Mechanism of vitamin D receptor action

Association between metabolic body composition status and vitamin D deficiency: A cross-sectional study

This study aimed to investigate the risk of vitamin D deficiency in a relatively healthy Asian population, with (i) metabolically healthy normal weight (MHNW) (homeostasis model assessment-insulin resistance [HOMA-IR] < 2. 5 without metabolic syndrome [MS], body mass index [BMI] < 25), (ii) metabolically healthy obesity (MHO) (HOMA-IR < 2.5, without MS, BMI ≥ 25), (iii) metabolically unhealthy normal weight (MUNW) (HOMA-IR ≥ 2.5, or with MS, BMI < 25), and (iv) metabolically unhealthy obesity (MUO) (HOMA-IR ≥ 2.5, or with MS, BMI ≥ 25) stratified by age and sex. This cross-sectional study involved 6,655 participants aged ≥ 18 years who underwent health checkups between 2013 and 2016 at the Chang Gung Memorial Hospital. Cardiometabolic and inflammatory markers including anthropometric variables, glycemic indices, lipid profiles, high-sensitivity C-reactive protein (hs-CRP), and serum 25-hydroxy vitamin D levels, were retrospectively investigated. Compared to the MHNW group, the MHO group showed a higher odds ratio (OR) [1.35, 95% confidence interval (CI) 1.05-1.73] for vitamin D deficiency in men aged < 50 years. By contrast, in men aged > 50 years, the risk of vitamin D deficiency was higher in the MUO group (OR 1.44, 95% CI 1.05-1.97). Among women aged < and ≥ 50 years, the MUO group demonstrated the highest risk for vitamin D deficiency, OR 2.33 vs. 1.54, respectively. Our study revealed that in women of all ages and men aged > 50 years, MUO is associated with vitamin D deficiency and elevated levels of metabolic biomarkers. Among men aged < 50 years, MHO had the highest OR for vitamin D deficiency.

Vitamin D Receptor Influences Intestinal Barriers in Health and Disease

Vitamin D receptor (VDR) executes most of the biological functions of vitamin D. Beyond this, VDR is a transcriptional factor regulating the expression levels of many target genes, such as genes for tight junction proteins claudin-2, -5, -12, and -15. In this review, we discuss the progress of research on VDR that influences intestinal barriers in health and disease. We searched PubMed and Google Scholar using key words vitamin D, VDR, tight junctions, cancer, inflammation, and infection. We summarize the literature and progress reports on VDR regulation of tight junction distribution, cellular functions, and mechanisms (directly or indirectly). We review the impacts of VDR on barriers in various diseases, e.g., colon cancer, infection, inflammatory bowel disease, and chronic inflammatory lung diseases. We also discuss the limits of current studies and future directions. Deeper understanding of the mechanisms by which the VDR signaling regulates intestinal barrier functions allow us to develop efficient and effective therapeutic strategies based on levels of tight junction proteins and vitamin D/VDR statuses for human diseases.

Upregulation of the Vitamin D Receptor in the Nasal Mucosa of Patients With Allergic Rhinitis

Background and Objectives: Vitamin D modulates immunity, including that of allergic diseases, and plays its roles through contact with vitamin D receptors (VDR). Recent studies have shown that patients with allergic rhinitis have low systemic serum vitamin D level. However, the expression of VDR in local tissue such as human nasal mucosa has not been investigated. Our study demonstrated that, in nasal mucosa of normal controls and patients with allergic rhinitis.Materials and Methods: Nasal mucosa were harvested from twenty-five patients who had normal nasal mucosa and twenty-five patients with allergic rhinitis. After the total RNA isolation, we performed reverse transcriptase-polymerase chain reaction, immunohistochemical staining and western blot analysis.Results: VDR were expressed in submucosal glands and the superficial layer of epithelial cell, and that inflammatory cells are expressed more highly in the nasal mucosa of patients with allergic rhinitis compared to those without. In the mucosa of patients with allergic rhinitis, VDR expression level was upregulated compared to that in normal nasal mucosa.Conclusion: This findings suggest that VDR plays a role in the pathogenesis of allergic rhinitis. Additional research is needed to determine the mechanism and consequences of VDR upregulation.

The Most Common Vitamin D Receptor Polymorphisms (ApaI,FokI, TaqI, BsmI, and BglI) in Children with Dental Caries: A Systematic Review and Meta-Analysis

Vitamin D participates in the calcification of enamel and dentin and the appropriate immune responses to oral microbial infections. We aimed to assess the association between the most common vitamin D receptor (VDR) polymorphisms (ApaI,FokI, TaqI, BsmI, and BglI) and the risk of dental caries in children.

METHODS

PubMed/MEDLINE, Cochrane Library, Web of Science, and Scopus databases were comprehensively searched until 19 January 2021. Meta-analysis with odds ratios as the effect estimate along with 95% confidence intervals and subgroup analysis were conducted using Review Manager 5.3 software. Publication bias and sensitivity analyses were conducted by Comprehensive Meta-Analysis, version 2.0 software.

RESULTS

Seventy-eight studies were retrieved from the databases, with nine studies included in the final analysis. Based on five genetic models, there was no association between ApaI (rs7975232), TaqI (rs731236), BsmI (rs1544410), FokI (rs2228570), and BglI (rs739837) polymorphisms and susceptibility to dental caries, except for the FokI (rs10735810) polymorphism.

CONCLUSION

Among the VDR polymorphisms considered, an association was found between the FokI (rs10735810) polymorphism and the risk of dental caries, with a protective role of the f allele and ff genotype.

1,25-Dihydroxyvitamin D3 modulates adipogenesis of human adipose-derived mesenchymal stem cells dose-dependently

Purpose

1,25-dihydroxyvitamin D3 may regulate adipogenesis in adipocytes in-vitro, but little is known about possible molecular mechanisms related to the inhibitory effect of 1,25-dihydroxyvitamin D3 on adipogenesis in humans҆ adipose tissue.

Methodology

In this study, human adipose-derived mesenchymal stem cells (hASCs) were cultured for 14 days in adipogenic differentiation media containing concentrations of 1,25-dihydroxyvitamin D3 (10⁻¹⁰–10⁻⁸ M). The extent of adipogenic differentiation in ASCs was assessed by Oil Red O staining and quantitative polymerase chain reaction (PCR) to determine expression levels of key adipogenic markers.

Results

Our results showed that vitamin D receptor (VDR), as a mediator of most actions of 1,25-dihydroxyvitamin D3, glucose trasporter-4 (GLUT4),and fatty acid binding protein-4 (FABP4) was expressed in vitamin D-treated hASCs. However, the protein level of these markers was lower than the control group. Treatment of human preadipocytes with 1,25-dihydroxyvitamin D3 significantly altered expression of adipogenic markers and triglyceride accumulation in a dose-dependent manner. 1,25-dihydroxyvitamin D3 at concentration of 10⁻⁸ M enhanced expression of sterol regulatory element-binding protein-1c (SREBP1c), CCAAT-enhancer-binding protein-β (C/EBPβ), a mitotic clonal expansion, peroxisome proliferator-activated receptor-gamma (PPARγ), fatty acid synthase (FASN), a marker of de novo lipogenesis,and lipoprotein lipase (LPL).

Conclusion

Our findings revealed that 1,25-dihydroxyvitamin D3 may provoke adipocyte development in critical periods of adipogenesis at concentration of 10⁻⁸ M, thereby leading to a greater risk of obesity in adulthood and an augmented risk of obesity-related diseases including diabetes, cardiovascular diseases, and some cancers.

Modulation of Intestinal Phosphate Transport in Young Goats Fed a Low Phosphorus Diet

The intestinal absorption of phosphate (P_i) takes place transcellularly through the active NaPi-cotransporters type IIb (NaPiIIb) and III (PiT1 and PiT2) and paracellularly by diffusion through tight junction (TJ) proteins. The localisation along the intestines and the regulation of P_i absorption differ between species and are not fully understood. It is known that 1,25-dihydroxy-vitamin D₃ (1,25-(OH)₂D₃) and phosphorus (P) depletion modulate intestinal P_i absorption in vertebrates in different ways. In addition to the apical uptake into the enterocytes, there are uncertainties regarding the basolateral excretion of P_i. Functional ex vivo experiments in Ussing chambers and molecular studies of small intestinal epithelia were carried out on P-deficient goats in order to elucidate the transepithelial P_i route in the intestine as well as the underlying mechanisms of its regulation and the proteins, which may be involved. The dietary P reduction had no effect on the duodenal and ileal P_i transport rate in growing goats. The ileal PiT1 and PiT2 mRNA expressions increased significantly, while the ileal PiT1 protein expression, the mid jejunal claudin-2 mRNA expression and the serum 1,25-(OH)₂D₃ levels were significantly reduced. These results advance the state of knowledge concerning the complex mechanisms of the P_i homeostasis in vertebrates.

Efficacy of Oral Administration of a Reliable AD3E Treatment on Vitamin D3 Deficiency in Najdi Sheep

This study was aimed to assess the efficacy of oral treatment of commercial product of vitamin D3 (VITOL-80 C ORAL®, Interchemie, Holland) in growing Najdi sheep suffering from musculoskeletal illness due to vitamin D3 deficiency in Basra province, Iraq. Using a Najdi sheep model bred in Iraq, here we focused on measuring the serum levels of total vitamin D3, calcium, phosphorus, parathyroid hormone (PTH), alkaline phosphatase (ALP) and alanine aminotransferase (ALT) as well as complete blood count (CBC) and clinical examinations pre and post-treatment with VITOL-80 C ORAL®. No significant changes (P > 0.05) of the vitamin D status were recorded in Najdi sheep with vitamin D3 deficiency post treatment with (VITOL-80 C ORAL®). However, a sharp (P < 0.0001) decline of the total serum vitamin D3 concentration were observed in those Najdi sheep per-administration (21.95 ± 1.82 ng/ml) and postadministration (22.29 ± 1.34 ng/ml) of vitamins therapy contrast to control healthy Najdi sheep (89.75 ± 6.84 ng/ml). An interaction between vitamin D3 status and the serum concentrations of calcium/phosphorus, PTH, ALP and ALT was observed. With vitamin D3-deficient Najdi sheep; values of CBC, and calcium/phosphorus concentrations were lower while PTH, ALP and ALT were higher than the healthy control Najdi sheep; thus, no significant changes (P > 0.05) of these values were recorded post treatment of (VITOL-80 C ORAL®). In conclusion, vitamin D3 deficiency threats the health of local Najdi sheep and has a potential role through suppressing their immunity. Oral administration of the commercial product as a source of vitamin D3 is not effective suggesting involvement of vitamin D receptors (VDR) and/or dysfunction of liver and kidneys.

Vitamin D Receptor Gene Polymorphisms and the Risk of Metabolic Syndrome (MetS): A Meta-Analysis

BACKGROUND

Several studies have assessed the association between the vitamin D receptor (VDR) polymorphism and the risk of metabolic syndrome (MetS). However, the results were inconsistent and inconclusive. Therefore, we conducted a meta-analysis to clarify the exact association between the vitamin D receptor (VDR) polymorphisms and the risk of MetS.

METHODS

All accessible studies reporting the association between the FokI (rs2228570) or/and TaqI (rs731236) or/and BsmI (rs1544410) or/and ApaI (rs7975232 polymorphisms of the Vitamin D Receptor and susceptibility to MetS published prior to February 2019 were systematically searched in Web of Science, Scopus, and PubMed. After that, Odds ratios (ORs) and their corresponding 95% confidence intervals (CIs) were estimated to evaluate the strength of the association in five genetic models.

RESULTS

A total of 9 articles based on four gene variations, and comprising 3348 participants with 1779 metabolic syndrome patients were included. The overall results suggested a significant association between BsmI (rs1544410) polymorphism and MetS susceptibility in recessive model (OR, 0.72, 95% CI, 0.55-0.95, fixed effect model), allelic model (OR, 0.83, 95% CI, 0.72-0.95, fixed effect model), and bb vs BB (OR, 0.65, 95% CI, 0.46-0.93, fixed effect). However, no significant association was identified between TaqI (rs731236) polymorphism, ApaI (rs7975232) polymorphism, and FokI (rs2228570) polymorphism and MetS.

CONCLUSION

This meta-analysis suggested an association between the BsmI (rs1544410) polymorphism and MetS. Indeed, BsmI (rs1544410) acts as a protective factor in the MetS. As a result, the VDR gene could be regarded as a promising pharmacological and physiological target in the prevention or treatment of the MetS.

Lactic Acid Bacteria Isolated From Korean Kimchi Activate the Vitamin D Receptor-autophagy Signaling Pathways

BACKGROUND

Probiotic lactic acid bacteria (LAB) have been used in the anti-inflammation and anti-infection process of various diseases, including inflammatory bowel disease (IBD). Vitamin D receptor (VDR) plays an essential role in pathogenesis of IBD and infectious diseases. Previous studies have demonstrated that the human VDR gene is a key host factor to shape gut microbiome. Furthermore, intestinal epithelial VDR conditional knockout (VDRΔIEC) leads to dysbiosis. Low expressions of VDR is associated with impaired autophagy, accompanied by a reduction of ATG16L1 and LC3B. The purpose of this study is to investigate probiotic effects and mechanism in modulating the VDR-autophagy pathways.

METHODS

Five LAB strains were isolated from Korean kimchi. Conditional medium (CM) from these strains was used to treat a human cell line HCT116 or intestinal organoids to measure the expression of VDR and autophagy. Mouse embryonic fibroblast (MEF) cells with or without VDR were used to investigate the dependence on the VDR signaling. To test the role of LAB in anti-inflammation, VDR+/+ organoids were treated with 121-CM before infection with Salmonella enterica serovar Enteritidis. In vivo, the role of LAB in regulating VDR-autophagy signaling was examined using LAB 121-CM orally administrated to VDRLoxp and VDRΔIEC mice.

RESULTS

The LAB-CM-treated groups showed higher mRNA expression of VDR and its target genes cathelicidin compared with the control group. LAB treatment also enhanced expressions of Beclin-1 and ATG16L1 and changed the ratio of LC3B I and II, indicating the activation of autophagic responses. Furthermore, 121-CM treatment before Salmonella enterica serovar Enteritidis infection dramatically increased VDR and ATG16L1 and inhibited the inflammation. Administration of 121-CM to VDRLoxp and VDRΔIEC mice for 12 and 24 hours resulted in an increase of VDR and LC3B II:I ratio. Furthermore, we identified that probiotic proteins P40 and P75 in the LAB-CM contributed to the anti-inflammatory function by increasing VDR.

CONCLUSIONS

Probiotic LAB exert anti-inflammation activity and induces autophagy. These effects depend on the VDR expression. Our data highlight the beneficial effects of these 5 LAB strains isolated from food in anti-infection and anti-inflammation.

Effects of acute hCG stimulation on serum INSL3 and 25-OH vitamin D in Klinefelter syndrome

BACKGROUND

It has recently been suggested that the hypergonadotropic hypogonadism characterizing Klinefelter syndrome (KS) might not be due to a steroidogenic dysfunction per se, but mainly to an altered testosterone (T) secretion into the bloodstream. However, the Leydig cell functionality remains incompletely studied in KS, and new markers should be considered. Previous data indicated that chronic hCG stimulation influences the production of both insulin-like peptide 3 (INSL3) and 25-hydroxy-vitamin D (25-VD) in eugonadal men.

AIM OF THE STUDY

To evaluate INSL3 and 25-VD serum levels, as markers of Leydig cell functionality, in association with sex steroids, after an acute hCG test in a group of KS patients and healthy volunteers.

METHODS

A retrospective analysis of a prospective case-control clinical trial was carried out. KS patients (n = 11) and age-matched healthy controls (n = 11) provided a basal blood sample (V0) immediately followed by a single intramuscular injection of hCG 5000 IU. Blood samples were taken in the following five days (V1-V5).

RESULTS

At baseline, INSL3 was lower in KS patients compared with controls (P = .007). When adjusted for INSL3 levels, the production of steroids was similar between KS patients and controls. 25-VD was in the insufficient range both in KS patients and in controls and was not different (P = .064). Acute hCG stimulation increased neither INSL3 nor 25-VD in both KS patients and controls. In controls, an inverse correlation was detected between INSL3 levels and body mass index (P = .020) and waist circumference (P = .020).

CONCLUSIONS

INSL3 secretion is independent from steroidogenesis, and its production is mostly not influenced by acute hCG stimulation both in KS men and in controls. INSL3 serum levels should be considered as a marker of Leydig cell differentiation and numbers rather than steroidogenesis. 25-VD serum levels are also not increased by a single acute hCG administration, which was not able to restore the normal concentrations of 25-VD.

Mechanisms Underlying Bone Loss Associated with Gut Inflammation

Patients with gastrointestinal diseases frequently suffer from skeletal abnormality, characterized by reduced bone mineral density, increased fracture risk, and/or joint inflammation. This pathological process is characterized by altered immune cell activity and elevated inflammatory cytokines in the bone marrow microenvironment due to disrupted gut immune response. Gastrointestinal disease is recognized as an immune malfunction driven by multiple factors, including cytokines and signaling molecules. However, the mechanism by which intestinal inflammation magnified by gut-residing actors stimulates bone loss remains to be elucidated. In this article, we discuss the main risk factors potentially contributing to intestinal disease-associated bone loss, and summarize current animal models, illustrating gut-bone axis to bridge the gap between intestinal inflammation and skeletal disease.

Impact of Vitamin D on Physical Efficiency and Exercise Performance-A Review

Vitamin D deficiency amongst athletes and the general population seems to be a prominent problem. The most recognized role of vitamin D is its regulation of calcium homeostasis; there is a strong relationship between vitamin D and bone health. Moreover, its concentrations are associated with muscle function and immune response in both the general and athletic populations. Vitamin D level is strongly connected with the presence of VDRs (vitamin D receptors) in most human extraskeletal cells. Expression of multiple myogenic transcription factors enhancing muscle cell proliferation and differentiation is caused by an exposure of skeletal muscles to vitamin D. The aim of this review is to summarize current understanding of the significance of vitamin D on exercise performance and physical efficiency, as well to analyze the impact of vitamin D on multiple potential mechanisms. More high-quality research studies, considering free 25(OH)D as a better marker of vitamin D status, the baseline level of 25(OH)D and multiple pathways of vitamin D acting and usage in athletes are required.

The Dependence of Running Speed and Muscle Strength on the Serum Concentration of Vitamin D in Young Male Professional Football Players Residing in the Russian Federation

Background: Vitamin D insufficiency is prevalent among athletes, and it can negatively affect physical performance. At the same time, most of the available data were obtained from untrained individuals of various ages, and published studies performed in athletes led to contradictory conclusions. Methods: This cohort prospective study examined the serum concentration of 25-hydroxycalciferol (25(OH)D) and its association with running speed and muscle power in 131 young football players (mean age 15.6 ± 2.4 years). Results: 25(OH)D levels were below reference in 42.8% (serum 25(OH)D <30 ng/mL) and above reference in 30.5% of the participants (serum 25(OH)D 61–130 ng/mL). A comparison of the results of 5, 15, and 30 m sprint tests and the standing long jump test found no statistically significant differences between the two groups. Athletes from the 25(OH)D-insufficient group were treated with 5000 IU cholecalciferol supplement daily for 60 days. After the treatment, the 25(OH)D concentration increased by 79.2% and was within reference in 84% of the treated athletes (serum 25(OH)D 30–60 ng/mL). Testing was repeated after the end of treatment, and a statistically significant increase in the results of the 5, 15, and 30 m sprint tests was observed (Cohen’s d was 0.46, 0.33, and 0.34, respectively), while the results of the standing long jump test remained unchanged. Body height, body weight, and lean body mass of the football players also increased. Conclusions: These findings indicate that there is likely no correlation between serum levels of 25(OH)D, muscle power, and running speed in young professional football players, and the changes observed post-treatment might have been caused by changes in the anthropometric parameters. During the study, all the anthropometric parameters changed, but the amount of lean body mass only correlated with the results of the 5 m sprint.

Determinants of vitamin D receptor gene expression in visceral and subcutaneous adipose tissue in non-obese, obese, and morbidly obese subjects

We aimed to illustrate determinants of VDR gene expression in visceral and subcutaneous adipose tissue among individuals without diabetes. We gathered visceral and subcutaneous adipose tissues during an elective abdominal surgery form 33 morbidly obese (BMI > 40 kg/m²), 23 obese (BMI = 30-40 kg/m²), and 35 non-obese (BMI<30 kg/m²) participants who were free of diabetes. Participants were classified according to their degree of obesity. Before the surgery, habitual dietary intake, physical activity, 25(OH)D, body mass index (BMI), waist circumference (WC), and HOMA-IR was gathered. Non-obese participants had significantly lower mean VDR gene expression in visceral adipose tissues than both the obese and morbidly obese ones and had also lower expression in subcutaneous adipose tissues than the morbidly obese participants. In multiple linear regression models, BMI and HOMA-IR were the independent positive predictors of VDR gene expression in subcutaneous fat. Among non-obese subjects, WC and 25(OH)D were the positive and negative independent predictors of visceral adipose tissue VDR gene expression, respectively. Among obese participants, 25(OH)D was negatively, and BMI and HOMA-IR were positively associated with VDR mRNA levels in visceral adipose tissue. In morbidly obese participants, the independent positive predictors of VDR gene expression in visceral fat were BMI and HOMA-IR, and negative predictors were 25(OH)D and calcium intake. Our findings suggested that 25(OH)D concentrations are the fundamental elements to determine VDR gene expression in visceral fat which by increasing fat depots, the subsequent insulin resistance became another predictor of VDR gene expression.

Lack of Vitamin D Receptor Leads to Hyperfunction of Claudin-2 in Intestinal Inflammatory Responses

BACKGROUND

Vitamin D3 and vitamin D receptor (VDR) are involved in the pathogenesis of inflammatory bowel disease (IBD) and bacterial infection. Claudin-2 is a junction protein that mediates paracellular water transport in epithelia. Elevation of Claudin-2 is associated with active IBD. However, VDR involved in epithelial junctions under inflammation and infection remains largely unknown. We investigated the mechanisms on how VDR and Claudin-2 are related in inflamed states.

METHODS

Using cultured VDR-/- enteroids, human intestinal epithelial cells, VDR-/- mice with Salmonella- or DSS-colitis, and human IBD samples, we investigated the mechanisms how VDR and Claudin-2 are related in inflamed states.

RESULTS

After Salmonella infection had taken place, we observed significantly enhanced Claudin-2 and an increased bacterial invasion and translocation. A lack of VDR regulation led to a robust increase of Claudin-2 at the mRNA and protein levels post-infection. In DSS-treated VDR-/- mice, Claudin-2 was significantly increased. Location and quantification of Claudin-2 protein in the mouse colons treated with DSS also confirmed these results. Inflammatory cytokines were significantly higher in the serum and mRNA levels in intestine, which are known to increase Claudin-2. Furthermore, in inflamed intestine of ulcerative colitis patients, VDR expression was low and Claudin-2 was enhanced. Mechanistically, we identified the enhanced Claudin-2 promoter activity through the binding sites of NF-κB and STAT in inflamed VDR-/- cells.

CONCLUSIONS

Our studies have identified a new role for intestinal epithelial VDR in regulating barrier functions in the context of infection and inflammation.

Impact of Paneth Cell Autophagy on Inflammatory Bowel Disease

Intestinal mucosal barrier, mainly consisting of the mucus layer and epithelium, functions in absorbing nutrition as well as prevention of the invasion of pathogenic microorganisms. Paneth cell, an important component of mucosal barrier, plays a vital role in maintaining the intestinal homeostasis by producing antimicrobial materials and controlling the host-commensal balance. Current evidence shows that the dysfunction of intestinal mucosal barrier, especially Paneth cell, participates in the onset and progression of inflammatory bowel disease (IBD). Autophagy, a cellular stress response, involves various physiological processes, such as secretion of proteins, production of antimicrobial peptides, and degradation of aberrant organelles or proteins. In the recent years, the roles of autophagy in the pathogenesis of IBD have been increasingly studied. Here in this review, we mainly focus on describing the roles of Paneth cell autophagy in IBD as well as several popular autophagy-related genetic variants in Penath cell and the related therapeutic strategies against IBD.

Association of Vitamin D receptor gene polymorphisms with metabolic syndrome and its components among adult Arabs from the United Arab Emirates

AIMS

The aim was to investigate relationships of Vitamin D receptor gene (VDR) polymorphisms to the components of MetS among Arabs adult residing in the United Arab Emirates.

METHODS

A cross-sectional study of 198 Arabs adult (50 males and 148 females). Serum levels of glucose, vitamin D, HDL-C, and TG, and blood pressure were measured. FokI, BsmI & TaqI genotyping of VDR were investigated using PCR-RFLP technique.

RESULTS

Age of the participants was 21(9) years with a BMI of 26.8(7.8) kg/m². About 15% had MetS with serum vitamin D levels of 25.5(18.2) nmol/L. VDR genotyping yielded: FokI: 57.1% FF and 38.9% Ff, BsmI: 29.8% bb and 51.5% Bb, while TaqI showed 39.4% TT and 43.4% Tt. The ff carriers had higher total cholesterol [174(12.4) mg/dl] than FF and Ff genotypes. Bb carriers showed higher BMI and LDL-C than BB and bb genotypes. In females, FokI VDR polymorphism showed significant association with systolic blood pressure (SBP) and F allele carriers were at higher risk of developing high SBP [x²=4.4, df1, OR=0.29 (95%CI: 0.087-0.98), p=0.035].

CONCLUSION

VDR gene polymorphisms were not associated with MetS, yet it may affect the severity of some of components of MetS, namely the association of BsmI with obesity, FokI and BsmI with dyslipidemia and FokI with SBP.

Identification of Novel Non-secosteroidal Vitamin D Receptor Agonists with Potent Cardioprotective Effects and devoid of Hypercalcemia

Vitamin D regulates many biological processes, but its clinical utility is limited by its hypercalcemic effect. Using a virtual screening platform to search novel chemical probes that activate the vitamin D signaling, we report discovery of novel non-steroidal small-molecule compounds that activate the vitamin D receptor (VDR), but are devoid of hypercalcemia. A lead compound (known as VDR 4-1) demonstrated potent transcriptional activities in a VDR reporter gene assay, and significantly ameliorated cardiac hypertrophy in cell culture studies and in animal models. VDR 4-1 also effectively suppressed secondary hyperparathyroidism in 1α-hydroxylase knockout mice. In contrast to 1α,25-dihydroxyvitamin D₃ (1,25-D₃ or calcitriol), a naturally occurring VDR agonist, VDR 4-1 therapy even at high doses did not induce hypercalcemia. These findings were accompanied by a lack of upregulation of calcium transport genes in kidney and in the gut providing a mechanism for the lack of hypercalcemia. Furthermore, VDR 4-1 therapy significantly suppressed cardiac hypertrophy and progression to heart failure in both vitamin D deficient and normal mice without inducing significant hypercalcemia. In conclusion, we have identified a unique VDR agonist compound with beneficial effects in mouse models of hyperparathyroidism and heart failure without inducing significant hypercalcemia.

Low vitamin D status and obesity: Role of nutritionist

Low vitamin D status and obesity have concomitantly reached epidemic levels worldwide. Up to now the direction of the association between low vitamin D status and obesity, the exact mechanisms responsible for this association and the clinical usefulness to increase vitamin D status for reducing adiposity still warrant further evaluation. The aim of the present review was to examine the current evidence linking low vitamin D status and obesity in relation to the role of the nutritionist. On the one side, considering obesity as a causal factor, low sun exposure in obese individuals due to their sedentary lifestyle and less outdoor activity, vitamin D sequestration in adipose tissue, and volumetric dilution of ingested or cutaneously synthesized vitamin D₃ in the large fat mass of obese patients, might represent some of the factors playing a major role in the pathogenesis of the low vitamin D status. On the other side, the expression of both vitamin D₃ receptors and enzymes responsible for vitamin D₃ metabolism in adipocytes depicted a role for the low vitamin D status per se in the development of obesity by modulating adipocyte differentiation and lipid metabolism. Nutritionists need to accurately address the aspects influencing the low vitamin D status in obesity and the vitamin D supplementation in obese individuals.

The Role of Vitamin D Receptor Polymorphisms on Dental Caries

OBJECTIVE

To determine the association between the ApaI, FokI, Cdx2 and TaqI polymorphisms of vitamin D receptor (VDR) gene in caries-active (high-moderate) and caries-free children.

STUDY DESIGN

A hundred and fifty children (75 males, 75 females, mean age: 10.19 ± 1.61 years) were included in the study. The subjects were divided into three groups as high caries risk group (DMFT, dft>4)(n=55), moderate caries risk group (DMFT, dft=1-4)(n=57) and caries-free group (n=38). From each individual, blood samples were collected and DNA was extracted. The VDR gene was genotyped for the polymorphisms ApaI, FokI, Cdx2 and TaqI using polymerase chain reaction and restriction fragment length polymorphism methods. All data were analyzed by chi-square test, Fisher's exact test and t test.

RESULTS

There was statistically significant difference in the frequency of TaqI genotypes (tt) between caries-active and caries-free children (p=0.029). No statistically significant differences were detected between ApaI, FokI, Cdx2 genotypes and dental caries.

CONCLUSION

In the future, VDR gene polymorphisms may be used as a marker for the identification of patients with high caries risk.

Characterization of cytochrome P450 CYP109E1 from Bacillus megaterium as a novel vitamin D3 hydroxylase

In this study the ability of CYP109E1 from Bacillus megaterium to metabolize vitamin D₃ (VD₃) was investigated. In an in vitro system using bovine adrenodoxin reductase (AdR) and adrenodoxin (Adx_4-108), VD₃ was converted by CYP109E1 into several products. Furthermore, a whole-cell system in B. megaterium MS941 was established. The new system showed a conversion of 95% after 24h. By NMR analysis it was found that CYP109E1 catalyzes hydroxylation of VD₃ at carbons C-24 and C-25, resulting in the formation of 24(S)-hydroxyvitamin D₃ (24S(OH)VD₃), 25-hydroxyvitamin D₃ (25(OH)VD₃) and 24S,25-dihydroxyvitamin D₃ (24S,25(OH)₂VD₃). Through time dependent whole-cell conversion of VD₃, we identified that the formation of 24S,25(OH)₂VD₃ by CYP109E1 is derived from VD₃ via the intermediate 24S(OH)VD₃. Moreover, using docking analysis and site-directed mutagenesis, we identified important active site residues capable of determining substrate specificity and regio-selectivity. HPLC analysis of the whole-cell conversion with the I85A-mutant revealed an increased selectivity towards 25-hydroxylation of VD₃ compared with the wild type activity, resulting in an approximately 2-fold increase of 25(OH)VD₃ production (45mgl^-1day^-1) compared to wild type (24.5mgl^-1day^-1).

Vitamin D and/or calcium deficient diets may differentially affect muscle fiber neuromuscular junction innervation

INTRODUCTION

There is evidence that supports a role for Vitamin D (Vit. D) in muscle. The exact mechanism by which Vit. D deficiency impairs muscle strength and function is not clear.

METHODS

Three-week-old mice were fed diets with varied combinations of Vit. D and Ca²⁺ deficiency. Behavioral testing, genomic and protein analysis, and muscle histology were performed with a focus on neuromuscular junction (NMJ) -related genes.

RESULTS

Vit. D and Ca²⁺ deficient mice performed more poorly on given behavioral tasks than animals with Vit. D deficiency alone. Genomic and protein analysis of the soleus and tibialis anterior muscles revealed changes in several Vit. D metabolic, NMJ-related, and protein chaperoning and refolding genes.

CONCLUSIONS

These data suggest that detrimental effects of a Vit. D deficient or a Vit. D and Ca²⁺ deficient diet may be a result of differential alterations in the structure and function of the NMJ and a lack of a sustained stress response in muscles. Muscle Nerve 54: 1120-1132, 2016.

New strategies in sport nutrition to increase exercise performance

Despite over 50 years of research, the field of sports nutrition continues to grow at a rapid rate. Whilst the traditional research focus was one that centred on strategies to maximise competition performance, emerging data in the last decade has demonstrated how both macronutrient and micronutrient availability can play a prominent role in regulating those cell signalling pathways that modulate skeletal muscle adaptations to endurance and resistance training. Nonetheless, in the context of exercise performance, it is clear that carbohydrate (but not fat) still remains king and that carefully chosen ergogenic aids (e.g. caffeine, creatine, sodium bicarbonate, beta-alanine, nitrates) can all promote performance in the correct exercise setting. In relation to exercise training, however, it is now thought that strategic periods of reduced carbohydrate and elevated dietary protein intake may enhance training adaptations whereas high carbohydrate availability and antioxidant supplementation may actually attenuate training adaptation. Emerging evidence also suggests that vitamin D may play a regulatory role in muscle regeneration and subsequent hypertrophy following damaging forms of exercise. Finally, novel compounds (albeit largely examined in rodent models) such as epicatechins, nicotinamide riboside, resveratrol, β-hydroxy β-methylbutyrate, phosphatidic acid and ursolic acid may also promote or attenuate skeletal muscle adaptations to endurance and strength training. When taken together, it is clear that sports nutrition is very much at the heart of the Olympic motto, Citius, Altius, Fortius (faster, higher, stronger).

Assessment of vitamin D receptors in alopecia areata and androgenetic alopecia

BACKGROUND

Alopecia areata (AA) is a frequent autoimmune disease, the pathogenesis of which is still unknown. Androgenetic alopecia (AGA) is a noncicatricial type of patterned hair loss. Expression of vitamin D receptors (VDRs) on keratinocytes is essential for maintenance of normal hair cycle, especially anagen initiation.

OBJECTIVE

To assess VDRs in the skin and blood of AA and AGA patients, in order to evaluate their possible role in these hair diseases.

METHODS

This study recruited 20 patients with AA, 20 patients with AGA, and 20 healthy controls. Blood samples and lesional scalp biopsies were taken from all participants for detection of VDR levels.

RESULTS

Serum and tissue VDR levels were lower in AA as well as AGA patients when compared to controls (P = 0.000). Serum and tissue VDR were positively correlated in each group. Tissue VDR was significantly lower in female patients with AA than males (P = 0.046) although serum and tissue VDR levels were significantly higher in female AGA patients than males (P = 0.004).

CONCLUSION

This study suggests an important role for VDR in the pathogenesis of AA and AGA through documenting lower serum and tissue VDR levels in AA and AGA patients in comparison with controls.

Calcitriol in Combination Therapy for Prostate Cancer: Pharmacokinetic and Pharmacodynamic Interactions

Epidemiological studies indicate that vitamin D insufficiency could have an etiological role in prostate cancer. In addition, calcitriol, used in combination with currently available drugs, has the potential to potentiate their anticancer effects or act synergistically by inhibiting distinct mechanisms involved in prostate cancer growth. Clinical data have not yet provided sufficient evidence to demonstrate benefit of vitamin D due to the limited and underpowered studies that have been published to date. Here, we review the preclinical and clinical studies that describe the activity of calcitriol, applied either alone or in combination and assessed the mechanistic basis of pharmacodynamic and pharmacokinetic interactions with calcitriol. Important considerations for calcitriol use in combination therapy with respect to safety and clinical outcomes have been discussed. Many of these combinations have therapeutic potential for the treatment of several cancer types and it is anticipated that future clinical research will put emphasis on well‑designed clinical trials to establish efficacy.

Vitamin D receptor pathway is required for probiotic protection in colitis

Low expression of vitamin D receptor (VDR) and dysfunction of vitamin D/VDR signaling are reported in patients with inflammatory bowel disease (IBD); therefore, restoration of VDR function to control inflammation in IBD is desirable. Probiotics have been used in the treatment of IBD. However, the role of probiotics in the modulation of VDR signaling to effectively reduce inflammation is unknown. We identified a novel role of probiotics in activating VDR activity, thus inhibiting inflammation, using cell models and VDR knockout mice. We found that the probiotics Lactobacillus rhamnosus strain GG (LGG) and Lactobacillus plantarum (LP) increased VDR protein expression in both mouse and human intestinal epithelial cells. Using the VDR luciferase reporter vector, we detected increased transcriptional activity of VDR after probiotic treatment. Probiotics increased the expression of the VDR target genes, such as antimicrobial peptide cathelicidin, at the transcriptional level. Furthermore, the role of probiotics in regulating VDR signaling was tested in vivo using a Salmonella-colitis model in VDR knockout mice. Probiotic treatment conferred physiological and histologic protection from Salmonella-induced colitis in VDR(+/+) mice, whereas probiotics had no effects in the VDR(-/-) mice. Probiotic treatment also enhanced numbers of Paneth cells, which secrete AMPs for host defense. These data indicate that the VDR pathway is required for probiotic protection in colitis. Understanding how probiotics enhance VDR signaling and inhibit inflammation will allow probiotics to be used effectively, resulting in innovative approaches to the prevention and treatment of chronic inflammation.

Breast Milk and Solid Food Shaping Intestinal Immunity

After birth, the intestinal immune system enters a critical developmental stage, in which tolerogenic and pro-inflammatory cells emerge to contribute to the overall health of the host. The neonatal health is continuously challenged by microbial colonization and food intake, first in the form of breast milk or formula and later in the form of solid food. The microbiota and dietary compounds shape the newborn immune system, which acquires the ability to induce tolerance against innocuous antigens or induce pro-inflammatory immune responses against pathogens. Disruption of these homeostatic mechanisms might lead to undesired immune reactions, such as food allergies and inflammatory bowel disease. Hence, a proper education and maturation of the intestinal immune system is likely important to maintain life-long intestinal homeostasis. In this review, the most recent literature regarding the effects of dietary compounds in the development of the intestinal immune system are discussed.

A therapeutic role for vitamin D on obesity-associated inflammation and weight-loss intervention

Vitamin D plays an essential role in the regulation of skeletal metabolism as well as calcium and phosphate homeostasis, while vitamin D receptor (VDR) regulates de novo lipid synthesis, thereby contributing to the development of obesity. Furthermore, obese individuals are at a greater risk for vitamin D deficiency which may increase the potential risk for chronic inflammation, insulin resistance, and metabolic syndrome. While acute exercise enhances the activation of inflammatory signaling pathways, chronic exercise training may attenuate elevated pro-inflammatory cytokine production, resulting in the improvement of cardiovascular and metabolic health in obese individuals. Supplementation with vitamin D coupled with exercise or mild caloric restriction has been shown to improve markers of fitness and inflammation as well as cholesterol. Therefore, this review primarily addresses the impact of vitamin D deficiency in obesity-related inflammatory imbalances and how exercise and weight-loss interventions may enhance the beneficial effects on vitamin D-mediated inflammation in obesity.

Intestinal epithelial vitamin D receptor deletion leads to defective autophagy in colitis

OBJECTIVE

Vitamin D and the vitamin D receptor (VDR) appear to be important immunological regulators of inflammatory bowel diseases (IBD). Defective autophagy has also been implicated in IBD, where interestingly, polymorphisms of genes such as ATG16L1 have been associated with increased risk. Although vitamin D, the microbiome and autophagy are all involved in pathogenesis of IBD, it remains unclear whether these processes are related or function independently.

DESIGN

We investigated the effects and mechanisms of intestinal epithelial VDR in healthy and inflamed states using cell culture models, a conditional VDR knockout mouse model (VDR(ΔIEC)), colitis models and human samples.

RESULTS

Absence of intestinal epithelial VDR affects microbial assemblage and increases susceptibility to dextran sulfate sodium-induced colitis. Intestinal epithelial VDR downregulates expressions of ATG16L1 and lysozyme, and impairs antimicrobial function of Paneth cells. Gain and loss-of-function assays showed that VDR levels regulate ATG16L1 and lysozyme at the transcriptional and translational levels. Moreover, low levels of intestinal epithelial VDR correlated with reduced ATG16L1 and representation by intestinal Bacteroides in patients with IBD. Administration of the butyrate (a fermentation product of gut microbes) increases intestinal VDR expression and suppresses inflammation in a colitis model.

CONCLUSIONS

Our study demonstrates fundamental relationship between VDR, autophagy and gut microbial assemblage that is essential for maintaining intestinal homeostasis, but also in contributing to the pathophysiology of IBD. These insights can be leveraged to define therapeutic targets for restoring VDR expression and function.

Abnormal calcium handling and exaggerated cardiac dysfunction in mice with defective vitamin d signaling

Aim

Altered vitamin D signaling is associated with cardiac dysfunction, but the pathogenic mechanism is not clearly understood. We examine the mechanism and the role of vitamin D signaling in the development of cardiac dysfunction.

Methods and Results

We analyzed 1α-hydroxylase (1α-OHase) knockout (1α-OHase^−/−) mice, which lack 1α-OH enzymes that convert the inactive form to hormonally active form of vitamin D. 1α-OHase^−/− mice showed modest cardiac hypertrophy at baseline. Induction of pressure overload by transverse aortic constriction (TAC) demonstrated exaggerated cardiac dysfunction in 1α-OHase^−/− mice compared to their WT littermates with a significant increase in fibrosis and expression of inflammatory cytokines. Analysis of calcium (Ca²⁺) transient demonstrated profound Ca²⁺ handling abnormalities in 1α-OHase^−/− mouse cardiomyocytes (CMs), and treatment with paricalcitol (PC), an activated vitamin D₃ analog, significantly attenuated defective Ca²⁺ handling in 1α-OHase^−/− CMs. We further delineated the effect of vitamin D deficiency condition to TAC by first correcting the vitamin D deficiency in 1α-OHase^−/− mice, followed then by either a daily maintenance dose of vitamin D or vehicle (to achieve vitamin D deficiency) at the time of sham or TAC. In mice treated with vitamin D, there was a significant attenuation of TAC-induced cardiac hypertrophy, interstitial fibrosis, inflammatory markers, Ca²⁺ handling abnormalities and cardiac function compared to the vehicle treated animals.

Conclusions

Our results provide insight into the mechanism of cardiac dysfunction, which is associated with severely defective Ca²⁺ handling and defective vitamin D signaling in 1α-OHase^−/− mice.

Vitamin D and the athlete: emerging insights

Interest in Vitamin D has risen considerably recently with many athletes now advised to take daily vitamin D supplements. The reason for this interest is partly not only attributed to the resurgence of the Vitamin D-deficient disease rickets but also due to the discovery of a Vitamin D receptor in many tissues suggesting a more global role for Vitamin D than previously considered. Unlike the other vitamins that are obtained through the diet, Vitamin D is unique since endogenous synthesis following ultraviolet B (UVB) exposure is the predominant route of entry into systemic circulation. Moreover, Vitamin D could be better classed as a seco-steroid, given that its structure is similar to that of a steroid, and its production is derived from a cholesterol precursor (7-dehydrocholesteol) in the skin. The classification of Vitamin D status is currently subject to considerable debate with many authors opposing governing body recommendations. Regardless of the suggested optimal concentration, there is now growing evidence to suggest that many athletes are in fact Vitamin D deficient, especially in the winter months largely as a consequence of inadequate sun exposure, combined with poor dietary practices, although the consequences of such deficiencies are still unclear in athletic populations. Impaired muscle function and reduced regenerative capacity, impaired immune function, poor bone health and even impaired cardiovascular function have all been associated with low Vitamin D in athletes, however, to date, the majority of studies on Vitamin D have described associations and much more research is now needed examining causation.

Calpain 1 inhibitor BDA-410 ameliorates α-klotho-deficiency phenotypes resembling human aging-related syndromes

Taking good care of elderly is a major challenge of our society, and thus identification of potential drug targets to reduce age-associated disease burden is desirable. α-klotho^-/- (α-kl) is a short-lived mouse model that displays multiple phenotypes resembling human aging-related syndromes. Such ageing phenotype of α-kl^-/- mice is associated with activation of a proteolytic enzyme, Calpain-1. We hypothesized that uncontrolled activation of calpain-1 might be causing age-related phenotypes in α-kl-deficient mice. We found that daily administration of BDA-410, a calpain-1 inhibitor, strikingly ameliorated multiple aging-related phenotypes. Treated mice showed recovery of reproductive ability, increased body weight, reduced organ atrophy, and suppression of ectopic calcifications, bone mineral density reduction, pulmonary emphysema and senile atrophy of skin. We also observed ectopic expression of FGF23 in calcified arteries of α-kl^-/- mice, which might account for the clinically observed association of increased FGF23 level with increased risk of cardiovascular mortality. These findings allow us to propose that modulation of calpain-1 activity is a potential therapeutic option for delaying age-associated organ pathology, particularly caused by the dysregulation of mineral ion homeostasis.

Testicular function and bone metabolism--beyond testosterone

Findings in the past few years have advanced understanding of the crosstalk between testis and bone and could contribute to defining an improved clinical approach to the biochemical diagnosis and therapeutic management of hypogonadism and male osteoporosis. This Review focuses on the Leydig cells of the testis. Other than being responsible for steroidogenesis and production of testosterone, the function of these cells is fundamental to bone health in at least two other ways: Leydig cells produce insulin-like 3 (INSL3), which has a role in osteoblast function, and they contribute to 25-hydroxylation of vitamin D. Impairment of testicular function leads to low levels of testosterone, INSL3 and 25-hydroxyvitamin D and consequently to an increased risk of osteopenia and osteoporosis.

1,25-dihydroxyvitamin D3 protects against macrophage-induced activation of NFκB and MAPK signalling and chemokine release in human adipocytes

Increased accumulation of macrophages in adipose tissue in obesity is linked to low-grade chronic inflammation, and associated with features of metabolic syndrome. Vitamin D3 may have immunoregulatory effects and reduce adipose tissue inflammation, although the molecular mechanisms remain to be established. This study investigated the effects of vitamin D3 on macrophage-elicited inflammatory responses in cultured human adipocytes, particularly the signalling pathways involved. Macrophage-conditioned (MC) medium (25% with adipocyte maintenance media) markedly inhibited protein expression of the nuclear factor-κB (NFκB) subunit inhibitor κBα (IκBα) (71%, P<0.001) and increased NFκB p65 (1.5-fold, P = 0.026) compared with controls. Treatment with 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) abolished macrophage-induced activation of NFκB signalling by increasing IκBα expression (2.7-fold, P = 0.005) and reducing NFκB p65 phosphorylation (68%; P<0.001). The mitogen-activated protein kinase (MAPK) signalling was activated by MC medium, which was also blunted by 1,25(OH)2D3 with a downregulation of phosphorylated p38 MAPK (32%, P = 0.005) and phosphorylated Erk1/2 (49%, P = 0.001). Furthermore, MC medium (12.5% or 25%) dose-dependently upregulated secretion of key proinflammatory chemokines/cytokines (22-368-fold; all P<0.001) and this was significantly decreased by 1,25(OH)2D3: IL-8 (61% and 31%, P<0.001), MCP-1 (37%, P<0.001 and 36%, P = 0.002), RANTES (78% and 62%, P<0.001) and IL-6 (29%, P<0.001 and 34%, P = 0.019). Monocyte migration-elicited by adipocytes treated with 1,25(OH)2D3 was also reduced (up to 25%, P<0.001). In conclusion, vitamin D3 could be anti-inflammatory in adipose tissue, decreasing macrophage-induced release of chemokines and cytokines by adipocytes and the chemotaxis of monocytes. Our data suggests these effects are mediated by inhibition of the NFκB and MAPK signalling pathways.

Inhibitory effect of tianeptine on catagen induction in alopecia areata-like lesions induced by ultrasonic wave stress in mice

BACKGROUND

Alopecia areata (AA) is characterized by rapid and complete hair loss in one or multiple areas of the scalp. Stress is an important triggering factor in AA.

AIM

To identify the inhibitory effect of tianeptine on catagen induction in C57BL/6 mice with AA-like lesions induced by ultrasonic wave stress (UWS).

METHODS

The mice were divided into four groups. Group 1 received oral tianeptine before and after UWS; group 2 received oral tianeptine only after UWS; group 3 was given UWS treatment only; and group 4 (negative control group) was not given any treatment. Phototrichigraphy and dermatoscopy were used for assessment. Histological analysis was performed using haematoxylin and eosin, toluidine blue, Masson trichrome and Verhoeff-van Gieson stains. Immunohistochemical analysis was also performed. The level of apoptosis and expression of neuropeptides in the skin were assessed by terminal deoxynucleotidyl transferase dUTP nick end labelling and immunofluorescence assays.

RESULTS

Mice in group 1 had an increased rate of hair growth and greater hair-shaft thickness compared with mice in groups 2 and 3. In addition, mice in group 1 had a higher number of anagen hair follicles, increased synthesis of collagen and elastic fibres, decreased mast-cell degranulation, reduction in cell apoptosis in hair follicles, and recovery of vitamin D receptor expression. Expression of neuropeptides (substance P, calcitonin gene-related peptide) was not altered.

CONCLUSIONS

Tianeptine might play a role in suppressing catagen induction in a stress-induced AA mouse model.

HIV compromises integrity of the podocyte actin cytoskeleton through downregulation of the vitamin D receptor

Alterations in the podocyte actin cytoskeleton have been implicated in the development of proteinuric kidney diseases. In the present study, we evaluated the effect of HIV on the podocyte actin cytoskeleton and the mechanism involved. We hypothesized that HIV may be compromising the actin cytoskeleton via downregulation of the vitamin D receptor (VDR) of conditionally immortalized differentiated human podocytes (CIDHPs). HIV-transduced podocytes (HIV/CIDHPs) not only displayed downregulation of VDR but also showed activation of the renin-angiotensin system (RAS) in the form of enhanced expression of renin and increased production of ANG II. Moreover, CIDHPs lacking VDR displayed enhanced ANG II production, and treatment of HIV/CIDHPs with EB1089 (vitamin D3; VD) attenuated ANG II production. HIV/CIDHPs as well as ANG II-treated CIDHPs exhibited enhanced expression of cathepsin (CTS) L. Additionally, losartan (an ANG II type I receptor blocker) inhibited both HIV- and ANG II-induced podocyte cathepsin L expression. Furthermore, VD downregulated HIV-induced podocyte CTSL expression. Both losartan and free radical scavengers attenuated HIV- and ANG II-induced podocyte reactive oxygen species (ROS) generation. HIV also led to cytosolic CTSL accumulation through enhancement of podocyte lysosomal membrane permeabilization; on the other hand, VD, losartan, and superoxide dismutase (SOD) attenuated HIV-induced enhanced podocyte cytosolic CTSL accumulation. Morphological evaluation of HIV/CIDHPs revealed sparse actin filaments and attenuated expression of dynamin. Interestingly, podocytes lacking CTSL displayed enhanced dynamin expression, and HIV/CIDHPs expressing CTSL exhibited downregulation of dynamin. These findings indicate that HIV-induced downregulation of podocyte VDR and associated RAS activation and cytosolic CTSL accumulation compromised the actin cytoskeleton.

Vitamin D, Vitamin D Receptor, and Tissue Barriers

Tissue barriers are critical in the pathogenesis of human diseases, such as atopic dermatitis, inflammatory bowel diseases and various cancers. Preserving or restoring barrier functions of the epithelia cells is a therapeutic strategy to prevent and treat the illness. Mounting evidence indicates that vitamin D and the vitamin D receptor (VDR) play key roles in the pathogenesis of human diseases. In particular, we note an interesting link between vitamin D/VDR signaling and tissue barriers. In the current review, we summarize the recent progress on vitamin D and cell junction complexes. We focus on the functions of VDR and VDR-associated intracellular junction proteins, such as β-catenin and claudins. We also discuss the potential therapeutic functions of vitamin D in treating defective tissue barriers that involve skin, intestine, lung, kidney and other organs. However, the mechanisms for the vitamin D/VDR signaling in tissue barriers remain largely unknown. Further studies on vitamin D/VDR’s multiple functions in physiological models will suggest new therapeutic targets for prevention and treatment diseases with defective barrier functions.

Diversity and substrate specificity in the structures of steroidogenic cytochrome P450 enzymes

Mammalian cytochrome P450 (CYP) comprise a large group of enzymes that play many important roles in the biosynthesis of steroid hormones and vitamins. In addition, they participate in the metabolism of drugs and xenobiotics. All known mammalian CYP enzymes are membrane-associated proteins, which complicated their X-ray crystallographic analysis. In recent years, however, significant progress has been made in the X-ray crystallographic analysis of mammalian CYP enzymes involved in the steroid hormone and vitamin D(3) metabolism. The knowledge from three-dimensional structures of mammalian CYP enzymes will benefit drug discovery and development.

Vitamin D signalling in adipose tissue

Vitamin D deficiency and the rapid increase in the prevalence of obesity are both considered important public health issues. The classical role of vitamin D is in Ca homoeostasis and bone metabolism. Growing evidence suggests that the vitamin D system has a range of physiological functions, with vitamin D deficiency contributing to the pathogenesis of several major diseases, including obesity and the metabolic syndrome. Clinical studies have shown that obese individuals tend to have a low vitamin D status, which may link to the dysregulation of white adipose tissue. Recent studies suggest that adipose tissue may be a direct target of vitamin D. The expression of both the vitamin D receptor and 25-hydroxyvitamin D 1α-hydroxylase (CYP27B1) genes has been shown in murine and human adipocytes. There is evidence that vitamin D affects body fat mass by inhibiting adipogenic transcription factors and lipid accumulation during adipocyte differentiation. Some recent studies demonstrate that vitamin D metabolites also influence adipokine production and the inflammatory response in adipose tissue. Therefore, vitamin D deficiency may compromise the normal metabolic functioning of adipose tissue. Given the importance of the tissue in energy balance, lipid metabolism and inflammation in obesity, understanding the mechanisms of vitamin D action in adipocytes may have a significant impact on the maintenance of metabolic health. In the present review, we focus on the signalling role of vitamin D in adipocytes, particularly the potential mechanisms through which vitamin D may influence adipose tissue development and function.

DDX5 is a multifunctional co-activator of steroid hormone receptors

The vitamin D receptor (VDR), an evolutionarily conserved member of the nuclear receptor superfamily, links the metabolically activated vitamin D ligand, calcitriol, with its vitamin D-responsive target genes that are implicated in diverse physiological processes. By genome-wide protein-protein interaction screening of a keratinocyte cDNA library using VDR as bait, we found that the DEAD box RNA helicase p68, also referred to as DDX5, directly interacts with VDR. Domain analysis reveals that the ligand-binding domain of VDR is responsible for the binding, an interaction typical of NR co-activators. Interestingly, the VDR interacting domain of DDX5 lacks a LXXLL-motif and interaction analysis of helix 12 VDR mutants E420K, E420Q and L417S, known to decrease binding affinity of LxxLL motif-containing co-activators showed no change in their interactions. As further support that this novel interactor might be involved in vitamin D-stimulated transcriptional regulation, we demonstrate that VDR and DDX5 co-localize within the nuclei of HaCaT keratinocytes and sub-cellular protein fractions. In vivo validation studies demonstrate, that overexpression of DDX5 has the capability to enhance both, calcitriol-dependent transcription of known response genes and an extrachromosomal DR3-type reporter response. In agreement with this, shRNA based knock-down of DDX5 in keratinocytes compensates for this particular response. Finally, our findings reveal parallels between the VDR-DDX5 interaction and the well-characterized interaction between DDX5 and human estrogen receptor α and the androgen receptor, thus underscoring the physiological significance of the novel protein-protein interaction.

Molecular aspects of vitamin D anticancer activity

Environment may influence the development and prevention of cancer. Calcitriol has been associated with calcium homeostasis regulation. Many epidemiological, biochemical, and genetic studies have shown non-classic effects of vitamin D, such as its involvement in the progression of different cancers. Although vitamin D induces cellular arrest, triggers apoptotic pathways, inhibits angiogenesis, and alters cellular adhesion, the precise mechanisms of its action are still not completely established. This article will present a revision about the molecular aspects proposed to be involved in the anticancer action of calcitriol. Adequate levels of vitamin D to prevent cancer development will also be discussed.

The SLCO1A2 gene, encoding human organic anion-transporting polypeptide 1A2, is transactivated by the vitamin D receptor

Organic anion-transporting polypeptide 1A2 (OATP1A2) (gene symbol, SLCO1A2) mediates cellular uptake of a wide range of endogenous substrates, as well as drugs and xenobiotics. OATP1A2 is expressed in several tissues, including apical membranes of small intestinal epithelial cells. Given its role in intestinal drug absorption, a detailed analysis of the mechanisms that regulate SLCO1A2 gene expression is potentially of great pharmacological relevance. We show here that treatment of human intestine-derived Caco-2 cells with vitamin D(3) markedly increased endogenous OATP1A2 mRNA and protein levels. Suppression of endogenous vitamin D receptor (VDR) expression with siRNAs significantly reduced this induction. Two alternative promoter regions exist in genomic databases for the SLCO1A2 gene. One putative VDR response element (VDRE) that was predicted to interact efficiently with VDR-retinoid X receptor α (RXRα) was identified in silico within SLCO1A2 promoter variant 1. This VDRE served as a strong binding site for the recombinant VDR-RXRα heterodimers in vitro and was potently activated by VDR in the presence of vitamin D(3) in heterologous promoter assays. In reporter assays using native promoter constructs, SLCO1A2 promoter variant 1 was strongly induced by VDR, and site-directed mutagenesis of a single VDRE within this region abolished this activation. Native VDR-RXRα also interacted with this element both in vitro and in living cells. We showed that expression of the SLCO1A2 gene is induced by vitamin D(3) at the transcriptional level through the VDR. Our results suggest that pharmacological administration of vitamin D(3) may allow modulation of intestinal absorption of OATP1A2 transport substrates.

The role of vitamin D receptor mutations in the development of alopecia

Hereditary Vitamin D Resistant Rickets (HVDRR) is a rare disease caused by mutations in the vitamin D receptor (VDR). The consequence of defective VDR is the inability to absorb calcium normally in the intestine. This leads to a constellation of metabolic abnormalities including hypocalcemia, secondary hyperparathyroidism and hypophosphatemia that cause the development of rickets at an early age in affected children. An interesting additional abnormality is the presence of alopecia in some children depending on the nature of the VDR mutation. The data indicate that VDR mutations that cause defects in DNA binding, RXR heterodimerization or absence of the VDR cause alopecia while mutations that alter VDR affinity for 1,25(OH)(2)D(3) or disrupt coactivator interactions do not cause alopecia. The cumulative findings indicate that hair follicle cycling is dependent on unliganded actions of the VDR. Further research is ongoing to elucidate the role of the VDR in hair growth and differentiation.

Vitamin D deficiency promotes skeletal muscle hypersensitivity and sensory hyperinnervation

Musculoskeletal pain affects nearly half of all adults, most of whom are vitamin D deficient. Previous findings demonstrated that putative nociceptors ("pain-sensing" nerves) express vitamin D receptors (VDRs), suggesting responsiveness to 1,25-dihydroxyvitamin D. In the present study, rats receiving vitamin D-deficient diets for 2-4 weeks showed mechanical deep muscle hypersensitivity, but not cutaneous hypersensitivity. Muscle hypersensitivity was accompanied by balance deficits and occurred before onset of overt muscle or bone pathology. Hypersensitivity was not due to hypocalcemia and was actually accelerated by increased dietary calcium. Morphometry of skeletal muscle innervation showed increased numbers of presumptive nociceptor axons (peripherin-positive axons containing calcitonin gene-related peptide), without changes in sympathetic or skeletal muscle motor innervation. Similarly, there was no change in epidermal innervation. In culture, sensory neurons displayed enriched VDR expression in growth cones, and sprouting was regulated by VDR-mediated rapid response signaling pathways, while sympathetic outgrowth was not affected by different concentrations of 1,25-dihydroxyvitamin D. These findings indicate that vitamin D deficiency can lead to selective alterations in target innervation, resulting in presumptive nociceptor hyperinnervation of skeletal muscle, which in turn is likely to contribute to muscular hypersensitivity and pain.

Regulating the levels of key factors in cell cycle and DNA repair: new pathways revealed by lamins

Spatial and temporal organization of the genome represents an additional step in the regulation of nuclear functions. The nuclear lamina, a polymeric meshwork formed by lamins (A/C and B type) and lamin-associated proteins, plays a key role in the maintenance of genome localization, structure and function. Specifically, mutations in the LMNA gene encoding lamins A/C or changes in its expression, either upregulation or silencing, are associated with defects in DNA replication, transcription and repair, as well as alterations in epigenetic modifications of chromatin. These data, together with the fact that defects in A-type lamins are associated with a whole variety of degenerative disorders, premature aging syndromes and cancer, support the notion that these proteins operate as caretakers of the genome. However, our understanding of their functions is limited due to the lack of well-defined mechanisms behind the genomic instability observed in lamin-related diseases. Here, we summarize our recent discovery of new pathways that are affected by the loss of A-type lamins. In particular, we found that A-type lamins control transcription and degradation of proteins with key roles in cell cycle regulation and DNA double-strand breaks (DSBs) repair by non-homologous end-joining (NHEJ) and homologous-recombination (HR). Importantly, the proteins regulated by A-type lamins--Rb family members, 53BP1, BRCA1 and RAD51--exert tumor suppressor functions, with their loss being associated with cancer susceptibility. Moreover, our studies revealed novel pathways that contribute to genomic instability and that can be activated in disease states independent of the status of A-type lamins.

Probiotics, nuclear receptor signaling, and anti-inflammatory pathways

There is increased investigation of the human microbiome as it relates to health and disease. Dysbiosis is implicated in various clinical conditions including inflammatory bowel disease (IBD). Probiotics have been explored as a potential treatment for IBD and other diseases. The mechanism of action for probiotics has yet to be fully elucidated. This paper discusses novel mechanisms of action for probiotics involving anti-inflammatory signaling pathways. We highlight recent progress in probiotics and nuclear receptor signaling, such as peroxisome-proliferator-activated receptor gamma (PPARγ) and vitamin D receptor (VDR). We also discuss future areas of investigation.

Bone mineral density and testicular failure: evidence for a role of vitamin D 25-hydroxylase in human testis

WORKING HYPOTHESIS

Mutations in the CYP2R1 gene, highly expressed in the testis and encoding vitamin D 25-hydroxylase, result in a vitamin D deficiency and a defective calcium homeostasis leading to rickets.

OBJECTIVE

Our aim was to investigate CYP2R1 expression in pathological testis samples and relate this to vitamin D metabolism in testiculopathic patients. DESIGN, PATIENTS, SETTING: Testis samples for in vitro study and 98 young men were transversally evaluated at Padova's Center for Male Gamete Cryopreservation.

METHODS

CYP2R1 mRNA expression and protein production were evaluated by quantitative RT-PCR, Western blot analysis, and immunofluorescence. Hormonal and bone-marker levels, and bone densitometry by dual-energy x-ray absorptiometry, were determined in patients with Sertoli-cell-only syndrome and severe hypospermatogenesis.

RESULTS

We found a lower gene and protein expression of CYP2R1 in samples with hypospermatogenesis and Sertoli-cell-only syndrome (P < 0.05) and a colocalization with INSL-3, a Leydig cell marker, at immunofluorescence. In all testiculopathic patients 25-hydroxyvitamin D levels were significantly lower and PTH levels higher compared to controls (P < 0.05). Furthermore, testiculopathic patients showed osteopenia and osteoporosis despite normal testosterone levels compared with controls both with increased bone-marker levels and altered dual-energy x-ray absorptiometry in the femoral neck and lumbar spine (for all parameters, P < 0.05).

CONCLUSIONS

Our data show an association between testiculopathy and alteration of the bone status, despite unvaried androgen and estrogen levels and no other evident cause of vitamin D reduction. Further studies in larger cohorts are needed to confirm our results.