Mimecan Regulates Corticosterone Secretion and Plays A Critical Role in Adrenal Responses to Stress

Background: A functional hypothalamic-pituitary-adrenal (HPA) axis is critical for host defenses to outside stimuli. The adrenal cortex is seemingly endowed with distinct functional units that are regulated by adrenocorticotropic hormone (ACTH). We have found that mimecan, a small leucine-rich proteoglycan expressed in the adrenal gland, has yet to be characterized in functional terms.Results: Herein, we have demonstrated the following properties: 1) adrenal mimecan expression in mouse models is significantly downregulated under hypoglycemia and scalded stress; 2) expression of mimecan in adrenal cells may be downregulated through ACTH or upregulated by glucocorticoid via related receptors (GRs); and 3) mimecan stimulates corticosterone secretion in adrenal tissues. The latter was proven using in vivo and in vitro studies to confirm the ACTH-independent activity of mimecan-maltose-binding protein (-MBP). Relative to litter-mate mice, the basal-state diurnal rhythm of corticosterone secretion is disrupted in mimecan knockout mice, and corticosterone secretion is increased under restraint stress conditions. Conclusions: These findings offer the first evidence that mimecan is key in regulating the HPA axis, assuming a critical role in adrenal responses to stress.