Regulation of aquaporin-2 in the kidney: A molecular mechanism of body-water homeostasis

Analysis of Kallikrein 6, Acetyl-α-Tubulin, and Aquaporin 1 and 2 Expression Patterns During Normal Human Nephrogenesis and in Congenital Anomalies of the Kidney and Urinary Tract (CAKUT)

Background/Objectives: The human kallikrein-related peptidase 6 (KLK6), a serine protease with trypsin-like properties, belongs to the 15-member kallikrein (KLK) gene family and is predominantly recognized for its role in oncogenesis, neurodegenerative disorders, and skin conditions. Aquaporins (AQPs) are integral membrane proteins that facilitate water transport across cell membranes. AQP1 is constitutively active in the kidneys and plays a crucial role in reabsorbing filtered water, while AQP2 is regulated by vasopressin and is essential for maintaining body fluid homeostasis. The primary objective of the present study is to investigate the spatio-temporal expression patterns of KLK6, AQP1, and AQP2 throughout normal human nephrogenesis and congenital kidney and urinary tract (CAKUT) abnormalities: duplex kidneys, horseshoe kidneys, and dysplastic kidneys. Methods: An immunofluorescence analysis of KLK6, AQP1, and AQP2 was performed on 37 paraffin-embedded fetal kidney samples. The area percentage of KLK6 in the kidney cortex was calculated in normal developing samples during developmental phases 2, 3, and 4 and compared with CAKUT samples. Results: KLK6 exhibits distinct spatiotemporal expression patterns during human kidney development, with consistent localization in proximal tubules. Its subcellular positioning shifts from the basolateral cytoplasm in early phases to the apical cytoplasm in later stages, which may be strategically positioned to act on its substrate in either the peritubular space or the tubular fluid. KLK6 expression followed a quadratic trajectory, peaking at Ph4. This marked increase in the final developmental phase aligns with its strong expression in mature kidneys, suggesting a potential role in proximal tubule differentiation and functional maturation through facilitating extracellular matrix remodeling and activating proteinase-activated receptors, modulating the signaling pathways that are essential for tubular development. In duplex kidneys, structural abnormalities such as ureteral obstruction and hydronephrosis may upregulate KLK6 as part of a reparative response, while its downregulation could impair epithelial remodeling and cytoskeletal integrity, exacerbating dysplastic phenotypes. Conclusions: These findings highlight the potential of KLK6 involvement in normal kidney development and the pathology of CAKUT.

Unravelling exosome paradigm: Therapeutic, diagnostic and theranostics application and regulatory consideration

In the recent decade, extracellular vesicles (EVs) have been released from nearly all the kingdoms, modulating intercellular communication and maintaining the human body's homeostasis by regulating different cellular processes. Among EVs, exosomes are the emerging field in biopharmaceuticals. They have lipid bilayer ranging from 30 to 150 nm in size and encompass DNA, RNA, protein lipids, etc. Their sources are widespread, easy to acquire, and cost-effective in manufacturing. This review focuses on the detailed classification of exosomes existing in nature, knowledge and application of omics, therapeutic, diagnostic and theranostic application of exosomes. It covers diseases such as cancer, infectious diseases (viral, bacterial, fungal infections), neurodegenerative diseases, metabolic diseases, lifestyle diseases (diabetes, cardiovascular, gastric disorder (IBD)), autoimmune disorders and their biodistribution. This article unfolds the recent progress in the exosomes arena and covers all the regulatory considerations (FDA, EMA, and other nations) involved with it. Moreover, a detailed discussion about clinical trials and its manifestation with exosomes and challenges associated with their isolation procedures, reproducibility, and safety concerns.

Insights into the renal pathophysiology in Hermansky-Pudlak syndrome-1 from urinary extracellular vesicle proteomics and a new mouse model

Hermansky-Pudlak syndrome type 1 (HPS-1) is a rare, autosomal recessive disorder caused by defects in the biogenesis of lysosome-related organelles complex-3 (BLOC-3). Impaired kidney function is among its clinical manifestations. To investigate HPS-1 renal involvement, we employed 1D-gel-LC-MS/MS and compared the protein composition of urinary extracellular vesicles (uEVs) from HPS-1 patients to normal control individuals. We identified 1029 proteins, 149 of which were altered in HPS-1 uEVs. Ingenuity Pathway Analysis revealed disruptions in mitochondrial function and the LXR/RXR pathway that regulates lipid metabolism, which is supported by our novel Hps1 knockout mouse. Serum concentration of the LXR/RXR pathway protein ApoA1 in our patient cohort was positively correlated with kidney function (with the estimated glomerular filtration rate or eGFR). uEVs can be used to study epithelial cell protein trafficking in HPS-1 and may provide outcome measures for HPS-1 therapeutic interventions.

Excess dietary sodium restores electrolyte and water homeostasis caused by loss of the endoplasmic reticulum molecular chaperone, GRP170, in the mouse nephron

The maintenance of fluid and electrolyte homeostasis by the kidney requires proper folding and trafficking of ion channels and transporters in kidney epithelia. Each of these processes requires a specific subset of a diverse class of proteins termed molecular chaperones. One such chaperone is GRP170, which is an Hsp70-like, endoplasmic reticulum (ER)-localized chaperone that plays roles in protein quality control and protein folding in the ER. We previously determined that loss of GRP170 in the mouse nephron leads to hypovolemia, electrolyte imbalance, and rapid weight loss. In addition, GRP170-deficient mice develop an acute kidney injury (AKI)-like phenotype, typified by tubular injury, elevation of kidney injury markers, and induction of the unfolded protein response (UPR). By using an inducible GRP170 knockout cellular model, we confirmed that GRP170 depletion induces the UPR, triggers apoptosis, and disrupts protein homeostasis. Based on these data, we hypothesized that UPR induction underlies hyponatremia and volume depletion in these rodents and that these and other phenotypes might be rectified by sodium supplementation. To test this hypothesis, control and GRP170 tubule-specific knockout mice were provided a diet containing 8% sodium chloride. We discovered that sodium supplementation improved electrolyte imbalance and kidney injury markers in a sex-specific manner but was unable to restore weight or tubule integrity. These results are consistent with UPR induction contributing to the kidney injury phenotype in the nephron-specific GR170 knockout model and indicate that GRP170 function in kidney epithelia is essential to both maintain electrolyte balance and ER homeostasis.NEW & NOTEWORTHY Loss of the endoplasmic reticulum chaperone, GRP170, results in widespread kidney injury and induction of the unfolded protein response (UPR). We now show that sodium supplementation is able to at least partially restore electrolyte imbalance and reduce kidney injury markers in a sex-dependent manner.

Approaching Ideal Selectivity with Bioinspired and Biomimetic Membranes

The applications of polymeric membranes have grown rapidly compared to traditional separation technologies due to their energy efficiency and smaller footprint. However, their potential is not fully realized due, in part, to their heterogeneity, which results in a "permeability-selectivity" trade-off for most membrane applications. Inspired by the intricate architecture and excellent homogeneity of biological membranes, bioinspired and biomimetic membranes (BBMs) aim to emulate biological membranes for practical applications. This Review highlights the potential of BBMs to overcome the limitations of polymeric membranes by utilizing the "division of labor" between well-defined permeable pores and impermeable matrix molecules seen in biological membranes. We explore the exceptional performance of membranes in biological organisms, focusing on their two major components: membrane proteins (biological channels) and lipid matrix molecules. We then discuss how these natural materials can be replaced with artificial mimics for enhanced properties and how macro-scale BBMs are developed. We highlight key demonstrations in the field of BBMs that draw upon the factors responsible for transport through biological membranes. Additionally, current state-of-the-art methods for fabrication of BBMs are reviewed with potential challenges and prospects for future applications. Finally, we provide considerations for future research that could enable BBMs to progress toward scale-up and enhanced applicability.

Investigating the biological significance of the TCM principle "promoting urination to regulate bowel movements" through the influence of the intestinal microbiota and their metabolites on the renal-intestinal axis

Treatment methods in traditional Chinese medicine (TCM) are foundational to their theoretical, methodological, formulaic, and pharmacological systems, significantly contributing to syndrome differentiation and therapy. The principle of "promoting urination to regulate bowel movements" is a common therapeutic approach in TCM. The core concept is "promoting the dispersion and drainage of water dampness, regulating urination to relieve diarrhea," yet its scientific underpinning remains unclear. Modern medical treatment for watery diarrhea primarily focuses on electrolyte replenishment, as diuretics may lead to dehydration and other side effects. Some reports suggest that this TCM approach lacks scientific validity. Microecology, an area associated with the origins of TCM, is closely related to the development, diagnosis, and treatment of diarrhea. The renal-intestinal axis offers a molecular biological basis for examining associated pathological mechanisms, advancing therapeutic targets such as "treating the intestine to address kidney issues" and highlighting the interactions within the "renal-intestinal microbiota-liquid metabolism" framework, thus providing an endogenous mechanism to support "treating the intestine through the kidney." An increasing number of studies have shown that the intestinal microbiota and its metabolites, as unique mediators, are involved in the physiological and pathological changes of the body. Therefore, this study explores the relationship between fluid metabolism and diarrhea from the perspective of the intestinal microbiota and its metabolites, aiming to elucidate the biological mechanisms underlying the "promoting urination to regulate bowel movements" therapeutic approach and to clarify the scientific basis for treating diarrhea via the renal-intestinal axis. This research provides new insights for the study of TCM microbiology.

Exploring Aquaporins in Human Studies: Mechanisms and Therapeutic Potential in Critical Illness

Aquaporins (AQPs) are membrane proteins facilitating water and other small solutes to be transported across cell membranes. They are crucial in maintaining cellular homeostasis by regulating water permeability in various tissues. Moreover, they regulate cell migration, signaling pathways, inflammation, tumor growth, and metastasis. In critically ill patients, such as trauma, sepsis, and patients with acute respiratory distress syndrome (ARDS), which are frequently encountered in intensive care units (ICUs), water transport regulation is crucial for maintaining homeostasis, as dysregulation can lead to edema or dehydration, with the latter also implicating hemodynamic compromise. Indeed, AQPs are involved in fluid transport in various organs, including the lungs, kidneys, and brain, where their dysfunction can exacerbate conditions like ARDS, acute kidney injury (AKI), or cerebral edema. In this review, we discuss the implication of AQPs in the clinical entities frequently encountered in ICUs, such as systemic inflammation and sepsis, ARDS, AKI, and brain edema due to different types of primary brain injury from a clinical perspective. Current and possible future therapeutic implications are also considered.

mRNA expression of kidney aquaporins and blood composition of meat-type chickens raised with or without glucose supplementation under cyclic heat or thermoneutral condition

Heat stress (HS) disrupts water homeostasis in broiler chickens. Kidney aquaporins (AQPs) facilitate water permeability in the renal tubules, thereby maintaining homeostasis of body water and metabolites. We evaluated the mRNA expression of kidney AQPs 1, 2, 3 and 4, and the blood composition of broilers raised under thermoneutral (TN) or cyclic HS condition with or without glucose supplementation. The treatments were TN+0% glucose (TN0), TN+6% glucose (TN6), HS+0% glucose (HS0), and HS+6% glucose (HS6). Each treatment had 6 replicates of 19 birds each. Groups with glucose (Glu) supplementation continuously received 6% Glu in water, and HS groups were exposed to a cyclic HS regime involving 35 °C from 8am to 8pm, and subsequently retuned to 25 °C (thermoneutral) from 8pm to 8am. Both heat and glucose supplementation were applied from d28 to d35. Blood and kidney were collected from 1 bird/replicate on d35. AQP-1, -2, and -3 were highly expressed (p < 0.05) in HS0 relative to TN0, TN6, and HS6. Birds in the TN6 and HS6 had a lower expression of AQP2 while HS0 and HS6 had a lower expression of AQP4. Birds in the HS0 group had a higher water consumption relative to TN0, TN6 and HS6. HS0 and HS6 had a higher water conversion ratio relative to TN0 and TN6. Heat stress lowered (p < 0.05) blood PCO2, TCO2, and HCO3. The blood pH, Na, K, and Cl composition were not affected (p > 0.05) with heat or glucose supplementation. Cyclic HS (p < 0.0001) and glucose supplementation (p = 0.0090) raised the blood glucose level. Kidney aquaporins 1, 2, and 3 are important indicators of water utilization in HS broiler chickens.

Effects of natural reduced water on cognitive functions in older adults: A RCT study

Oxidative stress and diabetes increase the risk of cognitive decline and dementia. Natural reduced water contains active hydrogen (hydrogen radicals), eliminates reactive oxygen species, and has antidiabetic effects. However, whether natural reduced water affects human cognitive function is unknown. Therefore, we implemented a double-blind intervention experiment in which participants consumed 1 L of natural reduced water or tap water daily for 6 months. The participants were healthy older adults living in Japan. The intervention group showed significant improvements in cognitive functions of attention function (p < 0.01) and short-term memory (p < 0.05). These results indicate that the continuous intake of natural reduced water improves several cognitive functions.

Aquaporin 2 in Cerebral Edema: Potential Prognostic Marker in Craniocerebral Injuries

Despite continuous medical advancements, traumatic brain injury (TBI) remains a leading cause of death and disability worldwide. Consequently, there is a pursuit for biomarkers that allow non-invasive monitoring of patients after cranial trauma, potentially improving clinical management and reducing complications and mortality. Aquaporins (AQPs), which are crucial for transmembrane water transport, may be significant in this context. This study included 48 patients, with 27 having acute (aSDH) and 21 having chronic subdural hematoma (cSDH). Blood plasma samples were collected from the participants at three intervals: the first sample before surgery, the second at 15 h, and the third at 30 h post-surgery. Plasma concentrations of AQP1, AQP2, AQP4, and AQP9 were determined using the sandwich ELISA technique. CT scans were performed on all patients pre- and post-surgery. Correlations between variables were examined using Spearman's nonparametric rank correlation coefficient. A strong correlation was found between aquaporin 2 levels and the volume of chronic subdural hematoma and midline shift. However, no significant link was found between aquaporin levels (AQP1, AQP2, AQP4, and AQP9) before and after surgery for acute subdural hematoma, nor for AQP1, AQP4, and AQP9 after surgery for chronic subdural hematoma. In the chronic SDH group, AQP2 plasma concentration negatively correlated with the midline shift measured before surgery (Spearman's ρ -0.54; p = 0.017) and positively with hematoma volume change between baseline and 30 h post-surgery (Spearman's ρ 0.627; p = 0.007). No statistically significant correlation was found between aquaporin plasma levels and hematoma volume for AQP1, AQP2, AQP4, and AQP9 in patients with acute SDH. There is a correlation between chronic subdural hematoma volume, measured radiologically, and serum AQP2 concentration, highlighting aquaporins' potential as clinical biomarkers.

Influence of previous plane of nutrition on molecular mechanisms regulating the expression of urea and water metabolism related genes in the rumen and kidney of finishing crossbred Angus steers

This study aimed to understand how molecular mechanisms controlling water and urea metabolism at the finishing phase can be affected by previous plane of nutrition of crossbred Angus beef steers. Twenty-four (n = 24) animals were randomly distributed into either a moderate (MP) or high plane of nutrition during the background phase for 85 d. Animals were then blocked by their previous plane and were moved onto a 105-d finishing phase in a 2 × 2 factorial arrangement. The forage-finished group received only high-quality alfalfa hay, whereas the grain-fed group received a high grain diet (80% whole corn and 20% alfalfa hay). By the end of the finishing phase, animals were harvested and tissue samples from the rumen and kidney were collected. Changes in gene expression of aquaporins (AQP)-2, -3, -4, -7, ATP1A1, ATP1B1, SGK1, CLIC1 (kidney and rumen), UT-A1 (kidney only) and UT-B (rumen only), were assayed via real-time qPCR; 18S rRNA was used as an endogenous control. One-way ANOVA followed by Tukey's post hoc analysis was conducted. When animals were from MP, forage-finishing increased the relative abundance of AQP3 (P ≤ 0.05), AQP7 (P ≤ 0.05), ATP1B1 (P ≤ 0.05), and SGK1 (P ≤ 0.05) in the kidney when compared to grain-fed animals. In the rumen, for the MP group, AQP7 was differentially expressed in both treatments at the finishing phase (P ≤ 0.01), with forage-finished steers having the highest expression of AQP7. For the MP group, UT-B had a tendency of presenting a higher expression on grain-fed animals (P = 0.075). Overall, these results suggest that previous plane can impact expression of genes associated with water and urea metabolism during the finishing phase, namely AQP3, AQP7, ATP1B1, and SGK1 in the kidney, and AQP7 and UT-B in the rumen. The greatest impact observed on gene expression changes of investigated genes at the finishing phase was reflective of animals backgrounded on the moderate previous plane.

Activation of TGR5 Increases Urine Concentration by Inducing AQP2 and AQP3 Expression in Renal Medullary Collecting Ducts

Introduction

G protein-coupled bile acid receptor (TGR5), the first G protein-coupled receptor for bile acids identified, is capable of activating a variety of intracellular signaling pathways after interacting with bile acids. TGR5 plays an important role in multiple physiological processes and is considered to be a potential target for the treatment of various metabolic diseases, including type 2 diabetes. Evidence has emerged that genetic deletion of TGR5 results in an increase in basal urine output, suggesting that it may play a critical role in renal water and salt reabsorption. The present study aims to elucidate the effect and mechanism of TGR5 activation on urine concentration.

Methods

Mice were treated with TGR5 agonists (LCA and INT-777) for 3 days. The 24-h urine of mice was collected and analyzed for urine biochemical parameters. The mRNA expressions were detected by real-time PCR, and the protein expressions were detected by western blot. Immunohistochemistry and immunofluorescence were performed to examine the cellular location of proteins. The cultured primary medullary collecting duct cells were pretreated with H89 (a PKA inhibitor) for 1 h, followed by 12-h treatment of LCA and INT-777. Luciferase reporter assays were used to detect the effect of CREB on the gene transcription of AQPs. Gel electrophoretic mobility shift assays were used to analyze DNA-protein interactions.

Results

Treatment of mice with the TGR5 agonist LCA and INT-777 markedly reduced urine output and increased urine osmolality, accompanied by a marked increase in AQP2 and AQP3 protein expression and membrane translocation. In cultured primary medullary collecting duct cells, LCA and INT-777 dose-dependently upregulated AQP2 and AQP3 expression in a cAMP/PKA-dependent manner. Mechanistically, both AQP2 and AQP3 gene promoter contains a putative CREB-binding site, which can be bound and activated by CREB as assessed by both gene promoter-driven luciferase and gel shift assays.

Conclusion

Collectively, our findings demonstrate that activation of TGR5 can promote urine concentration by upregulation of AQP2 and AQP3 expression in renal collecting ducts. TGR5 may represent an attractive target for the treatment of patients with urine concentration defect.

The relation between autophagy modulation by intermittent fasting and aquaporin 2 expression in experimentally induced diabetic nephropathy in albino rat

Polyuria is an early sign of diabetic nephropathy (DN) that produces dehydration in diabetic patients. This could be caused by alteration of renal aquaporin 2 (AQP2) expression. This study aimed to describe the relation between autophagy modulation via intermittent fasting (IF) and renal AQP2 expression and polyuria in case of DN. We divided the rats into control, DN and IF groups. After 2 and 4 weeks of diabetes induction, blood glucose (BG), serum creatinine (Scr), urine volume, and 24 hours urine protein (UP) were examined. Diabetic nephropathy histopathological index (DNHI) was calculated to evaluate histopathological changes. Immunohistochemistry and real-time PCR were performed to measure the levels of AQP2 and the autophagy marker; LC3 in kidney tissue. DNHI was correlated to the PCR and immunoexpression of AQP2 and LC3. Intermittent fasting significantly decreased the BG, Scr, urine volume, 24 hours UP, and DNHI as compared diabetes. Diabetes significantly elevated the immunoreactivity and mRNA expression levels of AQP2 and LC3 as compared to the control. However, the IF decreased AQP2 and stimulated autophagy in cyclic fashion. Our data revealed significant positive correlations between AQP2 and LC3 at the level of immunoexpression and mRNA at 2nd weeks. Taken together, these data showed that autophagy stimulation didn't regulate AQP2 expression in case of diabetic nephropathy, however IF decreased polyuria through improvement of glycemic state.

Adhesion G Protein-Coupled Receptor Gpr126 (Adgrg6) Expression Profiling in Diseased Mouse, Rat, and Human Kidneys

Uncovering the function of understudied G protein-coupled receptors (GPCRs) provides a wealth of untapped therapeutic potential. The poorly understood adhesion GPCR Gpr126 (Adgrg6) is widely expressed in developing kidneys. In adulthood, Gpr126 expression is enriched in parietal epithelial cells (PECs) and epithelial cells of the collecting duct and urothelium. Whether Gpr126 plays a role in kidney disease remains unclear. Here, we characterized Gpr126 expression in diseased kidneys in mice, rats, and humans. RT-PCR data show that Gpr126 expression is altered in kidney disease. A quantitative RNAscope® analysis utilizing cell type-specific markers revealed that Gpr126 expression upon tubular damage is mainly increased in cell types expressing Gpr126 under healthy conditions as well as in cells of the distal and proximal tubules. Upon glomerular damage, an increase was mainly detected in PECs. Notably, Gpr126 expression was upregulated in an ischemia/reperfusion model within hours, while upregulation in a glomerular damage model was only detected after weeks. An analysis of kidney microarray data from patients with lupus nephritis, IgA nephropathy, focal segmental glomerulosclerosis (FSGS), hypertension, and diabetes as well as single-cell RNA-seq data from kidneys of patients with acute kidney injury and chronic kidney disease indicates that GPR126 expression is also altered in human kidney disease. In patients with FSGS, an RNAscope® analysis showed that GPR126 mRNA is upregulated in PECs belonging to FSGS lesions and proximal tubules. Collectively, we provide detailed insights into Gpr126 expression in kidney disease, indicating that GPR126 is a potential therapeutic target.

Therapeutic Potential of Silymarin in Mitigating Paclitaxel-Induced Hepatotoxicity and Nephrotoxicity: Insights into Oxidative Stress, Inflammation, and Apoptosis in Rats

Background

Paclitaxel (PAX) is a widely used chemotherapy drug for various cancer types but often induces significant toxicity in multiple organ systems. Silymarin (SIL), a natural flavonoid, has shown therapeutic potential due to its multiple benefits.

Aims

To evaluate the therapeutic efficacy of SIL in mitigating liver and kidney damage induced by PAX in rats, focusing on oxidative stress, inflammation, and apoptosis pathways.

Study Design

Experimental animal model.

Methods

The study included 28 male Wistar rats aged 12-14 weeks weighing 270-300 g. The rats were divided into four groups: control, SIL, PAX, and PAX + SIL, with seven in each group. The rats received intraperitoneal (i.p.) injections at a dose of 2 mg per kilogram of body weight of PAX for 5 successive days, followed by oral gavage with 200 mg/kg body mass of SIL for 10 uninterrupted days. We examined the effect of SIL on specific serum biochemical parameters using an autoanalyzer and rat-specific kits. The spectrophotometric methods was used to investigate oxidative stress indicators in kidney and liver tissues. Aquaporin-2 (AQP-2), B-cell lymphoma-2 (Bcl-2), cysteine aspartate-specific protease-3 (caspase-3), interleukin-6 (IL-6), nuclear factor kappa B (NF-κB), and streptavidin-biotin staining were used to assess immunoreactivity in PAX-induced liver and kidney injury models.

Results

SIL treatment significantly reduced serum levels of alanine aminotransferase, aspartate aminotransferase, creatinine, urea, and C-reactive protein, indicating its effectiveness in treating PAX-induced liver and kidney injury. SIL treatment significantly reduced oxidative stress by increasing essential antioxidant parameters, such as superoxide dismutase, catalase, glutathione peroxidase, and glutathione. It also reduced malondialdehyde levels in liver and kidney tissues of SIL-PAX groups (p < 0.05). SIL administration reduced NF-κB, caspase-3, and IL-6 expression while increasing Bcl-2 and AQP2 levels in liver and kidney tissues of rats treated with SIL and PAX (p < 0.05).

Conclusion

Our findings indicate the potential of SIL to alleviate PAX-induced liver and kidney damage in rats by reducing oxidative stress, inflammation, and apoptotic processes.

Molecular Footprints on Osmoregulation-Related Genes Associated with Freshwater Colonization by Cetaceans and Sirenians

The genetic basis underlying adaptive physiological mechanisms has been extensively explored in mammals after colonizing the seas. However, independent lineages of aquatic mammals exhibit complex patterns of secondary colonization in freshwater environments. This change in habitat represents new osmotic challenges, and additional changes in key systems, such as the osmoregulatory system, are expected. Here, we studied the selective regime on coding and regulatory regions of 20 genes related to the osmoregulation system in strict aquatic mammals from independent evolutionary lineages, cetaceans, and sirenians, with representatives in marine and freshwater aquatic environments. We identified positive selection signals in genes encoding the protein vasopressin (AVP) in mammalian lineages with secondary colonization in the fluvial environment and in aquaporins for lineages inhabiting the marine and fluvial environments. A greater number of sites with positive selection signals were found for the dolphin species compared to the Amazonian manatee. Only the AQP5 and AVP genes showed selection signals in more than one independent lineage of these mammals. Furthermore, the vasopressin gene tree indicates greater similarity in river dolphin sequences despite the independence of their lineages based on the species tree. Patterns of distribution and enrichment of Transcription Factors in the promoter regions of target genes were analyzed and appear to be phylogenetically conserved among sister species. We found accelerated evolution signs in genes ACE, AQP1, AQP5, AQP7, AVP, NPP4, and NPR1 for the fluvial mammals. Together, these results allow a greater understanding of the molecular bases of the evolution of genes responsible for osmotic control in aquatic mammals.

Impact of Ring Finger Protein 20 and Its Downstream Regulation on Renal Tubular Injury in a Unilateral Nephrectomy Mouse Model Fed a High-Fat Diet

Abnormal lipid metabolism increases the relative risk of kidney disease in patients with a single kidney. Using transcriptome analysis, we investigated whether a high-fat diet leads to abnormalities in lipid metabolism and induces kidney cell-specific damage in unilateral nephrectomy mice. Mice with unilateral nephrectomy fed a high-fat diet for 12 weeks exhibited progressive renal dysfunction in proximal tubules, including lipid accumulation, vacuolization, and cell damage. Ring finger protein 20 (RNF20) is a ligase of nuclear receptor corepressor of peroxisome proliferator-activated receptors (PPARs). The transcriptome analysis revealed the involvement of RNF20-related transcriptome changes in PPAR signaling, lipid metabolism, and water transmembrane transporter under a high-fat diet and unilateral nephrectomy. In vitro treatment of proximal tubular cells with palmitic acid induced lipotoxicity by altering RNF20, PPARα, and ATP-binding cassette subfamily A member 1 (ABCA1) expression. PPARγ and aquaporin 2 (AQP2) expression decreased in collecting duct cells, regulating genetic changes in the water reabsorption process. In conclusion, a high-fat diet induces lipid accumulation under unilateral nephrectomy via altering RNF20-mediated regulation and causing functional damage to cells as a result of abnormal lipid metabolism, thereby leading to structural and functional kidney deterioration.

Bile acid receptors and renal regulation of water homeostasis

The kidney is the key organ responsible for maintaining the body's water and electrolyte homeostasis. About 99% of the primary urine filtered from the Bowman's capsule is reabsorbed along various renal tubules every day, with only 1-2 L of urine excreted. Aquaporins (AQPs) play a vital role in water reabsorption in the kidney. Currently, a variety of molecules are found to be involved in the process of urine concentration by regulating the expression or activity of AQPs, such as antidiuretic hormone, renin-angiotensin-aldosterone system (RAAS), prostaglandin, and several nuclear receptors. As the main bile acid receptors, farnesoid X receptor (FXR) and membrane G protein-coupled bile acid receptor 1 (TGR5) play important roles in bile acid, glucose, lipid, and energy metabolism. In the kidney, FXR and TGR5 exhibit broad expression across all segments of renal tubules, and their activation holds significant therapeutic potential for numerous acute and chronic kidney diseases through alleviating renal lipid accumulation, inflammation, oxidative stress, and fibrosis. Emerging evidence has demonstrated that the genetic deletion of FXR or TGR5 exhibits increased basal urine output, suggesting that bile acid receptors play a critical role in urine concentration. Here, we briefly summarize the function of bile acid receptors in renal water reabsorption and urine concentration.

Adhesion GPCR Gpr126 (Adgrg6) Expression Profiling in Zebrafish, Mouse, and Human Kidney

Adhesion G protein-coupled receptors (aGPCRs) comprise the second-largest class of GPCRs, the most common target for approved pharmacological therapies. aGPCRs play an important role in development and disease and have recently been associated with the kidney. Several aGPCRs are expressed in the kidney and some aGPCRs are either required for kidney development or their expression level is altered in diseased kidneys. Yet, general aGPCR function and their physiological role in the kidney are poorly understood. Here, we characterize in detail Gpr126 (Adgrg6) expression based on RNAscope® technology in zebrafish, mice, and humans during kidney development in adults. Gpr126 expression is enriched in the epithelial linage during nephrogenesis and persists in the adult kidney in parietal epithelial cells, collecting ducts, and urothelium. Single-cell RNAseq analysis shows that gpr126 expression is detected in zebrafish in a distinct ionocyte sub-population. It is co-detected selectively with slc9a3.2, slc4a4a, and trpv6, known to be involved in apical acid secretion, buffering blood or intracellular pH, and to maintain high cytoplasmic Ca2+ concentration, respectively. Furthermore, gpr126-expressing cells were enriched in the expression of potassium transporter kcnj1a.1 and gcm2, which regulate the expression of a calcium sensor receptor. Notably, the expression patterns of Trpv6, Kcnj1a.1, and Gpr126 in mouse kidneys are highly similar. Collectively, our approach permits a detailed insight into the spatio-temporal expression of Gpr126 and provides a basis to elucidate a possible role of Gpr126 in kidney physiology.

The use of Tablo continuous veno-venous haemodialysis to rapidly remove lithium in a patient with severe lithium toxicity

We report a case of severe, life-threatening lithium toxicity in a patient with bipolar I disorder who presented with altered mental status and acute renal failure. At admission, serum lithium level was well above toxic levels (>2 mEq/L). The signs and symptoms of lithium toxicity significantly improved after treatment with continuous veno-venous haemodialysis (CVVHD). The patient was discharged with no neurological or renal sequelae. Herein is the first case report using the Tablo CVVHD system to treat severe lithium toxicity.

Aquaporins: A new target for traditional Chinese medicine in the treatment of digestive system diseases

Aquaporins (AQPs) are a family of transmembrane proteins expressed in various organ systems. Many studies have shown that the abnormal expression of AQPs is associated with gastrointestinal, skin, liver, kidneys, edema, cancer, and other diseases. The majority of AQPs are expressed in the digestive system and have important implications for the physiopathology of the gastrointestinal tract as well as other tissues and organs. AQP regulators can prevent and treat most gastrointestinal-related diseases, such as colorectal cancer, gastric ulcer, and gastric cancer. Although recent studies have proposed clinically relevant AQP-targeted therapies, such as the development of AQP inhibitors, clinical trials are still lacking and there are many difficulties. Traditional Chinese medicine (TCM) has been used in China for thousands of years to prevent, treat and diagnose diseases, and is under the guidance of Chinese medicine (CM) theory. Herein, we review the latest research on the regulation of AQPs by TCMs and their active components, including Rhei Radix et Rhizoma, Atractylodis macrocephalae Rhizoma, Salviae miltiorrhizae Radix et Rhizoma, Poria, Astragali radix, and another 26 TCMs, as well as active components, which include the active components include anthraquinones, saponins, polysaccharides, and flavonoid glycosides. Through our review and discussion of numerous studies, we attempt to explore the regulatory effects of TCMs and their active components on AQP expression in the corresponding parts of the body in terms of the Triple Energizer concept in Chinese medicine defined as "upper energizer, middle energizer, and lower energizer,"so as to offer unique opportunities for the development of AQP-related therapeutic drugs for digestive system diseases.

Methotrexate-Induced Alteration of Renal Aquaporins 1 and 2, Oxidative Stress and Tubular Apoptosis Can Be Attenuated by Omega-3 Fatty Acids Supplementation

Methotrexate (MTX) is a potent anti-cancer drug, commonly associated with nephrotoxicity via the induction of oxidative stress and apoptosis with alteration of renal water channel proteins, namely aquaporins (AQPs). Omega-3 long-chain polyunsaturated fatty acids (LC-PUFA) have shown cytoprotective effects through their anti-oxidant and antiapoptotic activities. The present study aims for the first time to explore the role of LC-PUFA against MTX-induced nephrotoxicity. Rats were divided into the following groups: saline control, LC-PUFA control, MTX, MTX + LC-PUFA (150 mg/kg), or MTX + LC-PUFA (300 mg/kg). Then, H&E staining and immunohistochemical staining for the anti-apoptosis marker B-cell lymphoma 2 (BCL-2), the apoptosis marker BCL2-Associated X Protein (BAX), the proinflammatory marker Nuclear factor kappa B (NF-kB), AQPs 1 and 2 were performed in kidney sections with an assessment of renal oxidative stress. The MTX caused a renal histopathological alteration, upregulated renal BAX and NF-kB, downregulated Bcl-2 and AQP1, altered the distribution of AQP2, and caused oxidative stress. The LC-PUFA attenuated the pathological changes and decreased renal BAX and NF-kB, increased BCL-2 and AQP1, restored the normal distribution of AQP2, and decreased the oxidative stress. Therefore, LC-PUFA is a good adjuvant to MTX to prevent its adverse effects on kidneys through its antiapoptotic, antioxidant, and anti-inflammatory effect and its role in the restoration of the expression of AQPs 1 and 2.

Pathophysiology of Drug-Induced Hyponatremia

Drug-induced hyponatremia caused by renal water retention is mainly due to syndrome of inappropriate antidiuresis (SIAD). SIAD can be grouped into syndrome of inappropriate antidiuretic hormone secretion (SIADH) and nephrogenic syndrome of inappropriate antidiuresis (NSIAD). The former is characterized by uncontrolled hypersecretion of arginine vasopressin (AVP), and the latter is produced by intrarenal activation for water reabsorption and characterized by suppressed plasma AVP levels. Desmopressin is useful for the treatment of diabetes insipidus because of its selective binding to vasopressin V2 receptor (V2R), but it can induce hyponatremia when prescribed for nocturnal polyuria in older patients. Oxytocin also acts as a V2R agonist and can produce hyponatremia when used to induce labor or abortion. In current clinical practice, psychotropic agents, anticancer chemotherapeutic agents, and thiazide diuretics are the major causes of drug-induced hyponatremia. Among these, vincristine and ifosfamide were associated with sustained plasma AVP levels and are thought to cause SIADH. However, others including antipsychotics, antidepressants, anticonvulsants, cyclophosphamide, and thiazide diuretics may induce hyponatremia by intrarenal mechanisms for aquaporin-2 (AQP2) upregulation, compatible with NSIAD. In these cases, plasma AVP levels are suppressed by negative feedback. In rat inner medullary collecting duct cells, haloperidol, sertraline, carbamazepine, and cyclophosphamide upregulated V2R mRNA and increased cAMP production in the absence of vasopressin. The resultant AQP2 upregulation was blocked by a V2R antagonist tolvaptan or protein kinase A (PKA) inhibitors, suggestive of the activation of V2R-cAMP-PKA signaling. Hydrochlorothiazide can also upregulate AQP2 in the collecting duct without vasopressin, either directly or via the prostaglandin E2 pathway. In brief, nephrogenic antidiuresis, or NSIAD, is the major mechanism for drug-induced hyponatremia. The associations between pharmacogenetic variants and drug-induced hyponatremia is an area of ongoing research.

Renal transcriptome profiles in mice reveal the need for sufficient water intake irrespective of the drinking water type

This study sought to characterize the impact of long-term dehydration in terms of physiological and biochemical parameters, as well as renal transcriptomes. Furthermore, we assessed whether consumption of specific types of water elicit more beneficial effects on these health parameters. To this end, C57BL/6 mice were either provided water for 15 min/day over 2 and 4 weeks (water restricted; RES), or ad libitum access to distilled (CON), tap, spring, or purified water. Results show that water restriction decreases urine output and hematocrit levels while increasing brain vasopressin mRNA levels in RES mice compared to control mice (CON). Meanwhile, blood urea nitrogen and creatinine levels were higher in the RES group compared to the CON group. Kidney transcriptome analysis further identified kidney damage as the most significant biological process modulated by dehydration. Mechanistically, prolonged dehydration induces kidney damage by suppressing the NRF2-signaling pathway, which targets the cytoprotective defense system. However, type of drinking water does not appear to impact physiological or blood biochemical parameters, nor the renal transcriptome profile, suggesting that sufficient water consumption is critical, irrespective of the water type. Importantly, these findings also inform practical action for environmental sustainability by providing a theoretical basis for reducing bottled water consumption.

Bayesian analysis of dynamic phosphoproteomic data identifies protein kinases mediating GPCR responses

Background

A major goal in the discovery of cellular signaling networks is to identify regulated phosphorylation sites (“phosphosites”) and map them to the responsible protein kinases. The V2 vasopressin receptor is a G-protein coupled receptor (GPCR) that is responsible for regulation of renal water excretion through control of aquaporin-2-mediated osmotic water transport in kidney collecting duct cells. Genome editing experiments have demonstrated that virtually all vasopressin-triggered phosphorylation changes are dependent on protein kinase A (PKA), but events downstream from PKA are still obscure.

Methods

Here, we used: 1) Tandem mass tag-based quantitative phosphoproteomics to experimentally track phosphorylation changes over time in native collecting ducts isolated from rat kidneys; 2) a clustering algorithm to classify time course data based on abundance changes and the amino acid sequences surrounding the phosphosites; and 3) Bayes’ Theorem to integrate the dynamic phosphorylation data with multiple prior “omic” data sets covering expression, subcellular location, known kinase activity, and characteristic surrounding sequences to identify a set of protein kinases that are regulated secondary to PKA activation.

Results

Phosphoproteomic studies revealed 185 phosphosites regulated by vasopressin over 15 min. The resulting groups from the cluster algorithm were integrated with Bayes’ Theorem to produce corresponding ranked lists of kinases likely responsible for each group. The top kinases establish three PKA-dependent protein kinase modules whose regulation mediate the physiological effects of vasopressin at a cellular level. The three modules are 1) a pathway involving several Rho/Rac/Cdc42-dependent protein kinases that control actin cytoskeleton dynamics; 2) mitogen-activated protein kinase and cyclin-dependent kinase pathways that control cell proliferation; and 3) calcium/calmodulin-dependent signaling.

Conclusions

Our findings identify a novel set of downstream small GTPase effectors and calcium/calmodulin-dependent kinases with potential roles in the regulation of water permeability through actin cytoskeleton rearrangement and aquaporin-2 trafficking. The proposed signaling network provides a stronger hypothesis for the kinases mediating V2 vasopressin receptor responses, encouraging future targeted examination via reductionist approaches. Furthermore, the Bayesian analysis described here provides a template for investigating signaling via other biological systems and GPCRs.

Emerging roles for dynamic aquaporin-4 subcellular relocalization in CNS water homeostasis

Aquaporin channels facilitate bidirectional water flow in all cells and tissues. AQP4 is highly expressed in astrocytes. In the CNS, it is enriched in astrocyte endfeet, at synapses, and at the glia limitans, where it mediates water exchange across the blood-spinal cord and blood-brain barriers (BSCB/BBB), and controls cell volume, extracellular space volume, and astrocyte migration. Perivascular enrichment of AQP4 at the BSCB/BBB suggests a role in glymphatic function. Recently, we have demonstrated that AQP4 localization is also dynamically regulated at the subcellular level, affecting membrane water permeability. Ageing, cerebrovascular disease, traumatic CNS injury, and sleep disruption are established and emerging risk factors in developing neurodegeneration, and in animal models of each, impairment of glymphatic function is associated with changes in perivascular AQP4 localization. CNS oedema is caused by passive water influx through AQP4 in response to osmotic imbalances. We have demonstrated that reducing dynamic relocalization of AQP4 to the BSCB/BBB reduces CNS oedema and accelerates functional recovery in rodent models. Given the difficulties in developing pore-blocking AQP4 inhibitors, targeting AQP4 subcellular localization opens up new treatment avenues for CNS oedema, neurovascular and neurodegenerative diseases, and provides a framework to address fundamental questions about water homeostasis in health and disease.

Tolvaptan Improves Contrast-Induced Acute Kidney Injury

OBJECTIVE

Contrast-induced acute kidney injury (CI-AKI) is a serious side effect of contrast media use. The purpose of this study was to investigate the role and mechanism of tolvaptan (TOL) in CI-AKI.

METHODS

24 Wistar male rats were randomly divided into 4 groups (n = 6). And a rat model of CI-AKI was established. Then, the blood and urine of rats in each group were collected to detect relevant parameters. HE staining was utilized for the observation of the pathological changes of rat kidney tissues, TUNEL assay for the detection of tubular cell apoptosis, biochemical detection for the confirmation of oxidative stress level in kidney tissues, and western blot for the test of the expression of apoptotic proteins and the Nrf2 signaling pathway-related proteins in kidney tissues.

RESULTS

TOL could significantly reduce the serum level of urea nitrogen, creatinine, and neutrophil gelatinase-associated lipocalin and decrease serum Cys-C and urine KIM-1 in CI-AKI rats. The result above meant that TOL could improve kidney injury and reduce tubular cell apoptosis in CI-AKI rats. In addition, TOL contributed to a reduction of oxidative stress level by downregulating myeloperoxidase level and increasing the activities of superoxide dismutase and glutathione peroxidase in the kidney tissue of CI-AKI rats. After the pretreatment of TOL, the expression of proapoptotic proteins cleaved-caspase 3 and BAX, as well as mitochondrial fusion proteins DRP1 and MFN2 was downregulated, while the expression of Bcl-2 and PINK1 was upregulated in the kidney tissue of CI-AKI rats. Further, TOL could activate the Nrf2 signaling pathway, and the Nrf2 inhibitor ML385 reversed the effect of TOL on CI-AKI.

CONCLUSION

TOL can improve CI-AKI by activating the Nrf2/HO-1 signaling pathway, inhibiting oxidative stress response, and reducing tubular cell apoptosis.

The Role of Vasopressin V2 Receptor in Drug-Induced Hyponatremia

Hyponatremia is frequently encountered in clinical practice and usually induced by renal water retention. Many medications are considered to be among the various causes of hyponatremia, because they either stimulate the release of arginine vasopressin (AVP) or potentiate its action in the kidney. Antidepressants, anticonvulsants, antipsychotics, diuretics, and cytotoxic agents are the major causes of drug-induced hyponatremia. However, studies addressing the potential of these drugs to increase AVP release from the posterior pituitary gland or enhance urine concentration through intrarenal mechanisms are lacking. We previously showed that in the absence of AVP, sertraline, carbamazepine, haloperidol, and cyclophosphamide each increased vasopressin V2 receptor (V2R) mRNA and aquaporin-2 (AQP2) protein and mRNA expression in primary cultured inner medullary collecting duct cells. The upregulation of AQP2 was blocked by the V2R antagonist tolvaptan or protein kinase A (PKA) inhibitors. These findings led us to conclude that the nephrogenic syndrome of inappropriate antidiuresis (NSIAD) is the main mechanism of drug-induced hyponatremia. Previous studies have also shown that the V2R has a role in chlorpropamide-induced hyponatremia. Several other agents, including metformin and statins, have been found to induce antidiuresis and AQP2 upregulation through various V2R-independent pathways in animal experiments but are not associated with hyponatremia despite being frequently used clinically. In brief, drug-induced hyponatremia can be largely explained by AQP2 upregulation from V2R-cAMP-PKA signaling in the absence of AVP stimulation. This paper reviews the central and nephrogenic mechanisms of drug-induced hyponatremia and discusses the importance of the canonical pathway of AQP2 upregulation in drug-induced NSIAD.

Biological Functions and Activities of Rice Bran as a Functional Ingredient: A Review

Rice bran (RB) is a nutrient-rich by-product of the rice milling process. It consists of pericarp, seed coat, nucellus, and aleurone layer. RB is a rich source of a protein, fat, dietary fibers, vitamins, minerals, and phytochemicals (mainly oryzanols and tocopherols), and is currently mostly used as animal feed. Various studies have revealed the beneficial health effects of RB, which result from its functional components including dietary fiber, rice bran protein, and gamma-oryzanol. The health effects of RB including antidiabetic, lipid-lowering, hypotensive, antioxidant, and anti-inflammatory effects, while its consumption also improves bowel function. These health benefits have drawn increasing attention to RB in food applications and as a nutraceutical product to mitigate metabolic risk factors in humans. This review therefore focuses on RB and its health benefits.

Differential influences of dietary sodium on blood pressure regulation based on race and sex

There are clear differences between men and women, and differences among races, in the incidence and prevalence of hypertension. Furthermore, there is extensive inter-individual variability among humans in the extent to which sodium ingestion alters blood pressure. Orthostatic intolerance and orthostatic hypotension are more common in women; these are often treated with a high salt diet, which has variable efficacy in increasing blood volume and blood pressure. Conversely, people with certain forms of hypertension are often counseled to decrease their sodium intake. Non-Hispanic Black men and women have higher rates of hypertension compared to non-Hispanic White men and women and other racial/ethnic groups. In aggregate, Black women appear to have better orthostatic tolerance than White women. In the present paper, we summarize and evaluate the current evidence for mechanisms of blood pressure regulation in men and women, as well as differences between Black and White groups, with a focus on cardiovascular responses to salt and differences among these groups. We also provide a brief review of factors that are not traditionally considered to be "biological" - such as socio-economic disparities resulting from historic and contemporary inequity across racial groups. These non-biological factors have direct and substantial influences on cardiovascular mechanisms, as well as implications for the influences of salt and sodium intake on blood pressure and cardiovascular health. We conclude that both biological and socio-economic factors provide critical modulating influences when considering the impacts of sodium on cardiovascular health as functions of race and sex.

Immunohistochemical Expression of AQP2 and HSP70 in Broiler Kidney Tissue Treated with Salix tetrasperma Roxb. Extract under Heat Exposure

The administration of plant extracts to broilers may be a way to mitigate the effects of heat stress. The importance of AQP2 and HSP70 compounds in maintaining the homeostasis of the chicken body when it is subjected to heat stress is well established. This study aims to determine the effect of giving the ethanolic extract of the leaves of Salix tetrasperma Roxb. on the immunohistochemical expression of AQP2 and HSP70 in exposed and unexposed broiler kidney tissue. This study used 36 samples of 28-day-old chicken kidneys. Chickens were kept in individual cages, provided with feed and drinking water ad libitum. The design used was a completely randomized design with 6 treatments and 6 replications: (a) chickens were reared in conditions exposed to heat (HS + 0); (b) chickens were reared in conditions exposed to heat and given Salix extract at a dose of 50 mg/L drinking water (HS + 50); (c) chickens were reared under heat-exposed conditions and given Salix extract at a dose of 100 mg/L drinking water (HS + 100); (d) chickens were reared in conditions without exposure to heat (n-HS + 0); (e) chickens were reared in conditions without exposure to heat and given Salix extract at a dose of 50 mg/L drinking water (nHS + 50); and (f) chickens were reared in conditions exposed without exposure to heat and given 100 mg/L drinking water (nHS + 100) of Salix extract. Salix extract was given for 24 hours and was renewed every 6 hours. The results showed that giving Salix extract 100 mg/L in drinking water to chickens exposed to heat (HS + 100) reduced the value of the H/L ratio. Giving Salix extract 50–100 mg/L in drinking water caused an upregulated AQP2 expression; on the other hand, it downregulated HSP-70 expression, in chicken kidney tubules both exposed to heat stress and nonexposed to heat stress. In conclusion, exposure to heat stress in broiler chickens and giving Salix extract can increase the formation of aquaporin 2 compounds and suppress the formation of HSP70.

Effects of Natural Reduced Water on Cognitive Function, Body Composition, and Psychological Function in Older Adults: Study Protocol for a Randomized Controlled Trial

Natural reduced water is natural water that contains active hydrogen and reduces oxidation. It is rare in the world, and in Japan, it is produced in the Hita area of Oita Prefecture (Hita Tenryosui water). Previous studies in humans have examined the effects of natural reduced water on diabetes, which is one of the known risks for dementia. Animal studies of natural reduced water have revealed anti-obesity and anti-anxiety effects. However, the effects of natural reduced water on cognitive function, body composition, and psychological function in humans are unknown. Therefore, we investigated the relationship between these items in elderly people who continuously consume natural reduced water. In this study, we recruited participants aged between 65 and 74 years. The participants were randomly and blindly assigned to a natural reduced water (Hita Tenryosui water) group or a control (tap water) group and drank 1 L of water daily for 6 months. Cognitive function, body composition, and psychological function were measured before and after the 6-month intervention period.

Aquaporins in platelet function

Structurally, aquaporins (AQPs) are small channel proteins with monomers of ~ 30 kDa that are assembled as tetramers to form pores on cell membranes. Aquaporins mediate the conduction of water but at times also small solutes including glycerol across cell membranes and along osmotic gradients. Thirteen isoforms of AQPs have been reported in mammalian cells, and several of these are likely expressed in platelets. Osmotic swelling mediated by AQP1 sustains the calcium entry required for platelet phosphatidylserine exposure and microvesiculation, through calcium permeable stretch-activated or mechanosensitive cation channels. Notably, deletion of AQP1 diminishes platelet procoagulant membrane dynamics in vitro and arterial thrombosis in vivo, independent of platelet granule secretion and without affecting hemostasis. Water entry into platelets promotes procoagulant activity, and AQPs may also be critical for the initiation and progression of venous thrombosis. Platelet AQPs may therefore represent valuable targets for future development of a new class of antithrombotics, namely, anti-procoagulant antithrombotics, that are mechanistically distinct from current antithrombotics. However, the structure of AQPs does not make for easy targeting of these channels, hence they remain elusive drug targets. Nevertheless, thrombosis data in animal models provide compelling reasons to continue the pursuit of AQP-targeted antithrombotics. In this review, we discuss the role of aquaporins in platelet secretion, aggregation and procoagulation, the challenge of drugging AQPs, and the prospects of targeting AQPs for arterial and venous antithrombosis.

Comparative quantitation of aquaporin-2 and arginine vasopressin receptor-2 localizations among chronic kidney disease and healthy kidney in dogs

BACKGROUND AND AIM

Aquaporin-2 (AQP2) and arginine vasopressin receptor-2 (AVPR2) are proteins that control water homeostasis in principal cells. Chronic kidney disease (CKD) is defined as the impairment and irreversible loss of kidney function and/or structure, which causes water imbalances and polyuria. The study aimed to know the expression of AQPs and AVPR2 in the kidneys of a canine with CKD.

MATERIALS AND METHODS

The kidneys were collected from two dog carcasses from Small Animal Teaching Hospital, Faculty of Veterinary Medicine, Chiang Mai University. The kidney tissue was prepared for immunohistochemistry and investigated the expression and localization of tissue's AQP2 and AVPR2. For statistical analysis, the Mann-Whitney U-test was applied to the data.

RESULTS

By immunohistochemistry, AQP2 was expressed strongly in the basolateral and apical membranes of the principal cells, whereas AVPR2 was localized in the principal cell's basolateral membrane in both renal cortex and renal medulla. In the normal kidney, the semi-quantitative immunohistochemistry for the percentage of protein expression of AQP2 and AVPR2 was 5.062±0.4587 and 4.306±0.7695, respectively. In contrast, protein expression of AQP2 and AVPR2 in CKD was found to be 1.218±0.1719 and 0.8536±0.1396, respectively. The data shows that the percentage of AQP2 and AVPR2 expression was decreased, corresponding to a 4-fold and 5-fold in CKD (p<0.001).

CONCLUSION

Our findings revealed that CKD was a marked decrease in AQP2 and AVPR2 expression. The central role of specific AQP2 and AVPR2 in regulating water homeostasis will provide correlations in case of CKD with polyuria.

Actin-related protein 2/3 complex plays a critical role in the aquaporin-2 exocytotic pathway

The trafficking of proteins such as aquaporin-2 (AQP2) in the exocytotic pathway requires an active actin cytoskeleton network, but the mechanism is incompletely understood. Here, we show that the actin-related protein (Arp)2/3 complex, a key factor in actin filament branching and polymerization, is involved in the shuttling of AQP2 between the trans-Golgi network (TGN) and the plasma membrane. Arp2/3 inhibition (using CK-666) or siRNA knockdown blocks vasopressin-induced AQP2 membrane accumulation and induces the formation of distinct AQP2 perinuclear patches positive for markers of TGN-derived clathrin-coated vesicles. After a 20°C cold block, AQP2 formed perinuclear patches due to continuous endocytosis coupled with inhibition of exit from TGN-associated vesicles. Upon rewarming, AQP2 normally leaves the TGN and redistributes into the cytoplasm, entering the exocytotic pathway. Inhibition of Arp2/3 blocked this process and trapped AQP2 in clathrin-positive vesicles. Taken together, these results suggest that Arp2/3 is essential for AQP2 trafficking, specifically for its delivery into the post-TGN exocytotic pathway to the plasma membrane.NEW & NOTEWORTHY Aquaporin-2 (AQP2) undergoes constitutive recycling between the cytoplasm and plasma membrane, with an intricate balance between endocytosis and exocytosis. By inhibiting the actin-related protein (Arp)2/3 complex, we prevented AQP2 from entering the exocytotic pathway at the post-trans-Golgi network level and blocked AQP2 membrane accumulation. Arp2/3 inhibition, therefore, enables us to separate and target the exocytotic process, while not affecting endocytosis, thus allowing us to envisage strategies to modulate AQP2 trafficking and treat water balance disorders.

Renal expression and urinary excretion of aquaporin-2 in postobstructive uropathy in rats

This work assessed the time course of water renal management together with aquaporin-2 (AQP2) kidney expression and urinary AQP2 levels (AQP2u) in obstructive nephropathy. Adult male Wistar rats were monitored after 1, 2, and 7 days of bilateral ureteral release (bilateral ureteral obstruction (BUO); BUO-1, BUO-2 and BUO-7). Renal water handling was evaluated using conventional clearance techniques. AQP2 levels were assessed by immunoblotting and immunohistochemical techniques. AQP2 expression in apical membranes was downregulated in BUO-1 rats and upregulated both in BUO-2 and BUO-7 animals. AQP2 protein expression in whole cell lysate fraction from kidney cortex and medulla were significantly decreased in all the experimental groups. Concomitantly, mRNA levels of AQP2 decreased in renal medulla of all groups and in renal cortex from BUO-1; however, in renal cortex from BUO-2 and BUO-7 a recovery and an increase in the level of AQP2 mRNA were, respectively, observed. BUO-7 group showed a significant increase in AQP2u. The alterations observed in apical membranes AQP2 expression could explain, at least in part, the evolution time of water kidney management in the postobstructive phase of BUO. Additionally, the AQP2u increase after 7 days of ureteral release may be postulated as a biomarker of improvement in the kidney function.

The Transcription Factor Sox6 Controls Renin Expression during Renal Artery Stenosis

Background

Renal artery stenosis (RAStenosis) or renal artery occlusion is an intractable problem affecting about 6% of people >65 and up to 40% of people with coronary or peripheral vascular disease in the Unites States. The renal renin-angiotensin-aldosterone system plays a key role in RAStenosis, with renin (which is mainly produced in the kidney) being recognized as the driver of the disease. In this study, we will determine a new function for the transcription factor Sox6 in the control of renal renin during RAStenosis.

Methods

We hypothesize that knocking out Sox6 in Ren1d-positive cells will protect mice against renovascular hypertension and kidney injury. To test our hypothesis, we used a new transgenic mouse model, Ren1dcre/Sox6fl/fl (Sox6 KO), in which Sox6 is knocked out in renin-expressing cells. We used a modified two-kidney, one-clip (2K1C) Goldblatt mouse model to induce RAStenosis and renovascular hypertension. BP was measured using the tail-cuff method. Renin, prorenin, Sox6, and NGAL expressions levels were measured with Western blot, in situ hybridization, and immunohistochemistry. Creatinine levels were measured using the colorimetric assay.

Results

Systolic BP was significantly lower in Sox6 KO 2 weeks after RAStenosis compared with Sox6 WT (Ren1dcre/Sox6wt/wt). Renin, prorenin, and NGAL expression levels in the stenosed kidney were lower in Sox6 KO compared with Sox6 WT mice. Furthermore, creatinine clearance was preserved in Sox6 KO compared with Sox6 WT mice.

Conclusions

Our data indicate that Sox6 controls renal renin and prorenin expression and, as such, has a function in renovascular hypertension induced by RAStenosis. These results point to a novel transcriptional regulatory network controlled by Sox6.

The long-term effects of rapamycin-based immunosuppressive protocols on the expression of renal aquaporins 1, 2, 3 and 4 water channels in rats

BACKGROUND

To this day, the effect of multi-drug immunosuppressive protocols on renal expression of AQPs is unknown. This study aimed to determine the influence of rapamycin-based multi-drug immunosuppressive regimens on the expression of aquaporins (AQPs) 1, 2, 3, and 4 in the rat kidney.

METHODS

For 6 months, 24 male Wistar rats were administered immunosuppressants, according to the three-drug protocols used in patients after organ transplantation. The rats were divided into four groups: the control group, the TRP group (tacrolimus, rapamycin, prednisone), the CRP group (cyclosporine A, rapamycin, prednisone), and the MRP group (mycophenolate mofetil, rapamycin, prednisone). Selected red cell indices and total calcium were measured in the blood of rats and quantitative analysis of AQP1, AQP2, AQP3 and AQP4 immunoexpression in the kidneys were performed.

RESULTS

In the TRP and CRP groups, a mild increase of mean corpuscular hemoglobin concentration, hematocrit and total calcium were observed. Moreover, decreased expression of AQP1-4 was found in all experimental groups, with the highest decrease in the CRP group.

CONCLUSIONS

The long-term immunosuppressive treatment using multi-drug protocols decreased AQP1-4 expressions in renal tubules, possibly leading to impaired urine-concentrating ability in rat.

Renal Damages in Deoxycorticosterone Acetate-Salt Hypertensive Rats: Assessment with Diffusion Tensor Imaging and T2-mapping

PURPOSE

This study aimed to investigate the feasibility of diffusion tensor imaging (DTI) and T2-mapping to assess temporal renal damage in deoxycorticosterone acetate-salt (DOCA-salt) hypertensive rats and compare the results with histopathologic and immunohistochemical findings.

PROCEDURES

After baseline renal magnetic resonance imaging (MRI), 24 out of 30 uninephrectomized Sprague-Dawley rats with DOCA-salt-induced hypertension were divided equally into four groups. Group 1 had renal MRI at weeks 2, 4, 6, and 8, and groups 2, 3, and 4 had MRI at weeks 2, 4, and 6, respectively. The remaining 6 rats were used as sham controls. The renal cortex and outer and inner stripes of the outer medulla were examined over time using fractional anisotropy (FA), apparent diffusion coefficient (ADC), and T2-mapping, and the results were compared with baseline values. The degree of glomerular and tubular injury, endothelial cell thickening, hyaline arteriolosclerosis, macrophage infiltration, microcyst formation, and fibrosis in different zones at different time points in the DOCA-salt rats were compared with controls.

RESULTS

Compared with baseline values, DOCA-salt rats demonstrated a significant decrease in renal cortical FA from week 4 to week 8 (0.244 ± 0.015 vs 0.172 ± 0.014-0.150 ± 0.016, P = 0.018-0.002), corresponding to significantly more glomerular damage, arteriolosclerosis, macrophage infiltration, and fibrosis. The DOCA-salt rats had significantly increased cortical ADC and T2 values at weeks 6 and 8 (1.778 ± 0.051 × 10^-3 mm²/s vs 1.872 ± 0.058-1.917 ± 0.066 × 10^-3 mm²/s; 93.7 ± 4.9 ms vs 98.0 ± 2.9-100.7 ± 4.0 ms, respectively, all P < 0.05), consistent with excessively fluid-filled microcysts (aquaporin-2+). Despite DOCA-salt rats harbored markedly increased fibrosis in outer and inner stripes of the outer medulla at weeks 6 and 8, only nonsignificant decreases in FA were observed in comparison with the controls suggesting that only limited microstructural changes were present.

CONCLUSIONS

Renal cortical FA is useful for the early detection and monitoring of renal damage in DOCA-salt hypertensive rats.

Differential effects of sodium chloride and monosodium glutamate on kidney of adult and aging mice

Monosodium Glutamate (MSG) is used as flavour enhancer, with potential beneficial effects due to its nutritional value. Given the decline in kidney functions during aging, we investigated the impact of MSG voluntary intake on the kidney of male mice, aged 6 or 18 months. For 2 months, they freely consumed water (control group), sodium chloride (0.3% NaCl) or MSG (1% MSG) in addition to standard diet. Young animals consuming sodium chloride presented signs of proteinuria, hyperfiltration, enhanced expression and excretion of Aquaporin 2 and initial degenerative reactions suggestive of fibrosis, while MSG-consuming mice were similar to controls. In old mice, aging-related effects including proteinuria and increased renal corpuscle volume were observed in all groups. At an advanced age, MSG caused no adverse effects on the kidney compared to controls, despite the presence of a sodium moiety, similar to sodium chloride. These data show that prolonged MSG intake in mice has less impact on kidney compared to sodium chloride, that already in young animals induced some effects on kidney, possibly related to hypertension.

Pravastatin-induced changes in expression of long non-coding and coding RNAs in endothelial cells

OBJECTIVE

Atherosclerosis is the main cause of the cardiovascular disease (CVD). Elevated blood cholesterol and inflammation of the endothelium are two major mechanisms contributing to the establishment of atherosclerotic plaques. Statins, such as pravastatin, are blood-cholesterol lowering drugs commonly prescribed for patients with or at risk for CVDs. In addition to lowering blood cholesterols, statins have recently been shown to improve endothelial function in both hyper- and normocholesterolemic patients with atherosclerosis. To understand the molecular mechanisms underlying the endothelial function improvement by statins, we assessed the RNA profile of pravastatin-treated endothelial cells, particularly their mRNAs and long non-coding RNAs (lncRNAs).

METHODS

Human umbilical vein endothelial cells (HUVECs) treated with pravastatin (10 µM) for 24 hr were profiled for lncRNAs and mRNAs using the Arraystar Human lncRNA Expression Microarray V3.0.

RESULTS

Of the 30,584 different lncRNAs screened, 95 were significantly upregulated, while 86 were downregulated in HUVECs responding to pravastatin. LINC00281 and BC045663 were the most upregulated (~8-fold) and downregulated (~3.5-fold) lncRNAs, respectively. Of the 26,106 different mRNAs screened in the pravastatin-treated HUVEC samples, 190 were significantly upregulated, while 90 were downregulated. Assigning the differentially expressed genes by bioinformatics into functional groups revealed their molecular signaling involvement in the following physiological processes: osteoclast differentiation, Rap1 signaling pathway, hematopoiesis, immunity, and neurotrophin signaling pathway.

CONCLUSIONS

This is the first lncRNA and mRNA expression profiling of pravastatin-mediated changes in human endothelial cells. Our results reveal potential novel targets and mechanisms for pravastatin-mediated vascular protection in atherosclerosis.

Electrolyte handling in the isolated perfused rat kidney: demonstration of vasopressin V2-receptor-dependent calcium reabsorption

BACKGROUND

The most profound effect of vasopressin on the kidney is to increase water reabsorption through V₂-receptor (V₂R) stimulation, but there are also data suggesting effects on calcium transport. To address this issue, we have established an isolated perfused kidney model with accurate pressure control, to directly study the effects of V₂R stimulation on kidney function, isolated from systemic effects.

METHODS

The role of V₂R in renal calcium handling was studied in isolated rat kidneys using a new pressure control system that uses a calibration curve to compensate for the internal pressure drop up to the tip of the perfusion cannula.

RESULTS

Kidneys subjected to V₂R stimulation using desmopressin (DDAVP) displayed stable osmolality and calcium reabsorption throughout the experiment, whereas kidneys not administered DDAVP exhibited a simultaneous fall in urine osmolality and calcium reabsorption. Epithelial sodium channel (ENaC) inhibition using amiloride resulted in a marked increase in potassium reabsorption along with decreased sodium reabsorption.

CONCLUSIONS

A stable isolated perfused kidney model with computer-controlled pressure regulation was developed, which retained key physiological functions. The preparation responds to pharmacological inhibition of ENaC channels and activation of V₂R. Using the model, the dynamic effects of V₂R stimulation on calcium handling and urine osmolality could be visualised. The study thereby provides evidence for a stimulatory role of V₂R in renal calcium reabsorption.

Inhibition of Endothelin system during the postnatal nephrogenic period in the rat. Its relationship with hypertension and renal disease in adulthood

The aim of this work was to study the effect of a high sodium (HS) diet on blood pressure and renal function in male adult rats that have been treated with a dual Endothelin receptor antagonist (ERA) during their early postnatal period (day 1 to 20 of life). Male Sprague-Dawley rats were divided in four groups: C_NS: control rats with normosodic diet; ERA_NS: ERA-treated rats with normosodic diet; C_HS: control rats with high sodium diet; ERA_HS: ERA-treated rats with HS diet. Systolic blood pressure (SBP) was recorded before and after the diet and 24-hour metabolic cage studies were performed. AQP2 and α-ENac expressions were measured by western blot and real time PCR in the renal medulla. Vasopressin (AVP) pathway was evaluated by measuring V2 receptor and adenylyl cyclase 6 (AC6) expression and cAMP production in the renal medulla. Pre-pro ET-1mRNA was also evaluated in the renal medulla. Only rats that had been treated with an ERA during their postnatal period increased their SBP after consumption of a HS diet, showing an impaired capacity to excrete sodium and water, i.e. developing salt sensitivity. This salt sensitivity would be mediated by an increase in renomedullary expression and activity of AQP2 and α-ENaC as a consequence of increased AC6 expression and cAMP production and/or a decreased ET-1 production in the renal medulla. The knowledge of the molecular mechanisms underlying the perinatal programming of salt sensitive hypertension will allow the development of reprogramming strategies in order to avoid this pathology.

Protective effects of morin against acrylamide-induced hepatotoxicity and nephrotoxicity: A multi-biomarker approach

Acrylamide (ACR) is a heat-induced carcinogen substance that is found in some foods due to cooking or other thermal processes. The aim of present study was to assess the probable protective effects of morin against ACR-induced hepatorenal toxicity in rats. The rats were treated with ACR (38.27 mg/kg b.w., p.o.) alone or with morin (50 and 100 mg/kg b.w., p.o.) for 10 consecutive days. Morin treatment attenuated the ACR-induced liver and kidney tissue injury by diminishing the serum AST, ALP, ALT, urea and creatinine levels. Morin increased activities of SOD, CAT and GPx and levels of GSH, and suppressed lipid peroxidation in ACR induced tissues. Histopathological changes and immunohistochemical expressions of p53, EGFR, nephrin and AQP2 in the ACR-induced liver and kidney tissues were decreased after administration of morin. In addition, morin reversed the changes in levels of apoptotic, autophagic and inflammatory parameters such as caspase-3, bax, bcl-2, cytochrome c, beclin-1, LC3A, LC3B, p38α MAPK, NF-κB, IL-1β, IL-6, TNF-α and COX-2 in the ACR-induced toxicity. Morin also affected the protein levels by regulating the PI3K/Akt/mTOR signaling pathway and thus alleviated ACR-induced apoptosis and autophagy. Overall, these findings may shed some lights on new approaches for the treatment of ACR-induced hepatotoxicity and nephrotoxicity.

Protein misfolding in endoplasmic reticulum stress with applications to renal diseases

Protein misfolding may be the result of a variety of different processes that disrupt the ability of a protein to form a thermodynamically stable tertiary structure that allows it to perform its proper function. In this chapter, we explore the nature of a protein's form that allows it to have a stable tertiary structure, and examine specific mutation that are known to occur in the coding regions of DNA that disrupt a protein's ability to be folded into a thermodynamically stable tertiary structure. We examine the consequences of these protein misfoldings in terms of the endoplasmic reticulum stress response and resulting unfolded protein response. These conditions are specifically related to renal diseases. Further, we explore novel therapeutics, pharmacological chaperones, that are being developed to alleviate the disease burden associated with protein misfolding caused by mutations. These interventions aim to stabilize protein folding intermediates and allow proper folding to occur as well as prevent protein aggregation and the resulting pathophysiological consequences.

Aquaporin-2 expression in the kidney and urine is elevated in rats with monocrotaline-induced pulmonary heart disease

Objective

Little is known about how renal aquaporin-2 (AQP2) expression is affected by right heart failure caused by pulmonary heart disease (PHD). Therefore, we examined the expression of AQP2 in a rat model of PHD induced by monocrotaline (MCT).

Methods

After 4 weeks of treatment, urine and blood samples were collected from sham-treated and MCT-treated rats. Plasma arginine vasopressin (AVP) levels were measured by radioimmunoassay, and kidney Aqp2 mRNA expression was detected by reverse transcription (RT)-PCR. Kidney AQP2 protein expression was quantified by immunohistochemistry and western blotting assays. The concentration of urine AQP2 was determined by indirect enzyme-linked immunosorbent assay.

Results

We successfully established an animal model of MCT-induced PHD in rats. MCT-treated rats had significantly higher mRNA and protein levels of AQP2 in their kidney tissue. Following MCT treatment, rats also had markedly increased concentrations of both urine AQP2 and plasma AVP.

Conclusions

AQP2 expression was significantly increased in the kidney tissues and urine of rats with PHD induced by MCT. Our findings suggest that the evaluation of AQP2 expression contributes to an early diagnosis of PHD, and may also be an important reference to improve PHD therapeutics.

Gain-of-function mutations of the V2 vasopressin receptor in nephrogenic syndrome of inappropriate antidiuresis (NSIAD): a cell-based assay to assess constitutive water reabsorption

Nephrogenic syndrome of inappropriate antidiuresis (NSIAD) is a recently identified chromosome X-linked disease associated with gain-of-function mutations of the V2 vasopressin receptor (V2R), a G-protein-coupled receptor. It is characterized by inability to excrete a free water load, hyponatremia, and undetectable vasopressin-circulating levels. Hyponatremia can be quite severe in affected male children. To gain a deeper insight into the functional properties of the V2R active mutants and how they might translate into the pathological outcome of NSIAD, in this study, we have expressed the wild-type V2R and three constitutively active V2R mutants associated with NSIAD (R137L, R137C, and the F229V) in MCD4 cells, a cell line derived from renal mouse collecting duct, stably expressing the vasopressin-sensitive water channel aquaporin-2 (AQP2). Our findings indicate that in cells expressing each active mutant, AQP2 was constitutively localized to the apical plasma membrane in the absence of vasopressin stimulation. In line with these observations, under basal conditions, osmotic water permeability in cells expressing the constitutively active mutants was significantly higher compared to that of cells expressing the wild-type V2R. Our findings demonstrate a direct link between activating mutations of the V2R and the perturbation of water balance in NSIAD. In addition, this study provides a useful cell-based assay system to assess the functional consequences of newly discovered activating mutations of the V2R on water permeability in kidney cells and to screen the effect of drugs on the mutated receptors.