E3 Ligase-Mediated Immunosuppression in Acute Lung Injury

Abstract Acute respiratory Distress Syndrome (ARDS) is a devastating disorder with a high mortality. Prior studies have focused mainly on its hyper-inflammatory state and yet anti-inflammatories for ARDS have not shown benefit. Mounting data suggest that immune suppression partakes in this disorder, the molecular mechanisms of which remain unclear. This application investigates a unique molecular model whereby we discovered an immunosuppressive protein called Fbxo24, that disposes of a key transcriptional protein, called ELF2, that is indispensable for critical cytoprotective functions of epithelia including innate immune function and preservation of cell proliferative activity. By targeting the C-terminal molecular signature present in Fbxo24, we designed, synthesized, and tested a novel small molecule Fbxo24 antagonist that restores ELF2 levels and innate immune responses in ARDS models. Our hypothesis is that Fbxo24, in part, mediates immunosuppression in experimental ARDS through ubiquitin-mediated degradation of ELF2, a protein essential for host epithelial cell innate immune and reparative responses. Hence, in this application we will first elucidate if Fbxo24 targets ELF2 for its ubiquitin-mediated proteolysis in experimental ARDS (Aim 1). We will specifically elucidate the biologic relevance of reduced Fbxo24 levels in preclinical models of ARDS as an immune suppressor using gene transfer in our Fbxo24 knockout mice and the mechanisms by which Fbxo24 mediates ELF2 ubiquitination and degradation in a site-specific manner. Next, we will optimize the pharmacologic design and test a novel small molecule that exhibits distinct, and yet complementary cytoprotective and innate immune properties in ARDS models (Aim 2). We will employ complementary murine and 2-hit models of immune suppression and an ex vivo isolated human lung system. These studies will provide a new pathobiologic model of epithelial injury that will serve as a platform for generating small molecule modulators that optimize cellular repair and modulate immunity in subjects with severe critical illness.