Development of Knock-in Mutant Mice Carrying Human Catechol-O-Methyltransferase Met Mutation Mimicking the Functional Val158Met Polymorphism

The functional Val158Met polymorphism in human catechol-O-methyltransferase (COMT) gene affects cognition, arousal, pain sensitivity, and has been associated with psychiatric disorders including schizophrenia, obsessive-compulsive disorder and anxiety. The best characterized role of COMT in brain function is in termination of dopamine action in prefrontal cortex. Other than termination of dopamine action, it may play other roles in brain development and function related to its methyl transferase activity. COMT consumes S-adenosylmethionine (SAM), a key substrate for DNA methylation, and might affect epigenetic regulation of other genes in the brain. In addition, the dominant form of COMT in human brain is the membrane-bound COMT (MB-COMT), which is located on the cell membrane and might affect cell to cell communication involved in cell migration and survival. Although the complete COMT gene knockout mouse is a useful animal model for studying the roles of COMT in cognitive and emotional behaviors, the complete gene knockout mutation is quite different from the functional Val158Met polymorphism in terms of the effect on gene expression. Another problem with the complete COMT knockout mouse model is that the COMT gene is located in a high gene density region and the complete knockout of COMT might affect adjacent genes and complicate the interpretation of results. To mimic the Val158Met polymorphism, we replaced two nucleotides in the mouse COMT gene to replace the Leu, equivalent to Val in human COMT, with Met at the 158th amino acid position using knock-in targeted mutation technology. The knock-in mutant mice showed dramatic decreases in COMT protein and enzyme activity, which is very similar to the consequence of the ValMet mutation in human COMT. Our results suggest that the mutation in the COMT Met knock-in mutant mice resemble the functional Val/Met polymorphism better than the complete knockout and could be a better animal model for analyses of the molecular and cellular mechanisms underlying the differences in the cognitive and emotional controls due to the functional Val158Met polymorphism.