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A Single Amino Acid Deletion (ΔF1502) in the S6 Segment of CaV2.1 Domain III Associated with Congenital Ataxia Increases Channel Activity and Promotes Ca2+ Influx.

Bahamonde MI, Serra SA, Drechsel O, Rahman R, Marcé-Grau A, Prieto M, Ossowski S, Macaya A, Fernández-Fernández JM - PLoS ONE (2015)

Bottom Line: ΔF1502 strongly decreases the voltage threshold for channel activation (by ~ 21 mV), allowing significantly higher Ca2+ current densities in a range of depolarized voltages with physiological relevance in neurons, even though maximal Ca2+ current density through ΔF1502 CaV2.1 channels is 60% lower than through wild-type channels.ΔF1502 effects on CaV2.1 activation and deactivation properties seem to be of high physiological relevance.Thus, ΔF1502 strongly promotes Ca2+ influx in response to either single or trains of action potential-like waveforms of different durations.

View Article: PubMed Central - PubMed

Affiliation: Laboratori de Fisiologia Molecular i Canalopaties, Departament de Ciències Experimentals i de la Salut, Universitat Pompeu Fabra, Barcelona, Spain.

ABSTRACT
Mutations in the CACNA1A gene, encoding the pore-forming CaV2.1 (P/Q-type) channel α1A subunit, result in heterogeneous human neurological disorders, including familial and sporadic hemiplegic migraine along with episodic and progressive forms of ataxia. Hemiplegic Migraine (HM) mutations induce gain-of-channel function, mainly by shifting channel activation to lower voltages, whereas ataxia mutations mostly produce loss-of-channel function. However, some HM-linked gain-of-function mutations are also associated to congenital ataxia and/or cerebellar atrophy, including the deletion of a highly conserved phenylalanine located at the S6 pore region of α1A domain III (ΔF1502). Functional studies of ΔF1502 CaV2.1 channels, expressed in Xenopus oocytes, using the non-physiological Ba2+ as the charge carrier have only revealed discrete alterations in channel function of unclear pathophysiological relevance. Here, we report a second case of congenital ataxia linked to the ΔF1502 α1A mutation, detected by whole-exome sequencing, and analyze its functional consequences on CaV2.1 human channels heterologously expressed in mammalian tsA-201 HEK cells, using the physiological permeant ion Ca2+. ΔF1502 strongly decreases the voltage threshold for channel activation (by ~ 21 mV), allowing significantly higher Ca2+ current densities in a range of depolarized voltages with physiological relevance in neurons, even though maximal Ca2+ current density through ΔF1502 CaV2.1 channels is 60% lower than through wild-type channels. ΔF1502 accelerates activation kinetics and slows deactivation kinetics of CaV2.1 within a wide range of voltage depolarization. ΔF1502 also slowed CaV2.1 inactivation kinetic and shifted the inactivation curve to hyperpolarized potentials (by ~ 28 mV). ΔF1502 effects on CaV2.1 activation and deactivation properties seem to be of high physiological relevance. Thus, ΔF1502 strongly promotes Ca2+ influx in response to either single or trains of action potential-like waveforms of different durations. Our observations support a causative role of gain-of-function CaV2.1 mutations in congenital ataxia, a neurodevelopmental disorder at the severe-most end of CACNA1A-associated phenotypic spectrum.

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Brain MRI of the proband at the age of 14 months (A), 28 months (B), and 4 and a half years (C,D).After the initial normal findings (A), note the progressive cerebellar atrophy mainly involving the complete vermis (indicated by the arrows in B, C). The hemispheres, displaying prominence of the cerebellar folia, were eventually affected (D).
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pone.0146035.g001: Brain MRI of the proband at the age of 14 months (A), 28 months (B), and 4 and a half years (C,D).After the initial normal findings (A), note the progressive cerebellar atrophy mainly involving the complete vermis (indicated by the arrows in B, C). The hemispheres, displaying prominence of the cerebellar folia, were eventually affected (D).

Mentions: At the age of 7 years the patient has developed a complete ataxic syndrome. He is able to understand simple commands and speaks in short sentences. He is quite sociable and attends a special school. He is able to draw or self-feed with spoon. On examination, he is normocephalic and there are no telangiectasias or organomegalies. There is a fine, conjugate horizontal/rotary nystagmus and a complex alteration of ocular pursuit that resembles oculomotor apraxia, prominent head and trunk titubation, diffuse hypotonia, normal strength, brisk deep-tendon reflexes, flexor plantar responses and mild upper limb dysmetria with no tremor. He can adopt a quadrupedal position but is not able to stand or walk holding onto furniture. Ancillary tests included serum creatine kinase, vitamin E, alpha fetoprotein, immunoglobulins, thyroid hormones, amino acids, transferrin isoelectric focusing, urine organic acids, CSF lactate, pterins, folate and dopamine and serotonin metabolites. A comparative genomic hybridization array showed a 225 Kb segmental monosomy in the sexual chromosomes pseudoautosomal region (PAR2). Although this rearrangement affected the dose of SPRY3 and VAMP7, it was also found in his asymptomatic father. Fibroblast beta-galactosidase, beta-D-glucuronidase, beta-glucosidase, beta-N-acetyl-glucosaminidase, hexosaminidase A, alpha-galactosidase and alpha-glucosidase activities were normal. A neurophysiological study showed normality of motor and sensory neurography, EMG and somatosensory evoked responses. Visual evoked potentials (flash) and electroretinogram were normal. A muscle biopsy disclosed normal histochemistry and normal activities of the respiratory chain enzymes. A brain magnetic resonance imaging (MRI) at the age of 14 months did not reveal alterations. Subsequent studies performed at the ages of 28 months and 4 years showed a conspicuous and progressive, predominantly vermian, cerebellar atrophy with no involvement of other brain areas (Fig 1).


A Single Amino Acid Deletion (ΔF1502) in the S6 Segment of CaV2.1 Domain III Associated with Congenital Ataxia Increases Channel Activity and Promotes Ca2+ Influx.

Bahamonde MI, Serra SA, Drechsel O, Rahman R, Marcé-Grau A, Prieto M, Ossowski S, Macaya A, Fernández-Fernández JM - PLoS ONE (2015)

Brain MRI of the proband at the age of 14 months (A), 28 months (B), and 4 and a half years (C,D).After the initial normal findings (A), note the progressive cerebellar atrophy mainly involving the complete vermis (indicated by the arrows in B, C). The hemispheres, displaying prominence of the cerebellar folia, were eventually affected (D).
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4696675&req=5

pone.0146035.g001: Brain MRI of the proband at the age of 14 months (A), 28 months (B), and 4 and a half years (C,D).After the initial normal findings (A), note the progressive cerebellar atrophy mainly involving the complete vermis (indicated by the arrows in B, C). The hemispheres, displaying prominence of the cerebellar folia, were eventually affected (D).
Mentions: At the age of 7 years the patient has developed a complete ataxic syndrome. He is able to understand simple commands and speaks in short sentences. He is quite sociable and attends a special school. He is able to draw or self-feed with spoon. On examination, he is normocephalic and there are no telangiectasias or organomegalies. There is a fine, conjugate horizontal/rotary nystagmus and a complex alteration of ocular pursuit that resembles oculomotor apraxia, prominent head and trunk titubation, diffuse hypotonia, normal strength, brisk deep-tendon reflexes, flexor plantar responses and mild upper limb dysmetria with no tremor. He can adopt a quadrupedal position but is not able to stand or walk holding onto furniture. Ancillary tests included serum creatine kinase, vitamin E, alpha fetoprotein, immunoglobulins, thyroid hormones, amino acids, transferrin isoelectric focusing, urine organic acids, CSF lactate, pterins, folate and dopamine and serotonin metabolites. A comparative genomic hybridization array showed a 225 Kb segmental monosomy in the sexual chromosomes pseudoautosomal region (PAR2). Although this rearrangement affected the dose of SPRY3 and VAMP7, it was also found in his asymptomatic father. Fibroblast beta-galactosidase, beta-D-glucuronidase, beta-glucosidase, beta-N-acetyl-glucosaminidase, hexosaminidase A, alpha-galactosidase and alpha-glucosidase activities were normal. A neurophysiological study showed normality of motor and sensory neurography, EMG and somatosensory evoked responses. Visual evoked potentials (flash) and electroretinogram were normal. A muscle biopsy disclosed normal histochemistry and normal activities of the respiratory chain enzymes. A brain magnetic resonance imaging (MRI) at the age of 14 months did not reveal alterations. Subsequent studies performed at the ages of 28 months and 4 years showed a conspicuous and progressive, predominantly vermian, cerebellar atrophy with no involvement of other brain areas (Fig 1).

Bottom Line: ΔF1502 strongly decreases the voltage threshold for channel activation (by ~ 21 mV), allowing significantly higher Ca2+ current densities in a range of depolarized voltages with physiological relevance in neurons, even though maximal Ca2+ current density through ΔF1502 CaV2.1 channels is 60% lower than through wild-type channels.ΔF1502 effects on CaV2.1 activation and deactivation properties seem to be of high physiological relevance.Thus, ΔF1502 strongly promotes Ca2+ influx in response to either single or trains of action potential-like waveforms of different durations.

View Article: PubMed Central - PubMed

Affiliation: Laboratori de Fisiologia Molecular i Canalopaties, Departament de Ciències Experimentals i de la Salut, Universitat Pompeu Fabra, Barcelona, Spain.

ABSTRACT
Mutations in the CACNA1A gene, encoding the pore-forming CaV2.1 (P/Q-type) channel α1A subunit, result in heterogeneous human neurological disorders, including familial and sporadic hemiplegic migraine along with episodic and progressive forms of ataxia. Hemiplegic Migraine (HM) mutations induce gain-of-channel function, mainly by shifting channel activation to lower voltages, whereas ataxia mutations mostly produce loss-of-channel function. However, some HM-linked gain-of-function mutations are also associated to congenital ataxia and/or cerebellar atrophy, including the deletion of a highly conserved phenylalanine located at the S6 pore region of α1A domain III (ΔF1502). Functional studies of ΔF1502 CaV2.1 channels, expressed in Xenopus oocytes, using the non-physiological Ba2+ as the charge carrier have only revealed discrete alterations in channel function of unclear pathophysiological relevance. Here, we report a second case of congenital ataxia linked to the ΔF1502 α1A mutation, detected by whole-exome sequencing, and analyze its functional consequences on CaV2.1 human channels heterologously expressed in mammalian tsA-201 HEK cells, using the physiological permeant ion Ca2+. ΔF1502 strongly decreases the voltage threshold for channel activation (by ~ 21 mV), allowing significantly higher Ca2+ current densities in a range of depolarized voltages with physiological relevance in neurons, even though maximal Ca2+ current density through ΔF1502 CaV2.1 channels is 60% lower than through wild-type channels. ΔF1502 accelerates activation kinetics and slows deactivation kinetics of CaV2.1 within a wide range of voltage depolarization. ΔF1502 also slowed CaV2.1 inactivation kinetic and shifted the inactivation curve to hyperpolarized potentials (by ~ 28 mV). ΔF1502 effects on CaV2.1 activation and deactivation properties seem to be of high physiological relevance. Thus, ΔF1502 strongly promotes Ca2+ influx in response to either single or trains of action potential-like waveforms of different durations. Our observations support a causative role of gain-of-function CaV2.1 mutations in congenital ataxia, a neurodevelopmental disorder at the severe-most end of CACNA1A-associated phenotypic spectrum.

Show MeSH
Related in: MedlinePlus