Functional validation of a finding from a mouse genome-wide association study demonstrates that a mutant allele of Azi2 alters sensitivity to methamphetamine

Abstract

Methamphetamine is a widely abused psychostimulant. In a previous genome-wide association study (GWAS), we identified a locus that influenced the stimulant response to methamphetamine. That locus was also an eQTL for the gene Azi2. Based on those findings, we hypothesized that heritable differences in the expression of Azi2 were causally related to the differential response to methamphetamine. In this study, we created a mutant Azi2 allele that caused lower Azi2 expression and enhanced the locomotor response to methamphetamine; however, based on the GWAS findings, we had expected lower Azi2 to decrease rather than increase the stimulant response to methamphetamine. We then sought to explore the mechanism by which Azi2 influenced methamphetamine sensitivity. A recent publication had reported that the 3UTR of Azi2 mRNA downregulates the expression of Slc6a3, which encodes the dopamine transporter (DAT), which is a key target of methamphetamine. We evaluated the relationship between Azi2/Azi2 3UTR and Slc6a3 expression in the VTA in the mutant Azi2 mice and in a new cohort of CFW mice. We did not observe any correlation between Azi2 and Slc6a3 in the VTA in either cohort. However, RNA sequencing confirmed that the Azi2 mutation altered Azi2 expression and also revealed a number of potentially important genes and pathways that were regulated by Azi2, including the metabotropic glutamate receptor group III pathway and nicotinic acetylcholine receptor signaling pathway. Our results support a role for Azi2 in methamphetamine sensitivity; however, the exact mechanism does not appear to involve regulation of Slc6a3 and thus remains unknown.