A rare schizophrenia risk variant of CACNA1I disrupts CaV3.3 channel activity.

A. Andrade,A. Allen,J. Q. Pan,J. Hope,D. Lipscombe,V. Yorgan

doi:10.1038/srep34233

Abstract

CACNA1I is a candidate schizophrenia risk gene. It encodes the pore-forming human CaV3.3 α1 subunit, a subtype of voltage-gated calcium channel that contributes to T-type currents. Recently, two de novo missense variations, T797M and R1346H, of hCaV3.3 were identified in individuals with schizophrenia. Here we show that R1346H, but not T797M, is associated with lower hCaV3.3 protein levels, reduced glycosylation, and lower membrane surface levels of hCaV3.3 when expressed in human cell lines compared to wild-type. Consistent with our biochemical analyses, whole-cell hCaV3.3 currents in cells expressing the R1346H variant were ~50% of those in cells expressing WT hCaV3.3, and neither R1346H nor T797M altered channel biophysical properties. Employing the NEURON simulation environment, we found that reducing hCaV3.3 current densities by 22% or more eliminates rebound bursting in model thalamic reticular nucleus (TRN) neurons. Our analyses suggest that a single copy of Chr22: 39665939G > A CACNA1I has the capacity to disrupt CaV3.3 channel-dependent functions, including rebound bursting in TRN neurons, with potential implications for schizophrenia pathophysiology.

Highlights

CACNA1I encodes the pore-forming hCaV3.3 α1 subunit, one of three major CaV3 voltage-gated calcium (CaV) channels that contribute to low threshold T-type currents
By simulating thalamic reticular nucleus (TRN) neuron excitability in the NEURON environment[7] we show that: (i) rebound bursting is highly sensitive to CaV3.3 channel density; (ii) rebound bursting is eliminated when CaV3.3 channel density is reduced to 78% or less of initial WT values (Fig. 8b; black line shows WT relationship); and (iii) firing of TRN neurons evoked by depolarizing current injections is insensitive to changes in dendritic CaV3.3 current densities to 40% of initial WT values (Fig. 8a,c)
CACNA1I has been identified as a candidate schizophrenia risk gene based on genome wide association studies, and on the identification of de novo, rare missense variations in CACNA1I from exome sequencing of schizophrenia proband trios[19,31]

Summary

Introduction

CACNA1I encodes the pore-forming hCaV3.3 α1 subunit, one of three major CaV3 voltage-gated calcium (CaV) channels that contribute to low threshold T-type currents. Genetic analyses of large patient cohorts have identified loci associated with the risk of mental illnesses including schizophrenia, autism spectrum disorder and bipolar disorder[15,16,17,18,19]. Several of these candidate risk genes encode proteins involved in calcium signaling, including voltage-gated calcium channel subunits (CACNA1C, CACNB2 and CACNA1I), that may converge on a common disease mechanism[17,19,20,21,22,23,24]. Employing NEURON to simulate TRN neuron excitability, we show that R1346H disrupts rebound bursting mediated by CaV3.3 channels

Methods

Results

Conclusion