Identification of Extracellular Matrix Components and Their Integrin Receptors in the Human Fetal Adrenal Gland1

The development of the human fetal adrenal gland is characterized by a gradient of mitotic activity, cell migration, and cell apoptosis, all of which dictate its particular function. Such plasticity may possibly be under the control of the extracellular environment. The goal of this study was to identify components of the extracellular matrix in second-trimester fetal adrenal glands. Whereas collagen IV was expressed evenly throughout the gland, both fibronectin and laminin demonstrated a mirror-imaged distribution, with higher expression of fibronectin in the central portion and laminin at the periphery of the gland. The integrin subunit alpha1 was found mainly in the definitive zone and the alpha2-subunit mainly in the transitional zone, whereas integrin alpha3 (which binds both fibronectin and laminin) was detected only in the fetal zone. The beta2-subunit was observed solely in chromaffin cells. Such specific gradients of integrin and MEC component expression suggest that the extracellular environment does play a definite role during adrenal gland development. Indeed, compared with that in untreated plastic dishes, ACTH stimulation of dehydroepiandrosterone sulfate and cortisol was enhanced by collagen IV. In addition, fibronectin enhanced dehydroepiandrosterone sulfate but decreased cortisol secretion, compared with collagen IV substrates. These results provide fundamental insight into the contribution of the microenvironment in cellular processes leading to fetal adrenal gland development.