A NEW TRANSGENIC MOUSE MODEL FOR OSTEOGENESIS IMPERFECTA

Participants: E.P. Frankenburg, K.M. Kozloff, M.W. Stock, D.C. Kayner, A. Furling, C. Bergwitz, J.C. Marini, S.A. Goldstein

Keywords: osteogenesis imperfecta, bone mechanics, animal model

Introduction

Osteogenesis imperfecta is a disease that affects about 1 out of every 20,000 live births, in which there is a mutation in the extracellular matrix molecule type I collagen. The result is a disorder characterized by bone fractures with or without deformity, and later, osteopenia. The laboratory of Dr. Joan Marini at NIH has developed a mouse strain in which a glycene substitution on collagen genes resulted in mice with symptoms of osteogenesis imperfecta Type 4. The biologic similarities of this model to the disease are closer than previous models, and mice with this trait have resulted in spontaneous fractures. The new model may be valuable as a means to study a variety of therapeutic interventions including gene therapy or drug regiments. The specific objectives of this project are to determine through mechanical testing and image analysis whether this new model for osteogenesis imperfecta will better aid us in the study of this disease.

Materials and Methods

In order to compare the new model of osteogenesis imperfecta with additional models, we elected to follow established protocols from our laboratory which previously were used to characterize mouse models of osteogenesis imperfecta. We had 80 mice, both mutant and wild type, which were sacrificed at one month, two months, six months, or approximately 20 months. The femora are harvested, and frozen in separate saline filled containers. The femurs will be scanned on a micro-computed tomography system in order to determine the cross-sectional geometric properties of the femoral mid-diaphyses. After scanning, the left femurs will then be tested in four-point bending until failure in order to determine the structural properties of whole bone. Parallelepiped specimens will be machined from the mid-diaphysis of each right femur in order to perform a micro four-point bending test. This test will determine the local material properties of the cortical tissue. In addition, the right femurs may be tested by nano-indentation to determine tissue-level material properties.

Progress

All femora have been dissected free and stored frozen in individual containers. Micro ct scanning is currently underway. Forty femurs have all been tested in four-point bending, and the analysis of these test results is complete. In addition, protocols for micro-testing are currently being optimized.