No abstract

Post-transcriptional regulation of gene expression by microRNAs has been implicated in the regulation of chronic physiological and pathological responses. In this report, we demonstrate that changes in the expression of microRNAs (miRNAs) can also regulate acute inflammatory responses in human lung alveolar epithelial cells. Thus, stimulation with interleukin (IL)-1β results in a rapid time- and concentration-dependent increase in miRNA-146a and, to a lesser extent, miRNA-146b expression although these increases were only observed at high IL-1β concentration. Examination of miRNA function by over-expression and inhibition showed that increased miRNA-146a expression negatively regulated the release of the pro-inflammatory chemokines, IL-8 and RANTES. Subsequent examination of the mechanism demonstrated that the action of miRNA-146a was mediated at the translational level and not through down-regulation of proteins involved in the IL-1β signalling pathway or chemokine transcription or secretion. Overall, these studies indicate that rapid increase in miRNA-146a expression provides a novel mechanism for negative regulation of severe inflammation during the innate immune response.

It is increasingly clear that long non-coding RNAs (lncRNAs) regulate a variety biological responses, and that they do so by a diverse range of mechanisms. In the field of immunology, recent publications have shown widespread changes in the expression of lncRNAs during the activation of the innate immune response and T cell development, differentiation, and activation. These lncRNAs control important aspects of immunity such as production of inflammatory mediators, differentiation, and cell migration through regulating protein-protein interactions or via their ability to basepair with RNA and DNA. We review the current understanding of the mechanism of action of these immune-related lncRNAs, discuss their impact on physiological and pathological processes, and highlight important areas of inquiry at the intersection between immunology and lncRNA biology.

1 Cell-penetrating peptides such as antennapedia, TAT, transportan and polyarginine have been extensively employed for in vitro and in vivo delivery of biologically active peptides. However, little is known of the relative efficacy, toxicity and uptake mechanism of individual protein transduction domain-peptide conjugates, factors that will be critical in determining the most effective sequence. 2 In the present study, we show by FACS analysis that unconjugated antennapedia, TAT, transportan and polyarginine demonstrate similar kinetic uptake profiles, being maximal at 1-3 h and independent of cell type (HeLa, A549 and CHO cell lines). A comparison of the magnitude of uptake of cell-penetrating peptide conjugates demonstrated that polyarginine ¼ transportan4antennapedia4 TAT. 3 However, examination of cellular toxicity showed that antennapediaoTATotransportanopolyarginine, with antennapedia-peptide conjugates having no significant toxicity even at 100 mM. 4 Confocal studies of the mechanism of antennapedia-and TAT-peptide uptake showed that the time course of uptake and their cellular distribution did not correlate with transferrin, a marker of clathrin-mediated endocytosis. In contrast, the peptides co-localised with a marker of lipid rafts domains, cholera toxin, which was attenuated following the disruption of these domains using methylb-cyclodextrin. 5 Overall, comparison of the uptake and toxicity suggests that antennapedia provides the optimal cell-penetrating peptide for peptide delivery in vitro and that both antennapedia-and TAT-mediated peptide delivery occurs predominantly via lipid raft-dependent but clathrin-independent endocytosis.

Although the immune response is predominantly controlled at the transcriptional level, microRNA-mediated RNA interference is emerging as an important regulatory mechanism that operates at the translation level. Specifically, recent studies indicate that those miRNAs that are selectively and/or highly expressed in immune cells including the miR-17–92 cluster, miR-150, miR-155, miR-181 and miR-223 have a ‘permissive’ function in the maturation, proliferation and differentiation of myeloid and lymphoid cells. Importantly, these actions of miRNAs often involve interactions with transcription factors. In contrast, the rapid and transient induction of miR-9, miR-146a and miR-155 has been speculated to negatively regulate the acute responses following activation of innate immune through down-regulation of proteins involved in the receptor-induced signalling pathways.

The therapeutic application of siRNA shows promise as an alternative approach to small molecule inhibitors for the treatment of human disease. However, the major obstacle to its use has been the difficulty in delivering these large anionic molecules in vivo. In this study, we have investigated whether siRNA-mediated knockdown of p38 MAP kinase mRNA in mouse lung is influenced by conjugation to the non-viral delivery vector cholesterol and the cell penetrating peptides (CPP) TAT(48-60) and penetratin. Initial studies in the mouse fibroblast L929 cell line, showed that siRNA conjugated to cholesterol, TAT(48-60) and penetratin but not siRNA alone achieved a limited reduction of p38 MAP kinase mRNA expression. Intratracheal administration of siRNA resulted in localisation within macrophages and scattered epithelial cells and produced a 30-45% knockdown of p38 MAP kinase mRNA at 6hrs. As with increasing doses of siRNA, conjugation to cholesterol improved upon the duration but not the magnitude of mRNA knockdown whilst penetratin and TAT(48-60) had no effect. Importantly, administration of the penetratin or TAT(48-60) peptides alone caused significant reduction in p38 MAP kinase mRNA expression whilst the penetratin-siRNA conjugate activated the innate immune response. Overall, these studies suggest that conjugation to cholesterol may extend but not increase siRNA mediated p38 Figure S1, dose-dependent percentile p38 MAP kinase mRNA levels in vitro following lipofection with three mouse p38 MAP kinase siRNA or two mismatch controls; Figure S2, analytical HPLC and electrospray mass spectrograms of peptide-and cholesteryl-RNA constructs; Figure S3, analytical gels of CPP and cholesterol conjugate annealing products; Figure S4, cell viability following incubation with siRNA, CPP or siRNA conjugates; Figure S5, MAP kinase mRNA knockdown in the lung. Furthermore, the use of CPP may be limited due to as yet uncharacterized effects upon gene expression and a potential for immune activation.

Early reports indicate that long non-coding RNAs (lncRNAs) are novel regulators of biological responses. However, their role in the human innate immune response, which provides the initial defence against infection, is largely unexplored. To address this issue, here we characterize the long non-coding RNA transcriptome in primary human monocytes using RNA sequencing. We identify 76 enhancer RNAs (eRNAs), 40 canonical lncRNAs, 65 antisense lncRNAs and 35 regions of bidirectional transcription (RBT) that are differentially expressed in response to bacterial lipopolysaccharide (LPS). Crucially, we demonstrate that knockdown of nuclear-localized, NF-κB-regulated, eRNAs (IL1β-eRNA) and RBT (IL1β-RBT46) surrounding the IL1β locus, attenuates LPS-induced messenger RNA transcription and release of the proinflammatory mediators, IL1β and CXCL8. We predict that lncRNAs can be important regulators of the human innate immune response.

Background: At present, nothing is known of the role of miRNAs in the immune response in vivo despite the fact that inflammation is thought to underlie multiple acute and chronic diseases. In these circumstances, patients are commonly treated with corticosteroids such as dexamethasone.