Synthetic oligodeoxynucleotides containing suppressive TTAGGG motifs inhibit AIM2 inflammasome activation.

Synthetic oligodeoxynucleotides (ODNs) comprised of the immunosuppressive motif TTAGGG block TLR9 signaling, prevent STAT1 and STAT4 phosphorylation and attenuate a variety of inflammatory responses in vivo. In this study, we demonstrate that such suppressive ODN abrogate activation of cytosolic nucleic acid-sensing pathways. Pretreatment of dendritic cells and macrophages with the suppressive ODN-A151 abrogated type I IFN, TNF-α, and ISG induction in response to cytosolic dsDNA. In addition, A151 abrogated caspase-1-dependent IL-1ß and IL-18 maturation in dendritic cells stimulated with dsDNA and murine CMV. Inhibition was dependent on A151's phosphorothioate backbone, whereas substitution of the guanosine residues for adenosine negatively affected potency. A151 mediates these effects by binding to AIM2 in a manner that is competitive with immune-stimulatory DNA and as a consequence prevents AIM2 inflammasome complex formation. Collectively, these findings reveal a new route by which suppressive ODNs modulate the immune system and unveil novel applications for suppressive ODNs in the treatment of infectious and autoimmune diseases.

Endothelial cilia are fluid shear sensors that regulate calcium signaling and nitric oxide production through polycystin-1.

BACKGROUND: When challenged with extracellular fluid shear stress, vascular endothelial cells are known to release nitric oxide, an important vasodilator. Here, we show that the ability of cultured endothelial cells to sense a low range of fluid shear depends on apical membrane organelles, called cilia, and that cilia are compartments required for proper localization and function of the mechanosensitive polycystin-1 molecule. METHODS AND RESULTS: Cells with the Pkd1(null/null) or Tg737(orpk/orpk) mutation encoded for polycystin-1 or polaris, respectively, are unable to transmit extracellular shear stress into intracellular calcium signaling and biochemical nitric oxide synthesis. Cytosolic calcium and nitric oxide recordings further show that fluid shear sensing is a cilia-specific mechanism because other mechanical or pharmacological stimulation does not abolish calcium and nitric oxide signaling in polycystin-1 and polaris mutant endothelial cells. Polycystin-1 localized in the basal body of Tg737(orpk/orpk) endothelial cells is insufficient for a fluid shear stress response. Furthermore, the optimal shear stress to which the cells respond best does not alter the apical cilia structure but modifies the responsiveness of cells to higher shear stresses through proteolytic modification of polycystin-1. CONCLUSIONS: We demonstrate for the first time that polycystin-1 (required for cilia function) and polaris (required for cilia structure) are crucial mechanosensitive molecules in endothelial cells. We propose that a distinctive communication with the extracellular microenvironment depends on the proper localization and function of polycystin-1 in cilia.

Pattern recognition receptors and the innate immune response to viral infection.

The innate immune response to viral pathogens is critical in order to mobilize protective immunity. Cells of the innate immune system detect viral infection largely through germline-encoded pattern recognition receptors (PRRs) present either on the cell surface or within distinct intracellular compartments. These include the Toll-like receptors (TLRs), the retinoic acid-inducble gene I-like receptors (RLRs), the nucleotide oligomerization domain-like receptors (NLRs, also called NACHT, LRR and PYD domain proteins) and cytosolic DNA sensors. While in certain cases viral proteins are the trigger of these receptors, the predominant viral activators are nucleic acids. The presence of viral sensing PRRs in multiple cellular compartments allows innate cells to recognize and quickly respond to a broad range of viruses, which replicate in different cellular compartments. Here, we review the role of PRRs and associated signaling pathways in detecting viral pathogens in order to evoke production of interferons and cytokines. By highlighting recent progress in these areas, we hope to convey a greater understanding of how viruses activate PRR signaling and how this interaction shapes the anti-viral immune response.