Vitamin D interferes with glucocorticoid responsiveness in human peripheral blood mononuclear target cells

Abstract

Glucocorticoids (GCs) are widely used in the treatment of inflammatory and autoimmune diseases; however, patients are often resistant to GC effects. Current studies indicate that vitamin D reduces the risk or modifies the course of autoimmune diseases posing vitamin D supplementation as a prevention or therapeutic option. Herein, we investigated whether vitamin D can modify the response to GCs at the molecular level. To this end, peripheral blood mononuclear cells (PBMCs) were isolated from healthy vitamin D-deficient women and incubated with either the active metabolite 1,25(OH)D (VitD) for 11 days or dexamethasone (Dex) for the last 2 days in the presence or absence of VitD. Ex vivo GC sensitivity was assessed by the expression of the glucocorticoid receptor (GR) responsive gene GILZ with RT-PCR. Long-term incubation of PBMCs with VitD significantly decreased the Dex-induced augmentation of GILZ expression. Since the intracellular concentration of GR and the GR nuclear translocation are critical determinants of GC sensitivity, we next evaluated the effect of VitD on these factors. RT-PCR and western-blot analysis revealed that VitD reduced the expression of GR. This effect was abolished by the HDAC-specific inhibitor trichostatin A, implying that HDAC was implicated in this effect. Moreover, NCoR1 mRNA was significantly decreased upon treatment with VitD either alone or as pre-treatment to Dex, suggesting that a possible increase in expression of this co-repressor was not involved. In addition, immunofluorescence analysis showed that VitD hindered the Dex-induced GRα nuclear translocation, an effect verified by subcellular fractionation and western-blot experiments. To further explore the underpinning mechanism, we examined the potential of VitD to: (1) strengthen the FK506-binding protein 5 (FKBP5) negative feedback loop and (2) modify the phosphorylation status of GR. Remarkably, VitD decreased FKBP5 expression and decreased phosphorylation at Ser211, while enhancing phosphorylation of GR at Ser203. Overall, VitD decreases the ex vivo GC sensitivity and this effect is, at least in part, attributed both to decrease of GR expression owing to a mechanism that engages HDAC and inhibition of GR translocation to nucleus via differential modulation of the phosphorylation state of GR. Our study provides, for the first time, evidence that long-term action of VitD induces GC resistance in PBMCs from healthy volunteers and offers a possible mechanistic basis for VitD-triggered attenuation of GC effects.

Vitamin D deficiency and impaired placental function: potential regulation by glucocorticoids?

“…Similar observations have been made in a squamous cell carcinoma model whereby dexamethasone induces de novo transcription of the vitamin D receptor in a glucocorticoid receptor-dependent manner (Hidalgo et al 2011). Furthermore, vitamin D also appears to have direct effects on the glucocorticoid sensitivity of peripheral blood mononuclear cells, with evidence of direct downregulation of glucocorticoid receptor expression and inhibition of GR translocation to the nucleus (Kassi et al 2016). Moreover, in patients with steroid-resistant asthma, vitamin D administration beneficially alters the clinical response to glucocorticoids (Chambers et al 2015).…”

“…This suggests that vitamin D homeostasis during pregnancy likely involves communication between maternal, placental and fetal compartments. Indeed, recent research has shown an interaction between vitamin D pathways and glucocorticoids ('stress' hormones) in the context of the placenta, brain, lung and other tissues (Obradovic et al 2006, Hidalgo et al 2011, Chambers et al 2015, Tesic et al 2015, Kassi et al 2016. The current review aims to discuss the potential mechanisms by which placental function may be implicated in the adverse outcomes associated with vitamin D-deficient pregnancies.…”

Orexin-A Exerts Equivocal Role in Atherosclerosis Process Depending on the Duration of Exposure: In Vitro Study

“…Western blot analysis was performed as previously described [16]. Briefly, whole-cell lysates were prepared in lysis buffer (Cell Signaling Technology, MA, USA).…”

Vitamin D affects glucocorticoid action in target cells

“…We studied the effect of the long-term (11 days) repletion of vitamin D -the supplementation of which is often proposed for the prevention or even treatment of autoimmune / inflammatory diseases- on the sensitivity of peripheral blood mononuclear cells (PBMCs) to glucocorticoids [3]. …”

“…We found that long-term action of vitamin D downregulated GILZ expression thus inducing glucocorticoid resistance in PBMCs derived from healthy volunteers. Based on our results this effect can, at least in part, be attributed to: i) decrease of glucocorticoid receptor ( GR ) expression owing to a mechanism that engages histone deacetylase(s) (HDACs), and ii) inhibition of GR translocation to the nucleus via modulation of the phosphorylation state of GR; in fact, vitamin D decreased phosphorylation of GR at Ser211 whilst enhanced phosphorylation of GR at Ser203 [3]. …”