Differential and Spatial Expression Meta-Analysis of Genes Identified in Genome-Wide Association Studies of Depression
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bioRxiv preprint doi: https://doi.org/10.1101/2020.03.27.012435; this version posted May 13, 2020. The copyright holder for this preprint (which was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is made available under aCC-BY-NC-ND 4.0 International license. Differential and spatial expression meta-analysis of genes identified in genome-wide association studies of depression Running title: Expression patterns of depression risk genes 1,2,3 3 1,2,4,5 1,2,3,4 Wennie Wu , Derek Howard , Etienne Sibille , Leon French 1. Institute for Medical Science, University of Toronto, Toronto, Canada 2. Campbell Family Mental Health Research Institute, Centre for Addiction and Mental Health, Toronto, Canada 3. Krembil Centre for Neuroinformatics, Centre for Addiction and Mental Health, Toronto, ON, Canada 4. Department of Psychiatry, Faculty of Medicine, University of Toronto, Toronto, ON, Canada 5. Department of Pharmacology and Toxicology, University of Toronto, Toronto, ON, Canada Corresponding author: Leon French, Centre for Addiction and Mental Health, Toronto, Ontario, Canada, M5T 1R8. [email protected] Abstract Major depressive disorder (MDD) is the most prevalent psychiatric disorder worldwide and affects individuals of all ages. It causes significant psychosocial impairments and is a major cause of disability. A recent consortium study identified 102 genetic variants and 269 genes associated with depression. To provide targets for future depression research, we prioritized these recently identified genes using expression data. We examined differential expression of these genes in three studies that profiled gene expression of MDD cases and controls across multiple brain regions. In addition, we integrated anatomical expression information to determine which brain regions and transcriptomic cell-types highly express the candidate genes. We highlight 11 of the 269 genes with the most consistent differential expression: MANEA, UBE2M, CKB, ITPR3, SPRY2, SAMD5, TMEM106B, ZC3H7B, LST1, ASXL3 and HSPA1A. The majority of these top genes were found to have sex-specific differential expression. We place greater emphasis on MANEA as it is the top gene in a more conservative analysis of the 269. Specifically, differential expression of MANEA was strongest in cerebral cortex regions and had opposing sex-specific effects. Anatomically, our results suggest the importance of the dorsal lateral geniculate nucleus, cholinergic, monoaminergic, and enteric neurons. These findings provide a guide for targeted experiments to advance our understanding of the genetic underpinnings of depression. 1 bioRxiv preprint doi: https://doi.org/10.1101/2020.03.27.012435; this version posted May 13, 2020. The copyright holder for this preprint (which was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is made available under aCC-BY-NC-ND 4.0 International license. Introduction Major depressive disorder (MDD) is a leading cause of disability and a large contributor to morbidity and mortality, with an estimated annual prevalence affecting over 4.4% of the world’s 1 population . MDD is clinically diagnosed and characterized by prolonged periods of low mood or anhedonia in addition to physical and cognitive symptoms making it a complex and 2 heterogeneous disorder . The heritability of MDD, estimated through twin studies, is 31%-42%, 3,4 which is considered to be modest . Genome-wide association studies (GWAS) are performed to identify the common variants that increase the risk of a genetic disease. However, due to the complex nature of MDD, initial GWAS were unable to identify reproducible genetic loci, potentially suggesting that many genetic factors of small-effect contribute to the overall disease 5–8 manifestation . Moreover, genes and pathways affected differ between males and females 9–14 , which may explain some variability observed in depression phenotypes. To identify these genetic variants of smaller effect, the consortium acquired higher power by profiling larger sample sizes. This increase was achieved by including individuals that displayed broader phenotypes of depression. Cohorts that include individuals with MDD and broader depression 15 phenotypes were defined in the recent GWAS as depression . Howard et al. conducted the largest GWAS of depression to date (total n = 807 553) by 16 17 meta-analyzing data from three previous studies of depression: Hyde et al. , Howard et al. 18 and Wray et al. . This large sample size resulted in the identification of 102 independent 15 variants and 269 genes associated with depression . Additionally, they found that the genes near the identified variants were expressed at higher levels in the frontal cortex and within neuronal cell-types of the brain through a partitioned heritability approach using transcriptomic resources. Their results provided significant insights into the etiology of depression. However, few of the 269 genes have been studied in the context of the disorder. Furthermore, their enrichment results were based on 13 brain regions and 3 brain cell-types. To provide additional context, we examined these genes in studies that have profiled gene expression in postmortem brain samples of MDD cases. We hypothesized that genes with greater genetic associations would be differentially expressed in these transcriptomic studies of MDD. We performed a differential expression meta-analysis to prioritize the 269 genes and tested for evidence of opposing molecular signals between males and females. In addition, we used large transcriptomic atlases to obtain a finer perspective on the specific anatomy associated with the genetic findings. Our hypothesis for this analysis was that the prefrontal cortex and neuronal cell-types are more enriched for expression of the 269 genes. Figure 1 provides an overview of these analyses. Ultimately, we sought to provide guidance for future studies of depression by narrowing genetic and anatomical targets. 2 bioRxiv preprint doi: https://doi.org/10.1101/2020.03.27.012435; this version posted May 13, 2020. The copyright holder for this preprint (which was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is made available under aCC-BY-NC-ND 4.0 International license. Figure 1. Overview of this study. The 269 genes implicated with depression (top) are characterized in several transcriptomic studies (middle). Highlighted are the different brain regions sampled within each study (middle) that will help prioritize the genes (bottom). Other transcriptomic resources that were used (middle) will identify anatomical targets associated with the disease (bottom). Images are from the cited publications, and Wikimedia Commons (Gray’s Anatomy by Henry Vandyke Carter). Methods Depression GWAS data The latest GWAS of depression included 246 363 cases and identified 102 genetic variants. The included cohorts measured a broad range of phenotypes that included nerves, tension, self-reported depression and impairment, and clinically diagnosed depression. For example, the UK Biobank cohort included broad depression phenotypes and the 23andMe cohort assessed phenotypic status based on the responses provided in online surveys and that self-reported being diagnosed with depression by a professional. As the majority of the included participants 3 bioRxiv preprint doi: https://doi.org/10.1101/2020.03.27.012435; this version posted May 13, 2020. The copyright holder for this preprint (which was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is made available under aCC-BY-NC-ND 4.0 International license. 15 did not have MDD, this was defined as a study of depression . To summarize the variant to gene associations, Howard et al. used the MAGMA (Multi-marker Analysis of GenoMic 19 Annotation) tool . Genome-wide, MAGMA aggregated the genetic variants associated with depression to reveal the 269 of 17 842 tested genes that passed the multiple test correction threshold. Our analyses focused on these 269 depression risk genes. MDD transcriptomic studies MDD transcriptomic studies were selected based on the following criteria: transcriptomic profiles were obtained from human postmortem brain tissues, cases were diagnosed with MDD, results of the study included data from each sex, and the study was published within the past five years. A summary of the transcriptomic datasets used in our meta-analysis is presented in Table 1. The cases in each dataset were diagnosed with MDD through psychological autopsies that included interviews with family or individuals best-acquainted with the deceased. More 13,15,20,21 information is outlined in the respective studies . Ding et al. Transcriptomic Analyses Using microarray expression profiling, Ding et al. analyzed the transcriptome of 101 human 20 postmortem subjects (Table 1) . Eight studies were conducted between the two sexes in 3 corticolimbic regions: 4 studies were performed in the subgenual anterior cingulate cortex, 2 in the amygdala and 2 in the dorsolateral prefrontal cortex. Initially, 16 689 unique genes were assayed across all studies but were further reduced. Firstly, genes were ranked based on levels of expression, and the lowest 20% of genes