Review of the expression of peroxisome proliferator-activated receptors alpha (PPAR alpha), beta (PPAR beta), and gamma (PPAR gamma) in rodent and human development.

The peroxisome proliferator-activated receptors (PPAR) belong to the nuclear hormone receptor superfamily and there are three primary subtypes, PPARalpha, beta, and gamma. These receptors regulate important physiological processes that impact lipid homeostasis, inflammation, adipogenesis, reproduction, wound healing, and carcinogenesis. These nuclear receptors have important roles in reproduction and development and their expression may influence the responses of an embryo exposed to PPAR agonists. PPARs are relevant to the study of the biological effects of the perfluorinated alkyl acids as these compounds, including perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS), activate PPARalpha. Exposure of the rodent to PFOA or PFOS during gestation results in neonatal deaths, developmental delay and growth deficits. Studies in PPARalpha knockout mice demonstrate that the developmental effects of PFOA, but not PFOS, depend on expression of PPARalpha. This review provides an overview of PPARalpha, beta, and gamma protein and mRNA expression during mouse, rat, and human development. The review presents the results from many published studies and the information is organized by organ system and collated to show patterns of expression at comparable developmental stages for human, mouse, and rat. The features of the PPAR nuclear receptor family are introduced and what is known or inferred about their roles in development is discussed relative to insights from genetically modified mice and studies in the adult.