The Functional Glomerulosa Cells Define the Unicity of the Adult Human Adrenal Cortex

Abstract The zonation of the human adrenal cortex has long been established morphologically and histologically as three distinct layers of cells. The outer zona glomerulosa (ZG) comprises densely packed cells arranged in clusters that produce aldosterone; the zona fasciculata (ZF) is composed of cells with large cytoplasm, containing lipid droplets arranged in radial columns that synthetize cortisol; and the zona reticularis is composed of compact and pigmented cells producing androgens. The main purpose of this work was to study the expression of aldosterone synthase (CYP11B2 which catalyzes the last steps of aldosterone synthesis) and 11β-hydroxylase (CYP11B1 which catalyzes the last step of cortisol synthesis) in normal adrenal glands to address issues regarding the zonation and the fate of the cells constitutive of each zone through the expression of Ki-67 and cleaved Caspase-3. Thirty eight normal human adrenals (16 females, 22 males, ranging in age from 22 to 81 years old with a median age of 52 years old) were obtained from brain-dead organ donors (kindly provided by the Organ Transplant Clinics, University Hospital of Rouen). As early as 22 years old, we found that the histological ZG (h-ZG) does not correspond to the functional ZG (f-ZG) expressing CYP11B2. Moreover, the h-ZG CYP11B2- cells were CYP11B1+ showing that these cells ascribed to the h-ZG are in fact cortisol producing cells. The progressive replacement of CYP11B2+ cells by CYP11B1+ cells in the h-ZG might demonstrate the role of the extracellular matrix in the morphological maintenance of the adrenal cortex. Our analysis also showed that steroidogenic cells were either CYP11B1 or CYP11B2 positive. By immunofluorescence, we observed in many cases isolated or clusters of CYP11B2+ cells located deeply in the h-ZF and sometimes in the vicinity of the central vein. We were able to show that those cells were probably issued from CYP11B2+ cell clusters located in h-ZG which migrated centripetally. Ki-67 immunoreactivity was highly variable and observed throughout the entire cortex. We also found a positive correlation between the steroidogenic and endothelial cells proliferation. It is interesting to note that some Ki-67+ cells located in the h-ZG were CYP11B1+. Cortical cells positive for cleaved Caspase-3 were extremely rare but detected in all zones when present. These findings challenge the classic view of lineage conversion of differentiated ZG cells and show a new pathway where the CYP11B2+ cells migrate without changing their phenotype.