Uphill running does not exacerbate collagenase-induced pathological changes in the Achilles tendon of rats selectively bred for high-capacity running

Age and Intrinsic Fitness Affect the Female Rotator Cuff Tendon Tissue

The risk of the development of tendon disorders or ruptures increases with age, but it is unclear whether intrinsic fitness during lifetime might also affect tendon properties. To investigate this, a contrasting rat model of high-capacity runners (HCR with high intrinsic fitness) and low-capacity runners (LCR with low intrinsic fitness) was employed. Histological and molecular changes in rotator cuff (RC) tendons from 10 weeks old (young; HCR-10 and LCR-10) and 100 weeks old (old; HCR-100 and LCR-100) female rats were investigated. Age-dependent changes of RC tendons observed in HCR and LCR were increase of weight, decrease of tenocytes and RNA content, reduction of the wavy pattern of collagen and elastic fibers, repressed expression of Col1a1, Eln, Postn, Tnmd, Tgfb3 and Egr1 and reduction of the Col1:Col3 and Col1:Eln ratio. The LCR rats showed less physical activity, increased body weight, signs of metabolic disease and a reduced life expectancy. Their RC tendons revealed increased weight (more than age-dependent) and enlargement of the tenocyte nuclei (consistent with degenerative tendons). Low intrinsic fitness led to repressed expression of a further nine genes (Col3a1, Fbn1, Dcn, Tnc, Scx, Mkx, Bmp1, Tgfb1, Esr1) as well as the rise of the Col1:Col3 and Col1:Eln ratios (related to the lesser expression of Col3a1 and Eln). The intrinsic fitness influences the female RC tendons at least as much as age. Lower intrinsic fitness accelerates aging of RC tendons and leads to further impairment; this could result in decreased healing potential and elasticity and increased stiffness.

The Effect of Age and Intrinsic Aerobic Exercise Capacity on the Expression of Inflammation and Remodeling Markers in Rat Achilles Tendons

Old age, adiposity, and metabolic disorders are known as risk factors for chronic tendinopathy, which is a common problem in both athletes and the general population. However, the importance of these influencing factors has not yet been well understood. This study investigated alterations in gene expression and histology of Achilles tendons of young (10 weeks) and old (100 weeks) rats bred for low (low capacity runners, LCR) and high (high capacity runners, HCR) intrinsic aerobic exercise capacity. In this rat model, LCR displayed a phenotype of reduced exercise capacity, higher body weight, and metabolic dysfunctions compared to HCR. We hypothesized that the risk factors for tendinopathy in old LCR could lead to more pronounced impairments in Achilles tendon tissue. In quantitative real-time PCR (qPCR), age-related downregulation of tenocyte markers e.g., tenomodulin, genes related to matrix modeling and remodeling (e.g., collagens, elastin, biglycan, fibronectin, tenascin C) as well as transforming growth factor beta 3 (Tgfb3) have been detected. Inflammation marker cyclooxygenase 2 (Cox2) was downregulated in old rats, while microsomal prostaglandin E synthase 2 (Ptges2) was upregulated in old HCR and old LCR. In all groups, interleukin 6 (Il6), interleukin 1 beta (Il1b), and tumor necrosis factor alpha (Tnfa) showed no significant alteration. In histological evaluation, tendons of old rats had fewer and more elongated tenocyte nuclei than young rats. Even though a higher content of glycosaminoglycans, a sign of degeneration, was found in old HCR and LCR, no further signs of tendinopathy were detectable in tendons of old rats by histological evaluation. Low intrinsic aerobic exercise capacity and the associated phenotype did not show significant effects on gene expression and tendon histology. These findings indicate that aging seems to play a prominent role in molecular and structural alterations of Achilles tendon tissue and suggests that other risk factors associated with intrinsic aerobic exercise capacity are less influential in this rat model.

Mechanobiology of young and aging tendons: In vivo studies with treadmill running

Tendons are unique in the sense that they are constantly subjected to large mechanical loads and that they contain tendon-specific cells, including tenocytes and tendon stem/progenitor cells. The responses of these cells to mechanical loads can be anabolic or catabolic and as a result, change the biological properties of the tendon itself that may be beneficial or detrimental. On the other hand, aging also induces aberrant changes in cellular expression of various genes and production of various types of matrix proteins in the tendon, and consequently lead to tendon degeneration and impaired healing in aging tendons; both could be improved by moderate physiological mechanical loading such as treadmill running. This article gives an overview on the mechanobiology research of young and aging animal tendons using treadmill running model. The challenges in such treadmill running studies are also discussed. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:557-565, 2018.

[Effect of different intensity treadmill training on repair of micro-injured Achilles tendon in rats]

Objective

To explore the effect of different intensity treadmill training on the repair of micro-injured Achilles tendon induced by collagenase in rats.

Methods

Seventy-two 8-week-old male Sprague Dawley rats (weighing, 200-250 g) were selected. After adaptive treadmill training for 1 week, rats were injected with 30 μL type I collagenase solution (10 mg/mL) into both Achilles tendons to make micro-injured Achilles tendon models. After 1 week of cage feeding, the rats were randomly divided into 3 groups: the control group, the low-intensity group, and the high-intensity group, 24 rats each group. The rats in control group could move freely, and the rats underwent daily treadmill training at the intensity of 13 m/min and 20 min/d in the low-intensity group and at the intensity of 17 m/min and 60 min/d in the high-intensity group. At immediate, 1 week, and 4 weeks after training, bilateral Achilles tendons were collected from 8 rats of each group for gross observation, histological analysis, and mechanical testing.

Results

At immediate after training, there was no significant difference in the gross observation, histological observation, and biomechanical properties of the Achilles tendon between groups ( P>0.05). The gross observation showed connective tissue hyperplasia near Achilles tendon and lackluster tendon in each group at 1 week; hyperplasia significantly reduced in the low-intensity group when compared with the control group, and there were more connective tissue and a large number of neovascularization in the high-intensity group at 4 weeks. At 1 week, there was no significant difference in the semi-quantitative histological total score between groups ( P>0.05), but there were significant differences in vascularity between low-intensity group or high-intensity group and control group ( P<0.05). At 4 weeks, the semi-quantitative histological total score was significantly higher in high-intensity group than control group and low-intensity group ( P<0.05), and in control group than low-intensity group ( P<0.05). There were significant differences in collagen arrangement, cell morphology, abnormal cells, and vascularity between low-intensity group and high-intensity group or control group ( P<0.05). And there was significant difference in abnormal cells between high-intensity group and control group ( P<0.05). The mechanical testing showed that there was no significant difference in cross-sectional area of the Achilles tendon, the ultimate force, tensile strength, and elastic modulus between groups at 1 week ( P>0.05); the low-intensity group was significantly higher than the control group in the ultimate force and the tensile strength ( P<0.05), and than high-intensity group in the ultimate force and elastic modulus ( P<0.05), but no significant difference was found in the other indexes between groups ( P>0.05) at 4 weeks.

Conclusion

Low-intensity treadmill training can promote the repair of rat micro-injured Achilles tendon induced by collagenase.

The effect of dry needling and treadmill running on inducing pathological changes in rat Achilles tendon

Achilles tendinopathy is a common degenerative condition without a definitive treatment. An adequate chronic animal model of Achilles tendinopathy has not yet been developed. The purpose of this study was to evaluate the individual and combined effects of dry needling and treadmill running on the Achilles tendon of rats. Percutaneous dry needling, designed to physically replicate microrupture of collagen fibers in overloaded tendons, was performed on the right Achilles tendon of 80 Sprague-Dawley rats. The rats were randomly divided into two groups: a treadmill group, which included rats that underwent daily uphill treadmill running (n = 40), and a cage group, which included rats that could move freely within their cages (n = 40). At the end of weeks 1 and 4, 20 rats from each group were sacrificed, and bilateral Achilles tendons were collected. The harvested tendons were subjected to mechanical testing and histological analysis. Dry needling induced histological and mechanical changes in the Achilles tendons at week 1, and the changes persisted at week 4. The needled Achilles tendons of the treadmill group tended to show more severe histological and mechanical changes than those of the cage group, although these differences were not statistically significant. Dry needling combined with free cage activity or treadmill running produced tendinopathy-like changes in rat Achilles tendons up to 4 weeks after injury. Dry needling is an easy procedure with a short induction period and a high success rate, suggesting it may have relevance in the design of an Achilles tendinopathy model.

Increased mast cell numbers in a calcaneal tendon overuse model

Tendinopathy is often discovered late because the initial development of tendon pathology is asymptomatic. The aim of this study was to examine the potential role of mast cell involvement in early tendinopathy using a high-intensity uphill running (HIUR) exercise model. Twenty-four male Wistar rats were divided in two groups: running group (n = 12); sedentary control group (n = 12). The running-group was exposed to the HIUR exercise protocol for 7 weeks. The calcaneal tendons of both hind limbs were dissected. The right tendon was used for histologic analysis using Bonar score, immunohistochemistry, and second harmonic generation microscopy (SHGM). The left tendon was used for quantitative polymerase chain reaction (qPCR) analysis. An increased tendon cell density in the runners were observed compared to the controls (P = 0.05). Further, the intensity of immunostaining of protein kinase B, P = 0.03; 2.75 ± 0.54 vs 1.17 ± 0.53, was increased in the runners. The Bonar score (P = 0.05), and the number of mast cells (P = 0.02) were significantly higher in the runners compared to the controls. Furthermore, SHGM showed focal collagen disorganization in the runners, and reduced collagen density (P = 0.03). IL-3 mRNA levels were correlated with mast cell number in sedentary animals. The qPCR analysis showed no significant differences between the groups in the other analyzed targets. The current study demonstrates that 7-week HIUR causes structural changes in the calcaneal tendon, and further that these changes are associated with an increased mast cell density.