Clozapine-Related Brain Nrn1 Expression Patterns Are Associated With Methylation And Genetic Variants In Schizophrenia

The Neuritin-1 gene (NRN1), involved in neurodevelopment and synaptic plasticity, is associated with schizophrenia (SZ) and related clinical, cognitive, and neuroimaging phenotypes. Additionally, it is one of the most differentially methylated genes in the prefrontal cortex (PFC) in SZ and is responsive to neurotherapeutic agents. We aimed to investigate NRN1s molecular mechanisms in SZ by analyzing its expression, methylation, and genotypic profiles in PFC and hippocampus (HIPP) post-mortem samples from 30 control (CTL) subjects and 20 individuals with SZ (10 treated with clozapine, SZ-Clz, and 10 without antipsychotic drugs at death, SZ-ApFree). We compared the NRN1 mRNA expression between groups, measured by qPCR, and methylation levels across three CpG islands, assessed through EpiTYPER. Sparse Partial Least Square Discriminant Analysis identified key CpG units contributing to group differences. We then explored the relationship between NRN1 methylation and expression, considering the influence of 11 polymorphisms genotyped by qPCR. We found that SZ-Clz had lower NRN1 mRNA levels in the PFC than SZ-ApFree and CTL. SZ-Clz presented distinct methylation patterns across multiple CpG units in both brain regions compared to CTL. In the PFC, the methylation of the CpG units differentiating SZ-Clz from CTL correlated to NRN1 expression, and the NRN1-rs12333117 and NRN1-rs2208870 polymorphisms influenced this effect. These findings reveal distinct correlations between NRN1 epigenetic expression in SZ-Clz and CTL, shaped by genotypic variability. They emphasize region-specific alterations in SZ and underscore the importance of integrative approaches for a better understanding of the role of candidate genes in SZ etiology.