TNF-α inhibits aquaporin 5 expression in human salivary gland acinar cells via suppression of histone H4 acetylation

Application of anti-vascular endothelial growth factor antibody restores the function of saliva secretion in a type 2 diabetes mouse model

OBJECTIVES

Xerostomia, a common complication of type 2 diabetes, leads to an increased risk of caries, dysphagia, and dysgeusia. Although anti-vascular endothelial growth factor (VEGF) antibodies, such as ranibizumab (RBZ), have been used to treat diabetic retinopathy, their effects on the salivary glands are unknown. This study evaluated the effects of RBZ on salivary glands to reduce inflammation and restore salivary function in a mouse model of type 2 diabetes.

METHODS

Male KK-Ay mice with type 2 diabetes (10-12 weeks old) were used. The diabetes mellitus (DM) group received phosphate-buffered saline, while the DM + RBZ group received an intraperitoneal administration of RBZ (100 μg/kg) 24 h before the experiment.

RESULTS

Ex vivo perfusion experiments showed a substantial increase in salivary secretion from the submandibular gland (SMG) in the DM + RBZ group. In addition, the mRNA expression levels of TNF-α and IL-1β were considerably lower in this group. In contrast, those of aquaporin 5 were substantially higher in the DM + RBZ group, as revealed by quantitative reverse transcription PCR. Furthermore, the number of lymphocyte infiltration spots in the SMG was notably lower in the DM + RBZ group. Finally, intracellular Ca2+ signaling in acinar cells was considerably higher in the DM + RBZ group than that in the DM group.

CONCLUSION

Treating a type 2 diabetic mouse model with RBZ restored salivary secretion through its anti-inflammatory effects.

Chemokines and lymphocyte homing in Sjögren's syndrome

Sjögren's syndrome (SS) is a chronic systemic autoimmune disease that typically presents with lymphocyte, dendritic cell, and macrophage infiltration of exocrine gland ducts and the formation of ectopic germinal centers. The interactions of lymphocyte homing receptors and addressins and chemokines and their receptors, such as α4β7/MAdCAM-1, LFA-1/ICAM-1, CXCL13/CXCR5, CCL25/CCR9, CX3CL1/CX3CR1, play important roles in the migration of inflammatory cells to the focal glands and the promotion of ectopic germinal center formation in SS. A variety of molecules have been shown to be involved in lymphocyte homing, including tumor necrosis factor-α, interferon (IFN)-α, IFN-β, and B cell activating factor. This process mainly involves the Janus kinase-signal transducer and activator of transcription signaling pathway, lymphotoxin-β receptor pathway, and nuclear factor-κB signaling pathway. These findings have led to the development of antibodies to cell adhesion molecules, antagonists of chemokines and their receptors, compounds interfering with chemokine receptor signaling, and gene therapies targeting chemokines and their receptors, providing new targets for the treatment of SS in humans. The aim of this study was to explore the relationship between lymphocyte homing and the pathogenesis of SS, and to provide a review of recent studies addressing lymphocyte homing in targeted therapy for SS.

TNF inhibits AQP2 expression via a miR137-dependent pathway

As miR-137 is a regulator of aquaporin (AQP)2 expression and tumor necrosis factor (TNF) inhibits the expression of several extrarenal AQPs, we tested the hypothesis that TNF inhibits AQP2 in the kidney via a miR-137-dependent mechanism. AQP2 mRNA and protein expression decreased ∼70% and 53%, respectively, in primary renal inner medullary collecting duct (IMCD) cells transfected with a miRNA mimic of mmu-miR-137, suggesting that miR-137 directly targets AQP2 mRNA in these cells. Exposure of IMCD cells for 2 h to 400 mosmol/kgH2O medium increased mmu-miR-137 mRNA expression about twofold, conditions that also increased TNF production approximately fourfold. To determine if the increase in mmu-miR-137 mRNA expression was related to the concomitant increase in TNF, IMCD cells were transfected with a lentivirus construct to silence TNF. This construct decreased mmu-miR-137 mRNA expression by ∼63%, suggesting that TNF upregulates the expression of miR-137. Levels of miR-137 also increased approximately twofold in IMCD tubules isolated from male mice given 1% NaCl in the drinking water for 3 days. Intrarenal lentivirus silencing of TNF increased AQP2 mRNA levels and protein expression concomitant with a decrease in miR-137 levels in tubules isolated from mice given NaCl. The changes in AQP2 expression levels affected the diluting ability of the kidney, which was assessed by measuring urine osmolality and urine volume, as the decrease in these parameters after renal silencing of TNF was prevented on intrarenal administration of miR-137. The study reveals a novel TNF function via a miR-137-dependent mechanism that regulates AQP2 expression and function.NEW & NOTEWORTHY An emerging intratubular tumor necrosis factor system, functioning during normotensive noninflammatory conditions, acts as a breaking mechanism that attenuates both the increases in Na+-K+-2Cl- cotransporter and aquaporin-2 induced by arginine vasopressin, thereby contributing to the regulation of electrolyte balance and blood pressure. A greater appreciation for the role of cytokines as mediators of immunophysiological responses may help reveal the relationship between the immune system and other physiological systems.

Insights into the Function of Aquaporins in Gastrointestinal Fluid Absorption and Secretion in Health and Disease

Aquaporins (AQPs), transmembrane proteins permeable to water, are involved in gastrointestinal secretion. The secretory products of the glands are delivered either to some organ cavities for exocrine glands or to the bloodstream for endocrine glands. The main secretory glands being part of the gastrointestinal system are salivary glands, gastric glands, duodenal Brunner's gland, liver, bile ducts, gallbladder, intestinal goblet cells, exocrine and endocrine pancreas. Due to their expression in gastrointestinal exocrine and endocrine glands, AQPs fulfill important roles in the secretion of various fluids involved in food handling. This review summarizes the contribution of AQPs in physiological and pathophysiological stages related to gastrointestinal secretion.

Involvement of aquaporin 5 in Sjögren's syndrome

Sjögren's syndrome (SS) is a chronic autoimmune disease with the pathological hallmark of lymphoplasmacytic infiltration of exocrine glands - more specifically salivary and lacrimal glands - resulting in a diminished production of tears and saliva (sicca syndrome). The pathophysiology underscoring the mechanisms of the sicca symptoms in SS has still yet to be unraveled but recent advances have identified a cardinal role of aquaporin-5 (AQP5) as a key player in saliva secretion as well as salivary gland epithelial cell dysregulation. AQP5 expression and localization are significantly altered in salivary glands from patients and mice models of the disease, shedding light on a putative mechanism accounting for diminished salivary flow. Furthermore, aberrant expression and localization of AQP5 protein partners, such as prolactin-inducible protein and ezrin, may account for altered AQP5 localization in salivary glands from patients suffering from SS and are considered as new players in SS development. This review provides an overview of the role of AQP5 in SS salivary gland epithelial cell dysregulation, focusing on its trafficking and protein-protein interactions.

Aquaporin-5 Dynamic Regulation

Aquaporin-5 (AQP5), belonging to the aquaporins (AQPs) family of transmembrane water channels, facilitates osmotically driven water flux across biological membranes and the movement of hydrogen peroxide and CO₂. Various mechanisms have been shown to dynamically regulate AQP5 expression, trafficking, and function. Besides fulfilling its primary water permeability function, AQP5 has been shown to regulate downstream effectors playing roles in various cellular processes. This review provides a comprehensive overview of the current knowledge of the upstream and downstream effectors of AQP5 to gain an in-depth understanding of the physiological and pathophysiological processes involving AQP5.

A novel association of osmotic demyelination in Sjögren's syndrome prompts revisiting role of aquaporins in CNS demyelinating diseases: A literature review

BACKGROUND

Primary Sjögren's syndrome (SS) is a chronic systemic autoimmune disease with varied neurological manifestations. SS is associated with anti-aquaporin-4 antibody (AQP4-IgG)-positive neuromyelitis optica spectrum disorder (NMOSD), a demyelinating autoimmune disorder of the central nervous system (CNS). Intriguingly, there are reports of osmotic demyelinating syndrome (ODS), a supposedly non-inflammatory disorder, in the context of SS and renal tubular acidosis (RTA), both of which are not yet established risk factors for ODS.

METHODS

A literature search was undertaken to identify case reports of ODS in patients with SS. Details of the clinical and laboratory features of these patients were compiled. Additionally, we searched for NMOSD in patients with SS. We looked for co-existing RTA in patients with SS-ODS as well as SS-NMOSD. We also screened for reports of ODS in RTA without underlying SS.

RESULTS & DISCUSSION

We identified 15 patients (all women, median age 40 years) with ODS in SS, and all of these patients had comorbid RTA. There were only three reported cases of ODS in RTA without underlying SS. We identified a total of 67 patients with SS-NMOSD, of whom only 3 (4.5%) had RTA. Hence, unlike NMOSD, the development of ODS in SS requires a prolonged osmotic or electrolyte abnormality caused by the comorbid RTA. The 15 patients with ODS and SS -RTA, showed heterogeneous clinical manifestations and outcomes. The most common symptom was quadriparesis, seen in 14 of the 15 patients. Eleven of the 15 patients had one of the following features, either alone or in combination: worsening of the sensorium, extensor plantar response, dysphagia/dysarthria, and facial palsy. The latter four manifestations were present at the onset in 7 patients and later in the course of the illness in the remaining 4 patients. Ocular palsy was seen in only four of the 15 patients and was a late manifestation. One patient who had extensive long-segment myelitis and subsequent ODS died, but most patients recovered without significant sequelae. None had hyponatremia, while all patients had hypokalemia and/or hypernatremia. Hypokalemia causing nephrogenic diabetes insipidus (NDI) followed by rapid rise in sodium and the resultant osmotic stress could potentially explain the occurrence of ODS in SS-RTA. Aquaporin (AQP) in astrocytes is implicated in ODS, and renal AQP is downregulated in NDI. Antibodies against AQPs are present in some patients with SS. Defective AQP is therefore a common link underlying all the connected diseases, namely SS, NDI, and ODS, raising the possibility of immune-mediated AQP dysfunction in the pathogenesis.

CONCLUSION

The hitherto unreported association between SS-RTA and ODS may implicate SS and/or RTA in the development of ODS. In the setting of SS-RTA, ODS must be suspected when a patient with flaccid quadriparesis does not respond to the correction of potassium or develops additional neurological features along with a rise in sodium. Defective functions of AQPs may be a possible mechanism linking demyelinating CNS lesions, SS, and RTA. Studies evaluating AQP functions and serum antibodies against AQPs in these conditions are warranted.

Aquaporins in Glandular Secretion

Exocrine and endocrine glands deliver their secretory product, respectively, at the surface of the target organs or within the bloodstream. The release of their products has been shown to rely on secretory mechanisms often involving aquaporins (AQPs). This chapter will provide insight into the role of AQPs in secretory glands located within the gastrointestinal tract, including salivary glands, gastric glands, duodenal Brunner's glands, liver, gallbladder, intestinal goblets cells, and pancreas, as well and in other parts of the body, including airway submucosal glands, lacrimal glands, mammary glands, and eccrine sweat glands. The involvement of AQPs in both physiological and pathophysiological conditions will also be highlighted.

Ruscogenin Ameliorated Sjögren's Syndrome by Inhibiting NLRP3 Inflammasome Activation

This article investigated the role and the specific mechanism of Ruscogenin in Sjögren's syndrome (SS). NOD/ShiLtJ mice were treated with Ruscogenin, and acinar cells isolated from submandibular glands were treated with TNF-α, Ruscogenin and transfected with NLRP3 overexpression plasmid. Salivary flow rate (SFR) was measured at weeks 11, 13, 15, 17, and 20. Histological analysis of the submandibular glands was conducted by hematoxylin-eosin staining assay. IL-6, IL-17, TNF-α, and IL-1β mRNA expression was detected through qRT-PCR. AQP 5, AQP 4, P2X7R, NLRP3, caspase 1, IL-1β, Bax, and Bcl-2 protein levels were tested by western blot. Cell apoptosis was assessed through acridine orange and propidium iodide (AO/PI) staining assay and flow cytometry assay. Ruscogenin ameliorated the SFR and submandibular gland inflammation of NOD/ShiLtJ mice. Ruscogenin promoted the preservation of acinar cells and suppressed inflammation-related factors (P2X7R, NLRP3, caspase 1, and IL-1β) in submandibular gland tissues of NOD/ShiLtJ mice. Ruscogenin inhibited acinar cell apoptosis in NOD/ShiLtJ mice and reversed TNF-α-induced apoptosis and inflammation of acinar cells. NLRP3 overexpression reversed the repressive effect of Ruscogenin on TNF-α-induced inflammation and apoptosis of acinar cells. Ruscogenin ameliorated SS by inhibiting NLRP3 inflammasome activation.

Aquaporins: Unexpected actors in autoimmune diseases

Aquaporins (AQPs), transmembrane proteins allowing the passage of water and sometimes other small solutes and molecules, are involved in autoimmune diseases including neuromyelitis optica, Sjögren's syndrome and rheumatoid arthritis. Both autoantibodies against AQPs and altered expression and/or trafficking of AQPs in various tissue cell types as well as inflammatory cells are playing key roles in pathogenesis of autoimmune diseases. Detection of autoantibodies against AQP4 in the central nervous system has paved the way for a deeper understanding in disease pathophysiology as well as enabling diagnosis. This review provides a comprehensive summary of the roles of AQPs in autoimmune diseases.

Tonsil mesenchymal stem cells-derived extracellular vesicles prevent submandibular gland dysfunction in ovariectomized rats

Dry mouth that occurs after menopause significantly reduces the quality of life of the elderly. The extracellular vesicles derived from mesenchymal stem cells are being studied for application in various pathological conditions in the field of tissue regenerative medicine. This study is to investigate the therapeutic effect on salivary gland dysfunction occurring after ovariectomy using tonsil mesenchymal stem cells (T-MSCs)-derived extracellular vesicles. The rats were divided into the following groups: sham-operated rats (SHAM), rats that underwent ovariectomy (OVX), and rats that underwent OVX surgery and were simultaneously injected with T-MSC-derived extracellular vesicles (OVX+EV). The rats were sacrificed 6 weeks after ovariectomy. Estradiol levels decreased in the OVX group compared with those in the SHAM group. Extracellular vesicles had no effect on estradiol levels or estrogen receptor β expression. The evaluation of pro-inflammatory cytokines, TNF-α and IL-6, increased in the OVX group and decreased in the OVX+EV group. The expressions of collagen I and TGFβI increased in the OVX group but decreased in the OVX+EV group. Moreover, to examine submandibular gland function, AQP5 and α-amylase expressions were downregulated in the OVX group, but improved upon exosome injection. In conclusion, T-MSC-derived extracellular vesicles are useful for the prevented submandibular gland dysfunction that occurs after menopause.

Targeted Therapy for Primary Sjögren's Syndrome: Where are We Now?

Primary Sjögren's syndrome (pSS) is an autoimmune exocrinopathy characterized by dryness symptoms. This review briefly describes recent advances in the targeted therapies for pSS. Biologics evaluated for pSS treatment mainly include B cell-depleting agents, inhibitors of B cell activation, and agents that target co-signaling molecules or proinflammatory cytokines. Small molecule inhibitors that target signaling pathways have also been evaluated. However, current evidence for the efficacy of targeted therapies in pSS is still sparse. Although ianalumab (an anti-B cell-activating factor [BAFF]-receptor antibody) and iscalimab (an anti-CD40 antibody) are promising biologics for pSS, their efficacy still needs to be evaluated in larger clinical trials. For other biologics, clinical trials have found no differences versus placebo in the change from baseline in European League Against Rheumatism Sjögren's Syndrome Disease Activity Index (ESSDAI) score and fatigue score. Possible causes of the disappointing outcomes mainly include the inefficacy of those evaluated biologics in treating pSS, the high heterogeneous nature of pSS, irreversible exocrine glandular failure at advanced disease stages, inappropriate recruitment strategy in clinical trials, and outcome measures. Early diagnosis and glandular function-centered outcome measures may help to improve the current situation in the systemic therapy of pSS.

The Transcriptomic Profile of Monocytes from Patients With Sjögren's Syndrome Is Associated With Inflammatory Parameters and Is Mimicked by Circulating Mediators

Primary Sjögren's syndrome (pSS) is a systemic autoimmune disease characterized by infiltration of the exocrine glands and prominent B cell hyperactivity. Considering the key role of monocytes in promoting B cell hyperactivity, we performed RNA-sequencing analysis of CD14⁺ monocytes from patients with pSS, non-Sjögren's sicca (nSS), and healthy controls (HC). We demonstrated that the transcriptomic profile of pSS patients is enriched in intermediate and non-classical monocyte profiles, and confirmed the increased frequency of non-classical monocytes in pSS patients by flow-cytometry analysis. Weighted gene co-expression network analysis identified four molecular signatures in monocytes from pSS patients, functionally annotated for processes related with translation, IFN-signaling, and toll-like receptor signaling. Systemic and local inflammatory features significantly correlated with the expression of these signatures. Furthermore, genes highly associated with clinical features in pSS were identified as hub-genes for each signature. Unsupervised hierarchical cluster analysis of the hub-genes identified four clusters of nSS and pSS patients, each with distinct inflammatory and transcriptomic profiles. One cluster showed a significantly higher percentage of pSS patients with higher prevalence of anti-SSA autoantibodies, interferon-score, and erythrocyte sedimentation rate compared to the other clusters. Finally, we showed that the identified transcriptomic differences in pSS monocytes were induced in monocytes of healthy controls by exposure to serum of pSS patients. Representative hub-genes of all four signatures were partially inhibited by interferon-α/β receptor blockade, indicating that the circulating inflammatory mediators, including type I interferons have a significant contribution to the altered transcriptional profile of pSS-monocytes. Our study suggests that targeting key circulating inflammatory mediators, such as type I interferons, could offer new insights into the important pathways and mechanisms driving pSS, and holds promise for halting immunopathology in Sjögren's Syndrome.

Aquaporin5-Targeted Treatment for Dry Eye Through Bioactive Compounds and Gut Microbiota

Dry eye and dry mouth are the principal sources of morbidity for patients with Sjögren's syndrome (SS). There are few effective treatments, particularly systemic ones. Targeting aquaprin-5 (AQP5)-mediated tear secretion has been tested as a novel ancillary strategy and has proved promising. Patients have a great interest in using complementary medicine, including nutraceuticals and bioactive compounds to alleviate their symptoms. Potential mechanisms by which phytocompounds and bioactive compounds may benefit SS ocular and mouth symptoms through modulation of AQP5 activity are presented within this review. Supplementation with prebiotics (such as polyphenols with high bioavailability) in SS patients with lower Firmicutes/Bacteroides (F/B) community ratio phenotype, through administration of butyrate-producing diets, is proposed as ancillary strategy for dry eye and mouth. The potential use of natural bioactive compounds to treat dry eye could also apply to dry mouth occurring in the context of aging and SS. This novel hypothesis could have implications with respect to planning a successful dietary regimen for achieving and maintaining a normal gut microbiota in SS patients. This regimen would include augmenting butyrate-producing foodstuffs and/or polyphenol-rich syrups, and high amounts of some specific probiotic-rich foodstuffs such as yogurt, soy yogurt, or as probiotic supplements. There are applications for pharmaceutical and nutraceutical products aiming to relieve dry eye and mouth.

Candida Infection Associated with Salivary Gland-A Narrative Review

Candida species are common global opportunistic pathogens that could repeatedly and chronically cause oral mucosa infection and create an inflammatory environment, leading to organ dysfunction. Oral Candida infections may cause temporary or permanent damage to salivary glands, resulting in the destruction of acinar cells and the formation of scar tissue. Restricted function of the salivary glands leads to discomfort and diseases of the oral mucosa, such as dry mouth and associated infection. This narrative review attempts to summarize the anatomy and function of salivary glands, the associations between Candida and saliva, the effects of Candida infection on salivary glands, and the treatment strategies. Overall, clinicians should proactively manage Candida infections by educating patients on oral hygiene management for vulnerable populations, conducting frequent checks for a timely diagnosis, and providing an effective treatment plan.

A decrease in the tear secretion volume in a mouse model with ulcerative colitis

PURPOSE

Dry eye syndrome is known to develop from several systemic inflammatory diseases. Although dry eye may develop due to extraintestinal complications of ulcerative colitis (UC), the pathogenesis is not well-known. This study aimed to investigate whether there was decrease in the tear secretion volume in a mice model with UC; the difference between the control and dextran sodium sulphate (DSS)-treated group was also determined.

MATERIALS AND METHODS

This study included a mice model with UC induced by the oral administration of 5.0% DSS for 7 days. Following the DSS treatment, the tear volume was measured using the Schirmer's test. The colon and ocular tissues, including the lacrimal gland, were evaluated using histological and protein analyses. Additionally, tumour necrosis factor (TNF)-α and interleukin (IL)-6 in the plasma were determined. Differences between groups (DSS-treated versus control mice) were determined using Student's t-test.

RESULTS

The tear volume in DSS-treated mice was decreased compared to that in the control mice. Plasma levels of TNF-α and IL-6 in DSS-treated mice was higher than that of control. Morphological change was observed with the invasion of the inflammatory cell in the lacrimal gland of DSS-treated mice. Terminal deoxynucleotidyl transferase mediated deoxyuridine triphosphate nick end labelling (TUNEL)-positive cells were increased in the lacrimal glands of DSS-treated mice compared with control group. The distribution of aquaporin-5 expressed in the lacrimal gland of DSS-treated mice was decreased compared to that in the control group.

CONCLUSIONS

These findings suggest that a decrease in the tear volume in UC was associated with a functional decline in the inflamed lacrimal gland. This result therefore provides useful information that could contribute to the development of treatment approaches for dry eye associated with UC.

Inhibition of Alk signaling promotes the induction of human salivary-gland-derived organoids

Hyposalivation and xerostomia are the cause of several morbidities, such as dental caries, painful mucositis, oral fungal infections, sialadenitis and dysphagia. For these reasons, preservation of normal saliva secretion is critical for the maintenance of functionally normal oral homeostasis and for keeping good health. Several strategies for restoring salivary gland function have been reported, from different points of view, based on the use of salivary-gland-derived epithelial stem/progenitor cells and tissue engineering approaches to induce organoids that mimic in vivo salivary glands. In this study, we clarified that inhibition of activin receptor-like kinase (Alk) signaling was essential for the induction of human salivary-gland-derived organoids, and demonstrated the usefulness of such organoids as an inflammatory disease model. In inflammatory conditions like sialadenitis, in general, pro-inflammatory cytokines such as tumor necrosis factor-α (TNF-α, also known as TNF) are upregulated, but their function is still unclear. In our established human salivary-gland-derived organoid culture system, we successfully induced organoid swelling by stimulation with carbachol, a non-selective cholinergic agonist, and forskolin, an activator of cystic fibrosis transmembrane conductance regulator (CFTR). Furthermore, we found that this organoid swelling was inhibited by TNF-α. From these results, we could clarify the inhibitory function of TNF-α on saliva secretion in vitro Thus, our established human salivary-gland-derived organoids would be useful for in vitro analyses of the morphological and functional changes involved in salivary gland dysfunctions in several research fields, such as pathobiology, inflammation and regenerative medicine.This article has an associated First Person interview with the first author of the paper.

Current State of Knowledge on Primary Sjögren's Syndrome, an Autoimmune Exocrinopathy

Primary Sjögren's syndrome (pSS) is a chronic systemic autoimmune rheumatic disease characterized by lymphoplasmacytic infiltration of the salivary and lacrimal glands, whereby sicca syndrome and/or systemic manifestations are the clinical hallmarks, associated with a particular autoantibody profile. pSS is the most frequent connective tissue disease after rheumatoid arthritis, affecting 0.3-3% of the population. Women are more prone to develop pSS than men, with a sex ratio of 9:1. Considered in the past as innocent collateral passive victims of autoimmunity, the epithelial cells of the salivary glands are now known to play an active role in the pathogenesis of the disease. The aetiology of the "autoimmune epithelitis" still remains unknown, but certainly involves genetic, environmental and hormonal factors. Later during the disease evolution, the subsequent chronic activation of B cells can lead to the development of systemic manifestations or non-Hodgkin's lymphoma. The aim of the present comprehensive review is to provide the current state of knowledge on pSS. The review addresses the clinical manifestations and complications of the disease, the diagnostic workup, the pathogenic mechanisms and the therapeutic approaches.

Insight into Salivary Gland Aquaporins

The main role of salivary glands (SG) is the production and secretion of saliva, in which aquaporins (AQPs) play a key role by ensuring water flow. The AQPs are transmembrane channel proteins permeable to water to allow water transport across cell membranes according to osmotic gradient. This review gives an insight into SG AQPs. Indeed, it gives a summary of the expression and localization of AQPs in adult human, rat and mouse SG, as well as of their physiological role in SG function. Furthermore, the review provides a comprehensive view of the involvement of AQPs in pathological conditions affecting SG, including Sjögren's syndrome, diabetes, agedness, head and neck cancer radiotherapy and SG cancer. These conditions are characterized by salivary hypofunction resulting in xerostomia. A specific focus is given on current and future therapeutic strategies aiming at AQPs to treat xerostomia. A deeper understanding of the AQPs involvement in molecular mechanisms of saliva secretion and diseases offered new avenues for therapeutic approaches, including drugs, gene therapy and tissue engineering. As such, AQP5 represents a potential therapeutic target in different strategies for the treatment of xerostomia.

Epigenetics in Primary Sjögren's Syndrome

Primary Sjögren's syndrome (SjS) is a chronic and systemic autoimmune epithelitis with predominant female incidence, which is characterized by exocrine gland dysfunction. Incompletely understood, the etiology of SjS is multi-factorial and evidence is growing to consider that epigenetic factors are playing a crucial role in its development. Independent from DNA sequence mutations, epigenetics is described as inheritable and reversible processes that modify gene expression. Epigenetic modifications reported in minor salivary gland and lymphocytes from SjS patients are related to (i) an abnormal DNA methylation process inducing in turn defective control of normally repressed genes involving such matters as autoantigens, retrotransposons, and the X chromosome in women; (ii) altered nucleosome positioning associated with autoantibody production; and (iii) altered control of microRNA. Results from epigenome-wide association studies have further revealed the importance of the interferon pathway in disease progression, the calcium signaling pathway for controlling fluid secretions, and a cell-specific cross talk with risk factors associated with SjS. Importantly, epigenetic modifications are reversible thus opening opportunities for therapeutic procedures in this currently incurable disease.

Targeted TNF-α Overexpression Drives Salivary Gland Inflammation

Chronic inflammation of the salivary glands from pathologic conditions such as Sjögren's syndrome can result in glandular destruction and hyposalivation. To understand which molecular factors may play a role in clinical cases of salivary gland hypofunction, we developed an aquaporin 5 (AQP5) Cre mouse line to produce genetic recombination predominantly within the acinar cells of the glands. We then bred these mice with the TNF-αglo transgenic line to develop a mouse model with salivary gland-specific overexpression of TNF-α; which replicates conditions seen in sialadenitis, an inflammation of the salivary glands resulting from infection or autoimmune disorders such as Sjögren's syndrome. The resulting AQP5-Cre/TNF-αglo mice display severe inflammation in the salivary glands with acinar cell atrophy, fibrosis, and dilation of the ducts. AQP5 expression was reduced in the salivary glands, while tight junction integrity appeared to be disrupted. The immune dysregulation in the salivary gland of these mice led to hyposalivation and masticatory dysfunction.

Procaine stimulates aquaporin‑5 expression in human salivary gland ductal cells via the suppression of DNA methyltransferase‑1

The present study aimed to investigate whether procaine may upregulate the expression of aquaporin‑5 (AQP5) in human salivary gland ductal cells and the underlying mechanisms of this upregulation. Immortalized normal human salivary gland ductal cells (NS‑SV‑DC), lacking AQP5 protein expression, were used to measure the glandular secretion rate following treatment with procaine, and the protein expression levels of AQP5 in NS‑SV‑DC cells were measured by western blotting. In order to investigate the mechanism of procaine action on AQP5 protein expression, the protein expression and activity of DNA methyltransferase (DNMT)1, and the CpG methylation of AQP5, were investigated further. In NS‑SV‑DC cells treated with procaine, the mRNA and protein levels of AQP5, and the secretion rate of cells, were significantly increased. Although no significant alterations were observed in the protein expression of DNMT1 following procaine treatment, its enzymatic activity was reduced, resulting in CpG island demethylation at Sp1‑2 and Sp1‑3 sites of the AQP5 gene, which may contribute to the significantly upregulated AQP5 gene expression. The results of the present study indicate that procaine may upregulate the protein expression of AQP5 in human submandibular glands by inhibiting the activity of DNMT1 and promoting liquid secretion. The procaine‑mediated expression of AQP5 may provide a novel regimen for the treatment of SS syndrome.

The Expression of AQP5 and UTs in the Sweat Glands of Uremic Patients

PURPOSE

To research the distribution and quantitative changes of UT-A1, UT-B1, and AQP5 in uremic skin tissue.

METHODS

34 cases of uremic patients (UP) and 11 controls were recruited. Immunohistochemistry, immunofluorescence, RT-PCR, and Western Blot were used to identify the proteins in sweat glands.

RESULTS

AQP5, UT-A1, and UT-B1 were expressed and localized in human skin basal lines, skin sweat glands, and sweat ducts, both in UP and controls. Compared to controls, AQP5 mRNA abundance was significantly decreased in UP (P < 0.01), and, with the decrease of eGFR, the AQP5 expression was significantly decreased (P < 0.05). By contrast, UT-A1 and UT-B1 mRNA abundance was significantly increased in the skin of UP compared with the control (P < 0.01), and, with the decrease of eGFR, the AQP5 expression was significantly increased (P < 0.05). We found that the gene changes were coincident with the corresponding target proteins. The urea transporter subtypes, UT-A1 and UT-B1, were expressed in the skin basal cell layer and exocrine sweat glands. The abundance of UT-A1 and UT-B1 in uremic sweat glands was significantly increased in UP, while the expression of AQP5 was decreased.

CONCLUSION

Elimination of urea through the skin by producing sweat is a potential therapeutic strategy for renal failure patients.

Functional effects of proinflammatory factors present in Sjögren's syndrome salivary microenvironment in an in vitro model of human salivary gland

Primary Sjögren’s syndrome (pSS) is an autoimmune exocrinopathy in which the role that the immune response plays in reducing exocrine gland function, including the glandular microenvironment of cytokines, has not been fully understood. Epithelial cells from biopsies of human parotid gland (HPG) were used to establish a model of human salivary gland in vitro. In this model, the functional consequences of several proinflammatory soluble factors present in the pSS glandular microenvironment were assessed. Stimulation with isoproterenol and calcium produced a significant increase in the basal activity of amylase in the HPG cell supernatants. Under these conditions, the presence of TNF-α and CXCL12 increased amylase mRNA cellular abundance, but reduced the amylase activity in the cell-free supernatant in a dose-dependent manner. IL-1β and IFN-γ, but not TGF-β, also diminished amylase secretion by HPG cells. These results suggest that the glandular microenvironment of cytokine, by acting post-transcriptionally, may be responsible, at least in part, for the reduced exocrine function observed in pSS patients. These data may help to a better understanding of the pathogenesis of SS, which in turn would facilitate the identification of new therapeutic targets for this disorder.

Aquaporins and Gland Secretion

Aquaporins (AQPs ) are expressed in most exocrine and endocrine secretory glands. Consequently, summarizing the expression and functions of AQPs in secretory glands represents a daunting task considering the important number of glands present in the body, as well as the number of mammalian AQPs - thirteen. The roles played by AQPs in secretory processes have been investigated in many secretory glands. However, despite considerable research, additional studies are clearly needed to pursue our understanding of the role played by AQPs in secretory processes. This book chapter will focus on summarizing the current knowledge on AQPs expression and function in the gastrointestinal tract , including salivary glands, gastric glands, Duodenal Brunner's gland, liver and gallbladder, intestinal goblets cells, exocrine and endocrine pancreas, as well as few other secretory glands including airway submucosal glands, lacrimal glands, mammary glands and eccrine sweat glands.

Cell-specific expression of aquaporin-5 (Aqp5) in alveolar epithelium is directed by GATA6/Sp1 via histone acetylation

Epigenetic regulation of differentiation-related genes is poorly understood. We previously reported that transcription factors GATA6 and Sp1 interact with and activate the rat proximal 358-bp promoter/enhancer (p358P/E) of lung alveolar epithelial type I (AT1) cell-specific gene aquaporin-5 (Aqp5). In this study, we found that histone deacetylase (HDAC) inhibitor suberoylanilide hydroxamic acid (SAHA) increased AQP5 expression and Sp1-mediated transcription of p358P/E. HDAC3 overexpression inhibited Sp1-mediated Aqp5 activation, while HDAC3 knockdown augmented AQP5 protein expression. Knockdown of GATA6 or transcriptional co-activator/histone acetyltransferase p300 decreased AQP5 expression, while p300 overexpression enhanced p358P/E activation by GATA6 and Sp1. GATA6 overexpression, SAHA treatment or HDAC3 knockdown increased histone H3 (H3) but not histone H4 (H4) acetylation within the homologous p358P/E region of mouse Aqp5. HDAC3 binds to Sp1 and HDAC3 knockdown increased interaction of GATA6/Sp1, GATA6/p300 and Sp1/p300. These results indicate that GATA6 and HDAC3 control Aqp5 transcription via modulation of H3 acetylation/deacetylation, respectively, through competition for binding to Sp1, and suggest that p300 modulates acetylation and/or interacts with GATA6/Sp1 to regulate Aqp5 transcription. Cooperative interactions among transcription factors and histone modifications regulate Aqp5 expression during alveolar epithelial cell transdifferentiation, suggesting that HDAC inhibitors may enhance repair by promoting acquisition of AT1 cell phenotype.

Tumor necrosis factor-α decreases EC-SOD expression through DNA methylation

Extracellular-superoxide dismutase (EC-SOD) is a secreted antioxidative enzyme, and its presence in vascular walls may play an important role in protecting the vascular system against oxidative stress. EC-SOD expression in cultured cell lines is regulated by various cytokines including tumor necrosis factor-α (TNF-α). TNF-α is a major mediator of pathophysiological conditions and may induce or suppress the generation of various types of mediators. Epigenetics have been defined as mitotically heritable changes in gene expression that do not affect the DNA sequence, and include DNA methylation and histone modifications. The results of the present study demonstrated that TNF-α significantly decreased EC-SOD level in fibroblasts with an accompanying increase in methylated DNA. In DNA methylation and demethylation, cytosine is methylated to 5-methylcytosine (5mC) by DNA methyltransferase (DNMT), and 5mC is then converted to 5-hydroxymethylcytosine (5hmC) and cytosine in a stepwise manner by ten-eleven translocation methylcytosine dioxygenases (TETs). However, DNMT did not participate in TNF-α-induced DNA methylation within the EC-SOD promoter region. On the other hand, TNF-α significantly suppressed TET1 expression and EC-SOD mRNA levels were decreased by the silencing of TET1 in fibroblasts. These results demonstrate that the down-regulation of EC-SOD by TNF-α is regulated by DNA methylation through reductions in TET1.

Tumor necrosis factor-α decreases EC-SOD expression through DNA methylation

Extracellular-superoxide dismutase (EC-SOD) is a secreted antioxidative enzyme, and its presence in vascular walls may play an important role in protecting the vascular system against oxidative stress. EC-SOD expression in cultured cell lines is regulated by various cytokines including tumor necrosis factor-α (TNF-α). TNF-α is a major mediator of pathophysiological conditions and may induce or suppress the generation of various types of mediators. Epigenetics have been defined as mitotically heritable changes in gene expression that do not affect the DNA sequence, and include DNA methylation and histone modifications. The results of the present study demonstrated that TNF-α significantly decreased EC-SOD level in fibroblasts with an accompanying increase in methylated DNA. In DNA methylation and demethylation, cytosine is methylated to 5-methylcytosine (5mC) by DNA methyltransferase (DNMT), and 5mC is then converted to 5-hydroxymethylcytosine (5hmC) and cytosine in a stepwise manner by ten-eleven translocation methylcytosine dioxygenases (TETs). However, DNMT did not participate in TNF-α-induced DNA methylation within the EC-SOD promoter region. On the other hand, TNF-α significantly suppressed TET1 expression and EC-SOD mRNA levels were decreased by the silencing of TET1 in fibroblasts. These results demonstrate that the down-regulation of EC-SOD by TNF-α is regulated by DNA methylation through reductions in TET1.

Pathogenic role of endogenous TNF-α in the development of Sjögren's-like sialadenitis and secretory dysfunction in non-obese diabetic mice

Patients with Sjögren's syndrome (SS), an autoimmune disease primarily affecting exocrine glands, exhibit enhanced TNF-α expression in the saliva and salivary glands. However, the precise in vivo role of TNF-α during the initiation and development of SS is not clearly defined. The present study is undertaken to determine the function of endogenously produced TNF-α in the pathogenesis of SS in non-obese diabetic (NOD) mice, a model of this human disease. Administration of a neutralizing anti-TNF-α antibody to female NOD mice during the stage prior to disease onset significantly improved salivary secretion, indicating a remission of clinical symptoms of SS. TNF-α blockade also decreased the number of leukocyte foci and reduced the number of T cells and B cells in the submandibular glands (SMG). Moreover, TNF-α blockade reduced T-bet protein levels in the SMG, suggesting a decrease in T helper 1 and T cytotoxic 1 cells. These cellular changes induced by TNF-α neutralization were associated with a reduction in T- and B-cell chemoattractants CXCL9 and CXC13. In addition, TNF-α blockade markedly increased the expression level of tight junction protein claudin-1 and water channel protein aquaporin-5, two key factors required for normal salivary secretion, in the SMG. Collectively, these findings indicate that endogenous TNF-α has a pathogenic role in the development of SS in the NOD model of this disease.

Insight into pathogenesis of Sjögren's syndrome: Dissection on autoimmune infiltrates and epithelial cells

Sjögren's syndrome (SS) is a chronic autoimmune disease with broad clinical spectrum, extending from benign exocrinopathy to severe systemic disease and lymphoma development. The glandular and extraglandular dysfunction of SS is associated with lymphocytic infiltrates that invade the epithelial structures of affected organs. The in-depth study of autoimmune lesions in the minor salivary glands (MSG), which are the major target-organ of SS responses, revealed that the lymphocytic infiltrates vary in severity and composition among SS-patients, are full-blown at diagnosis and remain unchanged thereafter. Although the pathogenetic pathways underlying SS have not yet elucidated, it is well-established that glandular epithelial cells are central regulators of local autoimmune responses. Moreover, chronic inflammation affects epithelial function and phenotype, which strengthens or weakens their immunoregulatory/secretory function, leading to deterioration of autoimmune phenomena. Herein, the current findings regarding the autoimmune lesions, the role of epithelial cells and their interaction with infiltrating lymphocytic cells are discussed.

Molecular Biology of Aquaporins

Aquaporins (AQPs ) are a family of membrane water channels that basically function as regulators of intracellular and intercellular water flow. To date, thirteen AQPs , which are distributed widely in specific cell types in various organs and tissues, have been characterized in humans. Four AQP monomers, each of which consists of six membrane-spanning alpha-helices that have a central water-transporting pore, assemble to form tetramers, forming the functional units in the membrane. AQP facilitates osmotic water transport across plasma membranes and thus transcellular fluid movement. The cellular functions of aquaporins are regulated by posttranslational modifications , e.g. phosphorylation, ubiquitination, glycosylation, subcellular distribution, degradation, and protein interactions. Insight into the molecular mechanisms responsible for regulated aquaporin trafficking and synthesis is proving to be fundamental for development of novel therapeutic targets or reliable diagnostic and prognostic biomarkers.

Expression of aquaporins 1 and 5 in a model of ventilator-induced lung injury and its relation to tidal volume

NEW FINDINGS

What is the central question of this study? Although different studies have attempted to find factors that influence the expression of aquaporins (AQPs) in the lung in different situations, to date no research group has explored the expression of AQP1 and AQP5 jointly in rats mechanically ventilated with different tidal volumes in a model of ventilator-induced lung injury. What is the main finding? Mechanical ventilation with a high tidal volume causes lung injury and oedema, increasing lung permeability. In rats ventilated with a high tidal volume, the pulmonary expression of AQP1 decreases. We analysed the expression of aquaporins 1 and 5 and its relation with tidal volume in a model of ventilator-induced lung injury. Forty-two rats were used. Six non-ventilated animals were killed (control group). The remaining rats were ventilated for 2 h with different tidal volumes (group 7ML with 7 ml kg^-1 and group 20ML with 20 ml kg^-1 ) and a respiratory rate of 90 breaths min^-1 . Lung oedema was measured, and the expression of AQP1 and AQP5 was determined by Western immunoblotting and measurement of mRNA. Lung oedema and alveolar-capillary membrane permeability were significantly increased in the animals of group 20ML compared with the control group. Expression of AQP1 was decreased in groups 7ML and 20ML compared with the control group. In conclusion, mechanical ventilation with a high tidal volume causes lung injury and oedema, increasing lung permeability. In rats ventilated with a high tidal volume, the pulmonary expression of AQP1 decreases.

Understanding autoimmunity: The ion channel perspective

Ion channels are integral membrane proteins that orchestrate the passage of ions across the cell membrane and thus regulate various key physiological processes of the living system. The stringently regulated expression and function of these channels hold a pivotal role in the development and execution of various cellular functions. Malfunction of these channels results in debilitating diseases collectively termed channelopathies. In this review, we highlight the role of these proteins in the immune system with special emphasis on the development of autoimmunity. The role of ion channels in various autoimmune diseases is also listed out. This comprehensive review summarizes the ion channels that could be used as molecular targets in the development of new therapeutics against autoimmune disorders.

Aquaporins in Salivary Glands: From Basic Research to Clinical Applications

Salivary glands are involved in saliva secretion that ensures proper oral health. Aquaporins are expressed in salivary glands and play a major role in saliva secretion. This review will provide an overview of the salivary gland morphology and physiology of saliva secretion, and focus on the expression, subcellular localization and role of aquaporins under physiological and pathophysiological conditions, as well as clinical applications involving aquaporins. This review is highlighting expression and localization of aquaporins in human, rat and mouse, the most studied species and is pointing out possible difference between major salivary glands, i.e., parotid, submandibular and sublingual glands.

Low-intensity pulsed ultrasound rescues insufficient salivary secretion in autoimmune sialadenitis

Introduction

Low-intensity pulsed ultrasound (LIPUS) has been known to promote bone healing by nonthermal effects. In recent studies, LIPUS has been shown to reduce inflammation in injured soft tissues. Xerostomia is one of the most common symptoms in Sjögren syndrome (SS). It is caused by a decrease in the quantity or quality of saliva. The successful treatment of xerostomia is still difficult to achieve and often unsatisfactory. The aim of this study is to clarify the therapeutic effects of LIPUS on xerostomia in SS.

Methods

Human salivary gland acinar (NS-SV-AC) and ductal (NS-SV-DC) cells were cultured with or without tumor necrosis factor-α (TNF-α; 10 ng/ml) before LIPUS or sham exposure. The pulsed ultrasound signal was transmitted at a frequency of 1.5 MHz or 3 MHz with a spatial average intensity of 30 mW/cm² and a pulse rate of 20 %. Cell number, net fluid secretion rate, and expression of aquaporin 5 (AQP5) and TNF-α were subsequently analyzed. Inhibitory effects of LIPUS on the nuclear factor κB (NF-κB) pathway were determined by Western blot analysis. The effectiveness of LIPUS in recovering salivary secretion was also examined in a MRL/MpJ/lpr/lpr (MRL/lpr) mouse model of SS with autoimmune sialadenitis.

Results

TNF-α stimulation of NS-SV-AC and NS-SV-DC cells resulted in a significant decrease in cell number and net fluid secretion rate (p < 0.01), whereas LIPUS treatment abolished them (p < 0.05). The expression changes of AQP5 and TNF-α were also inhibited in LIPUS treatment by blocking the NF-κB pathway. Furthermore, we found that mRNA expression of A20, a negative feedback regulator, was significantly increased by LIPUS treatment after TNF-α or interleukin 1β stimulation (NS-SV-AC, p < 0.01; NS-SV-DC, p < 0.05). In vivo LIPUS exposure to MRL/lpr mice exhibited a significant increase in both salivary flow and AQP5 expression by reducing inflammation in salivary glands (p < 0.01).

Conclusions

These results suggest that LIPUS upregulates expression of AQP5 and inhibits TNF-α production. Thus, LIPUS may restore secretion by inflamed salivary glands. It may synergistically activate negative feedback of NF-κB signaling in response to inflammatory stimulation. Collectively, LIPUS might be a new strategic therapy for xerostomia in autoimmune sialadenitis with SS.

Electronic supplementary material

The online version of this article (doi:10.1186/s13075-015-0798-8) contains supplementary material, which is available to authorized users.

Human autoimmune diseases: a comprehensive update

There have been significant advances in our understanding of human autoimmunity that have led to improvements in classification and diagnosis and, most importantly, research advances in new therapies. The importance of autoimmunity and the mechanisms that lead to clinical disease were first recognized about 50 years ago following the pioneering studies of Macfarlane Burnett and his Nobel Prize-winning hypothesis of the 'forbidden clone'. Such pioneering efforts led to a better understanding not only of autoimmunity, but also of lymphoid cell development, thymic education, apoptosis and deletion of autoreactive cells. Contemporary theories suggest that the development of an autoimmune disease requires a genetic predisposition and environmental factors that trigger the immune pathways that lead, ultimately, to tissue destruction. Despite extensive research, there are no genetic tools that can be used clinically to predict the risk of autoimmune disease. Indeed, the concordance of autoimmune disease in identical twins is 12-67%, highlighting not only a role for environmental factors, but also the potential importance of stochastic or epigenetic phenomena. On the other hand, the identification of cytokines and chemokines, and their cognate receptors, has led to novel therapies that block pathological inflammatory responses within the target organ and have greatly improved the therapeutic effect in patients with autoimmune disease, particularly rheumatoid arthritis. Further advances involving the use of multiplex platforms for diagnosis and identification of new therapeutic agents should lead to major breakthroughs within the next decade.

Aquaporin 5 expression is altered in ovarian tumors and ascites-derived ovarian tumor cells in the chicken model of ovarian tumor

BACKGROUND

Aquaporin 5 (AQP5), a member of the aquaporin family of transmembrane channel proteins, is involved in water transport and cellular proliferation in various tumors. The objective of this study was to determine cellular localization of aquaporin 5 (AQP5) in the ovarian tumors of chicken, a preclinical model for human ovarian tumor and to determine if AQP5 mRNA and protein expression levels in cancerous chicken ovaries and in ascites-derived chicken ovarian cancer (COVCAR) cell lines are different from normal ovaries and normal ovarian surface epithelial (NOSE) cells, respectively.

METHODS

Immunohistochemical staining was performed to determine the localization of AQP5-immunoreactive (ir) cells in normal and cancerous ovaries. To determine AQP5 mRNA and protein concentrations in cancerous ovaries and COVCAR cell lines, quantitative real time PCR and Western blotting analysis were performed, respectively. Student's t-test was performed to compare the levels of AQP5 mRNA or protein in cancerous ovaries and COVCAR cell lines with that of normal ovaries and NOSE cells, respectively.

RESULTS

AQP5-ir cells were localized in granulosa and theca layers of normal ovarian follicles whereas cancerous ovaries showed AQP5 immunostaining in the surface epithelium, fibroblast cells of the stroma, and in the cells lining tumor cysts and acini. AQP5 mRNA concentration were significantly lesser while AQP5 protein concentrations were significantly greater in cancerous ovaries compared to that in normal ovaries (P < 0.05). Whereas AQP5 mRNA concentrations were significantly greater while AQP5 protein concentrations were lesser (P < 0.05) in COVCAR cell lines compared with that in NOSE cells.

CONCLUSION

AQP5 is differentially expressed in ovarian tumor and in COVCAR cell lines suggesting a potential involvement of AQP5 in ovarian tumorigenesis, metastasis, and survival of ovarian tumor cells in ascites.

Aqp5 is a new transcriptional target of Dot1a and a regulator of Aqp2

Dot1l encodes histone H3 K79 methyltransferase Dot1a. Mice with Dot1l deficiency in renal Aqp2-expressing cells (Dot1l(AC)) develop polyuria by unknown mechanisms. Here, we report that Aqp5 links Dot1l deletion to polyuria through Aqp2. cDNA array analysis revealed and real-time RT-qPCR validated Aqp5 as the most upregulated gene in Dot1l(AC) vs. control mice. Aqp5 protein is barely detectable in controls, but robustly expressed in the Dot1l(AC) kidneys, where it colocalizes with Aqp2. The upregulation of Aqp5 is coupled with reduced association of Dot1a and H3 dimethyl K79 with specific subregions in Aqp5 5' flanking region in Dot1l(AC) vs. control mice. In vitro studies in IMCD3, MLE-15 and 293Tcells using multiple approaches including real-time RT-qPCR, luciferase reporter assay, cell surface biotinylation assay, colocalization, and co-immunoprecipitation uncovered that Dot1a represses Aqp5. Human AQP5 interacts with AQP2 and impairs its cell surface localization. The AQP5/AQP2 complex partially resides in the ER/Golgi. Consistently, AQP5 is expressed in none of 15 normal controls, but in all of 17 kidney biopsies from patients with diabetic nephropathy. In the patients with diabetic nephropathy, AQP5 colocalizes with AQP2 in the perinuclear region and AQP5 expression is associated with impaired cellular H3 dimethyl K79. Taken together, these data for the first time identify Aqp5 as a Dot1a potential transcriptional target, and an Aqp2 binding partner and regulator, and suggest that the upregulated Aqp5 may contribute to polyuria, possibly by impairing Aqp2 membrane localization, in Dot1l(AC) mice and in patients with diabetic nephropathy.