A Role for AQP5 in Activation of TRPV4 by Hypotonicity: CONCERTED INVOLVEMENT OF AQP5 AND TRPV4 IN REGULATION OF CELL VOLUME RECOVERY

Indu Ambudkar,Tetsuji Nakamoto,Brij Singh,James E Melvin,Xibao Liu,Wolfgang Liedtke,Bidhan Bandyopadhyay

doi:10.1074/jbc.m600549200

Abstract

Regulation of cell volume in response to changes in osmolarity is critical for cell function and survival. However, the molecular basis of osmosensation and regulation of cell volume are not clearly understood. We have examined the mechanism of regulatory volume decrease (RVD) in salivary gland cells and report a novel association between osmosensing TRPV4 (transient receptor potential vanalloid 4) and AQP5 (aquaporin 5), which is required for regulating water permeability and cell volume. Exposure of salivary gland cells and acini to hypotonicity elicited an increase in cell volume and activation of RVD. Hypotonicity also activated Ca2+ entry, which was required for subsequent RVD. Ca2+ entry was associated with a distinct nonselective cation current that was activated by 4alphaPDD and inhibited by ruthenium red, suggesting involvement of TRPV4. Consistent with this, endogenous TRPV4 was detected in cells and in the apical region of acini along AQP5. Importantly, acinar cells from mice lacking either TRPV4 or AQP5 displayed greatly reduced Ca2+ entry and loss of RVD in response to hypotonicity, although the extent of cell swelling was similar. Expression of N terminus-deleted AQP5 suppressed TRPV4 activation and RVD but not cell swelling. Furthermore, hypotonicity increased the association and surface expression of AQP5 and TRPV4. Both these effects and RVD were reduced by actin depolymerization. These data demonstrate that (i) activation of TRPV4 by hypotonicity depends on AQP5, not on cell swelling per se, and (ii) TRPV4 and AQP5 concertedly control regulatory volume decrease. These data suggest a potentially important role for TRPV4 in salivary gland function.

Highlights

From the ‡Secretory Physiology Section, Gene Therapy and Therapeutics Branch, NIDCR, National Institutes of Health, Bethesda, Maryland 20892, the §Center for Oral Biology, University of Rochester, Rochester, New York 14642, the ¶Department of Biochemistry and Molecular Biology, University of North Dakota, Grand Forks, North Dakota 58203, and the ʈCenter for Translational Neuroscience, Duke University Medical Center, Durham, North Carolina 27710
We have examined the mechanism of regulatory volume decrease (RVD) in salivary gland cells and report a novel association between osmosensing TRPV4 and AQP5, which is required for regulating water permeability and cell volume
Hypotonicity Stimulates Changes in Cell Volume and Ca2ϩ Entry via a TRPV4-like Channel in Salivary Gland Cells—Fig. 1A shows that hypotonic external solution (HTS) induced a sustained increase in [Ca2ϩ]i in HSG

Summary

A Role for AQP5 in Activation of TRPV4 by Hypotonicity

VOLUME RECOVERY Xibao Liu, Bidhan Bandyopadhyay, Tetsuji Nakamoto, Brij Singh, Wolfgang Liedtke, James E. Myelin basic protein-primed T cells induce neurotrophins in glial cells via ␣v␤3 integrin. We request the readers to consider ␣5␤3 as ␣v␤3 and the title of the article as “Myelin Basic Protein-primed T Cells Induce Neurotrophins in Glial Cells via ␣v␤3 Integrin.”. 16-0512) for fluorescence-activated cell sorting analysis (Fig. 5) and neutralization experiments A role for AQP5 in activation of TRPV4 by hypotonicity: concerted involvement of AQP5 and TRPV4 in regulation of cell volume recovery. Dr Bandyopadhyay’s middle initial was inadvertently omitted. Secondary (abstract) services are urged to carry notice of these corrections as prominently as they carried the original abstracts

EXPERIMENTAL PROCEDURES

RESULTS

DISCUSSION