Lipid-filled vesicles modulate macrophages

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Science  01 Mar 2019:
Vol. 363, Issue 6430, pp. 931-932
DOI: 10.1126/science.aaw6765

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Adipose (fat) tissue is a major site of energy storage that responds to fluctuations in nutrient availability to maintain systemic metabolic homeostasis (1). Adipocytes take up circulating free fatty acids (FFAs) from the blood and store them in lipid droplets in response to increased insulin concentrations (which occur after feeding); they then hydrolyze lipids to release FFAs under conditions of nutrient deprivation. A variety of other cell types are present within adipose tissue, including fibroblasts, endothelial cells, and adipose tissue macrophages (ATMs). In addition to their roles in immune surveillance and clearance of cellular debris, ATMs are important for lipid buffering and regulate adipose tissue function in both healthy and diseased states (2). Owing to the rising global incidence of chronic obesity and associated health issues, there is renewed interest in understanding how adipose tissue functions in physiological and pathological settings. On page 989 of this issue, Flaherty et al. (3) report that adipocytes communicate with ATMs by releasing a distinct class of extracellular vesicles (EVs) called adipocyte-derived exosomes (AdExos), which are loaded with fat and appear to be derived directly from adipocyte lipid droplets. The uptake of AdExos by resident ATMs allows for the direct transfer of lipids, revealing a form of intercellular communication and nutrient exchange with important implications for obesity-associated pathologies.