Influence of decorin on the mechanical, compositional, and structural properties of the mouse patellar tendon

The interactions of small leucine-rich proteoglycans (SLRPs) with collagen fibrils, their association with water, and their role in fibrillogenesis suggests that SLRPs may play an important role in tendon mechanics. Some studies have assessed the role of SLRPs in the mechanical response of the tendon, but the relationships between sophisticated mechanics, assembly of collagen, and SLRPs have not been well characterized. Decorin content was varied in a dose dependent manner using decorin null, decorin heterozygote, and wild type mice. Quantitative measures of mechanical (tension and compression), compositional, and structural changes of the mouse patellar tendon were evaluated. Viscoelastic, tensile dynamic modulus was increased in the decorin heterozygous tendons compared to wild type. These tendons also had a significant decrease in total collagen and no structural changes compared to wild type. Decorin null tendons did not have any mechanical changes; however, a significant decrease in the average fibril diameter was found. No differences were seen between genotypes in elastic or compressive properties, and all tendons demonstrated viscoelastic mechanical dependence on strain rate and frequency. These results suggest that decorin, a member of the SLRP family, plays a role in tendon viscoelasticity that cannot be completely explained by its role in collagen fibrillogenesis. In addition, reductions in decorin do not cause large changes in indentation compressive properties, suggesting that other factors contribute to these properties. Understanding these relationships may ultimately help guide development of tissue engineered constructs or treatment modalities.