Inflammation involves a coordinated, sequential, and self limiting sequence of events controlled by positive and negative regulatory mechanisms. Recent studies have shown that microRNAs (miRNAs), an evolutionarily conserved class of endogenous 22-nucleotide noncoding RNAs, contribute to the regulation of inflammation by repressing gene expression at the posttranscriptional level. In this study, we characterize the profile of miRNAs induced by LPS in human polymorphonuclear neutrophils (PMN) and monocytes. In particular, we identify miR-9 as the only miRNA (among 365 analyzed) up-regulated in both cell types after TLR4 activation. miR-9 is also induced by TLR2 and TLR7/8 agonists and by the proinflammatory cytokines TNF-␣ and IL-1␤, but not by IFN␥. Among the 3 different genes encoding miR-9 precursors in humans, we show that LPS selectively induces the transcription of miR-9 -1 located in the CROC4 locus, in a MyD88-and NF-B-dependent manner. In PMN and monocytes, LPS regulates NFKB1 at both the transcriptional and posttranscriptional levels, and a conserved miR-9 seed sustained a miR-9-dependent inhibition of the NFKB1 transcript. Overall, these data suggest that TLR4-activated NF-B rapidly increases the expression of miR-9 that operates a feedback control of the NF-B-dependent responses by fine tuning the expression of a key member of the NF-B family.inflammation ͉ innate immunity ͉ Toll-like receptors ͉ cytokines ͉ NFKB1

Cytokines have been suggested to act as intermediates between the immune and the central nervous system, but little is known about the type of cells synthesizing them in the brain. We have immortalized with oncogenic retroviruses primary brain cell cultures from mouse embryos and have generated clones of microglial cells that have been characterized. Three of the clones studied produce interleukin 1 (IL 1); IL 6 and tumor necrosis factor-alpha as assessed by biological assays and by Northern blot analysis. Our data raise the question on the role of these cytokines in the brain and suggest that early resident microglial cells might play an important role in development processes and in the adult brain.

IL-10 is a potent anti-inflammatory molecule that, in phagocytes, negatively targets cytokine expression at transcriptional and posttranscriptional levels. Posttranscriptional checkpoints also represent the specific target of a recently discovered, evolutionary conserved class of small silencing RNAs known as "microRNAs" (miRNAs), which display the peculiar function of negatively regulating mRNA processing, stability, and translation. In this study, we report that activation of primary human monocytes up-regulates the expression of miR-187 both in vitro and in vivo. Accordingly, we identify miR-187 as an IL-10-dependent miRNA playing a role in IL-10-mediated suppression of TNF-α, IL-6, and the p40 subunit of IL-12 (IL12p40) produced by primary human monocytes following activation of Toll-like receptor 4 (TLR4). Ectopic expression of miR-187 consistently and selectively reduces TNFα, IL-6, and IL-12p40 produced by LPS-activated monocytes. Conversely, the production of LPS-induced TNF-α, IL-6, and IL-12p40 is increased significantly when miR-187 expression is silenced. Our data demonstrate that miR-187 directly targets TNF-α mRNA stability and translation and indirectly decreases IL-6 and IL-12p40 expression via down-modulation of IκBζ, a master regulator of the transcription of these latter two cytokines. These results uncover an miRNA-mediated pathway controlling cytokine expression and demonstrate a central role of miR-187 in the physiological regulation of IL-10-driven anti-inflammatory responses.