Adding exogenous biglycan or decorin improves tendon formation for equine peritenon and tendon proper cells in vitro

Characterization of an in vitro engineered ligament model

In vivo tendon and ligament research can be limited by the difficultly of obtaining tissue samples that can be biochemically analyzed. In this study, we characterize the most widely used in vitro engineered ligament model. Despite previous works suggesting multiple passages change gene expression in 2D primary tenocytes, we found no relationship between passage number and expression of classical tendon fibroblast markers across different biological donors. When engineered into 3D ligaments, there was an increase in maximal tensile load between 7 and 14 days in culture, that corresponded with an increase in collagen content. By contrast, percent collagen increased logarithmically from Day 7 to Day 14, and this was similar to the increase in the modulus of the tissue. Importantly, there was no relationship between passage number and mechanical function or collagen content in the two independent donors tested. These results suggest that the model develops quickly and is reliable across differing passage numbers. This provides the field with the ability to 1) consistently determine functional changes of interventions out to passage number 10; and 2) to time interventions to the appropriate developmental stage: developing/regenerating (Day 7) or mature (Day 14) tissue.

Examining the Potential of Vitamin C Supplementation in Tissue-Engineered Equine Superficial Digital Flexor Tendon Constructs

Because equine tendinopathies are slow to heal and often recur, therapeutic strategies are being considered that aid tendon repair. Given the success of utilizing vitamin C to promote tenogenesis in other species, we hypothesized that vitamin C supplementation would produce dose-dependent improvements in the tenogenic properties of tendon proper (TP) and peritenon (PERI) cells of the equine superficial digital flexor tendon (SDFT). Equine TP- and PERI-progenitor-cell-seeded fibrin three-dimensional constructs were supplemented with four concentrations of vitamin C. The gene expression profiles of the constructs were assessed with 3'-Tag-Seq and real-time quantitative polymerase chain reaction (RT-qPCR); collagen content and fibril ultrastructure were also analyzed. Moreover, cells were challenged with dexamethasone to determine the levels of cytoprotection afforded by vitamin C. Expression profiling demonstrated that vitamin C had an anti-inflammatory effect on TP and PERI cell constructs. Moreover, vitamin C supplementation mitigated the degenerative pathways seen in tendinopathy and increased collagen content in tendon constructs. When challenged with dexamethasone in two-dimensional culture, vitamin C had a cytoprotective effect for TP cells but not necessarily for PERI cells. Future studies will explore the effects of vitamin C on these cells during inflammation and within the tendon niche in vivo.

Hormonal, immune, and oxidative stress responses to blood flow-restricted exercise

INTRODUCTION

Heavy-load free-flow resistance exercise (HL-FFRE) is a widely used training modality. Recently, low-load blood-flow restricted resistance exercise (LL-BFRRE) has gained attention in both athletic and clinical settings as an alternative when conventional HL-FFRE is contraindicated or not tolerated. LL-BFRRE has been shown to result in physiological adaptations in muscle and connective tissue that are comparable to those induced by HL-FFRE. The underlying mechanisms remain unclear; however, evidence suggests that LL-BFRRE involves elevated metabolic stress compared to conventional free-flow resistance exercise (FFRE).

AIM

The aim was to evaluate the initial (<10 min post-exercise), intermediate (10-20 min), and late (>30 min) hormonal, immune, and oxidative stress responses observed following acute sessions of LL-BFRRE compared to FFRE in healthy adults.

METHODS

A systematic literature search of randomized and non-randomized studies was conducted in PubMed, Embase, Cochrane Central, CINAHL, and SPORTDiscus. The Cochrane Risk of Bias (RoB2, ROBINS-1) and TESTEX were used to evaluate risk of bias and study quality. Data extractions were based on mean change within groups.

RESULTS

A total of 12525 hits were identified, of which 29 articles were included. LL-BFRRE demonstrated greater acute increases in growth hormone responses when compared to overall FFRE at intermediate (SMD 2.04; 95% CI 0.87, 3.22) and late (SMD 2.64; 95% CI 1.13, 4.16) post-exercise phases. LL-BFRRE also demonstrated greater increase in testosterone responses compared to late LL-FFRE.

CONCLUSION

These results indicate that LL-BFRRE can induce increased or similar hormone and immune responses compared to LL-FFRE and HL-FFRE along with attenuated oxidative stress responses compared to HL-FFRE.

Examining the Effects of In Vitro Co-Culture of Equine Adipose-Derived Mesenchymal Stem Cells With Tendon Proper and Peritenon Cells

Tendinopathies remain the leading contributor to career-ending injuries in horses because of the complexity of tendon repair. As such, cell-based therapies like injections of adipose-derived mesenchymal stem cells (ADMSCs, or MSCs) into injured tendons are becoming increasingly popular though their long-term efficacy on a molecular and wholistic level remains contentious. Thus, we co-cultured equine MSCs with intrinsic (tendon proper) and extrinsic (peritenon) tendon cell populations to examine interactions between these cells. Gene expression for common tenogenic, perivascular, and differentiation markers was quantified at 48 and 120 hours. Additionally, cellular metabolism of proliferation was examined every 24 hours for peritenon and tendon proper cells co-cultured with MSCs. MSCs co-cultured with tendon proper or peritenon cells had altered expression profiles demonstrating trend toward tenogenic phenotype with the exception of decreases in type I collagen (COL1A1). Peritenon cells co-cultured with MSCs had a trending and significant decrease in biglycan (BGN) and CSPG4 at 48 hours and 120 hours but overall significant increases in lysyl oxidase (LOX), mohawk (MKX), and scleraxis (SCX) within 48 hours. Tendon proper cells co-cultured with MSCs also exhibited increases in LOX and SCX at 48 hours. Furthermore, cell proliferation improved overall for tendon proper cells co-cultured with MSCs. The co-culture study results suggest that adipose-derived MSCs contribute beneficially to tenogenic stimulation of peritenon or tendon proper cells.

Small leucine rich proteoglycans: Biology, function and their therapeutic potential in the ocular surface

Small leucine rich proteoglycans (SLRPs) are the largest family of proteoglycans, with 18 members that are subdivided into five classes. SLRPs are small in size and can be present in tissues as glycosylated and non-glycosylated proteins, and the most studied SLRPs include decorin, biglycan, lumican, keratocan and fibromodulin. SLRPs specifically bind to collagen fibrils, regulating collagen fibrillogenesis and the biomechanical properties of tissues, and are expressed at particularly high levels in fibrous tissues, such as the cornea. However, SLRPs are also very active components of the ECM, interacting with numerous growth factors, cytokines and cell surface receptors. Therefore, SLRPs regulate major cellular processes and have a central role in major fundamental biological processes, such as maintaining corneal homeostasis and transparency and regulating corneal wound healing. Over the years, mutations and/or altered expression of SLRPs have been associated with various corneal diseases, such as congenital stromal corneal dystrophy and cornea plana. Recently, there has been great interest in harnessing the various functions of SLRPs for therapeutic purposes. In this comprehensive review, we describe the structural features and the related functions of SLRPs, and how these affect the therapeutic potential of SLRPs, with special emphasis on the use of SLRPs for treating ocular surface pathologies.

Adipose and Bone Marrow Derived-Mesenchymal Stromal Cells Express Similar Tenogenic Expression Levels when Subjected to Mechanical Uniaxial Stretching In Vitro

The present study was conducted to determine whether adipose derived mesenchymal stromal cells (AD-MSCs) or bone marrow derived-MSCs (BM-MSCs) would provide superior tenogenic expressions when subjected to cyclical tensile loading. The results for this would indicate the best choice of MSCs source to be used for cell-based tendon repair strategies. Both AD-MSCs and BM-MSCs were obtained from ten adult donors (N = 10) and cultured in vitro. At passaged-2, cells from both groups were subjected to cyclical stretching at 1 Hz and 8% of strain. Cellular morphology, orientation, proliferation rate, protein, and gene expression levels were compared at 0, 24, and 48 hours of stretching. In both groups, mechanical stretching results in similar morphological changes, and the redirection of cell alignment is perpendicular to the direction of stretching. Loading at 8% strain did not significantly increase proliferation rates but caused an increase in total collagen expression and tenogenic gene expression levels. In both groups, these levels demonstrated no significant differences suggesting that in a similar loading environment, both cell types possess similar tenogenic potential. In conclusion, AD-MSCs and BM-MSCs both demonstrate similar tenogenic phenotypic and gene expression levels when subjected to cyclic tensile loading at 1 Hz and 8% strain, thus, suggesting that the use of either cell source may be suitable for tendon repair.

Challenges and perspectives of tendon-derived cell therapy for tendinopathy: from bench to bedside

Tendon is composed of dense fibrous connective tissues, connecting muscle at the myotendinous junction (MTJ) to bone at the enthesis and allowing mechanical force to transmit from muscle to bone. Tendon diseases occur at different zones of the tendon, including enthesis, MTJ and midsubstance of the tendon, due to a variety of environmental and genetic factors which consequently result in different frequencies and recovery rates. Self-healing properties of tendons are limited, and cell therapeutic approaches in which injured tendon tissues are renewed by cell replenishment are highly sought after. Homologous use of individual’s tendon-derived cells, predominantly differentiated tenocytes and tendon-derived stem cells, is emerging as a treatment for tendinopathy through achieving minimal cell manipulation for clinical use. This is the first review summarizing the progress of tendon-derived cell therapy in clinical use and its challenges due to the structural complexity of tendons, heterogeneous composition of extracellular cell matrix and cells and unsuitable cell sources. Further to that, novel future perspectives to improve therapeutic effect in tendon-derived cell therapy based on current basic knowledge are discussed.

Small Leucine-Rich Proteoglycans in Tendon Wound Healing

Significance: Tendon injury possesses a high morbidity rate and is difficult to achieve a satisfying prognosis with currently available treatment strategies. Current approaches used for tendon healing always lead to the formation of fibrovascular scar tissue, which significantly compromises the biomechanics of the healed tendon. Moreover, the related functional deficiency deteriorates over time with an increased injury recurrence risk. Small leucine-rich proteoglycans (SLRPs) link and interact with collagen fibrils to regulate tendon structure and biomechanics, which can provide a new and promising method in the field of tendon injury management. Recent Advances: The effect of SLRPs on tendon development has been extensively investigated. SLRP deficiency impairs tendon collagen fibril structure and biomechanic properties, while administration of SLRPs generally benefits tendon wound healing and regains better mechanical properties. Critical Issues: Current knowledge on the role of SLRPs in tendon development and regeneration mostly comes from uninjured knockout mice, and mainly focuses on the morphology description of collagen fibril profile and mechanical properties. Little is known about the regulatory mechanism on the molecular level. Future Directions: This article reviews the current knowledge in this highly translational topic and provides an evidence-based conclusion, thereby encouraging in-depth investigations of SLRPs in tendons and the development of SLRP-based treatments for desired tendon healing.

Extracellular Vesicles of Adipose-Derived Stem Cells Promote the Healing of Traumatized Achilles Tendons

Healing of ruptured tendons remains a clinical challenge because of its slow progress and relatively weak mechanical force at an early stage. Extracellular vesicles (EVs) derived from mesenchymal stem cells (MSCs) have therapeutic potential for tissue regeneration. In this study, we isolated EVs from adipose-derived stem cells (ADSCs) and evaluated their ability to promote tendon regeneration. Our results indicated that ADSC-EVs significantly enhanced the proliferation and migration of tenocytes in vitro. To further study the roles of ADSC-EVs in tendon regeneration, ADSC-EVs were used in Achilles tendon repair in rabbits. The mechanical strength, histology, and protein expression in the injured tendon tissues significantly improved 4 weeks after ADSC-EV treatment. Decorin and biglycan were significantly upregulated in comparison to the untreated controls. In summary, ADSC-EVs stimulated the proliferation and migration of tenocytes and improved the mechanical strength of repaired tendons, suggesting that ADSC-EV treatment is a potential highly potent therapeutic strategy for tendon injuries.

Biglycan: an emerging small leucine-rich proteoglycan (SLRP) marker and its clinicopathological significance

Extracellular matrix (ECM) plays an important role in the structural organization of tissue and delivery of external cues to the cell. Biglycan, a class I small leucine-rich proteoglycans (SLRP), is a key component of the ECM that participates in scaffolding the collagen fibrils and mediates cell signaling. Dysregulation of biglycan expression can result in wide range of clinical conditions such as metabolic disorder, inflammatory disorder, musculoskeletal defects and malignancies. In this review, we aim to update our current understanding regarding the link between altered expression of biglycan and different clinicopathological states. Biglycan interacts with toll like receptors (TLR)-2 and TLR-4 on the immune cells which initiates inflammation and aggravates inflammatory disorders. ECM unbound soluble biglycan acts as a DAMP (danger associated molecular pattern) resulting in sterile inflammation. Dysregulation of biglycan expression is also observed in inflammatory metabolic conditions such as atherosclerosis and obesity. In cancer, high-biglycan expression facilitates tumor growth, invasion and metastasis which is associated with poor clinical outcome. As a pivotal structural component of the ECM, biglycan strengthens the musculoskeletal system and its absence is associated with musculoskeletal defects. Thus, SLRP biglycan is a potential marker which is significantly altered in different clinicopathological states.

Plasma Activin A and Decorin in Exercised Purebred Arabian Horses - Preliminary Study

Development of the musculoskeletal system occurs, in part, through an impact on regulatory proteins, such as activin A and decorin. Activin A induces atrophic effects on skeletal muscle, and decorin regulates the formation of connective tissue proteins like collagen and elastin in tendons and ligaments. The aim of this study was to evaluate the influence of different intensities of exercise on blood plasma activin A and decorin concentrations in horses. Ten young purebred Arabian horses were subjected to routine training sessions on a racetrack, and another 11 adult horses of the same breed participated in endurance rides. Race horses were examined during gallop tests over a distance of 1200 m and endurance horses at distances from 20 to 80 km. Blood samples were collected at rest and after exercise to determine plasma concentrations of activin A, decorin and cortisol. Despite differences in the intensity of exercise, the plasma decorin concentration remained unchanged, and activin A tended to decrease in endurance horses only. The exercise-induced changes in plasma activin A concentrations correlated with the covered distance (r = -0.43; P < .05), but not with the changes in cortisol values. Further studies are needed to confirm the usefulness of plasma activin A as a potential indicator of a horse's endurance performance.