Specific inhibition of AQP1 water channels in human pulmonary microvascular endothelial cells by small interfering RNAs

Blood-nerve barrier enhances chronic postsurgical pain via the HIF-1α/ aquaporin-1 signaling axis

BACKGROUND

Blood nerve barrier (BNB) participates in the development of neuropathic pain. AQP1 is involved in peripheral pain perception and is negatively correlated with HIF-1α phenotype, which regulates endothelial permeability. However, the role of HIF-1α-AQP1-mediated BNB dysfunction in Chronic Postsurgical Pain (CPSP) has not been reported.

METHODS

Male Sprague-Dawley rats were randomized into 5 groups: (i) Naive group; (ii) Sham group; (iii) SMIR group: skin/muscle incision and retraction for one hour. Behavioral tests were performed for the three groups, BNB vascular permeability and western blotting were conducted to determine HIF-1α and AQP1 protein expression. (iv) The SMIR + HIF-1α inhibitor group; (v) SMIR + DMSO group. Rats in the two groups were administered with HIF-1α inhibitor (2ME2) or DMSO intraperitoneally on the third day post-SMIR surgery followed by performance of behavioral tests, BNB permeability assessment, and determination of HIF-1α, AQP1 and NF200 protein levels.

RESULTS

The permeability of BNB was significantly increased and the expression of AQP1 was downregulated on the 3rd and 7th days post-operation. AQP1 is mainly located in neurons and NF200, CGRP-positive nerve fibers. HIF-1α was highly expressed on the third day post-operation. HIF-1α inhibitor reversed the decrease in AQP1 expression and increase in NF200 expression, barrier permeability and hyperalgesia induced by SMIR on the 3rd day post-surgery.

CONCLUSIONS

Early dysfunction of BNB mediated by HIF-1α/AQP1 activated by SMIR may be an important mechanism to promote acute postoperative painful transformation of CPSP. Preadaptive protection of endothelial cells around nerve substructures may be an important countermeasure to inhibit CPSP transformation. Early impairment of BNB function mediated by HIF-1α/AQP1 activated by SMIR may be an important mechanism for promoting acute postoperative pain transformation of CPSP.

Naringin suppressed airway inflammation and ameliorated pulmonary endothelial hyperpermeability by upregulating Aquaporin1 in lipopolysaccharide/cigarette smoke-induced mice

Naringin is one of the natural flavonoids extracted from many Chinese medicines. It ameliorates endothelial dysfunctions in atherosclerosis, diabetes, and cardiovascular diseases through free radical scavenging and antioxidant activities. The aim of the present study was to investigate the protective effects of naringin against pulmonary endothelial permeability in addition to airway inflammation in lipopolysaccharide/cigarette smoke (LPS/CS)-induced chronic obstructive pulmonary disease (COPD) mice.The COPD mice were exposed to LPS twice through intranasal inhalation and then to cigarette smoke daily for 6 weeks. The mice were orally administrated with naringin at doses of 40 or 80 mg/kg one hour before cigarette smoke exposure since the first day of the experiment. Naringin significantly alleviated pulmonary histopathological injury, and suppressed inflammatory cell infiltration and cytokine release in bronchoalveolar lavage fluid. Naringin decreased fluorescence intensity of Evans Blue in the lung tissues, and elevated the expression levels of tight junctional proteins. Meanwhile, naringin decreased neutrophil/lymphocyte/platelet counts and MDA content in blood, and upregulated Aquaporin1 (AQP1) in the lung tissues. However, the effect of naringin on airway inflammation and pulmonary endothelial permeability was inhibited in LPS/CS-treatment AQP1 deficiency mice. These results indicated that naringin attenuated LPS/CS-induced airway inflammatory and pulmonary hyperpermeability via upregulating AQP1 expression.

Signaling Mechanisms and Pharmacological Modulators Governing Diverse Aquaporin Functions in Human Health and Disease

The aquaporins (AQPs) are a family of small integral membrane proteins that facilitate the bidirectional transport of water across biological membranes in response to osmotic pressure gradients as well as enable the transmembrane diffusion of small neutral solutes (such as urea, glycerol, and hydrogen peroxide) and ions. AQPs are expressed throughout the human body. Here, we review their key roles in fluid homeostasis, glandular secretions, signal transduction and sensation, barrier function, immunity and inflammation, cell migration, and angiogenesis. Evidence from a wide variety of studies now supports a view of the functions of AQPs being much more complex than simply mediating the passive flow of water across biological membranes. The discovery and development of small-molecule AQP inhibitors for research use and therapeutic development will lead to new insights into the basic biology of and novel treatments for the wide range of AQP-associated disorders.

Upregulation of Aquaporin 1 Mediates Increased Migration and Proliferation in Pulmonary Vascular Cells From the Rat SU5416/Hypoxia Model of Pulmonary Hypertension

Pulmonary arterial hypertension (PAH) is a progressive disorder characterized by exuberant vascular remodeling leading to elevated pulmonary arterial pressure, maladaptive right ventricular remodeling, and eventual death. The factors controlling pulmonary arterial smooth muscle cell (PASMC) and endothelial cell hyperplasia and migration, hallmark features of the vascular remodeling observed in PAH, remain poorly understood. We previously demonstrated that hypoxia upregulates the expression of aquaporin 1 (AQP1), a water channel, in PASMCs, and that this upregulation was required for hypoxia-induced migration and proliferation. However, whether the same is true in a model of severe PAH and in pulmonary microvascular endothelial cells (MVECs) is unknown. In this study, we used the SU5416 plus hypoxia (SuHx) rat model of severe pulmonary hypertension, which mimics many of the features of human PAH, to determine whether AQP1 levels were altered in PASMCs and MVECs and contributed to a hyperproliferative/hypermigratory phenotype. Rats received a single injection of SU5416 (20 mg/kg) and then were placed in 10% O2 for 3 weeks, followed by a return to normoxic conditions for an additional 2 weeks. We found that AQP1 protein levels were increased in both PASMCs and MVECs from SuHx rats, even in the absence of sustained hypoxic exposure, and that in MVECs, the increase in protein expression was associated with upregulation of AQP1 mRNA levels. Silencing of AQP1 had no significant effect on PASMCs from control animals but normalized enhanced migration and proliferation observed in cells from SuHx rats. Loss of AQP1 also reduced migration and proliferation in MVECs from SuHx rats. Finally, augmenting AQP1 levels in MVECs from control rats using forced expression was sufficient to increase migration and proliferation. These results demonstrate a key role for enhanced AQP1 expression in mediating abnormal migration and proliferation in pulmonary vascular cells from a rodent model that reflects many of the features of human PAH.

Vascular Inflammation Is Associated with Loss of Aquaporin 1 Expression on Endothelial Cells and Increased Fluid Leakage in SARS-CoV-2 Infected Golden Syrian Hamsters

Vascular changes represent a characteristic feature of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) infection leading to a breakdown of the vascular barrier and subsequent edema formation. The aim of this study was to provide a detailed characterization of the vascular alterations during SARS-CoV-2 infection and to evaluate the impaired vascular integrity. Groups of ten golden Syrian hamsters were infected intranasally with SARS-CoV-2 or phosphate-buffered saline (mock infection). Necropsies were performed at 1, 3, 6, and 14 days post-infection (dpi). Lung samples were investigated using hematoxylin and eosin, alcian blue, immunohistochemistry targeting aquaporin 1, CD3, CD204, CD31, laminin, myeloperoxidase, SARS-CoV-2 nucleoprotein, and transmission electron microscopy. SARS-CoV-2 infected animals showed endothelial hypertrophy, endothelialitis, and vasculitis. Inflammation mainly consisted of macrophages and lower numbers of T-lymphocytes and neutrophils/heterophils infiltrating the vascular walls as well as the perivascular region at 3 and 6 dpi. Affected vessels showed edema formation in association with loss of aquaporin 1 on endothelial cells. In addition, an ultrastructural investigation revealed disruption of the endothelium. Summarized, the presented findings indicate that loss of aquaporin 1 entails the loss of intercellular junctions resulting in paracellular leakage of edema as a key pathogenic mechanism in SARS-CoV-2 triggered pulmonary lesions.

Aquaporin 1 mediates early responses to osmotic stimuli in endothelial cells via the calmodulin pathway

The aquaporins (AQPs) are a family of integral membrane proteins which play critical roles in controlling transcellular water movement in various tissues throughout the body. AQP1 helps mediate the cellular response to osmotic stress and tissue water permeability. However, the mechanism by which AQP1 mediates changes in cell volume is not completely clear. Here, we investigated how AQP1 responds to and controls cell volume upon osmotic stimuli during the early phase after the immediate response. Cells overexpressing AQP1 were exposed to hypotonic or hypertonic medium in the presence or absence of staurosporine or W-7 hydrochloride, and fluorescence imaging was performed at 0, 5, 10, and 15 min later. Osmotic stimuli induced redistribution of AQP1 into the cell membrane, hypotonic stimuli caused cell enlargement, and hypertonic stimuli induced a reduction in cell size, which was blocked by T157A/T239A mutations. Changes in cell size induced by osmotic stimuli were blocked by an antagonist of calmodulin kinase, W-7 hydrochloride, but not by the PKC inhibitor staurosporine. These results suggest that calmodulin kinase regulates AQP1 activity during the early response to osmotic stimuli.

Pre-atherosclerotic flow and oncotically active solute transport across the arterial endothelium

Atherosclerosis starts with transmural (transwall) pressure-driven advective transport of blood-borne low-density lipoprotein (LDL) cholesterol across rare endothelial cell (EC) monolayer leaks into the arterial subendothelial intima (SI) wall layer where they can spread, bind to extracellular matrix and seed lesions. The local SI LDL concentration, which governs LDL's binding kinetics, depends on the overall diluting transmural liquid flow. Transmural pressures typically compress the SI at physiological pressures, which keeps this flow low. Nguyen et al. (2015) showed that aortic ECs express the water channel protein aquaporin-1 (AQP1) and the transEC (δP) portion of the transmural (ΔP) pressure difference drives, in parallel, water across AQP1s and plasma across interEC junctions. Since the lumen is isotonic, selective AQP1-mediated water flow should quickly render the ECs' lumen side hypertonic and the SI hypotonic; resulting transEC oncotic pressure differences, δπ, should oppose δP and quickly halt transEC flow. Yet Nguyen et al.'s (2015) transAQP1 flows persist for hours. To resolve this paradox, we extend our fluid filtration theory Joshi et al. (2015) to include mass transfer for oncotically active solutes like albumin. This addition nonlinearly couples mass transfer, fluid flow and wall mechanics. We simultaneously solve these problems at steady state. Surprisingly it finds that media layer filtration causes steady SI to exceed EC glycocalyx albumin concentration. Thus δπ reinforces rather than opposes δP, i.e., it sucks water from, rather than pushing water into the lumen from the SI. Endothelial AQP1s raise the overall driving force for flow across the EC above δP, most significantly at pressures too low to compress the SI, and they increase the ΔP needed for SI compression. This suggests the intriguing possibility that increasing EC AQP1 expression can raise this requisite compression pressure to physiological values. That is, increasing EC AQP1 may decompress the SI at physiological pressures, which would significantly increase SI thickness, flow and subsequently SI LDL dilution. This could retard LDL binding and delay preatherosclerotic lesion onset. The model also predicts that glycocalyx-degrading enzymes decrease overall transEC driving forces and thus lower, not raise, transmural water flux.

Aquaporin-1 plays a key role in erythropoietin-induced endothelial cell migration

Water influx through aquaporin-1 (AQP-1) has been linked to the ability of different cell types to migrate, and therefore plays an important part in processes like metastasis and angiogenesis. Since the erythroid growth factor erythropoietin (Epo) is now recognized as an angiogenesis promoter, we investigated the participation of AQP-1 as a downstream effector of this cytokine in the migration of endothelial cells. Inhibition of AQP-1 with either mercury ions (Hg²⁺) or a specific siRNA led to an impaired migration of EA.hy926 endothelial cells exposed to Epo (wound-healing assays). Epo also induced the expression of AQP-1 at mRNA and protein levels, an effect which was dependent on the influx of extracellular calcium through L-type calcium channels as well as TRPC3 channels. The relationship between Epo and AQP-1 was further confirmed at shorter exposure times, as the cytokine was unable to trigger calcium influxes in cells where AQP-1 had previously been knocked down. Moreover, Epo promoted changes in the subcellular localization of AQP-1 as well as rearrangements in the actin cytoskeleton, which are consistent with a migratory phenotype. Worthy of note, carbamylated erythropoietin (cEpo), the non-erythropoietic and non-promigratory derivative of Epo, was incapable of AQP-1 modulation. The therapeutical implications of aquaporin targeting in angiogenesis-related diseases highlight the importance of the present results in the context of the relationship between AQP-1 and Epo.

Simvastatin Ameliorates PAK4 Inhibitor-Induced Gut and Lung Injury

P21 activated kinase 4 (PAK4), a key regulator of cytoskeletal rearrangement and endothelial microparticles (EMPs), is released after lipopolysaccharide (LPS) stimulation. In addition, it participates in LPS-induced lung injury. In this study, forty-eight Sprague Dawley (SD) rats were divided into two groups, including PAK4 inhibitor (P) and PAK4 inhibitor + simvastatin (P + S) treatment groups. All rats were given PAK4 inhibitor (15 mg/kg/d) orally. Immediately after PAK4 inhibitor administration, simvastatin was injected intraperitoneally to P + S group animals at 20 mg/kg/day. Then, treatment effects on the intestinal mucosal barrier and lung injury caused by PAK4 inhibitor and simvastatin were assessed. The results showed that gut Zonula Occludens- (ZO-) 1, PAK4, mitogen-activated protein kinase 4 (MPAK4), and CD11c protein levels were reduced, while plasma endotoxin levels were increased after administration of PAK4 inhibitor. Furthermore, compared with normal rats, wet-to-dry (W/D) values of lung tissues and circulating EMP levels were increased in the treatment group, while PAK4 and CD11c protein amounts were reduced. Therefore, in this lung injury process induced by PAK4 inhibitor, the protective effects of simvastatin were reflected by intestinal mucosal barrier protection, inflammatory response regulation via CD11c+ cells, and cytoskeleton stabilization. In summary, PAK4 is a key regulator in the pathophysiological process of acute lung injury (ALI) and can be a useful target for ALI treatment.

Simvastatin Attenuates Acute Lung Injury via Regulating CDC42-PAK4 and Endothelial Microparticles

BACKGROUND

Simvastatin has lung vascular-protective effects via augmentation of endothelial barrier function. Accordingly, on the basis of our previous study, we hypothesized that endothelial cell (EC) protection by simvastatin is dependent on the stabilization on cytoskeletons.

METHODS

Sixty C57BL/6 mice were divided into two experimental groups: lipopolysaccharide (LPS) group (L group) and LPS+simvastatin treated group (L+S group). All mice in these two groups received an intraperitoneal injection of LPS (10 mg/kg/d). Simvastatin was administered intraperitoneally immediately after the LPS injection in animals of the L+S group at a dose of 20 mg/kg/day. Lung injury degree and the protective effects of simvastatin against LPS-induced lung injury were assessed at the time-points of 24, 48, and 72 h postinjection. Serum alanine transaminase (ALT), serum creatinine (Scr) were identified to assess the hepatic and renal side-effects of simvastatin.

RESULTS

LPS inhibited the cytoskeletal regulating proteins of Cdc42 and PAK4, and was accompanied by an increased circulating endothelial microparticles (EMPs) level. The adherent junction (AJ) protein of VE-cadherin was also decreased by LPS, and was accompanied by a thickening alveolar wall, increased lung W/D values, and high albumin concentration in bronchoalveolar lavage. Protective effects of simvastatin against LPS-induced lung injury were illustrated by regulating and stabilizing cytoskeletons, as well as intercellular AJs. The values of ALT and Scr were all lower than the common upper limits according to assay kits.

CONCLUSION

An increased serous EMP level associated with Cdc42-PAK4 can be deemed as a useful pulmonary injury marker in LPS-treated mice, and our results might be more relevant in guiding the clinical treatment of ALI by intervening Cdc42-PAK4 or EMPs.

Chronic hypertension increases aortic endothelial hydraulic conductivity by upregulating endothelial aquaporin-1 expression

Numerous studies have examined the role of aquaporins in osmotic water transport in various systems, but virtually none have focused on the role of aquaporin in hydrostatically driven water transport involving mammalian cells save for our laboratory's recent study of aortic endothelial cells. Here, we investigated aquaporin-1 expression and function in the aortic endothelium in two high-renin rat models of hypertension, the spontaneously hypertensive genetically altered Wistar-Kyoto rat variant and Sprague-Dawley rats made hypertensive by two-kidney, one-clip Goldblatt surgery. We measured aquaporin-1 expression in aortic endothelial cells from whole rat aortas by quantitative immunohistochemistry and function by measuring the pressure-driven hydraulic conductivities of excised rat aortas with both intact and denuded endothelia on the same vessel. We used them to calculate the effective intimal hydraulic conductivity, which is a combination of endothelial and subendothelial components. We observed well-correlated enhancements in aquaporin-1 expression and function in both hypertensive rat models as well as in aortas from normotensive rats whose expression was upregulated by 2 h of forskolin treatment. Upregulated aquaporin-1 expression and function may be a response to hypertension that critically determines conduit artery vessel wall viability and long-term susceptibility to atherosclerosis.NEW & NOTEWORTHY The aortic endothelia of two high-renin hypertensive rat models express greater than two times the aquaporin-1 and, at low pressures, have greater than two times the endothelial hydraulic conductivity of normotensive rats. Data are consistent with theory predicting that higher endothelial aquaporin-1 expression raises the critical pressure for subendothelial intima compression and for artery wall hydraulic conductivity to drop.

Increased Circulating Endothelial Microparticles Associated with PAK4 Play a Key Role in Ventilation-Induced Lung Injury Process

Inappropriate mechanical ventilation (MV) can result in ventilator-induced lung injury (VILI). Probing mechanisms of VILI and searching for effective methods are current areas of research focus on VILI. The present study aimed to probe into mechanisms of endothelial microparticles (EMPs) in VILI and the protective effects of Tetramethylpyrazine (TMP) against VILI. In this study, C57BL/6 and TLR4KO mouse MV models were used to explore the function of EMPs associated with p21 activated kinases-4 (PAK-4) in VILI. Both the C57BL/6 and TLR4 KO groups were subdivided into a mechanical ventilation (MV) group, a TMP + MV group, and a control group. After four hours of high tidal volume (20 ml/kg) MV, the degree of lung injury and the protective effects of TMP were assessed. VILI inhibited the cytoskeleton-regulating protein of PAK4 and was accompanied by an increased circulating EMP level. The intercellular junction protein of β-catenin was also decreased accompanied by a thickening alveolar wall, increased lung W/D values, and neutrophil infiltration. TMP alleviated VILI via decreasing circulating EMPs, stabilizing intercellular junctions, and alleviating neutrophil infiltration.

Endothelial Aquaporin-1 (AQP1) Expression Is Regulated by Transcription Factor Mef2c

Aquaporin 1 (AQP1) is expressed in most microvasculature endothelial cells and forms water channels that play major roles in a variety of physiologic processes. This study aimed to delineate the transcriptional regulation of AQP1 by Mef2c in endothelial cells. Mef2c cooperated with Sp1 to activate human AQP1 transcription by binding to its proximal promoter in human umbilical cord vein endothelial cells (HUVEC). Over-expression of Mef2c, Sp1, or Mef2c/Sp1 increased HUVEC migration and tube-forming ability, which can be abolished AQP1 knockdown. These data indicate that AQP1 is a direct target of Mef2c in regulating angiogenesis and vasculogenesis of endothelial cells.

Aquaporin-1 facilitates pressure-driven water flow across the aortic endothelium

Aquaporin-1, a ubiquitous water channel membrane protein, is a major contributor to cell membrane osmotic water permeability. Arteries are the physiological system where hydrostatic dominates osmotic pressure differences. In the present study, we show that the walls of large conduit arteries constitute the first example where hydrostatic pressure drives aquaporin-1-mediated transcellular/transendothelial flow. We studied cultured aortic endothelial cell monolayers and excised whole aortas of male Sprague-Dawley rats with intact and inhibited aquaporin-1 activity and with normal and knocked down aquaporin-1 expression. We subjected these systems to transmural hydrostatic pressure differences at zero osmotic pressure differences. Impaired aquaporin-1 endothelia consistently showed reduced engineering flow metrics (transendothelial water flux and hydraulic conductivity). In vitro experiments with tracers that only cross the endothelium paracellularly showed that changes in junctional transport cannot explain these reductions. Percent reductions in whole aortic wall hydraulic conductivity with either chemical blocking or knockdown of aquaporin-1 differed at low and high transmural pressures. This observation highlights how aquaporin-1 expression likely directly influences aortic wall mechanics by changing the critical transmural pressure at which its sparse subendothelial intima compresses. Such compression increases transwall flow resistance. Our endothelial and historic erythrocyte membrane aquaporin density estimates were consistent. In conclusion, aquaporin-1 significantly contributes to hydrostatic pressure-driven water transport across aortic endothelial monolayers, both in culture and in whole rat aortas. This transport, and parallel junctional flow, can dilute solutes that entered the wall paracellularly or through endothelial monolayer disruptions. Lower atherogenic precursor solute concentrations may slow their intimal entrainment kinetics.

Differential expression of HIF-1α, AQP-1, and VEGF under acute hypoxic conditions in the non-ventilated lung of a one-lung ventilation rat model

AIMS

One-lung ventilation (OLV) is a standard practice in thoracic surgery. However, OLV can give rise to arterial hypoxemia. Hypoxia-inducible transcription factor-1 alpha (HIF-1α), vascular endothelial growth factor (VEGF) and aquaporin-1 (AQP-1) may be involved in arterial hypoxemia and contribute to cellular injury. Therefore, in the present study, these moieties were investigated in an OLV rat model.

MAIN METHODS

Forty Sprague-Dawley (S-D) rats were randomly divided into four groups: right lung mechanical ventilation for 0.5 h (Group A); 1 h (Group B); 2 h (Group C) and mechanical ventilation of both lungs (control group). Rat lung tissue was examined using electron microscopy. Serum and lung tissue levels of VEGF were measured by ELISA, Western blot analyses were used to detect the protein expression of HIF-1α and immunohistochemical staining and real-time polymerase chain reaction (PCR) were performed to examine protein expression and gene levels, respectively, of VEGF and AQP-1 after hypoxia.

KEY FINDINGS

Electron microscopy revealed that increased duration of OLV was correlated with greater destruction of the non-ventilated lung. The protein expression of HIF-1α was significantly increased in the non-ventilated lungs of the experimental hypoxia groups (A-C) compared to the control group, whereas VEGF and AQP-1 protein expression and gene levels were decreased in the non-ventilated lungs of the hypoxia groups (A-C) compared to the control group.

SIGNIFICANCE

The OLV caused hypoxia in the non-ventilated lung and subsequent injury. The altered expression of HIF-1α, VEGF, and AQP-1 may be involved in the pathological process of lung injury caused by hypoxia.

Cardioprotective effect of valsartan in mice with short-term high-salt diet by regulating cardiac aquaporin 1 and angiogenic factor expression

Hypertension is the most common risk factor for various cardiovascular and cerebrovascular diseases that affects approximately 61 million, or 25% of the population in United States. The dietary salt intake is one of the most important but modifiable factors for hypertension. In the current study, we aim to elucidate the role of aquaporin 1 in high-salt-induced hypertension and cardiac injuries and whether angiotensin II receptor blocker valsartan could ameliorate the effect of high salt on blood pressure. Mice were fed with normal diet, high-salt diet in the presence or absence of valsartan for 4 weeks. The body weight gain, feeding behavior, blood pressure, and cardiac pathology changes were monitored after 4 weeks. The expression of aquaporin 1, vascular endothelial growth factor, transforming growth factor β1, and basic fibroblast growth factor were analyzed using quantitative real-time polymerase chain reaction, Western blot, and immunohistochemical staining. Valsartan partially reversed the effects of high-salt diet on hypertension, cardiac injuries such as fibrosis and inflammatory cell infiltration, and inhibition of aquaporin 1 and angiogenic factors; valsartan alone did not exert such effects. The current data demonstrated that the reduction of cardiac aquaporin 1 and angiogenic factor expression level might be associated with high-salt-induced hypertension and cardiac injuries in mice, which could be ameliorated by angiotensin II receptor blocker treatment.

Epoxyeicosatrienoic acids attenuating hypotonic-induced apoptosis of IMCD cells via γ-ENaC inhibition

Inner medulla collecting duct (IMCD) cells are the key part for urinary concentration. Hypotonic stress may trigger apoptosis of IMCD cells and induce renal injury. Epoxyeicosatrienoic acids (EETs) play an important role in anti-apoptosis, but their roles in hypotonic-induced apoptosis of IMCD cells are still unclear. Here we found increasing exogenous 11, 12-EET or endogenous EETs with Ad-CMV-CYP2C23-EGFP transfection decreased apoptosis of IMCD cells induced by hypotonic stress. Moreover, up-regulation of γ-ENaC induced by hypotonic stress was abolished by elevation of exogenous or endogenous EETs. Collectively, this study illustrated that EETs attenuated hypotonic-induced apoptosis of IMCD cells, and that regulation of γ-ENAC may be a possible mechanism contributing to the anti-apoptotic effect of EETs in response to hypotonic stress.