Impact of 27-Hydrocholesterol on Brown Adipose Tissue at the Single Cell Level

27-Hydroxycholesterol (27HC), the most abundant oxysterol in circulation, is produced from cholesterol by CYP27A1 enzyme, and is catabolized by CYP7B1 enzyme. In addition, previously we found that 27HC is an endogenous selective estrogen receptor modulator (SERM), which links cholesterol metabolism to estrogen receptor actions. Brown adipose tissue is the primary source of energy expenditure and energy homeostasis, as well as body temperature maintenance. While previously it was believed that BAT activity is limited to neonates and young children, it is now recognized that BAT is also active in adult humans and its function is impaired by metabolic diseases such as obesity. BAT is also a secretory organ and produces brown adipokines, although the exact function of BAT and adipokines from this tissue in obesity has not been completely understood. To examine the effect of 27HC on cellular diversity and gene expression in the BAT, we propose to use the single cell RNA-seq (scRNA-seq) approach to first identify the different cell populations in BAT and their gene expression patterns, then to compare the changes in cell diversity and gene expressions upon elevated 27HC levels using 27HC-catabolizing enzyme Cyp7b1-/- mice. Currently, there is no available scRNA-seq dataset from BAT except for that using brown adipocyte only. Therefore, our proposed study will provide a fundamental resource for BAT biology, and also enables us to identify the cells responsible for the 27HC action in BAT and explore the changes in BAT following 27HC up-regulation, all for the first time.