Mechanical loading plays an essential role in both tendon development and degradation. However, the underlying mechanism of how tendons sense and response to mechanical loading remains largely unknown. SPARC, a multifunctional extracellular matrix glycoprotein, modulates cell extracellular matrix contact, cell-cell interaction, ECM deposition and cell migration. Adult mice with SPARC deficiency exhibited hypoplastic tendons in load-bearing zone. By investigating tendon maturation in different stages, we found that hypoplastic tendons developed at around postnatal 3 weeks when the mice became actively mobile. The in vitro experiments on primary tendon derived stem cells demonstrated that mechanical loading induced SPARC production and AKT/S6K signalling activation, which was disrupted by deleting SPARC causing reduced collagen type I production, suggesting that mechanical loading was harmful to tendon homeostasis without SPARC. In vivo treadmill training further confirmed that increased loading led to reduced Achilles tendon size and eventually caused tendon rupture in SPARC-/− mice, whereas no abnormality was seen in WT mice after training. We then investigate whether paralysing the hindlimb of SPARC-/− mice using BOTOX from postnatal 2 weeks to 5 weeks would delay the hypoplastic tendon development. Increased patellar tendon thickness was shown in SPARC-/− mice by reducing mechanical loading, whereas opposite effect was seen in WT mice. Finally, we identified a higher prevalence of a missense SNP in the SPARC gene in patients who suffered from a rotator cuff tear. In conclusion, SPARC is a mechano-sensor that regulates tendon development and homeostasis.

Metabolic disorders are frequently associated with tendon degeneration and impaired healing after acute injury. However, the underlying cellular and molecular mechanisms remain largely unclear. We have previously shown that human and rat tendon cells responde to glucose stimulation in vitro by secretion of insulin. Therefore, we now hypothesize that nutritional glucose uptake affects tendon healing in a rat model.

In female rats (n=30/group), unilateral full-thickness Achilles tendon defects were created. Immediately after surgery animals were either fed a glucose rich- or a control diet for up to 4 weeks. Gait analysis (Catwalk, Noldus) was performed at three time points. In addition, tendon thickness measurements, biomechanical testing and immunohistochemical analysis were conducted. Subsequently, gene expression analysis, comparing cDNA pools (n=5) prepared from repair tissues of both groups was performed.

The repair tissues of the high glucose group were significantly thicker compared to the control group (p<0.001). The intermediate toe spread, an indicator of pain, were significantly improved in the high glucose group one and two weeks post surgery. Biomechanical analysis revealed that the repair tissues of the high glucose group were significantly stiffer (p<0.05) compared to the control group, no significant difference was detected for maximum tensile load…. The proportion of Ki67+ cells in the repair tissue was 3.3% in the control diet group and 9,8% in the high glucose group, indicating increased cell proliferation (p<0.001). Finally, gene expression analysis revealed the chondrogenic marker genes Collagen II, Aggrecan, COMP and SOX9 to be upregulated and genes involved in lipid metabolism like PPARgamma and Fabp2 to be downregulated in the glucose diet group.

Here we show fort he first time that a high-glucose diet affects gait pattern and tendon biomechanics, influences tendon thickness and cell proliferation. Gene expression analysis reveals a regulation of chondrogenic as well as adipogenic marker genes. The molecular mechanisms underlying these effects on cells and extracellular matrix are currently under investigation, potentially revealing targets for developing a dietary intervention scheme to support tendon regeneration after trauma or tendon disease.

Introduction

Metabolic disorders are among known risk factors for tendinopathies or spontaneous tendon ruptures. However, the underlying cellular and molecular mechanisms remain unclear. We have previously shown that human and rat tendon cells produce and secrete insulin upon glucose stimulation. Therefore, we hypothesize that nutritional glucose uptake affects tendon healing in a rat model.