Achilles Tendinopathy, A Brief Review and Update of Current Literature

Insertional Achilles Tendinopathy Treated With Botulinum Toxin: A Case Report

Chronic insertional Achilles tendinopathy (IAT) is a common cause of recalcitrant heel pain. Patients present with pain localized to the Achilles tendon insertion at the calcaneus and have tenderness to palpation in this area on physical exam. Conservative management often includes an exercise prescription focusing on eccentric loading with limited dorsiflexion. Extracorporeal shockwave therapy and injection therapies including hypertonic dextrose and platelet-rich plasma (PRP) have shown some therapeutic benefit but evidence for injections is limited. IAT can often be recalcitrant to non-operative treatments, and cases are often referred for surgical debridement and decompression. Botulinum toxin A (BTX-A) has been used to treat several different musculoskeletal injuries, but there have been no published studies assessing the efficacy of BTX-A injections specifically for Achilles tendinopathy. This is a case of recalcitrant IAT treated with ultrasound-guided BTX-A.

Evaluation of tendon and ligament microstructure and mechanical properties in a canine model of mucopolysaccharidosis I

Mucopolysaccharidosis (MPS) I is a lysosomal storage disorder characterized by deficient alpha-l-iduronidase activity, leading to abnormal accumulation of glycosaminoglycans (GAGs) in cells and tissues. Synovial joint disease is prevalent and significantly reduces patient quality of life. There is a strong clinical need for improved treatment approaches that specifically target joint tissues; however, their development is hampered by poor understanding of underlying disease pathophysiology, including how pathological changes to component tissues contribute to overall joint dysfunction. Ligaments and tendons, in particular, have received very little attention, despite the critical roles of these tissues in joint stability and biomechanical function. The goal of this study was to leverage the naturally canine model to undertake functional and structural assessments of the anterior (cranial) cruciate ligament (CCL) and Achilles tendon in MPS I. Tissues were obtained postmortem from 12-month-old MPS I and control dogs and tested to failure in uniaxial tension. Both CCLs and Achilles tendons from MPS I animals exhibited significantly lower stiffness and failure properties compared to those from healthy controls. Histological examination revealed multiple pathological abnormalities, including collagen fiber disorganization, increased cellularity and vascularity, and elevated GAG content in both tissues. Clinically, animals exhibited mobility deficits, including abnormal gait, which was associated with hyperextensibility of the stifle and hock joints. These findings demonstrate that pathological changes to both ligaments and tendons contribute to abnormal joint function in MPS I, and suggest that effective clinical management of joint disease in patients should incorporate treatments targeting these tissues.

Pristimerin suppresses AIM2 inflammasome by modulating AIM2-PYCARD/ASC stability via selective autophagy to alleviate tendinopathy

Macroautophagy/autophagy plays an important role in regulating cellular homeostasis and influences the pathogenesis of degenerative diseases. Tendinopathy is characterized by tendon degeneration and inflammation. However, little is known about the role of selective autophagy in tendinopathy. Here, we find that pristimerin (PM), a quinone methide triterpenoid, is more effective in treating tendinopathy than the first-line drug indomethacin. PM inhibits the AIM2 inflammasome and alleviates inflammation during tendinopathy by promoting the autophagic degradation of AIM2 through a PYCARD/ASC-dependent manner. A mechanistic study shows that PM enhances the K63-linked ubiquitin chains of PYCARD/ASC at K158/161, which serves as a recognition signal for SQSTM1/p62-mediated autophagic degradation of the AIM2-PYCARD/ASC complex. We further identify that PM binds the Cys53 site of deubiquitinase USP50 through the Michael-acceptor and blocks the binding of USP50 to PYCARD/ASC, thereby reducing USP50-mediated cleavage of K63-linked ubiquitin chains of PYCARD/ASC. Finally, PM treatment in vivo generates an effect comparable to inflammasome deficiency in alleviating tendinopathy. Taken together, these findings demonstrate that PM alleviates the progression of tendinopathy by modulating AIM2-PYCARD/ASC stability via SQSTM1/p62-mediated selective autophagic degradation, thus providing a promising autophagy-based therapeutic for tendinopathy.Abbreviations: 3-MA: 3-methyladenine; AIM2: absent in melanoma 2; AT: Achilles tenotomy; ATP: adenosine triphosphate; BMDMs: bone marrow-derived macrophages; CHX: cycloheximide; Col3a1: collagen, type III, alpha 1; CQ: chloroquine; Cys: cysteine; DARTS: drug affinity responsive target stability; DTT: dithiothreitol; DUB: deubiquitinase; gDNA: genomic DNA; GSH: glutathione; His: histidine; IL1B/IL-1β: interleukin 1 beta; IND: indomethacin; IP: immunoprecipitation; LPS: lipopolysaccharide; MMP: mitochondrial membrane potential; NLRP3: NLR family, pyrin domain containing 3; PM: pristimerin; PYCARD/ASC: PYD and CARD domain containing; SN: supernatants; SOX9: SRY (sex determining region Y)-box 9; SQSTM1: sequestosome 1; Tgfb: transforming growth factor, beta; TIMP3: tissue inhibitor of metalloproteinase 3; TNMD: tenomodulin; TRAF6: TNF receptor-associated factor 6; Ub: ubiquitin; USP50: ubiquitin specific peptidase 50; WCL: whole cell lysates.