Tumor necrosis factor-α decreases aquaporin-3 expression in DJM-1 keratinocytes

Expression analysis of genes important for maintaining skin function in a senescence-accelerated mouse prone model

AIM

Senescence-accelerated mouse prone (SAMP) mice can reproduce the same conditions as normal aging mice in a short period. Although SAMP mice have been widely used in aging research, research on skin function in SAMP mice is lacking. In this study, to investigate the skin function of SAMP mice, we analyzed the expression of genes important for maintaining skin function.

METHODS

Eight-month-old SAMP mice and senescence-accelerated mouse resistant (SAMR) mice with normal aging were used. The expression levels of various functional genes in the skin were analyzed.

RESULTS

The dermal water content of SAMP mice was significantly lower than that of SAMR mice, indicating dry skin. The mRNA expression levels of elastin (Ela), filaggrin (Flg), loricrin (Lor), collagen type I alpha 1 chain (Col1a1) and Col1a2 in the skin of SAMP mice were all significantly decreased compared with those of SAMR mice. Hyaluronan-degrading enzyme (Hyal1) expression levels in SAMP mice were similar to those in SAMR mice, but hyaluronan synthase (Has2) levels were significantly decreased. In addition, the expression level of aquaporin-3 in the skin of SAMP mice was significantly decreased at both the mRNA and protein levels.

CONCLUSIONS

In the skin of SAMP mice, the expression levels of various skin function-regulating genes were decreased, and this phenomenon might cause skin dryness. The SAMP mouse could be a tool for analyzing skin aging. Geriatr Gerontol Int 2023; 23: 951-957.

Abnormal nuclear expression of aquaporin-3 in lesional and perilesional skin of vitiligo patients: A novel immunohistochemical finding

BACKGROUND

Vitiligo is a skin disease characterized by a complex etiopathogenesis. Keratinocyte apoptosis may play a role in vitiligo pathogenesis. Aquaporin-3 (AQP-3) is an aqua-glyceroporin that controls keratinocyte proliferation and differentiation.

AIM

To assess the immunohistochemical expression of AQP-3 in lesional and perilesional skin of vitiligo patients compared to healthy control skin.

METHODS

A total of 20 patients with generalized non-segmental vitiligo and 20 age- and sex-matched healthy controls were included. Lesional and perilesional skin of vitiligo patients, as well as normal skin of control subjects, were biopsied. The immunohistochemical expression of AQP3 in the epidermis was examined.

RESULTS

Compared to control skin, both lesional and perilesional skin showed a significant reduction in the intensity of membranous staining of AQP-3 (p < 0.001, p = 0.002, respectively). Moreover, the membrano-cytoplasmic pattern of AQP-3 staining was significantly detected in 80% of lesions and 85% of perilesional biopsies, while it was absent in control skin (p < 0.001). Additionally, nuclear AQP-3 expression was significantly detected in 35% of lesions and 55% of perilesional biopsies, while it was not detected in control skin (p = 0.012, p < 0.001, respectively). No statistically significant difference was detected between lesional and perilesional skin.

CONCLUSIONS

To our knowledge, this is the first immunohistochemical research to show a significant abnormal nuclear expression of AQP-3 in lesional and perilesional skin of vitiligo patients. This abnormality may reflect impaired functions of AQP-3, leading to keratinocyte apoptosis with subsequent melanocyte death and development of vitiligo.

Effect of partially hydrolyzed guar gum on the expression of aquaporin-3 in the colon

In recent years, the development of functional foods targeting gastrointestinal disorders has been in progress. Partially hydrolyzed guar gum (PHGG), which is a water-soluble dietary fiber, is known to have a constipation-improving effect. However, many aspects of the mechanism remain unclear. In this study, we investigated the role of aquaporin-3 (AQP3), which regulates the water content of feces in ameliorative effect of PHGG on constipation. Rats were allowed to freely consume a normal diet or a diet containing 5% PHGG for 14 days, and defecation parameters were measured. We also analyzed the expression levels of genes involved in water transport in the colon. The defecation frequency and volume of rats treated with PHGG were not different from those from the control group, but the fecal water content was significantly increased, and soft stools were observed. The expressions of claudin-1, tight junction protein-1, and cadherin-1, which are involved in tight junctions or adherens junctions, were almost the same in the PHGG-treated group and the control group. The expression level of AQP3 in the colon was significantly decreased in the PHGG-treated group. In this study, PHGG decreased the colonic AQP3 expression, thereby suppressing water transport from the luminal side to the vascular side and improving constipation.

Role of Aquaporins in Inflammation-a Scientific Curation

Inflammation is a universal response mechanism existing as inter-communicator of biological systems. Uncontrolled or dysregulated inflammation addresses chronic low-grade effects eventually resulting in multimorbidity. Active solute transport across the membrane establishes varying osmotic gradients. Aquaporins (AQPs) are a class of critical ubiquitously expressed transmembrane proteins that aid in fluid and small solute transport via facilitated diffusion over established osmotic gradients. Numerous significant data features the biological functions of AQPs rendering them as an appropriate biomarker of health and diseases. Besides their physiological role in well-balanced inflammatory responses, it is worth noting the dysregulation of AQPs during any undesirable inflammatory event. Most literature to date clearly sets out AQPs as potential drug targets instigating AQP-based therapies. In light of this conception, the current review provides a compendious overview on the propitious and portentous out-turns of AQPs under inflammation.

Skin aquaporins as druggable targets: Promoting health by addressing the disease

Skin is the most vulnerable organ of the human body since it is the first line of defense, covering the entire external body surface. Additionally, skin has a critical role in thermoregulation, sensation, immunological surveillance, and biochemical processes such as Vitamin D₃ production by ultraviolet irradiation. The ability of the skin layers and resident cells to maintain skin physiology, such as hydration, regulation of keratinocytes proliferation and differentiation and wound healing, is supported by key proteins such as aquaporins (AQPs) that facilitate the movements of water and small neutral solutes across membranes. Various AQP isoforms have been detected in different skin-resident cells where they perform specific roles, and their dysregulation has been associated with several skin pathologies. This review summarizes the current knowledge of AQPs involvement in skin physiology and pathology, highlighting their potential as druggable targets for the treatment of skin disorders.

Role of Cutaneous Aquaporins in the Development of Xeroderma in Type 2 Diabetes

Xeroderma is induced by diabetes, reducing patients’ quality of life. We aimed to clarify the roles of cutaneous water channel aquaporin-3 (AQP3) in diabetic xeroderma using type 2 diabetes model db/db mice. Blood glucose levels were unchanged in 5-week-old db/db mice compared to db/+ mice (control mice), but the pathophysiology of type 2 diabetes was confirmed in 12-week-old db/db mice. The dermal water content and AQP3 expression in 5-week-old db/db mice were almost the same as those in the control mice. On the other hand, in 12-week-old db/db mice, the dermal water content and AQP3 expression were significantly decreased. The addition of glucose to HaCaT cells had no effect on AQP3, but tumor necrosis factor-α (TNF-α) decreased the AQP3 expression level. Blood TNF-α levels or skin inflammation markers in the 12-week-old db/db mice were significantly higher than those in control mice. AQP3 levels in the skin were decreased in type 2 diabetes, and this decrease in AQP3 may be one of the causes of xeroderma. Therefore, a substance that increases AQP3 may be useful for improving xeroderma. Additionally, a decrease in skin AQP3 may be triggered by inflammation. Therefore, anti-inflammatory drugs may be effective as new therapeutic agents for diabetic xerosis.

Unsaturated fatty acid-enriched extract from Hippophae rhamnoides seed reduces skin dryness through up-regulating aquaporins 3 and hyaluronan synthetases 2 expressions

Background

Seed oil of sea buckthorn (SBT) is well known to contain high amount of polyunsaturated fatty acid (PUFA), and PUFA is generally acknowledged to promote skin hydration by reducing trans‐epidermal water loss (TEWL).

Aims

The present study is aimed to investigate that skin hydration offered by SBT seed oil is whether through up‐regulating AQP3 or HAS2 expression.

Methods

MTT assay was performed to detect cytotoxicity of SBT seed oil, and then, PCR was carried out to explore whether SBT seed oil can increase AQP3 mRNA expression in normal human epidermis keratinocytes (NHEK) cells or not. Immunofluorescence (IF) and Western blot analysis were used to test the protein level expression of AQP3 and HAS2 influenced by SBT seed oil in NHEK cells or in reconstructed epidermis skin model.

Results

According to the result of MTT assay, all test concentration of SBT seed oil showed no cytotoxicity to cells. 10 μg/mL SBT seed oil treatment evidently increased AQP3 mRNA level compared to negative control (NC). IF and Western blot analysis results demonstrated that AQP3 and HAS2 protein levels in NHEK cells treated with 10 μg/mL SBT seed oil were much higher than that of NC. Finally, treatment with 10 μg/mL SBT seed oil substantially up‐regulated expression of AQP3 and HAS2 protein in reconstructed epidermis skin model in comparison to NC.

Conclusions

In summary, our study first proved that SBT seed oil can improve skin hydration through increasing AQP3 and HAS2 expressions.

Epidermal Growth Factor Receptor Tyrosine Kinase Inhibitor Erlotinib Induces Dry Skin via Decreased in Aquaporin-3 Expression

An adverse reaction of dry skin occurs frequently during treatment with anticancer epidermal growth factor receptor tyrosine kinase inhibitors (EGFR-TKIs). In this study, we conducted basic research to clarify the mechanism of EGFR-TKI-induced dry skin and propose new treatments or preventative measures. Dermal water content was significantly lower in the erlotinib-treated mice than in the control group. An assessment of the expression levels of functional genes in the skin revealed that only the expression of the water channel aquaporin-3 (AQP3) was significantly decreased in the erlotinib-treated group. When erlotinib was added to epidermal keratinocyte HaCaT cells, the expression levels of both AQP3 mRNA and protein decreased. Erlotinib treatment also significantly decreased the expression levels of phospho-EGFR and phospho-extracellular signal-regulated kinase (ERK), both in HaCaT cells and mouse skin. Dry skin due to erlotinib may be caused by the decreased expression of AQP3 in the skin, thereby limiting water transport from the vascular side to the corneum side. The decrease in AQP3 may also be attributable to ERK suppression via inhibition of EGFR activity by erlotinib. Therefore, substances that increase AQP3 expression may be effective for erlotinib-induced dry skin.

Study of the Mechanism Underlying the Onset of Diabetic Xeroderma Focusing on an Aquaporin-3 in a Streptozotocin-Induced Diabetic Mouse Model

Xeroderma is a frequent complication in diabetic patients. In this study, we investigated the mechanism underlying the onset of diabetic xeroderma, focusing on aquaporin-3 (AQP3), which plays an important role in water transport in the skin. Dermal water content in diabetic mice was significantly lower than that in control mice. The expression level of AQP3 in the skin was significantly lower in diabetic mice than in control mice. One week after streptozotocin (STZ) treatment, despite their increased blood glucose levels, mice showed no changes in the expression levels of AQP3, Bmal1, Clock, and D site-binding protein (Dbp) in the skin and 8-hydroxydeoxyguanosine (8-OHdG) in the urine. In contrast, two weeks after STZ treatment, mice showed increases in the blood glucose level, decreases in AQP3, Bmal1, Clock, and Dbp levels, and increases in the urinary levels of 8-OHdG. The results of this study suggest that skin AQP3 expression decreases in diabetes, which may limit water transport from the vessel side to the corneum side, causing dry skin. In addition, in diabetic mice, increased oxidative stress triggered decreases in the expression levels of Bmal1 and Clock in the skin, thereby inhibiting the transcription of Aqp3 by Dbp, which resulted in decreased AQP3 expression.

Changes in the Expression of Aquaporin-3 in the Gastrointestinal Tract Affect Drug Absorption

Aquaporin-3 (AQP3) plays an important role in water transport in the gastrointestinal (GI) tract. In this study, we conducted a Caco-2 cell permeability assay to examine how changes in the expression and function of AQP3 affect the rate at which a drug is absorbed via passive transport in the GI tract. When the function of AQP3 was inhibited by mercuric chloride or phloretin, there was no change in warfarin permeability. In contrast, when the expression of AQP3 protein was decreased by prostaglandin E₂ (PGE₂) treatment, warfarin permeability increased to approximately twice the control level, and membrane fluidity increased by 15%. In addition, warfarin permeability increased to an extent comparable to that after PGE₂ treatment when cell membrane fluidity was increased by 10% via boric acid/EDTA treatment. These findings suggest the possibility that the increased drug absorption under decreased AQP3 expression was attributable to increased membrane fluidity. The results of this study demonstrate that the rate of water transport has little effect on drug absorption. However, our findings also indicate that although AQP3 and other similar transmembrane proteins do not themselves transport drugs, changes in their expression levels can cause changes in cell membrane fluidity, thus affecting drug absorption rates.

Protein biomarker for psoriasis: A systematic review on their role in the pathomechanism, diagnosis, potential targets and treatment of psoriasis

Psoriasis is defined as a long-lasting multifactorial inflammatory autoimmune skin condition precisely characterized by delimited, erythematic papules with adherent shiny scales. The conditions are led by hyperproliferative responses of epidermis due to hyperactivation and immature keratinocytes production. The psoriatic skin consists of the thickened epidermal layer, in concurrence with inflammatory exudates in the dermis mainly of dendritic cells, neutrophils, T cells, and macrophages, contributing to the distinct manifestation of psoriatic lesions. It consents to multifaceted and discrete pathology due to the genetic and immunological alteration resulting from abnormal expression of various regulatory and structural proteins. These proteins are associated with various cellular and sub-cellular activities. Therefore, the presence of protein in a pathological cellular environment in the psoriatic lesions as well as in serum could be a great avenue for the insight of pathomechanism, anticipation and diagnosis of psoriasis. Research of protein biomarker in psoriasis is yet a developing realm to be explored by both fundamental and clinical researchers. This review is an attempt to assimilate the current discoveries and revelations of different proteins as a biomarker and their importance in pathogenesis, diagnosis, treatment, and anticipation of both the inflammatory and other dermatological aspects of psoriasis.

New Perspectives on the Potential Role of Aquaporins (AQPs) in the Physiology of Inflammation

Aquaporins (AQPs) are emerging, in the last few decades, as critical proteins regulating water fluid homeostasis in cells involved in inflammation. AQPs represent a family of ubiquitous membrane channels that regulate osmotically water flux in various tissues and sometimes the transport of small solutes, including glycerol. Extensive data indicate that AQPs, working as water channel proteins, regulate not only cell migration, but also common events essential for inflammatory response. The involvement of AQPs in several inflammatory processes, as demonstrated by their dysregulation both in human and animal diseases, identifies their new role in protection and response to different noxious stimuli, including bacterial infection. This contribution could represent a new key to clarify the dilemma of host-pathogen communications, and opens up new scenarios regarding the investigation of the modulation of specific AQPs, as target for new pharmacological therapies. This review provides updated information on the underlying mechanisms of AQPs in the regulation of inflammatory responses in mammals and discusses the broad spectrum of options that can be tailored for different diseases and their pharmacological treatment.

Tumor necrosis factor α decreases aquaporin 3 expression in intestinal epithelial cells through inhibition of constitutive transcription

Inflammatory diseases of the gut are associated with altered electrolyte and water transport, leading to the development of diarrhea. Epithelially expressed aquaporins (AQPs) are downregulated in inflammation, although the mechanisms involved are not known. We hypothesized that AQP3 expression in intestinal epithelial cells is altered in intestinal inflammation and that these changes are driven by tumor necrosis factor (TNF) α. Human colonic adenocarcinoma (HT‐29) cells were treated with TNFα to investigate signaling mechanisms in vitro. AQP3 expression was assessed by real‐time PCR and radiolabeled glycerol uptake, with select inhibitors and a luciferase reporter construct used to further elucidate intracellular signaling. AQP3 expression was downregulated in HT‐29 cells treated with TNFα. Luciferase reporter construct experiments revealed that TNFα downregulated constitutive transcriptional activity of the AQP3 promoter, and inhibition of MEK/ERK and nuclear factor κB (NF‐κB) signaling prevented the decrease in AQP3 mRNA expression. Constitutive AQP3 expression was suppressed by specificity protein (Sp) 3, and knockdown of this transcription factor bound to the AQP3 promoter was able to partially prevent the TNFα‐induced downregulation of AQP3. TNFα signals through MEK/ERK and NF‐κB to enhance the negative transcriptional control of AQP3 expression exerted by Sp3. Similar mechanisms regulate numerous ion channels, suggesting a common mechanism by which both ion and water transport are altered in inflammation.

Regulation of the Glycerol Transporter, Aquaporin-3, by Histone Deacetylase-3 and p53 in Keratinocytes

Aquaporin- (AQP) 3, a water and glycerol channel, plays an important role in epidermal function, with studies showing its involvement in keratinocyte proliferation, differentiation, and migration and in epidermal wound healing and barrier repair. Increasing speculation about the use of histone deacetylase (HDAC) inhibitors to treat skin diseases led us to investigate HDAC's role in the regulation of AQP3. The broad-spectrum HDAC inhibitor suberoylanilide hydroxamic acid induced AQP3 mRNA and protein expression in a dose- and time-dependent manner in normal keratinocytes. The SAHA-induced increase in AQP3 levels resulted in enhanced [³H]glycerol uptake in normal but not in AQP3-knockout keratinocytes, confirming that the expressed AQP3 was functional. Use of HDAC inhibitors with different specificities limited our exploration of the responsible HDAC member to HDAC1, HDAC2, or HDAC3. Cre-recombinase-mediated knockdown and overexpression of HDAC3 suggested a role for HDAC3 in suppressing AQP3 expression basally. Further investigation implicated p53 as a transcription factor involved in regulating HDAC inhibitor-induced AQP3 expression. Thus, our study supports the regulation of AQP3 expression by HDAC3 and p53. Because suberoylanilide hydroxamic acid is already approved to treat cutaneous T-cell lymphoma, it could potentially be used as a therapy for skin diseases like psoriasis, where AQP3 is abnormally expressed.

Epigenetic Signatures at AQP3 and SOCS3 Engage in Low-Grade Inflammation across Different Tissues

BACKGROUND

Elevated levels of C-reactive protein (CRP, determined by a high-sensitivity assay) indicate low-grade inflammation which is implicated in many age-related disorders. Epigenetic studies on CRP might discover molecular mechanisms underlying CRP regulation. We aimed to identify DNA methylation sites related to CRP concentrations in cells and tissues regulating low-grade inflammation.

RESULTS

Genome-wide DNA methylation was measured in peripheral blood in 1,741 participants of the KORA F4 study using Illumina HumanMethylation450 BeadChip arrays. Four CpG sites (located at BCL3, AQP3, SOCS3, and cg19821297 intergenic at chromosome 19p13.2, P ≤ 1.01E-07) were significantly hypomethylated at high CRP concentrations independent of various confounders including age, sex, BMI, smoking, and white blood cell composition. Findings were not sex-specific. CRP-related top genes were enriched in JAK/STAT pathways (Benjamini-Hochberg corrected P < 0.05). Results were followed-up in three studies using DNA from peripheral blood (EPICOR, n = 503) and adipose tissue (TwinsUK, n = 368) measured as described above and from liver tissue (LMU liver cohort, n = 286) measured by MALDI-TOF mass spectrometry using EpiTYPER. CpG sites at the AQP3 locus (significant p-values in peripheral blood = 1.72E-03 and liver tissue = 1.51E-03) and the SOCS3 locus (p-values in liver < 2.82E-05) were associated with CRP in the validation panels.

CONCLUSIONS

Epigenetic modifications seem to engage in low-grade inflammation, possibly via JAK/STAT mediated pathways. Results suggest a shared relevance across different tissues at the AQP3 locus and highlight a role of DNA methylation for CRP regulation at the SOCS3 locus.

Aquaporins in the Colon as a New Therapeutic Target in Diarrhea and Constipation

Aquaporins (AQPs) play important roles in the water transport system in the human body. There are currently 13 types of AQP, AQP0 through AQP12, which are expressed in various organs. Many members of the AQP family are expressed in the intestinal tract. AQP3 is predominantly expressed in the colon, ultimately controlling the water transport. Recently, it was clarified that several laxatives exhibit a laxative effect by changing the AQP3 expression level in the colon. In addition, it was revealed that morphine causes severe constipation by increasing the AQP3 expression level in the colon. These findings have shown that AQP3 is one of the most important functional molecules in water transport in the colon. This review will focus on the physiological and pathological roles of AQP3 in the colon, and discuss clinical applications of colon AQP3.

COX-2 inhibition attenuates lung injury induced by skeletal muscle ischemia reperfusion in rats

BACKGROUND

Skeletal muscle ischemia reperfusion accounts for high morbidity and mortality, and cyclooxygenase (COX)-2 is implicated in causing muscle damage. Downregulation of aquaporin-1 (AQP-1) transmembrane protein is implicated in skeletal muscle ischemia reperfusion induced remote lung injury. The expression of COX-2 in lung tissue and the effect of COX-2 inhibition on AQP-1 expression and lung injury during skeletal muscle ischemia reperfusion are not known. We investigated the role of COX-2 in lung injury induced by skeletal muscle ischemia reperfusion in rats and evaluated the effects of NS-398, a specific COX-2 inhibitor.

METHODS

Twenty-four Sprague Dawley rats were randomized into 4 groups: sham group (SM group), sham+NS-398 group (SN group), ischemia reperfusion group (IR group) and ischemia reperfusion+NS-398 group (IN group). Rats in the IR and IN groups were subjected to 3h of bilateral ischemia followed by 6h of reperfusion in hindlimbs, and intravenous NS-398 8 mg/kg was administered in the IN group. In the SM and SN groups, rubber bands were in place without inflation. At the end of reperfusion, myeloperoxidase (MPO) activity, COX-2 and AQP-1 protein expression in lung tissue, PGE2 metabolite (PGEM), tumor necrosis factor (TNF)-α and interleukin (IL)-1β levels in bronchoalveolar lavage (BAL) fluid were assessed. Histological changes in lung and muscle tissues and wet/dry (W/D) ratio were also evaluated.

RESULTS

MPO activity, COX-2 expression, W/D ratio in lung tissue, and PGEM, TNF-α and IL-1β levels in BAL fluid were significantly increased, while AQP-1 protein expression downregulated in the IR group as compared to that in the SM group (P<0.05). These changes were remarkably mitigated in the IN group (P<0.05). NS-398 treatment also alleviated histological signs of lung and skeletal muscle injury.

CONCLUSION

COX-2 protein expression was upregulated in lung tissue in response to skeletal muscle ischemia reperfusion. COX-2 inhibition may modulate pulmonary AQP-1 expression and attenuate lung injury.

Analysis of aquaporin 9 expression in human epidermis and cultured keratinocytes

Aquaporin 9 (AQP9) is a member of the aquaglyceroporin family that transports glycerol, urea and other small solutes as well as water. Compared to the expression and function in epidermal keratinocytes of AQP3, another aquaglyceroporin, our knowledge of epidermal AQP9 remains elusive. In this study, we investigated the expression of AQP9 in the human epidermis and cultured keratinocytes. Immunofluorescence studies revealed that AQP9 expression is highly restricted to the stratum granulosum of the human epidermis, where occludin is also expressed at the tight junctions. Interestingly, the AQP3 staining decreased sharply below the cell layers in which AQP9 is expressed. In cultured normal human epidermal keratinocytes (NHEK), knock-down of AQP9 expression in the differentiated cells induced by RNA interference reduced glycerol uptake, which was not as pronounced as was the case with AQP3 knock-down cells. In contrast, similar reduction of urea uptake was detected in AQP9 and AQP3 knock-down cells. These findings suggested that AQP9 expression in NHEK facilitates at least the transport of glycerol and urea. Finally, we analyzed the effect of retinoic acid (RA), a potent stimulator of keratinocyte proliferation, on AQP3 and AQP9 mRNA expression in differentiated NHEK. Stimulation with RA at 1 μM for 24 h augmented AQP3 expression and down-regulated AQP9 expression. Collectively, these results indicate that AQP9 expression in epidermal keratinocytes is regulated in a different manner from that of AQP3.

[The elucidation of the function and the expression control mechanism of aquaporin-3 in the colon]

Aquaporins (AQPs) are membrane channels that transport water within the human body and are therefore important for the regulation of water homeostasis. However, little is known regarding the details of the physiological role of AQP3, which is predominantly expressed in the colon. Thus, we investigated the role of AQP3 in the colon using laxative agents (magnesium sulfate and bisacodyl). The results suggest that the laxative effect produced by magnesium sulfate, which is classified as an osmotic laxative, is not simply a result of the changes in osmotic pressure but is also associated with the increased expression of AQP3 in the mucosal epithelial cells of the colon. In addition, magnesium sulfate increased colonic AQP3 expression through adenylate cyclase activation, which is caused by an increase in the intracellular Mg(2+) concentration. This effect may trigger CREB phosphorylation through PKA activation and promote AQP3 gene transcription. Meanwhile, bisacodyl, which is classified as a stimulant laxative, decreases the expression level of AQP3 in the mucosal epithelial cells of the colon, resulting in the inhibition of water transfer from the intestinal tract to the vascular side of the epithelium, eventually leading to the development of diarrhea. It was also observed that the direct activation of colon macrophages by bisacodyl increases the secretion of PGE2, which acts as a paracrine factor and decreases AQP3 expression in colon mucosal epithelial cells. Future studies of the enteric AQP3 expression level and water transport may aid in the development of new laxative and antidiarrheal agents that target AQP3.

An aquaporin 3-notch1 axis in keratinocyte differentiation and inflammation

Aquaporin 3 (AQP3) is an aquaglyceroporin which transports water, glycerol and small solutes across the plasma membrane. Its functions are not limited to fluid transport but also involve the regulation of cell proliferation, migration, skin hydration, wound healing and tumorigenesis. While AQP3 has been reported to play an important role in keratinocyte proliferation, its role in differentiation remains controversial. Our study demonstrated that the expression of AQP3 was regulated during differentiation and that it participated in keratinocyte differentiation control. We further revealed that AQP3 was a transcriptional target of Notch signaling, a critical pathway regulating keratinocyte differentiation and tumor suppression, and it regulated differentiation through a reciprocal negative feedback loop with Notch1. When the expression level of AQP3 was elevated, impaired barrier integrity and increased pro-inflammatory cytokine production ensued, mimicking the pathological conditions in Notch deficient mice and in atopic dermatitis. Dysregulation of AQP3 and Notch receptors has been reported in several skin diseases, including skin cancer. Our discovery of the novel AQP3-Notch1 axis may provide insight into epidermal homeostasis control and possible translational applications, including its potential use as a biomarker for molecular diagnosis in environmental studies.

Effects of COX-2 inhibitor on ventilator-induced lung injury in rats

BACKGROUND

Mechanical ventilation especially with large tidal volume has been demonstrated to activate inflammatory response inducing lung injury, which could be attenuated by cyclooxygenase (COX)-2 inhibitors. As the main small integral membrane proteins that selectively conduct water molecules' transportation, aquaporin (AQP)-1 downregulation significantly related to lung edema and inflammation. This study aims to investigate the role of AQP1 in ventilator-induced lung injury in rats and evaluates the effects of COX-2 inhibition.

METHODS

Forty rats were allocated into four groups, where rats in Groups LD (low volume+DMSO) and LN (low volume+NS-398) were given intravenously 2ml DMSO and 8mg/kg NS-398 (a specific COX-2 inhibitor, dissolved in 2ml DMSO) before 4-hour lower tidal volume ventilation (8ml/kg), respectively, while DMSO and NS-398 were administrated in the same manner before 4-hour injurious ventilation (40ml/kg) in Groups HD (high volume+DMSO) and HN (high volume+NS-398). The arachidonic acid metabolites (6-keto prostaglandin F1α, thromboxane B2), inflammatory cytokines (tumor necrosis factor-α, interleukin-1β, 6, 8) and total protein levels in bronchoalveolar lavage (BAL) fluid and COX-2 mRNA and AQP1 protein expression in lung tissue were detected; water content and lung morphology were also evaluated.

RESULTS

Compared to Groups LD and LN, the rats in Groups HD and HN suffered obvious lung morphological changes with higher wet-to-dry weight ratio and lung injury score, and the levels of arachidonic acid metabolites, inflammatory cytokines and total protein in BAL fluid were increased, the expression of COX-2 mRNA was significantly upregulated and AQP1 protein was downregulated in lung tissue (p<0.05). The changes in BAL fluid and the severity of lung injury were attenuated, and AQP1 expression was upregulated in Group HN as compared to HD (p<0.05).

CONCLUSIONS

Ventilation with large tidal volume causes inflammatory mediator production and AQP1 downregulation, which could be attenuated by COX-2 inhibition.

Aquaporin 3 expression is up-regulated by TGF-β1 in rat peritoneal mesothelial cells and plays a role in wound healing

Aquaporin 3 (AQP3) is expressed in many tissues including the peritoneum and kidney. In cultured mesothelial cells, glucose up-regulates AQP3, which may be important for water transport through the peritoneal membrane. However, there has been no research into the role of AQP3 in human peritoneal mesothelial cell (HPMC) migration or peritoneal fibrosis. We investigated the effects of transforming growth factor-β1 (TGF-β1) on AQP3 expression in HPMCs. We also investigated the role of AQP3 in the peritoneal wound healing process in rats. Chronic exposure to glucose-containing solution increased peritoneal myofibroblasts, with TGF-β1 and AQP3 expression in a model of long-term peritoneal dialysis. In vitro, TGF-β1 induced AQP3 expression in HPMCs. AQP3 knockdown by small-interfering RNA inhibited TGF-β1-induced AQP3 and α-smooth muscle actin expression and also slowed HPMC migration. AQP3 overexpression induced faster migration of HPMCs. Treatment with an extracellular signal-regulated kinase inhibitor and p38 kinase inhibitor attenuated TGF-β1-induced AQP3 expression in HPMCs. These data suggest that TGF-β1 induces AQP3 and that AQP3 has a critical role in TGF-β-induced HPMC migration. These findings provide evidence of a novel role for AQP3 in peritoneal fibrosis and wound healing. The effect of TGF-β1 on AQP3 expression in HPMCs is mediated, at least in part, by ERK and p38 signaling.

Changes in transepidermal water loss and skin hydration according to expression of aquaporin-3 in psoriasis

Background

Aquaporins (AQPs) are a family of water transporting proteins present in many mammalian epithelial and endothelial cell types. Among the AQPs, AQP3 is known to be a water/glycerol transporter expressed in human skin.

Objective

The relationship between the expression level of AQP3 and transpidermal water loss (TEWL) in the lesional and peri-lesional skin of psoriasis-affected patients, and skin hydration in the lesional and peri-lesional skin of psoriasis patients, was investigated.

Methods

The expression of AQP3 in psoriasis-affected and healthy control skin was determined using immunohistochemical and immunofluroscence staining. TEWL and skin hydration were measured using a Tewameter® TM210 (Courage & Khazaka, Cologne, Germany) and a Corneometer® CM 820 (Courage & Khazaka), respectively.

Results

AQP3 was mainly expressed in the plasma membrane of stratum corneum and the stratum spinosum in normal epidermis. Unlike the normal epidermis, AQP3 showed decreased expression in the lesional and peri-lesional epidermis of psoriasis. TEWL was increased, and skin hydration was decreased, in the lesional and peri-lesional skin of psoriasis patients, compared with the healthy control sample.

Conclusion

Although various factors contribute to reduced skin hydration in the lesional and peri-lesional skin of psoriasis, AQP3 appears to be a key factor in the skin dehydration of psoriasis-affected skin.

Impaired aquaporin 3 expression in reepithelialization of cutaneous wound healing in the diabetic rat

Impaired cutaneous wound healing is a serious complication of diabetes mellitus (DM). Currently, little is known about reepithelialization in DM. However, recent studies identified aquaporin 3 (AQP3), a transmembrane protein that functions as a pore-like passive transporter, to be a key molecule in cutaneous epidermal wound healing. AQP3 expression is downregulated in response to tumor necrosis factor-alpha (TNF- α). Given that systemic TNF-α levels are functionally connected to impaired healing in diabetic mice and that both diabetic and Aqp3-deficient animals exhibit impaired reepithelialization, the authors hypothesized that impaired AQP3 expression might contribute to diabetes-impaired wound healing. In the present study, the authors examined AQP3 expression in the regenerating epidermis during cutaneous full thickness wound healing and in intact skin of a streptozotocin-induced diabetic rat model. Aqp3 messenger RNA expression levels were decreased in wounds of DM rats compared to controls. Immunohistochemical analysis showed an absence of AQP3 in the stratum spinosum of the regenerating epidermis in the DM group, whereas the stratum basale was positive for AQP3 in both groups. In summary, these findings suggest that there may be a relationship between impaired AQP3 expression and diabetes-delayed reepithelialization. Thus, future nursing studies should focus on this mechanism in diabetic wound healing.

The channel physiology of the skin

During embryonic development, the skin, the largest organ of the human body, and nervous system are both derived from the neuroectoderm. Consequently, several key factors and mechanisms that influence and control central or peripheral nervous system activities are also present and hence involved in various regulatory mechanisms of the skin. Apparently, this is the case for the ion and non-ion selective channels as well. Therefore, in this review, we shall focus on delineating the regulatory roles of the channels in skin physiology and pathophysiology. First, we introduce key cutaneous functions and major characteristics of the channels in question. Then, we systematically detail the involvement of a multitude of channels in such skin processes (e.g. skin barrier formation, maintenance, and repair, immune mechanisms, exocrine secretion) which are mostly defined by cutaneous non-neuronal cell populations. Finally, we close by summarizing data suggesting that selected channels are also involved in skin diseases such as e.g. atopic dermatitis, psoriasis, non-melanoma cancers and malignant melanoma, genetic and autoimmune diseases, etc., as well as in skin ageing.

The laxative effect of bisacodyl is attributable to decreased aquaporin-3 expression in the colon induced by increased PGE2 secretion from macrophages

The purpose of this study was to investigate the role of aquaporin3 (AQP3) in the colon in the laxative effect of bisacodyl. After oral administration of bisacodyl to rats, AQP3, macrophages, cyclooxygenase 2 (COX2), and prostaglandin E(2) (PGE(2)) were examined in the colon. The mechanism by which bisacodyl decreases the expression of AQP3 was examined using HT-29 and Raw264.7 cells. When diarrhea occurred, a significant increase in the expression of PGE(2) and a decrease in AQP3 expression were observed. Immunostaining showed COX2 expression only in macrophages. The PGE(2) concentration increased significantly 30 min after the addition of bisacodyl to Raw264.7 cells. Thirty minutes after PGE(2) addition to HT-29 cells, the AQP3 expression level decreased to 40% of the control. When pretreated with indomethacin, bisacodyl did not induce an increase in the colon PGE(2) level, a decrease in the AQP3 expression level, or diarrhea. The results suggest that bisacodyl may decrease the expression of AQP3 in the colon, which inhibits water transfer from the luminal to the vascular side and leads to a laxative effect. This study also showed that direct activation of colon macrophages by bisacodyl increases the secretion of PGE(2), which acts as a paracrine factor and decreases AQP3 expression in colon mucosal epithelial cells.

Upregulation of aquaporin-3 is involved in keratinocyte proliferation and epidermal hyperplasia

Aquaporin-3 (AQP3) is a water/glycerol-transporting protein expressed in keratinocytes of the epidermis. We previously showed that AQP3-mediated transport of water and glycerol is involved in keratinocyte migration and proliferation, respectively. However, the involvement of AQP3 in epidermal hyperplasia in skin diseases, such as atopic dermatitis (AD), is unknown. In this study, we found significantly increased AQP3 transcript and protein expression in the epidermis of human AD lesions. The upregulation of AQP3 expression in human keratinocytes by transfection with human AQP3 DNA plasmid was associated with increased cellular glycerol and ATP, as well as increased cell proliferation. Among several cytokines and chemokines produced in the skin, CCL17, which is highly expressed in AD, was found to be a strong inducer of AQP3 expression and enhanced keratinocyte proliferation. In mouse AD models, AQP3 was strongly overexpressed in the epidermis in wild-type mice. Epidermal hyperplasia was reduced in AQP3-deficient mice, with a decreased number of proliferating keratinocytes. These results suggest the involvement of AQP3 in epidermal hyperplasia by a mechanism involving upregulated AQP3 expression and consequent enhancement of keratinocyte proliferation.