Dataset Information

Impaired Renal HCO₃ ^- Excretion in Cystic Fibrosis.

ABSTRACT:

Background

Patients with cystic fibrosis (CF) do not respond with increased urinary HCO₃ ^- excretion after stimulation with secretin and often present with metabolic alkalosis.

Methods

By combining RT-PCR, immunohistochemistry, isolated tubule perfusion, in vitro cell studies, and in vivo studies in different mouse models, we elucidated the mechanism of secretin-induced urinary HCO₃ ^- excretion. For CF patients and CF mice, we developed a HCO₃ ^- drinking test to assess the role of the cystic fibrosis transmembrane conductance regulator (CFTR) in urinary HCO₃ ^-excretion and applied it in the patients before and after treatment with the novel CFTR modulator drug, lumacaftor-ivacaftor.

Results

β-Intercalated cells express basolateral secretin receptors and apical CFTR and pendrin. In vivo application of secretin induced a marked urinary alkalization, an effect absent in mice lacking pendrin or CFTR. In perfused cortical collecting ducts, secretin stimulated pendrin-dependent Cl^-/HCO₃ ^- exchange. In collecting ducts in CFTR knockout mice, baseline pendrin activity was significantly lower and not responsive to secretin. Notably, patients with CF (F508del/F508del) and CF mice showed a greatly attenuated or absent urinary HCO₃ ^--excreting ability. In patients, treatment with the CFTR modulator drug lumacaftor-ivacaftor increased the renal ability to excrete HCO₃ ^-.

Conclusions

These results define the mechanism of secretin-induced urinary HCO₃ ^- excretion, explain metabolic alkalosis in patients with CF, and suggest feasibility of an in vivo human CF urine test to validate drug efficacy.

SUBMITTER: Berg P

PROVIDER: S-EPMC7460909 | biostudies-literature | 2020 Aug

REPOSITORIES: biostudies-literature

ACCESS DATA

Publications

Impaired Renal HCO<sub>3</sub><sup>-</sup> Excretion in Cystic Fibrosis.

Berg Peder P Svendsen Samuel L SL Sorensen Mads V MV Larsen Casper K CK Andersen Jesper Frank JF Jensen-Fangel Søren S Jeppesen Majbritt M Schreiber Rainer R Cabrita Ines I Kunzelmann Karl K Leipziger Jens J

Journal of the American Society of Nephrology : JASN 20200723 8

<h4>Background</h4>Patients with cystic fibrosis (CF) do not respond with increased urinary HCO<sub>3</sub><sup>-</sup> excretion after stimulation with secretin and often present with metabolic alkalosis.<h4>Methods</h4>By combining RT-PCR, immunohistochemistry, isolated tubule perfusion, <i>in vitro</i> cell studies, and <i>in vivo</i> studies in different mouse models, we elucidated the mechanism of secretin-induced urinary HCO<sub>3</sub><sup>-</sup> excretion. For CF patients and CF mice, w ...[more]

PMID: 32703846

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Project description:The interoceptive homeostatic mechanism that controls breathing, blood gases and acid-base balance in response to changes in CO2 /H+ is exquisitely sensitive, with convergent roles proposed for chemosensory brainstem neurons in the retrotrapezoid nucleus (RTN) and their supporting glial cells. For astrocytes, a central role for NBCe1, a Na+ -HCO3 - cotransporter encoded by Slc4a4, has been envisaged in multiple mechanistic models (i.e. underlying enhanced CO2 -induced local extracellular acidification or purinergic signalling). We tested these NBCe1-centric models by using conditional knockout mice in which Slc4a4 was deleted from astrocytes. In GFAP-Cre;Slc4a4fl/fl mice we found diminished expression of Slc4a4 in RTN astrocytes by comparison to control littermates, and a concomitant reduction in NBCe1-mediated current. Despite disrupted NBCe1 function in RTN-adjacent astrocytes from these conditional knockout mice, CO2 -induced activation of RTN neurons or astrocytes in vitro and in vivo, and CO2 -stimulated breathing, were indistinguishable from NBCe1-intact littermates; hypoxia-stimulated breathing and sighs were likewise unaffected. We obtained a more widespread deletion of NBCe1 in brainstem astrocytes by using tamoxifen-treated Aldh1l1-Cre/ERT2;Slc4a4fl/fl mice. Again, there was no difference in effects of CO2 or hypoxia on breathing or on neuron/astrocyte activation in NBCe1-deleted mice. These data indicate that astrocytic NBCe1 is not required for the respiratory responses to these chemoreceptor stimuli in mice, and that any physiologically relevant astrocytic contributions must involve NBCe1-independent mechanisms. KEY POINTS: The electrogenic NBCe1 transporter is proposed to mediate local astrocytic CO2 /H+ sensing that enables excitatory modulation of nearby retrotrapezoid nucleus (RTN) neurons to support chemosensory control of breathing. We used two different Cre mouse lines for cell-specific and/or temporally regulated deletion of the NBCe1 gene (Slc4a4) in astrocytes to test this hypothesis. In both mouse lines, Slc4a4 was depleted from RTN-associated astrocytes but CO2 -induced Fos expression (i.e. cell activation) in RTN neurons and local astrocytes was intact. Likewise, respiratory chemoreflexes evoked by changes in CO2 or O2 were unaffected by loss of astrocytic Slc4a4. These data do not support the previously proposed role for NBCe1 in respiratory chemosensitivity mediated by astrocytes.

Dataset Information

Impaired Renal HCO₃ ^- Excretion in Cystic Fibrosis.

Background

Methods

Results

Conclusions

Publications

Impaired Renal HCO<sub>3</sub><sup>-</sup> Excretion in Cystic Fibrosis.

Similar Datasets

OmicsDI is part of the ELIXIR infrastructure

Tweets

Dataset Information

Impaired Renal HCO3 - Excretion in Cystic Fibrosis.

Background

Methods

Results

Conclusions

Publications

Impaired Renal HCO<sub>3</sub><sup>-</sup> Excretion in Cystic Fibrosis.

Similar Datasets

OmicsDI is part of the ELIXIR infrastructure

Tweets

Impaired Renal HCO₃ ^- Excretion in Cystic Fibrosis.