Jianxia Chen

TLR3 regulates mycobacterial RNA-induced IL-10 production through the PI3K/AKT signaling pathway

Cytokine induction in response to Mycobacterium tuberculosis (Mtb) infection is critical for pathogen control, by (i) mediating innate immune effector functions and (ii) instructing specific adaptive immunity. IL-10 is an important anti-inflammatory cytokine involved in pathogenesis of tuberculosis (TB). Here, we show that TLR3, a sensor of extracellular viral or host RNA with stable stem structures derived from infected or damaged cells, is essential for Mtb-induced IL-10 production. Upon Mycobacterium bovis Bacillus Calmette-Guérin (BCG) infection, TLR3(-/-) macrophages expressed lower IL-10 but higher IL-12p40 production, accompanied by reduced phosphorylation of AKT at Ser473. BCG-infected TLR3(-/-) mice exhibited reduced IL-10 but elevated IL-12 expression compared to controls. Moreover, higher numbers of splenic Th1 cells and reduced pulmonary bacterial burden and tissue damage were observed in BCG-infected TLR3(-/-) mice. Finally, BCG RNA induced IL-10 in macrophages via TLR3-mediated activation of PI3K/AKT. Our findings demonstrate a critical role of TLR3-mediated regulation in the pathogenesis of mycobacterial infection involving mycobacterial RNA, which induces IL-10 through the PI3K/AKT signaling pathway.

Enteropathogenic Escherichia coli Tir recruits cellular SHP-2 through ITIM motifs to suppress host immune response.

Immune responses to pathogens are regulated by immune receptors containing either an immunoreceptor tyrosine-based activation motif (ITAM) or an immunoreceptor tyrosine-based inhibitory motif (ITIM). The important diarrheal pathogen enteropathogenic Escherichia coli (EPEC) require delivery and insertion of the bacterial translocated intimin receptor (Tir) into the host plasma membrane for pedestal formation. The C-terminal region of Tir, encompassing Y483 and Y511, shares sequence similarity with cellular ITIMs. Here, we show that EPEC Tir suppresses the production of inflammatory cytokines by recruitment of SHP-2 and subsequent deubiquitination of TRAF6 in an ITIM dependent manner. Our findings revealed a novel mechanism by which the EPEC utilize its ITIM motifs to suppress and evade the host innate immune response, which could lead to the development of novel therapeutics to prevent bacterial infection.

Induction of CCL8/MCP-2 by Mycobacteria through the Activation of TLR2/PI3K/Akt Signaling Pathway

Pleural tuberculosis (TB), together with lymphatic TB, constitutes more than half of all extrapulmonary cases. Pleural effusions (PEs) in TB are representative of lymphocytic PEs which are dominated by T cells. However, the mechanism underlying T lymphocytes homing and accumulation in PEs is still incompletely understood. Here we performed a comparative analysis of cytokine abundance in PEs from TB patients and non-TB patients by protein array analysis and observed that MCP-2/CCL8 is highly expressed in the TB-PEs as compared to peripheral blood. Meanwhile, we observed that CCR5, the primary receptor used by MCP-2/CCL8, is mostly expressed on pleural CD4+ T lymphocytes. Furthermore, we found that infection with either Mycobacterium bovis Bacillus Calmette-Guérin (BCG) or Mycobacterium tuberculosis H37Rv induced production of MCP-2/CCL8 at both transcriptional and protein level in Raw264.7 and THP-1 macrophage cells, mouse peritoneal macrophages as well as human PBMC monocyte-derived macrophages (MDMs). The induction of MCP-2/CCL8 by mycobacteria is dependent on the activation of TLR2/PI3K/Akt and p38 signaling pathway. We conclude that accumulation of MCP-2/CCL8 in TB-PEs may function as a biomarker for TB diagnosis.

The kinase CK1ɛ controls the antiviral immune response by phosphorylating the signaling adaptor TRAF3

The signaling adaptor TRAF3 is a highly versatile regulator of both innate immunity and adaptive immunity, but how its phosphorylation is regulated is still unknown. Here we report that deficiency in or inhibition of the conserved serine-threonine kinase CK1ɛ suppressed the production of type I interferon in response to viral infection. CK1ɛ interacted with and phosphorylated TRAF3 at Ser349, which thereby promoted the Lys63 (K63)-linked ubiquitination of TRAF3 and subsequent recruitment of the kinase TBK1 to TRAF3. Consequently, CK1ɛ-deficient mice were more susceptible to viral infection. Our findings establish CK1ɛ as a regulator of antiviral innate immune responses and indicate a novel mechanism of immunoregulation that involves CK1ɛ-mediated phosphorylation of TRAF3.

Porphyromonas gingivalis infected macrophages upregulate CD36 expression via ERK/NF-κB pathway.

CD36, a scavenger receptor, plays an important role in the progression of atherosclerosis through its interaction with oxidized low-density lipoprotein (ox-LDL). Porphyromonas gingivalis (P. gingivalis, Pg) has been shown to promote macrophage-derived foam cell formation by affecting the expression of CD36. However, the regulatory role of CD36 in macrophages infected with Pg remains largely unknown. Therefore, the aim of the present study was to explore the molecular mechanism of Pg induced CD36 expression in macrophages. Our results showed that Pg promoted ox-LDL uptake by macrophages and the formation of foam cells. Pg infection increased CD36 mRNA and protein levels in ox-LDL-untreated macrophages. Moreover, small interferon RNA (siRNA) targeting CD36 significantly reduced foam cell formation induced by Pg. Additionally, Pg stimulated nuclear translocation of p65, which directly bound to the promoters of CD36 to facilitate its transcription. Inhibition of p65, NF-κB or ERK1/2 blocked Pg-induced CD36 production; whereas, overexpression of NF-κB subunits p65 and p50 upregulated CD36. Furthermore, Ras inhibitors significantly attenuated ERK1/2 activation and CD36 expression. Taken together, the data indicated that stimulation of the ERK/NF-κB pathway by Pg led to transactivation of the CD36 promoters, thereby upregulating CD36 expression in the infected macrophages. These findings may help design new treatment strategies in atherosclerosis.

Epstein–Barr virus-induced gene 3 (EBI3) polymorphisms and expression are associated with susceptibility to pulmonary tuberculosis

Tuberculosis (TB) remains a major global health problem and host genetic factors play a critical role in susceptibility and resistance to TB. The aim of this study was to identify novel candidate genes associated with TB susceptibility. We performed a population-based case-control study to genotype 13 tag SNPs spanning Epstein-Barr virus-induced gene 3 (EBI3), colony stimulating factor 2 (CSF2), IL-4, interferon beta 1 (IFNB1), chemokine (C-X-C motif) ligand 14 (CXCL14) and myeloid differentiation primary response gene 88 (Myd88) genes in 435 pulmonary TB patients and 375 health donors from China. We observed that EBI3 gene rs4740 polymorphism was associated with susceptibility to pulmonary tuberculosis (PTB) and the allele G was associated with a protective effect against PTB. Furthermore, EBI3 deficiency led to reduced bacterial burden and histopathological impairment in the lung of mice infected with Mycobacterium bovis BCG. Meanwhile, higher abundance of EBI3 was observed in the granuloma of PTB patients and in the lung tissue of BCG-infected mice. Of note, the expression of EBI3 in macrophages was remarkably induced by mycobacteria infection at both mRNA and protein level. In conclusion, EBI3 gene rs4740 polymorphism is closely associated with susceptibility to PTB and the elevation and enrichment of EBI3 in the lung which at least partially derived from macrophages may contribute to the exacerbation of mycobacterial infection.

Lysine acetylation of DosR regulates the hypoxia response of Mycobacterium tuberculosis

Tuberculosis caused by Mycobacterium tuberculosis (Mtb) infection remains a large global public health problem. One striking characteristic of Mtb is its ability to adapt to hypoxia and trigger the ensuing transition to a dormant state for persistent infection, but how the hypoxia response of Mtb is regulated remains largely unknown. Here we performed a quantitative acetylome analysis to compare the acetylation profile of Mtb under aeration and hypoxia, and showed that 377 acetylation sites in 269 Mtb proteins were significantly changed under hypoxia. In particular, deacetylation of dormancy survival regulator (DosR) at K182 promoted the hypoxia response in Mtb and enhanced the transcription of DosR-targeted genes. Mechanistically, recombinant DosRK182R protein demonstrated enhanced DNA-binding activity in comparison with DosRK182Q protein. Moreover, Rv0998 was identified as an acetyltransferase that mediates the acetylation of DosR at K182. Deletion of Rv0998 also promoted the adaptation of Mtb to hypoxia and the transcription of DosR-targeted genes. Mice infected with an Mtb strain containing acetylation-defective DosRK182R had much lower bacterial counts and less severe histopathological impairments compared with those infected with the wild-type strain. Our findings suggest that hypoxia induces the deacetylation of DosR, which in turn increases its DNA-binding ability to promote the transcription of target genes, allowing Mtb to shift to dormancy under hypoxia.

IL-37 Confers Protection against Mycobacterial Infection Involving Suppressing Inflammation and Modulating T Cell Activation

Interleukin-37 (IL-37), a novel member of the IL-1 family, plays fundamental immunosuppressive roles by broadly reducing both innate inflammation and acquired immunity, but whether it is involved in the pathogenesis of tuberculosis (TB) has not been clearly elucidated. In this study, single nucleotide polymorphism (SNP) analysis demonstrated an association of the genetic variant rs3811047 of IL-37 with TB susceptibility. In line with previous report, a significant elevated IL-37 abundance in the sera and increased expression of IL-37 protein in the peripheral blood mononuclear cells (PBMC) were observed in TB patients in comparison to healthy controls. Moreover, release of IL-37 were detected in either macrophages infected with Mycobacterium tuberculosis (Mtb) or the lung of BCG-infected mice, concurrent with reduced production of proinflammatory cytokines including IL-6 and TNF-α. Furthermore, in contrast to wild-type mice, BCG-infected IL-37-Tg mice manifested with reduced mycobacterial burden and tissue damage in the lung, accompanied by higher frequency of Th1 cell and less frequencies of regulatory T cells and Th17 cells in the spleen. Taken together, our findings demonstrated that IL-37 conferred resistance to Mtb infection possibly involving suppressing detrimental inflammation and modulating T cell responses. These findings implicated that IL-37 may be employed as a new molecular target for the therapy and diagnosis of TB.

Notch4 Negatively Regulates the Inflammatory Response to Mycobacterium tuberculosis Infection by Inhibiting TAK1 Activation

Tuberculosis, caused by Mycobacterium tuberculosis infection, remains a global threat to human health, but knowledge of the molecular mechanisms underlying the pathogenesis of tuberculosis is still limited. Although Notch4, a member of the Notch receptor family, is involved in the initiation of mammary tumors, its function in M. tuberculosis infection remains unclear. In this study, we found that Notch4-deficient mice were more resistant to M. tuberculosis infection, with a much lower bacterial burden and fewer pathological changes in the lungs. Notch4 inhibited M. tuberculosis-induced production of proinflammatory cytokines by interaction with TAK1 and inhibition of its activation. Furthermore, we found that Notch intracellular domain 4 prevented TRAF6 autoubiquitination and suppressed TRAF6-mediated TAK1 polyubiquitination. Finally, Notch inhibitors made mice more resistant to M. tuberculosis infection. These results suggest that Notch4 is a negative regulator of M. tuberculosis-induced inflammatory response, and treatment with a Notch inhibitor could serve as a new therapeutic strategy for tuberculosis.

G protein-coupled receptor160 regulates mycobacteria entry into macrophages by activating ERK.

Mycobacterium tuberculosis (Mtb), the causative agent of tuberculosis, invades and replicates within susceptible hosts by disturbing host antimicrobial mechanisms. Although G protein-coupled receptors (GPCRs) are involved in most physiological and pathological activities of mammalian cells, the roles of GPCRs in Mtb invasion into host cell remain elusive. Here, we report that GPR160 expression is elevated at both mRNA and protein level in macrophages in response to BCG infection. Both the PiggyBac (PB) transposon-mediated mutation of gpr160 gene in mouse primary macrophages and siRNA-mediated knockdown of GPR160 in the human macrophage cell line THP-1 markedly reduced the entry of green fluorescent protein (GFP) expressing BCG (BCG-GFP), also operative in vivo. BCG infection-induced phosphorylation of ERK1/2 was significantly reduced in gpr160 mutated (gpr160(-/-)) macrophages relative to levels observed in wild type macrophages, while inhibition of ERK by specific inhibitor or knockdown ERK1/2 by specific siRNA markedly reduced entry of BCG. Finally, lower bacteria burdens and attenuated pathological impairments were observed in the lungs of BCG-infected gpr160(-/-) mice. Furthermore, gpr160(-/-) macrophages also exhibits reduced uptake of Escherichia coli and Francisella tularensis. Taken together, these findings suggest an important role of GPR160 in regulating the entry of BCG into macrophages by targeting the ERK signaling pathway. As GPCRs have proven to be successful drug targets in pharmaceutical industry, its tempting to speculate that compounds targeting GPR160, a G protein-coupled receptor, could intervene in Mtb infection.