Synapse-to-nucleus ERK-CREB transcriptional signaling requires dendrite-to-soma Ca2+propagation mediated by L-type voltage-gated Ca2+ channels

Abstract

The cAMP-response element binding protein (CREB) transcription factor controls the expression of the neuronal immediate early genes c-Fos, Arc, and Bdnf and is essential for long-lasting synaptic plasticity underlying learning and memory. Despite this critical role, there is still ongoing debate regarding the synaptic excitation-transcription (E-T) coupling mechanisms mediating CREB activation in the nucleus. Here we employed optical uncaging of glutamate to mimic synaptic excitation of distal dendrites in conjunction with simultaneous imaging of intracellular Ca²⁺ dynamics and transcriptional reporter gene expression to elucidate CREB E-T coupling mechanisms in hippocampal neurons cultured from both male and female rats. Using this approach, we found that CREB-dependent transcription was engaged following dendritic stimulation of N-methyl, D-aspartate receptors (NMDARs) only when Ca²⁺ signals propagated to the soma via subsequent activation of L-type voltage-gated Ca²⁺ channels resulting in activation of Extracellular signal-Regulated Kinase (ERK) MAP kinase signaling to sustain CREB phosphorylation in the nucleus. In contrast, dendrite-restricted Ca²⁺ signals generated by NMDARs failed to stimulate CREB-dependent transcription. Furthermore, Ca²⁺-CaM-dependent kinase (CaMK)-mediated signaling pathways that may transiently contribute to CREB-phosphorylation following stimulation were ultimately dispensable for downstream CREB-dependent transcription and c-Fos induction. These findings emphasize the essential role that L-type Ca²⁺ channels play in rapidly relaying signals over long distances from synapses located on distal dendrites to the nucleus to control gene expression.Significance Statement The transcription factor CREB controls gene expression programs required for long-lasting synaptic plasticity and learning and memory, yet the synapse-to-nucleus signaling mechanisms mediating CREB activation are still unclear. Using glutamate uncaging to mimic synaptic input to dendrites, this study shows that Ca²⁺ signals propagated to the soma by L-type voltage-gated Ca²⁺ channels engage the ERK MAP kinase cascade to mediate CREB phosphorylation and CREB-dependent transcription. In contrast, dendrite-restricted Ca²⁺ signals generated primarily by NMDARs failed to effectively engage this signaling pathway or CREB-dependent transcription. In addition, we found that while ERK and CaMK pathways may both contribute to increased CREB phosphorylation immediately following neuronal stimulation, sustained ERK signaling to CREB was necessary to effectively drive CREB-dependent transcription.