Changes In Aquaporin Expression Research Articles

Combined Soil Microorganism Amendments and Foliar Micronutrient Nanofertilization Increased the Production of Allium cepa L. through Aquaporin Gene Regulation.

The aim of this study was to investigate the impact of changes in aquaporin expression on the growth of onion (Allium cepa L.) plants when subjected to dual applications of microorganism-based soil amendments and foliar nanoencapsulated mineral nutrients. Multiple physiological parameters related to water, gas exchange, and nutrient content in leaf, root, and bulb tissues were determined. Additionally, the gene expression of aquaporins, specifically PIP1, PIP2 (aquaporin subfamily plasma membrane intrinsic protein), and TIP2 (aquaporin subfamily tonoplast intrinsic protein), was analyzed. The findings revealed that the foliar application of nutrients in a nanoencapsulated form significantly enhanced nutrient penetration, mobilization, and overall plant growth to a greater extent than free-form fertilizers. Amendments with microorganisms alone did not promote growth but influenced the production of secondary metabolites in the bulbs. The combination of microorganisms and nanoencapsulated mineral nutrients demonstrated synergistic effects, increasing dry matter, mineral content, and aquaporin gene expression. This suggests that aquaporins play a pivotal role in the transport of nutrients from leaves to storage organs, resulting in the overexpression of PIP2 aquaporins in bulbs, improved water uptake, and enhanced cell growth. Therefore, the combined treatment with microorganisms and nanoencapsulated mineral nutrients may be an optimal approach for enhancing onion productivity by regulating aquaporins under field conditions.

Aquaporin-mediated dysregulation of cell migration in disease states.

Dysregulated cell migration and invasion are hallmarks of many disease states. This dysregulated migratory behavior is influenced by the changes in expression of aquaporins (AQPs) that occur during pathogenesis, including conditions such as cancer, endometriosis, and arthritis. The ubiquitous function of AQPs in migration of diseased cells makes them a crucial target for potential therapeutics; this possibility has led to extensive research into the specific mechanisms underlying AQP-mediated diseased cell migration. The functions of AQPs depend on a diverse set of variables including cell type, AQP isoform, disease state, cell microenvironments, and even the subcellular localization of AQPs. To consolidate the considerable work that has been conducted across these numerous variables, here we summarize and review the last decade's research covering the role of AQPs in the migration and invasion of cells in diseased states.

Changes in aquaporins expression due to acute water restriction in naturally aging mice.

Aquaporins (AQPs) are water channels in the cell membrane that regulate osmosis in response to rapid changes in intracellular and extracellular fluid concentration caused by extrinsic factors. While there are so many studies on the association of AQPs with muscular atrophy, sarcopenia, and Duchenne muscular dystrophy (DMD), the expression of AQP has not been verified in naturally aging mice or humans. Notably, due to the characteristics of AQPs, the difference in function cannot be evaluated without extrinsic factors such as acute water restriction. The purpose of this study was to investigate the changes in AQPs expression and function due to natural aging under acute water restriction conditions in aging mice. The expression of AQP4 was shown to decrease with aging similar to previous studies. However, for the first time, this study results confirmed that AQP1 expression increased in aging mice. In addition, the expression of Aqp1 decreased in the acute water restricted group compared to the control group after acute water restriction in aging mice. These results suggest that although the expression of AQP1 increases with aging, its function is reduced. We also confirmed that overexpression of Aqp1 can inhibit myotube differentiation and that knockdown can promote myotube differentiation through in vitro experiments. In conclusion, based on our results, we suggest that the AQP1 is an important factor in sarcopenia caused by natural aging accompanied by chronic dehydration.

Differential regulation of the water channel protein aquaporins in chondrocytes of human knee articular cartilage by aging

Knee cartilage is in an aqueous environment filled with synovial fluid consisting of water, various nutrients, and ions to maintain chondrocyte homeostasis. Aquaporins (AQPs) are water channel proteins that play an important role in water exchange in cells, and AQP1, -3, and -4 are known to be expressed predominantly in cartilage. We evaluated the changes in AQP expression in chondrocytes from human knee articular cartilage in patients of different ages and identified the key factor(s) that mediate age-induced alteration in AQP expression. The mRNA and protein expression of AQP1, -3 and -4 were significantly decreased in fibrocartilage compared to hyaline cartilage and in articular cartilage from older osteoarthritis patients compared to that from young patients. Gene and protein expression of AQP1, -3 and -4 were altered during the chondrogenic differentiation of C3H10T1/2 cells. The causative factors for age-associated decrease in AQP included H2O2, TNFα, and HMGB1 for AQP1, -3, and -4, respectively. In particular, the protective effect of AQP4 reduction following HMGB1 neutralization was noteworthy. The identification of other potent molecules that regulate AQP expression represents a promising therapeutic approach to suppress cartilage degeneration during aging.

Cooling Treatment Induces Changes in Aquaporins Expression as a Protective Mechanism for Exertional Heat Stroke

Xiuzhen Liu1, Bing Zhang1, Yuanlong Liu2, Liye Zou3. 1Tsinghua University, Beijing, China.2Western Michigan University, Michigan, MI.3The Chinese University of Hong Kong, Hong Kong, China. (Sponsor: Yuanlong Liu, FACSM) ABSTRACT: Cooling treatment is important to ensure the survival of patients with Exertional Heat Stroke(EHS); however, the protective mechanism of aquaporins in the cooling treatment of EHS is not very clear. Cooling treatment induces changes in renal aquaporins and regulates homeostasis of water metabolism,which mechanism involves aquaporin gene expression. PURPOSE: To determine the role of AQP2 mRNA expression and AQP2 protein expression in kidney in the homeostasis of water metabolism when EHS rats were treated with cooling. METHODS: In this study, there were 4 groups of male SD rats, including normal control group(NC,n=8), EHS onset group(EHSO,n=9), EHS rest group(EHSR n=9) and EHS cooling group(EHSC,n = 8). We established the rat model of EHS by exercising to exhaustion in the environment of 36°C temperature and 75% humidity until rectal temperature reaching about 42°C. The cooling treatment for EHS was to immerse in cold water for 5 minutes at 19°C. Blood and kidney were taken. Hct in serum was measured by automatic blood cell analyzer. PCR and WB were used to detect AQP2 mRNA expression and AQP2 protein expression respectively. Data were analyzed with Mann-Whitney U in nonparametric test. RESULTS: When EHS occurs, Hct increased significantly(EHSO: 0.43±0.29 vs. 0.40±0.04L/L,p<0.05). To fit for water metabolism, AQP2 mRNA expression and AQP2 protein expression were up-regulated significantly (EHSO vs. NC)(mRNA: 3.45±0.95 vs. 1.19±0.37, p<0.01; Protein: 2.76±1.01 vs. 1.00±0.00g/L, p<0.01). After cold water immersion, No significant change of Hct was found, AQP2 mRNA expression and AQP2 protein expression were significantly down-regulated(EHSC vs. EHSO)(mRNA: 1.66±0.33 vs. 3.45±0.95, p<0.01; Protein: 1.52±0.85 vs. 2.76±1.01g/L, p<0.05). CONCLUSIONS: Hct, AQP2 mRNA expression and AQP2 protein expression are pathophysiological biomarkers of EHS. Cooling treatment restrain water reabsorption by down-regulating the expression of AQP2 mRNA and AQP2 protein in kidney.

Involvement of aquaporins on nitrogen-acquisition strategies of juvenile and adult plants of an epiphytic tank-forming bromeliad.

Depending on the N source and plant ontogenetic state, the epiphytic tank-forming bromeliad Vriesea gigantea can modulate aquaporin expression to maximize the absorption of the most available nitrogen source. Epiphytic bromeliads frequently present a structure formed by the overlapping of leaf bases where water and nutrients can be accumulated and absorbed, called tank. However, this structure is not present during the juvenile ontogenetic phase, leading to differences in nutrient acquisition strategies. Recent studies have shown a high capacity of the bromeliad Vriesea gigantea, an epiphytic tank-forming bromeliad, to absorb urea by their leaves. Since plant aquaporins can facilitate the diffusion of urea through the membranes, we cloned three foliar aquaporin genes, VgPIP1;1, VgPIP1;2 and VgTIP2;1 from V. gigantea plants. Through functional studies, we observed that besides water, VgTIP2;1 was capable of transporting urea while VgPIP1;2 may facilitate ammonium/ammonia diffusion. Moreover, aiming at identifying urea and ammonium-induced changes in aquaporin expression in leaves of juvenile and adult-tank plants, we showed that VgPIP1;1 and VgPIP1;2 transcripts were up-regulated in response to either urea or ammonium only in juvenile plants, while VgTIP2;1 was up-regulated in response to urea only in adult-tank plants. Thereby, an ontogenetic shift from juvenile to adult-tank-forming-plant appears to occur with metabolic changes regarding nitrogen metabolism regulation. Investigating urea metabolism in wild species that naturally cope with organic N sources, such as V. gigantea, may provide the knowledge to modify nitrogen use efficiency of crop plants.

Modulation of aquaporins expressions and its impact on alleviating diabetic complications in rats: role of Citrullus colocynthis

Background: Aquaporins (AQPs) belong to a class of small, integral membrane proteins that enable water transfer across the plasma membranes of cells as a reaction to osmotic gradients. There are 13 known types of AQPs in humans (AQP0 to AQP12), which are expressed in various organs such as the kidney, brain, liver, lungs, and salivary glands. In patient with diabetes mellitus, a reduction in salivary secretion is noted in concurrence with low salivary AQP5 levels. The Citrullus colocynthis (CC) extracts were reported to have beneficial effects on glucose homeostasis and body weight maintenance, in either alloxan- or streptozotocin (STZ)-induced diabetic rats through exerting insulinotropic effect. Aims and Objective: To check the changes in AQPs expression and to understand the antidiabetic effect of CC as a medicinal herb in STZ-induced diabetic rats. Materials and Methods: Forty-two male Wistar rats were assigned equally into six groups. The first and second groups were kept as control groups: the first remained without treatment, but the second received CC orally. Diabetes was induced by a single intraperitoneal (i.p) injection of STZ (60 mg/kg b.w.) in the remaining four groups. Three diabetic groups were treated with insulin or CC or both together for 4 weeks. The remaining diabetic group was left untreated as control diabetic group. Blood and organs were taken for biochemical, gene expression, and immunohistochemistry examinations. Result: Diabetic rats displayed increases in blood glucose, lipid profile, liver, and kidney parameters, which were restored significantly to normal with insulin or CC or both. At molecular level, diabetic rats showed significant downregulation in mRNA expressions of antioxidant enzymes, insulin receptor substrate 1 and 2, pyruvate kinase, GLUT-2 in liver and of AQP1, AQP5, AQP7, and AQP8 expressions in kidney, salivary gland, and pancreas, respectively, and normalized significantly by insulin or CC or in combination administrations. Expressions of phosphoenol pyruvate carboxykinase in liver and of AQP2 and AQP3 in kidney were upregulated in diabetic rats and returned to normal completely by insulin alone or CC or their combination. Values were statistically significant at p < 0.05. Immunohistochemical examinations revealed a downregulation of insulin and GLUT-2 in pancreas and upregulation of AQP2 in kidney of diabetic rats, but treatments with CC augmented insulin effect and restored their expression to normal levels. Conclusion: Current results concluded that AQPs could be a promising target for drug development. Moreover, Citrullus colocynthis extract acts as antidiabetic medicinal herb, which has been confirmed by its molecular and immunohistochemical effects.

The gene expression of aquaporins in various cutaneous tissues of the mouse

Objective: Aquaporins (AQP) are a family of water-transporting proteins that are expressed in many cell types where they play important physiological functions. The accurate distribution of AQP gene expression has not yet been examined in various cutaneous tissues of the mouse. Changes in AQP expression have been useful for understanding their functions. Due to the lack of information regarding the cutaneous tissue distribution of AQP genes, we first evaluated the cutaneous tissue distribution of AQP gene expression. Methods: To study the expression of potential reference genes and to validate the most stable ones as internal standards in the various cutaneous tissues, raw values were analyzed. The gene expression of AQPs in various cutaneous tissues was analyzed quantitatively by real-time reverse transcription polymerase chain reaction (RT-PCR). Results: The expression orders of AQP3 and 9 genes were tail = paw skin > auricle > abdominal skin > dorsal skin and abdominal skin > auricle = tail > dorsal skin > paw skin. The AQP4 gene was found in the dorsal and abdominal cutaneous tissues. The gene expression of AQP5 was expressed in only paw skins. The AQP6 gene was not found in all cutaneous tissues. The AQP0, 7, 8, 11 and 12 gene expressions were comparatively much lower in all cutaneous tissues. Conclusion: The present study suggests that multiple AQPs exist in the various skins.

Lipopolysaccharide decreases aquaporin 5, but not aquaporin 3 or aquaporin 4, expression in human primary bronchial epithelial cells

The aim of this study was to investigate the changes in expression of aquaporins (AQP) during differentiation of human bronchial epithelial cells and the role of lipopolysaccharide (LPS) in AQP expression. The levels of AQP3, AQP4 and AQP5 transcripts in human primary cultured bronchial epithelial cells were evaluated by real-time polymerase chain reaction at different time points before and after treatment with LPS. Western blotting was performed to assess the effects of LPS on AQP3, AQP4 and AQP5 expressions in normal human bronchial epithelial cells. Using pharmacological tools, the pathways involved in the regulation of LPS-induced changes in AQP5 were further explored. The levels of AQP3, AQP4 and AQP5 transcripts were increased during differentiation of human bronchial epithelial cells. Expression of AQP5, but not AQP3 or AQP4, was downregulated by LPS. LPS-induced downregulation of AQP5 was inhibited by p38 and c-Jun N-terminal kinase (JNK) inhibitors. This study demonstrated that LPS decreases AQP5, but not AQP3 or AQP4, expression in human primary bronchial epithelial cells. The downregulation of AQP5 expression is mediated through a p38/JNK signalling pathway.

Transient hyperosmolality modulates expression of cardiac aquaporins

PurposeHyperosmolarity is a common complication in intensive care patients, dysregulating water balance in many organs including brain and heart. The aquaporin (AQP) water channels, in particular AQP1 and −4, have been suggested to play an important role in fluid homeostasis of the myocardium. In many organs AQP expression is regulated by osmolarity, drastically altering water permeability of the cell membranes. The aim of our study was to investigate if plasma hyperosmolality may regulate cardiac expression of AQP1 and −4, and if so, at which magnitude and time frame such regulation takes place. MethodsC57Bl6 mice were injected intraperitoneally with either 1.5ml 0.154Mol (isoosmotic), 0.5ml 1Mol (mild hyperosmotic) or 0.5ml 2Mol (strong hyperosmotic) NaCl. Plasma, hearts, and forebrains were harvested before injection (“time 0”), and after 1, 4, 8 and 24h. AQP1 and −4 expression were analyzed using qPCR and Western blot. ResultsIsoosmotic and mild hyperosmotic injections caused no important changes in cardiac AQP expression. Strong hyperosmotic NaCl injections induced an upregulation of AQP1 mRNA and glycosylated fraction of AQP1 protein in the heart without changes of the total protein. AQP4 mRNA and protein decreased in the heart and increased in the brain after hyperosmotic NaCl. The change in AQP4 protein content in the brain preceded the increase of mRNA. ConclusionAs in the brain, expression of AQP1 and −4 in the heart is influenced by changes in plasma osmolality. Changes in AQP expression may alter cardiac function in hyperosmotic states.

Aquaporin Changes during Diabetic Retinopathy in Rats Are Accelerated by Systemic Hypertension and Are Linked to the Renin-Angiotensin System

We explored the relationship between the renin-angiotensin system (RAS) and aquaporins (AQP1 and AQP4 in Müller glia and astrocytes) in diabetic retinopathy (DR) with and without systemic hypertension. Diabetes was induced in spontaneously hypertensive rats (SHR) and normotensive control Wistar Kyoto (WKY) rats by intraperitoneal injections of streptozotocin. The diabetic and control non-diabetic rats were assigned randomly to receive no anti-hypertension treatment, or to be treated with the angiotensin II receptor blocker (ARB), valsartan (40 mg/kg/d) or the beta-blocker, metoprolol (50 mg/kg/day). Eight weeks later, retinas were evaluated by immunohistochemistry and Western blot to detect changes in the expression of AQP1, AQP4, and glial fibrillary acidic protein (GFAP). Hypertension increased expression of glial GFAP and AQP4 (P < 0.01), but not AQP1 (P > 0.05) in diabetic rats. Valsartan and metoprolol decreased GFAP, AQP1, and AQP4 expression in diabetic SHR rats (P < 0.01). Valsartan decreased GFAP and AQP1 expression in diabetic WKY rats (P < 0.01), while metoprolol did not. Activation of Müller glia and astrocytes was involved in the mechanism by which systemic hypertension affects DR. AQPs and macroglia were linked to changes in the RAS in DR. Changes in aquaporin expression in DR were increased by hypertension. This provides additional support for the early use of an ARB in the treatment of DR, especially in cases with retinal edema.

Effect of Hyperglycemia on Expression of Aquaporins in the Rat Vagina

To investigate the effect of hyperglycemia on the expression of the aquaporin (AQP) isoforms in the diabetic rat vagina. Female Sprague-Dawley rats (230-240 g, n = 45) were divided into control (n = 10) and experimental (n = 35) groups. Diabetes in the experimental group was induced by intraperitoneal injection of streptozotocin (STZ, 65 mg/kg). STZ-induced diabetic rats were left untreated or given subcutaneous injections of insulin (3 U/d). After 2 and 4 weeks, the blood glucose was measured, and the vaginal blood flow was assessed by Doppler flowmetry. The expression and cellular localization of AQP1 and AQP2 in the rat vagina were determined by Western blot and immunohistochemistry. The vaginal blood flow (mL/min/100 g tissue) after pelvic nerve stimulation was significantly lower in the STZ-induced diabetic rats (21.9 ± 6.5 at 2 weeks and 21 ± 2.8 at 4 weeks) compared with the control group (55.5 ± 8.9 at 2 weeks and 52.9 ± 6.5 at 4 weeks; P < .05). In contrast, the vaginal blood flow response was significantly greater in the insulin-treated diabetic groups (47.7 ± 8.7 at 2 weeks and 47.7 ± 8.4 at 4 weeks) and comparable to that of the control group. The protein expression of AQP2 was significantly lower in the STZ-induced diabetic rats and was restored to the control level after insulin treatment. However, no change was seen in AQP1 expression. Thus, hyperglycemia might cause downregulation of AQP2 expression in the diabetic rat vagina. These results suggest that decreased vaginal lubrication in diabetic women might result from changes in aquaporin expression, in addition to a reduction in the vaginal blood flow response.

Altered aquaporin expression and role in apoptosis during hepatic stellate cell activation

Hepatic stellate cells (HSCs) are effector cells of hepatic fibrosis contributing to excessive collagen deposition and scar matrix formation. Sustained HSC activation leads to hepatic cirrhosis, a leading cause of liver-related death. Reversal of hepatic fibrosis has been attributed to the induction of HSC apoptosis. Aquaporins (AQPs) are critical proteinacious channels that mediate cellular water loss during the initiation and progression of apoptosis. This study examined AQP expression in quiescent and activated HSCs and determined the responsiveness to AQP-dependent apoptosis. Aquaporin gene and protein expressions in quiescent and activated HSCs were determined by reverse transcription polymerase chain reaction and Western blot analyses. AQP function was determined by cell swelling and apoptotic assays in the absence and presence of HgCl(2) , a non-specific AQP inhibitor. In this study, we report that activated HSCs showed no detectable expression of AQP 1, 5, 8, 9 and 12 mRNAs but expression was observed in quiescent HSCs. Similarly, AQP 0, 1, 8 and 9 protein was not detected in activated HSCs but was measured in quiescent HSCs. Dual fluorescent immunohistochemistry confirmed that AQP expression is decreased in activated HSCs in a model of liver injury. Functional studies demonstrated that quiescent HSCs were highly susceptible to osmotic challenge and apoptotic stimulus, whereas activated HSCs were less responsive. Finally, apoptosis was abrogated by the inhibition of AQP-dependent water movement. These findings demonstrate that increased resistance to apoptosis in activated HSCs is due, at least in part, to the changes in AQP expression and function that occur following HSC activation.

Influence of nitrogen fertilization on xylem traits and aquaporin expression in stems of hybrid poplar

We studied the influence of nitrogen (N) on hydraulic traits and aquaporin (AQP) expression in the stem xylem of hybrid poplar saplings (Populus trichocarpa (Torr. & Gray) x deltoides Bartr. ex Marsh clone H11-11). Plants were grown in a controlled environment and were kept well watered throughout the experiments. Hydraulic measurements were done on basal and distal stem segments of plants receiving high N fertilization (high N plants) versus plants receiving only adequate N fertilization (adequate N plants). High N plants grew faster and exhibited more leaf area than adequate N controls. These morphological differences were paralleled by wider vessels and higher specific conductivities (K(S)) in high N plants. However, stems of high N plants were more vulnerable to xylem cavitation, at least in one of two experiments, and showed lower wood densities than stems of adequate N plants. Leaf area was strongly correlated with cross-sectional xylem area in both plant groups. Since higher K(S) in high N plants was accompanied by concomitant increases in leaf area, leaf-specific conductivities were similar in both plant groups. Influences of N on hydraulic traits were paralleled by changes in AQP expression. Seven AQPs were upregulated in the stem xylem of high N plants, five of which have been identified recently as water transporters. The enhanced growth of secondary xylem of high N plants has been shown to result from both increased cambial activity as well as increased cell size. We suggest that some of these water-transporting AQPs could play a role in xylogenesis, facilitating the influx of water into the zone of differentiating and maturing cells in secondary xylem, including expanding vessels.

Effect of salinity on water relations of wild barley plants differing in salt tolerance.

Certain lines of wild barley (Hordeum spontaneum) are more tolerant of salinity than others. The physiological basis of this difference is examined in a comparative study of a saline-tolerant and saline-intolerant line that emphasizes plant water relations. Effects of salt-treatment (75 mM maximum) extending from a few hours to 3 weeks were quantified in 8-day-old seedlings of a saline-sensitive wild barley line ('T-1') and a less saline-sensitive line ('20-45'). Plants were grown in nutrient culture. Levels of mRNA of the HtPIP2;4 aquaporin (AQP) gene were determined together with a range of physiological responses including root hydraulic conductivity, osmotic potential of root xylem sap, transpiration, leaf relative water content, root water content, leaf water potential, leaf sap osmolality, leaf length, leaf area and chlorophyll content. Salt treatment inhibited transpiration and hydraulic conductivity more in salt-tolerant '20-45' plants than in salt-sensitive 'T-1'. In '20-45', the effect was paralleled by a fast (within a few hours) and persistent (3 days) down-regulation of aquaporin. In salt-sensitive 'T-1' plants, aquaporin down-regulation was delayed for up to 24 h. Greater tolerance in '20-45' plants was characterized by less inhibition of leaf area, root fresh weight, leaf water content and chlorophyll concentration. Leaf water potentials were similar in both lines. (i) Decline in hydraulic conductivity in salt-treated barley plants is important for stomatal closure, (ii) lowered transpiration rate is beneficial for salt tolerance, at least at the seedling stage and (iii) changes in AQP expression are implicated in the control of whole plant hydraulic conductivity and the regulation of shoot water relations.

Effect of hyperosmotic stimulation on aquaporins gene expression in chick kidney

Birds can produce hyperosmotic urine, but their renal morphology differs from that of mammals. Recent studies in mammals, suggested that various aquaporins (AQPs) are present in the kidney and play crucial roles in urine production. To elucidate the role of AQPs in the avian kidney, we first examined for the presence of AQP1, 2, 3, 4, 7 and 9 mRNAs in the chick ( Gallus gallus) kidney by RT-PCR analysis. Next, we quantified variations of AQPs mRNAs levels in chick kidney after hyperosmotic stimulation (water-deprivation or salt-loading) by real-time RT-PCR analysis. Our study showed that in addition to AQP1, 2, 3, 4 and 7, chick kidney also expressed AQP9 and that hyperosmotic stimulation induced changes in AQPs expression. In particular, water-deprivation increased AQP2 and AQP3 mRNAs levels, whereas salt-loading induced a significant increase in AQP1, AQP2 and AQP9 mRNAs levels. AQP4 and AQP7 mRNA levels were not affected by any hyperosmotic stimulation. Taken together, these results indicated that the presence of AQPs in chick kidney is similar to that in mammals, that the chick kidney has an additional AQP9 and that AQP1, 2, 3 and 9 may play a crucial but different role in water permeability in this organ.

Ion channels profile expression in vestibular endorgans of patients with Meniere's disease and acoustic neuroma.

The regulation of ion concentration in the endolymph (K+, Na+, Ca2+ and pH homeostasis) and water permeability are critical for normal function of the vestibular endorgans (VE). Ion channels, transporters, cotransporters and aquaporins are involved in the homeostatic ionic concentration of endolymph. The gene expression profile of these molecules was investigated in utricular macula obtained in surgery for acoustic neuroma (AN) and compared with utricular macula obtained from patients with Meniere's disease (MD). We found in MD patients an up‐regulation of Na(+)/K(+)‐ATPase cotransporter, voltage gated Na+, neuronal Ca++, and K+ neuronal channels. In contrast, we found a down‐regulation of Cl− channels, vesicular monoamine transporters and neurotransmitter transporters to GABA, dopamine, serotonin and glycine. Finally, no significant changes in expression of aquaporins 1, 4 or 6 were detected in utricles form MD patients compared with the AN patients.

Early effects of salinity on water transport in Arabidopsis roots. Molecular and cellular features of aquaporin expression.

Aquaporins facilitate the uptake of soil water and mediate the regulation of root hydraulic conductivity (Lp(r)) in response to a large variety of environmental stresses. Here, we use Arabidopsis (Arabidopsis thaliana) plants to dissect the effects of salt on both Lp(r) and aquaporin expression and investigate possible molecular and cellular mechanisms of aquaporin regulation in plant roots under stress. Treatment of plants by 100 mm NaCl was perceived as an osmotic stimulus and induced a rapid (half-time, 45 min) and significant (70%) decrease in Lp(r), which was maintained for at least 24 h. Macroarray experiments with gene-specific tags were performed to investigate the expression of all 35 genes of the Arabidopsis aquaporin family. Transcripts from 20 individual aquaporin genes, most of which encoded members of the plasma membrane intrinsic protein (PIP) and tonoplast intrinsic protein (TIP) subfamilies, were detected in nontreated roots. All PIP and TIP aquaporin transcripts with a strong expression signal showed a 60% to 75% decrease in their abundance between 2 and 4 h following exposure to salt. The use of antipeptide antibodies that cross-reacted with isoforms of specific aquaporin subclasses revealed that the abundance of PIP1s decreased by 40% as early as 30 min after salt exposure, whereas PIP2 and TIP1 homologs showed a 20% to 40% decrease in abundance after 6 h of treatment. Expression in transgenic plants of aquaporins fused to the green fluorescent protein revealed that the subcellular localization of TIP2;1 and PIP1 and PIP2 homologs was unchanged after 45 min of exposure to salt, whereas a TIP1;1-green fluorescent protein fusion was relocalized into intracellular spherical structures tentatively identified as intravacuolar invaginations. The appearance of intracellular structures containing PIP1 and PIP2 homologs was occasionally observed after 2 h of salt treatment. In conclusion, this work shows that exposure of roots to salt induces changes in aquaporin expression at multiple levels. These changes include a coordinated transcriptional down-regulation and subcellular relocalization of both PIPs and TIPs. These mechanisms may act in concert to regulate root water transport, mostly in the long term (> or =6 h).

Changes in aquaporin expression in the inner ear of the rat after i.p. injection of steroids

The aquaporins (AQPs) are a family of small transmembrane water transporters. It has recently been revealed that they play a role in regulating homeostasis in the inner ear fluids. Steroid therapy is usually administered to patients with inner ear disorders; however, the mechanism of steroid effects has not been clearly determined. To elucidate the points of action of steroids in the inner ear, we recently examined the distributions of AQP isoform mRNAs in the rat inner ear and identified AQP1–6 mRNAs in the rat cochlea and AQP1, 3, 4, 5 and 6 mRNAs in the rat endolymphatic sac by means of reverse transcriptase polymerase chain reaction (PCR). In this study, we investigated changes in expression of AQP mRNAs in the rat inner ear after i.p. injections of steroids using real-time quantitative PCR and found that AQP3 mRNA in the endolymphatic sac was significantly upregulated in both dose- and time-dependent manners. This result suggests that steroids may effect water homeostasis in the rat inner ear via AQPs.

Molecular Mechanisms and Drug Development in Aquaporin Water Channel Diseases: Aquaporins in the Brain

Water homeostasis of the brain is essential for its neuronal activity. Changes in water content in the intra- and extra-cellular space affect ionic concentrations and therefore modify neuronal activity. Aquaporin (AQP) water channels may have a central role in keeping water homeostasis in the brain. Among AQP subtypes cloned in mammalian, only AQP1, AQP4, and AQP9 were identified in the brain. Changes in AQP expression may be correlated with edema formation of the brain. In this review, we describe the physiological function of AQPs and the regulatory mechanism of their expression in the brain.