Am J Physiol Lung Cell Mol Physiol 307: L817–L821, 2014; First published October 3, 2014; doi:10.1152/ajplung.00254.2014.
Editorial Focus
TRPV4: an exciting new target to promote alveolocapillary barrier function Rory E. Morty1,2 and Wolfgang M. Kuebler3,4,5 1
Department of Lung Development and Remodelling, Max Planck Institute for Heart and Lung Research, Bad Nauheim, Germany; 2Department of Internal Medicine (Pulmonology), University of Giessen and Marburg Lung Center (UGMLC), member of the German Center for Lung Research (DZL), Giessen, Germany; 3Institute of Physiology, Charité Universitätsmedizin Berlin, Germany; 4Departments of Surgery and Physiology, University of Toronto, Toronto, Ontario, Canada; and 5The Keenan Research Center for Biomedical Science of St. Michael’s, Toronto, Ontario, Canada Submitted 4 September 2014; accepted in final form 17 September 2014
Morty RE, Kuebler WM. TRPV4: an exciting new target to promote alveolocapillary barrier function. Am J Physiol Lung Cell Mol Physiol 307: L817–L821, 2014. First published October 3, 2014; doi:10.1152/ajplung.00254.2014.—Transient receptor potential (TRP) channels are emerging as important players and drug targets in respiratory disease. Amongst the vanilloid-type TRP channels (which includes the six members of the TRPV family), target diseases include cough, asthma, cancer, and more recently, pulmonary edema associated with acute respiratory distress syndrome. Here, we critically evaluate a recent report that addresses TRPV4 as a candidate target for the management of acute lung injury that develops as a consequence of aspiration of gastric contents, or acute chlorine gas exposure. By use of two new TRPV4 inhibitors (GSK2220691 or GSK2337429A) and a trpv4⫺/⫺ mouse strain, TRPV4 was implicated as a key mediator of pulmonary inflammation after direct chemical insult. Additionally, applied therapeutically, TRPV4 inhibitors exhibited vasculoprotective effects after chlorine gas exposure, inhibiting vascular leakage, and improving blood oxygenation. These observations underscore TRPV4 channels as candidate therapeutic targets in the management of lung injury, with the added need to balance these against the potential drawbacks of TRPV4 inhibition, such as the danger of limiting the immune response in settings of pathogen-provoked injury. ARDS; chlorine; edema; inflammation; TRPV4 TRANSIENT RECEPTOR POTENTIAL (TRP) channels comprise a group of nonselective cation channels that currently receive much attention in the cardiopulmonary system, both as pathogenic mediators and as targets for the treatment or prevention of lung and airway disease (17, 25). The TRP channels in mammals are currently organized, on the basis of protein and nucleotide sequence homology, into six families: the canonical (TRPC), vanilloid (TRPV), melastatin (TRPM), mucolipin (TRPML), polycystin (TRPP), and ankyrin (TRPA) families. Of these families, the six-member TRPV family is currently the subject of intense research in respiratory health and disease. Specifically, TRPV1 channels, which are expressed in nonmyelinated afferents innervating the airways and lungs (23), have evolved as novel pathogenic mediators and therapeutic targets in asthma and cough (4, 9, 17, 30, 35, 41). Recently, it has been demonstrated in rats that TRPV1 facilitates the activation of lung vagal C-fiber afferents by cigarette smoke (45), and some of the symptom control for cough afforded by tiotropium use has recently been attributed to effects of tiotropium on TRPV1 that are independent of its anticholinergic activity (3). Although less studied than TRPV1 channels, TRPV2 mRNA
Address for reprint requests and other correspondence: R. E. Morty, Dept. of Lung Development and Remodelling, Max Planck Institute for Heart and Lung Research, Parkstrasse 1, D-61231 Bad Nauheim, Germany (e-mail: rory.morty @mpi-bn.mpg.de). http://www.ajplung.org
expression is highest in the lung, of all organs examined (22), and a critical role for TRPV2 as mediator of strain-induced calcium entry into alveolar type II cells has recently been reported (13). Notably, the latter finding may relate to the physiologically relevant Ca2⫹-dependent mechanism of surfactant release from alveolar type II cells (51). TRPV3 is regarded largely as a thermosensitive channel in the skin and has not yet been ascribed any function in the lung or airway (34). TRPV5 and TRPV6 expression is only now just being considered in the lung, and reduced expression of both channels has been noted in human tumor tissues from non-small cell lung cancer patients; this reduced expression is associated with decreased median survival after surgical resection (11). This effect may be related to a role for TRPV6 in facilitating apoptosis, which has been reported for small cell lung cancer cells (29). In a recent report in the Journal, Balakrishna and colleagues (2) focus on TRPV4, a ubiquitously expressed cation channel that facilitates cellular responses to both physical (such as osmotic, mechanical, and heat) as well as chemical stimuli, that was first described in the airway epithelium in 2001 (8). Here, Balakrishna and colleagues (2) have examined the role of TRPV4 in lung injury resulting from exposure to two chemical stimuli, intratracheal instillation of hydrochloric acid or chlorine inhalation, using two novel and structurally unrelated TRPV4 inhibitors, GSK2220691 or GSK2337429A, as well as trpv4⫺/⫺ mice. These models mimic clinically relevant triggers of lung injury resulting from aspiration of gastric contents (modeled by intratracheal hydrochloric acid administration in mice) and acute chlorine gas exposure following an environmental accident or a chemical warfare attack (modeled by chlorine gas inhalation in mice) (14). The beauty of this study was that the inhibitors were not applied prophylactically, prior to induction of lung injury, but in a clinically more relevant treatment strategy, either immediately after chlorine exposure, or, in case of acid instillation, with a 30-min lag time. Application of TRPV4 inhibitors had potent anti-inflammatory effects in these two injury models, limiting neutrophil and macrophage infiltration and dampening the levels of proinflammatory cytokines and chemokines in the bronchoalveolar lavage fluid and serum. These observations were largely recapitulated in trpv4⫺/⫺ mice. In the chlorine inhalation model, postinjury application of TRPV4 inhibitors also improved blood oxygenation and reduced airway hyperreactivity. Interestingly, these effects are in part reminiscent of the attenuated inflammatory response and airway hyperresponsiveness in allergen-challenged trpc1⫺/⫺ mice (49), an idea with increasing relevance in view of the recent identification of TRPV4TRPC1 heterodimers, which can assemble to form a functional
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store-operated Ca2⫹ channel (31). The investigators went on to propose that under conditions of lung injury, TRPV4 may be activated by endogenously produced N-acylamine cannabinoids, fatty acid-derived products related to anandamide that can activate various TRP channels, levels of which were found to be elevated in the lungs of chlorine or hydrochloric acidtreated mice. Notably, anandamide has been shown to activate TRPV4 channels in an indirect manner via cytochrome P-450 epoxygenase-dependent formation of epoxyeicosatrienoic acids (EETs) (44). Intriguingly, EETs are also the dominant eicosanoids in human lungs upon microbial challenge and hence are considered to contribute substantially to inflammatory-infectious pulmonary injury. Whether induction of TRPV4mediated chlorine- and acid-induced lung injury similarly depends on the formation of EETs, or whether lung injury subsequent to microbial infections involves TRPV4, remains, however, to be demonstrated. This exciting study builds on a solid body of data that supports a role for TRPV4 in a broad spectrum of lung and airway functions and disease processes. TRPV4 has been implicated as a key regulator of lung endothelial barrier integrity, specifically, the integrity of the lung alveolar capillary endothelium, which is most relevant to alveolar flooding associated with acute lung injury (5, 21, 39). TRPV4 activation by the phorbol ester 4␣-phorbol 12,13-didecanoate (4␣PDD) increases lung capillary permeability and triggers the formation of alveolar edema (1, 46), whereas, conversely, hydrostatic lung edema formation and capillary leakage are reduced in trpv4⫺/⫺ mice (24, 50). In lung microvessels, hydrostatic stress activates TRPV4, presumably by circumferential vessel stretch, and the resulting increased endothelial Ca2⫹ concentration (27) triggers a diverse set of vascular responses. These responses include an increase in endothelial permeability through activation of myosin light chain kinase (50), the stimulation of endothelial NO synthesis (26), and the exocytosis of Weibel-Palade bodies with subsequent expression of Pselectin on the vascular surface (28). Although it should be noted that the latter response is confined to larger lung microvessels but is absent in alveolar capillaries, which are devoid of Weibel-Palade bodies (53) and do not express P-selectin in response to TRPV4 agonists (46), it may nevertheless be of considerable relevance in the context of the present study. Indeed, TRPV4-mediated exocytosis of Weibel-Palade bodies, P-selectin expression, and the concomitant release of chemokines such as interleukin-8 may provide a mechanistic explanation for the strikingly reduced infiltration of inflammatory cells following treatment with TRPV4 inhibitors. In addition to regulating endothelial permeability and as a result of Ca2⫹ entry channel function in pulmonary artery smooth muscle cells, TRPV4 also plays an important role in the regulation of lung myogenic tone. Inhibition or deficiency of TRPV4 has been documented to attenuate serotonin-induced Ca2⫹ elevations in pulmonary artery smooth muscle cells and thus attenuate the contraction of isolated pulmonary arteries (47). A similar role for TRPV4 was recently identified in the lung vascular responses to hypoxia, implicating TRPV4 in the complex signaling cascade that mediates hypoxic pulmonary vasoconstriction. Although this finding is essentially in line with the documented role of TRPV4 in lung vascular remodeling associated with exposure to chronic hypoxia (6, 48, 52),
it poses a potential threat to the clinical use of TRPV4 inhibitors for the treatment of acute lung injury. Lung injury is characteristically distributed in a heterogeneous fashion throughout the lungs, and redistribution of blood flow from poorly ventilated to better aerated lung areas by the von Euler-Liljestrand mechanism provides an intrinsic rescue mechanism by which an organism can maintain adequate arterial blood oxygenation even when significant parts of the lung have ceased to participate in gas exchange. Pharmacological inhibition of such a key physiological response would potentially be detrimental to any patient with acute lung disease. The fact that TRPV4 inhibition improved arterial oxygenation in the chlorine injury model seems to argue against such an effect, but the situation may differ in scenarios of more heterogeneous injury. In addition to effects in the pulmonary vasculature, TRPV4 has also been implicated in the maintenance of epithelial barrier function in the lung (38), and TRPV4 mediates the constriction of airway smooth muscle cells in a cysteinyl leukotriene-dependent manner (32). TRPV4 is also expressed in alveolar macrophages (18), implying a potential role in the regulation of inflammation. This has proven relevant in the context of lung injury, since adoptive transfer of macrophages from trpv4⫹/⫹ mice to trpv4⫺/⫺ mice restored susceptibility of trpv4⫺/⫺ lungs to mechanical injury induced by high peak inflation pressure ventilation (19). Given the broad spectrum of roles in lung and cellular function, TRPV4 has been conclusively identified as a mediator of hydrostatic lung edema (24, 50), as well as edema associated with experimental ventilator-induced lung injury (20). These observations have led to studies that have documented the usefulness of TRPV4 inhibition in models of pulmonary edema formation secondary to heart failure, in which application of an earlier-generation TRPV4 inhibitor GSK2193874 decreased extravascular lung water and increased arterial oxygenation (42). In the background of the emerging role of TRPV4 in cardiopulmonary physiology, the study by Balakrishna and colleagues (2) provides a foundation for further exciting work. Several important questions immediately emerge. A very striking observation made in the report is that TRPV4 inhibitors exhibit potent anti-inflammatory activity, which was comparable to that of glucocorticoids. Both TRPV4 inhibitors employed blocked inflammatory cell influx, dampened myeloperoxidase activity in the bronchoalveolar lavage as a measure of neutrophil infiltration and activation, and blunted proinflammatory cytokine and chemokine production. These effects were recapitulated in trpv4⫺/⫺ mice. However, the mechanisms underlying all of these effects are not understood. One possibility discussed above is that TRPV4 inhibitors act primarily on endothelial and epithelial cells, not only preventing changes in barrier function, but also blocking other Ca2⫹dependent processes such as the release of cytokines and adhesion molecules or the facilitation of neutrophil transit (40). Alternatively, do these inhibitors (and thus, TRPV4) directly impact macrophage and neutrophil function and mobility? Functional expression of TRPV4 in macrophages and its central role in the elicitation of ventilation-induced lung injury has been previously documented in isolated lung studies (19). In the present study, Balakrishna and colleagues furthermore analyzed RNAseq neutrophil transcriptome datasets in silico
AJP-Lung Cell Mol Physiol • doi:10.1152/ajplung.00254.2014 • www.ajplung.org
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and concluded that the frequency of TRPV4 transcripts in either noninduced or induced neutrophils was very low. This notion, however, is in contrast to quantitative real-time PCR analyses from murine neutrophils demonstrating an abundance of TRPV4 mRNA, compared with other TRP channels including TRPC3, TRPC6, TRPC7, and TRPM4 (7). The actual cell type (or types), through which TRPV4 inhibitors exert their anti-inflammatory effects remains, hence, so far unclear and may require extensive work using adoptive transfer models and
chimeric mice. The general notion, however, of a key role for TRPV4 in inflammatory disease processes is substantiated by recent reports that TRPV4 blockade can effectively protect against experimental colitis in mice (12), whereas, conversely, TRPV4 agonists trigger joint inflammation in rats (10). However, this anti-inflammatory potential also bears a serious risk for the therapeutic use of TRPV4 inhibitors in lung injury: the majority of patients with acute respiratory distress syndrome suffer from concomitant pulmonary (pneumonia) or systemic
Chemical injury (chlorine gas, acid)
Edema fluid
ROS NO
ATI cell
Alveolar macrophage
PASMC
PMN ?
Increased permeability Protein + fluid leak
ATII cell NO
P-selectin Vasoconstriction
EC Artery
TRPV4 channel
Capillary
Vein
Fig. 1. Role of TRPV4 in acute lung injury. Inhalation or intratracheal instillation of injurious chemicals such as chlorine gas or acid causes acute lung injury that is characterized by influx of inflammatory cells and failure of the alveolocapillary barrier, resulting in the formation of a cell- and protein-rich alveolar edema. Pharmacological inhibition or genetic deficiency of TRPV4 alleviates these effects, demonstrating that TRPV4, which is expressed on various lung parenchymatous and inflammatory cells, contributes critically to this scenario: In lung capillary endothelial cells (EC), TRPV4 activation increases vascular permeability, thus promoting protein and fluid leak. In extra-alveolar vessels, TRPV4 activation may stimulate endothelial P-selectin expression and nitric oxide (NO) synthesis. In pulmonary artery smooth muscle cells (PASMC), TRPV4 mediates vasoconstriction and may thus modulate ventilation/perfusion matching in injured lungs. In alveolar macrophages, TRPV4 activation results in the formation of reactive oxygen species (ROS) and NO, which in combination give rise to peroxynitrite, causing tyrosine nitrosylation of proteins. TRPV4 has also been reported to be expressed on alveolar epithelial cells and, according to some authors, neutrophils, yet their contribution to TRPV4-mediated acute lung injury remains to be resolved. The wide expression and multifold functions of TRPV4 in the lung render this channel a promising yet at the same time complex target for the treatment of acute lung injury. PMN, polymorphonuclear cell, neutrophil; ATI/ATII cell, alveolar type 1/type 2 cell. AJP-Lung Cell Mol Physiol • doi:10.1152/ajplung.00254.2014 • www.ajplung.org
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(sepsis) infections. Anti-inflammatory therapies that would dampen the body’s ability to clear invading pathogens could easily aggravate such infectious diseases with potentially fatal results. In their report, Balakrishna and colleagues (2) have addressed responses to HCl-induced damage in trpv4⫺/⫺ mice; however, for the chlorine-exposure studies, only the two TRPV4 inhibitors were employed. It remains to be demonstrated whether trpv4⫺/⫺ mice are protected from lung damage in response to chlorine gas inhalation. Along these lines, a further consideration with the mouse models would be to assess the responses to (and protection against) chlorine exposure in other mouse strains, which are notorious for strain-dependent variability in response to chlorine inhalation (14, 33). The combination of vascular protective effects and antiinflammatory properties also make TRPV4 inhibitors interesting candidates for investigation in animal models of pulmonary vascular disease with an inflammatory component, such as pulmonary arterial hypertension. TRPV4 has been directly implicated in pulmonary vascular remodeling, in response to chronic exposure of mice to hypoxia (47), a well-characterized animal model of pulmonary arterial hypertension (15, 43); however, perivascular inflammation is not appreciable in this model. In contrast, inflammation is a key player in the related rat monocrotaline model of pulmonary arterial hypertension (16). It would be interesting to explore the effect of TRPV4 inhibitors in that and other animal models of pulmonary disease with vascular and inflammatory components (37), particularly considering that pulmonary hypertension is a frequent complication of acute lung injury (36). The present work by Balakrishna and colleagues (2) identifies a novel pathogenic role for TRPV4 that extends its previously reported relevance in cardiogenic lung edema and ventilator-induced lung injury to scenarios of chemically induced lung injury (outlined in Fig. 1) and identifies TRPV4 inhibitors as promising therapeutic strategy for the treatment of related clinical conditions. Because of the ubiquitous expression of TRPV4, and the multitude of functions ascribed to TRPV4, including a role in lung vasomotor control, the inflammatory response, and the regulation of systemic blood pressure, TRPV4 blockade may represent a double-edged sword. The therapeutic benefits of TRPV4 inhibition will have to be carefully weighed against potential adverse effects on a caseby-case basis. GRANTS This work was supported by the Max Planck Society (R. E. Morty); by the German Centre for Lung Research (to R. E. Morty); by research grant 62589035 from the University Medical Center Giessen and Marburg (to R. E. Morty); by the Federal Ministry of Higher Education, Research, and the Arts of the State of Hessen LOEWE-Programm (to R. E. Morty); and by the German Research Foundation through Individual Grant Mo1789/1 (to R. E. Morty) and Excellence Cluster 147 Cardio-Pulmonary System (to R. E. Morty). W. M. Kuebler received support from the Canadian Institutes of Health Research, the German Research Foundation, and the Heart & Stroke Foundation of Canada. DISCLOSURES No conflicts of interest, financial or otherwise, are declared by the author(s).
AUTHOR CONTRIBUTIONS R.E.M. and W.M.K. analyzed data; R.E.M. and W.M.K. interpreted results of experiments; R.E.M. and W.M.K. drafted manuscript; R.E.M. and W.M.K. edited and revised manuscript; R.E.M. and W.M.K. approved final version of manuscript. REFERENCES 1. Alvarez DF, King JA, Weber D, Addison E, Liedtke W, Townsley MI. Transient receptor potential vanilloid 4-mediated disruption of the alveolar septal barrier: a novel mechanism of acute lung injury. Circ Res 99: 988 –995, 2006. 2. Balakrishna S, Song W, Achanta S, Doran SF, Liu B, Kaelberer MM, Yu Z, Sui A, Cheung M, Leishman E, Eidam HS, Ye G, Willette RN, Thorneloe KS, Bradshaw HB, Matalon S, Jordt SE. TRPV4 inhibition counteracts edema and inflammation and improves pulmonary function and oxygen saturation in chemically induced acute lung injury. Am J Physiol Lung Cell Mol Physiol 307: L158 –L172, 2014. 3. Birrell MA, Bonvini SJ, Dubuis E, Maher SA, Wortley MA, Grace MS, Raemdonck K, Adcock JJ, Belvisi MG. Tiotropium modulates transient receptor potential V1 (TRPV1) in airway sensory nerves: a beneficial off-target effect? J Allergy Clin Immunol 133: 679 –687.e9, 2014. 4. Cantero-Recasens G, Gonzalez JR, Fandos C, Duran-Tauleria E, Smit LA, Kauffmann F, Anto JM, Valverde MA. Loss of function of transient receptor potential vanilloid 1 (TRPV1) genetic variant is associated with lower risk of active childhood asthma. J Biol Chem 285: 27532–27535, 2010. 5. Cioffi DL, Lowe K, Alvarez DF, Barry C, Stevens T. TRPing on the lung endothelium: calcium channels that regulate barrier function. Antioxid Redox Signal 11: 765–776, 2009. 6. Dahan D, Ducret T, Quignard JF, Marthan R, Savineau JP, Esteve E. Implication of the ryanodine receptor in TRPV4-induced calcium response in pulmonary arterial smooth muscle cells from normoxic and chronically hypoxic rats. Am J Physiol Lung Cell Mol Physiol 303: L824 –L833, 2012. 7. Damann N, Owsianik G, Li S, Poll C, Nilius B. The calcium-conducting ion channel transient receptor potential canonical 6 is involved in macrophage inflammatory protein-2-induced migration of mouse neutrophils. Acta Physiol (Oxf) 195: 3–11, 2009. 8. Delany NS, Hurle M, Facer P, Alnadaf T, Plumpton C, Kinghorn I, See CG, Costigan M, Anand P, Woolf CJ, Crowther D, Sanseau P, Tate SN. Identification and characterization of a novel human vanilloid receptor-like protein, VRL-2. Physiol Genomics 4: 165–174, 2001. 9. Delescluse I, Mace H, Adcock JJ. Inhibition of airway hyper-responsiveness by TRPV1 antagonists (SB-705498 and PF-04065463) in the unanaesthetized, ovalbumin-sensitized guinea pig. Br J Pharmacol 166: 1822–1832, 2012. 10. Denadai-Souza A, Martin L, de Paula MA, de Avellar MC, Muscara MN, Vergnolle N, Cenac N. Role of transient receptor potential vanilloid 4 in rat joint inflammation. Arthritis Rheum 64: 1848 –1858, 2012. 11. Fan H, Shen YX, Yuan YF. Expression and prognostic roles of TRPV5 and TRPV6 in non-small cell lung cancer after curative resection. Asian Pac J Cancer Prev 15: 2559 –2563, 2014. 12. Fichna J, Mokrowiecka A, Cygankiewicz AI, Zakrzewski PK, Malecka-Panas E, Janecka A, Krajewska WM, Storr MA. Transient receptor potential vanilloid 4 blockade protects against experimental colitis in mice: a new strategy for inflammatory bowel diseases treatment? Neurogastroenterol Motil 24: e557–e560, 2012. 13. Fois G, Wittekindt O, Zheng X, Felder ET, Miklavc P, Frick M, Dietl P, Felder E. An ultra fast detection method reveals strain-induced Ca2⫹ entry via TRPV2 in alveolar type II cells. Biomech Model Mechanobiol 11: 959 –971, 2012. 14. Gessner MA, Doran SF, Yu Z, Dunaway CW, Matalon S, Steele C. Chlorine gas exposure increases susceptibility to invasive lung fungal infection. Am J Physiol Lung Cell Mol Physiol 304: L765–L773, 2013. 15. Gomez-Arroyo J, Saleem SJ, Mizuno S, Syed AA, Bogaard HJ, Abbate A, Taraseviciene-Stewart L, Sung Y, Kraskauskas D, Farkas D, Conrad DH, Nicolls MR, Voelkel NF. A brief overview of mouse models of pulmonary arterial hypertension: problems and prospects. Am J Physiol Lung Cell Mol Physiol 302: L977–L991, 2012. 16. Gomez-Arroyo JG, Farkas L, Alhussaini AA, Farkas D, Kraskauskas D, Voelkel NF, Bogaard HJ. The monocrotaline model of pulmonary hypertension in perspective. Am J Physiol Lung Cell Mol Physiol 302: L363–L369, 2012.
AJP-Lung Cell Mol Physiol • doi:10.1152/ajplung.00254.2014 • www.ajplung.org
Editorial Focus TRPV4 AND LUNG BARRIER FUNCTION 17. Grace MS, Baxter M, Dubuis E, Birrell MA, Belvisi MG. Transient receptor potential (TRP) channels in the airway: role in airway disease. Br J Pharmacol 171: 2593–2607, 2014. 18. Groot-Kormelink PJ, Fawcett L, Wright PD, Gosling M, Kent TC. Quantitative GPCR and ion channel transcriptomics in primary alveolar macrophages and macrophage surrogates. BMC Immunol 13: 57, 2012. 19. Hamanaka K, Jian MY, Townsley MI, King JA, Liedtke W, Weber DS, Eyal FG, Clapp MM, Parker JC. TRPV4 channels augment macrophage activation and ventilator-induced lung injury. Am J Physiol Lung Cell Mol Physiol 299: L353–L362, 2010. 20. Hamanaka K, Jian MY, Weber DS, Alvarez DF, Townsley MI, Al-Mehdi AB, King JA, Liedtke W, Parker JC. TRPV4 initiates the acute calcium-dependent permeability increase during ventilator-induced lung injury in isolated mouse lungs. Am J Physiol Lung Cell Mol Physiol 293: L923–L932, 2007. 21. Herold S, Gabrielli NM, Vadasz I. Novel concepts of acute lung injury and alveolar-capillary barrier dysfunction. Am J Physiol Lung Cell Mol Physiol 305: L665–L681, 2013. 22. Jang Y, Lee Y, Kim SM, Yang YD, Jung J, Oh U. Quantitative analysis of TRP channel genes in mouse organs. Arch Pharm Res 35: 1823–1830, 2012. 23. Jia Y, Lee LY. Role of TRPV receptors in respiratory diseases. Biochim Biophys Acta 1772: 915–927, 2007. 24. Jian MY, King JA, Al-Mehdi AB, Liedtke W, Townsley MI. High vascular pressure-induced lung injury requires P450 epoxygenase-dependent activation of TRPV4. Am J Respir Cell Mol Biol 38: 386 –392, 2008. 25. Jordt SE, Ehrlich BE. TRP channels in disease. Subcell Biochem 45: 253–271, 2007. 26. Kuebler WM, Uhlig U, Goldmann T, Schael G, Kerem A, Exner K, Martin C, Vollmer E, Uhlig S. Stretch activates nitric oxide production in pulmonary vascular endothelial cells in situ. Am J Respir Crit Care Med 168: 1391–1398, 2003. 27. Kuebler WM, Ying X, Bhattacharya J. Pressure-induced endothelial Ca2⫹ oscillations in lung capillaries. Am J Physiol Lung Cell Mol Physiol 282: L917–L923, 2002. 28. Kuebler WM, Ying X, Singh B, Issekutz AC, Bhattacharya J. Pressure is proinflammatory in lung venular capillaries. J Clin Invest 104: 495–502, 1999. 29. Lau JK, Brown KC, Dom AM, Witte TR, Thornhill BA, Crabtree CM, Perry HE, Brown JM, Ball JG, Creel RG, Damron CL, Rollyson WD, Stevenson CD, Hardman WE, Valentovic MA, Carpenter AB, Dasgupta P. Capsaicin induces apoptosis in human small cell lung cancer via the TRPV6 receptor and the calpain pathway. Apoptosis 19: 1190 – 1201, 2014. 30. Lieu TM, Myers AC, Meeker S, Undem BJ. TRPV1 induction in airway vagal low-threshold mechanosensory neurons by allergen challenge and neurotrophic factors. Am J Physiol Lung Cell Mol Physiol 302: L941– L948, 2012. 31. Ma X, Cao J, Luo J, Nilius B, Huang Y, Ambudkar IS, Yao X. Depletion of intracellular Ca2⫹ stores stimulates the translocation of vanilloid transient receptor potential 4-c1 heteromeric channels to the plasma membrane. Arterioscler Thromb Vasc Biol 30: 2249 –2255, 2010. 32. McAlexander MA, Luttmann MA, Hunsberger GE, Undem BJ. Transient receptor potential vanilloid 4 activation constricts the human bronchus via the release of cysteinyl leukotrienes. J Pharmacol Exp Ther 349: 118 –125, 2014. 33. Mo Y, Chen J, Schlueter CF, Hoyle GW. Differential susceptibility of inbred mouse strains to chlorine-induced airway fibrosis. Am J Physiol Lung Cell Mol Physiol 304: L92–L102, 2013. 34. Nilius B, Biro T, Owsianik G. TRPV3: time to decipher a poorly understood family member! J Physiol 592: 295–304, 2014. 35. Prakash YS. Airway smooth muscle in airway reactivity and remodeling: what have we learned? Am J Physiol Lung Cell Mol Physiol 305: L912–L933, 2013. 36. Price LC, McAuley DF, Marino PS, Finney SJ, Griffiths MJ, Wort SJ. Pathophysiology of pulmonary hypertension in acute lung injury. Am J Physiol Lung Cell Mol Physiol 302: L803–L815, 2012.
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37. Schneberger D, Aharonson-Raz K, Singh B. Pulmonary intravascular macrophages and lung health: what are we missing? Am J Physiol Lung Cell Mol Physiol 302: L498 –L503, 2012. 38. Sidhaye VK, Schweitzer KS, Caterina MJ, Shimoda L, King LS. Shear stress regulates aquaporin-5 and airway epithelial barrier function. Proc Natl Acad Sci USA 105: 3345–3350, 2008. 39. Stevens T. Functional and molecular heterogeneity of pulmonary endothelial cells. Proc Am Thorac Soc 8: 453–457, 2011. 40. Su WH, Chen HI, Huang JP, Jen CJ. Endothelial [Ca2⫹]i signaling during transmigration of polymorphonuclear leukocytes. Blood 96: 3816 – 3822, 2000. 41. Thomas KC, Roberts JK, Deering-Rice CE, Romero EG, Dull RO, Lee J, Yost GS, Reilly CA. Contributions of TRPV1, endovanilloids, and endoplasmic reticulum stress in lung cell death in vitro and lung injury. Am J Physiol Lung Cell Mol Physiol 302: L111–L119, 2012. 42. Thorneloe KS, Cheung M, Bao W, Alsaid H, Lenhard S, Jian MY, Costell M, Maniscalco-Hauk K, Krawiec JA, Olzinski A, Gordon E, Lozinskaya I, Elefante L, Qin P, Matasic DS, James C, Tunstead J, Donovan B, Kallal L, Waszkiewicz A, Vaidya K, Davenport EA, Larkin J, Burgert M, Casillas LN, Marquis RW, Ye G, Eidam HS, Goodman KB, Toomey JR, Roethke TJ, Jucker BM, Schnackenberg CG, Townsley MI, Lepore JJ, Willette RN. An orally active TRPV4 channel blocker prevents and resolves pulmonary edema induced by heart failure. Sci Transl Med 4: 159ra148, 2012. 43. Voelkel NF, Mizuno S, Bogaard HJ. The role of hypoxia in pulmonary vascular diseases: a perspective. Am J Physiol Lung Cell Mol Physiol 304: L457–L465, 2013. 44. Watanabe H, Vriens J, Prenen J, Droogmans G, Voets T, Nilius B. Anandamide and arachidonic acid use epoxyeicosatrienoic acids to activate TRPV4 channels. Nature 424: 434 –438, 2003. 45. Weng WH, Hsu CC, Chiang LL, Lin YJ, Lin YS, Su CL. Role of TRPV1 and P2X receptors in the activation of lung vagal C-fiber afferents by inhaled cigarette smoke in rats. Mol Med Rep 7: 1300 –1304, 2013. 46. Wu S, Jian MY, Xu YC, Zhou C, Al-Mehdi AB, Liedtke W, Shin HS, Townsley MI. Ca2⫹ entry via ␣1G and TRPV4 channels differentially regulates surface expression of P-selectin and barrier integrity in pulmonary capillary endothelium. Am J Physiol Lung Cell Mol Physiol 297: L650 –L657, 2009. 47. Xia Y, Fu Z, Hu J, Huang C, Paudel O, Cai S, Liedtke W, Sham JS. TRPV4 channel contributes to serotonin-induced pulmonary vasoconstriction and the enhanced vascular reactivity in chronic hypoxic pulmonary hypertension. Am J Physiol Cell Physiol 305: C704 –C715, 2013. 48. Yang XR, Lin AH, Hughes JM, Flavahan NA, Cao YN, Liedtke W, Sham JS. Upregulation of osmo-mechanosensitive TRPV4 channel facilitates chronic hypoxia-induced myogenic tone and pulmonary hypertension. Am J Physiol Lung Cell Mol Physiol 302: L555–L568, 2012. 49. Yildirim E, Carey MA, Card JW, Dietrich A, Flake GP, Zhang Y, Bradbury JA, Rebolloso Y, Germolec DR, Morgan DL, Zeldin DC, Birnbaumer L. Severely blunted allergen-induced pulmonary Th2 cell response and lung hyperresponsiveness in type 1 transient receptor potential channel-deficient mice. Am J Physiol Lung Cell Mol Physiol 303: L539 –L549, 2012. 50. Yin J, Hoffmann J, Kaestle SM, Neye N, Wang L, Baeurle J, Liedtke W, Wu S, Kuppe H, Pries AR, Kuebler WM. Negative-feedback loop attenuates hydrostatic lung edema via a cGMP-dependent regulation of transient receptor potential vanilloid 4. Circ Res 102: 966 –974, 2008. 51. Yin J, Kuebler WM. Mechanotransduction by TRP channels: general concepts and specific role in the vasculature. Cell Biochem Biophys 56: 1–18, 2010. 52. Yoo HY, Park SJ, Seo EY, Park KS, Han JA, Kim KS, Shin DH, Earm YE, Zhang YH, Kim SJ. Role of thromboxane A2-activated nonselective cation channels in hypoxic pulmonary vasoconstriction of rat. Am J Physiol Cell Physiol 302: C307–C317, 2012. 53. Zhou C, Chen H, King JA, Sellak H, Kuebler WM, Yin J, Townsley MI, Shin HS, Wu S. ␣1G T-type calcium channel selectively regulates P-selectin surface expression in pulmonary capillary endothelium. Am J Physiol Lung Cell Mol Physiol 299: L86 –L97, 2010.
AJP-Lung Cell Mol Physiol • doi:10.1152/ajplung.00254.2014 • www.ajplung.org
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Editorial Focus
TRPV4: an exciting new target to promote alveolocapillary barrier function Rory E. Morty1,2 and Wolfgang M. Kuebler3,4,5 1
Department of Lung Development and Remodelling, Max Planck Institute for Heart and Lung Research, Bad Nauheim, Germany; 2Department of Internal Medicine (Pulmonology), University of Giessen and Marburg Lung Center (UGMLC), member of the German Center for Lung Research (DZL), Giessen, Germany; 3Institute of Physiology, Charité Universitätsmedizin Berlin, Germany; 4Departments of Surgery and Physiology, University of Toronto, Toronto, Ontario, Canada; and 5The Keenan Research Center for Biomedical Science of St. Michael’s, Toronto, Ontario, Canada Submitted 4 September 2014; accepted in final form 17 September 2014
Morty RE, Kuebler WM. TRPV4: an exciting new target to promote alveolocapillary barrier function. Am J Physiol Lung Cell Mol Physiol 307: L817–L821, 2014. First published October 3, 2014; doi:10.1152/ajplung.00254.2014.—Transient receptor potential (TRP) channels are emerging as important players and drug targets in respiratory disease. Amongst the vanilloid-type TRP channels (which includes the six members of the TRPV family), target diseases include cough, asthma, cancer, and more recently, pulmonary edema associated with acute respiratory distress syndrome. Here, we critically evaluate a recent report that addresses TRPV4 as a candidate target for the management of acute lung injury that develops as a consequence of aspiration of gastric contents, or acute chlorine gas exposure. By use of two new TRPV4 inhibitors (GSK2220691 or GSK2337429A) and a trpv4⫺/⫺ mouse strain, TRPV4 was implicated as a key mediator of pulmonary inflammation after direct chemical insult. Additionally, applied therapeutically, TRPV4 inhibitors exhibited vasculoprotective effects after chlorine gas exposure, inhibiting vascular leakage, and improving blood oxygenation. These observations underscore TRPV4 channels as candidate therapeutic targets in the management of lung injury, with the added need to balance these against the potential drawbacks of TRPV4 inhibition, such as the danger of limiting the immune response in settings of pathogen-provoked injury. ARDS; chlorine; edema; inflammation; TRPV4 TRANSIENT RECEPTOR POTENTIAL (TRP) channels comprise a group of nonselective cation channels that currently receive much attention in the cardiopulmonary system, both as pathogenic mediators and as targets for the treatment or prevention of lung and airway disease (17, 25). The TRP channels in mammals are currently organized, on the basis of protein and nucleotide sequence homology, into six families: the canonical (TRPC), vanilloid (TRPV), melastatin (TRPM), mucolipin (TRPML), polycystin (TRPP), and ankyrin (TRPA) families. Of these families, the six-member TRPV family is currently the subject of intense research in respiratory health and disease. Specifically, TRPV1 channels, which are expressed in nonmyelinated afferents innervating the airways and lungs (23), have evolved as novel pathogenic mediators and therapeutic targets in asthma and cough (4, 9, 17, 30, 35, 41). Recently, it has been demonstrated in rats that TRPV1 facilitates the activation of lung vagal C-fiber afferents by cigarette smoke (45), and some of the symptom control for cough afforded by tiotropium use has recently been attributed to effects of tiotropium on TRPV1 that are independent of its anticholinergic activity (3). Although less studied than TRPV1 channels, TRPV2 mRNA
Address for reprint requests and other correspondence: R. E. Morty, Dept. of Lung Development and Remodelling, Max Planck Institute for Heart and Lung Research, Parkstrasse 1, D-61231 Bad Nauheim, Germany (e-mail: rory.morty @mpi-bn.mpg.de). http://www.ajplung.org
expression is highest in the lung, of all organs examined (22), and a critical role for TRPV2 as mediator of strain-induced calcium entry into alveolar type II cells has recently been reported (13). Notably, the latter finding may relate to the physiologically relevant Ca2⫹-dependent mechanism of surfactant release from alveolar type II cells (51). TRPV3 is regarded largely as a thermosensitive channel in the skin and has not yet been ascribed any function in the lung or airway (34). TRPV5 and TRPV6 expression is only now just being considered in the lung, and reduced expression of both channels has been noted in human tumor tissues from non-small cell lung cancer patients; this reduced expression is associated with decreased median survival after surgical resection (11). This effect may be related to a role for TRPV6 in facilitating apoptosis, which has been reported for small cell lung cancer cells (29). In a recent report in the Journal, Balakrishna and colleagues (2) focus on TRPV4, a ubiquitously expressed cation channel that facilitates cellular responses to both physical (such as osmotic, mechanical, and heat) as well as chemical stimuli, that was first described in the airway epithelium in 2001 (8). Here, Balakrishna and colleagues (2) have examined the role of TRPV4 in lung injury resulting from exposure to two chemical stimuli, intratracheal instillation of hydrochloric acid or chlorine inhalation, using two novel and structurally unrelated TRPV4 inhibitors, GSK2220691 or GSK2337429A, as well as trpv4⫺/⫺ mice. These models mimic clinically relevant triggers of lung injury resulting from aspiration of gastric contents (modeled by intratracheal hydrochloric acid administration in mice) and acute chlorine gas exposure following an environmental accident or a chemical warfare attack (modeled by chlorine gas inhalation in mice) (14). The beauty of this study was that the inhibitors were not applied prophylactically, prior to induction of lung injury, but in a clinically more relevant treatment strategy, either immediately after chlorine exposure, or, in case of acid instillation, with a 30-min lag time. Application of TRPV4 inhibitors had potent anti-inflammatory effects in these two injury models, limiting neutrophil and macrophage infiltration and dampening the levels of proinflammatory cytokines and chemokines in the bronchoalveolar lavage fluid and serum. These observations were largely recapitulated in trpv4⫺/⫺ mice. In the chlorine inhalation model, postinjury application of TRPV4 inhibitors also improved blood oxygenation and reduced airway hyperreactivity. Interestingly, these effects are in part reminiscent of the attenuated inflammatory response and airway hyperresponsiveness in allergen-challenged trpc1⫺/⫺ mice (49), an idea with increasing relevance in view of the recent identification of TRPV4TRPC1 heterodimers, which can assemble to form a functional
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store-operated Ca2⫹ channel (31). The investigators went on to propose that under conditions of lung injury, TRPV4 may be activated by endogenously produced N-acylamine cannabinoids, fatty acid-derived products related to anandamide that can activate various TRP channels, levels of which were found to be elevated in the lungs of chlorine or hydrochloric acidtreated mice. Notably, anandamide has been shown to activate TRPV4 channels in an indirect manner via cytochrome P-450 epoxygenase-dependent formation of epoxyeicosatrienoic acids (EETs) (44). Intriguingly, EETs are also the dominant eicosanoids in human lungs upon microbial challenge and hence are considered to contribute substantially to inflammatory-infectious pulmonary injury. Whether induction of TRPV4mediated chlorine- and acid-induced lung injury similarly depends on the formation of EETs, or whether lung injury subsequent to microbial infections involves TRPV4, remains, however, to be demonstrated. This exciting study builds on a solid body of data that supports a role for TRPV4 in a broad spectrum of lung and airway functions and disease processes. TRPV4 has been implicated as a key regulator of lung endothelial barrier integrity, specifically, the integrity of the lung alveolar capillary endothelium, which is most relevant to alveolar flooding associated with acute lung injury (5, 21, 39). TRPV4 activation by the phorbol ester 4␣-phorbol 12,13-didecanoate (4␣PDD) increases lung capillary permeability and triggers the formation of alveolar edema (1, 46), whereas, conversely, hydrostatic lung edema formation and capillary leakage are reduced in trpv4⫺/⫺ mice (24, 50). In lung microvessels, hydrostatic stress activates TRPV4, presumably by circumferential vessel stretch, and the resulting increased endothelial Ca2⫹ concentration (27) triggers a diverse set of vascular responses. These responses include an increase in endothelial permeability through activation of myosin light chain kinase (50), the stimulation of endothelial NO synthesis (26), and the exocytosis of Weibel-Palade bodies with subsequent expression of Pselectin on the vascular surface (28). Although it should be noted that the latter response is confined to larger lung microvessels but is absent in alveolar capillaries, which are devoid of Weibel-Palade bodies (53) and do not express P-selectin in response to TRPV4 agonists (46), it may nevertheless be of considerable relevance in the context of the present study. Indeed, TRPV4-mediated exocytosis of Weibel-Palade bodies, P-selectin expression, and the concomitant release of chemokines such as interleukin-8 may provide a mechanistic explanation for the strikingly reduced infiltration of inflammatory cells following treatment with TRPV4 inhibitors. In addition to regulating endothelial permeability and as a result of Ca2⫹ entry channel function in pulmonary artery smooth muscle cells, TRPV4 also plays an important role in the regulation of lung myogenic tone. Inhibition or deficiency of TRPV4 has been documented to attenuate serotonin-induced Ca2⫹ elevations in pulmonary artery smooth muscle cells and thus attenuate the contraction of isolated pulmonary arteries (47). A similar role for TRPV4 was recently identified in the lung vascular responses to hypoxia, implicating TRPV4 in the complex signaling cascade that mediates hypoxic pulmonary vasoconstriction. Although this finding is essentially in line with the documented role of TRPV4 in lung vascular remodeling associated with exposure to chronic hypoxia (6, 48, 52),
it poses a potential threat to the clinical use of TRPV4 inhibitors for the treatment of acute lung injury. Lung injury is characteristically distributed in a heterogeneous fashion throughout the lungs, and redistribution of blood flow from poorly ventilated to better aerated lung areas by the von Euler-Liljestrand mechanism provides an intrinsic rescue mechanism by which an organism can maintain adequate arterial blood oxygenation even when significant parts of the lung have ceased to participate in gas exchange. Pharmacological inhibition of such a key physiological response would potentially be detrimental to any patient with acute lung disease. The fact that TRPV4 inhibition improved arterial oxygenation in the chlorine injury model seems to argue against such an effect, but the situation may differ in scenarios of more heterogeneous injury. In addition to effects in the pulmonary vasculature, TRPV4 has also been implicated in the maintenance of epithelial barrier function in the lung (38), and TRPV4 mediates the constriction of airway smooth muscle cells in a cysteinyl leukotriene-dependent manner (32). TRPV4 is also expressed in alveolar macrophages (18), implying a potential role in the regulation of inflammation. This has proven relevant in the context of lung injury, since adoptive transfer of macrophages from trpv4⫹/⫹ mice to trpv4⫺/⫺ mice restored susceptibility of trpv4⫺/⫺ lungs to mechanical injury induced by high peak inflation pressure ventilation (19). Given the broad spectrum of roles in lung and cellular function, TRPV4 has been conclusively identified as a mediator of hydrostatic lung edema (24, 50), as well as edema associated with experimental ventilator-induced lung injury (20). These observations have led to studies that have documented the usefulness of TRPV4 inhibition in models of pulmonary edema formation secondary to heart failure, in which application of an earlier-generation TRPV4 inhibitor GSK2193874 decreased extravascular lung water and increased arterial oxygenation (42). In the background of the emerging role of TRPV4 in cardiopulmonary physiology, the study by Balakrishna and colleagues (2) provides a foundation for further exciting work. Several important questions immediately emerge. A very striking observation made in the report is that TRPV4 inhibitors exhibit potent anti-inflammatory activity, which was comparable to that of glucocorticoids. Both TRPV4 inhibitors employed blocked inflammatory cell influx, dampened myeloperoxidase activity in the bronchoalveolar lavage as a measure of neutrophil infiltration and activation, and blunted proinflammatory cytokine and chemokine production. These effects were recapitulated in trpv4⫺/⫺ mice. However, the mechanisms underlying all of these effects are not understood. One possibility discussed above is that TRPV4 inhibitors act primarily on endothelial and epithelial cells, not only preventing changes in barrier function, but also blocking other Ca2⫹dependent processes such as the release of cytokines and adhesion molecules or the facilitation of neutrophil transit (40). Alternatively, do these inhibitors (and thus, TRPV4) directly impact macrophage and neutrophil function and mobility? Functional expression of TRPV4 in macrophages and its central role in the elicitation of ventilation-induced lung injury has been previously documented in isolated lung studies (19). In the present study, Balakrishna and colleagues furthermore analyzed RNAseq neutrophil transcriptome datasets in silico
AJP-Lung Cell Mol Physiol • doi:10.1152/ajplung.00254.2014 • www.ajplung.org
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and concluded that the frequency of TRPV4 transcripts in either noninduced or induced neutrophils was very low. This notion, however, is in contrast to quantitative real-time PCR analyses from murine neutrophils demonstrating an abundance of TRPV4 mRNA, compared with other TRP channels including TRPC3, TRPC6, TRPC7, and TRPM4 (7). The actual cell type (or types), through which TRPV4 inhibitors exert their anti-inflammatory effects remains, hence, so far unclear and may require extensive work using adoptive transfer models and
chimeric mice. The general notion, however, of a key role for TRPV4 in inflammatory disease processes is substantiated by recent reports that TRPV4 blockade can effectively protect against experimental colitis in mice (12), whereas, conversely, TRPV4 agonists trigger joint inflammation in rats (10). However, this anti-inflammatory potential also bears a serious risk for the therapeutic use of TRPV4 inhibitors in lung injury: the majority of patients with acute respiratory distress syndrome suffer from concomitant pulmonary (pneumonia) or systemic
Chemical injury (chlorine gas, acid)
Edema fluid
ROS NO
ATI cell
Alveolar macrophage
PASMC
PMN ?
Increased permeability Protein + fluid leak
ATII cell NO
P-selectin Vasoconstriction
EC Artery
TRPV4 channel
Capillary
Vein
Fig. 1. Role of TRPV4 in acute lung injury. Inhalation or intratracheal instillation of injurious chemicals such as chlorine gas or acid causes acute lung injury that is characterized by influx of inflammatory cells and failure of the alveolocapillary barrier, resulting in the formation of a cell- and protein-rich alveolar edema. Pharmacological inhibition or genetic deficiency of TRPV4 alleviates these effects, demonstrating that TRPV4, which is expressed on various lung parenchymatous and inflammatory cells, contributes critically to this scenario: In lung capillary endothelial cells (EC), TRPV4 activation increases vascular permeability, thus promoting protein and fluid leak. In extra-alveolar vessels, TRPV4 activation may stimulate endothelial P-selectin expression and nitric oxide (NO) synthesis. In pulmonary artery smooth muscle cells (PASMC), TRPV4 mediates vasoconstriction and may thus modulate ventilation/perfusion matching in injured lungs. In alveolar macrophages, TRPV4 activation results in the formation of reactive oxygen species (ROS) and NO, which in combination give rise to peroxynitrite, causing tyrosine nitrosylation of proteins. TRPV4 has also been reported to be expressed on alveolar epithelial cells and, according to some authors, neutrophils, yet their contribution to TRPV4-mediated acute lung injury remains to be resolved. The wide expression and multifold functions of TRPV4 in the lung render this channel a promising yet at the same time complex target for the treatment of acute lung injury. PMN, polymorphonuclear cell, neutrophil; ATI/ATII cell, alveolar type 1/type 2 cell. AJP-Lung Cell Mol Physiol • doi:10.1152/ajplung.00254.2014 • www.ajplung.org
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(sepsis) infections. Anti-inflammatory therapies that would dampen the body’s ability to clear invading pathogens could easily aggravate such infectious diseases with potentially fatal results. In their report, Balakrishna and colleagues (2) have addressed responses to HCl-induced damage in trpv4⫺/⫺ mice; however, for the chlorine-exposure studies, only the two TRPV4 inhibitors were employed. It remains to be demonstrated whether trpv4⫺/⫺ mice are protected from lung damage in response to chlorine gas inhalation. Along these lines, a further consideration with the mouse models would be to assess the responses to (and protection against) chlorine exposure in other mouse strains, which are notorious for strain-dependent variability in response to chlorine inhalation (14, 33). The combination of vascular protective effects and antiinflammatory properties also make TRPV4 inhibitors interesting candidates for investigation in animal models of pulmonary vascular disease with an inflammatory component, such as pulmonary arterial hypertension. TRPV4 has been directly implicated in pulmonary vascular remodeling, in response to chronic exposure of mice to hypoxia (47), a well-characterized animal model of pulmonary arterial hypertension (15, 43); however, perivascular inflammation is not appreciable in this model. In contrast, inflammation is a key player in the related rat monocrotaline model of pulmonary arterial hypertension (16). It would be interesting to explore the effect of TRPV4 inhibitors in that and other animal models of pulmonary disease with vascular and inflammatory components (37), particularly considering that pulmonary hypertension is a frequent complication of acute lung injury (36). The present work by Balakrishna and colleagues (2) identifies a novel pathogenic role for TRPV4 that extends its previously reported relevance in cardiogenic lung edema and ventilator-induced lung injury to scenarios of chemically induced lung injury (outlined in Fig. 1) and identifies TRPV4 inhibitors as promising therapeutic strategy for the treatment of related clinical conditions. Because of the ubiquitous expression of TRPV4, and the multitude of functions ascribed to TRPV4, including a role in lung vasomotor control, the inflammatory response, and the regulation of systemic blood pressure, TRPV4 blockade may represent a double-edged sword. The therapeutic benefits of TRPV4 inhibition will have to be carefully weighed against potential adverse effects on a caseby-case basis. GRANTS This work was supported by the Max Planck Society (R. E. Morty); by the German Centre for Lung Research (to R. E. Morty); by research grant 62589035 from the University Medical Center Giessen and Marburg (to R. E. Morty); by the Federal Ministry of Higher Education, Research, and the Arts of the State of Hessen LOEWE-Programm (to R. E. Morty); and by the German Research Foundation through Individual Grant Mo1789/1 (to R. E. Morty) and Excellence Cluster 147 Cardio-Pulmonary System (to R. E. Morty). W. M. Kuebler received support from the Canadian Institutes of Health Research, the German Research Foundation, and the Heart & Stroke Foundation of Canada. DISCLOSURES No conflicts of interest, financial or otherwise, are declared by the author(s).
AUTHOR CONTRIBUTIONS R.E.M. and W.M.K. analyzed data; R.E.M. and W.M.K. interpreted results of experiments; R.E.M. and W.M.K. drafted manuscript; R.E.M. and W.M.K. edited and revised manuscript; R.E.M. and W.M.K. approved final version of manuscript. REFERENCES 1. Alvarez DF, King JA, Weber D, Addison E, Liedtke W, Townsley MI. Transient receptor potential vanilloid 4-mediated disruption of the alveolar septal barrier: a novel mechanism of acute lung injury. Circ Res 99: 988 –995, 2006. 2. Balakrishna S, Song W, Achanta S, Doran SF, Liu B, Kaelberer MM, Yu Z, Sui A, Cheung M, Leishman E, Eidam HS, Ye G, Willette RN, Thorneloe KS, Bradshaw HB, Matalon S, Jordt SE. TRPV4 inhibition counteracts edema and inflammation and improves pulmonary function and oxygen saturation in chemically induced acute lung injury. Am J Physiol Lung Cell Mol Physiol 307: L158 –L172, 2014. 3. Birrell MA, Bonvini SJ, Dubuis E, Maher SA, Wortley MA, Grace MS, Raemdonck K, Adcock JJ, Belvisi MG. Tiotropium modulates transient receptor potential V1 (TRPV1) in airway sensory nerves: a beneficial off-target effect? J Allergy Clin Immunol 133: 679 –687.e9, 2014. 4. Cantero-Recasens G, Gonzalez JR, Fandos C, Duran-Tauleria E, Smit LA, Kauffmann F, Anto JM, Valverde MA. Loss of function of transient receptor potential vanilloid 1 (TRPV1) genetic variant is associated with lower risk of active childhood asthma. J Biol Chem 285: 27532–27535, 2010. 5. Cioffi DL, Lowe K, Alvarez DF, Barry C, Stevens T. TRPing on the lung endothelium: calcium channels that regulate barrier function. Antioxid Redox Signal 11: 765–776, 2009. 6. Dahan D, Ducret T, Quignard JF, Marthan R, Savineau JP, Esteve E. Implication of the ryanodine receptor in TRPV4-induced calcium response in pulmonary arterial smooth muscle cells from normoxic and chronically hypoxic rats. Am J Physiol Lung Cell Mol Physiol 303: L824 –L833, 2012. 7. Damann N, Owsianik G, Li S, Poll C, Nilius B. The calcium-conducting ion channel transient receptor potential canonical 6 is involved in macrophage inflammatory protein-2-induced migration of mouse neutrophils. Acta Physiol (Oxf) 195: 3–11, 2009. 8. Delany NS, Hurle M, Facer P, Alnadaf T, Plumpton C, Kinghorn I, See CG, Costigan M, Anand P, Woolf CJ, Crowther D, Sanseau P, Tate SN. Identification and characterization of a novel human vanilloid receptor-like protein, VRL-2. Physiol Genomics 4: 165–174, 2001. 9. Delescluse I, Mace H, Adcock JJ. Inhibition of airway hyper-responsiveness by TRPV1 antagonists (SB-705498 and PF-04065463) in the unanaesthetized, ovalbumin-sensitized guinea pig. Br J Pharmacol 166: 1822–1832, 2012. 10. Denadai-Souza A, Martin L, de Paula MA, de Avellar MC, Muscara MN, Vergnolle N, Cenac N. Role of transient receptor potential vanilloid 4 in rat joint inflammation. Arthritis Rheum 64: 1848 –1858, 2012. 11. Fan H, Shen YX, Yuan YF. Expression and prognostic roles of TRPV5 and TRPV6 in non-small cell lung cancer after curative resection. Asian Pac J Cancer Prev 15: 2559 –2563, 2014. 12. Fichna J, Mokrowiecka A, Cygankiewicz AI, Zakrzewski PK, Malecka-Panas E, Janecka A, Krajewska WM, Storr MA. Transient receptor potential vanilloid 4 blockade protects against experimental colitis in mice: a new strategy for inflammatory bowel diseases treatment? Neurogastroenterol Motil 24: e557–e560, 2012. 13. Fois G, Wittekindt O, Zheng X, Felder ET, Miklavc P, Frick M, Dietl P, Felder E. An ultra fast detection method reveals strain-induced Ca2⫹ entry via TRPV2 in alveolar type II cells. Biomech Model Mechanobiol 11: 959 –971, 2012. 14. Gessner MA, Doran SF, Yu Z, Dunaway CW, Matalon S, Steele C. Chlorine gas exposure increases susceptibility to invasive lung fungal infection. Am J Physiol Lung Cell Mol Physiol 304: L765–L773, 2013. 15. Gomez-Arroyo J, Saleem SJ, Mizuno S, Syed AA, Bogaard HJ, Abbate A, Taraseviciene-Stewart L, Sung Y, Kraskauskas D, Farkas D, Conrad DH, Nicolls MR, Voelkel NF. A brief overview of mouse models of pulmonary arterial hypertension: problems and prospects. Am J Physiol Lung Cell Mol Physiol 302: L977–L991, 2012. 16. Gomez-Arroyo JG, Farkas L, Alhussaini AA, Farkas D, Kraskauskas D, Voelkel NF, Bogaard HJ. The monocrotaline model of pulmonary hypertension in perspective. Am J Physiol Lung Cell Mol Physiol 302: L363–L369, 2012.
AJP-Lung Cell Mol Physiol • doi:10.1152/ajplung.00254.2014 • www.ajplung.org
Editorial Focus TRPV4 AND LUNG BARRIER FUNCTION 17. Grace MS, Baxter M, Dubuis E, Birrell MA, Belvisi MG. Transient receptor potential (TRP) channels in the airway: role in airway disease. Br J Pharmacol 171: 2593–2607, 2014. 18. Groot-Kormelink PJ, Fawcett L, Wright PD, Gosling M, Kent TC. Quantitative GPCR and ion channel transcriptomics in primary alveolar macrophages and macrophage surrogates. BMC Immunol 13: 57, 2012. 19. Hamanaka K, Jian MY, Townsley MI, King JA, Liedtke W, Weber DS, Eyal FG, Clapp MM, Parker JC. TRPV4 channels augment macrophage activation and ventilator-induced lung injury. Am J Physiol Lung Cell Mol Physiol 299: L353–L362, 2010. 20. Hamanaka K, Jian MY, Weber DS, Alvarez DF, Townsley MI, Al-Mehdi AB, King JA, Liedtke W, Parker JC. TRPV4 initiates the acute calcium-dependent permeability increase during ventilator-induced lung injury in isolated mouse lungs. Am J Physiol Lung Cell Mol Physiol 293: L923–L932, 2007. 21. Herold S, Gabrielli NM, Vadasz I. Novel concepts of acute lung injury and alveolar-capillary barrier dysfunction. Am J Physiol Lung Cell Mol Physiol 305: L665–L681, 2013. 22. Jang Y, Lee Y, Kim SM, Yang YD, Jung J, Oh U. Quantitative analysis of TRP channel genes in mouse organs. Arch Pharm Res 35: 1823–1830, 2012. 23. Jia Y, Lee LY. Role of TRPV receptors in respiratory diseases. Biochim Biophys Acta 1772: 915–927, 2007. 24. Jian MY, King JA, Al-Mehdi AB, Liedtke W, Townsley MI. High vascular pressure-induced lung injury requires P450 epoxygenase-dependent activation of TRPV4. Am J Respir Cell Mol Biol 38: 386 –392, 2008. 25. Jordt SE, Ehrlich BE. TRP channels in disease. Subcell Biochem 45: 253–271, 2007. 26. Kuebler WM, Uhlig U, Goldmann T, Schael G, Kerem A, Exner K, Martin C, Vollmer E, Uhlig S. Stretch activates nitric oxide production in pulmonary vascular endothelial cells in situ. Am J Respir Crit Care Med 168: 1391–1398, 2003. 27. Kuebler WM, Ying X, Bhattacharya J. Pressure-induced endothelial Ca2⫹ oscillations in lung capillaries. Am J Physiol Lung Cell Mol Physiol 282: L917–L923, 2002. 28. Kuebler WM, Ying X, Singh B, Issekutz AC, Bhattacharya J. Pressure is proinflammatory in lung venular capillaries. J Clin Invest 104: 495–502, 1999. 29. Lau JK, Brown KC, Dom AM, Witte TR, Thornhill BA, Crabtree CM, Perry HE, Brown JM, Ball JG, Creel RG, Damron CL, Rollyson WD, Stevenson CD, Hardman WE, Valentovic MA, Carpenter AB, Dasgupta P. Capsaicin induces apoptosis in human small cell lung cancer via the TRPV6 receptor and the calpain pathway. Apoptosis 19: 1190 – 1201, 2014. 30. Lieu TM, Myers AC, Meeker S, Undem BJ. TRPV1 induction in airway vagal low-threshold mechanosensory neurons by allergen challenge and neurotrophic factors. Am J Physiol Lung Cell Mol Physiol 302: L941– L948, 2012. 31. Ma X, Cao J, Luo J, Nilius B, Huang Y, Ambudkar IS, Yao X. Depletion of intracellular Ca2⫹ stores stimulates the translocation of vanilloid transient receptor potential 4-c1 heteromeric channels to the plasma membrane. Arterioscler Thromb Vasc Biol 30: 2249 –2255, 2010. 32. McAlexander MA, Luttmann MA, Hunsberger GE, Undem BJ. Transient receptor potential vanilloid 4 activation constricts the human bronchus via the release of cysteinyl leukotrienes. J Pharmacol Exp Ther 349: 118 –125, 2014. 33. Mo Y, Chen J, Schlueter CF, Hoyle GW. Differential susceptibility of inbred mouse strains to chlorine-induced airway fibrosis. Am J Physiol Lung Cell Mol Physiol 304: L92–L102, 2013. 34. Nilius B, Biro T, Owsianik G. TRPV3: time to decipher a poorly understood family member! J Physiol 592: 295–304, 2014. 35. Prakash YS. Airway smooth muscle in airway reactivity and remodeling: what have we learned? Am J Physiol Lung Cell Mol Physiol 305: L912–L933, 2013. 36. Price LC, McAuley DF, Marino PS, Finney SJ, Griffiths MJ, Wort SJ. Pathophysiology of pulmonary hypertension in acute lung injury. Am J Physiol Lung Cell Mol Physiol 302: L803–L815, 2012.
L821
37. Schneberger D, Aharonson-Raz K, Singh B. Pulmonary intravascular macrophages and lung health: what are we missing? Am J Physiol Lung Cell Mol Physiol 302: L498 –L503, 2012. 38. Sidhaye VK, Schweitzer KS, Caterina MJ, Shimoda L, King LS. Shear stress regulates aquaporin-5 and airway epithelial barrier function. Proc Natl Acad Sci USA 105: 3345–3350, 2008. 39. Stevens T. Functional and molecular heterogeneity of pulmonary endothelial cells. Proc Am Thorac Soc 8: 453–457, 2011. 40. Su WH, Chen HI, Huang JP, Jen CJ. Endothelial [Ca2⫹]i signaling during transmigration of polymorphonuclear leukocytes. Blood 96: 3816 – 3822, 2000. 41. Thomas KC, Roberts JK, Deering-Rice CE, Romero EG, Dull RO, Lee J, Yost GS, Reilly CA. Contributions of TRPV1, endovanilloids, and endoplasmic reticulum stress in lung cell death in vitro and lung injury. Am J Physiol Lung Cell Mol Physiol 302: L111–L119, 2012. 42. Thorneloe KS, Cheung M, Bao W, Alsaid H, Lenhard S, Jian MY, Costell M, Maniscalco-Hauk K, Krawiec JA, Olzinski A, Gordon E, Lozinskaya I, Elefante L, Qin P, Matasic DS, James C, Tunstead J, Donovan B, Kallal L, Waszkiewicz A, Vaidya K, Davenport EA, Larkin J, Burgert M, Casillas LN, Marquis RW, Ye G, Eidam HS, Goodman KB, Toomey JR, Roethke TJ, Jucker BM, Schnackenberg CG, Townsley MI, Lepore JJ, Willette RN. An orally active TRPV4 channel blocker prevents and resolves pulmonary edema induced by heart failure. Sci Transl Med 4: 159ra148, 2012. 43. Voelkel NF, Mizuno S, Bogaard HJ. The role of hypoxia in pulmonary vascular diseases: a perspective. Am J Physiol Lung Cell Mol Physiol 304: L457–L465, 2013. 44. Watanabe H, Vriens J, Prenen J, Droogmans G, Voets T, Nilius B. Anandamide and arachidonic acid use epoxyeicosatrienoic acids to activate TRPV4 channels. Nature 424: 434 –438, 2003. 45. Weng WH, Hsu CC, Chiang LL, Lin YJ, Lin YS, Su CL. Role of TRPV1 and P2X receptors in the activation of lung vagal C-fiber afferents by inhaled cigarette smoke in rats. Mol Med Rep 7: 1300 –1304, 2013. 46. Wu S, Jian MY, Xu YC, Zhou C, Al-Mehdi AB, Liedtke W, Shin HS, Townsley MI. Ca2⫹ entry via ␣1G and TRPV4 channels differentially regulates surface expression of P-selectin and barrier integrity in pulmonary capillary endothelium. Am J Physiol Lung Cell Mol Physiol 297: L650 –L657, 2009. 47. Xia Y, Fu Z, Hu J, Huang C, Paudel O, Cai S, Liedtke W, Sham JS. TRPV4 channel contributes to serotonin-induced pulmonary vasoconstriction and the enhanced vascular reactivity in chronic hypoxic pulmonary hypertension. Am J Physiol Cell Physiol 305: C704 –C715, 2013. 48. Yang XR, Lin AH, Hughes JM, Flavahan NA, Cao YN, Liedtke W, Sham JS. Upregulation of osmo-mechanosensitive TRPV4 channel facilitates chronic hypoxia-induced myogenic tone and pulmonary hypertension. Am J Physiol Lung Cell Mol Physiol 302: L555–L568, 2012. 49. Yildirim E, Carey MA, Card JW, Dietrich A, Flake GP, Zhang Y, Bradbury JA, Rebolloso Y, Germolec DR, Morgan DL, Zeldin DC, Birnbaumer L. Severely blunted allergen-induced pulmonary Th2 cell response and lung hyperresponsiveness in type 1 transient receptor potential channel-deficient mice. Am J Physiol Lung Cell Mol Physiol 303: L539 –L549, 2012. 50. Yin J, Hoffmann J, Kaestle SM, Neye N, Wang L, Baeurle J, Liedtke W, Wu S, Kuppe H, Pries AR, Kuebler WM. Negative-feedback loop attenuates hydrostatic lung edema via a cGMP-dependent regulation of transient receptor potential vanilloid 4. Circ Res 102: 966 –974, 2008. 51. Yin J, Kuebler WM. Mechanotransduction by TRP channels: general concepts and specific role in the vasculature. Cell Biochem Biophys 56: 1–18, 2010. 52. Yoo HY, Park SJ, Seo EY, Park KS, Han JA, Kim KS, Shin DH, Earm YE, Zhang YH, Kim SJ. Role of thromboxane A2-activated nonselective cation channels in hypoxic pulmonary vasoconstriction of rat. Am J Physiol Cell Physiol 302: C307–C317, 2012. 53. Zhou C, Chen H, King JA, Sellak H, Kuebler WM, Yin J, Townsley MI, Shin HS, Wu S. ␣1G T-type calcium channel selectively regulates P-selectin surface expression in pulmonary capillary endothelium. Am J Physiol Lung Cell Mol Physiol 299: L86 –L97, 2010.
AJP-Lung Cell Mol Physiol • doi:10.1152/ajplung.00254.2014 • www.ajplung.org
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