Glucocorticoids and Fetal Programming; Necessary and Sufficient?

Abstract

Epidemiological evidence suggests that early life adversity, as marked by lower birth weight, associates with a substantially increased risk of cardiometabolic and neuropsychiatric disorders in later life, so called “fetal programming.” Fetal overexposure to glucocorticoids is a possible basis for this association. Indeed glucocorticoid treatment or maternal stress may reproduce programmed phenotypes in inbred models where genetic differences are minimised.

The placenta and developing fetal organs highly express 11β-hydroxysteroid dehydrogenase type 2 (11β-HSD2) which catalyses rapid inactivation of cortisol and corticosterone thus forming a functional barrier to cellular glucocorticoid action. By pass, gene deletion or inhibition of 11β-HSD2 reduces birth weight and programmes lasting changes in cardiometabolic and behavioural parameters in the offspring in mammals including humans. In contrast, whilst maternal malnutrition similarly programmes the offspring and also reduces placental 11β-HSD2 levels, the effects appear to be mediated more by premature activation of the fetal hypothalamic-pituitary-adrenal axis than trans-placental passage of maternal glucocorticoids.

At a molecular level, epigenetic alterations, notably in methylation of specific cytosine deoxynucleotide residues in the promoters of target genes, may underpin persisting alterations in cellular gene expression. However, the inconsistency of patterns of methylation and related gene expression, notably in phenotypically similar progeny of a second programmed generation, imply understanding of such processes is far from complete. This emerging biology and its pathophysiological implications is a ripe avenue for future study.