Identification of a novel caspase cleavage site in huntingtin that regulates mutant huntingtin clearance.
Huntington disease (HD) is a progressive neurodegenerative disease that initially affects the striatum leading to changes in behavior and loss of motor coordination. It is caused by an expansion in the polyglutamine repeat at the N-terminus of huntingtin (HTT) that leads to aggregation of mutant HTT. The loss of wildtype function, in combination with the toxic gain of function mutation, initiates various cell death pathways. Wildtype and mutant HTT are regulated by different post-translational modifications that can positively or negatively regulate their function or toxicity. In particular, we have previously shown that caspase cleavage of mutant HTT at amino acid position aspartate 586 (D586) by caspase-6 is critical for the pathogenesis of the disease in an HD mouse model. Herein, we describe the identification of a new caspase cleavage site at position D572 that is mediated by caspase-1. Inhibition of caspase-1 also inhibits cleavage at D586 through inhibition of caspase-6. Inhibition of caspase cleavage at D572 significantly decreases mutant HTT aggregation and significantly increased the turnover of soluble mutant HTT. This suggests that caspase-1 may be a viable target to inhibit caspase cleavage of mutant HTT at both D572 and D586 to promote mutant HTT clearance.