Secretion of Extracellular Vesicles Into the Mesenteric Lymph During Fasting and Lipid Absorption.

The intestine plays critical roles in nutrient homeostasis and systemic health. The small intestine is the major organ that packages dietary lipids into chylomicrons and secretes them into the mesenteric lymph. Extracellular vesicles (EVs) as a mechanism for cell-to-cell communication often exhibit organ specific characteristics. EV secretion from the intestine into the mesenteric lymph-a unique biofluid-remains unexplored. To characterize gut-derived EVs, Sprague-Dawley rats were surgically implanted with cannula in the mesenteric lymph duct (for lymph collection) and the duodenum (for lipid infusion). Lymph fluid was collected for assessment of EV secretion. EVs in lymph fluids collected before and after lipid infusion were characterized by transmission electron microscopy, nanoparticle tracking analysis, and further analyzed by flow cytometry with antibodies against CD63, CD81, CD9 and apolipoprotein B (ApoB). Lipid infusion increased lymph triglyceride output peaking at 2 h. Lymph fluids contained EVs with diameters in the range of 20 to 300 nm and the signals of specific EV markers CD63, CD81 and CD9 were significantly elevated following lipid infusion. Depletion of chylomicrons from lymph had differential effects on the percentage and intensity of CD63, CD81 and CD9. In addition, these EVs exhibited distinct patterns in ApoB+ particle population, with the median fluorescence intensity of CD63 and CD81 being significantly higher than that of CD9. To conclude, EVs secreted into the mesenteric lymph could rapidly respond to lipid supply. EVs may bind to and co-secrete with chylomicrons. Finally, gut-derived EVs during active lipid absorption may include multiple subtypes with different affinities to chylomicrons. Collectively, these findings highlight the intestine as an EV secretion organ and the mesenteric lymph as an important biofluid harboring EVs, which opens a new venue for future investigation of biological functions of gut-derived EVs.