Article

KCNJ10 gene mutations causing EAST syndrome (epilepsy, ataxia, sensorineural deafness, and tubulopathy) disrupt channel function

Department of Physiology, University of Regensburg, 93053 Regensburg, Germany.
Proceedings of the National Academy of Sciences (Impact Factor: 9.67). 08/2010; 107(32):14490-5. DOI: 10.1073/pnas.1003072107
Source: PubMed

ABSTRACT

Mutations of the KCNJ10 (Kir4.1) K(+) channel underlie autosomal recessive epilepsy, ataxia, sensorineural deafness, and (a salt-wasting) renal tubulopathy (EAST) syndrome. We investigated the localization of KCNJ10 and the homologous KCNJ16 in kidney and the functional consequences of KCNJ10 mutations found in our patients with EAST syndrome. Kcnj10 and Kcnj16 were found in the basolateral membrane of mouse distal convoluted tubules, connecting tubules, and cortical collecting ducts. In the human kidney, KCNJ10 staining was additionally observed in the basolateral membrane of the cortical thick ascending limb of Henle's loop. EM of distal tubular cells of a patient with EAST syndrome showed reduced basal infoldings in this nephron segment, which likely reflects the morphological consequences of the impaired salt reabsorption capacity. When expressed in CHO and HEK293 cells, the KCNJ10 mutations R65P, G77R, and R175Q caused a marked impairment of channel function. R199X showed complete loss of function. Single-channel analysis revealed a strongly reduced mean open time. Qualitatively similar results were obtained with coexpression of KCNJ10/KCNJ16, suggesting a dominance of KCNJ10 function in native renal KCNJ10/KCNJ16 heteromers. The decrease in the current of R65P and R175Q was mainly caused by a remarkable shift of pH sensitivity to the alkaline range. In summary, EAST mutations of KCNJ10 lead to impaired channel function and structural changes in distal convoluted tubules. Intriguingly, the metabolic alkalosis present in patients carrying the R65P mutation possibly improves residual function of KCNJ10, which shows higher activity at alkaline pH.

Download full-text

Full-text

Available from: Thomas Baukrowitz
    • "Cell cycle phase distribution analysis showed unchanged cell numbers in G1-, S-, and G2-phase of the cell cycle after siRNA-mediated depletion of Clcn4, Kcnq1 and Kcnj10 compared to siControl, excluding any possible cell cycle effect on the observed loss of cilia (Fig S3B). Immunofluorescence staining using specific antibodies to each of these ion channels shows that endogenous Clcn4, Kcnf1, Kcnq1 and Kcnj10 proteins localize to membrane subdomains at the base of primary cilia of human fibroblasts and mIMCD3 cells (Fig 2C, S2), in addition to the previously described localizations of these channels at the endosomal membrane for CLCN4 (Scheel et al., 2005), or basolateral membrane for KCNQ1 and KCNJ10 (Jespersen et al., 2004; Reichold et al., 2010). In human fibroblasts derived from two unrelated individuals, CLCN4 decorates the entire length of the cilium (Fig. 2C) whereas in murine renal cells it is restricted to the membrane subdomain at the base of the cilium, suggesting species-and tissue-specificity of localization. "
    [Show abstract] [Hide abstract]
    ABSTRACT: To investigate the contribution of ion channels to ciliogenesis we carried out an siRNA-based reverse genetics screen of all ion channels in the mouse genome in murine inner medullary collecting duct kidney cells. This screen revealed four candidate ion channel genes: Kcnq1, Kcnj10, Kcnf1 and Clcn4. We show that these four ion channels localize to renal tubules, specifically to the base of primary cilia. We report that human KCNQ1 Long QT syndrome disease alleles, regulate renal ciliogenesis; KCNQ1-p.R518X, -p.A178T and -p.K362R could not rescue ciliogenesis after Kcnq1 siRNA-mediated depletion in contrast to wild-type KCNQ1 and benign KCNQ1-p.R518Q, suggesting that the ion channel function of KCNQ1 regulates ciliogenesis. In contrast, we demonstrate that the ion channel function of KCNJ10 is independent of its effect on ciliogenesis. Our data suggest that these four ion channels possibly regulate renal ciliogenesis through the periciliary diffusion barrier or the ciliary pocket, with potential implication as genetic contributors to ciliopathy pathophysiology. The new functional roles of a subset of ion channels provide new insights into the disease pathogenesis of channelopathies and may suggest future therapeutic approaches.
    No preview · Article · Nov 2015 · Journal of Cell Science
  • Source
    • "Cite this article as Cold Spring Harb Perspect Med 2015;5:a022434 zation (Bockenhauer et al. 2009; Scholl et al. 2009; Reichold et al. 2010; Williams et al. 2010). The mutations increased the pH i -sensitivity of the channel and impeded its surface expression (Sala-Rabanal et al. 2010; Williams et al. 2010). "
    [Show abstract] [Hide abstract]
    ABSTRACT: Astrocytes express ion channels, transmitter receptors, and transporters and, thus, are endowed with the machinery to sense and respond to neuronal activity. Recent studies have implicated that astrocytes play important roles in physiology, but these cells also emerge as crucial actors in epilepsy. Astrocytes are abundantly coupled through gap junctions allowing them to redistribute elevated Kþ and transmitter concentrations from sites of enhanced neuronal activity. Investigation of specimens frompatients with pharmacoresistant temporal lobe epilepsy and epilepsy models revealed alterations in expression, localization, and function of astroglial Kþ and water channels. In addition, malfunction of glutamate transporters and the astrocytic glutamate-converting enzyme, glutamine synthetase, has been observed in epileptic tissue. These findings suggest that dysfunctional astrocytes are crucial players in epilepsy and should be considered as promising targets for new therapeutic strategies. © 2015 Cold Spring Harbor Laboratory Press; all rights reserved.
    Preview · Article · Mar 2015 · Cold Spring Harbor Perspectives in Medicine
  • Source
    • "In the DCT, the inwardly rectifying K + channel, comprising Kir4.1, likely with Kir5.1, appears to be the predominant conductive pathway for K + exit along the basolateral membrane (Lourdel et al., 2002; Zhang et al., 2014) (Figure S4B). When Kir4.1 mutations , which reduce conductive activity, are present in the DCT, a Gitelman-like tubulopathy, EAST/SeSAME syndrome, appears (Bandulik et al., 2011; Reichold et al., 2010). When EAST syndrome mutant channels were expressed in our system, the reversal potentials were less negative (Figures 5A and S4C), and the pNCC abundance was lower (Figure 5B and Table S4) than when wild-type channels were expressed. "
    [Show abstract] [Hide abstract]
    ABSTRACT: Dietary potassium deficiency, common in modern diets, raises blood pressure and enhances salt sensitivity. Potassium homeostasis requires a molecular switch in the distal convoluted tubule (DCT), which fails in familial hyperkalemic hypertension (pseudohypoaldosteronism type 2), activating the thiazide-sensitive NaCl cotransporter, NCC. Here, we show that dietary potassium deficiency activates NCC, even in the setting of high salt intake, thereby causing sodium retention and a rise in blood pressure. The effect is dependent on plasma potassium, which modulates DCT cell membrane voltage and, in turn, intracellular chloride. Low intracellular chloride stimulates WNK kinases to activate NCC, limiting potassium losses, even at the expense of increased blood pressure. These data show that DCT cells, like adrenal cells, sense potassium via membrane voltage. In the DCT, hyperpolarization activates NCC via WNK kinases, whereas in the adrenal gland, it inhibits aldosterone secretion. These effects work in concert to maintain potassium homeostasis. Copyright © 2015 Elsevier Inc. All rights reserved.
    Full-text · Article · Jan 2015 · Cell Metabolism
Show more