Exposure to the respirable toxicant crystalline silica (cSiO2) is etiologically linked to systemic lupus erythematosus and other human autoimmune diseases. An estimated 2 million Americans are exposed to cSiO2 occupationally, including approximately 100,000 exposed to levels above the National Institute for Occupational Safety and Health’s recommended exposure limit. Clearance of inhaled cSiO2 is very slow, thus repeated inhalation of cSiO2 activates a chronic immune response in the lungs. Animal models suggest that continued over-activation of immune cells results in production of antibodies against the host, ultimately culminating in the development of systemic autoimmunity. Intriguingly, previous studies performed in Dr. Pestka’s lab discovered that dietary supplementation with ω-3 polyunsaturated fatty acids (ω-3 PUFAs), an intervention known to improve disease status in patients with lupus and other autoimmune diseases, blocks cSiO2-triggered autoimmunity in lupus-prone NZBWF1 mice. In these studies, the dietary ω-3 PUFA docosahexaenoic acid (DHA) attenuated many of the inflammatory and autoimmune disease endpoints induced by cSiO2, including inflammatory gene expression; pulmonary immune cell infiltration; local and systemic chemokine, cytokine, and autoantibody production; and development of glomerulonephritis. This thesis builds upon previous work employing this model for environmenttriggered autoimmunity to determine 1) the effect of DHA supplementation in a Western style diet, 2) the associate between tissue ω-3 content and disease severity, and 3) the mechanisms of DHA protection and cSiO2 toxicity in in vitro macrophage models. Here, supplementation with DHA dose-dependently decreased several features of cSiO2-triggered autoimmunity in a lupus prone mouse model fed a diet mimicking the micro- and macro-nutrient composition of Western dietary patterns. DHA was as effective in this suboptimal diet as in previous studies where DHA is provided on the background of a diet optimized for rodent health. A meta-analysis of three publications employing DHA supplementation to protect against cSiO2-triggered lupus identified strong correlations between red blood cell ω-3 fatty PUFA levels and autoimmune and inflammatory endpoints, which highlights the benefits of monitoring patients’ fatty acid profiles when implementing a dietary intervention to augment ω-3 PUFA levels.A key event in the development of systemic inflammation in this model is cSiO2-induced toxicity of the alveolar macrophage (AM). In vitro studies in this thesis demonstrated that enriching the macrophage membrane with DHA influences macrophage phenotype and suppresses inflammatory and cytotoxic pathways induced by cSiO2 and other inflammatory stimuli. Specifically, it was identified that DHA inhibits cSiO2-induced inflammasome activation in part by interfering with gene expression of inflammasome components. Further investigations employing next generation RNA sequencing revealed that DHA suppressed many LPS-induced transcripts, and induced genes associated with inflammation resolution, identifying putative mechanisms for the protective effects of DHA supplementation in vitro. Lastly, a novel self-replicating AM model was used to investigate cSiO2 engulfment, cell death, and cytokine release in vitro. Here, DHA inhibited cSiO2-induced cell death and inflammatory cytokine release without influencing particle phagocytosis, highlighting the potential for this dietary intervention to protect against cSiO2-triggered autoimmunity by preventing cSiO2-induced toxicity in AMs.Taken together, these studies provide greater insight into ω-3 PUFA-mediated protection against inflammation and autoimmune disease triggered by the inhaled toxicant cSiO2.
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