MicroglioStress

Stress release of glucocorticoids (GCs) is a key adaptive response enabling the organism to cope with an ever-changing environment. When excessive or repeated, stress exposure may lead to chronic diseases, including psychiatric disorders. GCs exert thus both beneficial as well as detrimental actions, depending on the stressor and its duration. While it is firmly established that stress-induced GCs act within brain to modulate behavior and cognition by acting through their receptor GR, the underlying cellular mechanisms are not completely understood. In brain, GR acts in all cell types and it regulates gene transcription in cell-specific and context-dependent manner. The role of neuronal GR in stress-induced maladaptive behavior has been extensively reported in several preclinical models of psychiatric disorders. Yet, GR is also present in non-neural cells such as in microglia, the brain resident macrophage. In a healthy brain, microglia survey neuronal and synaptic activity, by regulating the formation and the elimination of synapses. A role is also suspected in the etiology of several brain disorders associated with inflammation. GC-GR is a potent inhibitor of inflammation and our previous work, in the context of Parkinson’s disease, revealed that GR can regulate multiple functions of microglia, including motility, proliferation, and lysosomal functions. In the MicroGlioStress project, we will test the hypotheses that microglial GR can regulate neuronal-microglial cross-talk and may participate in the etiology of stress-related psychopathologies. Our preliminary results show that microglial GR plays a state-dependent role in the regulation of cognitive processes. Indeed, while inactivation of GR in microglia decreases memory performance, it also improves cognition under chronic stress conditions. We will confirm this initial observation and will complete the behavioral characterization of microglia GR mutant mice, exposed or not to chronic stress protocols classically used as preclinical models of depression and inducing enduring changes in mood and cognition. We will combine gene expression and chromatin analyses to identify enduring molecular changes induced by chronic stress and/or that are relying on GR function. RNAseq using purified microglia will identify GR target genes. Single nucleus RNAseq on tissue explants will identify in other cell types, gene expression changes due to the lack of GR in microglia. In microglia, chromatin accessibility (ATACseq) and chromatin immunoprecipitation (ChIPseq) for GR, H3K27ac (tagging active promoters and enhancers), and BRG1 (a key GR partner) will give us insights on the mechanisms involved. Based on this knowledge, we will study the dynamics of these molecular changes after chronic stress. At the cellular level, we will study inflammation, the evolution of microglial processes (3D reconstruction), and microglia functional response (calcium imaging) to understand consequences of chronic stress and GR ablation. Finally, we will evaluate how these alteration of microglial physiology impacts the hippocampal neuronal network in freely moving animals (EEG) and ex vivo. The proposal should bring us conclusive data on the role of microglial GR in the etiology of stress-related behavioral disorders, a key knowledge to consider novel therapeutic strategies.