The role of GPR84 signaling during skin repair

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ABSTRACT Efficient wound healing requires complex cellular communication between tissue-resident non-immune cells and infiltrating immune cells. While much has been learned about how cytokines and growth factors contribute to acute wound healing, we know very little about how lipid signaling regulates acute inflammation and tissue repair, and identification of new mechanisms that govern acute inflammation and repair is needed. We previously demonstrated that inhibiting dermal adipocyte lipolysis led to reduced macrophage numbers during early inflammation and delayed repair, yet the mechanism(s) linking adipocyte lipolysis to efficient inflammation and repair have not been identified. Given the rising numbers of diabetic and aged patients, it is imperative to define molecular underpinnings that promote a healthy acute inflammatory response and to identify druggable mechanisms to treat inflammation and non- healing wounds. Inhibition of injury-induced dermal adipocyte lipolysis significantly reduces the abundance of medium-chain fatty acids (MCFAs). Recently, GPR84 was identified to be an MCFA receptor that is expressed by bone marrow-derived myeloid cells and during tissue inflammation. Activation of GPR84 in vitro increases macrophage migration and enhances pro-inflammatory gene expression; however, its role in skin and the in vivo mechanism of action is not well defined. We observe increased GPR84-expression during wound-induced inflammation and found that administration of a GPR84 agonist increases macrophage numbers. Additionally, systemic administration of a GPR84 antagonist decreases wound bed macrophages and delays tissue repair. Based on our preliminary data, we hypothesize that GPR84 signaling is required to support macrophage numbers and subsequent repair during injury-induced inflammation. We will combine our team’s tools and expertise in adipocyte, keratinocyte, and macrophage biology with single-cell data interrogation to validate this hypothesis with the following Specific Aims: (1) Use mouse models to determine how GPR84 signaling controls macrophage numbers and subsequent tissue repair after injury, and (2) define how MCFA/GPR84 signaling directly regulates myeloid cell function during skin wound healing and (3) define how epithelial GPR84 signaling contributes to keratinocyte function after injury. GPR84 signaling represents a new window to better understand mechanisms that regulate the injury response. Findings from this proposed work could lay a solid foundation for developing new tools that predict and enhance therapeutic treatment of wound healing.