scholarly journals Collecting‐duct‐principal‐cell‐select knockout (KO) of the mechanistic‐target‐of‐rapamycin (mTOR) alters sodium and acid/base homeostasis

2018 ◽  
Vol 32 (S1) ◽  
Author(s):  
Maurice B. Fluitt ◽  
Aaron L. Brown ◽  
Swasti Tiwari ◽  
Lijun Li ◽  
Carolyn M. Ecelbarger
Keyword(s):  
Collecting Duct ◽  
Principal Cell ◽  
Target Of Rapamycin ◽  
Acid Base ◽  
Mechanistic Target Of Rapamycin

scholarly journals Selective Deletion of the Mechanistic Target of Rapamycin From the Renal Collecting Duct Principal Cell in Mice Down-Regulates the Epithelial Sodium Channel

2022 ◽  
Vol 12 ◽  
Author(s):  
Bruce Chen ◽  
Maurice B. Fluitt ◽  
Aaron L. Brown ◽  
Samantha Scott ◽  
Anirudh Gadicherla ◽  
...  
Keyword(s):  
Sodium Channel ◽  
Collecting Duct ◽  
Epithelial Sodium Channel ◽  
Principal Cell ◽  
Target Of Rapamycin ◽  
Mtor Inhibition ◽  
Sodium Homeostasis ◽  
Mechanistic Target Of Rapamycin ◽  
Data Support ◽  
Body Sodium

The mechanistic target of rapamycin (mTOR), a serine-threonine-specific kinase, is a cellular energy sensor, integrating growth factor and nutrient signaling. In the collecting duct (CD) of the kidney, the epithelial sodium channel (ENaC) essential in the determination of final urine Na+ losses, has been demonstrated to be upregulated by mTOR, using cell culture and mTOR inhibition in ex vivo preparations. We tested whether CD-principal cell (PC) targeted deletion of mTOR using Cre-lox recombination would affect whole-body sodium homeostasis, blood pressure, and ENaC regulation in mice. Male and female CD-PC mTOR knockout (KO) mice and wild-type (WT) littermates (Cre-negative) were generated using aquaporin-2 (AQP2) promoter to drive Cre-recombinase. Under basal conditions, KO mice showed a reduced (∼30%) natriuretic response to benzamil (ENaC) antagonist, suggesting reduced in vivo ENaC activity. WT and KO mice were fed normal sodium (NS, 0.45% Na+) or a very low Na+ (LS, <0.02%) diet for 7-days. Switching from NS to LS resulted in significantly higher urine sodium losses (relative to WT) in the KO with adaptation occurring by day 2. Blood pressures were modestly (∼5–10 mm Hg) but significantly lower in KO mice under both diets. Western blotting showed KO mice had 20–40% reduced protein levels of all three subunits of ENaC under LS or NS diet. Immunohistochemistry (IHC) of kidney showed enhanced apical-vs.-cellular localization of all three subunits with LS, but a reduction in this ratio for γ-ENaC in the KO. Furthermore, the KO kidneys showed increased ubiquitination of α-ENaC and reduced phosphorylation of the serum and glucocorticoid regulated kinase, type 1 [serum glucocorticoid regulated kinase (SGK1)] on serine 422 (mTOR phosphorylation site). Taken together this suggests enhanced degradation as a consequence of reduced mTOR kinase activity and downstream upregulation of ubiquitination may have accounted for the reduction at least in α-ENaC. Overall, our data support a role for mTOR in ENaC activity likely via regulation of SGK1, ubiquitination, ENaC channel turnover and apical membrane residency. These data support a role for mTOR in the collecting duct in the maintenance of body sodium homeostasis.

scholarly journals Mechanistic target of rapamycin: integrating growth factor and nutrient signaling in the collecting duct

2018 ◽  
Vol 315 (3) ◽  
pp. F413-F416 ◽  
Author(s):  
Aaron L. Brown ◽  
Maurice B. Fluitt ◽  
Carolyn M. Ecelbarger
Keyword(s):  
Collecting Duct ◽  
Physiological Role ◽  
The Body ◽  
Fine Tuning ◽  
Target Of Rapamycin ◽  
In Vivo Studies ◽  
Whole Body ◽  
Mechanistic Target Of Rapamycin ◽  
Electrolyte Homeostasis

The renal collecting duct and other postmacula densa sites are the primary tubular regions for fine-tuning of electrolyte homeostasis in the body. A role for the mechanistic target of rapamycin (mTOR), a serine-threonine kinase, has recently been appreciated in this regulation. mTOR exists in two distinct multiprotein functional complexes, i.e., mTORC1 and mTORC2. Upregulation of mTORC1, by growth factors and amino acids, is associated with cell cycle regulation and hypertrophic changes. In contrast, mTORC2 has been demonstrated to have a role in regulating Na+ and K+ reabsorptive processes, including those downstream of insulin and serum- and glucocorticoid-regulated kinase (SGK). In addition, mTORC2 can upregulate mTORC1. A number of elegant in vitro and in vivo studies using cell systems and genetically modified mice have revealed mechanisms underlying activation of the epithelial Na+ channel (ENaC) and the renal outer medullary K+ channel (ROMK) by mTORC2. Overall, mTOR in its systematic integration of phosphorylative signaling facilitates the delicate balance of whole body electrolyte homeostasis in the face of changes in metabolic status. Thus, inappropriate regulation of renal mTOR has the potential to result in electrolyte disturbances, such as acidosis/alkalosis, hyponatremia, and hypertension. The goal of this minireview is to highlight the physiological role of mTOR in its complexes in regulating electrolyte homeostasis in the aldosterone-sensitive distal nephron.

scholarly journals Increased Na+/H+exchanger activity on the apical surface of a cilium-deficient cortical collecting duct principal cell model of polycystic kidney disease

2012 ◽  
Vol 302 (10) ◽  
pp. C1436-C1451 ◽  
Author(s):  
Dragos Olteanu ◽  
Xiaofen Liu ◽  
Wen Liu ◽  
Venus C. Roper ◽  
Neeraj Sharma ◽  
...  
Keyword(s):  
Kidney Disease ◽  
Polycystic Kidney Disease ◽  
Collecting Duct ◽  
Principal Cell ◽  
Cortical Collecting Duct ◽  
Wild Type ◽  
Polycystic Kidney ◽  
Acid Base ◽  
Collecting Ducts ◽  
Mutant Cells

Pathophysiological anomalies in autosomal dominant and recessive forms of polycystic kidney disease (PKD) may derive from impaired function/formation of the apical central monocilium of ductal epithelia such as that seen in the Oak Ridge polycystic kidney or orpk ( Ift88Tg737Rpw) mouse and its immortalized cell models for the renal collecting duct. According to a previous study, Na/H exchanger (NHE) activity may contribute to hyperabsorptive Na+movement in cilium-deficient (“mutant”) cortical collecting duct principal cell monolayers derived from the orpk mice compared with cilium-competent (“rescued”) monolayers. To examine NHE activity, we measured intracellular pH (pHi) by fluorescence imaging with the pH-sensitive dye BCECF, and used a custom-designed perfusion chamber to control the apical and basolateral solutions independently. Both mutant and rescued monolayers exhibited basolateral Na+-dependent acid-base transporter activity in the nominal absence of CO2/HCO3−. However, only the mutant cells displayed appreciable apical Na+-induced pHirecoveries from NH4+prepulse-induced acid loads. Similar results were obtained with isolated, perfused collecting ducts from orpk vs. wild-type mice. The pHidependence of basolateral cariporide/HOE-694-sensitive NHE activity under our experimental conditions was similar in both mutant and rescued cells, and 3.5- to 4.5-fold greater than apical HOE-sensitive NHE activity in the mutant cells (pHi6.23–6.68). Increased apical NHE activity correlated with increased apical NHE1 expression in the mutant cells, and increased apical localization in collecting ducts of kidney sections from orpk vs. control mice. A kidney-specific conditional cilium-knockout mouse produced a more acidic urine compared with wild-type littermates and became alkalotic by 28 days of age. This study provides the first description of altered NHE activity, and an associated acid-base anomaly in any form of PKD.

scholarly journals Lysosomes, Autophagy, and Hormesis in Cell Physiology, Pathology, and Age-Related Disease

Dose-Response ◽  
2020 ◽  
Vol 18 (3) ◽  
pp. 155932582093422 ◽  
Author(s):  
Michael N. Moore
Keyword(s):  
Intracellular Signaling ◽  
Adenosine Monophosphate ◽  
Target Of Rapamycin ◽  
Cell Physiology ◽  
Mechanistic Target Of Rapamycin ◽  
Age Related ◽  
Mechanistic Basis ◽  
The Many ◽  
Mtor Complex 1

Autophagy has been strongly linked with hormesis, however, it is only relatively recently that the mechanistic basis underlying this association has begun to emerge. Lysosomal autophagy is a group of processes that degrade proteins, protein aggregates, membranes, organelles, segregated regions of cytoplasm, and even parts of the nucleus in eukaryotic cells. These degradative processes are evolutionarily very ancient and provide a survival capability for cells that are stressed or injured. Autophagy and autophagic dysfunction have been linked with many aspects of cell physiology and pathology in disease processes; and there is now intense interest in identifying various therapeutic strategies involving its regulation. The main regulatory pathway for augmented autophagy is the mechanistic target of rapamycin (mTOR) cell signaling, although other pathways can be involved, such as 5′-adenosine monophosphate-activated protein kinase. Mechanistic target of rapamycin is a key player in the many highly interconnected intracellular signaling pathways and is responsible for the control of cell growth among other processes. Inhibition of mTOR (specifically dephosphorylation of mTOR complex 1) triggers augmented autophagy and the search is on the find inhibitors that can induce hormetic responses that may be suitable for treating many diseases, including many cancers, type 2 diabetes, and age-related neurodegenerative conditions.

Infektionen unter Immunsuppression nach Nierentransplantation

2020 ◽  
Vol 24 (08) ◽  
pp. 309-318
Author(s):  
Stephan Kemmner ◽  
Ulf Schönermarck
Keyword(s):  
Mtor Inhibitor ◽  
Pneumocystis Jirovecii ◽  
Target Of Rapamycin ◽  
Virale Infektionen ◽  
Mechanistic Target Of Rapamycin ◽  
Nach Transplantation ◽  
Polyomavirus Bk ◽  
Prophylaktische Therapie

ZUSAMMENFASSUNGUnter immunsuppressiver Therapie besteht ein deutlich erhöhtes Infektionsrisiko nach Nierentransplantation (NTx), insbesondere für virale Infektionen. Bereits vor einer geplanten NTx sollte auf einen aktuellen Impfstatus geachtet werden, da nach einer Transplantation unter immunsuppressiver Therapie einerseits Lebendimpfstoffe nicht mehr gegeben werden dürfen und andererseits eine adäquate Impfantwort schwieriger zu erreichen ist. Die saisonale Influenzaimpfung kann bereits einen Monat nach Transplantation gegeben werden, für alle anderen Impfungen wird ein Abwarten von 3–6 Monaten empfohlen. Eine prophylaktische Therapie kann das Auftreten bestimmter Infektionen effektiv verhindern. Nach NTx sollte für die ersten 6 Monate eine PjP-Prophylaxe (PjP: Pneumocystis-jirovecii-Pneumonie) mit Trimethoprim/Sulfamethoxazol verabreicht werden. Eine CMV-Prophylaxe (CMV: Zytomegalievirus) mit Valganciclovir erfolgt in Abhängigkeit vom Sero-Status von Empfänger und Spender i. d. R. für 3 bzw. 6 Monate. Im Falle einer Infektion kann in Abhängigkeit vom Schweregrad der Antimetabolit (meist MMF: Mycophenolatmofetil) dosishalbiert oder pausiert werden, jedoch ist dies mit einem erhöhten Rejektionsrisiko verbunden. Insbesondere bei Infektionen mit CMV und BKV (Polyomavirus BK) kann anstelle von MMF ein mTOR-Inhibitor (mTOR: „mechanistic target of rapamycin“) eingesetzt werden in Kombination mit einem niedrigdosierten Calcineurininhibitor (CNI). Bei einer COVID-19-Erkrankung (COVID-19: Coronavirus Disease 2019) nach NTx sollte wie bei anderen Infektionen in einer Kombinationstherapie zunächst der Antimetabolit bzw. der mTOR-Inhibitor dosisreduziert oder pausiert werden. Ein Absetzen des CNIs bei COVID-19 erscheint aus unserer Sicht nicht regelhaft indiziert, sondern bleibt schweren Verläufen im Einzelfall vorbehalten. Im Falle einer antiviralen Therapie bei COVID-19 muss immer an mögliche Interaktionen mit den Immunsuppressiva (v. a. mit CNI und mTOR-Inhibitoren) gedacht werden.

Histological and Immunohistochemical Evaluation of Phosphorylated Mechanistic Target of Rapamycin in Canine Skin Tumours

2021 ◽  
Vol 184 ◽  
pp. 60-64
Author(s):  
Raimon Mathew ◽  
Indira S. Sajitha ◽  
Dhanush K. Balakrishnan-Nair ◽  
Sudheesh S. Nair ◽  
Bibu J. Kariyil ◽  
...  
Keyword(s):  
Target Of Rapamycin ◽  
Skin Tumours ◽  
Mechanistic Target Of Rapamycin

Long-term regulation of renal Na-dependent cotransporters and ENaC: response to altered acid-base intake

2000 ◽  
Vol 279 (3) ◽  
pp. F459-F467 ◽  
Author(s):  
Gheun-Ho Kim ◽  
Stephen W. Martin ◽  
Patricia Fernández-Llama ◽  
Shyama Masilamani ◽  
Randall K. Packer ◽  
...  
Keyword(s):  
Collecting Duct ◽  
Na Channel ◽  
Thick Ascending Limb ◽  
Acid Base Balance ◽  
Acid Base ◽  
Opposite Pattern ◽  
Α Subunit ◽  
Base Balance ◽  
Acid Loading

Increased systemic acid intake is associated with an increase in apical Na/H exchange in the renal proximal tubule mediated by the type 3 Na/H exchanger (NHE3). Because NHE3 mediates both proton secretion and Na absorption, increased NHE3 activity could inappropriately perturb Na balance unless there are compensatory changes in Na handling. In this study, we use semiquantitative immunoblotting of rat kidneys to investigate whether acid loading is associated with compensatory decreases in the abundance of renal tubule Na transporters other than NHE3. Long-term (i.e., 7-day) acid loading with NH4Cl produced large decreases in the abundances of the thiazide-sensitive Na-Cl cotransporter (TSC/NCC) of the distal convoluted tubule and both the β- and γ-subunits of the amiloride-sensitive epithelial Na channel (ENaC) of the collecting duct. In addition, the renal cortical abundance of the proximal type 2 Na-dependent phosphate transporter (NaPi-2) was markedly decreased. In contrast, abundances of the bumetanide-sensitive Na-K-2Cl cotransporter of the thick ascending limb and the α-subunit of ENaC were unchanged. A similar profile of changes was seen with short-term (16-h) acid loading. Long-term (7-day) base loading with NaHCO3resulted in the opposite pattern of response with marked increases in the abundances of the β- and γ-subunits of ENaC and NaPi-2. These adaptations may play critical roles in the maintenance in Na balance when changes in acid-base balance occur.

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