Dual Influence of Aldosterone on AQP2 Expression in Cultured Renal Collecting Duct Principal Cells

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Besides its classical effects on salt homeostasis in renal epithelial cells, aldosterone promotes inflammation and fibrosis and modulates cell proliferation. The proinflammatory transcription factor NF-B has been implicated in cell proliferation, apoptosis, and regulation of transepithelial sodium transport. The effect of aldosterone on the NF-B pathway in principal cells of the cortical collecting duct, a major physiologic target of aldosterone, is unknown. Here, in both cultured cells and freshly isolated rat cortical collecting duct, aldosterone activated the canonical NF-B signaling pathway, leading to increased expression of several NF-B-targeted genes (IB␣, plasminogen activator inhibitor 1, monocyte chemoattractant protein 1, IL-1␤, and IL-6). Small interfering RNA-mediated knockdown of the serum and glucocorticoid-inducible kinase SGK1, a gene induced early in the response to aldosterone, but not pharmacologic inhibition of extracellular signal-regulated kinase and p38 kinase, attenuated aldosterone-induced NF-B activation. Pharmacologic antagonism or knockdown of the mineralocorticoid receptor prevented aldosterone-induced NF-B activity. In addition, activation of the glucocorticoid receptor inhibited the transactivation of NF-B by aldosterone. In agreement with these in vitro findings, spironolactone prevented NF-B-induced transcriptional activation observed in cortical collecting ducts of salt-restricted rats. In summary, aldosterone activates the canonical NF-B pathway in principal cells of the cortical collecting duct by activating the mineralocorticoid receptor and by inducing SGK1.

Section: Discussionmentioning

confidence: 99%

Aldosterone Activates NF-κB in the Collecting Duct

Leroy

Seigneux²,

Agassiz³

et al. 2009

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“…These cells, derived from microdissected collecting ducts of an SVPK/Tag transgenic mouse (11), develop into tight and highly differentiated epithelium when grown on permeable filters (11)(12)(13)(14). In addition, we have shown that mpkCCD cl4 cells maintain high levels of native AVP-inducible AQP2 expression, which can be exploited for analysis of intracellular mechanisms governing long-term AQP2 expression (15,16). …”

mentioning

confidence: 99%

Dual Effects of Hypertonicity on Aquaporin-2 Expression in Cultured Renal Collecting Duct Principal Cells

Hasler¹,

Vinciguerra²,

Vandewalle³

et al. 2005

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The driving force for renal water reabsorption is provided by the osmolarity gradient between the interstitium and the tubular lumen, which is subject to rapid physiologic variations as a consequence of water intake fluctuations. The effect of increased extracellular tonicity/osmolarity on vasopressin-inducible aquaporin-2 (AQP2) expression in immortalized mouse collecting duct principal cells (mpkCCD cl4 ) is investigated in this report. Increasing the osmolarity of the medium either by the addition of NaCl, sucrose, or urea first decreased AQP2 expression after 3 h. AQP2 expression then increased in cells exposed to NaClor sucrose-supplemented hypertonic medium after longer periods of time (24 h), while urea-supplemented hyperosmotic medium had no effect. Altered AQP2 expression induced by both short-term (3 h) and long-term ( A quaporin (AQP) water channels facilitate osmoticallydriven water movement across renal epithelial cells by forming aqueous pores across the plasma membrane. Currently, 10 members of the AQP family have been identified in mammals and at least 7 of these are expressed in the kidney (1,2). In the collecting duct (CD), the site of final adjustment of water excretion, water permeability is chiefly controlled by the antidiuretic hormone [8-arginine]vasopressin (AVP), which binds to vasopressin V 2 receptors of CD principal cells, leading to G s ␣/adenylyl cyclase activation, increased intracellular cAMP concentration, and cAMP-protein kinase (PKA) activation (2). An acute increase in plasma AVP concentration induces rapid AQP2 translocation from intracellular storage vesicles to the apical membrane (3) responsible for enhanced apical water permeability. Water exits the cells via basolateral AQP3 and AQP4 (4,5). Diminishing levels of circulating AVP leads to endocytotic retrieval of apical AQP2 and to reduced water permeability (3). Conversely, sustained increases in circulating AVP increase AQP2 and AQP3 abundance (6) and consequently maximal CD water permeability.Water excretion is dependent on the corticopapillary osmotic gradient which arises from interstitial accumulation of both urea and NaCl. This gradient decreases during water diuresis and increases under conditions of antidiuresis (2). Consequently, renal medullary cells are subject to fluctuations of interstitial osmolarity. Renal epithelial cells protect themselves from the effects of hypertonicity-induced cell shrinkage and osmotic stress chiefly by activating specific, immediate, early-regulated genes (7), heat shock genes (7,8), and genes that enhance accumulation of small organic solutes, known as compatible osmolytes, which in turn lower cellular ionic strength toward isotonic levels (9). Because water restriction increases AQP2 abundance in rat kidney despite chronic administration of V 2 -receptor antagonists (10), interstitial hyperosmolarity may regulate AQP2 expression as well. The aim of this study was to investigate the influence of increased extracellular tonicity/osmolarity on AQP2 abundance in the immortalized mouse...

“…When grown on permeable filters, these cells develop into tight and highly differentiated epithelium (18 -20) that displays low levels of native AQP2 mRNA and protein in the absence of AVP. AQP2 expression levels are increased dramatically when AVP is added to the basolateral medium (21)(22)(23). We recently showed that extracellular hyperosmolarity affects AQP2 mRNA and protein abundance in a time-dependent manner in mpkCCD cl4 cells and that this is due to changes in AQP2 gene transcription (17).…”

mentioning

confidence: 99%

Tonicity-Responsive Enhancer Binding Protein Is an Essential Regulator of Aquaporin-2 Expression in Renal Collecting Duct Principal Cells

Hasler¹,

Jeon²,

Kim³

et al. 2006

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119

107

Tonicity-responsive enhancer binding protein (TonEBP) plays a key role in protecting renal cells from hypertonic stress by stimulating transcription of specific genes. Under hypertonic conditions, TonEBP activity is enhanced via increased nuclear translocation, transactivation, and abundance. It was reported previously that hypertonicity exerted a dual, time-dependent effect on vasopressin-inducible aquaporin-2 (AQP2) expression in immortalized mouse collecting duct principal cells (mpkCCD cl4 ). Whereas AQP2 abundance decreased after 3 h of hyperosmotic challenge, it increased after 24 h of hypertonic challenge. This study investigated the role that TonEBP may play in these events by subjecting mpkCCD cl4 cells to 3 or 24 h of hypertonic challenge. Hypertonic challenge increased TonEBP mRNA and protein content and enhanced TonEBP activity as illustrated by both increased TonEBP-dependent luciferase activity and mRNA expression of several genes that are targeted by TonEBP. Irrespective of the absence or presence of vasopressin, decreased TonEBP activity in cells that were transfected with either TonEBP small interfering RNA or an inhibitory form of TonEBP strongly reduced AQP2 mRNA and protein content under iso-osmotic conditions and blunted the increase of AQP2 abundance that was induced after 24h of hypertonic challenge. Conversely, decreased TonEBP activity did not significantly alter reduced expression of AQP2 mRNA that was induced by 3 h of hypertonic challenge. Mutation of a TonE enhancer element located 489 bp upstream of the AQP2 transcriptional start site abolished the hypertonicity-induced increase of luciferase activity in cells that expressed AQP2 promoter-luciferase plasmid constructs, indicating that TonEBP influences AQP2 transcriptional activity at least partially by acting directly on the AQP2 promoter. These findings demonstrate that in collecting duct principal cells, TonEBP plays a central role in regulating AQP2 expression by enhancing AQP2 gene transcription.