Animal model for tendinopathy

Magnetic resonance Imaging for diagnosing and managing deep digital flexor tendinopathy in equine athletes: Insights, advances and future directions

Deep digital flexor (DDF) tendinopathy is a significant cause of lameness and poor performance in equine athletes with substantial implications for their return to athletic performance. Magnetic resonance imaging (MRI) is increasingly integrated into the diagnostic workup of horses with foot pain and has revolutionised the diagnosis and management of these injuries. This review discusses the principles of MRI in the context of deep digital flexor tendon (DDFT) injury, comparing high-field and low-field systems and highlighting the clinical relevance of technical parameters, including field strength and sequence selection, in achieving an accurate diagnosis. This review also critically evaluates how different configurations and/or imaging features of tendon lesions may impact patient prognosis, considers the complementary role of computed tomography and ultrasonography in cases where MRI may not be feasible, and discusses emerging imaging techniques including positron emission tomography (PET)-MRI and quantitative MRI. Lastly, this review underscores the importance of serial imaging to monitor lesion progression and guide rehabilitation, while identifying knowledge gaps and proposing future research directions. Ultimately, a multidisciplinary approach incorporating advanced imaging and tailored rehabilitation is essential to improving clinical outcomes in horses with DDFT injuries.

Targeting the IL-17A pathway for therapy in early-stage tendinopathy

OBJECTIVES

Tendinopathy is a frequent clinical problem and represents an extraordinary health economic and socioeconomic burden with high unmet medical needs. Recent clinical evidence suggests blockade of interleukin 17A (IL-17A) for tendinopathy therapy. The present preclinical study elucidates the biological mechanisms of IL-17A pathway stimulation and blockade in tendinopathy.

METHODS

We explored whether IL-17A and other IL-17 family members are differentially expressed in biopsies of healthy, early-stage and late-stage tendinopathic human rotator cuff tendons using RT-qPCR. IL-17 pathway signature genes in healthy human tendon-derived cells were identified following IL-17A stimulation using AmpliSeq RNA. The molecular, structural and functional consequences of IL-17A pathway stimulation were explored in healthy human tendon-derived cells and in a rat tendon fascicle model ex vivo. The effects of IL-17A pathway blockade were investigated in a rat model of rotator cuff tendinopathy in vivo.

RESULTS

We provide evidence of differential expression of IL-17A mRNA (IL17A) versus other IL-17 family members in human rotator cuff early-stage tendinopathy. In human tendon-derived cells, stimulation with IL-17A induced the expression of the selected IL-17A pathway signature genes NFKBIZ, ZC3H12A, CXCL1, IL6, MMP3. Expression was inhibited by IL-17A blockade. In the rat ex vivo and in vivo models, IL-17A blockade alleviated inflammatory immune effector release, tendon structural degeneration, tendon inflammation and impaired tendon function.

CONCLUSION

Our data provide evidence that IL-17A is a key contributor to the pathogenesis of tendinopathy by promoting tendon inflammation and degeneration and that IL-17A blockade may represent a potential therapy in early-stage tendinopathy.

Erroneous Differentiation of Tendon Stem/Progenitor Cells in the Pathogenesis of Tendinopathy: Current Evidence and Future Perspectives

Tendinopathy is a condition characterized by persistent tendon pain, structural damage, and compromised functionality. Presently, the treatment for tendinopathy remains a formidable challenge, partly because of its unclear pathogenesis. Tendon stem/progenitor cells (TSPCs) are essential for tendon homeostasis, regeneration, remodeling, and repair. An innovative theory has been previously proposed, with insufficient evidence, that the erroneous differentiation of TSPCs may constitute one of the fundamental mechanisms underpinning tendinopathy. Over the past few years, there has been accumulating evidence for plausibility of this theory. In this review, we delve into alterations in the differentiation potential of TSPCs and the underlying mechanisms in the context of injury-induced tendinopathy, diabetic tendinopathy, and age-related tendinopathy to provide updated evidence on the erroneous differentiation theory. Despite certain limitations inherent in the existing body of evidence, the erroneous differentiation theory emerges as a promising and highly pertinent avenue for understanding tendinopathy. In the future, advanced methodologies will be harnessed to further deepen comprehension of this theory, paving the way for prospective developments in clinical therapies targeting TSPCs for the management of tendinopathy.

Advancements in Therapeutic Approaches for Degenerative Tendinopathy: Evaluating Efficacy and Challenges

Degenerative tendinopathy results from the accumulation of minor injuries following unsuccessful tendon repair during acute tendon injuries. The process of tendon repair is prolonged and varies between individuals, making it susceptible to reinjury. Moreover, treating chronic tendinopathy often requires expensive and extensive rehabilitation, along with a variety of combined therapies to facilitate recovery. This condition significantly affects the quality of life of affected individuals, underscoring the urgent need for more efficient and cost-effective treatment options. Although traditional treatments have improved significantly and are being used as substitutes for surgical interventions, the findings have been inconsistent and conflicting. This review aims to clarify these issues by exploring the strengths and limitations of current treatments as well as recent innovations in managing various forms of degenerative tendinopathy.

Collagen denaturation in post-run Achilles tendons and Achilles tendinopathy: In vivo mechanophysiology and magnetic resonance imaging

Achilles tendinopathy is often attributed to overuse, but its pathophysiology remains poorly understood. Disruption to the molecular structure of collagen is fundamental for the onset and progression of tendinopathy but has mostly been investigated in vitro. Here, we interrogated the in vivo molecular structure changes of collagen in rat Achilles tendons following treadmill running. Unexpectedly, the tendons' collagen molecules were not mechanically unfolded by running but denatured through proteolysis during physiological post-run remodeling. We further revealed that running induces inflammatory gene expressions in Achilles tendons and that long-term running causes prolonged, elevated collagen degradation, leading to the accumulation of denatured collagen and tendinopathy development. For applications, we demonstrated magnetic resonance imaging of collagenase-induced Achilles tendon injury in vivo using a denatured collagen targeting contrast agent. Our findings may help close the knowledge gaps in the mechanobiology and pathogenesis of Achilles tendinopathy and initiate new strategies for its imaging-based diagnosis.

The roles and mechanisms of the NF-κB signaling pathway in tendon disorders

Both acute and chronic tendon injuries are the most frequently occurring musculoskeletal diseases in human and veterinary medicine, with a limited repertoire of successful and evidenced-based therapeutic strategies. Inflammation has been suggested as a key driver for the formation of scar and adhesion tissue following tendon acute injury, as well as pathological alternations of degenerative tendinopathy. However, prior efforts to completely block this inflammatory process have yet to be largely successful. Recent investigations have indicated that a more precise targeted approach for modulating inflammation is critical to improve outcomes. The nuclear factor-kappaB (NF-κB) is a typical proinflammatory signal transduction pathway identified as a key factor leading to tendon disorders. Therefore, a comprehensive understanding of the mechanism or regulation of NF-κB in tendon disorders will aid in developing targeted therapeutic strategies for human and veterinary tendon disorders. In this review, we discuss what is currently known about molecular components and structures of basal NF-κB proteins and two activation pathways: the canonical activation pathway and the non-canonical activation pathway. Furthermore, we summarize the underlying mechanisms of the NF-κB signaling pathway in fibrosis and adhesion after acute tendon injury, as well as pathological changes of degenerative tendinopathy in all species and highlight the effect of targeting this signaling pathway in tendon disorders. However, to gain a comprehensive understanding of its mechanisms underlying tendon disorders, further investigations are required. In the future, extensive scientific examinations are warranted to full characterize the NF-κB, the exact mechanisms of action, and translate findings into clinical human and veterinary practice.

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.

Treatment of Naturally Occurring Tendon Disease with Allogeneic Multipotent Mesenchymal Stromal Cells: A Randomized, Controlled, Triple-Blinded Pilot Study in Horses

The treatment of tendinopathies with multipotent mesenchymal stromal cells (MSCs) is a promising option in equine and human medicine. However, conclusive clinical evidence is lacking. The purpose of this study was to gain insight into clinical treatment efficacy and to identify suitable outcome measures for larger clinical studies. Fifteen horses with early naturally occurring tendon disease were assigned to intralesional treatment with allogeneic adipose-derived MSCs suspended in serum or with serum alone through block randomization (dosage adapted to lesion size). Clinicians and horse owners remained blinded to the treatment during 12 months (seven horses per group) and 18 months (seven MSC-group and five control-group horses) of follow-up including clinical examinations and diagnostic imaging. Clinical inflammation, lameness, and ultrasonography scores improved more over time in the MSC group. The lameness score difference significantly improved in the MSC group compared with the control group after 6 months. In the MSC group, five out of the seven horses were free of re-injuries and back to training until 12 and 18 months. In the control group, three out of the seven horses were free of re-injuries until 12 months. These results suggest that MSCs are effective for the treatment of early-phase tendon disease and provide a basis for a larger controlled study.