Inhibition of polyglutamine aggregate cytotoxicity by a structure-based elongation inhibitor

Huntington's disease and other expanded CAG repeat diseases are associated with the expression of proteins containing polyglutamine (polyGln) tracts expanded beyond a pathological repeat length threshold of approximately 38. Aggregation of these expanded polyGln proteins may trigger disease by recruiting and sequestering other polyGln-containing proteins in the cell, depriving the cellular environment of critical protein activities. We describe here proline-containing polyGln peptide sequences that are effective inhibitors of the ability of polyGln aggregates to be elongated by recruiting additional polyGln monomers. These peptides are also effective inhibitors of polyGln aggregate toxicity in a cell culture model based on delivery of preassembled polyGln aggregates into the cell nucleus. These results are not only consistent with a role for polyGln aggregates in the disease mechanisms of expanded CAG repeat disorders, but also directly implicate the elongation phase of aggregate growth in the toxicity mechanism, supporting the recruitment-sequestration model for polyGln toxicity. These results may be related to the ability of the glutamine/proline-rich protein PQE-1 to protect C. elegans against polyglutamine toxicity. Inhibition of aggregate elongation is a therapeutic strategy that, based on our results, may be effective even in neurons already compromised by polyGln aggregates.