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Importance of Water Transport in Mammalian Female Reproductive Tract. Vet Sci 2023; 10:vetsci10010050. [PMID: 36669051 PMCID: PMC9865491 DOI: 10.3390/vetsci10010050] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2022] [Revised: 12/26/2022] [Accepted: 12/30/2022] [Indexed: 01/13/2023] Open
Abstract
Aquaporins (AQPs) are involved in water homeostasis in tissues and are ubiquitous in the reproductive tract. AQPs are classified into classical aquaporins (AQP0, 1, 2, 4, 5, 6 and 8), aquaglycerolporins (AQP3, 7, 9, and 10) and superaquaporins (AQP11 and 12). Nine AQPs were described in the mammalian female reproductive tract. Some of their functions are influenced by sexual steroid hormones. The continuous physiological changes that occur throughout the sexual cycle, pregnancy and parturition, modify the expression of AQPs, thus creating at every moment the required water homeostasis. AQPs in the ovary regulate follicular development and ovulation. In the vagina and the cervix, AQPs are involved mainly in lubrication. In the uterus, AQPs are mostly mediated by estradiol and progesterone to prepare the endometrium for possible embryo implantation and fetal development. In the placenta, AQPs are responsible for the fluid support to the fetus to maintain fetal homeostasis that ensures correct fetal development as pregnancy goes on. This review is focused on understanding the role of AQPs in the mammalian female reproductive tract during the sexual cycle of pregnancy and parturition.
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Lei L, Huang M, Su L, Xie D, Mamuya FA, Ham O, Tsuji K, Păunescu TG, Yang B, Lu HAJ. Manganese promotes intracellular accumulation of AQP2 via modulating F-actin polymerization and reduces urinary concentration in mice. Am J Physiol Renal Physiol 2017; 314:F306-F316. [PMID: 29046300 DOI: 10.1152/ajprenal.00391.2017] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
Aquaporin-2 (AQP2) is a water channel protein expressed in principal cells (PCs) of the kidney collecting ducts (CDs) and plays a critical role in mediating water reabsorption and urine concentration. AQP2 undergoes both regulated trafficking mediated by vasopressin (VP) and constitutive recycling, which is independent of VP. For both pathways, actin cytoskeletal dynamics is a key determinant of AQP2 trafficking. We report here that manganese chloride (MnCl2) is a novel and potent regulator of AQP2 trafficking in cultured cells and in the kidney. MnCl2 treatment promoted internalization and intracellular accumulation of AQP2. The effect of MnCl2 on the intracellular accumulation of AQP2 was associated with activation of RhoA and actin polymerization without modification of AQP2 phosphorylation. Although the level of total and phosphorylated AQP2 did not change, MnCl2 treatment impeded VP-induced phosphorylation of AQP2 at its serine-256, -264, and -269 residues and dephosphorylation at serine 261. In addition, MnCl2 significantly promoted F-actin polymerization along with downregulation of RhoA activity and prevented VP-induced membrane accumulation of AQP2. Finally, MnCl2 treatment in mice resulted in significant polyuria and reduced urinary concentration, likely due to intracellular relocation of AQP2 in the PCs of kidney CDs. More importantly, the reduced urinary concentration caused by MnCl2 treatment in animals was not corrected by VP. In summary, our study identified a novel effect of MnCl2 on AQP2 trafficking through modifying RhoA activity and actin polymerization and uncovered its potent impact on water diuresis in vivo.
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Affiliation(s)
- Lei Lei
- Department of Pharmacology, School of Basic Medical Sciences, Peking University , Beijing , People's Republic of China.,Program in Membrane Biology, Center for Systems Biology, and Division of Nephrology, Department of Medicine, Massachusetts General Hospital , Boston, Massachusetts
| | - Ming Huang
- Department of Pharmacology, School of Basic Medical Sciences, Peking University , Beijing , People's Republic of China.,Program in Membrane Biology, Center for Systems Biology, and Division of Nephrology, Department of Medicine, Massachusetts General Hospital , Boston, Massachusetts
| | - Limin Su
- Department of Pharmacology, School of Basic Medical Sciences, Peking University , Beijing , People's Republic of China.,Program in Membrane Biology, Center for Systems Biology, and Division of Nephrology, Department of Medicine, Massachusetts General Hospital , Boston, Massachusetts
| | - Dongping Xie
- Program in Membrane Biology, Center for Systems Biology, and Division of Nephrology, Department of Medicine, Massachusetts General Hospital , Boston, Massachusetts
| | - Fahmy A Mamuya
- Program in Membrane Biology, Center for Systems Biology, and Division of Nephrology, Department of Medicine, Massachusetts General Hospital , Boston, Massachusetts.,Harvard Medical School , Boston, Massachusetts
| | - Onju Ham
- Program in Membrane Biology, Center for Systems Biology, and Division of Nephrology, Department of Medicine, Massachusetts General Hospital , Boston, Massachusetts.,Harvard Medical School , Boston, Massachusetts
| | - Kenji Tsuji
- Program in Membrane Biology, Center for Systems Biology, and Division of Nephrology, Department of Medicine, Massachusetts General Hospital , Boston, Massachusetts.,Harvard Medical School , Boston, Massachusetts
| | - Teodor G Păunescu
- Program in Membrane Biology, Center for Systems Biology, and Division of Nephrology, Department of Medicine, Massachusetts General Hospital , Boston, Massachusetts.,Harvard Medical School , Boston, Massachusetts
| | - Baoxue Yang
- Department of Pharmacology, School of Basic Medical Sciences, Peking University , Beijing , People's Republic of China
| | - Hua A Jenny Lu
- Program in Membrane Biology, Center for Systems Biology, and Division of Nephrology, Department of Medicine, Massachusetts General Hospital , Boston, Massachusetts.,Harvard Medical School , Boston, Massachusetts
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Kobayashi M, Igarashi T, Takahashi H, Fujimoto C, Suzuki H, Takahashi H. The correlation between plasma osmolarity and tear osmolarity. Int Ophthalmol 2017; 38:493-501. [PMID: 28255838 DOI: 10.1007/s10792-017-0484-8] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2016] [Accepted: 02/24/2017] [Indexed: 12/16/2022]
Abstract
PURPOSE To the correlation between plasma osmolarity (Posm) and tear osmolarity (Tosm) in patients (54 patients, 88 eyes) who underwent cataract surgery was evaluated. METHODS Before cataract surgery, routine pre-operative biochemical tests were performed, and Posm was determined from blood samples. Also, Tosm was measured using the TearLab system, and objective signs including tear break-up time (BUT), fluorescein staining, lissamine green staining, and Schirmer's test were evaluated. Dry eye (DE) was diagnosed according to the Japanese criteria for DE. RESULTS Of the 88 eyes, 4 were diagnosed as definite DE, 70 as probable DE, and 14 as normal. Since the number of definite DE was small, the eyes were divided into two groups: normal group (n = 14) and DE group (n = 74), which included definite DE (n = 4) and probable DE (n = 70). There was no correlation between Posm and Tosm, though Posm (293.32 mOsm/L) was significantly higher than Tosm (288.48 mOsm/L; p < 0.001). There was no significant difference in Tosm between the normal group (288.29 mOsm/L) and the DE group (288.51 mOsm/L). No patients had a Tosm higher than 310 mOsm/L even in the DE group. Correlations between Posm/Tosm and each DE sign value were not found. Of 54 patients, 18 were diabetic. Posm was significantly higher in diabetic (295.78 mOsm/L) than in non-diabetic (292.36 mOsm/L; p = 0.014) patients, while there was no significant difference in Tosm between diabetic and non-diabetic patients. CONCLUSIONS The results suggest that Tosm is independent of Posm, and Tosm elevation in DE occurs by some local mechanisms.
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Affiliation(s)
- Maika Kobayashi
- Department of Ophthalmology, Nippon Medical School, 1-1-5 Sendagi, Bunkyo-ku, Tokyo, 113-8602, Japan
| | - Tsutomu Igarashi
- Department of Ophthalmology, Nippon Medical School, 1-1-5 Sendagi, Bunkyo-ku, Tokyo, 113-8602, Japan.
| | - Hisatomo Takahashi
- Department of Ophthalmology, Nippon Medical School, 1-1-5 Sendagi, Bunkyo-ku, Tokyo, 113-8602, Japan
| | - Chiaki Fujimoto
- Department of Ophthalmology, Nippon Medical School, 1-1-5 Sendagi, Bunkyo-ku, Tokyo, 113-8602, Japan
| | - Hisaharu Suzuki
- Department of Ophthalmology, Musashikosugi Hospital, Nippon Medical School, 1-396 Kosugi-cho, Nakahara-ku, Kawasaki City, Kanagawa, 211-8533, Japan
| | - Hiroshi Takahashi
- Department of Ophthalmology, Nippon Medical School, 1-1-5 Sendagi, Bunkyo-ku, Tokyo, 113-8602, Japan
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Bogum J, Faust D, Zühlke K, Eichhorst J, Moutty MC, Furkert J, Eldahshan A, Neuenschwander M, von Kries JP, Wiesner B, Trimpert C, Deen PMT, Valenti G, Rosenthal W, Klussmann E. Small-molecule screening identifies modulators of aquaporin-2 trafficking. J Am Soc Nephrol 2013; 24:744-58. [PMID: 23559583 DOI: 10.1681/asn.2012030295] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
In the principal cells of the renal collecting duct, arginine vasopressin (AVP) stimulates the synthesis of cAMP, leading to signaling events that culminate in the phosphorylation of aquaporin-2 water channels and their redistribution from intracellular domains to the plasma membrane via vesicular trafficking. The molecular mechanisms that control aquaporin-2 trafficking and the consequent water reabsorption, however, are not completely understood. Here, we used a cell-based assay and automated immunofluorescence microscopy to screen 17,700 small molecules for inhibitors of the cAMP-dependent redistribution of aquaporin-2. This approach identified 17 inhibitors, including 4-acetyldiphyllin, a selective blocker of vacuolar H(+)-ATPase that increases the pH of intracellular vesicles and causes accumulation of aquaporin-2 in the Golgi compartment. Although 4-acetyldiphyllin did not inhibit forskolin-induced increases in cAMP formation and downstream activation of protein kinase A (PKA), it did prevent cAMP/PKA-dependent phosphorylation at serine 256 of aquaporin-2, which triggers the redistribution to the plasma membrane. It did not, however, prevent cAMP-induced changes to the phosphorylation status at serines 261 or 269. Last, we identified the fungicide fluconazole as an inhibitor of cAMP-mediated redistribution of aquaporin-2, but its target in this pathway remains unknown. In conclusion, our screening approach provides a method to begin dissecting molecular mechanisms underlying AVP-mediated water reabsorption, evidenced by our identification of 4-acetyldiphyllin as a modulator of aquaporin-2 trafficking.
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Affiliation(s)
- Jana Bogum
- Max Delbrueck Center for Molecular Medicine, Robert-Rössle Strasse, 10 D-13125, Berlin, Germany
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Sinke AP, Deen PMT. The physiological implication of novel proteins in systemic osmoregulation. FASEB J 2011; 25:3279-89. [PMID: 21737616 DOI: 10.1096/fj.11-188433] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Maintenance of the osmobalance is important for life. In this process, in which brain and kidney act in concert, mammals have to cope with significant deviations as drinking water reduces plasma osmolality, whereas salty food increases it. To restore homeostasis, specialized nuclei within the hypothalamus play a pivotal role in detecting changes in plasma osmolality and initiating appropriate responses. These responses are accomplished by either changing the intake of water or the excretion of water by the kidney. In the past decade, several novel findings have made significant contributions to our insights in the process of systemic osmoregulation. Novel proteins have been identified in the brain as well as in the kidney that are fulfilling important roles in the process of systemic osmoregulation. In this review, recent evidence of the involvement of TRPV channels (TRPV1, TRPV2, and TRPV4) and proteins, such as sodium channels NALCN and Na(x), in neuronal osmoregulation, as well as; e.g., the purinergic P2Y2 receptor in renal osmoregulation, are discussed, and integrated with existing knowledge of systemic osmoregulation.
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Affiliation(s)
- Anne P Sinke
- Department of Physiology, Radboud University Nijmegen Medical Centre, Nijmegen, The Netherlands
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Floyd RV, Mason SL, Proudman CJ, German AJ, Marples D, Mobasheri A. Expression and nephron segment-specific distribution of major renal aquaporins (AQP1-4) in Equus caballus, the domestic horse. Am J Physiol Regul Integr Comp Physiol 2007; 293:R492-503. [PMID: 17442782 DOI: 10.1152/ajpregu.00689.2005] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Aquaporins (AQPs) play fundamental roles in water and osmolyte homeostasis by facilitating water and small solute movement across plasma membranes of epithelial, endothelial, and other tissues. AQP proteins are abundantly expressed in the mammalian kidney, where they have been shown to play essential roles in fluid balance and urine concentration. Thus far, the majority of studies on renal AQPs have been carried out in laboratory rodents and sheep; no data have been published on the expression of AQPs in kidneys of equines or other large mammals. The aim of this comparative study was to determine the expression and nephron segment localization of AQP1-4 in Equus caballus by immunoblotting and immunohistochemistry with custom-designed rabbit polyclonal antisera. AQP1 was found in apical and basolateral membranes of the proximal convoluted tubules and thin descending limbs of the loop of Henle. AQP2 expression was specifically detected in apical membranes of cortical, medullary, and papillary collecting ducts. AQP3 was expressed in basolateral membranes of cortical, medullary, and papillary collecting ducts. Immunohistochemistry also confirmed AQP4 expression in basolateral membranes of cells lining the distal convoluted and connecting tubules. Western blots revealed high expression of AQP1-4 in the equine kidney. These observations confirm that AQPs are expressed in the equine kidney and are found in similar nephron locations to mouse, rat, and human kidney. Equine renal AQP proteins are likely to be involved in acute and chronic regulation of body fluid composition and may be implicated in water balance disorders brought about by colic and endotoxemia.
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Affiliation(s)
- R V Floyd
- Department of Physiology, Faculty of Veterinary Science, University of Liverpool, Liverpool, UK
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Cheong HI, Cho HY, Park HW, Ha IS, Choi Y. Molecular genetic study of congenital nephrogenic diabetes insipidus and rescue of mutant vasopressin V2 receptor by chemical chaperones. Nephrology (Carlton) 2007; 12:113-7. [PMID: 17371330 DOI: 10.1111/j.1440-1797.2006.00759.x] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
AIM X-linked nephrogenic diabetes insipidus is a rare disease caused by mutations in the arginine vasopressin V2 receptor (AVPR2) gene, which encodes vasopressin V2 receptor (V2R). More than a half of reported mutations in AVPR2 are missense mutations, and a large number of missense mutant receptors fail to fold properly and therefore are not routed to the cell surface. METHODS We analysed the AVPR2 gene in 14 unrelated patients with X-linked nephrogenic diabetes insipidus, and found 13 different mutations including eight missense point mutations. The cellular expression patterns of three missense mutant (A98P, L274P and R113W) and wild-type V2R were determined in transfected COS-7 cells. RESULTS In contrast to wild-type V2R, the cell-surface expressions of mutant receptors were totally (A98P and L274P) or partially (R113W) absent. Instead, they were retained intracellularly. However, treatment of cells with two chemical chaperones (100 mmol/L trimethylamine oxide or 2% dimethyl sulfoxide) or incubation at 26 degrees C restored the cell-surface expressions of mutant receptors. CONCLUSION These data show that some chemical chaperones correct the mistrafficking of misfolded A98P, L274P and R113W V2R. Thus, we believe that a therapeutic strategy based on chemical chaperones in patients with these mutations is worth trying.
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Affiliation(s)
- Hae Il Cheong
- Department of Pediatrics, Seoul National University Children's Hospital, Seoul, Korea.
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8
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Kondo Y, Morimoto T, Nishio T, Aslanova UF, Nishino M, Farajov EI, Sugawara N, Kumagai N, Ohsaga A, Maruyama Y, Takahashi S. Phylogenetic, ontogenetic, and pathological aspects of the urine-concentrating mechanism. Clin Exp Nephrol 2006; 10:165-74. [PMID: 17009073 DOI: 10.1007/s10157-006-0429-4] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2006] [Accepted: 08/09/2006] [Indexed: 12/21/2022]
Abstract
The urine-concentrating mechanism is one of the most fundamental functions of avian and mammalian kidneys. This particular function of the kidneys developed as a system to accumulate NaCl in birds and as a system to accumulate NaCl and urea in mammals. Based on phylogenetic evidence, the mammalian urine-concentrating mechanism may have evolved as a modification of the renal medulla's NaCl accumulating system that is observed in birds. This qualitative conversion of the urine-concentrating mechanism in the mammalian inner medulla of the kidneys may occur during the neonatal period. Human kidneys have several suboptimal features caused by the neonatal conversion of the urine-concentrating mechanism. The urine-concentrating mechanism is composed of various functional molecules, including water channels, solute transporters, and vasopressin receptors. Abnormalities in water channels aquaporin (AQP)1 and AQP2, as well as in the vasopressin receptor V2R, are known to cause nephrogenic diabetes insipidus. An analysis of the pathological mechanism involved in nephrogenic diabetes insipidus suggests that molecular chaperones may improve the intracellular trafficking of AQP2 and V2R, and, in the near future, such chaperones may become a new clinical tool for treating nephrogenic diabetes insipidus.
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Affiliation(s)
- Yoshiaki Kondo
- Department of Medical Informatics, Tohoku University Graduate School of Medicine, 1-1 Seiryo-machi, Aoba-ku, Sendai, 980-8574, Japan.
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Pitonzo D, Skach WR. Molecular mechanisms of aquaporin biogenesis by the endoplasmic reticulum Sec61 translocon. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2006; 1758:976-88. [PMID: 16782047 DOI: 10.1016/j.bbamem.2006.04.021] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/21/2005] [Revised: 03/27/2006] [Accepted: 04/14/2006] [Indexed: 11/29/2022]
Abstract
The past decade has witnessed remarkable advances in our understanding of aquaporin (AQP) structure and function. Much, however, remains to be learned regarding how these unique and vitally important molecules are generated in living cells. A major obstacle in this respect is that AQP biogenesis takes place in a highly specialized and relatively inaccessible environment formed by the ribosome, the Sec61 translocon and the ER membrane. This review will contrast the folding pathways of two AQP family members, AQP1 and AQP4, and attempt to explain how six TM helices can be oriented across and integrated into the ER membrane in the context of current (and somewhat conflicting) translocon models. These studies indicate that AQP biogenesis is intimately linked to translocon function and that the ribosome and translocon form a highly dynamic molecular machine that both interprets and is controlled by specific information encoded within the nascent AQP polypeptide. AQP biogenesis thus has wide ranging implications for mechanisms of translocon function and general membrane protein folding pathways.
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Affiliation(s)
- David Pitonzo
- Department of Biochemistry and Molecular Biology, Oregon Health and Sciences University Portland, Oregon, 3181 SW Sam Jackson Park Rd L-224 Portland, Oregon 97239, USA
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Li C, Wang W, Summer SN, Cadnapaphornchai MA, Falk S, Umenishi F, Schrier RW. Hyperosmolality in vivo upregulates aquaporin 2 water channel and Na-K-2Cl co-transporter in Brattleboro rats. J Am Soc Nephrol 2006; 17:1657-64. [PMID: 16672318 DOI: 10.1681/asn.2005121381] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022] Open
Abstract
There are considerable experimental results that indicate that arginine vasopressin (AVP)-independent factors are involved in urinary concentration. This study examined the role of hyperosmolality in vivo to modulate aquaporin 2 (AQP2) and Na-K-2Cl co-transporter (NKCC2), pivotal factors in urinary concentration, in AVP-deficient Brattleboro (BB) rats. Hyperglycemia with associated hyperosmolality occurred in diabetic BB rats (BBDM). Protein abundance of AQP2 increased and was reversed by insulin in the inner medulla (IM; control 100+/-5%; BBDM 146+/-8%; BBDM+Ins 122+/-9%; P<0.001) and inner stripe of outer medulla (ISOM; control 100+/-4%; BBDM 123+/-8%; BBDM+Ins 93+/-6%; P<0.05). These results were confirmed by immunohistochemistry studies. NKCC2 rose in the ISOM but was not reversed with insulin treatment. For investigation of the role of hyperosmolality in the absence of hyperglycemia on the regulation of the expression of renal AQP and NKCC2, studies were performed with hyperosmolality that was induced by 0.5% NaCl in drinking water in BB rats. Hyperosmolality that was induced by NaCl increased significantly the protein abundance of IM AQP2 (121+/-2 versus 100+/-5%; P<0.01), ISOM AQP2 (135+/-6 versus 100+/-5%; P<0.001), cortex plus outer stripe of outer medulla AQP2 (121+/-4 versus 100+/-1%; P<0.001), ISOM NKCC2 (133+/-1 versus 100+/-4%; P<0.05), and cortex plus outer stripe of outer medulla NKCC2 (142+/-16 versus 100+/-9%; P<0.05). In conclusion, hyperosmolality, secondary to either glucose or NaCl, upregulated renal AQP2 and NKCC2 in vivo in BB rats.
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Affiliation(s)
- Chunling Li
- Department of Medicine, University of Colorado School of Medicine, 4200 East 9th Avenue, Box B173, Denver, CO 80262, USA
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Holtbäck U, Aperia AC. Molecular determinants of sodium and water balance during early human development. ACTA ACUST UNITED AC 2004; 8:291-9. [PMID: 15001132 DOI: 10.1016/s1084-2756(03)00042-3] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The past decade has seen enormous progress in understanding the renal regulation of salt and water homeostasis. Most of the key transporters have been cloned, and their physiological importance has been revealed from studies of children with inherited diseases and from mutagenesis studies on a cellular level. We are beginning to understand the complexity with which the activity of these transporters is regulated by hormones. Studies on experimental animals have uniformly shown that the majority of renal salt and water transporters undergo profound changes in the postnatal period. There is generally a robust increase in the number of transporters expressed in a single tubular cell. Many of the transporters also shift their expression from one isoform to another with a somewhat different function. The short-term regulation of salt and water transporters, the key to a well-functioning homeostatic system, is often blunted in the early postnatal period. Taken together, these findings explain some phenomena well known in infants. The low urinary concentrating capacity can, for example, be at least partially attributed to immaturity of the expression of water channels, sodium losses in preterm infants to low expression of the energy generator for salt transport, Na(+),K(+)-ATPase, and the disposition to acidosis to immaturity of the Na(+)/H(+)exchanger. We propose that further studies on how these transporters are regulated will lead to the improved prevention and treatment of salt water balance disorders in infants.
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Affiliation(s)
- Ulla Holtbäck
- Department of Woman and Child Health, Karolinska Institute, Stockholm, Sweden.
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Akhter S, Kovbasnjuk O, Li X, Cavet M, Noel J, Arpin M, Hubbard AL, Donowitz M. Na(+)/H(+) exchanger 3 is in large complexes in the center of the apical surface of proximal tubule-derived OK cells. Am J Physiol Cell Physiol 2002; 283:C927-40. [PMID: 12176749 DOI: 10.1152/ajpcell.00613.2001] [Citation(s) in RCA: 55] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Cell biological approaches were used to examine the location and function of the brush border (BB) Na(+)/H(+) exchanger NHE3 in the opossum kidney (OK) polarized renal proximal tubule cell line. NHE3 epitope tagged with the vesicular stomatitis virus glycoprotein epitope (NHE3V) was stably expressed and called OK-E3V cells. On the basis of cell surface biotinylation studies, these cells had 10-15% of total NHE3 on the BB. Intracellular NHE3V largely colocalized with Rab11 and to a lesser extent with EEA1. The BB location of NHE3V was examined by confocal microscopy relative to the lectins wheat germ aggluttinin (WGA) and phytohemagluttin E (PHA-E), as well as the B subunit of cholera toxin (CTB). The cells were pyramidal, and NHE3 was located in microvilli in the center of the apical surface. In contrast, PHA-E, WGA, and CTB were diffusely distributed on the BB. Detergent extraction showed that total NHE3V was largely soluble in Triton X-100, whereas virtually all surface NHE3V was insoluble. Sucrose density gradient centrifugation demonstrated that total NHE3V migrated at the same size as approximately 400- and approximately 900-kDa standards, whereas surface NHE3V was enriched in the approximately 900-kDa form. Under basal conditions, NHE3 cycled between the cell surface and the recycling pathway through a phosphatidylinositol (PI) 3-kinase-dependent mechanism. Measurements of surface and intracellular pH were obtained by using FITC-WGA. Internalization of FITC-WGA occurred largely into the juxtanuclear compartment that contained Rab11 and NHE3V. pH values on the apical surface and in endosomes in the presence of the NHE3 blocker, S3226, were elevated, showing that NHE3 functioned to acidify both compartments. In conclusion, NHE3V in OK cells exists in distinct domains both in the center of the apical surface and in a juxtanuclear compartment. In the BB fraction, NHE3 is largely in the detergent-insoluble fraction in lipid rafts and/or in large heterogenous complexes ranging from approximately 400 to approximately 900 kDa.
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Affiliation(s)
- S Akhter
- Department of Medicine, Gastrointestinal Division, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205-2195, USA
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Sun TX, Van Hoek A, Huang Y, Bouley R, McLaughlin M, Brown D. Aquaporin-2 localization in clathrin-coated pits: inhibition of endocytosis by dominant-negative dynamin. Am J Physiol Renal Physiol 2002; 282:F998-1011. [PMID: 11997316 DOI: 10.1152/ajprenal.00257.2001] [Citation(s) in RCA: 90] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Before the identification of aquaporin (AQP) proteins, vasopressin-regulated "water channels" were identified by freeze-fracture electron microscopy as aggregates or clusters of intramembraneous particles (IMPs) on hormonally stimulated target cell membranes. In the kidney collecting duct, these IMP clusters were subsequently identified as possible sites of clathrin-coated pit formation on the plasma membrane, and a clathrin-mediated mechanism for internalization of vasopressin-sensitive water channels was suggested. Using an antibody raised against the extracellular C loop of AQP2, we now provide direct evidence that AQP2 is concentrated in clathrin-coated pits on the apical surface of collecting duct principal cells. Furthermore, by using a fracture-label technique applied to LLC-PK(1) cells expressing an AQP2-c-myc construct, we show that AQP2 is located in IMP aggregates and is concentrated in shallow membrane invaginations on the surface of forskolin-stimulated cells. We also studied the functional role of clathrin-coated pits in AQP2 trafficking by using a GTPase-deficient dynamin mutation (K44A) to inhibit clathrin-mediated endocytosis. Immunofluorescence labeling and freeze-fracture electron microscopy showed that dominant-negative dynamin 1 and dynamin 2 mutants prevent the release of clathrin-coated pits from the plasma membrane and induce an accumulation of AQP2 on the plasma membrane of AQP2-transfected cells. These data provide the first direct evidence that AQP2 is located in clathrin-coated pits and show that AQP2 recycles between the plasma membrane and intracellular vesicles via a dynamin-dependent endocytotic pathway. We propose that the IMP clusters previously associated with vasopressin action represent sites of dynamin-dependent, clathrin-mediated endocytosis in which AQP2 is concentrated before internalization.
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Affiliation(s)
- Tian-Xiao Sun
- Program in Membrane Biology and Renal Unit, Department of Medicine, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts 02114, USA
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Biner HL, Arpin-Bott MP, Loffing J, Wang X, Knepper M, Hebert SC, Kaissling B. Human cortical distal nephron: distribution of electrolyte and water transport pathways. J Am Soc Nephrol 2002; 13:836-847. [PMID: 11912242 DOI: 10.1681/asn.v134836] [Citation(s) in RCA: 121] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023] Open
Abstract
The exact distributions of the different salt transport systems along the human cortical distal nephron are unknown. Immunohistochemistry was performed on serial cryostat sections of healthy parts of tumor nephrectomized human kidneys to study the distributions in the distal convolution of the thiazide-sensitive Na-Cl cotransporter (NCC), the beta subunit of the amiloride-sensitive epithelial Na channel (ENaC), the vasopressin-sensitive water channel aquaporin 2 (AQP2), and aquaporin 3 (AQP3), the H(+) ATPase, the Na-Ca exchanger (NCX), plasma membrane calcium-ATPase, and calbindin-D28k (CaBP). The entire human distal convolution and the cortical collecting duct (CCD) display calbindin-D28k, although in variable amounts. Approximately 30% of the distal convolution profiles reveal NCC, characterizing the distal convoluted tubule. NCC overlaps with ENaC in a short portion at the end of the distal convoluted tubule. ENaC is displayed all along the connecting tubule (70% of the distal convolution) and the CCD. The major part of the connecting tubule and the CCD coexpress aquaporin 2 with ENaC. Intercalated cells, undetected in the first 20% of the distal convolution, were interspersed among the segment-specific cells of the remainder of the distal convolution, and of the CCD. The basolateral calcium extruding proteins, Na-Ca exchanger (NCX), and the plasma membrane Ca(2+)-ATPase were found all along the distal convolution, and, in contrast to other species, along the CCD, although in varying amounts. The knowledge regarding the precise distribution patterns of transport proteins in the human distal nephron and the knowledge regarding the differences from that in laboratory animals may be helpful for diagnostic purposes and may also help refine the therapeutic management of electrolyte disorders.
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Affiliation(s)
- Helena Lagger Biner
- *Anatomical Department, University of Zurich, Zurich, Switzerland; UMR CNRS 7519, University Louis Pasteur, Strasbourg, France; National Heart, Lung, and Blood Institute, Bethesda, Maryland; and Department of Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, Connecticut
| | - Marie-Pierre Arpin-Bott
- *Anatomical Department, University of Zurich, Zurich, Switzerland; UMR CNRS 7519, University Louis Pasteur, Strasbourg, France; National Heart, Lung, and Blood Institute, Bethesda, Maryland; and Department of Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, Connecticut
| | - Johannes Loffing
- *Anatomical Department, University of Zurich, Zurich, Switzerland; UMR CNRS 7519, University Louis Pasteur, Strasbourg, France; National Heart, Lung, and Blood Institute, Bethesda, Maryland; and Department of Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, Connecticut
| | - Xiaoyan Wang
- *Anatomical Department, University of Zurich, Zurich, Switzerland; UMR CNRS 7519, University Louis Pasteur, Strasbourg, France; National Heart, Lung, and Blood Institute, Bethesda, Maryland; and Department of Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, Connecticut
| | - Mark Knepper
- *Anatomical Department, University of Zurich, Zurich, Switzerland; UMR CNRS 7519, University Louis Pasteur, Strasbourg, France; National Heart, Lung, and Blood Institute, Bethesda, Maryland; and Department of Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, Connecticut
| | - Steve C Hebert
- *Anatomical Department, University of Zurich, Zurich, Switzerland; UMR CNRS 7519, University Louis Pasteur, Strasbourg, France; National Heart, Lung, and Blood Institute, Bethesda, Maryland; and Department of Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, Connecticut
| | - Brigitte Kaissling
- *Anatomical Department, University of Zurich, Zurich, Switzerland; UMR CNRS 7519, University Louis Pasteur, Strasbourg, France; National Heart, Lung, and Blood Institute, Bethesda, Maryland; and Department of Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, Connecticut
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15
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Affiliation(s)
- Anatoly I Masyuk
- The Center for Basic Research in Digestive Diseases, Division of Gastroenterology and Hepatology, Mayo Medical School, Clinic, and Foundation, Rochester, Minnesota 55905, USA
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16
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Nielsen S, Frøkiaer J, Marples D, Kwon TH, Agre P, Knepper MA. Aquaporins in the kidney: from molecules to medicine. Physiol Rev 2002; 82:205-44. [PMID: 11773613 DOI: 10.1152/physrev.00024.2001] [Citation(s) in RCA: 853] [Impact Index Per Article: 38.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The discovery of aquaporin-1 (AQP1) answered the long-standing biophysical question of how water specifically crosses biological membranes. In the kidney, at least seven aquaporins are expressed at distinct sites. AQP1 is extremely abundant in the proximal tubule and descending thin limb and is essential for urinary concentration. AQP2 is exclusively expressed in the principal cells of the connecting tubule and collecting duct and is the predominant vasopressin-regulated water channel. AQP3 and AQP4 are both present in the basolateral plasma membrane of collecting duct principal cells and represent exit pathways for water reabsorbed apically via AQP2. Studies in patients and transgenic mice have demonstrated that both AQP2 and AQP3 are essential for urinary concentration. Three additional aquaporins are present in the kidney. AQP6 is present in intracellular vesicles in collecting duct intercalated cells, and AQP8 is present intracellularly at low abundance in proximal tubules and collecting duct principal cells, but the physiological function of these two channels remains undefined. AQP7 is abundant in the brush border of proximal tubule cells and is likely to be involved in proximal tubule water reabsorption. Body water balance is tightly regulated by vasopressin, and multiple studies now have underscored the essential roles of AQP2 in this. Vasopressin regulates acutely the water permeability of the kidney collecting duct by trafficking of AQP2 from intracellular vesicles to the apical plasma membrane. The long-term adaptational changes in body water balance are controlled in part by regulated changes in AQP2 and AQP3 expression levels. Lack of functional AQP2 is seen in primary forms of diabetes insipidus, and reduced expression and targeting are seen in several diseases associated with urinary concentrating defects such as acquired nephrogenic diabetes insipidus, postobstructive polyuria, as well as acute and chronic renal failure. In contrast, in conditions with water retention such as severe congestive heart failure, pregnancy, and syndrome of inappropriate antidiuretic hormone secretion, both AQP2 expression levels and apical plasma membrane targetting are increased, suggesting a role for AQP2 in the development of water retention. Continued analysis of the aquaporins is providing detailed molecular insight into the fundamental physiology and pathophysiology of water balance and water balance disorders.
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Affiliation(s)
- Søren Nielsen
- The Water and Salt Research Center, Institute of Anatomy, and Institute of Experimental Clinical Research, University of Aarhus, Aarhus, Denmark.
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17
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Fernández-Llama P. [Aquaporins and renal water metabolism. Role in the physiopathology of water retention in cirrhosis]. GASTROENTEROLOGIA Y HEPATOLOGIA 2001; 24:205-9. [PMID: 11333660 DOI: 10.1016/s0210-5705(01)70151-3] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Affiliation(s)
- P Fernández-Llama
- Laboratorio de Hormonología. Hospital Clínic i Provincial. Universidad de Barcelona. Institut d'Investigacions Biomèdiques August Pi i Sunyer (IDIBAPS), Barcelona.
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18
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Chapter 6 Trafficking of native and mutant mammalian MIP proteins. CURRENT TOPICS IN MEMBRANES 2001. [DOI: 10.1016/s1063-5823(01)51008-x] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
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19
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Affiliation(s)
- P M Deen
- Department of Cell Physiology, University of Nijmegen, The Netherlands.
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20
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Deen PM, van Balkom BW, Kamsteeg EJ. Routing of the aquaporin-2 water channel in health and disease. Eur J Cell Biol 2000; 79:523-30. [PMID: 11001488 DOI: 10.1078/0171-9335-00075] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The identification of the first water channel in 1991 opened up a new field in cell biology and physiology that significantly increased our understanding of mammalian water balance regulation. Since then, nine other mammalian aquaporins have been identified. Although the physiological significance of many aquaporins is still to be elucidated, it has been clearly established for aquaporin-2. This water channel, which is expressed in the renal collecting duct, is redistributed to the apical membrane in response to a intracellular signaling cascade, initiated by binding of the antidiuretic hormone vasopressin to its receptor. In pathological conditions, characterized by a reduced reabsorption of water from urine, the expression of aquaporin-2 and the apical targeting is always found to be reduced or absent. Naturally-occurring AQP2 mutations that cause Nephrogenic Diabetes Insipidus, a disease in which the kidney is unable to concentrate urine in response to vasopressin, are extreme examples of this condition. In contrast, in diseases with increased renal water uptake, total and apical membrane expression of aquaporin-2 is increased. Since most aquaporins, including aquaporin-2, are considered to be constitutively open channels, much attention has been given to the regulation of the shuttling of aquaporin-2 to the apical membrane. This review focusses on the present understanding of the regulation of the routing of aquaporin-2 in collecting duct cells and the misrouting of aquaporin-2 mutants in Nephrogenic Diabetes Insipidus.
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Affiliation(s)
- P M Deen
- Department of Cell Physiology, University of Nijmegen, The Netherlands.
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21
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Brown D. Targeting of membrane transporters in renal epithelia: when cell biology meets physiology. Am J Physiol Renal Physiol 2000; 278:F192-201. [PMID: 10662723 DOI: 10.1152/ajprenal.2000.278.2.f192] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Epithelial cells in the kidney have highly specialized transport mechanisms that differ among the many tubule segments, and among the different cell types that are present in some regions. The purpose of this brief review is to examine some of the major intracellular mechanisms by which the membrane proteins that participate in these differentiated cellular functions are addressed, sorted, and delivered to specific membrane domains of epithelial cells. Unraveling these processes is important not only for our understanding of normal cellular function but is also critical for the interpretation of pathophysiological dysfunction in the context of newly generated molecular and cellular information concerning hereditary and acquired transporter abnormalities. Among the topics covered are sorting signals on proteins, role of the cytoskeleton, vesicle coat proteins, the fusion machinery, and exo- and endocytosis of recycling proteins. Examples of these events in renal epithelial cells are highlighted throughout this review and are related to the physiology of the kidney.
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Affiliation(s)
- D Brown
- Program in Membrane Biology, Massachusetts General Hospital, Department of Pathology, Harvard Medical School, Boston, Massachusetts 02114, USA.
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Abstract
Critical illness provides major stresses on all body systems, including those serving important regulatory functions. Endocrinologic and metabolic abnormalities are common on presentation and during hospitalization in the intensive care unit. Some of these abnormalities are the focus of this article. The authors review abnormalities of the adrenal and thyroid glands and in the metabolism of glucose, and include a brief review of abnormalities of sodium and calcium metabolism.
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Affiliation(s)
- F J Martinez
- Divisions of Pulmonary and Critical Care Medicine, University of Michigan Health System, Ann Arbor, USA
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