Temporal and spatial distribution of mast cells and steroidogenic enzymes in the human fetal adrenal

• Mast cells are present in the human fetal adrenal cortex from 18 WG
• Spatio-temporal correlation between mast cells and 3βHSD and CYP11B2.
• CYP11B1 is detected from 18 WG in both the transitional and fetal zones.
• CYP11B2 is detected from 24 WG in the definitive zone.

Mast cells are present in the human adult adrenal with a potential role in the regulation of aldosterone secretion in both normal cortex and adrenocortical adenomas. We have investigated the human developing adrenal gland for the presence of mast cells in parallel with steroidogenic enzymes profile and serotonin signaling pathway. RT-QPCR and immunohistochemical studies were performed on adrenals at 16–41 weeks of gestation (WG). Tryptase-immunopositive mast cells were found from 18 WG in the adrenal subcapsular layer, close to 3βHSD- and CYP11B2-immunoreactive cells, firstly detected at 18 and 24 WG, respectively. Tryptophan hydroxylase and serotonin receptor type 4 expression increased at 30 WG before the CYP11B2 expression surge. In addition, HDL and LDL cholesterol receptors were expressed in the subcapsular zone from 24 WG. Altogether, our findings suggest the implication of mast cells and serotonin in the establishment of the mineralocorticoid synthesizing pathway during fetal adrenal development.