Aquaporin water channels: roles beyond renal water handling

Genome-wide identification of aquaporin and their potential role in osmotic pressure regulation in Ruditapes philippinarum

Aquaporins (AQPs) are specialized membrane proteins that create selective water channels, facilitating the transport of water across cell membranes and playing a vital role in maintaining water balance and regulating osmotic pressure in aquatic animals. This study identified 9 aquaporin genes from the genome of R. philippinarum, and a comprehensive analysis was conducted on their gene structure, phylogenetic relationships, protein structure, and chromosome localization. RNA-seq data analysis revealed that aquaporin genes were differentially expressed at different developmental stages, in tissue distribution, and in response to salinity stress. In addition, qPCR results revealed that the expression levels of aquaporin genes (AQP1, AQP4d, and AQP3) were significantly elevated in response to both acute low and high salinity stress, suggesting their important role in osmotic pressure regulation in R. philippinarum. This study's results offer an important reference for further investigations into the regulation of osmotic pressure and salinity adaptation of aquaporin in R. philippinarum.

Advancements of aquaporin 1 in ultrafiltration failure secondary to peritoneal dialysis

For patients undergoing long-term peritoneal dialysis (PD), exposure to biologically incompatible PD solutions and the consequent peritoneal structure change can lead to progressive angiogenesis and fibrosis, and ultimately result in ultrafiltration failure (UFF). Peritoneal transport studies in aquaporin 1 (AQP1) knockout mice indicate that water transport across the peritoneum is mediated by AQP1, which accounts for up to 50% of ultrafiltration. Another recent study on a large cohort of PD patients with kidney failure further substantiated the impact of AQP1 genotype variation on water channel expression in the peritoneal membrane, influencing water transport, ultrafiltration, and patient prognosis. High-dose corticosteroid therapy in both patients and mice seems to be effective in regulating AQP1 to improve ultrafiltration. At present, increasing evidence suggests that AQP1 is relevant for the process of PD water osmotic transport and ultrafiltration. Despite a great deal of research having been done on the structure and function of aquaporin proteins, many fundamental issues remain unresolved.

Analysis of the impact of protein conformational dynamics and intermolecular interactions on water flux through TIP3;1 aquaporins of Zea mays L

The discovery of aquaporins (AQPs) in 1992 had a profound impact on our understanding of the mechanisms underlying the transport of substances across cell membranes. To further understand water mobilization through AQPs, this study focuses on the characterization of water flux through the TIP3;1 aquaporins of Zea mays L. using molecular dynamics. The primary objective is to elucidate how protein-water intermolecular interactions and protein conformational dynamics impact water mobility across the cell membrane. To conduct this analysis, the three-dimensional structure of TIP3;1 was modeled using AlphaFold2, from which the complete system was constructed. This system consisted of a homotetramer of TIP3;1 immersed in a fragment of cell membrane and solvated with water molecules and ions. Subsequently, molecular dynamics simulations were conducted for 90 ns, resulting in the determination of an osmotic permeability coefficient (pf) of 0.8172 ± 0.146 × 10-14 cm3 s-1. In general, the mobility of water along the single-file water channel is influenced by the complex interplay of protein conformational dynamics and hydrogen bonding. The conformational dynamics of the protein channel modify the pore radius available for the passage of water, which affects the frequency of protein-water interactions and consequently influences the mobility of water in the channel. This study contributes to our understanding of the molecular mechanisms by which AQP activity is modulated without involving changes in protein chemical composition.

Retention and pseudogenization of aquaporin-10 in Rodentia

Vertebrates exhibit diversity in the presence and number of aquaporin (Aqp)-10 genes. In Rodentia, mice possess an Aqp10 pseudogene, whereas guinea pigs possess an intact Aqp10. However, Aqp10 retention and pseudogenization history in various rodent lineages remains unclear. Therefore, in this study, we aimed to investigate the molecular evolution of Aqp10 using the recent increasingly decoded rodent genome sequences. We analyzed Aqp10 in the genomes of 43 rodent species belonging to 14 families and found that Aqp10 was pseudogenized in 13 species of three families in the Myomorpha suborder. In contrast, a single intact Aqp10 was retained in the other 30 rodent species, with no Aqp10 pseudogene found in the Castorimorpha, Hystricomorpha, and Sciuromorpha suborders. Additionally, we investigated the tissue expression levels of aquaglyceroporin genes in guinea pigs and rats via reverse transcription-polymerase chain reaction and detected Aqp10 expression in the guinea pig intestines. Notably, none of the examined rat organs expressed Aqp10; however, Aqp7 was expressed in the rat intestines. In situ hybridization showed that guinea pig Aqp10 was expressed in the intestinal epithelial cells. Moreover, AQP10 was permeable to water, glycerol, urea, and boric acid in Xenopus oocytes. Overall, these results clarify the Aqp10 pseudogenization history in Rodentia and suggest guinea pigs as excellent small animal models to analyze the intestinal AQP10 functions.

Lysine acetylation of aquaporin-3 promotes water permeability but is not essential for urine concentrating ability

Aquaporin-3 (AQP3) mediates basolateral water transport in the kidney principal cells contributing to urine concentration. We previously identified the acetylation of lysine 282 (K282) in the C-terminus of AQP3, which we hypothesized as a positive regulator of AQP3 water permeability. AQP3 acetylation (K282Q or Q) or deacetylation (K282R or R) mimetic mutant mice models were created using CRISPR/Cas9. Male and female wild-type (WT) and mutant mice were assigned to hydrating diets and water deprivation protocols. Urine and plasma osmolality in response to acute vasopressin receptor-2 activation with desmopressin (dDAVP) or inhibition by tolvaptan were determined. In vitro water permeability of murine principal kidney cortical collecting duct (mpkCCD) cells stably expressing AQP3 WT, Q, or R was measured. Acetylated AQP3 was prominent in the cortical to inner medullary collecting ducts of dehydrated versus hydrated mice. At baseline, the mutations did not affect the kidney transcriptome, AQP3 abundance, or subcellular localization. Urine osmolality of the mutant mice was within the normal range. With dehydration, all mice excreted concentrated urine; however, the female Q mutants exhibited significantly greater 24-h urine osmolality than WT, suggesting greater water reabsorption. In response to acute dDAVP, all mice produced concentrated urine; however, female Q mutants had a more dilute plasma than WT, further suggesting greater water retention. mpkCCD Q mutant cells exhibited greater water permeability than WT and R cells. We conclude that AQP3 K282 acetylation promotes principal cell water permeability in a sex-dependent manner; however, it is not essential for urine concentration.NEW & NOTEWORTHY The water channel, AQP3, is lysine 282 acetylated (acAQP3) in rodents and humans. When dehydrated, mouse cortical to inner medullary collecting ducts express acAQP3, suggesting that it promotes water reabsorption. acAQP3 expressing principal cells have high water permeability, and in vivo acute desmopressin resulted in a dilute plasma in female acAQP3 mice. However, all mice produced concentrated urine during water deprivation. Thus, acAQP3 promotes water permeability but is not essential for urine concentration during antidiuresis.

Fucoidan Alleviates Porcine Epidemic Diarrhea Virus-Induced Intestinal Damage in Piglets by Enhancing Antioxidant Capacity and Modulating Arginine Metabolism

Porcine epidemic diarrhea virus (PEDV) causes severe intestinal damage, posing significant threats to the swine industry. Fucoidan (FUC), a biologically active compound, exhibits antiviral activity against multiple viruses. This study aimed to investigate the protective effects of FUC on PEDV-induced intestinal injury in piglets and explore its underlying mechanisms. A total of 28 healthy crossbred piglets were randomly allocated into four experimental groups using a 2 × 2 factorial design: (1) a control group, (2) an FUC group, (3) a PEDV group, and (4) an FUC+PEDV group. From day 4 to day 10, the piglets in the FUC and FUC+PEDV groups were orally administered fucoidan at a dosage of 20 mg/kg body weight (BW) each day. On day 8, the piglets in the PEDV and FUC+PEDV groups were orally administered PEDV at a dose of 3 × 105.5 TCID50. The results show that FUC supplementation significantly decreased plasma DAO activity (p < 0.05) and increased the villus height, villus area, as well as the villus height/crypt depth (p < 0.05) in the intestine when compared to the PEDV-infected piglets. This indicates that FUC could alleviate the disruption of intestinal morphology and function caused by PEDV infection. FUC enhanced the antioxidant capacity of the piglets by increasing SOD and GSH-Px activity. Transcriptional profiling combined with quantitative analysis revealed that FUC regulates immune responses, substance transport, and arginine metabolism. Notably, FUC downregulated arginase 1 expression, which may redirect arginine toward nitric oxide synthesis, thereby establishing an antiviral state in the host. These findings highlight the potential application of FUC as a natural agent for mitigating PEDV-induced intestinal damage and improving gut health. Additionally, monitoring the health status of piglets is necessary when FUC is applied in practical applications.

Aquaporins as Membrane Proteins: The Current Status

BACKGROUND

The ambient conditions that ensure the expected protein folding activity are important in directing the protein folding process. Water favors the formation of a centrally located hydrophobic protein nucleus with exposed polar residues for preferable contact with polar water molecules. Different ambient conditions are created by the hydrophobic cell membrane, which also provides an environment for the activity of proteins, including channels responsible for transporting multiple molecules, the concentration of which is controlled as part of homeostasis. Aquaporins are transmembrane proteins responsible for primarily transporting water and low-molecular-weight compounds.

METHODS

The fuzzy oil drop (FOD) model was applied in its modified form, FOD-M, for the analysis. The FOD model allows quantitative assessment of protein structure adaptation to external conditions, ensuring its biological activity.

RESULTS

The aquaporins studied in this work revealed adaptations for stabilizing hydrophobic environments and transporting polar molecules.

CONCLUSIONS

A significant degree of similarity was demonstrated in the structure of human aquaporins using FOD-M. This model enabled a quantitative assessment of the degree of adaptation to biological function achieved through an appropriate balance between micelle-like decomposition and appropriate modification due to the specificity of the environment that ensures adequate activity.

Bifidobacterium animalis subsp. lactis BLa80 alleviates constipation in mice through modulating the stem cell factor (SCF)/c-Kit pathway and the gut microbiota

Probiotics, as health ingredients, have attracted widespread attention. However, due to the wide variety of probiotic species, their laxative effects and the underlying mechanisms remain elusive. In this study, we investigated the laxative effect of Bifidobacterium animalis subsp. lactis BLa80 (at concentrations of 1.0 × 108, 2.0 × 108, and 4.0 × 108 CFU per mL, with a dosage of 0.2 mL each) in mice, utilizing a functional constipation mouse model induced with loperamide hydrochloride (0.2 mL, 10 mg per kg BW) for 7 consecutive days. Meanwhile, a blank group (treated with 0.2 mL of 0.9% saline) and a positive control group (treated with mosapride at a dose of 5 mg per kg BW) were also set up. The body weight, fecal water content, intestinal propulsion rate, colon tissue histology, fecal microbial composition, serum indices, and colon mRNA levels of the mice were measured, employing histological and biochemical assays, GC-MS, RT-qPCR and 16S rRNA gene sequencing etc. Results showed BLa80 could accelerate intestinal peristalsis, maintain fecal moisture, prevent intestinal barrier disruption, increase short-chain fatty acid production, prevent gut microbe dysbiosis and constipation in mice. It also helped to keep the levels of 5-hydroxytryptamine (5-HT), motilin (MTL), and substance P (SP) normal, up-regulated the mRNAs of intestinal mucin 2 (MUC2), stem cell factor (SCF), and the tyrosine kinase receptor c-Kit, and down-regulated the mRNA of aquaporins (AQPs), especially at a high-dose. This study indicated that BLa80 held the potential to emerge as a novel ingredient in functional foods designed for constipation relief and as a treatment alternative.

Aquaporin-5 facilitates liver regeneration following hepatectomy via ROS/GSDMD pathway

During the proliferative phase of liver regeneration, insufficient regulation of hepatocyte hydrogen peroxide (H2O2) overproduction can result in oxidative stress and hepatocyte death. This study aims to investigate the influence of Aquaporin 5 (Aqp5) on liver regeneration by evaluating its role in reactive oxygen species (ROS) generation and NLRP3-GSDMD-mediated pyroptosis. A 70 % partial hepatectomy (PHx) model was established in Aqp5-/- mice to evaluate the pathological changes in the liver. Reactive oxygen species (ROS) production was assessed using a dichlorodihydrofluorescein diacetate (DCFH-DA) assay. Aqp5 deficiency significantly increased ROS production, the number of TUNEL-positive cells, and disrupted mitochondrial membrane potential in the liver of Aqp5-deficient mice. The impact of Aqp5 on ROS/NLRP3/Gasdermin-D (GSDMD)-mediated pyroptosis was examined through the administration of N-acetyl-L-cysteine (NAC, an ROS scavenger) or disulfiram (DSF, a GSDMD inhibitor). In Aqp5-deficient mice, the regenerative liver exhibited increased expression of NLRP3, enhanced activation of caspase-1 and GSDMD, as well as elevated secretion of IL-1β. Treatment with DSF significantly attenuated GSDMD-mediated pyroptosis triggered by Aqp5 deficiency in the regenerating liver. Furthermore, the administration of NAC to Aqp5-deficient mice resulted in a reduction in the expression levels of NLRP3, the activity levels of caspase-1 and GSDMD, as well as the release of IL-1β. Our findings indicate that the deficiency of Aqp5 facilitates GSDMD activation through the production of ROS. The suppression of ROS or inhibition of GSDMD significantly alleviates the damage and pyroptosis observed in Aqp5-deficient regenerative liver.

Aquaporin‑1 regulates microglial polarization and inflammatory response in traumatic brain injury

The present study investigated the mechanisms by which aquaporin 1 (AQP1) influences microglial polarization and neuroinflammatory processes in traumatic brain injury (TBI). A model of TBI was generated in AQP1‑knockout mice to assess the impact of AQP1 deletion on inflammatory cytokine release, neuronal damage and cognitive function. Immunofluorescence, reverse transcription‑quantitative PCR, western blotting and enzyme‑linked immunosorbent assay were employed to evaluate pro‑inflammatory and anti‑inflammatory markers. Behavioral assessments, including the Barnes maze, were performed to determine cognitive outcomes. Moreover, AQP1 knockout inhibited the activation of inflammation‑related signaling pathways, including nuclear factor‑κB, Janus kinase/signal transducer and activator of transcription, phosphoinositide 3‑kinase/protein kinase B and extracellular signal‑regulated kinase/mitogen‑activated protein kinase pathways. Further studies indicated that the AQP1 inhibitor m‑phenylenediacrylic acid demonstrated significant neuroprotective effects in a mouse model of TBI. These findings suggested that AQP1 may be essential in post‑TBI inflammatory responses and neuronal injury, establishing a theoretical foundation for future therapies aimed at AQP1.

The comprehensive potential of AQP1 as a tumor biomarker: evidence from kidney neoplasm cohorts, cell experiments and pan-cancer analysis

Aquaporin1 (AQP1) facilitates water transport. Its ability to be a biomarker at the pan-cancer level remains uninvestigated. We performed immunohistochemical staining on tissues from 370 individuals with kidney neoplasms to measure AQP1 expression. We utilized Kaplan-Meier survival analysis, Chi-square tests, and multivariate Cox regression analyses to assess the prognostic relevance of AQP1 expression. In the pan-cancer context, we explored AQP1's competing endogenous RNAs network, protein-protein interactions, genomic changes, gene set enrichment analysis (GSEA), the correlation of AQP1 expression with survival outcomes, drug sensitivity, drug molecular docking, tumor purity and immunity. AQP1 shRNA expressing 786-O cells were established. Cell proliferation was assessed by Cell Counting Kit-8 and colony formation. Transwell migration, invasion, and cell scratch assays were conducted. In our study, AQP1 expression was an independent protective factor for OS and PFS in renal cancer patients. AQP1 expression significantly correlated with survival outcomes in renal cancers, LGG, SARC, HNSC and UVM. PI-103 sensitivity was related to AQP1 expression and had potential binding cite with AQP1 protein. Knockdown of AQP1 reduced cell proliferation, migration and invasion. Our study uncovered AQP1 as a biomarker for favorable survival outcomes in renal cancers. Furthermore, the bioinformatic analysis promoted its implication in pan-cancer scope.

Water homeostasis gene expression in the kidney of broilers divergently selected for water conversion ratio

Divergent selection of broilers for water conversion ratio has established and high-(HWE) and low- water efficient (LWE) broiler lines. Two 2 × 2 factorial experiments were conducted to assess the gene expression profile of systems involved in renal water homeostasis. In Exp. 1, male and female HWE and LWE broilers were individually phenotyped between 4 and 6 wks of age to determine growth performance and water conversion ratio (g water intake/g body weight gain). Kidney samples were obtained from 5 males and 5 females from each line. In Exp. 2, HWE and modern random bred (MRB) broilers were placed in 12 controlled-environmental chambers (2 floor pens/chamber, 6 chambers/line, 11 birds per pen, 132 birds/line) on day of hatch. The broilers were brooded at thermoneutral temperatures from 0 to 4 wks. From 4 to 7 wks, broilers were maintained at thermoneutral (TN, 25 °C) or exposed to cyclic heat stress (HS, 35 °C, 8h/day) conditions. Body weight, feed intake, and water intake were recorded. Kidney samples were collected, flash frozen in liquid nitrogen, and kept at -80 °C for gene expression analysis. Data were analyzed by Two-way ANOVA and means compared by Tukey's HSD multiple comparison test. Molecular analyses from Exp. 1 showed that the renal expression of arginine vasopressin (AVP), angiotensinogen (AGT), angiotensin II receptor type 1 and 2 (AT1/2), sodium-potassium ATPase subunit B1 (ATP1B1), and aquaporin 3 (AQP3) were upregulated in HWE compared to the LWE line. In contrast, mRNA expression of mesotocin receptor (MTR), AT1/2, AQP1/2, and occludin were significantly higher in females than in males. In Exp. 2, target genes were regulated in environment and/or line-dependent manner. The renal expression of heat shock proteins 70 and 90, AVP receptor 2 (AVPR2), AGT, renin, AT1/2, and AQP1was significantly upregulated in HS compared to TN birds, however AVPR2 expression was significantly higher in HWE compared to MRB birds. Together, the up-regulation of AVP, the renin-angiotensin system (RAS), and AQP in HWE, female, or under HS conditions suggests a better renal water reabsorption to support water use efficiency.

Engineered crystalline polymers for effective contaminant removal from water

Herein, we discuss the structure-function of biomimetic imidazole-quartet substrates (I-quartets) obtained through the adaptive self-assembly of octyl-ureido-polyol structures in polyamide membranes designed as adsorbents. Molecular dynamics (MD) and well-tempered metadynamics simulations are utilized to examine ion contaminants' adsorption process and dynamic behaviors onto alkylureido-ethylimidazoles with well-defined supramolecular structures. Moreover, the atoms-in-molecules (AIM) analysis identified multiple types of atomic interactions between the contaminant molecules and the substrates. The results demonstrate that I-quartets with hydrophobic tails significantly enhance the adsorption of contaminant species in the aquatic environment. Descriptors involving interaction energies mean square displacement, radial distribution function, root-mean-square deviation, the number of hydrogen bonds, and solvent-accessible surface area are estimated from the simulation trajectories to study this process. The system containing PO43- exhibited notable stability, as indicated by data analysis. Electrostatic interactions primarily govern the adsorption process; however, the interaction between the active sites of alkylureido-ethylimidazole-based channels, such as N = C and O = C, and the investigated contaminant species (PO43-, NO3-, NO2-, and HNO3) can enhance adsorption due to these interactions. In addition, the free energy values for the adsorption process of PO43-, NO3-, NO2-, and HNO3 contaminants in water are - 604.77, - 532.63, - 461.24, and - 348.62 kJ mol-1, respectively. The obtained results confirm that alkylureido-ethylimidazoles are prominent adsorbents for removing pollutant ions from wastewater, thus contributing to the development of more efficient materials for water purification.

Arginine vasopressin and angiotensin II coregulate Aquaporin 2 expression in M-1 cells

OBJECTIVE

The aim of this study was to explore the impact of arginine vasopressin (AVP) and angiotensin II (Ang II) on aquaporin 2 (AQP2) expression in M - 1 cells.

METHODS

M - 1 cells were stimulated with desmopressin (dDAVP) and Ang II, followed by treatment with tolvaptan and losartan. The expression and protein levels of V2R, AT1R, AQP2, and p-S256AQP2 were measured via ELISA, western blotting, RT-qPCR, and immunofluorescence. Molecular docking was employed to assess the interaction affinities between Ang II, losartan, and V2R, as well as dDAVP, tolvaptan, and AT1R.

RESULTS

dDAVP stimulation significantly upregulated the expression of V2R, AQP2, and p-S256AQP2 in M - 1 cells. Ang II stimulation also resulted in significant increases in AT1R, AQP2, p-S256AQP2 expression. Interestingly, we found that dDAVP could stimulate the expression of AT1R, and Ang II could stimulate the expression of V2R. Following tolvaptan treatment, the expression levels of V2R, AQP2, p-S256AQP2, and AT1R were significantly reduced. Similarly, losartan treatment led to a marked decrease in AT1R, AQP2, p-S256AQP2, and V2R expression. Molecular docking analysis confirmed the binding interactions between Ang II and losartan with V2R, as well as between dDAVP and tolvaptan with AT1R.

CONCLUSION

AVP and Ang II collaboratively regulate the expression of V2R and AT1R in M - 1 cells, influencing AQP2 expression.

TRPML1 acts as a predisposing factor in lymphedema development by regulating the subcellular localization of aquaporin-3, -5

An imbalance in lymphatic fluid, whether it is caused by generation, transport, outflow, or dysfunctional vessels, can lead to lymphedema; however, the exact pathogenesis of this disease remains unclear. To explore the mechanism, we focused on the association among TRPML1, aquaporin-3 (AQP3), and aquaporin-5 (AQP5) in human lymphatic endothelial cells (HLECs). We explored the role of TRPML1 in altering the permeability of HLECs in lymphedema. Meanwhile, we constructed a disease model using gene-knockout mice to observe the effect of TRPML1 on inflammation and fibrosis in lymphedema sites. Our results indicate that TRPML1 not only regulates the localization of AQP3, -5 to the cell membrane but also increases HLEC permeability, disrupts lymphatic fluid transport, and mediates the development of chronic inflammation at the site of lymphedema. Our study suggests that TRPML1 is a precipitating factor in lymphedema. Our findings improve the understanding of TRPML1 and aquaporins in secondary lymphedema, providing valuable insights for future research.

The water channels aquaporin-1 and aquaporin-3 interact with and affect the cell polarity protein Scribble in 3D in vitro models of breast cancer

Cellular changes in carcinomas include alterations in cell proliferation, cell migration, cell-cell adhesion, and cellular polarity. In vitro studies have revealed that the water channels, aquaporin-1 (AQP1) and AQP3, can influence cell migration and cell-cell adhesion. Of note, we previously showed that AQP1 overexpression reduced levels of cell-cell adhesion proteins, whereas AQP3 increased levels when overexpressed in normal epithelial cells. Expression of AQP1 and AQP3 in breast carcinoma is associated with lymph node metastasis, recurrence, and poor survival of patients with breast cancer. In this study, we investigated if AQP1 and AQP3 affected cell polarity in breast cancer by studying the relationship between the major polarity protein Scribble and AQP1 and AQP3. In breast cancer tissue samples, the protein expression of AQP1, AQP3, and Scribble did not show an obvious correlation. However, in a GST pull-down assay, AQP1 and AQP3 interacted with Scribble. AQP1 overexpression reduced the size of 3D spheroids as well as reduced Scribble levels at cell-cell contacts, whereas AQP3 overexpression showed no significant change in spheroid size compared with control, AQP3 overexpression also reduced Scribble levels at cell-cell contacts. Of note, AQP1 overexpression increased cell migration and induced cell detachment and dissemination from migrating breast cancer cell sheets, whereas AQP3 overexpression did not. Thus, AQP1 and AQP3 differentially affect 3D-grown breast cancer spheroids, and especially AQP1 may contribute to cancer development and spread via negatively affecting cellular junctions and cell polarity proteins as well as increasing cell migration and cell detachment.NEW & NOTEWORTHY Overexpression of the water channels aquaporin-1 and aquaporin-3 reduced levels of the key polarity protein Scribble at cell-cell junctions, suggesting potential implications in breast cancer progression and metastasis.

Aquaporin-1 and Osmosis: From Physiology to Precision in Peritoneal Dialysis

The discovery of the aquaporin family of water channels has provided a molecular counterpart to the movement of water across biological membranes. The distribution of aquaporins in specific cell types, their selectivity and very high capacity for water permeation, and the control of their expression and/or trafficking are key to sustain osmosis in multiple tissues. Here, we review the convergent evidence demonstrating that aquaporin-1 (AQP1) facilitates water transport across endothelial cells in the peritoneal membrane, a key process for peritoneal dialysis-the leading modality of home-based dialysis therapy for patients with kidney failure. Genetic and pharmacologic studies in mouse and cell models indicated that AQP1 plays a critical role in crystalloid osmosis, with clinically relevant effects on water transport and risk of death and technique failure for patients on dialysis. By contrast, AQP1 plays no role in colloid osmosis. These studies substantiate potential strategies to improve free water transport and ultrafiltration in patients treated by peritoneal dialysis.

Aquaporin-3 is down-regulated by LMP1 in nasopharyngeal carcinoma cells to regulate cell migration and affect EBV latent infection

Epstein-Barr virus (EBV) infection has a strong correlation with the development of nasopharyngeal carcinoma (NPC). Aquaporin 3 (AQP3), a member of the aquaporin family, plays an important role in tumor development, especially in epithelial-mesenchymal transition. In this study, the expression of AQP3 in EBV-positive NPC cells was significantly lower than that in EBV-negative NPC cells. Western blot and qRT-PCR analysis showed that LMP1 down-regulated the expression of AQP3 by activating the ERK pathway. Cell biology experiments have confirmed that AQP3 affects the development of tumor by promoting cell migration and proliferation in NPC cells. In addition, AQP3 can promote the lysis of EBV in EBV-positive NPC cells. The inhibition of AQP3 expression by EBV through LMP1 may be one of the mechanisms by which EBV maintains latent infection-induced tumor progression.

Transcriptomics-based analysis reveals hexafluoropropylene oxide trimer acid (HFPO-TA) induced kidney damage and lipid metabolism disorders in SD rats

Hexafluoropropylene oxide trimer acid (HFPO-TA) is an emerging environmental pollutant that can accumulate in air and surface water. Currently, it has been widely used in fluoropolymer industry, which could cause serious environmental pollution. Due to the high bioaccumulation, the accumulation of pollutants may have an adverse effect on the normal physiological function of the kidneys. However, the toxic effects of HFPO-TA on the kidney are unknown. In this study, we investigated the toxic effects of HFPO-TA exposure on the rat kidney and its mechanism of action. Male SD rats were divided into 4 groups: control group (Ctrl group), L group (0.125 mg/kg/d), M group (0.5 mg/kg/d) and H group (2 mg/kg/d). After 14 consecutive days of gavage, periodic acid‑silver methenamine (PASM) and hematoxylin-eosin (HE) staining were used to examine the structure of the kidneys. We also used transcriptome sequencing (RNA-seq) to identify differentially expressed genes (DEGs) in the testes of rats in both the control and high dose groups. Besides, expression of key proteins was analyzed by immunohistochemistry. The results indicated that HFPO-TA can lead to injured renal capsule, change glomerular shape and have a significant impact on the protein expression levels of AQP2, p-AQP2 and PPARα. Additionally, the level of total cholesterol (TC) was obviously decreased after HFPO-TA exposure. RNA-seq analysis showed that HFPO-TA primarily affected peroxisome proliferator-activated receptor (PPAR) signaling pathway that is associated with lipid metabolism and cyclic adenosine monophosphate (cAMP) signaling pathway. In summary, exposure to HFPO-TA can lead to kidney damage and lipid metabolism disorders.

Comparison of aquaporin profile of advanced passage mesenchymal stem cells with early passage mesenchymal stem cells and determination of its effect on adipogenic differentiation efficiency

OBJECTIVE

Our study aimed to compare aquaporin profiles in advanced and early passage bone marrow-derived mesenchymal stem cells (BM-MSCs) and assess the impact of aquaporin changes after adipogenic differentiation. Aquaporins are crucial for stem cell survival and differentiation during their life cycle. We focused on the role of aquaporins in the cell structures of advanced and early passage stem cells.

METHODS

In our study, BM-MSCs were used for our objectives. Characterization of the cells was evaluated via flow cytometry using stem cell surface markers. The characterized BM-MSCs were divided into control and differentiation groups at passages 3 (P3) and 8 (P8). AQP1, AQP3, AQP7, AQP9, and AQP10 expression levels on days 0, 1, 3, 7, 14, and 21 were evaluated using Real Time-PCR, ELISA, and immunofluorescence studies.

RESULTS

The cells were characterized by flow cytometry and confirmed to exhibit BM-MSC characteristics. At P3 and P8, differentiation was initiated, and AQP protein expression was observed to initially increase and then decrease on subsequent days. The increase in AQP protein expression at P3 occurred earlier than that at P8. Gene expression analysis demonstrated a statistically significant increase in AQP gene expression on days when AQP protein expression decreased. Moreover, statistical differences were observed between late and early passage AQP profiles.

CONCLUSION

Our study examined the composition of AQPs in BM-MSCs in association with cell passage, and found that AQPs play a role in the differentiation process. The connection between the AQP profile and aging might be related to differentiation capacity, which could have implications for slowing down cellular aging and developing new therapeutic approaches.

Regulation of renal aquaporin water channels in acute pyelonephritis

Acute pyelonephritis (APN) is most frequently caused by uropathogenic Escherichia coli (UPEC), which ascends from the bladder to the kidneys during a urinary tract infection. Patients with APN have been reported to have reduced renal concentration capacity under challenged conditions, polyuria, and increased aquaporin-2 (AQP2) excretion in the urine. We have recently shown increased AQP2 accumulation in the plasma membrane in cell cultures exposed to E. coli lysates and in the apical plasma membrane of inner medullary collecting ducts in a 5-day APN mouse model. This study aimed to investigate if AQP2 expression in host cells increases UPEC infection efficiency and to identify specific bacterial components that mediate AQP2 plasma membrane insertion. As the transepithelial water permeability in the collecting duct is codetermined by AQP3 and AQP4, we also investigated whether AQP3 and AQP4 localization is altered in the APN mouse model. We show that AQP2 expression does not increase UPEC infection efficiency and that AQP2 was targeted to the plasma membrane in AQP2-expressing cells in response to the two pathogen-associated molecular patterns (PAMPs), lipopolysaccharide and peptidoglycan. In contrast to AQP2, the subcellular localizations of AQP1, AQP3, and AQP4 were unaffected both in lysate-incubated cell cultures and in the APN mouse model. Our finding demonstrated that cellular exposure to lipopolysaccharide and peptidoglycan can trigger the insertion of AQP2 in the plasma membrane revealing a new regulatory pathway for AQP2 plasma membrane translocation, which may potentially be exploited in intervention strategies.NEW & NOTEWORTHY Acute pyelonephritis (APN) is associated with reduced renal concentration capacity and increased aquaporin-2 (AQP2) excretion. Uropathogenic Escherichia coli (UPEC) mediates changes in the subcellular localization of AQP2 and we show that in vitro, these changes could be elicited by two pathogen-associated molecular patterns (PAMPs), namely, lipopolysaccharide and peptidoglycan. UPEC infection was unaltered by AQP2 expression and the other renal AQPs (AQP1, AQP3, and AQP4) were unaltered in APN.

Protective roles of peroxiporins AQP0 and AQP11 in human astrocyte and neuronal cell lines in response to oxidative and inflammatory stressors

In addition to aquaporin (AQP) classes AQP1, AQP4 and AQP9 known to be expressed in mammalian brain, our recent transcriptomic analyses identified AQP0 and AQP11 in human cortex and hippocampus at levels correlated with age and Alzheimer's disease (AD) status; however, protein localization remained unknown. Roles of AQP0 and AQP11 in transporting hydrogen peroxide (H2O2) in lens and kidney prompted our hypothesis that up-regulation in brain might similarly be protective. Established cell lines for astroglia (1321N1) and neurons (SHSY5Y, differentiated with retinoic acid) were used to monitor changes in transcript levels for human AQPs (AQP0 to AQP12) in response to inflammation (simulated with 10-100 ng/ml lipopolysaccharide [LPS], 24 h), and hypoxia (5 min N2, followed by 0 to 24 h normoxia). AQP transcripts up-regulated in both 1321N1 and SHSY5Y included AQP0, AQP1 and AQP11. Immunocytochemistry in 1321N1 cells confirmed protein expression for AQP0 and AQP11 in plasma membrane and endoplasmic reticulum; AQP11 increased 10-fold after LPS and AQP0 increased 0.3-fold. In SHSY5Y cells, AQP0 expression increased 0.2-fold after 24 h LPS; AQP11 showed no appreciable change. Proposed peroxiporin roles were tested using melondialdehyde (MDA) assays to quantify lipid peroxidation levels after brief H2O2. Boosting peroxiporin expression by LPS pretreatment lowered subsequent H2O2-induced MDA responses (∼50%) compared with controls; conversely small interfering RNA knockdown of AQP0 in 1321N1 increased lipid peroxidation (∼17%) after H2O2, with a similar trend for AQP11 siRNA. Interventions that increase native brain peroxiporin activity are promising as new approaches to mitigate damage caused by aging and neurodegeneration.

Aquaporin-8 promotes human dermal fibroblasts to counteract hydrogen peroxide-induced oxidative damage: A novel target for management of skin aging

The skin is subjected to various external factors that contribute to aging including oxidative stress from hydrogen peroxide (H2O2). This study investigated the distribution of aquaporin-8 (AQP8), a protein that transports H2O2 across biological membranes, in skin cells, and its effects in mitigating H2O2-induced oxidative damage. Human dermal fibroblasts were treated with increasing concentrations of H2O2 to evaluate oxidative damage. Cell viability, reactive oxygen species (ROS) generation, and the expression of specific genes associated with skin aging (IL-10, FPR2, COL1A1, KRT19, and Aggrecan) were evaluated and AQP8 expression was assessed via quantitative polymerase chain reaction and western blotting. Small-interfering RNA was used to silence the AQP8 gene and evaluate its significance. The results show that H2O2 treatment reduces cell viability and increases ROS generation, leading to oxidative damage that affects the expression of target molecules. Interestingly, H2O2-treated cells exhibit high levels of AQP8 expression and gene silencing of AQP8 reverses high levels of ROS and low levels of COL1A1, KRT19, and Aggrecan expression in stressed cells, indicating that AQP8 plays a vital role in preventing oxidative damage and consequent aging. In conclusion, AQP8 is upregulated in human dermal fibroblasts during H2O2-induced oxidative stress and may help prevent oxidative damage and aging. These findings suggest that AQP8 could be a potential therapeutic target for skin aging. Further research is necessary to explore the feasibility of using AQP8 as a preventive or therapeutic strategy for maintaining skin health.

Evidence That Aquaporin 11 (AQP11) in the Spiny Dogfish (Squalus acanthias) May Represent a Pseudogene

Various attempts to amplify an AQP11 cDNA from tissues of the spiny dogfish (Squalus acanthias) were made. Two pairs of deoxy-inosine-containing degenerate primers were designed based on conserved amino acid sequences from an AQP11 alignment. These primers yielded some faint bands from gill cDNA that were sequenced. Blast searches with the sequences showed they were not AQP11. An elasmobranch AQP11 nucleotide sequence alignment was produced to identify conserved regions to make further degenerate primers. One primer pair produced a short 148 bp fragment showing particularly strong amplification in gill and intestine. It was sequenced and represented a piece of the AQP11 gene. However, as the fragment may have resulted from contaminating genomic DNA (in total RNA used to make cDNA), 5' and 3' RACE were performed to amplify the two ends of the putative cDNA. Furthermore, 5' and 3' RACE amplifications depend on the presence of a 5' cap nucleotide and a poly A tail, respectively on the putative AQP11 mRNA. Hence, successful amplification was only possible from cDNA and not genomic DNA. Nested RACE amplifications were performed using gill and intestinal RACE cDNA, but none of the DNA fragments sequenced were AQP11. Consequently, the spiny dogfish AQP11 gene may represent a pseudogene.

Pathobiont and symbiont contribute to microbiota homeostasis through Malpighian tubules-gut countercurrent flow in Bactrocera dorsalis

Host-gut microbiota interactions are more complex than good or bad. Both gut symbiotic bacteria and pathobionts can provide essential functions to their host in one scenario and yet be detrimental to host health in another. So, these gut-dwelling bacteria must be tightly controlled to avoid harmful effects on the host. However, how pathobionts and other symbiotic bacteria coordinate to establish a host immune defense system remains unclear. Here, using a Tephritidae fruit fly Bactrocera dorsalis, we report that both pathobionts and other gut symbiotic bacteria release tyramine, which is recognized by the host insects. These tyramines induce the formation of insect-conserved Malpighian tubules-gut countercurrent flow upon bacterial infection, which requires tyramine receptors and aquaporins. At the same time, pathobionts but not gut symbiotic bacteria induce the generation of reactive oxygen species, which are preserved by the countercurrent flow, promoting bacteria elimination through increasing gut peristalsis. More importantly, our results show that the Malpighian tubules-gut countercurrent flow maintains proper microbiota composition. Our work suggests a model where pathobiont-induced reactive oxygen species are preserved by Malpighian tubules-gut countercurrent flow involving both pathobionts and symbiotic bacteria. Furthermore, our work provides a Malpighian tubules-gut interaction that ensures efficient maintenance of the gut microbiota.

Following the cellular itinerary of renal aquaporin-2 shuttling with 4.5x expansion microscopy

The shuttling of renal collecting duct aquaporin-2 (AQP2) between intracellular vesicles and the apical plasma membrane is paramount for regulation of renal water reabsorption. The binding of the circulating antidiuretic hormone arginine vasopressin (AVP) to the basolateral AVP receptor increases intracellular cAMP, which ultimately leads to AQP2 plasma membrane accumulation via a dual effect on AQP2 vesicle fusion with the apical plasma membrane and reduced AQP2 endocytosis. This AQP2 plasma membrane accumulation increases water reabsorption and consequently urine concentration. Conventional fluorescent microscopy provides a lateral resolution of ∼250 nm, which is insufficient to resolve the AQP2-containing endosomes/vesicles. Therefore, detailed information regarding the AQP2 vesicular population is still lacking. Newly established 4.5x Expansion Microscopy (ExM) can increase resolution to 60-70 nm. Using 4.5x ExM, we detected AQP2 vesicles/endosomes as small as 79 nm considering an average expansion factor of 4.3 for endosomes. Using different markers of the endosomal system provided detailed information of the cellular AQP2 itinerary upon changes in endogenous cAMP levels. Before cAMP elevation, AQP2 colocalized with early and recycling, but not late endosomes. Forskolin-induced cAMP increase was characterized by AQP2 insertion into the plasma membrane and AQP2 withdrawal from large perinuclear endosomes as well as some localization to lysosomal compartments. Forskolin washout promoted AQP2 endocytosis where AQP2 localized to not only early and recycling endosomes but also late endosomes and lysosomes indicating increased AQP2 degradation. Thus, our results show that 4.5 ExM is an attractive approach to obtain detailed information regarding AQP2 shuttling.NEW & NOTEWORTHY Renal aquaporin-2 (AQP2) imaged by expansion microscopy provides unprecedented 3-D information regarding the AQP2 itinerary in response to changes in cellular cAMP.

Aquaglyceroporins in Human Breast Cancer

Aquaporins are water channels that facilitate passive water transport across cellular membranes following an osmotic gradient and are essential in the regulation of body water homeostasis. Several aquaporins are overexpressed in breast cancer, and AQP1, AQP3 and AQP5 have been linked to spread to lymph nodes and poor prognosis. The subgroup aquaglyceroporins also facilitate the transport of glycerol and are thus involved in cellular metabolism. Transcriptomic analysis revealed that the three aquaglyceroporins, AQP3, AQP7 and AQP9, but not AQP10, are overexpressed in human breast cancer. It is, however, unknown if they are all expressed in the same cells or have a heterogeneous expression pattern. To investigate this, we employed immunohistochemical analysis of serial sections from human invasive ductal and lobular breast cancers. We found that AQP3, AQP7 and AQP9 are homogeneously expressed in almost all cells in both premalignant in situ lesions and invasive lesions. Thus, potential intervention strategies targeting cellular metabolism via the aquaglyceroporins should consider all three expressed aquaglyceroporins, namely AQP3, AQP7 and AQP9.