Downregulation of aquaporins (AQPs) in obstructive kidney disease has been well demonstrated with elusive mechanisms. Our previous study indicated that mitochondrial dysfunction played a crucial role ...in this process. However, it is still uncertain how mitochondrial dysfunction affected the AQPs in obstructive kidney disease. This study investigated the role of mitochondria-derived oxidative stress in mediating obstruction-induced downregulation of AQPs. After unilateral ureteral obstruction for 7 days, renal superoxide dismutase 2 (SOD2; mitochondria-specific SOD) was reduced by 85%. Meanwhile, AQP1, AQP2, AQP3, and AQP4 were remarkably downregulated as determined by Western blotting and/or quantitative real-time PCR. Administration of the SOD2 mimic manganese (III) tetrakis(4-benzoic acid)porphyrin chloride (MnTBAP) significantly attenuated AQP2 downregulation in line with complete blockade of thiobarbituric acid-reactive substances elevation, whereas the reduction of AQP1, AQP3, and AQP4 was not affected. The cyclooxygenase (COX)-2/prostaglandin (PG) E
pathway has been well documented as a contributor of AQP reduction in obstructed kidney; thus, we detected the levels of COX-1/2 and microsomal prostaglandin E synthase 1 (mPGES-1) in kidney and PGE
secretion in urine. Significantly, MnTBAP partially suppressed the elevation of COX-2, mPGES-1, and PGE
. Moreover, a marked decrease of V
receptor was significantly restored after MnTBAP treatment. However, the fibrotic response and renal tubular damage were unaffected by MnTBAP in obstructed kidneys. Collectively, these findings suggested an important role of mitochondrial oxidative stress in mediating AQP2 downregulation in obstructed kidney, possibly via modulating the COX-2/mPGES-1/PGE
/V
receptor pathway.
Aquaporins (AQPs) are among the best structural-characterized membrane proteins, fulfilling the role of allowing water flux across cellular membranes. Thus far, 34 single amino acid polymorphisms ...have been reported in HUMSAVAR for human aquaporins as disease-related. They affect AQP2, AQP5 and AQP8, where they are associated with nephrogenic diabetes insipidus, keratoderma and colorectal cancer, respectively. For half of these mutations, although they are mostly experimentally characterized in their dysfunctional phenotypes, a structural characterization at a molecular level is still missing. In this work, we focus on such mutations and discuss what the structural defects are that they appear to cause. To achieve this aim, we built a 3D molecular model for each mutant and explored the effect of the mutation on all of their structural features. Based on these analyses, we could collect the structural defects of all the pathogenic mutations (here or previously analysed) under few main categories, that we found to nicely correlate with the experimental phenotypes reported for several of the analysed mutants. Some of the structural analyses we present here provide a rationale for previously experimentally observed phenotypes. Furthermore, our comprehensive overview can be used as a reference frame for the interpretation, on a structural basis, of defective phenotypes of other aquaporin pathogenic mutants.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
The aquaporins (AQP) are expressed in the human follicle during ovulation with increased expressions of AQP2 and -3 during early stages of ovulation and of AQP1 during corpus luteum formation.
...Context:
Changes in vascular permeability and expansion of the fluid-filled antrum are major events in the LH-induced ovulatory process.
Objectives:
Our objective was to investigate the presence and expression levels of aquaporins (AQPs) in the granulosa and theca cell compartments of the follicle during defined phases of human ovulation.
Design and Setting:
We conducted a prospective experimental study at the Department of Obstetrics and Gynaecology at a university hospital.
Participants:
Twenty-eight women underwent laparoscopic sterilization and at the same time follicle retrieval at four periovulatory phases.
Main Outcome Measures:
mRNA levels of AQP1-4 were measured in separated granulosa and theca cells from preovulatory phase, early ovulatory (EO) phase, late ovulatory phase, and postovulatory phase. Immunohistochemistry was done for AQP1-4 in intact human follicles.
Results:
All four AQPs were expressed in both the theca and granulosa cells during ovulation. In granulosa cells, AQP1 levels increased in the late ovulatory and postovulatory phases. Expression of AQP2-3 followed a similar pattern with a marked increase in the EO phase, whereas AQP4 levels decreased from preovulatory to the EO phase. The presence of AQP1-4 in the human follicle was verified by immunohistochemistry.
Conclusions:
The results show for the first time the presence of AQP1-4 in human follicles during ovulation. The marked early rise in expression of AQP2 and AQP3 suggests a role during the process leading to follicular rupture, and the late rise of AQP1 suggests a role in corpus luteum formation.
Three aquaporins are expressed in the brain. AQP4, the predominant brain water channel, is expressed in astrocyte endfeet facing brain capillaries, perisynaptic spaces, and nodes of Ranvier. It is ...implicated in brain edema formation and resolution. It is also believed to assist clearance of K+ released during neuronal activity. AQP1 is expressed in epithelial cells of choroid plexus and is implicated in cerebrospinal fluid formation. AQP9, which has been reported to be present in astrocytes and in subpopulations of neurons, is implicated in the brain energy metabolism. All three brain AQPs are strongly upregulated in brain tumors and in injured brain tissue.
Water and solute transport via AQPs depends on concentration gradients across the membrane, but the magnitude of the transport is to a large extent determined by the single channel permeability of AQPs and by their abundance in the cell membrane. The future therapies will have to address not only the forces driving the water and solute transport (e.g. as mannitol infusion does in the treatment of brain edema), but also the regulation of AQPs, which provide the means for water entry to the brain, for water exit from the brain, and for redistribution of water and solutes within the brain compartments. This review summarizes the data concerning structure, permeability, role in the brain, short-term and long-term regulation of the three AQPs.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Aquaporins (AQP) conduct small, uncharged molecules, such as water (orthodox AQPs), ammonia (aquaammoniaporins) or glycerol (aquaglyceroporins). The physiological functions of AQPs are involved in ...osmotic volume regulation or the transport of biochemical precursors and metabolic waste products. The recent identification of hydrogen peroxide (H2O2) as a permeant of certain AQPs suggests additional roles in mitigating oxidative stress or enabling paracrine H2O2 signalling. Yet, an analysis of the structural requirements of the H2O2 permeability of AQPs is missing. We subjected a representative set of wild‐type and mutant AQPs to a newly established quantitative phenotypic assay. We confirmed high H2O2 permeability of the human aquaammoniaporin AQP8 and found intermediate H2O2 permeability of the prototypical orthodox water channel AQP1 from the rat. Differences from an earlier report showing an absence of H2O2 permeability of human AQP1 can be explained by expression levels. By generating point mutations in the selectivity filter of rat orthodox aquaporin AQP1, we established a correlation of H2O2 permeability primarily with water permeability and secondarily with the pore diameter. Even the narrowest pore of the test set (i.e. rat orthodox aquaporin AQP1 H180F with a pore diameter smaller than that of natural orthodox AQPs) conducted water and H2O2. We further found that H2O2 permeability of the aquaglyceroporin from the malaria parasite Plasmodium falciparum was lower despite its wider pore diameter. The data suggest that all water‐permeable AQPs are H2O2 channels, yet H2O2 permeability varies with the isoform. Thus, generally, AQPs must be considered as putative players in situations of oxidative stress (e.g. in Plasmodium‐infected red blood cells, immune cells, the cardiovascular system or cells expressing AQP8 in their mitochondria).
Aquaporins are not just water channels, but are also associated with other conductive activities such as the flux of glycerol and ammonia, and more recently hydrogen peroxide (H2O2). Using a cellular assay that probes the H2O2 pressure on yeast growth, Almasalmeh et al. demonstrate that molecular determinants of H2O2 permeability can be pinpointed. These results provide further evidence that different aquaporin isoforms are involved in the cell biology of oxidative stress.
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BFBNIB, DOBA, FZAB, GIS, IJS, IZUM, KILJ, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBMB, SIK, UILJ, UKNU, UL, UM, UPUK
Protein:protein interactions play key functional roles in the molecular machinery of the cell. A major challenge for structural biology is to gain high‐resolution structural insight into how membrane ...protein function is regulated by protein:protein interactions. To this end we present a method to express, detect, and purify stable membrane protein complexes that are suitable for further structural characterization. Our approach utilizes bimolecular fluorescence complementation (BiFC), whereby each protein of an interaction pair is fused to nonfluorescent fragments of yellow fluorescent protein (YFP) that combine and mature as the complex is formed. YFP thus facilitates the visualization of protein:protein interactions in vivo, stabilizes the assembled complex, and provides a fluorescent marker during purification. This technique is validated by observing the formation of stable homotetramers of human aquaporin 0 (AQP0). The method's broader applicability is demonstrated by visualizing the interactions of AQP0 and human aquaporin 1 (AQP1) with the cytoplasmic regulatory protein calmodulin (CaM). The dependence of the AQP0‐CaM complex on the AQP0 C‐terminus is also demonstrated since the C‐terminal truncated construct provides a negative control. This screening approach may therefore facilitate the production and purification of membrane protein:protein complexes for later structural studies by X‐ray crystallography or single particle electron microscopy.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Aquaporins (AQPs) are ubiquitous membrane proteins whose identification, pioneered by Peter Agre's team in the early nineties, provided a molecular basis for transmembrane water transport, which was ...previously thought to occur only by free diffusion. AQPs are members of the Major Intrinsic Protein (MIP) family and often referred to as water channels. In mammals and plants they are present in almost all organs and tissues and their function is mostly associated to water molecule movement. However, recent studies have pointed out a wider range of substrates for these proteins as well as complex regulation levels and pathways. Although their relative abundance in plants and mammals makes it difficult to investigate the role of a particular AQP, the use of knock-out and mutagenesis techniques is now bringing important clues regarding the direct implication of specific AQPs in animal pathologies or plant deficiencies. The present paper gives an overview about AQP structure, function and regulation in a broad range of living organisms. Emphasis will be given on plant AQPs where the high number and diversity of these transport proteins, together with some emerging aspects of their functionalities, make them behave more like multifunctional, highly adapted channels rather than simple water pores.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The present study, using a rodent model of closed-head diffuse traumatic brain injury (TBI), investigated the role of dysregulated aquaporins (AQP) 4 and 9, as well as hypoxia inducible factor - ...1alpha(HIF-1alpha) on brain edema formation, neuronal injury, and functional deficits.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Aquaporins play a crucial role in water homeostasis in the human body, and recently the physiological importance of aquaporins as glycerol channels have been demonstrated. The aquaglyceroporins ...(AQP3, AQP7, AQP9 and AQP10) represent key glycerol channels, enabling glycerol flux across the membranes of cells. Adipocytes are the major source of glycerol and during lipolysis, glycerol is released to be metabolized by other tissues through a well-orchestrated process. Here we show that both AQP3 and AQP7 bind to the lipid droplet protein perilipin 1 (PLIN1), suggesting that PLIN1 is involved in the coordination of the subcellular translocation of aquaglyceroporins in human adipocytes. Moreover, in addition to aquaglyceroporins, we discovered by transcriptome sequencing that AQP1 is expressed in human primary adipocytes. AQP1 is mainly a water channel and thus is thought to be involved in the response to hyper-osmotic stress by efflux of water during hyperglycemia. Thus, this data suggests a contribution of both orthodox aquaporin and aquaglyceroporin in human adipocytes to maintain the homeostasis of glycerol and water during fasting and feeding.
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•Orthodox aquaporins and aquaglyceroporins are expressed in human primary adipocytes.•Overexpression of the human lipid droplet protein perilipin 1 in E.coli.•Aquaglyceroporins bind to the C-terminus of perilipin 1.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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