Peroxisome proliferator-activated receptor-α-null mice have increased white adipose tissue glucose utilization, GLUT4, and fat mass:: Role in liver and brain

Activation of the peroxisome proliferator-activated receptor (PPAR)-alpha increases lipid catabolism and lowers the concentration of circulating lipid, but its role in the control of glucose metabolism is not as clearly established. Here we compared PPAR alpha knockout mice with wild type and confirmed that the former developed hypoglycemia during fasting. This was associated with only a slight increase in insulin sensitivity but a dramatic increase in whole-body and adipose tissue glucose use rates in the fasting state. The white sc and visceral fat depots were larger due to an increase in the size and number of adipocytes, and their level of GLUT4 expression was higher and no longer regulated by the fed-to-fast transition. To evaluate whether these adipocyte deregulations were secondary to the absence of PPAR alpha from liver, we reexpresssed this transcription factor in the liver of knockout mice using recombinant adenoviruses. Whereas more than 90% of the hepatocytes were infected and PPAR alpha expression was restored to normal levels, the whole-body glucose use rate remained elevated. Next, to evaluate whether brain PPAR alpha could affect glucose homeostasis, we activated brain PPAR alpha in wild-type mice by infusing WY14643 into the lateral ventricle and showed that whole-body glucose use was reduced. Hence, our data show that PPAR alpha is involved in the regulation of glucose homeostasis, insulin sensitivity, fat accumulation, and adipose tissue glucose use by a mechanism that does not require PPAR alpha expression in the liver. By contrast, activation of PPAR alpha in the brain stimulates peripheral glucose use. This suggests that the alteration in adipocyte glucose metabolism in the knockout mice may result from the absence of PPAR alpha in the brain.