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adipose tissue and to a lesser extent to monocytes, macrophages and Peyer patches
(Spiegelman and Flier 1996).
Although all PPARs are the members of the same receptor family, the functions
of different PPARs are found to be isoform specific. While PPAR cv is involved in the
regulation of polyunsaturated fatty acid oxidation, the function of PPAR 7is more limited
to the regulation of glucose metabolism (Issemann and Green 1990; Spiegelman and Flier
1996). The function of PPAR 0/ô is still unknown, however recent studies indicate that
PPAR plõ may play a significant role in the control of apoptosis and oxidative stress
(Cutler et al. 2003; O'Brien et al. 2005). A number of natural ligands for PPAR a
receptors are identified such as; polyunsaturated fatty acids, arachidonic and EPA acids
and lipoprotein lipase products (Ziouzenkova et al. 2003). The usage of synthetic ligands
such as fenofibrates is found to be beneficial in the treatment of hyperlipidemia (Forman
eI aI. 1997; Staels et al. 1998). Natural ligands for PPAR y are prostaglandin and oxidized
linoleic derivates while slmthetic ligands such as thiazolidinediones are widely used in a
treatment of diabetes (Marx et aI.2004). Natural ligands for PPAR Blõ are still unknown.
V.b.Mechanism of transcriptional regulation
PPAR receptors consist of a classical domain structure that is characteristic for all
of the members of thyroid/steroid super-receptor family. Similarly to the retinoic acid
receptors, PPAR have the NHz terminal region which consists of ligand-independent
transactivation domain (AF-l). Transactivation domain is foilowed by the DNA binding
domain which is stationed in a close proximity of ligand and dimerization domain. The
COOg-terminus is characfenzed by the existence of ligand dependent activation domain
(AF-2) (Fene 2004). The initial step in the regulation of gene transcription by ligand
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