Downregulation of the Cl-/HCO3-Exchanger Pendrin in Kidneys of Mice with Cystic Fibrosis: Role in the Pathogenesis of Metabolic Alkalosis

Abstract

Background/Aims: Patients with cystic fibrosis (CF) are prone to the development of metabolic alkalosis; however, the pathogenesis of this life threatening derangement remains unknown. We hypothesized that altered acid base transport machinery in the kidney collecting duct underlies the mechanism of impaired bicarbonate elimination in the CF kidney. Methods: Balance studies in metabolic cages were performed in WT and CFTR knockout (CF) mice with the intestinal rescue in response to bicarbonate loading or salt restriction, and the expression levels and cellular distribution of acid base and electrolyte transporters in the proximal tubule, collecting duct and small intestine were examined by western blots, northern blots and/or immunofluorescence labeling. Results: Baseline parameters, including acid-base and systemic vascular volume status were comparable in WT and CF mice, as determined by blood gas, kidney renin expression and urine chloride excretion. Compared with WT animals, CF mice demonstrated a significantly higher serum HCO₃^- concentration (22.63 in WT vs. 26.83 mEq/l in CF mice; n=4, p=0.013) and serum pH (7.33 in WT vs. 7.42 in CF mice; n=4, p=0.00792) and exhibited impaired kidney HCO₃^- excretion (urine pH 8.10 in WT vs. 7.35 in CF mice; n=7, p=0.00990) following a 3-day oral bicarbonate load. When subjected to salt restriction, CF mice developed a significantly higher serum HCO₃^- concentration vs. WT animals (29.26 mEq/L in CF mice vs. 26.72 in WT; n=5, p=0.0291). Immunofluorescence labeling demonstrated a profound reduction in the apical expression of the Cl^-/HCO₃^- exchanger pendrin in cortical collecting duct cells and western and northern blots indicated diminished plasma membrane abundance and mRNA expression of pendrin in CF kidneys. Conclusions: We propose that patients with cystic fibrosis are prone to the development of metabolic alkalosis secondary to the inactivation of the bicarbonate secreting transporter pendrin, specifically during volume depletion, which is a common occurrence in CF patients.

Tuberous sclerosis complex exhibits a new renal cystogenic mechanism

“…; Varasteh Kia et al. ). Briefly, animals were euthanized with an overdose of pentobarbital sodium, and kidneys were perfused with saline followed by 4% paraformaldehyde removed, cut in tissue blocks, and fixed in 4% paraformaldehyde solution overnight at 4°C.…”

“…Single and double immunofluorescence labeling was performed using established protocols (Xu et al 2011;Zahedi et al 2013;Barone et al 2018;Varasteh Kia et al 2018). Briefly, animals were euthanized with an overdose of pentobarbital sodium, and kidneys were perfused with saline followed by 4% paraformaldehyde removed, cut in tissue blocks, and fixed in 4% paraformaldehyde solution overnight at 4°C.…”

The therapeutic importance of acid-base balance

“…MAlk is a common finding in CF patients. CF-model mice are less capable of defending against HCO 3 – loads than their wild-type counterparts, due to downregulation of the renal HCO 3 – -secreting anion exchanger pendrin [256] and presumably loss of direct CFTR-mediated HCO 3 – secretion.…”

Pendrin stimulates a chloride absorption pathway to increase CFTR‐mediated chloride secretion from Cystic Fibrosis airway epithelia

“…This was confirmed using a TaqMan assay for pendrin mRNA (Figure 1B). CF‐dependent downregulation of pendrin has previously been described in CF animals 38 ; additionally, several interleukin cytokines have been shown to upregulate pendrin expression on the apical membrane of HBECs 39 . To confirm that cytokines could exert such an effect in our differentiated primary HBEC cultures, we performed Taqman qPCR analysis after 48 hours of treatment with 10 ng/mL IL‐13.…”