Protein expression changes in the Sprague Dawley rat liver proteome following administration of peroxisome proliferator activated receptor α and γ ligands

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Abstract
Peroxisome proliferator activated receptors (PPARs) are members of the nuclear receptor superfamily and are intimately involved in lipid metabolism and energy homeostasis. Activation of these receptors in rodents can lead to hepatomegaly and ultimately hepatic carcinogenesis although the mechanisms by which these processes occur are poorly understood. To further our understanding of these processes and to discriminate between different PPAR mediated signalling pathways, a proteomic approach has been undertaken to identify changes in protein expression patterns in Sprague Dawley rat liver following dosing with a PPARα agonist (Wyeth 14643), a PPARγ agonist (Troglitazone) and a compound with mixed PPARα/γ agonist activity (SB‐219994). Using one‐and‐two‐dimensional electrophoresis of tissue lysates a diverse range of protein abundance changes was observed in these tissues. Whilst a number of these proteins have PPAR response elements (PPREs) in their respective promoters, another group was detected whose expression has been documented to be sensitive to peroxisome proliferator administration. Most notably within these groups, proteins involved in lipid catabolism displayed increased expression following drug administration. A further subset of proteins, with less obvious biological implications, also showed altered expression patterns. Where available, sequences upstream of the coding regions of genes not previously known to have PPREs were searched with positional consensus matrices for the presence of PPREs in an attempt to validate these changes. Using such an approach putative PPARγ and PPARδ response elements were discovered upstream of the tubulin β coding region. There was limited overlap in observed protein abundance changes between the three groups, and where this was the case (cytosolic epoxide hydrolase, peroxisomal bifunctional enzyme, hydroxymethyl glutaryl CoA, synthase, long chain acyl‐CoA thioesterase), expression of these proteins had previously been shown to be under the control of PPAR activity.

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