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TRIP8b splice variants form a family of auxiliary subunits that regulate gating and trafficking of HCN channels in the brain.

ABSTRACT: Hyperpolarization-activated cyclic nucleotide-regulated (HCN) channels, which generate the I(h) current, mediate a number of important brain functions. The HCN1 isoform regulates dendritic integration in cortical pyramidal neurons and provides an inhibitory constraint on both working memory in prefrontal cortex and spatial learning and memory in the hippocampus. Altered expression of HCN1 following seizures may contribute to the development of temporal lobe epilepsy. Yet the regulatory networks and pathways governing HCN channel expression and function in the brain are largely unknown. Here, we report the presence of nine alternative N-terminal splice forms of the brain-specific cytoplasmic protein TRIP8b and demonstrate the differential effects of six isoforms to downregulate or upregulate HCN1 surface expression. Furthermore, we find that all TRIP8b isoforms inhibit channel opening by shifting activation to more negative potentials. TRIP8b thus functions as an auxiliary subunit that provides a mechanism for the dynamic regulation of HCN1 channel expression and function.

SUBMITTER: Santoro B

PROVIDER: S-EPMC2720631 | biostudies-literature | 2009 Jun

REPOSITORIES: biostudies-literature

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TRIP8b splice variants form a family of auxiliary subunits that regulate gating and trafficking of HCN channels in the brain.

Santoro Bina B Piskorowski Rebecca A RA Pian Phillip P Hu Lei L Liu Haiying H Siegelbaum Steven A SA

Neuron 20090601 6

Hyperpolarization-activated cyclic nucleotide-regulated (HCN) channels, which generate the I(h) current, mediate a number of important brain functions. The HCN1 isoform regulates dendritic integration in cortical pyramidal neurons and provides an inhibitory constraint on both working memory in prefrontal cortex and spatial learning and memory in the hippocampus. Altered expression of HCN1 following seizures may contribute to the development of temporal lobe epilepsy. Yet the regulatory networks ...[more]

PMID: 19555649

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Project description:Action potential-evoked neurotransmitter release is impaired in knock-out neurons lacking synaptic cell-adhesion molecules ?-neurexins (?Nrxns), the extracellularly longer variants of the three vertebrate Nrxn genes. Ca2+ influx through presynaptic high-voltage gated calcium channels like the ubiquitous P/Q-type (CaV2.1) triggers release of fusion-ready vesicles at many boutons. ?2? Auxiliary subunits regulate trafficking and kinetic properties of CaV2.1 pore-forming subunits but it has remained unclear if this involves ?Nrxns. Using live cell imaging with Ca2+ indicators, we report here that the total presynaptic Ca2+ influx in primary hippocampal neurons of ?Nrxn triple knock-out mice of both sexes is reduced and involved lower CaV2.1-mediated transients. This defect is accompanied by lower vesicle release, reduced synaptic abundance of CaV2.1 pore-forming subunits, and elevated surface mobility of ?2?-1 on axons. Overexpression of Nrxn1? in ?Nrxn triple knock-out neurons is sufficient to restore normal presynaptic Ca2+ influx and synaptic vesicle release. Moreover, coexpression of Nrxn1? together with ?2?-1 subunits facilitates Ca2+ influx further but causes little augmentation together with a different subunit, ?2?-3, suggesting remarkable specificity. Expression of defined recombinant CaV2.1 channels in heterologous cells validates and extends the findings from neurons. Whole-cell patch-clamp recordings show that Nrxn1? in combination with ?2?-1, but not with ?2?-3, facilitates Ca2+ currents of recombinant CaV2.1 without altering channel kinetics. These results suggest that presynaptic Nrxn1? acts as a positive regulator of Ca2+ influx through CaV2.1 channels containing ?2?-1 subunits. We propose that this regulation represents an important way for neurons to adjust synaptic strength.SIGNIFICANCE STATEMENT Synaptic transmission between neurons depends on the fusion of neurotransmitter-filled vesicles with the presynaptic membrane, which subsequently activates postsynaptic receptors. Influx of calcium ions into the presynaptic terminal is the key step to trigger vesicle release and involves different subtypes of voltage-gated calcium channels. We study the regulation of calcium channels by neurexins, a family of synaptic cell-adhesion molecules that are essential for many synapse properties. Using optical measurements of calcium influx in cultured neurons and electrophysiological recordings of calcium currents from recombinant channels, we show that a major neurexin variant facilitates calcium influx through P/Q-type channels by interacting with their ?2?-1 auxiliary subunits. These results propose a novel way how neurons can modulate the strength of distinct synapses.

Dataset Information

TRIP8b splice variants form a family of auxiliary subunits that regulate gating and trafficking of HCN channels in the brain.

Publications

TRIP8b splice variants form a family of auxiliary subunits that regulate gating and trafficking of HCN channels in the brain.

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