Vitamin D, multiple sclerosis and inflammatory bowel disease

It has now been more than 20years since the vitamin D receptor was identified in cells of the immune system. The immune system has now been established as an important target of vitamin D. Vitamin D receptor knockout and vitamin D deficient mice have a surplus of effector T cells that have been implicated in the pathology of multiple sclerosis (MS) and inflammatory bowel disease (IBD). The active form of vitamin D directly and indirectly suppresses the function of these pathogenic T cells while inducing several regulatory T cells that suppress MS and IBD development. There is reason to believe that vitamin D could be an environmental factor that may play a role in the development of these immune mediated diseases in the clinic but at present there has not been a causal relationship established. Nonetheless, current evidence suggests that improving vitamin D status and/or using vitamin D receptor agonists may be useful in MS and IBD.     

Vitamin D regulation of immune function in the gut: why do T cells have vitamin D receptors?

Low vitamin D status is associated with an increased risk of immune-mediated diseases like inflammatory bowel disease (IBD) in humans. Experimentally vitamin D status is a factor that shapes the immune response. Animals that are either vitamin D deficient or vitamin D receptor (VDR) deficient are prone to develop IBD. Conventional T cells develop normally in VDR knockout (KO) mice but over-produce IFN-γ and IL-17. Naturally occurring FoxP3+ regulatory T cells are present in normal numbers in VDR KO mice and function as well as wildtype T regs. Vitamin D and the VDR are required for the development and function of two regulatory populations of T cells that require non-classical MHC class 1 for development. The two vitamin D dependent cell types are the iNKT cells and CD4/CD8αα intraepithelial lymphocytes (IEL). Protective immune responses that depend on iNKT cells or CD8αα IEL are therefore impaired in the vitamin D or VDR deficient host and the mice are more susceptible to immune-mediated diseases in the gut.     

A crucial role for the vitamin D receptor in experimental inflammatory bowel diseases

The active form of vitamin D (1,25D3) suppressed the development of animal models of human autoimmune diseases including experimental inflammatory bowel disease (IBD). The vitamin D receptor (VDR) is required for all known biologic effects of vitamin D. Here we show that VDR deficiency (knockout, KO) resulted in severe inflammation of the gastrointestinal tract in two different experimental models of IBD. In the CD45RB transfer model of IBD, CD4+/CD45RBhigh T cells from VDR KO mice induced more severe colitis than wild-type CD4+/CD45RBhigh T cells. The second model of IBD used was the spontaneous colitis that develops in IL-10 KO mice. VDR/IL-10 double KO mice developed accelerated IBD and 100% mortality by 8 wk of age. At 8 wk of age, all of the VDR and IL-10 single KO mice were healthy. Rectal bleeding was observed in every VDR/IL-10 KO mouse. Splenocytes from the VDR/IL-10 double KO mice cells transferred IBD symptoms. The severe IBD in VDR/IL-10 double KO mice is a result of the immune system and not a result of altered calcium homeostasis, or gastrointestinal tract function. The data establishes an essential role for VDR signaling in the regulation of inflammation in the gastrointestinal tract.     

Vitamin D Status Is Positively Correlated with Regulatory T Cell Function in Patients with Multiple Sclerosis

Background

In several autoimmune diseases, including multiple sclerosis (MS), a compromised regulatory T cell (Treg) function is believed to be critically involved in the disease process. In vitro, the biologically active metabolite of vitamin D has been shown to promote Treg development. A poor vitamin D status has been linked with MS incidence and MS disease activity. In the present study, we assess a potential in vivo correlation between vitamin D status and Treg function in relapsing remitting MS (RRMS) patients.

Methodology/Principal Findings

Serum levels of 25-hydroxyvitamin D (25(OH)D) were measured in 29 RRMS patients. The number of circulating Tregs was assessed by flow-cytometry, and their functionality was tested in vitro in a CFSE-based proliferation suppression assay. Additionally, the intracellular cytokine profile of T helper cells was determined directly ex-vivo by flow-cytometry. Serum levels of 25(OH)D correlated positively with the ability of Tregs to suppress T cell proliferation (R = 0.590, P = 0.002). No correlation between 25(OH)D levels and the number of Tregs was found. The IFN-γ/IL-4 ratio (Th1/Th2-balance) was more directed towards IL-4 in patients with favourable 25(OH)D levels (R = −0.435, P = 0.023).

Conclusions/Significance

These results show an association of high 25(OH)D levels with an improved Treg function, and with skewing of the Th1/Th2 balance towards Th2. These findings suggest that vitamin D is an important promoter of T cell regulation in vivo in MS patients. It is tempting to speculate that our results may not only hold for MS, but also for other autoimmune diseases. Future intervention studies will show whether modulation of vitamin D status results in modulation of the T cell response and subsequent amelioration of disease activity.     

The ifng gene is essential for vdr gene expression and vitamin d3-mediated reduction of the pathogenic T cell burden in the central nervous system in experimental autoimmune encephalomyelitis, a multiple sclerosis model

Compelling evidence suggests that vitamin D(3) insufficiency may contribute causally to multiple sclerosis (MS) risk. Experimental autoimmune encephalomyelitis (EAE) research firmly supports this hypothesis. Vitamin D(3) supports 1,25-dihydroxyvitamin D(3) (1,25-[OH](2)D(3)) synthesis in the CNS, initiating biological processes that reduce pathogenic CD4(+) T cell longevity. MS is prevalent in Sardinia despite high ambient UV irradiation, challenging the vitamin D-MS hypothesis. Sardinian MS patients frequently carry a low Ifng expresser allele, suggesting that inadequate IFN-γ may undermine vitamin D(3)-mediated inhibition of demyelinating disease. Testing this hypothesis, we found vitamin D(3) failed to inhibit EAE in female Ifng knockout (GKO) mice, unlike wild-type mice. The two strains did not differ in Cyp27b1 and Cyp24a1 gene expression, implying equivalent vitamin D(3) metabolism in the CNS. The 1,25-(OH)(2)D(3) inhibited EAE in both strains, but 2-fold more 1,25-(OH)(2)D(3) was needed in GKO mice, causing hypercalcemic toxicity. Unexpectedly, GKO mice had very low Vdr gene expression in the CNS. Injecting IFN-γ intracranially into adult mice did not increase Vdr gene expression. Correlating with low Vdr expression, GKO mice had more numerous pathogenic Th1 and Th17 cells in the CNS, and 1,25-(OH)(2)D(3) reduced these cells in GKO and wild-type mice without altering Foxp3(+) regulatory T cells. Thus, the Ifng gene was needed for CNS Vdr gene expression and vitamin D(3)-dependent mechanisms that inhibit EAE. Individuals with inadequate Ifng expression may have increased MS risk despite high ambient UV irradiation because of low Vdr gene expression and a high encephalitogenic T cell burden in the CNS.     

间充质干细胞对Th17/Treg平衡的影响及与IBD的关系

辅助性T细胞17（Th17）/调节性T细胞（Treg）失衡是炎症性肠病（IBD）发病的重要因素,纠正Th17/Treg细胞失衡可以减缓或抑制IBD的发生发展,成为治疗IBD的靶点。间充质干细胞具有抗炎及免疫调节功能,通过可溶性因子、细胞接触及外泌体的方式调节适应性和先天性免疫,纠正Th17/Treg失衡缓解IBD,这给IBD的治疗提供新的方向。目前,MSCs和IBD的关系研究较少,本文综述了MSCs调节Th17/Treg平衡及与IBD的关系。     

Epigenetic reduction in invariant NKT cells following in utero vitamin D deficiency in mice

Vitamin D status changes with season, but the effect of these changes on immune function is not clear. In this study, we show that in utero vitamin D deficiency in mice results in a significant reduction in invariant NKT (iNKT) cell numbers that could not be corrected by later intervention with vitamin D or 1,25-dihydroxy vitamin D(3) (active form of the vitamin). Furthermore, this was intrinsic to hematopoietic cells, as vitamin D-deficient bone marrow is specifically defective in generating iNKT cells in wild-type recipients. This vitamin D deficiency-induced reduction in iNKT cells is due to increased apoptosis of early iNKT cell precursors in the thymus. Whereas both the vitamin D receptor and vitamin D regulate iNKT cells, the vitamin D receptor is required for both iNKT cell function and number, and vitamin D (the ligand) only controls the number of iNKT cells. Given the importance of proper iNKT cell function in health and disease, this prenatal requirement for vitamin D suggests that in humans, the amount of vitamin D available in the environment during prenatal development may dictate the number of iNKT cells and potential risk of autoimmunity.     

The Association of Vitamin D Receptor Polymorphisms with Multiple Sclerosis in a Case-Control Study from Kuwait

Vitamin D deficiency is associated with several diseases including multiple sclerosis (MS). Several factors influence vitamin D levels and its optimal multi-function maintenance. Our objective was to assess quantifiable variables influencing vitamin D level and metabolism in MS patients from Kuwait. In a case-control study involving 50 MS patients, and 50 healthy control individuals for which plasma vitamin D levels, supplement use, vitamin D receptor (VDR) variants, and skin pigmentation indices were ascertained; we found overall vitamin D levels to be deficient in both groups, and supplement use to be common practice. VDR variants TaqI and BsmI associated with MS risk, and ApaI associated with low disease progression. VDR variant FokI associated with higher vitamin D levels in both groups. We conclude that several quantifiable variables related to vitamin D associate with MS suggesting a possible clinical immuno-modulatory application of vitamin D for MS patients in Kuwait.     

Vitamin D and autoimmune diabetes

The biologically active form of vitamin D, 1,25(OH)(2)D(3), is a potent modulator of the immune system as well as a regulator of bone and mineral metabolism. Vitamin D-deficiency in infancy and vitamin D receptor gene polymorphisms may be risk factors for insulin-dependent Diabetes mellitus (IDDM). 1,25(OH)(2)D(3) and its analogs significantly repress the development of insulitis and diabetes in the non-obese diabetic (NOD) mouse, a model of human IDDM. 1,25(OH)(2)D(3) may modulate IDDM disease pathogenesis by repression of type I cytokines, inhibition of dendritic cell maturation, and upregulation of regulatory T cells. The function of vitamin D as a genetic and environmental determining factor for IDDM, the protective role of 1,25(OH)(2)D(3) and its analogs in a mouse model of IDDM, and the possible mechanisms by which this protection occurs will be reviewed.     

Novel role of the vitamin D receptor in maintaining the integrity of the intestinal mucosal barrier

Emerging evidence supports a pathological link between vitamin D deficiency and the risk of inflammatory bowel disease (IBD). To explore the mechanism we used the dextran sulfate sodium (DSS)-induced colitis model to investigate the role of the vitamin D receptor (VDR) in mucosal barrier homeostasis. While VDR(+/+) mice were mostly resistant to 2.5% DSS, VDR(-/-) mice developed severe diarrhea, rectal bleeding, and marked body weight loss, leading to death in 2 wk. Histological examination revealed extensive ulceration and impaired wound healing in the colonic epithelium of DSS-treated VDR(-/-) mice. Severe ulceration in VDR(-/-) mice was preceded by a greater loss of intestinal transepithelial electric resistance (TER) compared with VDR(+/+) mice. Confocal and electron microscopy (EM) revealed severe disruption in epithelial junctions in VDR(-/-) mice after 3-day DSS treatment. Therefore, VDR(-/-) mice were much more susceptible to DSS-induced mucosal injury than VDR(+/+) mice. In cell cultures, 1,25-dihydroxy-vitamin D(3) [1,25(OH)(2)D(3)] markedly enhanced tight junctions formed by Caco-2 monolayers by increasing junction protein expression and TER and preserved the structural integrity of tight junctions in the presence of DSS. VDR knockdown with small interfering (si)RNA reduced the junction proteins and TER in Caco-2 monolayers. 1,25(OH)(2)D(3) can also stimulate epithelial cell migration in vitro. These observations suggest that VDR plays a critical role in mucosal barrier homeostasis by preserving the integrity of junction complexes and the healing capacity of the colonic epithelium. Therefore, vitamin D deficiency may compromise the mucosal barrier, leading to increased susceptibility to mucosal damage and increased risk of IBD.     

Role of Vitamin D in the Onset,Progression, and Severity of Multiple Sclerosis

ObjectiveTo review and assess the role of vitamin D in the onset, progression, and relapse of multiple sclerosis (MS), based on evidence acquired from the analysis of preclinical, observational, and interventional studies.MethodsAll English language literature in MEDLINE (January 1969 through April 2012) was searched for observational and interventional studies on the dosage effect of vitamin D on the onset, progression, and relapse rate of MS. The medical subject heading (MeSH) terms used in the search included Vitamin D and Multiple Sclerosis. Additional publications and abstracts were identified from review articles and from the references cited in the previously found articles. In addition to the experimental studies, only those human studies that specified the population size, doses of vitamin D used, and the resulting effect on MS were considered.ResultsVitamin D deficiency is very common among MS patients. Multiple preclinical studies have shown that vitamin D is a potent regulator of inflammation in MS. Most observational studies support an association between high vitamin D levels and a reduced risk of developing MS. However, conflicting results have been reported by observational studies on the correlation between vitamin D and MS severity and by interventional studies using vitamin D as a therapeutic agent for MS.ConclusionVitamin D deficiency in MS patients should be avoided. In addition, the risk of developing MS might be reduced by maintaining optimal vitamin D levels in the healthy population. Larger randomized interventional trials are needed to clarify the therapeutic effect of vitamin D in MS. (Endocr Pract. 2013;19:129-136)     

Transcriptional profiling of gamma delta T cells identifies a role for vitamin D in the immunoregulation of the V gamma 9V delta 2 response to phosphate-containing ligands

Vitamin D is a steroid hormone that, in addition to its well-characterized role in calcium/phosphate metabolism, has been found to have regulatory properties for immune system function. The nuclear vitamin D receptor is widely expressed in tissues, but has also been shown to be regulated by hormones, growth factors, and cytokines. In this study we show that activation of human Vdelta2Vgamma9 T cells by nonpeptidic monoalkyl phosphates such as isopentenyl pyrophosphate leads to the up-regulation of the vitamin D receptor via a pathway that involves the classical isoforms of protein kinase C. We further show that this receptor is active by demonstrating that the ligand 1alpha,25-dihydroxyvitamin D3 (vitD3) significantly inhibits in a dose-dependent fashion phospholigand-induced gammadelta T cell expansion, IFN-gamma production, and CD25 expression. We also show that vitD3 negatively regulates signaling via Akt and ERK and, at high concentrations, potentiates Ag-induced cell death. As such, these data provide further support for the immunoregulatory properties of vitamin D, and suggest that the ability of vitD3 to negatively regulate the proinflammatory activity of gammadelta T cells may contribute to the protection this vitamin affords against inflammatory and autoimmune disorders dependent upon Th1-type responses.     

IL-10 signaling is essential for 1,25-dihydroxyvitamin D3-mediated inhibition of experimental autoimmune encephalomyelitis

Multiple sclerosis (MS) results from an aberrant, neuroantigen-specific, T cell-mediated autoimmune response. Because MS prevalence and severity decrease sharply with increasing sunlight exposure, and sunlight supports vitamin D(3) synthesis, we proposed that vitamin D(3) and 1,25-dihydroxyvitamin D(3) (1,25-(OH)(2)D(3)) may protect against MS. In support of this hypothesis, 1,25-(OH)(2)D(3) strongly inhibited experimental autoimmune encephalomyelitis (EAE). This inhibition required lymphocytes other than the encephalitogenic T cells. In this study, we tested the hypothesis that 1,25-(OH)(2)D(3) might inhibit EAE through the action of IL-10-producing regulatory lymphocytes. We report that vitamin D(3) and 1,25-(OH)(2)D(3) strongly inhibited myelin oligodendrocyte peptide (MOG(35-55))-induced EAE in C57BL/6 mice, but completely failed to inhibit EAE in mice with a disrupted IL-10 or IL-10R gene. Thus, a functional IL-10-IL-10R pathway was essential for 1,25-(OH)(2)D(3) to inhibit EAE. The 1,25-(OH)(2)D(3) also failed to inhibit EAE in reciprocal, mixed bone marrow chimeras constructed by transferring IL-10-deficient bone marrow into irradiated wild-type mice and vice versa. Thus, 1,25-(OH)(2)D(3) may be enhancing an anti-inflammatory loop involving hemopoietic cell-produced IL-10 acting on brain parenchymal cells and vice versa. If this interpretation is correct, and humans have a similar bidirectional IL-10-dependent loop, then an IL-10-IL-10R pathway defect could abrogate the anti-inflammatory and neuro-protective functions of sunlight and vitamin D(3). In this way, a genetic IL-10-IL-10R pathway defect could interact with an environmental risk factor, vitamin D(3) insufficiency, to increase MS risk and severity.     

Retinoic acid via RARalpha inhibits the expression of 24-hydroxylase in human prostate stromal cells

25-Hydroxyvitamin D(3)-24-hydroxylase (24-hydroxylase) is an important inactivating enzyme and its expression is induced by 25-hydroxyvitamin D3 (25OHD3) and 1alpha,25-dihydroxyvitamin D3 (1alpha,25-(OH)2D3) through action of heterodimers of vitamin D receptor (VDR) and retinoid X receptor (RXR). RXRs also act as heterodimer partners for retinoic acid receptors (RARs), mediating the action of all-trans-retinoic acid (ATRA). Prostate stroma plays a crucial role in prostate cancer development and benign prostatic hyperplasia. We demonstrate here that ATRA markedly reduced the expression of 24-hydroxylase mRNA induced by 25OHD3 and 1alpha,25-(OH)2D3 in human prostatic stromal cells P29SN and P32S but not in epithelial cells PrEC or cancer cells LNCaP. By using transfection and RAR-selective ligands, we found that the inhibitory effect of ATRA on 24-hydroxylase expression in stromal cells was mediated by RARalpha but not by RARbeta. Moreover, the ATRA-induced expression of RARbeta was also mediated by RARalpha. The combined treatment of 1alpha,25-(OH)2D3 and RARalpha agonist Am80 at 10 nM exhibited strong growth-inhibitory effect whereas either alone had no effect. Our data suggest that ATRA suppresses 24-hydroxylase expression through RARalpha-dependent signaling pathway and can enhance vitamin D action in suppression of cell growth.