Tenogenic differentiation protocol in xenogenic-free media enhances tendon-related marker expression in ASCs

Role of sodium-dependent vitamin C transporter 2 in human periodontal ligament fibroblasts

AIM

Ascorbic acid (AA) is a water-soluble vitamin that has antioxidant properties and regulates homeostasis of connective tissue through controlling various enzymatic activities. Two cell surface glycoproteins, sodium-dependent vitamin C transporter (SVCT) 1 and SVCT2, are known as ascorbate transporters. The purpose of this study was to investigate the expression pattern and functions of SVCTs in periodontal ligament (PDL) and PDL fibroblast (PDLF).

METHODS

Gene expression was examined using real-time polymerase chain reaction (PCR) and reverse transcription PCR. SVCT2 expression was determined by immunofluorescence staining, western blot and flow cytometry. ALP activity and collagen production were examined using ALP staining and collagen staining. Short interfering RNA was used to knock down the gene level of SVCT2. Change of comprehensive gene expression under SVCT2 knockdown condition was examined by RNA-sequencing analysis.

RESULTS

Real-time PCR, fluorescent immunostaining, western blot and flowy cytometry showed that SVCT2 was expressed in PDLF and PDL. ALP activity, collagen production, and SVCT2 expression were enhanced upon AA stimulation in PDLF. The enhancement of ALP activity, collagen production, and SVCT2 expression by AA was abolished under SVCT2 knockdown condition. RNA-sequencing revealed that gene expression of CLDN4, Cyclin E2, CAMK4, MSH5, DMC1, and Nidgen2 were changed by SVCT2 knockdown. Among them, the expression of MSH5 and DMC1, which are related to DNA damage sensor activity, was enhanced by AA, suggesting the new molecular target of AA in PDLF.

CONCLUSION

Our study reveals the SVCT2 expression in PDL and the pivotal role of SVCT2 in mediating AA-induced enhancements of ALP activity and collagen production in PDLF. Additionally, we identify alterations in gene expression profiles, highlighting potential molecular targets influenced by AA through SVCT2. These findings deepen our understanding of periodontal tissue homeostasis mechanisms and suggest promising intervention targeting AA metabolism.

Enthesitis on Chip - A Model for Studying Acute and Chronic Inflammation of the Enthesis and its Pharmacological Treatment

Enthesitis, the inflammation of the enthesis, which is the point of attachment of tendons and ligaments to bones, is a common musculoskeletal disease. The inflammation often originates from the fibrocartilage region of the enthesis as a consequence of mechanical overuse or -load and consequently tissue damage. During enthesitis, waves of inflammatory cytokines propagate in(to) the fibrocartilage, resulting in detrimental, heterotopic bone formation. Understanding of human enthesitis and its treatment options is limited, also because of lacking in vitro model systems that can closely mimic the pathophysiology of the enthesis and can be used to develop therapies. In this study, an enthes(it)is-on-chip model is developed. On opposite sides of a porous culture membrane separating the chip's two microfluidic compartments, human mesenchymal stromal cells are selectively differentiated into tenocytes and fibrochondrocytes. By introducing an inflammatory cytokine cocktail into the fibrochondrocyte compartment, key aspects of acute and chronic enthesitis, measured as increased expression of inflammatory markers, can be recapitulated. Upon inducing chronic inflammatory conditions, hydroxyapatite deposition, enhanced osteogenic marker expression and reduced secretion of tissue-related extracellular matrix components are observed. Adding the anti-inflammatory drug celecoxib to the fibrochondrocyte compartment mitigates the inflammatory state, demonstrating the potential of the enthesitis-on-chip model for drug testing.

Comparison of infant bone marrow- and umbilical cord-derived mesenchymal stem cells in multilineage differentiation

We compared infant bone marrow-derived mesenchymal stem cells (infant BMSCs) with umbilical cord-derived mesenchymal stem cells (UCSCs) by assessing multilineage differentiation. Proliferation was gauged through changes in cell numbers and doubling time. Senescence-related genes (p16, p21, and p53), senescence-associated β-galactosidase (SA-β-gal), and γH2AX immunofluorescence determined senescence presence. Superoxide dismutases (SODs) and genes related to various differentiations were analyzed using reverse transcription-quantitative polymerase chain reaction (RT-qPCR). Differentiation was confirmed through histochemical, immunohistochemical, and immunofluorescence staining. Infant BMSCs surpassed UCSCs in proliferation. Infant BMSCs exhibited lower senescence-related gene expression at late passages, upregulated antioxidant enzymes during early passages, and reduced SA-β-gal staining. Chondrogenic gene expression (SOX9, COL2, and COL10) was enhanced in infant BMSCs, along with improved immunohistochemical staining. Infant BMSCs showed higher expression of osteogenic (ALP and OCN) and adipogenic (PPARγ and LPL) genes, confirmed by histochemical staining. However, UCSCs had higher expression of tenogenic genes (MMP3, SCX, DCN, and TNC). Hepatogenic differentiation potential was similar, with no significant difference in hepatogenic gene expression (ALB and TAT). Compared to UCSCs, infant BMSCs demonstrated superior proliferation, reduced senescence, increased antioxidant capacity, and enhanced differentiation potential toward chondrogenic, osteogenic, and adipogenic lineages.

Viable tendon neotissue from adult adipose-derived multipotent stromal cells

Background: Tendon healing is frequently prolonged, unpredictable, and results in poor tissue quality. Neotissue formed by adult multipotent stromal cells has the potential to guide healthy tendon tissue formation. Objectives: The objective of this study was to characterize tendon neotissue generated by equine adult adipose-derived multipotent stromal cells (ASCs) on collagen type I (COLI) templates under 10% strain in a novel bioreactor. The tested hypothesis was that ASCs assume a tendon progenitor cell-like morphology, express tendon-related genes, and produce more organized extracellular matrix (ECM) in tenogenic versus stromal medium with perfusion and centrifugal fluid motion. Methods: Equine ASCs on COLI sponge cylinders were cultured in stromal or tenogenic medium within bioreactors during combined perfusion and centrifugal fluid motion for 7, 14, or 21 days under 10% strain. Viable cell distribution and number, tendon-related gene expression, and micro- and ultra-structure were evaluated with calcein-AM/EthD-1 staining, resazurin reduction, RT-PCR, and light, transmission, and scanning electron microscopy. Fibromodulin was localized with immunohistochemistry. Cell number and gene expression were compared between culture media and among culture periods (p < 0.05). Results: Viable cells were distributed throughout constructs for up to 21 days of culture, and cell numbers were higher in tenogenic medium. Individual cells had a round or rhomboid shape with scant ECM in stromal medium in contrast to clusters of parallel, elongated cells surrounded by highly organized ECM in tenogenic medium after 21 days of culture. Transcription factor, extracellular matrix, and mature tendon gene expression profiles confirmed ASC differentiation to a tendon progenitor-like cell in tenogenic medium. Construct micro- and ultra-structure were consistent with tendon neotissue and fibromodulin was present in the ECM after culture in tenogenic medium. Conclusion: Long-term culture in custom bioreactors with combined perfusion and centrifugal tenogenic medium circulation supports differentiation of equine adult ASCs into tendon progenitor-like cells capable of neotissue formation.

Proliferation and Differentiation Potential of Bone Marrow-Derived Mesenchymal Stem Cells From Children With Polydactyly and Adults With Basal Joint Arthritis

This study compared the proliferation and differentiation potential of bone marrow-derived mesenchymal stem cells (BMSCs) derived from infants with polydactyly and adults with basal joint arthritis. The proliferation rate of adult and infant BMSCs was determined by the cell number changes and doubling times. The γH2AX immunofluorescence staining, age-related gene expression, senescence-associated β-galactosidase (SA-β-gal) staining were analyzed to determine the senescence state of adult and infant BMSCs. The expression levels of superoxide dismutases (SODs) and genes associated with various types of differentiation were measured using Real-Time Quantitative Polymerase Chain Reaction (RT-qPCR). Differentiation levels were evaluated through histochemical and immunohistochemical staining. The results showed that infant BMSCs had a significantly higher increase in cell numbers and faster doubling times compared with adult BMSCs. Infant BMSCs at late stages exhibited reduced γH2AX expression and SA-β-gal staining, indicating lower levels of senescence. The expression levels of senescence-related genes (p16, p21, and p53) in infant BMSCs were also lower than in adult BMSCs. In addition, infant BMSCs demonstrated higher antioxidative ability with elevated expression of SOD1, SOD2, and SOD3 compared with adult BMSCs. In terms of differentiation potential, infant BMSCs outperformed adult BMSCs in chondrogenesis, as indicated by higher expression levels of chondrogenic genes (SOX9, COL2, and COL10) and positive immunohistochemical staining. Moreover, differentiated cells derived from infant BMSCs exhibited significantly higher expression levels of osteogenic, tenogenic, hepatogenic, and neurogenic genes compared with those derived from adult BMSCs. Histochemical and immunofluorescence staining confirmed these findings. However, adult BMSCs showed lower adipogenic differentiation potential compared with infant BMSCs. Overall, infant BMSCs demonstrated superior characteristics, including higher proliferation rates, enhanced antioxidative activity, and greater differentiation potential into various lineages. They also exhibited reduced cellular senescence. These findings, within the context of cellular differentiation, suggest potential implications for the use of allogeneic BMSC transplantation, emphasizing the need for further in vivo investigation.

The potential mechanism of hypoxia-induced tenogenic differentiation of mesenchymal stem cell for tendon regeneration

Tendon injuries account up to 50% of all musculoskeletal problems and remains a challenge to treat owing to the poor intrinsic reparative ability of tendon tissues. The natural course of tendon healing is very slow and often leads to fibrosis and disorganized tissues with inferior biomechanical properties. Mesenchymal stem cells (MSC) therapy is a promising alternative strategy to augment tendon repair due to its proliferative and multilineage differentiation potential. Hypoxic conditioning of MSC have been shown to enhance their tenogenic differentiation capacity. However, the mechanistic pathway by which this is achieved is yet to be fully defined. A key factor involved in this pathway is hypoxia-inducible factor-1-alpha (HIF-1α). This review aims to discuss the principal mechanism underlying the enhancement of MSC tenogenic differentiation by hypoxic conditioning, particularly the central role of HIF-1α in mediating activation of tenogenic pathways in the MSC. We focus on the interaction between HIF-1α with fibroblast growth factor-2 (FGF-2) and transforming growth factor-beta 1 (TGF-β1) in regulating MSC tenogenic differentiation pathways in hypoxic conditions. Strategies to promote stabilization of HIF-1α either through direct manipulation of oxygen tension or the use of hypoxia mimicking agents are therefore beneficial in increasing the efficacy of MSC therapy for tendon repair.

In Vitro and In Vivo Effects of IGF-1 Delivery Strategies on Tendon Healing: A Review

Tendon injuries suffer from a slow healing, often ending up in fibrovascular scar formation, leading to inferior mechanical properties and even re-rupture upon resumption of daily work or sports. Strategies including the application of growth factors have been under view for decades. Insulin-like growth factor-1 (IGF-1) is one of the used growth factors and has been applied to tenocyte in vitro cultures as well as in animal preclinical models and to human patients due to its anabolic and matrix stimulating effects. In this narrative review, we cover the current literature on IGF-1, its mechanism of action, in vitro cell cultures (tenocytes and mesenchymal stem cells), as well as in vivo experiments. We conclude from this overview that IGF-1 is a potent stimulus for improving tendon healing due to its inherent support of cell proliferation, DNA and matrix synthesis, particularly collagen I, which is the main component of tendon tissue. Nevertheless, more in vivo studies have to be performed in order to pave the way for an IGF-1 application in orthopedic clinics.

Tendon tissue engineering: Current progress towards an optimized tenogenic differentiation protocol for human stem cells

Tendons are integral to our daily lives by allowing movement and locomotion but are frequently injured, leading to patient discomfort and impaired mobility. Current clinical procedures are unable to fully restore the native structure of the tendon, resulting in loss of full functionality, and the weakened tissue following repair often re-ruptures. Tendon tissue engineering, involving the combination of cells with biomaterial scaffolds to form new tendon tissue, holds promise to improve patient outcomes. A key requirement for efficacy in promoting tendon tissue formation is the optimal differentiation of the starting cell populations, most commonly adult tissue-derived mesenchymal stem/stromal cells (MSCs), into tenocytes, the predominant cellular component of tendon tissue. Currently, a lack of consensus on the protocols for effective tenogenic differentiation is hampering progress in tendon tissue engineering. In this review, we discuss the current state of knowledge regarding human stem cell differentiation towards tenocytes and tendon tissue formation. Tendon development and healing mechanisms are described, followed by a comprehensive overview of the current protocols for tenogenic differentiation, including the effects of biochemical and biophysical cues, and their combination, on tenogenesis. Lastly, a synthesis of the key features of these protocols is used to design future approaches. The holistic evaluation of current knowledge should facilitate and expedite the development of efficacious stem cell tenogenic differentiation protocols with future impact in tendon tissue engineering. STATEMENT OF SIGNIFICANCE: The lack of a widely-adopted tenogenic differentiation protocol has been a major hurdle in the tendon tissue engineering field. Building on current knowledge on tendon development and tendon healing, this review surveys peer-reviewed protocols to present a holistic evaluation and propose a pathway to facilitate and expedite the development of a consensus protocol for stem cell tenogenic differentiation and tendon tissue engineering.

Stem cell sheet interpositioned between the tendon and bone would be better for healing than stem cell sheet overlaid above the tendon-to-bone junction in rotator cuff repair of rats

BACKGROUND

Although stem cells might enhance natural enthesis healing in surgical rotator cuff repair, not much attention has been given to the delivery and location of delivering stem cells. The purpose of this study to know where to locate those stem cells during repair.

METHODS

Animal model of chronic rotator cuff tear was created in 24 rats. Adipose-derived stem cells were engineered as a sheet and transplanted 1) between a torn tendon and humerus (interposition group) or 2) over a repaired tendon-to-bone junction (overlay group) at the time of surgical repair. Tracking of stem cells with overexpression of green fluorescent protein (GFP) were carried out at the time of sacrifice in additional 4 shoulders in each group. Histological and Biomechanical evaluation was performed to compare the differences in tendon-to-bone healing.

RESULTS

Histology showed increased fibrocartilage, a clear boundary at the mineralized fibrocartilage, abundant collagen type III, and higher total scores, especially in the interposition group. GFP-overexpression was observed at the transplanted site at 2 weeks after repair. Although two groups where stem cell sheets applied showed higher load to failure than the repair-only group, the load to failure was not different between the interposition and overlay group.

CONCLUSION

In the chronic rotator cuff repair model, stem cell sheets enhanced regeneration of the tendon-to-bone junction. This regeneration was effective when the stem cell sheet was interpositioned at the tendon-to-bone interface.

LEVEL OF EVIDENCE

Basic Science Study; In Vivo Animal Model; Histology and Biomechanics.

Comparison of the Infant and Adult Adipose-Derived Mesenchymal Stem Cells in Proliferation, Senescence, Anti-oxidative Ability and Differentiation Potential

BACKGROUND

Infant adipose-derived mesenchymal stem cells (ADSCs) collected from excised polydactyly fat tissue, which was surgical waste, could be cultured and expanded in vitro in this study. In addition, the collecting process would not cause pain in the host. In this study, the proliferation, reduction of senescence, anti-oxidative ability, and differentiation potential in the infant ADSCs were compared with those in the adult ADSCs harvested from thigh liposuction to determine the availability of infant ADSCs.

METHODS

Proliferation was determined by detecting the fold changes in cell numbers and doubling time periods. Senescence was analyzed by investigating the age-related gene expression levels and the replicative stress. The superoxide dismutase (SOD) gene expression, adipogenic, neurogenic, osteogenic, and tenogenic differentiation were compared by RT-qPCR. The chondrogenic differentiation efficiency was also determined using RT-qPCR and immunohistochemical staining.

RESULTS

The proliferation, SOD (SOD1, SOD2 and SOD3) gene expression, the stemness-related gene (c-MYC) and telomerase reverse transcriptase of the infant ADSCs at early passages were enhanced compared with those of the adults'. Cellular senescence related genes, including p16, p21 and p53, and replicative stress were reduced in the infant ADSCs. The adipogenic genes (PPARγ and LPL) and neurogenic genes (MAP2 and NEFH) of the infant ADSC differentiated cells were significantly higher than those of the adults' while the expression of the osteogenic genes (OCN and RUNX) and tenogenic genes (TNC and COL3A1) of both demonstrated opposite results. The chondrogenic markers (SOX9, COL2 and COL10) were enhanced in the infant ADSC differentiated chondrogenic pellets, and the expression levels of SODs were decreased during the differentiation process.

CONCLUSION

Cultured infant ADSCs demonstrate less cellular senescence and replicative stress, higher proliferation rates, better antioxidant defense activity, and higher potential of chondrogenic, adipogenic and neurogenic differentiation.

Autograft Long Head Biceps Tendon Can Be Used as a Scaffold for Biologically Augmenting Rotator Cuff Repairs

PURPOSE

We create a viable, mechanically expanded autograft long head biceps tendon (LHBT) scaffold for biologically augmenting the repair of torn rotator cuffs.

METHODS

The proximal aspect of the tenotomized LHBTs was harvested from patients during rotator cuff repair surgery and was mechanically formed into porous scaffolds using a surgical graft expander. LHBT scaffolds were evaluated for change in area, tensile properties, and tenocyte viability before and after expansion. The ability of endogenous tenocytes derived from the LHBT scaffold to promote tenogenic differentiation of human adipose-derived mesenchymal stromal cells (ADMSCs) was also determined.

RESULTS

Autograft LHBTs were successfully expanded using a modified surgical graft expander to create a porous scaffold containing viable resident tenoctyes from patients undergoing rotator cuff repair. LHBT scaffolds had significantly increased area (length: 24.91 mm [13.91, 35.90] × width: 22.69 mm [1.87, 34.50]; P = .011) compared with the native LHBT tendon (length: 27.16 mm [2.70, 33.62] × width: 6.68 mm [5.62, 7.74]). The structural properties of the autograft were altered, including the ultimate tensile strength (LHBT scaffold: .56 MPa [.06, 1.06] vs. native LHBT: 2.35 MPa [1.36, 3.33]; P = .002) and tensile modulus (LHBT scaffold: 4.72 MPa [-.80, 1.24] versus native LHBT: 37.17 MPa [24.56, 49.78]; P = .001). There was also a reduction in resident tenocyte percent viability (LHBT scaffold: 38.52% [17.94, 59.09] vs. native LHBT: 68.87% [63.67, 74.37]; P =.004). Tenocytes derived from the LHBT scaffold produced soluble signals that initiated ADMSC differentiation into an immature tenocyte-like phenotype, as indicated by an 8.7× increase in scleraxis (P = .040) and a 3.6× increase in collagen type III mRNA expression (P = .050) compared with undifferentiated ADMSC controls.

CONCLUSIONS

The ability to produce a viable autologous scaffold from the proximal biceps tendon having dimensions, porosity, mechanical characteristics, native ECM components, and viable tenocytes that produce bioactive signals conducive to supporting the biologic augmentation of rotator cuff repair surgery has been demonstrated.

CLINICAL RELEVANCE

This biologically active construct may help to improve the quality of healing and regeneration at the repair site of rotator cuff tears, especially those at high risk for retear.

Tendon and multiomics: advantages, advances, and opportunities

Tendons heal by fibrosis, which hinders function and increases re-injury risk. Yet the biology that leads to degeneration and regeneration of tendons is not completely understood. Improved understanding of the metabolic nuances that cause diverse outcomes in tendinopathies is required to solve these problems. 'Omics methods are increasingly used to characterize phenotypes in tissues. Multiomics integrates 'omic datasets to identify coherent relationships and provide insight into differences in molecular and metabolic pathways between anatomic locations, and disease stages. This work reviews the current literature pertaining to multiomics in tendon and the potential of these platforms to improve tendon regeneration. We assessed the literature and identified areas where 'omics platforms contribute to the field: (1) Tendon biology where their hierarchical complexity and demographic factors are studied. (2) Tendon degeneration and healing, where comparisons across tendon pathologies are analyzed. (3) The in vitro engineered tendon phenotype, where we compare the engineered phenotype to relevant native tissues. (4) Finally, we review regenerative and therapeutic approaches. We identified gaps in current knowledge and opportunities for future study: (1) The need to increase the diversity of human subjects and cell sources. (2) Opportunities to improve understanding of tendon heterogeneity. (3) The need to use these improvements to inform new engineered and regenerative therapeutic approaches. (4) The need to increase understanding of the development of tendon pathology. Together, the expanding use of various 'omics platforms and data analysis resulting from these platforms could substantially contribute to major advances in the tendon tissue engineering and regenerative medicine field.

The interaction between human rotator cuff tendon and subacromial bursal tissue in co-culture

BACKGROUND

The role of subacromial bursa in rotator cuff pathology is unclear. Along with recognized inflammatory potential, current data demonstrate the presence of mesenchymal stem cells and potential regenerative properties of the bursa. The purpose of this study was to (1) approximate an in vitro co-culture model that represents interaction between torn rotator cuff tendon and subacromial bursa, (2) quantify the cellular activity of tendon and bursa and their interactions, (3) use this model to induce a state of inflammation present with rotator cuff pathology.

METHODS

In part 1, tendon and bursa samples were obtained from 6 patients undergoing rotator cuff repair. Tendon and bursa were cultured alone and together in co-culture wells for 21 days. Markers specific for tenocyte gene expression (tenascin C, decorin, etc) were measured in both tendon and bursa alone and compared to co-culture models. In part 2 of the study, an inflammatory state was induced with interleukin-1β treatment, and markers of inflammation were measured via protein assay at 0 and 21 days in samples from 7 additional patients.

RESULTS

There was an increase in tendon and bursa markers in nearly all groups as evidenced by increased gene expression of known tendon and bursa markers. There was a significant increase in gene expression when torn tendon was co-cultured with bursa compared with culturing alone. Additionally, a state of inflammation was induced as evidenced by increased markers of inflammation, inflammatory protein concentration, and inflammatory cells and disruption of histologic morphology.

CONCLUSION

There is a clear interaction between rotator cuff tendon and the milieu produced by the subacromial bursa in this in vitro co-culture system that is significantly different when compared to an isolated culture of tendon and bursa. This system was successfully used to induce a state of inflammation that may represent in vivo inflammation. This in vitro model of rotator cuff pathology can aid investigators in testing effects of agents proposed to improve rotator cuff healing. This can lead to further knowledge regarding effective treatment options.

The Effect of L-Ascorbic Acid and Serum Reduction on Tenogenic Differentiation of Human Mesenchymal Stromal Cells

Background and Objectives

Despite significant improvement in the treatment of tendon injuries, the full tissue recovery is often not possible because of its limited ability to auto-repair. The transplantation of mesenchymal stromal cells (MSCs) is considered as a novel approach in the treatment of tendinopathies. The question about the optimal culture conditions remains open. In this study we aimed to investigate if serum reduction, L-ascorbic acid supplementation or a combination of both factors can induce tenogenic differentiation of human adipose-derived MSCs (ASCs).

Methods and Results

Human ASCs from 3 healthy donors were used in the study. The tested conditions were: 0.5 mM of ascorbic acid 2-phosphate (AA-2P), reduced serum content (2% FBS) or combination of these two factors. The combination of AA-2P and 2% FBS was the only experimental condition that caused a significant increase of the expression of all analyzed genes related to tenogenesis (SCLERAXIS, MOHAWK, COLLAGEN_1, COLLAGEN_3, DECORIN) in comparison to the untreated control (evaluated by RT-PCR, 5^th day of experiment). Moreover, this treatment significantly increased the synthesis of SCLERAXIS, MOHAWK, COLLAGEN_1, COLLAGEN_3 proteins at the same time point (evaluated by Western blot method). Double immunocytochemical staining revealed that AA-2P significantly increased the extracellular deposition of both types of collagens. Semi-quantitative Electron Spin Resonance analysis of ascorbyl free radical revealed that AA-2P do not induce harmful transition metals-driven redox reactions in cell culture media.

Conclusions

Obtained results justify the use of reduced content of serum with the addition of 0.5 mM of AA-2P in tenogenic inducing media.

3D Bioprinting of Human Adipose-Derived Stem Cells and Their Tenogenic Differentiation in Clinical-Grade Medium

Defining the best combination of cells and biomaterials is a key challenge for the development of tendon tissue engineering (TE) strategies. Adipose-derived stem cells (ASCs) are ideal candidates for this purpose. In addition, controlled cell-based products adherent to good manufacturing practice (GMP) are required for their clinical scale-up. With this aim, in this study, ASC 3D bioprinting and GMP-compliant tenogenic differentiation were investigated. In detail, primary human ASCs were embedded within a nanofibrillar-cellulose/alginate bioink and 3D-bioprinted into multi-layered square-grid matrices. Bioink viscoelastic properties and scaffold ultrastructural morphology were analyzed by rheology and scanning electron microscopy (SEM). The optimal cell concentration for printing among 3, 6 and 9 × 10⁶ ASC/mL was evaluated in terms of cell viability. ASC morphology was characterized by SEM and F-actin immunostaining. Tenogenic differentiation ability was then evaluated in terms of cell viability, morphology and expression of scleraxis and collagen type III by biochemical induction using BMP-12, TGF-β3, CTGF and ascorbic acid supplementation (TENO). Pro-inflammatory cytokine release was also assessed. Bioprinted ASCs showed high viability and survival and exhibited a tenocyte-like phenotype after biochemical induction, with no inflammatory response to the bioink. In conclusion, we report a first proof of concept for the clinical scale-up of ASC 3D bioprinting for tendon TE.

Development of collagen-poly(caprolactone)-based core-shell scaffolds supplemented with proteoglycans and glycosaminoglycans for ligament repair

Core-shell scaffolds offer a promising regenerative solution to debilitating injuries to anterior cruciate ligament (ACL) thanks to a unique biphasic structure. Nevertheless, current core-shell designs are impaired by an imbalance between permeability, biochemical and mechanical cues. This study aimed to address this issue by creating a porous core-shell construct which favors cell infiltration and matrix production, while providing mechanical stability at the site of injury. The developed core-shell scaffold combines an outer shell of electrospun poly(caprolactone) fibers with a freeze-dried core of type I collagen doped with proteoglycans (biglycan, decorin) or glycosaminoglycans (chondroitin sulphate, dermatan sulphate). The aligned fibrous shell achieved an elastic modulus akin of the human ACL, while the porous collagen core is permeable to human mesenchymal stem cell (hMSC). Doping of the core with the aforementioned biomolecules led to structural and mechanical changes in the pore network. Assessment of cellular metabolic activity and scaffold contraction shows that hMSCs actively remodel the matrix at different degrees, depending on the core's doping formulation. Additionally, immunohistochemical staining and mRNA transcript levels show that the collagen-chondroitin sulphate formulation has the highest matrix production activity, while the collagen-decorin formulation featured a matrix production profile more characteristic of the undamaged tissue. Together, this demonstrates that scaffold doping with target biomolecules leads to distinct levels of cell-mediated matrix remodeling. Overall, this work resulted in the development of a versatile and robust platform with a combination of mechanical and biochemical features that have a significant potential in promoting the repair process of ACL tissue.

Induction of tenogenic differentiation of equine adipose-derived mesenchymal stem cells by platelet-derived growth factor-BB and growth differentiation factor-6

Managing tendon healing process is complicated mainly due to the limited regeneration capacity of tendon tissue. Mesenchymal stem cells (MSCs) have potential applications in regenerative medicine and have been considered for tendon repair and regeneration. This study aimed to evaluate the capacity of equine adipose tissue-derived cells (eASCs) to differentiate into tenocytes in response to platelet-derived growth factor-BB (PDGF-BB) and growth differentiation factor-6 (GDF-6) in vitro. Frozen characterized eASCS of 3 mares were thawed and the cells were expanded in basic culture medium (DMEM supplemented with 10% FBS). The cells at passage 5 were treated for 14 days in different conditions including: (1) control group in basic culture medium (CM), (2) induction medium as IM (CM containing L-prolin, and ascorbic acid (AA)) supplemented with PDGF-BB (20 ng/ml), (3) IM supplemented with GDF-6 (20 ng/ml), and (4) IM supplemented with PDGF-BB and GDF-6. At the end of culture period (14th day), tenogenic differentiation was evaluated. Sirius Red staining was used to assess collagen production, and H&E was used for assessing cell morphology. mRNA levels of collagen type 1 (colI), scleraxis (SCX), and Mohawk (MKX), as tenogenic markers, were analyzed using real-time reverse-transcription polymerase chain reaction (qPCR). H&E staining showed a stretching and spindle shape (tenocyte-like) cells in all treated groups compared to unchanged from of cells in control groups. Also, Sirius red staining data showed a significant increase in collagen production in all treated groups compared with the control group. MKX expression was significantly increased in PDGF-BB and mixed groups and COLI expression was significantly increased only in PDGF-BB group. In conclusion, our results showed that PDGF-BB and GDF-6 combination could induce tenogenic differentiation in eASCs. These in vitro findings could be useful for cell therapy in equine regenerative medicine.

Induction of Tendon-Specific Markers in Adipose-Derived Stem Cells in Serum-Free Culture Conditions

IMPACT STATEMENT

Herein, we describe the tenogenic effect of bone morphogenetic protein-12 and transforming growth factor-β1 in cultured adipose-derived stem cells (ADSCs) in serum-free conditions. This culture system provides an insight into serum-free culture conditions in stem cell differentiation protocols. A positive response of the ADSCs to the tenogenic induction was observed. In particular, the different growth factors used in this study displayed notable differences both on the gene and on the protein expression of the tendon-specific markers. The results underline the positive outcome of the serum removal in tenogenic differentiation protocols, contributing to the development of future cell-based therapies for tendon regeneration and repair.

Structure and ingredient-based biomimetic scaffolds combining with autologous bone marrow-derived mesenchymal stem cell sheets for bone-tendon healing

Tendon attaches to bone across a robust fibrocartilaginous tissue termed the bone-tendon interface (BTI), commonly injured in the field of sports medicine and orthopedics with poor prognosis. So far, there is still a lack of effective clinical interventions to achieve functional healing post BTI injury. However, tissue-engineering may be a promising treatment strategy. In this study, a gradient book-type triphasic (bone-fibrocartilage-tendon) scaffold is fabricated based on the heterogeneous structure and ingredient of BTI. After decellularization, the scaffold exhibits no residual cells, while the characteristic extracellular matrix of the original bone, fibrocartilage and tendon is well preserved. Meanwhile, the bone, fibrocartilage and tendon regions of the acellular scaffold are superior in osteogenic, chondrogenic and tenogenic inducibility, respectively. Furthermore, autologous bone marrow mesenchymal stem cell (BMSC) sheets (CS) combined with the acellular scaffolds is transplanted into the lesion site of a rabbit BTI injury model to investigate the therapeutic effects. Our results show that the CS modified scaffold not only successfully achieves triple biomimetic of BTI in structure, ingredient and cell distribution, but also effectively accelerates bone-tendon (B-T) healing. In general, this work demonstrates book-type acellular triphasic scaffold combined with autologous BMSCs sheets is a promising graft for repairing BTI injury.

Supporting Cell-Based Tendon Therapy: Effect of PDGF-BB and Ascorbic Acid on Rabbit Achilles Tenocytes in Vitro

Cell-based tendon therapies with tenocytes as a cell source need effective tenocyte in vitro expansion before application for tendinopathies and tendon injuries. Supplementation of tenocyte culture with biomolecules that can boost proliferation and matrix synthesis is one viable option for supporting cell expansion. In this in vitro study, the impacts of ascorbic acid or PDGF-BB supplementation on rabbit Achilles tenocyte culture were studied. Namely, cell proliferation, changes in gene expression of several ECM and tendon markers (collagen I, collagen III, fibronectin, aggrecan, biglycan, decorin, ki67, tenascin-C, tenomodulin, Mohawk, α-SMA, MMP-2, MMP-9, TIMP1, and TIMP2) and ECM deposition (collagen I and fibronectin) were assessed. Ascorbic acid and PDGF-BB enhanced tenocyte proliferation, while ascorbic acid significantly accelerated the deposition of collagen I. Both biomolecules led to different changes in the gene expression profile of the cultured tenocytes, where upregulation of collagen I, Mohawk, decorin, MMP-2, and TIMP-2 was observed with ascorbic acid, while these markers were downregulated by PDGF-BB supplementation. Vice versa, there was an upregulation of fibronectin, biglycan and tenascin-C by PDGF-BB supplementation, while ascorbic acid led to a downregulation of these markers. However, both biomolecules are promising candidates for improving and accelerating the in vitro expansion of tenocytes, which is vital for various tendon tissue engineering approaches or cell-based tendon therapy.