Vitamin D up-regulates the vitamin D receptor by protecting it from proteasomal degradation in human CD4+ T cells

Vitamin D-induced up-regulation of human keratinocyte cathelicidin anti-microbial peptide expression involves retinoid X receptor α

The biologically active form of vitamin D, 1α,25-dihydroxyvitamin D3 (1,25D3), has been reported to positively regulate the human cathelicidin anti-microbial peptide (CAMP) gene coding for LL-37, but the mechanisms are not completely understood. We have determined the expression of CAMP, vitamin D receptor (VDR), and the retinoid X receptor (RXR) isoforms in human skin and gingival tissue biopsies and investigated the signaling pathways involved in 1,25D3-induced upregulation of CAMP. Human skin and gingival biopsies exhibited few VDR-immunoreactive cells within the stratum basale, whereas rat colon enterocytes (positive control) possessed abundant VDR immunoreactivity. Nuclear VDR immunoreactivity was demonstrated in human skin keratinocytes (HaCaT cells). Gene analysis revealed that human skin biopsies expressed higher levels of both CAMP and RXRα mRNA than human gingival biopsies, whereas VDR and RXRβ transcript levels were similar in skin and gingiva. In HaCaT cells, treatment with 1,25D3 (5 nM and 1 μM) for 4 and 24 h up-regulated CAMP mRNA several fold, and treatment with 1,25D3 for 24 h increased protein expression of the pro-form of LL-37 (hCAP-18) by about 13 times. The 1,25D3-evoked stimulation of HaCaT CAMP expression was associated with attenuated VDR mRNA and protein expression. Treatment with RXRα short interfering RNA reversed the 1,25D3-induced CAMP expression in HaCaT cells, showing that RXRα is involved in the up-regulation of CAMP by 1,25D3. We conclude that the 1,25D3-evoked stimulation of CAMP expression in human skin keratinocytes is dependent on RXRα but is not associated with the up-regulation of VDR expression.

Comparative effect of 25(OH)D3 and 1,25(OH)2D3 on Th17 cell differentiation

Vitamin D is a secosteroid hormone that plays an important regulatory role in calcium homeostasis and bone metabolism. Immune cells can both produce and respond to 1,25(OH)2D3. CD4+ T cells from vitamin D receptor (VDR) KO mice produce higher levels of IFN-γ and IL-17 than their wild type counterparts, and play a crucial role in the pathogenesis of autoimmune diseases (AID). We are particularly interested in studying the effect of vitamin D on pathogenic Th17 cells in humans. We investigated the in vitro effect of 1,25(OH)2D3 and 25(OH)D3 on the differentiation and cytokine production of primary CD4+ T cells from normal donors, and cultured in Th17 polarizing conditions. Both forms of vitamin D reduced the expression of pathogenic Th17 markers and their secretion of pro-inflammatory cytokines (IL-17A, IFN-γ). Furthermore, both vitamin D forms induced an expansion of CD25hi cells and upregulated their expression of CTLA-4 and Foxp3 regulatory markers.

Vitamin D Supplementation Modulates T Cell-Mediated Immunity in Humans: Results from a Randomized Control Trial

CONTEXT

Although studies have linked vitamin D deficiency with immune-mediated diseases, data demonstrating a direct effect on T-cell function are sparse.

OBJECTIVE

Our objective was to determine whether oral vitamin D3 influences T-cell activation in humans with vitamin D deficiency.

DESIGN

This was a single-center ancillary study within Vitamin D Therapy in Individuals at High Risk of Hypertension, a double-blind, multicenter, randomized controlled trial.

SETTING

This study was undertaken in a single academic medical center.

PARTICIPANTS

Adults with vitamin D deficiency and untreated pre- or early stage I hypertension were included.

INTERVENTION

In Vitamin D Therapy in Individuals at High Risk of Hypertension, participants were randomized to either low- (400 IU daily) or high- (4000 IU daily) dose oral vitamin D3 for 6 months. In this ancillary study of 38 patients, we measured CD4+ T-cell activation estimated by intracellular ATP release after stimulation of whole blood with plant lectin phytohemagglutinin collected at baseline (pretreatment) and 2-month follow-up.

MAIN OUTCOME MEASURE

Determining whether ATP level changes were significantly different between treatment groups was the main outcome measure.

RESULTS

Treatment with 4000 IU of vitamin D3 decreased intracellular CD4+ ATP release by 95.5 ng/ml (interquartile range, -219.5 to 105.8). In contrast, 400 IU of vitamin D3 decreased intracellular CD4+ ATP release by 0.5 ng/ml (interquartile range, -69.2 to 148.5). In a proportional odds model, high-dose vitamin D3 was more likely than low-dose vitamin D3 to decrease CD4+ ATP release (odds ratio, 3.43; 95% confidence interval, 1.06-1.11).

CONCLUSIONS

In this ancillary study of a randomized controlled trial, we found that high-dose vitamin D3 significantly reduced CD4+ T-cell activation compared to low-dose vitamin D3, providing human evidence that vitamin D can influence cell-mediated immunity.

Vitamin D3 enhances bactericidal activity of macrophage against Pseudomonas aeruginosa

BACKGROUND

The bioactive form of vitamin D3, i.e.1,25-dihydroxyvitamin D3 (1,25(OH)2D3) vitamin D has been shown to modulate monocytes/macrophages physiology and its response against bacterial infections. Pseudomonas aeruginosa (P. aeruginosa) is an opportunistic bacterial pathogen that can most frequently be fatal in immunocompromised infected people.

METHODS

We investigated the ex vivo effect of 1,25(OH)2D3 on monocyte-derived macrophages function against P. aeruginosa infection.

RESULTS

Relative vitamin D receptor (VDR) mRNA expression was significantly increased in infected and 1,25(OH)2D3-treated macrophages compared to controls (p<0.01). Treatment with 1,25(OH)2D3 markedly resulted in up-regulation of nitric oxide (NO) and IL-1β production and down-regulation of IL-10 levels (respectively, p=0.029, p=0.048 and p=0.008). Additionally, 1,25(OH)2D3 significantly increased M1/M2 macrophage ratio (p<0.05) and slightly reduced intracellular bacterial development. Furthermore, the arginase activity, P. aeruginosa phagocytosis and killing were significantly increased in cells that were both infected and 1,25(OH)2D3-treated compared to the infected, but not 1,25(OH)2D3-treated macrophages (respectively, p<0.001, p<0.01 and p<0.001).

CONCLUSIONS

We show in this study that bioactive from of vitamin D [1,25-dihydroxyvitamin D3 (1,25D3)] can enhance M1 macrophage polarization and their bactericidal protective activity against P. aeruginosa. Future works would involve improving the treatment response through dose-dependent effect studies, both in ex vivo and in vivo models.

The potential regulatory role of vitamin D in the bioenergetics of inflammation

PURPOSE OF REVIEW

The extraskeletal health benefits of vitamin D still need scientific endorsement. Obesity and related chronic diseases are pathogenically linked by inflammation, which carries a considerable energetic cost. Recent techniques for the determination of the bioenergetic demand of inflammation, offer an avenue to cement the regulatory role of vitamin D in this process.

RECENT FINDINGS

Nuclear vitamin D receptors may be translocated into mitochondria of certain cell types, opening up a pathway for direct action on cellular bioenergetics. Classical M1 (inflammatory)/M2(anti-inflammatory) phenotypes can vary with the clinical context. M2 macrophages do not always depend on oxidative metabolism/fatty acid oxidation. Newer methodologies offer real-time bioenergetic measurements that can be used as an index of metabolic health.

SUMMARY

Vitamin D may prove to be a therapeutic agent for inflammation of chronic disease and understanding its role in cellular bioenergetics may offer a diagnostic/prognostic indicator of its action.

Vitamin D every day to keep the infection away?

Within the last decade, vitamin D has emerged as a central regulator of host defense against infections. In this regard, vitamin D triggers effective antimicrobial pathways against bacterial, fungal and viral pathogens in cells of the human innate immune system. However, vitamin D also mediates potent tolerogenic effects: it is generally believed that vitamin D attenuates inflammation and acquired immunity, and thus potentially limits collateral tissue damage. Nevertheless, several studies indicate that vitamin D promotes aspects of acquired host defense. Clinically, vitamin D deficiency has been associated with an increased risk for various infectious diseases in epidemiological studies; yet, robust data from controlled trials investigating the use of vitamin D as a preventive or therapeutic agent are missing. In this review, we summarize the current knowledge regarding the effect of vitamin D on innate and acquired host defense, and speculate on the difficulties to translate the available molecular medicine data into practical therapeutic or preventive recommendations.

Flow cytometry detection of vitamin D receptor changes during vitamin D treatment in Crohn's disease

Crohn's disease (CD) is a chronic inflammatory disease associated with a dysregulated T cell response towards intestinal microflora. Vitamin D has immune modulatory effects on T cells through the nuclear vitamin D receptor (VDR) in vitro. It is unclear how oral vitamin D treatment affects VDR expression. The aim of this study was to establish a flow cytometry protocol, including nuclear and cytoplasmic VDR expression, and to investigate the effects of vitamin D treatment on T cell VDR expression in CD patients. The flow cytometry protocol for VDR staining was developed using the human acute monocytic leukaemia cell line (THP-1). The protocol was evaluated in anti-CD3/CD28-stimulated peripheral blood mononuclear cells (PBMCs) from vitamin D3- (n = 9) and placebo-treated (n = 9) CD patients. Anti-VDR-stained PBMCs were examined by flow cytometry, and their cytokine production was determined by cytokine bead array. VDR, CYP27B1 and RXRα mRNA expression levels in CD4(+) T cells were measured by quantitative reverse transcriptase polymerase chain reaction. The flow cytometry protocol enabled detection of cytoplasmic and nuclear VDR expression. The results were confirmed by confocal microscopy and supported by correlation with VDR mRNA expression. VDR expression in CD4(+) T cells increased following stimulation. This VDR up-regulation was inhibited with 30% by vitamin D treatment compared to placebo in CD patients (P = 0027). VDR expression was correlated with in-vitro interferon-γ production in stimulated PBMCs (P = 0.01). Flow cytometry is a useful method with which to measure intracellular VDR expression. Vitamin D treatment in CD patients reduces T cell receptor-mediated VDR up-regulation.

Vitamin D and 1,25(OH)2D regulation of T cells

Vitamin D is a direct and indirect regulator of T cells. The mechanisms by which vitamin D directly regulates T cells are reviewed and new primary data on the effects of 1,25 dihydroxyvitamin D (1,25(OH)2D) on human invariant natural killer (iNK)T cells is presented. The in vivo effects of vitamin D on murine T cells include inhibition of T cell proliferation, inhibition of IFN-γ, IL-17 and induction of IL-4. Experiments in mice demonstrate that the effectiveness of 1,25(OH)2D requires NKT cells, IL-10, the IL-10R and IL-4. Comparisons of mouse and human T cells show that 1,25(OH)2D inhibits IL-17 and IFN-γ, and induces T regulatory cells and IL-4. IL-4 was induced by 1,25(OH)2D in mouse and human iNKT cells. Activation for 72 h was required for optimal expression of the vitamin D receptor (VDR) in human and mouse T and iNKT cells. In addition, T cells are potential autocrine sources of 1,25(OH)2D but again only 48-72 h after activation. Together the data support the late effects of vitamin D on diseases like inflammatory bowel disease and multiple sclerosis where reducing IL-17 and IFN-γ, while inducing IL-4 and IL-10, would be beneficial.

Vitamin D-binding protein controls T cell responses to vitamin D

Background

In vitro studies have shown that the active form of vitamin D₃, 1α,25-dihydroxyvitamin D3 (1,25(OH)₂D₃), can regulate differentiation of CD4⁺ T cells by inhibiting Th1 and Th17 cell differentiation and promoting Th2 and Treg cell differentiation. However, the serum concentration of 1,25(OH)₂D₃ is far below the effective concentration of 1,25(OH)₂D₃ found in in vitro studies, and it has been suggested that 1,25(OH)₂D₃ must be produced locally from the inactive precursor 25-hydroxyvitamin D3 (25(OH)D₃) to affect ongoing immune responses in vivo. Although it has been reported that activated T cells express the 25(OH)D-1α-hydroxylase CYP27B1 that converts 25(OH)D₃ to 1,25(OH)₂D₃, it is still controversial whether activated T cells have the capacity to produce sufficient amounts of 1,25(OH)₂D₃ to affect vitamin D-responsive genes. Furthermore, it is not known how the vitamin D-binding protein (DBP) found in high concentrations in serum affects T cell responses to 25(OH)D₃.

Results

We found that activated T cells express CYP27B1 and have the capacity to produce sufficient 1,25(OH)₂D₃ to affect vitamin D-responsive genes when cultured with physiological concentrations of 25(OH)D₃ in serum-free medium. However, if the medium was supplemented with serum or purified DBP, DBP strictly inhibited the production of 1,25(OH)₂D₃ and 25(OH)D₃-induced T cell responses. In contrast, DBP did not inhibit the effect of exogenous 1,25(OH)₂D₃. Actin, arachidonic acid and albumin did not affect the sequestration of 25(OH)D₃ by DBP, whereas carbonylation of DBP did.

Conclusions

Activated T cells express CYP27B1 and can convert 25(OH)D₃ to 1,25(OH)₂D₃ in sufficiently high concentrations to affect vitamin D-responsive genes when cultured in serum-free medium. However, DBP sequesters 25(OH)D₃ and inhibits the production of 1,25(OH)₂D₃ in T cells. To fully exploit the immune-regulatory potential of vitamin D, future studies of the mechanisms that enable the immune system to exploit 25(OH)D₃ and convert it to 1,25(OH)₂D₃in vivo are required.

Electronic supplementary material

The online version of this article (doi:10.1186/s12865-014-0035-2) contains supplementary material, which is available to authorized users.