A novel long non-coding RNA, Nostrill, regulates iNOS gene transcription and neurotoxicity in microglia.

Background Microglia are resident immunocompetent and phagocytic cells in the CNS. Pro-inflammatory microglia, stimulated by environmental microbial signals such as bacterial lipopolysaccharide (LPS), viral RNAs, or inflammatory cytokines, are neurotoxic and associated with pathogenesis of several neurodegenerative diseases. Long non-coding RNA (lncRNA) are emerging as important tissue-specific regulators directing cell differentiation and functional states and may help direct proinflammatory responses of microglia. Methods Microglial gene expression array analyses and qRT-PCR was used to identify a novel intergenic long-noncoding RNA that was upregulated in LPS-stimulated microglial cell lines, LPS-stimulated primary microglia, and LPS-injected mouse cortical tissue. Silencing and overexpression studies, RNA immunoprecipitation, chromatin immunoprecipitation, chromatin RNA immunoprecipitation assays, and qRT-PCR were used to study the function of this long-noncoding RNA in microglia. In vitro cytotoxicity assays were used to examine the effects of silencing the novel long-noncoding RNA in LPS-stimulated microglia on neurotoxicity. Results We report here that the previously uncharacterized intergenic lncRNA we termed Nostrill is induced by LPS stimulation in both BV2 cells and primary murine microglia, as well as in cortical tissue of LPS-injected mice. Induction of Nostrill is NF-κB dependent and silencing of Nostrill decreased inducible nitric oxide synthase (iNOS) expression and nitric oxide production in BV2 and primary microglial cells. Overexpression of Nostrill increased iNOS expression and nitric oxide production. RNA immunoprecipitation assays demonstrated that Nostrill is physically associated with NF-κB subunit p65 following LPS stimulation. Silencing of Nostrill significantly reduced NF-κB p65 and RNA polymerase II recruitment to the iNOS promoter and decreased H3K4me3 activating histone modifications at iNOS gene loci. In vitro studies demonstrate that silencing of Nostrill in microglia reduced LPS-stimulated microglia neurotoxicity. Conclusions Our data indicate a new regulatory role of NF-κB-induced Nostrill and suggest that Nostrill acts as a co-activator of transcription of iNOS resulting in the production of nitric oxide in microglia through modulation of epigenetic chromatin remodeling. Nostrill may be a target for reducing the neurotoxicity associated with iNOS-mediated inflammatory processes in microglia during neurodegeneration.