Staphylococcus aureus is a dangerous pathogen that can cause necrotizing infections characterized by massive inflammatory responses and tissue destruction. Staphylococcal α-hemolysin is an essential virulence factor in severe S. aureus pneumonia. It activates the nucleotide-binding domain and leucine-rich repeat containing gene family, pyrin domain containing 3 (NLRP3) inflammasome to induce production of interleukin-1β and programmed necrotic cell death. We sought to determine the role of α-hemolysin-mediated activation of NLRP3 in the pathogenesis of S. aureus pneumonia. We show that α-hemolysin activates the NLRP3 inflammasome during S. aureus pneumonia, inducing necrotic pulmonary injury. Moreover, Nlrp3(-/-) mice have less-severe pneumonia. Pulmonary injury induced by isolated α-hemolysin or live S. aureus is independent of interleukin-1β signaling, implicating NLRP3-induced necrosis in the pathogenesis of severe infection. This work demonstrates the exploitation of host inflammatory signaling by S. aureus and suggests the NLRP3 inflammasome as a potential target for pharmacologic interventions in severe S. aureus infections.

(PGE2) has complex effects on airway tone, and the existence of four PGE2 [E-prostanoid (EP)] receptors, each with distinct signaling characteristics, has provided a possible explanation for the seemingly contradictory actions of this lipid mediator. To identify the receptors mediating the actions of PGE2 on bronchomotor tone, we examined its effects on the airways of wild-type and EP receptor-deficient mice. In conscious mice the administration of PGE2 increased airway responsiveness primarily through the EP1 receptor, although on certain genetic backgrounds a contribution of the EP3 receptor was detected. These effects of PGE2 were eliminated by pretreatment with either atropine or bupivacaine and were undetectable in anesthetized mice or in denervated tracheal rings, where only EP2-mediated relaxation of airway smooth muscle was observed. Together, our findings are consistent with a model in which PGE2 modulates airway tone by activating multiple receptors expressed on various cell populations and in which the relative contribution of these receptors might depend on the expression of modifier alleles. PGE2/EP1/EP3-induced airway constriction occurs indirectly through activation of neural pathways, whereas PGE2-induced bronchodilation results from direct activation of EP2 receptors on airway smooth muscle. This segregation of EP receptor function within the airway suggests that PGE2 analogs that selectively activate the EP2 receptor without activating the EP1/EP3 receptors might prove useful in the treatment of asthma. PGE2 receptor; bronchoconstriction; bronchodilation; knockout; nerves SHORTLY AFTER ITS DISCOVERY in the 1960s, prostaglandin E 2 (PGE 2 ) was observed to have potent relaxant effects on airway smooth muscle, making this endogenous lipid an attractive candidate drug for asthma (18,34). However, human studies with aerosolized PGE 2 have demonstrated inconsistent effects on airway tone, with most asthmatics showing a bronchodilator response but some developing profound bronchoconstriction requiring beta agonist rescue (6,19). Ex vivo studies from humans and animals have also shown that PGE 2 can both relax and constrict airway smooth muscle, a paradox explained when it was recognized that PGE 2 could act through more than one receptor (9,20,26).Four distinct cell surface receptors for PGE 2 [E-prostanoid (EP)] have been identified and cloned, each with unique signal transduction mechanisms as a result of coupling to different G proteins (23). Activation of one or a combination of receptors, each which may be differentially expressed on airway smooth muscle, epithelia, neurons, and immune effector cells, results in a specific physiological response. EP2 and EP4 receptors couple to G s , and activation of these receptors results in stimulation of adenylyl cyclase and increases in intracellular cAMP. Various EP3 isoforms, arising from the differential splicing of the EP3 gene, have been identified both in humans and in mice (1,24). Differences in the cytoplasmic domain of the EP3 receptor leads to th...

The contribution of NLRP3, a member of the nucleotide-binding domain leucine-rich repeat containing (NLR) family, in the development of allergic airway disease is currently controversial. Here, we used multiple allergic asthma models to examine the physiologic role of NLRP3. We found no significant differences in airway eosinophilia, histopathology, mucus production and airway hyperreactivity between wild type and Nlrp3-/- mice in either acute (alum-dependent) or chronic (alum-independent) OVA models. In addition to the OVA model, we also did not detect a role for NLRP3 in the development of allergic airway disease induced by either acute or chronic house dust mite (HDM) antigen exposure. While we did not observe significant phenotypic differences in any of the models tested, we did observe a significant reduction of IL-13 and IL-33 in Nlrp3-/- mice compared to wild type controls in the chronic OVA model without added alum. In all of the allergic airway disease models, the levels of the NLRP3 inflammasome associated cytokines IL-1β and IL-18 in the lung were below the level of detection. In sum, this report surveyed four different allergic asthma models and found a modest and selected role for NLRP3 in the alum-free OVA model. However this difference did not greatly alter the clinical outcome of the disease. This suggests that the role of NLRP3 in allergic asthma has to be re-evaluated.

Primary ciliary dyskinesia (PCD) is a genetic disorder in which impaired ciliary function leads to chronic airway disease. Exome sequencing of a PCD subject identified an apparent homozygous frameshift variant, c.887_890delTAAG (p.Val296Glyfs*13), in exon 5; this frameshift introduces a stop codon in amino acid 308 of the growth arrest-specific protein 2-like 2 (GAS2L2). Further genetic screening of unrelated PCD subjects identified a second proband with a compound heterozygous variant carrying the identical frameshift variant and a large deletion (c.867_*343þ1207del; p.?) starting in exon 5. Both individuals had clinical features of PCD but normal ciliary axoneme structure. In this research, using human nasal cells, mouse models, and X.laevis embryos, we show that GAS2L2 is abundant at the apical surface of ciliated cells, where it localizes with basal bodies, basal feet, rootlets, and actin filaments. Cultured GAS2L2deficient nasal epithelial cells from one of the affected individuals showed defects in ciliary orientation and had an asynchronous and hyperkinetic (GAS2L2-deficient ¼ 19.8 Hz versus control ¼ 15.8 Hz) ciliary-beat pattern. These results were recapitulated in Gas2l2 À/À mouse tracheal epithelial cell (mTEC) cultures and in X. laevis embryos treated with Gas2l2 morpholinos. In mice, the absence of Gas2l2 caused neonatal death, and the conditional deletion of Gas2l2 impaired mucociliary clearance (MCC) and led to mucus accumulation. These results show that a pathogenic variant in GAS2L2 causes a genetic defect in ciliary orientation and impairs MCC and results in PCD.

Among the 22 members of the nucleotide binding-domain, leucine rich repeat-containing (NLR) family, less than half have been functionally characterized. Of those that have been well studied, most form caspase-1 activating inflammasomes. NLRP12 is a unique NLR that has been shown to attenuate inflammatory pathways in biochemical assays and mediate the lymph node homing of activated skin dendritic cells in contact hypersensitivity responses. Since the mechanism between these two important observations remains elusive, we further evaluated the contribution of NLRP12 to organ specific adaptive immune responses by focusing on the lung, which, like skin, is exposed to both exogenous and endogenous inflammatory agents. In models of allergic airway inflammation induced by either acute ovalbumin (OVA) exposure or chronic house dust mite (HDM) antigen exposure, Nlrp12−/− mice displayed subtle differences in eosinophil and monocyte infiltration into the airways. However, the overall development of allergic airway disease and airway function was not significantly altered by NLRP12 deficiency. Together, the combined data suggest that NLRP12 does not play a vital role in regulating Th2 driven airway inflammation using common model systems that are physiologically relevant to human disease. Thus, the allergic airway inflammation models described here should be appropriate for subsequent studies that seek to decipher the contribution of NLRP12 in mediating the host response to agents associated with asthma exacerbation.