Xikun Zhou

MicroRNA-302b augments host defense to bacteria by regulating inflammatory responses via feedback to TLR/IRAK4 circuits

Summary MicroRNAs (miRNAs) have been implicated in a spectrum of physiological and pathological conditions, including immune responses. miR-302b has been implicated in stem cell differentiation but its role in immunity remains unknown. Here we show that miR-302b is induced by TLR2 and TLR4 through ERK-p38-NF-κB signaling upon Gram-negative bacterium Pseudomonas aeruginosa infection. Suppression of inflammatory responses to bacterial infection is mediated by targeting IRAK4, a protein required for the activation and nuclear translocation of NF-κB. Through negative feedback, enforced expression of miR-302b or IRAK4 siRNA silencing inhibits downstream NF-κB signaling and airway leukocyte infiltration, thereby alleviating lung injury and increasing survival in P. aeruginosa-infected mice. In contrast, miR-302b inhibitors exacerbate inflammatory responses and decrease survival in P. aeruginosa-infected mice and lung cells. These findings reveal that miR-302b is a novel inflammatory regulator of NF-κB activation in respiratory bacterial infections by providing negative feedback to TLRs-mediated immunity.

Lyn regulates inflammatory responses in Klebsiella pneumoniae infection via the p38/NF-κB pathway

Klebsiella pneumoniae (Kp) is one of the most common pathogens in nosocomial infections and is becoming increasingly multidrug resistant. However, the underlying molecular pathogenesis of this bacterium remains elusive, limiting the therapeutic options. Understanding the mechanism of its pathogenesis may facilitate the development of anti‐bacterial therapeutics. Here, we show that Lyn, a pleiotropic Src tyrosine kinase, is involved in host defense against Kp by regulating phagocytosis process and simultaneously downregulating inflammatory responses. Using acute infection mouse models, we observed that lyn−/− mice were more susceptible to Kp with increased mortality and severe lung injury compared with WT mice. Kp infected‐lyn−/− mice exhibited elevated inflammatory cytokines (IL‐6 and TNF‐α), and increased superoxide in the lung and other organs. In addition, the phosphorylation of p38 and NF‐κB p65 subunit increased markedly in response to Kp infection in lyn−/− mice. We also demonstrated that the translocation of p65 from cytoplasm to nuclei increased in cultured murine lung epithelial cells by Lyn siRNA knockdown. Furthermore, lipid rafts clustered with activated Lyn and accumulated in the site of Kp invasion. Taken together, these findings revealed that Lyn may participate in host defense against Kp infection through the negative modulation of inflammatory cytokines.

Atg7 Enhances Host Defense against Infection via Downregulation of Superoxide but Upregulation of Nitric Oxide

Pseudomonas aeruginosa is an opportunistic bacterium that can cause serious infection in immunocompromised individuals. Although autophagy may augment immune responses against P. aeruginosa infection in macrophages, the critical components and their role of autophagy in host defense are largely unknown. In this study, we show that P. aeruginosa infection–induced autophagy activates JAK2/STAT1α and increases NO production. Knocking down Atg7 resulted in increased IFN-γ release, excessive reactive oxygen species, and increased Src homology-2 domain-containing phosphatase 2 activity, which led to lowered phosphorylation of JAK2/STAT1α and subdued expression of NO synthase 2 (NOS2). In addition, we demonstrated the physiological relevance of dysregulated NO under Atg7 deficiency as atg7−/− mice were more susceptible to P. aeruginosa infection with increased mortality and severe lung injury than wild-type mice. Furthermore, P. aeruginosa–infected atg7−/− mice exhibited increased oxidation but decreased bacterial clearance in the lung and other organs compared with wild-type mice. Mechanistically, atg7 deficiency suppressed NOS2 activity by downmodulating JAK2/STAT1α, leading to decreased NO both in vitro and in vivo. Taken together, these findings revealed that the JAK2/STAT1α/NOS2 dysfunction leads to dysregulated immune responses and worsened disease phenotypes.

Lyn Delivers Bacteria to Lysosomes for Eradication through TLR2-Initiated Autophagy Related Phagocytosis

Extracellular bacteria, such as Pseudomonas aeruginosa and Klebsiella pneumoniae, have been reported to induce autophagy; however, the role and machinery of infection-induced autophagy remain elusive. We show that the pleiotropic Src kinase Lyn mediates phagocytosis and autophagosome maturation in alveolar macrophages (AM), which facilitates eventual bacterial eradication. We report that Lyn is required for bacterial infection-induced recruitment of autophagic components to pathogen-containing phagosomes. When we blocked autophagy with 3-methyladenine (3-MA) or by depleting Lyn, we observed less phagocytosis and subsequent bacterial clearance by AM. Both morphological and biological evidence demonstrated that Lyn delivered bacteria to lysosomes through xenophagy. TLR2 initiated the phagocytic process and activated Lyn following infection. Cytoskeletal trafficking proteins, such as Rab5 and Rab7, critically facilitated early phagosome formation, autophagosome maturation, and eventual autophagy-mediated bacterial degradation. These findings reveal that Lyn, TLR2 and Rab modulate autophagy related phagocytosis and augment bactericidal activity, which may offer insight into novel therapeutic strategies to control lung infection.

Atg7 deficiency impairs host defense against Klebsiella pneumoniae by impacting bacterial clearance, survival and inflammatory responses in mice.

Klebsiella pneumoniae (Kp) is a Gram-negative bacterium that can cause serious infections in humans. Autophagy-related gene 7 (Atg7) has been implicated in certain bacterial infections; however, the role of Atg7 in macrophage-mediated immunity against Kp infection has not been elucidated. Here we showed that Atg7 expression was significantly increased in murine alveolar macrophages (MH-S) upon Kp infection, indicating that Atg7 participated in host defense. Knocking down Atg7 with small-interfering RNA increased bacterial burdens in MH-S cells. Using cell biology assays and whole animal imaging analysis, we found that compared with wild-type mice atg7 knockout (KO) mice exhibited increased susceptibility to Kp infection, with decreased survival rates, decreased bacterial clearance, and intensified lung injury. Moreover, Kp infection induced excessive proinflammatory cytokines and superoxide in the lung of atg7 KO mice. Similarly, silencing Atg7 in MH-S cells markedly increased expression levels of proinflammatory cytokines. Collectively, these findings reveal that Atg7 offers critical resistance to Kp infection by modulating both systemic and local production of proinflammatory cytokines.

Transient Receptor Potential Channel 1 Deficiency Impairs Host Defense and Proinflammatory Responses to Bacterial Infection by Regulating Protein Kinase Cα Signaling

ABSTRACT Transient receptor potential channel 1 (TRPC1) is a nonselective cation channel that is required for Ca2+ homeostasis necessary for cellular functions. However, whether TRPC1 is involved in infectious disease remains unknown. Here, we report a novel function for TRPC1 in host defense against Gram-negative bacteria. TRPC1−/− mice exhibited decreased survival, severe lung injury, and systemic bacterial dissemination upon infection. Furthermore, silencing of TRPC1 showed decreased Ca2+ entry, reduced proinflammatory cytokines, and lowered bacterial clearance. Importantly, TRPC1 functioned as an endogenous Ca2+ entry channel critical for proinflammatory cytokine production in both alveolar macrophages and epithelial cells. We further identified that bacterium-mediated activation of TRPC1 was dependent on Toll-like receptor 4 (TLR4), which induced endoplasmic reticulum (ER) store depletion. After activation of phospholipase Cγ (PLC-γ), TRPC1 mediated Ca2+ entry and triggered protein kinase Cα (PKCα) activity to facilitate nuclear translocation of NF-κB/Jun N-terminal protein kinase (JNK) and augment the proinflammatory response, leading to tissue damage and eventually mortality. These findings reveal that TRPC1 is required for host defense against bacterial infections through the TLR4-TRPC1-PKCα signaling circuit.

FIP200 is Involved in Murine Pseudomonas Infection by Regulating HMGB1 Intracellular Translocation

Background: FIP200, a critical autophagy initiating protein, can participate in numerous cellular functions including cancer development; however, its functional role in P. aeruginosa infection of alveolar macrophages is unknown. Methods: To investigate the role of FIP200 in host defense, we transfected murine alveolar macrophage MH-S cells with FIP200 siRNA. Having confirmed that FIP200 knockdown inhibited PAO1-induced autophagosme formation, we sought to characterize the underlying signaling pathways by immunoblotting. Further, we used fip200 KO mice to study the effects of fip200 deficiency on HMGB1 translocation. Results: We showed that Pseudomonas PAO1 strain infection facilitated autophagosome formation, whereas knockdown of FIP200 inhibited autophagosome formation and HMGB1 expression in MH-S cells. Silencing FIP200 impaired the translocation of HMGB1 to cytosol of MH-S cells and almost abolished acetylation of HMGB1 during PAO1 infection. In contrast, FIP200 overexpression facilitated the cytosol translocation of HMGB1 from nuclei and increased acetylation of HMGB1 in PAO1-infected MH-S cells. Importantly, expression and acetylation of HMGB1 were also significantly down-regulated in fip200 KO mice following PAO1 infection. Conclusions: Collectively, these findings elucidate that FIP200 may regulate expression and translocation of HMGB1 during PAO1 infection, which may indicate novel therapeutic targets to control pulmonary infection.

Photosensitive Fluorescent Dye Contributes to Phototoxicity and Inflammatory Responses of Dye-doped Silica NPs in Cells and Mice

Dye-doped fluorescent silica nanoparticles provide highly intense and photostable fluorescence signals. However, some dopant dye molecules are photosensitive. A widely-used photosensitive fluorescent dopant, RuBpy, was chosen to systematically investigate the phototoxicity of the dye-doped silica nanoparticles (NPs). We investigated cell viability, DNA damage, and Reactive Oxygen Species (ROS) levels in alveolar macrophages using the dye-doped NPs with or without irradiation. Our results showed that the RuBpy-doped silica NPs could induce significant amount of ROS, DNA damage, apoptosis and impaired proliferation in MH-S cells. In vivo studies in mice showed that RuBpy-doped silica NPs induced significant inflammatory cytokine production and lowered expression in signaling proteins such as ERK1/2 and NF-κB as well as increased lung injury determined by myeloperoxidase and lipid peroxidation. Strikingly, we also found that both RuBpy alone and NPs induced systemic signaling activation in the kidney compared to the liver and lung where showed highly selective signaling patterns, which is more pronounced than RuBpy-doped silica NPs. Moreover, we discovered a critical biomarker (e.g., HMGB1) for silica NPs-induced stress and toxicity and demonstrated differentially-regulated response patterns in various organs. Our results indicate for the first time that the RuBpy-doped silica NPs may impose less inflammatory responses but stronger thermotherapeutic effects on target cells in animals than naked NPs in a time- and dose-dependent manner.

Pseudomonas aeruginosa infection augments inflammation through miR-301b repression of c-Myb-mediated immune activation and infiltration

MicroRNAs (miRNAs) play critical roles in various biological processes, including cell proliferation, development and host defence. However, the molecular mechanism for miRNAs in regulating bacterial-induced inflammation remains largely unclear. Here, we report that miR-301b augments pro-inflammatory response during pulmonary infection, and caffeine suppresses the effect of miR-301b and thereby augments respiratory immunity. LPS treatment or Pseudomonas aeruginosa infection induces miR-301b expression via a TLR4/MyD88/NF-κB pathway. Importantly, caffeine decreases miR-301b expression through negative regulation of the cAMP/PKA/NF-κB axis. Further, c-Myb is identified as a target of miR-301b, which positively modulates anti-inflammatory cytokines IL-4 and TGF-β1, but negatively regulates pro-inflammatory cytokines MIP-1α and IL-17A. Moreover, repression of miR-301b results in increased transcription of c-Myb and elevated levels of neutrophil infiltration, thereby alleviating infectious symptoms in mice. These findings reveal miR-301b as a new controller of inflammatory response by repressing c-Myb function to inhibit the anti-inflammatory response to bacterial infection, representing a novel mechanism for balancing inflammation.

DNA repair interacts with autophagy to regulate inflammatory responses to pulmonary hyperoxia

Oxygen is supplied as a supportive treatment for patients suffering from acute respiratory distress syndrome. Unfortunately, high oxygen concentration increases reactive oxygen species generation, which causes DNA damage and ultimately cell death in the lung. Although 8-oxoguanine-DNA glycosylase (OGG-1) is involved in repairing hyperoxia-mediated DNA damage, the underlying molecular mechanism remains elusive. In this study, we report that ogg-1–deficient mice exhibited a significant increase of proinflammatory cytokines (TNF-α, IL-6, and IFN-γ) in the lung after being exposed to 95% oxygen. In addition, we found that ogg-1 deficiency downregulated (macro)autophagy when exposed to hyperoxia both in vitro and in vivo, which was evident by decreased conversion of LC3-I to LC3-II, reduced LC3 punctate staining, and lower Atg7 expression compared with controls. Using a chromatin immunoprecipitation assay, we found that OGG-1 associated with the promoter of Atg7, suggesting a role for OGG1 in regulation of Atg7 activity. Knocking down OGG-1 decreased the luciferase reporter activity of Atg7. Further, inflammatory cytokine levels in murine lung epithelial cell line cells were downregulated following autophagy induction by starvation and rapamycin treatment, and upregulated when autophagy was blocked using 3-methyladenine and chloroquine. atg7 knockout mice and Atg7 small interfering RNA-treated cells exhibited elevated levels of phospho–NF-κB and intensified inflammatory cytokines, suggesting that Atg7 impacts inflammatory responses to hyperoxia. These findings demonstrate that OGG-1 negatively regulates inflammatory cytokine release by coordinating molecular interaction with the autophagic pathway in hyperoxia-induced lung injury.