The nuclear export signal mediates mutant atrophin-1-induced neuropathology in a mouse model of DRPLA

Dentatorubral and pallidoluysian atrophy (DRPLA) is an autosomal dominant neurodegenerative disorder, caused by a CAG expansion in the atrophin-1 gene. The clinical features include chorea, ataxia, incoordination, emotional changes and dementia, progressing to early mortality. The atrophin-1 protein sequence contains a putative N-terminal nuclear localization signal (NLS) and a putative C-terminal nuclear export signal (NES). To investigate whether nuclear localization of atrophin-1 plays a role in the pathogenesis of DRPLA, we designed alterations of the NLS and NES by site-directed mutagenesis. We generated transgenic mice expressing mutant full-length atrophin-1 (repeat length = 65) with alteration of either the nuclear export signal (At65QmNES, predicted to result in a higher ratio of nuclear to cytosolic atrophin-1 than in control), or the nuclear localization signal (At65QmNLS, predicated to retain more cytosolic atrophin-1), respectively. With equivalent levels of atrophin-1 expression, At65QmNES mice displayed more nuclear accumulation of atrophin-1 and its fragments than At65QmNLS or control mice expressing endogenous normal Atrophin-1. Moreover, At65QmNES mice had a shorter life span and more severe locomotor defects than did At65QmNLS (and non-transgenic control) mice. Additionally, we found that At65QmNES caused more pathology in mouse brains than did At65QmNLS. These results provide evidence that nuclear localization enhances the phenotype of mutant atrophin-1-linked neuropathology. In addition, our findings indicate that the AT65QmNES transgenic mouse will be a valuable model for future studies of DRPLA pathogenesis and potential therapeutics.