The Role of Reactive Oxygen Species in Osteocyte Mechano-Transduction and Sclerostin Regulation

摘要

ABSTRACT The development of low bone mass caused by aging, disuse due to paralysis, or extended space flights impacts many individuals of all ages. Current therapeutics aim to slow the loss of bone mass, but none currently target the lack of mechanical loading that leads to declining bone mass in these situations. We have recently described a novel pathway in vitro in which NADPH Oxidase 2 (NOX2) produces reactive oxygen species following the onset of fluid shear stress that, in turn, activates transient receptor potential vanilloid 4 (TRPV4) channels to allow for calcium influx. This ultimately results in calcium/calmodulin-dependent kinase II (CaMKII) activation and sclerostin degradation, lifting the inhibition on osteoblasts to allow for bone formation. Though the mechano- transduction cascade controlling sclerostin abundance has been described in in vitro osteocytes, the fidelity and impact of this signaling pathway's impact on sclerostin regulation and bone mass has not been examined in vivo. This proposal will examine how the loss of NOX2, a necessary early step in the mechano-transduction cascade, affects bone quality, both in unstimulated and mechanically-stimulated conditions, in an in vivo animal model. Supported by in vitro and in vivo preliminary data, we hypothesize that the mechano-transduction pathway controlling sclerostin in vitro is conserved in vivo and that disrupting NOX2-dependent ROS production will affect basal bone properties and impair bone acquisition in response to mechanical load. We will address this hypothesis in one aim with three independent experiments: (1) Examine how NOX2 deletion in osteocytes impacts basal bone properties and mechano-responsiveness in vivo. Given the in vitro nature of our prior work on this pathway, the contribution of this mechano-transduction pathway to in vivo bone mechano-responsiveness remained unresolved. To extend these in vitro findings, this proposal will use in vitro and in vivo models, specifically a conditional deletion model, to address several knowledge gaps, including the cell autonomous role of NOX2 in osteocytes and the contribution of NOX2-mediated ROS to skeletal physiology and function. This proposal will validate novel therapeutic targets, such as ROS production, which can be exploited to mimic load in populations where traditional mechanical load is not possible.