Expression of aromatase P450AROM in the human fetal and early postnatal cerebral cortex

Abstract Aromatase (P450 AROM ), the enzyme responsible for the conversion of testosterone (T) into 17-β estradiol (E 2 ), plays a crucial role in the sexual differentiation of specific hypothalamic nuclei. Moreover, recent findings indicate that local E 2 synthesis has an impact on other brain areas including hippocampus, temporal cortex and cerebellum, and may thus influence also cognitive functions. Numerous studies have described the expression and the distribution of P450 AROM throughout ontogenesis and postnatal development of the central nervous system in several mammals, but data referring to humans are scarce. In the adult human brain, P450 AROM has been detected in the hypothalamus, limbic areas, and in the basal forebrain, and described in glial cells of the cerebral cortex and hippocampus. In this study we report the expression, distribution and cellular localization of P450 AROM in the human fetal and early postnatal cerebral cortex. In our series of fetal brains of the second trimester, P450 AROM expression appeared at gestational week (GW) 17 and resulted limited to groups of cells localized close to the growing neuroepithelium in the ventricular and subventricular zones. At GWs 20–24, scattered P450 AROM immunoreactive (-ir) neural cells were identified in the intermediate plate and subplate, and in the parietal cortical plate. In perinatal and early postnatal individuals the quantity of P450 AROM -ir elements increased, and revealed the morphology typical of glial cells. Double labeling immunostaining with anti-GFAP and anti-P450 AROM antisera, and subsequent confocal analysis, confirmed this observation. Our data show that the expression of P450 AROM in the fetal cortex starts approx at the end of the fourth gestational month, but increases steadily only in the last trimester or in the early postnatal period. This temporal trend may suggest that P450 AROM could act as a differentiation-promoting factor, based on timing of the steroid actions.