New insights into the transcriptional regulation of aquaporin-2 and the treatment of X-linked hereditary nephrogenic diabetes insipidus

The kidney collecting duct (CD) is a tubular segment of the kidney where the osmolality and final flow rate of urine are established, enabling urine concentration and body water homeostasis. Water reabsorption in the CD depends on the action of arginine vasopressin (AVP) and a transepithelial osmotic gradient between the luminal fluid and surrounding interstitium. AVP induces transcellular water reabsorption across CD principal cells through associated signaling pathways after binding to arginine vasopressin receptor 2 (AVPR2). This signaling cascade regulates the water channel protein aquaporin-2 (AQP2). AQP2 is exclusively localized in kidney connecting tubules and CDs. Specifically, AVP stimulates the intracellular translocation of AQP2-containing vesicles to the apical plasma membrane, increasing the osmotic water permeability of CD cells. Moreover, AVP induces transcription of the Aqp2 gene, increasing AQP2 protein abundance. This review provides new insights into the transcriptional regulation of the Aqp2 gene in the kidney CD with an overview of AVP and AQP2. It summarizes current therapeutic approaches for X-linked nephrogenic diabetes insipidus caused by AVPR2 gene mutations.

A Minireview on Vasopressin-regulated Aquaporin-2 in Kidney Collecting Duct Cells

The kidney collecting duct is an important renal tubular segment for the regulation of body water and salt homeostasis. Water reabsorption in the collecting duct cells is regulated by arginine vasopressin (AVP) via the vasopressin V2-receptor (V2R). AVP increases the osmotic water permeability of the collecting duct cells through aquaporin-2 (AQP2) and aquaporin-3 (AQP3). AVP induces the apical targeting of AQP2 and transcription of AQP2 gene in the kidney collecting duct principal cells. The signaling transduction pathways resulting in the AQP2 trafficking to the apical plasma membrane of the collecting duct principal cells, include AQP2 phosphorylation, RhoA phosphorylation, actin depolymerization and calcium mobilization, and the changes of AQP2 protein abundance in water balance disorders have been extensively studied. These studies elucidate the underlying cellular and molecular mechanisms of body water homeostasis and provide the basis for the treatment of body water balance disorders.

Physiology and pathophysiology of cyclooxygenase-2 and prostaglandin E2 in the kidney

The cyclooxygenase (COX) enzyme system is the major pathway catalyzing the conversion of arachidonic acid into prostaglandins (PGs). PGs are lipid mediators implicated in a variety of physiological and pathophysiological processes in the kidney, including renal hemodynamics, body water and sodium balance, and the inflammatory injury characteristic in multiple renal diseases. Since the beginning of 1990s, it has been confirmed that COX exists in 2 isoforms, referred to as COX-1 and COX-2. Even though the 2 enzymes are similar in size and structure, COX-1 and COX-2 are regulated by different systems and have different functional roles. This review summarizes the current data on renal expression of the 2 COX isoforms and highlights mainly the role of COX-2 and PGE2 in several physiological and pathophysiological processes in the kidney.

Development of intestinal ischemia/reperfusion-induced acute kidney injury in rats with or without chronic kidney disease: Cytokine/chemokine response and effect of alpha-melanocyte-stimulating hormone

BACKGROUND: The primary aim of the study was to investigate the cytokine/chemokine response in the kidney, lung, and liver following acute kidney injury (AKI). The secondary aim was to test whether alpha-melanocyte-stimulating hormone (alpha-MSH) could prevent a reduction in organ function, and attenuate the inflammatory cytokine/chemokine response within the kidney, lung, and liver following AKI in rats with or without preexisting chronic kidney disease (CKD). METHODS: A two-stage animal model, in which AKI was induced in rats with preexisting CKD, induced by 5/6 nephrectomy (Nx), was used. Six weeks later, AKI was induced by intestinal ischemia and reperfusion (IIR). Sham procedures [S(Nx) and S(IIR)] were also performed. RESULTS: Increasing levels of serum creatinine (sCr) demonstrated progressive development of CKD in response to Nx, and following IIR sCr levels increased further significantly, except in the S(Nx) group treated with alpha-MSH. However, no significant differences in the fractional increase in sCr were observed between any of the groups exposed to IIR. In kidney, lung, and liver tissue the levels of interleukin (IL)-1beta were significantly higher in rats undergoing IIR when compared to the S(IIR) and control rats. The same pattern was observed for the chemokine monocyte chemoattractant protein (MCP)-1 in lung and liver tissue. Furthermore, kidney IL-1beta and RANTES levels were significantly increased after IIR in the Nx rats compared to the S(Nx) rats. CONCLUSION: Both the functional parameters and the cytokine/chemokine response are as dramatic when AKI is superimposed onto CKD as onto non-CKD. No convincing protective effect of alpha-MSH was detected.

Regulation of aquaporin-2 in the kidney : A molecular mechanism of body-water homeostasis

The kidneys play a key role in the homeostasis of body water and electrolyte balance. Aquaporin-2 (AQP2) is the vasopressin-regulated water-channel protein expressed at the connecting tubule and collecting duct, and plays a key role in urine concentration and body-water homeostasis through short-term and long-term regulation of collecting duct water permeability. The signaling transduction pathways resulting in the AQP2 trafficking to the apical plasma membrane of the collecting duct principal cells, including AQP2 phosphorylation, RhoA phosphorylation, actin depolymerization, and calciumm obilization, and the changes of AQP2 abundance in water-balance disorders have been extensively studied. Dysregulation of AQP2 has been shown to be importantly associated with a number of clinical conditions characterized by body-water balance disturbances, including hereditary nephrogenic diabetes insipidus (NDI), lithium-induced NDI, electrolytes disturbance, acute and chronic renal failure, ureteral obstruction, nephrotic syndrome, congestive heart failure, and hepatic cirrhosis. Recent studies exploiting omics technology further demonstrated the comprehensive vasopressin signaling pathways in the collecting ducts. Taken together, these studies elucidate the underlying molecular mechanisms of body-water homeostasis and provide the basis for the treatment of body-water balance disorders.

Membrane Trafficking of Collecting Duct Water Channel Protein AQP2 Regulated by Akt/AS160

Akt (protein kinase B (PKB)) is a serine/threonine kinase that acts in the phosphatidylinositol 3-kinase (PI3K)/Akt signaling pathway. The PI3K/Akt signaling pathway, triggered by growth factors and hormones including vasopressin, is an important pathway that is widely involved in cellular mechanisms regulating transcription, translation, cell growth and death, cell proliferation, migration, and cell cycles. In particular, Akt and Akt substrate protein of 160 kDa (AS160) are likely to participate in the trafficking of aquaporin-2 (AQP2) in the kidney collecting duct. In this study, we demonstrated that 1) small interfering RNA (siRNA)-mediated gene silencing of Akt1 significantly decreased Akt1 and phospho-AS160 protein expression; and 2) confocal laser scanning microscopy of AQP2 in mouse cortical collecting duct cells (M-1 cells) revealed AS160 knockdown by siRNA increased AQP2 expression in the plasma membrane compared with controls, despite the absence of dDAVP stimulation. Thus, the results suggest that PI3K/Akt pathways could play a role in AQP2 trafficking via the AS160 protein.

Ubiquitination of Aquaporin: in the kidney

Ubiquitination is known to be important for endocytosis and lysosomal degradation of aquaporin-2 (AQP2). Ubiquitin (Ub) is covalently attached to the lysine residue of the substrate proteins and activation and attachment of Ub to a target protein is mediated by the action of three enzymes (i.e., E1, E2, and E3). In particular, E3 Ub-protein ligases are known to have substrate specificity. This minireview will discuss the ubiquitination of AQP2 and identification of potential E3 Ub-protein ligases for 1-deamino-8-D-arginine vasopressin (dDAVP)-dependent AQP2 regulation.

Fluorescence Quenching to Measure dDAVP-induced Cell Volume Changes in Kidney Collecting Duct Cell / 대한신장학회지

PURPOSE: Cell volume regulation is critical in kidney collecting duct cells which are subjected to large transepithelial osmotic gradients and stimulation of vasopressin. The present study aimed at validating the usefulness of the fluorescence quenching method to measure rapid changes in the cell volume of the kidney collecting duct cells in response to changes of extracellular osmolality and/or dDAVP (V2 receptor agonist) stimulation. METHODS: M-1 cell (a mouse cortical collecting duct cell line) was used and the data presented traces of cellular fluorescence in M-1 cells loaded with calcein collected over time as extracellular osmolality was repeatedly changed or dDAVP was treated. And the "initial relative rate of cell volume changes" was calculated. RESULTS: M-1 cells loaded with calcein revealed that fluorescence was increased when exposed to low extracellular osmolality (250 mOsm/KgH2O), whereas it was decreased by high extracellular osmolality (350 mOsm/KgH2O). This could reflect volume-dependent changes in fluorescence intensity in the range of quenching concentrations. The calculated "initial relative rate of cell volume changes" in M-1 cells during 1 sec was increased-7-fold by dDAVP treatment (10(-8)M, 2 min), compared with vehicle treatment when extracellular osmolality was changed from 350 to 250 mOsm/KgH2O. CONCLUSION: This study suggests that a fluorescence quenching method could be exploited for investigating an effect of dDAVP or other drugs/chemicals on the relative rate of cell volume changes in the kidney collecting duct cells.

The Protective Effect of Simvastatin on Monocrotaline-Induced Pulmonary Hypertension in Rats

BACKGROUND AND OBJECTIVES: Pulmonary hypertension is characterized by abnormal proliferation of vascular endothelial cells and smooth muscle cells, and progressive pulmonary microvascular leakage that leads to pulmonary edema. This study was designed to investigate the protective effect of simvastatin on monocrotaline (MCT)-induced pulmonary hypertension and the role of the aquaporin (AQP) water channels. MATERIALS AND METHODS: Twenty one 8-week-old rats were randomized to the control, MCT (60 mg/kg, sc) and the MCT plus simvastatin (5 mg/kg/day, po) groups. Four weeks later, the systolic right ventricular pressure, the right ventricular hypertrophy, the medial wall thickness of the peribronchiolar artery and pulmonary arterioles and the renal function were measured to examine the effects of MCT and simvastatin in the rats. Western blotting for lung aquaporin1 (AQP1) and renal aquaporin2 (AQP2) was performed to analyze the effects of MCT and simvastatin on the AQP water channels. RESULTS: Treatment with simvastatin reduced the MCT-induced enhanced right ventricular pressure (32.3+/-2.1 vs. 52.4+/-3.9 mmHg, respectively; p<0.05), the right ventricular hypertrophy (0.32+/-0.03 vs. 0.48+/-0.07, respectively; p<0.05) and the increased medial wall thickness of the peribronchiolar artery (0.14+/-0.02 vs. 0.28+/-0.02, respectively; p<0.05) and pulmonary arterioles (0.15+/-0.04 vs. 0.29+/-0.11, respectively; p<0.05). The decreased expression of lung AQP1 and renal AQP2 protein after MCT treatment was normalized by simvastatin treatment (p<0.05). Additionally, simvastatin treatment significantly reduced the perivascular and interstitial edema in the rats' lungs without major alterations of renal function. CONCLUSION: These results suggest that simvastatin attenuates the MCT-induced pulmonary hypertension and the pulmonary edema by up-regulation of lung AQP1. Modulation of AQP may be one of the important mechanism of simvastatin.

Kidney Tubular Cell Regeneration Starts in the Deep Cortex after Ischemia / 대한신장학회지

PURPOSE: In kidneys exposed to ischemia/reperfusion (I/R), the periodic and regional changes of loss and restoration of tubular epithelial cells and the influence of these processes for renal function remain to be defined. We investigated the loss and regeneration of tubular cells in each nephron segment at various times after I/R. METHODS: Mice were subjected to 30 min of bilateral renal ischemia and were administered 5-bromo-2'-deoxyuridine (BrdU) 20 hours before harvest kidneys. The numbers of tubular cell nuclei, BrdUincorporating cells and proliferative cell nuclear antigen (PCNA)-positive cells were analyzed by PASstaining and immunohistochemistry. RESULTS: Thirty minutes of ischemia induced loss of tubular epithelial cells in the outer stripe of the outer medulla. The loss of tubular epithelial cells peaked 24 hours after ischemia. After the maximum decrease, recovery of number of tubular epithelial cells was observed from 3 days after I/R in the outer medulla and from 5 days in the cortex. The tubular cell numbers were inversely correlated with the changes in concentrations of plasma creatinine and BUN by Pearson correlation, indicating that the decrease and increase of tubular epithelial cell numbers reflect functional failure and recovery, respectively. Cell proliferation as determined by BrdU-incorporating appeared in the deep cortex from 3 days after ischemia. CONCLUSION: The recovery of renal function was found to significantly correlate with the restoration of tubular cells. Furthermore, the regeneration of tubular cells started in the tubules of the deep cortex, suggesting that it may be a great proliferative cell niche.

Regulation of AQP2 in Collecting Duct: An emphasis on the Effects of Angiotensin II or Aldosterone

Vasopressin, angiotensin II (AngII), and aldosterone are essential hormones in the regulation of body fluid homeostatsis. We examined the effects of AngII or aldosterone on the regulation of body water balance. We demonstrated that 1) short-term treatment with AngII in the primary cultured inner medullary collecting duct cells played a role in the regulation of AQP2 targeting to the plasma membrane through AT1 receptor activation. This potentiated the effects of dDAVP on cAMP accumulation, AQP2 phosphorylation, and AQP2 plasma membrane targeting; 2) pharmacological blockade of the AngII AT1 receptor in rats co-treated with dDAVP and dietary NaCl-restriction (to induce high plasma endogenous AngII) resulted in an increase in urine production, a decrease in urine osmolality, and blunted the dDAVP-induced upregulation of AQP2; 3) long-term aldosterone infusion in normal rats or in rats with diabetes insipidus was associated with polyuria and decreased urine concentration, accompanied by decreased apical but increased basolateral AQP2 labeling intensity in the connecting tubule and cortical collecting duct; and 4) in contrast to the effects of dDAVP and AngII, short-term aldosterone treatment does not alter the intracellular distribution of AQP2. In conclusion, angiotensin II, and aldosterone could play a role in the regulation of renal water reabsorption by changing intracellular AQP2 targeting and/or AQP2 abundance, in addition to the vasopressin.

Dysregulation of Renal Cyclooxygenase-2 in Rats with Lithium-induced Nephrogenic Diabetes Insipidus

This study aimed to examine whether the expression of major prostaglandin E2 (PGE2) synthesis enzyme, cyclooxygenase-2 (COX-2), is changed in the kidneys of the rats with lithium-induced nephrogenic diabetes insipidus (Li-NDI). Sprague- Dawley rats treated with lithium for 4 weeks were used as the NDI model and expression of renal COX-2 was determined by immunoblotting and immunohistochemistry. In Li-NDI where urine output was markedly increased and urine osmolality was significantly decreased, COX-2 expression in the inner medulla was decreased (28% of control), while it increased 18-fold in the cortex and outer medulla. Consistent with this, labeling intensity of COX-2 in macula densa region was increased, whereas it was decreased in the interstitial cells in the inner medulla, indicating a differential regulation of COX-2 between the cortex and inner medulla in Li-NDI. Accordingly, urinary PGE2 excretion was significantly increased in Li-NDI. In conclusion, there is a differential regulation of COX-2 between cortex and inner medulla in Li- NDI and urinary PGE2 excretion is increased in Li-NDI, possibly due to an increased renal production. This may suggest that increased renal production of PGE2 could play a role in modulating water reabsorption in the renal collecting duct in Li-NDI.

Identification of TGF-beta-induced Gene Product, betaig-h3 in Ischemic Acute Renal Failure / 대한신장학회지

PURPOSE: Acute renal failure remains a potentially devastating clinical problem. This study aimed to examine whether the expression of TGF-beta-induced gene product, betaig-h3, is altered in ischemia- reperfusion (I/R) injury and urinary excretion of betaig-h3 is changed in I/R injury. METHODS: I/R injury was performed by clamping both renal arteries. Daily urine output, serum creatinine and urinary TGF-beta and betaig-h3 were measured after I/R injury. Also, the renal expression of betaig-h3 by western blotting and immunohistochemistry were investigated. In the second step, urinary betaig-h3 was measured at 4, 10, 16, and 24 hours after I/R injury to investigate whether it could be used as an early and sensitive marker for detecting I/R injury. RESULTS: Urinary betaig-h3 was significantly elevated at 24 hours and maintained higher than the controls until 2 days after I/R injury. In contrast, western blotting did not reveal any changes of betaig-h3 expression. Immunohistochemistry showed that labeling of betaig-h3 was seen at the basement membranes of proximal tubule cells mainly located at the medullary ray (S3 segment) in both groups. Following I/R injury, the labeling was also seen in the basement membrane of injured or regenerated proximal tubular epithelial cells. Within 24 hours, urinary betaig-h3 was significantly increased at 4 hours after I/R injury. Importantly, the urinary appearance of betaig-h3 preceded that of N-acetyl-beta-D-glucosaminidase. CONCLUSION: These results suggest that endogenous renal betaig-h3 may serve to promote tissue regeneration in I/R injury and urinary betaig-h3 could be used as an early and sensitive marker demonstrating I/R injury.

Altered Expression of Peritoneal Aquaporin-1 and Water Transport during Long-term Peritoneal Dialysis in Rats / 대한신장학회잡지

BACKGROUND: The present work was designed to examine the altered expression of peritoneal AQP-1 and water transport of peritoneal membrane during the long-term peritoneal dialysis with hypertonic glucose solution in rats. METHODS: Eighteen Sprague-Dawley male rats were randomly divided into 2 groups: control rats (n=6) with peritoneal catheter but not dialyzed; rats with peritoneal dialysis (PD) (n=12) were dialyzed with 4.25% glucose dialysate for all exchanges. Before completion of the study, 4 animals in PD group were euthanized owing to nonfunctional catheters or peritonitis, leaving 14 animals for the analysis. Dialysis exchanges were performed 3 times a day with 25 mL/each exchange for 12 weeks. Immunoperoxidase staining was performed using monoclonal anti-AGE antibody and polyclonal anti-AQP-1 antibody. The slides were read by 5 different examiners in a blind fashion. The staining intensity was graded semiquantitively from 0 to 3. The peritoneal membrane function was assessed by performing one-hour peritoneal equilibration tests every 6 week for comparing transport characteristics. Peritoneal membrane transport rate was assessed by D/P of urea nitrogen and D/Do of glucose. Water transport of peritoneal membrane was assessed by D/P of sodium at 12 week. RESULTS: The expression of peritoneal AQP-1 was increased in rats with PD, compared to control rats. Consistent with this, D/P of sodium in rats with PD was significantly decreased compared to control rats (0.58+/-0.04 vs 0.86+/-0.07, p<0.05), indicating high peritoneal water permeability in response to long-term peritoneal dialysis. Moreover, rats with PD were associated with significantly lower D/Do of glucose and higher D/P of urea nitrogen, suggesting high peritoneal membrane transport. CONCLUSION: High expression of peritoneal AQP-1 was associated with an increased peritoneal water permeability in response to long-term peritoneal dialysis with 4.25% glucose for 12 weeks. The underlying mechanisms for the increased AQP-1 expression need to be examined whether it is due to the continuous exposure to the dialysis solution containing high glucose concentration itself or compensatory effects of slowly developed concomitant ultrafiltration failure in chronic peritoneal dialysis.

Altered Regulation of Renal Aquaporins and Sodium Transporters in Experimental Chronic Renal Failure

Chronic renal failure, which has an increased single nephron glomerular filtration rate in remnant kidney, is known to cause characteristic structural alterations in renal tubule epithelia in association with impaired urinary concentration and deranged urinary sodium excretion. This mini-review will deal with the changes in the renal expression of aquaporins (AQPs) and sodium transporters for elucidating the underlying cellular and molecular mechanisms for the urinary abnormalities of decreased urinary concentration and increased urinary sodium excretion.

Angiotensin II AT1 Receptor Blockade Changes Expression of Renal Sodium Transporters in Rats with Chronic Renal Failure

We aimed to examine the effects of angiotensin II AT1 receptor blocker on the expression of major renal sodium transporters and aquaporin-2 (AQP2) in rats with chronic renal failure (CRF). During 2 wks after 5/6 nephrectomy or sham operation, both CRF rats (n=10) and sham-operated control rats (n=7) received a fixed amount of low sodium diet and had free access to water. CRF rats (n=10) were divided into two groups which were either candesartan-treated (CRF-C, n=4) or vehicletreated (CRF-V, n=6). Both CRF-C and CRF-V demonstrated azotemia, decreased GFR, polyuria, and decreased urine osmolality compared with sham-operated rats. When compared with CRF-V, CRF-C was associated with significantly higher BUN levels and lower remnant kidney weight. Semiquantitative immunoblotting demonstrated decreased AQP2 expression in both CRF-C (54% of control levels) and CRF-V (57%), whereas BSC-1 expression was increased in both CRF groups. Particularly, CRF-C was associated with higher BSC-1 expression (611%) compared with CRF-V (289%). In contrast, the expression of NHE3 (25%) and TSC (27%) was decreased in CRF-C, whereas no changes were observed in CRF-V. In conclusion, 1) candesartan treatment in an early phase of CRF is associated with decreased renal hypertrophy and increased BUN level; 2) decreased AQP2 level in CRF is likely to play a role in the decreased urine concentration, and the downregulation is not altered in response to candesartan treatment; 3) candesartan treatment decreases NHE3 and TSC expression; and 4) an increase of BSC-1 is prominent in candesartan-treated CRF rats, which could be associated with the increased delivery of sodium and water to the thick ascending limb.

Beta ig-h3 promotes renal proximal tubular epithelial cell adhesion, migration and proliferation through the interaction with alpha3beta1 integrin

Betaig-h3 (betaig-h3) is a secretory protein composed of fasciclin I-like repeats containing sequences that allows binding of integrins and glycosaminoglycans in vivo. Expression of betaig-h3 is responsive to TGF-beta and the protein is found to be associated with extracellular matrix (ECM) molecules, implicating betaig-h3 as an ECM adhesive protein of developmental processes. We previously observed predominant expression of betaig-h3 expression in the basement membrane of proximal tubules of kidney. In this study, the physiological relevance of such localized expression of betaig-h3 was examined in the renal proximal tubular epithelial cells (RPTEC). RPTEC constitutively expressed betaig-h3 and the expression was dramatically induced by exogenous TGF-beta1 treatment. betaig-h3 and its second and fourth FAS1 domain were able to mediate RPTEC adhesion, spreading and migration. Two known alpha3beta1 integrin-interaction motifs including aspartatic acid and isoleucine residues, NKDIL and EPDIM in betaig-h3 were responsible to mediate RPTEC adhesion, spreading, and migration. By using specific antibodies against integrins, we confirmed that alpha3beta1 integrin mediates the adhesion and migration of RPTECs on betaig-h3. In addition, it also enhanced proliferation of RPTECs through NKDIL and EPDIM. These results indicate that betaig-h3 mediates adhesion, spreading, migration and proliferation of RPTECs through the interaction with alpha3beta1 integrin and is intimately involved in the maintenance and the regeneration of renal proximal tubular epithelium.

Altered Expression of Renal AQP1, AQP2 and NHE3 in Puromycin Aminonucleoside Induced Nephrotic Syndrome: Intervention by Alpha-MSH Treatment / 대한신장학회잡지

BACKGROUND: We examined whether puromycin aminonucleoside (PAN)-induced nephrotic syndrome (NS) is associated with altered renal handling of water and sodium along with changes of renal abundance of aquaporins (AQP1 and AQP2) and NHE3. Next we tested the effects of alpha-melanocyte stimulating hormone (alpha- MSH), a potent anti-inflammatory drug, on the PAN-induced renal functional derangement and the changes of renal AQPs and NHE3 abundance. METHODS: PAN was administered to Sprague-Dawley rats using two protocols: protocol 1 (180 mg/kg, single iv injection) and protocol 2 (100 mg/kg, single iv injection). RESULTS: In both protocols, PAN-induced NS was associated with decreased urine concentration, manifested by an increased urine output and decreased urine osmolality and TcH2O. Consistent with this, a marked downregulation of vasopressin-regulated collecting duct AQP2 expression was seen in PAN-induced NS. In protocol 2 where rats treated with moderate dose of PAN, alpha-MSH cotreatment prevented the reduction of urine osmolality and the increase of the FENa in the PAN-induced NS. This suggests that alpha-MSH may have protective effects against the renal functional deterioration induced by PAN. The renal abundance of the AQP1, AQP2 and NHE3 was reduced in PAN-induced NS in protocol 2, as seen in protocol 1. In contrast to the functional improvement, alpha-MSH cotreatment had marginal effects in the prevention of renal AQP1, AQP2 and NHE3 downregulation in PAN-induced NS. CONCLUSION: PAN-induced NS was associated with decreased urine concentration along with reduced renal AQP2, AQP1 and NHE3 abundance. Alpha-MSH may have protective effects against the renal functional deterioration (e.g., urine osmolality and FENa). However, alpha-MSH treatment alone is less likely to prevent the marked reduction of AQP2, AQP1 and NHE3 abundance in PAN-induced NS, in contrast to the previously known dramatic effects against the ischemia-reperfusion injury in kidney and small intestine.

Aquaporins in the Kidney: Localization and Clinical Physiology / 대한신장학회잡지

No abstract available.

Immunolocalization of AQP5 in Salivary Glands of Rat / 대한해부학회지

Exocrine glands secrete large volumes of fluid in response to neural or hormonal stimulation. In the present studies, we examined the immunolocalization of AQP1-5 in salivary glands of rat to clarify the potential roles of these for fluid secretion. Immunohistochemistry using cryosections of rat submandibular glands revealed that AQP1 was located in the capillary endothelia between secretory gland cells. Secretory gland cells and ductal cells were not labeled with anti-AQP1, AQP2 and AQP3 were not present in either salivary gland cells, intercalated ductal cells or striated ducts. AQP4 was localized in the basolateral plasma membrane domains of the intercalated ductal cells in rat submandibular glands whereas either secretory gland cells or striated ducts were not labeled. AQP5 was abundant in the apical domains of the secretory gland cells as well as of the secretory canaliculi and intercalated ductal cells, consistent with RT-PCR analyses as well as previous data (Nielsen et al., 1997). Importantly, AQP5 labeling was associated with the apical part of the secretory gland cells, raising the possibility for trafficking of AQP5 from intracellular vesicles to the apical plasma membranes following neuronal or hormonal stimulation. In parotid and sublingual glands, the immunolabeling pattern of AQPs was identical with that seen in submandibular glands, while the AQP5 immunolabeling was sparse in the sublingual glands which is mainly composed of mucinous glands. In conclusion, the basolateral localization of AQP4 in the intercalated ductal cells and presence of AQP5 in the apical plasma membrane of secretory acinar cells, canaliculi and intercalated ductal cells of submandibular gland suggest that both AQP4 and AQP5 may provide a critical pathway for osmotic water flow into the secreted fluid.