Neuroprogesterone synthesis in hypothalamic astrocytes is associated with a pubertal increase in membrane ERα levels

ABSTRACTThe development of estrogen positive feedback is a hallmark of female puberty. Both estrogen and progesterone signaling are required for the functioning of this neuroendocrine feedback loop but the physiological changes that underlie the emergence of estrogen positive feedback remain unknown. Only after puberty does estradiol (E2) facilitate progesterone synthesis in female hypothalamic astrocytes (neuroP) (Mohr et al. 2018), an event critical for estrogen positive feedback and the LH surge. We hypothesize that prior to puberty, these astrocytes have low levels of membrane estrogen receptor alpha (ERα), making them unable to respond to E2 with increased neuroP synthesis prior to puberty. To test this hypothesis, pure populations of primary astrocyte cultures were derived from female mice at three different stages of development: pre-puberty (postnatal week 3), pubertal onset (week 5), and post-puberty (week 8). Hypothalamic astrocyte responses were measured after treatment with E2. Hypothalamic astrocytes increased progesterone synthesis across pubertal development. Prior to puberty, mERα expression was low in hypothalamic astrocytes, but expression increased across puberty. The increase in mERα expression in hypothalamic astrocytes also corresponded with an increase in caveolin-1 protein, PKA phosphorylation, and a more rapid [Ca2+]i flux in response to E2. Together, these results indicate that increased mERα in hypothalamic astrocytes contributed to the post-pubertal response to E2 that results in neuroP synthesis, critical for ovulation.SIGNIFICANCE STATEMENTHypothalamic astrocytes, when exposed to estradiol, make progesterone that is necessary for estrogen positive feedback during adulthood in the female rodent. However, little is known about what cellular changes occur during puberty that allow for the estradiol facilitation of progesterone synthesis. In this study, we compared cell excitability, progesterone synthesis, and levels of membrane estrogen receptor in hypothalamic astrocytes derived from pre-, mid-, and post-pubertal female mice to characterize their maturation that allows them to increase progesterone synthesis facilitating estrogen positive feedback. This study suggests that hypothalamic astrocytes acquire the necessary cellular machinery during puberty to enable E2-facilitated progesterone synthesis.