Specific Regulation of StAR Expression in the Rat Adrenal Zona Glomerulosa: an In Situ Hybridization Study

Abstract

Steroid acute regulatory protein (StAR) plays an essential role in steroidogenesis because it is responsible for the transfer of cholesterol from cellular stores to the inner mitochondrial membrane. We investigated the distribution and regulation of StAR expression in association with aldosterone production in the rat adrenal gland in vivo. Using nonradioactive in situ hybridization, we demonstrate that the outermost five to seven parenchymal cell layers express the StAR gene only weakly and inhomogeneously. The strongest expression is found in the zona fasciculata and zona reticularis. In addition, some cells in the adrenal medulla also stained positively. To differentiate between functionally active glomerulosa and inactive intermediate cells, we compared the expression pattern of StAR with that of aldosterone synthase. The expression of the latter is localized to two or three cell layers only, located immediately below the capsule. However, the cells of the intermedia are capable of expressing both genes prominently, as shown after stimulation with bilateral nephrectomy for 2 days. All zones of the adrenal cortex by then expressed StAR gene to the same extent. This was accompanied by a 50-fold elevated plasma aldosterone concentration. Our data demonstrate that the width of the aldosterone-producing zone can increase within a short period of time by recruiting hormonally inactive cells to steroidogenesis.