Pleiotropic effects of dihydrotestosterone in immortalized mouse proximal tubule cells. Technical note

Aldosterone-induced microRNAs act as feedback regulators of mineralocorticoid receptor signaling in kidney epithelia

The final steps in the Renin-Angiotensin-Aldosterone signaling System (RAAS) involve binding of the corticosteroid hormone, aldosterone to its mineralocorticoid receptor (MR). The bound MR interacts with response elements to induce or repress the transcription of aldosterone-regulated genes. A well characterized aldosterone-induced gene is the serum and glucocorticoid-induced kinase (SGK1), which acts downstream to increase sodium transport in distal kidney nephron epithelial cells. The role of microRNAs (miRs) induced by extended aldosterone stimulation in regulating MR and SGK1 has not been reported. In these studies, miRs predicted to bind to the 3'-UTR of mouse MR were profiled by qRT-PCR after aldosterone stimulation. The miR-466a/b/c/e family was upregulated in mouse kidney cortical collecting duct epithelial cells. A luciferase reporter assay confirmed miR-466 binding to both MR and SGK1 3'-UTRs. Inhibition of miR-466 increased MR and SGK1 mRNA and protein levels. Inhibiting miR-466b and preventing its upregulation after aldosterone stimulation increased amiloride-sensitive sodium transport and sensitivity to aldosterone stimulation. In vivo upregulation of miR-466 was confirmed in distal nephrons of mice on low Na+ diets. Repression of MR and SGK1 by aldosterone-induced miRs may represent a negative feedback loop that contributes to a form of aldosterone escape in vivo.

p-Cresol sulfate and indoxyl sulfate induce similar cellular inflammatory gene expressions in cultured proximal renal tubular cells

BACKGROUND

p-Cresol sulfate (PCS) and indoxyl sulfate (IS) have important roles in the kidney injury. The aim of this study was to determine the inflammatory response to PCS and IS.

METHODS

Cultured mouse proximal renal tubular cells were treated with PCS or IS and analyzed by polymerase chain reaction array with an inflammation and immune panel. Gene annotation enrichment and functional annotation clustering were analyzed with the Database for Annotation, Visualization, and Integrated Discovery (DAVID). Functional networks of the target genes were analyzed with the algorithm GeneMANIA.

RESULTS

PCS and IS increased the expression of inflammation associated genes. Sixteen upregulated gene clusters of cells treated with PCS or IS were found. The major cytokines in the functional networks generated by PCS or IS treatment were Tgfb1, Fasl, Il6/15, Il15, Csf1/3 and Cxcl10. The major intracellular signal triggered by PCS or IS included Stats, Smads, Nfkb2, Ikbkb, Bcl2 and Bax. In both PCS- and IS-treated cells, Col4a5, Cxc10, Fasl, Stat1 and Ikbkb were the target genes in the predicted molecular functional networks connected to Tgfb1.

CONCLUSIONS

PCS and IS stimulate significant cellular inflammation. Similar immune and cellular inflammatory responses were induced by PCS or IS on cultured proximal renal tubular cells.

Uremic toxins induce kidney fibrosis by activating intrarenal renin-angiotensin-aldosterone system associated epithelial-to-mesenchymal transition

Background

Uremic toxins are considered to have a determinant pathological role in the progression of chronic kidney disease. The aim of this study was to define the putative pathological roles of the renal renin–angiotensin–aldosterone system (RAAS) and renal tubular epithelial-to-mesenchymal transition (EMT) in kidney fibrosis induced by (indoxyl sulfate) IS and (p-cresol sulfate) PCS.

Methods

Mouse proximal renal tubular cells (PKSV-PRs) treated with IS or PCS were used. Half-nephrectomized B-6 mice were treated with IS or PCS for 4 weeks. In the losartan treatment study, the study animal was administrated with IS+losartan or PCS+losartan for 4 weeks.

Results

IS and PCS significantly activated the intrarenal RAAS by increasing renin, angiotensinogen, and angiotensin 1 (AT1) receptor expression, and decreasing AT2 receptor expression in vitro and in vivo. IS and PCS significantly increased transforming growth factor-β1 (TGF-β1) expression and activated the TGF-β pathway by increasing Smad2/Smad2-P, Smad3/Smad3-P, and Smad4 expression. The expression of the EMT-associated transcription factor Snail was increased by IS and PCS treatment. IS and PCS induced the phenotype of EMT-like transition in renal tubules by increasing the expression of fibronectin and α-smooth muscle actin and decreasing the expression of E-cadherin. Losartan significantly attenuated the expression of TGF-β1 and Snail, and decreased kidney fibrosis induced by IS and PCS in vivo.

Conclusion

Activating the renal RAAS/TGF-β pathway has an important pathological role in chronic kidney injury caused by IS and PCS. IS and PCS may increase Snail expression and induce EMT-like transition.

Gender differences in kidney function

Sex hormones influence the development of female (F) and male (M) specific traits and primarily affect the structure and function of gender-specific organs. Recent studies also indicated their important roles in regulating structure and/or function of nearly every tissue and organ in the mammalian body, including the kidneys, causing gender differences in a variety of characteristics. Clinical observations in humans and studies in experimental animals in vivo and in models in vitro have shown that renal structure and functions under various physiological, pharmacological, and toxicological conditions are different in M and F, and that these differences may be related to the sex-hormone-regulated expression and action of transporters in the apical and basolateral membrane of nephron epithelial cells. In this review we have collected published data on gender differences in renal functions, transporters and other related parameters, and present our own microarray data on messenger RNA expression for various transporters in the kidney cortex of M and F rats. With these data we would like to emphasize the importance of sex hormones in regulation of a variety of renal transport functions and to initiate further studies of gender-related differences in kidney structure and functions, which would enable us to better understand occurrence and development of various renal diseases, pharmacotherapy, and drug-induced nephrotoxicity in humans and animals.

Hormonal status affects the progression of STZ-induced diabetes and diabetic renal damage in the VCD mouse model of menopause

Changes in the estrogen/testosterone balance at menopause may negatively influence the development of diabetic kidney disease. Furthermore, recent studies suggest that changes in hormone levels during perimenopause may influence disease development. Injection of 4-vinylcyclohexene diepoxide (VCD) in B(6)C(3)F(1) mice induces gradual ovarian failure, preserving both the perimenopausal (peri-ovarian failure) and menopausal (post-ovarian failure) periods. To address the impact of the transition into menopause on the development of diabetes and diabetic kidney damage, we used streptozotocin (STZ)-induced diabetes in the VCD model of menopause. After 6 wk of STZ-induced diabetes, blood glucose was significantly increased in post-ovarian failure (post-OF) diabetic mice compared with cycling diabetic mice. In peri-ovarian failure (peri-OF) diabetic mice, blood glucose levels trended higher but were not significantly different from cycling diabetic mice, suggesting a continuum of worsening blood glucose across the menopausal transition. Cell proliferation, an early marker of damage in the kidney, was increased in post-OF diabetic mice compared with cycling diabetic mice, as measured by PCNA immunohistochemistry. In post-OF diabetic mice, mRNA abundance of early growth response-1 (Egr-1), collagen-4alpha1, and matrix metalloproteinase-9 were increased and 3beta-hydroxysteroid dehydrogenase 4 (3beta-HSD4) and transforming growth factor-beta(2) (TGF-beta(2)) were decreased compared with cycling diabetic mice. In peri-OF diabetic mice, mRNA abundance of Egr-1 and 3beta-HSD4 were increased, and TGF-beta(2) was decreased compared with cycling diabetic mice. This study highlights the importance and utility of the VCD model of menopause, as it provides a physiologically relevant system for determining the impact of the menopausal transition on diabetes and diabetic kidney damage.

Transimmortalized proximal tubule and collecting duct cell lines derived from the kidneys of transgenic mice

This review summarizes the strategy of cellular immortalization based on the principle of targeted oncogenesis in transgenic mice, used to establish models of transimmortalized renal proximal tubule cells, referred to as PKSV-PCT and PKSV-PR-cells, and collecting duct principal cells, referred to as mpkCCD(cl4) cells. These cell lines have maintained for long-term passages the main biochemical and functional properties of the parental cells from which they were derived. Proximal tubule PKSV-PCT and PKSV-PR cells have been proved to be suitable cell systems for toxicological and pharmacological studies. They also permitted the establishment of a model of multidrug-resistant (MDR) renal epithelial tubule cells, PKSV-PR(col50), which have served for the study of both MDR-dependent extrusion of chemotherapeutic drugs and inappropriate accumulation of weak base anthracyclines in intracellular acidic organelles. The novel collecting duct cell line mpkCCD(cl4), which has maintained the characteristics of tight epithelial cells, in particular Na(+) absorption stimulated by aldosterone, has been extensively used for pharmacological studies related to the regulation of ion transport. These cells have permitted the identification of several aldosterone-induced proteins playing a key role in the regulation of Na(+) absorption mediated by the epithelial Na(+) channel ENaC. Recent studies have also provided evidence that these cell lines represent valuable cell systems for the study of host-pathogen interactions and the analysis of the role of renal tubule epithelial cells in the induction of inflammatory response caused by uropathogens that may lead to severe renal damage.

Regulation of NaCl transport in the renal collecting duct: lessons from cultured cells

The fine control of NaCl absorption regulated by hormones takes place in the distal nephron of the kidney. In collecting duct principal cells, the epithelial sodium channel (ENaC) mediates the apical entry of Na(+), which is extruded by the basolateral Na(+),K(+)-ATPase. Simian virus 40-transformed and "transimmortalized" collecting duct cell lines, derived from transgenic mice carrying a constitutive, conditionally, or tissue-specific promoter-regulated large T antigen, have been proven to be valuable tools for studying the mechanisms controlling the cell surface expression and trafficking of ENaC and Na(+),K(+)-ATPase. These cell lines have made it possible to identify sets of aldosterone- and vasopressin-stimulated proteins, and have provided new insights into the concerted mechanism of action of serum- and glucocorticoid-inducible kinase 1 (Sgk1), ubiquitin ligase Nedd4-2 (neural precursor cell-expressed, developmentally down-regulated protein 4-2), and 14-3-3 regulatory proteins in modulating ENaC-mediated Na(+) currents. Epidermal growth factor and induced leucine zipper protein have also been shown to repress and stimulate ENaC-dependent Na(+) absorption, respectively, by activating or repressing the mitogen-activated protein kinase externally regulated kinase(1/2). Overall, these findings have provided evidence suggesting that multiple pathways are involved in regulating NaCl absorption in the distal nephron.

Expression of androgen receptor and androgen regulation of NDRG2 in the rat renal collecting duct

Androgens are known to regulate gene expression in the renal proximal tubule. Whether the distal parts of the nephron, in particular the cortical collecting duct (CCD), where sodium reabsorption is controlled tightly by aldosterone, are also targets for these hormones is unknown. Real-time PCR on rat isolated renal tubules showed that androgen receptor mRNA is not only, as expected, expressed in the proximal tubule, but also in the CCD. We examined the effects of adrenalectomy (ADX) plus castration and in-vivo administration of the active metabolite of testosterone, dihydrotestosterone (DHT), on the intrarenal expression of N-myc downstream regulated gene 2 (NDRG2), an early aldosterone-induced gene located specifically in the CCD. NDRG2 belongs to a newly identified family of differentiation-related genes; although the function of these genes remains elusive, regulation of NDRG1 by androgens has been suggested. Castration plus ADX increased NDRG2 expression (RNase protection assay) significantly in the whole kidney, and a single i.p. injection of DHT caused a significant decrease in NDRG2 expression 4 h afterwards (up to 24 h). Furthermore, real-time PCR on microdissected tubules revealed that the decrease in NDRG2 expression caused by DHT is restricted to the CCD. Thus, aldosterone and androgens have opposite effects on NDRG2 expression in the renal CCD. These results are the first demonstration of androgen-dependent gene regulation in the rat renal CCD.

Testosterone enhances calcium reabsorption by the kidney

The kidney is a target tissue for androgens, but the role of these hormones in the regulation of calcium (Ca2+) reabsorption remains unclear. The present study examines the effects of testosterone on Ca2+ transport by the luminal membranes of proximal and distal nephrons of the rabbit kidney. Tubule suspensions were pre-incubated in the presence or absence of the hormone, and 45C2+ uptake by the luminal membranes was measured using the rapid filtration technique. In the proximal tubules, testosterone did not influence Ca2+ uptake. In the distal tubules, a 5 min incubation with the hormone increased this uptake with a maximal response at 10(-10)M. Ca2+ transport by the distal membranes shows a dual kinetics. Testosterone enhanced the Vmax value of the low affinity component. In an attempt to identify the underlying mechanisms involved in this action, several messenger inhibitors were introduced in the tubule suspension. PD 98059 and U0 126 as well as AG 99 and genistein interfered with the hormone action suggesting the implication of a MEK kinase and a tyrosine kinase. To determine the type of the channels involved in this effect, Ca2+ uptake was measured in the presence of diltiazem, omega-conotoxin MVIIC and mibefradil, i.e. selective inhibitors of the L-type, P/Q type and T-type channels. An inhibition of Ca2+ transport was observed exclusively with mibefradil. These results indicate that testosterone enhances Ca2+ transport by opening a T-type Ca2+ channel in the distal luminal membrane, via MEK kinase and tyrosine kinase dependent mechanisms.

Estrogen and androgen regulation of plasma membrane calcium pump activity in immortalized distal tubule kidney cells

The ATP dependent plasma membrane calcium pump (PMCA) is a regulator of renal calcium reabsorption. The effect of estrogen and dihydrotestosterone to increase the activity of the PMCA in membrane vesicle preparations from a distal tubule cell line was investigated. 17beta Estradiol (10(-10)M) increased PMCA activity (1.5 +/- 0.2-fold increase compared to control) with 24 h, but not 1 or 5 h, of exposure, an effect that was blocked by the addition of the estrogen antagonist ICI 164384. alpha Estradiol did not increase PMCA activity. Dihydrotestosterone (10(-11)M ) resulted in a dose dependent increase in PMCA activity (1.5+/-0.1-fold increase compared to control) with 24h, but not 1 or 5h, of exposure, an effect that was blocked by the androgen receptor agonist flutamide. Testosterone (10(-5)M) also increased PMCA activity (1.9+/-0.3-fold increase compared to control). Neither estrogen nor dihydrotestosterone increased PMCA protein expression in MDBK cells, indicating that these hormones increase PMCA activity by regulating PMCA activity rather than PMCA expression. These results demonstrate receptor dependent stimulatory effects of both estrogen and dihydrotestosterone to increase PMCA activity. and have significance for our understanding of estrogen and androgen deficient states on calcium transport.

Gender- and age-dependent changes in kidney androgen protein mRNA expression in a knockout mouse model for nephrolithiasis

Kidney androgen-regulated protein (Kap) is the most abundant protein in the mouse kidney, but its function is unknown. We previously observed a significant decrease in Kap mRNA expression in whole kidney tissue from male mice with adenine phosphoribosyltransferase (APRT) deficiency and 2,8-dihydroxyadenine (DHA) nephrolithiasis. The disease phenotype is more severe in male mice and is age-dependent. To identify the cellular basis for differential Kap expression, we used in situ hybridization (ISH) and reverse transcription-polymerase chain reaction ISH (RT-PCR ISH) to identify the cell types expressing this mRNA in paraffin-embedded kidney sections. In 1-month-old wild-type male mice, Kap was detected primarily in S3 proximal tubule segments, but expression was very low in female mice. In 1-month-old APRT-deficient male mice, Kap expression was decreased significantly and was undetectable in female mice. Kap mRNA was not detected in 3- or 6-month-old mice using our standard ISH protocol, but we observed intense cytoplasmic staining in S3 proximal tubules in wild-type male mice of these age groups using an improved RT-PCR ISH procedure. Our studies demonstrate age-, gender-, and APRT genotype-dependent changes in Kap mRNA expression in mouse kidney. Kap expression is under multihormonal control, and hormonal changes in DHA-induced nephrolithiasis may account for the decreased Kap expression in APRT-deficient mice.

Hormone-specific regulation of the kidney androgen-regulated gene promoter in cultured mouse renal proximal-tubule cells

The kidney androgen-regulated protein (KAP) is specifically expressed and differentially regulated by androgens and tri-iodothyronine (T(3)) in intact mouse early (PCT) and late (PR) proximal-tubule cells. Until now, detailed characterization of the molecular elements mediating androgen-responsive gene expression in the kidney has been hampered by the lack of appropriate cultured cell systems suitable for DNA transfection studies. In the present study we have analysed the hormone-dependent transactivation of the KAP gene promoter in immortalized differentiated PCT and PR proximal-tubule cells derived from L-PK/Tag1 transgenic mice. Transient transfection studies with different KAP promoter constructs indicated that a 224 bp-truncated fragment was sufficient to mediate cell-specific expression of the KAP promoter. Dihydrotestosterone (DHT) stimulated in an androgen-dependent manner the transactivation of KAP in PCT and PR cells, while mutation of a putative androgen-response element (ARE) sequence located at -39 bp from the transcription initiation site abolished the transactivation induced by DHT. Furthermore, insulin-like growth factor 1 (IGF-1), but not T(3), enhanced the androgen-dependent transactivation of KAP in cultured PCT cells. These results demonstrate that the short 224 bp fragment of the KAP promoter is sufficient to drive the proximal-tubule androgen-specific regulated expression of KAP and reveal synergistic interactions between IGF-1 and androgens for KAP regulation in PCT cells.

Kidney androgen-regulated protein interacts with cyclophilin B and reduces cyclosporine A-mediated toxicity in proximal tubule cells

The gene for kidney androgen-regulated protein (KAP) is the most abundant and specific gene expressed in mouse kidney proximal tubule cells, where it is tightly regulated by steroid and thyroid hormones in different tubule segments. Despite the cell-specific expression, strict regulatory mechanisms, and relative abundance, nothing is known of the function of its encoded protein, which does not exhibit known structural or functional domains, or homologies with other sequences in the data bases. We raised monoclonal antibodies against KAP, which specifically recognize a protein with an apparent molecular mass of 20 kDa in crude kidney homogenates, the distribution and regulation of which parallel that of its mRNA. To gain insight into its function, we performed a yeast two hybrid screen and determined that KAP specifically interacts with cyclophilin B. Furthermore, cyclosporine A (CsA)-treated mice exhibited a significant decrease in KAP levels, and tetracycline-controlled overexpression of KAP in stably transfected proximal tubule cells significantly decreased the toxic effects of CsA. Taken together, these results indicate a functional relationship among KAP-, cyclophilin B-, and CsA-mediated nephrotoxicity and suggest an important role of KAP in renal physiology, providing new data on the molecular mechanisms implied in the toxic effects of CsA.

Immortalized kidney cells derived from transgenic mice harboring L-type pyruvate kinase and vimentin promoters

Targeted oncogenesis in transgenic mice, where an oncogene is placed under the control of the regulatory sequences of a cell-specific gene, has been used to derive several new types of differentiated nonepithelial and epithelial cell lines. This review summarizes the properties of cell lines derived from proximal, distal and collecting duct cells. The cells were obtained from kidneys of transgenic mice harboring the 5' regulatory sequences of the L-type pyruvate kinase or vimentin genes controlling the expression of either the large T and little t antigens or the temperature-sensitive large T antigen.

Immortalized kidney epithelial cells as tools for hormonally regulated ion transport studies

The development of transgenic mice carrying the simian virus-40 large T antigen gene or the temperature-sensitive simian virus-40 large T antigen gene, either alone or placed under the control of the 5'-regulatory regions of tissue-specific or ubiquitous genes, has permitted the production of differentiated, polarized kidney epithelial cells. This review covers the immortalized cell lines issued from the various parts of the renal tubule and, in particular, the recently established collecting duct cell lines that have been used as ex-vivo cell models to analyze the regulation of ion transport processes by hormones.