PROJECT SUMMARY Inflammation is involved in an abundant number of acute and chronic skin pathologies, which together contribute to high patient and healthcare burden. Topical immunosuppressants such as topical corticosteroids are first-line treatments despite their association with a myriad of adverse effects such as skin atrophy, striae, and rosacea, among others. Further, while many inflammatory skin conditions involve similar pathways of immune activation and disease progression, the development of targeted anti-inflammatory therapies would aid in delineating our understanding of the shared and unique molecular mechanisms that accompany inflammation in the skin. Cholesterol is integral to the normal functioning of skin and recently, excess intracellular cholesterol has been associated with inflammatory activation by interleukin-17A (IL-17A) in cultured keratinocytes. Interestingly, these findings resemble the cholesterol-dependent inflammatory processes found in activated macrophages, suggesting keratinocytes could be subjected to similar mechanisms of cholesterol regulation in the setting of inflammation. Therefore, research is required to delineate the relationship between cholesterol metabolism and keratinocyte-induced inflammation. Our lab pioneered a synthetic high-density lipoprotein-like nanoparticle (HDL NP) capable of modulating cellular cholesterol through specifically binding to scavenger receptor class B type 1 (SR-B1), a transporter responsible for cellular cholesterol flux. Application of HDL NPs in the skin is attractive due to the well-established presence of SR-B1 in the epidermis and the favorable physical properties of HDL NPs that may enable keratinocyte targeting and localization to all layers of the epidermis. Further, topical HDL NP administration in wounded corneal epithelial cells has demonstrated anti-inflammatory benefit, further supporting a link between cholesterol modulation and immune activation. We aim to use HDL NPs as a powerful tool to mechanistically study how changes in cholesterol metabolism affect inflammation in the skin. Our overarching hypothesis is the following: keratinocyte cholesterol levels control inflammatory signaling in the skin. In the first aim of the study, we will understand how HDL NP modulates keratinocyte cholesterol in the setting of IL-17A activation. In the second aim, we will investigate IL-17A-dependent inflammatory signaling in keratinocytes with a particular focus in measuring the expression of chemoattractants that are known to perpetuate skin inflammation. In the final aim of the study, we will investigate the therapeutic potential of targeting cholesterol modulation in vivo using the imiquimod-induced psoriasis-like mouse model as a model of skin inflammation. Project success will better delineate the role of cholesterol metabolism in inflammatory skin disease to develop novel topical therapies to reduce inflammation.