Endocrine Abstracts

Introduction: Glucocorticoids (GCs) are used in the treatment of chronic inflammatory or autoimmune diseases. However, patients are often resistant to the GC effects. Response to GCs is triggered through glucocorticoid receptor (GR). An important regulator of GR activity is the FKBP5. FKBP5 binds to co-chaperones promoting a conformation with lower cortisol affinity. The number of GRs is another determinant of GC sensitivity; GR expression is regulated by the nuclear receptor co-repressor-1 (NCoR-1). An anti-inflammatory/immunomodulatory role of 1,25(OH)₂D₃ has been demonstrated. We aimed to investigate the effect of 1,25(OH)₂D₃ on the in vitro GC sensitivity.

Participants and methods: PBMCs were isolated from eight healthy women and incubated with dexamethasone for the last 48 h, with or without pre-incubation with 1,25(OH)₂D₃ for 11 days. Co-incubation experiments with dexamethasone and 1,25(OH)₂D₃ were also performed. In vitro GC sensitivity was assessed with dexamethasone-induced effects on GILZ mRNA expression (real-time PCR). FKBP5 and NCoR1 mRNA expression as well as GRα mRNA and protein expression (western blot analysis) were assessed. Intracellular distribution of GR was visualised by IF.

Results: After 11 days of culture, incubation of PBMCs with dexamethasone for the last 48-h resulted in 12-fold increase in GILZ-mRNA levels. When PBMCs were pre-incubated with 1,25(OH)₂D_3, dexamethasone (last 48-h) induced a significant down-regulation of GILZ mRNA expression. When PBMCs were pre-treated with 1,25(OH)₂D₃ for 11 days, dexamethasone (last 48-h) caused a significant down-regulation of GRα mRNA expression, confirmed at protein level. Treatment of PBMCs with 1,25(OH)₂D₃, led to significant decrease in FKBP5 and NCoR1 mRNA levels. IF staining showed that vitamin D causes a GR translocation from nucleus to cytoplasm.

Conclusion: 1,25(OH)₂D₃ decreased the in vitro glucocorticoid sensitivity in PBMCs isolated from healthy women. This effect is, at least in part, attributed to the reduction of GRα expression due to a mechanism that did not appear to implicate NCoR1 or FKBP5 expression. Moreover a 1,25(OH)₂D₃-induced GR translocation from nucleus to cytoplasm is also involved. The mechanism through which vitamin D modulates response to glucocorticoids remains to be fully delineated.

Disclosure: General Secretariat for Research and Technology.