Serum Starvation Affects the Transcriptomic and Proliferative Response to ACTH in Primary Cultures of Rat Adrenocortical Cells

The adrenocorticotropic hormone (ACTH) is a key regulator of adrenal cortex function, promoting glucocorticoid synthesis and modulating cell proliferation. However, the role of extracellular steroid availability in shaping ACTH responses is still not fully defined. In this study, the functional and transcriptomic effects of ACTH were investigated in primary rat adrenocortical cells cultured under standard conditions and under simulating serum starvation (charcoal-stripped serum). The cells were treated with ACTH (10 nM), and proliferation was monitored using xCELLigence RTCA, while corticosterone secretion was assessed via ELISA. The RNA extracted from these samples was then utilised for the purpose of microarray-based gene expression profiling. The present study revealed that charcoal-stripped serum markedly improved ACTH-induced corticosterone output, suggesting that the absence of endogenous steroids sensitises cells to ACTH stimulation possibly by removing negative feedback constraints. This enhanced steroidogenic response was accompanied by a significant suppression of proliferation, confirming that the stimulation of specialised functions (such as steroid secretion) reduces proliferative capacity of adrenocortical cells. Transcriptomic data revealed that the steroids stimulating effect on corticosterone output was mainly mediated via steroid biosynthetic and lipid metabolic processes while inhibitory effect on proliferation rate was mediated mainly by cell adhesion molecules. These results suggest that, in primary culture of rat adrenocortical cells, the stimulatory effect of ACTH on their specialised function (corticosteroid secretion) simultaneously reduces their basal function, which is their proliferation process. Changes in this type are also observed in cells cultured in steroid-depleted conditions.