Regulatory role of Transcription factor-EB (TFEB) in parasite control through alteration of antigen presentation in visceral leishmaniasis.

Leishmania donovani, an obligate intracellular parasite, the causative agent of visceral leishmaniasis is known to subvert the host immune system for its own survival. Although the precise mechanism is still unknown, emerging evidences indicate that L. donovani efficiently suppress MHC I mediated antigen presentation, rendering inadequate CD8+T cell activation and weakening host defense against parasite. The role of transcription factor EB (TFEB) was recognized in modulating antigen presentation besides its role in lysosomal biogenesis and function. Here, we investigated the regulatory role of TFEB in the modulation of presentation of Leishmania antigen in host tissue. Our results showed an increased expression of TFEB after Leishmania infection both in vitro and in vivo and there was a decrease in the expression of Th-1 cytokine IFNγ along with MHC class I and CD8+T cells indicating attenuation of cell mediated immunity and possibly MHC I restricted antigen presentation. Silencing of TFEB resulted in increased expression of IFNγ and MHC I along with increased CD8+T cells population without any significant change in CD4+T cell number. We also observed a decreased parasite burden in TFEB silenced condition which indicates enhanced parasite clearance by alteration of immunological response possibly through induction of presentation of Leishmania antigen through MHC I. The present study explains the role of TFEB silencing in parasite clearance through regulating the antigen presentation of Leishmania antigen thereby promises to formulate a potential therapeutic strategy against visceral leishmaniasis.

Disruption of Cxcr3 chemotactic signaling alters lysosomal function and renders macrophages more microbicidal.

Chemotaxis and lysosomal function are closely intertwined processes essential for the inflammatory response and clearance of intracellular bacteria. We used the zebrafish model to examine the link between chemotactic signaling and lysosome physiology in macrophages during mycobacterial infection and wound-induced inflammation in vivo. Macrophages from zebrafish larvae carrying a mutation in a chemokine receptor of the Cxcr3 family display upregulated expression of vesicle trafficking and lysosomal genes and possess enlarged lysosomes that enhance intracellular bacterial clearance. This increased microbicidal capacity is phenocopied by inhibiting the lysosomal transcription factor EC, while its overexpression counteracts the protective effect of chemokine receptor mutation. Tracking macrophage migration in zebrafish revealed that lysosomes of chemokine receptor mutants accumulate in the front half of cells, preventing macrophage polarization during chemotaxis and reaching sites of inflammation. Our work shows that chemotactic signaling affects the bactericidal properties and localization during chemotaxis, key aspects of the inflammatory response.

Virucidal activity of Moringa A from Moringa oleifera seeds against Influenza A Viruses by regulating TFEB.

Influenza A viruses (IAVs) are highly contagious pathogens infecting human and numerous animals. The viruses cause millions of infection cases and thousands of deaths every year, making IAVs a continual threat to global health. Our study demonstrated the virucidal activity of Moringa A as a new compound from Moringa oleifera seeds against IAVs. It inhibits virus replication in host cells and protects infected cells from the cytopathic effect induced by IAVs. The EC50andEC90 values of Moringa A for IAVs were 1.27 and 5.30 µM, respectively, when RAW264.7 cells were infected at MOI of 1. The different treatment experiments revealed that Moringa A has a significant inhibitory effect on the IAVs both before and afterdrug addition. Moringa A was observed to decrease the inflammatory cytokines TNF-α, IL-6, IL-1ß, and IFN-ß in H1N1 infected RAW264.7 cells. Finally, Moringa A was found to inhibit the expression and nuclear transfer of the cellular protein transcription factor EB (TFEB) and weaken the autophagy in infected cells, which could be an important antiviral mechanism. Our study demonstrates Moringa A has potent antiviral activity against IVAs, which could be due to the autophagy inhibition property.

MXD1 regulates the H9N2 and H1N1 influenza A virus-induced chemokine expression and their replications in human macrophage.

Human infection with influenza A/Hong Kong/156/97 (H5N1) avian influenza virus is associated with a high mortality rate of 60%. This virus is originated from influenza A/Quail/Hong Kong/G1/97 (H9N2/G1) avian influenza virus. Since the 1990s, four lineages of H9N2 viruses have been circulating in poultry and cause occasional infection in humans in different countries. Due to its zoonotic and genetic reassortment potential, H9N2/G1 and H5N1 viruses are believed to be the next pandemic candidates. Previous reports, including ours, showed that the virulence of avian virus strains correlates with their ability to dysregulate cytokine expression, including TNF-α, CXCL10, and related chemokines in the virus-infected cells. However, the transcriptional factors required for this cytokine dysregulation remains undefined. In light of our previous report showing the unconventional role of MYC, an onco-transcriptional factor, for regulating the antibacterial responses, we hypothesize that the influenza virus-induced cytokine productions may be governed by MYC/MAX/MXD1 network members. Here, we demonstrated that the influenza A/Hong Kong/54/98 (H1N1)- or H9N2/G1 virus-induced CXCL10 expressions can be significantly attenuated by knocking down the MXD1 expression in primary human blood macrophages. Indeed, only the MXD1 expression was up-regulated by both H1N1 and H9N2/G1 viruses, but not other MYC/MAX/MXD1 members. The MXD1 expression and the CXCL10 hyperinduction were dependent on MEK1/2 activation. By using EMSAs, we revealed that MXD1 directly binds to the CXCL10 promoter-derived oligonucleotides upon infection of both viruses. Furthermore, silencing of MXD1 decreased the replication of H9N2 but not H1N1 viruses. Our results provide a new insight into the role of MXD1 for the pathogenicity of avian influenza viruses.

Inhibition of Ctsk modulates periodontitis with arthritis via downregulation of TLR9 and autophagy.

OBJECTIVES: The mechanisms underlying the effects of Toll-like receptor 9 (TLR9) and autophagy on rheumatoid arthritis (RA)-aggravated periodontitis are unclear. We aimed to explore a novel target, cathepsin K (Ctsk)-mediated TLR9-related autophagy, during the progress of periodontitis with RA. MATERIALS AND METHODS: DBA/J1 mouse model of periodontitis with RA was created by local colonization of Porphyromonas gingivalis (Pg) and injection of collagen. The expression of Ctsk was inhibited by adeno-associated virus (AAV). Micro-CT, immunohistochemistry (IHC), Western blot and quantitative real-time polymerase chain reaction (qRT-PCR) were used to detect the expression of TLR9-related autophagy in periodontitis with RA. Small interfering RNA (siRNA) and CpG oligodeoxynucleotides (CpG ODN) were applied in macrophages. Western blot, immunofluorescence (IF) and qRT-PCR were used to verify the in vivo results. RESULTS: RA can promote periodontitis bone destruction in the lesion area, while inhibiting Ctsk could effectively alleviate this effect. The infiltration of macrophages, TLR9, autophagy proteins (TFEB and LC3) and inflammatory cytokines increased in the periodontitis-with-RA group and was reduced by the inhibition of Ctsk in the periodontal region. Macrophage stimulation confirmed the in vivo results. With the activation of TLR9 by CpG ODN, inhibition of Ctsk could suppress both TLR9 downstream signalling proteins and autophagy-related proteins. CONCLUSIONS: This study advanced a novel role for Ctsk in TLR9 and autophagy to explain the interaction between periodontitis and RA.

Vasoactive intestinal peptide alleviates food allergy via restoring regulatory B cell functions.

The immune regulatory cell dysfunction is associated with many immune diseases including food allergy (FA). This study aims to investigate the role of vasoactive intestinal peptide (VIP) in the maintenance of regulatory B cell (Br cell)'s immune suppressive functions by stabilizing thrombospondin (TSP1) expression. In this study, blood samples were collected from patients with food allergy (FA) and healthy control (HC) subjects. Br cells were isolated from the samples through flow cytometry cell sorting and analyzed by immunological approaches to determine the immune regulatory capacity. We found that the immune suppressive functions of Br cells were impaired in FA patients. The serum VIP levels were associated with the production of immune suppressive function-related mediators (interleukin-10, IL-10) of Br cells in FA patients. VIP counteracted IL-10 mRNA decay in Br cells by up regulating the TSP1 expression. TSP1 inhibited tristetraprolin (TTP) to prevent IL-10 mRNA decay in Br cells. Administration of VIP inhibited FA response through restoration of immune suppressive functions in Br cells. In conclusion, administration of VIP can alleviate FA response through up regulating expression of TSP1 to stabilize IL-10 expression in FA Br cells and recover the immune regulatory functions. The results have translational potential for the treatment of FA and other disorders associated with immune regulatory dysfunction of Br cells.

Myeloid Folliculin balances mTOR activation to maintain innate immunity homeostasis.

The mTOR pathway is central to most cells. How mTOR is activated in macrophages and modulates macrophage physiology remain poorly understood. The tumor suppressor Folliculin (FLCN) is a GAP for RagC/D, a regulator of mTOR. We show here that LPS potently suppresses FLCN in macrophages, allowing nuclear translocation of the transcription factor TFE3, leading to lysosome biogenesis, cytokine production, and hypersensitivity to inflammatory signals. Nuclear TFE3 additionally activates a transcriptional RagD positive feedback loop that stimulates FLCN-independent canonical mTOR signaling to S6K and increases cellular proliferation. LPS thus simultaneously suppresses the TFE3 arm and activates the S6K arm of mTOR. In vivo, mice lacking myeloid FLCN reveal chronic macrophage activation, leading to profound histiocytic infiltration and tissue disruption, with hallmarks of human histiocytic syndromes like Erdheim-Chester Disease. Our data thus identify a critical FLCN-mTOR-TFE3 axis in myeloid cells, modulated by LPS, that balances mTOR activation and curbs innate immune responses.

Carbohydrate response element binding protein (ChREBP) modulates the inflammatory response of mesangial cells in response to glucose.

Diabetic nephropathy (DN) is one of the most devastating complications of diabetes mellitus. Carbohydrate response element binding protein (ChREBP) is a basic helix-loop-helix leucine zipper transcription factor that primarily mediates glucose homeostasis in the body. The present study investigated the role of ChREBP in the pathogenesis of DN. The expression of ChREBP was detected in patients with type 2 diabetes mellitus (T2DM), diabetic mice, and mesangial cells. ELISA was used to measure cytokine production in mesangial cells. Flow cytometry analysis was performed to detect the apoptosis of mesangial cells in the presence of high glucose. The expression levels of ChREBP and several cytokines (TNF-α, IL-1ß, and IL-6) were up-regulated in T2DM patients. The mRNA and protein levels of ChREBP were also significantly elevated in the kidneys of diabetic mice. Moreover, glucose treatment promoted mRNA levels of TNF-α, IL-1ß, and IL-6 in mesangial cells. Glucose stimulation induced significant apoptosis of SV40 MES 13 cells. In addition, transfection with ChREBP siRNA significantly inhibited ChREBP expression. Consequently, the inflammatory responses and apoptosis were inhibited in SV40 MES 13 cells. These results demonstrated that ChREBP could mediate the inflammatory response and apoptosis of mesangial cells, suggesting that ChREBP may be involved in the pathogenesis of DN.

Lysosomal Protein Lamtor1 Controls Innate Immune Responses via Nuclear Translocation of Transcription Factor EB.

Amino acid metabolism plays important roles in innate immune cells, including macrophages. Recently, we reported that a lysosomal adaptor protein, Lamtor1, which serves as the scaffold for amino acid-activated mechanistic target of rapamycin complex 1 (mTORC1), is critical for the polarization of M2 macrophages. However, little is known about how Lamtor1 affects the inflammatory responses that are triggered by the stimuli for TLRs. In this article, we show that Lamtor1 controls innate immune responses by regulating the phosphorylation and nuclear translocation of transcription factor EB (TFEB), which has been known as the master regulator for lysosome and autophagosome biogenesis. Furthermore, we show that nuclear translocation of TFEB occurs in alveolar macrophages of myeloid-specific Lamtor1 conditional knockout mice and that these mice are hypersensitive to intratracheal administration of LPS and bleomycin. Our observation clarified that the amino acid-sensing pathway consisting of Lamtor1, mTORC1, and TFEB is involved in the regulation of innate immune responses.

PPAR-α Activation Mediates Innate Host Defense through Induction of TFEB and Lipid Catabolism.

The role of peroxisome proliferator-activated receptor α (PPAR-α) in innate host defense is largely unknown. In this study, we show that PPAR-α is essential for antimycobacterial responses via activation of transcription factor EB (TFEB) transcription and inhibition of lipid body formation. PPAR-α deficiency resulted in an increased bacterial load and exaggerated inflammatory responses during mycobacterial infection. PPAR-α agonists promoted autophagy, lysosomal biogenesis, phagosomal maturation, and antimicrobial defense against Mycobacterium tuberculosis or M. bovis bacillus Calmette-Guérin. PPAR-α agonists regulated multiple genes involved in autophagy and lysosomal biogenesis, including Lamp2, Rab7, and Tfeb in bone marrow-derived macrophages. Silencing of TFEB reduced phagosomal maturation and antimicrobial responses, but increased macrophage inflammatory responses during mycobacterial infection. Moreover, PPAR-α activation promoted lipid catabolism and fatty acid ß-oxidation in macrophages during mycobacterial infection. Taken together, our data indicate that PPAR-α mediates antimicrobial responses to mycobacterial infection by inducing TFEB and lipid catabolism.

Jasmonate response decay and defense metabolite accumulation contributes to age-regulated dynamics of plant insect resistance.

Immunity deteriorates with age in animals but comparatively little is known about the temporal regulation of plant resistance to herbivores. The phytohormone jasmonate (JA) is a key regulator of plant insect defense. Here, we show that the JA response decays progressively in Arabidopsis. We show that this decay is regulated by the miR156-targeted SQUAMOSA PROMOTER BINDING PROTEIN-LIKE9 (SPL9) group of proteins, which can interact with JA ZIM-domain (JAZ) proteins, including JAZ3. As SPL9 levels gradually increase, JAZ3 accumulates and the JA response is attenuated. We provide evidence that this pathway contributes to insect resistance in young plants. Interestingly however, despite the decay in JA response, older plants are still comparatively more resistant to both the lepidopteran generalist Helicoverpa armigera and the specialist Plutella xylostella, along with increased accumulation of glucosinolates. We propose a model whereby constitutive accumulation of defense compounds plays a role in compensating for age-related JA-response attenuation during plant maturation.

Isoform-Specific Expression and Feedback Regulation of E Protein TCF4 Control Dendritic Cell Lineage Specification.

The cell fate decision between interferon-producing plasmacytoid DC (pDC) and antigen-presenting classical DC (cDC) is controlled by the E protein transcription factor TCF4 (E2-2). We report that TCF4 comprises two transcriptional isoforms, both of which are required for optimal pDC development in vitro. The long Tcf4 isoform is expressed specifically in pDCs, and its deletion in mice impaired pDCs development and led to the expansion of non-canonical CD8+ cDCs. The expression of Tcf4 commenced in progenitors and was further upregulated in pDCs, correlating with stage-specific activity of multiple enhancer elements. A conserved enhancer downstream of Tcf4 was required for its upregulation during pDC differentiation, revealing a positive feedback loop. The expression of Tcf4 and the resulting pDC differentiation were selectively sensitive to the inhibition of enhancer-binding BET protein activity. Thus, lineage-specifying function of E proteins is facilitated by lineage-specific isoform expression and by BET-dependent feedback regulation through distal regulatory elements.

Phagocytosis Enhances Lysosomal and Bactericidal Properties by Activating the Transcription Factor TFEB.

Macrophages internalize pathogens through phagocytosis, entrapping them into organelles called phagosomes. Phagosomes then fuse with lysosomes to mature into phagolysosomes, acquiring an acidic and hydrolytic lumen that kills the pathogens. During an ongoing infection, macrophages can internalize dozens of bacteria. Thus, we hypothesized that an initial round of phagocytosis might boost lysosome function and bactericidal ability to cope with subsequent rounds of phagocytosis. To test this hypothesis, we employed Fcγ-receptor-mediated phagocytosis and endocytosis, which internalize immunoglobulin G (IgG)-opsonized particles and polyvalent IgG immune complexes, respectively. We report that Fcγ receptor activation in macrophages enhances lysosome-based proteolysis and killing of subsequently phagocytosed E. coli compared to naive macrophages. Importantly, we show that Fcγ receptor activation causes nuclear translocation of TFEB, a transcription factor that boosts expression of lysosome genes. Indeed, Fc receptor activation is accompanied by increased expression of specific lysosomal proteins. Remarkably, TFEB silencing represses the Fcγ-receptor-mediated enhancements in degradation and bacterial killing. In addition, nuclear translocation of TFEB requires phagosome completion and fails to occur in cells silenced for MCOLN1, a lysosomal Ca(2+) channel, suggesting that lysosomal Ca(2+) released during phagosome maturation activates TFEB. Finally, we demonstrate that non-opsonic phagocytosis of E. coli also enhances lysosomal degradation in a TFEB-dependent manner, suggesting that this phenomenon is not limited to Fcγ receptors. Overall, we show that macrophages become better killers after one round of phagocytosis and suggest that phagosomes and lysosomes are capable of bi-directional signaling.

Molecular functions of the transcription factors E2A and E2-2 in controlling germinal center B cell and plasma cell development.

E2A is an essential regulator of early B cell development. Here, we have demonstrated that E2A together with E2-2 controlled germinal center (GC) B cell and plasma cell development. As shown by the identification of regulated E2A,E2-2 target genes in activated B cells, these E-proteins directly activated genes with important functions in GC B cells and plasma cells by inducing and maintaining DNase I hypersensitive sites. Through binding to multiple enhancers in the Igh 3' regulatory region and Aicda locus, E-proteins regulated class switch recombination by inducing both Igh germline transcription and AID expression. By regulating 3' Igk and Igh enhancers and a distal element at the Prdm1 (Blimp1) locus, E-proteins contributed to Igk, Igh, and Prdm1 activation in plasmablasts. Together, these data identified E2A and E2-2 as central regulators of B cell immunity.

Dynamic changes in Id3 and E-protein activity orchestrate germinal center and plasma cell development.

The generation of high-affinity antibodies requires germinal center (GC) development and differentiation of long-lived plasma cells in a multilayered process that is tightly controlled by the activity of multiple transcription factors. Here, we reveal a new layer of complexity by demonstrating that dynamic changes in Id3 and E-protein activity govern both GC and plasma cell differentiation. We show that down-regulation of Id3 in B cells is essential for releasing E2A and E2-2, which in a redundant manner are required for antigen-induced B cell differentiation. We demonstrate that this pathway controls the expression of multiple key factors, including Blimp1, Xbp1, and CXCR4, and is therefore critical for establishing the transcriptional network that controls GC B cell and plasma cell differentiation.

The transcription factor TFEB acts as a molecular switch that regulates exogenous antigen-presentation pathways.

Dendritic cells (DCs) can initiate immune responses by presenting exogenous antigens to T cells via both major histocompatibility complex (MHC) class I pathways and MHC class II pathways. Lysosomal activity has an important role in modulating the balance between these two pathways. The transcription factor TFEB regulates lysosomal function by inducing lysosomal activation. Here we report that TFEB expression inhibited the presentation of exogenous antigen by MHC class I while enhancing presentation via MHC class II. TFEB promoted phagosomal acidification and protein degradation. Furthermore, we found that the activation of TFEB was regulated during DC maturation and that phagosomal acidification was impaired in DCs in which the gene encoding TFEB was silenced. Our data indicate that TFEB is a key participant in the differential regulation of the presentation of exogenous antigens by DCs.

ß-catenin promotes regulatory T-cell responses in tumors by inducing vitamin A metabolism in dendritic cells.

Tumors actively suppress antitumor immunity, creating formidable barriers to successful cancer immunotherapy. The molecular mechanisms underlying tumor-induced immune tolerance are largely unknown. In the present study, we show that dendritic cells (DC) in the tumor microenvironment acquire the ability to metabolize vitamin A to produce retinoic acid (RA), which drives regulatory T-cell responses and immune tolerance. Tolerogenic responses were dependent on induction of vitamin A-metabolizing enzymes via the ß-catenin/T-cell factor (TCF) pathway in DCs. Consistent with this observation, DC-specific deletion of ß-catenin in mice markedly reduced regulatory T-cell responses and delayed melanoma growth. Pharmacologic inhibition of either vitamin A-metabolizing enzymes or the ß-catenin/TCF4 pathway in vivo had similar effects on tumor growth and regulatory T-cell responses. Hence, ß-catenin/TCF4 signaling induces local regulatory DC and regulatory T-cell phenotypes via the RA pathway, identifying this pathway as an important target for anticancer immunotherapy.

MHC Class II-restricted antigen presentation by plasmacytoid dendritic cells drives proatherogenic T cell immunity.

BACKGROUND: Plasmacytoid dendritic cells (pDCs) bridge innate and adaptive immune responses and are important regulators of immuno-inflammatory diseases. However, their role in atherosclerosis remains elusive. METHODS AND RESULTS: Here, we used genetic approaches to investigate the role of pDCs in atherosclerosis. Selective pDC deficiency in vivo was achieved using CD11c-Cre × Tcf4(-/flox) bone marrow transplanted into Ldlr(-/-) mice. Compared with control Ldlr(-/-) chimeric mice, CD11c-Cre × Tcf4(-/flox) mice had reduced atherosclerosis levels. To begin to understand the mechanisms by which pDCs regulate atherosclerosis, we studied chimeric Ldlr(-/-) mice with selective MHCII deficiency on pDCs. Significantly, these mice also developed reduced atherosclerosis compared with controls without reductions in pDC numbers or changes in conventional DCs. MHCII-deficient pDCs showed defective stimulation of apolipoprotein B100-specific CD4(+) T cells in response to native low-density lipoprotein, whereas production of interferon-α was not affected. Finally, the atheroprotective effect of selective MHCII deficiency in pDCs was associated with significant reductions of proatherogenic T cell-derived interferon-γ and lesional T cell infiltration, and was abrogated in CD4(+) T cell-depleted animals. CONCLUSIONS: This study supports a proatherogenic role for pDCs in murine atherosclerosis and identifies a critical role for MHCII-restricted antigen presentation by pDCs in driving proatherogenic T cell immunity.

Of worms and men: HLH-30 and TFEB regulate tolerance to infection.

In this issue of Immunity, Visvikis et al. (2014) use the model host Caenorhabditis elegans to discover a role in innate immunity for the basic helix-loop-helix transcription factor, HLH-30. The finding inspires study of the mammalian ortholog TFEB, in which a similar role in immune response is ascertained.