Objectives: Excessive levels of serum free fatty acids, particularly saturated fatty acid, are known to result in lipotoxicity in skeletal muscle. Various tissues including liver, adipose tissue and skeletal muscle release exosomes, a type of extracellular microvesicles containing nucleic acids, proteins and lipids. Exosomes are known to regulate physiological processes in recipient cells by delivering signal molecules from donor cells. However, the effects of exosomes derived from myocytes treated with different fatty acids on the growth of cancer cell lines remain unclear. Here, we investigated whether exosomes derived from C2C12 treated with either palmitate or oleate differentially affect the growth of hepatoma cells.
Methods: After differentiation with horse serum, C2C12 cells were treated with 0.5 mmol/L palmitate or oleate for 48 h. Culture media were used for the isolation of exosomes (PA-Exo and OA-Exo) using ExoQuick-TC solution. Mouse Hepa1-6 hepatoma cells were treated with various concentrations of exosomes and cell growth was detected by MTT assay. Proliferation and apoptosis of Hepa1-6 cells were evaluated by Western blot.
Results: PA-Exo promoted Hepa1-6 growth in comparison to OA-Exo in a dose-dependent manner. Higher increase in cell proliferation was observed in cells treated with PA-Exo, based on the activation of extracellular signal-regulated kinase (ERK) and increases in the expression level of proliferating cell nuclear antigen (PCNA). In addition, PA-Exo inhibited apoptosis compared to OA-Exo by decreasing cleaved-poly (ADP-ribose) polymerase (PARP) and phosphorylated p53 lelves in Hepa1-6 cells. Consistently, we observed in lower levels of phosphorylated AMP-activated protein kinase (AMPK) in cells in response to the treatment of PA-Exo compared to OA-Exo.
Conclusions: Palmitate mediated-lipotoxicity in myocyte significantly increased hepatoma cell growth via exosome. Further studies are needed to reveal the target genes and regulatory mechanisms associated with cell growth in response to myocytes-derived exosomes.
Funding Sources: This research was supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science and ICT.
