776. Bridging the divide: can we use human living cell models to link studies in human postmortem brain and live participants?

Abstract

Abstract Background Investigations on the biological underpinnings of psychosis spectrum disorders (PSDs) point to the involvement of both neuronal and glia populations, within neural circuits involved in emotion regulation and executive functions. A key question is how changes in these different cell types relate to one another, i.e. whether the biological underpinnings of PSDs arise from primarily from one cell type or are instead the result of coordinated changes across many cell populations. Our published and ongoing human brain postmortem studies point to this latter possibility. We show that, in healthy subjects, neuronal and glial cell types robustly coordinate gene expression programs (GEPs) related to key functions, such as synaptic regulation, lipid metabolism and immune signaling. In subjects with PSDs, these pan-cellular GEPs are greatly reduced, although still strongly correlated across cell types. Aims & Objectives Important questions arising from these results related how pan-cellular GEPs are coordinated and what are the consequences of their dysregulation. Toward answering these questions, we developed approaches to obtain primary as well as iPSC-derived cell cultures from human brains, which can be combined in co-cultures of different cell types (e.g. neurons and astrocytes). Method Primary glial cells are derived from fresh preparation of gray and white matter from fresh human postmortem brain. MACS MicroBeads-isolated cells are collected and cryopreserved. These cells are tested on several assays, including responses to immune activation, and assessed in parallel with brain tissue from the same donors on single cell (nucleus) transcriptomics (snRNA-seq). Human fibroblasts are derived from cryopreserved human postmortem dura mater, cultured for several weeks, dissociated and reseeded for proliferation, expansion and cryopreservation. These cells are then reprogrammed into iPSCs, then expanded, and differentiated in astrocytes, microglia and brain endothelial cells. Results SnRNA-seq results show highly concordant gene expression in cultured cells and their counterparts in tissue from the same brain region/donors. In vitro human primary astrocytes, BECs microglia, macrophages: response to immune challenge. Each cell type responded to an immune challenge with robust, cell specific, cytokine secretion, while control macrophage cultures show a distinct pattern, indicating that the functional phenotype of primary human microglia is conserved. Discussion & Conclusions These approaches allow mechanistic studies in parallel with investigations on the same brain regions/donor of origin. Comparisons of cell-level gene expression in brain tissue as well as primary and iPSC-derived cells from the same donors allow for mechanistic studies anchored in the brain tissue of origin and offer a unique opportunity to investigate non-cell autonomous GEPs in parallel in vitro and in situ paradigms. These comparisons will inform result interpretation from a vast field of investigations using human iPSCs and guide future technological developments. These studies will offer a much-needed vocabulary to integrate live human iPSC and postmortem studies.