Soluble amyloid triggers a myeloid differentiation factor 88 and interferon regulatory factor 7 dependent neuronal type-1 interferon response in vitro

Background: neuro-inflammation has long been implicated as a contributor to the progression of alzheimer's disease in both humans and animal models. type-1 interferons (ifns) are pleiotropic cytokines critical in mediating the innate immune pro-inflammatory response. the production of type-1 ifns following pathogen detection is,in part,through the activation of the toll-like receptors (tlrs) and subsequent signalling through myeloid differentiation factor-88 (myd88) and interferon regulatory factors (irfs). we have previously identified that neuronal type-1 ifn signalling,through the type-1 interferon alpha receptor-1 (ifnar1),is detrimental in models of ad. using an in vitro approach,this study investigated the tlr network as a potential production pathway for neuronal type-1 ifns in response to aβ. methods: wildtype and myd88-/- primary cultured cortical and hippocampal neurons were treated with 2.5 μm aβ1-42 for 24 to 72 h or 1 to 10 μm aβ1-42 for 72 h. human be(2)m17 neuroblastoma cells stably expressing an irf7 small hairpin rna (shrna) or negative control shrna construct were subjected to 7.5 μm aβ1-42/aβ42-1 for 24 to 96 h,2.5 to 15 μm aβ1-42 for 96 h or 100 ng/ml lps for 0.5 to 24 h. q-pcr was used to analyse ifnα,ifnβ,il-1β,il-6 and tnfα mrna transcript levels. phosphorylation of stat-3 was detected by western blot analysis,and cell viability was assessed by mts assay. results: reduced ifnα,ifnβ,il-1β,il-6 and tnfα expression was detected in aβ1-42-treated myd88-/- neurons compared to wildtype cells. this correlated with reduced phosphorylation of stat-3,a downstream type-1 ifn signalling mediator. significantly,myd88-/- neuronal cultures were protected against aβ1-42-induced neurotoxicity compared to wildtype as determined by mts assay. knockdown of irf7 in m17 cells was sufficient in blocking ifnα,ifnβ and p-stat-3 induction to both aβ1-42 and the tlr4 agonist lps. m17 irf7 kd cells were also protected against aβ1-42-induced cytotoxicity. conclusions: this study confirms that the neuronal type-1 ifn response to soluble amyloid is mediated primarily through tlrs. this production is dependent upon myd88 and irf7 signalling. this study suggests that targeting this pathway to modulate neuronal type-1 ifn levels may be beneficial in controlling aβ-induced neurotoxicity. © 2015 minter et al; licensee biomed central.