, is characterized by the progressive destruction of cartilage, leading to disability. The Current early clinical treatment strategy for OA often centers on anti-inflammatory or analgesia medication, weight loss, improved muscular function and articular cartilage repair. Although these treatments can relieve symptoms, OA tends to be progressive, and most patients require arthroplasty at the terminal stages of OA. Recent studies have shown a close correlation between joint pain, inflammation, cartilage destruction and synovial cells. Consequently, understanding the potential mechanisms associated with the action of synovial cells in OA could be beneficial for the clinical management of OA. Therefore, this review comprehensively describes the biological functions of synovial cells, the synovium, together with the pathological changes of synovial cells in OA, and the interaction between the cartilage and synovium, which is lacking in the present literature. Additionally, therapeutic approaches based on synovial cells for OA treatment are further discussed from a clinical perspective, highlighting a new direction in the treatment of OA.

Allogenic Synovia-Derived Mesenchymal Stem Cells for Treatment of Equine Tendinopathies and Desmopathies-Proof of Concept

Tendon and ligament injuries are frequent in sport horses and humans, and such injuries represent a significant therapeutic challenge. Tissue regeneration and function recovery are the paramount goals of tendon and ligament lesion management. Nowadays, several regenerative treatments are being developed, based on the use of stem cell and stem cell-based therapies. In the present study, the preparation of equine synovial membrane mesenchymal stem cells (eSM-MSCs) is described for clinical use, collection, transport, isolation, differentiation, characterization, and application. These cells are fibroblast-like and grow in clusters. They retain osteogenic, chondrogenic, and adipogenic differentiation potential. We present 16 clinical cases of tendonitis and desmitis, treated with allogenic eSM-MSCs and autologous serum, and we also include their evaluation, treatment, and follow-up. The concerns associated with the use of autologous serum as a vehicle are related to a reduced immunogenic response after the administration of this therapeutic combination, as well as the pro-regenerative effects from the growth factors and immunoglobulins that are part of its constitution. Most of the cases (14/16) healed in 30 days and presented good outcomes. Treatment of tendon and ligament lesions with a mixture of eSM-MSCs and autologous serum appears to be a promising clinical option for this category of lesions in equine patients.

Extracellular vesicles from equine mesenchymal stem cells decrease inflammation markers in chondrocytes in vitro

BACKGROUND

Mesenchymal stem cells (MSCs) have been used therapeutically in equine medicine. MSCs release extracellular vesicles (EVs), which affect cell processes by inhibiting cell apoptosis and regulating inflammation. To date, little is known about equine EVs and their regenerative properties.

OBJECTIVES

To characterise equine MSC-derived extracellular vesicles (EVs) and evaluate their effect on equine chondrocytes treated with pro-inflammatory cytokines in vitro.

STUDY DESIGN

In vitro experiments with randomised complete block design.

METHODS

Mesenchymal stem cells from bone marrow, adipose tissue, and synovial fluid were cultured in vitro. The MSC culture medium was centrifuged and filtered. Isolated particles were analysed for size and concentration (total number of particles per mL). Transmission electron microscopy analysis was performed to evaluate the morphology and CD9 expression of the particles. Chondrocytes from healthy equines were treated with the inflammatory cytokines interleukin (IL)-1β and tumour necrosis factor-alpha. MSC-derived EVs from bone marrow and synovial fluid cells were added as co-treatments in vitro. Gene expression analysis by real-time PCR was performed to evaluate the effects of EVs.

RESULTS

The particles isolated from MSCs derived from different tissues did not differ significantly in size and concentration. The particles had a round-like shape and positively expressed CD9. EVs from bone marrow cells displayed reduced expression of metalloproteinase-13.

MAIN LIMITATIONS

Sample size and characterisation of the content of EVs.

CONCLUSIONS

EVs isolated from equine bone marrow MSCs reduced metalloproteinase 13 gene expression; this gene encodes an enzyme related to cartilage degradation in inflamed chondrocytes in vitro. EVs derived from MSCs can reduce inflammation and could potentially be used as an adjuvant treatment to improve tissue and cartilage repair in the articular pathologies.

Osteochondral regeneration of the femoral medial condyle by using a scaffold-free 3D construct of synovial membrane-derived mesenchymal stem cells in horses

Background

Medical interventions for subchondral bone cysts in horses have been extensively studied. This study investigated the regeneration of articular cartilage and subchondral bone with scaffold-free three-dimensional (3D) constructs of equine synovial membrane-derived mesenchymal stem cells (SM-MSCs) isolated from three ponies and expanded until over 1.0 × 107 cells at passage 2 (P2).

Results

SM-MSCs were strongly positive for CD11a/CD18, CD44, and major histocompatibility complex (MHC) class I; moderately positive for CD90, CD105, and MHC class II; and negative for CD34 and CD45 on flow cytometry and differentiated into osteogenic, chondrogenic, and adipogenic lineages in the tri-lineage differentiation assay. After culturing SM-MSCs until P3, we prepared a construct (diameter, 6.3 mm; height, 5.0 mm) comprising approximately 1920 spheroids containing 3.0 × 104 cells each. This construct was confirmed to be positive for type I collagen and negative for type II collagen, Alcian blue, and Safranin-O upon histological analysis and was subsequently implanted into an osteochondral defect (diameter, 6.8 mm; depth, 5.0 mm) at the right femoral medial condyle. The contralateral (left femoral) defect served as the control. At 3 and 6 months after surgery, the radiolucent volume (RV, mm3) of the defects was calculated based on multiplanar reconstruction of computed tomography (CT) images. Magnetic resonance (MR) images were evaluated using a modified two-dimensional MR observation of cartilage repair tissue (MOCART) grading system, while macroscopic (gross) and microscopic histological characteristics were scored according to the International Cartilage Repair Society (ICRS) scale. Compared to the control sites, the implanted defects showed lower RV percentages, better total MOCART scores, higher average gross scores, and higher average histological scores.

Conclusions

Implantation of a scaffold-free 3D-construct of SM-MSCs into an osteochondral defect could regenerate the original structure of the cartilage and subchondral bone over 6 months post-surgery in horses, indicating the potential of this technique in treating equine subchondral bone cysts.

Synovial membrane mesenchymal stem cells for cartilaginous tissues repair

BACKGROUND

The present review is focused on general aspects of the synovial membrane as well as specialized aspects of its cellular constituents, particularly the composition and location of synovial membrane mesenchymal stem cells (S-MSCs). S-MSC multipotency properties are currently at the center of translational medicine for the repair of multiple joint tissues, such as articular cartilage and meniscus lesions.

METHODS AND RESULTS

We reviewed the results of in vitro and in vivo research on the current clinical applications of S-MSCs, surface markers, cell culture techniques, regenerative properties, and immunomodulatory mechanisms of S-MSCs as well as the practical limitations of the last twenty-five years (1996 to 2021).

CONCLUSIONS

Despite the poor interest in the development of new clinical trials for the application of S-MSCs in joint tissue repair, we found evidence to support the clinical use of S-MSCs for cartilage repair. S-MSCs can be considered a valuable therapy for the treatment of repairing joint lesions.

Expression profile of the Kisspeptin/Kiss1r system and angiogenic and immunological mediators in the ovary of cyclic and pregnant cats

The Kisspeptin/Kiss1r system has been studied in mammalian ovaries. However, there are still no studies on the modulation of this system and its relationship with angiogenic and immunological mediators in the ovary of domestic cats, especially during pregnancy. We evaluated the expression of Kisspeptin/Kiss1r and angiogenic and immunological mediators during folliculogenesis, luteogenesis and luteal regression of cyclic and pregnant cats. The ovary exhibited moderate to intense expression for Kiss1, VEGF, Flk-1, INFγ and MIF in oocytes and the follicular wall, while Kiss1r expression was low in granulosa cells. In these cells, there was also a greater expression of Kiss1, INFγ and MIF, mainly in secondary follicles, while tertiary and preovulatory follicles exhibited greater expression of VEGF and Flk-1 in this layer. In luteogenesis, Kiss1 immunostaining was higher in mature corpora lutea (MCL) of pregnant cats compared to vacuolated CL (VCL) and corpus albicans (CA). Pregnancy also increased the luteal gene expression of Kiss1 as well as Kiss1, Kiss1r, Flk-1, and MIF immunostaining in MCL, while reduced the area of VEGF expression in VCL and luteal mRNA expression of Mif when compared to non-pregnant animals. In addition, positive gene correlation between Kiss1r and Mif was observed in the CL. Kiss1, Kiss1r, Vegf and Mif expression were lower in the CA of cats in anestrus. These findings reveal that the expression of Kisspeptin/Kiss1r and angiogenic and immunological mediators, in the ovary of domestic cats, depend on the follicular and luteal stage, and the luteal expression of these mediators is influenced by pregnancy.

Synovial Fluid Mesenchymal Stem Cells for Knee Arthritis and Cartilage Defects: A Review of the Literature

Mesenchymal stem cells (MSCs) are adult stem cells that have the ability to self-renew and differentiate into several cell lineages including adipocytes, chondrocytes, tenocytes, bones, and myoblasts. These properties make the cell a promising candidate for regenerative medicine applications, especially when dealing with sports injuries in the knee. MSCs can be isolated from almost every type of adult tissue. However, most of the current research focuses on MSCs derived from bone marrow, adipose, and placenta derived products. Synovial fluid-derived MSCs (SF-MSCs) are relatively overlooked but have demonstrated promising therapeutic properties including possessing higher chondrogenic proliferation capabilities than other types of MSCs. Interestingly, SF-MSC population has shown to increase exponentially in patients with joint injury or disease, pointing to a potential use as a biomarker or as a treatment of some orthopaedic disorders. In this review, we go over the current literature on synovial fluid-derived MSCs including the characterization, the animal studies, and discuss future perspectives.

Effects of Normal Synovial Fluid and Interferon Gamma on Chondrogenic Capability and Immunomodulatory Potential Respectively on Equine Mesenchymal Stem Cells

Synovial fluid contains cytokines, growth factors and resident mesenchymal stem cells (MSCs). The present study aimed to (1) determine the effects of autologous and allogeneic synovial fluid on viability, proliferation and chondrogenesis of equine bone marrow MSCs (BMMSCs) and (2) compare the immunomodulatory properties of equine synovial fluid MSCs (SFMSCs) and BMMSCs after stimulation with interferon gamma (INF-γ). To meet the first aim of the study, the proliferation and viability of MSCs were evaluated by MTS and calcein AM staining assays. To induce chondrogenesis, MSCs were cultured in a medium containing TGF-β1 or different concentrations of synovial fluid. To meet the second aim, SFMSCs and BMMSCs were stimulated with IFN-γ. The concentration of indoleamine-2,3-dioxygenase (IDO) and nitric oxide (NO) were examined. Our results show that MSCs cultured in autologous or allogeneic synovial fluid could maintain proliferation and viability activities. Synovial fluid affected chondrocyte differentiation significantly, as indicated by increased glycosaminoglycan contents, compared to the chondrogenic medium containing 5 ng/mL TGF-β1. After culturing with IFN-γ, the conditioned media of both BMMSCs and SFMSCs showed increased concentrations of IDO, but not NO. Stimulating MSCs with synovial fluid or IFN-γ could enhance chondrogenesis and anti-inflammatory activity, respectively, suggesting that the joint environment is suitable for chondrogenesis.

Kisspeptin/Kiss1r system and angiogenic and immunological mediators at the maternal-fetal interface of domestic cats

The Kisspeptin/Kiss1r system is a key regulator of reproduction by stimulating gonadotrophin-releasing hormone and luteinizing hormone release, and in vitro studies have shown that Kisspeptin can modulate angiogenesis and immune function, factors that are also essential for reproduction However, there are no studies on the expression of Kisspeptin/Kiss1r at the maternal-fetal interface in domestic cats and its relationship with angiogenic and immunological mediators. Thus, our objective was to evaluate the spatiotemporal expression profile of Kisspeptin/Kiss1r and angiogenic and immunological mediators in the uterus and placenta of domestic cats during pregnancy. Uterus and placenta samples were collected from cats in mid pregnancy (N = 6) and late pregnancy (N = 6), in addition to uterus from non-pregnant cats in diestrus (N = 7), to evaluate protein and gene expression of kisspeptin (Kiss1), kisspeptin receptor (Kiss1r), vascular endothelial growth factor (VEGF), tyrosine kinase receptor (Flk-1), placental growth factor (PLGF), interferon gamma (INFγ), migration inhibiting factor (MIF), tumor necrosis factor (TNFα), interleukins (IL6 and IL10) by immunohistochemistry and quantitative polymerase chain reaction. Pregnancy increased the uterine expression of Kiss1 and Kiss1r, especially at the late pregnancy, in addition to upregulating INFy, MIF, Vegf, Il10, and Tnf and downregulating Plgf. Higher placental expression of Kiss1r and Plgf mRNA occurred at the late pregnancy, while the expression of Kiss1, VEGF, Flk-1, INFy, TNFα, Il6, and IL10 was higher in the mid of pregnancy. A positive correlation between Kiss1 and Tnf was observed in the placenta, while Kiss1r had a negative correlation with Infγ, Il6, and Il10. The findings reveal that Kisspeptin/Kiss1r and angiogenic and immunological mediators at the maternal-fetal interface of pregnant cat have a gene correlation and are modulated by the gestational age. These data suggest possible functional links of Kisspeptin in placental angiogenesis and immunology.

Cartilage repair using stem cells & biomaterials: advancement from bench to bedside

Osteoarthritis (OA) involves gradual destruction of articular cartilagemanifested by pain, stiffness of joints, and impaired movement especially in knees and hips. Non-vascularity of this tissue hinders its self-regenerative capacity and thus, the application of reparative or restorative modalities becomes imperative in OA treatment. In recent years, stem cell-based therapies have been explored as potential modalities for addressing OA complications. While mesenchymal stem cells (MSCs) hold immense promise, the recapitulation of native articular cartilage usingMSCs remains elusive. In this review, we have highlighted the chondrogenic potential of MSCs, factors guiding in vitro chondrogenic differentiation, biomaterials available for cartilage repair, their current market status, and the outcomes of major clinical trials. Our search on ClinicalTrials.gov using terms "stem cell" and "osteoarthritis" yielded 83 results. An analysis of the 29 trials that have been completed revealed differences in source of MSCs (bone marrow, adipose tissue, umbilical cord etc.), cell type (autologous or allogenic), and dose administered. Moreover, only 02 out of 29 studies have reported the use of matrix for cartilage repair. From future perspective, aconsensus on choice of cells, differentiation inducers, biomaterials, and clinical settings might pave a way for concocting robust strategies to improve the clinical applicability of biomimetic neocartilage constructs.

Stem Cells in Veterinary Medicine-Current State and Treatment Options

Regenerative medicine is a branch of medicine that develops methods to grow, repair, or replace damaged or diseased cells, organs or tissues. It has gained significant momentum in recent years. Stem cells are undifferentiated cells with the capability to self—renew and differentiate into tissue cells with specialized functions. Stem cell therapies are therefore used to overcome the body's inability to regenerate damaged tissues and metabolic processes after acute or chronic insult. The concept of stem cell therapy was first introduced in 1991 by Caplan, who proposed that massive differentiation of cells into the desired tissue could be achieved by isolation, cultivation, and expansion of stem cells in in vitro conditions. Among different stem cell types, mesenchymal stem cells (MSC) currently seem to be the most suitable for therapeutic purposes, based on their simple isolation and culturing techniques, and lack of ethical issues regarding their usage. Because of their remarkable immunomodulatory abilities, MSCs are increasingly gaining recognition in veterinary medicine. Developments are primarily driven by the limitations of current treatment options for various medical problems in different animal species. MSCs represent a possible therapeutic option for many animal diseases, such as orthopedic, orodental and digestive tract diseases, liver, renal, cardiac, respiratory, neuromuscular, dermal, olfactory, and reproductive system diseases. Although we are progressively gaining an understanding of MSC behavior and their mechanisms of action, some of the issues considering their use for therapy are yet to be resolved. The aim of this review is first to summarize the current knowledge and stress out major issues in stem cell based therapies in veterinary medicine and, secondly, to present results of clinical usage of stem cells in veterinary patients.

Coronary corium, a new source of equine mesenchymal stromal cells

Mesenchymal stromal cells (MSCs) have attracted great attention for therapeutic applications. Since cells derived from different tissues have different properties, using the right tissue source may impact their efficiency in regenerative medicine. This study describes for the first time the isolation and characterization of MSCs derived from the equine coronary corium, which may be useful for treating diseases such as laminitis. Seven coronary corium samples were used for isolation of cells (ccMSCs). Adherent cells were characterized for morphology, immunophenotype, proliferation and differentiation potential, in vitro migration and colony-forming capacity. The cells displayed the characteristic fibroblastoid morphology, with population doubling time increasing until passage 7 and reaching a plateau in passage 10. Cells were negative for CD14 and CD45, and positive for CD73 and CD90. ccMSCs showed chondrogenic and osteogenic, but not adipogenic differentiation, and migrated with nearly total closing of the empty area in 48 h, in the scratch assay. The clonogenic potential was in average 18% to 23%. This study describes for the first time the establishment of mesenchymal stromal cell cultures from the equine coronary corium. The results are similar to MSCs isolated from many other equine tissues, except for restricted differentiation potential. As coronary corium stem cell regulation may contribute to the pathogenesis of equine chronic laminitis, the use of ccMSCs in cell therapy for this significantly debilitating disease should be further investigated.

Nomenclature clarification: synovial fibroblasts and synovial mesenchymal stem cells

Synovial-derived cells, found in the synovial membrane of human joints, were obtained by digestion of the synovial membrane and were subsequently expanded in vitro. The identity of synovial-derived cells has long been a topic of debate. The terms "type B synoviocytes," "fibroblast-like synoviocytes (FLS)," "synovium-derived mesenchymal stem cells (MSCs)," and "synovial fibroblasts (SF)" appeared in different articles related to human synovial-derived cells in various disease models, yet they seemed to be describing the same cell type. However, to date, there is no clear standard to distinguish these terms; thus, the hypothesis that they represent the same cell type is currently inconclusive. Therefore, this review aims to clarify the similarities and differences between these terms and to diffuse the chaotic nomenclature of synovial-derived cells.

The effect of hypoxia on chondrogenesis of equine synovial membrane-derived and bone marrow-derived mesenchymal stem cells

BACKGROUND

Joint injury is extremely common in equine athletes and post-traumatic osteoarthritis (PTOA), a progressive and debilitating disease, is estimated to affect 60% of horses in the USA. The limited potential for intrinsic healing of articular cartilage has prompted intense efforts to identify a cell-based repair strategy to prevent progression of PTOA. Mesenchymal stem cells (MSCs) have the potential to become an ideal source for cell-based treatment of cartilage lesions; however, full chondrogenic differentiation remains elusive. Due to the relatively low oxygen tension in articular cartilage, hypoxia has been proposed as a method of increasing MSC chondrogenesis. The objective of this study was to investigate the effect of hypoxic culture conditions on chondrogenesis in equine synovial membrane-derived MSCs (SM-MSCs) and bone marrow-derived MSCs (BM-MSCs). MSCs were isolated from synovial membrane and bone marrow collected from 5 horses. Flow cytometric analysis was used to assess cell surface marker expression including CD29, CD44, CD90, CD105, CD45, CD-79α, MHCI and MHCII. MSC pellets were cultured in normoxic (21% O₂) or in hypoxic (5% O₂) culture conditions for 28 days. Following the culture period, chondrogenesis was assessed by histology, biochemical analyses and gene expression of chondrogenic-related genes including ACAN, COL2b, SOX9, and COL10A1.

RESULTS

Both cell types expressed markers consistent with stemness including CD29, CD44, CD90, CD105, and MHCI and were negative for exclusion markers (CD45, CD79α, and MHCII). Although the majority of outcome variables of chondrogenic differentiation were not significantly different between cell types or culture conditions, COL10A1 expression, a marker of chondrocyte hypertrophy, was lowest in hypoxic SM-MSCs and was significantly lower in hypoxic SM-MSCs compared to hypoxic BM-MSCs.

CONCLUSIONS

Hypoxic culture conditions do not appear to increase chondrogenesis of equine SM-MSCs or BM-MSCs; however, hypoxia may downregulate the hypertrophic marker COL10A1 in SM-MSCs.

Comparison of the Chondrogenic Differentiation Potential of Equine Synovial Membrane-Derived and Bone Marrow-Derived Mesenchymal Stem Cells

Focal cartilage injury occurs commonly and often precipitates OA. Mesenchymal stem cells (MSCs) may be useful for repairing cartilage lesions, thereby preventing joint degeneration. Although MSCs isolated from bone marrow have been shown to have chondrogenic potential, synovial membrane-derived MSCs (SM-MSCs) may have superior chondrogenic abilities due to a common progenitor cell between synovium and cartilage. The objective of this study was to directly compare the immunophenotype, proliferative capabilities, and chondrogenic potential of equine SM-MSCs and bone marrow-derived MSCs (BM-MSCs). In order to do this, MSCs were isolated from synovial membrane and bone marrow collected from 6 adult horses. Flow cytometric analysis was used to assess cell surface marker expression including CD29, CD44, CD90, CD105, CD45, CD-79α, MHCI, and MHCII. Proliferation rates and doubling time were quantified in P1 and P2 cells. Trilineage differentiation assays were performed. MSC pellets were cultured in chondrogenic induction media for 28 days. Pellets were stained with toluidine blue to assess proteoglycan deposition. Expression of the chondrogenic-related genes ACAN, COL2b, and SOX9 was quantified using qRT-PCR. The immunophenotypes of BM-MSCs and SM-MSCs were similar with both cell types being positive for expression of stem cell markers (CD29, CD44, CD90, CD105, and MHCI) and negative for exclusion markers (CD45 and CD79α). Although SM-MSCs did not express the exclusion marker, MHCII, expression of MHCII was moderate in BM-MSCs. Overall, chondrogenic differentiation was not significantly between the cell types with histologic parameters, proteoglycan content and gene expression being similar. BM-MSCs showed enhanced osteogenic differentiation compared to SM-MSCs. Synovial membrane is a feasible source of MSCs in the horse, however, superior chondrogenesis in vitro should not be expected under currently described culture conditions.

Osteoarthritic Synovial Fluid Modulates Cell Phenotype and Metabolic Behavior In Vitro

Synovial fluid holds a population of mesenchymal stem cells (MSC) that could be used for clinical treatment. Our goal was to characterize the inflammatory and metabolomic profile of the synovial fluid from osteoarthritic patients and to identify its modulatory effect on synovial fluid cells. Synovial fluid was collected from non-OA and OA patients, which was centrifuged to isolate cells. Cells were cultured for 21 days, characterized with specific markers for MSC, and exposed to a specific cocktail to induce chondrogenic, osteogenic, and adipogenic differentiation. Then, we performed a MTT assay exposing SF cells from non-OA and OA patients to a medium containing non-OA and OA synovial fluid. Synovial fluid from non-OA and OA patients was submitted to ELISA to evaluate BMP-2, BMP-4, IL-6, IL-10, TNF-α, and TGF-β1 concentrations and to a metabolomic evaluation using ¹H-NMR. Synovial fluid cells presented spindle-shaped morphology in vitro. Samples from OA patients formed a higher number of colonies than the ones from non-OA patients. After 21 days, the colony-forming cells from OA patients differentiated into the three mesenchymal cell lineages, under the appropriated induction protocols. Synovial fluid cells increased its metabolic activity after being exposed to the OA synovial fluid. ELISA assay showed that OA synovial fluid samples presented higher concentration of IL-10 and TGF-β1 than the non-OA, while the NMR showed that OA synovial fluid presents higher concentrations of glucose and glycerol. In conclusion, SFC activity is modulated by OA synovial fluid, which presents higher concentration of IL-10, TGF-β, glycerol, and glucose.

A pilot study of regenerative therapy by implanting synovium-derived mesenchymal stromal cells in equine osteochondral defect models

Synovium-derived mesenchymal stromal cells (SM-MSCs) from seven Thoroughbreds with naturally occurring intra-articular fracture proliferated to over ten million cells by the second passage. Using three experimental Thoroughbreds, columnar osteochondral defects were made arthroscopically at the bilateral distal radius. Five million allogenic SM-MSCs were implanted into the right defect, and another five million were injected into the right radio-carpal joint (implantation site). No SM-MSCs were implanted into the left defect or the same joint (control site). At 3 and 6 weeks after surgery, ten million autologous SM-MSCs were injected into the right joints. Radiolucent volumes of defects calculated by analysis of postmortem CT images 9 weeks after surgery were decreased in implanted sites compared with control sites in all horses. The average scores for ICRS gross and histopathological grading scales in implanted sites were equal to or higher than those of the controls. These results suggest that allogenic implantation and subsequent autologous injection of SM-MSCs might not obstruct subchondral bone formation in defects.

Equine Mesenchymal Stem Cells: Properties, Sources, Characterization, and Potential Therapeutic Applications

Properties like sustained multiplication and self-renewal, and homing and multilineage differentiation to undertake repair of the damaged tissues make stem cells the lifeline for any living system. Therefore, stem cell therapy is regarded to carry immense therapeutic potential. Though the dearth of understanding about the basic biological properties and pathways involved in therapeutic benefits currently limit the application of stem cells in humans as well as animals, there are innumerable reports that suggest clinical benefits of stem cell therapy in equine. Among various stem cell sources, currently adult mesenchymal stem cells (MSCs) are preferred for therapeutic application in horse owing to their easy availability, capacity to modulate inflammation, and promote healing. Also the cells carry very limited teratogenic risk compared to the pluripotent stem cells. Mesenchymal stem cells were earlier considered mainly for musculoskeletal tissues, but now may also be utilized in other diverse clinical problems in horse, and the results may be extrapolated even for human medicine. The current review highlights biological properties, sources, mechanisms, and potential therapeutic applications of stem cells in equine practice.

Magnetic-Activated Cell Sorting Strategies to Isolate and Purify Synovial Fluid-Derived Mesenchymal Stem Cells from a Rabbit Model

Mesenchymal stem cells (MSCs) are the main cell source for cell-based therapy. MSCs from articular cavity synovial fluid could potentially be used for cartilage tissue engineering. MSCs from synovial fluid (SF-MSCs) have been considered promising candidates for articular regeneration, and their potential therapeutic benefit has made them an important research topic of late. SF-MSCs from the knee cavity of the New Zealand white rabbit can be employed as an optimized translational model to assess human regenerative medicine. By means of CD90-based magnetic activated cell sorting (MACS) technologies, this protocol successfully obtains rabbit SF-MSCs (rbSF-MSCs) from this rabbit model and further fully demonstrates the MSC phenotype of these cells by inducing them to differentiate to osteoblasts, adipocytes, and chondrocytes. Therefore, this approach can be applied in cell biology research and tissue engineering using simple equipment and procedures.

Practical considerations for clinical use of mesenchymal stem cells: From the laboratory to the horse

Since the clinical use of mesenchymal stem cells (MSCs) for treating musculoskeletal injuries is gaining popularity, practitioners should be aware of the factors that may affect MSCs from tissue harvesting for MSC isolation to cell delivery into the injury site. This review provides equine practitioners with up-to-date, practical knowledge for the treatment of equine patients using MSCs. A brief overview of laboratory procedures affecting MSCs is provided, but the main focus is on shipping conditions, routes of administration, injection methods, and which commonly used products can be combined with MSCs and which products should be avoided as they have deleterious effects on cells. There are still several knowledge gaps regarding MSC-based therapies in horses. Therefore, it is important to properly manage the factors which are currently known to affect MSCs, to further strengthen the evidence basis of this treatment.

Mesenchymal Stem/Progenitor Cells Derived from Articular Cartilage, Synovial Membrane and Synovial Fluid for Cartilage Regeneration: Current Status and Future Perspectives

Large articular cartilage defects remain an immense challenge in the field of regenerative medicine because of their poor intrinsic repair capacity. Currently, the available medical interventions can relieve clinical symptoms to some extent, but fail to repair the cartilaginous injuries with authentic hyaline cartilage. There has been a surge of interest in developing cell-based therapies, focused particularly on the use of mesenchymal stem/progenitor cells with or without scaffolds. Mesenchymal stem/progenitor cells are promising graft cells for tissue regeneration, but the most suitable source of cells for cartilage repair remains controversial. The tissue origin of mesenchymal stem/progenitor cells notably influences the biological properties and therapeutic potential. It is well known that mesenchymal stem/progenitor cells derived from synovial joint tissues exhibit superior chondrogenic ability compared with those derived from non-joint tissues; thus, these cell populations are considered ideal sources for cartilage regeneration. In addition to the progress in research and promising preclinical results, many important research questions must be answered before widespread success in cartilage regeneration is achieved. This review outlines the biology of stem/progenitor cells derived from the articular cartilage, the synovial membrane, and the synovial fluid, including their tissue distribution, function and biological characteristics. Furthermore, preclinical and clinical trials focusing on their applications for cartilage regeneration are summarized, and future research perspectives are discussed.

Repair of articular cartilage defects with intra-articular injection of autologous rabbit synovial fluid-derived mesenchymal stem cells

Background

The role of rabbit synovial fluid-derived mesenchymal stem cells (rbSF-MSCs) in cartilage defect repair remains undefined. This work evaluates the in vivo effects of rbSF-MSCs to repair knee articular cartilage defects in a rabbit model.

Methods

Cartilage defects were made in the patellar grooves of New Zealand white rabbits. The rbSF-MSCs were generated from the knee cavity by arthrocentesis. Passage 5 rbSF-MSCs were assayed by flow cytometry. The multipotency of rbSF-MSCs was confirmed after 3 weeks induction in vitro and the autologous rbSF-MSCs and predifferentiated rbSF-MSCs were injected into the synovial cavity. The intra-articular injection was performed once a week for 4 weeks. The animals were euthanized and the articular surfaces were subjected to macroscopic and histological evaluations at 8 and 12 weeks after the first intra-articular injection.

Results

Hyaline-like cartilage was detected in the defects treated with rbSF-MSCs, while fibrocartilage tissue formed in the defects treated with chondrocytes induced from rbSF-MSCs.

Conclusions

Our results suggest that autologous undifferentiated rbSF-MSCs are favorable to articular cartilage regeneration in treating cartilage defects.

Electronic supplementary material

The online version of this article (10.1186/s12967-018-1485-8) contains supplementary material, which is available to authorized users.

Cell viability assessed in a reproducible model of human osteoblasts derived from human adipose-derived stem cells

Human adipose tissue-derived stem cells (hASCs) have been subjected to extensive investigation because of their self-renewal properties and potential to restore damaged tissues. In the literature, there are several protocols for differentiating hASCs into osteoblasts, but there is no report on the control of cell viability during this process. In this study, we used osteoblasts derived from hASCs of patients undergoing abdominoplasty. The cells were observed at the beginning and end of bone matrix formation, and the expression of proteins involved in this process, including alkaline phosphatase and osteocalcin, was assessed. RANKL, Osterix, Runx2, Collagen3A1, Osteopontin and BSP expression levels were analyzed using real-time PCR, in addition to a quantitative assessment of protein levels of the markers CD45, CD105, STRO-1, and Nanog, using immunofluorescence. Rhodamine (Rho123), cytochrome-c, caspase-3, P-27, cyclin D1, and autophagy cell markers were analyzed by flow cytometry to demonstrate potential cellular activity and the absence of apoptotic and tumor cell processes before and after cell differentiation. The formation of bone matrix, along with calcium nodules, was observed after 16 days of osteoinduction. The gene expression levels of RANKL, Osterix, Runx2, Collagen3A1, Osteopontin, BSP and alkaline phosphatase activity were also elevated after 16 days of osteoinduction, whereas the level of osteocalcin was higher after 21 days of osteoinduction. Our data also showed that the cells had a high mitochondrial membrane potential and a low expression of apoptotic and tumor markers, both before and after differentiation. Cells were viable after the different phases of differentiation. This proposed methodology, using markers to evaluate cell viability, is therefore successful in assessing different phases of stem cell isolation and differentiation.

Concepts and challenges in the use of mesenchymal stem cells as a treatment for cartilage damage in the horse

Osteoarthritis (OA), the most common form of joint disease affecting humans and horses, is characterized by the advance and decline of cartilage and loss of function of the affected joint. The progression of OA is steadily accompanied with biochemical events, which interfere with the cytokines and proteolytic enzymes responsible for progress of the disease. Recently, regenerative therapies have been used with an assumption that mesenchymal stem cells (MSCs) possess the potential to prevent the advancement of cartilage damage and potentially regenerate the injured tissue with an ultimate goal of preventing OA. We believe that despite various challenges, the use of allogenic versus autologous MSCs in cartilage regeneration, is a major issue which can directly or indirectly affect the other factors including, the timing of implantation, dose or cell numbers for implantation, and the source of MSCs. Current knowledge reporting some of these challenges that the clinicians might face in the treatment of cartilage damage in horses are presented. In this regard we conducted two independent studies. In the first study we compared donor matched bone marrow and synovial fluid - derived equine MSCs in vitro, and showed that the SFMSCs were similar to the BMMSCs in their proliferation, expression of CD29, CD44 and CD90, but, exhibited a significantly different chondrogenesis. Additionally, 3.2-21% of all SFMSCs were positive for MHC II, whereas, BMMSCs were negative. In the second study we observed that injection of both the autologous and allogenic SFMSCs into the tarsocrural joint resulted in elevated levels of total protein and total nucleated cell counts. Further experiments to evaluate the in vivo acute or chronic response to allogenic or autologous MSCs are imperative.

Mammalian MSC from selected species: Features and applications

Mesenchymal stromal/stem cells (MSC) are promising candidates for cellular therapy of different diseases in humans and in animals. Following the guidelines of the International Society for Cell Therapy, human MSC may be identified by expression of a specific panel of cell surface markers (CD105+, CD73+, CD90+, CD34-, CD14-, or CD11b-, CD79- or CD19-, HLA-DR-). In addition, multiple differentiation potential into at least the osteogenic, adipogenic, and chondrogenic lineage is a main criterion for MSC definition. Human MSC and MSC of a variety of mammals isolated from different tissues meet these criteria. In addition to the abovementioned, they express many more cell surface markers. Yet, these are not uniquely expressed by MSC. The gross phenotypic appearance like marker expression and differentiation potential is similar albeit not identical for MSC from different tissues and species. Similarly, MSC may feature different biological characteristics depending on the tissue source and the isolation and culture procedures. Their versatile biological qualities comprising immunomodulatory, anti-inflammatory, and proregenerative capacities rely largely on the migratory and secretory capabilities of MSC. They are attracted to sites of tissue lesion and secrete factors to promote self-repair of the injured tissue. This is a big perspective for clinical MSC applications in both veterinary and human medicine. Phase I/II clinical trials have been initiated to assess safety and feasibility of MSC therapies in acute and chronic disease settings. Yet, since the mode of MSC action in a specific disease environment is still unknown at large, it is mandatory to unravel the response of MSC from a given source onto a specific disease environment in suitable animal models prior to clinical applications. © 2017 International Society for Advancement of Cytometry.

Donor-Matched Comparison of Chondrogenic Potential of Equine Bone Marrow- and Synovial Fluid-Derived Mesenchymal Stem Cells: Implications for Cartilage Tissue Regeneration

Mesenchymal stem cells (MSCs) have been demonstrated to be useful for cartilage tissue regeneration. Bone marrow (BM) and synovial fluid (SF) are promising sources for MSCs to be used in cartilage regeneration. In order to improve the clinical outcomes, it is recommended that prior to clinical use, the cellular properties and, specifically, their chondrogenic potential must be investigated. The purpose of this study is to compare and better understand the in vitro chondrogenic potential of equine bone marrow-derived mesenchymal stem cells (BMMSCs) and synovial fluid-derived mesenchymal stem cells (SFMSCs) populated from the same equine donor. BM- and SF-derived MSCs cultures were generated from five equine donors, and the MSCs were evaluated in vitro for their morphology, proliferation, trilineage differentiation, and immunophenotyping. Differences in their chondrogenic potentials were further evaluated quantitatively using glycosaminoglycan (GAG) content and via immunofluorescence of chondrogenic differentiation protein markers, SRY-type HMG box9, Aggrecan, and collagen II. The BMMSCs and SFMSCs were similar in cellular morphology, viability, and immunophenotype, but, varied in their chondrogenic potential, and expression of the key chondrogenic proteins. The SFMSCs exhibited a significant increase in GAG content compared to the BMMSCs (P < 0.0001) in three donors, suggesting increased levels of chondrogenesis. The expression of the key chondrogenic proteins correlated positively with the GAG content, suggesting that the differentiation process is dependent on the expression of the target proteins in these three donors. Our findings suggest that even though SFMSCs were hypothesized to be more chondrogenic relative to BMMSCs, there was considerable donor-to-donor variation in the primary cultures of MSCs which can significantly affect their downstream application.

Comparative study of equine mesenchymal stem cells from healthy and injured synovial tissues: an in vitro assessment

Background

Bone marrow and adipose tissues are known sources of mesenchymal stem cells (MSCs) in horses; however, synovial tissues might be a promising alternative. The aim of this study was to evaluate phenotypic characteristics and differentiation potential of equine MSCs from synovial fluid (SF) and synovial membrane (SM) of healthy joints (SF-H and SM-H), joints with osteoarthritis (SF-OA and SM-OA) and joints with osteochondritis dissecans (SF-OCD and SM-OCD) to determine the most suitable synovial source for an allogeneic therapy cell bank.

Methods

Expression of the markers CD90, CD105, CD44, and CD34 in SF-H, SM-H, SF-OA, SM-OA, SF-OCD and SM-OCD was verified by flow cytometry, and expression of cytokeratin, vimentin, PGP 9.5, PCNA, lysozyme, nanog, and Oct4 was verified by immunocytochemistry. MSCs were cultured and evaluated for their chondrogenic, osteogenic and adipogenic differentiation potential. Final quantification of extracellular matrix and mineralized matrix was determined using AxioVision software. A tumorigenicity test was conducted in Balb-C^nu/nu mice to verify the safety of the MSCs from these sources.

Results

Cultured cells from SF and SM exhibited fibroblastoid morphology and the ability to adhere to plastic. The time elapsed between primary culture and the third passage was approximately 73 days for SF-H, 89 days for SF-OCD, 60 days for SF-OA, 68 days for SM-H, 57 days for SM-OCD and 54 days for SM-OA. The doubling time for SF-OCD was higher than that for other cells at the first passage (P < 0.05). MSCs from synovial tissues showed positive expression of the markers CD90, CD44, lysozyme, PGP 9.5, PCNA and vimentin and were able to differentiate into chondrogenic (21 days) and osteogenic (21 days) lineages, and, although poorly, into adipogenic lineages (14 days). The areas staining positive for extracellular matrix in the SF-H and SM-H groups were larger than those in the SF-OA and SM-OA groups (P < 0.05). The positive mineralized matrix area in the SF-H group was larger than those in all the other groups (P < 0.05). The studied cells exhibited no tumorigenic effects.

Conclusions

SF and SM are viable sources of equine MSCs. All sources studied provide suitable MSCs for an allogeneic therapy cell bank; nevertheless, MSCs from healthy joints may be preferable for cell banking purposes because they exhibit better chondrogenic differentiation capacity.