The apoptosis pathway and the genetic predisposition to Achilles tendinopathy

Challenges and opportunities of medicines for treating tendon inflammation and fibrosis: A comprehensive and mechanistic review

BACKGROUND

Tendinopathy refers to conditions characterized by collagen degeneration within tendon tissue, accompanied by the proliferation of capillaries and arteries, resulting in reduced mechanical function, pain, and swelling. While inflammation in tendinopathy can play a role in preventing infection, uncontrolled inflammation can hinder tissue regeneration and lead to fibrosis and impaired movement.

OBJECTIVES

The inability to regulate inflammation poses a significant limitation in tendinopathy treatment. Therefore, an ideal treatment strategy should involve modulation of the inflammatory process while promoting tissue regeneration.

METHODS

The current review article was prepared by searching PubMed, Scopus, Web of Science, and Google Scholar databases. Several treatment approaches based on biomaterials have been developed.

RESULTS

This review examines various treatment methods utilizing small molecules, biological compounds, herbal medicine-inspired approaches, immunotherapy, gene therapy, cell-based therapy, tissue engineering, nanotechnology, and phototherapy.

CONCLUSION

These treatments work through mechanisms of action involving signaling pathways such as transforming growth factor-beta (TGF-β), mitogen-activated protein kinases (MAPKs), and nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB), all of which contribute to the repair of injured tendons.

Exploring pathogenic pathways in carpal tunnel syndrome: sterile inflammation and oxidative stress

OBJECTIVES

The main objective of the current study was to find the association between oxidative stress, inflammatory markers, and electrophysiological profile with symptom severity in patients of carpal tunnel syndrome (CTS).

METHODS

Thirty-two carpal tunnel syndrome patients and 32 controls were included in the study. Boston CTS questionnaire along with plasma oxidative stress markers including superoxide dismutase, malondialdehyde, and nitric oxide and inflammatory markers including IL-6 and TNF-α were compared with the electrophysiological parameters derived from nerve conduction studies. Statistical significance of the levels between groups was calculated using unpaired-t test after checking for normality with D'Agostino & Pearson omnibus normality test.

RESULTS

We found that the median nerve conduction velocity was prolonged, amplitude was decreased, while the levels of oxidative stress markers like malondialdehyde (MDA), superoxidase dismutase (SOD), and nitric oxide (NO) were increased in CTS patients compared to controls. Inflammatory markers like interleukin-6 (IL-6) and tumor necrosis factor-alpha (TNF-α) were also increased in CTS patients. We found that plasma SOD and TNF-α correlated well with the median motor amplitude. There was no other significant correlation between oxidative stress markers and inflammatory markers with nerve conduction studies or disease severity. Patients with mild disease also showed lesser levels of SOD, NO, IL-6, and TNF-α markers than patients with severe disease.

CONCLUSIONS

CTS is probably a disease of sterile inflammation and disbalance of oxidative stress, with higher inflammatory and oxidative stress markers pointing to a more severe disease.

Collagen Gene Polymorphisms Previously Associated with Resistance to Soft-Tissue Injury Are More Common in Competitive Runners Than Nonathletes

ABSTRACT

Dines, HR, Nixon, J, Lockey, SJ, Herbert, AJ, Kipps, C, Pedlar, CR, Day, SH, Heffernan, SM, Antrobus, MR, Brazier, J, Erskine, RM, Stebbings, GK, Hall, ECR, and Williams, AG. Collagen gene polymorphisms previously associated with resistance to soft-tissue injury are more common in competitive runners than nonathletes. J Strength Cond Res 37(4): 799-805, 2023-Single-nucleotide polymorphisms (SNPs) of collagen genes have been associated with soft-tissue injury and running performance. However, their combined contribution to running performance is unknown. We investigated the association of 2 collagen gene SNPs with athlete status and performance in 1,429 Caucasian subjects, including 597 competitive runners (354 men and 243 women) and 832 nonathletes (490 men and 342 women). Genotyping for COL1A1 rs1800012 (C > A) and COL5A1 rs12722 (C > T) SNPs was performed by a real-time polymerase chain reaction. The numbers of "injury-resistant" alleles from each SNP, based on previous literature (rs1800012 A allele and rs12722 C allele), were combined as an injury-resistance score (RScore, 0-4; higher scores indicate injury resistance). Genotype frequencies, individually and combined as an RScore, were compared between cohorts and investigated for associations with performance using official race times. Runners had 1.34 times greater odds of being rs12722 CC homozygotes than nonathletes (19.7% vs. 15.5%, p = 0.020) with no difference in the rs1800012 genotype distribution ( p = 0.659). Fewer runners had an RScore 0 of (18.5% vs. 24.7%) and more had an RScore of 4 (0.6% vs. 0.3%) than nonathletes ( p < 0.001). Competitive performance was not associated with the COL1A1 genotype ( p = 0.933), COL5A1 genotype ( p = 0.613), or RScore ( p = 0.477). Although not associated directly with running performance among competitive runners, a higher combined frequency of injury-resistant COL1A1 rs1800012 A and COL5A1 rs12722 C alleles in competitive runners than nonathletes suggests these SNPs may be advantageous through a mechanism that supports, but does not directly enhance, running performance.

Challenges and perspectives of tendon-derived cell therapy for tendinopathy: from bench to bedside

Tendon is composed of dense fibrous connective tissues, connecting muscle at the myotendinous junction (MTJ) to bone at the enthesis and allowing mechanical force to transmit from muscle to bone. Tendon diseases occur at different zones of the tendon, including enthesis, MTJ and midsubstance of the tendon, due to a variety of environmental and genetic factors which consequently result in different frequencies and recovery rates. Self-healing properties of tendons are limited, and cell therapeutic approaches in which injured tendon tissues are renewed by cell replenishment are highly sought after. Homologous use of individual’s tendon-derived cells, predominantly differentiated tenocytes and tendon-derived stem cells, is emerging as a treatment for tendinopathy through achieving minimal cell manipulation for clinical use. This is the first review summarizing the progress of tendon-derived cell therapy in clinical use and its challenges due to the structural complexity of tendons, heterogeneous composition of extracellular cell matrix and cells and unsuitable cell sources. Further to that, novel future perspectives to improve therapeutic effect in tendon-derived cell therapy based on current basic knowledge are discussed.

Investigation of multiple populations highlight VEGFA polymorphisms to modulate anterior cruciate ligament injury

Polymorphisms in VEGFA and KDR encoding proteins have been associated with anterior cruciate ligament (ACL) injury risk. We leveraged a collective sample from Sweden, Poland, and Australia to investigate the association of functional polymorphisms in VEGFA and KDR with susceptibility to ACL injury risk. Using a case-control genetic association approach, polymorphisms in VEGFA and KDR were genotyped and haplotypes inferred from 765 controls, and 912 cases clinically diagnosed with ACL rupture. For VEGFA, there was a significant overrepresentation of the rs2010963 CC genotype (p = 0.0001, false discovery rate [FDR]: p = 0.001, odds ratio [OR]: 2.16, 95% confidence interval [CI]: 1.47-3.19) in the combined ACL group (18%) compared to the combined control group (11%). The VEGFA (rs699947 C/A, rs1570360 G/A, rs2010963 G/C) A-A-G haplotype was significantly (p = 0.010, OR: 0.85, 95% CI: 0.69-1.05) underrepresented in the combined ACL group (23%) compared to the combined control group (28%). In addition, the A-G-G construct was significantly (p = 0.036, OR: 0.81, 95% CI: 0.64-1.02) underrepresented in the combined ACL group (12%) compared to the combined CON group (16%). Our findings support the association of the VEGFA rs2010963 CC genotype with increased risk and (ii) the VEGFA A-A-G haplotype with a reduced risk, and are in alignment with the a priori hypothesis. Collectively identifying a genetic interval within VEGFA to be implicated in ACL risk modulation and highlight further the importance of vascular regulation in ligament biology.

Tendon and Ligament Genetics: How Do They Contribute to Disease and Injury? A Narrative Review

A significant proportion of patients requiring musculoskeletal management present with tendon and ligament pathology. Our understanding of the intrinsic and extrinsic mechanisms that lead to such disabilities is increasing. However, the complexity underpinning these interactive multifactorial elements is still not fully characterised. Evidence highlighting the genetic components, either reducing or increasing susceptibility to injury, is increasing. This review examines the present understanding of the role genetic variations contribute to tendon and ligament injury risk. It examines the different elements of tendon and ligament structure and considers our knowledge of genetic influence on form, function, ability to withstand load, and undertake repair or regeneration. The role of epigenetic factors in modifying gene expression in these structures is also explored. It considers the challenges to interpreting present knowledge, the requirements, and likely pathways for future research, and whether such information has reached the point of clinical utility.

Advances in sports genomics

Sports genomics is the scientific discipline that focuses on the organization and function of the genome in elite athletes, and aims to develop molecular methods for talent identification, personalized exercise training, nutritional need and prevention of exercise-related diseases. It postulates that both genetic and environmental factors play a key role in athletic performance and related phenotypes. This update on the panel of genetic markers (DNA polymorphisms) associated with athlete status and soft-tissue injuries covers advances in research reported in recent years, including one whole genome sequencing (WGS) and four genome-wide association (GWAS) studies, as well as findings from collaborative projects and meta-analyses. At end of 2020, the total number of DNA polymorphisms associated with athlete status was 220, of which 97 markers have been found significant in at least two studies (35 endurance-related, 24 power-related, and 38 strength-related). Furthermore, 29 genetic markers have been linked to soft-tissue injuries in at least two studies. The most promising genetic markers include HFE rs1799945, MYBPC3 rs1052373, NFIA-AS2 rs1572312, PPARA rs4253778, and PPARGC1A rs8192678 for endurance; ACTN3 rs1815739, AMPD1 rs17602729, CPNE5 rs3213537, CKM rs8111989, and NOS3 rs2070744 for power; LRPPRC rs10186876, MMS22L rs9320823, PHACTR1 rs6905419, and PPARG rs1801282 for strength; and COL1A1 rs1800012, COL5A1 rs12722, COL12A1 rs970547, MMP1 rs1799750, MMP3 rs679620, and TIMP2 rs4789932 for soft-tissue injuries. It should be appreciated, however, that hundreds and even thousands of DNA polymorphisms are needed for the prediction of athletic performance and injury risk.

Using Genomic Techniques in Sports and Exercise Science: Current Status and Future Opportunities

ABSTRACT

The past two decades have built on the successes of the Human Genome Project identifying the impact of genetics and genomics on human traits. Given the importance of exercise in the physical and psychological health of individuals across the lifespan, using genomics to understand the impact of genes in the sports medicine field is an emerging field. Given the complexity of the systems involved, high-throughput genomics is required to understand genetic variants, their functions, and ultimately their effect on the body. Consequently, genomic studies have been performed across several domains of sports medicine with varying degrees of success. While the breadth of these is great, they focus largely on the following three areas: 1) performance; 2) injury susceptibility; and 3) sports associated chronic conditions, such as osteoarthritis. Herein, we review literature on genetics and genomics in sports medicine, offer suggestions to bolster existing studies, and suggest ways to ideally impact clinical care.

Identification of Three Loci Associated with Achilles Tendon Injury Risk from a Genome-wide Association Study

PURPOSE

This study aimed to screen the entire genome for genetic markers associated with risk for Achilles tendon injury.

METHODS

A genome-wide association analysis was performed using data from the Kaiser Permanente Research Board and the UK Biobank. Achilles tendon injury cases were identified based on electronic health records from the Kaiser Permanente Research Board databank and the UK Biobank from individuals of European ancestry. Genome-wide association analyses from both cohorts were tested for Achilles tendon injury using a logistic regression model adjusting for sex, height, weight, and race/ethnicity using allele counts for single nucleotide polymorphisms (SNP). Previously identified genes within the literature were also tested for association with Achilles tendon injury.

RESULTS

There were a total of 12,354 cases of Achilles tendon injury and 483,080 controls within the two combined cohorts, with 67 SNP in three chromosomal loci demonstrating a genome-wide significant association with Achilles tendon injury. The first locus contains a single SNP (rs183364169) near the CDCP1 and TMEM158 genes on chromosome 3. The second locus contains 65 SNP in three independently segregating sets near the MPP7 gene on chromosome 10. The last locus contains a single SNP (rs4454832) near the SOX21 and GPR180 genes on chromosome 13. The current data were used to test 14 candidate genes previously reported to show an association with Achilles tendon injury, but none showed a significant association (all P > 0.05).

CONCLUSION

Three loci were identified as potential risk factors for Achilles tendon injury and deserve further validation and investigation of molecular mechanisms.

Use of a Virtual Reality Simulator for Tendon Repair Training: Randomized Controlled Trial

BACKGROUND

Virtual reality (VR) simulators have become widespread tools for training medical students and residents in medical schools. Students using VR simulators are provided with a 3D human model to observe the details by using multiple senses and they can participate in an environment that is similar to reality.

OBJECTIVE

The aim of this study was to promote a new approach consisting of a shared and independent study platform for medical orthopedic students, to compare traditional tendon repair training with VR simulation of tendon repair, and to evaluate future applications of VR simulation in the academic medical field.

METHODS

In this study, 121 participants were randomly allocated to VR or control groups. The participants in the VR group studied the tendon repair technique via the VR simulator, while the control group followed traditional tendon repair teaching methods. The final assessment for the medical students involved performing tendon repair with the "Kessler tendon repair with 2 interrupted tendon repair knots" (KS) method and the "Bunnell tendon repair with figure 8 tendon repair" (BS) method on a synthetic model. The operative performance was evaluated using the global rating scale.

RESULTS

Of the 121 participants, 117 participants finished the assessment and 4 participants were lost to follow-up. The overall performance (a total score of 35) of the VR group using the KS method and the BS method was significantly higher (P<.001) than that of the control group. Thus, participants who received VR simulator training had a significantly higher score on the global rating scale than those who received traditional tendon repair training (P<.001).

CONCLUSIONS

Our study shows that compared with the traditional tendon repair method, the VR simulator for learning tendon suturing resulted in a significant improvement of the medical students in the time in motion, flow of operation, and knowledge of the procedure. Therefore, VR simulator development in the future would most likely be beneficial for medical education and clinical practice.

TRIAL REGISTRATION

Chinese Clinical Trial Registry ChiCTR2100046648; http://www.chictr.org.cn/hvshowproject.aspx?id=90180.

Mitochondrial dysfunction and potential mitochondrial protectant treatments in tendinopathy

Tendinopathy is a common musculoskeletal condition that affects a wide range of patients, including athletes, laborers, and older patients. Tendinopathy is often characterized by pain, swelling, and impaired performance and function. The etiology of tendinopathy is multifactorial, including both intrinsic and extrinsic mechanisms. Various treatment strategies have been described, but outcomes are often variable, as tendons have poor intrinsic healing potential compared with other tissues. Therefore, several novel targets for tendon regeneration have been identified and are being explored. Mitochondria are organelles that generate adenosine triphosphate, and they are considered to be the power generators of the cell. Recently, mitochondrial dysfunction verified by increased reactive oxygen species (ROS), decreased superoxide dismutase activity, cristae disorganization, and decreased number of mitochondria has been identified as a mechanism that may contribute to tendinopathy. This has provided new insights for studying tendinopathy pathogenesis and potential treatments via antioxidant, metabolic modulation, or ROS inhibition. In this review, we present the current understanding of mitochondrial dysfunction in tendinopathy. The review summarizes the potential mechanism by which mitochondrial dysfunction contributes to the development of tendinopathy, as well as the potential therapeutic benefits of mitochondrial protectants in the treatment of tendinopathy.

Photobiomodulation therapy on expression of HSP70 protein and tissue repair in experimental acute Achilles tendinitis

The aim of the present study was to investigate the effects of photobiomodulation (PBM) therapy on the expression of heat shock protein 70 (HSP70) and tissue repair in an experimental model of collagenase-induced Achilles tendinitis. Thirty Wistar rats (aged 12 weeks) were randomly distributed among control group (n = 8), tendinitis group (n = 11), and LED group (n = 11). Tendinitis was induced in the tendinitis and LED groups through a peritendinous injection of collagenase (100 μl). The LED group animals received the first irradiation 1 h after injury. A 630 ± 20 nm, 300-mW continuous wave light-emitting diode (LED), spot size 1 cm², was placed in contact with the skin. One point over the tendon was irradiated for 30 s, delivering 9 J (9 J/cm²). LED irradiation was performed once daily for 7 days, with the total energy delivered being 63 J. The tendons were surgically removed and expression of the HSP70 protein was calculated using semi-quantitative analyses of immunohistochemistry (HSCORE). Number of fibroblasts and amount of collagen were measured using histological and histochemical analyses. An increase in the mean HSCORE for HSP70, in the number of fibroblasts, and in the amount of collagen were found in the LED group compared with those in the tendinitis and control group (P ≤ 0.05). PBM therapy increased the expression of the HSP70, number of fibroblasts, and amount of collagen in the acute Achilles tendinitis in rats.

Elevated lipid levels in patients with achilles tendon ruptures: a retrospective matching study

Background

Achilles tendon rupture (ATR) can lead to significant disability of patients. However, whether serum lipid levels are associated with ATR is still unclear. This study aimed to examine the difference in lipid levels between patients with and those without ATR.

Methods

Patients who received ATR surgery during January 2017 to December 2017 were categorized into the case group, and those who had physical examinations during the same period without ATR were in the control group. Different matching methods [case-control matching (CCM) and propensity score matching (PSM)] were used to match the cases and controls at a 1:1 ratio.

Results

Among a total of 216 pairs of subjects with CCM, cholesterol, triglyceride, and low-density lipoprotein (LDL) levels were significantly higher (all P<0.05) in the case group than in the control group. Among 241 pairs of subjects with PSM, the same results as those with CCM were obtained. Abnormal rates of cholesterol, triglyceride, and LDL levels in the case group were also significantly higher than those in the control group in CCM and PSM (all P<0.05). After adjusting for the factors of height and weight, there were still significant differences in cholesterol, triglyceride, and LDL levels, as well as high-density lipoprotein levels, between the case and control groups (all P<0.05).

Conclusions

Cholesterol, triglyceride, and LDL levels in patients with ATR are higher than those in healthy people. Further studies are required to verify the effect of some components of lipids on Achilles tendon structure.

Serum levels of inflammatory cytokines in patients with idiopathic carpal tunnel syndrome

Objectives: Carpal tunnel syndrome (CTS) is a disorder caused by median nerve pressure inside the carpal tunnel in the wrist area. Recent evidences have demonstrated a role of cytokines in CTS. It is still controversial whether idiopathic CTS is an inflammatory or non-inflammatory disorder. Accordingly, the purpose of the current research was to assess serum levels of inflammatory cytokines in patients with idiopathic carpal tunnel syndrome in comparison with healthy participants.Methods: This case-control research was performed on 40 female patients with idiopathic carpal tunnel syndrome and 40 healthy controls. After identifying the participants, the serum levels of four cytokines (TNF-α, IL-2, IL-4, IL-6, and IL-10) were calculated by ELIZA method. SPSS statistical analysis was performed after entering data. p-values ≤ 0.05 was deliberated statistically significant.Results: The mean age was 45.07 ± 8.52 years in the patient group and 45.32 ± 8.42 years in the control group. The concentration of TNFα, IL1, IL6 and IL10 was 3.84 ± 0.44, 3.20 ± 0.71, 3.37 ± 1.26 and 6.21 ± 3.38 in patient group. The current study results demonstrated that there was no statistically significant difference among the case and control groups.Conclusions: This study showed that, serum levels of inflammatory cytokines (IL1, IL6, IL10 and TNFα) had no meaningful changes in patients with carpal tunnel syndrome and the role of these inflammatory mediators in this disease is still unclear.

The Apoptosis Pathway and CASP8 Variants Conferring Risk for Acute and Overuse Musculoskeletal Injuries

Rotator cuff tendinopathy (RCT), anterior cruciate ligament (ACL) ruptures, and carpal tunnel syndrome (CTS), are examples of chronic (RCT and CTS) and acute (ACL ruptures) musculoskeletal soft tissue injuries. These injuries are multifactorial in nature, with several identified intrinsic and extrinsic risk factors. Previous studies have implicated specific sequence variants within genes encoding structural and regulatory components of the extracellular matrix of tendons and/ligaments to predispose individuals to these injuries. An example, includes the association of sequence variants within the apoptotic regulatory gene, caspase-8 (CASP8) with other musculoskeletal injury phenotypes, such as Achilles tendinopathy. The primary aim of this study was, therefore, to investigate previously implicated DNA sequence variants within CASP8: rs3834129 (ins/del) and rs1045485 (G/C), and the rs13113 (T/A) identified using a whole exome sequencing approach, with risk of musculoskeletal injury phenotypes (RCT, ACL ruptures, and CTS) in three independent studies. In addition, the aim was to implicate a CASP8 genomic interval in the modulation of risk of RCT, ACL ruptures, or CTS. It was found that the AA genotype of CASP8 rs13113 (T/A) was independently associated with increased risk for CTS. In addition, it was found that the del-C haplotype (rs3834129-rs1045485) was significantly associated with non-contact ACL ruptures, which is in alignment with previous research findings. Collectively, the results of this study implicate the apoptosis pathway as biologically significant in the underlying pathogenesis of musculoskeletal injury phenotypes. These findings should be repeated in larger sample cohorts and across different populations. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 38:680-688, 2020.

Inhibition of CD44 induces apoptosis, inflammation, and matrix metalloproteinase expression in tendinopathy

Apoptosis has emerged as a primary cause of tendinopathy. CD44 signaling pathways exert anti-apoptotic and -inflammatory effects on tumor cells, chondrocytes, and fibroblast-like synoviocytes. The aim of this study was to examine the association among CD44, apoptosis, and inflammation in tendinopathy. Expression of CD44 and apoptotic cell numbers in tendon tissue from patients with long head of biceps (LHB) tendinopathy were determined according to the histological grades of tendinopathy. Primary tenocytes from Achilles tendon of Sprague-Dawley rats 1 week after collagenase injection were cultured with an antagonizing antibody against CD44. Treatment responses were determined by evaluating cell viability and expression of tendon-related proliferation markers, inflammatory mediators, and apoptosis. The expression of CD44 and apoptosis were positively correlated with the severity of tendinopathy in the human LHB tendinopathy. Furthermore, CD44 expression and apoptotic cells were co-stained in tendinopathic tendon. Blocking the CD44 signaling pathways in rat primary tenocytes by OX-50 induced cell apoptosis and the elevated levels of cleaved caspase-3. Furthermore, they had decreased cell viability and expression of collagen type I, type III, tenomodulin, and phosphorylated AKT. In contrast, there were elevated levels of inflammatory mediators, including interleukin (IL)-1β, IL-6, tumor necrosis factor-α, cyclooxygenase-2, and phosphorylated NF-κB, as well as matrix metalloproteinase (MMP) family members including MMP-1, -3, -9, and -13 in tenocytes upon OX-50 treatment. This study is the first to demonstrate the association of CD44 and apoptosis in tendinopathy. Our data imply that CD44 may play a role in tendinopathy via regulating apoptosis, inflammation, and extracellular matrix homeostasis.

Variability within the human iNOS gene and Achilles tendon injuries: Evidence for a heterozygous advantage effect

OBJECTIVES

The aim of this case control genetic association study was to explore whether two variants within the inducible nitric oxide synthase (iNOS) gene, rs2779249 (C/A) and rs2248814 (A/G), influenced the risk of Achilles tendinopathy in a British population.

DESIGN

Candidate gene, case control association study.

METHOD

We recruited 145 individuals diagnosed with Achilles tendon pathology and 132 asymptomatic controls. All participants were genotyped for the iNOS variants using qPCR and significant associations were discovered using a combination of Chi squared and ANOVA type analysis.

RESULTS

The CA genotype of the iNOS rs2779249 variant was protective and conformed to a heterozygous advantage model of inheritance as it was overrepresented in the control participants (p=0.009). In sex specific analysis the protective association persisted in male participants (p=0.016) but not in females. Unlike the rs2779249 variant, the rs2248814 variant was not associated with Achilles tendinopathy or Achilles tendon rupture.

CONCLUSION

The rs2779249 CA genotype within the human iNOS gene appears to protect individuals from Achilles tendinopathy. This study further supports a genetic contribution to modifying the risk of Achilles tendon problems. The study also infers an important role for nitric oxide in tendon healing and/or degradation.

Additional evidence supports association of common genetic variants in MMP3 and TIMP2 with increased risk of chronic Achilles tendinopathy susceptibility

OBJECTIVES

To systematically evaluate the effects of matrix metalloproteinase-3 (MMP3) and tissue inhibitor of metalloproteinase-2 (TIMP2) on chronic Achilles tendinopathy (AT) susceptibility. Chronic AT is one of the most prevalent and severe injuries in athletes. Early studies suggested that tendon extracellular matrix (ECM) may be involved in the pathogenesis of chronic AT. MMP3 is an important member of the MMP family and is important to ECM integrity. In addition, tissue inhibitor of metalloproteinase-2 (TIMP2) can indirectly limit the activity of MMP3 activity.

DESIGN

Case-control genetic association study.

METHODS

A total of 1084 chronic AT patients and 2188 controls with Chinese Han ancestry were recruited. Twenty-one SNPs, 4 mapped to MMP3 and 17 mapped to TIMP2, were selected and genotyped. Genetic association analyses and eQTL analyses were performed. In addition, we also examined the potential effects of epistasis using a case-only study design.

RESULTS

Two SNPs, rs679620 (OR=0.82, P=0.0006, MMP3) and rs4789932 (OR=1.2, P=0.0002, TIMP2) were identified to be significantly associated with chronic AT risk. No significant results were obtained from epistasis analyses. SNP rs4789932 was identified to be strongly associated with the gene expression level of TIMP2 in two types of human tissues: atrial appendage (P=0.0003) and tibial artery (P=0.0009).

CONCLUSIONS

We have identified genetic polymorphisms in MMP3 and TIMP2 to be significantly associated with chronic AT risk. Further eQTL analyses indicated that SNP rs4789932 of TIMP2 was related to the gene expression levels of TIMP2. These results suggest important roles for MMP3 and TIMP2 in the pathophysiology of chronic AT.

Tendon and Ligament Injuries in Elite Rugby: The Potential Genetic Influence

This article reviews tendon and ligament injury incidence and severity within elite rugby union and rugby league. Furthermore, it discusses the biological makeup of tendons and ligaments and how genetic variation may influence this and predisposition to injury. Elite rugby has one of the highest reported injury incidences of any professional sport. This is likely due to a combination of well-established injury surveillance systems and the characteristics of the game, whereby high-impact body contact frequently occurs, in addition to the high intensity, multispeed and multidirectional nature of play. Some of the most severe of all these injuries are tendon and ligament/joint (non-bone), and therefore, potentially the most debilitating to a player and playing squad across a season or World Cup competition. The aetiology of these injuries is highly multi-factorial, with a growing body of evidence suggesting that some of the inter-individual variability in injury susceptibility may be due to genetic variation. However, little effort has been devoted to the study of genetic injury traits within rugby athletes. Due to a growing understanding of the molecular characteristics underpinning the aetiology of injury, investigating genetic variation within elite rugby is a viable and worthy proposition. Therefore, we propose several single nucleotide polymorphisms within candidate genes of interest; COL1A1, COL3A1, COL5A1, MIR608, MMP3, TIMP2, VEGFA, NID1 and COLGALT1 warrant further study within elite rugby and other invasion sports.

The VEGFA gene and anterior cruciate ligament rupture risk in the Caucasian population

The aim of the present study was to analyse VEGFA rs699947, rs1570360, and rs2010963 polymorphisms with susceptibility to anterior cruciate ligament rupture (ACLR) in a Polish population. The study included 412 physically active Caucasian participants. The study group consisted of 222 individuals with surgically diagnosed primary ACLR qualified for ligament reconstruction (ACLR group). The control group consisted of 190 apparently healthy participants without any history of ACLR (CON group). Three polymorphisms within the VEGFA (rs699947, rs1570360, and rs2010963) gene were chosen for investigation due to their significance in the angiogenesis signalling pathway and previous associations with risk of ACLRs. Both single-locus and haplotype-based analyses were conducted. No significant differences in the allele and genotype frequency distributions were noted for the rs699947 and rs1570360 polymorphisms. In contrast, rs2010963 was associated with risk of ACLR in the codominant (p=0.047) and recessive model (p=0.017). In the latter, the CC genotype was overrepresented among individuals with ACL rupture (23.4% vs 14.2%, OR=1.85 [1.11-3.08]). Two VEGFA haplotypes were associated with ACLR under the additive (global score=11.39, p=0.022) and dominant model (global score=11.61, p=0.020). The [C;G;G] haplotype was underrepresented in the ACLR group (52.2% vs. 60.3%), whereas the [C;G;C] haplotype was overrepresented (2.9% vs 0.5%). The results obtained suggest a potential correlation between the VEGFA rs2010963 polymorphism and ACLR risk, suggesting that harbouring this specific C allele may be an unfavourable risk factor for a knee injury in Caucasian participants from Poland.

Clinical risk factors for Achilles tendinopathy: a systematic review

Background

Achilles tendinopathy is a common problem, but its exact aetiology remains unclear.

Objective

To evaluate the association between potential clinical risk factors and Achilles tendinopathy.

Design

Systematic review.

Data sources

The databases Embase, MEDLINE Ovid, Web of Science, Cochrane Library and Google Scholar were searched up to February 2018.

Eligibility criteria

To answer our research question, cohort studies investigating risk factors for Achilles tendinopathy in humans were included. We restricted our search to potential clinical risk factors (imaging studies were excluded).

Results

We included 10 cohort studies, all with a high risk of bias, from 5111 publications identified. There is limited evidence for nine risk factors: (1) prior lower limb tendinopathy or fracture, (2) use of ofloxacin (quinolone) antibiotics, (3) an increased time between heart transplantation and initiation of quinolone treatment for infectious disease, (4) moderate alcohol use, (5) training during cold weather, (6) decreased isokinetic plantar flexor strength, (7) abnormal gait pattern with decreased forward progression of propulsion, (8) more lateral foot roll-over at the forefoot flat phase and (9) creatinine clearance of <60 mL/min in heart transplant patients. Twenty-six other putative risk factors were not associated with Achilles tendinopathy, including being overweight, static foot posture and physical activity level.

Conclusion

From an ocean of studies with high levels of bias, we extracted nine clinical risk factors that may increase a person’s risk of Achilles tendinopathy. Clinicians may consider ofloxacin use, alcohol consumption and a reduced plantar flexor strength as modifiable risk factors when treating patients with Achilles tendinopathy.

Trial registration number

CRD42017053258.

Mid-portion Achilles tendinopathy in runners with metabolic disorders

INTRODUCTION

Running is a very popular modality of physical activity, which may help to lose weight and normalize pathological values of blood parameters in subjects suffering from metabolic disorders. Given that both overuse and metabolic pathologies are responsible for the onset of tendon damage, aim of the present study was to evaluate whether the first group of pathogenetic factors or the latter was more responsible for mid-portion Achilles tendinopathy.

METHOD

Thirty-six and 28 subjects with and without mid-portion Achilles tendinopathy, who were regular runners and started running for metabolic disorders, were enrolled, respectively. Information about body weight and blood parameters at baseline was collected. The characteristics of running practice, dietary habits and anthropometric measures were registered. An ultrasound evaluation of the tendon was performed, and the blood metabolic parameters were evaluated.

RESULTS

The amount of running years and mileage was equivalent in both groups. A similar weight loss was observed; the subjects with mid-portion Achilles tendinopathy showed a worse metabolic profile (Hb1aC%, p = 0.008; total cholesterol, p = 0.04; HDL cholesterol, p = 0.003; triglycerides, p = 0.009).

CONCLUSIONS

These findings suggest that the subjects with less evident positive effects of running on metabolism are more exposed to the onset of mid-portion Achilles tendinopathy.

Chronic inflammation is a feature of Achilles tendinopathy and rupture

Background

Recent investigation of human tissue and cells from positional tendons such as the rotator cuff has clarified the importance of inflammation in the development and progression of tendon disease. These mechanisms remain poorly understood in disease of energy-storing tendons such as the Achilles. Using tissue biopsies from patients, we investigated if inflammation is a feature of Achilles tendinopathy and rupture.

Methods

We studied Achilles tendon biopsies from symptomatic patients with either mid-portion tendinopathy or rupture for evidence of abnormal inflammatory signatures. Tendon-derived stromal cells from healthy hamstring and diseased Achilles were cultured to determine the effects of cytokine treatment on expression of inflammatory markers.

Results

Tendinopathic and ruptured Achilles highly expressed CD14+ and CD68+ cells and showed a complex inflammation signature, involving NF-κB, interferon and STAT-6 activation pathways. Interferon markers IRF1 and IRF5 were highly expressed in tendinopathic samples. Achilles ruptures showed increased PTGS2 and interleukin-8 expression. Tendinopathic and ruptured Achilles tissues expressed stromal fibroblast activation markers podoplanin and CD106. Tendon cells isolated from diseased Achilles showed increased expression of pro-inflammatory and stromal fibroblast activation markers after cytokine stimulation compared with healthy hamstring tendon cells.

Conclusions

Tissue and cells derived from tendinopathic and ruptured Achilles tendons show evidence of chronic (non-resolving) inflammation. The energy-storing Achilles shares common cellular and molecular inflammatory mechanisms with functionally distinct rotator cuff positional tendons. Differences seen in the profile of ruptured Achilles are likely to be attributable to a superimposed phase of acute inflammation and neo-vascularisation. Strategies that target chronic inflammation are of potential therapeutic benefit for patients with Achilles tendon disease.

Genetic Factors in Tendon Injury: A Systematic Review of the Literature

BACKGROUND

Tendon injury such as tendinopathy or rupture is common and has multiple etiologies, including both intrinsic and extrinsic factors. The genetic influence on susceptibility to tendon injury is not well understood.

PURPOSE

To analyze the published literature regarding genetic factors associated with tendon injury.

STUDY DESIGN

Systematic review; Level of evidence, 3.

METHODS

A systematic review of published literature was performed in concordance with the Preferred Reporting Items of Systematic Reviews and Meta-analysis (PRISMA) guidelines to identify current evidence for genetic predisposition to tendon injury. PubMed, Ovid, and ScienceDirect databases were searched. Studies were included for review if they specifically addressed genetic factors and tendon injuries in humans. Reviews, animal studies, or studies evaluating the influence of posttranscription factors and modifications (eg, proteins) were excluded.

RESULTS

Overall, 460 studies were available for initial review. After application of inclusion and exclusion criteria, 11 articles were ultimately included for qualitative synthesis. Upon screening of references of these 11 articles, an additional 15 studies were included in the final review, for a total of 26 studies. The genetic factors with the strongest evidence of association with tendon injury were those involving type V collagen A1, tenascin-C, matrix metalloproteinase-3, and estrogen-related receptor beta.

CONCLUSION

The published literature is limited to relatively homogenous populations, with only level 3 and level 4 data. Additional research is needed to make further conclusions about the genetic factors involved in tendon injury.

Biomedical Risk Factors of Achilles Tendinopathy in Physically Active People: a Systematic Review

Background

Achilles tendinopathy is the most prevalent tendon disorder in people engaged in running and jumping sports. Aetiology of Achilles tendinopathy is complex and requires comprehensive research of contributing risk factors. There is relatively little research focussing on potential biomedical risk factors for Achilles tendinopathy. The purpose of this systematic review is to identify studies and summarise current knowledge of biomedical risk factors of Achilles tendinopathy in physically active people.

Methods

Research databases were searched for relevant articles followed by assessment in accordance with PRISMA statement and standards of Cochrane collaboration. Levels of evidence and quality assessment designation were implemented in accordance with OCEBM levels of evidence and Newcastle-Ottawa Quality Assessment Scale, respectively.

Results

A systematic review of the literature identified 22 suitable articles. All included studies had moderate level of evidence (2b) with the Newcastle-Ottawa score varying between 6 and 9. The majority (17) investigated genetic polymorphisms involved in tendon structure and homeostasis and apoptosis and inflammation pathways.

Overweight as a risk factor of Achilles tendinopathy was described in five included studies that investigated non-genetic factors. COL5A1 genetic variants were the most extensively studied, particularly in association with genetic variants in the genes involved in regulation of cell-matrix interaction in tendon and matrix homeostasis. It is important to investigate connections and pathways whose interactions might be disrupted and therefore alter collagen structure and lead to the development of pathology. Polymorphisms in genes involved in apoptosis and inflammation, and Achilles tendinopathy did not show strong association and, however, should be considered for further investigation.

Conclusions

This systematic review suggests that biomedical risk factors are an important consideration in the future study of propensity to the development of Achilles tendinopathy. The presence of certain medical comorbidities and genetic markers should be considered when contemplating the aetiology of Achilles tendinopathy. Further elucidation of biomedical risk factors will aid in the understanding of tendon pathology and patient risk, thereby informing prevention and management strategies for Achilles tendinopathy.

Trial Registration

PROSPERO CRD42016036558

Investigation of angiogenesis genes with anterior cruciate ligament rupture risk in a South African population

The angiogenesis-signalling pathway is a physiological response after mechanical loading to promote matrix remodelling and thereby maintain tissue homeostasis. Studies have shown increased expression of angiogenic molecules in response to loading and in ruptured ligaments. Recently, polymorphisms within the vascular endothelial growth factor A (VEGFA) and kinase insert-domain receptor (KDR) genes were associated with risk of anterior cruciate ligament (ACL) ruptures and Achilles tendinopathy in Caucasian study groups. A case-control genetic association study was conducted on 100 controls and 98 participants with surgically-diagnosed ACL ruptures; of which 51 participants reported non-contact mechanism of injury (NON). All participants were genotyped for five functional polymorphisms: VEGFA (rs699947, rs1570360, rs2010963) and KDR (rs2071559, rs1870377). Haplotypes were inferred. In the male participants, the KDR rs2071559 AG genotype was significantly over-represented (P = 0.048, OR: 1.90, 95% CI: 1.00-3.59) in the controls. Furthermore, the GG genotype was significantly under-represented in the male controls compared to the male ACL group (P = 0.018, OR: 2.77, 95% CI: 1.17-6.55) and the male NON subgroup (P = 0.013, OR: 3.26, 95% CI: 1.24-8.58). Haplotype analysis implicated the KDR gene in all participants and in male participants separately. Collectively, these results implicate the angiogenesis-signalling pathway as a potentially key biological pathway contributing to ACL injury susceptibility.

The investigation of association between IL-1Ra and ACE I/D polymorphisms in carpal tunnel syndrome

BACKGROUND

Carpal tunnel syndrome (CTS) is a common neurologic impairment caused by injury on the median nerve in the wrist, characterized by pain and loss of sensory. CTS usually occurs through three factors, such as a mechanical pressure on median nerve, immunologic changes, and oxidative stress. The aim of this study was to evaluate the influence of interleukin-1 receptor antagonist (IL-1Ra) and angiotensin-converting enzyme (ACE) I/D polymorphisms on the susceptibility of patients to the CTS.

METHODS

One hundred fifty-eight patients with CTS and 151 healthy controls were enrolled in this study. Each patient was analyzed according to diseases symptoms, such as gender, a positive Tinel's sign, a positive Phalen maneuver, disease sides, EMG findings, and clinical stage. We applied the polymerase chain reaction (PCR) to determine the polymorphisms of IL-1Ra and ACE I/D.

RESULTS

The statistically significant relation was not found between IL-1Ra, ACE I/D polymorphisms and CTS (respectively, P>.05; P>.05, OR: 1.51, CI: 0.82-1.61). Additionally, in the result of the statistical analysis compared with gene polymorphisms and clinical characteristics, we did not find any correlation (P>.05).

CONCLUSIONS

Our findings showed that there are no associations of IL-1Ra and ACE I/D polymorphisms with susceptibility of a person for the development of CTS. So, it means that these polymorphisms do not create a risk for the development of CTS. Further studies with larger populations will be required to confirm these findings in different study populations.

Noninsertional Achilles Tendinopathy Pathologic Background and Clinical Examination

The term tendinopathy includes a series of pathologies, all of which have a combination of pain, swelling, and impaired performance. The terms tendinosis, tendinitis and peritendinitis are all within the main heading of tendinopathy; this terminology provides a more accurate understanding of the condition and highlights the uniformity of clinical findings while distinguishing the individual histopathological findings of each condition. Understanding the clinical features and the underlying histopathology leads to a more accurate clinical diagnosis and subsequent treatment selection. Misuse of the term tendinitis can lead to the underestimation of chronic degenerative nature of many tendinopathies, affecting the treatment selection.

Genome-wide association screens for Achilles tendon and ACL tears and tendinopathy

Achilles tendinopathy or rupture and anterior cruciate ligament (ACL) rupture are substantial injuries affecting athletes, associated with delayed recovery or inability to return to competition. To identify genetic markers that might be used to predict risk for these injuries, we performed genome-wide association screens for these injuries using data from the Genetic Epidemiology Research on Adult Health and Aging (GERA) cohort consisting of 102,979 individuals. We did not find any single nucleotide polymorphisms (SNPs) associated with either of these injuries with a p-value that was genome-wide significant (p<5x10-8). We found, however, four and three polymorphisms with p-values that were borderline significant (p<10-6) for Achilles tendon injury and ACL rupture, respectively. We then tested SNPs previously reported to be associated with either Achilles tendon injury or ACL rupture. None showed an association in our cohort with a false discovery rate of less than 5%. We obtained, however, moderate to weak evidence for replication in one case; specifically, rs4919510 in MIR608 had a p-value of 5.1x10-3 for association with Achilles tendon injury, corresponding to a 7% chance of false replication. Finally, we tested 2855 SNPs in 90 candidate genes for musculoskeletal injury, but did not find any that showed a significant association below a false discovery rate of 5%. We provide data containing summary statistics for the entire genome, which will be useful for future genetic studies on these injuries.

Tendinopathy in diabetes mellitus patients-Epidemiology, pathogenesis, and management

Chronic tendinopathy is a frequent and disabling musculo-skeletal problem affecting the athletic and general populations. The affected tendon is presented with local tenderness, swelling, and pain which restrict the activity of the individual. Tendon degeneration reduces the mechanical strength and predisposes it to rupture. The pathogenic mechanisms of chronic tendinopathy are not fully understood and several major non-mutually exclusive hypotheses including activation of the hypoxia-apoptosis-pro-inflammatory cytokines cascade, neurovascular ingrowth, increased production of neuromediators, and erroneous stem cell differentiation have been proposed. Many intrinsic and extrinsic risk/causative factors can predispose to the development of tendinopathy. Among them, diabetes mellitus is an important risk/causative factor. This review aims to appraise the current literature on the epidemiology and pathology of tendinopathy in diabetic patients. Systematic reviews were done to summarize the literature on (a) the association between diabetes mellitus and tendinopathy/tendon tears, (b) the pathological changes in tendon under diabetic or hyperglycemic conditions, and (c) the effects of diabetes mellitus or hyperglycemia on the outcomes of tendon healing. The potential mechanisms of diabetes mellitus in causing and exacerbating tendinopathy with reference to the major non-mutually exclusive hypotheses of the pathogenic mechanisms of chronic tendinopathy as reported in the literature are also discussed. Potential strategies for the management of tendinopathy in diabetic patients are presented.

Modulators of the extracellular matrix and risk of anterior cruciate ligament ruptures

OBJECTIVES

The extracellular matrix (ECM) of ligaments continuously undergoes remodelling in order to maintain tissue homeostasis. Several key mediators of ECM remodelling were chosen for investigation in the present study. It is thought that polymorphisms within genes encoding signalling molecules may contribute to inter-individual variation in the responses to mechanical loading, potentially altering risk of injury.

DESIGN

A genetic association study was conducted on 232 asymptomatic controls (CON) and 234 participants with surgically diagnosed anterior cruciate ligament (ACL) ruptures; of which 135 participants reported a non-contact mechanism of injury (NON subgroup).

METHODS

All participants were genotyped for ten variants in eight genes encoding ECM remodelling proteins. Haplotypes and allele combinations were also inferred.

RESULTS

The CASP8 rs3834129 ins allele was significantly over-represented in the male CON group compared to the male NON subgroup (p=0.047, OR: 1.46, 95% CI: 1.01-2.12). In female participants, the IL1B rs16944 TT genotype was significantly under-represented in the CON group compared to the NON subgroup (p=0.039, OR: 3.06, 95% CI: 1.09-8.64). Haplotype analysis revealed an under-representation of the CASP8 rs3834129-rs1045485 del-G haplotype in the CON group compared to both the ACL group (p=0.042; haplo.score:2.03) and the NON subgroup (p=0.037; haplo.score:2.09). Furthermore, following a pathway-based approach, genetic variants involved in the cell signalling cascade were associated with ACL injury risk.

CONCLUSIONS

The novel independent associations and allele combinations observed implicate the apoptosis and cell signalling cascades as potential contributors to ACL injury susceptibility. Furthermore, these genetic variants may potentially modulate ECM remodelling in response to loading and ultimately contribute to ligament capacity.

Polymorphisms within the COL5A1 gene and regulators of the extracellular matrix modify the risk of Achilles tendon pathology in a British case-control study

Several genetic loci have been associated with risk of Achilles tendon pathology (ATP) within South African and Australian populations. The aim of this study was, therefore, to evaluate eight previously implicated genetic variants in an independent British population. A total of 130 asymptomatic controls (CON) and 112 participants clinically diagnosed with ATP comprising 87 individuals with chronic Achilles tendinopathy (TEN) and 25 with Achilles tendon ruptures (RUP) were included. All participants were genotyped for variants within the COL5A1, MIR608, IL-1β, IL-6 and CASP8 genes. Primary findings implicated COL5A1 and CASP8. Three inferred allele combinations constructed from COL5A1 rs12722, rs3196378 and rs71746744 were identified as risk modifiers. The T-C-D combination was associated with increased risk of ATP (P = 0.023) and RUP (P < 0.001), the C-A-I combination was associated with increased risk of ATP (P = 0.011), TEN (P = 0.011) and RUP (P = 0.011) and the C-C-D combination was associated with decreased risk of ATP (P = 0.011) and RUP (P = 0.004). The CASP8 rs3834129 DD genotype was associated with decreased risk of TEN (P = 0.020, odds ratio: 0.45, 95% confidence interval: 0.22-0.90) and the CASP8 I-G (rs3834129-rs1045485) inferred allele combination was associated with increased risk of TEN (P = 0.031). This study further highlights the importance of polymorphisms within COL5A1 and CASP8 in the aetiology of ATP.

Semantic interrogation of a multi knowledge domain ontological model of tendinopathy identifies four strong candidate risk genes

Tendinopathy is a multifactorial syndrome characterised by tendon pain and thickening, and impaired performance during activity. Candidate gene association studies have identified genetic factors that contribute to intrinsic risk of developing tendinopathy upon exposure to extrinsic factors. Bioinformatics approaches that data-mine existing knowledge for biological relationships may assist with the identification of candidate genes. The aim of this study was to data-mine functional annotation of human genes and identify candidate genes by ontology-seeded queries capturing the features of tendinopathy. Our BioOntological Relationship Graph database (BORG) integrates multiple sources of genomic and biomedical knowledge into an on-disk semantic network where human genes and their orthologs in mouse and rat are central concepts mapped to ontology terms. The BORG was used to screen all human genes for potential links to tendinopathy. Following further prioritisation, four strong candidate genes (COL11A2, ELN, ITGB3, LOX) were identified. These genes are differentially expressed in tendinopathy, functionally linked to features of tendinopathy and previously implicated in other connective tissue diseases. In conclusion, cross-domain semantic integration of multiple sources of biomedical knowledge, and interrogation of phenotypes and gene functions associated with disease, may significantly increase the probability of identifying strong and unobvious candidate genes in genetic association studies.

Towards an Understanding of the Genetics of Tendinopathy

To date, more than 18 genomic intervals, which underpin the complex myriad of extracellular matrix interactions of tendons, have been implicated in risk models for tendinopathy. It is these relationships that most likely regulate the tissue's response to loading and unloading, thereby dictating the overall capacity of tendons and influencing injury susceptibility. The evidence suggesting a genetic contribution to the susceptibility of sustaining a tendon injury is growing. However, only a few of the loci have been repeated in independent studies, of which some have included a range of musculoskeletal soft tissues injuries. Case-control study designs can be effective in capturing risk, provided that the cases and controls are equally well-defined and carefully considered. The genome consists of 3.6 × 10(9) sequences and therefore we realise that we are far from decoding all the genomic signatures. We are indeed fortunate to be living in such exciting times where high-throughput technologies are at our disposal. Through collaboration, our chances of harnessing these "omics" technologies to further our clinical understanding of tendinopathy will increase.

Extracellular matrix proteins interact with cell-signaling pathways in modifying risk of achilles tendinopathy

The aim of this study was to investigate interactions between variants within genes encoding components of the collagen fibril and components of cell-signaling pathways within the extracellular matrix, and determine the relative contribution of these variants to Achilles tendinopathy risk in a polygenic model. A total of 339 asymptomatic control participants and 179 participants clinically diagnosed with Achilles tendinopathy were genotyped for variants within six genes encoding components of the collagen fibril and three genes encoding components of cell-signaling pathways. Logistic regression, stepwise selection, and receiver operating characteristic curve (ROC) analysis was used to select and evaluate genetic interactions and determine the relative contribution of these variants to overall genetic risk. The strongest, best fit polygenic risk model included the variables sex, three COL27A1 variants (rs4143245; rs1249744; rs946053), COL5A1 rs12722, CASP8 rs1045485, and CASP8 rs2824129 with an area under the ROC curve of 0.737 and the maximum sum of sensitivity and specificity indicators equal to 134%. Significant interactions between genes encoding components of the collagen fibril and genes encoding components of the cell-signaling pathways modify risk of Achilles tendinopathy.

Applying personal genetic data to injury risk assessment in athletes

Recent studies have identified genetic markers associated with risk for certain sports-related injuries and performance-related conditions, with the hope that these markers could be used by individual athletes to personalize their training and diet regimens. We found that we could greatly expand the knowledge base of sports genetic information by using published data originally found in health and disease studies. For example, the results from large genome-wide association studies for low bone mineral density in elderly women can be re-purposed for low bone mineral density in young endurance athletes. In total, we found 124 single-nucleotide polymorphisms associated with: anterior cruciate ligament tear, Achilles tendon injury, low bone mineral density and stress fracture, osteoarthritis, vitamin/mineral deficiencies, and sickle cell trait. Of these single nucleotide polymorphisms, 91% have not previously been used in sports genetics. We conducted a pilot program on fourteen triathletes using this expanded knowledge base of genetic variants associated with sports injury. These athletes were genotyped and educated about how their individual genetic make-up affected their personal risk profile during an hour-long personal consultation. Overall, participants were favorable of the program, found it informative, and most acted upon their genetic results. This pilot program shows that recent genetic research provides valuable information to help reduce sports injuries and to optimize nutrition. There are many genetic studies for health and disease that can be mined to provide useful information to athletes about their individual risk for relevant injuries.

Achilles tendon injuries in elite athletes: lessons in pathophysiology from their equine counterparts

Superficial digital flexor tendon (SDFT) injury in equine athletes is one of the most well-accepted, scientifically supported companion animal models of human disease (i.e., exercise-induced Achilles tendon [AT] injury). The SDFT and AT are functionally and clinically equivalent (and important) energy-storing structures for which no equally appropriate rodent, rabbit, or other analogues exist. Access to equine tissues has facilitated significant advances in knowledge of tendon maturation and aging, determination of specific exercise effects (including early life), and definition of some of the earliest stages of subclinical pathology. Access to human surgical biopsies has provided complementary information on more advanced phases of disease. Importantly, equine SDFT injuries are only a model for acute ruptures in athletes, not the entire spectrum of human tendonopathy (including chronic tendon pain). In both, pathology begins with a potentially prolonged phase of accumulation of (subclinical) microdamage. Recent work has revealed remarkably similar genetic risk factors, including further evidence that tenocyte dysfunction plays an active role. Mice are convenient but not necessarily accurate models for multiple diseases, particularly at the cellular level. Mechanistic studies, including tendon cell responses to combinations of exercise-associated stresses, require a more thorough investigation of cross-species conservation of key stress pathway auditors. Molecular evidence has provided some context for the poor performance of mouse models; equines may provide better systems at this level. The use of horses may be additionally justifiable based on comparable species longevity, lifestyle factors, and selection pressure by similar infectious agents (e.g., herpesviruses) on general cell stress pathway evolution.

The association of genes involved in the angiogenesis-associated signaling pathway with risk of anterior cruciate ligament rupture

Angiogenesis-associated signaling is a fundamental component in the remodeling of the extracellular matrix in response to loading. Genes encoding protein components within this signaling cascade are therefore suitable candidates for investigation into ACL injury susceptibility: namely, vascular endothelial growth factor A isoform (VEGFA), kinase insert-domain receptor (KDR), nerve growth factor (NGF), and hypoxia inducible factor-1α (HIF1A). A case-control genetic association study was conducted on 227 asymptomatic control participants and 227 participants with surgically diagnosed ACL ruptures of which 126 participants reported a non-contact mechanism of rupture. All participants were genotyped for seven polymorphisms within the four genes. The VEGFA rs699947 CC genotype (p=0.010, OR: 1.92, 95% CI: 1.17-3.17) was significantly over-represented within participants with non-contact ACL ruptures. The VEGFA rs1570360 GA genotype was significantly over-represented in the CON group (p=0.007, OR: 1.70, 95% CI: 1.16-2.50). Furthermore, the KDR rs2071559 GA genotype was significantly over-represented in the female controls (p=0.023, OR: 2.16, 95% CI: 1.11-4.22). Inferred haplotype analyses also implicated genomic regions spanning the VEGFA and KDR genes. These novel findings suggest that regions within VEGFA and KDR may be implicated in the pathophysiology of ACL ruptures; highlighting the potential biological significance of angiogenesis-associated signaling in the aetiology of ACL ruptures.

The pathogenesis of Achilles tendinopathy: a systematic review

Achilles tendinopathy is a degenerative, not an inflammatory, condition. It is prevalent in athletes involved in running sports. A systematic literature review on Achilles tendon tendinopathy has been performed according to the intrinsic (age, sex, body weight, tendon temperature, systemic diseases, muscle strength, flexibility, previous injuries and anatomical variants, genetic predisposition and blood supply) and extrinsic risk factors (drugs and overuse), which can cause tendon suffering and degeneration. Different theories have been found: Neurogenic, Angiogenic, Impingement and "Iceberg" Hypotheses. Multiple databases were utilized for articles published between 1964 and 2013. The different hypothesis were analyzed, differently considering those concerning the pathogenesis of tendinopathy and those concerning the etiology of complaints in patients. This review of the literature demonstrates the heterogeneity of Achilles tendinopathy pathogenesis. Various risk factors have been identified and have shown an interaction between them such as genes, age, circulating and local cytokine production, sex, biomechanics and body composition.

Tendon healing, edema, and resistance to flexor tendon gliding: clinical implications

Early flexor tendon healing is characterized by peak cellular apoptosis of both inflammatory and tendon cells in the first week, followed by progressively greater tenocyte proliferation in the second and third weeks. Tenocyte apoptosis is a predominant event, but proliferation of tenocytes is minimal in the middle and late healing periods. Edematous subcutaneous tissues, edema of the tendon, the intact annular pulleys, and extensor tendons all greatly contribute to the resistance. Careful consideration of the contributing factors and dynamics offers insight into strategies to reduce repair rupture and maximize tendon gliding through surgery and postoperative motion protocols.

Pathology of the tendo Achillis: do our genes contribute?

The incidence of acute and chronic conditions of the tendo Achillis appear to be increasing. Causation is multifactorial but the role of inherited genetic elements and the influence of environmental factors altering gene expression are increasingly being recognised. Certain individuals' tendons carry specific variations of genetic sequence that may make them more susceptible to injury. Alterations in the structure or relative amounts of the components of tendon and fine control of activity within the extracellular matrix affect the response of the tendon to loading with failure in certain cases. This review summarises present knowledge of the influence of genetic patterns on the pathology of the tendo Achillis, with a focus on the possible biological mechanisms by which genetic factors are involved in the aetiology of tendon pathology. Finally, we assess potential future developments with both the opportunities and risks that they may carry.

Polymorphic variation within the ADAMTS2, ADAMTS14, ADAMTS5, ADAM12 and TIMP2 genes and the risk of Achilles tendon pathology: a genetic association study

OBJECTIVES

Achilles tendon pathology (ATP) is a multifactorial condition for which genetic risk factors have been identified. The ADAMTS, ADAM12 and TIMP2 genes encode enzymes that are important regulators of tendon homeostasis. ADAMTS2 and ADAMTS14 proteins are procollagen N-propeptidases for pro-collagen type I, type II, and type III. ADAMTS2, like COL5A1, has been linked to Ehlers-Danlos syndrome. Variants within ADAMTS5 and ADAM12 have been associated with osteoarthritis. TIMP2, a metalloprotease inhibitor, maintains homeostasis in the ECM by inhibiting ADAM, ADAMTS and MMP functions. We sought to determine whether single nucleotide polymorphisms (SNPs) within the ADAMTS2, ADAMTS5, ADAMTS14, ADAM12 and TIMP2 genes were associated with the risk of ATP in two independent populations.

DESIGN

213 (115 ATP cases and 98 asymptomatic controls) South African Caucasian participants and 209 (60 ATP cases and 149 asymptomatic controls) Australian Caucasian participants were recruited for this case-control genetic association study.

METHODS

All participants were genotyped using TaqMan technology for the ADAMTS2 rs1054480, ADAMTS5 rs226794, ADAMTS14 rs4747096, ADAM12 rs3740199, and TIMP2 rs4789932 SNPs.

RESULTS

We report for the first time a significant (p=0.016) genotypic association between the TIMP2 rs4789932 variant and ATP in a combined Caucasian cohort. We also identify an interaction between the ADAMTS14 rs4747096 variant and age of onset of ATP (p=0.024).

CONCLUSIONS

Our data show that DNA sequence variation within the TIMP2 gene is a risk factor for ATP in Caucasians. Furthermore, carriage of the ADAMTS14 rs4747096 GG variant appears to delay onset of the injury in the ATP group.

Polymorphisms within the COL5A1 3'-UTR that alters mRNA structure and the MIR608 gene are associated with Achilles tendinopathy

COL5A1 encodes for the α1 chain of type V collagen, an important regulator of fibril assembly in tendons, ligaments and other connective tissues. A polymorphism (rs12722) within the functional COL5A1 3'-untranslated region (UTR) has been shown to associate with chronic Achilles tendinopathy and other exercise-related phenotypes. The COL5A1 3'-UTR contains several putative cis-acting elements including a functional Hsa-miR-608 binding site. The aim of this study was to determine whether previously uncharacterized polymorphisms within a functional region of the COL5A1 3'-UTR or the MIR608 gene are associated with chronic Achilles tendinopathy. The effect of these COL5A1 3'-UTR polymorphisms on the 3'-UTR predicted mRNA secondary structure was also investigated. One hundred and sixty Caucasian chronic Achilles tendinopathic and 342 control participants were genotyped for the COL5A1 3'-UTR markers rs71746744, rs16399 and rs1134170, as well as marker rs4919510 within MIR608. All four genetic markers were independently associated with chronic Achilles tendinopathy. The COL5A1 polymorphisms appear to alter the predicted secondary structure of the 3'-UTR. We propose that the secondary structure plays a role in the regulation of the COL5A1 mRNA stability and by implication type V collagen production.