scholarly journals Rapamycin inhibition of mTORC1 reverses lithium-induced proliferation of renal collecting duct cells

2013 ◽  
Vol 305 (8) ◽  
pp. F1201-F1208 ◽  
Author(s):  
Yang Gao ◽  
Melissa J. Romero-Aleshire ◽  
Qi Cai ◽  
Theodore J. Price ◽  
Heddwen L. Brooks
Keyword(s):  
Collecting Duct ◽  
Control Cell ◽  
Renal Cysts ◽  
Lithium Therapy ◽  
Mtor Inhibition ◽  
Duct Cells ◽  
Mtorc1 Signaling ◽  
Collecting Ducts ◽  
Collecting Duct Cells ◽  
Bipolar Affective Disorders

Nephrogenic diabetes insipidus (NDI) is the most common renal side effect in patients undergoing lithium therapy for bipolar affective disorders. Approximately 2 million US patients take lithium of whom ∼50% will have altered renal function and develop NDI ( 2 , 37 ). Lithium-induced NDI is a defect in the urinary concentrating mechanism. Lithium therapy also leads to proliferation and abundant renal cysts (microcysts), commonly in the collecting ducts of the cortico-medullary region. The mTOR pathway integrates nutrient and mitogen signals to control cell proliferation and cell growth (size) via the mTOR Complex 1 (mTORC1). To address our hypothesis that mTOR activation may be responsible for lithium-induced proliferation of collecting ducts, we fed mice lithium chronically and assessed mTORC1 signaling in the renal medulla. We demonstrate that mTOR signaling is activated in the renal collecting ducts of lithium-treated mice; lithium increased the phosphorylation of rS6 (Ser240/Ser244), p-TSC2 (Thr1462), and p-mTOR (Ser2448). Consistent with our hypothesis, treatment with rapamycin, an allosteric inhibitor of mTOR, reversed lithium-induced proliferation of medullary collecting duct cells and reduced levels of p-rS6 and p-mTOR. Medullary levels of p-GSK3β were increased in the renal medullas of lithium-treated mice and remained elevated following rapamycin treatment. However, mTOR inhibition did not improve lithium-induced NDI and did not restore the expression of collecting duct proteins aquaporin-2 or UT-A1.

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

2019 ◽  
Vol 317 (3) ◽  
pp. F632-F637 ◽  
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.

Fluorescent characterization of collecting duct cells: a second H+-secreting type

1988 ◽  
Vol 255 (5) ◽  
pp. F1003-F1014 ◽  
Author(s):  
G. J. Schwartz ◽  
L. M. Satlin ◽  
J. E. Bergmann
Keyword(s):  
Collecting Duct ◽  
Apical Surface ◽  
Cortical Collecting Duct ◽  
Cytosolic Ph ◽  
Duct Cells ◽  
Physiological Properties ◽  
Collecting Ducts ◽  
Outer Stripe ◽  
Collecting Duct Cells ◽  
Medullary Collecting Duct

We have used three fluorescent probes to label acid-base transporting cells with specific physiological properties in the rabbit collecting duct. Rhodamine albumin identified cells active in luminal endocytosis; rhodamine peanut agglutinin (PNA) identified cells with apical surface PNA ligands; and 6-carboxyfluorescein (6-CF) diacetate identified cells with alkaline pH or acetazolamide-sensitive esterase activity. More than 90% of all cells identified by PNA or rhodamine albumin selectively concentrated 6-CF. Axial heterogeneity of the identified cells was clearly evident along the collecting duct. In the midcortical collecting duct the predominant labeled cell (108 +/- 15/mm) was positive for PNA and 6-CF. These cells were less prevalent (69 +/- 10/mm) in inner cortical collecting ducts and absent from the outer medullary collecting duct. Cells that labeled only with 6-CF (with no detectable luminal endocytosis or PNA binding) showed the opposite distribution. They were the predominant identified cell in the inner stripe of the outer medulla (126 +/- 20/mm), and were less common in the cortical collecting duct. Because the former segment secretes H+, it was likely that these cells were H+-secreting cells. We used excitation ratio microspectrofluorometry of 6-CF to measure cytosolic pH (pHi approximately 7.2) and found evidence for a basolateral DIDS-sensitive Cl- -HCO3- exchanger and a Na+-independent luminal H+ pump. The previously described endocytic H+-secreting cell was seen at its highest concentration in the outer stripe (39 +/- 6/mm). Finally, 5-10% of identified cells did not stain selectively with 6-CF in cortical collecting ducts (solely endocytic or PNA binding). The function of these latter types could not be established. These studies suggest that the distribution and number of these populations of cells may determine the direction and magnitude of H+ transport along the collecting duct.

Changes in cellular composition of kidney collecting duct cells in rats with lithium-induced NDI

2004 ◽  
Vol 286 (4) ◽  
pp. C952-C964 ◽  
Author(s):  
Birgitte Mønster Christensen ◽  
David Marples ◽  
Young-Hee Kim ◽  
Weidong Wang ◽  
Jørgen Frøkiær ◽  
...  
Keyword(s):  
Collecting Duct ◽  
Lithium Treatment ◽  
Intercalated Cells ◽  
Cellular Organization ◽  
Principal Cells ◽  
Duct Cells ◽  
Collecting Ducts ◽  
Collecting Duct Cells ◽  
Principal And Intercalated Cells ◽  
Double Immunolabeling

Lithium treatment for 4 wk caused severe polyuria, dramatic downregulation in aquaporin-2 (AQP-2) expression, and marked decrease in AQP-2 immunoreactivity with the appearance of a large number of cells without AQP-2 labeling in the collecting ducts after lithium treatment. Surprisingly, this was not all due to an increase in AQP-2-negative principal cells, because double immunolabeling revealed that the majority of the AQP-2-negative cells displayed [H+]ATPase labeling, which identified them as intercalated cells. Moreover, multiple [H+]ATPase-labeled cells were adjacent, which was never seen in control rats. Quantitation confirmed a significant decrease in the fraction of collecting duct cells that exhibited detectable AQP-2 labeling compared with control rats: in cortical collecting ducts, 40 ± 3.4 vs. 62 ± 1.8% of controls ( P < 0.05; n = 4) and in inner medullary collecting ducts, 58 ± 1.6 vs. 81 ± 1.3% of controls ( P < 0.05; n = 4). In parallel, a significant increase in the fraction of intercalated ([H+]ATPase-positive) cells was shown. Urine output, whole kidney AQP-2 expression, cellular organization, and the fractions of principal and intercalated cells in cortex and inner medulla returned to control levels after 4 wk on a lithium-free diet following 4 wk on a lithium-containing diet. In conclusion, lithium treatment not only decreased AQP-2 expression, but dramatically and reversibly reduced the fraction of principal cells and altered the cellular organization in collecting ducts. These effects are likely to be important in lithium-induced nephrogenic diabetes insipidus.

scholarly journals Slc4a8 in the Kidney: Expression, Subcellular Localization and Role in Salt Reabsorption

2018 ◽  
Vol 50 (4) ◽  
pp. 1361-1375 ◽  
Author(s):  
Jie Xu ◽  
Sharon Barone ◽  
Kamyar Zahedi ◽  
Marybeth Brooks ◽  
Manoocher Soleimani
Keyword(s):  
In Situ Hybridization ◽  
Subcellular Localization ◽  
Collecting Duct ◽  
Basolateral Membrane ◽  
Acid Base ◽  
Duct Cells ◽  
Collecting Ducts ◽  
Collecting Duct Cells ◽  
Medullary Collecting Duct

Background/Aims: The sodium-dependent bicarbonate transporter Slc4a8 (a.k.a NDCBE) mediates the co-transport of sodium and bicarbonate in exchange for chloride. It is abundantly detected in the brain, with low expression levels in the kidney. The cell distribution and subcellular localization of Slc4a8 in the kidney and its role in acid/base and electrolyte homeostasis has been the subject of conflicting reports. There are no conclusive localization or functional studies to pinpoint the location and demonstrate the function of Slc4a8 in the kidney. Methods: Molecular techniques, including RT-PCR and in situ hybridization, were performed on kidney sections and tagged epitopes were used to examine the membrane targeting of Slc4a8 in polarized kidney cells. Crispr/Cas9 was used to generate and examine Slc4a8 KO mice. Results: Zonal distribution and in situ hybridization studies showed very little expression for Slc4a8 (NDCBE) in the cortex or in cortical collecting ducts (CCD). Slc4a8 was predominantly detected in the outer and inner medullary collecting ducts (OMCD and IMCD), and was targeted to the basolateral membrane of osmotically tolerant MDCK cells. Slc4a8 KO mice did not show any abnormal salt or bicarbonate wasting under baseline conditions or in response to bicarbonate loading, salt restriction or furosemide-induced diuresis. Conclusion: Slc4a8 (NDCBE) is absent in the CCD and is predominantly localized on the basolateral membrane of medullary collecting duct cells. Further, Slc4a8 deletion does not cause significant acid base or electrolyte abnormalities in pathophysiologic states. Additional studies are needed to examine the role of Slc4a8 (NDCBE) in intracellular pH and volume regulation in medullary collecting duct cells.

scholarly journals Gender-Dependent Phenotype in Polycystic Kidney Disease Is Determined by Differential Intracellular Ca2+ Signals

2021 ◽  
Vol 22 (11) ◽  
pp. 6019
Author(s):  
Khaoula Talbi ◽  
Inês Cabrita ◽  
Rainer Schreiber ◽  
Karl Kunzelmann
Keyword(s):  
Cell Proliferation ◽  
Kidney Disease ◽  
Polycystic Kidney Disease ◽  
Collecting Duct ◽  
Primary Cells ◽  
Loss Of Function ◽  
Polycystic Kidney ◽  
Chloride Currents ◽  
Duct Cells ◽  
Collecting Duct Cells

Autosomal dominant polycystic kidney disease (ADPKD) is caused by loss of function of PKD1 (polycystin 1) or PKD2 (polycystin 2). The Ca2+-activated Cl− channel TMEM16A has a central role in ADPKD. Expression and function of TMEM16A is upregulated in ADPKD which causes enhanced intracellular Ca2+ signaling, cell proliferation, and ion secretion. We analyzed kidneys from Pkd1 knockout mice and found a more pronounced phenotype in males compared to females, despite similar levels of expression for renal tubular TMEM16A. Cell proliferation, which is known to be enhanced with loss of Pkd1−/−, was larger in male when compared to female Pkd1−/− cells. This was paralleled by higher basal intracellular Ca2+ concentrations in primary renal epithelial cells isolated from Pkd1−/− males. The results suggest enhanced intracellular Ca2+ levels contributing to augmented cell proliferation and cyst development in male kidneys. Enhanced resting Ca2+ also caused larger basal chloride currents in male primary cells, as detected in patch clamp recordings. Incubation of mouse primary cells, mCCDcl1 collecting duct cells or M1 collecting duct cells with dihydrotestosterone (DHT) enhanced basal Ca2+ levels and increased basal and ATP-stimulated TMEM16A chloride currents. Taken together, the more severe cystic phenotype in males is likely to be caused by enhanced cell proliferation, possibly due to enhanced basal and ATP-induced intracellular Ca2+ levels, leading to enhanced TMEM16A currents. Augmented Ca2+ signaling is possibly due to enhanced expression of Ca2+ transporting/regulating proteins.

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