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.

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Available from: Thomas Baukrowitz, Sep 28, 2015
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    • "Genetic variations of Kir4.1 channels in humans and animals underlie severe disorders in the brain and in the retina, such as epilepsy, disruption of electroretinogram, glaucoma, stroke, ataxia, hypokalemia, hypomagnesemia, and metabolic alkalosis [27], [30], [31], [32], [33]. In addition, recently identified Kir4.1 mutations were found to result in autoimmune inhibition, contributing to pathogenesis of multiple sclerosis [34], hearing loss [35], autism [36] and seizures [30], [33]. The mutated Kir4.1 protein is not inserted in the membrane or the channels are blocked, as revealed by the absence of representative potassium currents [37]. "
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    ABSTRACT: Müller cells, the principal glial cells of the vertebrate retina, are fundamental for the maintenance and function of neuronal cells. In most vertebrates, including humans, Müller cells abundantly express Kir4.1 inwardly rectifying potassium channels responsible for hyperpolarized membrane potential and for various vital functions such as potassium buffering and glutamate clearance; inter-species differences in Kir4.1 expression were, however, observed. Localization and function of potassium channels in Müller cells from the retina of crocodiles remain, hitherto, unknown. We studied retinae of the Spectacled caiman (Caiman crocodilus fuscus), endowed with both diurnal and nocturnal vision, by (i) immunohistochemistry, (ii) whole-cell voltage-clamp, and (iii) fluorescent dye tracing to investigate K+ channel distribution and glia-to-neuron communications. Immunohistochemistry revealed that caiman Müller cells, similarly to other vertebrates, express vimentin, GFAP, S100β, and glutamine synthetase. In contrast, Kir4.1 channel protein was not found in Müller cells but was localized in photoreceptor cells. Instead, 2P-domain TASK-1 channels were expressed in Müller cells. Electrophysiological properties of enzymatically dissociated Müller cells without photoreceptors and isolated Müller cells with adhering photoreceptors were significantly different. This suggests ion coupling between Müller cells and photoreceptors in the caiman retina. Sulforhodamine-B injected into cones permeated to adhering Müller cells thus revealing a uni-directional dye coupling. Our data indicate that caiman Müller glial cells are unique among vertebrates studied so far by predominantly expressing TASK-1 rather than Kir4.1 K+ channels and by bi-directional ion and uni-directional dye coupling to photoreceptor cells. This coupling may play an important role in specific glia-neuron signaling pathways and in a new type of K+ buffering.
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    • "Another compelling, although indirect, evidence for the Kir involvement in the generation of epileptiform activities is the finding that mutations or polymorphisms of KCNJ10, the gene encoding Kir4.1 subunits, have been associated with increased seizure susceptibility and epileptic phenotypes in mice (Ferraro et al., 2004; Inyushin et al., 2010). Humans KCNJ10 mutations are also associated to seizure susceptibility, idiopathic generalized epilepsy (Buono et al., 2004; Lenzen et al., 2005) or to complex syndromes that encompass epilepsy (Bockenhauer et al., 2009; Scholl et al., 2009; Reichold et al., 2010). Notably, a reduced Kir4.1-mediated "
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    • "These mutations cause a disorder characterized by salt wasting, epilepsy, ataxia, and sensorineural deafness. These mutations all lead to channels that are unable to pass current in the physiologically relevant pH range (Reichold et al., 2010). "
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