A peptidylic inhibitor for neutralizing expandedCAGRNA-induced nucleolar stress in polyglutamine diseases

Polyglutamine (polyQ) diseases are a class of progressive neurodegenerative disorders characterized by the expression of both expandedCAGRNA and misfolded polyQ protein. We previously reported that the direct interaction between expandedCAGRNA and nucleolar protein nucleolin (NCL) impedespreribosomalRNA (pre-rRNA) transcription, and eventually triggers nucleolar stress-induced apoptosis in polyQ diseases. Here, we report that a 21-amino acid peptide, named “beta-structured inhibitor for neurodegenerative diseases” (BIND), effectively suppresses toxicity induced by expandedCAGRNA. When administered to a cell model, BIND potently inhibited cell death induced by expandedCAGRNA with an IC50value of ∼0.7 µM. We showed that the function of BIND is dependent on Glu2, Lys13, Gly14, Ile18, Glu19, and Phe20. BIND treatment restored the subcellular localization of nucleolar marker protein and the expression level ofpre-45s rRNA. Through isothermal titration calorimetry analysis, we demonstrated that BIND suppresses nucleolar stress via a direct interaction withCAGRNA in a length-dependent manner. The mean binding constants (KD) of BIND toSCA2CAG22,SCA2CAG42,SCA2CAG55, andSCA2CAG72RNA are 17.28, 5.60, 4.83, and 0.66 µM, respectively. In vivo, BIND ameliorates retinal degeneration and climbing defects, and extends the lifespan ofDrosophilaexpressing expandedCAGRNA. These effects suggested that BIND can suppress neurodegeneration in diverse polyQ disease models in vivo and in vitro without exerting observable cytotoxic effect. Our results collectively demonstrated that BIND is an effective inhibitor of expandedCAGRNA-induced toxicity in polyQ diseases.