Abstract:
The prevalence of nonalcoholic fatty liver disease (NAFLD) is on the rise. It is characterized by an increase in hepatic lipid accumulation due to an impaired lipid metabolism. A correlation has been found lately between NAFLD and sphingosine-1- phosphate (S1P) but the role of the sphingolipid in steatosis remained controversial. The aim of this study is to investigate how S1P interferes in altering lipid metabolism in HepG2 cells using its analogue FTY720P and to uncover its mode of action. Lipid accumulation was induced by incubating the cells in a mixture of oleic and palmitic acids and quantified using Oil red O as a stain. The lipid level was then determined by measuring the absorbance of the extracted dye using a microplate reader. The involvement of signaling mediators was studied using pharmacological inhibitors and western blot analysis. The presence of FTY720P increased lipid accumulation, but this increase wasn’t maintained in the presence of inhibitors of S1PR3, Gq, PI3K, mTOR, SREBP, and PPAR indicating their involvement in the process. The results revealed that FTY720P alters lipid metabolism through binding to S1PR3 which activates Gq, PI3K then mTOR leading to an increase in SREBP expression and activation of PPAR γ.
