Neuroprotective Effects of Calmodulin Peptide 76-121aa: Disruption of Calmodulin Binding to Mutant Huntingtin

Huntington's disease (HD) is a neurodegenerative disease caused by mutant huntingtin protein containing an expanded polyglutamine tract, which may cause abnormal protein-protein interactions such as increased association with calmodulin (CaM). We previously demonstrated in HEK293 cells that a peptide containing amino acids 76-121 of CaM (CaM-peptide) interrupted the interaction between CaM and mutant huntingtin, reduced mutant huntingtin-induced cytotoxicity and reduced transglutaminase (TG)-modified mutant huntingtin. We now report that adeno-associated virus (AAV)-mediated expression of CaM-peptide in differentiated neuroblastoma SH-SY5Y cells, stably expressing an N-terminal fragment of huntingtin containing 148 glutamine repeats, significantly decreases the amount of TG-modified huntingtin and attenuates cytotoxicity. Importantly, the effect of the CaM-peptide shows selectivity, such that total TG activity is not significantly altered by expression of CaM-peptide nor is the activity of another CaM-dependent enzyme, CaM kinase II. In vitro, recombinant exon 1 of huntingtin with 44 glutamines (htt-exon1-44Q) binds to CaM-agarose; the addition of 10 mu M of CaM-peptide significantly decreases the interaction of htt-exon1-44Q and CaM but not the binding between CaM and calcineurin, another CaM-binding protein. These data support the hypothesis that CaM regulates TG-catalyzed modifications of mutant huntingtin and that specific and selective disruption of the CaM-huntingtin interaction is potentially a new target for therapeutic intervention in HD.