Introduction: Glucocorticoids exert pleiotropic effects on all tissues, are essential for life, and are used therapeutically for a range of conditions. Exposure to excess glucocorticoid (as commonly seen with therapeutic dosing) is associated with a range of serious adverse events and increased mortality. Glucocorticoids act via the glucocorticoid receptor (GR), a nuclear transcription factor, to exert their actions. A range of GR splice and translational isoforms have been identified, expression of which have been shown to affect glucocorticoid sensitivity. To date, these have been characterised in vitro and in vivo in a range of healthy and diseased tissues, here we report the first in vivo study of GR isoform expression in PBMCs of patients with varying states of glucocorticoid excess and deficiency.
Methods: PBMCs were isolated from whole blood of adult patient with normal HPA axis, glucocorticoid deficiency and glucocorticoid excess. Proteins from cytoplasmic and nuclear lysates were extracted. GR protein isoforms were measured via western blot and normalised to β-actin expression. PBMC gene expression was measured via RNA-Seq.
Results: GR protein isoforms detected in PBMCs of each group included GRα-A, GRα-C, GRα-D1-3, GR-A and GR-P. All GR isoforms were downregulated in the exogenous glucocorticoid group with some differences between other groups for individual isoforms. Isoform expression was downregulated across the day in women with AI. GR isoforms were correlated with expression of both shared, and unique genes, and gene expression profiles were markedly different in AI compared to the other groups.
Conclusion: The presence of multiple GR isoforms in PBMCs may regulate the sensitivity and specificity of the response to glucocorticoids under different conditions and disease states. This may be an important consideration when assessing glucocorticoid responsiveness in patients with endocrine disorders associated with altered HPA function or requiring exogenous glucocorticoid treatment.