Hypoxia-induced gene expression of aquaporin-4, cyclooxygenase-2 and hypoxia-inducible factor 1α in rat cortical astroglia is inhibited by 17ß-estradiol and progesterone.

ABSTRACT

17ß-Estradiol (E2) and progesterone (P) are neuroprotective in acute brain injury by attenuating neuropathophysiological processes and regulating local glial function. Besides controlling brain-intrinsic immune responses, astrocytes are cellular targets for sex steroids in health and disease and typically resist to hypoxic damage. In this in vitro study, we aimed at uncovering astroglia-specific reactions to sublethal hypoxic conditions and astroglia-specific effects of both sex steroid hormones on these parameters. Short-term hypoxia for 3 h increased reactive oxygen species production, but had no influence on cell viability of cerebral cortical rat astroglia. Astrocytes expressed classical estrogen receptors (ER), progesterone receptor (PR), and a set of nonclassical steroid hormone receptors. Hypoxia specifically induced ERα and PR isoform A gene expression. Oxygen deprivation increased gene expression of aquaporin-4 (AQP4), hypoxia-inducible factor 1α (Hif1α), and cyclooxygenase-2 (COX2). The application of E2 and P selectively prevented this induction. Effects on protein levels of these genes appeared to be delayed. These data show that astrocytes change their receptivity for sex steroid hormones by switching steroid hormone receptor expression and that E2 and P modify or antagonize proinflammatory COX2 synthesis, edema-promoting AQP4 expression, and the Hif1α increase. In vivo studies have to address whether these cell responses contribute to steroid-mediated neuroprotection in stroke.