Contributions of human C4A overexpression to schizophrenia pathogenesis.

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The pathophysiology of schizophrenia has been unknown, resulting in a lack of innovative therapeutics with novel mechanisms of action. The Conte Center for Neuroimmune Studies was created to build on our discovery that the biology underlying the most significant schizophrenia common genetic risk variants involves neuroimmune mechanisms of synaptic pruning. We have found that risk variants of the complement component C4 genes are correlated with increased C4A expression in the brain and CSF, and that overexpression of human C4A in a mouse model results in excess synaptic pruning and social behavioral deficits. We have further shown that additional neuroimmune molecules encoded at schizophrenia risk loci, CD47 and CSMD1, influence synaptic pruning and complement activity. Lastly, schizophrenia is unusual among neurodevelopmental disorders in its late-adolescent/early-adult onset, and childhood adversity is a major non-genetic risk factor for schizophrenia; yet the biological underpinnings of adolescent psychiatric vulnerability are wholly unknown. We have identified a critical period of circuit refinement in the mouse frontal cortex that we propose can be exploited to better understand the unique vulnerability of adolescent brain development to psychiatric risk factors. The goals of the Center in our next five years are to both deepen the focus on C4-mediated synaptic pruning as a pathophysiological mechanism, and expand the scope of our investigations to create a fuller picture of neuroimmune pathways, their upstream regulators, their cellular effectors, and their downstream circuit-level and behavioral impacts. Project 1 will investigate the role of astrocytes, the main source of C4 in the brain, by manipulating schizophrenia risk genes in these cells and assaying the impacts on synapse formation and function. Project 2 will spatially map the brain’s transcriptional response to C4 overexpression, and test the therapeutic hypothesis that inhibition of C4 activity may rescue over-pruning and associated behavioral phenotypes. Project 3 will examine the circuit specificity of the adolescent critical period, the impacts of gene-by-environment risk factor interactions, and the roles of the brain borders. Project 4 will explore circuit-level interactions between the basal ganglia and frontal cortex in the context of adolescent development, psychiatric risk factors, and risk/reward decision-making. We will also lay the groundwork for expanding neuroimmune studies of psychiatric risk to a non-human primate model, the marmoset. Finally, our Administrative Core will facilitate interdisciplinary collaboration that exploits the full range of expertise across the four labs, and coordinate outward- facing activities including the annual research symposium.