Lack of estrogen receptor a in astrocytes of progranulin-deficient mice

Progranulin (PGRN) is a multifunctional growth factor with functions in neuroprotection, anti-inflammation, and neural progenitor cell proliferation. These functions largely overlap with the actions of estrogen in the brain. Indeed, we have previously shown that PGRN mediates the functions of estrogen, such as masculinizing the rodent brain and promoting adult neurogenesis. To evaluate the underlying mechanism of PORN in mediating the actions of estrogen, the localization of estrogen receptor alpha (ER alpha) in the brains of wild-type (WT) and PGRN-deficient (KO) mice was investigated. First, double labeling immunofluorescence was performed for ER alpha with neuronal nuclei (NeuN), ionized calcium-binding adaptor molecule 1 (Iba1), and glial fibrillary acidic protein (GFAP), as markers for neurons, microglia, and astrocytes, respectively, in female mice in diestrous and estrous stages. ER alpha-immunoreactive (IR) cells were widespread and co-localized with NeuN in brain sections analyzed (bregma -1.06 to -3.16 mm) of both WT and KO mice. In contrast, expression of ERa was not observed in Ibal-IR cells from both genotypes. Interestingly, although ER alpha was co-localized with GFAP in WT mice, virtually no ER alpha expression was discernible in GFAP-IR cells in KO mice. Next, the brains of ovariectomized adult female, adult male, and immature female mice were subjected to immunostaining for ER alpha and GFAP. Again, co-localization of ER alpha with GFAP was observed in WT mice, whereas this co-localization was not detected in KO mice. These results suggest that PGRN plays a crucial role in the expression of ER alpha in astrocytes regardless of the estrous cycle stage, sex, and maturity.