First proteomic profiling of exosomes in rodent intestinal lymph

Abstract

Introduction: Exosomes are released by many cell types and can be taken up by other cells. They may play an important role in cell-to-cell communication and disease pathogenesis. Exosomes derived from plasma or urine have been extensively studied, but that of intestinal lymph has not been reported due to the difficulty in obtaining these samples. Intestinal lymph is continuously draining from the intestine and enters the veins just before the heart and lungs. These organs may therefore be directly influenced by intestinal exosomes. Methods: Intestinal lymph was collected from a rodent experimental model of critical illness. Exosomes were isolated from the intestinal lymph using a commercially available exosome isolation kit. Particle size and concentration were determined by Nanosight. Proteomic profiling of lymph exosomes and its changes in critical illness were analysed by LC-MS. Results: The size and concentration of “exosomes” isolated from the intestinal lymph did not change significantly in the critical illness. The exosome preparation contained proteins previously identified in microparticles or exosomes (e.g. inter-alpha trypsin inhibitor), but also the highly abundant plasma proteins (e.g. complement C3, albumin). Common exosomal markers (e.g. TSG101, CD63) were not detected. Instead, substantial amounts of Apo B and A-I were found, indicating presumed co-isolation of chylomirons. Lymph chylomicrons are similar to size of “exosomes”, and produced in high concentration from the intestine. Our study indicates the unexpected difficulty in isolating pure exosomes using a commercial kit in this unique fluid. Conclusion: This present study provides the first attempt at a proteomic profile of an exosome preparation from intestinal lymph. Collectively, multiple proteins were identified, but found to have come from both exosomes and chylomicrons. New purification methods will be needed to study pure isolates of each particle type in this unique fluid.