Airway epithelial control of Pseudomonas aeruginosa infection in cystic fibrosis

Defective expression or function of the cystic fibrosis transmembrane conductance regulator (CFTR) underlies the hypersusceptibility of cystic fibrosis (CF) patients to chronic airway infections, particularly with Pseudomonas aeruginosa. CFTR is involved in the specific recognition of P. aeruginosa, thereby contributing to effective innate immunity and proper hydration of the airway surface layer (ASL). In CF, the airway epithelium fails to initiate an appropriate innate immune response, allowing the microbe to bind to mucus plugs that are then not properly cleared because of the dehydrated ASL. Recent studies have identified numerous CFTR-dependent factors that are recruited to the epithelial plasma membrane in response to infection and that are needed for bacterial clearance, a process that is defective in CF patients hypersusceptible to infection with this organism.     

IL-18通过MyD88依赖信号途径调控CSF-1表达

IL-18是IL-1家族的一个成员,最初发现被命名为IFN-γ诱导因子.现在研究表明,IL-18是炎症反应的重要标志,参与许多慢性炎症和自身免疫性疾病炎性反应.证明了IL-18在JurkatT淋巴细胞的炎症反应中能够调节CSF-1的表达,其信号机制是IL-18通过MyD88-NF-κB-CSF-1信号途径上调CSF-1的基因转录.     

IL-1 receptor-mediated signal is an essential component of MyD88-dependent innate response to Mycobacterium tuberculosis infection

MyD88, the common adapter involved in TLR, IL-1, and IL-18 receptor signaling, is essential for the control of acute Mycobacterium tuberculosis (MTB) infection. Although TLR2, TLR4, and TLR9 have been implicated in the response to mycobacteria, gene disruption for these TLRs impairs only the long-term control of MTB infection. Here, we addressed the respective role of IL-1 and IL-18 receptor pathways in the MyD88-dependent control of acute MTB infection. Mice deficient for IL-1R1, IL-18R, or Toll-IL-1R domain-containing adaptor protein (TIRAP) were compared with MyD88-deficient mice in an acute model of aerogenic MTB infection. Although primary MyD88-deficient macrophages and dendritic cells were defective in cytokine production in response to mycobacterial stimulation, IL-1R1-deficient macrophages exhibited only a reduced IL-12p40 secretion with unaffected TNF, IL-6, and NO production and up-regulation of costimulatory molecules CD40 and CD86. Aerogenic MTB infection of IL-1R1-deficient mice was lethal within 4 wk with 2-log higher bacterial load in the lung and necrotic pneumonia but efficient pulmonary CD4 and CD8 T cell responses, as seen in MyD88-deficient mice. Mice deficient for IL-18R or TIRAP controlled acute MTB infection. These data demonstrate that absence of IL-1R signal leads to a dramatic defect of early control of MTB infection similar to that seen in the absence of MyD88, whereas IL-18R and TIRAP are dispensable, and that IL-1, together with IL-1-induced innate response, might account for most of MyD88-dependent host response to control acute MTB infection.     

MyD88/IL-18-dependent pathways rather than TLRs control early parasitaemia in non-lethal Plasmodium yoelii infection

Plasmodium falciparum GPI contributes to malaria pathology by inducing cytokine release. It has been shown to be recognized through TLR2 and to a lesser extent TLR4 in vitro. However, previous findings on the role of TLRs in parasite clearance or pathology in vivo are conflicting. Thus, we analyzed the impact of TLR-signalling on protection using the P. yoelii infection model. Deficiency of single TLRs as well as triple TLR2/4/9-deficiency had no impact on parasitaemia. In contrast, mice deficient for the adaptor protein MyD88 were more susceptible to P. yoelii infection in that they exhibited an increased parasitaemia in the early phase of the infection and a higher lethality. This phenotype was caused mainly by impaired IL-18 signalling since parasitaemia in IL-18-deficient mice was also increased at early time points during P. yoelii infection compared to wild-type control mice. However, no lethality was observed in IL-18-deficient mice. Since parasitaemia in IL-1R-deficient mice was also slightly increased during P. yoelii infection, impaired IL-1R signalling contributed to the increased susceptibility of MyD88-deficient mice to a lesser extent. These findings correlated with a reduced IFN-gamma production in MyD88- and IL-18-deficient mice, but not in TLR2/4/9-deficient mice. We conclude that mainly IL-18/MyD88-dependent signalling but not TLR2/4/9-signalling is important for early parasite control in our model.     

Role of interleukin-1 and MyD88-dependent signaling in rhinovirus infection

Rhinoviral infection is an important trigger of acute inflammatory exacerbations in patients with underlying airway disease. We have previously established that interleukin-1β (IL-1β) is central in the communication between epithelial cells and monocytes during the initiation of inflammation. In this study we explored the roles of IL-1β and its signaling pathways in the responses of airway cells to rhinovirus-1B (RV-1B) and further determined how responses to RV-1B were modified in a model of bacterial coinfection. Our results revealed that IL-1β dramatically potentiated RV-1B-induced proinflammatory responses, and while monocytes did not directly amplify responses to RV-1B alone, they played an important role in the responses observed with our coinfection model. MyD88 is the essential signaling adapter for IL-1β and most Toll-like receptors. To examine the role of MyD88 in more detail, we created stable MyD88 knockdown epithelial cells using short hairpin RNA (shRNA) targeted to MyD88. We determined that IL-1β/MyD88 plays a role in regulating RV-1B replication and the inflammatory response to viral infection of airway cells. These results identify central roles for IL-1β and its signaling pathways in the production of CXCL8, a potent neutrophil chemoattractant, in viral infection. Thus, IL-1β is a viable target for controlling the neutrophilia that is often found in inflammatory airway disease and is exacerbated by viral infection of the airways.     

Sex hormone affects the severity of non-alcoholic steatohepatitis through the MyD88-dependent IL-6 signaling pathway

Recent research has shown that the occurrence of gender disparity in liver cancer associated with sex differences in MyD88-dependent IL-6 production, but the role of this signaling pathway in sex differences of non-alcoholic steatohepatitis (NASH) remains unknown. To investigate the effects of sex hormone-specific intervention on pathology and progression of NASH, and on the inflammatory TLR-MyD88-IL-6 signaling pathway NASH was modeled in C57/BL6 mice by feeding a methionine and choline-deficient (MCD) diet for 4 weeks. Male mice were subjected to sex hormone-related interventions such as orchidectomy, and orchidectomy combined with administration of either testosterone propionate or estradiol benzoate. Next, the degree of non-alcoholic fatty liver disease activity score (NAS), serum levels of alanine aminotransferase (ALT) and aspartate aminotransferase (AST), and the expression level of MyD88 and IL-6, were compared between these groups. Males developed more serious inflammatory problems and had a higher NAS than the females. Sex-specific intervention in male mice by orchidectomy reduced NAS, ALT, and AST, and the expression level of MyD88 and IL-6. But administration of exogenous androgen had no influence on either NAS or the expression of ALT, AST, MyD88, and IL-6. On the other hand, exogenous estrogen could alleviate the pathological damage caused by NASH, as well as reduce NAS, ALT and AST, and the expression of MyD88 and IL-6. The result show different sex hormone-related interventions affected the severity of NASH, possibly by modulating the level of sex hormones and regulating the TLR-MyD88-IL-6 signaling pathway.     

MyD88-dependent pathway accelerates the liver damage of Concanavalin A-induced hepatitis

We have explored the pathological role of the MyD88 signaling pathway via Toll-like receptors (TLRs) that mediate the recognition of pathogen-associated molecular patterns (PAMPs) in a murine model of autoimmune hepatitis induced by administering Concanavalin A (ConA). We first found that various TLRs and MyD88 molecules were expressed in liver of Con A-treated and untreated wild-type (WT) mice including liver macrophages. Flowcytometric analysis revealed that liver CD11b⁺CD11c⁻ and CD11b⁺CD11c⁺ antigen-presenting cells express TLR2, although NK and NKT cells did not. When WT and MyD88^−/− mice were intravenously administered with Con A, the severity of hepatitis was significantly lower in Con A-injected MyD88^−/− mice than in WT mice in terms of the histopathology, the levels of serum transaminase and pro-inflammatory cytokines (TNF-α, IFN-γ, and IL-6), and upregulation of CD80/CD86 and TNF-α on/in liver macrophages. The results provide evidence of a possible contribution of the TLRs-MyD88 signaling pathway in activating TLR-expressing liver macrophages in the autoimmune hepatitis model, and thus indicate that the strategy of blockade of pathological pathogens via the intestinal lumen may be feasible for the treatment of the disease.     

MyD88-dependent IFN-gamma production by NK cells is key for control of Legionella pneumophila infection

Legionella pneumophila (Lpn) is a ubiquitous Gram-negative bacterium in aquatic systems and an opportunistic intracellular pathogen in immunocompromised humans causing a severe pneumonia known as Legionnaires' disease. Using a mouse model, we investigated molecular and cellular players in the innate immune response to infection with Lpn. We observed robust levels of inflammatory cytokines in the serum upon intranasal or i.v. infection with live, virulent Lpn, but not with inactivated or avirulent bacteria lacking the Icm/Dot type IV secretion system. Interestingly, Lpn-induced serum cytokines were readily detectable regardless of the capacity of Icm/Dot-proficient Lpn to replicate in host cells and the Lpn permissiveness of the host mice. We found NK cell-derived IFN-gamma to be the key cytokine in the resolution of Lpn infection, whereas type I IFNs did not appear to play a major role in our model. Accordingly, NK cell-depleted or IFN-II-R-deficient mice carried severely increased bacterial burdens or failed to control Lpn infection, respectively. Besides the dependence of inflammatory cytokine induction on Lpn virulence, we also demonstrate a strict requirement of MyD88 for this process, suggesting the involvement of TLRs in the recognition of Lpn. However, screening of several TLR-deficient hosts did not reveal a master TLR responsible for the sensing of an Lpn infection, but provided evidence for either redundancy of individual TLRs in Lpn recognition or TLR-independent induction of inflammatory responses.     

Regulation of MyD88 Aggregation and the MyD88-dependent Signaling Pathway by Sequestosome 1 and Histone Deacetylase 6

MyD88 is an essential adaptor molecule for Toll-like receptors (TLRs) and interleukin (IL)-1 receptor. MyD88 is thought to be present as condensed forms or aggregated structures in the cytoplasm, although the reason has not yet been clear. Here, we show that endogenous MyD88 is present as small speckle-like condensed structures, formation of which depends on MyD88 dimerization. In addition, formation of large aggregated structures is related to cytoplasmic accumulation of sequestosome 1 (SQSTM1; also known as p62) and histone deacetylase 6 (HDAC6), which are involved in accumulation of polyubiquitinated proteins. A gene knockdown study revealed that SQSTM1 and HDAC6 were required for MyD88 aggregation and exhibited a suppressive effect on TLR ligand-induced expression of IL-6 and NOS2 in RAW264.7 cells. SQSTM1 and HDAC6 were partially involved in suppression of several TLR4-mediated signaling events, including activation of p38 and JNK, but they hardly affected degradation of IκBα (inhibitor of nuclear factor κB). Biochemical induction of MyD88 oligomerization induced recruitment of SQSTM1 and HDAC6 to the MyD88-TRAF6 signaling complex. Repression of SQSTM1 and HDAC6 enhanced formation of the MyD88-TRAF6 complex and conversely decreased interaction of the ubiquitin-specific negative regulator CYLD with the complex. Furthermore, ubiquitin-binding regions on SQSTM1 and HDAC6 were essential for MyD88 aggregation but were not required for interaction with the MyD88 complex. Thus, our study reveals not only that SQSTM1 and HDAC6 are important determinants of aggregated localization of MyD88 but also that MyD88 activates a machinery of polyubiquitinated protein accumulation that has a modulatory effect on MyD88-dependent signal transduction.     

Streptococcus pneumoniae induces expression of the antibacterial CXC chemokine MIG/CXCL9 via MyD88-dependent signaling in a murine model of airway infection

MIG/CXCL9 belongs to the CXC family of chemokines and participates in the regulation of leukocyte-trafficking and angiogenesis. Certain chemokines, including human MIG/CXCL9, exert strong antibacterial activity in vitro, although the importance of this property in vivo is unknown. In the present study, we investigated the expression and a possible role for MIG/CXCL9 in host defense during mucosal airway infection caused by Streptococcus pneumoniae in vivo. We found that intranasal challenge of C57BL/6 wild-type mice with pneumococci elicited production of high levels of MIG/CXCL9 in the lungs via the MyD88-dependent signaling pathway. Whereas both human and murine MIG/CXCL9 showed efficient killing of S. pneumoniae in vitro, MIG/CXCL9 knock-out mice were not more susceptible to pneumococcal infection. Our data demonstrate that, in vivo this chemokine probably has a redundant role, acting together with other antibacterial peptides and chemokines, in innate and adaptive host defense mechanisms against pneumococcal infections.     

Central role of MyD88-dependent dendritic cell maturation and proinflammatory cytokine production to control Brucella abortus infection

Brucella abortus is a facultative intracellular bacterium that infects humans and domestic animals. The enhanced susceptibility to virulent B. abortus observed in MyD88 knockout (KO) mice led us to investigate the mechanisms involved in MyD88-dependent immune responses. First, we defined the role of MyD88 in dendritic cell (DC) maturation. In vitro as well as in vivo, B. abortus-exposed MyD88 KO DCs displayed a significant impairment on maturation as observed by expression of CD40, CD86, and MHC class II on CD11c+ cells. In addition, IL-12 and TNF-alpha production was totally abrogated in MyD88 KO DCs and macrophages. Furthermore, B. abortus-induced IL-12 production was found to be dependent on TLR2 in DC, but independent on TLR2 and TLR4 in macrophages. Additionally, we investigated the role of exogenous IL-12 and TNF-alpha administration on MyD88 KO control of B. abortus infection. Importantly, IL-12, but not TNF-alpha, was able to partially rescue host susceptibility in MyD88 KO-infected animals. Furthermore, we demonstrated the role played by TLR9 during virulent B. abortus infection. TLR9 KO-infected mice showed 1 log Brucella CFU higher than wild-type mice. Macrophages and DC from TLR9 KO mice showed reduced IL-12 and unaltered TNF-alpha production when these cells were stimulated with Brucella. Together, these results suggest that susceptibility of MyD88 KO mice to B. abortus is due to impaired DC maturation and lack of IL-12 synthesis. Additionally, DC activation during Brucella infection plays an important regulatory role by stimulating and programming T cells to produce IFN-gamma.     

IFN-alphabeta-mediated inflammatory responses and antiviral defense in liver is TLR9-independent but MyD88-dependent during murine cytomegalovirus infection

Chemokine responses critical for inflammation and promotion of effective innate control of murine CMV (MCMV) in liver have been shown to be dependent on immunoregulatory functions elicited by IFN-alphabeta. However, it remains to be determined whether upstream factors that promote viral sensing resulting in the rapid secretion of IFN-alphabeta in liver differ from those described in other tissues. Because plasmacytoid dendritic cells (pDCs) are known producers of high levels of systemic IFN-alpha in response to MCMV, this study examines the in vivo contribution of pDCs to IFN-alpha production in the liver, and whether production of the cytokine and ensuing inflammatory events are dependent on TLR9, MyD88, or both. We demonstrate that whereas MyD88 deficiency markedly impaired secretion of IFN-alpha, production of the cytokine was largely independent of TLR9 signaling, in the liver. MyD88 and TLR9 were needed for IFN-alpha production in the spleen. Moreover, hepatic but not splenic pDCs produced significant amounts of intracellular IFN-alpha in the absence of TLR9 function during infection. Furthermore, production of CCL2, CCL3, and IFN-gamma, as well as the accumulation of macrophages and NK cells, was not affected in the absence of functional TLR9 in the liver. In contrast, these responses were dramatically reduced in MyD88(-/-) mice. Additionally, MyD88(-/-) but not TLR9(-/-) mice exhibited increased sensitivity to virus infection in liver. Collectively, our results define contrasting compartmental functions for TLR9 and MyD88, and suggest that the infected tissue site uniquely contributes to the process of virus sensing and regulation of localized antiviral responses.     

Cutting edge: TNFR-associated factor (TRAF) 6 is essential for MyD88-dependent pathway but not toll/IL-1 receptor domain-containing adaptor-inducing IFN-beta (TRIF)-dependent pathway in TLR signaling

Signaling pathways from TLRs are mediated by the Toll/IL-1R (TIR) domain-containing adaptor molecules. TNF receptor-associated factor (TRAF) 6 is thought to activate NF-kappaB and MAPKs downstream of these TIR domain-containing proteins to induce production of inflammatory cytokines. However, the precise role of TRAF6 in signaling from individual TLRs has not been appropriately addressed. We analyzed macrophages from TRAF6-deficient mice and made the following observations. In the absence of TRAF6, 1) ligands for TLR2, TLR5, TLR7, and TLR9 failed to induce activation of NF-kappaB and MAPKs or production of inflammatory cytokines; 2) TLR4 ligand-induced cytokine production was remarkably reduced and activation of NF-kappaB and MAPKs was observed, albeit with delayed kinetics; and 3) in contrast with previously reported findings, TLR3 signaling was not affected. These results indicate that TRAF6 is essential for MyD88-dependent signaling but is not required for TIR domain-containing adaptor-inducing IFN-beta (TRIF)-dependent signaling.     

Heterotrimeric Gi/Go proteins modulate endothelial TLR signaling independent of the MyD88-dependent pathway

The innate immune recognition of bacterial lipopolysaccharide (LPS) is mediated by Toll-like receptor 4 (TLR4) and results in activation of proinflammatory signaling including NF-κB and MAPK pathways. Heterotrimeric G proteins have been previously implicated in LPS signaling in macrophages and monocytes. In the present study, we show that pertussis toxin sensitive heterotrimeric G proteins (Gα(i/o)) are involved in the activation of MAPK and Akt downstream of TLR2, TLR3, and TLR4 in endothelial cells. Gα(i/o) are also required for full activation of interferon signaling downstream of TLR3 and TLR4 but are not required for the activation of NF-κB. We find that Gα(i/o)-mediated activation of the MAPK is independent of the canonical MyD88, interleukin-1 receptor-associated kinase, and tumor necrosis factor receptor-associated factor 6 signaling cascade in LPS-stimulated cells. Taken together, the data presented here suggest that heterotrimeric G proteins are widely involved in TLR pathways along a signaling cascade that is distinct from MyD88-TRAF6.     

大鼠海马神经元TLR4介导的MyD88依赖途径在神经炎症中的作用

目的:研究大鼠海马神经元是否有Toll样受体4(TLR4)介导的的髓样分化因子88(MyD88)依赖途径及该途径的激活在神经炎症中的作用。方法:采用体外培养7 d的新生大鼠海马神经元,细胞免疫荧光双标法鉴定海马神经元纯度。用TLR4配体脂多糖(LPS)或TLR4抗体预处理海马神经元,以激活或阻断TLR4的作用。实时定量PCR(RT-qPCR)方法检测海马神经元中MyD88、肿瘤坏死因子受体相关因子6(TRAF6)mRNA的表达;Westernblot方法测定海马神经元MyD88和TRAF6蛋白水平;细胞免疫荧光双标法观察海马神经元中核因子κB/P65(NF-κB/P65)的表达定位及TLR4激活或阻断后NF-κB/P65核易位情况;ELISA检测培养上清液中肿瘤坏死因子-α(TNF-α)、白细胞介素-1β(IL-1β)和一氧化氮(NO)的水平。结果:LPS能上调海马神经元MyD88和肿瘤坏死因子受体相关因子(TRAF6)mRNA水平;促使NF-κB/P65转位至核;增加MyD88和TRAF6蛋白的表达;增加海马神经元培养上清中TNF-α、IL-1β和NO含量;TLR4抗体预处理能减弱LPS对海马神经元NF-κB/P65核易位作用及降低培养上清中TNF-α、IL-1β和NO的水平。结论:大鼠海马神经元有TLR4介导的的MyD88依赖途径,该途径的激活能导致TNF-α、IL-lβ和NO含量的增加。海马神经元TLR4介导的MyD88依赖途径参与了神经炎症反应,神经元不是神经炎症反应中的被动者。     

The MyD88-dependent, but not the MyD88-independent, pathway of TLR4 signaling is important in clearing nontypeable haemophilus influenzae from the mouse lung

TLRs are important for the recognition of conserved motifs expressed by invading bacteria. TLR4 is the signaling receptor for LPS, the major proinflammatory component of the Gram-negative cell wall, whereas CD14 serves as the ligand-binding part of the LPS receptor complex. Triggering of TLR4 results in the activation of two distinct intracellular pathways, one that relies on the common TLR adaptor MyD88 and one that is mediated by Toll/IL-1R domain-containing adaptor-inducing IFN-beta (TRIF). Nontypeable Haemophilus influenzae (NTHi) is a common Gram-negative respiratory pathogen that expresses both TLR4 (LPS and lipooligosaccharide) and TLR2 (lipoproteins) ligands. To determine the roles of CD14, TLR4, and TLR2 during NTHi pneumonia, the following studies were performed: 1) Alveolar macrophages from CD14 and TLR4 knockout (KO) mice were virtually unresponsive to NTHi in vitro, whereas TLR2 KO macrophages displayed a reduced NTHi responsiveness. 2) After intranasal infection with NTHi, CD14 and TLR4 KO mice showed an attenuated early inflammatory response in their lungs, which was associated with a strongly reduced clearance of NTHi from the respiratory tract; in contrast, in TLR2 KO mice, lung inflammation was unchanged, and the number of NTHi CFU was only modestly increased at the end of the 10-day observation period. 3) MyD88 KO, but not TRIF mutant mice showed an increased bacterial load in their lungs upon infection with NTHi. These data suggest that the MyD88-dependent pathway of TLR4 is important for an effective innate immune response to respiratory tract infection caused by NTHi.