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Mechanical, compositional, and structural properties of the mouse patellar tendon with changes in biglycan gene expression.

ABSTRACT: Tendons have complex mechanical properties that depend on their structure and composition. Some studies have assessed the role of small leucine-rich proteoglycans (SLRPs) in the mechanical response of tendon, but the relationships between sophisticated mechanics, assembly of collagen and SLRPs have not been well characterized. In this study, biglycan gene expression was varied in a dose dependent manner using biglycan null, biglycan heterozygote and wild type mice. Measures of mechanical (tension and compression), compositional and structural changes of the mouse patellar tendon were evaluated. Viscoelastic, tensile dynamic modulus was found to be increased in the biglycan heterozygous and biglycan null tendons compared to wild type. Gene expression analyses revealed biglycan gene expression was closely associated in a dose-dependent allelic manner. No differences were seen between genotypes in elastic or compressive properties or quantitative measures of collagen structure. These results suggest that biglycan, a member of the SLRP family, plays a role in tendon viscoelasticity that cannot be completely explained by its role in collagen fibrillogenesis.

SUBMITTER: Dourte LM

PROVIDER: S-EPMC3801205 | biostudies-literature | 2013 Sep

REPOSITORIES: biostudies-literature

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Mechanical, compositional, and structural properties of the mouse patellar tendon with changes in biglycan gene expression.

Dourte Leann M LM Pathmanathan Lydia L Mienaltowski Michael J MJ Jawad Abbas F AF Birk David E DE Soslowsky Louis J LJ

Journal of orthopaedic research : official publication of the Orthopaedic Research Society 20130416 9

Tendons have complex mechanical properties that depend on their structure and composition. Some studies have assessed the role of small leucine-rich proteoglycans (SLRPs) in the mechanical response of tendon, but the relationships between sophisticated mechanics, assembly of collagen and SLRPs have not been well characterized. In this study, biglycan gene expression was varied in a dose dependent manner using biglycan null, biglycan heterozygote and wild type mice. Measures of mechanical (tensio ...[more]

PMID: 23592048

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Project description:IntroductionThe effect of chronic patellar tendinopathy on tissue function and integrity is currently unclear and underinvestigated. The aim of this cohort comparison was to examine morphological, material, and mechanical properties of the patellar tendon and to extend earlier findings by measuring the ability to store and return elastic energy in symptomatic tendons.MethodsSeventeen patients with chronic (>3 months, VISA-P < 80), inferior pole patellar tendinopathy (24 ± 4 years; male = 12, female = 5) were carefully matched to controls (25 ± 3 years) for training status, pattern, and history of loading of the patellar tendon. Individual knee extension force, patellar tendon stiffness, stress, strain, Young's modulus, hysteresis, and energy storage capacity, were obtained with combined dynamometry, ultrasonography, magnetic resonance imaging, and electromyography.ResultsAnthropometric parameters did not differ between groups. VISA-P scores ranged from 28 to 78 points, and symptoms had lasted from 10 to 120 months before testing. Tendon proximal cross-sectional area was 61% larger in the patellar tendinopathy group than in the control group. There were no differences between groups in maximal voluntary isometric knee extension torque (p = 0.216; d < -0.31) nor in tensile tendon force produced during isometric ramp contractions (p = 0.185; d < -0.34). Similarly, tendon strain (p = 0.634; d < 0.12), hysteresis (p = 0.461; d < 0.18), and strain energy storage (p = 0.656; d < 0.36) did not differ between groups. However, patellar tendon stiffness (-19%; p = 0.007; d < -0.74), stress (-27%; p< 0.002; d < -0.90) and Young's modulus (-32%; p = 0.001; d < -0.94) were significantly lower in tendinopathic patients compared to healthy controls.DiscussionIn this study, we observed lower stiffness in affected tendons. However, despite the substantial structural and histological changes occurring with tendinopathy, the tendon capacity to store and dissipate energy did not differ significantly.

Project description:The aging population is at an increased risk of tendon injury and tendinopathy. Elucidating the molecular basis of tendon aging is crucial to understanding the age-related changes in structure and function in this vulnerable tissue. In this study, the structural and functional features of tendon aging are investigated. In addition, the roles of decorin and biglycan in the aging process were analyzed using transgenic mice at both mature and aged time points. Our hypothesis is that the increase in tendon injuries in the aging population is the result of altered structural properties that reduce the biomechanical function of the tendon and consequently increase susceptibility to injury. Decorin and biglycan are important regulators of tendon structure and therefore, we further hypothesized that decreased function in aged tendons is partly the result of altered decorin and biglycan expression. Biomechanical analyses of mature (day 150) and aged (day 570) patellar tendons revealed deteriorating viscoelastic properties with age. Histology and polarized light microscopy demonstrated decreased cellularity, alterations in tenocyte shape, and reduced collagen fiber alignment in the aged tendons. Ultrastructural analysis of fibril diameter distributions indicated an altered distribution in aged tendons with an increase of large diameter fibrils. Aged wild type tendons maintained expression of decorin which was associated with the structural and functional changes seen in aged tendons. Aged patellar tendons exhibited altered and generally inferior properties across multiple assays. However, decorin-null tendons exhibited significantly decreased effects of aging compared to the other genotypes. The amelioration of the functional deficits seen in the absence of decorin in aged tendons was associated with altered tendon fibril structure. Fibril diameter distributions in the decorin-null aged tendons were comparable to those observed in the mature wild type tendon with the absence of the subpopulation containing large diameter fibrils. Collectively, our findings provide evidence for age-dependent alterations in tendon architecture and functional activity, and further show that lack of stromal decorin attenuates these changes.

Dataset Information

Mechanical, compositional, and structural properties of the mouse patellar tendon with changes in biglycan gene expression.

Publications

Mechanical, compositional, and structural properties of the mouse patellar tendon with changes in biglycan gene expression.

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