Mapping Metabolic Pathways for Mucosal Health at the Host-microbe Interface PDF Download

Author: Katti R. Crakes
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Languages : en
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Book Description
Background: Human body surfaces are lined by mucosal membranes composed of epithelial cells which serve as the primary barrier for protection against pathogens. These mucous membranes function in a shared environment with resident microbes, creating a complex ecosystem with communal sources of nutrients for the host as well as its microbes. Encounters with viral, fungal, and bacterial pathogens can directly or indirectly damage epithelial cells, disrupting tight junctions that keep mucosal barriers intact. Disruption of epithelial barriers lead to downstream inflammation, translocation of microbial products into the bloodstream, and exacerbation of disease. For example, Human immunodeficiency virus-1 (HIV) proteins can target zonula occludens for viral entry and dissemination, Clostridium perfringens utilizes claudin proteins as receptors for entry, and candidalysin toxin from Candida albicans targets junctional complexes for translocation, all of which induce permeability in epithelial barriers. Furthermore, autoimmune diseases such as inflammatory bowel disease and diabetes exhibit similar pathologies in intestinal barrier disruption and microbial dysbiosis. While these barrier defects have been observed across a broad range of diseases, there is a lack of understanding in how tight junctions are regulated by epithelial cells and which therapeutic targets will be effective. My dissertation takes two approaches to address this issue: 1) mucosal repair in chronic inflammation and 2) mucosal protection against pathogens. I hypothesized that strategies targeting entry of pathogens and cellular metabolism at mucosal sites will be fundamental for effective prevention and treatment of chronic diseases. This dissertation presents three studies that advance our knowledge about mucosal repair/protection by leveraging host-microbial metabolic pathways and mucoadhesive drug delivery systems. 1: Repair of gut epithelial barriers during SIV-induced chronic gut inflammation through the mitochondria-microbiota crosstalk. Chronic gut inflammatory diseases are associated with disruption of intestinal epithelial barriers and impaired mucosal immunity. HIV causes depletion of mucosal CD4+ T cells early in infection and disruption of gut epithelium, resulting in chronic inflammation and immunodeficiency. Although antiretroviral therapy is effective in suppressing viral replication, it is incapable of restoring the "leaky gut," which poses an impediment for HIV cure efforts. Using the intestinal loop model in SIV-infected rhesus macaques, we found rapid repair of gut epithelial barriers within five hours of administering Lactobacillus plantarum into virally inflamed gut. The rapid recovery was driven by peroxisome proliferator-activated receptor (PPAR[alpha]) activation and occurred independent of mucosal CD4+ T cell recovery, highlighting a metabolic repair pathway in mitochondrial [beta]-oxidation that can be targeted for epithelial repair prior to complete immune recovery. These findings highlight the critical role of PPAR[alpha] at the intersection between microbial metabolism and epithelial repair in virally inflamed gut and as a potential mitochondrial target for restoring gut barriers in infectious or inflammatory diseases. Study 2: Renewal of gut epithelial barriers in metabolic disease through PPAR[alpha] signaling at the host-microbe interface in metabolic disease. Metabolic disease affects approximately one-third of the US adult population, and is defined by pathological conditions associated with obesity, insulin resistance, hypertension, and hyperlipidemia. Metabolic disease is concomitant to dysfunctions in the intestinal barrier and an increased risk for mucosal infection and systemic inflammation, all of which are poorly understood. Using a canine model of diabetes mellitus (DM), we translated our findings in Study 1 and tested the clinical translation of PPAR[alpha] activation on gut epithelial barriers using fenofibrate, a known PPAR[alpha] agonist. We found that a 3-week oral dosage of fenofibrate alleviates small intestinal barrier disruption and improves lipid metabolism in dogs with DM. Reduction of plasma triglycerides after 3 weeks correlated with lower immune activation and reduction of intraepithelial T lymphocytes in the duodenum. The gut microbial composition remained stable after fenofibrate administration, suggesting that repair of intestinal barriers can be achieved independent of surrounding microbiota. These findings indicate that lipid metabolism is essential to functionality of the gut epithelium, which can be rescued by PPAR[alpha] activation in DM. Study 3: Protection of genital mucosal surfaces against HIV and SHIV viruses using Silk fibroin mucoadhesive delivery platform. Efforts to end the AIDS epidemic using anti-retroviral therapy have been widely successful in reducing HIV-related deaths. However, challenges for the prevention of new HIV infections have not been fully resolved. Most new HIV infections occur through mucosal transmission, so it is imperative that HIV prevention platforms are effective at mucosal sites, can be produced inexpensively, and are accessible to vulnerable populations. In these cases, protection against HIV transmission must overcome individual-to-individual variation in the context of mucosal microbiota composition, host metabolic status, and immune response. In this study, we developed a silk fibroin (SF)-based drug delivery platform that encapsulates a potent HIV entry inhibitor Griffithsin (Grft) that can be readily administered into genital mucosal sites for HIV prevention. The SF formulation, capable of holding several anti-HIV proteins, is thermodynamically stable for over one year, can be released over the course of one month, and provides an innovative platform that is safe and effective against transmission of HIV. We demonstrate the safety and efficacy of SF-Grft in both vaginal and rectal compartments using a non-human primate model in vivo and human explant cultures ex vivo. Effective release and mucosal adherence of SF-Grft protected against HIV and SHIV challenge with negligible changes in local microbiota or inflammatory responses. These findings provide support for the development of SF as an effective HIV prevention modality at mucosal sites to help address the global disparity in HIV infection. Conclusion: These studies provide novel insights into new metabolic targets to repair inflamed gut mucosa and impart protection against pathogens at mucosal surfaces through innovative mucoadhesive technology. This dissertation deciphers the molecular, cellular, and microbial components involved in chronic gut inflammatory diseases, identifies molecular mechanisms of reversing mucosal damage, and defines the significance of addressing this complexity to bolster systemic and mucosal health.