Role Of Aquaporins Research Articles

Transport of Reactive Oxygen and Nitrogen Species across Aquaporin: A Molecular Level Picture.

Aquaporins (AQPs) are transmembrane proteins that conduct not only water molecules across the cell membrane but also other solutes, such as reactive oxygen and nitrogen species (RONS), produced (among others) by cold atmospheric plasma (CAP). These RONS may induce oxidative stress in the cell interior, which plays a role in cancer treatment. The underlying mechanisms of the transport of RONS across AQPs, however, still remain obscure. We apply molecular dynamics simulations to investigate the permeation of both hydrophilic (H2O2 and OH) and hydrophobic (NO2 and NO) RONS through AQP1. Our simulations show that these RONS can all penetrate across the pores of AQP1. The permeation free energy barrier of OH and NO is lower than that of H2O2 and NO2, indicating that these radicals may have easier access to the pore interior and interact with the amino acid residues of AQP1. We also study the effect of RONS-induced oxidation of both the phospholipids and AQP1 (i.e., sulfenylation of Cys191) on the transport of the above-mentioned RONS across AQP1. Both lipid and protein oxidation seem to slightly increase the free energy barrier for H2O2 and NO2 permeation, while for OH and NO, we do not observe a strong effect of oxidation. The simulation results help to gain insight in the underlying mechanisms of the noticeable rise of CAP-induced RONS in cancer cells, thereby improving our understanding on the role of AQPs in the selective anticancer capacity of CAP.

Cerebrospinal fluid flow. Part 2. Aquaporins and their role in CNS water homeostasis

The capabilities of the central nervous system to receive, integrate and process the incoming information, as well as to ensure an adequate timely response, are directly determined by the ability to maintain the electrochemical gradient of ions, a certain concentration of organic molecules and the transport of water through the plasma membrane of nerve cells. This dynamic disequilibrium is a key mechanism in the generation and transmission of information in neuronal intercellular communication, in the activation of extracellular signaling molecules, and in the metabolic support of the neural tissue. It is obvious that maintaining stable homeostasis in the central nervous system is strictly regulated by the mechanisms of ion transport, organic and inorganic molecules, and water. Astrocytes provided with proteins of ionic and aqueous transmembrane channels communicate with neurons and cells lining the cavities filled with fluid. So astroglia is the basic element in achieving such homeostatic regulation of the CNS. Astroglial-mediated homeostasis is highly dynamic, and it has been proven that the disruption of surface expression and the polarization of transport proteins in astroglial cells underlies various pathological conditions. The discovery and further investigation of functional characteristics of specialized water channels — aquaporins was one of the milestones in the study of the mechanisms for maintaining water homeostasis of CNS. The present review deals with base ideas concerning the role of aquaporins in the processes of water transport, such as regulating cell volume, controlling the size of extracellular space, production and drainage of cerebrospinal fluid. Certain pathological conditions caused by a violation of water homeostasis and the drainage system of the central nervous system are considered.

Aquaporin 4 Suppresses Neural Hyperactivity and Synaptic Fatigue and Fine-Tunes Neurotransmission to Regulate Visual Function in the Mouse Retina

The bidirectional water channel aquaporin 4 (AQP4) is abundantly expressed in the neural tissue. The advantages and disadvantages of AQP4 neural tissue deficiency under pathological conditions, such as inflammation, and relationship with neural diseases, such as Alzheimer’s disease, have been previously reported. However, the physiological functions of AQP4 are not fully understood. Here, we evaluated the role of AQP4 in the mouse retina using Aqp4 knockout (KO) mice. Aqp4 was expressed in Müller glial cells surrounding the synaptic area between photoreceptors and bipolar cells. Both scotopic and photopic electroretinograms showed hyperactive visual responses in KO mice, gradually progressing with age. Moreover, the amplitude reduction after frequent stimuli and synaptic fatigue was more severe in KO mice. Glutamine synthetase, glutamate aspartate transporter, synaptophysin, and the inward potassium channel Kir2.1, but not Kir4.1, were downregulated in KO retinas. KIR2.1 colocalized with AQP4 in Müller glial cells at the synaptic area, and its expression was affected by Aqp4 levels in primary Müller glial cell cultures. Intraocular injection of potassium in wild-type mice led to visual function hyperactivity, as observed in Aqp4 KO mice. Mitochondria molecules, such as Pgc1α and CoxIV, were downregulated, while apoptotic markers were upregulated in KO retinas. AQP4 may fine-tune synaptic activity, most likely by regulating potassium metabolism, at least in part, via collaborating with KIR2.1, and possibly indirectly regulating glutamate kinetics, to inhibit neural hyperactivity and synaptic fatigue which finally affect mitochondria and cause neurodegeneration.

Targeting Water in the Brain: Role of Aquaporin-4 in Ischemic Brain Edema.

Brain edema primarily occurs as a consequence of various cerebral injuries including ischemic stroke. Excessive accumulation of brain water content causes a gradual expansion of brain parenchyma, decreased blood flow and increased intracranial pressure and, ultimately, cerebral herniation and death. Current clinical treatment for ischemic edema is very limited, therefore, it is urgent to develop novel treatment strategies. Mounting evidence has demonstrated that AQP4, a water channel protein, is closely correlated with brain edema and could be an optimal therapeutic target for the reduction of ischemic brain edema. AQP4 is prevalently distributed in the central nervous system, and mainly regulates water flux in brain cells under normal and pathological conditions. This review focuses on the underlying mechanisms of AQP4 related to its dual role in edema formation and elimination.

Aquaporin-4 reduces neuropathology in a mouse model of Alzheimer\u2019s disease by remodeling peri-plaque astrocyte structure

Redistribution of the water channel aquaporin-4 (AQP4) away from astrocyte endfeet and into parenchymal processes is a striking histological feature in mouse models of Alzheimer’s disease (AD) and other neurological conditions with prominent astrogliosis. AQP4 redistribution has been proposed to impair bulk Aβ clearance in AD, resulting in increased amyloid deposition in the brain; however, this finding is controversial. Here, we provide evidence in support of a different and novel role of AQP4 in AD. We found that Aqp4 deletion significantly increased amyloid deposition in cerebral cortex of 5xFAD mice, with an increase in the relative number of fibrillar vs. dense core plaques. AQP4 deficient 5xFAD mice also showed a significant reduction in the density of GFAP labeled peri-plaque astrocyte processes. Microglial plaque coverage was also significantly reduced, suggesting astrocyte involvement in organizing the peri-plaque glial response. The alterations in peri-plaque glial structure were accompanied by increased neuronal uptake of Aβ and an increase in the number of dystrophic neurites surrounding plaques. On the basis of these findings, we propose that redistribution of AQP4 into the parenchymal processes facilitates astrocyte structural plasticity and the formation of a reactive glial net around plaques that protects neurons from the deleterious effects of Aβ aggregates. AQP4 redistribution may thus facilitate plaque containment and reduce neuropathology in AD.

The role of Aquaporin-4 in T cell activation

Abstract Aquaporins (AQPs) are membrane channels that mediate a variety of biological processes via water and other small molecule movement. Several aquaglyceroporins have been shown to regulate key immune functions. However, the role of AQP4 in immune cells is poorly characterized. We recently reported that AQP4 is expressed by both naïve and memory CD4 and CD8 T cells. Furthermore, AQP4 blockade with a small molecule inhibitor, AER-270, reduced T cell activation and proliferation leading to a significant prolongation of fully MHC-mismatched murine heart allograft survival. The goal of this study was to determine the mechanisms by which AQP4 facilitates T cell activation and TCR signaling. Wild-type (WT) but not AQP4−/− T cells treated with AER-270 were protected from lysis in a hypoosmotic shock assay demonstrating AQP4 requirement for water transport in T cells. Following αCD3/αCD28 stimulation, AQP4−/− T cells demonstrated inferior activation compared to WT T cells. Similar decreased activation was observed after treatment of WT T cells with AER-270. Consistent with reduced T cell activation, AQP4 inhibition diminished Ca2+flux in WT but not AQP4−/− T cells in response to TCR crosslinking. AQP4 inhibition also resulted in altered pattern of protein tyrosine phosphorylation at 2 min following TCR crosslinking. These results indicate that despite T cell expression of several water channels, AQP4 function is critical for optimal T cell activation and functions. Our study identifies a novel role of water channels in T cell biology and suggests AQP4 inhibition as a promising strategy to modulate T cell alloresponses following transplantation.

Time course effects of methotrexate on renal handling of water and electrolytes in rats. Role of aquaporin-2 and Na-K-2Cl-cotransporter

Methotrexate (MTX) is a derivate of folic acid, commonly used as an anchor drug for the treatment and management of malignant diseases and autoimmune disorders. However, nephrotoxicity is an important drawback of MTX therapy. Unfortunately, there are not enough studies reporting the nature of the renal failure induced by MTX. Thus, the aim of this study was to evaluate the time course of renal handling of water and electrolytes in male Wistar rats, after the exposure to a unique dose of MTX (80 mg/kg b.w.). Experiments were carried out at day 2, day 4, day 8 and day 14 after MTX administration. Several parameters of kidney function related to water and electrolytes handling were evaluated. Renal expression and urinary excretion of aquaporin-2 (AQP2) and Na-K-2Cl-cotransporter (NKCC2) were determined by Western blotting. MTX produced alterations on water handling on the second day after treatment, showing a significant increase in solute free water reabsorption which might be mediated by the increased expression of AQP2 in apical membranes. On the other hand, MTX produced alterations on electrolytes handling on the fourth day after treatment, showing a significant decrease of sodium chloride excretion, mediated at least in part, by the increase renal expression of NKCC2. These results provide valuable information to clinical practice in order to be able to find therapeutic targets that diminish adverse effects and health deterioration. Moreover, MTX treatment altered AQP2 and NKCC2 urinary excretion allowing postulating these transporters as potential biomarkers of MTX induced nephrotoxicity.

Aquaporin 4 Blockade Attenuates Acute Lung Injury Through Inhibition of Th17 Cell Proliferation in Mice

Acute lung injury (ALI) is a syndrome characterized by damage to the alveolar-capillary wall, pulmonary edema and recruitment of inflammatory cells. Previous studies have indicated that aquaporin 4 (AQP4) plays a key role in brain edema formation and resolution. However, the role of AQP4 in the development and progression of ALI is not clear and needs to be resolved. In our current study, mouse ALI was induced by intratracheal instillation of lipopolysaccharide (LPS) at a concentration of 30mg/kg. For the inhibition of AQP4, 200mg/kg of TGN-020 (Sigma, USA) was administered intraperitoneally every 6h starting at 30min before intratracheal instillation of LPS. The results of the present work indicate, for the first time, that mice treated with the AQP4 inhibitor TGN-020 had attenuated LPS-induced lung injury, reduced proinflammatory cytokine release (including IL-1α, IL-1β, IL-6, TNF-α, IL-23, and IL-17A), and an improved survival rate. Additionally, we found that the attenuated lung injury scores, increased survival rate, and decreased BALF total protein concentration in TGN-020-treated mice were all abrogated by rIL-17A administration. Furthermore, TGN-020 treatment downregulated the phosphorylation of PI3K and Akt, increased the expression of SOCS3, and decreased the expression of p-STAT3 and RORγt. In conclusion, inhibition of AQP4 by TGN-020 has a detectable protective effect against lung tissue injury induced by LPS, and this effect is associated with inhibition of IL-17A through the downregulation of the PI3K/Akt signaling pathway and upregulation of SOCS3 protein.

That's Swell! The Role of Aquaporin in an Inflammatory Response

Death due to lung inflammation has increased 31 percent over the last 35 years. A protein that influences this mortality rate is aquaporin‐4. This tetramer protein is a water channel that is water permeable. This integral protein, made up of six transmembrane helices and two pore helices, creates an hourglass shape. The structure of aquaporin is vital to its function due to pore helices preventing large molecules from passing through the membrane, only facilitating the movement of water molecules or small solutes. These two pore helices allow one molecule to pass at a time, making the net water movement facilitation easier. All types of aquaporins have NPA (asparagine‐proline‐alanine) motifs which are located in the central channel and are responsible for water permeation and intracellular processing. In aquaporin‐4, there are two NPA motifs at residues 97–99 and 213–215. Scientists discovered that aquaporin's response to bacterial stimuli can alter its pore size. Trauma, toxins or injury to tissue can cause a cell to become hypotonic. Aquaporin‐4 is specifically related to lung injury and inflammation because it is highly expressed in humans. The HUHS MAPS Team (Modeling A Protein Story) has designed a model of the wild form of AQP4 with 3D printing technology to investigate structure‐function relationships. The extensive research on aquaporins in relation to lung inflammation can contribute to the scientific and medical world and eventually target new pharmacological therapies.Support or Funding InformationThe MSOE Center for BioMolecular Modeling would like to acknowledge and thank the National Institutes of Health Clinical and Translational Science Award (NIH_CTSA UL1RR031973) and the Milwaukee School of Engineering for their support in funding the 2018_2019 SMART Team program.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Pharmacotherapy for Neuromyelitis Optica Spectrum Disorders: Current Management and Future Options.

Neuromyelitis optica (NMO) is an inflammatory and demyelinating disease of the central nervous system. Although the prevalence of NMO is low, the rapid and severe impairment observed in patients has led to extensive development of research in the fields of diagnostic criteria and therapy in the past 15years. With improved understanding of the pathophysiology of NMO and the role of aquaporin-4 (AQP4) or myelin oligodendrocyte glycoprotein antibodies, numerous therapeutic approaches have been proposed and are currently undergoing evaluation. In this review, we describe the rationale for existing therapeutics and their benefit/risk ratio. We also discuss the pharmacological and clinical interest of future approaches targeting, among others, B or T cells, the blood-central nervous system barrier, complement, polynuclear cells, AQP4-antibody linkage and AQP4 activity. The numerous agents under development are the result of a major collaborative effort all over the world. After the considerable progress on diagnosis, we are now close to class I evidence for a therapeutic effect of several drugs in NMO spectrum disorders, most notably with the anti-interleukin-6 receptor antibody (satralizumab) and anti-complement-5 antibody (eculizumab).

Variation in Aquaporin and Physiological Responses Among Pinus contorta Families Under Different Moisture Conditions.

A population of eight open pollinated families of Pinus contorta was selected from sites varying in precipitation regimes and elevation to examine the possible role of aquaporins in adaptation to different moisture conditions. Five Pinus contorta aquaporins encoding PiconPIP2;1, PiconPIP2;2, PiconPIP2;3, PiconPIP1;2, and PiconTIP1;1 were cloned and detailed structural analyses were conducted to provide essential information that can explain their biological and molecular function. All five PiconAQPs contained hydrophilic aromatic/arginine selective filters to facilitate the transport of water. Transcript abundance patterns of PiconAQPs varied significantly across the P. contorta families under varying soil moisture conditions. The transcript abundance of five PiconPIPs remained unchanged under control and water-stress conditions in two families that originated from the sites with lower precipitation levels. These two families also displayed a different adaptive strategy of photosynthesis to cope with drought stress, which was manifested by reduced sensitivity in photosynthesis (maintaining the same rate) while exhibiting a reduction in stomatal conductance. In general, root:shoot ratios were not affected by drought stress, but some variation was observed between families. The results showed variability in drought coping mechanisms, including the expression of aquaporin genes and plant biomass allocation among eight families of Pinus contorta.

Aqp-1 Gene Knockout Attenuates Hypoxic Pulmonary Hypertension of Mice.

Objective- Hypoxic pulmonary hypertension (HPH) is characterized by proliferative vascular remodeling. Abnormal pulmonary artery smooth muscle cells proliferation and endothelial dysfunction are the primary cellular bases of vascular remodeling. AQP1 (aquaporin-1) is regulated by oxygen level and has been observed to play a role in the proliferation and migration of pulmonary artery smooth muscle cells. The role of AQP1 in HPH pathogenesis has not been directly determined to date. To determine the possible roles of AQP1 in the pathogenesis of HPH and explore its possible mechanisms. Approach and Results- Aqp1 knockout mice were used, and HPH model was established in this study. Primary pulmonary artery smooth muscle cells, primary mouse lung endothelial cells, and lung tissue sections from HPH model were used. Immunohistochemistry, immunofluorescence and Western blot, cell cycle, apoptosis, and migration analysis were performed in this study. AQP1 expression was upregulated by chronic hypoxia exposure, both in pulmonary artery endothelia and medial smooth muscle layer of mice. Aqp1 deficiency attenuated the elevation of right ventricular systolic pressures and mitigated pulmonary vascular structure remodeling. AQP1 deletion reduced abnormal cell proliferation in pulmonary artery and accompanied with accumulation of HIF (hypoxia-inducible factor). In vitro, Aqp1 deletion reduced hypoxia-induced proliferation, apoptosis resistance, and migration ability of primary cultured pulmonary artery smooth muscle cells and repressed HIF-1α protein stability. Furthermore, Aqp1 deficiency protected lung endothelial cells from apoptosis in response to hypoxic injury. Conclusions- Our data showed that Aqp1 deficiency could attenuate hypoxia-induced vascular remodeling in the development of HPH. AQP1 may be a potential target for pulmonary hypertension treatment.

Aquaporin4 (AQP4) in brain disorder

Two third of our body is composed of water molecules. Regulation of water and electrolytes is indeed the most important homeostatic functions. Many diseases, such as heart failure, are associated with disturbance in fluid homeostasis. Surprisingly, water dynamics inside the brain is still largely unknown. In 2012, a new concept referred as "glymphatic system" was proposed by Nedergaard's group, where aquaporin4 (AQP4) may play an important role as well as sleep. AQP4 is mainly expressed in the central nervous system, especially in the foot processes of astrocytes; surrounding the capillary, beneath pia matter and lining the ventricles. The unique distribution of AQP4 suggest that AQP4 might play a role in brain water homeostasis. The concept of "glymphatic system" is still controversial, and needs to be clarified with new experimental data. This approach will lead to the better understanding of roles of astrocytes in neurodegenerative diseases and pharmacokinetics inside the brain, and eventually will facilitate the development of new drugs for sleep or mental disorders. It has been accumulating evidence that sleep disturbance is related to several kinds of chronic diseases such as hypertension and diabetes. In addition, the number of patients with dementia are significantly increasing. It is therefore critical to understand the physiological and pathological mechanisms of brain lymphatic system from the medical and social point of views. Here I will discuss about the roles of AQP4 in neurodegenerative diseases and introduce new knowledge regarding to "glymphatic system".

Role of Aquaporins in Cancer Diagnosis and Treatment: A Review

Role of Aquaporins in Cancer Diagnosis and Treatment: A Review

The Relationship between Hematoma Expansion Induced by Hypertension and Hyperglycemia and Blood-Brain Barrier Disruption and Its Possible Mechanism: Role of Aquaporin-4 and Connexin43

The Relationship between Hematoma Expansion Induced by Hypertension and Hyperglycemia and Blood-Brain Barrier Disruption and Its Possible Mechanism: Role of Aquaporin-4 and Connexin43

The brain’sglymphatic system:physiological anatomy and clinical perspectives

The recently discovered glymphatic system (GS) ensures the efficient clearance of interstitial fluid and soluble compounds from the central nervous system into cerebrospinal fluid (CSF), which compensates for the lack of conventional lymphatic vessels in the brain parenchyma. This unique anatomical and physiological phenomenon had been unknown until 2012. GS lacks inherent proper vessels Р the current of CSF and interstitial fluid is carried out directly inside the arterial walls (the perivascular pathway) or near the walls of the cerebral arteries and veins (the paravascular pathway). Current biorheological technologies could establish a special role of aquaporin-4 in the filtration of CSF and interstitial fluid. The close link between GS and the CSF circulatory system allows the established views on fluid dynamics within the brain to be reconsidered. The discovery of GS can contribute to our understanding of the pathogenesis of increased intracranial pressure and neurodegenerative diseases, as well as to the elaboration of new therapeutic approaches to their treatment.

Aquaporins in human platelets: intracellular localization and possible role in granule and lysosome secretion.

This study was undertaken to establish the presence and the role of aquaporins (AQPs) in human platelets. Immunodetection with polyclonal antibodies and fluorescent microscopy suggest the presence of AQP isoforms - 0-7 and 9-12 - localized (in resting platelets) in the plasma membrane and in the dense and alpha granules. In thrombin- or monensin-treated platelets, the granules' AQPs become visible in the whole cell body, indicating the granules' swelling. In our studies on the role of AQPs in platelet responses we used tetrachloroauric acid (HAuCl4), a classical water channel blocker. We found that 10-100 µM of Au(III) inhibited the hypotonicity-, monensin (simulating the action of Na+/H+ exchanger)-, and collagen-evoked platelet swelling and reduced tritiated water uptake by platelets treated by collagen or monensin, indicating its ability to block water channels in these cells. HAuCl4, at the concentrations reducing water influx, did not induce cell lysis, alter the plasma membrane shape or the -SH group content. The inhibitor also failed to affect Na+ and Cl--related osmotic gradient formation and protein kinase D2 phosphorylation. In platelets activated by threshold concentrations of collagen, the thrombin receptor activating peptide, ADP, calcium ionophore A23187, phorbol ester and arachidonic acid, HAuCl4 (100 µM) completely inhibited secretion of ATP from dense granules but failed to reduce platelet aggregation. In collagen-stimulated platelets, HAuCl4 (10-100 µM) reduced secretion from dense and alpha granules, as well as lysosomes, in a dose-dependent manner. We conclude that human platelets possess numerous AQPs subtypes localized in the plasma and granule membranes. AQP-mediated water fluxes may be crucial for platelet volume regulation as well as secretion from dense and alpha granules and lysosomes.

Fluid resuscitation via the rectum ameliorates hemodynamic disorders through adjusting aquaporin expression in an experimental severe acute pancreatitis model

Acute pancreatitis is an acute abdominal disease, with 10-20% of the cases deteriorating rapidly, accompanied by persistent organ failure and further development into severe acute pancreatitis (SAP). The aim of the present study was to investigate the mechanism of fluid resuscitation via the rectum in the early stages of SAP and the role of aquaporins (AQPs). An SAP model was constructed by injection of 5% sterile sodium taurocholate into the biliopancreatic duct of Sprague Dawley rats, and the mean arterial pressure (MAP) was continuously monitored via femoral artery catheterization. At 30 min after the construction of the SAP model, the rats in the fluid resuscitation groups were resuscitated with normal saline at a rate of 4 ml/kg/h through the venous or the rectal route. The AQP and Na+-K+-ATPase levels, and the correlation of the MAP and colon AQPs at the early stages of SAP were analyzed. The results demonstrated that the mRNA level of AQP-3 and AQP-4 in the distal colon decreased significantly in the group subjected to fluid resuscitation via the rectum, while no significant differences were identified in the Na+-K+-ATPase levels of the colon in that group. Furthermore, a negative correlation was identified between the expression of AQPs and the MAP (P<0.01). Thus, fluid resuscitation via the rectum appears to ameliorate hemodynamic disorders through adjusting the expression of AQP-3 and AQP-4 in the distal colon in an experimental SAP model.

Aquaporin 9 Contributes to the Maturation Process and Inflammatory Cytokine Secretion of Murine Dendritic Cells.

Dendritic cells (DCs) are the most potent antigen-presenting cells able to trigger the adaptive immune response to specific antigens. When non-self-antigens are captured, DCs switch from an “immature” to a “mature” state to fulfill their function. Among the several surface proteins involved in DCs maturation, the role of aquaporins (AQPs) is still poorly understood. Here we investigated the expression profile of Aqps in murine bone marrow derived dendritic cells (BMDCs). Among the Aqps analyzed, Aqp9 was the most expressed by DCs. Its expression level was significantly upregulated 6 h following LPS exposure. Chemical inhibition of Aqp9 led to a decreased inflammatory cytokines secretion. BMDCs from AQP9-KO mice release lower amount of inflammatory cytokines and chemokines and increased release of IL-10. Despite the reduced release of inflammatory cytokines, Aqp9-KO mice were not protected from DSS induced colitis. All together, our data indicate that AQP9 blockade can be an efficient strategy to reduce DCs inflammatory response but it is not sufficient to protect from acute inflammatory insults such as DSS induced colitis.

Evidence of positive selection suggests possible role of aquaporins in the water-to-land transition of mudskippers

Aquaporins are integral membrane proteins that exchange water and small solutes. They played an important role in the colonisation of terrestrial environments by tetrapod ancestors via the appearance of three exclusive paralogs. Like early tetrapods, mudskippers represent an independent case of amphibious lifestyle evolution that is unparalleled by other extant fish groups. Given this lifestyle parallelism and that aquaporins were relevant for tetrapod terrestrialisation, this study examines the aquaporins in mudskippers to investigate whether similar changes in aquaporins could have possibly occurred during their water-to-land transition. We have catalogued aquaporin genes in four mudskipper genomes and studied their diversity and molecular evolution (including detection of positive selection) in a broad phylogenetic context of vertebrates. Our genomic screening returned 55 aquaporin genes for mudskippers (none of them constituting novel paralogs) that can be assigned to 10 different known classes. We detected signatures of positive selection in AQP10a and AQP11b in mudskippers (both the entire clade and the clade containing the most terrestrial species, implying different evolutionary times). This suggests possible alteration of the molecular function of such paralogs caused by changes at specific protein sequence positions, some of them located in relatively close proximity to parts of the molecule involved in pore formation and substrate selectivity. Given the importance of aquaporins for osmotic regulation in fishes, it might be possible that these selective changes (perhaps allowing permeability to new solutes) could have played a role during the adaptation of mudskippers to an amphibious lifestyle.