Bile acids and nonalcoholic fatty liver disease: An intriguing relationship

Ursodeoxycholic acid ameliorates hepatic lipid metabolism in LO2 cells by regulating the AKT/mTOR/SREBP-1 signaling pathway

BACKGROUND

Nonalcoholic fatty liver disease (NAFLD), the most common chronic liver disease, can progress into nonalcoholic steatohepatitis (NASH), cirrhosis, and even hepatocellular carcinoma. Bile acids such as ursodeoxycholic acid (UDCA) play an essential role in the pathogenesis of NAFLD by regulating the level of sterol regulatory element-binding protein (SREBP) 1c, but the underlying regulatory mechanism remains elusive. Increased evidence indicates that the AKT/mTOR/SREBP-1 signaling pathway is a key pathway to regulate hepatic cellular lipid metabolism. UDCA may regulate the AKT/mTOR/SREBP-1 signaling pathway to ameliorate hepatic lipid metabolism.

AIM

To investigate the functional mechanism of UDCA in an oleic acid (OA)-induced cellular model of NAFLD.

METHODS

The cellular model of NAFLD was established using OA and treated with UDCA. First, the best concentration of UDCA was selected. For the best time-dependent assay, cells were stimulated with OA only or co-treated with OA and 2 mmol/L UDCA for 24 h, 48 h, and 72 h. Oil red O staining was used to observe the accumulation of intracellular lipids, while the intracellular contents of triglyceride, alanine aminotransferase (ALT), gamma-glutamyl transpeptidase (GGT), and aspartate aminotransferase (AST) were detected by enzymatic methods. Meanwhile, the expression levels of AKT/mTOR/SREBP-1 signaling pathway-related proteins were detected by real-time PCR and Western blot.

RESULTS

In the NAFLD cell model established with LO2 cells induced using OA, lipid accumulation was obvious. UDCA significantly inhibited lipid accumulation at different concentrations (especially 2 mmol/L) and decreased cell growth ability at different time points. The biochemical parameters like ALT, AST, and GGT were significant improved by UDCA. UDCA treatment vividly repressed the activation of AKT, mTOR, and CRTC2 and the expression of nSREBP-1 in LO2 cells induced with OA.

CONCLUSION

Our findings demonstrate the effect of UDCA in improving NAFLD. UDCA attenuates OA-induced hepatic steatosis mainly by regulation of AKT/mTOR/SREBP-1 signal transduction.