PROJECT SUMMARY/ABSTRACT The proposed research plan focuses on improving our understanding of the effects of acidosis on pneumonia and establishing the conceptual basis for diagnostic and therapeutic translation. Acidosis is common in critically ill pneumonia patients, and is associated with high mortality. The pathophysiology of acidosis in pneumonia is poorly understood, and current therapies fail to improve major outcomes. Our studies have shown that pulmonary microvascular endothelial cells (PMVECs) utilize the carbonic anhydrase IX (CA IX) isoform to regulate pH, metabolism and migration. We also demonstrated that Pseudomonas aeruginosa infection of PMVECs induces release of cytotoxic amyloid proteins, which disrupts the alveolar capillary membrane. These cytotoxic amyloids induce soluble CA IX shedding from PMVECs which compromises their repair potential. Based on these preliminary studies, we test the hypothesis that P. aeruginosa infection induces cytotoxic amyloid production that leads to shedding of soluble CA IX in PMVECs, increasing lung injury. Specific aims test the hypotheses that: 1) CA IX is critical to the acid regulation, metabolism and migration of PMVECs and pulmonary endothelial barrier integrity; and, 2) P. aeruginosa infection elicits cytotoxic amyloid production, causing CA IX shedding in PMVECs, which increases lung injury. In vitro, we will use genetic approaches and endothelial cell functional assays to evaluate the effects of acidosis and the role of specific CA IX functional domains during physiologic and infectious conditions. In vivo and ex vivo, we will use acidosis, pneumonia and isolated lung perfusion mouse models to translate in vitro findings. Successful completion of this study will provide new insights into the mechanisms underlying acidosis in pneumonia and help identify CA IX and cytotoxic amyloids as biomarkers and therapeutic targets for pneumonia.