Ca_V2.1 P/Q-type calcium channel alternative splicing affects the functional impact of familial hemiplegic migraine mutations: Implications for calcium channelopathies

Abstract

Alternative splicing is known to generate multiple functionally distinct calcium channel variants that exhibit unique spatial and temporal expression patterns. In humans, naturally occurring mutations in genes encoding calcium channel pore forming α 1 -subunits are associated with several severe hereditary disorders although it remains to be described whether there exists any relationship between the physiological effects of these mutations and calcium channel splice variation. In the present study, we systematically compare the biophysical effects of three type-1 familial hemiplegic migraine (FHM-1) mutations in two predominant splice variants of the neuronal Ca V 2.1 P/Q-type channel. All three FHM-1 mutations cause a greater hyperpolarizing shift in voltage-dependent properties when expressed in the short carboxyl terminus variant (Ca V 2.1 Δ47) compared to the long variant (Ca V 2.1 +47). Furthermore, the FHM-1 mutations also exhibit differential splice variant-specific effects on recovery from inactivation and accumulation of inactivation during tonic and burst firing. Our findings provide important insight concerning the role of calcium channel alternatively spliced variants and the molecular pathophysiology of FHM-1 and potentially of other calcium channelopathies.

Gating defects of disease-causing de novo mutations in Cav1.3 Ca2+ channels

“…The inclusion of this exon slowed recovery from inactivation as compared to channels devoid of exon 25, and the mutation offset this effect. Likewise, alternative splicing in the C-terminal tail of Ca v 2.1 α1-subunits of P/Q-type channels ( CACNA1A ) affected the functional changes of several gain-of-function missense mutations causing Familial Hemiplegic Migraine Type 1 [8], including S218L. It is possible that this mechanism also contributes to the differential effects of this mutation on neurotransmission at cortical pyramidal (gain-of-function of excitatory neurotransmission) and multipolar interneurons (unaltered inhibitory neurotransmission) in S218L knockin mice [37].…”

“…Their subcellular targeting as well as the dynamics of Ca 2+ entry need to be tightly controlled by accessory subunits, post-translational modification, lipid- and protein interactions, as well as alternative splicing [1,2]. The occurrence of human channelopathies resulting from even minor changes in Ca 2+ channel activity [4–8] further emphasizes the importance of strictly regulated channel gating and targeting for normal physiological function.…”

Contribution of calcium-dependent facilitation to synaptic plasticity revealed by migraine mutations in the P/Q-type calcium channel

“…In brief, HEK 293 cells were transiently transfected with WT, R192Q, or S218L human Ca v 2.1 in combination with β2, α 2 δ, and CD8 as previously described (24). Cerebellar PCs from WT or homozygous R192Q and S218L mice between postnatal days 15 to 25 were enzymatically isolated using similar dissociation techniques previously described (49)(50)(51).…”

In vivo imaging reveals that pregabalin inhibits cortical spreading depression and propagation to subcortical brain structures

“…FHM-1 mutations introduced into the orthologous Cacna1a gene produce transgenic mice with phenotypes that closely mimic both the milder (R192Q) and more severe (S218L) symptoms described in FHM-1 patients with these mutations (8,9). FHM-1 mutations have been shown to produce an overall gain-of-function increase in calcium conductance at physiological membrane potentials (10,11); given the wellestablished role of the channels in the calcium-mediated release of vesicular neurotransmitters, this increase can explain the increased synaptic activity observed in the mutant animals (12)(13)(14)(15)(16).…”