Differential subcellular localization of the glucocorticoid receptor in distinct neural stem and progenitor populations of the mouse telencephalon in vivo

Abstract

Glucocorticoids are given to pregnant women at risk for premature delivery to promote lung maturation. Despite reports of detrimental effects of glucocorticoids on telencephalic neural stem/progenitor cells (NSPCs), the regional and cellular expression of the glucocorticoid receptor (GR) in various NSPC populations in the intact brain has not been thoroughly assessed. Therefore in this study we performed a detailed analysis of GR protein expression in the developing mouse ventral and dorsal telencephalon in vivo. At embryonic day 11.5 (E11.5), the majority of Pax6-positive radial glial cells (RGCs) and Tbr2-positive intermediate progenitor cells (IPCs) expressed nuclear GR, while a small number of RGCs on the apical ventricular zone (aVZ), expressed cytoplasmic GR. However, on E13.5, the latter population of RGCs increased in size, whereas abventricular NSPCs and especially neurons of the cortical plate, expressed nuclear GR. In IPCs, GR was always nuclear. A similar expression profile was observed throughout the ventral telencephalon, hippocampus and olfactory bulb, with NSPCs of the aVZ primarily expressing cytoplasmic GR, while abventricular NSPCs and mature cells primarily expressed nuclear GR. Close to birth, nuclear GR accumulated within specific cortical areas such as layer V, the subplate and CA1 area of the hippocampus. In summary, our data show that GR protein is present in early NSPCs of the dorsal and ventral telencephalon at E11.5 and primarily occupies the nucleus. Moreover, our study suggests that the subcellular localization of the receptor may be subjected to region and neurodevelopmental stage-specific regulation.

Effects of antenatal glucocorticoids on the developing brain

“…Typically, endogenous GC levels in fetal circulation increase rapidly late in gestation to promote the development of fetal organs including the lungs, kidney and brain, utilizing the receptor for cortisol, GR, which is expressed throughout gestation, a finding confirmed in studies from our lab in mice 2,3,33 . Throughout development, the placenta tightly regulates fetal GC levels, while the HPA axis regulates maternal GC.…”

“…The timing of neurogenesis and gliogenesis are tightly controlled and regulated such that neurogenesis occurs before birth in humans, followed by the subsequent formation of oligodendrocytes and astrocytes 48–52 . Human and mice NSPCs express GR from early developmental stages and have been shown to respond to GC stimulation in-vitro indicating that the developing brain is poised to respond to premature GC administration and activate downstream signaling 33,53 . Since GCs have been shown to have anti-proliferative effects on NSPCs 51,54 , GC exposure is likely to have effects on neurogenesis and gliogenesis.…”

Glucocorticoid-independent modulation of GR activity: Implications for immunotherapy

“…As mentioned in section 4, changing levels of nuclear versus cytoplasmic versus membrane-associated unliganded GR are possible mechanisms whereby GC-independent GR signalling could be modulated, although this has not been much investigated. Relatively little is known about signals that regulate subcellular localization of the unliganded GR; however evidence suggests a role for cell cycle phase and developmental stage (Matthews et al, 2011; Matthews et al, 2015; Tsiarli et al, 2013). Matthews et al reported that the heterogeneity in unliganded GR subcellular distribution is reflective of cell cycle phase and that mitotic index contributes to tissue GC sensitivity (Matthews et al, 2011).…”

“…Matthews et al reported that the heterogeneity in unliganded GR subcellular distribution is reflective of cell cycle phase and that mitotic index contributes to tissue GC sensitivity (Matthews et al, 2011). Recent work in neural stem/progenitor cells of the developing mouse ventral telencephalon suggests that the unliganded GR may be subjected to region and neurodevelopmental stage-specific regulation, with the GR being mostly nuclear in some neurons in the absence of GCs (Tsiarli et al, 2013). A recent study has reported a requirement for the unliganded GR in chromosome segregation (Matthews et al, 2015).…”

“…Interestingly, there are some reports showing that the GR is mainly nuclear in primary untransformed cells, such as cortical astrocytes (Unemura et al, 2012), some neural stem and progenitor cell populations (Tsiarli et al, 2013), human monocytes and mouse gonadotropes (Hapgood et al, unpublished data) as well as in some transformed cell lines (Verhoog et al, 2011), even in the absence of serum. Moreover, a substantial proportion of unliganded GR is nuclear in the absence of serum in primary normal human bronchial epithelial (NHBE) cells (Hakim et al, 2013) and other cells isolated from the sputum of healthy patients (macrophages, epithelial cells, neutrophils and Eosinophils) (Usmani et al, 2005), all key targets for immunotherapy.…”