Expression of peroxisome proliferator-activated receptors in urinary tract of rabbits and humans

Peroxisome proliferator-activated receptors (PPARs, α, β/δ, and γ) are members of the nuclear receptor superfamily of ligand-activated transcription factors. PPARs regulate the expression of genes involved in lipid metabolism. 8(S)-hydroxyeicosatetraenoic acid (8-S-HETE), leukotriene B₄ (LTB₄), and hypolipidemic fibrates activate PPARα, whereas PPARγ is activated by prostaglandin metabolites. The present studies examined the intrarenal and tissue distribution of rabbit and human PPARα, -β/δ, and - γ mRNAs. Nuclease protection showed PPARα predominated in liver, heart, and kidney, whereas PPARγ, a putative adipose-specific transcription factor, was in white adipose tissue, bladder, and ileum, followed by kidney and spleen. Lower expression levels of PPARβ/δ were observed in several tissues. In situ hybridization of kidney showed PPARα mRNA predominated in proximal tubules and medullary thick ascending limbs of both rabbit and human. PPARγ was exclusively expressed in medullary collecting duct and papillary urothelium. Immunoblot confirmed the expression of PPARγ protein in freshly isolated inner medullary collecting ducts. mRNAs for all the PPARs were expressed in the ureter and bladder in both rabbit and human, but PPARγ expression was greatest. This distinct distribution of PPAR isoforms has important implications for lipid-activated gene transcription in urinary epithelia.