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Research Papers

Influence of Decorin on the Mechanical, Compositional, and Structural Properties of the Mouse Patellar Tendon

[+] Author and Article Information
LeAnn M. Dourte, Lydia Pathmanathan

McKay Orthopaedic Research Laboratory,  University of Pennsylvania, Philadelphia, PA 19104

Abbas F. Jawad

Department of Pediatrics: Biostatistics and Epidemiology,  University of Pennsylvania Perelman School of Medicine and Children’s Hospital of Philadelphia, Philadelphia, PA 19104

Renato V. Iozzo

Department of Pathology, Anatomy and Cell Biology,  Thomas Jefferson University, Philadelphia, PA 19107

Michael J. Mienaltowski, David E. Birk

Department of Pathology and Cell Biology,  University of South Florida, Tampa, FL 33612

Louis J. Soslowsky1

McKay Orthopaedic Research Laboratory,  University of Pennsylvania, Philadelphia, PA 19104soslowsk@upenn.edu

1

Corresponding author. Present address: McKay Orthopaedic Research Laboratory, University of Pennsylvania, 424 Stemmler Hall, 36th Street and Hamilton Walk, Philadelphia, PA 19104-6081.

J Biomech Eng 134(3), 031005 (Mar 23, 2012) (8 pages) doi:10.1115/1.4006200 History: Received December 07, 2011; Revised February 17, 2012; Posted February 23, 2012; Published March 21, 2012; Online March 23, 2012

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.

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Copyright © 2012 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Viscoelastic mechanical testing protocol

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Figure 2

Percent relaxation was significantly decreased with increasing strain level. There was a trend toward an effect of genotype. Mean and standard deviation shown. Strain level significantly different (p ≤ 0.05/3) from 4% (*) and 6% (#), respectively.

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Figure 3

At every frequency level, Dcn+/− is significantly increased from WT. Mean and standard deviation shown pooled across strain level. At the given frequency, p ≤ 0.05/3 * Dcn+/− .

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Figure 4

(a) At every frequency level, dynamic modulus significantly increased with increasing strain level. (b) At a given strain level, all combinations of frequencies were significantly different from each other (paired comparisons) except 0.01 Hz versus 0.1 Hz at 6% and 8% as well as 5 Hz versus 10 Hz at 8%. Mean and standard deviation shown pooled across all genotypes. At the given frequency level, p ≤ 0.05/3 for * 4% versus 6%, # 4% versus 8%, +6% versus 8%. At the given strain level, bar denotes p ≤ 0.05/10, paired comparisons.

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Figure 5

Dynamic modulus of representative WT samples at 4% strain demonstrating frequency dependence. Similar trends were seen in all genotypes.

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Figure 6

(a) At all frequencies, phase shift is significantly decreased between 4% and 6% as well as 4% and 8%. At 0.1 Hz, 1 Hz it is also decreased between 6% and 8%. (b) At a given strain level, all frequency combinations are significantly different from each other (paired comparisons) except 0.01 Hz versus 0.1 Hz at 4%. At the given frequency level, p ≤ 0.05/3 for * 4% versus 6%, # 4% versus 8%, +6% versus 8%. Mean and standard deviation shown pooled across all genotypes. At the given strain level, bar denotes p ≤ 0.05/10, paired comparisons.

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Figure 7

The relative expression of decorin was significantly reduced between the WT and Dcn−/− groups as well as between Dcn+/− and Dcn−/− . (b) There was a trend toward an effect of genotype in the biglycan relative expression (p = 0.1). No significant difference was found in (c) fibromodulin or (d) lumican. Mean and standard deviation shown. Bar denotes p ≤ 0.05/3.

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Figure 8

Representative TEM images of fibril cross sections in (a) wild type, (b) Dcn+/− , and (c) Dcn−/− . Scale bar 200 nm.

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Figure 9

Histograms of fibril diameters. Qualitatively (a) the shape of the Dcn+/− distribution is similar to WT while (b) the Dcn−/− has an increased small fibril population

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