Although MDD has been predominantly studied in the context of neuronal function, emerging evidence indicates that dysregulation of glia may be equally important ? particularly during chronic neuroinflammation in response to stress, which is known to contribute to the pathophysiology of MDD. However, the cell-type specific transcriptional dynamics driving these processes remain unclear because traditional epigenetic chromatin accessibility profiling methods are not compatible with cell-type specific approaches. Our laboratory has recently implemented the newly developed technique FANS (Fluorescence-Activated Nuclear Sorting)-coupled ATAC- seq (Assay for Transposase-Accessible Chromatin-Sequencing) to profile the cell type-specific regulatory landscape in human MDD in orbitofrontal cortex (OFC), a brain region that processes reward-based decision- making and may mediate anhedonic symptoms in MDD. Interestingly, we only detected MDD-specific open chromatin regions (OCRs) in the glial, but not the neuronal OFC cell population. Gene set analyses of MDD- specific OCRs showed significant enrichment of astrocyte-specific genes regulating NF-KB inflammation response. Using motif discovery, I identified ZBTB7A, a chromatin remodeling protein with recognition sequences significantly overrepresented in MDD-specific OCRs. Recently, ZBTB7A has been shown to orchestrate chromatin accessibility for a distinct subset of delayed induction NF-Kb target genes, suggesting that ZBTB7A may regulate the transduction of chronic NF-Kb stress signals from adaptive to pathological. My pilot data has shown that ZBTB7A is upregulated in the OFC of both human MDD and in OFC astrocytes of a preclinical chronic social defeat stress (CSDS) mouse model, as well as in cultured murine primary astrocytes treated with LPS (a compound which induces NF-KB and inflammation). Given these preliminary data, I hypothesize that upregulation of ZBTB7A in OFC astrocytes acts as a pathogenic driver of pro- inflammatory NF-Kb activation in MDD through modulation of chromatin accessibility at key downstream target genes, leading to MDD-related behavioral deficits.
In Aim 1, I will characterize the basic mechanisms of manipulating this chromatin remodeler at baseline and during inflammation stress by manipulating ZBTB7A levels in a cultured human primary astrocyte system, then treating with LPS or saline followed by assessment of astrocyte reactivity (IHC), chromatin accessibility (via ATAC-seq), epigenetic regulation (ChIP-seq) and gene expression (RNA-seq).
In Aim 2, I will explore the therapeutic potential of targeting Zbtb7a by using novel astrocyte-specific viral vectors to determine if Zbtb7a is necessary and sufficient in the OFC to affect vulnerability to inflammation stress-induced behavioral deficits in a preclinical mouse model of social defeat stress. Together these experiments will offer enormous potential for new mechanistic insights into disease pathology in the context of a relatively understudied cell-type, astrocytes, in neuroinflammation and stress.
Major Depressive Disorder (MDD) arises from a complex interaction of genetic composition and environmental influences like stress, which are transduced into persistent changes in frontolimbic gene expression mediated by epigenetic processes that regulate chromatin accessibility. This project will take a cross-species approach to investigate the role of a novel chromatin remodeling factor in the regulation of chromatin accessibility, gene transcription, and stress-induced behavioral deficits in astrocytes ? a cell-type that is known to be intricately involved in inflammation stress and neurotransmission, but to date has not been well characterized in MDD. Therapeutic agents that would act to dampen the coordinated inflammation response in MDD would be of great clinical value, and the data generated in this project will offer enormous potential for new mechanistic insights into how astrocytes contribute to affective disease pathology.
