Synaptic dysglycosylation caused by the schizophrenia-risk variant in SLC39A8

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PROJECT SUMMARY/ABSTRACT Schizophrenia is a severe mental illness with strong heritability, and advances in genetics have started to unravel the complex molecular underpinnings of this disorder. GWAS have identified over 250 loci linked to schizophrenia which are enriched near genes expressed in CNS neurons and involved in synaptic biology. Most schizophrenia-associated variants are in the non-coding region of the genome, though a small number result in a mutation within a known protein. The most significantly associated coding variant in schizophrenia GWAS is rs13107325 in SLC39A8, resulting in a missense mutation (A391T) in the eponymous manganese (Mn2+) transporter. Mn2+ transport by SLC39A8 is critical for glycosylation, the enzymatic attachment of carbohydrates to proteins and lipids, which is involved in neurodevelopment and synaptic function. Here, the applicant will investigate a novel molecular mechanism underlying increased schizophrenia risk in A391T carriers using a mouse model of genetic risk. Having shown that A391T mice have altered glycosylation of synaptic proteins, including neurotransmitter receptors and cell adhesion molecules, the applicant will test if altered glycosylation of these proteins changes their trafficking and localization, deposition of complement, and the number of dendritic spines in the frontal cortex (Aim 1). Next, he will attempt to reverse previously identified glycome changes with oral Mn2+ supplementation, overcoming impaired SLC39A8 transport from A391T. These studies will employ existing genetically engineered mouse lines, glycobiology techniques pioneered by the applicant, and cutting-edge neuroscience training in analysis of the synapse. Together, these aims will define the molecular alterations caused by A391T at the synapse and provide critical preclinical data for Mn2+ supplementation in carriers of A391T during critical periods of brain development and maturation. The applicant, Dr. Robert Mealer, is well qualified to execute the proposed experiments with his background in neuroscience, psychiatric genetics, and glycobiology. The four-year training plan will foster development towards independent investigator status and generate the preliminary data necessary for a future R01 application with clear therapeutic potential. He will continue his mentee relationships with Drs. Smoller and Cummings, while receiving additional training and mentorship from Dr. Morgan Sheng on the molecular analysis of the synapse. He has also enlisted Dr. Michael Aschner, a world leader on Mn2+ in the brain, and Dr. Maurizio Fava, a clinician researcher with extensive experience in psychopharmacology and trial design, as members of his research advisory committee. Finally, the collaborative research environment is ideal for furthering the applicant’s goal of becoming an independent researcher in academic psychiatry.