PhD Defense: Steven Proulx

In Vivo Imaging of TNF-Transgenic Murine Arthritis

Abstract

Research of mouse models of inflammatory arthritis is limited by the lack of longitudinal outcome measures that can track progression of the disease and response to effective therapy. These measures can improve the statistical power of preclinical trials by allowing each animal to serve as its own control. The goal of this study was to develop several in vivo imaging biomarkers of arthritis using magnetic resonance imaging and micro-computed tomography.

A mouse knee coil was built that interfaces with a clinical 3T MRI to allow acquisition of high resolution (~100) images. A T1-weighted FLASH sequence was used to generate images before and after injection of gadolinium contrast agent. Using commercially available software, biomarkers for synovial inflammation, bone marrow edema, and the draining lymph node were developed. Micro-CT was employed for analysis of bone erosion. These biomarkers were tested in longitudinal studies of the natural history of arthritis and in response to therapeutic intervention using histology and cellular analyses.

Seven independent biomarkers were developed and validated: synovial volume, popliteal lymph node volume, normalized lymph node contrast enhancement, normalized bone marrow intensity, normalized marrow contrast enhancement, patellar bone volume, and talar bone volume. Progression of arthritis was demonstrated through significant changes in these biomarkers from 2 to 5 months of age versus wild type animals. All biomarkers significantly improved in response to anti-TNF therapy. A diffuse bone marrow edema pattern was investigated with histology and flow cytometry methods and was found to be a highly vascularized cellular marrow with increased myelopoiesis and contrast agent perfusion. Initial insights on a possibly beneficial role of the draining lymph node were found by investigating the relationship of this tissue with adjacent synovial inflammation.

This study demonstrates the importance of developing in vivo imaging techniques for translational science that may extend beyond biomarkers for preclinical studies. Since these outcome measures were developed using clinical imaging approaches, there may be potential in applying these outcome measures to humans. In addition, insights gained by visualizing the pathogenesis of the disease may lead to novel therapies that can, in turn, be evaluated with these biomarkers.