Molecular mechanisms underlying increased susceptibility to bacterial infections and impaired antimicrobial responsiveness observed in patients with hypoinflammatory syndromes are poorly understood. Such states could result from impaired recognition of bacterial structures with TLRs as a consequence of mutations in the TLR ectodomains. Secondly, faulty cell activation by microbial products may be mediated by mutations in principal intracellular adapter molecules and kinases (e.g., IRAK-4) that affect their abilities to form signaling complex and/or activate downstream signaling intermediates. Finally, development of tolerance-like hypoinflammatory states in septic patients and smokers may compromise the hostâ?Ts ability to counteract subsequent bacterial challenge, leading to an increased incidence of bacterial infections. My research program focuses on the following projects:
1. Molecular mechanisms of microbial tolerance;
2. Role of post-translational modifications of TLRs and adapter proteins in TLR signaling and tolerance;
3. The effect of tobacco smoking on TLR sensing of Gram positive, Gram negative bacteria, mycobacteria and their structural components; and
4. Delineation of molecular basis by which polymorphisms/mutations in TLR2, TLR4, and IRAK-4 affect bacterial sensing and signal transduction.
Within these projects, my laboratory has recently demonstrated an important functional role of tyrosine phosphorylation of TLR4 and adapter protein MAL, and is now focused on the identification of protein kinases involved in TLR4 tyrosine phosphorylation. Ongoing studies address functional role of phosphorylation and glycosylation statuses of TLRs, adapter proteins, and kinases in mediating their signal-transducing functions. In addition, we study TLR-inducible activation of signaling cascades in control cells and upon induction of tolerant-like states. These include studies on TLR recruitment/cellular distribution/posttranslational modifications of adapter proteins and kinases IRAK-4, IRAK-1, and TBK-1; activation of IRAK-4/IRAK-1/TBK-1 kinase activities, expression and functions of negative regulators of TLR signaling Tollip, SHIP, SOCS-1, SARM and IRAK-M; induction of MAP kinases and transcription factors NF-kB, AP-1, CREB and ATF-2. Having characterized these signaling events in tolerant cells, my laboratory is planning to use findings obtained in the model of endotoxin tolerance as a methodological platform to extend these studies to signaling network analyses in patients with sepsis, burns, trauma and other pathologies.
Medvedev AE, W Piao, J Shoenfelt, SH Rhee, H Chen, S Basu, LM Wahl, MJ Fenton, and SN Vogel. 2007. Role of TLR4 tyrosine phosphorylation in signal transduction and tolerance. J Biol Chem. 282: 16042-16053.
Medvedev A. E., I. Sabroe, and S. N. Vogel. 2006. Tolerance to microbial pathogens: molecular mechanisms and relevance to disease. J. Endotoxin Res. 12: 133-150.
Vogel S. N., A. Awomoyi, P. Rallabhandi, and A. E. Medvedev. 2005. Mutations in TLR4 Signaling that Lead to Increased Susceptibility to Infection in Humans: An Overview. J. Endotoxin Res. 11:333-339.
Medvedev, A.E., Thomas K., Awomoyi A, Kuhns D.B., Gallin J.I., Li X., and Vogel S.N. 2005. Cutting Edge: IRAK-4 Mutations Identified in a Patient with Recurrent Bacterial Infections Alter IRAK-4 Interaction with Components of the IL-1 Receptor Complex. J. Immunol. 174:6587-6591.
Medvedev, A.E., Lentschat, A., Kuhns, D.B., Blanco, J.C.G., Salkowksi, C., Zhang, S., Arditi, M., Gallin, J.I., and Vogel, S.N. 2003. Distinct mutations in IRAK-4 confer hyporesponsiveness to lipopolysaccharide and Interleukin-1 in a patient with recurrent infections. J Exp Med 198:521-531.
Medvedev, A.E. and Vogel, S.N. (2003) Overexpression of CD14, TLR4, and MD-2 in HEK 293 cells does not prevent induction of in vitro endotoxin tolerance. J Endotoxin Res 9: 60-4.
Medvedev, A.E., A. Lentschat, L. M. Wahl, D. T. Golenbock, and S.N. Vogel. (2002) Dysregulation of LPS-induced TLR4-MyD88 complex formation and IRAK-1 activation in endotoxin-tolerant cells. J. Immunol. 169: 5209-16.
Medvedev, A.E., Henneke, P., Schromm, A., Lien, E., Ingalls, R., Fenton, M.J., Golenbock, D.T., and Vogel, S.N. 2001. Induction of tolerance to lipopolysaccharide and mycobacterial components in Chinese hamster ovary/CD14 cells is not affected by overexpression of Toll-like receptors 2 or 4. J. Immunol. 167:2257.
Lakics, V., Medvedev, A.E., Okada, S., and Vogel, S.N. 2000. Inhibition of LPS-induced cytokines by Bcl-xL in a murine macrophage cell line. J Immunol. 165:2729.
Medvedev, A.E., Kopydlowski, K.M., and Vogel, S.N. 2000. Inhibition of lipopolysaccharide-induced signal transduction in endotoxin-tolerized mouse macrophages: dysregulation of cytokine, chemokine, and toll-like receptor 2 and 4 gene expression. J Immunol. 164:5564.
Vogel, S.N., Johnson, D., Perera, P.Y., Medvedev, A., Lariviere, L., Qureshi, S.T., and Malo, D. 1999. Cutting edge: functional characterization of the effect of the C3H/HeJ defect in mice that lack an Lpsn gene: in vivo evidence for a dominant negative mutation. J. Immunol. 162:5666.
Medvedev, A.E., Blanco, J.C., Qureshi, N., and Vogel, S.N. 1999. Limited role of ceramide in lipopolysaccharide-mediated mitogen-activated protein kinase activation, transcription factor induction, and cytokine release. J Biol Chem. 274:9342.