Deveroux Ferguson - US grants

[unreadable] DESCRIPTION (provided by applicant): The differential effects of basal and stress levels of glucocorticoids (GCs) on cognition can be explained by the presence of two types of GC receptors, the type I mineralocorticoid receptor (MR) which has a high affinity for GCs and mediates the beneficial effects of GC secretion on cognition. In contrast, the type II glucocorticoid receptor has a low affinity for GCs and is only activated at a high GC concentration, which is implicated in impairing spatial discrimination and synaptic plasticity. This research proposal aims are to construct a vector expressing the MR and characterize the effects of overexpression on basal cognitive functions and synaptic plasticity. In addition, we will assess the neuroprotective potential of MR overexpression against stress-induced memory impairments and synaptic plasticity. A modified herpes simplex virus amplicon system has made it feasible to introduce and overexpress foreign DNA into the central nervous system. In the present study we will use a HSV amplicon overexpressing MR to investigate its neuroprotective potential against stress-induced impairments in hippocampal-dependent cognition and its potential to enhance cognition and synaptic plasticity. [unreadable] [unreadable]

DESCRIPTION (provided by applicant): Epigenetic factors may play a key role in unraveling the molecular mechanisms underlying the pathogenesis of several neuropsychiatric disorders, including depression and drug addiction. Genes appear to explain only part of the risk factor for developing these disorders. The NIH Pathway to Independence Award (K99/R00) will significantly facilitate the candidate's ability to begin his career as an independent scientist, allowing him to study the epigenetic mechanisms underlying the gene-environment interactions observed in the onset of major mood disorders. Under the primary mentorship of Dr. Eric Nestler, Chairman of the Department of Neuroscience, and Director of the Friedman Brain Institute, at Mount Sinai School of Medicine in New York, the Pathway to Independence Awards would provide the candidate the opportunity to extend and develop his training and expertise in next generation sequencing technologies and cell type specific signaling analysis. The Award would advance the candidate's long term career objectives to: (1) determine how the environment interacts with genes and identify mechanisms by which experience confers enduring changes in gene expression, and (2) discover novel susceptibility (or resilience) genes to understand how they influence behavior. Despite the prevalence of depression and its considerable impact, knowledge about its pathophysiology is rudimentary. Thus, there is an urgent need to discover novel signaling pathways contributing to the development of depression so that better diagnostic tests, treatments, and preventive measures can be attained. The objectives of this program of research are to evaluate the role of SIRT1 and its downstream targets as potential new candidates for the treatment of neuropsychiatric disorders by performing chromatin immunoprecipitation followed by genome-wide profiling (ChIP-seq) in nucleus accumbens (NAc) tissue from control and socially defeated stressed mice. Preliminary data from our lab show that chronic social defeat stress, an ethologically validated model of depression and other stress-related disorders, modulates SIRT1 levels in the NAc and is a pro-depressant sufficient to increase stress sensitivity. The SIRT1 protein is the founding member of a family of NAD+-dependent deacetylases and ADP-ribosyltransferases, termed sirtuins. In this grant we propose to test the hypothesis that modulation of SIRT1 constitutes a novel candidate therapeutic target for antidepressants. In the mentored K-phase of this grant (Specific Aim 1 and Specific Aim 2) we will directly determine the role of sirtuins in regulating depressive- and anxiety-like behaviors using pharmacological and genetic tools. First, we will inhibit or increase the activity of sirtuins by direct intra-NAc infusion of a pharmacological inhibitior (sirtinol) or activator (resveratrol) to assess the effects of sirtuins on the development of stress-induced depressive and anxiety-like behaviors. Next, we will specifically target SIRT1 using a genetic approach to overexpress HSV-Cre viral vectors in the NAc of floxed SIRT1 (SIRT1flx) mice to knock-down SIRT1 levels, or to increase SIRT1 levels by overexpressing SIRT1 using HSV-SIRT1 vectors in the NAc. In Specific Aim 2 we also will identify transcriptional targets of SIRT1 in the NAc regulated by social defeat and antidepressants in susceptible and resilient mice by performing ChIP-Seq for SIRT1 in addition to markers of gene activation and repression. In the independent phase (R00), Specific Aim 3, will characterize the effects of social defeat on sirtuin signaling in a cell type specific manner in the NAc using drd1-GFP and drd2-GFP transgenic mice, allowing for the identification of striatonigral and striatopallidal medium spiny neurons (MSNs). In summary, the research proposed in this Pathway to Independence Award will prepare the candidate to develop a fully independent research program capable of integrating a wide range of molecular and behavioral approaches in a technically advanced and high impact manner, including: (i) lines of genetically engineered mice to target cell type specific regulation of sirtuin signaling after exposure to chronic stress, (ii) the ability to isolate chromatin from bain tissue, (iii) ChIP followed by genome-wide profiling, (iv) a rodent model of depression with high validity, and (v) automated behavioral assays measuring many depression- and anxiety-like behavioral responses. . PUBLIC HEALTH RELEVANCE: The objective of this project is to prepare Dr. Deveroux Ferguson to transition to a position as an independent, tenure-track academic investigator. This project focuses on the role of the histone deacetylase, SIRT1, in depression models and in antidepressant action. The improved knowledge of depression and antidepressant mechanisms derived from this project promises to lead to the development of more effective treatments.

Project Summary/Abstract Major depressive disorder (MDD) is a leading cause of disability, with ~20% of individuals suffering from clinical depression during their lifetime. Depression is a heterogeneous syndrome consisting of several subtypes and abnormalities in multiple brain regions. Despite the prevalence of depression and its considerable impact, knowledge about its pathophysiology is limited. Thus, there is an urgent need to discover novel signaling pathways contributing to the development of depression so that better diagnostic tests, treatments, and preventive measures can be attained. A recent ground breaking report revealed SIRT1 as one of the first two genes successfully linked to MDD in a genome-wide study. SIRT1, a member of the sirtuin family, is characterized as a Class III histone deacetylase (HDAC), which regulates the acetylation state of histones and non-histone proteins and thereby influences gene expression and cellular physiology. Preliminary data from our lab show that chronic social defeat stress (CSDS), an ethologically validated model of depression and other stress-related disorders, regulates SIRT1 levels in the NAc, a key brain reward region. Additionally we demonstrate that SIRT1 overexpression in the NAc increases anxiety and despair-like behaviors. What is not understood is how SIRT1 influences anxiety and despair-like behaviors in a cell and circuit-specific manner. This is of particular importance due to the opposing role of D1 medium spiny neurons (MSNs) and D2 MSNs in reward- and depression-related behaviors. A central hypothesis of this project is that SIRT1 signaling acts through the D1 pathway to mediate anxiety- and despair-like behaviors. To test this hypothesis, first we will use Cre-inducible RiboTag (RT) mice, which have been crossed with D1-Cre and D2- Cre bacterial artificial chromosome (BAC) transgenic mice, allowing for the cell-type specific isolation of mRNA from D1 or D2 MSNs. Following CSDS we will measure SIRT1 mRNA from D1 and D2 MSN isolated from RiboTag-D1 Cre and RiboTag-D2 Cre mice. Second, to determine through which MSN subtype SIRT1 acts to mediate anxiety- and depressive- like behaviors we will selectively overexpress SIRT1 in D1 or D2 MSNs in the NAc and third we will utilize electrophysiology and morphological approaches, to uncover cell-type specific SIRT1 dependent neural circuits that mediate depression-like behaviors. If successful this study will have several positive impacts: 1) it would have identified the SIRT1-signaling pathway as a potential target in the development of urgently needed novel antidepressants; 2) it will provide additional support for the development of non-monoaminergic medications to treat depression; and 3) it will identify the neural circuit and cell-type specific mechanisms through which SIRT1 mediates depression-like behaviors.

PROJECT SUMMARY / ABSTRACT Depression is a complex, severe debilitating mental disorder that affects about 10% of Americans. While it is well established that environmental factors, such as stress, plays an etiology role, the brain mechanisms, particularly the role of specific neural circuits mediating the pathogenesis of depression, remain to be elucidated. Chronic social defeat stress (cSDS) in mice is a highly relevant, validated model to study brain mechanisms of depression. This behavior paradigm has been shown to induce morphological and functional changes in multiple brain regions including the prefrontal cortex (PFC), which is interconnected with other limbic brain regions such as the nucleus accumbens (NAc), ventral tegmental area, hippocampus and amygdala. It is not clear whether a particular neuronal type in the PFC, defined by its synaptic connectivity, is more relevant to the pathogenesis of depression. Using a recently developed neuronal activity reporter mouse line, termed fosTRAP, the applicant's lab has determined that acute and chronic social defeat stress activate distinct populations of projection neurons in the PFC. This raises the question of whether specific circuit connectivity is pertinent to depression and if future therapeutic strategies could be devised, using a `precision medicine in psychiatry' approach, to target the relevant circuits to combat the core symptoms of depression while alleviating off target effects. In this R21 proposal, the expertise of two junior faculty laboratories (Qiu, neurophysiology and functional circuit mapping; Ferguson, mouse depression behavior and optogenetics), will be merged to test the hypothesis that chronic social defeat-induced, depression-related behaviors are encoded within a specific neural circuit in the PFC. These PIs will employ the fosTRAP:AI14 reporter mouse combined with tamoxifen to gain genetic access to the prefrontal neurons that are activated by cSDS. They will further explore whether disrupted synaptic homeostasis selectively occurs in the proportion of L5 neurons that are activated by the chronic social defeat stress. This will be investigated using whole cell patch clamp electrophysiology and laser scanning photostimulation for functional circuit mapping studies in NAc-projecting L5 prefrontal neurons in fosTRP:AI14 reporter mice following cSDS (Aim 1). They will also test whether disrupted synaptic homeostasis occurs selectively in the susceptible mice populations. In Aim 2, they will use targeted optogenetic manipulation of neural activity in the L5 PFC projection neurons that are selectively activated by cSDS and also selectively express opsins. These investigators will test the novel hypothesis that optogenetic inhibition of this specific neuron ensemble during the acquisition of depressive-like behavior confers resistance, while repeated activation of these neurons leads to susceptibility. This study could reveal a paradigm-shifting practice in circuit-based therapeutics aimed at restoring prefrontal synaptic homeostasis and could establish a specific corticolimbic circuit as a lead target for preventing the development of depression, which is otherwise not possible by previous studies examining an indiscriminate population of PFC neurons.