Oleic acid-induced hepatic steatosis is coupled with downregulation of aquaporin 3 and upregulation of aquaporin 9 via activation of p38 signaling.

Abstract

Excess lipid deposition in hepatocytes is a hallmark feature of nonalcoholic fatty liver disease (NAFLD). The present study was designed to explore the expression and regulation of aquaporin (AQP) 3 and AQP9 in oleic acid-induced hepatic steatosis. HepG2 cells were incubated with oleic acid at different concentrations and time points. Oil-Red-O staining and triglyceride content measurement were done to assess the extent of hepatic steatosis. The expression of AQP3 and AQP9 was assessed using quantitative real-time PCR and Western blot analyses. The mitogen-activated protein kinase (MAPK) pathways involved in the regulation of AQP3 and AQP9 expression were checked. Compared to untreated control cells, oleic acid treatment significantly (p<0.05) induced hepatic steatosis in HepG2 cells in a dose- and time-dependent fashion. Oleic acid-treated cells showed a significant reduction in the AQP3 expression and a concomitant increase in the AQP9 expression. Oleic acid exposure led to enhanced phosphorylation of p38, but not ERK1/2 or JNK MAPK. Pharmacological inhibition of p38 rather than ERK1/2 signaling significantly blocked the regulation of AQP3 and AQP9 expression by oleic acid. Oleic acid-induced hepatic steatosis in HepG2 cells is associated with the coordinated regulation of AQP3 and AQP9 via activation of p38 signaling. These findings warrant functional studies of aquaglyceroporins in NAFLD.