Characterization and Comprehensive Proteome Profiling of Exosomes Secreted by Hepatocytes

Abstract

Synopsis Exosomes constitute a discrete population of nanometer-sized (30-150 nm) vesicles formed in endocytic compartments and released to the extracellular environment by different cell types. In this work we demonstrated by electron microscopic, western blotting and proteomic analyses that primary hepatocytes secrete exosome-like vesicles containing proteins involved in metabolizing lipoproteins, endogenous compounds as well as xenobiotics. These new findings contribute to improve our knowledge about biology's hepatocyte and may have important diagnostic, prognosis and therapeutic implications in liver diseases Exosomes represent a discrete population of vesicles that are secreted from various cell types to the extracellular media. Their protein and lipid composition are a consequence of sorting events at the level of the multivesicular body, a central organelle which integrates endocytic and secretory pathways. Characterization of exosomes from different biological samples has shown the presence of common as well as cell-type specific proteins. Remarkably, the protein content of the exosomes is modified upon pathological or stress conditions. Hepatocytes play a central role in the body response to stress metabolizing potentially harmful endogenous substances as well as xenobiotics. In the present study we described and characterized for first time exosome secretion in non-tumoral hepatocytes, and using a systematic proteomic approach, we establish the first extensive proteome of a hepatocyte-derived exosome population which should be useful in furthering our understanding of the hepatic function and in the identification of components that may serve as biomarkers for hepatic alterations. Our analysis identifies a significant number of proteins previously described among exosomes derived from others cell types as well as proteins involved in metabolizing lipoproteins, endogenous compounds and xenobiotics, not previously described in exosomes. Furthermore, we demonstrated that exosomal membrane proteins can constitute an interesting tool to express non-exosomal proteins into exosomes with therapeutic purposes.

Extracellular Vesicles Exploit Viral Entry Routes for Cargo Delivery

“…TSPANs consist of four transmembrane regions, with intracellular amino-and carboxy-terminal tails. According to several studies, tetraspanins CD9, CD63, CD81, CD82, CD151, Tspan8 (D6.1A), CD37, and CD53 are enriched in exosomes (78)(79)(80)(81)(82). The exact composition of the tetraspanin web on exosomes may have implications for target cell selection (83).…”

Exosome-mediated transmission of hepatitis C virus between human hepatoma Huh7.5 cells

“…Exosomes are formed in the endocytic compartment of multivesicular bodies (1) and are secreted in various body fluids under normal and pathological conditions (2,3). Extensive studies have now implicated exosomes in many biological processes such as tissue injury and immune responses by transfer of antigens, antigen presentation (2,4), and the shuttling of proteins, mRNAs, and microRNAs (miRNA) between cells (5).…”

Exosomes as a novel pathway for regulating development and diseases of the skin (Review)

“…Exosomes may be internalized by target cells to participate in various physiological or pathological processes (33). Exosomes have multiple specific marker proteins, including membrane transport and fusion proteins (GTPases, annexins and flotillin), tetraspannins (34), heat shock proteins (Hsps; heat shock cognate 70 and Hsp90), proteins involved in MVB biogenesis (Alix and tumor susceptibility gene 101 protein), as well as lipid-related proteins and phospholipases (35).…”