Repetitive mechanical stretching modulates transforming growth factor-β induced collagen synthesis and apoptosis in human patellar tendon fibroblasts

In vitro collagen biomarkers in mechanically stimulated human tendon cells: a systematic review

OBJECTIVE

The aim of this study was to comprehensively examine and summarize the available in vitro evidence regarding the relationship between mechanical stimulation and biomarkers of collagen synthesis in human-derived tendon cells.

METHODS

Systematic review with narrative analyses and risk of bias assessment guided by the Health Assessment and Translation tool. The electronic databases MEDLINE (Ovid), EMBASE (Ovid), CENTRAL (Ovid) and COMPENDEX (Engineering Village) were systematically searched from inception to 3 August 2023. Inclusion criteria encompassed English language, original experimental, or quasi-experimental in vitro publications that subjected human tendon cells to mechanical stimulation, with collagen synthesis (total collagen, type I, III, V, XI, XII, and XIV) and related biomarkers (matrix metalloproteinases, transforming growth factor β, scleraxis, basic fibroblast growth factor) as outcomes.

RESULTS

Twenty-one publications were included. A pervasive definite high risk of bias was evident in all included studies. Owing to incomplete outcome reporting and heterogeneity in mechanical stimulation protocols, planned meta-analyses were unfeasible. Reviewed data suggested that human tendon cells respond to mechanical stimulation with increased synthesis of collagen (e.g., COL1A1, procollagen, total soluble collagen, etc.), scleraxis and several matrix metalloproteinases. Results also indicate that mechanical stimulation dose magnitude may influence synthesis in several biomarkers.

CONCLUSIONS

A limited number of studies, unfortunately characterized by a definite high risk of bias, suggest that in vitro mechanical stimulation primarily increases type I collagen synthesis by human tendon cells. Findings from this systematic review provide researchers and clinicians with biological evidence concerning the possible beneficial influence of exercise and loading on cellular-level tendon adaptation.

Transforming growth factor-β signalling pathway in tendon healing

Transforming growth factor-β(TGF-β) plays an important but diverse role in tendon injuries, such as collagen synthesis, cell proliferation, cell differentiation, and cell adhesion, leading to tendon healing and tendon fibrosis. In the well-known canonical TGF-β signalling pathway, TGF-β activates Smad signalling through its two cell surface receptors, which leads to Smad-mediated transcriptional regulation and is also regulated by inhibitory Smads, forming a negative feedback regulatory pathway. In the context of the canonical TGF-β signalling mechanism mediated by Smad, the activated receptors also send signals through other signal transducers, which in the backdrop of TGF-β signaling are collectively known as non-Smad signalling pathways. Activated TGF-β binds to the receptor and acts through these signalling pathways. Understanding the mechanism of the TGF-β signalling pathway and its role in tendon repair is of great significance for targeting the TGF-β signalling pathway to accelerate tendon healing and reduce tendon fibrosis.

Ultrastructural and Molecular Development of the Myotendinous Junction Triggered by Stretching Prior to Resistance Exercise

The myotendinous junction (MTJ) is a highly specialized region of the locomotor apparatus. Here, we investigated the ultrastructural and molecular effects in the MTJ region after static stretching prior to the ladder-based resistance training. Thirty-two male, 60-day old Wistar rats were divided into four groups: Sedentary, Resistance Training, Stretching, and Stretching-Resistance Training. The gastrocnemius muscle was processed for transmission electron microscopy techniques and Western blot assay. We observed that the static stretching prior to the ladder-based resistance training increased the MTJ components, the fibroblast growth factor (FGF)-2 and FGF-6 protein expression. Also, we demonstrated the lower transforming growth factor expression and no difference in the lysyl oxidase expression after combined training. The MTJ alterations in response to combined training demonstrate adaptive mechanisms which can be used for the prescription or development of methods to reduce or prevent injuries in humans and promote the myotendinous interface benefit.

Transfection of TGF-β shRNA by Using Ultrasound-targeted Microbubble Destruction to Inhibit the Early Adhesion Repair of Rats Wounded Achilles Tendon In vitro and In vivo

BACKGROUND

Tendon injury is a major orthopedic disorder. Ultrasound-targeted microbubble destruction (UTMD) provides a promising method for gene transfection, which can be used for the treatment of injured tendons.

OBJECTIVE

The purpose of this study was to investigate the optimal transforming growth factor beta (TGF-β) short hairpin RNA (shRNA) sequence and transfection conditions using UTMD in vitro and to identify its ability for inhibiting the early adhesion repair of rats wounded achilles tendons in vivo.

METHODS

The optimal sequence was selected analyzing under a fluorescence microscope and quantitative real-time reverse transcription polymerase chain reaction in vitro. In vivo, 40 rats with wounded Achilles tendons were divided into five groups: (1) control group, (2) plasmid group (3) plasmid + ultrasound group, (4) plasmid + microbubble group, (5) plasmid + microbubble + ultrasound group, and were euthanized at 14 days post treatment. TGF-β expression was evaluated using adhesion scores and pathological examinations.

RESULTS

The optimal condition for UTMD delivery in vitro was 1W/cm2 of output intensity and a 30% duty cycle with 60 s irradiation time (P < 0.05). The transfection efficiency of the plasmid in group 5 was higher than that in other groups (P < 0.05). Moreover, the lowest adhesion index score and the least expression of TGF-β were shown in group 5 (P < 0.05). When compared with the other groups, group 5 had a milder inflammatory reaction.

CONCLUSION

The results suggested that UTMD delivery of TGF-β shRNA offers a promising treatment approach for a tendon injury in vivo.

Risk modelling further implicates the angiogenesis pathway in anterior cruciate ligament ruptures

The aim of this study was to explore the interactions between the interleukins and the angiogenesis signalling pathway, following a pathway-based approach. Statistical modelling tools were used to develop a preliminary polygenic risk assessment model for anterior cruciate ligament (ACL) ruptures, incorporating the angiogenesis signalling genes (VEGFA and KDR) and interleukins (IL1B, IL6, IL6R) which also function to regulate angiogenesis. Multivariate logistic regression analysis was used to identify the most informative contributors to ACL rupture risk from a range of eleven potential intrinsic risk factors: age, sex, BMI and eight genetic polymorphisms within five genes, namely, IL1B rs16944 C/T, IL6 rs1800795 G/C, IL6R rs2228145 C/A, VEGFA rs699947 C/A, VEGFA rs1570360 G/A, VEGFA rs2010963 C/G, KDR rs2071559 A/G and KDR rs1870377 T/A. A total of 232 asymptomatic controls (CON) and 234 participants with surgically diagnosed ACL ruptures, of which 135 participants reported a non-contact mechanism of injury (NON subgroup), were previously genotyped for the selected polymorphisms. The polygenic risk model identified the VEGFA rs699947 CC genotype (p = 0.024, odds ratio (OR): 3.35, 95% confidence interval (CI): 1.17-9.62), VEGFA rs2010963 GC genotype (p = 0.049, OR: 2.43, 95% CI: 1.00-5.87), age (p = 0.011, OR: 0.97, 95% CI: 0.95-0.99) and BMI (p = 0.009, OR:1.09, 95% CI: 0.57-2.11) as the most significant predictors of ACL rupture risk from the data included. The results of this study highlight VEGFA, age and BMI as biologically significant components of this network requiring further investigation in the context of musculoskeletal soft tissue injury risk. HighlightsThe findings of this study highlight the VEGFA gene, age and BMI as biologically significant contributors to ACL rupture susceptibility.Upon further validation of these risk factors, they may be included in genetic risk assessment tools to design pre-habilitation strategies, prescribe appropriate treatment strategies after injury or to assess how an individual is likely to respond to load.Polygenic risk models aid in highlighting the components of the complex ECM remodelling pathway requiring further investigation, using a multidisciplinary approach.VEGFA is a key angiogenic protein contributing to ECM homeostasis and may therefore have potential therapeutic implications that need to be explored.

Proliferation and tenogenic differentiation of bone marrow mesenchymal stem cells in a porous collagen sponge scaffold

BACKGROUND

Collagen is one of the most commonly used natural biomaterials for tendon tissue engineering. One of the possible practical ways to further enhance tendon repair is to combine a porous collagen sponge scaffold with a suitable growth factor or cytokine that has an inherent ability to promote the recruitment, proliferation, and tenogenic differentiation of cells. However, there is an incomplete understanding of which growth factors are sufficient and optimal for the tenogenic differentiation of rat bone marrow mesenchymal stem cells (BMSCs) in a collagen sponge-based 3D culture system.

AIM

To identify one or more ideal growth factors that benefit the proliferation and tenogenic differentiation of rat BMSCs in a porous collagen sponge scaffold.

METHODS

We constructed a 3D culture system based on a type I collagen sponge scaffold. The surface topography of the collagen sponge scaffold was observed by scanning electron microscopy. Primary BMSCs were isolated from Sprague-Dawley rats. Cell survival on the surfaces of the scaffolds with different growth factors was assessed by live/dead assay and CCK-8 assay. The mRNA and protein expression levels were confirmed by quantitative real-time polymerase chain reaction and Western blot, respectively. The deposited collagen was assessed by Sirius Red staining.

RESULTS

Transforming growth factor β1 (TGF-β1) showed great promise in the tenogenic differentiation of BMSCs compared to growth differentiation factor 7 (GDF-7) and insulin-like growth factor 1 (IGF-1) in both the 2D and 3D cultures, and the 3D culture enhanced the differentiation of BMSCs into tenocytes well beyond the level of induction in the 2D culture after TGF-β1 treatment. In the 2D culture, the proliferation of the BMSCs showed no significant changes compared to the control group after TGF-β1, IGF-1, or GDF-7 treatment. However, TGF-β1 and GDF-7 could increase the cell proliferation in the 3D culture. Strangely, we also found more dead cells in the BMSC-collagen sponge constructs that were treated with TGF-β1. Moreover, TGF-β1 promoted more collagen deposition in both the 2D and 3D cultures.

CONCLUSION

Collagen sponge-based 3D culture with TGF-β1 enhances the responsiveness of the proliferation and tenogenic differentiation of rat BMSCs.

Fibroblasts From Common Anterior Cruciate Ligament Tendon Grafts Exhibit Different Biologic Responses to Mechanical Strain

BACKGROUND

Different tendons are chosen for anterior cruciate ligament (ACL) reconstruction based on perceived advantages and disadvantages, yet there is a relative paucity of information regarding biologic responsiveness of commonly used tendon grafts to mechanical strain.

PURPOSE

To evaluate the in vitro responses of graft fibroblasts derived from tendons used for ACL reconstruction to clinically relevant strain levels.

STUDY DESIGN

Controlled laboratory study.

METHODS

Twelve quadriceps tendons (QTs), 12 patellar tendons (PTs), and 9 hamstring tendons (HTs) were harvested from skeletally mature dogs (n = 16). Tendon fibroblasts were isolated and seeded onto BioFlex plates (1 × 10⁵ cells/well). Cells were subjected to 3 strain conditions (stress deprivation, 0%; physiologic, 4%; high, 10%) for 5 days. Media were collected for proinflammatory and metabolic assays. RNA was extracted for gene expression analysis using real-time reverse transcription polymerase chain reaction.

RESULTS

Stress deprivation elicited significantly higher metabolic activity from HT and PT cells than from QT cells (P < .001 and P = .001, respectively). There were no differences in metabolic activity among all 3 graft fibroblasts at physiologic and high strain. COL-1 expression was significantly higher in PT versus HT during physiologic strain (P = .007). No significant differences with COL-3 expression were seen. TIMP-1 (P = .01) expression was higher in PT versus HT under physiologic strain. Scleraxis expression was higher in PT versus HT (P = .007) under physiologic strain. A strain-dependent increase in PGE2 levels occurred for all grafts. At physiologic strain conditions, HT produced significantly higher levels of PGE2 versus QT (P < .001) and PT (P = .005).

CONCLUSION

Fibroblasts from common ACL graft tissues exhibited different metabolic responses to mechanical strain. On the basis of these data, we conclude that early production of extracellular matrix and proinflammatory responses from ACL grafts are dependent on mechanical loading and graft source.

CLINICAL RELEVANCE

Graft-specific differences in ACL reconstruction outcomes are known to exist. Our results suggest that there are differences in the biologic responsiveness of cells from the tendon grafts used in ACL reconstruction, which are dependent on strain levels and graft source. The biologic properties of the tissue used for ACL reconstruction should be considered when selecting graft source.

In Vivo and In Vitro Mechanical Loading of Mouse Achilles Tendons and Tenocytes-A Pilot Study

Mechanical force is a key factor for the maintenance, adaptation, and function of tendons. Investigating the impact of mechanical loading in tenocytes and tendons might provide important information on in vivo tendon mechanobiology. Therefore, the study aimed at understanding if an in vitro loading set up of tenocytes leads to similar regulations of cell shape and gene expression, as loading of the Achilles tendon in an in vivo mouse model. In vivo: The left tibiae of mice (n = 12) were subject to axial cyclic compressive loading for 3 weeks, and the Achilles tendons were harvested. The right tibiae served as the internal non-loaded control. In vitro: tenocytes were isolated from mice Achilles tendons and were loaded for 4 h or 5 days (n = 6 per group) based on the in vivo protocol. Histology showed significant differences in the cell shape between in vivo and in vitro loading. On the molecular level, quantitative real-time PCR revealed significant differences in the gene expression of collagen type I and III and of the matrix metalloproteinases (MMP). Tendon-associated markers showed a similar expression profile. This study showed that the gene expression of tendon markers was similar, whereas significant changes in the expression of extracellular matrix (ECM) related genes were detected between in vivo and in vitro loading. This first pilot study is important for understanding to which extent in vitro stimulation set-ups of tenocytes can mimic in vivo characteristics.

Are TNC gene variants associated with anterior cruciate ligament rupture susceptibility?

OBJECTIVES

To investigate the role of inter-individual variations in a particular glycoprotein, TNC, and its potential contribution to anterior cruciate ligament (ACL) injury susceptibility in Polish Caucasian participants. ACL rupture is one of the most prevalent and severe knee injury that predominantly occurs during sports participation, primarily via a non-contact mechanism. Several polymorphisms in genes encoding glycoproteins either independently or as allelic combinations, modulate the risk of musculoskeletal soft tissue injuries. Specifically, the TNC rs1330363 (C>T), rs2104772 (T>A) and rs13321 (G>C) variants, independently or in haplotype combinations, were analysed in this context.

DESIGN

Case-control genetic association study.

METHODS

A group of 421 physically active, unrelated participants were recruited where 229 individuals with surgically diagnosed primary ACL rupture and 192 apparently healthy participants without any history of ACL injuries. Participants were genotyped for the above variants.

RESULTS

Genotype and allele frequencies of TNC variants did not differ between cases and controls. Haplotype analysis revealed no association between TNC and predisposition to ACL rupture.

CONCLUSIONS

Our analyses did not reveal a significant association between these TNC variants and risk of ACL rupture in Polish Caucasian participants.

Construction of tendon replacement tissue based on collagen sponge and mesenchymal stem cells by coupled mechano-chemical induction and evaluation of its tendon repair abilities

Tissue engineering is an ideal therapeutic strategy for the development of functional tendon replacement tissue for tendon repair in the clinic. Currently, the synergistic roles of mechano-chemical factors and the mechanisms involved in tendon repair and regeneration are not fully understood. In this study, we developed a three-dimensional (3D) culture system based on a silicone chamber and collagen sponge scaffold that can deliver cyclic mechanical stretch and biochemical stimulation to bone marrow-derived mesenchymal stem cells (BMSCs) seeded on the scaffold. We found that the combined stimulation of cyclic stretch and transforming growth factor beta 1 (TGF-β1) treatment not only increased cell viability but also synergistically promoted the differentiation of BMSCs into tenocytes in a 3D culture environment. Meanwhile, the combined stimulation increased the Young's modulus of the BMSC-collagen sponge constructs by reducing the porosity of the scaffold compared to the non-treated constructs. Furthermore, a rat Achilles tendon in situ repair experiment showed that enhanced tendon regeneration was achieved using the BMSC-collagen sponge construct combined with cyclic stretch and TGF-β1, as confirmed by Achilles functional index (AFI) measurement, morphological observation, histological analysis, and mechanical testing. These results suggest that this approach could offer a practical benefit in tendon healing and future tendon tissue engineering.

STATEMENT OF SIGNIFICANCE

This study aims to disclose the crucial roles of the coupled induction by mechano-chemical stimulation in tendon tissue engineering and clarifies their collaborative control mechanisms. We developed a three-dimensional (3D) culture system based on a silicone chamber and collagen sponge scaffold that could deliver cyclic mechanical stretch and biochemical stimulation to bone marrow-derived mesenchymal stem cells (BMSCs). We found that the combined stimulation of cyclic stretch and transforming growth factor beta 1 (TGF-β1) could result in an improvement of tissue-engineered construct for enhancing tendon healing. These results suggest that this approach could offer a practical benefit in tendon healing and future tendon tissue engineering.

Improving tissue expansion protocols through computational modeling

Tissue expansion is a common technique in reconstructive surgery used to grow skin in vivo for correction of large defects. Despite its popularity, there is a lack of quantitative understanding of how stretch leads to growth of new skin. This has resulted in several arbitrary expansion protocols that rely on the surgeon's personal training and experience rather than on accurate predictive models. For example, choosing between slow or rapid expansion, or small or large inflation volumes remains controversial. Here we explore four tissue expansion protocols by systematically varying the inflation volume and the protocol duration in a porcine model. The quantitative analysis combines three-dimensional photography, isogeometric kinematics, and finite growth theory. Strikingly, all four protocols generate similar peak stretches, but different growth patterns: Smaller filling volumes of 30 ml per inflation did not result in notable expander-induced growth neither for the short nor for the long protocol; larger filling volumes of 60 ml per inflation trigger skin adaptation, with larger expander-induced growth in regions of larger stretch, and more expander-induced growth for the 14-day compared to the 10-day expansion protocol. Our results suggest that expander-induced growth is not triggered by the local stretch alone. While stretch is clearly a driver for growth, the local stretch at a given point is not enough to predict the expander-induced growth at that location. From a clinical perspective, our study suggests that longer expansion protocols are needed to ensure sufficient growth of sizable skin patches.

Human Genetic Variation, Sport and Exercise Medicine, and Achilles Tendinopathy: Role for Angiogenesis-Associated Genes

Sport and Exercise Medicine is one of the important subspecialties of 21st century healthcare contributing to improving the physical function, health, and vitality of populations while reducing the prevalence of lifestyle-related diseases. Moreover, sport and exercise are associated with injuries such as Achilles tendinopathy, which is a common tendon injury. The angiogenesis-associated signaling pathway plays a key role in extracellular matrix remodeling, with increased levels of angiogenic cytokines reported after cyclic stretching of tendon fibroblasts. We investigated the variants in angiogenesis genes in relation to the risk of Achilles tendinopathy in two population samples drawn independently from South Africa (SA) and the United Kingdom (UK). The study sample comprised 120 SA and 130 UK healthy controls, and 108 SA and 87 UK participants with Achilles tendinopathy. All participants were genotyped for five functional polymorphisms in the vascular endothelial growth factor, A isoform (VEGFA) (rs699947, rs1570360, rs2010963) and kinase insert-domain receptor (KDR) genes (rs1870377, rs2071559). The VEGFA A-G-G inferred haplotype was associated with an increased risk of Achilles tendinopathy in the SA group (15% in controls vs. 20% in cases, p = 0.048) and the combined SA+UK group (14% in controls vs. 20% in cases, p = 0.009). These new findings implicate the VEGFA gene with Achilles tendinopathy risk, while highlighting the potential biological significance of the angiogenesis signaling pathway in the etiology of Achilles tendinopathy. The evidence suggesting a genetic contribution to the susceptibility of sustaining a tendon injury is growing. We anticipate that high-throughput and multi-omics approaches, building on genomics, proteomics, and metabolomics, may soon uncover the pathophysiology of many diseases in the field of Sports and Exercise Medicine, as a new frontier of global precision medicine.

In vitro loading models for tendon mechanobiology

Tendons are the connective tissue responsible for transferring force from muscles to bones. A key factor in tendon development, maturation, repair, and degradation is its biomechanical environment. Understanding tendon mechanobiology is essential for the development of injury prevention strategies, rehabilitation protocols and potentially novel treatments in tendon injury and degeneration. Despite the simple overall loading on tendon tissue, cells within the tissue in vivo experience a much more complex mechanical environment including tension, compression and shear forces. This creates a substantial challenge in the establishment of in vitro loading models of the tendon. This article reviews multiple loading models used for the study of tendon mechanobiology and summarizes the main findings. Although impressive progress has been achieved in the functionality and mimicry of in vitro loading models, an ideal platform is yet to be developed. Multidisciplinary approaches and collaborations will be the key to unveiling the tendon mechanobiology. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:566-575, 2018.

Impact of TGF-β inhibition during acute exercise on Achilles tendon extracellular matrix

The purpose of this study was to evaluate the role of TGF-β₁ in regulating tendon extracellular matrix after acute exercise. Wistar rats exercised (n = 15) on a treadmill for four consecutive days (60 min/day) or maintained normal cage activity. After each exercise bout, the peritendinous space of each Achilles tendon was injected with a TGF-β₁ receptor inhibitor or sham. Independent of group, tendons injected with inhibitor exhibited ~50% lower Smad 3 (Ser^423/425) (P < 0.05) and 2.5-fold greater ERK1/2 phosphorylation (P < 0.05) when compared with sham (P < 0.05). Injection of the inhibitor did not alter collagen content in either group (P > 0.05). In exercised rats, hydroxylyslpyridinoline content and collagen III expression were lower (P < 0.05) in tendons injected with inhibitor when compared with sham. In nonexercised rats, collagen I and lysyl oxidase (LOX) expression was lower (P < 0.05) in tendons injected with inhibitor when compared with sham. Decorin expression was not altered by inhibitor in either group (P > 0.05). On the basis of evaluation of hematoxylin and eosin (H&E) stained cross sections, cell numbers were not altered by inhibitor treatment in either group (P > 0.05). Evaluation of H&E-stained sections revealed no effect of inhibitor on collagen fibril morphology. In contrast, scores for regional variation in cellularity decreased in exercised rats (P < 0.05). No differences in fiber arrangement, structure, and nuclei form were noted in either group (P > 0.05). Our findings suggest that TGF-β₁ signaling is necessary for the regulation of tendon cross-link formation, as well as collagen and LOX gene transcription in an exercise-dependent manner.

Influence of repetitive mechanical loading on MMP2 activity in tendon fibroblasts

Matrix metalloproteinase2 has been implicated in tendon pathology caused by repetitive movements. However, its activity in the early stages of the tendon's response to overuse, and its presence in the circulation as a possible indicator of tendon degradation, remain unknown. Human tendon cells were repetitively stretched for 5 days, and the rabbit Achilles tendon complex underwent repetitive motion 3× per week for 2 weeks. Quantitative polymer chain reaction analysis was performed to detect matrix metalloproteinase2/14 and tissue inhibitor of matrix metalloproteinase2 messenger ribonucleic acid of cells and rabbit tissue, and matrix metalloproteinase2 protein levels were determined with an enzyme linked immunoassay. Matrix metalloproteinase2 activity was examined using zymography of the conditioned media, tendon and serum. Immunohistochemistry was used to localize matrix metalloproteinase2 in tendon tissue, and the density of fibrillar collagen in tendons was examined using second harmonic generation microscopy. Tendon cells stretched with high strain or high frequency demonstrated increased matrix metalloproteinase2 messenger ribonucleic acid and protein levels. Matrix metalloproteinase2 activity was increased in the rabbit Achilles tendon tissue at weeks 1 and 2; however, serum activity was only increased at week 1. After 2 weeks of exercise, the collagen density was lower in specific regions of the exercised rabbit Achilles tendon complex. Matrix metalloproteinase2 expression in exercised rabbit Achilles tendons was detected surrounding tendon fibroblasts. Repetitive mechanical stimulation of tendon cells results in a small increase in matrix metalloproteinase2 levels, but it appears unlikely that serum matrix metalloproteinase2 will be a useful indicator of tendon overuse injury. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:1991-2000, 2016.

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.

Effect of Different Exercise Intensities on the Myotendinous Junction Plasticity

Myotendinous junctions (MTJs) are anatomical regions specialized in transmission of contractile strength from muscle to tendon and, for this reason, a common site where acute injuries occur during sport activities. In this work we investigated the influence of exercise intensity on MTJ plasticity, as well as on the expression of insulin-like growth factor 1 (IGF-1) and transforming growth factor beta (TGF-β) and their receptors in muscle and tendon. Three groups of rats were analyzed: control (CTRL), slow-runner (RUN-S) and fast-runner (RUN-F) trained using a treadmill. Ultrastructural and morphometric analyses of distal MTJs from extensor digitorum longus muscles have been performed. Contractile strength and hypertrophy were investigated by using in vivo tension recordings and muscle cross-sectional area (CSA) analysis, respectively. mRNA levels of PGC-1α, vinculin, IGF-1Ea and TGF-β have been quantified in muscle belly, while IGF-1Ea, TGF-β and their receptors in tendon. Morphometry revealed an increased MTJ complexity and interaction surface between tissues in trained rats according to training intensity. CSA analysis excluded hypertrophy among groups, while muscle strength was found significantly enhanced in exercised rats in comparison to controls. In muscle tissue, we highlighted an increased mRNA expression of PGC-1α and vinculin in both trained conditions and of TGF-β in RUN-F. In tendon, we mainly noted an enhancement of TGF-β mRNA expression only in RUN-F group and a raise of Betaglycan tendon receptor mRNA levels proportional to exercise intensity. In conclusion, MTJ plasticity appears to be related to exercise intensity and molecular analysis suggests a major role played by TGF-β.

Enalapril stimulates collagen biosynthesis through prolidase-dependent mechanism in cultured fibroblasts

The mechanism of a lower incidence of dermatological manifestations in patients treated with enalapril compared to patients treated with other ACE-inhibitors, e.g., captopril, is not known. The finding that prolidase plays an important role in collagen biosynthesis and that some angiotensin-converting enzyme inhibitors affect prolidase activity led us to evaluate its effect on collagen biosynthesis in cultured human skin fibroblasts. Since insulin-like growth factor (IGF-I) and transforming growth factor beta 1 (TGF-β1) are the most potent stimulators of both collagen biosynthesis and prolidase activity, and prolidase is regulated by β₁ integrin signaling, the effect of enalapril and enalaprilat on IGF-IR, TGF-β1, and β₁ integrin receptor expressions was evaluated. Cells were treated with milimolar concentrations (0.3 and 0.5 mM) of enalapril and enalaprilat for 24 h. The activity of prolidase was determined by colorimetic assay. Collagen biosynthesis was evaluated by radiometric assay. Expression of signaling proteins was evaluated using Western blot. It was found that enalapril- and enalaprilat-dependent increase in prolidase activity and expression was accompanied by parallel increase in collagen biosynthesis. The exposure of the cells to 0.5 mM enalapril and enalaprilat contributed to increase in IGF-IR and α₂β₁ integrin receptor as well as TGF-β1 and NF-κB p65 expressions. Enalapril- and enalaprilat-dependent increase of collagen biosynthesis in fibroblasts results from increase of prolidase activity and expression, which may undergo through activation of α₂β₁ integrin and IGF-IR signaling as well as upregulation of TGF-β1 and NF-κB p65, the inhibitor of collagen gene expression.

Enhanced collagen type I synthesis by human tenocytes subjected to periodic in vitro mechanical stimulation

Background

Mechanical stimulation (e.g. slow heavy loading) has proven beneficial in the rehabilitation of chronic tendinopathy, however the optimal parameters of stimulation have not been experimentally determined. In this study of mechanically stimulated human tenocytes, the influence of rest insertion and cycle number on (1) the protein and mRNA levels of type I and III collagen; (2) the mRNA levels of transforming growth factor beta (TGFB1) and scleraxis (SCXA); and (3) tenocyte morphology, were assessed.

Methods

Human hamstring tenocytes were mechanically stimulated using a Flexcell® system. The stimulation regimens were 1) continuous and 2) rest-inserted cyclic equiaxial strain at a frequency of 0.1 Hz for 100 or 1000 cycles. Data were normalized to unstimulated (non-stretched) control groups for every experimental condition. qPCR was performed to determine relative mRNA levels and quantitative immunocytochemistry image analysis was used to assess protein levels and cell morphology.

Results

Collagen type I mRNA level and pro-collagen protein levels were higher in tenocytes that were subjected to rest-inserted mechanical stimulation, compared to continuous stretching (p < 0.05). Rest insertion and increased cycle number also had significant positive effects on the levels of mRNA for TGFB1 and SCXA (p < 0.05). There was no direct relation between cell morphology and gene expression, however mechanical stimulation, overall, induced a metabolically active tenocyte phenotype as evidenced by cells that on average demonstrated a decreased major-minor axis ratio (p < 0.05) with greater branching (p < 0.01).

Conclusions

The incorporation of rest periods in a mechanical stretching regimen results in greater collagen type I synthesis. This knowledge may be beneficial in refining rehabilitation protocols for tendon injury.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2474-15-386) contains supplementary material, which is available to authorized users.