MECHANICAL PROPERTIES OF VERTEBRA IN BIGLYCAN DEFICIENT MICE

Participants: T. Adachi, M. Young*, P. Gehron Robey*, X.-D. Chen*, M. Moalli, S. A. Goldstein,

*National Institute of Dental Research, NIH

Keywords: mechanical properties, biglycan knockout, osteoporosis

Introduction

Biglycan (Bgn) is an extracellular matrix (ECM) proteoglycan that is enriched in bone. Bgn-deficient mice were generated and have been used to study the role of Bgn in vivo, and it was found that these mice display a phenotype characterized by a reduced growth rate and decreased bone mass [1]. Marked by low bone mass that becomes more obvious with age, these mice may serve as an animal model to study the role of ECM proteins in osteoporosis. Biomechanical tests were reported for cortical bone as a primary measure of its structural and material properties of bone. However, more detailed analysis and biomechanical characterization of regions rich in trabecular bone is required for a critical assessment of the osteopenia. The purpose of this study was (a) to develop the miniature experimental apparatus for the compression test of the mice caudal vertebrae, and (b) to investigate the mechanical and structural properties of vertebrae with trabecular microstructure in Bgn-deficient mice.

Materials and Methods

The caudal vertebrae (coccygea) were dissected from 33 Bgn knockout and 15 wild type mice at 5 (n = 13 & 5), 10 (n = 12 & 7), and 16 (n = 8 & 3) weeks of age acquired from collaborators at the Craniofacial and Skeletal Diseases Branch, National Institute of Dental Research, NIH. All vertebrae were stored at —20C in PBS until thawed and tested. After the measurement of the original length, the 5th, 7th, and 9th caudal vertebrae were cut at the both longitudinal ends into 3.0 mm in length using a rotary cutter. Specimens were then tested under the uniaxial compression on the miniature testing machine developed in our laboratory with 50lb load cell and LVDT at a cross-head speed of 10m/s under moist conditions. Load-displacement curves were acquired, and failure load, maximum stiffness and energy to failure were measured.

Progress

To date, 144 (=3(18+19+11)) vertebrae have been tested. They are currently under analysis. The 6th and/or 8th caudal vertebrae will be scanned on a micro-CT system to quantitatively investigate the structural parameters of the trabecular architecture. Statistical comparisons will be made between Bgn knockout and wild type, gender and vertebral body using multi-way analysis of variance. Further testing of vertebrae from older mice will also be performed.

References

1.  
2. T. Xu, et al.: "Targeted disruption of the biglycan gene leads to an osteoporosis-like phenotype in mice," Nature Genetics, Vol. 20, pp. 78-82 (1998).