Increased expression of FABP1 and cFLIPL by free fatty acid treatment is associated with reduced death-receptor mediated apoptosis in human primary hepatocytes

Aims: The non-alcoholic fatty liver disease (NAFLD) is associated with excessive accumulation of lipid-droplets in hepatocytes and causes increased death-receptor expression, altered apoptosis-induction, liver damage and fibrosis. Investigation of fatty acid transport protein expression and lipid accumulation in steatotic hepatocytes may elucidate the correlation of FFA transport mechanisms, death-receptor expression and apoptosis. Methods: Human primary hepatocytes were treated with 0.5mM and 1mM free fatty acids (FFA; oleate: palmitate=2: 1) for 24–96h. Expression of the FFA transport proteins FABP-1, FATP-5, CD36/FAT and Caveolin-1 as well as the death-receptors DR4, DR5, CD95/Fas and TNFR-1 and the apoptosis-related proteins PUMA, NOXA, cFLIPL was investigated. Activation of the stress-responsive kinase ERK was determined by Western-blot. Results: Expression of CD36 (0.5±0.1,p<0.01;means±SEM) and Caveolin-1 (0.5±0.1,p<0.01) was reduced in hepatocytes after treatment with FFA for 96h while FABP-1 (2.2±0.2,p<0.01) expression-levels were elevated. FATP-5-expression was not changed significantly under FFA-treatment. FFA-incubation for 96h slightly decreased the expression of DR4 (0.7±0.1,p=0.014) and DR5 (0.6±0.1,p=0.011). Expression-levels of CD95/Fas (2.7±0.1, p=0.04) and TNFR-1 (2.1±0.1,p<0.01) were increased after incubation with 0.5mM FFA. Furthermore the expression of the pro-apoptotic molecule NOXA (0.4±0.1,p<0.01) was repressed. FFA-treatment did not affect apoptosis-induction (M30) significantly but activated the expression of the anti-apoptotic protein cFLIPL (2.9±0.5,p=0.017). Western-blot analyses showed increased phosphorylation of the stress-responsive kinase ERK after FFA-treatment. Conclusions: FFA-treatment induces FABP-1-expression consequently FFA-uptake seems to be an active mechanism. FFA-incubation activates the expression of CD95/Fas and TNFR-1 but does not activate apoptosis, which may be due to increased cFLIPL expression and ERK activation.