Humanized CYP2C19 transgenic mouse as an animal model of cerebellar ataxia

Abstract

Background: Animal models are essential for understanding aetiology and pathophysiology of movement disorders. Previously, it had been found that mice transgenic for the human CYP2C19 gene, which is expressed in the liver and developing brain, exhibit altered neurodevelopment associated with impairments of their motor function and emotionality [1, 2]. The aim of this study was to characterize motoric phenotype of the CYP2C19 transgenic mouse and validate its potential usefulness as an animal model for ataxia.

Methods: Experiments were performed on CYP2C19 transgenic mice and control wild-type littermate mice. Body weight of mice was measured between the 21st and 42nd postnatal day. Mouse gait was analysed with footprint test [3] in young animals at four time points and once in adult mice. The maximal height of hindpaw elevation while walking was measured offline from the video footage of the footprint test. Motoric function was quantified by the rotarod and beam-walking tests. Structural differences in 20 brain regions of wild-type and transgenic mice were investigated with 9.4T gadolinium-enhanced postmortem neuroimaging. Antioxidative enzyme status was determined in the brain tissue in order to assess potential differences in the brain oxidative-antioxidative balance between wild-type and transgenic mice. When multiple brain regions or multiple antioxidant enzyme activities were analysed, p-values were FDR corrected for multiple comparisons.

Results: CYP2C19 transgenic (TG) animals exhibited approximately 5-10% reduced body weight (p=0.015) during 3rd and 4th postnatal week, while after postnatal day 31, the differences in the body weight were no longer statistically significant. The TG animals exhibited approximately two fold higher maximal hindpaw elevation in young (2.1-fold [CI95%: 2.0, 2.2], p<0.0001) and adult mice (1.9-fold [CI95%: 1.8, 2.1], p<0.0001), compared to wild-types. In the 5th postnatal week, all transgenic mice exhibited increase in elevation of both hindpaws, while after this point they gradually started exhibiting unilateral phenotype until almost all (49 of 51) animals became unilaterally affected in the adulthood. Footprint analysis and rotarod test did not detect significant differences (p>0.1) between TG and control mice in any of the analysed parameters, accounting for all examined time points. CYP2C19 transgenic mice exhibited 14% increase in beam crossing time (14%, [95%CI: 6.4, 22], p=0.0014) and 5.6-fold more paw-slips (p<0.0001, n=89) in the beam-walking test. CYP2C19 transgenic mice exhibited profound reduction in cerebellar volume (-11.8% [95%CI: -14.7, -9.0], q<0.0001, n=59) and moderate reduction in hippocampal volume (-4.2% [95%CI: -6.4%, -1.9%], q=0.015, n=59); compared to the corresponding volumes measured in WT mice. Superoxide dismutase activity was slightly increased (1.14-fold [CI95%: 1.06, 1.23], p=0.0010, q=0.023) in the cerebelli and moderately increased (1.3-fold, [CI95%: 1.18, 1.47], p<0.0001, q=0.0013) in the hippocampi of transgenic mice compared to wild-types, while glutathione reductase activity was significantly increased (1.2-fold [CI95%: 1.13, 1.35], p<0.0001, q=0.0021) in the hippocampi of TG mice.

Conclusions: Humanized CYP2C19 transgenic mice exhibit altered motoric function, functional motoric impairments and reduced cerebellar volume. CYP2C19 transgenic mice can be a useful tool for the studies focused on understanding the physiology of cerebellar development, as well as aetiology and pathophysiology of cerebellum-related disorders.