Hepatic Autophagy Deficiency Leads to Increased Production of Extracellular Vesicles

Abstract

As an evolutionarily conserved metabolic process autophagy functions in transporting intracellular components by the autophagosome to the lysosome for degradation. Extracellular vehicles (EVs) are defined as membrane-surrounded, nanometer-sized vesicles released by cells into the extracellular space in a highly regulated manner. Exosomes (40 to 160 nm in diameter) are a widely studied subclass of EVs, which are generated inside multivesicular bodies (MVBs) and released into the extracellular space when MVBs are fused with the plasma membrane. Both autophagy and EVs are related to vesicular trafficking process, and they share some common pathways. However, the relationship of EVs production and autophagy function is largely unknown. In the present study, we found an increased production of exosomes under the condition of hepatic autophagy deficiency. Transmission electron microscopy (TEM) and nanoparticle tracking analysis (NTA) showed that the average size of exosomes isolated from the serum of hepatic Atg7-deficient was around 100 nm, which was about the same size as the exosome from the Atg7-floxed mice. In addition to the commonly defined markers in hepatocyte-derived exosome, such as TSG101 and CYP2E1, exosomes produced by autophagy deficient hepatocytes also carry unique protein markers, such as Syntenin-2, which is a Syndecan-binding protein and is closely related to the formation of MVBs. Compared to those in Atg7-floxed livers, both the mRNA and protein levels of Syntenin-2 were increased in Atg7 -/- livers. Interestingly, increased expression of Syntenin-2 and increased production of exosomesin Atg7 -/- deficient mice were reversed by co-deletion of an anti-oxidative gene, Nrf2. In summary, liver-specific autophagy deficiency enhances the Nrf2-dependent expression of Syntenin-2, thereby promoting the production of exosomes, perhaps via increased activity of MVB.