Regulation of lipid metabolism in grass carp primary hepatocytes by exosomes derived from fatty hepatocytes though GRP78.

Exosomes regulate lipid metabolism by carrying miRNAs, nucleic acids, and proteins, thereby influencing the function of receptor cells. Glucose-regulated protein 78 (GRP78) is also involved in the regulation of lipid metabolism. However, it remains unclear whether exosomes derived from fatty hepatocytes (OA-Exo) regulate lipid metabolism through the enrichment of GRP78. In this study, we observed the expression of GRP78 was significantly increased in fatty hepatocytes (incubating hepatocytes with oleic acid (OA) for 24 h) and OA-Exo (P < 0.05). In addition, OA-Exo (50 μg/mL) and GRP78 protein (1 μg/mL) significant increased the content of triacylglycerol (TG) and total cholesterol (TC), as well as up-regulated the expression of GRP78 and inositol-requiring enzyme-1alpha (IRE1α) protein (P < 0.05). We further used YUM70 (an inhibitor of GRP78) to inhibit endogenous GRP78, and compared with the YUM70 group, OA-Exo reversed the effect of YUM70 and increased the content of TG, TC, and the expression of GRP78 protein in hepatocytes (P < 0.05). Furthermore, the inhibition of the IRE1α pathway with 4μ8C resulted in a significant decrease in TG content compared to the control group (P < 0.05). However, when compared with the 4μ8C group, OA-Exo and GRP78 reversed the effect of 4μ8C and significantly increased TG content (P < 0.05). Taken together, these results indicated that OA-Exo activated IRE1α to promote lipid accumulation in hepatocytes through the enrichment of GRP78. This study provided a new perspective for further exploration of exosomal lipid metabolism in fish.