Aquaporin-5 regulation of cell-cell adhesion proteins: an elusive "tail" story

Novel signalling pathways in nephrogenic syndrome of inappropriate antidiuresis: functional implication of site-specific AQP2 phosphorylation

Nephrogenic syndrome of inappropriate antidiuresis (NSIAD) is a rare X-linked disease caused by gain-of-function mutations of arginine vasopressin receptor 2 (V2R). Patients with NSIAD are characterized by the inability to excrete a free water load and by inappropriately increased urinary osmolality despite very low levels of plasma vasopressin, resulting in euvolaemic hyponatraemia. To dissect the signalling downstream V2R constitutively active variants, Flp-In T-REx Madin-Darby canine kidney (FTM) cells, stably transfected with V2R mutants (R137L, R137C and F229V) and AQP2-wt or non-phosphorylatable AQP2-S269A/AQP2-S256A, were used as cellular models. All three activating V2R mutations presented constitutive plasma membrane expression of AQP2-wt and significantly higher basal water permeability. In addition, V2R-R137L/C showed significantly higher activity of Rho-associated kinase (ROCK), a serine/threonine kinase previously suggested to be involved in S269-AQP2 phosphorylation downstream of these V2R mutants. Interestingly, FTM cells expressing V2R-R137L/C mutants and AQP2-S269A showed a significant reduction in AQP2 membrane abundance and a significant reduction in ROCK activity, indicating the crucial importance of S269-AQP2 phosphorylation in the gain-of-function phenotype. Conversely, V2R-R137L/C mutants retained the gain-of-function phenotype when AQP2-S256A was co-expressed. In contrast, cells expressing the F229V mutant and the non-phosphorylatable AQP2-S256A had a significant reduction in AQP2 membrane abundance along with a significant reduction in basal osmotic water permeability, indicating a crucial role of Ser256 for this mutant. These data indicate that the constitutive AQP2 trafficking associated with the gain-of-function V2R-R137L/C mutants causing NSIAD is protein kinase A independent and requires an intact Ser269 in AQP2 under the control of ROCK phosphorylation. KEY POINTS: Nephrogenic syndrome of inappropriate antidiuresis is caused by two constitutively active variant phenotypes of AVPR2, one sensitive to vaptans (V2R-F229V) and the other vaptan resistant (V2R-R137C/L). In renal cells, all three activating arginine vasopressin receptor 2 (V2R) variants display constitutive AQP2 plasma membrane expression and high basal water permeability. In cells expressing V2R-R137L/C mutants, disruption of the AQP2-S269 phosphorylation site caused the loss of the gain-of-function phenotype, which, in contrast, was retained in V2R-F229V-expressing cells. Cells expressing the V2R-F229V mutant were instead sensitive to disruption of the AQP2-S256 phosphorylation site. The serine/threonine kinase Rho-associated kinase (ROCK) was found to be involved in AQP2-S269 phosphorylation downstream of the V2R-R137L/C mutants. These findings might have clinical relevance for patients with nephrogenic syndrome of inappropriate antidiuresis.

Peroxiporins in Triple-Negative Breast Cancer: Biomarker Potential and Therapeutic Perspectives

Triple-negative breast cancer (TNBC) remains one of the most challenging subtypes since it is initially characterized by the absence of specific biomarkers and corresponding targeted therapies. Advances in methodology, translational informatics, genomics, and proteomics have significantly contributed to the identification of therapeutic targets. The development of innovative treatments, such as antibody-drug conjugates and immune checkpoint inhibitors, alongside chemotherapy, has now become the standard of care. However, the quest for biomarkers defining therapy outcomes is still ongoing. Peroxiporins, which comprise a subgroup of aquaporins, which are membrane pores facilitating the transport of water, glycerol, and hydrogen peroxide, have emerged as potential biomarkers for therapy response. Research on peroxiporins reveals their involvement beyond traditional channeling activities, which is also reflected in their cellular localization and roles in cellular signaling pathways. This research on peroxiporins provides fresh insights into the mechanisms of therapy resistance in tumors, offering potential avenues for predicting treatment outcomes and tailoring successful TNBC therapies.

Recovery of extracorporeal lungs using cross-circulation with injured recipient swine

OBJECTIVE

Lung transplantation remains limited by the shortage of healthy organs. Cross-circulation with a healthy swine recipient provides a durable physiologic environment to recover injured donor lungs. In a clinical application, a recipient awaiting lung transplantation could be placed on cross-circulation to recover damaged donor lungs, enabling eventual transplantation. Our objective was to assess the ability of recipient swine with respiratory compromise to tolerate cross-circulation and support recovery of donor lungs subjected to extended cold ischemia.

METHODS

Swine donor lungs (n = 6) were stored at 4 °C for 24 hours while recipient swine (n = 6) underwent gastric aspiration injury before cross-circulation. Longitudinal multiscale analyses (blood gas, bronchoscopy, radiography, histopathology, cytokine quantification) were performed to evaluate recipient swine and extracorporeal lungs on cross-circulation.

RESULTS

Recipient swine lung injury resulted in sustained, impaired oxygenation (arterial oxygen tension/inspired oxygen fraction ratio 205 ± 39 mm Hg vs 454 ± 111 mm Hg at baseline). Radiographic, bronchoscopic, and histologic assessments demonstrated bilateral infiltrates, airway cytokine elevation, and significantly worsened lung injury scores. Recipient swine provided sufficient metabolic support for extracorporeal lungs to demonstrate robust functional improvement (0 hours, arterial oxygen tension/inspired oxygen fraction ratio 138 ± 28.2 mm Hg; 24 hours, 539 ± 156 mm Hg). Multiscale analyses demonstrated improved gross appearance, aeration, and cellular regeneration in extracorporeal lungs by 24 hours.

CONCLUSIONS

We demonstrate that acutely injured recipient swine tolerate cross-circulation and enable recovery of donor lungs subjected to extended cold storage. This proof-of-concept study supports feasibility of cross-circulation for recipients with isolated lung disease who are candidates for this clinical application.

The Involvement of Peroxiporins and Antioxidant Transcription Factors in Breast Cancer Therapy Resistance

Breast cancer is still the leading cause of death in women of all ages. The reason for this is therapy resistance, which leads to the progression of the disease and the formation of metastases. Multidrug resistance (MDR) is a multifactorial process that leads to therapy failure. MDR involves multiple processes and many signaling pathways that support each other, making it difficult to overcome once established. Here, we discuss cellular-oxidative-stress-modulating factors focusing on transcription factors NRF2, FOXO family, and peroxiporins, as well as their possible contribution to MDR. This is significant because oxidative stress is a consequence of radiotherapy, chemotherapy, and immunotherapy, and the activation of detoxification pathways could modulate the cellular response to therapy and could support MDR. These proteins are not directly responsible for MDR, but they support the survival of cancer cells under stress conditions.

Aquaporin water channels: roles beyond renal water handling

Aquaporin (AQP) water channels are pivotal to renal water handling and therefore in the regulation of body water homeostasis. However, beyond the kidney, AQPs facilitate water reabsorption and secretion in other cells and tissues, including sweat and salivary glands and the gastrointestinal tract. A growing body of evidence has also revealed that AQPs not only facilitate the transport of water but also the transport of several small molecules and gases such as glycerol, H2O2, ions and CO2. Moreover, AQPs are increasingly understood to contribute to various cellular processes, including cellular migration, adhesion and polarity, and to act upstream of several intracellular and intercellular signalling pathways to regulate processes such as cell proliferation, apoptosis and cell invasiveness. Of note, several AQPs are highly expressed in multiple cancers, where their expression can correlate with the spread of cancerous cells to lymph nodes and alter the response of cancers to conventional chemotherapeutics. These data suggest that AQPs have diverse roles in various homeostatic and physiological systems and may be exploited for prognostics and therapeutic interventions.

Aquaglyceroporins in Human Breast Cancer

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

The multifaceted role of aquaporins in physiological cell migration

Cell migration is an essential process that underlies many physiological processes, including the immune response, organogenesis in the embryo, and angiogenesis, as well as pathological processes such as cancer metastasis. Cells have at their disposal a variety of migratory behaviors and mechanisms that seem to be specific to cell type and the microenvironment. Research over the past two decades has elucidated the water channel protein family of aquaporins (AQPs) as a regulator of many cell migration-related processes, from physical phenomena to biological signaling pathways. The roles that AQPs play in cell migration are both cell type- and isoform-specific; thus, a large swath of information has accumulated as researchers seek to identify the responses across these distinct variables. There does not seem to be a universal role that AQPs play in cell migration; the complex interplay between AQPs and cell volume management, signaling pathway activation, and in a few identified circumstances, gene expression regulation, has shown the intricate, and perhaps paradoxical, role of AQPs in cell migration. The objective of this review is to provide an organized and integrated collection of recent work that has elucidated the many mechanisms by which AQPs regulate cell migration.NEW & NOTEWORTHY Research has elucidated the water channel protein family of aquaporins (AQPs) as a regulator of many cell migration-related processes, from physical phenomena to biological signaling pathways. The roles that AQPs play in cell migration are both cell type- and isoform-specific; thus, a large swath of information has accumulated as researchers seek to identify the responses across these distinct variables. This review compiles insights into the recent findings linking AQPs to physiological cell migration.

Genetic studies of heat stress regulation in goat during hot climatic condition

Various direct and indirect environmental constraints have an impact on livestock performance. The physiological parameters, such as rectal temperature, heart rate, and respiratory rate, are the primary indicators of thermal stress. Under a stressed environment temperature humidity index (THI) had established as a vital measurement to identify the thermal stress in livestock. THI in association with climatic variations can define the environmental effect as stressful or comfortable for livestock. Goats are small ruminants that adapt to a wide range of ecological variations due to their anatomical and physiological characteristics. However, the productivity of animals declines at the individual level during thermal stress. Stress tolerance can be determined through genetic studies associated with at the cellular level using physiological as well as molecular approaches. Information on genetic association with thermal stress in goats is scanty, this severely affects their survival and hence productivity of livestock. The ever-increasing demand for food across the globe needs deciphering novel molecular markers as well as stress indicators that play a vital role in livestock improvement. This review represents an analysis of current knowledge of phenotypic differences during thermal stress and signifies the importance of physiological responses and their association at the cellular level in goats. The regulation of vital genes associated with thermal stress such as Aquaporins (AQP 0, 1, 2, 4, 5, 6, 8), aquaglyceroporins (AQP3, 7, 9, and 10) and super-aquaporins (AQP 11, 12); BAX inhibitors such as PERK (PKR like ER kinase), IRE 1(inositol-requiring-1); Redox regulating genes such as NOX; Transport of Na+ and K+ such as ATPase (ATP1A1) and several heat shock proteins have been implicated in heat-stress related adaptations have been elucidated. As these changes have a significant impact on production performance as well as on livestock productivity. Such efforts may help in the development of molecular markers and will assist the breeders to develop heat-tolerant goats with improved productivity.

Role of aquaporins in corneal healing post chemical injury

Aquaporins (AQPs) are transmembrane water channel proteins that regulate the movement of water through the plasma membrane in various tissues including cornea. The cornea is avascular and has specialized microcirculatory mechanisms for homeostasis. AQPs regulate corneal hydration and transparency for normal vision. Currently, there are 13 known isoforms of AQPs that can be subclassified as orthodox AQPs, aquaglyceroporins (AQGPs), or supraquaporins (SAQPs)/unorthodox AQPs. AQPs are implicated in keratocyte function, inflammation, edema, angiogenesis, microvessel proliferation, and the wound-healing process in the cornea. AQPs play an important role in wound healing by facilitating the movement of corneal stromal keratocytes by squeezing through tight stromal matrix and narrow extracellular spaces to the wound site. Deficiency of AQPs can cause reduced concentration of hepatocyte growth factor (HGF) leading to reduced epithelial proliferation, reduced/impaired keratocyte migration, reduced number of keratocytes in the injury site, delayed and abnormal wound healing process. Dysregulated AQPs cause dysfunction in osmolar homeostasis as well as wound healing mechanisms. The cornea is a transparent avascular tissue that constitutes the anterior aspect of the outer covering of the eye and aids in two-thirds of visual light refraction. Being the outermost layer of the eye, the cornea is prone to injury. Of the 13 AQP isoforms, AQP1 is expressed in the stromal keratocytes and endothelial cells, and AQP3 and AQP5 are expressed in epithelial cells in the human cornea. AQPs can facilitate wound healing through aid in cellular migration, proliferation, migration, extracellular matrix (ECM) remodeling and autophagy mechanism. Corneal wound healing post-chemical injury requires an integrative and coordinated activity of the epithelium, stromal keratocytes, endothelium, ECM, and a battery of cytokines and growth factors to restore corneal transparency. If the chemical injury is mild, the cornea will heal with normal clarity, but severe injuries can lead to partial and/or permanent loss of corneal functions. Currently, the role of AQPs in corneal wound healing is poorly understood in the context of chemical injury. This review discusses the current literature and the role of AQPs in corneal homeostasis, wound repair, and potential therapeutic target for acute and chronic corneal injuries.

The cell polarity protein Scribble is downregulated by the water channel aquaporin-5 in breast cancer cells

Breast carcinomas originate from cells in the terminal duct-lobular unit. Carcinomas are associated with increased cell proliferation and migration, altered cellular adhesion, as well as loss of epithelial polarity. In breast cancer, aberrant and high levels of aquaporin-5 (AQP5) are associated with increased metastasis, poor prognosis, and cancer recurrence. AQP5 increases the proliferation and migration of cancer cells, and ectopic expression of AQP5 in normal epithelial cells reduces cell-cell adhesion and increases cell detachment and dissemination from migrating cell sheets, the latter via AQP5-mediated activation of the Ras pathway. Here, we investigated if AQP5 also affects cellular polarity by examining the relationship between the essential polarity protein Scribble and AQP5. In tissue samples from invasive lobular and ductal carcinomas, the majority of cells with high AQP5 expression displayed low Scribble levels, indicating an inverse relationship. Probing for interactions via a Glutathione S-transferase pull-down experiment revealed that AQP5 and Scribble interacted. Moreover, overexpression of AQP5 in the breast cancer cell line MCF7 reduced both size and circularity of three-dimensional (3-D) spheroids and induced cell detachment and dissemination from migrating cell sheets. In addition, Scribble levels were reduced. An AQP5 mutant cell line, which cannot activate Ras (AQP5^S156A) signaling, displayed unchanged spheroid size and circularity and an intermediate level of Scribble, indicating that the effect of AQP5 on Scribble is, at least in part, dependent on AQP5-mediated activation of Ras. Thus, our results suggest that high AQP5 expression negatively regulates the essential polarity protein Scribble and thus, can affect cellular polarity in breast cancer.

Aquaporins Display a Diversity in their Substrates

Aquaporins constitute a family of transmembrane proteins that function to transport water and other small solutes across the cell membrane. Aquaporins family members are found in diverse life forms. Aquaporins share the common structural fold consisting of six transmembrane alpha helices with a central water-transporting channel. Four such monomers assemble together to form tetramers as their biological unit. Initially, aquaporins were discovered as water-transporting channels, but several studies supported their involvement in mediating the facilitated diffusion of different solutes. The so-called water channel is able to transport a variety of substrates ranging from a neutral molecule to a charged molecule or a small molecule to a bulky molecule or even a gas molecule. This article gives an overview of a diverse range of substrates conducted by aquaporin family members. Prime focus is on human aquaporins where aquaporins show a wide tissue distribution and substrate specificity leading to various physiological functions. This review also highlights the structural mechanisms leading to the transport of water and glycerol. More research is needed to understand how one common fold enables the aquaporins to transport an array of solutes.

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.

Aquaporin water channels affect the response of conventional anticancer therapies of 3D grown breast cancer cells

Aquaporin (AQP) water channels facilitate water transport across cellular membranes and are essential in regulation of body water balance. Moreover, several AQPs are overexpressed or ectopically expressed in breast cancer. Interestingly, several in vitro studies have suggested that AQPs can affect the response to conventional anticancer chemotherapies. Therefore, we took a systematic approach to test how AQP1, AQP3 and AQP5, which are often over-/ectopically expressed in breast cancer, affect total viability of 3-dimensional (3D) breast cancer cell spheroids when treated with the conventional anticancer chemotherapies Cisplatin, 5-Fluorouracil (5-FU) and Doxorubicin, a Combination of the three drugs as well as the Combination plus the Ras inhibitor Salirasib. Total viability of spheroids overexpressing AQP1 were decreased by all treatments except for 5-FU, which increased total viability by 20% compared to DMSO treated controls. All treatments reduced viability of spheroids overexpressing AQP3. In contrast, only Doxorubicin, Combination and Combination + Salirasib reduced total viability of spheroids overexpressing AQP5. Thus, this study supports a significant role of AQPs in the response to conventional chemotherapies. Evaluating the role of individual proteins that contribute to resistance to chemotherapies is essential in advancing personalized medicine in breast carcinomas.

Aquaporin-5 in breast cancer

The water channel aquaporin‐5 (AQP5) is essential in transepithelial water transport in secretory glands. AQP5 is ectopically overexpressed in breast cancer, where expression is associated with lymph node metastasis and poor prognosis. Besides the role in water transport, AQP5 has been found to play a role in cancer metastasis, migration, and proliferation. AQP5 has also been shown to be involved in the dysregulation of epithelial cell–cell adhesion; frequently observed in cancers. Insight into the underlying molecular mechanisms of how AQP5 contributes to cancer development and progression is essential for potentially implementing AQP5 as a prognostic biomarker and to develop targeted intervention strategies for the treatment of breast cancer patients.

Aquaporins in pancreatic ductal adenocarcinoma

Aquaporins are water channel proteins facilitating passive transport of water across cellular membranes. Aquaporins are over- or ectopically expressed in a multitude of cancers, including pancreatic ductal adenocarcinoma, which is a highly aggressive cancer with low survival rate. Evidence suggests that aquaporins can affect multiple cellular processes involved in cancer development and progression including epithelial-mesenchymal transition, cellular migration, cell proliferation, invasion, and cellular adhesions. In pancreatic ductal adenocarcinoma, aquaporin-1, aquaporin-3, and aquaporin-5 are overexpressed and have been associated with metastatic processes and poor survival. Thus, aquaporin expression has been suggested as diagnostic markers and therapeutic targets in pancreatic ductal adenocarcinoma.

Aquaporin-1 in breast cancer

The canonical function of aquaporin (AQP) water channels is to facilitate passive transport of water across cellular membranes making them essential in the regulation of body water homeostasis. Moreover, AQPs, including AQP1, have been found to be overexpressed in multiple cancer types, including breast cancer, where AQP1 overexpression is associated with poor prognosis. AQPs have been shown to affect cellular processes associated with cancer progression and spread including cell migration, angiogenesis, and proliferation. Moreover, AQPs can regulate levels of adhesion proteins at cell-cell junctions, a regulatory role, which is still largely unexplored in cancer. Understanding the molecular mechanisms of how AQP1 contributes to breast cancer progression and metastatic processes is essential to establish AQP1 as a biomarker and to develop targeted anticancer treatments for breast cancer patients. This mini-review focuses on the role of AQP1 in breast cancer.

Unraveling Human AQP5-PIP Molecular Interaction and Effect on AQP5 Salivary Glands Localization in SS Patients

Saliva secretion requires effective translocation of aquaporin 5 (AQP5) water channel to the salivary glands (SGs) acinar apical membrane. Patients with Sjögren’s syndrome (SS) display abnormal AQP5 localization within acinar cells from SGs that correlate with sicca manifestation and glands hypofunction. Several proteins such as Prolactin-inducible protein (PIP) may regulate AQP5 trafficking as observed in lacrimal glands from mice. However, the role of the AQP5-PIP complex remains poorly understood. In the present study, we show that PIP interacts with AQP5 in vitro and in mice as well as in human SGs and that PIP misexpression correlates with an altered AQP5 distribution at the acinar apical membrane in PIP knockout mice and SS hMSG. Furthermore, our data show that the protein-protein interaction involves the AQP5 C-terminus and the N-terminal of PIP (one molecule of PIP per AQP5 tetramer). In conclusion, our findings highlight for the first time the role of PIP as a protein controlling AQP5 localization in human salivary glands but extend beyond due to the PIP-AQP5 interaction described in lung and breast cancers.

Aquaporin 5 Facilitates Corneal Epithelial Wound Healing and Nerve Regeneration by Reactivating Akt Signaling Pathway

Aquaporins (AQPs) are normally expressed in the corneal epithelium. The aim of this study was to determine whether AQP5 played a role in corneal epithelial wound healing. AQP5 knockout (AQP5^-/-) mice were constructed using CRISPR/Cas9 technology. A corneal wound healing model was performed using epithelial debridement on corneas. The time to corneal epithelial and nerve regeneration was significantly delayed in the AQP5^-/- mice. Reduced Ki-67-positive cells and nerve growth factor (NGF) expression were confirmed in the AQP5^-/- mice during healing. The epithelial and nerve regeneration rates were significantly promoted in the AQP5^-/- mice by treatment with NGF, which was accompanied by recovered levels of phosphorylated Akt. NGF treatment also improved the recovery of corneal nerve fiber density and sensitivity in the AQP5^-/- mice. However, the promotion of NGF induced corneal epithelial and nerve regeneration rates, and Akt reactivation was reversed by Akt inhibitor. The significant impairment of corneal wound healing in the AQP5^-/- mice resulted from distinct defects in corneal epithelial cell proliferation and nerve regeneration. The results provided evidence for the involvement of aquaporin in cell proliferation and suggested that AQP5 induction could be a potential therapy for accelerating the resurfacing of corneal defects.

Aquaporin water channels as regulators of cell-cell adhesion proteins

Aquaporin (AQP) water channels facilitate passive transport of water across cellular membranes following an osmotic gradient. AQPs are expressed in a multitude of epithelia, endothelia, and other cell types where they play important roles in physiology, especially in the regulation of body water homeostasis, skin hydration, and fat metabolism. AQP dysregulation is associated with many pathophysiological conditions, including nephrogenic diabetes insipidus, chronic kidney disease, and congestive heart failure. Moreover, AQPs have emerged as major players in a multitude of cancers where high expression correlates with metastasis and poor prognosis. Besides water transport, AQPs have been shown to be involved in cellular signaling, cell migration, cell proliferation, and regulation of junctional proteins involved in cell-cell adhesion; all cellular processes which are dysregulated in cancer. This review focuses on AQPs as regulators of junctional proteins involved in cell-cell adhesion.