ESPE Abstracts

Background: Animal studies have reported that exposure to synthetic glucocorticoids (sGCs) may lead to inter- and transgenerational effects on offspring phenotype. However, many of these studies are poorly designed, do not account for possible non-epigenetic confounds, and cannot determine the mechanism(s) by which gamete epimutations are induced.

Objectives: Firstly, to determine whether developmental exposure of mice to sGCs at human-relevant doses and routes causes intergenerational and/or transgenerational effects on phenotype through the paternal line; and secondly, to determine whether intergenerational effects of sGCs are due to germline inheritance (including specifically glucocorticoid receptor [GR] activation in germ cells or epididymis only) or confounding by other factors.

Methods: First, wild-type gestating C57BL/6J mice were treated with subcutaneous vehicle or dexamethasone (0.2 mg/kg/day) on gestational days 16-17, and their patrilineal F1-F3 offspring phenotyped. Next, sperm from F1 males exposed antenatally to vehicle or dexamethasone were used to generate F2 offspring via in vitro fertilisation, which were also phenotyped. Finally, heterozygous C57BL/6NTac mice expressing a constitutively active GR (ΔGR) under a germ cell- (males and females) or epididymis-specific (males only) promoter were mated with wild-type mice and their wild-type offspring phenotyped and compared to controls with two wild-type parents. Phenotypic outcomes assessed were growth, glucose and insulin tolerance, body composition, and various reproductive metrics.

Results: Gestational dexamethasone treatment caused impaired glucose tolerance in F1 and F2 males, and heavier internal genitalia in F2 females, but these findings were not replicated in F2 mice generated by IVF, suggesting a non-germline effect. The F3 phenotype was of increased body weight (males) and altered thyroid hormone levels and body composition (females). Founder mice heterozygous for ΔGR had no obvious phenotype, but their wild-type adult male offspring had improved glycaemia regardless of which parental reproductive tissue (male/female germ cells or epididymis) expressed ΔGR; paternal and maternal germ cell, but not paternal epididymal, ΔGR expression also affected offspring body composition in a sexually dimorphic manner.

Conclusions: Patrilineal intergenerational effects of gestational dexamethasone treatment appear to be transmitted independent of the germline. Constitutive activation of the GR in germ cells of either parent causes sexually dimorphic changes in offspring body composition, and improves male glycaemia; the latter effect is also seen with paternal epididymal GR activation. More evidence is required to determine the public health significance of these findings.