Subject(s)
Autoreceptors/metabolism , Dopaminergic Neurons/physiology , Prefrontal Cortex/physiopathology , Receptors, Dopamine D2/metabolism , Animals , Autoreceptors/genetics , Behavior, Animal/physiology , Chromatin/metabolism , DNA-Binding Proteins , Epigenesis, Genetic , Gene Expression , Histones/metabolism , Methylation , Mice, Knockout , Nerve Tissue Proteins/metabolism , Nuclear Proteins/metabolism , Receptors, Dopamine D2/geneticsABSTRACT
Alterations of the dopaminergic system are associated with the cognitive and functional dysfunctions that characterize complex neuropsychiatric disorders. We modeled a dysfunctional dopaminergic system using mice with targeted ablation of dopamine (DA) D2 autoreceptors in mesencephalic dopaminergic neurons. Loss of D2 autoreceptors abolishes D2-mediated control of DA synthesis and release. Here, we show that this mutation leads to a profound alteration of the genomic landscape of neurons receiving dopaminergic afferents at distal sites, specifically in the prefrontal cortex. Indeed, we observed a remarkable downregulation of gene expression in this area of ~2000 genes, which involves a widespread increase in the histone repressive mark H3K9me2/3. This reprogramming process is coupled to psychotic-like behaviors in the mutant mice. Importantly, chronic treatment with a DA agonist can revert the genomic phenotype. Thus, cortical neurons undergo a profound epigenetic reprogramming in response to dysfunctional D2 autoreceptor signaling leading to altered DA levels, a process that may underlie a number of neuropsychiatric disorders.
Subject(s)
Autoreceptors/metabolism , Corpus Striatum/physiopathology , Dopaminergic Neurons/physiology , Epigenesis, Genetic , Prefrontal Cortex/physiopathology , Receptors, Dopamine D2/metabolism , Animals , Autoreceptors/genetics , Corpus Striatum/drug effects , Dopamine/metabolism , Dopamine Agonists/pharmacology , Dopaminergic Neurons/drug effects , Down-Regulation , Gene Expression , Histones/metabolism , Mice, Transgenic , Prefrontal Cortex/drug effects , Psychotic Disorders/drug therapy , Psychotic Disorders/physiopathology , Quinpirole/pharmacology , Receptors, Dopamine D2/agonists , Receptors, Dopamine D2/geneticsABSTRACT
Understanding the regulation of the apoptotic program in neurons by intracellular pathways is currently a subject of great interest. Recent results suggest that c-Jun N-terminal kinases (JNK), mitogen-activated protein kinases and the transcription factor c-Jun are important regulators of this cell death program in post-mitotic neurons following survival-factor withdrawal. Our study demonstrates that ceramide levels increase upon survival-factor withdrawal in primary cultured cortical neurons. Furthermore, survival-factor withdrawal or addition of exogenous c(2)-ceramide induces JNK pathway activation in these cells. Western blot analyses of JNK and c-Jun using phospho-specific antibodies reveal that JNK and subsequent c-Jun phosphorylation occur hours before the initiation of apoptosis, reflected morphologically by neurite retraction and fragmentation, cell-body shrinkage and chromatin fragmentation. Immunocytochemistry using the same antibodies shows that phospho-JNK are localized in the neurites of control neurons and translocate to the nucleus where phospho-c-Jun concurrently appears upon ceramide-induced apoptosis. To determine if ceramide-induced c-Jun activation is responsible for the induction of the apoptotic program, we performed transient transfections of a dominant negative form of c-Jun, truncated in its transactivation region. Our results show that DNc-Jun partially protects cortical neurons from ceramide-induced apoptosis. Treatment of dominant negative c-Jun-expressing neurons with the pharmacological inhibitor of p38 kinase, SB203580, completely blocked neuronal death. Thus our data show that p38 and JNK/c-Jun pathways cooperate to induce neuronal apoptosis.