Proteomics perspectives in rotator cuff research: a systematic review of gene expression and protein composition in human tendinopathy

Cervical and Thoracic Spine Mobility in Rotator Cuff Related Shoulder Pain: A Comparative Analysis with Asymptomatic Controls

Rotator cuff related shoulder pain (RCRSP) is a prevalent clinical presentation characterized by substantial diagnostic uncertainty. Some of this uncertainty relates to the involvement of the cervical and thoracic spine as a source of or contributing factor to RCRSP. Thirty-two RCRSP cases and thirty-two asymptomatic controls (AC), recruited from Hospital La Paz-Carlos III between March 2023 and September 2023, were matched for age, gender and hand dominance. Assessed variables included cervical, thoracic range of motion (ROM) and neck disability index (NDI). Independent t-tests were used to compare each of these measurements and multiple linear regression was used to examine the capacity of neck or psychosocial variables to predict the variability of the NDI. The RCRSP group had significantly reduced cervical rotation [RCRSP (111.14 ± 22.98); AC (130.23 ± 21.20), d = 0.86, p < 0.01] and flexo-extension ROM [RCRSP (112.47 ± 2.07); AC (128.5 ± 17.85), d = 0.80, p < 0.01] as well as thoracic spine flexion [RCRSP (33.02 ± 1.14); AC (34.14 ± 1.01), d = 1.04, p < 0.01], extension [RCRSP (28.63 ± 0.89); AC (27.37 ± 0.89), d = -1.40, p < 0.01], right rotation [RCRSP (40.53 ± 10.39); AC (54.45 ± 9.75), d = 1.38, p < 0.01], left rotation [RCRSP (39.00 ± 11.26); AC (54.10 ± 10.51), d = 1.39, p < 0.01] and a significantly increased NDI score [RCRSP (17.56 ± 7.25); AC (2.47 ± 3.25), d = -2.69, p < 0.01]. The variables best explaining neck disability were central sensitization index and SF-12 total score (adjusted R2 = 0.75; p < 0.01). These results suggest that clinicians should assess cervical and thoracic spine mobility in patients with RCRSP.

Shoulder mobility and strength impairments in patients with rotator cuff related shoulder pain: a systematic review and meta analysis

Background

The methods previously proposed in the literature to assess patients with rotator cuff related shoulder pain, based on special orthopedic tests to precisely identify the structure causing the shoulder symptoms have been recently challenged. This opens the possibility of a different way of physical examination.

Objective

To analyze the differences in shoulder range of motion, strength and thoracic kyphosis between rotator cuff related shoulder pain patients and an asymptomatic group.

Method

The protocol of the present research was registered in the International Prospective Register of Systematic Review (PROSPERO) (registration number CRD42021258924). Database search of observational studies was conducted in MEDLINE, EMBASE, WOS and CINHAL until July 2023, which assessed shoulder or neck neuro-musculoskeletal non-invasive physical examination compared to an asymptomatic group. Two investigators assessed eligibility and study quality. The Newcastle Ottawa Scale was used to evaluate the methodology quality.

Results

Eight studies (N = 604) were selected for the quantitative analysis. Meta-analysis showed statistical differences with large effect for shoulder flexion (I2 = 91.7%, p < 0.01, HG = -1.30), external rotation (I2 = 83.2%, p < 0.01, HG = -1.16) and internal rotation range of motion (I2 = 0%, p < 0.01, HG = -1.32). Regarding to shoulder strength; only internal rotation strength showed statistical differences with small effect (I2 = 42.8%, p < 0.05, HG = -0.3).

Conclusions

There is moderate to strong evidence that patients with rotator cuff related shoulder pain present less shoulder flexion, internal and external rotation range of motion and less internal rotation strength than asymptomatic individuals.

Sex Differences in the Serum Proteomic Profile During Acute Low Back Pain-A Preliminary Study of the Relationship to Future Low Back Pain

The molecular processes driving the transition from acute to chronic low back pain (LBP) remain poorly understood and are likely to be sexually dimorphic. This study aimed to explore sex differences in the serum proteomic profile of people experiencing an acute LBP episode and determine if serum protein concentrations were associated with three-month outcome. Serum samples were collected through venepuncture from 30 female and 29 male participants experiencing an acute LBP episode. Serum samples underwent trypsin digestion and fractionation using hydrophobic interaction chromatography and were then analysed using mass-spectrometry. Mass-spectrometry spectra were searched in the Swissprot database for protein identification. Sex differences in protein abundance changes were evident upon inspection of fold changes. Multivariable data analysis identified 21 serum proteins during the acute episode that correctly classified 93% of males and 23 serum proteins that correctly classified 90% of females with ongoing LBP at 3 months. Pathway analysis suggested the differentially expressed proteins during acute LBP were frequently involved in immune, inflammatory, complement, or coagulation responses. This data provides preliminary evidence that biological processes during an acute LBP episode may contribute to the resolution, or persistence, of LBP symptoms at 3 months, however, these processes differ between males and females. PERSPECTIVE: Differential expression of serum proteins was observed between male and female participants during an acute LBP episode. This preliminary work provides a foundation for future research targeting distinct immune system processes in males and females that may interfere with the transition from acute to chronic LBP.

iTRAQ-based proteomics reveals potential markers and treatment pathways for acute Achilles tendon rupture

BACKGROUND

Due to its limited blood supply and irregular mechanical loading, the Achilles tendon is the most frequently ruptured tendon. Despite the rising incidence of acute Achilles tendon rupture (AATR), the optimal treatment remains controversial. Missed diagnoses and delayed treatments lead to poor outcomes and limited treatment options. This study aimed to identify potential biomarkers for diagnosing and developing therapies for AATR.

METHODS

We employed the coupled isobaric tag for relative and absolute quantitation-liquid chromatography-electrospray ionization-tandem mass spectrometry approach to investigate protein expression in tissues from AATR patients. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses were conducted to identify differentially expressed proteins (DEPs) between AATR patients and healthy individuals. A protein-protein interaction (PPI) network of DEPs was constructed using the Search Tool for the Retrieval of Interacting Genes. The screened hub genes were selectively verified by immunohistochemical staining.

RESULTS

We identified 410 DEPs between AATR patients and controls. The DEPs were significantly enriched in GO terms such as the extracellular region, extracellular region part, and defense response, as well as KEGG pathways, including complement and coagulation cascades, focal adhesion, and regulation of actin cytoskeleton. The main hub nodes in the PPI network comprised fibronectin 1 (FN1), major histocompatibility complex, class I, B (HLA-B), filamin A (FLNA), heat shock 27-kDa protein 1 (HSPB1), heat shock protein family A member 5 (HSPA5), apolipoprotein A4 (APOA4), and myosin IC (MYO1C). Although APOA4 and collagens I, II, and III were detectable in healthy tendons, immunohistochemical staining confirmed higher expression of these proteins in the acutely ruptured Achilles tendon.

CONCLUSIONS

Our findings lay a foundation for further molecular studies of AATR. Inflammation and age-related degeneration may contribute to the pathogenesis of AATR. Moreover, the identified DEPs could be potential biomarkers for AATR diagnosis and treatment.

Association Between COL5a1, COL11a1, and COL11a2 Gene Variations and Rotator Cuff Tendinopathy in Young Athletes

OBJECTIVE

Tendinopathy is a prevalent condition in young athletes and in older nonathletic people. Recent tendinopathy research has shown a growing interest in the role played by genetic factors, basically genes involved in collagen synthesis and regulation, in view of collagen disorganization typically present in tendon pathologies.

DESIGN

A case-control, genotype-phenotype association study.

SETTING

La Ribera Hospital, Valencia, Spain.

PARTICIPANTS

A group of 137 young athletes (49 with rotator cuff tendon pathology and 88 healthy counterparts) who played upper-limb-loading sports were clinically and ultrasound (US) assessed for rotator cuff tendinopathy were included.

INTERVENTION

Genetic analysis was performed to determine whether there was a relationship between rotator cuff pathology and the genotype.

MAIN OUTCOME MEASURES

We hypothesized that the following single nucleotide polymorphisms: COL5a1 rs12722, COL11a1 rs3753841, COL11a1 rs1676486, and COL11a2 rs1799907 would be associated with rotator cuff tendinopathy.

RESULTS

A direct relationship between CC genotype and bilateral US pathological images was statistically significant (χ 2 = 0.0051) and confirmed by the Fisher test, with a correlation coefficient of 0.345 and a Cramer's v of 0.26.

CONCLUSION

A significant association was found between COL5a1 rs12722 genotype and rotator cuff pathology, with the CC genotype conferring increased risk of tendon abnormalities and being associated with rotator cuff pathology.

Association between the rs820218 Variant within the SAP30BP Gene and Rotator Cuff Rupture in an Amazonian Population

BACKGROUND

Rotator cuff disease is one of the leading causes of musculoskeletal pain and disability, and its etiology is most likely multifactorial but remains incompletely understood. Therefore, the objective of this research was to investigate the relationship of the single-nucleotide rs820218 polymorphism of the SAP30-binding protein (SAP30BP) gene with rotator cuff tears in the Amazonian population.

METHODS

The case group consisted of patients who were operated on due to rotator cuff tears in a hospital in the Amazon region between 2010 and 2021, and the control group was composed of individuals who were selected after negative physical examinations for rotator cuff tears. Genomic DNA was obtained from saliva samples. For the genotyping and allelic discrimination of the selected single nucleotide polymorphism (rs820218) in the SAP30BP gene, real-time PCR was performed.

RESULTS

The frequency of the A allele in the control group was four times as high as that in the case group (AA homozygotes); an association of the genetic variant rs820218 of the SAP30BP gene with rotator cuff tears was not established (p = 0.28 and 0.20), as the A allelic frequency is ordinarily low in the general population.

CONCLUSIONS

The presence of the A allele indicates protection against rotator cuff tears.

Pharmacologic Enhancement of Rotator Cuff Repair: A Narrative Review

INTRODUCTION

As rotator cuff repairs (RCRs) are among the most common procedures in upper extremity orthopedics, healing augmentation using pharmacologic enhancement of the repaired rotator cuff muscle is of particular interest.

OBJECTIVE

The purpose of this study is to review the current understanding of Matrix Metalloproteinases (MMPs), Doxycycline, Testosterone, Estrogen, Growth hormone/ IGF-1, Vitamin D, and Vitamin C as a means to mitigate deleterious effects and propagate factors that support healing following RCR.

METHODS

A review of English language articles in PubMed and Medline was conducted in December of 2020. All articles describing the current understanding of the aforementioned therapies were reviewed. Studies were excluded if they were non-English or reported incomplete results.

RESULTS

Matrix metalloproteinases (MMP's) are fundamental to the healing process after rotator cuff tears through a delicate balance of various proteases that can be modulated by doxycycline through inhibition. While testosterone has shown to induce replication and differentiation of the tendon stem-cells, estrogen agonists have been shown to decrease inflammation and muscle atrophy. Though growth hormone being associated with elevated collagen synthesis and decreased anoxic damage when present, clinical studies have shown inconclusive and adverse effects on rotator cuff healing. Patients with Vitamin D deficiency have shown to have increased fatty infiltration in rotator cuff muscle while Vitamin C functions as an antioxidant that increases collagen and fibroblast proliferation.

CONCLUSION

As manipulation of pharmacologic factors shows potential for enhancing healing following RCRs, future studies are needed to establish a viable augmentation strategy to improve patient outcomes.

A Global Phosphorylation Atlas of Proteins Within Pathological Site of Rotator Cuff Tendinopathy

Rotator cuff tendinopathy (RCT) is the most common cause of shoulder pain, therefore posing an important clinical problem. Understanding the mechanism and biochemical changes of RCT would be of crucial importance and pave the path to targeting novel and effective therapeutic strategies in translational perspectives and clinical practices. Phosphorylation, as one of the most important and well-studied post-translational modifications, is tightly associated with protein activity and protein functional regulation. Here in this study, we generated a global protein phosphorylation atlas within the pathological site of human RCT patients. By using Tandem Mass Tag (TMT) labeling combined with mass spectrometry, an average of 7,741 phosphorylation sites (p-sites) and 3,026 proteins were identified. Compared with their normal counterparts, 1,668 p-sites in 706 proteins were identified as upregulated, while 73 p-sites in 57 proteins were downregulated. GO enrichment analyses have shown that majority of proteins with upregulated p-sites functioned in neutrophil-mediated immunity whereas downregulated p-sites are mainly involved in muscle development. Furthermore, pathway analysis identified NF-κB–related TNF signaling pathway and protein kinase C alpha type (PKCα)–related Wnt signaling pathway were associated with RCT pathology. At last, a weighted kinase-site phosphorylation network was built to identify potentially core kinase, from which serine/threonine-protein kinase 39 (STLK3) and mammalian STE20-like protein kinase 1 (MST1) were proposed to be positively correlated with the activation of Wnt pathway.

Molecular Big Data in Sports Sciences: State-of-Art and Future Prospects of OMICS-Based Sports Sciences

Together with environment and experience (that is to say, diet and training), the biological and genetic make-up of an athlete plays a major role in exercise physiology. Sports genomics has shown, indeed, that some DNA single nucleotide polymorphisms (SNPs) can be associated with athlete performance and level (such as elite/world-class athletic status), having an impact on physical activity behavior, endurance, strength, power, speed, flexibility, energetic expenditure, neuromuscular coordination, metabolic and cardio-respiratory fitness, among others, as well as with psychological traits. Athletic phenotype is complex and depends on the combination of different traits and characteristics: as such, it requires a “complex science,” like that of metadata and multi-OMICS profiles. Several projects and trials (like ELITE, GAMES, Gene SMART, GENESIS, and POWERGENE) are aimed at discovering genomics-based biomarkers with an adequate predictive power. Sports genomics could enable to optimize and maximize physical performance, as well as it could predict the risk of sports-related injuries. Exercise has a profound impact on proteome too. Proteomics can assess both from a qualitative and quantitative point of view the modifications induced by training. Recently, scholars have assessed the epigenetics changes in athletes. Summarizing, the different omics specialties seem to converge in a unique approach, termed sportomics or athlomics and defined as a “holistic and top-down,” “non-hypothesis-driven research on an individual’s metabolite changes during sports and exercise” (the Athlome Project Consortium and the Santorini Declaration) Not only sportomics includes metabonomics/metabolomics, but relying on the athlete’s biological passport or profile, it would enable the systematic study of sports-induced changes and effects at any level (genome, transcriptome, proteome, etc.). However, the wealth of data is so huge and massive and heterogenous that new computational algorithms and protocols are needed, more computational power is required as well as new strategies for properly and effectively combining and integrating data.

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.

A genome-wide association study for shoulder impingement and rotator cuff disease

BACKGROUND

The purpose of the study was to identify genetic variants associated with rotator cuff disease by performing a genome-wide association study (GWAS) for shoulder impingement using the UK Biobank (UKB) cohort and then combining the GWAS data with a prior GWAS for rotator cuff tears. The loci identified by the GWAS and meta-analysis were examined for changes in expression following rotator cuff tearing using RNA sequencing.

METHODS

A GWAS was performed using data from UKB with 3864 cases of shoulder impingement. The summary statistics from shoulder impingement and a prior study on rotator cuff tears were combined in a meta-analysis. Also, the previous association of 2 single-nucleotide polymorphisms (SNPs) with shoulder impingement from a published GWAS using the UKB was tested. Rotator cuff tendon biopsies were obtained from 24 patients with full-thickness rotator cuff tears who underwent arthroscopic rotator cuff repair (cases) and 9 patients who underwent open reduction internal fixation for a proximal humeral fracture (controls). Total RNA was extracted and differential gene expression was measured by RNA sequencing for genes with variants associated with rotator cuff tearing.

RESULTS

The shoulder impingement GWAS identified 4 new loci: LOC100506457, LSP1P3, LOC100506207, and MIS18BP1/LINC00871. Combining data with a prior GWAS for rotator cuff tears in a meta-analysis resulted in the identification of an additional 7 loci: SLC39A8/UBE2D3, C5orf63, ASTN2, STK24, FRMPD4, ACOT9/SAT1, and LINC00890/ALG13. Many of the identified loci have known biologic functions or prior associations with diseases, suggesting possible biologic pathways leading to rotator cuff disease. RNA sequencing experiments show that expression of STK24 increases whereas expression of SAT1 and UBE2D3 decreases following rotator cuff tearing. Two SNPs previously reported to show an association with shoulder impingement from a prior UKB GWAS were not validated in our study.

CONCLUSION

This is the first GWAS for shoulder impingement in which new data from UKB enabled the identification of 4 loci showing a genetic association. A meta-analysis with a prior GWAS for rotator cuff tearing identified an additional 7 loci. The known biologic roles of many of the 11 loci suggest plausible biologic mechanisms underlying the etiology of rotator cuff disease. The risk alleles from each of the genetic loci can be used to assess the risk for rotator cuff disease in individual patients, enabling preventative or restorative actions via personalized medicine.

The inflammatory response of the supraspinatus muscle in rotator cuff tear conditions

BACKGROUND

Rotator cuff (RC) disorders involve a spectrum of shoulder conditions from early tendinopathy to full-thickness tears leading to impaired shoulder function and pain. The pathology of RC disorder is, nonetheless, still largely unknown. Our hypothesis is that a supraspinatus (SS) tendon tear leads to sustained inflammatory changes of the SS muscle along with fatty infiltration and muscle degeneration, which are threshold markers for poor RC muscle function. The aim of this study was to determine the extent of this muscle inflammation in conjunction with lipid accumulation and fibrosis in RC tear conditions.

METHODS

We used proteomics, histology, electrochemiluminescence immunoassay, and quantitative polymerase chain reaction analyses to evaluate inflammatory and degenerative markers and fatty infiltration in biopsies from 22 patients undergoing surgery with repair of a full-thickness SS tendon tear.

RESULTS

Bioinformatic analysis showed that proteins involved in innate immunity, extracellular matrix organization, and lipid metabolism were among the most upregulated, whereas mitochondrial electronic transport chain along with muscle fiber function was among the most downregulated. Histologic analysis confirmed changes in muscle fiber organization and the presence of inflammation and fatty infiltration. Inflammation appeared to be driven by a high number of infiltrating macrophages, accompanied by elevated matrix metalloprotease levels and changes in transforming growth factor-β and cytokine levels in the SS compared with the deltoid muscle.

CONCLUSIONS

We demonstrated massive SS muscle inflammation after the tendon tear combined with fatty infiltration and degeneration. The regulation of tissue repair is thus extremely complex, and it may have opposite effects at different time points of healing. Inhibition or stimulation of muscle inflammation may be a potential target to enhance the outcome of the repaired torn RC.

Tendinopathy

Tendinopathy describes a complex multifaceted pathology of the tendon, characterized by pain, decline in function and reduced exercise tolerance. The most common overuse tendinopathies involve the rotator cuff tendon, medial and lateral elbow epicondyles, patellar tendon, gluteal tendons and the Achilles tendon. The prominent histological and molecular features of tendinopathy include disorganization of collagen fibres, an increase in the microvasculature and sensory nerve innervation, dysregulated extracellular matrix homeostasis, increased immune cells and inflammatory mediators, and enhanced cellular apoptosis. Although diagnosis is mostly achieved based on clinical symptoms, in some cases, additional pain-provoking tests and imaging might be necessary. Management consists of different exercise and loading programmes, therapeutic modalities and surgical interventions; however, their effectiveness remains ambiguous. Future research should focus on elucidating the key functional pathways implicated in clinical disease and on improved rehabilitation protocols.

Recent advances in tendinopathy

Tendinopathy refers to the clinical diagnosis of activity-related pain resulting in a decline in tendon function. In the last few years, much has been published concerning the basic science and clinical investigation of tendinopathy and debates and discussions to new questions and points of view started many years ago. This advances review will discuss the current thinking on the basic science and clinical management of tendinopathy and in particular new findings in the tendon repair space that are relevant to the pathophysiology of tendinopathy. We will further discuss potential novel therapies on the horizon in human tendon disease.

Genetic Aspects in Shoulder Disorders

The influence of genetic inheritance has been increasingly investigated in shoulder disorders, such as rotator cuff injury, instability and frozen shoulder. Although the initial findings are enlightening, it is necessary to progressively build a database of genetic markers to catalog genomic profiles that, later, may contribute for predicting the risk of the disease, as well as to the development of better diagnostic and treatment tools. The present article seeks to update what is evidence of genetic studies in the literature for these diseases, from polymorphism analyses, expression of candidate genes in tissues and broad genomic association studies (GWAS). However, it is necessary to point out that there is great difficulty in replicating and using the findings, mainly due to the lack of statistical power, the high rate of false-positive results and the large number of variables involved.

In Vitro Innovation of Tendon Tissue Engineering Strategies

Tendinopathy is the term used to refer to tendon disorders. Spontaneous adult tendon healing results in scar tissue formation and fibrosis with suboptimal biomechanical properties, often resulting in poor and painful mobility. The biomechanical properties of the tissue are negatively affected. Adult tendons have a limited natural healing capacity, and often respond poorly to current treatments that frequently are focused on exercise, drug delivery, and surgical procedures. Therefore, it is of great importance to identify key molecular and cellular processes involved in the progression of tendinopathies to develop effective therapeutic strategies and drive the tissue toward regeneration. To treat tendon diseases and support tendon regeneration, cell-based therapy as well as tissue engineering approaches are considered options, though none can yet be considered conclusive in their reproduction of a safe and successful long-term solution for full microarchitecture and biomechanical tissue recovery. In vitro differentiation techniques are not yet fully validated. This review aims to compare different available tendon in vitro differentiation strategies to clarify the state of art regarding the differentiation process.

Augmenting endogenous repair of soft tissues with nanofibre scaffolds

As our ability to engineer nanoscale materials has developed we can now influence endogenous cellular processes with increasing precision. Consequently, the use of biomaterials to induce and guide the repair and regeneration of tissues is a rapidly developing area. This review focuses on soft tissue engineering, it will discuss the types of biomaterial scaffolds available before exploring physical, chemical and biological modifications to synthetic scaffolds. We will consider how these properties, in combination, can provide a precise design process, with the potential to meet the requirements of the injured and diseased soft tissue niche. Finally, we frame our discussions within clinical trial design and the regulatory framework, the consideration of which is fundamental to the successful translation of new biomaterials.

Efficacy of Combining PRP and MMP Inhibitors in Treating Moderately Damaged Tendons Ex Vivo

Platelet-rich plasma (PRP) and broad-spectrum matrix metalloproteinase inhibitors (MMPIs) have been used as therapeutic options for tendinopathy. However, mixed results have been reported regarding their efficacy. We posited that the combination of these two treatment strategies would be more beneficial for healing tendons than each treatment alone. Rat tail tendons were harvested and cultured without mechanical stress for 0, 4, or 10 days. Single and combination treatment with PRP and MMPIs with either broad- or narrow-spectrum (MMP-13 selective), was administered to 4-day stress-deprived (SD) tendons, an ex vivo model for moderate tendinopathy. This treatment was applied to the damaged tendons over 6 days. At the end of their culture time, the tendons were subjected to traction testing and pathohistology, immunohistochemistry, and viability assays. The results showed better histological features for the PRP + narrow-spectrum MMPI group compared with all individual treatment modalities. Moreover, higher fiber density, more elongated nucleus shape, smaller space between fibers, and a trend toward higher mechanical strength were noted for PRP + narrow-spectrum MMPI group compared with 10-day SD tendons. This study shows that the combination of PRP + narrow-spectrum MMPI is a potentially effective treatment approach for tendinopathy. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 37:1838-1847, 2019.

Molecular profile of ultrastructure changes of the ligamentum flavum related to lumbar spinal canal stenosis

Lumbar spinal canal stenosis (LSCS) is a degenerative disease observed by hypertrophy of the ligamentum flavum (LF) that cause compression of the lumbar neural content. Diabetes mellitus (DM) is a risk factor for the disease and we have shown previously that DM increases the fibrosis and elastic fiber loss in patients with LSCS. The purpose of this study was to find the proteins that play a role in the development of this clinical pathogenesis and the effect of DM on protein expression. LF tissue retrieved from patients diagnosed with LSCS, some were also diagnosed with DM, were compared with LF from patients diagnosed with herniated nucleus pulposus (HNP). The tissues were analyzed by mass spectrometry for proteins profile alteration. We found that LF of LSCS/DM patients exhibited significantly higher levels of proteoglycan proteins and latent transforming growth factor β-binding protein (LTBP2 and LTBP4). Additionally, an increase of HTRA serine protease 1 and insulin-like growth factor binding protein-5 were noted. The higher fibrosis was also associated with proteins related to inflammation and slower tissue repair. Collagen 6 and transforming growth factor inhibitor are related to activation of the anti-inflammatory M2 pathway that is associated with tissue repair. The decrease of these proteins expression in LSCS/DM is associated with increased levels and activation of M1 pro-inflammatory pathways. Interestingly, C3 and C4b members of the complement complex and mannose receptor-like protein (CLEC18) paralogous proteins were detectable solely at the LSCS/DM patients' samples. Histology analysis shows that inflammatory was induced by the hyperglycemic conditions in diabetic patients involve in altering the matrix compositions. Thus, the protein profiles associated with inflammatory pathways affecting the LF suggested increasing susceptibility of developing the degeneration under hyperglycemic conditions.

Doxycycline improves cage activity, but not exercised, supraspinatus tendon and muscle in a rat model

The objective of this study was to investigate the effects of doxycycline, a broad-spectrum MMP inhibitor, on cage activity and exercised supraspinatus tendon and muscle using a Sprague-Dawley rat model of non-injurious exercise. Because exercise may alter muscle and tendon MMP activity and matrix turnover, we hypothesized that doxycycline would abolish the beneficial adaptations found with exercise but have no effect on cage activity muscle and tendon properties. Rats were divided into acute or chronic exercise (EX) or cage activity (CA) groups, and half of the rats received doxycycline orally. Animals in acute EX groups were euthanized 24 h after a single bout of exercise (10 m/min, 1 h) on a flat treadmill. Animals in chronic EX groups walked on a flat treadmill and were euthanized at 2 or 8 week time points. Assays included supraspinatus tendon mechanics and histology and muscle fiber morphologic and type analysis. Doxycycline improved tendon mechanical properties and collagen organization in chronic cage activity groups, which was not consistently evident in exercised groups. Combined with exercise, doxycycline decreased average muscle fiber cross-sectional area. Results of this study suggest that administration of doxycycline at pharmaceutical doses induces beneficial supraspinatus tendon adaptations without negatively affecting the muscle in cage activity animals, supporting the use of doxycycline to combat degenerative processes associated with underuse; however, when combined with exercise, doxycycline does not consistently produce the same beneficial adaptations in rat supraspinatus tendons and reduces muscle fiber cross-sectional area, suggesting that doxycycline is not advantageous when combined with activity.

A Systematic Summary of Systematic Reviews on the Topic of the Rotator Cuff

BACKGROUND

The number of systematic reviews and meta-analyses published on the rotator cuff (RC) has increased markedly.

PURPOSE

To quantify the number of systematic reviews and meta-analyses published on the RC and to provide a qualitative summary of the literature.

STUDY DESIGN

Systematic review; Level of evidence, 4.

METHODS

A systematic search for all systematic reviews and meta-analyses pertaining to the RC published between January 2007 and September 2017 was performed with PubMed, MEDLINE, and the Cochrane Database of Systematic Reviews. Narrative reviews and non-English language articles were excluded.

RESULTS

A total of 1078 articles were found, of which 196 met the inclusion criteria. Included articles were summarized and divided into 15 topics: anatomy and function, histology and genetics, diagnosis, epidemiology, athletes, nonoperative versus operative treatment, surgical repair methods, concomitant conditions and surgical procedures, RC tears after total shoulder arthroplasty, biological augmentation, postoperative rehabilitation, outcomes and complications, patient-reported outcome measures, cost-effectiveness of RC repair, and quality of randomized controlled trials.

CONCLUSION

A qualitative summary of the systematic reviews and meta-analyses published on the RC can provide surgeons with a single source of the most current literature.

Effects of Redox Modulation on Cell Proliferation, Viability, and Migration in Cultured Rat and Human Tendon Progenitor Cells

Tendon healing is slow and usually results in inferior fibrotic tissue formation. Recently, application of tendon derived stem cells (TDSCs) improved tendon healing in animal studies. In a chicken model, local injection of antioxidants reduced tendon adhesion after tendon injury. An in vitro study demonstrated that supplementation of H₂O₂ reduced tenogenic marker expression in TDSCs. These findings suggested that the possibility of TDSCs is involved in tendon healing and the cellular activities of TDSCs might be affected by oxidative stress of the local environment. After tendon injury, oxidative stress is increased. Redox modulation might affect healing outcomes via affecting cellular activities in TDSCs. To study the effect of oxidative stress on TDSCs, the cellular activities of rat/human TDSCs were measured under different dosages of vitamin C or H₂O₂ in this study. Lower dose of vitamin C increased cell proliferation, viability and migration; H₂O₂ affected colony formation and suppressed cell migration, cell viability, apoptosis, and proliferation. Consistent with previous studies, oxidative stresses (H₂O₂) affect both recruitment and survival of TDSCs, while the antioxidant vitamin C may exert beneficial effects at low doses. In conclusion, redox modulation affected cellular activities of TDSCs and might be a potential strategy for tendon healing treatment.

A quantitative label-free analysis of the extracellular proteome of human supraspinatus tendon reveals damage to the pericellular and elastic fibre niches in torn and aged tissue

Tears of the human supraspinatus tendon are common and often cause painful and debilitating loss of function. Progressive failure of the tendon leading to structural abnormality and tearing is accompanied by numerous cellular and extra-cellular matrix (ECM) changes in the tendon tissue. This proteomics study aimed to compare torn and aged rotator cuff tissue to young and healthy tissue, and provide the first ECM inventory of human supraspinatus tendon generated using label-free quantitative LC-MS/MS. Employing two digestion protocols (trypsin and elastase), we analysed grain-sized tendon supraspinatus biopsies from older patients with torn tendons and from healthy, young controls. Our findings confirm measurable degradation of collagen fibrils and associated proteins in old and torn tendons, suggesting a significant loss of tissue organisation. A particularly marked reduction of cartilage oligomeric matrix protein (COMP) raises the possibility of using changes in levels of this glycoprotein as a marker of abnormal tissue, as previously suggested in horse models. Surprisingly, and despite using an elastase digestion for validation, elastin was not detected, suggesting that it is not highly abundant in human supraspinatus tendon as previously thought. Finally, we identified marked changes to the elastic fibre, fibrillin-rich niche and the pericellular matrix. Further investigation of these regions may yield other potential biomarkers and help to explain detrimental cellular processes associated with tendon ageing and tendinopathy.

Molecular signatures of age-associated chronic degeneration of shoulder muscles

Chronic muscle diseases are highly prevalent in the elderly causing severe mobility limitations, pain and frailty. The intrinsic molecular mechanisms are poorly understood due to multifactorial causes, slow progression with age and variations between individuals. Understanding the underlying molecular mechanisms could lead to new treatment options which are currently limited. Shoulder complaints are highly common in the elderly, and therefore, muscles of the shoulder's rotator cuff could be considered as a model for chronic age-associated muscle degeneration. Diseased shoulder muscles were characterized by muscle atrophy and fatty infiltration compared with unaffected shoulder muscles. We confirmed fatty infiltration using histochemical analysis. Additionally, fibrosis and loss of contractile myosin expression were found in diseased muscles. Most cellular features, including proliferation rate, apoptosis and cell senescence, remained unchanged and genome-wide molecular signatures were predominantly similar between diseased and intact muscles. However, we found down-regulation of a small subset of muscle function genes, and up-regulation of extracellular region genes. Myogenesis was defected in muscle cell culture from diseased muscles but was restored by elevating MyoD levels. We suggest that impaired muscle functionality in a specific environment of thickened extra-cellular matrix is crucial for the development of chronic age-associated muscle degeneration.

Chondroitin sulphate glycosaminoglycans contribute to widespread inferior biomechanics in tendon after focal injury

Both mechanical and structural properties of tendon change after injury however the causal relationship between these properties is presently unclear. This study aimed to determine the extent of biomechanical change in post-injury tendon pathology and whether the sulphated glycosaminoglycans (glycosaminoglycans) present are a causal factor in these changes. Equine superficial digital flexor tendons (SDF tendons) were surgically-injured in vivo (n=6 injured, n=6 control). Six weeks later they were harvested and regionally dissected into twelve regions around the lesion (equal medial/lateral, proximal/distal). Glycosaminoglycans were removed by enzymatic (chondroitinase) treatment. Elastic modulus (modulus) and ultimate tensile strength (UTS) were measured under uniaxial tension to failure, and tendon glycosaminoglycan content was measured by spectrophotometry. Compared to healthy tendons, pathology induced by the injury decreased modulus (-38%; 95%CI -49% to -28%; P<0.001) and UTS (-38%; 95%CI -48% to -28%; P<0.001) and increased glycosaminoglycan content (+52%; 95%CI 39% - 64%; P<0.001) throughout the tendon. Chondroitinase-mediated glycosaminoglycan removal (50%; 95%CI 21-79%; P<0.001) in surgically-injured pathological tendons caused a significant increase in modulus (5.6MPa/µg removed; 95%CI 0.31-11; P=0.038) and UTS (1.0MPa per µg removed; 95%CI 0.043-2; P=0.041). These results demonstrate that the chondroitin/dermatan sulphate glycosaminoglycans that accumulate in pathological tendon post-injury are partly responsible for the altered biomechanical properties.