Zebrafish screen of schizophrenia risk genes reveals convergent dysregulation of cholesterol metabolism

Abstract

Rare coding variants provide a tractable entry point for understanding the molecular mechanisms underlying schizophrenia risk. Here, we generated and characterized zebrafish lines with mutations in the orthologs of >20 human schizophrenia-associated genes, including eight of the top ten SCHEMA genes, genes disrupted in childhood-onset schizophrenia (COS), and genes located within recurrent copy number variants. Whole-brain phospho-Erk activity mapping and behavioral profiling identified phenotypes in multiple mutant lines. We prioritized a protein-truncating mutation in sp4, which encodes an activity-dependent transcription factor, and a COS-associated missense mutation in atp1a3a, which encodes a Na+/K+ ATPase pump, for additional characterization. Both knockout and point mutations in atp1a3a disrupted brain activity and behavior in larvae and impaired navigation of a Y-maze in juveniles. Bulk RNA sequencing data from adult sp4 and atp1a3a brains highlighted convergent upregulation of sterol biosynthesis pathways, including increased expression of srebf2 and msmo1. Analysis of previously published telencephalon single-cell data demonstrated that cholesterol synthesis genes are enriched in astrocyte-like cells and increase in expression during post-larval development. Consistent with transcriptomic findings, filipin staining indicated increased free cholesterol in juvenile sp4 and atp1a3a mutant brains. Our findings identify dysregulation of glial and sterol-associated programs as a shared molecular consequence of two distinct schizophrenia risk mutations. Although whether sterol pathway dysregulation represents a primary pathogenic mechanism or a secondary response to changes in neuronal activity requires further investigation, the convergence observed between genetic models and developmental stages suggests that disruptions to lipid homeostasis could represent a shared feature of schizophrenia disease biology.