AcScapeStress · Cell type-specific effects of HDAC1 on stress vulnerability, hippocampal gene regulation and genome-wide acetylation landscape

Periodic Report Summary 1 - ACSCAPESTRESS (Cell type-specific effects of HDAC1 on stress vulnerability, hippocampal gene regulation and genome-wide acetylation landscape)

Cell type-specific effects of HDAC1 on stress vulnerability, hippocampal gene regulation and genome-wide acetylation landscape The project was based on the observation that stress effects can be alleviated by treatment with broad spectrum histone deacetylase inhibitors (HDACis) and levels of HDACs are deregulated following stress exposure in the rodent model or in post mortem tissue of patients with major depression or bipolar disorder. Specific aim of this research was to systematically investigate the role of a single histone deacetylase in stress vulnerability. To this end, Dr. Jakovcevski used conditional Hdac1 knockout mice with Cre recombinase expression under the control of a neuron specific CamK2a promoter, to obtain Hdac1 deficiency, specifically in neurons, at first. These mice were exposed to a chronic stressor and their stress induced behavior was evaluated using a test battery, probing anxiety and depression-like behaviors, typically affected by stressors. To better understand the behavioral stress reactivity, data was compared to the pre-stress, baseline, behavior. Interestingly, under basal conditions Hdac1 knockout mice, displayed behaviors, indicative of stress vulnerability such as increased locomotion in the unfamiliar environment of an open field and anhedonia. Likewise, when tested for their behavioral stress response, Hdac1 knockout mice were affected stronger than wildtypes. To link these behavioral phenotypes to molecular pathways, Dr. Jakovcevski investigated potential gene expression changes in the hippocampus of Hdac1 knockout mice under basal conditions using a conventional microarray for coding mRNA transcripts. This approach identified only a small number of differentially regulated genes, in line with results in cell culture, demonstrating that Hdac1 mostly affects expression levels of non-coding RNAs. Thus, the fellow has switched to RNAseq to include non-coding transcripts in her analysis. Also, since, major differences in gene expression between wildtype and knockout mice might arise only after stress exposure, Dr. Jakovcevski did now include this condition in the experimental setup. Similar, to determine if gene expression changes are linked to a modified histone acetylation landscape, the fellow initially tested which histone acetylation marks are differently regulated at bulk level using Western blot in wildtype versus knockout mice under basal and stressed conditions. Dr. Jakovcevski identified several histone acetylation marks to be changed through Hdac1 inactivation and by stress exposure. For one of the histone acetylation marks, changed the most by both conditions, the fellow performed ChIPseq experiments on hippocampi from all four groups of mice. This set of data, passed quality controls such as read numbers and rate of duplicates. We are still in the process of finalizing the analysis, but preliminary data look very promising. Finally, Dr. Jakovcevski will compare the RNAseq data with the ChIPseq data to understand how the molecular stress response in wildtype mice is different from Hdac1 knockout mice. Here, it will be interesting if changes in the acetylation landscape correlate straight with changes in gene expression, or if changes to the histone landscape at basal conditions might be predictive for gene expression changes after stress exposure and most importantly, if this relationship will be the same for both genotypes. Most prominent changes/ loci will be further tested for their cell type specificity using sorted neural cells. Required technology has been established by the fellow. Thereafter, Dr. Jakovcevski will rescue the phenotype of Hdac1 knockout mice by re-expression or knockdown of the two or three most regulated genes in the most affected neural cell type. From the scientific point of view this research facilitated knowledge on the role of Hdac1 in stress vulnerability. Moreover, the study will significantly increase the knowledge on the cell type specific interaction between histone acetylation and gene regulation in the brain and during adaption/ maladaption to environmental challenges. Since, Hdac1 is target of many broad spectrum HDACis and we have demonstrated an important role of Hdac1 in the response to stress, this project might help to develop more specific treatment options for stress related disorders on the long run. Perhaps, these options might be already focused on cell type-specific downstream targets of Hdac1. Another important aspect of this project is its potential for increasing public awareness on the importance of environmental factors such as stress exposure, which interact with an organism’s genetics through the interface of epigenetic mechanisms, in the development of stress related disorders. This increased awareness may give rise to preventive actions such as stress reduction programs at the work place. Altogether, indirect long-term effects of the project might help to alleviate the personal tragedy of neuropsychiatric disorders from on an individual perspective and reduce the financial burden caused by these disorders from the perspective of society.

Data: CORDIS, © European Union