Protection against amyloid beta cytotoxicity by sulforaphane: Role of the proteasome

The 26S proteasome plays a major role in degradation of abnormal proteins within the cell. The indirect antioxidant including sulforaphane (SFN) protects cells from oxidative damage by increasing the expression of Nrf2-target genes. It has been observed that the expression of multiple subunits of the proteasome was up-regulated by indirect antioxidants through the Nrf2 pathway. In the current study, the role of SFN in amyloid β_1-42 (Aβ_1-42)-induced cytotoxicity has been investigated in murine neuroblastoma cells. Treatment with SFN protected cells from Aβ_1-42-mediated cell death in Neuro2A and N1E 115 cells. Inhibition of proteasome activities by MG132 could abolish the protective effect of SFN against Aβ_1-42. Neuro2A cells, which were stably overexpressing the catalytic subunit of the proteasome PSMB5, showed an elevated resistance toward Aβ_1-42 toxicity compared to control cells. Furthermore, the in vitro assay demonstrated that the Aβ_1-42 peptide is degraded by the proteasome fraction. These results suggest that proteasome-inducing indirect antioxidants may facilitate the removal of the Aβ_1-42 peptide and lead to the amelioration of abnormal protein-associated etiologies.