Glucocorticoid receptor isoforms and effects of glucocorticoids in ovulated mouse oocytes and preimplantation embryos†

Abstract

To investigate possible involvement of glucocorticoid receptor (GR) in mediating effects of maternal stress or therapeutically administered glucocorticoids on early embryo we analyzed the expression of GR subtypes in ovulated mouse oocytes and preimplantation embryos. RT-PCR analysis results showed that GRα and GRγ transcripts are relatively highly expressed in mouse oocytes, and both transcripts are present at lower amounts in preimplantation embryos. We also detected low expression of two other splice variants, GRβ and a transcript orthologous to the human GR-P subtype, mainly at the blastocyst stage. Using Western blot analysis, we detected several GR protein bands that differed in size between oocytes and preimplantation embryos. To compare the effects of corticosterone (a major endogenous glucocorticoid in rodents) and dexamethasone (a synthetic glucocorticoid) on early embryos, we cultured mouse preimplantation embryos in the presence of these glucocorticoids. Corticosterone showed a strong inhibitory effect on embryo development (starting from a 50 μM concentration), without a significant influence on apoptosis incidence. On the other hand, dexamethasone induced apoptosis in early embryo cells (starting from a 1.5 μM concentration), and its effect on embryo development was less detrimental than that found with the same dose of corticosterone. In summary, our results showed that different GR subtypes are expressed in ovulated mouse oocytes and preimplantation embryos and that the composition of GR subtypes changes during early embryo development. Moreover, we found significant differences in the effects of the two glucocorticoids on early embryo development, which might be associated with activation of different GR subtypes.

Glucocorticoids, Stress and Delta-9 Tetrahydrocannabinol (THC) during Early Embryonic Development

“…The impact of glucocorticoids on their target organs is primarily modulated by the local number of glucocorticoid receptors (GRs) and the concentration of active hormone available to bind to the GRs ( Table 1 ) [ 22 , 48 , 49 ]. NR3C1 is one of the main GR subtypes that has been shown to be expressed in the ovaries of many different mammalian species [ 17 , 20 , 21 , 22 , 50 , 51 , 52 ] and is part of the nuclear receptor subfamily ligand-dependent transcription factors [ 50 ]. NR3C1 forms a receptor complex upon binding to cortisol, which translocates from the cytoplasm to the nucleus and binds to glucocorticoid response elements (GREs) on DNA to alter transcription and downstream gene expression ( Figure 1 ) [ 17 , 50 , 52 , 53 ].…”

“…NR3C1 is one of the main GR subtypes that has been shown to be expressed in the ovaries of many different mammalian species [ 17 , 20 , 21 , 22 , 50 , 51 , 52 ] and is part of the nuclear receptor subfamily ligand-dependent transcription factors [ 50 ]. NR3C1 forms a receptor complex upon binding to cortisol, which translocates from the cytoplasm to the nucleus and binds to glucocorticoid response elements (GREs) on DNA to alter transcription and downstream gene expression ( Figure 1 ) [ 17 , 50 , 52 , 53 ]. Two main enzymes, 11b-hydroxysteroid dehydrogenase type 1 (HSD11B1) and type 2 (HSD11B2), are responsible for controlling the concentration of active glucocorticoids within target organs [ 21 , 22 ].…”

“…HSD11B1 is responsible for reducing inactive cortisone into active cortisol, while HSD11B2 is a dehydrogenase that oxidizes active cortisol to inactive cortisone [ 21 , 22 ]. Across various mammalian species, HSD11s and GRs have been shown to be expressed and regulate the hormonal microenvironment in many of the same cells and tissues as the ECS, including GCs, CCs, oocytes, embryos, follicular fluid, ovary, and placenta [ 17 , 21 , 22 , 49 , 50 , 52 , 54 ]. The hormonal microenvironment is tightly regulated throughout oocyte maturation, given that oocyte competence, quality, and capacity to produce an embryo can be altered by disruption to such processes [ 20 , 21 , 22 ].…”

“…Therefore, it is important to evaluate the validity of previously used animal models to study relationships between molecular stress levels and THC in humans. Mammalian animal models previously utilized to study the effects of THC or molecular stress include mice, pigs, goats, lambs, primates, and cow [ 12 , 14 , 15 , 17 , 18 , 20 , 21 , 22 , 49 , 50 , 52 , 60 , 61 , 62 ]. Evaluation of such animal models has revealed that the bovine oocyte, granulosa cells (GC), and CCs are the most translationally relevant to human reproduction [ 13 , 63 , 64 , 65 ].…”

Reduced growth capacity of preimplantation mouse embryos in chronic unpredictable stress model

“…Clinical study showed that both increased stress levels and serum levels of cortisol (CORT) are associated with missed abortion (Tian & Kang, 2014). Corticosterone treatment during in vitro culture inhibits early embryo development from the two‐cell stage to blastocysts in mice (Čikoš et al, 2019). Administration of dexamethasone (a synthetic glucocorticoid) during gestation results in increased follicular atresia and reduction of the pool of healthy primordial follicles in the ovary of neonatal spiny mice (Hulas‐Stasiak et al, 2016).…”