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Background Huntington’s disease (HD) is a protein misfolding disorder involving a mutant form of the huntingtin protein (Htt) with a polyglutamine expansion. Heat shock proteins (Hsp) are key therapeutic targets in protein misfolding diseases given their role in protein folding, aggregation, and degradation. YM-1 is an Hsp70 modulator (ATPase domain inhibitor) which was found protective in the polyglutamine disorder SBMA. However, given that the consequences of modulating a specific Hsp seem to depend on the nature of the client protein and the drug pharmacodynamics, it remains uncertain whether YM-1 might be protective in HD. Aims Assess the effects of YM-1 on Htt proteostasis. Methods PC12 cells with inducible full-length Htt(Q23/Q145); U2OS cells transfected with N-terminal GFP-Htt(Q23/Q74). Western Blot and immunoprecipitation were used to determine the levels of Htt, Hsp and their interaction. Htt aggregation was monitored by fluorescence microscopy. Results Concerning full-length Htt, treatment with YM-1 alone decreased mutant Htt (mHtt) in PC12 cells, without altering the levels of wild-type Htt. The effect of YM-1 was potentiated by heat shock conditions (HS; 42°C, 1 hour), leading to higher decreases in mHtt than HS alone. Since HS increased levels of Hsp70, these results are consistent with an Hsp70-dependent effect of YM-1. Concerning aggregation of N-terminal Htt, treatment with YM-1 increased the proportion of cells with mHtt aggregates. Conclusions: These results suggest that YM-1 alters mHtt proteostasis in an Hsp70-dependent manner, decreasing levels of full-length mHtt, possibly by enhancing its Hsp70-mediated degradation, and increasing aggregation of N-terminal mHtt, possibly by affecting the formation of Hsp70/40/110 disaggregation complex. Acknowledgments: Fundacao para a Ciencia e a Tecnologia P2020-PTDC/NEU-NMC/0412/2014, POCI-01-0145-FEDER-016577, 3599-PPCDT, UID/QUI/50006/2013, PD/BD/113567/2015, SFRH/BPD/102259/2014. |
