Evaluation of early cellular influences of bone morphogenetic proteins 12 and 2 on equine superficial digital flexor tenocytes and bone marrow-derived mesenchymal stem cells in vitro

Interleukin-1β in tendon injury enhances reparative gene and protein expression in mesenchymal stem cells

Tendon injury in the horse carries a high morbidity and monetary burden. Despite appropriate therapy, reinjury is estimated to occur in 50–65% of cases. Although intralesional mesenchymal stem cell (MSC) therapy has improved tissue architecture and reinjury rates, the mechanisms by which they promote repair are still being investigated. Additionally, reevaluating our application of MSCs in tendon injury is necessary given recent evidence that suggests MSCs exposed to inflammation (deemed MSC licensing) have an enhanced reparative effect. However, applying MSC therapy in this context is limited by the inadequate quantification of the temporal cytokine profile in tendon injury, which hinders our ability to administer MSCs into an environment that could potentiate their effect. Therefore, the objectives of this study were to define the temporal cytokine microenvironment in a surgically induced model of equine tendon injury using ultrafiltration probes and subsequently evaluate changes in MSC gene and protein expression following in vitro inflammatory licensing with cytokines of similar concentration as identified in vivo. In our in vivo surgically induced tendon injury model, IL-1β and IL-6 were the predominant pro-inflammatory cytokines present in tendon ultrafiltrate where a discrete peak in cytokine concentration occurred within 48 h following injury. Thereafter, MSCs were licensed in vitro with IL-1β and IL-6 at a concentration identified from the in vivo study; however, only IL-1β induced upregulation of multiple genes beneficial to tendon healing as identified by RNA-sequencing. Specifically, vascular development, ECM synthesis and remodeling, chemokine and growth factor function alteration, and immunomodulation and tissue reparative genes were significantly upregulated. A significant increase in the protein expression of IL-6, VEGF, and PGE2 was confirmed in IL-1β-licensed MSCs compared to naïve MSCs. This study improves our knowledge of the temporal tendon cytokine microenvironment following injury, which could be beneficial for the development and determining optimal timing of administration of regenerative therapies. Furthermore, these data support the need to further study the benefit of MSCs administered within the inflamed tendon microenvironment or exogenously licensed with IL-1β in vitro prior to treatment as licensed MSCs could enhance their therapeutic benefit in the healing tendon.

The combination of BMP12 and KY02111 enhances tendon differentiation in bone marrow-derived equine mesenchymal stromal cells (BM-eMSCs)

The Wingless and Int-1 (WNT) and bone morphogenic protein/growth differentiation factor (BMP/GDF) signalling pathways contribute significantly to the development of the musculoskeletal system. The mechanism by which they contribute is as follows: BMP/GDF signalling usually promotes tendon differentiation, whereas WNT signalling inhibits it. We hypothesised that inhibiting WNT and subsequently stimulating BMP signalling may enhance the tenogenic differentiation of stem cells. The objective of this study was to determine whether a combination of WNT inhibitor (KY02111) and BMP12/GDF7 protein could enhance the differentiation of bone marrow-derived equine mesenchymal stromal cells (BM-eMSCs) into tenocytes. Cells were cultured in five treatments: control, BMP12, and three different combinations of BMP12 and KY02111. The results indicated that a 1-day treatment with KY02111 followed by a 13-day treatment with BMP12 resulted in the highest tenogenic differentiation score in this experiment. The effect of KY02111 is dependent on the incubation time, with 1 day being better than 3 or 5 days. This combination increased tenogenic gene marker expression, including SCX, TNMD, DCN, and TNC, as well as COL1 protein expression. In conclusion, we propose that a combination of BMP12 and KY02111 can enhance the in vitro tenogenic differentiation of BM-eMSCs more than BMP12 alone. The findings of this study might be useful for improving tendon differentiation protocols for stem cell transplantation and application to tendon regeneration.

Strategies of tenogenic differentiation of equine stem cells for tendon repair: current status and challenges

Tendon injuries, as one of the most common orthopedic disorders, are the major cause of early retirement or wastage among sport horses which mainly affect the superficial digital flexor tendon (SDFT). Tendon repair is a slow process, and tendon tissue is often replaced by scar tissue. The current treatment options are often followed by an incomplete recovery that increases the susceptibility to re-injury. Recently, cell therapy has been used in veterinary medicine to treat tendon injuries, although the risk of ectopic bone formation after cell injection is possible in some cases. In vitro tenogenic induction may overcome the mentioned risk in clinical application. Moreover, a better understanding of treatment strategies for musculoskeletal injuries in horse may have future applications for human and vice versa. This comprehensive review outlines the current strategies of stem cell therapy in equine tendon injury and in vitro tenogenic induction of equine stem cell.

Identification of Novel Equine (Equus caballus) Tendon Markers Using RNA Sequencing

Although several tendon-selective genes exist, they are also expressed in other musculoskeletal tissues. As cell and tissue engineering is reliant on specific molecular markers to discriminate between cell types, tendon-specific genes need to be identified. In order to accomplish this, we have used RNA sequencing (RNA-seq) to compare gene expression between tendon, bone, cartilage and ligament from horses. We identified several tendon-selective gene markers, and established eyes absent homolog 2 (EYA2) and a G-protein regulated inducer of neurite outgrowth 3 (GPRIN3) as specific tendon markers using RT-qPCR. Equine tendon cells cultured as three-dimensional spheroids expressed significantly greater levels of EYA2 than GPRIN3, and stained positively for EYA2 using immunohistochemistry. EYA2 was also found in fibroblast-like cells within the tendon tissue matrix and in cells localized to the vascular endothelium. In summary, we have identified EYA2 and GPRIN3 as specific molecular markers of equine tendon as compared to bone, cartilage and ligament, and provide evidence for the use of EYA2 as an additional marker for tendon cells in vitro.

Early cellular responses of BMSCs genetically modified with bFGF/BMP2 co-cultured with ligament fibroblasts in a three-dimensional model in vitro

Currently, a number of strategies including the implantation of bone marrow-derived mesenchymal stem cells (BMSCs) and growth factors have been developed to regenerate the tendon-to-bone interface after performing anterior cruciate ligament reconstruction. However, the mechanisms behind the interactions of the implanted BMSCs and tendon cells remain to be elucidated. The aim of this study was to evaluate the early cellular responses of BMSCs genetically modified with basic growth factor growth factor (bFGF)/bone morphogenic protein 2 (BMP2) and ligament fibroblasts in a three-dimensional co-culture model. BMSCs and ligament fibroblasts were both isolated from male Wistar rats. The BMSCs were then transfected with an adenoviral vector carrying bFGF or BMP2. The transfected BMSCs and ligament fibroblasts both encapsulated in alginate beads were co-cultured for 6 days in three-dimensional model. On days 0, 3 and 6, cell proliferation was assayed. On day 6, the expression of several tendon-bone related markers was evaluated. In the co-culture system, bFGF and BMP2 were highly expressed at the mRNA and protein level. During the process, bFGF significantly promoted cell proliferation, as well as the expression of scleraxis (SCX) and collagen (COL) type Ⅰ (COL1) in the BMSCs; however, it markedly decreased the expression of phenotype markers in the ligament fibroblasts, including COL1 and COL3. BMP2 markedly increased the expression of alkaline phosphatase and osteocalcin in the BMSCs and ligament fibroblasts, whereas it had no obvious effect on cell proliferation and collagen synthesis in the ligament fibroblasts. The combination of bFGF and BMP2 resulted in the similarly enhanced proliferation of BMSCs and ligament fibroblasts as observed with bFGF alone; however, this combination more potently promoted osteogenic differentiation than did BMP2 alone. The findings of our study demonstrate the superiority of the combined use of growth factors in inducing osteogenic differentiation and provide a theoretical foundation for the regeneration of the tendon-to-bone interface.

Progress in cell-based therapies for tendon repair

The last decade has seen significant developments in cell therapies, based on permanently differentiated, reprogrammed or engineered stem cells, for tendon injuries and degenerative conditions. In vitro studies assess the influence of biophysical, biochemical and biological signals on tenogenic phenotype maintenance and/or differentiation towards tenogenic lineage. However, the ideal culture environment has yet to be identified due to the lack of standardised experimental setup and readout system. Bone marrow mesenchymal stem cells and tenocytes/dermal fibroblasts appear to be the cell populations of choice for clinical translation in equine and human patients respectively based on circumstantial, rather than on hard evidence. Collaborative, inter- and multi-disciplinary efforts are expected to provide clinically relevant and commercially viable cell-based therapies for tendon repair and regeneration in the years to come.

Bone morphogenetic protein-12 induces tenogenic differentiation of mesenchymal stem cells derived from equine amniotic fluid

Tendon injuries are common in race horses, and mesenchymal stem cells (MSCs) isolated from adult and foetal tissue have been used for tendon regeneration. In the present study, we evaluated equine amniotic fluid (AF) as a source of MSCs and standardised methodology and markers for their in vitro tenogenic differentiation. Plastic-adherent colonies were isolated from 12 of 20 AF samples by day 6 after seeding and 70-80% cell confluency was reached by day 17. These cells expressed mesenchymal surface markers [cluster of differentiation (CD)73, CD90 and CD105] by reverse transcription (RT)-polymerase chain reaction (PCR) and immunocytochemistry, but did not express haematopoietic markers (CD34, CD45 and CD14). In flow cytometry, the expression of CD29, CD44, CD73 and CD90 was observed in 68.83 ± 1.27, 93.66 ± 1.80, 96.96 ± 0.44 and 93.7 ± 1.89% of AF-MSCs, respectively. Osteogenic, chondrogenic and adipogenic differentiation of MSCs was confirmed by von Kossa and Alizarin red S, Alcian blue and oil red O staining, respectively. Upon supplementation of MSC growth media with 50 ng/ml bone morphogenetic protein (BMP)-12, AF-MSCs differentiated to tenocytes within 14 days. The differentiated cells were more slender, elongated and spindle shaped with thinner and longer cytoplasmic processes and showed expression of tenomodulin and decorin by RT-PCR and immunocytochemistry. In flow cytometry, 96.7 ± 1.90 and 80.9 ± 6.4% of differentiated cells expressed tenomodulin and decorin in comparison to 1.6 and 3.1% in undifferentiated control cells, respectively. Our results suggest that AF is an easily accessible and effective source of MSCs. On BMP-12 supplementation, AF-MSCs can be differentiated to tenocytes, which could be exploited for regeneration of ruptured or damaged tendon in race horses.

Relationship between muscle fatty infiltration and the biological characteristics and stimulation potential of tenocytes from rotator cuff tears

The healing after rotator cuff surgery is still dissatisfying, and increased muscle fatty infiltration even more impairs the healing success. To achieve sufficient healing after rotator cuff reconstructions, the use of growth factors may be one possibility. The aim of the study was to identify a possible relationship between fatty infiltration of the supraspinatus muscle and cellular biological characteristics and stimulation potential of tenocyte-like cells (TLCs). TLCs of 3 donor groups differing in grade of muscle fatty infiltration were analyzed for their cellular characteristics and were stimulated with BMP-2 or BMP-7 in a 3D scaffold culture. The cell count and potency for self-renewal were significantly decreased in TLCs from donors with high muscle fatty infiltration compared to the lower fatty infiltration groups. Cell count and collagen-I expression as well as protein synthesis were stimulated by growth factors. Interestingly, TLCs of the high fatty infiltration group exhibited a weaker stimulation potential compared to the other groups. TLCs from donors with high muscle fatty infiltration generally revealed inferior characteristics compared to cells of lower fatty infiltration groups, which may be one reason for a weaker healing potential and may represent a possible starting point for the development of future treatment options.

Culture conditions for equine bone marrow mesenchymal stem cells and expression of key transcription factors during their differentiation into osteoblasts

BACKGROUND

The use of equine bone marrow mesenchymal stem cells (BMSC) is a novel method to improve fracture healing in horses. However, additional research is needed to identify optimal culture conditions and to determine the mechanisms involved in regulating BMSC differentiation into osteoblasts. The objectives of the experiments were to determine: 1) if autologous or commercial serum is better for proliferation and differentiation of equine BMSC into osteoblasts, and 2) the expression of key transcription factors during the differentiation of equine BMSC into osteoblasts. Equine BMSC were isolated from the sterna of 3 horses, treated with purchased fetal bovine serum (FBS) or autologous horse serum (HS), and cell proliferation determined. To induce osteoblast differentiation, cells were incubated with L-ascorbic acid-2-phosphate and glycerol-2-phosphate in the presence or absence of human bone morphogenetic protein2 (BMP2), dexamethasone (DEX), or combination of the two. Alkaline phosphatase (ALP) activity, a marker of osteoblast differentiation, was determined by ELISA. Total RNA was isolated from differentiating BMSC between d 0 to 18 to determine expression of runt-related transcription factor2 (Runx2), osterix (Osx), and T-box3 (Tbx3). Data were analyzed by ANOVA.

RESULTS

Relative to control, FBS and HS increased cell number (133 ± 5 and 116 ± 5%, respectively; P < 0.001) and 5-bromo-2'-deoxyuridine (BrdU) incorporation (167 ± 6 and 120 ± 6%, respectively; P < 0.001). Treatment with DEX increased ALP activity compared with control (1,638 ± 38%; P < 0.001). In the absence and presence of Dex, BMP-2 did not alter ALP activity (P > 0.8). Runt-related transcription factor2 expression increased 3-fold (P < 0.001) by d 6 of culture. Osterix expression increased 9-fold (P < 0.05) by d 18 of culture. Expression of Tbx3 increased 1.8-fold at d 3 (P < 0.01); however expression was reduced 4-fold at d 18 (P < 0.01).

CONCLUSIONS

Dexamethasone, but not BMP-2, is required for differentiation of equine BMSC into osteoblasts. In addition, expression of Runx2 and osterix increased and expression of Tbx3 is reduced during differentiation.

Inflammatory effects of autologous, genetically modified autologous, allogeneic, and xenogeneic mesenchymal stem cells after intra-articular injection in horses

OBJECTIVES

To compare the clinical and inflammatory joint responses to intra-articular injection of bone marrow-derived mesenchymal stem cells (MSC) including autologous, genetically modified autologous, allogeneic, or xenogeneic cells in horses.

METHODS

Six five-year-old Thoroughbred mares had one fetlock joint injected with Gey's balanced salt solution as the vehicle control. Each fetlock joint of each horse was subsequently injected with 15 million MSC from the described MSC groups, and were assessed for 28 days for clinical and inflammatory parameters representing synovitis, joint swelling, and pain.

RESULTS

There were not any significant differences between autologous and genetically modified autologous MSC for synovial fluid total nucleated cell count, total protein, interleukin (IL)-6, IL-10, fetlock circumference, oedema score, pain-free range-of-motion, and soluble gene products that were detected for at least two days. Allogeneic and xenogeneic MSC produced a greater increase in peak of inflammation at 24 hours than either autologous MSC group.

CLINICAL SIGNIFICANCE

Genetically engineered MSC can act as vehicles to deliver gene products to the joint; further investigation into the therapeutic potential of this cell therapy is warranted. Intra-articular MSC injection resulted in a moderate acute inflammatory joint response that was greater for allogeneic and xenogeneic MSC than autologous MSC. Clinical management of this response may minimize this effect.

Modulation of osteoblastic/odontoblastic differentiation of adult mesenchymal stem cells through gene introduction: a brief review

Bone tissue engineering is one of the important therapeutic approaches to the regeneration of bones in the entire field of regeneration medicine. Mesenchymal stem cells (MSCs) are actively discussed as material for bone tissue engineering due to their ability to differentiate into autologous bone. MSCs are able to differentiate into different lineages: osteo/odontogenic, adipogenic, and neurogenic. The tissue of origin for MSCs defines them as bone marrow-derived stem cells, adipose tissue-derived stem cells, and, among many others, dental stem cells. According to the tissue of origin, DSCs are further stratified into dental pulp stem cells, periodontal ligament stem cells, stem cells from apical papilla, stem cells from human exfoliated deciduous teeth, dental follicle precursor cells, and dental papilla cells. There are numerous in vitro/in vivo reports suggesting successful mineralization potential or osteo/odontogenic ability of MSCs. Still, there is further need for the optimization of MSCs-based tissue engineering methods, and the introduction of genes related to osteo/odontogenic differentiation into MSCs might aid in the process. In this review, articles that reported enhanced osteo/odontogenic differentiation with gene introduction into MSCs will be discussed to provide a background for successful bone tissue engineering using MSCs with artificially introduced genes.

BMP-2 and BMP-7 affect human rotator cuff tendon cells in vitro

BACKGROUND

Rotator cuff repair is prone to incomplete regeneration. To explore biological improvements of tendon-bone healing, it was the aim of this study to investigate the influence of growth factors bone morphogenetic protein (BMP)-2 and BMP-7 on tenocyte cell activity and matrix gene expression and production. A beneficial effect of these factors would be promising to improve tendon-bone healing in vivo.

METHODS

Tenocyte-like cells were isolated from human rotator cuff tissue samples (supraspinatus and long head of biceps tendon) and incubated with BMP-2 (100-1000 ng/mL) and BMP-7 (100-2000 ng/mL), both alone and in combination. At days 0, 3, and 6, cell activity was assessed. At day 6, collagen type I production and the expression of several tendon-, bone-, and cartilage-related markers (collagen types I-III, osteocalcin, scleraxis) were evaluated.

RESULTS

Dose-dependent effects of both investigated growth factors on tenocyte-like cells were observed. Application of BMP-2 increased collagen type I production significantly but its expression only slightly. Cell activity was decreased in higher doses over time. For BMP-7, a significant increase in collagen type I production and expression, as well as increased cell activity, was observed. The addition of both factors resulted in decreased parameters when compared with BMP-7 alone. The expression of collagen types II and III, osteocalcin, and scleraxis was not significantly affected by application of BMPs.

CONCLUSION

Besides the well-known effects of BMP-2 and BMP-7 on osteoblasts, this study describes further effects on rotator cuff tendon cell biology. Both tissue types potentially need to be addressed to improve tendon-bone healing of the rotator cuff.

Chondrogenic effects of exogenous retinoic acid or a retinoic acid receptor antagonist (LE135) on equine chondrocytes and bone marrow-derived mesenchymal stem cells in monolayer culture

OBJECTIVE

To determine effects of various concentrations of retinoic acid (RA) or a synthetic RA receptor antagonist (LE135) on equine chondrocytes or bone marrow-derived equine mesenchymal stem cells (BMDMSCs) in monolayer cultures.

SAMPLE

Articular cartilage and BMDMSCs from 5 clinically normal horses.

PROCEDURES

Monolayers of chondrocytes cultured in standard media and of BMDMSCs cultured in chondrogenic media were treated with RA at concentrations of 0, 0.1, 1, or 10 μM or LE135 at concentrations of 0, 0.1, 1, or 10 μM on day 0. On days 7 and 14, samples were analyzed for DNA concentration, chondrocyte morphology or features consistent with chondrogenesis (ie, chondral morphology [scored from 0 to 4]), and gene expression of collagen type Ia (CI), collagen type II (CII), and aggrecan.

RESULTS

Chondrocytes treated with RA had more mature chondral morphology (range of median scores, 3.0 to 4.0) than did untreated controls (range of median scores, 0.5 to 0.5). Chondrocytes treated with LE135 did not sustain chondrocyte morphology. All BMDMSCs had evidence of chondral morphology or high CII:CI ratio. Retinoic acid (1 or 10 μM) or LE135 (10 μM) treatment decreased DNA content of BMDMSC cultures. At 0.1 and 1 μM concentrations, LE135 weakly but significantly increased chondral morphology scores, compared with untreated controls, but lack of aggrecan expression and lack of increased CII:CI ratio, compared with that of controls, did not affect chondrogenesis.

CONCLUSIONS AND CLINICAL RELEVANCE

RA promoted maturation and hypertrophy in chondrocytes but not BMDMSCs in monolayer cultures. Deficiency or blockade of RA may prevent hypertrophy and maturation of differentiated chondrocytes.

Biological aspects of rotator cuff healing

Tendon tears of the rotator cuff show a high prevalence in today's population. Patients suffer from permanent pain and disability, and surgical reconstruction may be the only possibility for abatement. The complex process of tendon-bone healing leads to mechanically inferior scar-tissue, which often results in retears or non-healing. In the current literature, factors such as patients age, sex and fatty muscle infiltration are highly correlated to the presence of rotator cuff tears and the incidence of retears. To improve the tendon tissue quality after surgical reconstructions biologically based strategies with use of growth factors arouse more and more interest in the last years. However, to optimize the treatment of rotator cuff tears the biological background of tears and retears must be investigated in more detail. This article will elucidate different aspects that have an impact on rotator cuff healing and give a brief insight in tendon/ligament cell culture and animal studies focusing on growth factor treatments.

The regenerative medicine laboratory: facilitating stem cell therapy for equine disease

This article focuses on the emerging field of equine regenerative medicine with an emphasis on the use of mesenchymal stem cells (MSCs) for orthopedic diseases. We detail laboratory procedures and protocols for tissue handling and MSC isolation, characterization, expansion, and cryopreservation from bone marrow, fat, and placental tissues. We provide an overview of current clinical uses for equine MSCs and how MSCs function to heal tissues. Current laboratory practices in equine regenerative medicine mirror those in the human field. However, the translational use of autologous and allogeneic MSCs for patient therapy far exceeds what is currently permitted in human medicine.

Equine clinical genomics: A clinician's primer

The objective of this review is to introduce equine clinicians to the rapidly evolving field of clinical genomics with a vision of improving the health and welfare of the domestic horse. For 15 years a consortium of veterinary geneticists and clinicians has worked together under the umbrella of The Horse Genome Project. This group, encompassing 22 laboratories in 12 countries, has made rapid progress, developing several iterations of linkage, physical and comparative gene maps of the horse with increasing levels of detail. In early 2006, the research was greatly facilitated when the US National Human Genome Research Institute of the National Institutes of Health added the horse to the list of mammalian species scheduled for whole genome sequencing. The genome of the domestic horse has now been sequenced and is available to researchers worldwide in publicly accessible databases. This achievement creates the potential for transformative change within the horse industry, particularly in the fields of internal medicine, sports medicine and reproduction. The genome sequence has enabled the development of new genome-wide tools and resources for studying inherited diseases of the horse. To date, researchers have identified 11 mutations causing 10 clinical syndromes in the horse. Testing is commercially available for all but one of these diseases. Future research will probably identify the genetic bases for other equine diseases, produce new diagnostic tests and generate novel therapeutics for some of these conditions. This will enable equine clinicians to play a critical role in ensuring the thoughtful and appropriate application of this knowledge as they assist clients with breeding and clinical decision-making.