Peroxisome Proliferator Activated Receptor a Activation Induces Hepatic Steatosis, Suggesting an Adverse Effect
Non alcoholic fatty liver disease (NAFLD) is characterized by hepatic triglyceride accumulation, ranging from steatosis to steatohepatitis and cirrhosis. NAFLD is a risk factor for cardiovascular diseases and is associated with metabolic syndrome. Antihyperlipidemic drugs are recommended as part of the treatment for NAFLD patients. Although fibrates activate peroxisome proliferator activated receptor a (PPARa) leading to the reduction of serum triglyceride levels, the effects of these drugs on NAFLD remain controversial. Clinical studies have reported that PPARa activation does not improve hepatic steatosis. In the present study, we focused on exploring the effect and mechanism of PPARa activation on hepatic triglyceride accumulation and hepatic steatosis. Male C57BL/6J mice, Ppara null mice and HepG2 cells were treated with fenofibrate, one of the most commonly used fibrate drugs. Both low and high doses of fenofibrate were administered. Hepatic steatosis was detected through oil red O staining and electron microscopy. Notably, in fenofibrate treated mice, the serum triglyceride levels were reduced and the hepatic triglyceride content was increased in a dose dependent manner. Oil red O staining of liver sections demonstrated that fenofibrate fed mice accumulated abundant neutral lipids. Fenofibrate also increased the intracellular triglyceride content in HepG2 cells. The expression of sterol regulatory element binding protein 1c (SREBP 1c) and the key genes associated with lipogenesis were increased in fenofibrate treated mouse livers and HepG2 cells in a dose dependent manner. However, the effect was strongly impaired in Ppara null mice treated with fenofibrate. Fenofibrate treatment induced mature SREBP 1c expression via the direct binding of PPARa to the DR1 motif of the SREBP 1c gene. Taken together, these findings indicate the molecular mechanism by which PPARa activation increases liver triglyceride accumulation and suggest an adverse effect of fibrates on the pathogenesis of hepatic steatosis.
PloS one