¹University of Wollongong, Molecular Horizons and School of Science, Wollongong, Australia, ²University of Sydney, Charles Perkins Centre and School of Medical Sciences, Sydney, Australia, ³Max Planck Institute of Psychiatry, Department Genes and Environment, Munich, Germany, ⁴Helmholtz Zentrum München, Institute of Computational Biology, Neuherberg, Germany, ⁵Max-Planck Institute of Psychiatry, Department of Translational Research in Psychiatry, Munich, Germany, ⁶University of Münster, Department of Psychiatry, Münster, Germany, ⁷Emory University School of Medicine, Department of Psychiatry and Behavioral Sciences, Atlanta, United States

Background: Despite affecting millions of people worldwide, psychiatric disorders are inadequately treated. Understanding how adversity, one of the major risk factors for these disorders, raises risk for psychopathology is essential for identifying new treatments. The orbitofrontal cortex (OFC), a sub-region of prefrontal cortex (PFC), is involved in higher cognitive processes and is highly vulnerable to adverse experiences. However, the impacts of adversity on various cell-types across the cortical layers of the OFC are largely unknown. Here, we interrogated human postmortem OFC (BA11) samples to unravel adversity-induced cell-type-specific transcriptomic changes in psychiatric disorders. Explorations of single-cell epigenomic, as well as, spatial transcriptomic alterations within the same samples are currently underway.

Aims & Objectives: The primary objective of this study is to disentangle adversity-induced cell-type- and cortical layer-specific molecular changes in the OFC of psychiatric patients. The overarching goal is to determine if adversity is associated with a transdiagnostic subtype of psychiatric disorders that may benefit from targeted therapy.

Method: We examined 86 individuals (n=32 controls vs n=54 cases with mixed major psychiatric disorders: schizophrenia, major depression and bipolar disorder) with or without history of profound psychological adversity exposure (n=23 with severe adversity and n=31 without). To capture the cell-type-specific effects, we generated single-nucleus Assay for Transposase-Accessible Chromatin sequencing (snATAC-seq) and single-nucleus RNA sequencing (snRNA-seq) datasets using 10x Chromium (10x Genomics, USA). To dissect spatial heterogeneity, we produced spatial transcriptomic dataset using Visium (10x Genomics, USA). We performed compositional and differential gene expression analyses, followed by gene ontology and disease enrichment analyses, on the snRNA-seq data.

Results: After filtering out low-quality nuclei from the snRNA-seq dataset, about ~800,000 nuclei from 15 different cell types were retained. The proportions of inhibitory neurons and astrocytes were significantly lower in individuals exposed to adversity vs those without adversity, while the proportion of oligodendrocytes was higher (Log2FoldChange of -0.51, -1.02 and 0.33, respectively). We identified a large number of differentially expressed genes (DEGs) in oligodendrocytes and reelin-expressing inhibitory neurons (160 and 265, respectively) only when the contrast was performed among cases based on their history of adversity. Overall, the DEGs showed significant enrichment of psychopathology-associated metabolic processes and phenotypes, including synaptic signaling and inflammatory responses.

Discussion & Conclusions: These results highlight the striking cell-type-specific impacts of adverse experiences on gene expressions and cellular abundances in the OFC of individuals with psychiatric disorders. The glial cells such as astrocytes and oligodendrocytes, which are known to be involved in stress response, as well as inhibitory neuronal subtypes, known to be affected in stress-related disorders, showed marked impacts of adversity in the context of psychopathology. In general, synaptic signaling, transmembrane transports, energy metabolism and immune response pathways were affected, all of which are implicated in psychopathology.
Experiments and analyses are underway to further disentangle the regulatory changes affecting transcription by delineating epigenomic modifications and gene co-expression networks within these cell types and to unmask the changes in transcript and cellular abundances across the cortical layers. The study will thus help decompose adversity-induced transcriptomic and gene regulatory changes into cell-type-specific alterations across cortical layers.