Molecular and Cellular Mechanisms of Lipid Droplet Breakdown in the Liver of Chinese Soft-Shelled Turtle (Pelodiscus sinensis)

The Chinese Soft-shelled Turtle (Pelodicus sinensis) is a kind of the most primitive amphibians and reptiles in nature. On account of its environmental suitability and unique hibernation habit, the peculiar physiological phenomenon in Pelodicus sinensis attracted the attentions of researchers in marine science. The aim of the present study was to investigate the molecular mechanisms underlying the periodic variation of lipid droplet (LD) in the liver of Pelodicus sinensis. Histological results indicated that accumulated LD in the liver of Pelodiscus sinensis during non-hibernation was gradually consumed in hibernation. RNA-Seq results revealed that genes responsible for carbohydrate catabolism are down-regulated during hibernation, while genes involved in lipid oxidation were up-regulated. These results illustrated that energy metabolism in the liver of Pelodiscus sinensis during hibernation involved an important shift, that the energy generation mode was transformed from carbohydrate catabolism (non-hibernation) to lipid oxidation (hibernation). Further analysis of RNA-Seq results indicated that both lipolysis and autophagy could promote the degradation of hepatic LD during hibernation. To further determine the relationship between lipolysis and autophagy in the process of LD breakdown, we applied the inhibitors of lipolysis and autophagy (DEUP and 3MA) in cultured primary hepatocytes from Pelodiscus sinensis. And the results indicated that lipolysis is the main way for LD degradation in the hepatocyte of Pelodiscus sinensis. Taken all together, the present study made a major contribution to understanding the adaptive mechanism in the liver of Pelodicus sinensis during hibernation and provided us with new inspirations for improving survival rates of marine life.