Control of HIV infection by IFN-α: implications for latency and a cure.

Viral infections, including HIV, trigger the production of type I interferons (IFNs), which in turn, activate a signalling cascade that ultimately culminates with the expression of anti-viral proteins. Mounting evidence suggests that type I IFNs, in particular IFN-α, play a pivotal role in limiting acute HIV infection. Highly active anti-retroviral treatment reduces viral load and increases life expectancy in HIV positive patients; however, it fails to fully eliminate latent HIV reservoirs. To revisit HIV as a curable disease, this article reviews a body of literature that highlights type I IFNs as mediators in the control of HIV infection, with particular focus on the anti-HIV restriction factors induced and/or activated by IFN-α. In addition, we discuss the relevance of type I IFN treatment in the context of HIV latency reversal, novel therapeutic intervention strategies and the potential for full HIV clearance.

Interdependent and independent roles of type I interferons and IL-6 in innate immune, neuroinflammatory and sickness behaviour responses to systemic poly I:C.

Type I interferons (IFN-I) are expressed in the brain during many inflammatory and neurodegenerative conditions and have multiple effects on CNS function. IFN-I is readily induced in the brain by systemic administration of the viral mimetic, poly I:C (synthetic double-stranded RNA). We hypothesised that IFN-I contributes to systemically administered poly I:C-induced sickness behaviour, metabolic and neuroinflammatory changes. IFN-I receptor 1 deficient mice (IFNAR1(-/-)) displayed significantly attenuated poly I:C-induced hypothermia, hypoactivity and weight loss compared to WT C57BL/6 mice. This amelioration of sickness was associated with equivalent IL-1ß and TNF-α responses but much reduced IL-6 responses in plasma, hypothalamus and hippocampus of IFNAR1(-/-) mice. IFN-ß injection induced trivial IL-6 production and limited behavioural change and the poly I:C-induced IFN-ß response did not preceed, and would not appear to mediate, IL-6 induction. Rather, IFNAR1(-/-) mice lack basal IFN-I activity, have lower STAT1 levels and show significantly lower levels of several inflammatory transcripts, including stat1. Basal IFN-I activity appears to play a facilitatory role in the full expression of the IL-6 response and activation of the tryptophan-kynurenine metabolism pathway. The deficient IL-6 response in IFNAR1(-/-) mice partially explains the observed incomplete sickness behaviour response. Reconstitution of circulating IL-6 revealed that the role of IFNAR in burrowing activity is mediated via IL-6, while IFN-I and IL-6 have additive effects on hypoactivity, but the role of IFN-I in anorexia is independent of IL-6. Hence, we have demonstrated both interdependent and independent roles for IFN-I and IL-6 in systemic inflammation-induced changes in brain function.

TRIF-mediated TLR3 and TLR4 signaling is negatively regulated by ADAM15.

TLRs are a group of pattern-recognition receptors that play a crucial role in danger recognition and induction of the innate immune response against bacterial and viral infections. The TLR adaptor molecule, Toll/IL-1R domain-containing adaptor inducing IFN (TRIF), facilitates TLR3 and TLR4 signaling and concomitant activation of the transcription factors, NF-κB and IFN regulatory factor 3, leading to proinflammatory cytokine production. Whereas numerous studies have been undertaken toward understanding the role of TRIF in TLR signaling, little is known about the signaling components that regulate TRIF-dependent TLR signaling. To this end, TRIF-interacting partners were identified by immunoprecipitation of the TRIF signaling complex, followed by protein identification using liquid chromatography mass spectrometry. Following stimulation of cells with a TLR3 or TLR4 ligand, we identified a disintegrin and metalloprotease (ADAM)15 as a novel TRIF-interacting partner. Toward the functional characterization of the TRIF:ADAM15 interaction, we show that ADAM15 acts as a negative regulator of TRIF-mediated NF-κB and IFN-ß reporter gene activity. Also, suppression of ADAM15 expression enhanced polyriboinosinic polyribocytidylic acid and LPS-mediated proinflammatory cytokine production via TRIF. In addition, suppression of ADAM15 expression enhanced rhinovirus 16 and vesicular stomatitis virus-mediated proinflammatory cytokine production. Interestingly, ADAM15 mediated the proteolytic cleavage of TRIF. Thus, ADAM15 serves to curtail TRIF-dependent TLR3 and TLR4 signaling and, in doing so, protects the host from excessive production of proinflammatory cytokines and matrix metalloproteinases. In conclusion, to our knowledge, our study clearly shows for the first time that ADAM15 plays an unexpected role in TLR signaling, acting as an anti-inflammatory molecule through impairment of TRIF-mediated TLR signaling.

14-3-3ε and 14-3-3σ inhibit Toll-like receptor (TLR)-mediated proinflammatory cytokine induction.

Toll-like receptors (TLRs) are a group of pattern recognition receptors that play a crucial role in the induction of the innate immune response against bacterial and viral infections. TLR3 has emerged as a key sensor of viral double-stranded RNA. Thus, a clearer understanding of the biological processes that modulate TLR3 signaling is essential. Limited studies have applied proteomics toward understanding the dynamics of TLR signaling. Herein, a proteomics approach identified 14-3-3ε and 14-3-3σ proteins as new members of the TLR signaling complex. Toward the functional characterization of 14-3-3ε and 14-3-3σ in TLR signaling, we have shown that both of these proteins impair TLR2, TLR3, TLR4, TLR7/8, and TLR9 ligand-induced IL-6, TNFα, and IFN-ß production. We also show that 14-3-3ε and 14-3-3σ impair TLR2-, TLR3-, TLR4-, TLR7/8-, and TLR9-mediated NF-κB and IFN-ß reporter gene activity. Interestingly, although the 14-3-3 proteins inhibit poly(I:C)-mediated RANTES production, 14-3-3 proteins augment Pam(3)CSK(4), LPS, R848, and CpG-mediated production of RANTES (regulated on activation normal T cell expressed and secreted) in a Mal (MyD88 adaptor-like)/MyD88-dependent manner. 14-3-3ε and 14-3-3σ also bind to the TLR adaptors and to both TRAF3 and TRAF6. Our study conclusively shows that 14-3-3ε and 14-3-3σ play a major regulatory role in balancing the host inflammatory response to viral and bacterial infections through modulation of the TLR signaling pathway. Thus, manipulation of 14-3-3 proteins may represent novel therapeutic targets for inflammatory conditions and infections.

The microtubule-associated protein doublecortin-like regulates the transport of the glucocorticoid receptor in neuronal progenitor cells.

In neuronal cells, activated glucocorticoid receptor (GR) translocates to the nucleus guided by the cytoskeleton. However, the detailed mechanisms underlying GR translocation remain unclear. Using gain and loss of function studies, we report here for the first time that the microtubule-associated protein doublecortin-like (DCL) controls GR translocation to the nucleus. DCL overexpression in COS-1 cells, neuroblastoma cells, and rat hippocampus organotypic slice cultures impaired GR translocation and decreased GR-dependent transcriptional activity, measured by a specific reporter gene assay, in COS-1 cells. Moreover, DCL and GR directly interact on microtubule bundles formed by DCL overexpression. A C-terminal truncated DCL with conserved microtubule-bundling activity did not influence GR translocation. In N1E-115 mouse neuroblastoma cells and neuronal progenitor cells in rat hippocampus organotypic slice cultures, laser-scanning confocal microscopy showed colabeling of endogenously expressed DCL and GR. In these systems, RNA-interference-mediated DCL knockdown hampered GR translocation. Thus, we conclude that DCL expression is tightly regulated to adequately control GR transport. Because DCL is primarily expressed in neuronal progenitor cells, our results introduce this microtubule-associated protein as a new modulator of GR signaling in this cell type and suggest the existence of cell-specific mechanisms regulating GR translocation to the nucleus.

In vitro Characterization of Gut Microbiota-Derived Bacterial Strains With Neuroprotective Properties.

Neurodegenerative diseases are disabling, incurable, and progressive conditions characterized by neuronal loss and decreased cognitive function. Changes in gut microbiome composition have been linked to a number of neurodegenerative diseases, indicating a role for the gut-brain axis. Here, we show how specific gut-derived bacterial strains can modulate neuroinflammatory and neurodegenerative processes in vitro through the production of specific metabolites and discuss the potential therapeutic implications for neurodegenerative disorders. A panel of fifty gut bacterial strains was screened for their ability to reduce pro-inflammatory IL-6 secretion in U373 glioblastoma astrocytoma cells. Parabacteroides distasonis MRx0005 and Megasphaera massiliensis MRx0029 had the strongest capacity to reduce IL-6 secretion in vitro. Oxidative stress plays a crucial role in neuroinflammation and neurodegeneration, and both bacterial strains displayed intrinsic antioxidant capacity. While MRx0005 showed a general antioxidant activity on different brain cell lines, MRx0029 only protected differentiated SH-SY5Y neuroblastoma cells from chemically induced oxidative stress. MRx0029 also induced a mature phenotype in undifferentiated neuroblastoma cells through upregulation of microtubule-associated protein 2. Interestingly, short-chain fatty acid analysis revealed that MRx0005 mainly produced C1-C3 fatty acids, while MRx0029 produced C4-C6 fatty acids, specifically butyric, valeric and hexanoic acid. None of the short-chain fatty acids tested protected neuroblastoma cells from chemically induced oxidative stress. However, butyrate was able to reduce neuroinflammation in vitro, and the combination of butyrate and valerate induced neuronal maturation, albeit not to the same degree as the complex cell-free supernatant of MRx0029. This observation was confirmed by solvent extraction of cell-free supernatants, where only MRx0029 methanolic fractions containing butyrate and valerate showed an anti-inflammatory activity in U373 cells and retained the ability to differentiate neuroblastoma cells. In summary, our results suggest that the pleiotropic nature of live biotherapeutics, as opposed to isolated metabolites, could be a promising novel drug class in drug discovery for neurodegenerative disorders.

Motor neuron disease-associated mutant vesicle-associated membrane protein-associated protein (VAP) B recruits wild-type VAPs into endoplasmic reticulum-derived tubular aggregates.

The vesicle-associated membrane protein-associated proteins (VAPs) VAPA and VAPB interact with lipid-binding proteins carrying a short motif containing two phenylalanines in an acidic tract (FFAT motif) and targets them to the cytosolic surface of the endoplasmic reticulum (ER). A genetic mutation (P56S) in the conserved major sperm protein homology domain of VAPB has been linked to motor-neuron degeneration in affected amyotrophic lateral sclerosis (ALS) patients. We report that in the CNS, VAPB is abundant in motor neurons and that the P56S substitution causes aggregation of mutant VAPB in immobile tubular ER clusters, perturbs FFAT-motif binding, and traps endogenous VAP in mutant aggregates. Expression of mutant VAPB or reduction of VAP by short hairpin RNA in primary neurons causes Golgi dispersion and cell death. VAPA and VAPB are reduced in human ALS patients and superoxide dismutase 1 (SOD1)-ALS-transgenic mice, suggesting that VAP family proteins may be involved in the pathogenesis of sporadic and SOD1-linked ALS. Our data support a model in which reduced levels of VAP family proteins result in decreased ER anchoring of lipid-binding proteins and cause motor neuron degeneration.

HIV-1 Promotes the Degradation of Components of the Type 1 IFN JAK/STAT Pathway and Blocks Anti-viral ISG Induction.

Anti-retroviral therapy successfully suppresses HIV-1 infection, but fails to provide a cure. During infection Type 1 IFNs normally play an essential role in viral clearance, but in vivo IFN-α only has a modest impact on HIV-1 infection, suggesting its possible targeting by HIV. Here, we report that the HIV protein, Vif, inhibits effective IFN-α signalling via degradation of essential JAK/STAT pathway components. We found that STAT1 and STAT3 are specifically reduced in HEK293T cells expressing Vif and that full length, infectious HIV-1 IIIB strain promotes their degradation in a Vif-dependent manner. HIV-1 IIIB infection of myeloid ThP-1 cells also reduced the IFN-α-mediated induction of the anti-viral gene, ISG15, but not MxA, revealing a functional consequence of this HIV-1-mediated immune evasion strategy. Interestingly, while total STAT levels were not reduced upon in vitro IIIB infection of primary human PBMCs, IFN-α-mediated phosphorylation of STAT1 and STAT3 and ISG induction were starkly reduced, with removal of Vif (IIIBΔVif), partially restoring pSTATs, ISG15 and MxB induction. Similarly, pSTAT1 and pSTAT3 expression and IFN-α-induced ISG15 were reduced in PBMCs from HIV-infected patients, compared to healthy controls. Furthermore, IFN-α pre-treatment of a CEM T lymphoblast cells significantly inhibited HIV infection/replication (measured by cellular p24), only in the absence of Vif (IIIBΔVif), but was unable to suppress full length IIIB infection. When analysing the mechanism by which Vif might target the JAK/STAT pathway, we found Vif interacts with both STAT1 and STAT3, (but not STAT2), and its expression promotes ubiquitination and MG132-sensitive, proteosomal degradation of both proteins. Vif's Elongin-Cullin-SOCS-box binding motif enables the formation of an active E3 ligase complex, which we found to be required for Vif's degradation of STAT1 and STAT3. In fact, the E3 ligase scaffold proteins, Cul5 and Rbx2, were also found to be essential for Vif-mediated proteasomal degradation of STAT1 and STAT3. These results reveal a target for HIV-1-Vif and demonstrate how HIV-1 impairs the anti-viral activity of Type 1 IFNs, possibly explaining why both endogenous and therapeutic IFN-α fail to activate more effective control over HIV infection.

Hepatitis C virus (HCV)-induced suppressor of cytokine signaling (SOCS) 3 regulates proinflammatory TNF-α responses.

TNF-α is a proinflammatory cytokine, dramatically elevated during pathogenic infection and often responsible for inflammation-induced disease pathology. SOCS proteins are inhibitors of cytokine signaling and regulators of inflammation. In this study, we found that both SOCS1 and SOCS3 were transiently induced by TNF-α and negatively regulate its NF-κB-mediated signal transduction. We discovered that PBMCs from HCV-infected patients have elevated endogenous SOCS3 expression but less TNF-α-mediated IκB degradation and proinflammatory cytokine production than healthy controls. HCV protein expression in Huh7 hepatocytes also induced SOCS3 and directly inhibited TNF-α-mediated IL-8 production. Furthermore, we found that SOCS3 associates with TRAF2 and inhibits TRAF2-mediated NF-κB promoter activity, suggesting a mechanism by which SOCS3 inhibits TNF-α-mediated signaling. These results demonstrate a role for SOCS3 in regulating proinflammatory TNF-α signal transduction and reveal a novel immune-modulatory mechanism by which HCV suppresses inflammatory responses in primary immune cells and hepatocytes, perhaps explaining mild pathology often associated with acute HCV infection.