Temporal Expression of Extracellular Matrix in PPTJ in Vivo Cyclical Loading Model

Abstract

Patella-Patella Tendon Junction (PPTJ) overuse injury is common athletic and occupational problems. But early pathophysiologic processes are not well known. Extracellular Matrix (ECM) links tissues of the body together and plays an important role in the force transmission and tissue structure maintenance especially in tendons. PURPOSE: Based on our previous study established PPTJ overuse injury model, this study aimed to evaluate expression of Tenascin-C(TN-C) and Collagen type III in PPTJ during the early stage of PPTJ overuse injury. METHOD: 45 female New Zealand rabbits(2.37±0.14 kg) were randomly divided into 5 groups according to cyclical loading times. The left rectus femoris muscles were electrically stimulated to contract repetitively for 60 repetitions/min at 30% peak tetanic force for 2h, 4h, 6h, 12h and 24h cumulative loading respectively. We randomly choosed 9 contralateral limbs served as controls. The PPTJ were harvested, and sections were stained with HE and immunostained TN-C and Collagen type III. Collagen fiber arrangement was asseesed by Bonar scale in HE stained sections under polarized light. 5 regions of interest in PPTJ were digitally photographed at 400× for immunostained sections. Positive staining cells were manually counted in each region and we calculated mean positive stained cell densities of each sample. Polynomial contrasts were used to assess the trend of TN-C positive staining cell desity among five groups. One way ANOVA with Tukey adjusted post hoc pairwise comparisons were used to compare mean collagen fiber arrangement and mean positive staining cell desity of collagen type III in five groups. RESULT: Collagen fiber arrangement in 4h, 6h, 12h and 24h group disordered significantly compared with control group (1.56±0.24, 1.67±0.24, 1.56±0.24, 1.67±0.24 vs 0.40±0.16 respectively, All p<0.01). For mean positive stained cell densities of TN-C, we observed a significant quadratic trend (p< 0.05). Compared with control group(139.7±36.6 cells/mm2), the mean positive stained cell densities of Collagen-III in 2h(278.4±35.2 cells/mm2) and 24h(255.9±31.0 cells/mm2) were significantly higher (All p<0.05). CONCLUSION: Expression changes in ECM in PPTJ may play a role in the eraly progession of PPTJ overuse. Supported by Fundamental Research Funds for Central Universities 2011038