Calcitriol is a positive effector of adipose differentiation in the OB 17 cell line: relationship with the adipogenic action of triiodothyronine

Murine in vitro cellular models to better understand adipogenesis and its potential applications

Adipogenesis has been extensively studied using in vitro models of cellular differentiation, enabling long-term regulation of fat cell metabolism in human adipose tissue (AT) material. Many studies promote the idea that manipulation of this process could potentially reduce the prevalence of obesity and its related diseases. It has now become essential to understand the molecular basis of fat cell development to tackle this pandemic disease, by identifying therapeutic targets and new biomarkers. This review explores murine cell models and their applications for study of the adipogenic differentiation process in vitro. We focus on the benefits and limitations of different cell line models to aid in interpreting data and selecting a good cell line model for successful understanding of adipose biology.

Physiological functions of Vitamin D in adipose tissue

Adipose tissue has long been identified as the major site of vitamin D storage. Recent studies have demonstrated that VDR and vitamin D metabolizing enzymes are expressed in adipocytes. Furthermore, it has been shown that vitamin D regulates adipogenic gene expression as well as adipocyte apoptosis. Vitamin D is active in adipocytes at all levels. It interacts with membrane receptors, adaptor molecules, and nuclear coregulator proteins. Several functions of unliganded nVDR were discovered by studying human samples from patients having hereditary vitamin D resistant rickets, transgenic mice overexpressing the VDR and VDR knockout mice. Through its genomic action, vitamin D participates in the regulation of energy metabolism by controlling the expression of uncoupling proteins. In vitro, vitamin D stimulates lipogenesis and inhibits lipolysis by interacting with mVDR. mVDR is present in caveolae of the plasma membrane and is the same as the classic nVDR. In addition, vitamin D affects directly the expression of the appetite regulating hormone, leptin. Some researchers reported also that vitamin D regulates the expression of the insulin sensitizing hormone, adiponectin. Vitamin D reduced cytokine release and adipose tissue inflammation through the inhibition of NF-κB signaling. Scientific research investigating the role of adipose tissue resident immune cells in the pathogenesis of obesity-associated inflammation is scarce. Obesity is associated with vitamin D deficiency. However there is no scientific evidence to prove that vitamin D deficiency predispose to obesity. Vitamin D supplementation may prevent obesity but it does not lead to weight loss in obese subjects.

Association of serum 25-hydroxyvitamin D and serum total cholesterol with depressive symptoms in Korean adults: the Fifth Korean National Health and Nutrition Examination Survey (KNHANES V, 2010–2012)

Objective

To examine the hypothesis that the association between vitamin D deficiency and depressive symptoms is dependent upon total cholesterol level in a representative national sample of the South Korean population.

Design

This was a population-based cross-sectional study.

Setting

The Fifth Korean National Health and Nutrition Examination Survey (KNHANES V, 2010–2012).

Subjects

We included 7198 adults aged 20–88 years.

Results

The incidence of depressive symptoms in individuals with vitamin D deficiency (serum 25-hydroxyvitamin D<20 ng/ml) was 1·54-fold (95 % CI 1·20, 1·98) greater than in individuals without vitamin D deficiency (serum 25-hydroxyvitamin D ≥20 ng/ml). The relationship was stronger in individuals with normal-to-borderline serum total cholesterol (serum total cholesterol<240 mg/dl; OR=1·60; 95 % CI 1·23, 2·08) and non-significant in individuals with high serum total cholesterol (OR=0·97; 95 % CI 0·52, 1·81) after adjustment for confounding variables (age, sex, BMI, alcohol consumption, smoking status, regular exercise, income level, education level, marital status, changes in body weight, perceived body shape, season of examination date and cholesterol profiles).

Conclusions

The association between vitamin D deficiency and depressive symptoms was weakened by high serum total cholesterol status. These findings suggest that both vitamin D and total cholesterol are important targets for the prevention and treatment of depression.

Causes of Vitamin D Deficiency and Effect of Vitamin D Supplementation on Metabolic Complications in Obesity: a Review

Obese subjects are often characterized by low plasma 25-hydroxy-vitamin D (25OHD) levels. Many explanations for this association have been proposed. Low plasma 25OHD is associated with obesity-related comorbidities such as insulin resistance, type 2 diabetes mellitus, and low-grade inflammation. In this review, we discuss the proposed mechanisms for low 25OHD in obesity and explore the results of recent RCTs on vitamin D (VD) supplementation on obesity and its metabolic complications such as insulin resistance and type 2 diabetes. Although the results from these clinical randomized controlled trials vary, the general picture is that VD treatment of obese individuals does not seem to be an effective treatment of obesity-related metabolic complications.

Genetic variation in the vitamin D receptor gene and vitamin D serum levels in Egyptian women with polycystic ovary syndrome

Obesity, insulin resistance, and hyperandrogenism are considered crucial parameters of polycystic ovary syndrome (PCOS) which might be related to vitamin D metabolism. The aim of this study was to investigate the associations between polymorphisms (TaqI and ApaI) in the vitamin D receptor gene (VDR) and PCOS among Egyptian women. We aimed also to elucidate the impact of these polymorphisms on vitamin D level, hormonal and metabolic parameters of PCOS. One hundred and fifty Egyptian women with PCOS and 150 unrelated controls were enrolled in this study. Polymorphisms of VDR Taq-I T/C (rs731236) and Apa-I A/C (rs7975232) gene were genotyped using polymerase chain reaction restriction fragment length polymorphism (PCR–RFLP). Serum 25 hydroxy vitamin D [25(OH) D] levels were measured by high-performance liquid chromatography. PCOS women had significantly lower levels of 25(OH) D compared to healthy women. Our results revealed that Taq-I CC genotype and C allele were associated with increased risk of PCOS, while the Apa-I polymorphism was not. Haplotype Taq-I C/ Apa-I C was associated with a higher PCOS risk more than controls. Moreover, there was a significant decrease of 25(OH) D levels in carriers of haplotype Taq-I C/ Apa-I C (with variant alleles) compared to the non-carriers. Results showed also that there was an obesity- VDR Taq-I genotypes interactions. These results suggested that, VDR Taq-I gene polymorphism is associated with increased risk of PCOS in Egyptian women.

Induction of STEAP4 correlates with 1,25-dihydroxyvitamin D3 stimulation of adipogenesis in mesenchymal progenitor cells derived from human adipose tissue

The vitamin D receptor (VDR) is expressed in human adipocytes and is transiently induced during early adipogenesis in mesenchymal progenitor cell models. VDR null mice exhibit enhanced energy expenditure and reduced adiposity even when fed high fat diets. Adipocyte-specific transgenic-expression of human VDR in mice enhances adipose tissue mass, indicating that VDR activation in adipocytes enhances lipid storage in vivo. In these studies, we conducted genomic profiling and differentiation assays in primary cultures of human adipose-derived mesenchymal progenitor cells to define the role of the VDR and its ligand 1,25-dihydroxyvitamin D3 (1,25D) in adipogenesis. In the presence of adipogenic media, 1,25D promoted lipid accumulation and enhanced the expression of FABP4, FASN, and PPARγ. Mesenchymal cells derived from 6-month old VDR null mice exhibited impaired adipogenesis ex vivo but differentiation was restored by stable expression of human VDR. STEAP4, a gene that encodes a metalloreductase linked to obesity, insulin sensitivity, metabolic homeostasis and inflammation, was highly induced in human adipose cells differentiated in the presence of 1,25D but was minimally affected by 1,25D in undifferentiated precursors. These studies provide a molecular basis for recent epidemiological associations between vitamin D status, body weight and insulin resistance which may have relevance for prevention or treatment of metabolic syndrome and obesity.

Hypovitaminosis D and Obesity - Coincidence or Consequence?

Vitamin D has attracted much scientific interest in recent years, mostly due to its newly described roles in metabolism regulation and cell proliferation. Along with hypovitaminosis D, the incidence of obesity has risen and has become a public health concern. The association between these two conditions is not merely coincidence and is being deeply investigated regarding its prevalence, mechanism, and even a possible causal relation. The data are still inconclusive but there is important evidence indicating that vitamin D is involved with fat accumulation, the responsible mechanism however still the principal question. The three main hypotheses are: adipose tissue sequestration, genetic modulation, such as polymorphism of the vitamin D receptor (VDR), or an organism evolutionary adaptation to cold weather. In conclusion, more evidence is needed to determine what the correct direction of this connection is and the possible therapeutic strategies of vitamin D replenishment and obesity control.

Calcitriol imparts neuroprotection in vitro to midbrain dopaminergic neurons by upregulating GDNF expression

During development a tightly controlled signaling cascade dictates the differentiation, maturation and survival of developing neurons. Understanding this signaling mechanism is important for developing therapies for neurodegenerative illnesses. In previous work we have sought to understand the complex signaling pathways responsible for the development of midbrain dopamine neurons using a proteomic approach. One protein we have identified as being expressed in developing midbrain tissue is the vitamin D receptor. Therefore we investigated the effect of the biologically active vitamin D3 metabolite, calcitriol, on primary fetal ventral mesencephalic cultures of dopamine neurons. We observed a dose responsive increase in numbers of rat primary dopamine neurons when calcitriol was added to culture media. Western blot data showed that calcitriol upregulated the expression of glial derived neurotrophic factor (GDNF). Blocking GDNF signaling could prevent calcitriol's ability to increase numbers of dopamine neurons. An apoptosis assay and cell birth dating experiment revealed that calcitriol increases the number of dopamine neurons through neuroprotection and not increased differentiation. This could have implications for future neuroprotective PD therapies.

Epigenetic mechanisms in anti-cancer actions of bioactive food components--the implications in cancer prevention

The hallmarks of carcinogenesis are aberrations in gene expression and protein function caused by both genetic and epigenetic modifications. Epigenetics refers to the changes in gene expression programming that alter the phenotype in the absence of a change in DNA sequence. Epigenetic modifications, which include amongst others DNA methylation, covalent modifications of histone tails and regulation by non-coding RNAs, play a significant role in normal development and genome stability. The changes are dynamic and serve as an adaptation mechanism to a wide variety of environmental and social factors including diet. A number of studies have provided evidence that some natural bioactive compounds found in food and herbs can modulate gene expression by targeting different elements of the epigenetic machinery. Nutrients that are components of one-carbon metabolism, such as folate, riboflavin, pyridoxine, cobalamin, choline, betaine and methionine, affect DNA methylation by regulating the levels of S-adenosyl-L-methionine, a methyl group donor, and S-adenosyl-L-homocysteine, which is an inhibitor of enzymes catalyzing the DNA methylation reaction. Other natural compounds target histone modifications and levels of non-coding RNAs such as vitamin D, which recruits histone acetylases, or resveratrol, which activates the deacetylase sirtuin and regulates oncogenic and tumour suppressor micro-RNAs. As epigenetic abnormalities have been shown to be both causative and contributing factors in different health conditions including cancer, natural compounds that are direct or indirect regulators of the epigenome constitute an excellent approach in cancer prevention and potentially in anti-cancer therapy.

The relationship of vitamin D with non-traditional risk factors for cardiovascular disease in subjects with metabolic syndrome

INTRODUCTION

Several studies implicate an inverse relationship between 25-hydroxy vitamin D (25(OH)Vit D) serum levels and metabolic syndrome (MetS). We sought to investigate a possible relationship between 25(OH)Vit D and emerging risk factors associated with MetS, such as small dense low-density lipoprotein cholesterol (sdLDL-C) concentration, lipoprotein-associated phospholipase A(2) (Lp-PLA(2)) activity and high-sensitivity C-reactive protein (hsCRP) levels.

MATERIAL AND METHODS

We studied 110 consecutive otherwise healthy individuals. Of these, 52 were diagnosed with MetS and 58 who did not meet the MetS criteria served as controls. Low-density lipoprotein (LDL) subclass analysis was performed by polyacrylamide gel electrophoresis. Lp-PLA(2) activity was determined in total plasma by the trichloroacetic acid precipitation procedure. Serum 25(OH)Vit D was determined quantitatively by an enzyme immunoassay method.

RESULTS

Metabolic syndrome subjects had significantly lower 25(OH)Vit D levels (11.8 [0.6-48.3] ng/ml; 29.5 [1.5-120.75] nmol/l) compared with controls (17.2 [4.8-62.4] ng/ml; 43 [12-156] nmol/l, p = 0.027). Univariate regression analysis showed that 25(OH)Vit D concentration was inversely related to triglycerides (r= - 0.416, p = 0.003) and sdLDL-C (r= - 0.305, p = 0.004). There was no association of 25(OH)Vit D with waist circumference, blood pressure, high-density lipoprotein cholesterol (HDL-C), fasting glucose, Lp-PLA(2) and hsCRP. In multivariate regression analysis the relationship between 25(OH)Vit D and sdLDL-C became insignificant when triglycerides were included in the model.

CONCLUSIONS

Subjects with MetS exhibit lower 25(OH)Vit D serum levels compared with non-MetS individuals. Low 25(OH)Vit D is associated with higher sdLDL-C levels possibly through elevated triglycerides. No association between 25(OH)Vit D and Lp-PLA(2) or hsCRP was found.

Vitamin D and metabolic health with special reference to the effect of vitamin D on serum lipids

Considering that the vitamin D receptor as well as the 1-α-hydroxylase enzyme that converts 25-hydroxyvitamin D (25(OH)D) to its active form 1,25-dihydroxyvitamin D have been found in tissues throughout the body, it is likely that vitamin D is important for more than the calcium balance. Accordingly, low serum levels of 25(OH)D have been associated with mortality, cardiovascular disease, type 2 diabetes, hypertension and obesity. Low serum levels of 25(OH)D have also been associated with an unfavourable lipid profile, which could possible explain the relation with cardiovascular disease and mortality. However, the relation between vitamin D and lipids have so far received little attention and is therefore the main focus of the present review. A PubMed search identified 22 cross-sectional studies where serum levels of 25(OH)D and lipids were related and that included a minimum of 500 subjects, and 10 placebo-controlled double-blind intervention studies with vitamin D where more than 50 subjects were included. In all the cross-sectional studies serum 25(OH)D was positively associated with high-density lipoprotein cholesterol (HDL-C) resulting in a favourable low-density lipoprotein cholesterol (LDL-C) (or total cholesterol) to HDL-C ratio. There was also a uniform agreement between studies on a negative relation between serum 25(OH)D and triglycerides (TG). On the other hand, the intervention studies gave divergent results, with some showing a positive and some a negative effect of vitamin D supplementation. However, none of the intervention studies were specifically designed for evaluating the relation between vitamin D and lipids, none had hyperlipemia as an inclusion criterion, and none were sufficiently powered. In only one study was a significant effect seen with an 8% (0.28 mmol/L) increase in serum LDL-C and a 16% (0.22 mmol/L) decrease in serum TG in those given vitamin D as compared to the placebo group. Accordingly, the effect of vitamin D supplementation on serum lipids is at present uncertain. Considering the numerous other promising vitamins and minerals that when properly tested have been disappointing, one should wait for the results of forthcoming vitamin D intervention studies before drawing conclusions on potential beneficial effects of vitamin D.

Impact of vitamin D metabolism on clinical epigenetics

The bioactive vitamin D (VD) metabolite, 1,25-dihydroxyvitamin D₃ regulates essential pathways of cellular metabolism and differentiation via its nuclear receptor (VDR). Molecular mechanisms which are known to play key roles in aging and cancer are mediated by complex processes involving epigenetic mechanisms contributing to efficiency of VD-activating CYP27A1 and CYP27B1 or inactivating CYP24 enzymes as well as VDR which binds to specific genomic sequences (VD response elements or VDREs). Activity of VDR can be modulated epigenetically by histone acetylation. It co-operates with other nuclear receptors which are influenced by histone acetyl transferases (HATs) as well as several types of histone deacetylases (HDACs). HDAC inhibitors (HDACi) and/or demethylating drugs may contribute to normalization of VD metabolism. Studies link VD signaling through the VDR directly to distinct molecular mechanisms of both HAT activity and the sirtuin class of HDACs (SIRT1) as well as the forkhead transcription factors thus contributing to elucidate complex epigenetic mechanisms for cancer preventive actions of VD.

Vitamin D receptor gene polymorphisms are associated with adiposity phenotypes

BACKGROUND

Emerging data suggest a role for the vitamin D receptor (VDR) in lipogenesis and adipocyte differentiation.

OBJECTIVE

Our objective was to evaluate the association of VDR gene variants and adiposity phenotypes in an epidemiologic study.

DESIGN

In a sample of 1773 healthy female adults recruited from western New York, we tested for the association of 14 VDR single nucleotide polymorphisms (SNPs) with the following 3 adiposity phenotypes: body mass index (in kg/m²), waist circumference (in cm), and abdominal height (in cm). We examined age, education, total energy intake, smoking status, alcohol intake, and menopausal status as potential covariates.

RESULTS

One SNP, rs3782905, remained associated with all 3 adiposity phenotypes after multiple-testing correction (Bonferroni-adjusted P = 0.004). The mean waist circumference for women with the rs3782905 homozygous rare genotype was 4.4 cm larger than for women with the common homozygous genotype. Two other VDR SNPs were associated with waist circumference and abdominal height, but the associations did not survive multiple-testing correction. Adjustment for covariates did not influence the results.

CONCLUSION

The study results and the biological activity of VDR in adipocyte differentiation suggest that 3' VDR variants may play a role in adiposity phenotypes.

Stimulation of Sirt1-regulated FoxO protein function by the ligand-bound vitamin D receptor

Hormonal vitamin D, 1,25-dihydroxyvitamin D (1,25D), signals through the nuclear vitamin D receptor (VDR). 1,25D regulates cell proliferation and differentiation and has been identified as a cancer chemopreventive agent. FoxO proteins are transcription factors that control cell proliferation and survival. They function as tumor suppressors and are associated with longevity in several organisms. Accumulating data have revealed that 1,25D and FoxO proteins regulate similarly common target genes. We show here that the ligand-bound VDR regulates the posttranslational modification and function of FoxO proteins. 1,25D treatment enhances binding of FoxO3a and FoxO4 within 4 h to promoters of FoxO target genes and blocks mitogen-induced FoxO protein nuclear export. The VDR associates directly with FoxO proteins and regulators, the sirtuin 1 (Sirt1) class III histone deacetylase (HDAC), and protein phosphatase 1. In addition, phosphatase activity and trichostatin A-resistant HDAC activity coimmunoprecipitate with the VDR. 1,25D treatment rapidly (in <4 h) induces FoxO deacetylation and dephosphorylation, consistent with activation. In contrast, ablation of VDR expression enhances FoxO3a phosphorylation, as does knockdown of Sirt1, consistent with the coupling of FoxO acetylation and phosphorylation. 1,25D regulation of common VDR/FoxO target genes is attenuated by blockade of phosphatase activity or by small interfering RNA (siRNA)-mediated knockdown of Sirt1 or FoxO protein expression. Finally, 1,25D-dependent cell cycle arrest is blocked in FoxO3a-deficient cells, indicating that FoxO proteins are key downstream mediators of the antiproliferative actions of 1,25D. These studies link 1,25D signaling through the VDR directly to Sirt1 and FoxO function and provide a molecular basis for the cancer chemopreventive actions of 1,25D.

Vitamin D status in relation to nutritional depletion and muscle function in patients with advanced pulmonary disease

Muscle weakness is an important complication of advanced pulmonary disease and it is associated with reduced functional activity and lower survival. Vitamin D may be involved in muscle function. The aim of this study was to investigate determinants of calcidiol (25-hydroxycholecalciferol, the major circulating indicator of vitamin D) status and associations between vitamin D metabolites and muscle function in relation to nutritional depletion. Fifty-two percent of the underweight patients (n = 42) and 55% of the normal-weight ones (n = 29) had vitamin D deficiency (< 37.5 nmol/L). The resulting models of linear regression showed that, for the calcidiol model, 24.7% of the variation for calcidiol was explained by fat mass index, vitamin D intake, and FEV(1)/FVC. The results further suggested that vitamin D intake was a stronger predictor of calcidiol status in the underweight patients than in the normal-weight ones. In the resulting models for 6-minute walking distance, calcidiol was a significant predictor, which tended to be more marked in the underweight patients than in the normal-weight ones. Low serum calcidiol concentration was associated with fat mass, lung obstruction, and low intake of vitamin D, especially in the underweight patients, and calcidiol was a predictor of walking distance.

Association between VDR and ESR1 gene polymorphisms with bone and obesity phenotypes in Chinese male nuclear families

AIM

The goal of this study was to determine whether polymorphisms in the vitamin D receptor (VDR) and estrogen receptor alpha (ESR1) genes are associated with variations of peak bone mineral density (BMD) and obesity phenotypes in young Chinese men.

METHODS

A total of 1215 subjects from 400 Chinese nuclear families were genotyped by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) and allele-specific multiple PCR (ASM-PCR) analysis at the ApaI, FokI, and CDX2 sites in the VDR gene and the PvuII and XbaI sites in the ESR1 gene. BMD at the lumbar spine and hip, total fat mass, and total lean mass were measured using dual energy X-ray absorptiometry. The associations between VDR and ESR1 gene polymorphisms with peak BMD, body mass index (BMI), total fat mass, total lean mass, and percentage fat mass (PFM) were determined using quantitative transmission disequilibrium tests (QTDTs).

RESULTS

Using QTDTs, no significant within-family associations were obtained between genotypes or haplotypes of the VDR and ESR1 genes and peak BMD. For the obesity phenotypes, the within-family associations were significant between CDX2 genotypes and BMI (P=0.046), fat mass (P=0.004), and PFM (P=0.020). Further, PvuII was significantly associated with the variation of fat mass and PFM (P=0.002 and P=0.039, respectively). A subsequent 1000 permutations were in agreement with these within-family association results.

CONCLUSION

Our findings showed that VDR and ESR1 polymorphisms were associated with total fat mass in young Chinese men, but we failed to find a significant association between VDR and ESR1 genotypes and peak BMD. These findings suggested that the VDR and ESR1 genes are quantitative trait loci (QTL) underlying fat mass variation in young Chinese men.

Lean phenotype and resistance to diet-induced obesity in vitamin D receptor knockout mice correlates with induction of uncoupling protein-1 in white adipose tissue

Increased adiposity is a feature of aging in both mice and humans, but the molecular mechanisms underlying age-related changes in adipose tissue stores remain unclear. In previous studies, we noted that 18-month-old normocalcemic vitamin D receptor (VDR) knockout (VDRKO) mice exhibited atrophy of the mammary adipose compartment relative to wild-type (WT) littermates, suggesting a role for VDR in adiposity. Here we monitored body fat depots, food intake, metabolic factors, and gene expression in WT and VDRKO mice on the C57BL6 and CD1 genetic backgrounds. Regardless of genetic background, both sc and visceral white adipose tissue depots were smaller in VDRKO mice than WT mice. The lean phenotype of VDRKO mice was associated with reduced serum leptin and compensatory increased food intake. Similar effects on adipose tissue, leptin and food intake were observed in mice lacking Cyp27b1, the 1alpha-hydroxylase enzyme that generates 1,25-dihydroxyvitamin D(3), the VDR ligand. Although VDR ablation did not reduce expression of peroxisome proliferator-activated receptor-gamma or fatty acid synthase, PCR array screening identified several differentially expressed genes in white adipose tissue from WT and VDRKO mice. Uncoupling protein-1, which mediates dissociation of cellular respiration from energy production, was greater than 25-fold elevated in VDRKO white adipose tissue. Consistent with elevation in uncoupling protein-1, VDRKO mice were resistant to high-fat diet-induced weight gain. Collectively, these studies identify a novel role for 1,25-dihydroxyvitamin D(3) and the VDR in the control of adipocyte metabolism and lipid storage in vivo.

The vitamin D receptor gene BsmI polymorphism is not associated with anthropometric and biochemical parameters describing metabolic syndrome in postmenopausal women

AIM

Vitamin D could have a direct effect on adipocyte differentiation and metabolism and might be involved in glucose regulation of insulin secretion. In recent years several polymorphisms in the gene encoding the vitamin D receptor (VDR), which are potent to alter the activity of VDR protein, have been described. The present study aimed to investigate the prevalence of the VDR BsmI polymorphism and its association with anthropometric and biochemical features of metabolic syndrome in postmenopausal women.

MATERIALS AND METHODS

We studied 351 randomly selected healthy postmenopausal women, with mean age of 55.43 +/- 2.75 years and mean body mass index (BMI) of 27.5 +/- 4.78 kg/m2, to evaluate the frequency of BsmI polymorphism (by restriction fragment length polymorphism-polymerase chain reaction) in the VDR gene and to find out whether there is an association between this polymorphism and BMI, total fat volume and visceral fat (as determined by total body dual-energy X-ray absorptiometry), blood pressure, lipid profile (total cholesterol, low-density lipoprotein cholesterol (LDL-C), high-density lipoprotein cholesterol, triglycerides) glucose and fasting insulin in the whole group, as well as subgroups of obese and non-obese women.

RESULTS

The prevalence of BsmI genotypes in the study group was 51.0% Bb, 37.3% bb and 11.7% BB. Genotype distribution did not differ from that expected under Hardy-Weinberg equilibrium conditions (chi2 = 2.95, p = 0.22). Apart from LDL-C levels (F = 3.46, p = 0.032), there were no significant differences in anthropometric or metabolic parameters between genotypes.

CONCLUSIONS

The BsmI polymorphism in the VDR gene does not seem to predispose to obesity and insulin resistance, but the BB genotype is connected with an unfavorable lipid profile.

Role of vitamin D in the pathogenesis of type 2 diabetes mellitus

Vitamin D deficiency has been shown to alter insulin synthesis and secretion in both humans and animal models. It has been reported that vitamin D deficiency may predispose to glucose intolerance, altered insulin secretion and type 2 diabetes mellitus. Vitamin D replenishment improves glycaemia and insulin secretion in patients with type 2 diabetes with established hypovitaminosis D, thereby suggesting a role for vitamin D in the pathogenesis of type 2 diabetes mellitus. The presence of vitamin D receptors (VDR) and vitamin D-binding proteins (DBP) in pancreatic tissue and the relationship between certain allelic variations in the VDR and DBP genes with glucose tolerance and insulin secretion have further supported this hypothesis. The mechanism of action of vitamin D in type 2 diabetes is thought to be mediated not only through regulation of plasma calcium levels, which regulate insulin synthesis and secretion, but also through a direct action on pancreatic beta-cell function. Therefore, owing to its increasing relevance, this review focuses on the role of vitamin D in the pathogenesis of type 2 diabetes mellitus.

Vitamin D endocrine system and the genetic susceptibility to diabetes, obesity and vascular disease. A review of evidence

The Vitamin D endocrine system regulates multiple aspects of calcium metabolism and cellular differentiation and replication in the immune system, endocrine pancreas, liver, skeletal muscles and adipocytes. It plays an important role in glucose homeostasis, notably, in the mechanism of insulin release. Actions of vitamin D are mediated by the binding of 1, 25-(OH)2D3 to a specific cytosolic/nuclear vitamin D receptor (VDR), a member of the steroid/thyroid hormone receptor superfamily. Several frequent polymorphisms are found in the VDR gene and were reported to be associated with a variety of physiological and pathological phenotypes in many populations. In this paper, we will review the evidences suggesting associations of allelic variations in the VDR gene and phenotypes related to body weight, glucose homeostasis, diabetes and its vascular complications.

Increased adipogenesis in bone marrow but decreased bone mineral density in mice devoid of thyroid hormone receptors

Mice deficient for all known thyroid hormone receptors, TRalpha1-/-beta-/- mice, display a clear skeletal phenotype characterized by growth retardation, delayed maturation of long bones and decreased trabecular and total bone mineral density (BMD; -14.6 +/- 2.8%, -14.4 +/- 1.5%). The aim of the present study was to investigate the molecular mechanisms behind the skeletal phenotype in TRalpha1-/-beta-/- mice. Global gene expression analysis was performed on total vertebrae from wild-type (WT) and TRalpha1-/-beta-/- mice using DNA microarray and the results were verified by real-time PCR. The mRNA levels of six genes (AdipoQ, Adipsin, Fat-Specific Protein 27 (FSP 27), lipoprotein lipase (LPL), retinol-binding protein (RBP) and phosphoenolpyruvate carboxykinase (PEPCK)) expressed by mature adipocytes were increased in TRalpha1-/-beta-/- compared with WT mice. An increased amount of fat (225% over WT) due to an increased number but unchanged mean size of adipocytes in the bone marrow of TRalpha1-/-beta-/- mice was revealed. Interestingly, the mRNA levels of the key regulator of osteoclastogenesis, receptor activator of NF-varkappab ligand (RANKL), were dramatically decreased in TRalpha1-/-beta-/- mice. In conclusion, TRalpha1-/-beta-/- mice demonstrated increased expression of adipocyte specific genes and an increased amount of bone marrow fat. Thus, these mice have increased adipogenesis in bone marrow associated with decreased trabecular bone mineral density (BMD). One may speculate that these effects either could be caused by an imbalance in the differentiation of the osteoblast and the adipocyte lineages at the expense of osteoblastogenesis, or by independent effects on the regulation of both osteoblastogenesis and adipogenesis.

The pleiotropic actions of vitamin D

General knowledge of the role of vitamin D3 in human physiology has been shaped by its discovery as a preventive agent of nutritional rickets, a defect in bone development due to inadequate uptake of dietary calcium. Studies on the function of the hormonal form of vitamin D3, 1alpha,25-dihydroxyvitamin D3, have been greatly accelerated by the molecular cloning and structural analysis of the vitamin D3 receptor, which is a ligand-activated regulator of gene transcription. Molecular genetic techniques including genomics have helped reveal that 1alpha,25-dihydroxyvitamin D3 can control more than calcium homeostasis. It has widespread effects on cellular differentiation and proliferation, and can modulate immune responsiveness, and central nervous system function. Moreover, accumulating epidemiological and molecular evidence suggests that 1alpha,25-dihydroxyvitamin D3 acts as a chemopreventive agent against several malignancies including cancers of the prostate and colon. Here, we survey the most-recent findings and discuss their implications for the potential therapeutic uses of vitamin D analogues.

Association study of the vitamin D: 1alpha-hydroxylase (CYP1alpha) gene and type 2 diabetes mellitus in a Polish population

OBJECTIVES

Type 2 diabetes mellitus (T2DM) is a complex disease. Genetic and environmental factors cooperate together to form its clinical picture. Polymorphisms in genes involved in the metabolism of vitamin D may influence susceptibility to T2DM. One of them is the vitamin D 1alpha-hydroxylase (CYP1alpha) gene. In this study we searched for the association of two markers, one in its intron 6 and the another one located upstream from the 5' end of CYP1alpha gene, with T2DM in a Polish population.

METHODS

Overall 522 individuals were included in this study: 291 T2DM patients and 231 controls. The sequences, which contain both examined variants, were amplified by polymerase chain reaction (PCR). The T-->C polymorphism in intron 6 was assessed by the dot-blotting method using P(32). Genotyping of the other variant in the 5' end of CYP1alpha gene was carried out by restriction fragment length polymorphism (RFLP) method. Since variants of both SNPs were in very strong linkage disequilibrium, haplotypes could be assigned to phase-unknown individuals. The distribution of alleles, genotypes, haplotypes and haplotype combinations was compared between the groups by chi(2) test.

RESULTS

The frequency of T/C alleles of the 5'end variant was 81.7%/18.3% in T2DM patients and 82.8%/17.2% in the controls (chi(2)=0.2, 1.d.f., p=0.65). For a T-->C polymorphism in intron 6 the frequency of alleles was 65.1%/34.9% and 67.5%/32.5% in T2DM patients and controls, respectively (chi(2)=0.413, 1.d.f., p=0.669). Distribution of genotypes, haplotypes and haplotype combinations were similar in both groups. In stratified analysis, we observed that the T-C/T-T heterozygous haplotype combination was more prevalent in the subgroup of obese T2DM patients (BMI >=30) than in the controls (41.5% vs 28.6%, p=0.01).

CONCLUSIONS

Vitamin D 1alpha-hydroxylase is not a major gene for T2DM in a Polish population. However, this gene may be associated with T2DM in subjects with obesity. Thus, to definitely determine the role of this gene in T2DM further studies are necessary in other populations using larger sample size.

1alpha,25-dihydroxyvitamin D3 inhibits uncoupling protein 2 expression in human adipocytes

We recently demonstrated that suppressing 1alpha,25-(OH)2-D3 by increasing dietary calcium decreases adipocyte intracellular Ca2+ ([Ca2+]i), stimulates lipolysis, and inhibits lipogenesis. High calcium diets also increase core temperature and white adipose tissue uncoupling protein 2 (UCP2) expression in aP2-agouti transgenic mice. Accordingly, we have evaluated the role of 1alpha,25-(OH)2-D3 in regulating human adipocyte UCP2 expression. Treatment of human adipocytes for 48 h with 1 nM 1alpha,25-(OH)2-D3 inhibited UCP2 mRNA and protein levels by 50% (P<0.002) and completely blocked isoproterenol- or fatty acid-stimulated two- to threefold increases in UCP2 expression. However, a specific agonist for the membrane vitamin D receptor (mVDR), 1alpha,25-dihydroxylumisterol3, was unable to inhibit basal, isoproterenol-stimulated, or fatty acid-stimulated UCP2 expression, whereas a specific mVDR antagonist,1beta,25-dihydroxyvitamin D3, was unable to prevent the 1alpha,25-(OH)2-D3 inhibition of UCP2 expression. In contrast, nuclear vitamin D receptor (nVDR) knockout via antisense oligodeoxynucleotide (ODN) prevented the inhibitory effect of 1alpha,25-(OH)2-D3 on adipocyte UCP2 expression and protein levels. These data indicate that 1a,25-(OH)2-D3 exerts an inhibitory effect on adipocyte UCP2 expression via the nVDR. Thus, suppression of 1alpha,25-(OH)2-D3 and consequent up-regulation of UCP2 may contribute to our previous observation of increased thermogenesis in mice fed with high calcium diets.

Expression profiling in squamous carcinoma cells reveals pleiotropic effects of vitamin D3 analog EB1089 signaling on cell proliferation, differentiation, and immune system regulation

The active form of vitamin D3, 1alpha,25-dihydroxyvitamin D3 [1,25-(OH)2D3] is key mediator of calcium homeostasis and is a component of the complex homeostatic system of the skin. 1,25-(OH)2D3 regulates cellular differentiation and proliferation and has broad potential as an anticancer agent. Oligonucleotide microarrays were used to assess profiles of target gene regulation at several points over a 48 h period by the low calcemic 1,25-(OH)2D3 analog EB1089 in human SCC25 head and neck squamous carcinoma cells. One hundred fifty-two targets were identified, composed of 89 up- and 63 down-regulated genes distributed in multiple profiles of regulation. Results are consistent with EB1089 driving SCC25 cells toward a less malignant phenotype, similar to that of basal keratinocytes. Targets identified control inter- and intra-cellular signaling, G protein-coupled receptor function, intracellular redox balance, cell adhesion, and extracellular matrix composition, cell cycle progression, steroid metabolism, and more than 20 genes modulating immune system function. The data indicate that EB1089 performs three key functions of a cancer chemoprevention agent; it is antiproliferative, it induces cellular differentiation, and has potential genoprotective effects. While no evidence was found for gene-specific differences in efficacy of 1,25-(OH)2D3 and EB1089, gene regulation by 1,25-(OH)2D3 was generally more transient. Treatment of cells with 1,25-(OH)2D3 and the cytochrome P450 inhibitor ketoconazole produced profiles of regulation essentially identical to those observed with EB1089 alone, indicating that the more sustained regulation by EB1089 was due to its resistance to inactivation by induced 24-hydroxylase activity. This suggests that differences in action of the two compounds arise more from their relative sensitivities to metabolism than from differing effects on VDR function.

Effects of antiretroviral drug combinations on the differentiation of adipocytes

OBJECTIVE

Preadipocyte cell lines present a cell model with which to understand the physiopathological mechanisms underlying lipodystrophy syndrome, a common complication observed in patients treated with highly active antiretroviral therapy (HAART) that, in general, is associated with the use of protease inhibitors (PI) and nucleoside reverse transcriptase inhibitors (NRTI). The aim of this study was to evaluate the effects of NRTI and of PI and NRTI combinations in this cell model.

METHODS

The differentiation of 3T3-F442A cells was studied by monitoring the expression of specific genes in the presence of therapeutic concentrations of antiretroviral drugs. Messenger RNA (mRNA) was quantified by two reverse transcription-PCR-based methods.

RESULTS

In the presence of 2 microM saquinavir, 30 microM ritonavir or 1 microM zidovudine preadipocytes delayed their differentiation, whereas the use of 10 microM nelfinavir led to cell death. Indinavir (10 microM) promoted lipoprotein lipase expression whereas 1 microM lamivudine or 1 microM stavudine enhanced slightly the expression of the malic enzyme gene. However, the combination of indinavir, lamivudine and stavudine led to a large increase in both lipoprotein lipase and malic enzyme mRNA transcription whereas the combination of indinavir, lamivudine and zidovudine led to a 2.5-fold increase in the expression of the lipogenic malic enzyme gene. Similar potentiating effects of NRTI and PI were observed on the expression of the fatty acid synthase gene.

CONCLUSIONS

Our data suggest that, like PI (although to a lesser extent) NRTI interfere with the differentiation process of adipocytes. In addition, we demonstrate that the effects produced by combinations of NRTI and PI are different from those elicited by each drug separately. This point may be particularly relevant in understanding the physiopathological mechanisms underlying the lipodystrophic syndrome.

Rat oligodendrocytes express the vitamin D(3) receptor and respond to 1,25-dihydroxyvitamin D(3)

The present study investigates the presence of vitamin D receptor (VDR) in cells of the rat oligodendrocyte (OL) lineage. VDR transcripts were detected by in situ hybridization in a fraction of rat OL in secondary cultures. The VDR protein was shown to be co-localized in cells that are also recognized by an anti-myelin basic protein (MBP) antibody. Likewise, in vivo, VDR-positive cells were found in the brain white matter, such as the internal capsule of the striatum or the corpus callosum but also in the spinal cord. At least part of these positive cells in vivo correspond to OL, since they were co-stained by an anti-carbonic anhydrase II antiserum. Northern blot analyses of the CG-4 OL cell line demonstrated that the VDR transcripts are already found in the O-2A precursors. There was a two-fold increase in the relative abundance of these transcripts in differentiated OL or in type-2 astrocytes. 1, 25-dihydroxyvitamin D(3) [1,25-(OH)(2)D(3)] increased the pool of transcripts encoding its own receptor, the VDR. The hormone also enhanced the abundance of the mRNA of the nerve growth factor (NGF) and of its low-affinity receptor, the p75(NTR) protein. By contrast, the hormone had no effect on the levels of MBP or proteolipid protein (PLP) mRNA. This finding suggests that unlike retinoic acid (RA) or thyroid hormone, 1,25-(OH)(2)D(3) has no regulatory action on the synthesis of myelin proteins.

Transient expression of c-erbAbeta1 messenger ribonucleic acid and beta1 thyroid hormone receptor early in adipogenesis of Ob 17 cells

In the murine Ob 17 preadipocyte cell line, the thyroid hormone T3 is an adipogenic factor necessary at an early stage for differentiation into adipocyte. We demonstrate here that this T3 dependence may involve a transient expression (at both the messenger RNA and the protein levels) of c-ErbA beta-type receptors (T3R), although a large body of T3R remained the product of the c-erbAalpha gene, as previously described. c-ErbAbeta1 (and not beta2) expression emerged significantly at growth arrest, peaked 2 days later, and almost disappeared in maturing adipocytes. This expression is related to the presence of T3, as total deprivation of culture medium from T3 prevented it, and the addition of 1.5 nM T3 to preconfluent cultures was able to restore it. When cells were cultured in the presence of T3 and thus were able to differentiate, the c-erbAbeta peak was accompanied by sequential rapid increases in CAAT/enhancer-binding protein-delta(C/EBPdelta), peroxisome proliferator-activated-gamma receptor (PPARgamma), and C/EBPalpha gene expressions. On the contrary, under thyroid hormone-deprived culture conditions that result in nondifferentiation of the preadipocytes, c-erbAbeta1, PPARgamma, and the large C/EBPalpha expressions were blunted, and a moderate early increase in c-erbAalpha1 transcripts was sustained for a longer period. Addition of T3 to T3-deprived preconfluent cells restored PPARgamma and C/EBPalpha expressions. Taken together, the results highlight the important role of T3 in the adipogenesis of Ob 17 cells through the involvement of both beta1 and alpha1 T3R subtypes.

1,25-Dihydroxy vitamin D3 inhibits adipocyte differentiation and gene expression in murine bone marrow stromal cell clones and primary cultures

Bone marrow stromal stem cells differentiate into adipocytes and osteoblasts. These two lineages are thought to be reciprocally related, in part due to the observation that the osteoblast-inducing factor, 1,25 dihydroxy vitamin D3 [1,25(OH)2D3], inhibited adipogenesis of rat femoral-derived stromal cell cultures. However, the literature is divided concerning the adipogenic effects of this steroid hormone. This work examined the effect of 1,25(OH)2D3 (10(-12)-10(-8) M) on murine femoral-derived bone marrow stromal cell differentiation in response to adipogenic agonists employing two different classes of nuclear hormone receptors: the glucocorticoid receptor (hydrocortisone) or peroxisome proliferator-activated receptors (thiazolidinediones). Experiments used the multipotent murine bone marrow stromal cell line, BMS2, and its subclones, as well as primary-derived murine bone marrow stromal cell cultures. In all systems examined, 1,25(OH)2D3 blocked adipogenesis induced by hydrocortisone, methylisobutylxanthine, and indomethacin based on flow cytometric analysis of lipid accumulation. This correlated with reduced messenger RNA levels of the late adipocyte gene markers, aP2 and adipsin. In the BMS2 subclone no. 24, the 1,25(OH)2D3 actions were concentration dependent. Whereas 1,25(OH)2D3 partially inhibited thiazolidinedione-induced adipogenesis in the parental BMS2 cell line, it had minimal effect on the thiazolidinedione-induced differentiation of the BMS2 subclone and primary cultures. These findings indicate that 1,25(OH)2D3, at nanomolar concentrations, completely inhibits murine bone marrow stromal cell differentiation in response to glucocorticoid-based adipogenic agonists but is a less effective adipogenic antagonist following induction with thiazolidinediones. This work supports the conclusion that 1,25(OH)2D3 inhibits murine femoral-derived bone marrow stromal cell adipogenesis.