Scrapie infection in experimental rodents and SMB-S15 cells decreased the brain endogenous levels and activities of Sirt1.

Prion diseases are composed of a group of fatal neurodegenerative disorders resulting from misfolding of cellular prion (PrP(C)) into scrapie prion (PrP(Sc)). Sirt1, a class III histone deacetylase, has been reported to protect neuronal cells against PrP (106-126)-induced cell death. To address the potential role of Sirt1 during prion infection, the levels and enzyme activities of Sirt1 in the brains of scrapie-infected rodents, including hamsters infected with strain 263K, mice infected with strains 139A and ME7, and in prion infected SMB-S15 cells, were analyzed. Western blots revealed that endogenous Sirt1 levels were significantly decreased in all tested scrapie-infected models. Dynamic assays of brain Sirt1 levels in 263K-infected hamsters during incubation period showed a time-dependent decrease. The acetylating forms of Sirt1 target proteins, P53, PGC-1, and STAT3, markedly increased both in the brains of scrapie-infected rodents and in SMB-S15 cells, representing decreased Sirt1 activity. Immunofluorescent assays illustrated that Sirt1 predominately localized in cytosol of SMB-S15 cells but clearly distributed in nucleus of its normal partner cell line, SMB-PS. Moreover, accompanying with increase of Sirt1 level and decrease of acetyl-P53 level, treatments with Sirt1 activators SRT1720 and resveratrol in SMB-S15 cells significantly reduced PrP(Sc); at the same time, the cellular distribution of PrP proteins became normal, and the cell proliferating state was slightly improved. These data indicate that prion infection notably attenuates the Sirt1 activity in host cells. Sensitivity of the PrP(Sc) to Sirt1 activators highlights a potential role of Sirt1 in prion therapeutics.