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Gekara, Nelson O
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Publications (10 of 20) Show all publications
Kurhade, C., Zegenhagen, L., Weber, E., Nair, S., Michaelsen-Preusse, K., Spanier, J., . . . Överby, A. K. (2016). Type I Interferon response in olfactory bulb, the site of tick-borne flavivirus accumulation, is primarily regulated by IPS-1. Journal of Neuroinflammation, 13, Article ID 22.
Open this publication in new window or tab >>Type I Interferon response in olfactory bulb, the site of tick-borne flavivirus accumulation, is primarily regulated by IPS-1
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2016 (English)In: Journal of Neuroinflammation, ISSN 1742-2094, E-ISSN 1742-2094, Vol. 13, 22Article in journal (Refereed) Published
Abstract [en]

Background: Although type I interferons (IFNs)—key effectors of antiviral innate immunity are known to be induced via different pattern recognition receptors (PRRs), the cellular source and the relative contribution of different PRRs in host protection against viral infection is often unclear. IPS-1 is a downstream adaptor for retinoid-inducible gene I (RIG-I)-like receptor signaling. In this study, we investigate the relative contribution of IPS-1 in the innate immune response in the different brain regions during infection with tick-borne encephalitis virus (TBEV), a flavivirus that causes a variety of severe symptoms like hemorrhagic fevers, encephalitis, and meningitis in the human host.

Methods: IPS-1 knockout mice were infected with TBEV/Langat virus (LGTV), and viral burden in the peripheral and the central nervous systems, type I IFN induction, brain infiltrating cells, and inflammatory response was analyzed.

Results: We show that IPS-1 is indispensable for controlling TBEV and LGTV infections in the peripheral and central nervous system. Our data indicate that IPS-1 regulates neuropathogenicity in mice. IFN response is differentially regulated in distinct regions of the central nervous system (CNS) influencing viral tropism, as LGTV replication was mainly restricted to olfactory bulb in wild-type (WT) mice. In contrast to the other brain regions, IFN upregulation in the olfactory bulb was dependent on IPS-1 signaling. IPS-1 regulates basal levels of antiviral interferon-stimulated genes (ISGs) like viperin and IRF-1 which contributes to the establishment of early viral replication which inhibits STAT1 activation. This diminishes the antiviral response even in the presence of high IFN-β levels. Consequently, the absence of IPS-1 causes uncontrolled virus replication, in turn resulting in apoptosis, activation of microglia and astrocytes, elevated proinflammatory response, and recruitment of inflammatory cells into the CNS.

Conclusions: We show that LGTV replication is restricted to the olfactory bulb and that IPS-1 is a very important player in the olfactory bulb in shaping the innate immune response by inhibiting early viral replication and viral spread throughout the central nervous system. In the absence of IPS-1, higher viral replication leads to the evasion of antiviral response by inhibiting interferon signaling. Our data suggest that the local microenvironment of distinct brain regions is critical to determine virus permissiveness.

Keyword
Tick-borne encephalitis, IPS-1, Brain, Olfactory bulb, Type I interferons, Antiviral mechanism, Immune asion
National Category
Microbiology in the medical area
Identifiers
urn:nbn:se:umu:diva-116737 (URN)10.1186/s12974-016-0487-9 (DOI)000368886900003 ()26819220 (PubMedID)
Available from: 2016-02-19 Created: 2016-02-11 Last updated: 2018-01-10Bibliographically approved
Panda, S., Nilsson, J. A. & Gekara, N. O. (2015). Deubiquitinase MYSM1 Regulates Innate Immunity through Inactivation of TRAF3 and TRAF6 Complexes. Immunity, 43(4), 647-659.
Open this publication in new window or tab >>Deubiquitinase MYSM1 Regulates Innate Immunity through Inactivation of TRAF3 and TRAF6 Complexes
2015 (English)In: Immunity, ISSN 1074-7613, E-ISSN 1097-4180, Vol. 43, no 4, 647-659 p.Article in journal (Refereed) Published
Abstract [en]

Pattern-recognition receptors (PRRs) including Toll-like receptors, RIG-I-like receptors, and cytoplasmic DNA receptors are essential for protection against pathogens but require tight control to avert inflammatory diseases. The mechanisms underlying this strict regulation are unclear. MYSM1 was previously described as a key component of epigenetic signaling machinery. We found that in response to microbial stimuli, MYSM1 accumulated in the cytoplasm where it interacted with and inactivated TRAF3 and TRAF6 complexes to terminate PRR pathways for pro-inflammatory and type I interferon responses. Consequently, Mysm1 deficiency in mice resulted in hyper-inflammation and enhanced viral clearance but also susceptibility to septic shock. We identified two motifs in MYSM1 that were essential for innate immune suppression: the SWIRM domain that interacted with TRAF3 and TRAF6 and the metalloproteinase domain that removed K63 polyubiquitins. This study identifies MYSM1 as a key negative regulator of the innate immune system that guards against an overzealous self-destructive immune response.

Place, publisher, year, edition, pages
Elsevier, 2015
National Category
Microbiology in the medical area
Identifiers
urn:nbn:se:umu:diva-111482 (URN)10.1016/j.immuni.2015.09.010 (DOI)000363478700009 ()26474655 (PubMedID)
Available from: 2015-12-08 Created: 2015-11-13 Last updated: 2018-01-10Bibliographically approved
Härtlova, A., Erttmann, S. F., Raffi, F. A. M., Schmalz, A. M., Resch, U., Anugula, S., . . . Gekara, N. O. (2015). DNA Damage Primes the Type I Interferon System via the Cytosolic DNA Sensor STING to Promote Anti-Microbial Innate Immunity. Immunity, 42(2), 332-343.
Open this publication in new window or tab >>DNA Damage Primes the Type I Interferon System via the Cytosolic DNA Sensor STING to Promote Anti-Microbial Innate Immunity
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2015 (English)In: Immunity, ISSN 1074-7613, E-ISSN 1097-4180, Vol. 42, no 2, 332-343 p.Article in journal (Refereed) Published
Abstract [en]

Dysfunction in Ataxia-telangiectasia mutated (ATM), a central component of the DNA repair machinery, results in Ataxia Telangiectasia (AT), a cancer-prone disease with a variety of inflammatory manifestations. By analyzing AT patient samples and Atm(-/-) mice, we found that unrepaired DNA lesions induce type I interferons (IFNs), resulting in enhanced anti-viral and anti-bacterial responses in Atm(-/-) mice. Priming of the type I interferon system by DNA damage involved release of DNA into the cytoplasm where it activated the cytosolic DNA sensing STING-mediated pathway, which in turn enhanced responses to innate stimuli by activating the expression of Toll-like receptors, RIG-I-like receptors, cytoplasmic DNA sensors, and their downstream signaling partners. This study provides a potential explanation for the inflammatory phenotype of AT patients and establishes damaged DNA as a cell intrinsic danger signal that primes the innate immune system for a rapid and amplified response to microbial and environmental threats.

National Category
Medical Biotechnology (with a focus on Cell Biology (including Stem Cell Biology), Molecular Biology, Microbiology, Biochemistry or Biopharmacy)
Identifiers
urn:nbn:se:umu:diva-101396 (URN)10.1016/j.immuni.2015.01.012 (DOI)000349916400016 ()25692705 (PubMedID)
Available from: 2015-07-02 Created: 2015-03-30 Last updated: 2017-12-04Bibliographically approved
Erttmann, S. F., Gekara, N. O. & Fällman, M. (2014). Bacteria Induce Prolonged PMN Survival via a Phosphatidylcholine-Specific Phospholipase C- and Protein Kinase C-Dependent Mechanism. PLoS ONE, 9(1), e87859.
Open this publication in new window or tab >>Bacteria Induce Prolonged PMN Survival via a Phosphatidylcholine-Specific Phospholipase C- and Protein Kinase C-Dependent Mechanism
2014 (English)In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 9, no 1, e87859- p.Article in journal (Refereed) Published
Abstract [en]

Polymorphonuclear leukocytes (PMNs) are essential for the human innate immune defense, limiting expansion of invading microorganisms. PMN turnover is controlled by apoptosis, but the regulating signaling pathways remain elusive, largely due to inherent differences between mice and humans that undermine use of mouse models for understanding human PMN biology. Here, we aim to elucidate signal transduction mediating survival of human peripheral blood PMNs in response to bacteria, such as Yersinia pseudotuberculosis, an enteropathogen that causes the gastro-intestinal disease yersiniosis, as well as Escherichia coli and Staphylococcus aureus. Determinations of cell death reveal that uninfected control cells undergo apoptosis, while PMNs infected with either Gram-positive or -negative bacteria show profoundly increased survival. Infected cells exhibit decreased caspase 3 and 8 activities, increased mitochondrial integrity and are resistant to apoptosis induced by a death receptor ligand. This bacteria-induced response is accompanied by pro-inflammatory cytokine production including interleukin-8 and tumor necrosis factor-a competent to attract additional PMNs. Using agonists and pharmacological inhibitors, we show participation of Toll-like receptor 2 and 4, and interestingly, that protein kinase C (PKC) and phosphatidylcholine-specific phospholipase C (PC-PLC), but not tyrosine kinases or phosphatidylinositol-specific phospholipase C (PI-PLC) are key players in this dual PMN response. Our findings indicate the importance of prolonged PMN survival in response to bacteria, where general signaling pathways ensure complete exploitation of PMN anti-microbial capacity.

National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:umu:diva-87041 (URN)10.1371/journal.pone.0087859 (DOI)000330621900186 ()
Available from: 2014-04-07 Created: 2014-03-18 Last updated: 2017-12-05Bibliographically approved
Härtlova, A., Link, M., Balounova, J., Benesova, M., Resch, U., Straskova, A., . . . Stulik, J. (2014). Quantitative proteomics analysis of macrophage-derived lipid rafts reveals induction of autophagy pathway at the early time of Francisella tularensis LVS infection. Journal of Proteome Research, 13(2), 796-804.
Open this publication in new window or tab >>Quantitative proteomics analysis of macrophage-derived lipid rafts reveals induction of autophagy pathway at the early time of Francisella tularensis LVS infection
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2014 (English)In: Journal of Proteome Research, ISSN 1535-3893, E-ISSN 1535-3907, Vol. 13, no 2, 796-804 p.Article in journal (Refereed) Published
Abstract [en]

Francisella tularensis is a highly infectious intracellular pathogen that has evolved an efficient strategy to subvert host defense response to survive inside the host. The molecular mechanisms regulating these host-pathogen interactions and especially those that are initiated at the time of the bacterial entry via its attachment to the host plasma membrane likely predetermine the intracellular fate of pathogen. Here, we provide the evidence that infection of macrophages with F. tularensis leads to changes in protein composition of macrophage-derived lipid rafts, isolated as detergent-resistant membranes (DRMs). Using SILAC-based quantitative proteomic approach, we observed the accumulation of autophagic adaptor protein p62 at the early, stages of microbe-host cell interaction. We confirmed the colocalization of the p62 with ubiquitinated and LC3-decorated intracellular F. tularensis microbes with its maximum at 1 h postinfection. Furthermore, the infection of p62-knockdown host cells led to the transient increase in the intracellular number of microbes up to 4 h after in vitro infection. Together, these data suggest that the activation of the autophagy pathway in F. tularensis infected macrophages, which impacts the early phase of microbial proliferation, is subsequently circumvented by ongoing infection.

National Category
Biochemistry and Molecular Biology
Identifiers
urn:nbn:se:umu:diva-87175 (URN)10.1021/pr4008656 (DOI)000331164100040 ()
Available from: 2014-03-31 Created: 2014-03-24 Last updated: 2017-12-05Bibliographically approved
Weber, E., Finsterbusch, K., Lindquist, R., Nair, S., Lienenklaus, S., Gekara, N. O., . . . Kröger, A. (2014). Type I interferon protects mice from fatal neurotropic infection with Langat virus by systemic and local antiviral responses. Journal of Virology, 89(21), 12202-12212.
Open this publication in new window or tab >>Type I interferon protects mice from fatal neurotropic infection with Langat virus by systemic and local antiviral responses
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2014 (English)In: Journal of Virology, ISSN 0022-538X, E-ISSN 1098-5514, Vol. 89, no 21, 12202-12212 p.Article in journal (Refereed) Published
Abstract [en]

Vector-borne flaviviruses, such as tick-borne encephalitis virus (TBEV), West Nile virus, and dengue virus, cause millions of infections in humans. TBEV causes a broad range of pathological symptoms, ranging from meningitis to severe encephalitis or even hemorrhagic fever, with high mortality. Despite the availability of an effective vaccine, the incidence of TBEV infections is increasing. Not much is known about the role of the innate immune system in the control of TBEV infections. Here, we show that the type I interferon (IFN) system is essential for protection against TBEV and Langat virus (LGTV) in mice. In the absence of a functional IFN system, mice rapidly develop neurological symptoms and succumb to LGTV and TBEV infections. Type I IFN system deficiency results in severe neuroinflammation in LGTV-infected mice, characterized by breakdown of the blood-brain barrier and infiltration of macrophages into the central nervous system (CNS). Using mice with tissue-specific IFN receptor deletions, we show that coordinated activation of the type I IFN system in peripheral tissues as well as in the CNS is indispensable for viral control and protection against virus induced inflammation and fatal encephalitis. IMPORTANCE: The type I interferon (IFN) system is important to control viral infections; however, the interactions between tick-borne encephalitis virus (TBEV) and the type I IFN system are poorly characterized. TBEV causes severe infections in humans that are characterized by fever and debilitating encephalitis, which can progress to chronic illness or death. No treatment options are available. An improved understanding of antiviral innate immune responses is pivotal for the development of effective therapeutics. We show that type I IFN, an effector molecule of the innate immune system, is responsible for the extended survival of TBEV and Langat virus (LGTV), an attenuated member of the TBE serogroup. IFN production and signaling appeared to be essential in two different phases during infection. The first phase is in the periphery, by reducing systemic LGTV replication and spreading into the central nervous system (CNS). In the second phase, the local IFN response in the CNS prevents virus-induced inflammation and the development of encephalitis.

Place, publisher, year, edition, pages
American Society for Microbiology, 2014
National Category
Medical Biotechnology (with a focus on Cell Biology (including Stem Cell Biology), Molecular Biology, Microbiology, Biochemistry or Biopharmacy)
Identifiers
urn:nbn:se:umu:diva-96495 (URN)10.1128/JVI.01215-14 (DOI)000343314900004 ()
Available from: 2014-12-01 Created: 2014-11-21 Last updated: 2017-12-05Bibliographically approved
Łyszkiewicz, M., Zietara, N., Rohde, M., Gekara, N. O., Jabłońska, J., Dittmar, K. E. & Weiss, S. (2011). SIGN-R1+MHC II+ cells of the splenic marginal zone: a novel type of resident dendritic cells. Journal of Leukocyte Biology, 89(4), 607-615.
Open this publication in new window or tab >>SIGN-R1+MHC II+ cells of the splenic marginal zone: a novel type of resident dendritic cells
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2011 (English)In: Journal of Leukocyte Biology, ISSN 0741-5400, E-ISSN 1938-3673, Vol. 89, no 4, 607-615 p.Article in journal (Refereed) Published
Abstract [en]

In the spleen, the MZ forms an interface between red and white pulp. Its major function is to trap blood-borne antigens and to reorient them to APCs and lymphocytes. SIGN-R1(+) cells are of the MZ inherent cell population, which for a long time, have been considered as macrophages. We now show that one subpopulation of SIGN-R1(+) cells that express MHC II molecules should be considered as a resident DC. Histological analysis indicated that SIGN-R1(+) cells have dendritic-like protrusions extending into T and B cell areas. Flow cytometry analysis revealed an expression profile of adhesion, costimulatory, and MHC molecules similar to cDCs but distinct from macrophages. Most importantly, SIGN-R1(+)MHC(+) cells were able to present antigen to naïve CD4 T cells, as well as to cross-present soluble, particulate antigens secreted by Listeria monocytogenes to CD8 T cells in vitro and in vivo. Our experiments identified SIGN-R1(+)MHC II(+) cells as professional APCs and indicate their nature as splenic resident DCs.

Keyword
macrophages, antigen presentation, T cell activation
Identifiers
urn:nbn:se:umu:diva-46328 (URN)10.1189/jlb.0610368 (DOI)21208895 (PubMedID)
Available from: 2011-08-30 Created: 2011-08-30 Last updated: 2017-12-08Bibliographically approved
Gekara, N. O., Zietara, N., Geffers, R. & Weiss, S. (2010). Listeria monocytogenes induces T cell receptor unresponsiveness through pore-forming toxin listeriolysin O. Journal of Infectious Diseases, 202(11), 1698-1707.
Open this publication in new window or tab >>Listeria monocytogenes induces T cell receptor unresponsiveness through pore-forming toxin listeriolysin O
2010 (English)In: Journal of Infectious Diseases, ISSN 0022-1899, E-ISSN 1537-6613, Vol. 202, no 11, 1698-1707 p.Article in journal (Refereed) Published
Abstract [en]

Background.  The success of many pathogens relies on their ability to circumvent the innate and adaptive immune defenses. How bacterial pathogens subvert adaptive immune defenses is not clear. Cholesterol-dependent cytolysins (CDCs) represent an expansive family of homologous pore-forming toxins that are produced by more than 20 gram-positive bacterial species. Listeriolysin O (LLO), a prototype CDC, is the main virulence factor of Listeria monocytogenes. Methods.  We employed flow cytometric and microarray techniques to analyze the effect of LLO on T cell activation in vitro and in vivo. Results.  In vivo and in vitro proliferation of CD4(+) T cells upon T cell receptor (TCR) activation was highly diminished in the presence of LLO or wild-type L. monocytogenes but not in the presence of LLO-deficient L. monocytogenes. This block in T cell proliferation was specific to T cell activation via the TCR and not by phorbol 12-myristate 13-acetate-ionomycin, which bypasses the proximal TCR signaling event. The results of microarray analysis suggest that LLO-induced T cell unresponsiveness is due to the induction of a calcium-nuclear factor of activated T cells-dependent transcriptional program that drives the expression of negative regulators of TCR signaling. Conclusion. These findings provide important insights into how bacterial toxins silence adaptive immune responses and thus enable prolonged survival of the pathogen in the host.

National Category
Immunology in the medical area
Identifiers
urn:nbn:se:umu:diva-46329 (URN)10.1086/657145 (DOI)20961225 (PubMedID)
Available from: 2011-08-30 Created: 2011-08-30 Last updated: 2018-01-12Bibliographically approved
Dietrich, N., Rohde, M., Geffers, R., Kröger, A., Hauser, H., Weiss, S. & Gekara, N. O. (2010). Mast cells elicit proinflammatory but not type I interferon responses upon activation of TLRs by bacteria.. Proceedings of the National Academy of Sciences of the United States of America, 107(19), 8748-8753.
Open this publication in new window or tab >>Mast cells elicit proinflammatory but not type I interferon responses upon activation of TLRs by bacteria.
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2010 (English)In: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 107, no 19, 8748-8753 p.Article in journal (Refereed) Published
Abstract [en]

Balanced induction of proinflammatory and type I IFN responses upon activation of Toll-like receptors (TLRs) determines the outcome of microbial infections and the pathogenesis of autoimmune and other inflammatory diseases. Mast cells, key components of the innate immune system, are known for their debilitating role in allergy and autoimmunity. However, their role in antimicrobial host defenses is being acknowledged increasingly. How mast cells interact with microbes and the nature of responses triggered thereby is not well characterized. Here we show that in response to TLR activation by Gram-positive and -negative bacteria or their components, mast cells elicit proinflammatory but not type I IFN responses. We demonstrate that in mast cells, bound bacteria and TLR ligands remain trapped at the cell surface and do not undergo internalization, a prerequisite for type I IFN induction. Such cells, however, can elicit type I IFNs in response to vesicular stomatitis virus which accesses the cytosolic retinoic acid-inducible gene I receptor. Although important for antiviral immunity, a strong I IFN response is known to contribute to pathogenesis of several bacterial pathogens such as Listeria monocytogenes. Interestingly, we observed that the mast cell-dependent neutrophil mobilization upon L. monocytogenes infection is highly impaired by IFN-beta. Thus, the fact that mast cells, although endowed with the capacity to elicit type I IFNs in response to viral infection, elicit only proinflammatory responses upon bacterial infection shows that mast cells, key effector cells of the innate immune system, are well adjusted for optimal antibacterial and antiviral responses.

Identifiers
urn:nbn:se:umu:diva-46331 (URN)10.1073/pnas.0912551107 (DOI)20421474 (PubMedID)
Available from: 2011-08-30 Created: 2011-08-30 Last updated: 2017-12-08Bibliographically approved
Dietrich, N., Lienenklaus, S., Weiss, S. & Gekara, N. O. (2010). Murine toll-like receptor 2 activation induces type I interferon responses from endolysosomal compartments.. PloS one, 5(4), e10250.
Open this publication in new window or tab >>Murine toll-like receptor 2 activation induces type I interferon responses from endolysosomal compartments.
2010 (English)In: PloS one, ISSN 1932-6203, Vol. 5, no 4, e10250- p.Article in journal (Refereed) Published
Abstract [en]

The results indicate that TLR2 activation induces pro-inflammatory and type I interferon responses from distinct subcellular sites: the plasma membrane and endolysosomal compartments respectively. Apart from identifying and characterizing a novel pathway for induction of type I interferons, the present study offers new insights into how TLR signaling discriminates and regulates the nature of responses to be elicited against extracellular and endocytosed microbes. These findings may also have clinical implication. Excessive production of pro-inflammatory cytokines and type I IFNs following activation of TLRs is a central pathologic event in several hyper-inflammatory conditions. The discovery that the induction of pro-inflammatory and type I IFN responses can be uncoupled through pharmacological manipulation of endolysosomal acidification suggests new avenues for potential therapeutic intervention against inflammations and sepsis.

Identifiers
urn:nbn:se:umu:diva-46330 (URN)10.1371/journal.pone.0010250 (DOI)20422028 (PubMedID)
Available from: 2011-08-30 Created: 2011-08-30 Last updated: 2011-11-11Bibliographically approved
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