Gene expression profiles of changes underlying different-sized human rotator cuff tendon tears

The major pain source of rotator cuff-related shoulder pain: A narrative review on current evidence

BACKGROUND

Rotator cuff-related shoulder pain (RCRSP) was proposed to have a complex pain mechanism, but the exact aetiology is still unclear. A recent review summarised the updated research to analyse the traditional concept of shoulder impingement which may not be accurate. Current studies have demonstrated that mechanical factors including a reduction in subacromial space, scapular dyskinesia and different acromial shapes are unlikely directly contributing to RCRSP.

AIMS

Since the precise RCRSP pain mechanism remains unclear, the aim of this narrative review is to discuss possible sources of pain contributing to RCRSP according to the mechanisms-based pain classifications.

RESULTS AND DISCUSSION

Research findings on potential mechanical nociceptive factors of RCRSP are conflicting; investigations of neuropathic and central pain mechanisms of RCRSP are limited and inconclusive. Overall, available evidence has indicated moderate to strong correlations between RCRSP and chemical nociceptive sources of pain.

CONCLUSION

Results from current research may provide new directions for future studies on the aetiology of RCRSP and its clinical management towards a biochemical view instead of the traditional mechanical hypothesis.

Transcriptional time course after rotator cuff repair in 6 month old female rabbits

Introduction: Rotator cuff tears are prevalent in the population above the age of 60. The disease progression leads to muscle atrophy, fibrosis, and fatty infiltration, which is not improved upon with surgical repair, highlighting the need to better understand the underlying biology impairing more favorable outcomes. Methods: In this study, we collected supraspinatus muscle tissue from 6 month old female rabbits who had undergone unilateral tenotomy for 8 weeks at 1, 2, 4, or 8 weeks post-repair (n = 4/group). RNA sequencing and enrichment analyses were performed to identify a transcriptional timeline of rotator cuff muscle adaptations and related morphological sequelae. Results: There were differentially expressed (DE) genes at 1 (819 up/210 down), 2 (776/120), and 4 (63/27) weeks post-repair, with none at 8 week post-repair. Of the time points with DE genes, there were 1092 unique DE genes and 442 shared genes, highlighting that there are changing processes in the muscle at each time point. Broadly, 1-week post-repair differentially expressed genes were significantly enriched in pathways of metabolism and energetic activity, binding, and regulation. Many were also significantly enriched at 2 weeks, with the addition of NIF/NF-kappaB signaling, transcription in response to hypoxia, and mRNA stability alongside many additional pathways. There was also a shift in transcriptional activity at 4 weeks post-repair with significantly enriched pathways for lipids, hormones, apoptosis, and cytokine activity, despite an overall decrease in the number of differentially expressed genes. At 8 weeks post-repair there were no DE genes when compared to control. These transcriptional profiles were correlated with the histological findings of increased fat, degeneration, and fibrosis. Specifically, correlated gene sets were enriched for fatty acid metabolism, TGF-B-related, and other pathways. Discussion: This study identifies the timeline of transcriptional changes in muscle after RC repair, which by itself, does not induce a growth/regenerative response as desired. Instead, it is predominately related to metabolism/energetics changes at 1 week post-repair, unclear or asynchronous transcriptional diversity at 2 weeks post-repair, increased adipogenesis at 4 weeks post-repair, and a low transcriptional steady state or a dysregulated stress response at 8 weeks post-repair.

Characterization of Histone Modifications in Late-Stage Rotator Cuff Tendinopathy

The development and progression of rotator cuff tendinopathy (RCT) is multifactorial and likely to manifest through a combination of extrinsic, intrinsic, and environmental factors, including genetics and epigenetics. However, the role of epigenetics in RCT, including the role of histone modification, is not well established. Using chromatin immunoprecipitation sequencing, differences in the trimethylation status of H3K4 and H3K27 histones in late-stage RCT compared to control were investigated in this study. For H3K4, 24 genomic loci were found to be significantly more trimethylated in RCT compared to control (p < 0.05), implicating genes such as DKK2, JAG2, and SMOC2 in RCT. For H3K27, 31 loci were shown to be more trimethylated (p < 0.05) in RCT compared to control, inferring a role for EPHA3, ROCK1, and DEFβ115. Furthermore, 14 loci were significantly less trimethylated (p < 0.05) in control compared to RCT, implicating EFNA5, GDF6, and GDF7. Finally, the TGFβ signaling, axon guidance, and regulation of focal adhesion assembly pathways were found to be enriched in RCT. These findings suggest that the development and progression of RCT is, at least in part, under epigenetic control, highlighting the influence of histone modifications in this disorder and paving the way to further understand the role of epigenome in RCT.

Pathological alterations in the expression status of rotator cuff tendon matrix components in hyperlipidemia

Hyperlipidemia is an important risk factor in the development and progression of tendon pathology, however its role in aggravating rotator cuff tendon injury (RCTI) is largely unknown. We aimed to assess the expression status of key extracellular matrix (ECM) components in the tendon tissues and tenocytes under hyperlipidemia. Shoulder rotator cuff (RC) tendon tissues harvested from the swine model of hyperlipidemia displayed alterations in histomorphometry and the expression status of major ECM component proteins including COL-I, COL-III, COL-IV, COL-V, COL-VI, MMP2, and MMP9. Similarly, the LDL- and oxLDL-challenged tenocytes displayed altered expression of the same proteins at both transcriptional and translational levels. In addition, the lipid uptake and cellular reactive oxygen radicals predominated in the lipid-challenged tenocytes compared to the control. Overall, the LDL-treated cells displayed predominant pathological alterations compared to the ox-LDL-treated cells. Further understanding regarding the underlying molecular mechanisms driving the tendon matrisome alteration and subsequent aggravated RCTI pathology in hyperlipidemia could open novel translational avenues in the management of RCTI.

RNA-Seq analysis reveals sex-dependent transcriptomic profiles of human subacromial bursa stratified by tear etiology

Rotator cuff tendinopathy, a major cause of shoulder disability, occurs due to trauma or degeneration. Our molecular understanding of traumatic and degenerative tears remains elusive. Here, we probed transcript level differences between traumatic and degenerative tears. Subacromial bursa tissues were collected from patients with traumatic or degenerative tears during arthroscopy (N = 32). Transcripts differentially expressed by tear etiology were detected by RNA-seq. RNA-seq results were validated by real-time quantitative polymerase chain reaction. We identified 334 protein-coding transcripts differentially expressed between traumatic and degenerative tears in females and 167 in males at a fold-change greater than 2. In females, XIRP2, MYL1, MYBPC1, TNNT1, and LMOD2, were highly expressed in traumatic tears whereas TPSD1, CDSN, RCVRN, LTBP4, and PTGS1 were elevated in degen tears. Transcripts elevated in traumatic tears represented muscle cell differentiation and development, and muscle contraction whereas those elevated in degenerative tears represented cell activation and immune response. In males, AZGP1, CNTFR, COL9A1, ZNF98, and EREG were highly elevated in traumatic tears whereas MYL2, HOXD11, SLC6A7, CADM1, and MMP17 were highly expressed in degenerative tears. Transcripts elevated in traumatic tears represented metabolic/catabolic processes, and transmembrane protein transport while processes related to cell cycle were mainly enriched in degenerative tears. Numerous long noncoding RNAs were differentially expressed between traumatic and degenerative tears in both sexes. In summary, this study provides insights into molecular biology of bursa in patients with rotator cuff tendon disease based on tear acuity and novel sex-based transcript differences that could inform clinical decision making in treating patients with traumatic or degenerative shoulder injuries.

The Usefulness of Serological Inflammatory Markers in Patients with Rotator Cuff Disease—A Systematic Review

Background and Objectives: Rotator cuff disease (RCD) is a prominent musculoskeletal pain condition that spans a variety of pathologies. The etiology and precise diagnostic criteria of this condition remain unclear. The current practice of investigating the biochemical status of RCD is by conducting biopsy studies but their invasiveness is a major limitation. Recent biochemical studies on RCD demonstrate the potential application of serological tests for evaluating the disease which may benefit future clinical applications and research. This systematic review is to summarize the results of available studies on serological biochemical investigations in patients with RCD. Methods: An electronic search on databases PubMed and Virtual Health Library was conducted from inception to 1 September 2021. The inclusion criteria were case-control, cross-sectional, and cohort studies with serological biochemical investigations on humans with RCD. Methodological quality was assessed using the Study Quality Assessment Tool for Observational Cohort and Cross-sectional studies from the National Heart, Lung, and Blood Institute. Results: A total of 6008 records were found in the databases; of these, 163 full-text studies were checked for inclusion and exclusion criteria. Nine eligible studies involving 984 subjects with RCD emerged from this systematic review. The quality of the studies found ranged from poor to moderate. In summarizing all the studies, several fatty acids, nonprotein nitrogen, interleukin-1 β, interleukin-8, and vascular endothelial growth factor were found to be significantly higher in blood samples of patients with RCD than with control group patients, while Omega-3 Intex, vitamin B12, vitamin D, phosphorus, interleukin-10, and angiogenin were observed to be significantly lower. Conclusions: This is the first systematic review to summarize current serological studies in patients with RCD. Results of the studies reflect several systemic physiological changes in patients with RCD, which may prove helpful to better understand the complex pathology of RCD. In addition, the results also indicate the possibility of using serological tests in order to evaluate RCD; however, further longitudinal studies are required.

Tendon healing is adversely affected by low-grade inflammation

BACKGROUND

Tendinopathy is common, presents with pain and activity limitation, and is associated with a high risk of recurrence of the injury. Tendinopathy usually occurs as a results of a disrupted healing response to a primary injury where cellular and molecular pathways lead to low grade chronic inflammation.

MAIN FINDINGS

There has been a renewed interest in investigating the role of Inflammation in the pathogenesis of tendinopathy, in particular during the initial phases of the condition where it may not be clinically evident. Understanding the early and late stages of tendon injury pathogenesis would help develop new and effective treatments addressed at targeting the inflammatory pathways.

CONCLUSION

This review outlines the role of low-grade Inflammation in the pathogenesis of tendinopathy, stressing the role of proinflammatory cytokines, proteolytic enzymes and growth factors, and explores how Inflammation exerts a negative influence on the process of tendon healing.

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 and multiomics: advantages, advances, and opportunities

Tendons heal by fibrosis, which hinders function and increases re-injury risk. Yet the biology that leads to degeneration and regeneration of tendons is not completely understood. Improved understanding of the metabolic nuances that cause diverse outcomes in tendinopathies is required to solve these problems. 'Omics methods are increasingly used to characterize phenotypes in tissues. Multiomics integrates 'omic datasets to identify coherent relationships and provide insight into differences in molecular and metabolic pathways between anatomic locations, and disease stages. This work reviews the current literature pertaining to multiomics in tendon and the potential of these platforms to improve tendon regeneration. We assessed the literature and identified areas where 'omics platforms contribute to the field: (1) Tendon biology where their hierarchical complexity and demographic factors are studied. (2) Tendon degeneration and healing, where comparisons across tendon pathologies are analyzed. (3) The in vitro engineered tendon phenotype, where we compare the engineered phenotype to relevant native tissues. (4) Finally, we review regenerative and therapeutic approaches. We identified gaps in current knowledge and opportunities for future study: (1) The need to increase the diversity of human subjects and cell sources. (2) Opportunities to improve understanding of tendon heterogeneity. (3) The need to use these improvements to inform new engineered and regenerative therapeutic approaches. (4) The need to increase understanding of the development of tendon pathology. Together, the expanding use of various 'omics platforms and data analysis resulting from these platforms could substantially contribute to major advances in the tendon tissue engineering and regenerative medicine field.

Transcriptional Time Course After Rotator Cuff Tear

Rotator cuff (RC) tears are prevalent in the population above the age of 60. The disease progression leads to muscle atrophy, fibrosis, and fatty infiltration in the chronic state, which is not improved with intervention or surgical repair. This highlights the need to better understand the underlying dysfunction in muscle after RC tendon tear. Contemporary studies aimed at understanding muscle pathobiology after RC tear have considered transcriptional data in mice, rats and sheep models at 2–3 time points (1 to 16 weeks post injury). However, none of these studies observed a transition or resurgence of gene expression after the initial acute time points. In this study, we collected rabbit supraspinatus muscle tissue with high temporal resolution (1, 2, 4, 8, and 16 weeks) post-tenotomy (n = 6/group), to determine if unique, time-dependent transcriptional changes occur. RNA sequencing and analyses were performed to identify a transcriptional timeline of RC muscle changes and related morphological sequelae. At 1-week post-tenotomy, the greatest number of differentially expressed genes was observed (1,069 up/873 down) which decreases through 2 (170/133), 4 (86/41), and 8 weeks (16/18), followed by a resurgence and transition of expression at 16 weeks (1,421/293), a behavior which previously has not been captured or reported. Broadly, 1-week post-tenotomy is an acute time point with expected immune system responses, catabolism, and changes in energy metabolism, which continues into 2 weeks with less intensity and greater contribution from mitochondrial effects. Expression shifts at 4 weeks post-tenotomy to fatty acid oxidation, lipolysis, and general upregulation of adipogenesis related genes. The effects of previous weeks’ transcriptional dysfunction present themselves at 8 weeks post-tenotomy with enriched DNA damage binding, aggresome activity, extracellular matrix-receptor changes, and significant expression of genes known to induce apoptosis. At 16 weeks post-tenotomy, there is a range of enriched pathways including extracellular matrix constituent binding, mitophagy, neuronal activity, immune response, and more, highlighting the chaotic nature of this time point and possibility of a chronic classification. Transcriptional activity correlated significantly with histological changes and were enriched for biologically relevant pathways such as lipid metabolism. These data provide platform for understanding the biological mechanisms of chronic muscle degeneration after RC tears.

Distinct Gene Expression Profile in Patients With Poor Postoperative Outcomes After Rotator Cuff Repair: A Case-Control Study

BACKGROUND

Impaired healing after rotator cuff repair is a major concern, with retear rates as high as 94%. A method to predict whether patients are likely to experience poor surgical outcomes would change clinical practice. While various patient factors, such as age and tear size, have been linked to poor functional outcomes, it is currently very challenging to predict outcomes before surgery.

PURPOSE

To evaluate gene expression differences in tissue collected during surgery between patients who ultimately went on to have good outcomes and those who experienced a retear, in an effort to determine if surgical outcomes can be predicted.

STUDY DESIGN

Case-control study; Level of evidence, 3.

METHODS

Rotator cuff tissue was collected at the time of surgery from 140 patients. Patients were tracked for a minimum of 6 months to identify those with good or poor outcomes, using clinical functional scores and follow-up magnetic resonance imaging to confirm failure to heal or retear. Gene expression differences between 8 patients with poor outcomes and 28 patients with good outcomes were assessed using a multiplex gene expression analysis via NanoString and a custom-curated panel of 145 genes related to various stages of rotator cuff healing.

RESULTS

Although significant differences in the expression of individual genes were not observed, gene set enrichment analysis highlighted major differences in gene sets. Patients who had poor healing outcomes showed greater expression of gene sets related to extracellular matrix production (P < .0001) and cellular biosynthetic pathways (P < .001), while patients who had good healing outcomes showed greater expression of genes associated with the proinflammatory (M1) macrophage phenotype (P < .05).

CONCLUSION

These results suggest that a more proinflammatory, fibrotic environment before repair may play a role in poor healing outcome. With validation in a larger cohort, these results may ultimately lead to diagnostic methods to preoperatively predict those at risk for poor surgical outcomes.

Regulatory VCAN polymorphism is associated with shoulder pain and disability in breast cancer survivors

Background and purpose

Shoulder morbidity following breast cancer treatment is multifactorial. Despite several treatment- and patient-related factors being implicated, unexplained inter-individual variability exists in the development of such morbidity. Given the paucity of relavant genetic studies, we investigate the role of polymorphisms in candidate proteoglycan genes.

Patients and methods

We conducted a cross-sectional study on 254 South African breast cancer survivors, to evaluate associations between shoulder pain/disability and ten single nucleotide polymorphisms (SNPs) within four proteoglycan genes: ACAN (rs1126823 G>A, rs1516797 G>T, rs2882676 A>C); BGN (rs1042103 G>A, rs743641 A>T, rs743642 G>T); DCN rs516115 C>T; and VCAN (rs11726 A>G, rs2287926 G>A, rs309559). Participants were grouped into no–low and moderate–high shoulder pain/disability based on total pain/disability scores: < 30 and ≥ 30, respectively using the Shoulder Pain and Disability Index (SPADI).

Results

The GG genotype of VCAN rs11726 was independently associated with an increased risk of being in the moderate-to-high shoulder pain (P = 0.005, OR = 2.326, 95% CI = 1.259–4.348) or disability (P = 0.011, OR = 2.439, 95% CI = 1.235–4.762) categories, after adjusting for participants’ age. In addition, the T-T-G inferred allele combination of BGN (rs74364–rs743642)–VCAN rs11726 was associated with an increased risk of being in the moderate-to-high shoulder disability category (0 = 0.002, OR = 2.347, 95% CI = 1.215–4.534).

Conclusion

Our study is first to report that VCAN rs11726, independently or interacting with BGN polymorphisms, is associated with shoulder pain or disability in breast cancer survivors. Whereas our findings suggest an involvement of proteoglycans in the etiology of shoulder pain/disability, further studies are recommended.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40246-021-00337-0.

Transcriptome profiling of digital flexor tendons after injury in a chicken model

BACKGROUND

Modulation of tendon healing remains a challenge because of our limited understanding of the tendon repair process. Therefore, we performed the present study to provide a global perspective of the gene expression profiles of tendons after injury and identify the molecular signals driving the tendon repair process.

RESULTS

The gene expression profiles of flexor digitorum profundus tendons in a chicken model were assayed on day 3, weeks 1, 2, 4, and 6 after injury using the Affymetrix microarray system. Principal component analysis (PCA) and hierarchical cluster analysis of the differentially expressed genes showed three distinct clusters corresponding to different phases of the tendon healing period. Gene ontology (GO) analysis identified regulation of cell proliferation and cell adhesion as the most enriched biological processes. Kyoto encyclopedia of genes and genomes (KEGG) pathway analysis revealed that the cytokine-cytokine receptor interaction and extracellular matrix (ECM)-receptor interaction pathways were the most impacted. Weighted gene co-expression network analysis (WGCNA) demonstrated four distinct patterns of gene expressions during tendon healing. Cell adhesion and ECM activities were mainly associated with genes with drastic increase in expression 6 weeks after injury. The protein-protein interaction (PPI) networks were constructed to identify the key signaling pathways and hub genes involved.

CONCLUSIONS

The comprehensive analysis of the biological functions and interactions of the genes differentially expressed during tendon healing provides a valuable resource to understand the molecular mechanisms underlying tendon healing and to predict regulatory targets for the genetic engineering of tendon repair. Tendon healing, Adhesion, Gene Ontology, Kyoto Encyclopedia of Genes and Genomes, Weighted Gene Co-expression Network Analysis, Protein-protein Interaction.

Electrospun Scaffold Micro-Architecture Induces an Activated Transcriptional Phenotype within Tendon Fibroblasts

Biomaterial augmentation of surgically repaired rotator cuff tendon tears aims to improve the high failure rates (∼40%) of traditional repairs. Biomaterials that can alter cellular phenotypes through the provision of microscale topographical cues are now under development. We aimed to systematically evaluate the effect of topographic architecture on the cellular phenotype of fibroblasts from healthy and diseased tendons. Electrospun polydioxanone scaffolds with fiber diameters ranging from 300 to 4000 nm, in either a highly aligned or random configuration, were produced. Healthy tendon fibroblasts cultured for 7 days on scaffolds with highly aligned fibers demonstrated a distinctive elongated morphology, whilst those cultured on randomly configured fibers demonstrated a flattened and spread morphology. The effect of scaffold micro-architecture on the transcriptome of both healthy and diseased tendon fibroblasts was assessed with bulk RNA-seq. Both healthy (n = 3) and diseased tendon cells (n = 3) demonstrated a similar transcriptional response to architectural variants. Gene set enrichment analysis revealed that large diameter (≥2000 nm) aligned scaffolds induced an upregulation of genes involved in cellular replication and a downregulation of genes defining inflammatory responses and cell adhesion. Similarly, PDPN and CD248, markers of inflammatory or "activated" fibroblasts, were downregulated during culture of both healthy and diseased fibroblasts on aligned scaffolds with large (≥2000 nm) fiber diameters. In conclusion scaffold architectures resembling that of disordered type III collagen, typically present during the earlier phases of wound healing, resulted in tendon fibroblast activation. Conversely, scaffolds mimicking aligned diameter collagen I fibrils, present during tissue remodelling, did not activate tendon derived fibroblasts. This has implications for the design of scaffolds used during rotator cuff repair augmentation.

Polymorphisms and alterations in gene expression associated with rotator cuff tear and healing following surgical repair: a systematic review

BACKGROUND

Rotator cuff tears (RCTs) are a common cause of shoulder disability, yet both conservative and surgical treatment strategies can lead to poor results in some patient populations. Enhanced understanding of the genetic processes associated with RCTs can assist in the development of more effective management options and help predict individual responses to surgical treatment. This systematic review analyzes the current literature on the genetic footprint associated with RCTs and interprets these findings to enhance the current understanding of RCT pathogenesis, potential treatment regimens, and prognostic biomarkers of outcomes after surgical repair.

METHODS

A systematic search of the Embase, PubMed, and Web of Science electronic databases was performed. Medical Subject Headings (MeSH) and Emtree index terms were formulated from the concept terms "rotator cuff tear," "genetics," and "human," and synonyms of these concepts were applied to the Web of Science search. Articles were screened against predefined inclusion and exclusion criteria. Eligible studies compared gene expression patterns and genetic polymorphisms between cases (with RCTs) and controls (without RCTs). Quality assessment was performed with studies being rated as high, moderate, or poor quality. A modified best-evidence synthesis was applied, and studies were determined to be of strong, moderate, or limited evidence.

RESULTS

The search identified 259 articles. Of these studies, 26 were eligible for review. Two studies were considered poor quality; 15 studies, moderate quality; and 9 studies, high quality. Analysis of these articles found that RCTs were associated with alterations in genes that code for the extracellular matrix, cell apoptosis, immune and inflammatory responses, and growth factor pathways. In particular, there was strong evidence of a significant association between RCTs and the genes MMP3, TNC, and ESRRB. Strong evidence of an association between BMP5 upregulation and successful healing after surgical repair was also found.

CONCLUSION

This review provides strong evidence of an genetic association with RCTs. The genotype and gene expression patterns detailed within this review can assist in deciphering the biological mechanisms resulting in RCTs, as well as predicting an individual's response to surgical repair. Future research could investigate whether manipulating these genes-or their associated signaling pathways-could assist in RCT healing and whether genetic biomarkers could be used clinically to predict patient outcomes after surgical repair of RCTs.

Decreased Synovial Fluid Biomarkers Levels Are Associated with Rehabilitation of Function and Pain in Rotator Cuff Tear Patients Following Electroacupuncture Therapy

Background

The aim of this study was to assess inflammatory cytokines levels in synovial fluid (SF) before and after electroacupuncture (EA) treatment and to explore whether these biomarkers are associated with function of rotator cuff tear (RCT) patients.

Material/Methods

We recruited 54 patients with RCT and separated them into an EA group and a control group. The SF biomarker levels were detected at baseline and at 6-week and 6-month follow-up. The symptomatic severity was evaluated by visual analog scale (VAS), Constant-Murley score, and American Shoulder and Elbow Surgeons score (ASES). We also investigated the correlation between symptomatic severity and biomarker levels in SF of the shoulder joint.

Results

The reductions in VAS and improved functional score (ASES and Constant-Murley score) were significantly different between the 2 groups, and SF biomarker concentrations were significantly lower in the EA group. IL-1β levels were significantly negatively correlated with Constant-Murley score (r=−0.73, P=0.04) and ASES score (r=−0.59, P<0.001) and positively correlated with VAS scores (r=0.81, P=0.004). IL-6 levels were significantly negatively correlated with Constant-Murley score (r=−0.67, P=0.03) and positively correlated with VAS score (r=0.7, P=0.01). MMP-1 levels were significantly negatively correlated with ASES score (r=−0.57, P<0.001).

Conclusions

The biomarkers in SF were directly associated with shoulder pain and shoulder function in rotator cuff tear. EA, as a safe and effective conservative therapy, obviously decreased the level of inflammatory cytokines in RCT patients, accompanied by a reduction in shoulder pain and improved function.

Gene Expression in Torn Rotator Cuff Tendons Determined by RNA Sequencing

Background:

Although the cause of rotator cuff tearing is likely multifactorial and a genetic predisposition has been proposed, the biochemical basis remains unknown.

Purpose:

To determine gene expression profiles in torn rotator cuff tendon tissue through use of RNA sequencing.

Study Design:

Controlled laboratory study.

Methods:

The supraspinatus tendon edge was biopsied in 24 patients undergoing arthroscopic rotator cuff repair for full-thickness supraspinatus rotator cuff tears. The supraspinatus tendon was also biopsied in 9 patients undergoing open reduction and internal fixation for a proximal humeral fracture (controls). Total RNA was extracted and sequenced. Differential gene expression was analyzed between the tear and control groups, and a secondary analysis was conducted between groups defined by an unbiased clustering.

Results:

Tear and control transcriptomes demonstrated significant differential expression in more than 3000 genes. The identified differential genes were highlighted in pathways involved in inflammation in control patients and extracellular matrix generation in patients with tears. Secondary analysis using unsupervised and thus unbiased hierarchical clustering revealed 2 clusters (c2 and c3). Cluster c3 contained smaller (P < .001) and less retracted (P = .018) tears (ie, tears earlier in the progression of rotator cuff disease) with increased expression of hypoxia target genes. Cluster c2 contained larger, more retracted tears (ie, tears further in the progression of rotator cuff disease) with increased expression of endothelial cell markers and chronic inflammation target genes. Tears in c2 had significantly worse healing rates compared with tears in c3 (0% vs 89%; P = .007).

Conclusion:

Smaller, less retracted tears had increased expression of hypoxia target genes and improved healing, whereas larger, more retracted tears were associated with endothelial cell markers and worse healing. Thus, hypoxia may be the inciting event for tear development, whereas with tear enlargement, a chronic, inflammatory, angiogenic process may predominate.

Clinical Relevance:

Identification of differential gene expression in rotator cuff tears may be a reliable tool to predict repair healing in the future.

Conjoint analysis of lncRNA and mRNA expression in rotator cuff tendinopathy

Background

Rotator cuff tendinopathy (RCT) is a common musculoskeletal disorder in the shoulder, whose underlying mechanism is unknown. Long non-coding RNAs (lncRNAs) are involved in the development of various diseases, but little is known about their potential roles in RCT.

Methods

In this study, we profiled lncRNAs and mRNAs involved in RCT in comparison with the normal tendon (NT) by RNA sequencing (RNA-Seq), to identify potential therapeutic targets. Gene ontology (GO), Kyoto encyclopedia of genes and genomes (KEGG) pathway, competing endogenous RNA (ceRNA), and co-expression network construction were used to identify the potential functions of these RNAs. Three lncRNAs and three mRNAs were validated by quantitative reverse transcription-polymerase chain reaction (qRT-PCR).

Results

In total, 419 lncRNAs and 1,541 mRNAs were differentially expressed between the RCT and NT groups with a fold change of >2 and P of <0.01. The GO and KEGG pathway analyses showed that the differentially expressed mRNAs were mainly enriched in complement activation and involved in the citrate cycle. The ceRNA network showed the interaction of differentially expressed RNAs, comprising 139 lncRNAs, 126 mRNAs, and 35 miRNAs. NONHSAT209114.1, ENST00000577806, NONHSAT168464.1, PLK2, TMEM214, and IGF2 were validated by PCR. We constructed a co-expressed network of these validated RNAs.

Conclusions

We preliminarily analyzed the profile of lncRNAs and mRNAs in RCT. The bioinformatic analysis revealed several potential therapeutic targets for RCT.

Gene expression profiling of progenitor cells isolated from rat rotator cuff musculotendinous junction

Background

Rotator cuff tendon tears are typically degenerative and usually affect the region of tendon insertion on bone. The remnant torn tendon is degenerative and may not be an ideal source for progenitor cells for cell-based therapies. Therefore, the aim of this study was to determine if musculotendinous junction (MTJ), which is adjacent to tendon would be a viable alternate source of progenitor stem cells. We also sought to study the gene expression profile MTJ progenitors and compare it with progenitors isolated from RC tendon, RC muscle and other existing tissue sources (bone marrow, adipose tissue, and Achilles tendon).

Methods

Rotator cuff tendon (RCT), muscle (RCM), and RCMTJ as well as Achilles tendon (AT) tissues were harvested from healthy male Lewis rats and progenitor cultures were established from these tissues and also from bone marrow and adipose tissue. Quantitative RT-PCR was performed on RNA extracts from intact tissues and progenitor cells using a custom array for the mesenchymal stem cell (MSC) differentiation marker genes. The gene expression profile of MSC differentiation markers within four tissues types, six progenitor cells, and between tissue and their corresponding progenitors were compared.

Results

Progenitors cells can be isolated from rat rotator cuff musculotendinous tissue and their pattern of MSC gene expression was similar to the rotator cuff tendon progenitors for majority of the genes tested. However, there were significant differences between the MSC gene expression patterns of RCMTJ and RCM progenitors. Furthermore, there were differences in gene expression between the RCMTJ tissue and its progenitor cells with respect to MSC differentiation markers. The gene expression pattern of RCMTJ tissue was similar to RCM tissue with respect to markers of chondrogenesis, myogenesis, tenogenesis, and MSC specific markers.

Conclusion

We demonstrate that the musculotendinous junction contains distinct set of progenitor cells and their MSC gene expression pattern is similar to rotator cuff tendon progenitors. RCMTJ progenitors will be an attractive option for cell-based regenerative treatment of chronic rotator cuff tears.

A systematic review of inflammatory cells and markers in human tendinopathy

BACKGROUND

This article systematically reviews the current evidence regarding inflammation in Tendinopathy with the aim to increase understanding of a potential common pathophysiology.

METHODS

Following the PRISMA statements, the terms: (tendinopathy OR (tendons AND rupture)) AND (inflammation OR (inflammation AND cells) OR immune system OR inflammation mediators OR bacteria) were used. One thousand four hundred thirty-one articles were identified which was screened down to 53.

RESULTS

39/53 studies mentioned inflammatory cells but had contradicting conclusions. Macrophages were the most common cell type and inflammatory markers were detectable in all the articles which measure them.

CONCLUSIONS

The included studies show different conclusions, but this heterogeneity is not unexpected since the clinical criteria of 'tendinopathy' encompass a huge clinical spectrum. Different 'tendinopathy' conditions may have different pathophysiology, and even the same clinical condition may be at different disease stages during sampling, which can alter the histological and biochemical picture. Control specimen sampling was suboptimal since the healthy areas of the pathological-tendon may actually be sub-clinically diseased, as could the contralateral tendon in the same subject. Detection of inflammatory cells is most sensitive using immunohistochemistry targeting the cluster of differentiation markers, especially when compared to the conventional haematoxylin and eosin staining methods. The identified inflammatory cell types favour a chronic inflammatory process; which suggests a persistent stimulus. This means NSAID and glucocorticoids may be useful since they suppress inflammation, but it is noted that they may hinder tendon healing and cause long term problems. This systematic review demonstrates a diversity of data and conclusions in regard to inflammation as part of the pathogenesis of Tendinopathy, ranging from ongoing or chronic inflammation to non-inflammatory degeneration and chronic infection. Whilst various inflammatory markers are present in two thirds of the reviewed articles, the heterogenicity of data and lack of comparable studies means we cannot conclude a common pathophysiology from this systematic review.

Tendon healing in presence of chronic low-level inflammation: a systematic review

BACKGROUND

Tendinopathy is a common musculoskeletal condition affecting subjects regardless of their activity level. Multiple inflammatory molecules found in ex vivo samples of human tendons are related to the initiation or progression of tendinopathy. Their role in tendon healing is the subject of this review.

SOURCES OF DATA

An extensive review of current literature was conducted using PubMed, Embase and Cochrane Library using the term 'tendon', as well as some common terms of tendon conditions such as 'tendon injury OR (tendon damage) OR tendonitis OR tendinopathy OR (chronic tendonitis) OR tendinosis OR (chronic tendinopathy) OR enthesitis' AND 'healing' AND '(inflammation OR immune response)' as either key words or MeSH terms.

AREAS OF AGREEMENT

An environment characterized by a low level of chronic inflammation, together with increased expression of inflammatory cytokines and growth factors, may influence the physiological tendon healing response after treatment.

AREAS OF CONTROVERSY

Most studies on this topic exhibited limited scientific translational value because of their heterogeneity. The evidence associated with preclinical studies is limited.

GROWING POINTS

The role of inflammation in tendon healing is still unclear, though it seems to affect the overall outcome. A thorough understanding of the biochemical mediators of healing and their pathway of pain could be used to target tendinopathy and possibly guide its management.

AREAS TIMELY FOR DEVELOPING RESEARCH

We require further studies with improved designs to effectively evaluate the pathogenesis and progression of tendinopathy to identify cellular and molecular targets to improve outcomes.

Anisotropic cytocompatible electrospun scaffold for tendon tissue engineering elicits limited inflammatory response in vitro

Tendon tears are a relevant concern for today's national health systems because of their social impact and high recurrence rate. The current gold standard for fixing tendon tears is surgical repair; however, this strategy is not able to fully re-establish tendon integrity and functionality. Tissue engineering approaches aim at promoting tissue regeneration by delivering the opportune signals to the injured site combining biomaterials, cells and biochemical cues. Electrospinning is currently one of the most versatile polymer processing techniques that allows manufacturing of nano- and micro-fibres substrates. Such fibrous morphology is deemed to be an ideal substrate to convey topographical cues to cells. Here we evaluated the potential of polycaprolactone processed by means of electrospinning technology for tendon tissue engineering. Fibrous free-of-defects substrate with random and aligned fibres were successfully fabricated. Rat tenocytes were used to assess the cytocompatibility of the substrates for application as tendon tissue engineered devices. Tenocytes were able to proliferate and adapt to the substrates topography acquiring an elongated morphology, which is the precondition for oriented collagen deposition, when seeded on aligned fibres. Real time Polymerase Chain Reaction (Rt-PCR) also revealed the overall maintenance of tenocyte phenotype over 7 days culture. To verify suitability for in vivo implantation, the level of inflammatory cytokine genes expressed by THP-1 cells cultured in presence of electrospun polycaprolactone substrates was evaluated. Inflammatory response was limited. The novel preliminary in vitro work presented herein showing tenocytes compatibility and limited inflammatory cytokines synthesis suggests that electrospun polycaprolactone may be taken into consideration as substrate for tendon healing applications.

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.

Safe time frame of staged bilateral arthroscopic rotator cuff repair

BACKGROUND

Few studies have assessed the outcomes of staged bilateral arthroscopic rotator cuff repair (ARCR). This study aimed to determine the influencing factors related to the outcomes of patients who underwent staged bilateral ARCR and to verify an optimal interval for performing the second rotator cuff repair in staged bilateral ARCR.

METHODS

We analyzed 166 shoulders that underwent staged bilateral ARCR. The average interval between the first- and second-side surgical procedures was 21.9 ± 19.7 months. The minimum follow-up period was 2 years.

RESULTS

Clinical outcomes and retear rates were not significantly different according to the order of surgical procedures, sex, arm dominance, age, and tear size (P > .05 for all). The cutoff value for the optimal interval between the first and second surgical procedures for the University of California, Los Angeles score and American Shoulder and Elbow Surgeons score was 9 months, with the area under the curve equal to 0.815 (P < .001) for the University of California, Los Angeles score and 0.806 (P < .001) for the American Shoulder and Elbow Surgeons score. The group with an interval of 9 months or less between the first- and second-side surgical procedures showed significantly inferior clinical outcomes and a higher retear rate (35%) compared with the group with an interval greater than 9 months (retear rate, 10%) (P < .05).

CONCLUSION

Staged bilateral ARCR resulted in significant improvements in clinical outcomes regardless of the order of surgical procedures, sex, arm dominance, age, and tear size. To optimize clinical outcomes of staged bilateral ARCR, second-side surgery should be delayed until 9 months after the first-side surgical procedure.

Fibroblast Growth Factor 2 Enhances Tendon-to-Bone Healing in a Rat Rotator Cuff Repair of Chronic Tears

BACKGROUND

The effects of fibroblast growth factor 2 (FGF-2) on healing after surgical repair of chronic rotator cuff (RC) tears remain unclear.

HYPOTHESIS

FGF-2 enhances tenogenic healing response, leading to biomechanical and histological improvement of repaired chronic RC tears in rats.

STUDY DESIGN

Controlled laboratory study.

METHODS

Adult male Sprague-Dawley rats (n = 117) underwent unilateral surgery to refix the supraspinatus tendon to its insertion site 3 weeks after detachment. Animals were assigned to either the FGF-2 group or a control group. The effects of FGF-2 were assessed via biomechanical tests at 3 weeks after detachment and at 6 and 12 weeks postoperatively and were assessed histologically and immunohistochemically for proliferating cell nuclear antigen and mesenchymal stem cell (MSC)-related markers at 2, 6, and 12 weeks postoperatively. The expression of tendon/enthesis-related markers, including SRY-box 9 (Sox9), scleraxis (Scx), and tenomodulin (Tnmd), were assessed by real-time reverse transcription polymerase chain reaction, in situ hybridization, and immunohistochemistry. The effect of FGF-2 on comprehensive gene expressions at the healing site was evaluated by microarray analysis.

RESULTS

The FGF-2 group showed a significant increase in mechanical strength at 6 and 12 weeks compared with control; the FGF-2 group also showed significantly higher histological scores at 12 weeks than control, indicating the presence of more mature tendon-like tissue. At 12 weeks, Scx and Tnmd expression increased significantly in the FGF-2 group, whereas no significant differences in Sox9 were found between groups over time. At 2 weeks, the percentage of positive cells expressing MSC-related markers increased in the FGF-2 group. Microarray analysis at 2 weeks after surgery showed that the expression of several growth factor genes and extracellular matrix-related genes was influenced by FGF-2 treatment.

CONCLUSION

FGF-2 enhanced the formation of tough tendon-like tissues including an increase in Scx- or Tnmd-expressing cells at 12 weeks after surgical repair of chronic RC tears. The increase in mesenchymal progenitors and the changes in gene expression upon FGF-2 treatment in the early phase of healing appear to be related to a certain favorable microenvironment for tenogenic healing response of chronic RC tears.

CLINICAL RELEVANCE

These findings may provide advantages in therapeutic strategies for patients with RC tears.

Bioinformatics analysis of differentially expressed genes in rotator cuff tear patients using microarray data

Background

Rotator cuff tear (RCT) is a common shoulder disorder in the elderly. Muscle atrophy, denervation and fatty infiltration exert secondary injuries on torn rotator cuff muscles. It has been reported that satellite cells (SCs) play roles in pathogenic process and regenerative capacity of human RCT via regulating of target genes. This study aims to complement the differentially expressed genes (DEGs) of SCs that regulated between the torn supraspinatus (SSP) samples and intact subscapularis (SSC) samples, identify their functions and molecular pathways.

Methods

The gene expression profile GSE93661 was downloaded and bioinformatics analysis was made.

Results

Five hundred fifty one DEGs totally were identified. Among them, 272 DEGs were overexpressed, and the remaining 279 DEGs were underexpressed. Gene ontology (GO) and pathway enrichment analysis of target genes were performed. We furthermore identified some relevant core genes using gene–gene interaction network analysis such as GNG13, GCG, NOTCH1, BCL2, NMUR2, PMCH, FFAR1, AVPR2, GNA14, and KALRN, that may contribute to the understanding of the molecular mechanisms of secondary injuries in RCT. We also discovered that GNG13/calcium signaling pathway is highly correlated with the denervation atrophy pathological process of RCT.

Conclusion

These genes and pathways provide a new perspective for revealing the underlying pathological mechanisms and therapy strategy of RCT.

Enthesis Repair: Challenges and Opportunities for Effective Tendon-to-Bone Healing

On May 22, 2017, the National Institutes of Health (NIH)/National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS) hosted a roundtable on "Innovative Treatments for Enthesis Repair." A summary of the roundtable discussion, as well as a list of the extramural participants, can be found at https://www.niams.nih.gov/about/meetings-events/roundtables/roundtable-innovative-treatments-enthesis-repair. This paper reviews the challenges and opportunities for developing effective treatment strategies for enthesis repair that were identified at the roundtable discussion.

Synovial fluid biomarkers: association with chronic rotator cuff tear severity and pain

BACKGROUND

We tested the hypothesis that biomarkers in the synovial fluid of the glenohumeral (shoulder) joint are correlated with visual analog scale (VAS) scores, functional scores, and ultrasound findings of chronic rotator cuff tear (RCT) severity.

METHODS

We measured biomarkers in shoulder joint synovial fluid of 42 patients with partial-thickness (21), nonmassive full-thickness (10), and massive full-thickness (11) RCTs. Pain duration, tear severity, and VAS and functional scores were compared with interleukin (IL) 1β, IL-6, matrix metalloproteinase (MMP) 1, and MMP-13 levels.

RESULTS

Both MMP-1 and MMP-13 levels were significantly highest in the massive full-thickness group. MMP-13 levels were significantly different between groups, but proinflammatory cytokine IL-1β and IL-6 levels were not. However, IL-1β levels were significantly positively correlated with VAS (r = 0.66; P <.01) and functional scores (r = 0.61; P <.01), but IL-6, MMP-1, and MMP-13 levels were not.

CONCLUSIONS

IL-1β levels in shoulder synovial fluid correlated positively with shoulder pain and functional scores in patients with chronic RCTs. Both MMP-1 and MMP-13 levels were altered and increased with cuff tear severity.

Involvement of synovial matrix degradation and angiogenesis in oxidative stress-exposed degenerative rotator cuff tears with osteoarthritis

BACKGROUND

Shoulder osteoarthritis is a gradual wearing of the articular cartilage concomitant with degenerative rotator cuff tears (RCTs). This pathologic disorder is related to inflammation, oxidative stress, and angiogenesis. Degenerative alterations may prompt production of cytokines and angiogenesis-related proteins, evoking rotator cuff diseases. This study tested the hypothesis that oxidative stress-responsive mediators can influence joint inflammation of patients with RCT.

METHODS

Twelve healthy RCT patients not suffering shoulder osteoarthritis were categorized as the control group, and 24 patients were allocated to 2 RCT groups (RCTP1 and RCTP2), according to severity of RCT and glenohumeral arthritis. Cytokines, growth factors, and angiogenic biomarkers in synovial fluids, blood, platelet-rich plasma (PRP), and tendon tissues were analyzed with enzyme-linked immunosorbent assay, immunoblotting, and collagen zymography.

RESULTS

Induction of interleukin 8, tumor necrosis factor α, and interleukin 1β was considerably elevated in synovial fluids of RCTP groups (P = .0398, P = .0428, P = .0828, respectively). The joint inflammation highly enhanced insulin-like growth factor 1 and transforming growth factor β1 (TGF-β1) in the synovial fluids and serum. Angiogenesis-related angiopoietin (Ang) 1 and 2, Tie-2, and hypoxia-inducible factor 1α were upregulated in reactive oxygen species-exposed RCTP synovium (P < .05). The production of matrix metalloproteinase 1 markedly increased in synovial fluids of the RCTP group (P = .043), whereas tissue collagen type I expression diminished with reduction of connective tissue growth factor expression (P = .032). Although the secretion of platelet-derived growth factor AB and vascular endothelial growth factor was marginal in the circulation (P = .714, P = .335), platelet-derived growth factor AB, TGF-β1, Ang-1, and matrix metalloproteinase 1 were enriched in PRP of the RCTP group (P < .001, P = .002, P = .0389, respectively).

CONCLUSIONS

Synovial matrix degradation and oxidative stress-triggered angiogenesis may be involved in inducing RCT with joint inflammation. TGF-β1, Ang-1, and Ang-2 are the major components to repair RCT and to alleviate joint inflammation in PRP therapy.

Cytokines in tendon disease: A Systematic Review

OBJECTIVES

Emerging evidence indicates that tendon disease is an active process with inflammation that is critical to disease onset and progression. However, the key cytokines responsible for driving and sustaining inflammation have not been identified.

METHODS

We performed a systematic review of the literature using MEDLINE (U.S. National Library of Medicine, Bethesda, Maryland) in March 2017. Studies reporting the expression of interleukins (ILs), tumour necrosis factor alpha (TNF-α) and interferon gamma in diseased human tendon tissues, and animal models of tendon injury or exercise in comparison with healthy control tissues were included.

RESULTS

IL-1β, IL-6, IL-10, and TNF-α are the cytokines that have been most frequently investigated. In clinical samples of tendinopathy and tendon tears, the expression of TNF-α tended not to change but IL-6 increased in tears. Healthy human tendons showed increased IL-6 expression after exercise; however, IL-10 remained unchanged. Animal tendon injury models showed that IL-1β, IL-6, and TNF-α tend to increase from the early phase of tendon healing. In animal exercise studies, IL-1β expression showed a tendency to increase at the early stage after exercise, but IL-10 expression remained unchanged with exercise.

CONCLUSIONS

This review highlights the roles of IL-1β, IL-6, IL-10, and TNF-α in the development of tendon disease, during tendon healing, and in response to exercise. However, there is evidence accumulating that suggests that other cytokines are also contributing to tendon inflammatory processes. Further work with hypothesis-free methods is warranted in order to identify the key cytokines, with subsequent mechanistic and interaction studies to elucidate their roles in tendon disease development.Cite this article: W. Morita, S. G. Dakin, S. J. B. Snelling, A. J. Carr. Cytokines in tendon disease: A Systematic Review. Bone Joint Res 2017;6:656-664. DOI: 10.1302/2046-3758.612.BJR-2017-0112.R1.

Novel Tenascin-C Haplotype Modifies the Risk for a Failure to Heal After Rotator Cuff Repair

BACKGROUND

Several single-nucleotide polymorphisms (SNPs) in the TNC gene have recently been found to be associated with degenerative rotator cuff tears.

HYPOTHESIS

Exonic SNPs in the TNC gene are related to the risk for a failure to heal after rotator cuff repair.

STUDY DESIGN

Case-control study; Level of evidence, 3.

METHODS

A total of 302 patients from the Vienna area and European Caucasian ancestry underwent mini-open rotator cuff repair for a full-thickness superior or posterosuperior tear and were assessed for the integrity of the repair 1 year postoperatively with a real-time 7.5- to 10-MHz ultrasound linear array transducer. Outcomes were classified as intact (complete footprint coverage), small (<200 mm²), or large (≥200 mm²) recurrent defect. Patients were genotyped for 15 previously identified risk SNPs within a 49-kbp segment of the TNC gene with the KASP genotyping technology or the Ion-Torrent Personal Genome Machine System.

RESULTS

All recurrent defects were atraumatic failures, and the overall failure rate was 39.7%. Of the traditional risk factors, only the initial tear size was significantly associated with a failure to heal. In a multinomial logistic regression model, the T allele at rs1138545 [C>T] was protective for a large recurrent defect (odds ratio = 0.16; 95% CI, 0.09-0.31). The role of rs1138545 was further backed by haplotype analysis, which showed that the combination of the C allele at rs1138545 [C>T], the A allele at rs2104772 [A>T], and the G allele at rs10759752 [A>G] formed the risk-related haplotype [CAG]. The CAG haplotype was associated with large recurrent defects ( P < .0001; haplotype frequency, 0.394; haplotype score, 4.518). Exonic marker rs1138545 transcribed into all isoforms of the TNC protein, whereas exonic marker rs2104772, which has been associated with Achilles tendinopathy before, transcribed only into large isoforms of the TNC protein.

CONCLUSION

Recurrent defects after rotator cuff repairs are clinically relevant, and a heritable component of the disorder is plausible on the basis of a genetic association with 8 TNC variants. Characterization of TNC sequences that favor tendon healing will help engineer new products in regenerative medicine.

Epigenetic regulation of metalloproteinases and their inhibitors in rotator cuff tears

Rotator cuff tear is a common orthopedic condition. Metalloproteinases (MMP) and their inhibitors (TIMP) seem to play a role in the development of joint injuries and in the failure of tissue healing. However, the mechanisms of regulation of gene expression in tendons are still unknown. Epigenetic mechanisms, such as DNA methylation and microRNAs regulation, are involved in the dynamic control of gene expression. Here, the mRNA expression and DNA methylation status of MMPs (MMP1, MMP2, MMP3, MMP9, MMP13, and MMP14) and TIMPs (TIMP1-3) and the expression of miR-29 family members in ruptured supraspinatus tendons were compared with non-injured tendons of individuals without this lesion. Additionally, the gene expression and methylation status at the edge of the ruptured tendon were compared with macroscopically non-injured rotator cuff tendon samples from the anterior and posterior regions of patients with tendon tears. Moreover, the possible associations between the molecular alterations and the clinical and histologic characteristics were investigated. Dysregulated expression and DNA methylation of MMP and TIMP genes were found across the rotator cuff tendon samples of patients with supraspinatus tears. These alterations were influenced at least in part by age at surgery, sex, smoking habit, tear size, and duration of symptoms. Alterations in the studied MMP and TIMP genes may contribute to the presence of microcysts, fissures, necrosis, and neovascularization in tendons and may thus be involved in the tendon healing process. In conclusion, MMPs and their inhibitors are regulated by epigenetic modifications and may play a role in rotator cuff tears.

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.

The Biology of Bone and Ligament Healing

This review describes the normal healing process for bone, ligaments, and tendons, including primary and secondary healing as well as bone-to-bone fusion. It depicts the important mediators and cell types involved in the inflammatory, reparative, and remodeling stages of each healing process. It also describes the main challenges for clinicians when trying to repair bone, ligaments, and tendons with a specific emphasis on Charcot neuropathy, fifth metatarsal fractures, arthrodesis, and tendon sheath and adhesions. Current treatment options and research areas are also reviewed.