Expression of peroxisome proliferator-activated receptors in zebrafish (Danio rerio) depending on gender and developmental stage

Peroxisome proliferator-activated receptors (PPARs) are members of the superfamily of nuclear hormone receptors involved in embryo development and differentiation of several tissues in mammals. The aim of the present study was to investigate the possible differential expression of the three PPAR subtypes (PPARalpha, PPARbeta, and PPARgamma) in relation to gender and developmental stage in zebrafish. For this purpose PPAR expression was assessed by immunohistochemistry in 7-day-old larvae, 1-month-old juveniles, and 1-year-old adults. Additionally, the activity of peroxisomal acyl-CoA oxidase (AOX), a gene regulated by PPARs, and the volume density of catalase-immunolabeled liver peroxisomes (V-VP) was examined. No significant gender-related differences were detected in the tissue distribution of the three PPAR subtypes or in peroxisomal AOX activity and V-VP. The percentage of PPARbeta-positive hepatocytes was significantly higher in females than in males suggesting a specific regulatory role of this subtype in female zebrafish. The three PPAR subtypes were already expressed at the larval stage, with a similar tissue distribution pattern to that found in adults. For all stages, PPARalpha and PPARbeta were expressed at higher levels than PPARbeta, and PPARbeta immunolabeling was stronger in juveniles than in larval or adult stages. The percentages of hepatocyte nuclei immunolabeled for PPARs was higher in early developmental stages than in adults, similarly to AOX activity and V-VP. In conclusion, our results indicate that PPAR expression, the activity of its target gene AOX, and peroxisomal biogenesis are developmentally modulated in zebrafish.