Activating Transcription Factor 4 (ATF4) Regulates Neuronal Activity by Controlling GABA_BR Trafficking

Abstract

Activating Transcription Factor 4 (ATF4) has been postulated as a key regulator of learning and memory. We previously reported that specific hippocampal ATF4 downregulation causes deficits in synaptic plasticity and memory and reduction of glutamatergic functionality. Here we extend our studies to address ATF4's role in neuronal excitability. We find that long-term ATF4 knockdown in cultured rat hippocampal neurons significantly increases the frequency of spontaneous action potentials. This effect is associated with decreased functionality of metabotropic GABA receptors (GABARs). Knocking down ATF4 results in significant reduction of GABAR-induced GIRK currents and increased mIPSC frequency. Furthermore, reducing ATF4 significantly decreases expression of membrane-exposed, but not total, GABAR 1a and 1b subunits, indicating that ATF4 regulates GABAR trafficking. In contrast, ATF4 knockdown has no effect on surface expression of GABAR2s, several GABAR-coupled ion channels or β2 and γ2 GABARs. Pharmacologic manipulations confirmed the relationship between GABAR functionality and action potential frequency in our cultures. Specifically, the effects of ATF4 downregulation cited above are fully rescued by transcriptionally active, but not by transcriptionally inactive, shRNA-resistant, ATF4. We previously reported that ATF4 promotes stabilization of the actin-regulatory protein Cdc42 by a transcription-dependent mechanism. To test the hypothesis that this action underlies the mechanism by which ATF4 loss affects neuronal firing rates and GABAR trafficking, we downregulated Cdc42 and found that this phenocopies the effects of ATF4 knockdown on these properties. In conclusion, our data favor a model in which ATF4, by regulating Cdc42 expression, affects trafficking of GABARs, which in turn modulates the excitability properties of neurons. GABA receptors (GABARs), the metabotropic receptors for the inhibitory neurotransmitter GABA, have crucial roles in controlling the firing rate of neurons. Deficits in trafficking/functionality of GABARs have been linked to a variety of neurological and psychiatric conditions, including epilepsy, anxiety, depression, schizophrenia, addiction, and pain. Here we show that GABARs trafficking is influenced by Activating Transcription Factor 4 (ATF4), a protein that has a pivotal role in hippocampal memory processes. We found that ATF4 downregulation in hippocampal neurons reduces membrane-bound GABAR levels and thereby increases intrinsic excitability. These effects are mediated by loss of the small GTPase Cdc42 following ATF4 downregulation. These findings reveal a critical role for ATF4 in regulating the modulation of neuronal excitability by GABARs.

Activation of GCN2/ATF4 signals in amygdalar PKC-δ neurons promotes WAT browning under leucine deprivation

“…In addition, signals mediating the activated PKC-δ neurons to the SNS, remain unclear in light of our study's results. Our results showed that deletion of GCN2 in the amygdala stimulated the activity of PKC-δ neurons, which might be mediated by increasing ATF4 expression which induces neuronal firing, as previously shown 50,51 . PKC-δ neurons are a class of GABAergic neurons, and activation of PKC-δ neurons increases GABA release thus inhibiting feeding 21 .…”

ATF4 selectively regulates heat nociception and contributes to kinesin-mediated TRPM3 trafficking

“…Studies have shown that ATF4 directly interacts with GABA B receptors in the soma and at the dendritic membrane surface of both cultured hippocampal neurons and retinal amacrine cells [41][42][43] . Research has also shown that knocking down ATF4 significantly decreases the membrane expression of GABA B receptors but does not change the total abundance of GABA B receptors in hippocampal neurons, indicating that ATF4 regulates GABA B receptor trafficking 44 . Therefore, despite being a transcription factor, ATF4 may also be involved in nontranscriptional regulation.…”

Spinal Inhibition of GABAB Receptors by the Extracellular Matrix Protein Fibulin-2 in Neuropathic Rats

“…Alternatively, the interaction between fibulin-2 and the Sushi domains may also interfere with the receptor trafficking and regulate GABAB inhibition as demonstrated for ATF4, another interactor ( Corona et al, 2018 ).…”