PROJECT SUMMARY An effective epidermal permeability barrier (EPB) protects the skin from dehydration, inflammation, premature aging, environmental exposure, and infection. Epidermal barrier dysfunction is an important feature of atopic dermatitis, as well as numerous skin diseases including psoriasis, acne, and rosacea. A fundamental and holistic understanding of mechanisms regulating homeostatic barrier function is essential to effectively prevent and manage barrier abnormalities. The EPB function resides in the skin epidermis, which is home to diverse microbial communities. The microbiome is recognized as a functional unit of the skin barrier. The skin ecosystem is continuously challenged by the external exposome that includes ultraviolet radiation (UVR), air pollutants and allergens. Critical for the barrier defense and homeostasis are xenobiotic sensors that recognize external signals and help identify beneficial (e.g., commensal microbes) from harmful (e.g., pollutants, pathogens) xenobiotics to regulate barrier defenses. Recently, I have demonstrated that commensal microbes regulate epidermal differentiation and barrier permeability of the skin by activating xenobiotic sensor, the aryl hydrocarbon receptor (AHR). However, the mechanisms by which commensal microbes regulate EPB through AHR under homeostasis, and in presence of environmental insults such as UVR are unexplored. The central hypothesis of this proposal is that tuning of epithelial responses by modulating AHR-commensal interactions can alter barrier permeability. This project utilizes ‘multi-omics’ approaches by integrating transcriptomics, metagenomics, and metabolomics to understand host-microbiota interactions in skin barrier repair. In Aim 1, I will identify microbial signals from a synthetic commensal community that can activate AHR. These studies will lead to identification of microbial ligands that can be used to target AHR in barrier diseases. In Aim 2, I will test contributions of commensal microbiome in protecting against UV-induced barrier damage and use multiomics approaches to characterize microbiome-host-UV interactome in the context of AHR signaling. These studies will provide a framework to generate therapies that leverage understanding of environmental-host-microbiome interactions. During the K99 phase, I will be trained in metabolomics to identify microbial metabolites. I will receive advanced training in bioinformatics and systems biology approaches that focus on integrating multiple omics datasets. The outstanding training environment at the University of Pennsylvania coupled with the excellent advisory committee I have assembled, will greatly facilitate my research during the mentored phase as well as launch my career with the skills necessary for understanding the role of the microbiome-host- environment interactome in regulating skin barrier repair.