Role of HMGB1 and mitochondria in organic dust induced airway inflammation
Due to a sharp increase in global demand for protein of animal origin, animal production systems have transformed into industrial-scale operations known as concentrated animal feeding operations (CAFOs). Due to the high animal density within CAFOs, these facilities generate and accumulate various of contaminants such as airborne dust, gases, and microbes. Organic dust (OD) from such large animal confinement facilities is a complex mixture of microbial-associated components and particulate matter known to elicit chronic respiratory diseases in exposed workers. Examination of clinical samples from exposed workers revealed the prevalence of fevers, airway hyperresponsiveness, and an increase in neutrophils, macrophages, and proinflammatory mediators including TNFα, IL-6, and IL-8 (CXCL8) in bronchoalveolar lavage (BAL) fluid. Studies have also shown the release of damage-associated molecular patterns (DAMPs) and activation of multiple overlapping signaling pathways on OD exposure. In the following dissertation, we investigated the role of high mobility group box 1 (HMGB1), a ubiquitously present transcription factor and DAMP, in OD-mediated airway inflammation. HMGB1 has been shown to mediate the activation of innate immune responses and plays a critical role at the intersection of host inflammatory response to sterile and to infectious threats. The goal of our research was to understand the role and impact of HMGB1 in OD-mediated airway inflammation. We show that OD-mediated HMGB1 release amplifies cytokine release and tissue damage. Using experimental strategies that selectively target HMGB1, we effectively reversed activation of specific immune signaling molecules and cytokine release and significantly attenuated damage in OD exposed in vitro and in vivo models. In addition to the myriad of immune signaling and responses, inflammation contributes to cellular structural and functional changes as well. Recently, mitochondria are emerging as therapeutic targets in addition to their essential role in cellular respiration. Emerging evidence shows that exposure to contaminants damages mitochondrial structure and alters function. We identified that OD exposure would induce ultrastructural changes in mitochondria and transcriptional changes in genes encoding proteins related to mitochondrial structure and function. We further investigated how the pathologic (secreted) and physiologic (nuclear) roles of HMGB1 would influence OD-exposure induced mitochondrial dysfunction, and airway inflammation. By using targeted HMGB1 antagonists we identified that HMGB1 could be a critical regulator of mitochondrial structure and function. We showed that neutralization of HMGB1 rescues OD-induced mitochondrial damages at structural and transcriptomic levels. Overall, our results highlight a critical role HMGB1, and mitochondria play in the progression of OD mediated airway inflammation. Identifying a mechanistic correlation between these two factors will likely help develop effective therapeutic strategies.