Cardiolipin (CL) is an important phospholipid component of mitochondrial and bacterial membranes that has emerged as a critical factor in the apoptotic program. To date, there is very limited data on the metabolism, processing, and physiologic role of CL in human disease states. Normally, very little CL is detected in lung fluid or in association with surfactant, but levels increase in patients with chronic obstructive pulmonary disease (COPD), and in chemical and sepsis-induced lung injury models. Preliminary data in the PI's laboratory shows that CL is elevated in lung fluid of patients with ventilator- associated pneumonia and in murine models of pneumonitis. Further, CL potently elevates lung surface- tension and impairs lung compliance. These original observations suggest a new role for CL as an important mediator of acute and chronic inflammatory lung injury. The data also suggest the existence of a CL-alveolar transport protein that may evacuate this phospholipid from pulmonary fluid, thereby preserving lung structure and function. ATP8b1 is a relatively newly discovered lipid pump that functions to translocate a phospholipid, phosphatidylserine, across biological membranes. Preliminary data show that ATP8b1 is highly expressed in alveolar epithelia, that ATP8b1 binds CL, and stable overexpression of this pump increases uptake and internalization of CL in murine lung epithelia. ATP8b1 mutant mice exhibit impairment of lung biophysical properties and are severely prone to acute bacterial inflammatory lung injury. Collectively, the above observations led to the overall hypothesis in this project that cardiolipin is a key mediator of inflammatory lung injury, and its intra-alveolar availability is tightly regulated by the lipid pump, ATP8b1. The PI will conditionally express ATP8b1 in a cell line and generate distal lung epithelial-targeted ATP8b1 double transgenic mice to ascertain the role of this lipid pump in regulating CL availability in lung fluid after E. coli and P. aeruginosa infection. Studies also assess ATP8b1 protein apical targeting, delivery of ATP8b1 CL-binding decoy peptides, and gene transfer of ATP8b1 in mutant mice after E. coli and P. aeruginosa infection as a means to attenuate inflammatory lung injury. Last, studies will assay CL levels and molecular species of CL in patients with acute lung injury at a University-based, patient-oriented teaching hospital. Execution of these studies will provide novel information of ATP8b1 molecular regulation that will impact the field of lung inflammatory disease.
We have recently discovered that in pneumonia, there is marked elevation of a rare lipid, termed cardiolipin, that potently inhibits lung function. We have also discovered a lipid pump, termed FIC1, that is rapidly degraded after bacterial infection. We propose in this application to use several tools to confirm that FIC1 is indispensable for controlling the availability of cardiolipin in lung fluid, to identify the molecular and biochemical mechanisms for FIC1 breakdown after bacterial infection, and to correlate cardiolipin levels in lung fluid of patients having pneumonia with illness severity.
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