Sex differences in hypothalamic astrocyte response to estradiol stimulation

Abstract

BackgroundReproductive functions controlled by the hypothalamus are highly sexually differentiated. One of the most dramatic differences involves estrogen positive feedback, which leads to ovulation. A crucial feature of this positive feedback is the ability of estradiol to facilitate progesterone synthesis in female hypothalamic astrocytes. Conversely, estradiol fails to elevate hypothalamic progesterone levels in male rodents, which lack the estrogen positive feedback-induced luteinizing hormone (LH) surge. To determine whether hypothalamic astrocytes are sexually differentiated, we examined the cellular responses of female and male astrocytes to estradiol stimulation.MethodsPrimary adult hypothalamic astrocyte cultures were established from wild type rats and mice, estrogen receptor-α knockout (ERKO) mice, and four core genotype (FCG) mice, with the sex determining region of the Y chromosome (Sry) deleted and inserted into an autosome. Astrocytes were analyzed for Sry expression with reverse transcription PCR. Responses to estradiol stimulation were tested by measuring free cytoplasmic calcium concentration ([Ca2+]i) with fluo-4 AM, and progesterone synthesis with column chromatography and radioimmunoassay. Membrane estrogen receptor-α (mERα) levels were examined using surface biotinylation and western blotting.ResultsEstradiol stimulated both [Ca2+]i release and progesterone synthesis in hypothalamic astrocytes from adult female mice. Male astrocytes had a significantly elevated [Ca2+]i response but it was significantly lower than in females, and progesterone synthesis was not enhanced. Surface biotinylation demonstrated mERα in both female and male astrocytes, but only in female astrocytes did estradiol treatment increase insertion of the receptor into the membrane, a necessary step for maximal [Ca2+]i release. Regardless of the chromosomal sex, estradiol facilitated progesterone synthesis in astrocytes from mice with ovaries (XX and XY-), but not in mice with testes (XY-Sry and XXSry).ConclusionsAstrocytes are sexually differentiated, and in adulthood reflect the actions of sex steroids during development. The response of hypothalamic astrocytes to estradiol stimulation was determined by the presence or absence of ovaries, regardless of chromosomal sex. The trafficking of mERα in female, but not male, astrocytes further suggests that cell signaling mechanisms are sexually differentiated.

Sex differences in astrocyte and microglia responses immediately following middle cerebral artery occlusion in adult mice

“…In cell culture models, estradiol is shown to promote signaling mechanisms that increase intracellular Ca 2+ concentrations and corresponding astrocyte Ca 2+ dependent functions (Chaban et al, 2004; Kelly and Ronnekleiv, 2009). While not tested in our preparation, estradiol was reported to increase cytoplasmic Ca 2+ release in cultured hypothalamic astrocytes collected from both males and females but not in females with estrogen receptor knockout (Kuo et al, 2010). It has also been shown that elevated intracellular Ca 2+ stimulates astrocyte mitochondrial metabolism to maintain vital energy resources during the first few hours after ischemia.…”

Regulation of astroglia by gonadal steroid hormones under physiological and pathological conditions

“…Certain functions of astrocytes also present sex-dimorphic characteristics, such as glutamate uptake, the response to glutamate (Hsu et al, 2001;Morizawa et al, 2012), the response to cannabinoids (Lopez-Gallardo et al, 2012) or even the response to gonadal hormones (Arnold et al, 2008;Gulinello and Etgen, 2005;Kuo et al, 2010a;Zhang et al, 2002). Sex also influences the response of astrocytes to harmful stimuli such as prenatal or neonatal stress (Garcia-Caceres et al, 2010;Llorente et al, 2009Llorente et al, , 2008Lopez-Gallardo et al, 2012), exposure to toxins (Santos-Galindo et al, 2011) and to environmental contaminants (Astiz et al, 2014;Miller et al, 2010;Sundar Boyalla et al, 2011) or deprivation of oxygen and glucose (Liu et al, 2008(Liu et al, , 2007 (Figure 1).…”

“…The increase in the activity of StAR and TSPO leads to an increase in progesterone synthesis in the astrocyte (Chaban et al, 2004;Chen et al, 2014;Dewing et al, 2007;Kuo et al, 2010b;Micevych et al, 2007). In female rodents, the production of progesterone by hypothalamic astrocytes in response to estradiol is involved in the initiation of luteinizing hormone surge and the subsequent ovulation (Kuo et al, 2010a). In addition to play this role in the control of reproduction, the synthesis of progesterone by astrocytes in response to estradiol may also be involved in the regulation of many aspects of brain function under physiological and pathological conditions (Melcangi et al, 2014).…”

Astrocytic response to cerebral ischemia is influenced by sex differences and impaired by aging

“…Astrocytes from both males and females express estrogen receptor (ER) α, ERβ, the transmembrane ER, GPR30, and progesterone and androgen receptors (Azcoitia et al, 1999; Pawlak et al, 2005b; Arnold et al, 2008; Duncan et al, 2013; Kuo et al, 2010b) and estradiol facilitates the synthesis of progesterone in astrocytes (Micevych et al, 2007; Chaban et al, 2004). In addition, astrocytes were found to be the most steroidogenic brain cells producing several neurosteroids, such as progesterone, testosterone, and estradiol, and expressing enzymes involved in hormone synthesis, including aromatase (Zwain and Yen, 1999).…”