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

Objective: Examination of the pattern of expression of peroxisome prolifera tor-activated receptor (PPAR) isoforms alpha and gamma in a model of obesit y. Design: Examination of adipose tissue and primary adipocyte cultures from l ean 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 PPAR alpha and gamma mRNA were present in br own adipose tissue (BAT), followed by liver and white adipose tissue (WAT) for the alpha and gamma subtypes, respectively, at both ages examined, PPAR alpha was expressed 100-fold higher in BAT compared with WAT, and PPAR gam ma mRNA levels were 2-fold higher in the WAT of obese compared with lean ra ts. PPAR alpha and gamma expression was minimal in m. soleus, although high er levels of PPAR gamma were found in the diaphragm. In marked contrast to the findings in vivo, virtually no PPAR alpha mRNA could be detected in BAT cultures differentiated in vitro. Conclusion: PPAR alpha and gamma are most highly expressed in BAT in vivo. However, PPAR alpha is undetectable in brown adipose cells in vitro, sugges ting that the expression of this receptor is induced by some external stimu li. In addition, the expression of PPAR gamma was increased in WAT from you ng obese animals, compatible with an early adaptive phenomenon, Finally, th e presence of PPAR gamma mRNA is detectable only in particular muscles, suc h as the diaphragm, suggesting the possibility of an influence of fiber typ e on its expression, although exercise did not influence the expression of PPAR gamma in other skeletal muscles.