SA102 - A COGNITIVE AND MOLECULAR ANALYSIS OF SDCCAG8, A SCHIZOPHRENIA RISK GENE THAT FUNCTIONS IN THE CENTROSOME

Abstract

Background Schizophrenia affects 1% of adults and is a major global health problem. Although aetiology is complex, genetics represents a vital tool for probing the neurobiology of the disorder in the absence of biomarkers. We undertook an interdisciplinary project investigating the role of centrosome genes in schizophrenia. The centrosome, an organelle within cells, plays a crucial role in brain development where it directs cell shape, polarity and motility. The centrosome also seeds the growth of antenna-like signalling structures called primary cilia. Rare mutations in centrosome genes cause disorders that present with severe cognitive deficits and variable neuropsychiatric phenotypes. Methods We mined online databases to generate a list of genes encoding proteins with centrosome function. These were cross-referenced with schizophrenia risk genes identified in the 2014 PGC GWAS. Neurocognitive analysis: prioritised candidate genes were taken forward to analysis in a sample of Irish psychosis patients and controls (n=1,200). Participants were grouped by genotype at genome-wide significant SNPs and linear regression was used to test if genotype at schizophrenia risk SNPs was significantly associated with different domains of cognitive function. Molecular analysis: CRISPR-Cas9 genome editing technology was used to generate SDCCAG8 knockout cell lines in hTERT-RPE1 epithelial cells and in SH-SY5Y cells, a neuronal cell line. After serum starvation, cilia and centrosome markers were used to perform ciliation counts by immunofluorescence. Centrosome amplification was induced by exposing cells to 5 Gy ionising radiation and the number of centrosomes was counted after 72 hours by immunofluorescence. Results We identified 7 schizophrenia risk genes that have centrosomal functions: SDCCAG8, NEK4, MPHOSPH9, MAD1L1, PRKD1, MAPK3 and GIGYF2. Neurocognitive analysis of schizophrenia risk SNPs within these seven genes identified nominally significant associations with at least one domain of cognition for 5 of these 7 genes. Most of the significant associations were identified for social cognition, with the effect of SDCCAG8 on this domain being the most significant finding (p=0.001). SDCCAG8 is also associated with educational attainment and the genome-wide significant SNPs for the two phenotypes are in high linkage disequilibrium indicating a pleiotropic effect. We successfully generated SDCCAG8 knockout in RPE1 cells and in SH-SY5Y cells. Preliminary data shows that SDCCAG8 knockout clones, while viable in a p53 wildtype background, have slower proliferation rates. The capacity of the clones to ciliate is also reduced, by 50% in RPE1 clones and 75% in SH-SY5Y clones. In response to DNA damage there was an increase in centrosome amplification in RPE1 knockout clones when compared to wildtype cells. Discussion SDCCAG8 is a schizophrenia risk gene that we find is also associated with social cognition and educational attainment. Our data suggest that loss of SDCCAG8 impairs cells’ ability to make primary cilia and that their capacity to repair genome damage may be reduced. Further work will address whether SDCCAG8 affects activities that may contribute to schizophrenia, including cell migration and cell signalling. This could identify molecular mechanisms by which SDCCAG8 mutations contribute to schizophrenia risk and cognition, and help uncover the biological processes that implicate centrosome genes in various neurodevelopmental phenotypes.