Functional interaction between AQP2 and TRPV4 in renal cells

Abstract

We have previously demonstrated that renal cortical collecting duct cells (RCCD 1 ), responded to hypotonic stress with a rapid activation of regulatory volume decrease (RVD) mechanisms. This process requires the presence of the water channel AQP2 and calcium influx, opening the question about the molecular identity of this calcium entry path. Since the calcium permeable nonselective cation channel TRPV4 plays a crucial role in the response to mechanical and osmotic perturbations in a wide range of cell types, the aim of this work was to test the hypothesis that the increase in intracellular calcium concentration and the subsequent rapid RVD, only observed in the presence of AQP2, could be due to a specific activation of TRPV4. We evaluated the expression and function of TRPV4 channels and their contribution to RVD in WT-RCCD 1 (not expressing aquaporins) and in AQP2-RCCD 1 (transfected with AQP2) cells. Our results demonstrated that both cell lines endogenously express functional TRPV4, however, a large activation of the channel by hypotonicity only occurs in cells that express AQP2. Blocking of TRPV4 by ruthenium red abolished calcium influx as well as RVD, identifying TRPV4 as a necessary component in volume regulation. Even more, this process is dependent on the translocation of TRPV4 to the plasma membrane. Our data provide evidence of a novel association between TRPV4 and AQP2 that is involved in the activation of TRPV4 by hypotonicity and regulation of cellular response to the osmotic stress, suggesting that both proteins are assembled in a signaling complex that responds to anisosmotic conditions. J. Cell. Biochem. 113: 580-589, 2012. ß 2011 Wiley Periodicals, Inc.KEY WORDS: AQUAPORIN 2; TRANSIENT RECEPTOR POTENTIAL VANILLOID 4; CELL VOLUME REGULATION; INTRACELLULAR CALCIUM M any cell types have evolved specialized mechanisms of volume regulation to counteract damage induced by either cell swelling or shrinking. Under hypotonic conditions, cells first respond by swelling and second by initiating a mechanism that allows them to recover their original volume, this mechanism is called regulatory volume decrease (RVD) [O'Neill, 1999;Okada et al., 2001;Lang, 2007]. Essentially all cells respond to hypotonic swelling with this complex mechanism but the response is usually incomplete probably due to the fact that a new steady-state volume is achieved [O'Neill, 1999]. RVD depends on the release of inorganic and organic osmolytes that reverse the osmotic gradient and direction of water flow [Okada et al., 2001;Strange, 2004;Lang, 2007]. A number of ion channels and transporters were identified as the pathways for volume-regulatory ionic flux [Lang, 2007], however, the underlying mechanism that senses the change in osmolarity and/or cell volume to initiate volume regulation is not yet completely understood.We have previously demonstrated, in a rat cortical collecting duct cell line (RCCD 1 ) which exhibits many major functional properties of the cortical collecting duct (CCD) [Blot-Chabaud et al., 1996;Dje...

Discrete Control of TRPV4 Channel Function in the Distal Nephron by Protein Kinases A and C

“…This indicates that TRPV4 trafficking in distal nephron cells might be at least partially under the control of antidiuretic hormone (vasopressin). TRPV4 was recently shown to functionally interact with AQP2, the well known end effector of vasopressin, and the trafficking of TRPV4 to the plasma membrane in M1 collecting duct cells occurs only in the presence of AQP2 (26). Although this was associated with enhanced responses to hypotonicity, we failed to observe an augmented response to flow in forskolin-treated distal nephrons (Fig.…”

Transient Receptor Potential Channels as Drug Targets: From the Science of Basic Research to the Art of Medicine

“…Direct mechanoactivation of TRPV4 was recently demonstrated (Loukin et al, 2010b). TRPV4 interacts (or even forms heteromers) with TRPP1 (Köttgen et al, 2008), aquaporin 4 (Benfenati et al, 2011), aquaporin 2 (Galizia et al, 2012), TRPC1 , and/or calcium-activated potassium channel (KCa2.3 cells) . TRPV4 can be activated by a number of endogenous agonists.…”

Role of aquaporins in cell proliferation: What else beyond water permeability?

“…34 Moreover, in renal cortical collecting ducts expressing AQP2, hypotonic stress caused translocation of TRPV4 to the plasma membrane, indicating a functional interaction between the two proteins and suggesting that AQP2 forms part of a sensory and signaling pathway that results in TRPV4 translocation, possibly via sensing of extracellular osmolality. 35 Hypotonicity-induced translocation of AQP1 has also been described in HEK293 cells. 36 Another example that illustrates the role of AQPs in cell volume regulation can be seen in sperm, where AQP3 is actively involved in the signaling pathway that activates RVD to protect sperm from excess cell swelling, thereby optimizing postcopulatory sperm behavior.…”