PPARα-Deficient ob/ob Obese Mice Become More Obese and Manifest Severe Hepatic Steatosis Due to Decreased Fatty Acid Oxidation

Obesity poses an increased risk of developing metabolic syndrome and closely associated nonalcoholic fatty liver disease, including liver cancer. Satiety hormone leptin-deficient (ob/ob) mice, considered paradigmatic of nutritional obesity, develop hepatic steatosis but are less prone to developing liver tumors. Sustained activation of peroxisome proliferator-activated receptor alpha (PPAR alpha) in ob/ob mouse liver increases fatty acid oxidation (FAO), which contributes to attenuation of obesity but enhances liver cancer risk. To further evaluate the role of PPAR alpha-regulated hepatic FAO and energy burning in the progression of fatty liver disease, we generated PPAR alpha-deficient ob/ob (PPAR alpha(Delta)ob/ob) mice. These mice become strikingly more obese compared to ob/ob littermates, with increased white and brown adipose tissue content and severe hepatic steatosis. Hepatic steatosis becomes more severe in fasted PPAR alpha(Delta)ob/ob mice as they fail to up-regulate FAO systems. PPAR alpha(Delta)ob/ob mice also do not respond to peroxisome proliferative and mitogenic effects of PPAR alpha agonist Wy-14,643. Although PPAR alpha(Delta)ob/ob mice are severely obese, there was no significant increase in liver tumor incidence, even when maintained on a diet containing Wy-14,643. We conclude that sustained PPAR alpha activation-related increase in FAO in fatty livers of obese ob/ob mice increases liver cancer risk, whereas deletion of PPAR alpha in ob/ob mice aggravates obesity and hepatic steatosis. However, it does not lead to liver tumor development because of reduction in FAO and energy burning.