Increased vulnerability to kainate-induced seizures in utrophin-knockout mice

Utrophin, the autosomal homologue of dystrophin, the Duchenne muscular dystrophy gene product, is a cytoskeletal protein found in many tissues. In muscle fibers, the level and localization of utrophin depend on their state of differentiation and innervation. Transgenic overexpression of utrophin prevents degeneration of dystrophin‐deficient muscle fibers. In brain, in addition to its enrichment in blood vessels, utrophin is associated primarily with the plasma membrane of large sensory and motor brainstem neurons, suggesting a contribution to their structural stability. Here, we examined the role of utrophin for long‐term survival of dentate granule cells, which become markedly hypertrophic in a mouse model of temporal lobe epilepsy. This morphogenetic change is induced several weeks after a unilateral intrahippocampal injection of kainic acid (KA), while mice experience chronic focal seizures. Using in situ hybridization and immunohistochemistry, we show that dispersion and hypertrophy of granule cells in KA‐treated wildtype mice are accompanied by a strong and long‐lasting expression of utrophin in somata and proximal dendrites. Utrophin knockout mice had a normal hippocampal cytoarchitecture but were more sensitive to KA‐induced excitotoxicity, as shown by increased mortality and faster progression of the lesion. At 6 weeks post‐KA, the numerical density of granule cells and thickness of the granule cell layer were significantly reduced ipsilaterally in mutant mice, indicating a profound reduction in total cell number in the absence of utrophin. These findings suggest that utrophin contributes to protect CNS neurons against pathological insults, in particular, stimuli leading to massive neuronal hypertrophy.