Functional analysis of missense variants in the TRESK (KCNK18) K+ channel

Abstract

A loss of function mutation in the TRESK K2P potassium channel (KCNK18), has recently been linked with typical familial migraine with aura. We now report the functional characterisation of additional TRESK channel missense variants identified in unrelated patients. Several variants either had no apparent functional effect, or they caused a reduction in channel activity. However, the C110R variant was found to cause a complete loss of TRESK function, yet is present in both sporadic migraine and control cohorts, and no variation in KCNK18 copy number was found. Thus despite the previously identified association between loss of TRESK channel activity and migraine in a large multigenerational pedigree, this finding indicates that a single non-functional TRESK variant is not alone sufficient to cause typical migraine and highlights the genetic complexity of this disorder.

Nonmigraine-associated TRESK K+ channel variant C110R does not increase the excitability of trigeminal ganglion neurons

“…Moreover, they exert a dominant-negative effect on the currents through wild-type (WT) TRESK channels and result in hyperexcitability of small-diameter TG neurons (Lafreniere et al 2010;Liu et al 2013), suggesting that the frameshift mutation may increase the gain of the neuronal circuit underlying migraine headache. In support of a genotype-phenotype correlation between the TRESK function and migraine susceptibility, the missense TRESK variant A34V identified in a migraine patient but not in the control cohort exhibits the same effect on whole cell TRESK current as the frameshift mutation in Xenopus oocytes (Andres-Enguix et al 2012). The TRESK variants R10G, S231P, and A233V have been found in both migraine and control cohorts.…”

“…The migraine-associated frameshift deletion and the CR variant of human TRESK were introduced into the corresponding region of the mouse TRESK cDNA using the Stratagene QuikChange site-directed mutagenesis kit. The human TRESK CR variant contains the cysteine to arginine substitution at amino acid 110 (Andres-Enguix et al 2012;Lafreniere et al 2010), corresponding to the cysteine to arginine change at amino acid 121 of mouse TRESK subunit (Andres-Enguix et al 2012). The enhanced green fluorescent protein (EGFP)-or mCherry-tagged constructs were generated by fusing TRESK CR cDNA in frame at the COOH termini of EGFP and mCherry coding region (EGFP-CR and mCherry-CR), respectively.…”

“…It is present in both migraineurs and unaffected individuals. However, the CR variant forms a nonfunctional channel per se in Xenopus oocytes and exhibits the same dominant-negative effect on WT TRESK currents as the frameshift mutation (Andres-Enguix et al 2012). This calls into question a direct causal relationship between TRESK dysfunction and migraine phenotype (Andres-Enguix et al 2012;Eising et al 2013;Lafreniere et al 2010).…”

“…However, the CR variant forms a nonfunctional channel per se in Xenopus oocytes and exhibits the same dominant-negative effect on WT TRESK currents as the frameshift mutation (Andres-Enguix et al 2012). This calls into question a direct causal relationship between TRESK dysfunction and migraine phenotype (Andres-Enguix et al 2012;Eising et al 2013;Lafreniere et al 2010). On the other hand, previous works have illustrated the importance of studying migraine-associated gene mutations in neurons involved in migraine pathophysiology (Fioretti et al 2011;Hullugundi et al 2014;Liu et al 2013;Tao et al 2012;Tottene et al 2009;van Den Maagdenberg et al 2004).…”

“…The TRESK variants R10G, S231P, and A233V have been found in both migraine and control cohorts. None of them affect the magnitude of the TRESK currents in Xenopus oocytes (Andres-Enguix et al 2012). …”