Lack of Renal Tubular Glucocorticoid Receptor Decreases the Thiazide-Sensitive Na+/Cl– Cotransporter NCC and Transiently Affects Sodium Handling

Abstract

Chronic glucocorticoid infusion impairs NCC activity and induces a non-dipping profile in mice, suggesting that glucocorticoids are essential for daily blood pressure variations. In this paper, we studied mice lacking the renal tubular glucocorticoid receptor (GR) in adulthood (GR knockouts, Nr3c1 Pax8/LC1 ). Upon standard salt diet, Nr3c1 Pax8/LC1 mice grow normally, but show reduced NCC activity despite normal plasma aldosterone levels. Following diet switch to low sodium, Nr3c1 Pax8/LC1 mice exhibit a transient but significant reduction in the activity of NCC and expression of NHE3 and NKCC2 accompanied by significant increased Spak activity. This is followed by transiently increased urinary sodium excretion and higher plasma aldosterone concentrations. Plasma corticosterone levels and 11βHSD2 mRNA expression and activity in the whole kidney remain unchanged. High salt diet does not affect whole body Na + and/or K + balance and NCC activity is not reduced, but leads to a significant increase in diastolic blood pressure dipping in Nr3c1 Pax8/LC1 mice. When high sodium treatment is followed by 48 h of darkness, NCC abundance is reduced in knockout mice although activity is not different. Our data show that upon Na + restriction renal tubular GR-deficiency transiently affects Na + handling and transport pathways. Overall, upon standard, low Na + and high Na + diet exposure Na + and K + balance is maintained as evidenced by normal plasma and urinary Na + and K + and aldosterone concentrations.

Deletion of the serine protease CAP2/Tmprss4 leads to dysregulated renal water handling upon dietary potassium depletion

“…To study the renal function of the GR upon potassium depletion, we fed inducible nephron-specific GR knockout mice (Nr3c1 Pas8/LC1 ) 28 a LK diet. Knockout animals lost bodyweight, and displayed opposite features to CAP2/ Tmprss4 knockouts, namely increased water intake, increased urine output, reduced urine osmolality, decreased cumulative urinary sodium and potassium excretion, and increased urinary pH and calcium excretion, whereas phosphate excretion was unchanged compared to controls and daily urinary Na + and K + excretions tended to decrease in knockouts (Fig.…”

“…However, RU486 cross-reacts with GR, thereby further reducing HKA2 expression 49 , as RU486 is also commonly used as GR antagonist in the treatment of Cushing’s syndrome 58,59 , and one side-effect in patients is the reduction of kalemia 58 . However, given the unavailability of a specific PR sparing GR antagonist, we further explored the function of the GR upon K + depletion by using nephron-specific GR knockout mice (Nr3c1 Pax8/LC1 ) 28 . Strikingly, GR deletion led to the mirrored phenotype of CAP2/ Tmprss4 knockout mice including HKA2, NKCC2 and AQP2 protein expressions, and additionally impacted body weight and kalemia (Figs.…”

“…Age-matched (3–5 months old, C57BL6/N inbred) male CAP2/ Tmprss4 homozygous mutant (CAP2/ Tmprss4 ∆/∆ , ∆/∆, knockout), heterozygous mutant (CAP2/ Tmprss4 ∆/+ , ∆/+) and wildtype (CAP2/ Tmprss4 +/+ , +/+, WT) littermates 26 were treated either with regular K + diet (RK, 0.97% K + ), or low K + diet (LK, <0.003% K + ) (Ssniff, Spezialdiäten GmbH, Germany). Age-matched (triple transgenic C57BL6/N-mixed background) male GR control mice (Nr3c1 +/+ , controls) and doxycycline-induced kidney-specific knockouts (Nr3c1 Pax8/LC1 ) were used 28 . Tubule-specific doxycycline-induced deletion of GR was achieved as previously described 28 .…”

“…Age-matched (triple transgenic C57BL6/N-mixed background) male GR control mice (Nr3c1 +/+ , controls) and doxycycline-induced kidney-specific knockouts (Nr3c1 Pax8/LC1 ) were used 28 . Tubule-specific doxycycline-induced deletion of GR was achieved as previously described 28 . Mice were kept in metabolic cages with free access to food and water for 6 consecutive days, and diet was switched after 2 days from RK to LK.…”

Effect of Hydrocortisone on Angiotensinogen (AGT) Mutation–Causing Autosomal Recessive Renal Tubular Dysgenesis

“…We found that this AGT mutation led to truncated AGT that excluded the amino acids that contained the potential binding motif (LQDLL) for nuclear receptor [ 27 ]. Since GR, one of nuclear receptors, is abundant in proximal convoluted tubule during the tubular development [ 18 , 19 , 28 ]. In mouse and rat, the AGT is primarily detected in proximal tubules at early gestation [ 29 , 30 , 31 , 32 ].…”