Fatty Acid Amide Hydrolase Determines Anandamide-induced Cell Death in the Liver

Sören V Siegmund,Ekihiro Seki,Yosuke Osawa,Hiroshi Uchinami,Benjamin F Cravatt,Robert F Schwabe

doi:10.1074/jbc.m509706200

Abstract

The endocannabinoid anandamide (AEA) induces cell death in many cell types, but determinants of AEA-induced cell death remain unknown. In this study, we investigated the role of the AEA-degrading enzyme fatty acid amide hydrolase (FAAH) in AEA-induced cell death in the liver. Primary hepatocytes expressed high levels of FAAH and were completely resistant to AEA-induced cell death, whereas primary hepatic stellate cells (HSCs) expressed low levels of FAAH and were highly sensitive to AEA-induced cell death. Hepatocytes that were pretreated or with the FAAH inhibitor URB597 isolated from FAAH(-/-) mice displayed increased AEA-induced reactive oxygen species (ROS) formation and were susceptible to AEA-mediated death. Conversely, overexpression of FAAH in HSCs prevented AEA-induced death. Since FAAH inhibition conferred only partial AEA sensitivity in hepatocytes, we analyzed additional factors that might regulate AEA-induced death. Hepatocytes contained significantly higher levels of glutathione (GSH) than HSCs. Glutathione depletion by dl-buthionine-(S,R)-sulfoximine rendered hepatocytes susceptible to AEA-mediated ROS production and cell death, whereas GSH ethyl ester prevented ROS production and cell death in HSCs. FAAH inhibition and GSH depletion had additive effects on AEA-mediated hepatocyte cell death resulting in almost 70% death after 24 h at 50 microm AEA and lowering the threshold for cell death to 500 nm. Following bile duct ligation, FAAH(-/-) mice displayed increased hepatocellular injury, suggesting that FAAH protects hepatocytes from AEA-induced cell death in vivo. In conclusion, FAAH and GSH are determinants of AEA-mediated cell death in the liver.

Highlights

Major roles in the central nervous system, where they regulate food intake, pain perception, and sleep
We have demonstrated that also termed anandamide (AEA) efficiently mediates cell death in primary hepatic stellate cells (HSCs), the main fibrogenic cell type in the liver, but not in primary hepatocytes [6]
Our study focuses on two candidate systems that may contribute to the resistance to AEA: (i) the AEA degrading enzyme fatty acid amide hydrolase (FAAH), which is highly expressed and active in the liver and represents the main mechanism that determines the biological half-life of AEA (24 –26), and (ii) GSH, a major determinant of apoptotic and necrotic cell death in hepatocytes that renders hepatocytes resistant to TNF-induced cell death [27, 28]

Summary

Fatty Acid Amide Hydrolase Determines Anandamideinduced Cell Death in the Liver*

We investigated the role of the AEAdegrading enzyme fatty acid amide hydrolase (FAAH) in AEA-induced cell death in the liver. We have demonstrated that AEA efficiently mediates cell death in primary hepatic stellate cells (HSCs), the main fibrogenic cell type in the liver, but not in primary hepatocytes [6]. Our study focuses on two candidate systems that may contribute to the resistance to AEA: (i) the AEA degrading enzyme fatty acid amide hydrolase (FAAH), which is highly expressed and active in the liver and represents the main mechanism that determines the biological half-life of AEA (24 –26), and (ii) GSH, a major determinant of apoptotic and necrotic cell death in hepatocytes that renders hepatocytes resistant to TNF-induced cell death [27, 28]. Our study shows that high expression levels of GSH and FAAH correlate with resistance to AEA-mediated cell death in primary hepatic cell populations and that FAAH is a determinant of cell death in the liver in vivo

EXPERIMENTAL PROCEDURES

RESULTS

DISCUSSION