Immunohistochemical localization of aromatase cytochrome P-450 and estradiol dehydrogenase in the syncytiotrophoblast of the human placenta

Immunocytochemical localization of aromatase in the brain

An immunocytochemical peroxidase-antiperoxidase procedure using a purified polyclonal antibody raised against human placental aromatase was used to localize aromatase-containing cells in the Japanese quail brain. Immunoreactive cells were found only in the preoptic area and hypothalamus, with a high density of positive cells being present in the sexually dimorphic medial preoptic nucleus, in the ventromedial nucleus of the hypothalamus and in the infundibulum. The positive material was localized in the perikarya and in adjacent cytoplasmic processes. Aromatase-containing cells were a specific marker for the sexually dimorphic preoptic nucleus. Treatment with testosterone produced a 6-fold increase in the aromatase activity of the preoptic area and a 4-fold increase in the number of immunoreactive cells in the medial preoptic nucleus. Thus, the increase in aromatase activity observed after testosterone administration is caused by a change in enzyme concentration.

Aromatase in human fetal tissues

The placenta has been shown to be the major source of estrogen production during pregnancy. This investigation was undertaken to compare the content and activity of aromatase in the placenta and various other human fetal tissues. Tissues were obtained from first- and second-trimester human abortuses. The amount of aromatase P-450 (aromatase cytochrome P-450) in tissue homogenates was determined after sodium dodecyl sulfate-polyacrylamide gel electrophoresis and immunoblotting by use of a polyclonal antibody directed against aromatase cytochrome P-450. The activity of aromatase in microsomal preparations was assayed by determining the rate of incorporation of tritium from 1-[3H]androstenedione into [3H]water. The greatest amount of aromatase cytochrome P-450 (55 kd) was detected in placenta and lesser amounts were detected in other tissues. Aromatase activity also was highest in placental microsome fractions (368 +/- 62.4 pmol/mg/hr [mean +/- SE], n = 9). A significant amount of aromatase activity was also detected in fetal liver (19 +/- 4.8 pmol/mg/hr, n = 7). Much less activity was found in brain (2.8 +/- 1.0 pmol/mg/hr, n = 6) and intestine (2.7 +/- 1.3 pmol/mg/hr, n = 7). Minimal activity was noted in adrenal (n = 5), spleen (n = 4), stomach (n = 4), and muscle (n = 5) (1.2 to 1.5 pmol/mg/hr). Activity in kidney (n = 7), heart (n = 4), and lung (n = 4) was extremely low (less than 0.8 pmol/mg/hr). In conclusion, the placenta is a major site of conversion of C19 steroid precursors to estrogens because of the amount of enzyme and the high rate of activity of aromatase compared with those of other fetal tissues. However, considering the size and rate of aromatase activity in other fetal tissues such as liver, brain, and intestine, these tissues also may contribute to the total estrogen production in the fetal-placental unit.

Human placental sterylsulfatase: immunocytochemical and biochemical localization

Human placental sterylsulfatase was localised in situ by light and electron microscope immunocytochemical techniques as well as in homogenate and tissue extract fractions by enzyme assays. Light microscope observations on frozen sections of term and preterm placenta revealed sterylsulfatase immunoactivity primarily in the syncytiotrophoblast. Electron microscope observations confirmed the light microscope findings; in addition, they showed that the sulfatase is present in the endoplasmic reticulum of endothelial cells, too. In the syncytiotrophoblast, the enzyme was detectable in the cytoplasmic membrane of the nuclear evelope, in the membranes of the rough endoplasmic reticulum, in the plasma membrane with predominant localisation in coated pits, and in the membranes of endosomes and multivesicular bodies; little or no reactivity was detectable over the membranes of the Golgi complex and of lysosomes. Sterylsulfatase immunoactivity was absent in placentas with hereditary sterylsulfatase deficiency. The observations indicate that human placental sterylsulfatase is normally present in the membranes of compartments along the secretory pathway and the endocytic route of cells lining the fetal and maternal blood. Homogenates of normal term placenta as well as membrane vesicle preparations obtained by extraction of trophoblast tissue with isotonic saline were fractionated by differential centrifugation; the fractions were assayed for specific activities of sterylsulfatase and several marker enzymes of cellular topography. In agreement with our immunocytochemical findings, the results of these biochemical localisation experiments indicate the repeatedly described association of the placental sterylsulfatase with microsomal membranes but also point to the presence of the enzyme's activity in the microvillous plasma membrane of the syncytiotrophoblast. This localisation of sterylsulfatase may have functional implications in the placental uptake of circulating steroid sulfates.

Oestrogen synthetase (aromatase) and hormone secretion in primary cultures of human placental trophoblast cells. Effects of cyclic AMP addition at the start of culture in attached and unattached cell populations

Term placental trophoblast cells, released by trypsin digestion of placental villi, purified on a Percoll gradient and grown in serum-containing medium, differentiate within 24 to 48 h in culture from mononucleated cytotrophoblast-like cells at the start of culture to highly multinucleated giant (syncytiotrophoblast-like) cells that are more active in hormonogenesis. To determine the changes in hormone biosynthesis and secretion that occur early in the trophoblast differentiation process in vitro, freshly isolated placental cells were cultured in Dulbecco's Modified Eagle's Medium (DMEM) containing 20 per cent FBS, in the presence and absence of cAMP for up to 48 h. Cell attachment and growth, oestrogen synthetase (aromatase) activity in attached and unattached cells, and secretion of human chorionic gonadotropin (hCG) and progesterone were studied. The aromatase specific activity, low in freshly isolated cells, increased fourfold in attached cells by 3 h, and achieved a 10- to 15-fold increase by 40 to 48 h. In attached cells grown with cAMP, aromatase activity was further stimulated by about fourfold, relative to the control. The aromatase activity of the unattached cells removed from the culture dishes at various times up to 48 h showed a biphasic response: the activity decreased by 18 h and then increased back to the fresh cell levels. The effect of cAMP on aromatase in these unattached cells was manifested by a two-fold stimulation of activity by 18 h, relative to control unattached cells. Secretion of hCG from both attached and unattached cells remained at a low level (less than 200 ng/mg protein) in control cells; in the presence of cAMP, hCG secretion was stimulated by tenfold after 40 h.(ABSTRACT TRUNCATED AT 250 WORDS)