PROJECT SUMMARY/ABSTRACT Studies have shown much broader roles for macrophages in responding to inflammation and tissue injury than previously recognized, such as promoting inflammation resolution, tissue repair and restoring tissue homeostasis and this recognition of macrophage plasticity has shifted the focus away from the simple notion of M1 and M2 dichotomies. Project 3 focuses on delineating the signals mediating monocyte transition to tissue macrophages and their potentially essential role in tissue repair in acute lung injury (ALI). As the lung endothelium is the entry point of the monocytes transmigrating into tissue, endothelial cells (ECs) may modify the downstream macrophage phenotype, and thus the interaction between cells may be of great consequence. Project 3 will delineate mechanisms of generation of how ECs instruct macrophages and their role in resolving ALI. We will address fundamental questions including: What are the EC signals mediating transition to the reparative macrophage populations? What signals in macrophages in turn convert the cells to repair tissue? What are the epigenetic and transcriptomic features of these phenotype-shifted macrophages? In Project 3 we will test the hypothesis that the lung endothelium via Wnt signaling mediates macrophage phenotype transition through modifying mitochondrial metabolism and epigenome that initiates specific transcriptional programs. In Aim 1, we will define the role of endothelial Wnt signaling in regulating the differentiation of monocytes to macrophages in lungs. Here we will determine the role of the Wnt signaling regulator Rspondin 3 (Rspo3) derived from ECs in signaling the transition of monocytes to lung macrophages. In Aim 2, we will determine the role of metabolic reprogramming and epigenetic modifications of macrophages in mediating phenotype transition and thereby reducing the extent of lung injury as well as promoting its resolution.

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