Rat PPARs: Quantitative analysis in adult rat tissues and regulation in fasting and refeeding

PPARs are members of the nuclear hormone receptor superfamily and are prima rily involved in lipid metabolism. The expression patterns of all 3 PPAR is otypes in 22 adult rat organs were analyzed by a quantitative ribonuclease protection assay. The data obtained allowed comparison of the expression of each isotype to the others and provided new insight into the less studied PPAR beta (NR1C2) expression and function. This isotype shows a ubiquitous expression pattern and is the most abundant of the three PPARs in all analy zed tissues except adipose tissue. Its expression is especially high in the digestive tract, in addition to kidney, heart, diaphragm, and esophagus. A fter an overnight fast, PPAR beta mRNA levels are dramatically down-regulat ed in liver and kidney by up to 80% and are rapidly restored to control lev els upon refeeding. This tight nutritional regulation is independent of the circulating glucocorticoid levels and the presence of PPAR alpha, whose ac tivity is markedly up-regulated in the liver and small intestine during fas ting. Finally, PPAR gamma2 mRNA levels are decreased by 50% during fasting in both white and brown adipose tissue. In conclusion, fasting can strongly influence PPAR expression, but in only a few selected tissues.