Variable loss of Kir4.1 channel function in SeSAME syndrome mutations

Department of Neuroscience, University of Minnesota, Minneapolis, MN 55455,USA.
Biochemical and Biophysical Research Communications (Impact Factor: 2.3). 09/2010; 399(4):537-41. DOI: 10.1016/j.bbrc.2010.07.105
Source: PubMed


SeSAME syndrome is a complex disease characterized by seizures, sensorineural deafness, ataxia, mental retardation and electrolyte imbalance. Mutations in the inwardly rectifying potassium channel Kir4.1 (KCNJ10 gene) have been linked to this condition. Kir4.1 channels are weakly rectifying channels expressed in glia, kidney, cochlea and possibly other tissues. We determined the electrophysiological properties of SeSAME mutant channels after expression in transfected mammalian cells. We found that a majority of mutations (R297C, C140R, R199X, T164I) resulted in complete loss of Kir4.1 channel function while two mutations (R65P and A167V) produced partial loss of function. All mutant channels were rescued upon co-transfection of wild-type Kir4.1 but not Kir5.1 channels. Cell-surface biotinylation assays indicate significant plasma membrane expression of all mutant channels with exception of the non-sense mutant R199X. These results indicate the differential loss of Kir channel function among SeSAME syndrome mutations.

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Available from: Paulo Kofuji, Aug 29, 2015
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    • "Seizure susceptibility has been linked to mutations in four selected candidate genes; Pex19 [81], Kcnj10 [82], Pigm [83], and Cabc1 [84]. There is a reduction in LS area as well as the number of GABAergic neurons in rats with pilocarpine-induced status epilepticus [85]. "
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    ABSTRACT: The lateral septum has strong efferent projections to hypothalamic and midbrain regions, and has been associated with modulation of social behavior, anxiety, fear conditioning, memory-related behaviors, and the mesolimbic reward pathways. Understanding natural variation of lateral septal anatomy and function, as well as its genetic modulation, may provide important insights into individual differences in these evolutionarily important functions. Here we address these issues by using efficient and unbiased stereological probes to estimate the volume of the lateral septum in the BXD line of recombinant inbred mice. Lateral septum volume is a highly variable trait, with a 2.5-fold difference among animals. We find that this trait covaries with a number of behavioral and physiological phenotypes, many of which have already been associated with behaviors modulated by the lateral septum, such as spatial learning, anxiety, and reward-seeking. Heritability of lateral septal volume is moderate (h(2) = 0.52), and much of the heritable variation is caused by a locus on the distal portion of chromosome (Chr) 1. Composite interval analysis identified a secondary interval on Chr 2 that works additively with the Chr 1 locus to increase lateral septum volume. Using bioinformatic resources, we identified plausible candidate genes in both intervals that may influence the volume of this key nucleus, as well as associated behaviors.
    PLoS ONE 08/2012; 7(8):e44236. DOI:10.1371/journal.pone.0044236 · 3.23 Impact Factor
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    • "Heterologous expression demonstrated that the mutations indeed affected Kir4.1 function and produced depolarization and reduced transmembrane currents (Bockenhauer et al., 2009; Reichold et al., 2010; Williams et al., 2010). The EAST/SeSAME syndrome-related decrease in K 1 conductance could not be rescued by co-expression with Kir5.1, and mutated Kir4.1 had no dominant-negative effect when co-expressing wildtype Kir4.1 (Tang et al., 2010). The mutations increased pH i -sensitivity of the channel and impeded its surface expression (Sala-Rabanal et al., 2010; Williams et al., 2010). "
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    ABSTRACT: Astrocytes are endowed with the machinery to sense and respond to neuronal activity. Recent work has demonstrated that astrocytes play important physiological roles in the CNS, e.g., they synchronize action potential firing, ensure ion homeostasis, transmitter clearance and glucose metabolism, and regulate the vascular tone. Astrocytes are abundantly coupled through gap junctions, which is a prerequisite to redistribute elevated K(+) from sites of excessive neuronal activity to sites of lower extracellular K(+) concentration. Recent studies identified dysfunctional astrocytes as crucial players in epilepsy. Investigation of specimens from patients with pharmacoresistant temporal lobe epilepsy and epilepsy models revealed alterations in expression, localization, and function of astroglial inwardly rectifying K(+) (Kir) channels, particularly Kir4.1, which is suspected to entail impaired K(+) buffering. Gap junctions in astrocytes appear to play a dual role: on the one hand they counteract the generation of hyperactivity by facilitating clearance of elevated extracellular K(+) levels while in contrast, they constitute a pathway for energetic substrate delivery to fuel neuronal (hyper)activity. Recent work suggests that astrocyte dysfunction is causative of the generation or spread of seizure activity. Thus, astrocytes should be considered as promising targets for alternative antiepileptic therapies.
    Glia 08/2012; 60(8):1192-202. DOI:10.1002/glia.22313 · 6.03 Impact Factor
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    • "Thus, the functional expression of Kir4.1 channels in glial membranes is important for voltage-dependent transport processes, such as glutamate uptake [12], [13]. The important role of the Kir4.1 channels is demonstrated by a number of studies identifying mutations in the Kir4.1 gene (KCNJ10) as a reason for symptoms found in the EAST syndrome (epilepsy, ataxia, sensorineural deafness, and tubulopathy) [14]–[18]. Moreover, possible associations between polymorphisms of the gene for aquaporin-4 and epilepsy have been described [19]. "
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    ABSTRACT: Glial cells such as retinal Müller glial cells are involved in potassium ion and water homeostasis of the neural tissue. In these cells, inwardly rectifying potassium (Kir) channels and aquaporin-4 water channels play an important role in the process of spatial potassium buffering and water drainage. Moreover, Kir4.1 channels are involved in the maintenance of the negative Müller cell membrane potential. The subcellular distribution of Kir4.1 and aquaporin-4 channels appears to be maintained by interactions with extracellular and intracellular molecules. Laminins in the extracellular matrix, dystroglycan in the membrane, and dystrophins in the cytomatrix form a complex mediating the polarized expression of Kir4.1 and aquaporin-4 in Müller cells. The aim of the present study was to test the function of the β2 and γ3 containing laminins in murine Müller cells. We used knockout mice with genetic deletion of both β2 and γ3 laminin genes to assay the effects on Kir4.1 and aquaporin-4. We studied protein and mRNA expression by immunohistochemistry, Western Blot, and quantitative RT-PCR, respectively, and membrane currents of isolated cells by patch-clamp experiments. We found a down-regulation of mRNA and protein of Kir4.1 as well as of aquaporin-4 protein in laminin knockout mice. Moreover, Müller cells from laminin β2 and γ3 knockout mice had reduced Kir-mediated inward currents and their membrane potentials were more positive than those in age-matched wild-type mice. These findings demonstrate a strong impact of laminin β2 and γ3 subunits on the expression and function of both aquaporin-4 and Kir4.1, two important membrane proteins in Müller cells.
    PLoS ONE 01/2011; 6(1):e16106. DOI:10.1371/journal.pone.0016106 · 3.23 Impact Factor
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