Nuclear Calcium Signaling Controls Expression of a Large Gene Pool: Identification of a Gene Program for Acquired Neuroprotection Induced by Synaptic Activity

Abstract

Synaptic activity can boost neuroprotection through a mechanism that requires synapse-to-nucleus communication and calcium signals in the cell nucleus. Here we show that in hippocampal neurons nuclear calcium is one of the most potent signals in neuronal gene expression. The induction or repression of 185 neuronal activity-regulated genes is dependent upon nuclear calcium signaling. The nuclear calcium-regulated gene pool contains a genomic program that mediates synaptic activity-induced, acquired neuroprotection. The core set of neuroprotective genes consists of 9 principal components, termed Activity-regulated Inhibitor of Death (AID) genes, and includes Atf3, Btg2, GADD45β, GADD45γ, Inhibin β-A, Interferon activated gene 202B, Npas4, Nr4a1, and Serpinb2, which strongly promote survival of cultured hippocampal neurons. Several AID genes provide neuroprotection through a common process that renders mitochondria more resistant to cellular stress and toxic insults. Stereotaxic delivery of AID gene-expressing recombinant adeno-associated viruses to the hippocampus confers protection in vivo against seizure-induced brain damage. Thus, treatments that enhance nuclear calcium signaling or supplement AID genes represent novel therapies to combat neurodegenerative conditions and neuronal cell loss caused by synaptic dysfunction, which may be accompanied by a deregulation of calcium signal initiation and/or propagation to the cell nucleus.

Nuclear Calcium Signaling Controls Methyl-CpG-binding Protein 2 (MeCP2) Phosphorylation on Serine 421 following Synaptic Activity

“…Recombinant Adeno-associated Virus and Virus InfectionRecombinant adeno-associated virus (rAAV) vector with a CMV/CBA hybrid promoter for the expression of hrGFP (humanized Renilla reniformis green fluorescent protein), CaMBP4, or CaMKIV(1-313) have previously been described (18,19). A rAAV vector containing the mouse CaMKII promoter (a gift from Ali Cetin and Peter Seeburg, Max Planck Institute for Medical Research Heidelberg, Germany), was used to generate rAAV-CaMKII(1-290)-Flag, rAAV-CaMKII(1-290)NLS-Flag, and rAAV-CaMKVI(1-313)NLS-Flag.…”

“…Knock-in mice that lack either serine 421 of MeCP2 or serine 421 as well as serine 424, a second site of synaptic activity-induced phosphorylation, show alterations in synaptogenesis, synaptic plasticity, and spatial memory (9,17), underscoring the importance of these phosphorylation sites in vivo. The calcium-dependent modulation of MeCP2 function suggests that its role in neural circuit development could be mediated by one or several components of a pool of about 1000 genes that are induced or repressed within a few hours following NMDA receptor stimulation and the activation of calcium signaling pathways (18,19). Because calcium can act in different subcellular compartments (in particular cytosol versus nucleus) to differentially regulate transcription (20), it is important to determine the precise spatial requirement of the calcium signal needed to induce MeCP2 serine 421 phosphorylation.…”

“…Because calcium can act in different subcellular compartments (in particular cytosol versus nucleus) to differentially regulate transcription (20), it is important to determine the precise spatial requirement of the calcium signal needed to induce MeCP2 serine 421 phosphorylation. In this study, we focused on nuclear calcium, which has emerged as a key signal in several transcription-dependent forms of neuronal adaptations, including acquired neuroprotection and memory (19,(21)(22)(23)(24). In hippocampal neurons, nuclear calcium transients are required for activity-dependent regulation of about 200 genes, many of which are targets of CREB and CBP, the prototypical transcription factor complex activated by nuclear calcium and the nuclear calcium/calmodulin-dependent protein (CaM) kinase IV (19).…”

“…In this study, we focused on nuclear calcium, which has emerged as a key signal in several transcription-dependent forms of neuronal adaptations, including acquired neuroprotection and memory (19,(21)(22)(23)(24). In hippocampal neurons, nuclear calcium transients are required for activity-dependent regulation of about 200 genes, many of which are targets of CREB and CBP, the prototypical transcription factor complex activated by nuclear calcium and the nuclear calcium/calmodulin-dependent protein (CaM) kinase IV (19). Here we identify MeCP2 as an alternative target of nuclear calcium signaling and provide evidence that unlike CREB/CBP regulation, a nuclear localized CaMKII mediates the effects of nuclear calcium on MeCP2.…”

Microdissection and transcriptional profiling

“…15 Comparing our early gene expression alterations with other molecular signatures reported in the literature revealed the presence of a molecular signature reminiscent of that induced by synaptic N-methyl-D-aspartate receptor (NMDAR) stimulation in primary mouse hippocampal neurons. 31,32 In fact, our preclinical signature included at least 60% of the genes that was reported by Zhang and colleagues 32 to be deregulated by synaptic NMDAR stimulation that acts primarily through nuclear Ca 2+ signaling and transcription. NMDAR is an ionotropic glutamate receptor that is primarily involved in synaptic formation and memory function.…”