Biology subjects

Kaczmarek, L. K.

Publications and source records attributed to Kaczmarek, L. K..

4 recordsLinked to original sources

bioRxiv2024

Neuronal potassium channel activity triggers initiation of mRNA translation through binding of translation regulators

Neuronal activity stimulates mRNA translation crucial for learning and development. While FMRP (Fragile X Mental Retardation Protein) and CYFIP1 (Cytoplasmic FMR1 Interacting Protein 1) regulate translation, the mechanism linking translation to neuronal activity is not understood. We now find that translation is stimulated when FMRP and CYFIP1 translocate to the potassium channel Slack (KCNT1, Slo2.2). When Slack is activated, both factors are released from eIF4E (Eukaryotic Initiation Factor 4E), where they normally inhibit translation initiation. A constitutively active Slack mutation and pharmacological stimulation of the wild-type channel both increase binding of FMRP and CYFIP1 to the channel, enhancing the translation of a reporter for {beta}-actin mRNA in cell lines and the synthesis of {beta}-actin in neuronal dendrites. Slack activity-dependent translation is abolished when both FMRP and CYFIP1 expression are suppressed. The effects of Slack mutations on activity-dependent translation may explain the severe intellectual disability produced by these mutations in humans. HIGHLIGHTSO_LIActivation of Slack channels triggers translocation of the FMRP/CYFIP1 complex C_LIO_LISlack channel activation regulates translation initiation of a {beta}-actin reporter construct C_LIO_LIA Slack gain-of-function mutation increases translation of {beta}-actin reporter construct and endogenous cortical {beta}-actin C_LIO_LIFMRP and CYFIP1 are required for Slack activity-dependent translation C_LI IN BRIEFMalone et al. show that the activation of Slack channels triggers translocation of the FMRP/CYFIP1 complex from the translation initiation factor eIF4E to the channel. This translocation releases eIF4E and stimulates mRNA translation of a reporter for {beta}-actin and cortical {beta}-actin mRNA, elucidating the mechanism that connects neuronal activity with translational regulation.

neuroscience↗

bioRxiv2023

Hidden HCN channels permit pathway-specific synaptic amplification in L2/3 pyramidal neurons

Layer 2/3 pyramidal cells (L2/3 PCs) play a crucial role in cortical information transfer. Although the dendritic arbors of L2/3 PCs are impressive, they often lack the distinct anatomical compartments characteristic of deeper L5 PCs. For example, many L2/3 PCs do not display an apparent distal tuft region. However, L2/3 PCs receive inputs from both thalamic (bottom-up) and cortical (top-down) inputs, which preferentially synapse onto their proximal and distal dendrites, respectively. Nonuniform organization of channels and NMDA receptors in L2/3 dendrites could serve to independently modulate these information streams to affect learning and behavior, yet whether L2/3 PC dendrites possess this capability has not been established. Here we found a previously unappreciated, non-uniform HCN channel distribution in L2/3 PCs, allowing for pathway-specific gating of NMDA receptor recruitment at bottom-up (proximal) but not top-down (distal) synapses. HCN availability shifted depending on developmental stage and neuromodulation, suggesting that the gain of thalamic and cortical-cortical signals in L2/3 may be independently modified in vivo across different timescales.

neuroscience↗

bioRxiv2023

Interaction Between HCN and Slack Channels Regulates mPFC Pyramidal Cell Excitability and Working Memory

The ability of monkeys and rats to carry out spatial working memory tasks has been shown to depend on the persistent firing of pyramidal cells in the prefrontal cortex (PFC), arising from recurrent excitatory connections on dendritic spines. These spines express hyperpolarization-activated cyclic nucleotide-gated (HCN) channels whose open state is increased by cAMP signaling, and which markedly alter PFC network connectivity and neuronal firing. In traditional neural circuits, activation of these non-selective cation channels leads to neuronal depolarization and increased firing rate. Paradoxically, cAMP activation of HCN channels in PFC pyramidal cells reduces working memory-related neuronal firing. This suggests that activation of HCN channels may hyperpolarize rather than depolarize these neurons. The current study tested the hypothesis that Na+ influx through HCN channels activates Na+-activated K+ (KNa or Slack) channels to hyperpolarize the membrane. We have found that HCN and Slack KNa channels co-immunoprecipitate in cortical extracts and that, by immunoelectron microscopy, they colocalize at postsynaptic spines of PFC pyramidal neurons. A specific blocker of HCN channels, ZD7288, reduces KNa current in pyramidal cells that express both HCN and Slack channels, indicating that blockade of HCN channels reduced K+ current indirectly by lowering Na+ influx. In contrast, ZD7288 has no effect on KNa currents in an HEK cell line stably expressing this Slack channels but no HCN channels, demonstrating that ZD7288 does not block Slack channels directly. Activation of HCN channels by cAMP in a cell line expressing a Ca2+ reporter results in elevation of cytoplasmic Ca2+, but the effect of cAMP is completely reversed if the HCN channels are co-expressed with Slack channels. Finally, we have used a novel pharmacological blocker of Slack channels to show that inhibition of either Slack or HCN channels in rat PFC improves working memory performance, and that the actions of Slack and HCN channel blockers occlude each other in the memory task. Our results suggest that the regulation of working memory by HCN channels in PFC pyramidal neurons is mediated by an HCN-Slack channel complex that links activation HCN channels to suppression of neuronal excitability.

neuroscience↗

bioRxiv2023

Disease-causing Slack potassium channel mutations produce opposite effects on excitability of excitatory and inhibitory neurons

KCNT1 encodes the sodium-activated potassium channel Slack (KCNT1, KNa1.1), an important mediator of neuronal membrane excitability. Gain-of-function (GOF) mutations in humans lead cortical network hyperexcitability and seizures, as well as very severe intellectual disability. Using a mouse model of Slack GOF-associated epilepsy, we found that both excitatory and inhibitory neurons of the cerebral cortex have increased Na+-dependent K+ (KNa) currents and voltage-dependent sodium (NaV) currents. The characteristics of the increased KNa currents were, however, different in the two cell types such that the intrinsic excitability of excitatory neurons was enhanced but that of inhibitory neurons was suppressed. We further showed that the expression of NaV channel subunits, particularly that of NaV1.6, is upregulated and that the length of the axon initial segment (AIS) and of axonal NaV immunostaining is increased in both neuron types. We found that the proximity of the AIS to the soma is shorter in excitatory neurons than in inhibitory neurons of the mutant animals, potentially contributing to the different effects on membrane excitability. Our study on the coordinate regulation of KNa currents and the expression of NaV channels may provide a new avenue for understanding and treating epilepsies and other neurological disorders. In briefIn a genetic mouse model of Na+-activated K+ potassium channel gene Slack-related childhood epilepsy, Wu et al. show that a disease-causing gain-of-function (GOF) mutation R455H in Slack channel causes opposite effects on excitability of cortical excitatory and inhibitory neurons. In contrast to heterologous expression systems, they find that the increase in potassium current substantially alters the expression of sodium channel subunits, resulting in increased lengths of axonal initial segments. HighlightsGOF mutations in Slack potassium channel cause elevated outward K+currents and inward voltage-dependent Na+ (NaV) currents in cortical neurons Slack GOF does not alter the expression of Slack channel but upregulates the expression of NaV channel Slack GOF enhances the excitability of excitatory neurons but suppresses the firing of inhibitory interneurons Slack GOF alters the length of AIS in both excitatory and inhibitory neurons Proximity of AIS to the soma is different between excitatory neuron and inhibitory neuron

neuroscience↗