Second Harmonic Generation Imaging and the Musculoskeletal Systems of Hypophosphatasia

Hypophosphatasia (HPP) is a rare metabolic bone disorder characterized by low levels of alkalinephosphatase that causes poor mineralization of the bone and an unexpected muscle impairment in patients. In this thesis we pursued 2 lines of research: first developing technology to evaluate the impact of HPP on bone microstructure; and second investigating the impact of HPP on muscle function. Bone mineral directly strengthensthe bone and assistsin assembly of the bone collagen matrix. Therefore, we developed polarimetric second harmonic generation to study bone matrix assembly in bone collagen. We found that we could detect collagen organization in the bone with polarized SHG, and that while resolution diminishes with depth, within the outer ~50 µm polarization can be used to describe collagen secondary structures. We then applied our findings to evaluate loss of bone collagen microstructure in HPP and developed a polarimetric gray-level co-occurrence matrix imaging analysis technique that can effectively discriminate between healthy and diseased bone. Finally, we turned our attention to the understudied effects of HPP on muscle function. We determined that HPP muscles in the mouse model are weak and have different fiber types while retaining their mitochondrial content. However, significant impairment in mitochondrial Complex I function was detected- which may suggest a toxic mitochondrial environment that is overloaded with ATP. Together, this dissertation provides methodsforstudying the musculoskeletalsystem and further insight into the pathology of HPP.