Splice variants of the CYP27b1 gene and the regulation of 1,25-dihydroxyvitamin D3 production

What is known about the effects of vitamin D in neuropsychiatric lupus?

Systemic lupus erythematosus (SLE) is an autoimmune disease that can affect several organs and systems. The central and/or peripheral nervous system can suffer from complications known as neuropsychiatric lupus (NPSLE). Studies have associated the manifestations of SLE or NPSLE with vitamin D deficiency. It has been shown that hypovitaminosis D can lead to cognition deficits and cerebral hypoperfusion in patients with NPSLE. In this review article, we will address the main features related to vitamin D supplementation or serum vitamin D levels with neuropsychiatric manifestations, either in patients or in animal models of NPSLE.

Expression of renal vitamin D receptors and metabolizing enzymes in IgA nephropathy

AIM

One of the main causes of end-stage renal disease (ESRD) in the world is IgA nephropathy (IgAN). Since kidney is a key player in vitamin D metabolism, we investigated the expression of renal vitamin D receptors (VDR) and metabolizing enzymes in IgA nephropathy patients (IgAN-P).

METHODS

The sample included twelve IgAN-P who underwent ultrasound-guided renal biopsies and five controls who underwent nephrectomy due to clear renal carcinoma. Immunofluorescent staining was used to determine the expression of VDR, 25-hydroxyvitamin D3 -alpha-hydroxylase (1alpha-OHase) and vitamin D3 24-hydroxylase (CYP24A1).

RESULTS

Significant increase in expression of VDR, which was prominent in distal tubular cells (DTCs) in tissues from IgAN-P, was found in comparison to the controls (p = 0.0368). The expression of 1alpha-OHase, calcitriol synthesizing enzyme, was significantly lower in IgAN-P, in comparison with controls (p < 0.0001). The opposite, expression of CYP24A1 (vitamin D degrading enzyme), was significantly higher in IgAN-P in comparison with controls (p = 0.0003). Additionally, we found significant negative correlation between percentage of CYP24A1 immunoreactive nuclei in proximal tubular cells (PTCs) and estimated glomerular filtration rate (eGFR) in IgAN-P (r = -0.6139; p = 0.0337).

CONCLUSIONS

Our research indicates substantially decreased renal calcitriol production and increased vitamin D degradation in kidneys of IgAN-P, but larger studies are needed to confirm our results.

The vitamin D activator CYP27B1 is upregulated in muscle fibers in denervating disease and can track progression in amyotrophic lateral sclerosis

Extra-renal expression of Cytochrome P450 Family 27 Subfamily B Member 1 (CYP27B1) has been well recognized and reflects the importance of intracrine/paracrine vitamin D signaling in different tissues under physiological and pathological conditions. In a prior RNA sequencing project, we identified CYP27B1 mRNA as upregulated in muscle samples from patients with amyotrophic lateral sclerosis (ALS) compared to normal controls. Our aims here were: (1) to validate this finding in a larger sample set including disease controls, (2) to determine which cell type is expressing CYP27B1 protein in muscle tissue, (3) to correlate CYP27B1 mRNA expression with disease progression in the SOD1G93A ALS mouse and in ALS patients. We assessed CYP27B1 expression by qPCR, western blot, and immunohistochemistry in a repository of muscle samples from ALS, disease controls (myopathy and non-ALS neuropathic disease), normal subjects, and muscle samples from the SOD1G93A mouse. Eight ALS patients were studied prospectively over 6-12 months with serial muscle biopsies. We found that CYP27B1 mRNA and protein levels were significantly increased in ALS versus normal and myopathy muscle samples. Neuropathy samples had increased CYP27B1 mRNA and protein expression but at a lower level than the ALS group. Immunohistochemistry showed that CYP27B1 localized to myofibers, especially those with features of denervation. In the SOD1G93A mouse, CYP27B1 mRNA and protein were detected in skeletal muscle in early pre-symptomatic stages and increased through end-stage. In the human study, increases in CYP27B1 mRNA in muscle biopsies correlated with disease progression rates over the same time period. In summary, we show for the first time that CYP27B1 mRNA and protein expression are elevated in muscle fibers in denervating disease, especially ALS, where mRNA levels can potentially serve as a surrogate marker for tracking disease progression. Its upregulation may reflect a local perturbation of vitamin D signaling, and further characterization of this pathway may provide insight into underlying molecular processes linked to muscle denervation.

Pleiotropic effects of vitamin D3 on CD4+ T lymphocytes mediated by human periodontal ligament cells and inflammatory environment

Aims

Both, vitamin D₃ and human periodontal ligament cells (hPDLCs) possess immunosuppressive properties, but their combined effect on immune cells has never been investigated. Here, we analysed the impact of vitamin D₃ on the immunosuppressive properties of hPDLCs towards CD4⁺ T lymphocytes.

Material and Methods

Allogenic CD4⁺ T lymphocytes were activated by phytohemagglutinin either in monoculture or co‐culture with hPDLCs, in the presence or absence of IFN‐γ and 1,25(OH)₂D₃. After 5 days, CD4⁺ T‐lymphocyte proliferation, CD4⁺ CD25⁺ FoxP3⁺ regulatory T lymphocytes (T_regs) proportion and IL‐10, TGF‐β1 and IL‐17A production were analysed.

Results

In monoculture, 1,25(OH)₂D₃ suppressed CD4⁺ T‐lymphocyte proliferation, increased the percentage of CD4⁺ FoxP3⁺ CD25⁺ FoxP3⁺ T_regs and enhanced IL‐10 and TGF‐β1 production. In the presence of IFN‐γ treated hPDLCs, 1,25(OH)₂D₃ significantly increased CD4⁺ T‐lymphocyte proliferation and decreased the percentage of CD4⁺ CD25⁺ FoxP3⁺ T_regs. IL‐10 and IL‐17A expression was significantly diminished by 1,25(OH)₂D₃, whereas TGF‐β1 was slightly increased. The effects of 1,25(OH)₂D₃ in co‐culture were reversed by inhibition of indoleamine‐2,3‐dioxygenase‐1, prostaglandin‐endoperoxide synthase and programmed cell death 1 ligand 1. 1,25(OH)₂D₃ also suppressed the expression of these proteins in hPDLCs.

Conclusion

Effects of vitamin D₃ on CD4⁺ T lymphocyte are modified by hPDLCs depending on the microenvironment.

1,25(OH)2D3 Differently Affects Immunomodulatory Activities of Mesenchymal Stem Cells Depending on the Presence of TNF-α, IL-1β and IFN-γ

Periodontal ligament-derived mesenchymal stem cells (hPDLSCs) possess immunomodulatory abilities which are strongly enhanced by various inflammatory cytokines. Vitamin D₃ has anti-inflammatory effects on hPDLSCs and immune cells. However, no study to date has directly compared the influence of 1,25(OH)₂D₃ on the immunomodulatory activities of hPDLSCs in the presence of different cytokines. In the present study, the effects of hPDLSCs treated with tumor necrosis factor (TNF)-α, interleukin (IL)-1β, or interferon (IFN)-γ in the presence of 1,25(OH)₂D₃ on the proliferation of allogenic CD4⁺ T lymphocyte or on the functional status of primary CD68⁺ macrophages were analyzed in coculture models. Additionally, the effects of 1,25(OH)₂D₃ on TNF-α-, IL-1β-, and IFN-γ-induced gene expression of some immunomodulatory factors in hPDLSCs were compared. Under coculture conditions, 1,25(OH)₂D₃ increased or decreased CD4⁺ T lymphocyte proliferation via hPDLSCs, depending on the cytokine. hPDLSCs primed with 1,25(OH)₂D₃ and different cytokines affected pro- and anti-inflammatory cytokine expression in macrophages variably, depending on the priming cytokine. With one exception, 1,25(OH)₂D₃ significantly reduced TNF-α-, IL-1β-, and IFN-γ-induced expression of all the investigated immunomediators in hPDLSCs, albeit to different extents. These results suggest that 1,25(OH)₂D₃ influences the immunomodulatory activities of hPDLSCs depending qualitatively and quantitatively on the presence of certain inflammatory cytokines.

Human cytochrome P450 enzymes 5-51 as targets of drugs and natural and environmental compounds: mechanisms, induction, and inhibition - toxic effects and benefits

Cytochrome P450 (P450, CYP) enzymes have long been of interest due to their roles in the metabolism of drugs, pesticides, pro-carcinogens, and other xenobiotic chemicals. They have also been of interest due to their very critical roles in the biosynthesis and metabolism of steroids, vitamins, and certain eicosanoids. This review covers the 22 (of the total of 57) human P450s in Families 5-51 and their substrate selectivity. Furthermore, included is information and references regarding inducibility, inhibition, and (in some cases) stimulation by chemicals. We update and discuss important aspects of each of these 22 P450s and questions that remain open.

Primary Vitamin D Target Genes of Human Monocytes

The molecular basis of vitamin D signaling implies that the metabolite 1α,25-dihydroxyvitamin D₃ (1,25(OH)₂D₃) of the secosteroid vitamin D₃ activates the transcription factor vitamin D receptor (VDR), which in turn modulates the expression of hundreds of primary vitamin D target genes. Since the evolutionary role of nuclear receptors, such as VDR, was the regulation of cellular metabolism, the control of calcium metabolism became the primary function of vitamin D and its receptor. Moreover, the nearly ubiquitous expression of VDR enabled vitamin D to acquire additional physiological functions, such as the support of the innate immune system in its defense against microbes. Monocytes and their differentiated phenotypes, macrophages and dendritic cells, are key cell types of the innate immune system. Vitamin D signaling was most comprehensively investigated in THP-1 cells, which are an established model of human monocytes. This includes the 1,25(OH)₂D₃-modulated cistromes of VDR, the pioneer transcription factors PU.1 and CEBPA and the chromatin modifier CTCF as well as of the histone markers of promoter and enhancer regions, H3K4me3 and H3K27ac, respectively. These epigenome-wide datasets led to the development of our chromatin model of vitamin D signaling. This review discusses the mechanistic basis of 189 primary vitamin D target genes identified by transcriptome-wide analysis of 1,25(OH)₂D₃-stimulated THP-1 cells and relates the epigenomic basis of four different regulatory scenarios to the physiological functions of the respective genes.

Parameters of the Immune System and Vitamin D Levels in Old Individuals

Aim

The increased number of individuals older than 80 years, centenarians, and supercentenarians is not a synonym for healthy aging, since severe infections, hospitalization, and disability are frequently observed. In this context, a possible strategy is to preserve the main characteristics/functions of the immune system with the aim to cause less damage to the organism during the aging process. Vitamin D acts on bone marrow, brain, breast, malignant cells, and immune system and has been recommended as a supplement. We aimed to evaluate whether immune parameters and vitamin D serum levels are correlated.

Methods

We evaluated some features of the immune system using the peripheral blood of individuals older than 80 years (n = 12) compared to young subjects (n = 10). In addition, we correlated these findings with vitamin D serum levels.

Results

Old individuals presented metabolic parameters of healthy aging and maintained preserved some features of immunity such as CD4/CD8 ratio, and low production of pro-inflammatory cytokines after stimulus. On the other hand, we observed increase in the frequency of myeloid-derived suppressor cells, reduction in circulating leukocytes, in the percentage of total CD8+, and in CD8+ Naïve T cells, in addition to increase in the percentage of CD8+ effector memory re-expressing CD45RA (EMRA) T cells. We found seropositivity for CMV in 97.7%, which was correlated with the decrease of CD8+ Naïve T cells and increase in CD8+ EMRA T cells. Vitamin D levels were insufficient in 50% of old individuals and correlated positively with total CD8+ T cells and negatively with CD8+ EMRA T cells.

Conclusion

In the studied population, longevity was correlated to maintenance of some immune parameters. Considering the limitations of the study as size of the sample and lack of functional assays, it was found that vitamin D in old individuals was correlated to some features of the immune system, mainly in the CD8 compartment.

Physiologic and pathophysiologic roles of extra renal CYP27b1: Case report and review

Although the kidney was initially thought to be the sole organ responsible for the production of 1,25(OH)₂D via the enzyme CYP27b1, it is now appreciated that the expression of CYP27b1 in tissues other than the kidney is wide spread. However, the kidney is the major source for circulating 1,25(OH)₂D. Only in certain granulomatous diseases such as sarcoidosis does the extra renal tissue produce sufficient 1,25(OH)₂D to contribute to the circulating levels, generally associated with hypercalcemia, as illustrated by the case report preceding the review. Therefore the expression of CYP27b1 outside the kidney under normal circumstances begs the question why, and in particular whether the extra renal production of 1,25(OH)₂D has physiologic importance. In this chapter this question will be discussed. First we discuss the sites for extra renal 1,25(OH)₂D production. This is followed by a discussion of the regulation of CYP27b1 expression and activity in extra renal tissues, pointing out that such regulation is tissue specific and different from that of CYP27b1 in the kidney. Finally the physiologic significance of extra renal 1,25(OH)₂D₃ production is examined, with special focus on the role of CYP27b1 in regulation of cellular proliferation and differentiation, hormone secretion, and immune function. At this point the data do not clearly demonstrate an essential role for CYP27b1 expression in any tissue outside the kidney, but several examples pointing in this direction are provided. With the availability of the mouse enabling tissue specific deletion of CYP27b1, the role of extra renal CYP27b1 expression in normal and pathologic states can now be addressed definitively.

Vitamin D metabolic loci and vitamin D status in Black and White pregnant women

BACKGROUND

Several candidate genes and genome wide association studies have reported significant associations between vitamin D metabolism genes and 25-hydroxyvitamin D. Few studies have examined these relationships in pregnancy.

OBJECTIVE

We evaluated the relationship between maternal allelic variants in three vitamin D metabolism genes and 25-hydroxyvitamin D (25(OH)D) concentration in pregnancy.

STUDY DESIGN

In two case-control studies, samples were drawn from women who delivered at Magee Womens Hospital in Pittsburgh, PA from 1999 to 2010 and twelve recruiting sites across the United States from 1959 to 65. For 882 Black and 1796 White pregnant women from these studies, 25(OH)D concentration was measured and single nucleotide polymorphisms (SNPs) were genotyped 50 kilobases up- and down-stream in three genes (VDR, GC, and CYP27B1). Using multivariable linear regression, we estimated the associations between allelic variation of each locus and log-transformed 25(OH)D concentration separately by race and study group. Meta-analysis was used to estimate the association across the four groups for each SNP.

RESULTS

Minor alleles of several variants in VDR, GC, and CYP27B1 were associated with differences in log-transformed 25(OH)D concentration compared to the corresponding major alleles [beta, 95% confidence intervals (CI)]. The meta-analysis confirmed the associations for differences in log-transformed 25(OH)D by allelic loci for one intron VDR variant [rs2853559 0.08 (0.02, 0.13), p<0.01] and a variant in the GC flanking region [rs13150174: 0.04 (0.02, 0.07), p<0.01], and a GC missense mutation [rs7041 0.05 (0.01, 0.09), p<0.01]. The meta-analysis also revealed possible associations for SNPs in linkage disequilibrium with variants in the VDR 3-prime untranslated region, another GC missense variant (rs4588), and a variant of the 3-prime untranslated region of CYP27B1.

CONCLUSION

We observed associations between VDR, GC, and CYP27B1 variants and maternal 25-hydroxyvitamin D concentration. Our results provide additional support for a possible role of genetic variation in vitamin D metabolism genes on vitamin D status during pregnancy.

Vascular Calcification Induced by Chronic Kidney Disease Is Mediated by an Increase of 1α-Hydroxylase Expression in Vascular Smooth Muscle Cells

Vascular calcification (VC) is a complication of chronic kidney disease that predicts morbidity and mortality. Uremic serum promotes VC, but the mechanism involved is unknown. A role for 1,25(OH)₂ D₃ in VC has been proposed, but the mechanism is unclear because both low and high levels have been shown to increase it. In this work we investigate the role of 1,25(OH)₂ D₃ produced in vascular smooth muscle cells (VSMCs) in VC. Rats with subtotal nephrectomy and kidney recipient patients showed increased arterial expression of 1α-hydroxylase in vivo. VSMCs exposed in vitro to serum obtained from uremic rats also showed increased 1α-hydroxylase expression. Those increases were parallel to an increase in VC. After 6 days with high phosphate media, VSMCs overexpressing 1α-hydroxylase show significantly higher calcium content and RUNX2 expression than control cells. 1α-hydroxylase null mice (KO) with subtotal nephrectomy and treated with calcitriol (400 ng/kg) for 2 weeks showed significantly lower levels of vascular calcium content, Alizarin red staining, and RUNX2 expression than wild-type (WT) littermates. Serum calcium, phosphorus, blood urea nitrogen (BUN), PTH, and 1,25(OH)₂ D₃ levels were similar in both calcitriol-treated groups. In vitro, WT VSMCs treated with uremic serum also showed a significant increase in 1α-hydroxylase expression and higher calcification that was not observed in KO cells. We conclude that local activation of 1α-hydroxylase in the artery mediates VC observed in uremia. © 2016 American Society for Bone and Mineral Research.

Cytochrome P450 Vitamin D Hydroxylases in Inflammation and Cancer

Vitamin D insufficiency correlates with increased incidence of inflammatory disorders and cancer of the colon, breast, liver, and prostate. Preclinical studies demonstrated that the hormonally active form of vitamin D, 1,25(OH)2D3, has antiproliferative, proapoptotic, anti-inflammatory, and immunomodulatory effects. Tissue levels of 1,25(OH)2D3 are determined by expression and activity of specific vitamin D hydroxylases expressed at renal and extrarenal sites. In order to understand how perturbations in the vitamin D system affect human health, we need to understand the steps involved in the synthesis and catabolism of the active metabolite. This review provides an overview about recent findings on the altered vitamin D metabolism in inflammatory conditions and carcinogenesis. We will summarize existing data on the pathophysiological regulation of vitamin D hydroxylases and outline the role of adequate levels of 1,25(OH)2D3 on tissue homeostasis.

Vitamin D and alternative splicing of RNA

The active form of vitamin D (1α,25-dihydroxyvitamin D, 1,25(OH)2D) exerts its genomic effects via binding to a nuclear high-affinity vitamin D receptor (VDR). Recent deep sequencing analysis of VDR binding locations across the complete genome has significantly expanded our understanding of the actions of vitamin D and VDR on gene transcription. However, these studies have also promoted appreciation of the extra-transcriptional impact of vitamin D on gene expression. It is now clear that vitamin D interacts with the epigenome via effects on DNA methylation, histone acetylation, and microRNA generation to maintain normal biological functions. There is also increasing evidence that vitamin D can influence pre-mRNA constitutive splicing and alternative splicing, although the mechanism for this remains unclear. Pre-mRNA splicing has long been thought to be a post-transcription RNA processing event, but current data indicate that this occurs co-transcriptionally. Several steroid hormones have been recognized to coordinately control gene transcription and pre-mRNA splicing through the recruitment of nuclear receptor co-regulators that can both control gene transcription and splicing. The current review will discuss this concept with specific reference to vitamin D, and the potential role of heterogeneous nuclear ribonucleoprotein C (hnRNPC), a nuclear factor with an established function in RNA splicing. hnRNPC, has been shown to be involved in the VDR transcriptional complex as a vitamin D-response element-binding protein (VDRE-BP), and may act as a coupling factor linking VDR-directed gene transcription with RNA splicing. In this way hnRNPC may provide an additional mechanism for the fine-tuning of vitamin D-regulated target gene expression. This article is part of a Special Issue entitled '17th Vitamin D Workshop'.

Decreased expression of CYP27B1 correlates with the increased aggressiveness of ovarian carcinomas

CYP27B1 hydroxylates 25-hydroxyvitamin D3 in position C1α into biologically active 1,25-dihydroxyvitamin D3, calcitriol. CYP27B1 is expressed in normal tissues and tumors. Since calcitriol indicates anticancer activities and CYP27B1 expression can be deregulated during malignant progression, we analyzed its expression in ovarian cancers in relation to pathomorphological features of tumors and overall survival (OS). Expression of CYP27B1 was evaluated in 61 ovarian tumors, 18 metastases and 10 normal ovaries. Normal ovarian epithelium showed the highest levels CYP27B1 with a significant decrease in its expression in ovarian cancers. Both poorly differentiated primary tumors and metastases showed the lowest level of CYP27B1 expression, while non-metastasizing tumors showed a higher CYP27B1 level than tumors that developed metastases. The expression of CYP27B1 was positively correlated with a lower proliferation rate, lower dynamism of tumor growth and tumor infiltrating lymphocyte response. Furthermore, CYP27B1 expression was negatively correlated with tumor cell modeling of their microenvironment. CYP27B1 expression was also associated with longer OS time. In summary, our results suggest that local expression of CYP27B1 in ovarian tumor cells can modify their behavior and promote a less aggressive phenotype by affecting local concentrations of active of vitamin D levels within the tumor microenvironment.

Vitamin D level and risk of community-acquired pneumonia and sepsis

Previous research has reported reduced serum 25-hydroxyvitamin D (25(OH)D) levels is associated with acute infectious illness. The relationship between vitamin D status, measured prior to acute infectious illness, with risk of community-acquired pneumonia (CAP) and sepsis has not been examined. Community-living individuals hospitalized with CAP or sepsis were age-, sex-, race-, and season-matched with controls. ICD-9 codes identified CAP and sepsis; chest radiograph confirmed CAP. Serum 25(OH)D levels were measured up to 15 months prior to hospitalization. Regression models adjusted for diabetes, renal disease, and peripheral vascular disease evaluated the association of 25(OH)D levels with CAP or sepsis risk. A total of 132 CAP patients and controls were 60 ± 17 years, 71% female, and 86% Caucasian. The 25(OH)D levels <37 nmol/L (adjusted odds ratio (OR) 2.57, 95% CI 1.08-6.08) were strongly associated with increased odds of CAP hospitalization. A total of 422 sepsis patients and controls were 65 ± 14 years, 59% female, and 91% Caucasian. The 25(OH)D levels <37 nmol/L (adjusted OR 1.75, 95% CI 1.11-2.77) were associated with increased odds of sepsis hospitalization. Vitamin D status was inversely associated with risk of CAP and sepsis hospitalization in a community-living adult population. Further clinical trials are needed to evaluate whether vitamin D supplementation can reduce risk of infections, including CAP and sepsis.

Fructus ligustri lucidi ethanol extract improves bone mineral density and properties through modulating calcium absorption-related gene expression in kidney and duodenum of growing rats

Optimizing peak bone mass in early life is one of key preventive strategies against osteoporosis. Fructus ligustri lucidi (FLL), the fruit of Ligustrum lucidum Ait., is a commonly prescribed herb in many kidney-tonifying traditional Chinese medicinal formulas to alleviate osteoporosis. Previously, FLL extracts have been shown to have osteoprotective effect in aged or ovariectomized rats. In the present study, we investigated the effects of FLL ethanol extract on bone mineral density (BMD) and mechanical properties in growing male rats and explored the underlying mechanisms. Male weaning Sprague-Dawley rats were randomized into four groups and orally administrated for 4 months an AIN-93G formula-based diet supplementing with different doses of FLL ethanol extract (0.40, 0.65, and 0.90 %) or vehicle control, respectively. Then calcium balance, serum level of Ca, P, 25(OH)2D3, 1,25(OH)2D3, osteocalcin (OCN), C-terminal telopeptide of type I collagen (CTX-I), and parathyroid hormone, bone microarchitecture, and calcium absorption-related genes expression in duodenum and kidney were analyzed. The results demonstrated that FLL ethanol extract increased BMD of growing rats and improved their bone microarchitecture and mechanical properties. FLL ethanol extract altered bone turnover, as evidenced by increasing a bone formation maker, OCN, and decreasing a bone resorption maker, CTX-I. Intriguingly, both Ca absorption and Ca retention rate were elevated by FLL ethanol extract treatment, possibly through the mechanisms of up-regulating the transcriptions of calcitropic genes in kidney (1α-hydroxylase) and duodenum (vitamin D receptor, calcium transporter calbindin-D9k, and transient receptor potential vanilloid 6). In conclusion, FLL ethanol extract increased bone mass gain and improved bone properties via modulating bone turnover and up-regulating calcium absorption-related gene expression in kidney and duodenum, which could then activate 1,25(OH)2D3-dependent calcium transport in male growing rats.

Cytochrome P450-mediated metabolism of vitamin D

The vitamin D signal transduction system involves a series of cytochrome P450-containing sterol hydroxylases to generate and degrade the active hormone, 1α,25-dihydroxyvitamin D3, which serves as a ligand for the vitamin D receptor-mediated transcriptional gene expression described in companion articles in this review series. This review updates our current knowledge of the specific anabolic cytochrome P450s involved in 25- and 1α-hydroxylation, as well as the catabolic cytochrome P450 involved in 24- and 23-hydroxylation steps, which are believed to initiate inactivation of the vitamin D molecule. We focus on the biochemical properties of these enzymes; key residues in their active sites derived from crystal structures and mutagenesis studies; the physiological roles of these enzymes as determined by animal knockout studies and human genetic diseases; and the regulation of these different cytochrome P450s by extracellular ions and peptide modulators. We highlight the importance of these cytochrome P450s in the pathogenesis of kidney disease, metabolic bone disease, and hyperproliferative diseases, such as psoriasis and cancer; as well as explore potential future developments in the field.

Fibroblast growth factor 23 inhibits extrarenal synthesis of 1,25-dihydroxyvitamin D in human monocytes

Vitamin D is a potent stimulator of monocyte innate immunity, and this effect is mediated via intracrine conversion of 25-hydroxyvitamin D (25OHD) to 1,25-dihydroxyvitamin D (1,25(OH)(2) D). In the kidney, synthesis of 1,25(OH)(2) D is suppressed by fibroblast growth factor 23 (FGF23), via transcriptional suppression of the vitamin D-activating enzyme 1α-hydroxylase (CYP27B1). We hypothesized that FGF23 also suppresses CYP27B1 in monocytes, with concomitant effects on intracrine responses to 1,25(OH)(2) D. Healthy donor peripheral blood mononuclear cell monocytes (PBMCm) and peritoneal dialysate monocyte (PDm) effluent from kidney disease patients were assessed at baseline to confirm the presence of mRNA for FGF23 receptors (FGFRs), with Klotho and FGFR1 being more strongly expressed than FGFR2/3/4 in both cell types. Immunohistochemistry showed coexpression of Klotho and FGFR1 in PBMCm and PDm, with this effect being enhanced following treatment with FGF23 in PBMCm but not PDm. Treatment with FGF23 activated mitogen-activated protein kinase (MAPK) and protein kinase B (Akt) pathways in PBMCm, demonstrating functional FGFR signaling in these cells. FGF23 treatment of PBMCm and PDm decreased expression of mRNA for CYP27B1. In PBMCm this was associated with downregulation of 25OHD to 1,25(OH)(2) D metabolism, and concomitant suppression of intracrine induced 24-hydroxylase (CYP24A1) and antibacterial cathelicidin (LL37). FGF23 suppression of CYP27B1 was particularly pronounced in PBMCm treated with interleukin-15 to stimulate synthesis of 1,25(OH)(2) D. These data indicate that FGF23 can inhibit extra-renal expression of CYP27B1 and subsequent intracrine responses to 1,25(OH)(2) D in two different human monocyte models. Elevated expression of FGF23 may therefore play a crucial role in defining immune responses to vitamin D and this, in turn, may be a key determinant of infection in patients with chronic kidney disease (CKD).

Vitamin D, immune tolerance, and prevention of type 1 diabetes

Vitamin D is a secosteroid hormone that resembles other nuclear steroid hormones such as thyroid, gluco-, and mineralocorticoids, as well as gonadal effector systems. Primarily understood as a master regulator of bone and calcium/phosphate physiology, it is now increasingly recognized as orchestrating numerous aspects of cell growth and differentiation in many tissues, including those of innate and acquired immunity. This review addresses recently discovered aspects that highlight vitamin D's potential for immune intervention and how the vitamin D pathway is utilized for anti-infective and antineoplastic immunity. This provides the rationale for novel therapeutic strategies in the context both of prevention and of therapy of immune dysregulation in type 1 diabetes.

Vitamin D and the immune system

It is now clear that vitamin D has important roles in addition to its classic effects on calcium and bone homeostasis. As the vitamin D receptor is expressed on immune cells (B cells, T cells, and antigen-presenting cells), and these immunologic cells are all capable of synthesizing the active vitamin D metabolite, vitamin D has the capability of acting in an autocrine manner in a local immunologic milieu. Vitamin D can modulate the innate and adaptive immune responses. Deficiency in vitamin D is associated with increased autoimmunity and an increased susceptibility to infection. As immune cells in autoimmune diseases are responsive to the ameliorative effects of vitamin D, the beneficial effects of supplementing vitamin D-deficient individuals with autoimmune disease may extend beyond the effects on bone and calcium homeostasis.

Vitamin D and the immune system

It is now clear that vitamin D has important roles in addition to its classic effects on calcium and bone homeostasis. As the vitamin D receptor is expressed on immune cells (B cells, T cells, and antigen-presenting cells), and these immunologic cells are all capable of synthesizing the active vitamin D metabolite, vitamin D has the capability of acting in an autocrine manner in a local immunologic milieu. Vitamin D can modulate the innate and adaptive immune responses. Deficiency in vitamin D is associated with increased autoimmunity and an increased susceptibility to infection. As immune cells in autoimmune diseases are responsive to the ameliorative effects of vitamin D, the beneficial effects of supplementing vitamin D-deficient individuals with autoimmune disease may extend beyond the effects on bone and calcium homeostasis.

Ethanol extract of Fructus Ligustri Lucidi increases circulating 1,25-dihydroxyvitamin D3 by inducing renal 25-hydroxyvitamin D-1α hydroxylase activity

OBJECTIVE

The present study was designed to determine whether Fructus Ligustri Lucidi (FLL) ethanol extract can directly regulate vitamin D metabolism both in vivo and in vitro.

METHODS

Eleven-month-old, aged Sprague-Dawley sham-operated and ovariectomized (OVX) female rats were fed a normal-calcium (Ca) diet (0.6% Ca, 0.65% phosphorus) and received either FLL (700 mg/kg) or vehicle daily for 12 weeks. The in vitro effects of FLL on vitamin D metabolism were studied using primary cultures of the rat renal proximal tubules. mRNA and protein expressions of 25-hydroxyvitamin D-1α hydroxylase (1-OHase) and vitamin D receptor (VDR) in the kidney and proximal tubule were measured using real-time polymerase chain reaction and Western blotting, respectively. The concentrations of 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) synthesized by renal 1-OHase were measured by a competitive enzyme immunoassay.

RESULTS

FLL treatment significantly increased serum 1,25(OH)2D3 levels in both sham (P < 0.01) and OVX (P < 0.05) rats. FLL increased renal 1-OHase and VDR protein and mRNA expressions in sham rats. Protein expression of renal 1-OHase, but not VDR, was also up-regulated in OVX rats during FLL treatment. 1-OHase mRNA and 1-OHase activity were increased by FLL treatment in primary cultures of renal proximal tubule cells.

CONCLUSIONS

FLL could increase the circulating levels of 1,25(OH)2D3 in vivo in aged female rats by directly stimulating 1-OHase activity. Thus, it might be an ideal oral agent that can help to improve the ability to induce 1,25(OH)2D3 synthesis and Ca balance in postmenopausal women who are of high risk of developing osteoporosis.

DNA methylation-related vitamin D receptor insensitivity in breast cancer

Calcitriol (1α, 25(OH)(2)-Vitamin D3) binds to the vitamin D receptor (VDR) and regulates differentiation of the normal mammary gland, and may therefore be useful in breast cancer treatment or prevention. Many breast cancer cells are, however, resistant to Calcitriol. In this study, we investigated the resistance mechanism and the role of epigenetic silencing of VDR by promoter hypermethylation. Bisulfite sequencing of the VDR promoter region revealed methylated CpG islands at -700 base pairs (bp) upstream and near the transcription start site. VDR CpG islands were demethylated by 5'deoxy-azacytidine treatment, and this was accompanied by a parallel increase in VDR mRNA levels in breast cancer cell lines. Quantitative methylation-specific PCR analyses confirmed hypermethylation of these CpG islands in primary tumors, and its absence in normal breast tissue. VDR transcripts detected in breast cancers were predominantly 5'-truncated, while normal breast tissue expressed full-length transcripts. Consistent with this observation, genes containing the VDR-responsive element (VDRE), such as cytochrome p450 hydroxylases, p21 or C/EBP were underexpressed in breast cancers compared to normal breast samples. Expression of the active longer transcripts of VDR was restored with 5'deoxy-Azacytidine (AZA) treatment, with a concurrent increase in expression of VDRE-containing genes. Thus, promoter methylation-mediated silencing of expression of the functional variants of VDR may contribute to reduced expression of downstream effectors of the VDR pathway and subsequent Calcitriol insensitivity in breast cancer. These data suggest that pharmacological reversal of VDR methylation may re-establish breast cancer cell susceptibility to differentiation therapy using Calcitriol.

Vitamin D and molecular actions on the immune system: modulation of innate and autoimmunity

Vitamin D has received increased attention recently for its pleiotropic actions on many chronic diseases. The importance of vitamin D on the regulation of cells of the immune system has gained increased appreciation over the past decade with the discovery of the vitamin D receptor (VDR) and key vitamin D metabolizing enzymes expressed by cells of the immune system. Animal studies, early epidemiologic and clinical studies have supported a potential role for vitamin D in maintaining immune system balance. The hormonal form of vitamin D up-regulates anti-microbial peptides, namely cathelicidin, to enhance clearance of bacteria at various barrier sites and in immune cells. Vitamin D modulates the adaptive immune system by direct effects on T cell activation and on the phenotype and function of antigen-presenting cells (APCs), particularly of DCs. The purpose of this manuscript is to review the molecular and clinical evidence for vitamin D as a modulator of the innate and adaptive immune system.

Vitamin d-directed rheostatic regulation of monocyte antibacterial responses

The active form of vitamin D, 1,25-dihydroxyvitamin D (1,25(OH)(2)D) enhances innate immunity by inducing the cathelicidin antimicrobial peptide (hCAP). In monocytes/macrophages, this occurs primarily in response to activation of TLR, that induce expression of the vitamin D receptor and localized synthesis of 1,25(OH)(2)D from precursor 25-hydroxyvitamin D(3) (25OHD). To clarify the relationship between vitamin D and innate immunity, we assessed changes in hCAP expression in vivo and ex vivo in human subjects attending a bone clinic (n = 50). Of these, 38% were vitamin D-insufficient (<75 nM 25OHD) and received supplementation with vitamin D (50,000 IU vitamin D(2) twice weekly for 5 wk). Baseline 25OHD status or vitamin D supplementation had no effect on circulating levels of hCAP. Therefore, ex vivo changes in hCAP for each subject were assessed using peripheral blood monocytes cultured with 10% autologous serum (n = 28). Under these vitamin D "insufficient" conditions the TLR2/1 ligand 19 kDa lipopeptide or the TLR4 ligand LPS, monocytes showed increased expression of the vitamin D-activating enzyme CYP27b1 (5- and 5.5-fold, respectively, both p < 0.01) but decreased expression of hCAP mRNA (10-fold and 30-fold, both p < 0.001). Following treatment with 19 kDa, expression of hCAP: 1) correlated with 25OHD levels in serum culture supplements (R = 0.649, p < 0.001); 2) was significantly enhanced by exogenous 25OHD (5 nM); and 3) was significantly enhanced with serum from vivo vitamin D-supplemented patients. These data suggest that a key role of vitamin D in innate immunity is to maintain localized production of antibacterial hCAP following TLR activation of monocytes.

Mammary epithelial cell transformation is associated with deregulation of the vitamin D pathway

The vitamin D endocrine system mediates anti-proliferative and pro-differentiating signaling in multiple epithelial tissues, including mammary gland and breast tumors. The vitamin D metabolite 1alpha,25(OH)2D3 mediates growth inhibitory signaling via activation of the vitamin D receptor (VDR), a ligand dependent transcription factor. 1alpha,25(OH)(2)D3 is synthesized from 25(OH)D3 (the major circulating form of the vitamin) by the mitochondrial enzyme CYP27b1 in renal and other tissues. Human mammary epithelial (HME) cells express VDR and CYP27b1 and undergo growth inhibition when exposed to physiological concentrations of 25(OH)D3, suggesting that autocrine or paracrine vitamin D signaling contributes to maintenance of differentiation and quiescence in the mammary epithelium. In the current studies we tested the hypothesis that cancer cells would exhibit reduced sensitivity to vitamin D mediated negative growth regulation. We used a series of progressively transformed HME cell lines expressing known oncogenic manipulations to study the effects of transformation per se on the vitamin D pathway. We report that mRNA and protein levels of VDR and CYP27b1 were reduced greater than 70% upon stable introduction of known oncogenes (SV40 T antigens and H-rasV12) into HME cells. Oncogenic transformation was also associated with reduced 1alpha,25(OH)2D3 synthesis, and cellular sensitivity to growth inhibition by 1alpha,25(OH)2D3 and 25(OH)D3 was decreased approximately 100-fold in transformed cells. These studies provide evidence that disruption of the vitamin D signaling pathway occurs early in the cancer development process.

Reduction of the vitamin D hormonal system in kidney disease is associated with increased renal inflammation

To examine any potential role for 1,25-dihydroxyvitamin D (1,25(OH)2D) in inflammation associated with chronic kidney disease we measured vitamin D metabolites, markers of inflammation and gene expression in 174 patients with a variety of kidney diseases. Urinary MCP-1 protein and renal macrophage infiltration were each significantly but inversely correlated with serum 1,25(OH)2D levels. Logistic regression analysis with urinary MCP-1 as binary outcome showed that a 10-unit increase in serum 1,25(OH)2D or 25OHD resulted in lower renal inflammation. Analysis of 111 renal biopsies found that renal injury was not associated with a compensatory increase in mRNA for the vitamin D-activating enzyme 25-hydroxyvitamin D-1alpha-hydroxylase (CYP27B1), its catabolic counterpart 24-hydroxylase, or the vitamin D receptor. There was, however, a significant association between tissue MCP-1 and CYP27B1. Patients with acute renal inflammation had a significant increase in urinary and tissue MCP-1, macrophage infiltration, and macrophage and renal epithelial CYP27B1 expression but significantly lower levels of serum 1,25(OH)2D in comparison to patients with chronic ischemic disease despite similar levels of renal damage. In vitro, 1,25(OH)2D attenuated TNFalpha-induced MCP-1 expression by human proximal tubule cells. Our study indicates that renal inflammation is associated with decreased serum vitamin D metabolites and involves activation of the paracrine/autocrine vitamin D system.

Specific regulation of CYP27B1 and VDR in proximal versus distal renal cells

In this study, we utilized murine renal proximal (MPCT-G) and distal (DKC-8) tubular epithelial cell lines to compare the gene expressions and promoter activities of 1,25(OH)(2)D(3) receptor (VDR) and 25-hydroxyvitamin D-1alpha-hydroxylase (CYP27B1) in response to 50 nM of parathyroid hormone (PTH) and changes in extracellular calcium (Ca(2+)) concentration. In MPCT-G cells, VDR gene expression was suppressed by PTH, whereas CYP27B1 gene expression was elevated in response to PTH. In DKC-8 cells, treatment of PTH significantly increased the relative gene expression of VDR by 6.5-fold while CYP27B1 gene expression was unchanged. High Ca(2+) exposure stimulated VDR gene expression and repressed CYP27B1 gene expression in both dose and time-dependent fashion in MPCT-G but not DKC-8 cells. The analysis of promoter activities and VDR protein levels corresponded with the gene expression data. We conclude that PTH-mediated decrease in VDR and increase in renal CYP27B1 is proximal cell-specific.