RAPAMYCIN INCREASES LENGTH AND MECHANOSENSORY FUNCTION OF PRIMARY CILIA IN RENAL EPITHELIAL AND VASCULAR ENDOTHELIAL CELLS.

Primary cilia arebiophysically-sensitive organelles responsible for sensing fluid-flow and transducing this stimulus into intracellular responses. Previous studies have shown that the primary cilia mediate flow-induced calcium influx, and sensitivity of cilia function to flow is correlated to cilia length. Cells with abnormal cilia length or function can lead to a host of diseases that are collectively termed as ciliopathies. Rapamycin, a potent inhibitor of mTOR (mammalian target of rapamycin), has been demonstrated to be a potential pharmacological agent against the aberrant mTOR signaling seen in ciliopathies such as polycystic kidney disease (PKD) and tuberous sclerosis complex (TSC). Here we look at the effects of rapamycin on ciliary length and function for the first time. Compared to controls, primary cilia in rapamycin-treated porcine renal epithelial and mouse vascular endothelial cells showed a significant increase in length. Graded increases in fluid-shear stress further indicates that rapamycin enhances cilia sensitivity to fluid flow. Treatment with rapamycin led to G0 arrest in porcine epithelial cells while no significant change in cell cycle were observed in rapamycin-treated mouse epithelial or endothelial cells, indicating a species-specific effect of rapamycin. Given the previousin vitro and in vivo studies establishing rapamycin as a potential therapeutic agent for ciliopathies, such as PKD and TSC, our studies show that rapamycin enhances ciliary function and sensitivity to fluid flow. The results of our studies suggest a potential ciliotherapeutic effect of rapamycin.