Project Summary Chronic overconsumption of high fructose-containing food and beverages has emerged as a significant risk factor for development of obesity, nonalcoholic fatty liver disease, and type 2 diabetes mellitus. Fructose metabolism has been extensively investigated in the hepatocyte, where 50-70% of dietary fructose is metabolized as well as in the small intestine and kidneys, where the fructose transporter Glut5 is highly expressed. However, much less is known in other metabolic organs including skeletal muscle, brain and white adipose tissue. Thus far, the impact of Glut5 and fructose metabolism in intrascapular brown adipose tissue (iBAT) has not been investigated. While analyzing the diet/feeding-stimulated iBAT transcriptomes to gain mechanistic insights, we observed a dramatic but transient upregulation of facilitated glucose/fructose transporter type 5 (Glut5, [Slc2a5]) in iBAT as early as 1 h after feeding from both male and female C57BL/6J mice but not in antibiotic-treated mice. Consistently, we also observed similar Glut5 upregulation in differentiated human brown adipocytes after incubation with serum from fed mice. In addition, we also observed that chronic high fructose consumption dysregulates iBAT basal Glut5 expression. This is unexpected because Glut5 expression in white fat is fructose-independent. Our data showed for the first time that iBAT Glut5 regulates circulating fructose homeostasis and mediates fructose-dependent iBAT whitening and obesity. Fructose metabolism is important for glycogen and lipid accumulation in hepatocyte. Increase in iBAT fructose metabolism due to fructose-induced Glut5 dysregulation could potentially leads to iBAT whitening. Together with our preliminary findings that feeding-induced Glut5 expression in iBAT is eliminated in antibiotic-treated mice, we hypothesize that high-fructose consumption promotes whitening and impairs iBAT metabolic activity via microbiome-dependent iBAT Glut5 expression. In this proposal, we plan to delineate how brown adipocyte Glut5 impacts iBAT metabolism. We will also determine whether high-fructose diet increase Glut5 via microbiota-derived hyodeoxycholic acid (HDCA) to inhibit iBAT function. Finally, we will determine liver-x-receptors (LXRs) expressed in brown adipocyte are required for whitening and metabolic activity impairment in iBAT induced by high-fructose diet. Successful completion of this proposed study will contribute to our understanding of high fructose diet-induced brown fat whitening and metabolic dysfunction.