The control of adrenocortical cytodifferentiation by extracellular matrix

Adult rat adrenal cortical cells maintained in medium supplemented with horse serum (HS) from cohesive epithelial islands secrete large amounts of corticosterone. Such cells do not produce detectable extracellular material (ECM) and are not motile. Cultures exposed to fetal calf serum supplements (FCS) produce metachromatic ECM, modulate to a fibroblastic morphology, and become motile. Within 24 h, steroid production by these cells drop 100-fold. Cells now resemble myofibroblastic "stem" cells of the adrenal cortical capsule, and express structural and functional bimorphism by exhibiting a myofibroblastic phenotype while retaining responsiveness to adrenocorticotropic hormone (ACTH) and limited corticosteroid secreting capacity. Exposure of the myofibroblastic cells to ACTH in FCS overrides the effect of FSC: ECM disappears, steroid production increases several fold, and cells develop an epithelial morphology. The possibility that ECM produced in response to FCS may be responsible for the alteration from a highly differentiated, non-motile adrenocortical cell to a less differentiated, motile adrenocortical stem cell was investigated by inhibition studies using 6-diazo-5-oxo-L-nor-leucine (DON) and by exogenously added components of ECM. DON, a glutamine analogue, inhibited the synthesis of metachromatic ECM in FCS, and prevented the modulation to a fibroblastic morphology, onset of motility, and decrease in steroid production. Addition of hyaluronic acid, but not of chondroitin sulfate, to the epithelioid secretory cells promoted a drop in steroid production and slight alteration in morphology and movement. Both results are consistent with the possibility that metachromatic ECM production is responsible for the reversion of the steroid secretory to the myofibroblastic phenotype. This effect was mimicked by maintaining cells on polystyrene surfaces that were sulfonated to a negative charge density similar to that of ECM. This result implies that the negative charge of ECM may contribute to the expression of the adrenocortical stem cell phenotype, and that its effect is extracellular. A possible physiologic role for ECM-mediated control of adrenal cortical differentiation is proposed.