Regulation and Function of the Rhomboid Pseudoproteases iRhom1 and iRhom2 in Lung Inflammation

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Lung inflammation can be critically modulated by limited proteolysis of cell surface molecules. These so called shedding processes regulate vascular permeability, edema formation, leukocyte recruitment, inflammatory mediator production and fibrotic responses. This involves the activity of several surface molecules such as TNF, EGF family members, IL-6 receptor, transmembrane chemokines, junctional cell adhesion molecules, or syndecans which all undergo shedding by the metalloprotease ADAM17. By cell specific knockout or pharmacological inhibition of ADAM17 we have demonstrated a critical role of endothelial and smooth muscle expressed ADAM17 in a murine model of acute lung inflammation. ADAM17 is known to be tightly regulated by several mechanism. Transcriptional induction of the protease is per se not sufficient and requires further translational events including the trafficking from the ER to the Golgi, maturation and surface expression of the protease. It became clear that these events strictly depend on the interaction of ADAM17 with the rhomboid like pseudoproteases (iRhom1 and 2). We recently observed differential induction of iRhom2 by inflammatory stimuli and iRhom1 by flow conditions. We could show that inflammatory upregulation of endothelial iRhom2 causes enhanced maturation and surface expression of ADAM17. On the other hand upregulation of iRhom1 in flow exposed endothelial cells correlated with enhanced induction and surface expression of ADAM15. We propose that the upregulation of iRhom2 in lung tissue plays a critical role in boosting the inflammatory response, while high expression of iRhom1 could be more important in maintaining some surface expression of ADAM proteases under non-inflammatory conditions. The central aim of this proposal is to study the role of iRhom1 and 2 in lung inflammation at molecular, cellular and systemic levels. The in vitro investigations address the differential role of iRhoms in inflammatory and physiological responses of primary lung cell types including endothelial and smooth muscle cells. This comprises endothelial barer function, permeability changes, mediator production, smooth muscle transactivation, leukocyte transmigration and protection against apoptosis. We observed that in inflamed mouse lungs iRhom2 rather than iRhom1 becomes upregulated. We therefore want to further investigate and correlate the time kinetics of iRhom regulation with the inflammatory events in our model of LPS induced inflammation. We will then use or generate new mice with knockout of iRhom1 and/or 2 or iRhom2 overexpression and investigate them for vascular permeability, mediator production, leukocyte recruitment and fibrotic responses. We expect that our findings allow a deeper understanding of the pathways promoting pathogenic functions of ADAM17 which in turn could support the rationale to target iRhom2 in inflammatory lung diseases.