Striatal expression of a calmodulin fragment improved motor function, weight loss, and neuropathology in the R6/2 mouse model of Huntington's disease

Huntington's disease (HD) is an autosomal dominant neurodegenerative disorder, caused by a polyglutamine expansion in the huntingtin protein (htt). Increasing evidence suggests that transglutaminase (TGase) plays a critical role in the pathophysiology of HD possibly by stabilizing monomeric, polymeric and aggregated htt. We previously reported that in HEK293 and SH-SY5Y cells expression of a calmodulin (CaM)-fragment, consisting of amino acids 76-121 of CaM, decreased binding of CaM to mutant htt, TGase-modified htt and cytotoxicity associated with mutant htt and normalized intracellular calcium release. In this study, an adeno-associated virus (AAV) that expresses the CaM-fragment was injected into the striatum of HD transgenic R6/2 mice. The CaM-fragment significantly reduced body weight loss and improved motor function as indicated by improved rotarod performance, longer stride length, lower stride frequency, fewer low mobility bouts and longer travel distance than HD controls. A small but insignificant increase in survival was observed in R6/2 mice with CaM-fragment expression. Immunoprecipitation studies show that expression of the CaM-fragment reduced TGase-modified htt in the striatum of R6/2 mice. The percentage of htt-positive nuclei and the size of intranuclear htt aggregates were reduced by the CaM-fragment without striatal volume changes. The effects of CaM-fragment appear to be selective, as activity of another CaM-dependent enzyme, CaM-dependent kinase II, was not altered. Moreover, inhibition of TGase-modified htt was substrate-specific since overall TGase activity in the striatum was not altered by treatment with the CaM-fragment. Together, these results suggest that disrupting CaM-htt interaction may provide a new therapeutic strategy for HD.