Animal models for the study of tendinopathy

Proteins Derived From MRL/MpJ Tendon Provisional Extracellular Matrix and Secretome Promote Pro-Regenerative Tenocyte Behavior

Tendinopathies are prevalent musculoskeletal conditions that have no effective therapies to attenuate scar formation. In contrast to other adult mammals, the tendons of Murphy Roths Large (MRL/MpJ) mice possess a superior healing capacity following acute and overuse injuries. Here, we hypothesized that the application of biological cues derived from the local MRL/MpJ tendon environment would direct otherwise scar-mediated tenocytes towards a pro-regenerative MRL/MpJ-like phenotype. We identified soluble factors enriched in the secretome of MRL/MpJ tenocytes using bioreactor systems and quantitative proteomics. We then demonstrated that the combined administration of structural and soluble constituents isolated from decellularized MRL/MpJ tendon provisional ECM (dPECM) and the secretome stimulate scar-mediated rodent tenocytes towards enhanced mechanosensitivity, proliferation, intercellular communication, and ECM deposition associated with MRL/MpJ cell behavior. Our findings highlight key biological mechanisms that drive MRL/MpJ tenocyte activity and their interspecies utility to be harnessed for therapeutic strategies that promote pro-regenerative healing outcomes.

Teaser

Proteins enriched in a super-healer mouse strain elicit interspecies utility in promoting pro-regenerative tenocyte behavior.

Tissue-engineered mesenchymal stem cell constructs alleviate tendinopathy by suppressing vascularization

Tendinopathy leads to low-grade tissue inflammation and chronic damage, which progresses due to pathological imbalance in angiogenesis. Reducing early pathological vascularization may be a new approach in helping to regenerate tendon tissue. Conventional stem cell therapy and tissue engineering scaffolds have not been highly effective at treating tendinopathy. In this study, tissue engineered stem cells (TSCs) generated using human umbilical cord mesenchymal stem cells (hUC-MSCs) were combined with microcarrier scaffolds to limit excessive vascularization in tendinopathy. By preventing VEGF receptor activation through their paracrine function, TSCs reduced in vitro angiogenesis and the proliferation of vascular endothelial cells. TSCs also decreased the inflammatory expression of tenocytes while promoting their anabolic and tenogenic characteristics. Furthermore, local injection of TSCs into rats with collagenase-induced tendinopathy substantially reduced early inflammation and vascularization. Mechanistically, transcriptome sequencing revealed that TSCs could reduce the progression of pathological angiogenesis in tendon tissue, attributed to Rap1-mediated vascular inhibition. TSCs may serve as a novel and practical approach for suppressing tendon vascularization, and provide a promising therapeutic agent for early-stage clinical tendinopathy.

Carpaine alleviates tendinopathy in mice by promoting the ubiquitin-proteasomal degradation of p65 via targeting the E3 ubiquitin ligase LRSAM1

BACKGROUND

Currently, there are no specific drugs or targets available for the treatment of tendinopathy. However, inflammation has recently been found to play a pivotal role in tendinopathy progression, thereby identifying it as a potential therapeutic target. Carpaine (CA) exhibits potential anti-inflammatory pharmacological properties and may offer a therapeutic option for tendinopathy.

PURPOSE

This study aimed to investigate the effectiveness of CA in addressing tendinopathy and uncovering its underlying mechanisms.

METHODS

Herein, the efficacy of CA by local administration in vivo in comparison to the first-line drug indomethacin was evaluated in a mouse collagenase-induced tendinopathy (CIT) model. Furthermore, IL-1β induced a simulated pathological inflammatory microenvironment in tenocytes to investigate its underlying mechanisms in vitro. Further confirmation experiments were performed by overexpressing or knocking down the selective targets of CA in vivo.

RESULTS

The findings demonstrated that CA was dose-dependent in treating tendinopathy and that the high-dose group outperformed the first-line drug indomethacin. Mechanistically, CA selectively bound to and enhanced the activity of the E3 ubiquitin ligase LRSAM1 in tendinopathy. This effect mediated the ubiquitination of p65 at lysine 93, subsequently promoting its proteasomal degradation. As a result, the NF-κB pathway was inactivated, leading to a reduction in inflammation of tendinopathy. Consequently, CA effectively mitigated the progression of tendinopathy. Moreover, the LRSAM1 overexpression demonstrated effectiveness in mitigating the tendinopathy progression and its knockdown abolished the therapeutic effects of CA.

CONCLUSION

CA attenuates the progression of tendinopathy by promoting the ubiquitin-proteasomal degradation of p65 via increasing the enzyme activity of LRSAM1. The exploration of LRSAM1 has also unveiled a new potential target for treating tendinopathy based on the ubiquitin-proteasomal pathway.

Characterization of Rabbit Mesenchymal Stem/Stromal Cells after Cryopreservation

Adipose tissues (ADPs) are an alternative source for mesenchymal stem/stromal cells (MSCs), given that conventional bone marrow (BM) collection is painful and yields limited cell numbers. As the need for easily accessible MSCs grows, cryopreservation's role in regenerative medicine is becoming increasingly vital. However, limited research exists on the characteristics and functional properties of rabbit-derived MSCs from various anatomical sources before and after cryopreservation. We examined the effects of cryopreservation using Bambanker. We found that cryopreservation did not adversely affect the morphology, viability, and adipogenic or chondrogenic differentiation abilities of ADP MSCs or BM MSCs. However, there was a notable drop in the proliferation rate and osteogenic differentiation capability of BM MSCs post-cryopreservation. Additionally, after cryopreservation, the surface marker gene expression of CD90 was not evident in ADP MSCs. As for markers, ADIPOQ can serve as an adipogenic marker for ADP MSCs. ACAN and CNMD can act as chondrogenic markers, but these two markers are not as effective post-cryopreservation on ADP MSCs, and osteogenic markers could not be validated. The study highlights that compared to BM MSCs, ADP MSCs retained a higher viability, proliferation rate, and differentiation potential after cryopreservation. As such, in clinical MSC use, we must consider changes in post-cryopreservation cell functions.

A review on the use of porcine in tendon research

PURPOSE OF REVIEW

Large animals have been increasingly employed in tendon research; the objective of this review was to summarize the employment of porcine in tendon research.

RECENT FINDINGS

Literature before 2022-03-31 was searched using the following strategy: (pig[MeSH Terms]) AND (tendon[MeSH Terms]); (pig[MeSH Terms]) AND (tendon[title]); (tendon[MeSH Terms]) AND (porcine[title]); (tendon[title]) AND (porcine[title]); (tendon[MeSH Terms]) AND (pig[title]); (tendon[title]) AND (pig[title]); (tendon[MeSH Terms]) AND (swine[title]); (tendon[title]) AND (swine[title]). 296 studies were included in this review. There were wide application areas of porcine tendon, including tissue engineering tendons, training of surgical skills. Porcine tendon was used both in in vitro studies, such as anatomy, biomechanics, cytology, and material science as well as in in vivo studies. The research techniques of porcine tendon are relatively common.

SUMMARY

In conclusion, pigs have been widely used as a good animal model of tendon research. However, the limitations of porcine tendon research (the lack of anatomical research and in vivo studies) should be given more attention in future studies.

Animal model for tendinopathy

Background

Tendinopathy is a common motor system disease that leads to pain and reduced function. Despite its prevalence, our mechanistic understanding is incomplete, leading to limited efficacy of treatment options. Animal models contribute significantly to our understanding of tendinopathy and some therapeutic options. However, the inadequacies of animal models are also evident, largely due to differences in anatomical structure and the complexity of human tendinopathy. Different animal models reproduce different aspects of human tendinopathy and are therefore suitable for different scenarios. This review aims to summarize the existing animal models of tendinopathy and to determine the situations in which each model is appropriate for use, including exploring disease mechanisms and evaluating therapeutic effects.

Methods

We reviewed relevant literature in the PubMed database from January 2000 to December 2022 using the specific terms ((tendinopathy) OR (tendinitis)) AND (model) AND ((mice) OR (rat) OR (rabbit) OR (lapin) OR (dog) OR (canine) OR (sheep) OR (goat) OR (horse) OR (equine) OR (pig) OR (swine) OR (primate)). This review summarized different methods for establishing animal models of tendinopathy and classified them according to the pathogenesis they simulate. We then discussed the advantages and disadvantages of each model, and based on this, identified the situations in which each model was suitable for application.

Results

For studies that aim to study the pathophysiology of tendinopathy, naturally occurring models, treadmill models, subacromial impingement models and metabolic models are ideal. They are closest to the natural process of tendinopathy in humans. For studies that aim to evaluate the efficacy of possible treatments, the selection should be made according to the pathogenesis simulated by the modeling method. Existing tendinopathy models can be classified into six types according to the pathogenesis they simulate: extracellular matrix synthesis-decomposition imbalance, inflammation, oxidative stress, metabolic disorder, traumatism and mechanical load.

Conclusions

The critical factor affecting the translational value of research results is whether the selected model is matched with the research purpose. There is no single optimal model for inducing tendinopathy, and researchers must select the model that is most appropriate for the study they are conducting.

The translational potential of this article

The critical factor affecting the translational value of research results is whether the animal model used is compatible with the research purpose. This paper provides a rationale and practical guide for the establishment and selection of animal models of tendinopathy, which is helpful to improve the clinical transformation ability of existing models and develop new models.

Overload in a Rat In Vivo Model of Synergist Ablation Induces Tendon Multiscale Structural and Functional Degeneration

Tendon degeneration is typically described as an overuse injury with little distinction made between magnitude of load (overload) and number of cycles (overuse). Further, in vivo, animal models of tendon degeneration are mostly overuse models, where tendon damage is caused by a high number of load cycles. As a result, there is a lack of knowledge of how isolated overload leads to degeneration in tendons. A surgical model of synergist ablation (SynAb) overloads the target tendon, plantaris, by ablating its synergist tendon, Achilles. The objective of this study was to evaluate the structural and functional changes that occur following overload of plantaris tendon in a rat SynAb model. Tendon cross-sectional area (CSA) and shape changes were evaluated by longitudinal MR imaging up to 8 weeks postsurgery. Tissue-scale structural changes were evaluated by semiquantified histology and second harmonic generation microscopy. Fibril level changes were evaluated with serial block face scanning electron microscopy (SBF-SEM). Functional changes were evaluated using tension tests at the tissue and microscale using a custom testing system allowing both video and microscopy imaging. At 8 weeks, overloaded plantaris tendons exhibited degenerative changes including increases in CSA, cell density, collagen damage area fraction (DAF), and fibril diameter, and decreases in collagen alignment, modulus, and yield stress. To interpret the differences between overload and overuse in tendon, we introduce a new framework for tendon remodeling and degeneration that differentiates between the inputs of overload and overuse. In summary, isolated overload induces multiscale degenerative structural and functional changes in plantaris tendon.

Platelet-rich plasma in the pathologic processes of tendinopathy: a review of basic science studies

Tendinopathy is a medical condition that includes a spectrum of inflammatory and degenerative tendon changes caused by traumatic or overuse injuries. The pathological mechanism of tendinopathy has not been well defined, and no ideal treatment is currently available. Platelet-rich plasma (PRP) is an autologous whole blood derivative containing a variety of cytokines and other protein components. Various basic studies have found that PRP has the therapeutic potential to promote cell proliferation and differentiation, regulate angiogenesis, increase extracellular matrix synthesis, and modulate inflammation in degenerative tendons. Therefore, PRP has been widely used as a promising therapeutic agent for tendinopathy. However, controversies exist over the optimal treatment regimen and efficacy of PRP for tendinopathy. This review focuses on the specific molecular and cellular mechanisms by which PRP manipulates tendon healing to better understand how PRP affects tendinopathy and explore the reason for the differences in clinical trial outcomes. This article has also pointed out the future direction of basic research and clinical application of PRP in the treatment of tendinopathy, which will play a guiding role in the design of PRP treatment protocols for tendinopathy.

A pilot study testing an Achilles tendinopathy human cadaver model using intratendinous injection of collagenase

BACKGROUND

Achilles tendinopathy is one of the most frequently occurring soft-tissue injuries. Despite decades of research, there is still much that is unknown about the progression of tendinopathy. Animal models, such as collagenase injection, allow researchers to gain insight into disease progression and investigate clinical interventions, yet are limited in their direct application to humans. Establishment of a cadaver model of tendinopathy would provide another method of investigating clinical interventions in human tissues. The purpose of this study is to develop such a model and evaluate biomechanical changes in cadaveric Achilles tendons using ultrasound elastography.

METHODS

Achilles tendons of five female foot/ankle cadavers were injected with two different concentrations (three with 10 mg/mL, two 20 mg/mL) of collagenase and incubated for 24 h. Ultrasound elastography images were collected at baseline, 16 and 24 h post-injection. Elasticity of tendons was calculated using a custom image analysis program.

FINDINGS

Elasticity decreased over time in both dosage groups. In the 10 mg/mL group, mean elasticity decreased from 642 ± 246 kPa at baseline to 392 ± 38.3 kPa at 16 h and 263 ± 87.3 kPa at 24 h. In the 20 mg/mL group, mean elasticity decreased from 628 ± 206 kPa at baseline to 176 ± 152 kPa at 16 h and 188 ± 120 kPa at 24 h.

INTERPRETATION

Injection of collagenase into cadaveric Achilles tendons resulted in decreases in elasticity. Decreases were observed in tendons that received injections with both 10 and 20 mg/mL collagenase dosages. Further biomechanical and histological testing is needed to evaluate this cadaveric tendinopathy.

Development and application of a novel in vivo overload model of the Achilles tendon in rat

Repetitive overload is a primary factor in tendon injury, causing progressive accumulation of matrix damage concurrent with a cellular response. However, it remains unclear how these events occur at the initial stages of the disease, making it difficult to identify appropriate treatment approaches. Here, we describe the development of a new model to cyclically load the Achilles tendon (AT) of rats in vivo and investigate the initial structural and cellular responses. The model utilizes controlled dorsiflexion of the ankle joint applied near maximal dorsiflexion, for 10,000 cycles at 3 Hz. Animals were subjected to a single bout of in vivo loading under anaesthesia, and either culled immediately (without recovery from anaesthesia), or 48 h or 4-weeks post-loading. Macro strains were assessed in cadavers, whilst tendon specific microdamage was assessed through collagen-hybridizing peptide (CHP) immunohistochemistry which highlighted a significant rise in CHP staining in loaded ATs compared to contralateral controls, indicating an accumulation of overload-induced damage. Staining for pro-inflammatory mediators (IL-6 and COX-2) and matrix degradation markers (MMP-3 and -13) also suggests an initial cellular response to overload. Model validation confirmed our approach was able to explore early overload-induced damage within the AT, with microdamage present and no evidence of broader musculoskeletal damage. The new model may be implemented to map the progression of tendinopathy in the AT, and thus study potential therapeutic interventions.

Subacromial bursa increases the failure force in a mouse model of supraspinatus detachment and repair

BACKGROUND

It has been shown that subacromial bursa (SAB) harbors connective tissue progenitor cells. The purpose of this study was to evaluate the effects of implantation of SAB-derived cells (SBCs) suspended in a fibrin sealant bead and implantation of SAB tissue at rotator cuff repair site on biomechanical properties of the repair in a mouse (C57Bl/6) model of supraspinatus tendon (ST) detachment and repair.

METHODS

Part 1: Murine SAB tissue was harvested and cultured. Viability of SBCs suspended in 10 μL of fibrin sealant beads was confirmed in vitro and in vivo. Eighty mice underwent right ST detachment and repair augmented with either fibrin sealant bead (control group) or fibrin sealant bead with 100,000 SBCs (study group) applied at the repair site. Part 2: 120 mice underwent right ST detachment and repair and were randomized equally into 4 groups: (1) a tissue group, which received a piece of freshly harvested SAB tissue; (2) a cell group, which received SBCs suspended in fibrin sealant bead; (3) a fibrin sealant group, which received plain fibrin sealant bead without cells; and (4) a control group, which received nothing at the ST repair site. An equal number of mice in each group were killed at 2 and 4 weeks. Specimens underwent biomechanical testing to evaluate failure force (part 1 and 2) and histologic analysis of the repair site (part 1 only).

RESULTS

Part 1: The mean failure force in the study group was significantly higher than controls at 2 and 4 weeks (3.25 ± 1.03 N vs. 2.43 ± 0.56 N, P = .01, and 4.08 ± 0.99 N vs. 3.02 ± 0.8 N, P = .004, respectively). Mean cell density of the ST at the repair site was significantly lower in the study group at 2 weeks than in controls (18,292.13 ± 1706.41 vs. 29,501.90 ± 3627.49, P = .001). Study group specimens had lower proteoglycan contents than controls, but this difference was not statistically significant. Part 2: There was no difference in failure force between cell and tissue groups at the 2- and 4-week time points (P = .994 and P = .603, respectively). There was no difference in failure force between fibrin sealant bead and control groups at the 2- and 4-week time points (P = .978 and P = .752, respectively).

CONCLUSION

This study shows that the application of SBCs and SAB tissue at the rotator cuff repair site increases the strength of repair in a murine model of rotator cuff detachment and repair.

Large animal models for the study of tendinopathy

Tendinopathy has a high incidence in athletes and the aging population. It can cause pain and movement disorders, and is one of the most difficult problems in orthopedics. Animal models of tendinopathy provide potentially efficient and effective means to develop understanding of human tendinopathy and its underlying pathological mechanisms and treatments. The selection of preclinical models is essential to ensure the successful translation of effective and innovative treatments into clinical practice. Large animals can be used in both micro- and macro-level research owing to their similarity to humans in size, structure, and function. This article reviews the application of large animal models in tendinopathy regarding injuries to four tendons: rotator cuff, patellar ligament, Achilles tendon, and flexor tendon. The advantages and disadvantages of studying tendinopathy with large animal models are summarized. It is hoped that, with further development of animal models of tendinopathy, new strategies for the prevention and treatment of tendinopathy in humans will be developed.

The tendon microenvironment: Engineered in vitro models to study cellular crosstalk

Tendinopathy is a multi-faceted pathology characterized by alterations in tendon microstructure, cellularity and collagen composition. Challenged by the possibility of regenerating pathological or ruptured tendons, the healing mechanisms of this tissue have been widely researched over the past decades. However, so far, most of the cellular players and processes influencing tendon repair remain unknown, which emphasizes the need for developing relevant in vitro models enabling to study the complex multicellular crosstalk occurring in tendon microenvironments. In this review, we critically discuss the insights on the interaction between tenocytes and the other tendon resident cells that have been devised through different types of existing in vitro models. Building on the generated knowledge, we stress the need for advanced models able to mimic the hierarchical architecture, cellularity and physiological signaling of tendon niche under dynamic culture conditions, along with the recreation of the integrated gradients of its tissue interfaces. In a forward-looking vision of the field, we discuss how the convergence of multiple bioengineering technologies can be leveraged as potential platforms to develop the next generation of relevant in vitro models that can contribute for a deeper fundamental knowledge to develop more effective treatments.

Slowed-Down Rehabilitation Following Percutaneous Repair of Achilles Tendon Rupture

BACKGROUND

Following percutaneous repair of acute Achilles tendon (AT) ruptures, early postoperative weightbearing is advocated; however, it is debatable how aggressive rehabilitation should be. We compared the clinical and functional outcomes in 2 groups of patients who followed either our "traditional" or a "slowed down" rehabilitation after percutaneous surgical repair.

METHODS

Sixty patients were prospectively recruited to a slowed down (29 patients) or a traditional (31 patients) rehabilitation program. Both groups were allowed immediate weightbearing postoperatively; a removable brace with 5 heel wedges was applied at 2 weeks. In the slowed-down group, 1 wedge was removed after 4 weeks. Gradual removal of the boot took place after 4 wedges were kept for 4 weeks. In the traditional group, 1 wedge was removed every 2 weeks, with removal of the boot after 2 wedges had been kept for 2 weeks. The AT Resting Angle (ATRA) evaluated tendon elongation. Patient reported functional outcomes were assessed using the AT Rupture Score (ATRS). Calf circumference difference and the isometric plantarflexion strength of the gastro-soleus complex were evaluated.

RESULTS

At the 12-month follow-up, both ATRA and ATRS were more favorable in the slowed-down group. The isometric strength and the calf circumference were more similar to the contralateral leg in the slowed-down group than in the traditional one.

CONCLUSION

Following percutaneous repair of acute Achilles tendon patients undergoing slowed down rehabilitation performed better than the traditional one. These conclusions must be considered within the limitations of the present study.

LEVEL OF EVIDENCE

Level II, prospective comparative study.

Allergy-induced systemic inflammation impairs tendon quality

Background

Treatment of degenerating tendons still presents a major challenge, since the aetiology of tendinopathies remains poorly understood. Besides mechanical overuse, further known predisposing factors include rheumatoid arthritis, diabetes, obesity or smoking all of which combine with a systemic inflammation.

Methods

To determine whether the systemic inflammation accompanying these conditions contributes to the onset of tendinopathy, we studied the effect of a systemic inflammation induced by an allergic episode on tendon properties. To this end, we induced an allergic response in mice by exposing them to a timothy grass pollen allergen and subsequently analysed both their flexor and Achilles tendons. Additionally, we analysed data from a health survey comprising data from more than 10.000 persons for an association between the occurrence of an allergy and tendinopathy.

Findings

Biomechanical testing and histological analysis revealed that tendons from allergic mice not only showed a significant reduction of both elastic modulus and tensile stress, but also alterations of the tendon matrix. Moreover, treatment of 3D tendon-like constructs with sera from allergic mice resulted in a matrix-remodelling expression profile and the expression of macrophage-associated markers and matrix metalloproteinase 2 (MMP2) was increased in allergic Achilles tendons. Data from the human health study revealed that persons suffering from an allergy have an increased propensity to develop a tendinopathy.

Interpretation

Our study demonstrates that the presence of a systemic inflammation accompanying an allergic condition negatively impacts on tendon structure and function.

Funding

This study was financially supported by the Fund for the Advancement of Scientific Research at Paracelsus Medical University (PMU-FFF E-15/22/115-LEK), by the Land Salzburg, the Salzburger Landeskliniken (SALK, the Health Care Provider of the University Hospitals Landeskrankenhaus and Christian Doppler Klinik), the Paracelsus Medical University, Salzburg and by unrestricted grants from Bayer, AstraZeneca, Sanofi-Aventis, Boehringer-Ingelheim.

Controlled vitamin D delivery with injectable hyaluronic acid-based hydrogel for restoration of tendinopathy

Tendinopathy is a term used to describe tendon disorders that are marked by pain and a loss of function. Recent studies demonstrated that inflammation plays an important role throughout the broad spectrum of tendinopathy. Conventional treatments such as steroid injections, analgesics, and physical modalities simply give pain relief and do not alter the disease progression without the tendon regeneration effect. Tenocytes are responsible for maintaining the tendon matrix and understanding how they function is essential to studying new treatments for tendinopathy. Our previous study showed the protective effects of vitamin D (Vit D) on damaged tenocytes. Besides its well-known effects on bone metabolism, the non-classical action of Vit D is the pleiotropic effects on modulating immune function. In the present study, we developed a Vit D delivery system with hyaluronic acid (HA), which is one of the major components of the extracellular matrix that has anti-inflammation and wound-healing properties. A novel Vit D delivery system with cross-linked HA hydrogel (Gel) and Tween 80 (T80), Vit D@Gel/T80, could be a new regeneration technique for the treatment of tendinopathy. Vit D@Gel/T80 reduced TNF-α induced damage to human tenocytes in vitro. In an animal study, the Vit D@Gel/T80 injected group demonstrated tendon restoration features. As a result, this Vit D@Gel/T80 system might be a local injection material in the treatment for tendinopathy.

Collagenase-Induced Patellar Tendinopathy with Neovascularization: First Results towards a Piglet Model of Musculoskeletal Embolization

Background: Therapeutic strategies targeting neovessels responsible for musculoskeletal chronic pain have emerged, including neovessels embolization. Our study aimed to develop a large animal model of patellar tendinopathy with neovascularization. Methods: Nine 3-month-old male piglets (18 patellar tendons) received percutaneous injections of increasing doses of collagenase (0 to 50 mg) at day 0 (D0). Tendinopathy was evaluated by ultrasound (D7 and D14). Neovascularization was evaluated visually and on angiographies. Bonar score was used for histological analysis (D14). Correlations were evaluated using Spearman’s rank (Rs) test. Results: Research protocol was well tolerated. All tendons were enlarged with a median increase of 31.58% [25–40.28] at D7 (p = 0.244) at D7 and 57.52% [48.41–91.45] at D14 (p = 0.065). Tendons with collagenase injection had more hypoechoic changes, with one tendon rupture (p = 0.012). Neovascularization was reported above 5 mg collagenase (p < 0.01) at D7 and D14 with dose-related neovessels induction (Rs = 0.8, p < 0.001). The Bonar score increased above 5 mg collagenase, correlated with the dose (Rs = 0.666, p = 0.003). Conclusions: The study shows the feasibility, safety and reproducibility of this new large animal model of patellar tendinopathy with neovascularization after collagenase injection. It will allow studying new treatments on direct embolization of neovessels by endovascular approach.

CTRP3 exacerbates tendinopathy by dysregulating tendon stem cell differentiation and altering extracellular matrix composition

Tendinopathy, the most common disorder affecting tendons, is characterized by chronic disorganization of the tendon matrix, which leads to tendon tear and rupture. The goal was to identify a rational molecular target whose blockade can serve as a potential therapeutic intervention for tendinopathy. We identified C1q/TNF-related protein-3 (CTRP3) as a markedly up-regulated cytokine in human and rodent tendinopathy. Overexpression of CTRP3 enhanced the progression of tendinopathy by accumulating cartilaginous proteoglycans and degenerating collagenous fibers in the mouse tendon, whereas CTRP3 knockdown suppressed the tendinopathy pathogenesis. Functional blockade of CTRP3 using a neutralizing antibody ameliorated overuse-induced tendinopathy of the Achilles and rotator cuff tendons. Mechanistically, CTRP3 elicited a transcriptomic pattern that stimulates abnormal differentiation of tendon stem/progenitor cells and ectopic chondrification as an effect linked to activation of Akt signaling. Collectively, we reveal an essential role for CTRP3 in tendinopathy and propose a potential therapeutic strategy for the treatment of tendinopathy.

Chronic subacromial impingement leads to supraspinatus muscle functional and morphological changes: Evaluation in a murine model

Muscle atrophy and fatty infiltration have been directly correlated with higher rates of incomplete or failed healing following surgical repair of the rotator cuff. The purpose of this study was to evaluate clinically relevant functional and morphological changes in the supraspinatus muscle at various time points in this model of rotator cuff tendinopathy. Subacromial impingement was induced in 47, male C57BL/6 mice (total 94 limbs) by implantation of a metal clip in the subacromial space. Specimens were evaluated at 4, 6, and 12 weeks postoperatively. Gait analysis was used to measure various kinematic parameters. Supraspinatus muscle wet weight, histology, and quantitative reverse-transcription polymerase chain reaction analysis of genes related to muscle atrophy and adipogenesis were performed to characterize the structural, cellular, and molecular changes. Muscle atrophy and fatty infiltration was evident beginning at 6 weeks, with progression out to 12 weeks. Gait analysis identified significant functional changes in many aspects of gait and abnormal stance tracing as early as 4 weeks, verifying alterations in upper extremity function. We have demonstrated that clinically relevant changes to the supraspinatus muscle are seen starting 6 weeks after induction of subacromial impingement. Furthermore, the gait analysis provides key functional outcome measurements that may be useful for future evaluation of new therapeutic strategies.

Tendon: Principles of Healing and Repair

Tendon stores, releases, and dissipates energy to efficiently transmit contractile forces from muscle to bone. Tendon injury is exceedingly common, with the spectrum ranging from chronic tendinopathy to acute tendon rupture. Tendon generally develops according to three main steps: collagen fibrillogenesis, linear growth, and lateral growth. In the setting of injury, it also repairs and regenerates in three overlapping steps (inflammation, proliferation, and remodeling) with tendon-specific durations. Acute injury to the flexor and extensor tendons of the hand are of particular clinical importance to plastic surgeons, with tendon-specific treatment guided by the general principle of minimum protective immobilization followed by hand therapy to overcome potential adhesions. Thorough knowledge of the underlying biomechanical principles of tendon healing is required to provide optimal care to patients presenting with tendon injury.

Species variations in tenocytes' response to inflammation require careful selection of animal models for tendon research

For research on tendon injury, many different animal models are utilized; however, the extent to which these species simulate the clinical condition and disease pathophysiology has not yet been critically evaluated. Considering the importance of inflammation in tendon disease, this study compared the cellular and molecular features of inflammation in tenocytes of humans and four common model species (mouse, rat, sheep, and horse). While mouse and rat tenocytes most closely equalled human tenocytes’ low proliferation capacity and the negligible effect of inflammation on proliferation, the wound closure speed of humans was best approximated by rats and horses. The overall gene expression of human tenocytes was most similar to mice under healthy, to horses under transient and to sheep under constant inflammatory conditions. Humans were best matched by mice and horses in their tendon marker and collagen expression, by horses in extracellular matrix remodelling genes, and by rats in inflammatory mediators. As no single animal model perfectly replicates the clinical condition and sufficiently emulates human tenocytes, fit-for-purpose selection of the model species for each specific research question and combination of data from multiple species will be essential to optimize translational predictive validity.

Animal models for study on rotator cuff injury

Rotator cuff injuries are the most common cause of shoulder pain and dysfunction. Ideal animal shoulder models should have similar shoulder anatomy and function as human, and are able to replicate the microenvironment change after tendon injury. At present, a variety of animal models including rat, mouse, rabbit, sheep, canine, bovine, and primate have been used to study the mechanism of rotator cuff injury, effects of different repair techniques, and factors affecting tendon to bone healing. Although large animal models are more anatomically similar to humans, small animal models are more convenient in revealing the biological mechanism of rotator cuff injury and healing. Choosing appropriate animal models based on research objectives and establishing new small animal models play a critical role in revealing the mechanism of rotator cuff diseases and developing novel treating strategies.

Engineering multi-tissue units for regenerative Medicine: Bone-tendon-muscle units of the rotator cuff

Our body systems are comprised of numerous multi-tissue units. For the musculoskeletal system, one of the predominant functional units is comprised of bone, tendon/ligament, and muscle tissues working in tandem to facilitate locomotion. To successfully treat musculoskeletal injuries and diseases, critical consideration and thoughtful integration of clinical, biological, and engineering aspects are necessary to achieve translational bench-to-bedside research. In particular, identifying ideal biomaterial design specifications, understanding prior and recent tissue engineering advances, and judicious application of biomaterial and fabrication technologies will be crucial for addressing current clinical challenges in engineering multi-tissue units. Using rotator cuff tears as an example, insights relevant for engineering a bone-tendon-muscle multi-tissue unit are presented. This review highlights the tissue engineering strategies for musculoskeletal repair and regeneration with implications for other bone-tendon-muscle units, their derivatives, and analogous non-musculoskeletal tissue structures.

Failed Surgery for Patellar Tendinopathy in Athletes: Midterm Results of Further Surgical Management

Background:

Tendon injuries are commonly seen in sports medicine practice. Many elite players involved in high-impact activities develop patellar tendinopathy (PT) symptoms. Of them, a small percentage will develop refractory PT and need to undergo surgery. In some of these patients, surgery does not resolve these symptoms.

Purpose:

To report the clinical results in a cohort of athletes who underwent further surgery after failure of primary surgery for PT.

Study Design:

Case series; Level of evidence, 4.

Methods:

A total of 22 athletes who had undergone revision surgery for failed surgical management of PT were enrolled in the present study. Symptom severity was assessed through the Victorian Institute of Sport Assessment Scale for Patellar Tendinopathy (VISA-P) upon admission and at the final follow-up. Time to return to training, time to return to competition, and complications were also recorded.

Results:

The mean age of the athletes was 25.4 years, and the mean symptom duration from the index intervention was 15.3 months. At a mean follow-up of 30.0 ± 4.9 months, the VISA-P score improved 27.8 points (P < .0001). The patients returned to training within a mean of 9.2 months. Fifteen patients (68.2%) returned to competition within a mean of 11.6 months. Of these 15 patients, a further 2 had decreased their performance, and 2 more had abandoned sports participation by the final follow-up. The overall rate of complications was 18.2%. One patient (4.5%) had a further revision procedure.

Conclusion:

Revision surgery was feasible and effective in patients in whom PT symptoms persisted after previous surgery for PT, achieving a statistically significant and clinically relevant improvement of the VISA-P score as well as an acceptable rate of return to sport at a follow-up of 30 months.

2017 Marathon of Rome: Anthropometry and Sport Profile in 350 Runners and Association With Achilles and Patellar Tendinopathy

BACKGROUND

Achilles and patellar tendinopathy are common in runners. Despite the relevance of the problem, causative factors remain poorly understood. This cross-sectional study evaluated the association between Achilles and patellar tendinopathy and age, sex, weight, height, number of marathons, and impact profile in runners who participated in the 2017 Marathon of Rome.

METHODS

At the 2017 Marathon of Rome, 350 athletes (256 men and 94 women; mean age: 44.8 years, range 12-80 years) filled in the VISA-A and VISA-P questionnaires. A fully trained orthopedic surgeon made a diagnosis of Achilles and patellar tendinopathy according to clinical criteria.

RESULTS

Ninety-five participants were diagnosed with Achilles tendinopathy and 96 with patellar tendinopathy. There was evidence of a statistically significant positive association between age and Achilles and patellar tendinopathy, with no effect of sex, weight, and height on the presence of Achilles tendinopathy. There was no evidence of a statistically significant positive association between the number of marathons and impact profile and VISA-A score. There was a statistically significant association between VISA-P score and impact profile. Finally, there was evidence of a statistically significant positive association between VISA-A score and VISA-P score (P = 0.007).

CONCLUSIONS

In marathon runners, there was no evidence of a statistically significant association between sex, weight, height, number of marathons, and Achilles and patellar tendinopathy. However, age was associated with Achilles and patellar tendinopathy, and impact profile was associated with patellar tendinopathy.

Superiority of synovial membrane mesenchymal stem cells in chondrogenesis, osteogenesis, myogenesis and tenogenesis in a rabbit model

Engineering complex tissues is perhaps the most ambitious goal of all tissue engineers. Despite significant advances in tissue engineering, which have resulted in successful engineering of simple tissues such as skin and cartilage, there are a number of challenges that remain in engineering of complex, hybrid tissue structures, such as osteochondral tissue. Mesenchymal stem cells (MSCs) have the capacity to highly proliferate in an undifferentiated state and the potential to differentiate into a variety of different lineages, providing a promising single cell source to produce multiple cell types. MSC obtained from adult human contribute to the regeneration of mesenchymal tissues such as bone, cartilage, fat, muscle, tendon and marrow stroma. In the present study, the regeneration capacity of multipotent MSCs derived from different tissues in the rabbit were compared. Specifically the aim of this study was to isolate and characterize rabbit adult stem cell populations from bone marrow, adipose, synovial membrane, rotator cuff, ligament and tendon and assess their cell morphology, growth rate, cell surface markers and differentiation capacity. MSCs derived from synovial membrane showed superiority in terms of chondrogenesis, osteogenesis, myogenesis and tenogenesis, suggesting that synovial membrane-derived MSCs would be a good candidate for efforts to regenerate musculoskeletal tissues.

Sustained Exposure of Substance P Causes Tendinopathy

Recently, neuromediators such as substance P (SP) have been found to be important factors in tendon homeostasis. Some studies have found SP to be the cause of inflammation and tendinopathy, whereas others have determined it to be a critical component of tendon healing. As demonstrated by these conflicting findings, the effects of SP on tendinopathy remain unclear. In this study, we hypothesized that the duration of SP exposure determines its effect on the tendons, with repetitive long-term exposure leading to the development of tendinopathy. First, we verified the changes in gene and protein expression using in vitro tenocytes with 10-day exposure to SP. SP and SP + Run groups were injected with SP in their Achilles tendon every other day for 14 days. Achilles tendons were then harvested for biomechanical testing and histological processing. Notably, tendinopathic changes with decreased tensile strength, as observed in the Positive Control, were observed in the Achilles in the SP group compared to the Negative Control. Subsequent histological analysis, including Alcian blue staining, also revealed alterations in the Achilles tendon, which were generally consistent with the findings of tendinopathy in SP and SP + Run groups. Immunohistochemical analysis revealed increased expression of SP in the SP group, similar to the Positive Control. In general, the SP + Run group showed worse tendinopathic changes. These results suggest that sustained exposure to SP may be involved in the development of tendinopathy. Future research on inhibiting SP is warranted to target SP in the treatment of tendinopathy and may be beneficial to patients with tendinopathy.

Molecular and Structural Effects of Percutaneous Interventions in Chronic Achilles Tendinopathy

Achilles tendinopathy (AT) is a common problem, especially in people of working age, as well as in the elderly. Although the pathogenesis of tendinopathy is better known, therapeutic management of AT remains challenging. Various percutaneous treatments have been applied to tendon lesions: e.g., injectable treatments, platelet-rich plasma (PRP), corticosteroids, stem cells, MMP inhibitors, and anti-angiogenic agents), as well as percutaneous procedures without any injection (percutaneous soft tissue release and dry needling). In this review, we will describe and comment on data about the molecular and structural effects of these treatments obtained in vitro and in vivo and report their efficacy in clinical trials. Local treatments have some impact on neovascularization, inflammation or tissue remodeling in animal models, but evidence from clinical trials remains too weak to establish an accurate management plan, and further studies will be necessary to evaluate their value.

Sequential inflammation model for Achilles tendinopathy by elastin degradation with treadmill exercise

Background & objective

Tendinopathy is a tendon disease with abnormal mechanical loading to induce chronic repetitive injury. However, lack of a comparable animal model to demonstrate clinical progressions has hindered the understanding of anatomical and pathological changes. The major extracellular matrix (ECM) in the tendon consists of abundant type I collagen (COL) and minimal amount of elastin (ELN).

Methods

To study the ECM breakdown and inflammation, rat Achilles tendon was harvested and ex vivo incubated with specific enzymes of elastase (ELNase) or collagenase (COLase).

Results

The ELNase broke down ELN, loosened the tendon structure, and increased the COL composition. Increases in cyclooxygenase-2 expression levels in tenocytes were revealed to induce inflammation with either ELNase or COLase. However, incubation of COLase for 12 hours severely digested the tendon. To create a proper ELN degradation in rats, the present study used high-frequency ultrasound to guide the injection of ELNase at the paratendon tissue of the Achilles tendon. The effect of mechanically triggered inflammatory responses was investigated by applying treadmill exercise (15 m/min for 20 min per day). After ELNase injection for 14 and 28 days, a significant loss of ELN was observed, and exercise further facilitated the pathological transition of COL. The dynamics of inflammatory cell recruitments was revealed by specific staining of CD-11b (neutrophils) and CD-68 (macrophage) after in vivo injection of ELNase or COLase for 1, 3, 7, 14, and 28 days. The combination of ELNase and exercise caused early recruitment of neutrophil on day 1 and sequential expression of macrophage on day 7 in peritendinous tissue.

Conclusion

These results suggested that ELN degradation with repetitive mechanical loading may present a suitable model for the pathogenesis of tendinopathy.

The Translational potential of this article

This discover the role of elastin degradation in tendinopathy and the interaction of exercise in the histological changes. The established the pathological model mimicking the pathogenesis to the human disease by injecting the elastase using ultrasound guidance and then applying treadmill exercise. The loss of elastin and change of collagen composition in clinical tendinopathy samples were observed in the rats. In addition, the sequential inflammation cascades were observed in the histological outcomes with combination of elastase injection and treadmill exercise. Thus, this model may be used to test the clinical treatment of tendinopathy in different stages.

Pathogenesis and Development of Patellar Tendon Fibrosis in a Rabbit Overuse Model

BACKGROUND

The pathogenesis of patellar tendon fibrosis caused by overuse remains unclear. In an effort to further investigate effective treatments for patellar tendon fibrosis attributed to overuse, it is necessary to construct a reliable animal model.

PURPOSE

A rabbit patellar tendon fibrosis model was developed with the use of electrical stimulation to induce jumping. The pathogenesis and development of patellar tendon fibrosis were subsequently investigated with this model.

STUDY DESIGN

Controlled laboratory study.

METHODS

A total of 32 New Zealand White rabbits were randomly divided into a jumping group and a control group. Rabbits in the control group did not receive any treatment, while those in the jumping group jumped 150 times daily, 5 days per week. At 2, 4, 6, and 8 weeks after the initiation of treatment, the patellar tendons of 4 rabbits from each group were harvested and subjected to hematoxylin and eosin staining, immunohistochemical staining, and real-time polymerase chain reaction. The influence of jumping training on the expressions of histology- and fibrosis-related factors in the patellar tendon was assessed.

RESULTS

The histological changes of patellar tendon fibrosis in the jumping group were most pronounced at 4 weeks. When compared with the control group at corresponding time points, the mRNA and protein expressions of TGF-β1, CTGF, COL-I, and COL-III were upregulated significantly in the patellar tendon after jumping training for 4 weeks (P < .05). Intragroup comparison at different time points indicated that the mRNA and protein expressions of TGF-β1, COL-I, and COL-III were the highest at 4 weeks in the jumping group (P < .01).

CONCLUSION

It was found that patellar tendon fibrosis occurred because of overuse and the peak changes occurred at 4 weeks. Jumping load increased the secretions of TGF-β1 and Smad3 in the patellar tendon, with CTGF upregulation and higher synthesis of COL-I and COL-III, which were considered the pathogenesis of fibrosis.

CLINICAL RELEVANCE

This study simulated the effects of jumping load on tendon fibrosis at different time points. Moreover, the time course relationship between jumping training and patellar tendon fibrosis in the rabbit model was determined, which provided a new animal model for the study of patellar tendon fibrosis.

Histopathological changes in patellar tendon enthesis of rabbit induced by electrical stimulation intensity

BACKGROUND

Enthesis injury is a common problem in athletes and workers, which is considered closely related to overuse. However, the early pathophysiologic changes of osteotendinous junction are not well understood, and moreover, few studies investigated the relationship between intensity and pathological changes. The purpose of this study was to evaluate microstructural changes induced by different loading intensities and to find out the threshold intensity.

METHODS

Forty-eight New Zealand White rabbits were randomly divided into six groups. One control group, the others were electrically stimulated to contract repetitively for 2 h per day, three days a week. 30% of peak tetanic force (7.06 N) was adopted to stimulate the rabbits in the 100% cyclic loading group. Other groups were stimulated with 20%, 40%, 60% and 80% of this force. After four weeks, prepared samples were stained with hematoxylin and eosin.

RESULTS

After 4 weeks of cyclic loading, the shape and the distribution of tendon cells in patellar enthesis changed, the arrangement of collagen fibers became disordered and the tidemark had become irregular or even disappeared. Different stimulus intensity caused a significant change of cell density in different groups (F = 10.19, P < 0.001). The cell densities of tendon were 34.3 ± 7.9 cells/100 μm² (L60), 38.2 ± 5.9 cells/100 μm² (L80), 43.8 ± 10.3 cells/100 μm² (L100) respectively, which had significant difference with CON group 22.5 ± 3.5 cells/100 μm². The thickness of fibrocartilage zone had no significant difference among the groups.

CONCLUSIONS

The changes of histomorphology with the increasing exercise intensity elucidated that the degree of enthesis microdamage was directly related to the intensity of exercises. The findings demonstrated that 18% (used in L60 group) of peak tetanic force was the threshold intensity which could induce pathological changes in enthesis in four weeks.

Therapeutic Efficacy of Intratendinous Delivery of Dexamethasone Using Porous Microspheres for Amelioration of Inflammation and Tendon Degeneration on Achilles Tendinitis in Rats

Achilles tendinitis caused by overuse, aging, or gradual wear induces pain, swelling, and stiffness of Achilles tendon and leads to tendon rupture. This study was performed to investigate the suppression of inflammation responses in interleukin-1β- (IL-1β-) stimulated tenocytes in vitro and the suppression of the progression of Achilles tendinitis-induced rat models in vivo using dexamethasone-containing porous microspheres (DEX/PMSs) for a sustained intratendinous DEX delivery. DEX from DEX/PMSs showed the sustained release of DEX. Treatment of IL-1β-stimulated tenocytes with DEX/PMSs suppressed the mRNA levels for COX-2, IL-1β, IL-6, and TNF-α. The intratendinous injection of DEX/PMSs into Achilles tendinitis rats both decreased the mRNA levels for these cytokines and increased mRNA levels for anti-inflammatory cytokines IL-4 and IL-10 in tendon tissues. Furthermore, DEX/PMSs effectively prevented tendon degeneration by enhancing the collagen content and biomechanical properties. Our findings suggest that DEX/PMSs show great potential as a sustained intratendinous delivery system for ameliorating inflammation responses as well as tendon degeneration in Achilles tendinitis.

Aspirin promotes tenogenic differentiation of tendon stem cells and facilitates tendinopathy healing through regulating the GDF7/Smad1/5 signaling pathway

Tendinopathy is a common musculoskeletal system disorder in sports medicine, but regeneration ability of injury tendon is limited. Tendon stem cells (TSCs) have shown the definitive treatment evidence for tendinopathy and tendon injuries due to their tenogenesis capacity. Aspirin, as the representative of nonsteroidal anti-inflammatory drugs for its anti-inflammatory and analgestic actions, has been commonly used in treating tendinopathy in clinical, but the effect of aspirin on tenogenesis of TSCs is unclear. We hypothesized that aspirin could promote injury tendon healing through inducing TSCs tenogenesis. The aim of the present study is to make clear the effect of aspirin on TSC tenogenesis and tendon healing in tendinopathy, and thus provide new treatment evidence and strategy of aspirin for clinical practice. First, TSCs were treated with aspirin under tenogenic medium for 3, 7, and 14 days. Sirius Red staining was performed to observe the TSC differentiation. Furthermore, RNA sequencing was utilized to screen out different genes between the induction group and aspirin treatment group. Then, we identified the filtrated molecules and compared their effect on tenogenesis and related signaling pathway. At last, we constructed the tendinopathy model and compared biomechanical changes after aspirin intake. From the results, we found that aspirin promoted tenogenesis of TSCs. RNA sequencing showed that growth differentiation factor 6 (GDF6), GDF7, and GDF11 were upregulated in induction medium with the aspirin group compared with the induction medium group. GDF7 increased tenogenesis and activated Smad1/5 signaling. In addition, aspirin increased the expression of TNC, TNMD, and Scx and biomechanical properties of the injured tendon. In conclusion, aspirin promoted TSC tenogenesis and tendinopathy healing through GDF7/Smad1/5 signaling, and this provided new treatment evidence of aspirin for tendinopathy and tendon injuries.

Aspirin inhibits adipogenesis of tendon stem cells and lipids accumulation in rat injury tendon through regulating PTEN/PI3K/AKT signalling

Tendon injury repairs are big challenges in sports medicine, and fatty infiltration after tendon injury is very common and hampers tendon injury healing process. Tendon stem cells (TSCs), as precursors of tendon cells, have shown promising effect on injury tendon repair for their tenogenesis and tendon extracellular matrix formation. Adipocytes and lipids accumulation is a landmark event in pathological process of tendon injury, and this may induce tendon rupture in clinical practice. Based on this, it is important to inhibit TSCs adipogenesis and lipids infiltration to restore structure and function of injury tendon. Aspirin, as the representative of non‐steroidal anti‐inflammatory drugs (NSAIDs), has been widely used in tendon injury for its anti‐inflammatory and analgesic actions, but effect of aspirin on TSCs adipogenesis and fatty infiltration is still unclear. Under adipogenesis conditions, TSCs were treated with concentration gradient of aspirin. Oil red O staining was performed to observe changes of lipids accumulation. Next, we used RNA sequencing to compare profile changes of gene expression between induction group and aspirin‐treated group. Then, we verified the effect of filtrated signalling on TSCs adipogenesis. At last, we established rat tendon injury model and compared changes of biomechanical properties after aspirin treatment. The results showed that aspirin decreased lipids accumulation in injury tendon and inhibited TSCs adipogenesis. RNA sequencing filtrated PTEN/PI3K/AKT signalling as our target. After adding the signalling activators of VO‐Ohpic and IGF‐1, inhibited adipogenesis of TSCs was reversed. Still, aspirin promoted maximum loading, ultimate stress and breaking elongation of injury tendon. In conclusion, by down‐regulating PTEN/PI3K/AKT signalling, aspirin inhibited adipogenesis of TSCs and fatty infiltration in injury tendon, promoted biomechanical properties and decreased rupture risk of injury tendon. All these provided new therapeutic potential and medicine evidence of aspirin in treating tendon injury and tendinopathy.

Combined approach for characterization and quality assessment of rabbit bone marrow-derived mesenchymal stem cells intended for gene banking

Rabbit mesenchymal stem cells (rMSCs) are promising agents for the preservation of genetic biodiversity in domestic rabbit breeds. However, rMSCs must meet certain requirements to be used for cryopreservation in animal gene banks. Currently, there are numerous discrepancies in the published data regarding the rMSC phenotype, which may complicate efforts to evaluate their purity and suitability for reuse after cryopreservation in gene and tissue banks. We propose a combined approach (flow cytometry, PCR, differentiation and ultrastructure studies) for the characterization and recovery of rMSCs after cryopreservation. Flow cytometric analyses of rMSCs confirmed the expression of CD29, CD44, vimentin, desmin and α-SMA. RT-PCR revealed the expression of other markers at the mRNA level (SSEA-4, CD73, CD90, CD105, CD146 and CD166). rMSCs showed efficient multilineage differentiation into adipo-, chondro- and osteogenic lineages, SOX2 expression (pluripotency) and typical MSC morphology and ultrastructure. The confirmed rMSCs were subsequently used for cryopreservation. Efficient recovery of rMSCs after cryogenic freezing was demonstrated by high cell viability, normal ultrastructure of reseeded rMSCs, high expression of CD29 and CD44 and lineage differentiation capacity. The proposed combined approach could be used for characterization, cryopreservation and recovery of rMSCs as genetic resources for native rabbit breeds.

Use of Human Placenta-Derived Cells in a Preclinical Model of Tendon Injury

BACKGROUND

Emerging data suggest that human cells derived from extraembryonic tissues may have favorable musculoskeletal repair properties. The purpose of this study was to determine whether the injection of human placenta-derived mesenchymal-like stromal cells, termed placental expanded cells (PLX-PAD), would improve tendon healing in a preclinical model of tendinopathy.

METHODS

Sixty male Sprague-Dawley rats underwent bilateral patellar tendon injection with either saline solution (control) or PLX-PAD cells (2 × 10 cells/100 µL) 6 days after collagenase injection to induce tendon degeneration. Animals were killed at specific time points for biomechanical, histological, and gene expression analyses of the healing patellar tendons.

RESULTS

Biomechanical testing 2 weeks after the collagenase injury demonstrated better biomechanical properties in the tendons treated with PLX-PAD cells. The load to failure of the PLX-PAD-treated tendons was higher than that of the saline-solution-treated controls at 2 weeks (77.01 ± 10.51 versus 58.87 ± 11.97 N, p = 0.01). There was no significant difference between the 2 groups at 4 weeks. There were no differences in stiffness at either time point. Semiquantitative histological analysis demonstrated no significant differences in collagen organization or cellularity between the PLX-PAD and saline-solution-treated tendons. Gene expression analysis demonstrated higher levels of interleukin-1β (IL-1β) and IL-6 early in the healing process in the PLX-PAD-treated tendons.

CONCLUSIONS

Human placenta-derived cell therapy induced an early inflammatory response and a transient beneficial effect on tendon failure load in a model of collagenase-induced tendon degeneration.

CLINICAL RELEVANCE

Human extraembryonic tissues, such as the placenta, are an emerging source of cells for musculoskeletal repair and may hold promise as a point-of-care cell therapy for tendon injuries.

Patella tendinopathy Zoobiquity - What can we learn from dogs?

BACKGROUND

Patella tendinopathy is an overuse condition. Pathogenesis and identification of intrinsic risk factors have largely eluded the orthopaedic world. The cranial cruciate ligament (CrCL) in dogs is the equivalent to the human anterior cruciate ligament (ACL). We report the effect of two canine proximal tibial osteotomy procedures in the veterinary literature on patella tendon moment arm and describe the biomechanical rationale for a tibial tubercle osteotomy for treatment of patella tendinopathy in the human.

METHODS

A literature review of studies reporting clinical complications of TTA and TPLO to form an observational animal cohort study in dogs.

RESULTS

The veterinary literature reports an overall clinical complication rate of up to 61% for TTA and up to 50% for TPLO respectively. Complications associated with the extensor mechanism of the knee are <1% for TTA compared to 1.9-19% for TPLO. Radiographic thickening of the patella tendon and tendinopathy is seen in one to 80% of TPLO cases. The TPLO decreases the moment arm of the extensor mechanism meaning increased force is required in the patella tendon to achieve the same torque when compared to the TTA which increases the efficiency of the extensor mechanism. This difference may account, in part, for the post-operative complications reported to the patella and patella tendon following TPLO.

CONCLUSION

This observational animal cohort study demonstrates a biomechanical rationale for investigating diagnostic and potential treatment options, including a tibial tubercle osteotomy, for patella tendinopathy in humans based on this principle.

A Novel Microplate 3D Bioprinting Platform for the Engineering of Muscle and Tendon Tissues

Two-dimensional (2D) cell cultures do not reflect the in vivo situation, and thus it is important to develop predictive three-dimensional (3D) in vitro models with enhanced reliability and robustness for drug screening applications. Treatments against muscle-related diseases are becoming more prominent due to the growth of the aging population worldwide. In this study, we describe a novel drug screening platform with automated production of 3D musculoskeletal-tendon-like tissues. With 3D bioprinting, alternating layers of photo-polymerized gelatin-methacryloyl-based bioink and cell suspension tissue models were produced in a dumbbell shape onto novel postholder cell culture inserts in 24-well plates. Monocultures of human primary skeletal muscle cells and rat tenocytes were printed around and between the posts. The cells showed high viability in culture and good tissue differentiation, based on marker gene and protein expressions. Different printing patterns of bioink and cells were explored and calcium signaling with Fluo4-loaded cells while electrically stimulated was shown. Finally, controlled co-printing of tenocytes and myoblasts around and between the posts, respectively, was demonstrated followed by co-culture and co-differentiation. This screening platform combining 3D bioprinting with a novel microplate represents a promising tool to address musculoskeletal diseases.

Characterization of a Novel Calcific Achilles Tendinopathy Model in Mice: Contralateral Tendinopathy Induced by Unilateral Tenotomy

Achilles tendinopathy is a significant clinical disease characterized by activity-related pain, focal movement limitation, and intratendinous imaging changes. However, treatment of Achilles tendinopathy has been based mainly on theoretical rationale and clinical experience because of its unclear underlying pathogenesis and mechanism. The purpose of the study was to develop a simple but reproducible overuse-induced animal model of Achilles tendinopathy in mice to better understand the underlying mechanism and prevent calcific Achilles tendinopathy. A total of 80 C57/B6 mice (8 or 9 weeks old) were employed and randomly divided into control and experimental groups. Unilateral Achilles tenotomy was performed on the right hind limbs in the experiment group. 12 weeks after unilateral Achilles tenotomy, the onset of Achilles tendinopathy in the contralateral Achilles tendon was determined by radiological assessment, histologic analysis, electron microscopy observation, and biomechanical test. The onset of calcific Achilles tendinopathy in contralateral Achilles tendon was confirmed after 12 weeks of unilateral tenotomy. The contralateral Achilles tendon in the experimental group was characterized as hypercellularity, neovascularization, and fused collagen fiber disarrangement, compared with the control group. Importantly, intra-tendon endochondral ossification and calcaneus deformity were featured in contralateral Achilles tendon. In addition, poor biomechanical properties in the contralateral Achilles tendon revealed the incidence of Achilles tendinopathy. We hereby introduce a novel, simple, but reproducible spontaneous contralateral calcific Achilles tendinopathy model in mice, which represents overuse conditions during tendinopathy development in humans. It should be a useful tool to further study the underlying pathogenesis of calcific Achilles tendinopathy.

The use of an IL1-receptor antagonist to reverse the changes associated with established tendinopathy in a rat model

Interleukin-1 (IL1) is a cytokine that plays a role in inflammation and is a potential contributor to the inflammation present in tendinopathy. Its inhibition may be of use in the treatment of tendinopathy and has been a target for treatment. To evaluate how an IL1-receptor antagonist (IL1-RA) reverses pathologic changes associated with established patellar tendinopathy, we randomized 48 Sprague-Dawley retired breeder rats into three groups having weekly bilateral patellar tendon injections for 6 weeks. The control group received 0.1 mL saline for 6 weeks. The intervention groups were treated with 0.1 mL 2% carrageenan for 4 weeks. Beginning at week three, the IL1-RA group received 0.94 mg of the IL1-RA (2.5 mg/kg) added to the 0.1 mL 2% carrageenan and 0.94 mg of the IL1-RA alone for the final 2 weeks, while the CAR received 0.1 mL saline for the final 2 weeks. Animals were euthanized 6 weeks after initial injection. The CAR group demonstrated significantly (P < 0.05) shorter tendon lengths (7.81 ± 0.44 mm) than the control (8.25 ± 0.58 mm) and IL1-RA (8.34 ± 0.52 mm) group (P < 0.05). Macroscopically, plaque-like formations were reduced and margins of the tendon were more evident in the IL1-RA group compared to the CAR group. CAR group demonstrated significantly greater histopathologic changes (inflammatory cell density, disorganization of collagen, nuclear rounding, and angiogenesis) than the control and IL1-RA group. No significant difference in mechanical properties of the tendon was noted. These findings demonstrate IL1-RA can reduce pathologic changes in the patellar tendon in an established tendonitis model although did not demonstrate a difference in mechanical properties.

Evaluating the role of subacromial impingement in rotator cuff tendinopathy: Development and analysis of a novel murine model

Subacromial impingement of the rotator cuff is understood as a contributing factor in the development of rotator cuff tendinopathy. However, changes that occur in the impinged tendon are poorly understood and warrant further study. To enable further study of rotator cuff tendinopathy, we performed a controlled laboratory study to determine feasibility and baseline characteristics of a new murine model for subacromial impingement. This model involves surgically inserting a microvascular clip into the subacromial space in adult C57Bl/6 mice. Along with a sham surgery arm, 90 study animals were distributed among time point groups for sacrifice up to 6 weeks. All animals underwent bilateral surgery (total N = 180). Biomechanical, histologic, and molecular analyses were performed to identify and quantify the progression of changes in the supraspinatus tendon. Decreases in failure force and stiffness were found in impinged tendon specimens compared to sham and no-surgery controls at all study time points. Semi-quantitative scoring of histologic specimens demonstrated significant, persistent tendinopathic changes over 6 weeks. Quantitative real-time polymerase chain reaction analysis of impinged tendon specimens demonstrated persistently increased expression of genes related to matrix remodeling, inflammation, and tendon development. Overall, this novel murine subacromial impingement model creates changes consistent with acute tendonitis, which may mimic the early stages of rotator cuff tendinopathy. A robust, simple, and reproducible animal model of rotator cuff tendinopathy is a valuable research tool to allow further studies of cellular and molecular mechanisms and evaluation of therapeutic interventions in rotator cuff tendinopathy. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:2780-2788, 2018.

Rescue plan for Achilles: Therapeutics steering the fate and functions of stem cells in tendon wound healing

Due to the increasing age of our society and a rise in engagement of young people in extreme and/or competitive sports, both tendinopathies and tendon ruptures present a clinical and financial challenge. Tendon has limited natural healing capacity and often responds poorly to treatments, hence it requires prolonged rehabilitation in most cases. Till today, none of the therapeutic options has provided successful long-term solutions, meaning that repaired tendons do not recover their complete strength and functionality. Our understanding of tendon biology and healing increases only slowly and the development of new treatment options is insufficient. In this review, following discussion on tendon structure, healing and the clinical relevance of tendon injury, we aim to elucidate the role of stem cells in tendon healing and discuss new possibilities to enhance stem cell treatment of injured tendon. To date, studies mainly apply stem cells, often in combination with scaffolds or growth factors, to surgically created tendon defects. Deeper understanding of how stem cells and vasculature in the healing tendon react to growth factors, common drugs used to treat injured tendons and promising cellular boosters could help to develop new and more efficient ways to manage tendon injuries.

Evaluation of Stem Cell Therapies in a Bilateral Patellar Tendon Injury Model in Rats

Regenerative medicine provides novel alternatives to conditions that challenge traditional treatments. The prevalence and morbidity of tendinopathy across species, combined with the limited healing properties of this tissue, have prompted the search for cellular therapies and propelled the development of experimental models to study their efficacy. Umbilical cord matrix-derived mesenchymal stem cells (UCM-MSC) are appealing candidates because they are abundant, easy to collect, circumvent the ethical concerns and risk of teratoma formation, yet resemble primitive embryonic stem cells more closely than adult tissue-derived MSCs. Significant interest has focused on chitosan as a strategy to enhance the properties of MSCs through spheroid formation. This paper details techniques to isolate UCM-MSCs, prepare spheroids on chitosan film, and analyze the effect of spheroid formation on surface marker expression. Consequently, creation of a bilateral patellar tendon injury model in rats is described for in vivo implantation of UCM-MSC spheroids formed on chitosan film. No complication was observed in the study with respect to morbidity, stress rising effects, or tissue infection. The total functional score of the operated rats at 7 days was lower than that of normal rats, but returned to normal within 28 days after surgery. Histological scores of tissue-healing confirmed the presence of a clot in treated defects evaluated at 7 days, absence of foreign body reaction, and progressing healing at 28 days. This bilateral patella tendon defect model controls inter-individual variation via creation of an internal control in each rat, was associated with acceptable morbidity, and allowed detection of differences between untreated tendons and treatments.

Novel animal model for Achilles tendinopathy: Controlled experimental study of serial injections of collagenase in rabbits

Our goal was to develop a novel technique for inducing Achilles tendinopathy in animal models which more accurately represents the progressive histological and biomechanical characteristic of chronic Achilles tendinopathy in humans. In this animal research study, forty-five rabbits were randomly assigned to three groups and given bilateral Achilles injections. Low dose (LD group) (n = 18) underwent a novel technique with three low-dose (0.1mg) injections of collagenase that were separated by two weeks, the high dose group (HD) (n = 18) underwent traditional single high-dose (0.3mg) injections, and the third group were controls (n = 9). Six rabbits were sacrificed from each experimental group (LD and HD) at 10, 12 and 16 weeks. Control animals were sacrificed after 16 weeks. Histological and biomechanical properties were then compared in all three groups. At 10 weeks, Bonar score and tendon cross sectional area was highest in HD group, with impaired biomechanical properties compared to LD group. At 12 weeks, Bonar score was higher in LD group, with similar biomechanical findings when compared to HD group. After 16 weeks, Bonar score was significantly increased for both LD group (11,8±2,28) and HD group (5,6±2,51), when compared to controls (2±0,76). LD group showed more pronounced histological and biomechanical findings, including cross sectional area of the tendon, Young’s modulus, yield stress and ultimate tensile strength. In conclusion, Achilles tendinopathy in animal models that were induced by serial injections of low-dose collagenase showed more pronounced histological and biomechanical findings after 16 weeks than traditional techniques, mimicking better the progressive and chronic characteristic of the tendinopathy in humans.

Mechanobiology of young and aging tendons: In vivo studies with treadmill running

Tendons are unique in the sense that they are constantly subjected to large mechanical loads and that they contain tendon-specific cells, including tenocytes and tendon stem/progenitor cells. The responses of these cells to mechanical loads can be anabolic or catabolic and as a result, change the biological properties of the tendon itself that may be beneficial or detrimental. On the other hand, aging also induces aberrant changes in cellular expression of various genes and production of various types of matrix proteins in the tendon, and consequently lead to tendon degeneration and impaired healing in aging tendons; both could be improved by moderate physiological mechanical loading such as treadmill running. This article gives an overview on the mechanobiology research of young and aging animal tendons using treadmill running model. The challenges in such treadmill running studies are also discussed. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:557-565, 2018.

Tendon injury and repair - A perspective on the basic mechanisms of tendon disease and future clinical therapy

Tendon is an intricately organized connective tissue that efficiently transfers muscle force to the bony skeleton. Its structure, function, and physiology reflect the extreme, repetitive mechanical stresses that tendon tissues bear. These mechanical demands also lie beneath high clinical rates of tendon disorders, and present daunting challenges for clinical treatment of these ailments. This article aims to provide perspective on the most urgent frontiers of tendon research and therapeutic development. We start by broadly introducing essential elements of current understanding about tendon structure, function, physiology, damage, and repair. We then introduce and describe a novel paradigm explaining tendon disease progression from initial accumulation of damage in the tendon core to eventual vascular recruitment from the surrounding synovial tissues. We conclude with a perspective on the important role that biomaterials will play in translating research discoveries to the patient.

STATEMENT OF SIGNIFICANCE

Tendon and ligament problems represent the most frequent musculoskeletal complaints for which patients seek medical attention. Current therapeutic options for addressing tendon disorders are often ineffective, and the need for improved understanding of tendon physiology is urgent. This perspective article summarizes essential elements of our current knowledge on tendon structure, function, physiology, damage, and repair. It also describes a novel framework to understand tendon physiology and pathophysiology that may be useful in pushing the field forward.

Degradation of elastic fiber and elevated elastase expression in long head of biceps tendinopathy

Tendinopathy of the long head of the biceps (TLHB) involves various types of extracellular matrix degeneration, but previous studies have not evaluated elastic fibers. The purpose of this study was to investigate elastic fiber distribution in long head of the biceps (LHB). The TLHB tendons of 16 consecutive patients (eight men and eight women; average age of 55.75 years; age range of 40-71 years) were transected and harvested. Three cadaveric LHB tendons were used as the control group. The expression of collagen type I was decreased, but type III was increased in TLHB. Disruption of elastic fibers was particularly observed in grade II specimens where the level of elastase-positive staining was significantly higher than in grade I specimens. Elastic fibers were not observed in the grade III area, implying a higher expression of elastase than in the grade I area. Results of Western blotting showed that the expression of elastin was higher in the control group and the levels of elastin significantly decreased in grades II and III of TLHB. Levels of osteopontin and elastase were increased in primary culture of human tenocytes after experiencing elastic derived peptide treatment. These results suggested that elastase may be caused by the disruption of elastic fibers in the development of chronic tendinopathy and that elastic derived peptide may enhance elastase and osteopontin expression. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:1919-1926, 2017.