Receptor-interacting protein 2 gene silencing attenuates allergic airway inflammation.

Persistent activation of NF-κB has been associated with the development of asthma. Receptor-interacting protein 2 (Rip2) is a transcriptional product of NF-κB activation. It is an adaptor protein with serine/threonine kinase activity and has been shown to positively regulate NF-κB activity. We investigated potential protective effects of Rip2 gene silencing using small interfering RNA (siRNA) in an OVA-induced mouse asthma model. Rip2 protein level was found to be upregulated in allergic airway inflammation. A potent and selective Rip2 siRNA given intratracheally knocked down Rip2 expression in OVA-challenged lungs and reduced OVA-induced increases in total and eosinophil counts, and IL-4, IL-5, IL-13, IL-1ß, IL-33, and eotaxin levels in bronchoalveolar lavage fluid. Rip2 silencing blocked OVA-induced inflammatory cell infiltration and mucus hypersecretion as observed in lung sections, and mRNA expression of ICAM-1, VCAM-1, E-selectin, RANTES, IL-17, IL-33, thymic stromal lymphopoietin, inducible NO synthase, and MUC5ac in lung tissues. In addition, elevation of serum OVA-specific IgE level in mouse asthma model was markedly suppressed by Rip2 siRNA, together with reduced IL-4, IL-5, and IL-13 production in lymph node cultures. Furthermore, Rip2 siRNA-treated mice produced significantly less airway hyperresponsiveness induced by methacholine. Mechanistically, Rip2 siRNA was found to enhance cytosolic level of IκBα and block p65 nuclear translocation and DNA-binding activity in lung tissues from OVA-challenged mice. Taken together, our findings clearly show that knockdown of Rip2 by gene silencing ameliorates experimental allergic airway inflammation, probably via interruption of NF-κB activity, confirming Rip2 a novel therapeutic target for the treatment of allergic asthma.

Carbonylation caused by cigarette smoke extract is associated with defective macrophage immunity.

Oxidants in cigarette smoke inhibit pathogen recognition receptor function and phagocytosis, but the molecular basis of this inhibition remains obscure. We sought to identify the inhibitory mechanisms that impair alveolar macrophage function. Balb/c mice were acutely exposed to four cigarettes for 4 hours before treatment with intranasal LPS (1 µg). The mice exhibited significantly reduced airway neutrophilia and expression of TNF-α. Balb/c-derived MH-S alveolar macrophage cells exposed to cigarette smoke extract (CSE) displayed a similar inhibitory response to stimulation with LPS. The induction of inflammatory genes by recombinant (r) TNF-α (100 ng/ml) was also impaired by CSE. Because both pathways converge on NF-κB, the degradation of IκBα and the phosphorylation of p65 were assessed and shown to be blunted by CSE. CSE also blocked the activity of activator protein-1 (AP-1) by inhibiting p38 mitogen activated protein kinase (MAPK) in a reduced glutathione (GSH)-reversible manner. The induction of specific Toll-like receptor (TLR)-negative regulators (suppressor of cytokine signaling-1 [SOCS-1], interleukin-1 receptor associated kinase-M [IRAK-M], and IL-10) did not account for the impaired responses of TLRs. As free radical species are abundant in CSE and GSH restored function, a panel of oxidative/nitrosative stress markers was screened using immunocytochemistry. The panel identified protein carbonylation as the major CSE-inducible marker. Oxyblot analysis confirmed that CSE potently introduced carbonyl groups to many proteins in a dose-dependent and time-dependent manner that inversely correlated with the expression of TNF-α. The formation of pseudopodia was not prevented, but these membrane extensions were heavily carbonylated, and primary alveolar macrophages were also targeted for carbonylation. Oxidants in cigarette smoke drive a rapid, persistent, and global protein carbonylation that may represent a common pathway to altered immunity in disease.