Aging Effects on Mechanoregulation of Osteocytes using Multiscale Multiphysics

Project Summary This is a highly interdisciplinary research proposal to study the effects of aging on the responsiveness of osteocytes to mechanical loading in both sexes of mice. The proposal will engage undergraduate and graduate students alongside established investigators who will mentor these students in various aspects of bone

mechanobiology, computer-based modeling to build in silico models of how osteocytes respond to load and 3D printing of osteocyte-lacuna-dendrite-canalicular models. The osteocytes with their interconnected dendritic network are thought to be the primary mechanosensory cells in bone. Aging produces changes in morphological

aspects of the lacunar canalicular system. The long-term goal of this proposal is to determine how mechanical strain and fluid flow shear stress induce the biological activation (mechanotransduction) of bone forming pathways, such as the Wnt/β-catenin pathway, in osteocytes. Activation of this signaling pathway will be used to

correlate with the mechanics that induce the cellular response. This will be done using sophisticated finite element (FE) and fluid-structure interaction (FSI) modeling, using confocal imaging, at the level of the osteocyte and its dendritic membranes using real data generated from loaded and unloaded bones as input into the models.

The specific aims are to a) Develop multiplexed imaging models to predict osteocyte activation in response to altered mechanical loads encountered with aging, b) Develop macro and micro level 3D finite element and fluid- structure interaction models of osteocyte lacunae and determine the strains and shear stresses on

osteocytes/dendrites as a function of age, at three different load levels and c) Correlate mechanical strain determined by in silico modeling to Wnt/β-catenin signaling for different load levels. Male and female TOPGAL (β-catenin reporter) mice at 6 and 18 months of age will be used. Activation of β-catenin signaling in osteocytes

in the ulna in response to loading will be determined using novel multiplexed confocal imaging approaches to build multi-length-scale finite element models to study the loading response. From the 3D finite element and fluid-structure interaction models, strain fields in the lacuna and wall shear stress will be determined. Mechanical

strain responses from in silico modeling will be correlated with the activation of osteocyte β-catenin signaling determined using confocal imaging in each of the osteocyte/dendrite systems (β-galactosidase activity) to determine a strain threshold for pathway activation. Fluid flow shear stress responses on the cell/dendrites will

be studied using FSI models and magnitudes at the activation levels. Novel 3D printed models of the lacuna- canaliculi system will be used to study the overall flow of fluids through the system. The interdisciplinary research team, from the fields of bone biology and engineering, will train engineering and health science students in a

collaborative team giving valuable experience to methods of working in diverse fields to research a scientific problem.