Expression of peroxisome proliferator-activated receptors in lean and obese Zucker rats

Abstract

Objective: Examination of the pattern of expression of peroxisome proliferator-activated receptor (PPAR) isoforms α and γ in a model of obesity. Design: Examination of adipose tissue and primary adipocyte cultures from lean and obese Zucker rats at different ages (28 days and 12 weeks). Methods: mRNA levels were measured by RNase protection assay. Results: The highest levels of PPARα and γ mRNA were present in brown adipose tissue (BAT), followed by liver and white adipose tissue (WAT) for the α and γ subtypes, respectively, at both ages examined. PPARα was expressed 100-fold higher in BAT compared with WAT, and PPARγ mRNA levels were 2-fold higher in the WAT of obese compared with lean rats. PPARα and γ expression was minimal in m. soleus, although higher levels of PPARγ were found in the diaphragm. In marked contrast to the findings in vivo, virtually no PPARα mRNA could be detected in BAT cultures differentiated in vitro. Conclusion: PPARα and γ are most highly expressed in BAT in vivo. However, PPARα is undetectable in brown adipose cells in vitro, suggesting that the expression of this receptor is induced by some external stimuli. In addition, the expression of PPARγ was increased in WAT from young obese animals, compatible with an early adaptive phenomenon. Finally, the presence of PPARγ mRNA is detectable only in particular muscles, such as the diaphragm, suggesting the possibility of an influence of fiber type on its expression, although exercise did not influence the expression of PPARγ in other skeletal muscles.