The Relationship Between NF-?B Signal Pathway And Prion Disease

Nuclear factor ?B(NF-?B)functions as a pleiotropic regulator of target genes controlling physiological function as well as pathological processes of many different diseases,including some neurodegeneration diseases.However,the role of NF-?B in the pathogenesis of prion disease remains ambiguous.In this study,the status of NF-?B(p65)in a prion infected cell line SMB-S15 was firstly evaluated.Significantly lower levels of p65 and phosphorylated form of p65(p-p65)were detected in SMB-S15 cells,comparing with its normal partner cell line SMB-PS.Markedly slow responses of NF-?B system to the stimulation of tumor necrosis factor(TNF-a)were observed in SMB-S15 cells.Removal of PrPSc replication in SMB-S15 cells rescued the expression and activity of NF-?B.However,overexpression of p65 in SMB-S15 cells did not influence the propagation of PrPSc.Moreover,significant decline of p65 level was also observed in the brain tissues of the mice infected with the lysates of SMB-S15 cells and the hamsters infected with scrapie agent 263K at terminal stage.IFA assays on the brain sections from either normal or scrapie-infected rodents revealed colocalization of p65 with Feminizing Locus on X-3(NeuN)positive cells,but not with glial fibrillary acidic protein(GFAP)positive cells.Assays of the agents involving in the regulation for NF-?B showed down-regulated Phosphoinositide 3-kinase(PI3K)and Protein Kinase B(Akt)both in SMB-S15 cells and in the brains of scrapie infected rodents.Those data indicate a remarkable repression of classical NF-?B pathway during prion infection both in vitro and in vivo.The alteration of NF-?B(p65)shows close association with the replication and accumulation of PrPSc in the cells.Microglia activation is one of the pathological features of prion disease,often accompanied by the production of a number of inflammatory factors,such as TNF-a,Interleukin-6(IL-6),etc.TNF-a participates in not only pro-inflammatory responses but also in cellular communication,cell differentiation,cell death and so on.In this study,we explored initially the effect of TNF-a on the development of prion diseases.SMB-S15 cells are more vulnerable to the conditioned medium of BV2 cells activated by lipopolysaccharide(LPS),in which the cytokine TNF-? is increased obviously.Futher,we found that SMB-S15 cells are also vulnerable to the cytokine TNF-? alone represented by the decreased cell viability.In SMB-S15 cells stimulated by TNF-?,the cleavage forms of apoptosis-related proteins caspase-3 and RIP1 did not increase significantly,and caspase-8 activity was significantly lower than that of SMB-PS cells.In contrast,the necroptosis related protein,phosphorylated mixed lineage kinase domain-like(p-MLKL),was significantly increased in TNF-?-stimulated SMB-S15 cells.Our data suggest that,the cell viability of SMB-S15 cells decreased more obviously was mainly due to the outcome of necroptosis.Meanwhile,removal of PrPSc propagation in SMB-S15 cells partly rescues the tolerance of cells to TNF-?.It is further shown that necroptosis is closely related to the replication and accumulation of PrPSc in cells.The remarkable repression of the classical NF-?B pathway during prion infection increased the damage of inflammatory factors to prion-infected cells to a certain extent,thereby accelerating the occurrence and development of the disease.