The innate immune system is integral for defense against infectious diseases. Characterized by Pattern Recognition Receptors (PRRs), which sense conserved molecular motifs known as Pathogen-Associated Molecular Patterns (PAMPs), the innate immune system sets a system of checks and balances to regulate inflammation in host defense. In this dissertation, we focus on one class of PRRs known as the NOD-like Receptors (NLRs) in response to bacterial diseases. This class consists of pro-inflammatory receptors that form a multi-protein complex termed the inflammasome, as well as regulatory NLRs that modulate inflammation. Here, we investigated the roles of inflammasomes and negative regulatory NLRX1 in response to bacterial diseases. First, we studied brucellosis, a zoonotic, chronic disease often transmitted in unpasteurized dairy products from livestock. Using murine models and bone marrow-derived macrophages (BMDMs) challenged with Brucella abortus, we found that canonical inflammasomes in murine models were protective against brucellosis through the initiation of inflammatory cell death called pyroptosis. In contrast, the inhibition of inflammation by NLRX1 adversely led to increased pathology in the spleen and liver in infected murine models. Despite these contrasting results, Brucella genomic DNA was an effective PAMP for NLR recognition. These results suggest the importance of DNA recognition by NLRs during brucellosis. Second, we investigated NLRX1 regulation of Borrelia burgdorferi in Lyme arthritis using murine models. Characterized by persistent inflammation of the joints, Lyme arthritis is an enigmatic and difficult inflammatory condition to resolve. We found that NLRX1 was protective against arthritis. By characterizing changes in gene and protein expression of infected ankle joints, in addition to in vitro studies in BMDMs and fibroblasts, we found that NLRX1 enhances cell migration and regulates cell metabolism. Our results suggest that NLRX1 may metabolically shift macrophages toward a more favorable wound-healing environment for arthritis resolution. Ultimately, this work emphasizes the importance of balance in NLR signaling, which occurs within NLRs and from crosstalk with other inflammatory pathways. Further, NLR signaling is highly multifaceted and context-specific for the cell type and bacterial disease, showcasing the complexity of host-pathogen interactions when battling bacteria. / National Institute of Health/National Institute of Allergy & Infectious Diseases: R03AI151494, R21AI159800
Virginia Tech/University of Maryland Joint Seed Grant
VMCVM Office of Research and Graduate Studies and DVM/PhD Student Support / Doctor of Philosophy / The immune system consists of two arms: a specialized adaptive response that forms long-lasting defense and a generalized innate response that provokes immediate protection. Consequently, the innate immune system is our first line of defense against infectious diseases. It operates in part through proteins called Pattern Recognition Receptors (PRRs), which work by recognizing foreign signals in the body, known as Pathogen-Associated Molecular Patterns (PAMPs). The innate immune system’s job is to enforce a system of checks and balances to regulate inflammation in host defense. In this dissertation, we focus on the NOD-like Receptor (NLR) class of PRRs. NLRs consist of a group of pro-inflammatory proteins that form a complex called the inflammasome, as well as NLRs like NLRX1 that instead control and change inflammation. Here, we investigated the role that inflammasomes and anti-inflammatory NLRX1 play in response to bacterial diseases.
First, we studied brucellosis, a chronic bacterial disease often transmitted in unpasteurized dairy products from livestock. We found that inflammasome-forming NLRs in murine models were protective against brucellosis through the initiation of inflammation and inflammatory cell death. In contrast, NLRX1 in mouse models adversely led to increased disease in the spleen and liver and decreased inflammation. Despite these contrasting results, Brucella DNA was an effective signal, or PAMP, for the activation of both NLRs in cells. These results suggest the importance of DNA recognition by NLRs, and that inflammation is protective during brucellosis.
Second, we investigated NLRX1 regulation of the bacterium Borrelia burgdorferi in Lyme arthritis. Characterized by persistent inflammation of the joints, Lyme arthritis is a difficult inflammatory condition to resolve. We found that in mouse models, NLRX1 was protective against arthritis. Using immune and wound healing cells, we found that NLRX1 promotes faster cell migration and regulates cell metabolism. Encouragingly, our results suggest that NLRX1 may change cell metabolism in joints to provide enhanced energy in order to increase wound healing and resolve arthritis.
Ultimately, this work emphasizes the importance of balance in NLR signaling. Further, NLR signaling is highly dependent on the specific cell type and bacterial disease, showcasing the complexity of host-pathogen interactions when battling bacteria.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/121251 |
| Date | 19 August 2024 |
| Creators | Tupik, Juselyn D. |
| Contributors | Allen, Irving Coy, Jutras, Brandon L., Reilly, Christopher M., Caswell, Clayton C., Coutermarsh-Ott, Sheryl, Zhang, Yan-Jin |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Language | English |
| Detected Language | English |
| Type | Dissertation, Text |
| Format | ETD, application/pdf, application/pdf, application/pdf |
| Rights | Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International, http://creativecommons.org/licenses/by-nc-sa/4.0/ |
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