Primary Cilia Mediate Intracellular cAMP Responses in Bone Cells Exposed to Dynamic Fluid Flow

It is well accepted that fluid flow is an important mechanical signal in regulating bone structure and function. Primary cilia, which are non-motile, microtubule based organelles that extend from the centrosome and project into extracellular space in many cell types, have recently been shown to mediate fluid flow-induced osteogenic responses in MLO-Y4 osteocyte-like cells [1]. However, primary cilia did not mediate increases in intracellular Ca2+ concentration, and the second messenger system(s) involved in primary cilia-mediated mechanosensing has yet to be elucidated. In this study, our goals were to (1) determine whether exposing bone cells to oscillatory fluid flow modulates intracellular levels of cyclic adenosine monophosphate (cAMP), another ubiquitous second messenger molecule, and (2) investigate whether this modulation may be mediated by primary cilia.