Seasonal and gender variation of peroxisome proliferator activated receptors expression in brown trout liver.

PPAR isotypes have been previously identified in the teleost brown trout (Salmo trutta f. fario) and their organ distribution pattern established. Being that the liver is a vital metabolic organ presenting expression of all isotypes and also knowing that estrogens/estrogen receptors seem to interact with PPARs, we hypothesized that the latter may very well change seasonally. So, we studied the expression of these receptors in the liver, along the annual reproductive cycle and in both genders. According to real-time RT-PCR, PPARalpha mRNA expression in females was significantly higher in May and lower in September than in other seasons. No significant variation was observed along the year in males. A significant difference between genders occurred in May, when PPARalpha expression was higher for females. PPARbeta expression showed little variation along the reproductive cycle in females, but in males it was significantly higher in December than in the other seasons. No significant differences existed between genders. PPARgamma was more expressed in February than in September and December, for females. As to males, it was more expressed in February than in all other seasons. No significant differences were observed between genders. The study proved our hypothesis that PPARs gene expression varies along the year. Moreover, PPARalpha expression in females followed the same annual variation pattern as peroxisome volumes and enzyme activities, and an inverse pattern relatively to the salmonid type annual plasma estradiol levels. The data agrees with the idea that PPARalpha is under estradiol modulation and that cross-talk between this receptor and the estrogen receptor possibly exists.