Viral infection stimulates the immune response to produce many cytokines and chemokines, the proteins imperative to fight a brewing infection. This response begins through recognition of pathogen-associated molecular patterns (PAMPs) from the virus, or from other signatures characteristic of tissue damage, damage-associated molecular patterns (DAMPs), by pattern recognition receptors (PRRs) that in turn stimulate pro-inflammatory signaling cascades. The results of these signaling pathways include the release of cytokines and chemokines that work to further upregulate immune responses and attract immune cells to the site of infection, respectively. In the case of SARS-CoV-2 infection, these responses can become problematic if they go unmitigated or unresolved, resulting in the severe COVID-19 manifestation of the 'cytokine storm,' or multisystem inflammatory syndrome in children (MIS-C). One classically increased protein in cytokine storm of COVID-19 patients is C-X-C motif chemokine 10 (CXCL10), which has been explored as a prognostic marker as it is shown to be predictive of disease outcome in hospitalized patients. To prevent severe outcomes like cytokine storm, a delicate balance must be struck, to ensure that this inflammation does not result in high levels of diffuse tissue damage. To achieve this, anti-inflammatory pathways exist within the immune system and help dampen the signals being induced. One such unique anti-inflammatory protein is a pattern recognition receptor known as NLRX1 (Nucleotide binding oligomerization domain, leucine rich repeat containing X1), that can interact with two main pathways involved with anti-viral immunity, the NFB and interferon pathways, downregulating them to keep off-target tissue damage at bay. NLRX1 is also involved in several other cellular processes, including modulating cell death processes and cellular metabolism which can also impact viral replication and clearance indirectly.
In this work, we investigated both the pro- and anti-inflammatory arms of the anti-SARS-CoV-2 response focusing on two key proteins – pro-inflammatory chemokine CXCL10 and immunoregulatory PRR NLRX1. The roles of these two proteins were explored utilizing transcriptomic analysis of both human and mouse RNA samples, immortalized cell culture work, humanized mouse models of SARS-CoV-2 infection, and mouse-adapted virus models to be able to utilize deficient mouse models. In this work we better characterize the immune response to SARS-CoV-2 and its related immune-driven pathobiology of disease. The data presented in this work continues to elucidate CXCL10's role as an important driver of viral clearance of SARS-CoV-2, translating data from human patient nasal swabs to the animal model of disease, exploring differential inflammation and immune responses in the absence of CXCL10. Additionally, the work shown here provides further understanding of NLRX1 and its role in antiviral immunity with the context of SARS-CoV-2 infection. The interactions between this protein and the virus remains to be fully characterized, however, it appears they have some degree of mutual inhibition as determined by animal and cell culture models. The culmination of work here emphasizes the importance for both the pro- and anti-inflammatory responses in SARS-CoV-2 infection and offers insight into two possible related targets for future drug development. / Doctor of Philosophy / When a virus invades the body, the immune system kicks off many signaling cascades to keep the virus from replicating, clear virus already established in cells, and clean up the tissues surrounding the infected area of the remnants of cells that already succumbed to the virus. While this immune response is important to fight off the virus that has made its way into the body, overactive immune responses can result in hospital stays requiring supportive care to aid recovery from possible off-target tissue damage. One such case of this happening is when SARS-CoV-2 induces such a strong response, the immune system becomes overzealous and results in overproduction of pro-inflammatory cytokines and chemokines, signaling proteins in the immune system, which can lead to the characteristic 'cytokine storm' of severe COVID-19 disease. One of the proteins most often overproduced is the chemokine CXCL10, and this protein has been used as a biomarker in clinical practice to successfully predict severe disease outcomes in COVID-19 patients. To help combat severe disease outcomes and high levels of tissue damage, the immune system has inborn checks and balances to ensure that proteins like CXCL10 do not reach the level of overproduction as in the cytokine storm of COVID-19. One of these natural checkpoints is a protein called NLRX1, which interacts with two of the main pathways that can lead to the overproduction of cytokines seen overproduced in the case of cytokine storm. NLRX1 also has other roles in other interesting facets important for viral infections, including the metabolism of the cell and cellular death processes. The culmination of these roles could offer up NLRX1 as a possible target for treatments in the future.
The work put together here explores both sides of the immune response, turning it 'on' with pro-inflammatory signaling, and turning it 'off' with anti-inflammatory signaling, trying to find just the right amount of inflammation to clear a viral invader while also impeding off target and diffuse tissue damage as the body fights the virus. This work focuses on two key proteins, CXCL10 to represent pro-inflammatory responses, and NLRX1 to represent the anti-inflammatory signaling. Understanding both arms of the immune response to SARS-CoV-2 infection is crucial to being able to identify potential targets for future treatments to help combat severe outcomes of SARS-CoV-2 infection. Using multiple levels across the translational spectrum, including cell culture, animal models, and human patient RNA from COVID test swabs, we explore both facets of SARS-CoV-2 immunity, focusing on these two proteins. Utilizing mouse models bearing deletions of the genes required to make these proteins and a mouse-adapted strain of SARS-CoV-2, this work characterizes how important these individual proteins are in the immune response to SARS-CoV-2, and work as proxies to understand the broader impacts of either the positive or negative regulation of immune signaling. Because of the work culminated here, these two tangentially related proteins are also offered up as possible future drug targets for the development of treatments in severe COVID-19 disease with cytokine storm presentation.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/118977 |
| Date | 14 May 2024 |
| Creators | Ivester, Hannah Marie |
| Contributors | Graduate School, Allen, Irving Coy, Bertke, Andrea S., Duggal, Nisha, Smyth, James, Zhang, Yanjin, Weger, James David |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Language | English |
| Detected Language | English |
| Type | Dissertation |
| Format | ETD, application/pdf, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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