Fluvastatin modulates renal water reabsorption in vivo through increased AQP2 availability at the apical plasma membrane of collecting duct cells

It is widely accepted that in vivo the function of the papilla of the mammalian kidney is supported primarily by anaerobic metabolism. As a result, the major source of energy for support of function in the papilla is considered to be derived from glycolysis. This orientation originates from two concepts: 1) that in vivo the gaseous environment of the papilla has such a low PO2 that O2 availability limits O2 consumption, and 2) that papillary tissue has a high rate of glycolysis when compared with either cortical tissue or extrarenal tissues. It has also been tacitly assumed that papillary tissue has a "low" O2 uptake. Review of the measurements of PO2 of papillary tissue and of urine PO2 indicates that the PO2 of papillary tissue should not limit its aerobic mitochondrial oxidative metabolism. While the rate of aerobic glycolysis in papillary tissue is high, simultaneously papillary tissue has a rate of O2 uptake similar to that of liver and higher than that of muscle. The major (two-thirds) source of energy for papillary tissue in vitro is from O2 uptake. That papillary tissue is not exclusively dependent on glucose for its energy requirements is indicated by the greater stimulation of papillary tissue QO2 by succinate than by glucose. Thus, papillary tissue has both a high aerobic mitochondrial oxidative metabolism and a high aerobic glycolytic metabolism. It is suggested that the mechanism for the high rate of aerobic glycolysis in the presence of an adequate O2 supply is due to the relatively small mass of mitochondria in papillary tissue in relation to the amount of work done by the tissue. As a result of the limited rate of ATP production by the mitochondrial electron transport chain, the phosphorylation state ([ATP]/[ADP][Pi]) is reduced and the cytoplasmic redox state ([NAD+]/[NADH]) of the papillary collecting duct cells also becomes more reduced; changes in both ratios enhance the rate of glycolysis. This limited metabolic capacity of the collecting duct cells may permit an excess volume of solute and water to be excreted during volume expansion diuresis. The metabolic characteristics of the papilla, when compared to cortex, also provide a basis for the observed differences in substrate selectivity of cortex and medulla with respect to utilization of glucose and lactate. The experimental approaches that may provide information bearing on the suggested mechanisms for regulation of papillary metabolism in relation to tubular work functions are indicated.

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Rab7 involves Vps35 to mediate AQP2 sorting and apical trafficking in collecting duct cells

AJP Renal Physiology ◽

10.1152/ajprenal.00297.2019 ◽

2020 ◽

Vol 318 (4) ◽

pp. F956-F970 ◽

Cited By ~ 4

Author(s):

Wei-Ling Wang ◽

Shih-Han Su ◽

Kit Yee Wong ◽

Chan-Wei Yang ◽

Chin-Fu Liu ◽

...

Keyword(s):

Plasma Membrane ◽

Apical Membrane ◽

Collecting Duct ◽

Water Channel ◽

Small Gtpase ◽

Apical Plasma Membrane ◽

Water Reabsorption ◽

Recycling Endosomes ◽

Early Endosomes ◽

Vacuolar Protein

Aquaporin-2 (AQP2) is a vasopressin-regulated water channel protein responsible for osmotic water reabsorption by kidney collecting ducts. In response to vasopressin, AQP2 traffics from intracellular vesicles to the apical plasma membrane of collecting duct principal cells, where it increases water permeability and, hence, water reabsorption. Despite continuing efforts, gaps remain in our knowledge of vasopressin-regulated AQP2 trafficking. Here, we studied the functions of two retromer complex proteins, small GTPase Rab7 and vacuolar protein sorting 35 (Vps35), in vasopressin-induced AQP2 trafficking in a collecting duct cell model (mpkCCD cells). We showed that upon vasopressin removal, apical AQP2 returned to Rab5-positive early endosomes before joining Rab11-positive recycling endosomes. In response to vasopressin, Rab11-associated AQP2 trafficked to the apical plasma membrane before Rab5-associated AQP2 did so. Rab7 knockdown resulted in AQP2 accumulation in early endosomes and impaired vasopressin-induced apical AQP2 trafficking. In response to vasopressin, Rab7 transiently colocalized with Rab5, indicative of a role of Rab7 in AQP2 sorting in early endosomes before trafficking to the apical membrane. Rab7-mediated apical AQP2 trafficking in response to vasopressin required GTPase activity. When Vps35 was knocked down, AQP2 accumulated in recycling endosomes under vehicle conditions and did not traffic to the apical plasma membrane in response to vasopressin. We conclude that Rab7 and Vps35 participate in AQP2 sorting in early endosomes under vehicle conditions and apical membrane trafficking in response to vasopressin.

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A Role for VAMP8/Endobrevin in Surface Deployment of the Water Channel Aquaporin 2

Molecular and Cellular Biology ◽

10.1128/mcb.00814-09 ◽

2009 ◽

Vol 30 (1) ◽

pp. 333-343 ◽

Cited By ~ 26

Author(s):

Cheng-Chun Wang ◽

Chee Peng Ng ◽

Hong Shi ◽

Hwee Chien Liew ◽

Ke Guo ◽

...

Keyword(s):

Plasma Membrane ◽

Membrane Protein ◽

Collecting Duct ◽

Water Channel ◽

Snare Proteins ◽

Snare Protein ◽

Aquaporin 2 ◽

Duct Cells ◽

Collecting Duct Cells ◽

Intracellular Vesicles

ABSTRACT Vesicle-associated-membrane protein 8 (VAMP8) is highly expressed in the kidney, but the exact physiological and molecular functions executed by this v-SNARE protein in nephrons remain elusive. Here, we show that the depletion of VAMP8 in mice resulted in hydronephrosis. Furthermore, the level of the vasopressin-responsive water channel aquaporin 2 (AQP2) was increased by three- to fivefold in VAMP8-null mice. Forskolin and [desamino-Cys1, D-Arg8]-vasopressin (DDAVP)-induced AQP2 exocytosis was impaired in VAMP8-null collecting duct cells. VAMP8 was revealed to colocalize with AQP2 on intracellular vesicles and to interact with the plasma membrane t-SNARE proteins syntaxin4 and syntaxin3, suggesting that VAMP8 mediates the regulated fusion of AQP2-positive vesicles with the plasma membrane.

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Glucocorticoid Receptor Maintains Vasopressin‐Regulated Water Reabsorption Pathway in the Kidney Collecting Duct Cells

The FASEB Journal ◽

10.1096/fasebj.2020.34.s1.05129 ◽

2020 ◽

Vol 34 (S1) ◽

pp. 1-1

Author(s):

Shih-Han Su ◽

Cheng-Hsuan Ho ◽

Ming-Jiun Yu

Keyword(s):

Glucocorticoid Receptor ◽

Collecting Duct ◽

Water Reabsorption ◽

Kidney Collecting Duct ◽

Duct Cells ◽

Collecting Duct Cells

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Structure and regulation of the mDot1 gene, a mouse histone H3 methyltransferase

Biochemical Journal ◽

10.1042/bj20030839 ◽

2004 ◽

Vol 377 (3) ◽

pp. 641-651 ◽

Cited By ~ 42

Author(s):

Wenzheng ZHANG ◽

Yoshihide HAYASHIZAKI ◽

Bruce C. KONE

Keyword(s):

Alternative Splicing ◽

Fluorescent Protein ◽

Expressed Sequence Tag ◽

Collecting Duct ◽

Signal Transduction Pathway ◽

Dependent Manner ◽

Coding Region ◽

Duct Cells ◽

Collecting Duct Cells

Recently, a new class of histone methyltransferases that plays an indirect role in chromatin silencing by targeting a conserved lysine residue in the nucleosome core was described, namely the Dot1 (disruptor of telomeric silencing) family [Feng, Wang, Ng, Erdjument-Bromage, Tempst, Struhl and Zhang (2002) Curr. Biol. 12, 1052–1058; van Leeuwen, Gafken and Gottschling (2002) Cell (Cambridge, Mass.) 109, 745–756; Ng, Feng, Wang, Erdjument-Bromage, Tempst, Zhang and Struhl (2002) Genes Dev. 16, 1518–1527]. In the present study, we report the isolation, genomic organization and in vivo expression of a mouse Dot1 homologue (mDot1). Expressed sequence tag analysis identified five mDot1 mRNAs (mDot1a–mDot1e) derived from alternative splicing. mDot1a and mDot1b encode 1540 and 1114 amino acids respectively, whereas mDot1c–mDot1e are incomplete at the 5´-end. mDot1a is closest to its human counterpart (hDot1L), sharing 84% amino acid identity. mDot1b is truncated at its N- and C-termini and contains an internal deletion. The five mDot1 isoforms are encoded by 28 exons on chromosome 10qC1, with exons 24 and 28 further divided into two and four sections respectively. Alternative splicing occurs in exons 3, 4, 12, 24, 27 and 28. Northern-blot analysis with probes corresponding to the methyltransferase domain or the mDot1a-coding region detected 7.6 and 9.5 kb transcripts in multiple tissues, but only the 7.6 kb transcript was evident in mIMCD3-collecting duct cells. Transfection of mDot1a–EGFP constructs (where EGFP stands for enhanced green fluorescent protein) into human embryonic kidney (HEK)-293T or mIMCD3 cells increased the methylation of H3-K79 but not H3-K4, -K9 or -K36. Furthermore, DMSO induced mDot1 gene expression and methylation specifically at H3-K79 in mIMCD3 cells in a time- and dose-dependent manner. Collectively, these results add new members to the Dot1 family and show that mDot1 is involved in a DMSO-mediated signal-transduction pathway in collecting duct cells.

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Low aquaporin-2 levels in polyuric DI +/+ severe mice with constitutively high cAMP-phosphodiesterase activity

AJP Renal Physiology ◽

10.1152/ajprenal.1999.276.2.f179 ◽

1999 ◽

Vol 276 (2) ◽

pp. F179-F190 ◽

Cited By ~ 16

Author(s):

Jørgen Frøkiaer ◽

David Marples ◽

Heinz Valtin ◽

John F. Morris ◽

Mark A. Knepper ◽

...

Keyword(s):

Plasma Membrane ◽

Collecting Duct ◽

Northern Blotting ◽

Apical Plasma Membrane ◽

Phosphodiesterase Activity ◽

Camp Phosphodiesterase ◽

Aquaporin 2 ◽

Acute Response ◽

Camp Levels

In the renal collecting duct, vasopressin acutely activates cAMP production, resulting in trafficking of aquaporin-2 water channels (AQP2) to the apical plasma membrane, thereby increasing water permeability. This acute response is modulated by long-term changes in AQP2 expression. Recently, a cAMP-responsive element has been identified in the AQP2 gene, raising the possibility that changes in cAMP levels may control AQP2 expression. To investigate this possibility, we determined AQP2 protein levels in a strain of mice, DI +/+ severe (DI), which have genetically high levels of cAMP-phosphodiesterase activity, and hence low cellular cAMP levels, and severe polyuria. Semiquantitative immunoblotting of membrane fractions prepared from whole kidneys revealed that AQP2 levels in DI mice were only 26 ± 7% (±SE) of those in control mice ( n = 10, P < 0.01). In addition, semiquantitative Northern blotting revealed a significantly lower AQP2 mRNA expression in kidneys from DI mice compared with control mice (43 ± 6% vs. 100 ± 10%; n = 6 in each group, P < 0.05). AQP3 levels were also reduced. The mice were polyuric and urine osmolalities were accordingly substantially lower in the DI mice than in controls (496 ± 53 vs. 1,696 ± 105 mosmol/kgH2O, respectively). Moreover, there was a linear correlation between urine osmolalities and AQP2 levels ( P < 0.05). Immunoelectron microscopy confirmed the markedly lower expression of AQP2 in collecting duct principal cells in kidneys of DI mice and, furthermore, demonstrated that AQP2 was almost completely absent from the apical plasma membrane. Thus expression of AQP2 and AQP2 trafficking were severely impaired in DI mice. These results are consistent with the view that in vivo regulation of AQP2 expression by vasopressin is mediated by cAMP.

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Loss of primary cilia increases polycystin-2 and TRPV4 and the appearance of a nonselective cation channel in the mouse cortical collecting duct

AJP Renal Physiology ◽

10.1152/ajprenal.00210.2019 ◽

2019 ◽

Vol 317 (3) ◽

pp. F632-F637 ◽

Cited By ~ 5

Author(s):

Takamitsu Saigusa ◽

Qiang Yue ◽

Marlene A. Bunni ◽

P. Darwin Bell ◽

Douglas C. Eaton

Keyword(s):

Collecting Duct ◽

Cation Channel ◽

Conditional Knockout ◽

Nonselective Cation Channel ◽

Channel Activity ◽

Open Probability ◽

Duct Cells ◽

Collecting Ducts ◽

Collecting Duct Cells

Flow-related bending of cilia results in Ca2+ influx through a polycystin-1 (Pkd1) and polycystin-2 (Pkd2) complex, both of which are members of the transient receptor potential (TRP) family (TRPP1 and TRPP2, respectively). Deletion of this complex as well as cilia result in polycystic kidney disease. The Ca2+ influx pathway has been previously characterized in immortalized collecting duct cells without cilia and found to be a 23-pS channel that was a multimere of TRPP2 and TRPV4. The purpose of the present study was to determine if this TRPP2 and TRPV4 multimere exists in vivo. Apical channel activity was measured using the patch-clamp technique from isolated split-open cortical collecting ducts from adult conditional knockout mice with ( Ift88flox/flox) or without ( Ift88−/−) cilia. Single tubules were isolated for measurements of mRNA for Pkd1, Pkd2, Trpv4, and epithelial Na+ channel subunits. The predominant channel activity from Ift88flox/flox mice was from epithelial Na+ channel [5-pS Na+-selective channels with long mean open times (475.7 ± 83.26 ms) and open probability > 0.2]. With the loss of cilia, the predominant conductance was a 23-pS nonselective cation channel (reversal potential near 0) with a short mean open time (72 ± 17 ms), open probability < 0.08, and a characteristic flickery opening. Loss of cilia increased mRNA levels for Pkd2 and Trpv4 from single isolated cortical collecting ducts. In conclusion, 23-pS channels exist in vivo, and activity of this channel is elevated with loss of cilia, consistent with previous finding of an elevated-unregulated Ca2+-permeable pathway at the apical membrane of collecting duct cells that lack cilia.

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