Developmental changes in KCNQ2 and KCNQ3 expression in human brain: Possible contribution to the age-dependent etiology of benign familial neonatal convulsions

doi:10.1016/j.braindev.2007.11.003

Brain and Development

Volume 30, Issue 5, May 2008, Pages 362-369

https://doi.org/10.1016/j.braindev.2007.11.003 Get rights and content

Abstract

Several mutations of KCNQ2 and KCNQ3 are considered to be associated with benign familial neonatal convulsions (BFNC). BFNC is characterized by seizures starting within several days of life and spontaneous remission within weeks to months. KCNQ channel is a heteromeric voltage-dependent potassium channel consisting of KCNQ2 and KCNQ3 subunits. To clarify the age-dependent etiology of BFNC, we examined the developmental changes in KCNQ2 and KCNQ3 expression in human hippocampus, temporal lobe, cerebellum and medulla oblongata obtained from 23 subjects who died at 22 gestation weeks to adulthood. Formalin-fixed and paraffin-embedded specimens were used for immunohistochemistry. Unique developmental changes in KCNQ2 and KCNQ3 were found in each region. A high expression of KCNQ2 was identified in the hippocampus, temporal cortex, cerebellar cortex and medulla oblongata in fetal life, but such expression decreased after birth. The expression of KCNQ3 increased in late fetal life to infancy. Simultaneous and high expressions of KCNQ2 and KCNQ3 were observed in each region from late fetal life to early infancy, coinciding with the time when BFNC occurs. Such coexpression may contribute to the pathogenesis of BFNC.

Introduction

Epilepsy is a common neurological disorder afflicting 1–2% of the general population worldwide. The pathogenesis of epilepsy has a genetic component and the phenotypes often show age-dependence. Genetic abnormalities have been identified recently in age-dependent familial epilepsy syndromes [1], [2]. However, the etiology of such age-dependency of epilepsy remains mostly unclear.

Benign familial neonatal convulsion (BFNC) is an age-dependent familial epilepsy syndrome characterized by clusters of generalized seizures exclusively afflicting neonates, with spontaneous remission [3], [4]. Mutations in the genes encoding two subunits of KCNQ channels, KCNQ2 and KCNQ3, have been identified as causes of BFNC [1], [5], [6], [7], [8]. However, the exact pathogenic mechanisms of age-dependent onset and spontaneous remission of BFNC remain to be elucidated.

The KCNQ channel is a voltage-dependent potassium channel. Potassium current generated by KCNQ channels is called M-current. The M-current was first described in sympathetic neurons [9] and later recorded in mammalian brain neurons [10], [11]. Hence, it is currently known to have a major influence on neuronal excitability governing the responsiveness of neurons to incoming inputs.

The KCNQ channel is a heteromeric tetramer consisting of KCNQ2 and KCNQ3 subunits [12]. KCNQ2 and KCNQ3 are widely expressed mainly in the hippocampus, neocortex and cerebellar cortex, presenting a specific regionalized distribution [13], [14], [15], [16]. In these regions, KCNQ2 and KCNQ3 are co-expressed and co-assembled [15], and thus both subunits are thought to fully function when they are assembled as a heterotetramer, because KCNQ2/KCNQ3 heteromeric channels generate 15-fold larger current than homomeric channels [6], [12], [13], [14], [15], [17], [18], [19], [20]. The developmental pattern of KCNQ2 and KCNQ3 subunits may contribute to the age-dependent etiology of BFNC. To our knowledge, there is no information about the development of the subunits in human brain. Therefore, we investigated the developmental changes in KCNQ2 and KCNQ3 expression in the hippocampus, temporal lobe, cerebellum and medulla oblongata in human brain.

Section snippets

Western blotting

Specimens of normal human brain were used in Western blotting. Western blot analysis was performed as described previously [21]. Briefly, supernatants of cerebral cortex and cerebelli homogenates were collected after centrifugation, and the amounts of protein were assayed by the method of Bradford. Samples (50 lg/lane) were separated on a 7.5% SDS polyacrylamide gel and then electrophoretically transferred to a nitrocellulose membrane (HyBond-P; Amersham; NJ, USA). Blocking with 8% skimmed milk

Results

Table 1 summarizes the extent of immunoreactivities to KCNQ2 and KCNQ3 in the developing human hippocampus, temporal lobe, cerebellum and medulla oblongata. Unique developmental changes in KCNQ2 and KCNQ3 immunostaining were found in each region.

Discussion

We reported the developmental changes in KCNQ2 and KCNQ3 expression in human hippocampus, temporal lobe, cerebellum and medulla oblongata. Our results showed unique developmental changes in KCNQ2 and KCNQ3 expression in each region and these changes varied spatially and temporally. A high expression of KCNQ2 was identified in the hippocampus, temporal cortex, cerebellar cortex and medulla oblongata in fetal life, but such expression decreased after birth. The expression of KCNQ3 increased in

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Original articleDevelopmental changes in KCNQ2 and KCNQ3 expression in human brain: Possible contribution to the age-dependent etiology of benign familial neonatal convulsions

Abstract

Introduction

Section snippets

Western blotting

Results

Discussion

Epilepsy Res

Pediatr Neurol

Pediatr Neurol

Brain Res

FEBS Lett

J Biol Chem

J Biol Chem

J Biol Chem

Brain Res

Neurosci Lett

Cell

Epilepsy Res

Epilepsy Res

A novel mutation of KCNQ3 (c.925T–>C) in a Japanese family with benign familial neonatal convulsions

Ann Neurol

A reduced K+ current due to a novel mutation in KCNQ2 causes neonatal convulsions

Ann Neurol

A potassium channel mutation in neonatal human epilepsy

Science

A pore mutation in a novel KQT-like potassium channel gene in an idiopathic epilepsy family

Nat Genet

Original article
Developmental changes in KCNQ2 and KCNQ3 expression in human brain: Possible contribution to the age-dependent etiology of benign familial neonatal convulsions