Despite advances of modern medicine, bacterial sepsis remains one of the major threats to human health worldwide. In the U.S.A alone, it affects approximately 750,000 Americans per year, with an associated mortality rate >28%. The lipopolysaccharide (LPS), an outer membrane component of Gram negative bacteria, and various structures of Gram positive bacteria and Mycobacterium tuberculosis, represent the initiating stimuli in the activation of the innate immune response. Effective recognition of these bacterial structures by Toll-like receptors (TLR) expressed on monocytes and macrophages is critical for mounting a strong first line defense and prevention of sepsis. Many patients with sepsis develop a hypoinflammatory state that is manifested by marked inhibition of monocyte functions, including suppressed production of a number of cytokines. This state is highly reminiscent of bacterial tolerance defined as a transient state of cell refractoriness following a prior exposure to bacterial components. Therefore, induction of bacterial tolerance can be used as a model to delineate mechanisms that underlie decreased monocyte responsiveness in patients with sepsis. Despite numerous studies, the molecular mechanisms that underlie induction of bacterial tolerance are still largely unknown. The overall goal of this project is to gain a better understanding of the molecular mechanisms of host responses to microbes. Our objective is to define the role of receptors and signal transducing molecules of the TLR pathway in induction and maintenance of bacterial tolerance in monocytes. The central hypothesis is that induction of bacterial tolerance in human monocytes dramatically alters signal-induced complex formation among key components of the TLR pathway, leading to development of a state of suppressed antibacterial responsiveness. The following Specific Aims are proposed to: 1. Examine post-translational modifications and interactions of key molecules of TLR4 complexes associated with tolerance to TLR4 and TLR2 agonists. 2. Analyze the effect of bacterial tolerance on expression, recruitment, post-translational modifications of key adapter proteins and activation of IRAK-4. 3. Characterize suppressors of TLR-mediated signaling in tolerized cells that interfere with agonist-induced interactions among TLRs, adapter proteins, and IRAK kinases. It is expected that at the completion of this grant, we will have identified key molecular mechanisms responsible for development of bacterial tolerance, and have provided strategies for development of new therapeutic approaches for treatment of patients with bacterial sepsis to target components of the TLR signaling pathway that are compromised in tolerance and sepsis.

Agency
National Institute of Health (NIH)
Institute
National Institute of Allergy and Infectious Diseases (NIAID)
Type
Research Project (R01)
Project #
5R01AI059524-05
Application #
7565898
Study Section
Special Emphasis Panel (ZRG1-IHD (01))
Program Officer
Minnicozzi, Michael
Project Start
2005-05-15
Project End
2011-07-31
Budget Start
2009-02-01
Budget End
2011-07-31
Support Year
5
Fiscal Year
2009
Total Cost
$310,793
Indirect Cost
Name
University of Maryland Baltimore
Department
Microbiology/Immun/Virology
Type
Schools of Medicine
DUNS #
188435911
City
Baltimore
State
MD
Country
United States
Zip Code
21201
Pattabiraman, Goutham; Murphy, Michael; Agliano, Federica et al. (2018) IRAK4 activity controls immune responses to intracellular bacteria Listeria monocytogenes and Mycobacterium smegmatis. J Leukoc Biol 104:811-820
Murphy, Michael B; Medvedev, Andrei E (2016) Long noncoding RNAs as regulators of Toll-like receptor signaling and innate immunity. J Leukoc Biol 99:839-50
Xiong, Yanbao; Murphy, Michael; Manavalan, Tissa T et al. (2016) Endotoxin Tolerance Inhibits Lyn and c-Src Phosphorylation and Association with Toll-Like Receptor 4 but Increases Expression and Activity of Protein Phosphatases. J Innate Immun 8:171-84
Leifer, Cynthia A; Medvedev, Andrei E (2016) Molecular mechanisms of regulation of Toll-like receptor signaling. J Leukoc Biol 100:927-941
Murphy, Michael; Xiong, Yanbao; Pattabiraman, Goutham et al. (2015) Pellino-1 Positively Regulates Toll-like Receptor (TLR) 2 and TLR4 Signaling and Is Suppressed upon Induction of Endotoxin Tolerance. J Biol Chem 290:19218-32
Medvedev, Andrei E; Murphy, Michael; Zhou, Hao et al. (2015) E3 ubiquitin ligases Pellinos as regulators of pattern recognition receptor signaling and immune responses. Immunol Rev 266:109-22
Murphy, Michael B; Xiong, Yanbao; Pattabiraman, Goutham et al. (2015) Pellino-3 promotes endotoxin tolerance and acts as a negative regulator of TLR2 and TLR4 signaling. J Leukoc Biol 98:963-74
Medvedev, Andrei E (2013) Toll-like receptor polymorphisms, inflammatory and infectious diseases, allergies, and cancer. J Interferon Cytokine Res 33:467-84
Xiong, Yanbao; Pennini, Meghan; Vogel, Stefanie N et al. (2013) IRAK4 kinase activity is not required for induction of endotoxin tolerance but contributes to TLR2-mediated tolerance. J Leukoc Biol 94:291-300
Xiong, Yanbao; Song, Chang; Snyder, Greg A et al. (2012) R753Q polymorphism inhibits Toll-like receptor (TLR) 2 tyrosine phosphorylation, dimerization with TLR6, and recruitment of myeloid differentiation primary response protein 88. J Biol Chem 287:38327-37

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