The Molecular Physiology of the Urinary Concentrating Mechanism

Mark A . Knepper 대한신장학회 1998 춘계학술대회 초록집 Vol.1998 No.-

Aquaporins in Health and Disease

Mark A . knepper 대한신장학회 1998 춘계학술대회 초록집 Vol.1998 No.-

Molecular physiology of water balance.

Knepper, Mark A,Kwon, Tae-Hwan,Nielsen, Soren Massachusetts Medical Society 2015 The New England journal of medicine Vol.372 No.14

Biphasic effects of ANP infusion in conscious, euvolumic rats: roles of AQP2 and ENaC trafficking.

Wang, Weidong,Li, Chunling,Nejsum, Lene N,Li, Hongyan,Kim, Soo Wan,Kwon, Tae-Hwan,Jonassen, Thomas E N,Knepper, Mark A,Thomsen, Klaus,Frokiaer, Jorgen,Nielsen, Soren American Physiological Society 2006 American journal of physiology. Renal physiology Vol.290 No.2

<P>Atrial natriuretic peptide (ANP) acutely promotes water and sodium excretion, whereas subchronic effects involve water retention. Renal hemodynamics, water and sodium excretion, and aquaporin-2 (AQP2) and epithelial Na channel (ENaC) subcellular trafficking were determined in response to continuous ANP infusion in conscious rats, where body sodium and fluid balance was constantly maintained. ANP (0.5 microg x kg(-1) x min(-1)) evoked a transient (peak at 10 min) fivefold diuresis followed by reduced urine production to control levels (30- to 90-min period). The fractional distal water excretion was significantly increased initially and then decreased in response to ANP. There was no change in the subcellular localization of AQP2 and AQP2 phosphorylated in PKA consensus site S256 (p-AQP2) 10 min after ANP infusion. In contrast, after 90 min a marked increase in apical labeling of AQP2 and p-AQP2 was observed in the inner and outer medullary collecting ducts but not in cortical collecting ducts. In support of this, ANP induced plasma membrane targeting of AQP2 in transiently AQP2-transfected cells. ANP infusion evoked an instant increase in renal sodium excretion, which persisted for 90 min. Ten minutes of ANP infusion induced no changes in the subcellular localization of ENaC subunits, whereas a marked increase in apical targeting of alpha- and gamma-subunits was observed after 90 min. In conclusion, 1) ANP infusion induced a sustained natriuresis and transient diuresis; 2) there were no changes in the subcellular localization of AQP2 and ENaC subunits after 10 min of ANP infusion; and 3) there was a marked increase in apical targeting of AQP2, p-AQP2, and alpha- and gamma-ENaC after 90 min of ANP infusion. The increased targeting of ENaC and AQP2 likely represents direct or compensatory effects to increase sodium and water reabsorption and to prevent volume depletion in response to prolonged ANP infusion.</P>

Maintained ENaC trafficking in aldosterone-infused rats during mineralocorticoid and glucocorticoid receptor blockade.

Nielsen, Jakob,Kwon, Tae-Hwan,Frokiaer, Jorgen,Knepper, Mark A,Nielsen, Soren American Physiological Society 2007 American Journal of Physiology Vol.292 No.1

<P>Aldosterone induces redistribution of epithelial sodium channel (ENaC) to the apical plasma membrane from intracellular vesicles in renal connecting tubule (CNT) and cortical collecting duct (CCD). The role of the classical mineralocorticoid receptor (MR) in ENaC trafficking is still debated. We examined whether the MR antagonist spironolactone affects ENaC regulation in the kidney cortex of aldosterone-infused rats. Aldosterone infusion for 7 days resulted in a plasma aldosterone concentration in the high physiological range (3 to 4 nM). Aldosterone infusion decreased plasma K(+) concentration compared with untreated control rats. Cotreatment with spironolactone completely blocked the aldosterone-induced decrease in plasma K(+). Immunoblotting and immunohistochemistry showed increased protein abundance of Na-K-ATPase alpha(1)-subunit and NCC in the kidney cortex, in response to aldosterone infusion that was blocked by spironolactone. In contrast, aldosterone-induced redistribution of ENaC subunits from the cytoplasm to the apical plasma membrane domain in CNT and CCD was unaffected by spironolactone. Immunoblotting of alphaENaC showed increased protein abundance in aldosterone-infused rats that was not blocked by spironolactone treatment. To exclude possible glucocorticoid receptor (GR)-mediated effects of aldosterone, we treated aldosterone-infused rats with both spironolactone and the GR antagonist RU486. Combined MR and GR blockade prevented neither ENaC trafficking nor the upregulation of alphaENaC protein abundance in aldosterone-infused rats. We provide new evidence for ENaC trafficking occurring independent of MR and GR activation in aldosterone-infused rats.</P>

Identification of β-catenin-interacting proteins in nuclear fractions of native rat collecting duct cells

Hwang, Jacqueline R.,Chou, Chung-Lin,Medvar, Barbara,Knepper, Mark A.,Jung, Hyun Jun American Physiological Society 2017 American Journal of Physiology Vol.313 No.1

<P>The gene encoding the aquaporin-2 water channel is regulated transcriptionally in response to vasopressin. In the renal collecting duct, vasopressin stimulates the nuclear translocation and phosphorylation (at Ser<SUP>552</SUP>) of β-catenin, a multifunctional protein that acts as a transcriptional coregulator in the nucleus. The purpose of this study was to identify β-catenin-interacting proteins that might be involved in transcriptional regulation in rat inner medullary collecting duct (IMCD) cells, using experimental and computational approaches. We used a standard chromatin immunoprecipitation procedure coupled to mass spectrometry (ChIP-MS) in a nuclear fraction isolated from rat IMCD suspensions. Over four biological replicates, we reproducibly identified 43 β-catenin-binding proteins, including several known β-catenin-binding partners as well as novel interacting proteins. Multiple proteins involved in transcriptional regulation were identified (Taf1, Jup, Tdrd3, Cdh1, Cenpj, and several histones). Many of the identified β-catenin-binding partners were found in prior studies to translocate to the nucleus in response to vasopressin. There was only one DNA-binding transcription factor (TF), specifically Taf1, part of the RNA-polymerase II preinitiation complex. To identify sequence-specific TFs that might interact with β-catenin, Bayes’ theorem was used to integrate data from several information sources. The analysis identified several TFs with potential binding sites in the <I>Aqp2</I> gene promoter that could interact with β-catenin in the regulation of <I>Aqp2</I> gene transcription, specifically Jun, Junb, Jund, Atf1, Atf2, Mef2d, Usf1, Max, Pou2f1, and Rxra. The findings provide information necessary for modeling the transcriptional response to vasopressin.</P>

Altered Renal Sodium Transporter Expression in an Animal Model of Type 2 Diabetes Mellitus

주권욱,Jay Wook Lee,Un Sil Jeon,임춘수,Jin Suk Han,Mark A. Knepper,나기영,오윤규 대한의학회 2007 Journal of Korean medical science Vol.22 No.6

Hemodynamic factors play an important role in the development and/or progression of diabetic nephropathy. We hypothesized that renal sodium transporter dysregulation might contribute to the hemodynamic alterations in diabetic nephropathy. Otsuka Long Evans Tokushima Fatty (OLETF) rats were used as an animal model for type 2 diabetes. Long Evans Tokushima (LETO) rats were used as controls. Renal sodium transporter regulation was investigated by semiquantitative immunoblotting and immunohistochemistry of the kidneys of 40-week-old animals. The mean serum glucose level in OLETF rats was increased to 235±25 mg/dL at 25 weeks, and the hyperglycemia continued up to the end of 40 weeks. Urine protein/ creatinine ratios were 10 times higher in OLETF rats than in LETO rats. At 40th week, the abundance of the epithelial sodium channel (ENaC) -subunit was increased in OLETF rats, but the abundance of the ENaC -subunit was decreased. No significant differences were observed in the ENaC -subunit or other major sodium transporters. Immunohistochemistry for the ENaC -subunit showed increased immunoreactivity in OLETF rats, whereas the ENaC -subunit showed reduced immunoreactivity in these rats. In OLETF rats, ENaC -subunit upregulation and ENaC -subunit downregulation after the development of diabetic nephropathy may reflect an abnormal sodium balance.

Single-tubule RNA-Seq uncovers signaling mechanisms that defend against hyponatremia in SIADH

Lee, Jae Wook,Alsady, Mohammad,Chou, Chung-Lin,de Groot, Theun,Deen, Peter M.T.,Knepper, Mark A.,Ecelbarger, Carolyn M. Springer-Verlag 2018 Kidney international Vol.93 No.1

Altered Renal Sodium Transporter Expression in an Animal Model of Type 2 Diabetes Mellitus

Oh, Yun Kyu,Joo, Kwon Wook,Lee, Jay Wook,Jeon, Un Sil,Lim, Chun Soo,Han, Jin Suk,Knepper, Mark A.,Na, Ki Young The Korean Academy of Medical Sciences 2007 JOURNAL OF KOREAN MEDICAL SCIENCE Vol.22 No.6

<P>Hemodynamic factors play an important role in the development and/or progression of diabetic nephropathy. We hypothesized that renal sodium transporter dysregulation might contribute to the hemodynamic alterations in diabetic nephropathy. Otsuka Long Evans Tokushima Fatty (OLETF) rats were used as an animal model for type 2 diabetes. Long Evans Tokushima (LETO) rats were used as controls. Renal sodium transporter regulation was investigated by semiquantitative immunoblotting and immunohistochemistry of the kidneys of 40-week-old animals. The mean serum glucose level in OLETF rats was increased to 235±25 mg/dL at 25 weeks, and the hyperglycemia continued up to the end of 40 weeks. Urine protein/creatinine ratios were 10 times higher in OLETF rats than in LETO rats. At 40th week, the abundance of the epithelial sodium channel (ENaC) β-subunit was increased in OLETF rats, but the abundance of the ENaC γ-subunit was decreased. No significant differences were observed in the ENaC α-subunit or other major sodium transporters. Immunohistochemistry for the ENaC β-subunit showed increased immunoreactivity in OLETF rats, whereas the ENaC γ-subunit showed reduced immunoreactivity in these rats. In OLETF rats, ENaC β-subunit upregulation and ENaC γ-subunit downregulation after the development of diabetic nephropathy may reflect an abnormal sodium balance.</P>

alpha-MSH prevents impairment in renal function and dysregulation of AQPs and Na-K-ATPase in rats with bilateral ureteral obstruction.

Li, Chunling,Shi, Yimin,Wang, Weidong,Sardeli, Chrysanthi,Kwon, Tae-Hwan,Thomsen, Klaus,Jonassen, Thomas,Djurhuus, Jens Christian,Knepper, Mark A,Nielsen, Soren,Frokiaer, Jorgen American Physiological Society 2006 American Journal of Physiology Vol.290 No.2

<P>The purpose of this study was to evaluate the effects of the anti-inflammatory hormone alpha-melanocyte-stimulating hormone (alpha-MSH) treatment on renal function and expression of aquaporins (AQPs) and Na-K-ATPase in the kidney in response to 24 h of bilateral ureteral obstruction (BUO) or release of BUO (BUO-R). In rats with 24-h BUO, immunoblotting revealed that downregulation of AQP2 and AQP3 was attenuated (AQP2: 38 +/- 5 vs. 13 +/- 4%; AQP3: 44 +/- 3 vs. 19 +/- 4% of sham levels; P < 0.05), whereas downregulation of Na-K-ATPase was prevented by alpha-MSH treatment (Na-K-ATPase: 94 +/- 7 vs. 35 +/- 5% of sham levels; P < 0.05). Immunocytochemistry confirmed the changes in AQP1 and Na-K-ATPase expression. Renal tubular cell apoptosis was confirmed in BUO kidneys, and alpha-MSH treatment virtually completely abolished apoptosis. Furthermore, we measured glomerular filtration rate (GFR) and effective renal plasma flow (ERPF), respectively. Forty-eight hours after BUO-R demonstrated that alpha-MSH treatment almost completely prevented the decrease in GFR (nontreated: 271 +/- 50; alpha-MSH: 706 +/- 85; sham: 841 +/- 105 microl x min(-1).100 g body wt(-1), P < 0.05) and ERPF (nontreated: 1,139 +/- 217; alpha-MSH: 2,598 +/- 129; sham: 2,633 +/- 457 microl x min(-1).100 g body wt(-1), P < 0.05). alpha-MSH treatment also partly prevented the downregulation of AQP1 and Na-K-ATPase expression in rats after BUO-R for 48 h. In conclusion, alpha-MSH treatment significantly prevents impairment in renal function and also prevents downregulation of AQP2, AQP3, and Na-K-ATPase during BUO or AQP1 and Na-K-ATPase after BUO-R, demonstrating a marked renoprotective effect of alpha-MSH treatment in conditions with urinary tract obstruction.</P>