Male kidney-specific BMAL1 knockout mice are protected from K+-deficient, high-salt diet-induced blood pressure increases.

The circadian clock protein basic helix-loop-helix aryl hydrocarbon receptor nuclear translocator-like protein 1 (BMAL1) is a transcription factor that impacts kidney function, including blood pressure (BP) control. Previously, we have shown that male, but not female, kidney-specific cadherin Cre-positive BMAL1 knockout (KS-BMAL1 KO) mice exhibit lower BP compared with littermate controls. The goal of this study was to determine the BP phenotype and immune response in male KS-BMAL1 KO mice in response to a low-K+ high-salt (LKHS) diet. BP, renal inflammatory markers, and immune cells were measured in male mice following an LKHS diet. Male KS-BMAL1 KO mice had lower BP following the LKHS diet compared with control mice, yet their circadian rhythm in pressure remained unchanged. Additionally, KS-BMAL1 KO mice exhibited lower levels of renal proinflammatory cytokines and immune cells following the LKHS diet compared with control mice. KS-BMAL1 KO mice were protected from the salt-sensitive hypertension observed in control mice and displayed an attenuated immune response following the LKHS diet. These data suggest that BMAL1 plays a role in driving the BP increase and proinflammatory environment that occurs in response to an LKHS diet.NEW & NOTEWORTHY We show here, for the first time, that kidney-specific BMAL1 knockout mice are protected from blood pressure (BP) increases and immune responses to a salt-sensitive diet. Other kidney-specific BMAL1 knockout models exhibit lower BP phenotypes under basal conditions. A salt-sensitive diet exacerbates this genotype-specific BP response, leading to fewer proinflammatory cytokines and immune cells in knockout mice. These data demonstrate the importance of distal segment BMAL1 in BP and immune responses to a salt-sensitive environment.

Aldosterone: Renal Action and Physiological Effects.

Aldosterone exerts profound effects on renal and cardiovascular physiology. In the kidney, aldosterone acts to preserve electrolyte and acid-base balance in response to changes in dietary sodium (Na+ ) or potassium (K+ ) intake. These physiological actions, principally through activation of mineralocorticoid receptors (MRs), have important effects particularly in patients with renal and cardiovascular disease as demonstrated by multiple clinical trials. Multiple factors, be they genetic, humoral, dietary, or otherwise, can play a role in influencing the rate of aldosterone synthesis and secretion from the adrenal cortex. Normally, aldosterone secretion and action respond to dietary Na+ intake. In the kidney, the distal nephron and collecting duct are the main targets of aldosterone and MR action, which stimulates Na+ absorption in part via the epithelial Na+ channel (ENaC), the principal channel responsible for the fine-tuning of Na+ balance. Our understanding of the regulatory factors that allow aldosterone, via multiple signaling pathways, to function properly clearly implicates this hormone as central to many pathophysiological effects that become dysfunctional in disease states. Numerous pathologies that affect blood pressure (BP), electrolyte balance, and overall cardiovascular health are due to abnormal secretion of aldosterone, mutations in MR, ENaC, or effectors and modulators of their action. Study of the mechanisms of these pathologies has allowed researchers and clinicians to create novel dietary and pharmacological targets to improve human health. This article covers the regulation of aldosterone synthesis and secretion, receptors, effector molecules, and signaling pathways that modulate its action in the kidney. We also consider the role of aldosterone in disease and the benefit of mineralocorticoid antagonists. © 2023 American Physiological Society. Compr Physiol 13:4409-4491, 2023.

Adrenal-Specific KO of the Circadian Clock Protein BMAL1 Alters Blood Pressure Rhythm and Timing of Eating Behavior.

Brain and muscle ARNT-like 1 (BMAL1) is a core circadian clock protein and transcription factor that regulates many physiological functions, including blood pressure (BP). Male global Bmal1 knockout (KO) mice exhibit ∼10 mmHg reduction in BP, as well as a blunting of BP rhythm. The mechanisms of how BMAL1 regulates BP remains unclear. The adrenal gland synthesizes hormones, including glucocorticoids and mineralocorticoids, that influence BP rhythm. To determine the role of adrenal BMAL1 on BP regulation, adrenal-specific Bmal1 (ASCre/+ ::Bmal1) KO mice were generated using aldosterone synthase Cre recombinase to KO Bmal1 in the adrenal gland zona glomerulosa. We confirmed the localization and efficacy of the KO of BMAL1 to the zona glomerulosa. Male ASCre/+ ::Bmal1 KO mice displayed a shortened BP and activity period/circadian cycle (typically 24 h) by ∼1 h and delayed peak of BP and activity by ∼2 and 3 h, respectively, compared with littermate Cre- control mice. This difference was only evident when KO mice were in metabolic cages, which acted as a stressor, as serum corticosterone was increased in metabolic cages compared with home cages. AS Cre/+ ::Bmal1 KO mice also displayed altered diurnal variation in serum corticosterone. Furthermore, these mice have altered eating behaviors where they have a blunted night/day ratio of food intake, but no change in overall food consumed compared with controls. Overall, these data suggest that adrenal BMAL1 has a role in the regulation of BP rhythm and eating behaviors.

Kidney-specific KO of the circadian clock protein PER1 alters renal Na+ handling, aldosterone levels, and kidney/adrenal gene expression.

PERIOD 1 (PER1) is a circadian clock transcription factor that is regulated by aldosterone, a hormone that increases blood volume and Na+ retention to increase blood pressure. Male global Per1 knockout (KO) mice develop reduced night/day differences in Na+ excretion in response to a high-salt diet plus desoxycorticosterone pivalate treatment (HS + DOCP), a model of salt-sensitive hypertension. In addition, global Per1 KO mice exhibit higher aldosterone levels on a normal-salt diet. To determine the role of Per1 in the kidney, male kidney-specific Per1 KO (KS-Per1 KO) mice were generated using Ksp-cadherin Cre recombinase to remove exons 2-8 of Per1 in the distal nephron and collecting duct. Male KS-Per1 KO mice have increased Na+ retention but have normal diurnal differences in Na+ excretion in response to HS + DOCP. The increased Na+ retention is associated with altered expression of glucocorticoid and mineralocorticoid receptors, increased serum aldosterone, and increased medullary endothelin-1 compared with control mice. Adrenal gland gene expression analysis revealed that circadian clock and aldosterone synthesis genes have altered expression in KS-Per1 KO mice compared with control mice. These results emphasize the importance of the circadian clock not only in maintaining rhythms of physiological functions but also for adaptability in response to environmental cues, such as HS + DOCP, to maintain overall homeostasis. Given the prevalence of salt-sensitive hypertension in the general population, these findings have important implications for our understanding of how circadian clock proteins regulate homeostasis.NEW & NOTEWORTHY For the first time, we show that knockout of the circadian clock transcription factor PERIOD 1 using kidney-specific cadherin Cre results in increased renal Na+ reabsorption, increased aldosterone levels, and changes in gene expression in both the kidney and adrenal gland. Diurnal changes in renal Na+ excretion were not observed, demonstrating that the clock protein PER1 in the kidney is important for maintaining homeostasis and that this effect may be independent of time of day.

Benzamil-mediated urine alkalization is caused by the inhibition of H+-K+-ATPases.

Epithelial Na+ channel (ENaC) blockers elicit acute and substantial increases of urinary pH. The underlying mechanism remains to be understood. Here, we evaluated if benzamil-induced urine alkalization is mediated by an acute reduction in H+ secretion via renal H+-K+-ATPases (HKAs). Experiments were performed in vivo on HKA double-knockout and wild-type mice. Alterations in dietary K+ intake were used to change renal HKA and ENaC activity. The acute effects of benzamil (0.2 µg/g body wt, sufficient to block ENaC) on urine flow rate and urinary electrolyte and acid excretion were monitored in anesthetized, bladder-catheterized animals. We observed that benzamil acutely increased urinary pH (ΔpH: 0.33 ± 0.07) and reduced NH4+ and titratable acid excretion and that these effects were distinctly enhanced in animals fed a low-K+ diet (ΔpH: 0.74 ± 0.12), a condition when ENaC activity is low. In contrast, benzamil did not affect urine acid excretion in animals kept on a high-K+ diet (i.e., during high ENaC activity). Thus, urine alkalization appeared completely uncoupled from ENaC function. The absence of benzamil-induced urinary alkalization in HKA double-knockout mice confirmed the direct involvement of these enzymes. The inhibitory effect of benzamil was also shown in vitro for the pig α1-isoform of HKA. These results suggest a revised explanation of the benzamil effect on renal acid-base excretion. Considering the conditions used here, we suggest that it is caused by a direct inhibition of HKAs in the collecting duct and not by inhibition of the ENaC function.NEW & NOTEWORTHY Bolus application of epithelial Na+ channel (EnaC) blockers causes marked and acute increases of urine pH. Here, we provide evidence that the underlying mechanism involves direct inhibition of the H+-K+ pump in the collecting duct. This could provide a fundamental revision of the previously assumed mechanism that suggested a key role of ENaC inhibition in this response.

A noninvasive method to study the evolution of extracellular fluid volume in mice using time-domain nuclear magnetic resonance.

Maintaining water homeostasis is fundamental for cellular function. Many diseases and drugs affect water balance and plasma osmolality. Water homeostasis studies in small animals require the use of invasive or terminal methods that make intracellular fluid volume and extracellular fluid volume (ECF) monitoring over time stressful and time consuming. We examined the feasibility of monitoring mouse ECF by a noninvasive method using time-domain nuclear magnetic resonance (TD-NMR). This technique allows differentiation of protons in a liquid environment (free fluid) from protons in soft tissues containing a majority of either small molecules (lean) or large molecules (fat). Moreover, this apparatus enables rapid, noninvasive, and repeated measurements on the same animal. We assessed the feasibility of coupling TD-NMR analysis to a longitudinal metabolic cage study by monitoring mice daily. We determined the effect of 24-h water deprivation on mouse body parameters and detected a sequential and overlapping decrease in free fluid and lean mass during water deprivation. Finally, we studied the effect of mineralocorticoids that are known to induce a transient increase in ECF but for which no direct measurements have been performed in mice. We showed, for the first time, that mineralocorticoids induced a transient ~15% increase in free fluid in conscious mice. TD-NMR is, therefore, the first method to allow direct measurement of discrete changes in ECF in conscious small animals. This method allows analysis of kinetic changes to stimuli before investigating with terminal methods and will allow further understanding of fluid disorders.

Knockout of the circadian clock protein PER1 results in sex-dependent alterations of ET-1 production in mice in response to a high-salt diet plus mineralocorticoid treatment.

Previously, we showed that global knockout (KO) of the circadian clock transcription factor PER1 in male, but not female, mice fed a high-salt diet plus mineralocorticoid treatment (HS/DOCP) resulted in nondipping hypertension and decreased night/day ratio of sodium (Na) excretion. Additionally, we have shown that the endothelin-1 (ET-1) gene is targeted by both PER1 and aldosterone. We hypothesized that ET-1 would exhibit a sex-specific response to HS/DOCP treatment in PER1 KO. Here we show that male, but not female, global PER1 KO mice exhibit a decreased night/day ratio of urinary ET-1. Gene expression analysis revealed significant genotype differences in ET-1 and endothelin A receptor (ETA) expression in male, but not female, mice in response to HS/DOCP. Additionally, both wild-type and global PER1 KO male mice significantly increase endothelin B receptor (ETB) expression in response to HS/DOCP, but female mice do not. Finally, siRNA-mediated knockdown of PER1 in mouse cortical collecting duct cells (mpkCCDc14) resulted in increased ET-1 mRNA expression and peptide secretion in response to aldosterone treatment. These data suggest that PER1 is a negative regulator of ET-1 expression in response to HS/DOCP, revealing a novel mechanism for the regulation of renal Na handling in response to HS/DOCP treatment.

EDN1-AS, A Novel Long Non-coding RNA Regulating Endothelin-1 in Human Proximal Tubule Cells.

Endothelin-1 (ET-1) is a peptide hormone that functions as a vasoconstrictor in the vasculature, whereas in the collecting duct of the kidney it exerts blood pressure-lowering effects via natriuretic actions. Aberrant ET-1 signaling is associated with several pathological states including hypertension and chronic kidney disease. ET-1 expression is regulated largely through transcriptional control of the gene that encodes ET-1, EDN1. Here we report a long, non-coding RNA (lncRNA) that appears to be antisense to the EDN1 gene, called EDN1-AS. Because EDN1-AS represents a potential novel mechanism to regulate ET-1 expression, we examined the regulation of EDN1-AS expression and action. A putative glucocorticoid receptor response (GR) element upstream of the predicted EDN1-AS transcription start site was identified using the ENCODE database and the UCSC genome browser. Two homozygous deletion clones of the element were generated using CRISPR/Cas9. This deletion resulted in a significant increase in the expression of EDN1-AS, which was associated with increased secretion of ET-1 peptide from HK-2 cells (two-fold increase in KO cells vs. CNTL, n = 7, P < 0.05). Phenotypic characterization of these CRISPR clones revealed a difference in cell growth rates. Using a standard growth assay, we determined that the KO1 clone exhibited a three-fold increase in growth over 8 days compared to control cells (n = 4, P < 0.01) and the KO2 clone exhibited a two-fold increase (n = 4, P < 0.01). These results support a role for EDN1-AS as a novel regulatory mechanism of ET-1 expression and cellular proliferation.

Differences in renal BMAL1 contribution to Na+ homeostasis and blood pressure control in male and female mice.

The renal circadian clock has a major influence on the function of the kidney. Aryl hydrocarbon receptor nuclear translocator-like protein 1 [ARNTL; also known as brain and muscle ARNT-like 1 (BMAL1)] is a core clock protein and transcription factor that regulates the expression of nearly half of all genes. Using male and female kidney-specific cadherin BMAL1 knockout (KS-BMAL1 KO) mice, we examined the role of renal distal segment BMAL1 in blood pressure control and solute handling. We confirmed that this mouse model does not express BMAL1 in thick ascending limb, distal convoluted tubule, and collecting duct cells, which are the final locations for solute and fluid regulation. Male KS-BMAL1 KO mice displayed a substantially lower basal systolic blood pressure compared with littermate control mice, yet their circadian rhythm in pressure remained unchanged [male control mice: 127 ± 0.7 mmHg (n = 4) vs. male KS-BMAL KO mice: 119 ± 2.3 mmHg (n = 5), P < 0.05]. Female mice, however, did not display a genotype difference in basal systolic blood pressure [female control mice: 120 ± 1.6 mmHg (n = 5) vs. female KS-BMAL1 KO mice: 119 ± 1.5 mmHg (n = 7), P = 0.4]. In addition, male KS-BMAL1 KO mice had less Na+ retention compared with control mice in response to a K+-restricted diet (15% less following 5 days of treatment). However, there was no genotype difference in Na+ handling after a K+-restricted diet in female mice. Furthermore, there was evidence indicating a sex-specific response to K+ restriction where female mice reabsorbed less Na+ in response to this dietary challenge compared with male mice. We propose that BMAL1 in the distal nephron and collecting duct contributes to blood pressure regulation and Na+ handling in a sex-specific manner.

NBCe1-A is required for the renal ammonia and K+ response to hypokalemia.

Hypokalemia increases ammonia excretion and decreases K+ excretion. The present study examined the role of the proximal tubule protein NBCe1-A in these responses. We studied mice with Na+-bicarbonate cotransporter electrogenic, isoform 1, splice variant A (NBCe1-A) deletion [knockout (KO) mice] and their wild-type (WT) littermates were provided either K+ control or K+-free diet. We also used tissue sections to determine the effect of extracellular ammonia on NaCl cotransporter (NCC) phosphorylation. The K+-free diet significantly increased proximal tubule NBCe1-A and ammonia excretion in WT mice, and NBCe1-A deletion blunted the ammonia excretion response. NBCe1-A deletion inhibited the ammoniagenic/ammonia recycling enzyme response in the cortical proximal tubule (PT), where NBCe1-A is present in WT mice. In the outer medulla, where NBCe1-A is not present, the PT ammonia metabolism response was accentuated by NBCe1-A deletion. KO mice developed more severe hypokalemia and had greater urinary K+ excretion during the K+-free diet than did WT mice. This was associated with blunting of the hypokalemia-induced change in NCC phosphorylation. NBCe1-A KO mice have systemic metabolic acidosis, but experimentally induced metabolic acidosis did not alter NCC phosphorylation. Although KO mice have impaired ammonia metabolism, experiments in tissue sections showed that lack of ammonia does impair NCC phosphorylation. Finally, urinary aldosterone was greater in KO mice than in WT mice, but neither expression of epithelial Na+ channel α-, ß-, and γ-subunits nor of H+-K+-ATPase α1- or α2-subunits correlated with changes in urinary K+. We conclude that NBCe1-A is critical for the effect of diet-induced hypokalemia to increase cortical proximal tubule ammonia generation and for the expected decrease in urinary K+ excretion.

TRPV4 deletion protects against hypokalemia during systemic K+ deficiency.

Tight regulation of K+ balance is fundamental for normal physiology. Reduced dietary K+ intake, which is common in Western diets, often leads to hypokalemia and associated cardiovascular- and kidney-related pathologies. The distal nephron, and, specifically, the collecting duct (CD), is the major site of controlled K+ reabsorption via H+-K+-ATPase in the state of dietary K+ deficiency. We (Mamenko MV, Boukelmoune N, Tomilin VN, Zaika OL, Jensen VB, O'Neil RG, Pochynyuk OM. Kidney Int 91: 1398-1409, 2017) have previously demonstrated that the transient receptor potential vanilloid type 4 (TRPV4) Ca2+ channel, abundantly expressed in the CD, contributes to renal K+ handling by promoting flow-induced K+ secretion. Here, we investigated a potential role of TRPV4 in controlling H+-K+-ATPase-dependent K+ reabsorption in the CD. Treatment with a K+-deficient diet (<0.01% K+) for 7 days reduced serum K+ levels in wild-type (WT) mice from 4.3 ± 0.2 to 3.3 ± 0.2 mM but not in TRPV4-/- mice (4.3 ± 0.1 and 4.2 ± 0.3 mM, respectively). Furthermore, we detected a significant reduction in 24-h urinary K+ levels in TRPV4-/- compared with WT mice upon switching to K+-deficient diet. TRPV4-/- animals also had significantly more acidic urine on a low-K+ diet, but not on a regular (0.9% K+) or high-K+ (5% K+) diet, which is consistent with increased H+-K+-ATPase activity. Moreover, we detected a greatly accelerated H+-K+-ATPase-dependent intracellular pH extrusion in freshly isolated CDs from TRPV4-/- compared with WT mice fed a K+-deficient diet. Overall, our results demonstrate a novel kaliuretic role of TRPV4 by inhibiting H+-K+-ATPase-dependent K+ reabsorption in the CD. We propose that TRPV4 inhibition could be a novel strategy to manage certain hypokalemic states in clinical settings.

Direct and indirect inhibition of the circadian clock protein Per1: effects on ENaC and blood pressure.

Circadian rhythms govern physiological functions and are important for overall health. The molecular circadian clock comprises several transcription factors that mediate circadian control of physiological function, in part, by regulating gene expression in a tissue-specific manner. These connections are well established, but the underlying mechanisms are incompletely understood. The overall goal of this study was to examine the connection among the circadian clock protein Period 1 (Per1), epithelial Na+ channel (ENaC), and blood pressure (BP) using a multipronged approach. Using global Per1 knockout mice on a 129/sv background in combination with a high-salt diet plus mineralocorticoid treatment, we demonstrated that loss of Per1 in this setting is associated with protection from hypertension. Next, we used the ENaC inhibitor benzamil to demonstrate a role for ENaC in BP regulation and urinary Na+ excretion in 129/sv mice. We targeted Per1 indirectly using pharmacological inhibition of Per1 nuclear entry in vivo to demonstrate altered expression of known Per1 target genes as well as a BP-lowering effect in 129/sv mice. Finally, we directly inhibited Per1 via genetic knockdown in amphibian distal nephron cells to demonstrate, for the first time, that reduced Per1 expression is associated with decreased ENaC activity at the single channel level.

Female C57BL/6J mice lacking the circadian clock protein PER1 are protected from nondipping hypertension.

The circadian clock is integral to the maintenance of daily rhythms of many physiological outputs, including blood pressure. Our laboratory has previously demonstrated the importance of the clock protein period 1 (PER1) in blood pressure regulation in male mice. Briefly, a high-salt diet (HS; 4% NaCl) plus injection with the long-acting mineralocorticoid deoxycorticosterone pivalate (DOCP) resulted in nondipping hypertension [<10% difference between night and day blood pressure (BP) in Per1-knockout (KO) mice but not in wild-type (WT) mice]. To date, there have been no studies that have examined the effect of a core circadian gene KO on BP rhythms in female mice. The goal of the present study was to determine whether female Per1-KO mice develop nondipping hypertension in response to HS/DOCP treatment. For the first time, we demonstrate that loss of the circadian clock protein PER1 in female mice does not significantly change mean arterial pressure (MAP) or the BP rhythm relative to female C57BL/6 WT control mice. Both WT and Per1-KO female mice experienced a significant increase in MAP in response to HS/DOCP. Importantly, however, both genotypes maintained a >10% dip in BP on HS/DOCP. This effect is distinct from the nondipping hypertension seen in male Per1-KO mice, demonstrating that the female sex appears to be protective against PER1-mediated nondipping hypertension in response to HS/DOCP. Together, these data suggest that PER1 acts in a sex-dependent manner in the regulation of cardiovascular rhythms.

Renal Na-handling defect associated with PER1-dependent nondipping hypertension in male mice.

Many physiological functions have a circadian rhythm, including blood pressure (BP). BP is highest during the active phase, whereas during the rest period, BP dips 10-20%. Patients that do not experience this dip at night are termed "nondippers." Nondipping hypertension is associated with increased risk of cardiovascular disease. The mechanisms underlying nondipping hypertension are not understood. Without the circadian clock gene Per1, C57BL/6J mice develop nondipping hypertension on a high-salt diet plus mineralocorticoid treatment (HS/DOCP). Our laboratory has shown that PER1 regulates expression of several genes related to sodium (Na) transport in the kidney, including epithelial Na channel (ENaC) and Na chloride cotransporter (NCC). Urinary Na excretion also demonstrates a circadian pattern with a peak during active periods. We hypothesized that PER1 contributes to circadian regulation of BP via a renal Na-handling-dependent mechanism. Na-handling genes from the distal nephron were inappropriately regulated in KO mice on HS/DOCP. Additionally, the night/day ratio of Na urinary excretion by Per1 KO mice is decreased compared with WT (4 × vs. 7×, P < 0.001, n = 6 per group). Distal nephron-specific Per1 KO mice also show an inappropriate increase in expression of Na transporter genes αENaC and NCC. These results support the hypothesis that PER1 mediates control of circadian BP rhythms via the regulation of distal nephron Na transport genes. These findings have implications for the understanding of the etiology of nondipping hypertension and the subsequent development of novel therapies for this dangerous pathophysiological condition.

ENaC activity in the cortical collecting duct of HKα1 H+,K+-ATPase knockout mice is uncoupled from Na+ intake.

Modulation of the epithelial Na+ channel (ENaC) activity in the collecting duct (CD) is an important mechanism for normal Na+ homeostasis. ENaC activity is inversely related to dietary Na+ intake, in part due to inhibitory paracrine purinergic regulation. Evidence suggests that H+,K+-ATPase activity in the CD also influences Na+ excretion. We hypothesized that renal H+,K+-ATPases affect Na+ reabsorption by the CD by modulating ENaC activity. ENaC activity in HKα1 H+,K+-ATPase knockout (HKα1-/-) mice was uncoupled from Na+ intake. ENaC activity on a high-Na+ diet was greater in the HKα1-/- mice than in WT mice. Moreover, dietary Na+ content did not modulate ENaC activity in the HKα1-/- mice as it did in WT mice. Purinergic regulation of ENaC was abnormal in HKα1-/- mice. In contrast to WT mice, where urinary [ATP] was proportional to dietary Na+ intake, urinary [ATP] did not increase in response to a high-Na+ diet in the HKα1-/- mice and was significantly lower than in the WT mice. HKα1-/- mice fed a high-Na+ diet had greater Na+ retention than WT mice and had an impaired dipsogenic response. These results suggest an important role for the HKα1 subunit in the regulation of purinergic signaling in the CD. They are also consistent with HKα1-containing H+,K+-ATPases as important components for the proper regulation of Na+ balance and the dipsogenic response to a high-salt diet. Such observations suggest a previously unrecognized element in Na+ regulation in the CD.

Obstructive Nephropathy Without Hydronephrosis: Suspicion Is the Key.

Urinary tract obstruction leading to acute kidney injury is usually associated with bilateral hydroureters and hydronephrosis, often accompanied by oliguria. We present an atypical case of obstructive uropathy without these features that presented with severe acute kidney injury. A 64-year-old male with no known medical history has presented with a 2-week history of nausea, decreased appetite, flank pain, and lower extremity edema, and was found to have an elevated creatinine of 10.5 mg/dL. Renal ultrasound showed mild prominence of the bilateral renal collecting systems with no evidence of hydronephrosis. Computed tomography scan showed findings suggestive of retroperitoneal fibrosis involving ureteral region and bilateral ureteral stent placement has led to dramatic improvement of creatinine to 1.3 mg/dL over the next 4 days.

Aldosterone alters the chromatin structure of the murine endothelin-1 gene.

UNLABELLED: Aldosterone increases sodium reabsorption in the renal collecting duct and systemic blood pressure. Paradoxically, aldosterone also induces transcription of the endothelin-1 (Edn1) gene to increase protein (ET-1) levels, which inhibits sodium reabsorption. AIMS: Here we investigated changes in the chromatin structure of the Edn1 gene of collecting duct cell lines in response to aldosterone treatment. The Edn1 gene has a CpG island that encompasses the transcription start site and four sites in the 5' regulatory region previously linked to transcriptional regulation. MATERIALS AND METHODS: The chromatin structure of the Edn1 gene was investigated using a quantitative PCR-based DNaseI hypersensitivity assay in murine hepatocyte (AML12), renal cortical collecting duct (mpkCCDC14), outer medullary collecting duct1 (OMCD1), and inner medullary collecting duct-3 (IMCD-3) cell lines. KEY FINDINGS: The CpG island was uniformly accessible. One calcium-responsive NFAT element remained at low chromatin accessibility in all cell lines under all conditions tested. However, the second calcium responsive NFAT element located at -1563bp upstream became markedly more accessible in IMCD-3 cells exposed to aldosterone. Importantly, one established aldosterone hormone response element HRE at -671bp relative to the transcription start site was highly accessible, and another HRE (-551bp) became more accessible in aldosterone-treated IMCD-3 and OMCD1 cells. SIGNIFICANCE: The evidence supports a model in which aldosterone activation of the mineralocorticoid receptor (MR) results in the MR-hormone complex binding at HRE at -671bp to open chromatin structure around other regulatory elements in the Edn1 gene.