Genetic ablation and chemical inhibition of IP3R1 reduce mutant huntingtin aggregation

Huntington's disease (HD) is a dominantly inherited neurodegenerative disease caused by an expansion of the polyglutamine (polyQ) stretch in huntingtin (htt). Previously, it has been shown that inhibition of the inositol 1,4,5-trisphosphate receptor type 1 (IP3R1) activity reduced aggregation of pathogenic polyQ proteins. Experimentally, this effect was achieved by modification of the intracellular IP3 levels or by application of IP3R1 inhibitors, such as 2-aminoethyl diphenylborinate (2-APB). Unfortunately, there are certain concerns about the 2-APB specificity and cytotoxicity. Moreover, a direct link between IP3R1 and polyQ aggregation has not been shown yet. In this study we show, that down-regulation of the IP3R1 levels by shRNA reduced the aggregation of mutant htt. We tested 2-APB analogs in an attempt to identify less toxic and more IP3R1-specific compounds and found that the effect of these analogs on the reduction of the mutant htt aggregation did weakly correlate with their inhibitory action toward the IP3-induced Ca(2+) release (IICR). Their effect on aggregation was not correlated with the store-operated Ca(2+) entry (SOCE), which is another target of the 2-APB related compounds. Our findings suggest that besides functional contribution of the IP3R inhibition on the mutant htt aggregation there are additional mechanisms for the anti-aggregation effect of the 2-APB related compounds.