Primary cilia regulate the osmotic stress response of renal epithelial cells through TRPM3.

Pri-mary cilia sense environmental conditions, including osmolality, butwhether cilia participate in the osmotic response in renal epithelialcells is not known. The transient receptor potential (TRP) channelsTRPV4 and TRPM3 are osmoresponsive. TRPV4 localizes to cilia incertain cell types, while renal subcellular localization of TRPM3 is notknown. We hypothesized that primary cilia are required for maximalactivation of the osmotic response of renal epithelial cells and thatciliary TRPM3 and TRPV4 mediate that response. Ciliated [murineepithelial cells from the renal inner medullary collecting duct(mIMCD-3) and 176-5] and nonciliated (176-5Δ) renal cells ex-pressedTrpv4andTrpm3. Ciliary expression of TRPM3 was observedin mIMCD-3 and 176-5 cells and in wild-type mouse kidney tissue.TRPV4 was identified in cilia and apical membrane of mIMCD-3cells by electrophysiology and in the cell body by immunofluores-cence. Hyperosmolal stress at 500 mOsm/kg (via NaCl addition)induced the osmotic response genes betaine/GABA transporter (Bgt1)and aldose reductase (Akr1b3) in all ciliated cell lines. This inductionwas attenuated in nonciliated cells. A TRPV4 agonist abrogatedBgt1andAkr1b3induction in ciliated and nonciliated cells. A TRPM3agonist attenuatedBgt1andAkr1b3induction in ciliated cells only.TRPM3 knockout attenuatedAkr1b3induction. Viability under os-motic stress was greater in ciliated than nonciliated cells.Akr1b3induction was also less in nonciliated than ciliated cells when man-nitol was used to induce hyperosmolal stress. These findings suggestthat primary cilia are required for the maximal osmotic response inrenal epithelial cells and that TRPM3 is involved in this mechanism.TRPV4 appears to modulate the osmotic response independent ofcilia. [ABSTRACT FROM AUTHOR]