Effects And Signaling Mechanisms Of Endogenous Heat Shock Factor 1 In Inducible Nitric Oxide Synthase Induction In Murine Microglia

Background Inducible nitric oxide synthase(iNOS)makes a great contribution to host defense and inflammation.In many settings,lipopolysaccharide(LPS)induces iNOS expression through activation of the inhibitor of ?B-?(I?B-?)-nuclear factor-?B(NF-?B)cascade,whereas interferon-?(IFN-?)acts through Janus kinase(JAK)-signal transducer and activator of transcription 1(STAT1)signals.Heat shock factor 1(HSF1),a major regulator of heat shock protein transcription,has been shown to regulate the production of pro-inflammatory cytokines such as tumor necrosis factor-?(TNF-?)and interleukin-6(IL-6).But it remains obscure whether and how HSF1 affects iNOS induction.Methods Western blot was used to measure the protein expression.The mRNA level was measured by real time-PCR.Silence of HSF1 was achieved by small interfering RNA.Nitric oxide(NO)content and NF-?B binding activity were assayed by commercial kits.Chromatin immunoprecipitation(ChIP)was used to measure the binding activity of NF-?B and STAT1 to iNOS promoters.Results HSF1 inhibition or knockdown prevented the LPSand/or IFN-?-stimulated iNOS protein expression in cultured microglia.HSF1 inhibition blocked iNOS mRNA transcription.These inhibitory effects of HSF1 inhibition on iNOS expression were confirmed in brain tissues from endotoxemic mice.Further analysis showed that HSF1 inhibition had no effect on I?B-? degradation and NF-?B or STAT1 phosphorylation in LPS/IFN-?-stimulated cells.The nuclear transport of active NF-?B or STAT1 was also not affected by HSF1 inhibition.But HSF1 inhibition reduced the binding of NF-?B and STAT1 to their DNA elements.In addition,HSF1 inhibition reduced NF-?B and STAT1 bindings to i NOS promoter inside the LPS/IFN-?-stimulated cells.Conclusions 1.HSF1 inhibition reduced iNOS protein expression and mRNA transcription.2.The HSF1 inhibitor did not affect the LPS-or IFN-?-induced I?B-? degradation ? NF-?B or STAT1 phosphorylation.3.The HSF1 inhibitor attenuated the LPS-or IFN-?-induced binding of NF-?B or STAT1 to iNOS promoters.