| Particulate matter (PM) has long been established as a notable hazard to public health. Nonetheless, regardless of its strong association with a number of adverse cardiopulmonary outcomes the underlying mechanisms responsible remain unclear. Especially mechanisms that may provide insight into the physiological basis of differential sensitivities that have been shown to exist amongst PM-exposed human sub-populations. Therefore, further evaluation / identification of novel mechanisms that elucidate: 1) the pathophysiological pathways by which PM may exploit; 2) pathways that may explain inherent vulnerabilities in susceptible individuals, are of great interest to regulatory and academic scientists.;In response to these needs, the primary aim of this dissertation was to comprehensively evaluate the role of RAGE, a latent pattern recognition receptor (PRR) intimately involved in the pathobiology of a diverse range of chronic inflammatory diseases, in the context of inhaled PM toxicity. Therein, characterizing the contributions / involvement of a receptor with significant physiological / pathophysiological cardiopulmonary importance to a ubiquitous toxicant with well-established adverse cardiopulmonary effect. The basis of this hypothesis is rooted in the fact that RAGE is: 1) the pre-eminent pathological factor in chronic-inflammatory diseases such as diabetes and cardiovascular disease, both of which constitute sub-populations that have been established as susceptible cohorts to PM exposure; 2) a functional PRR that is highly responsive / potentiated by an array of damage-associated molecular patterns; 3) inherently localized in lung tissues. To comprehensively characterize RAGE, a multi-faceted approach utilizing specimens derived from naturally-exposed human cohorts, as well as in vitro and in vivo exposures were incorporated.;As a result of the work encompassed in this thesis, for the first time ambient PM exposure was found to significantly modulate sRAGE levels in sera of humans, while heavy metal components of atmospheric PM, Ni, Cu, As and Se, were found to significantly influence AGE levels. Bioassays in cultured bronchial / alveolar epithelial cells and alveolar macrophages exposed to PM revealed distinct cell-type-specific and PM-type-specific RAGE-related response profiles. More specifically, while epithelial cells were found to significantly contribute to labile DAMP pools, macrophages were found to be the major pulmonary contributors of HMGB-1 and select s100s, as well as RAGE activation. Furthermore, penultimate outcomes of RAGE activation (i.e. NF-kappaB activation and ROS generation) were found across all exposed cell-types to varying degrees generally influenced by dose and composition. Lastly, validation experiments using wild-type and RAGE null mice clearly distinguish the pro-inflammatory contributions of RAGE as a mediator of PM-induced pulmonary inflammation. RNA and protein expression of exposed lungs in these mice confirmed the significance of macrophage-specific contributions in these PM-derived inflammatory processes.;Taken together, these findings along with those from tertiary studies involving LPS-stimulated cell models, human endothelial cells, as well as diabetic-specific murine models add to a relatively scarce body-of-literature pertaining to RAGE in the context of inhalation toxicology. Moreover, these findings clearly support my hypothesis that RAGE is indeed a significant mediator of PM-induced toxicity yet elucidate the unexpected significance of PM-derived DAMP contributions (e.g. HMGB-1, S100A9, and S100A12) to the process of PM-induced pulmonary injury. Lastly, the work encompassed in this dissertation provide foundational evidence that supports the use of sRAGE as a potential biomarker of chronic PM-exposure and potential influence of inhaled heavy-metals on AGE modulation. In conclusion, these results indicate that exposure to ambient PM as well as related constituents such as cigarette smoke and diesel PM are indeed modulated by RAGE but more importantly result in the production / release of DAMPs that are likely to harbor significant tertiary implications from nearby pro-inflammatory PRRs. |
