Membrane localization, Caveolin-3 association and rapid actions of vitamin D receptor in cardiac myocytes

The effects of vitamin D on different types of cells

Vitamin D is neccessary for regulation of calcium and phosphorus metabolism in bones, affects imunity, the cardiovascular system, muscles, skin, epithelium, extracellular matrix, the central nervous system, and plays arole in prevention of aging-associated diseases. Vitamin D receptor is expressed in almost all types of cells and its activation leads to modulation of different signaling pathways. In this review, we have analysed the current knowledge of 1,25-dihydroxyvitamin D3 or 25-hydroxyvitamin D3 effects on metabolism of cells important for the function of the cardiovascular system (endothelial cells, vascular smooth muscle cells, cardiac cells and pericytes), tissue healing (fibroblasts), epithelium (various types of epithelial cells) and the central nervous system (neurons, astrocytes and microglia). The goal of this review was to compare the effects of vitamin D on the above mentioned cells in in vitro conditions and to summarize what is known in this field of research.

Vitamin D and cardiovascular disease risk. A literature overview

BACKGROUND

Atherosclerosis and cerebro and cardiovascular disease associated represent the major cause of morbidity and mortality worldwide. Recently, vitamin D deficiency has been considered a new potential risk factor of these conditions.

METHODS AND RESULTS

In this reviw we briefly describe the biological role of vitamin D, analyze the pathophysiological associations between cardiovascular disease and vitamin D, summarize and synthesize the evidence from literature about the association between vitamin D and cardiovascular disease.

RESULTS

Vit D is an essential vitamin for bone metabolism and homeostasis. The maintenance of optimal blood levels contributes to the correct homeostasis by influencing different metabolic processes, including those underlying cardiovascular diseases. However, the evidence does not support vitamin D routine administration for the prevention and treatment of cardiovascular disease and intake to achieve specific cardiovascular effects. Evidence shows that maintaining optimal levels of vitamin D, ensures cardiovascular protection.

Vitamin D and Hypoxia: Points of Interplay in Cancer

Vitamin D is a hormone that, through its action, elicits a broad spectrum of physiological responses ranging from classic to nonclassical actions such as bone morphogenesis and immune function. In parallel, many studies describe the antiproliferative, proapoptotic, antiangiogenic effects of calcitriol (the active hormonal form) that contribute to its anticancer activity. Additionally, epidemiological data signify the inverse correlation between vitamin D levels and cancer risk. On the contrary, tumors possess several adaptive mechanisms that enable them to evade the anticancer effects of calcitriol. Such maladaptive processes are often a characteristic of the cancer microenvironment, which in solid tumors is frequently hypoxic and elicits the overexpression of Hypoxia-Inducible Factors (HIFs). HIF-mediated signaling not only contributes to cancer cell survival and proliferation but also confers resistance to anticancer agents. Taking into consideration that calcitriol intertwines with signaling events elicited by the hypoxic status cells, this review examines their interplay in cellular signaling to give the opportunity to better understand their relationship in cancer development and their prospect for the treatment of cancer.

Vitamin D3 Treatment Alters Thyroid Functional Morphology in Orchidectomized Rat Model of Osteoporosis

Vitamin D plays an essential role in prevention and treatment of osteoporosis. Thyroid hormones, in addition to vitamin D, significantly contribute to regulation of bone remodeling cycle and health. There is currently no data about a possible connection between vitamin D treatment and the thyroid in the context of osteoporosis. Middle-aged Wistar rats were divided into: sham operated (SO), orchidectomized (Orx), and cholecalciferol-treated orchidectomized (Orx + Vit. D₃; 5 µg/kg b.m./day during three weeks) groups (n = 6/group). Concentration of 25(OH)D in serum of the Orx + Vit. D₃ group increased 4 and 3.2 times (p < 0.0001) respectively, compared to Orx and SO group. T_4, TSH, and calcitonin in serum remained unaltered. Vit. D₃ treatment induced changes in thyroid functional morphology that indicate increased utilization of stored colloid and release of thyroid hormones in comparison with hormone synthesis, to maintain hormonal balance. Increased expression of nuclear VDR (p < 0.05) points to direct, TSH independent action of Vit. D on thyrocytes. Strong CYP24A1 immunostaining in C cells suggests its prominent expression in response to Vit. D in this cell subpopulation in orchidectomized rat model of osteoporosis. The indirect effect of Vit. D on bone, through fine regulation of thyroid function, is small.

The Role of Classical and Novel Forms of Vitamin D in the Pathogenesis and Progression of Nonmelanoma Skin Cancers

Nonmelanoma skin cancers including basal and squamous cell carcinomas (SCC and BCC) represent a significant clinical problem due to their relatively high incidence, imposing an economic burden to healthcare systems around the world. It is accepted that ultraviolet radiation (UVR: λ = 290-400 nm) plays a crucial role in the initiation and promotion of BCC and SCC with UVB (λ = 290-320 nm) having a central role in this process. On the other hand, UVB is required for vitamin D3 (D3) production in the skin, which supplies >90% of the body's requirement for this prohormone. Prolonged exposure to UVB can also generate tachysterol and lumisterol. Vitamin D3 itself and its canonical (1,25(OH)2D3) and noncanonical (CYP11A1-intitated) D3 hydroxyderivatives show photoprotective functions in the skin. These include regulation of keratinocyte proliferation and differentiation, induction of anti-oxidative responses, inhibition of DNA damage and induction of DNA repair mechanisms, and anti-inflammatory activities. Studies in animals have demonstrated that D3 hydroxyderivatives can attenuate UVB or chemically induced epidermal cancerogenesis and inhibit growth of SCC and BCC. Genomic and non-genomic mechanisms of action have been suggested. In addition, vitamin D3 itself inhibits hedgehog signaling pathways which have been implicated in many cancers. Silencing of the vitamin D receptor leads to increased propensity to develop UVB or chemically induced epidermal cancers. Other targets for vitamin D compounds include 1,25D3-MARRS, retinoic orphan receptors α and γ, aryl hydrocarbon receptor, and Wnt signaling. Most recently, photoprotective effects of lumisterol hydroxyderivatives have been identified. Clinical trials demonstrated a beneficial role of vitamin D compounds in the treatment of actinic keratosis. In summary, recent advances in vitamin D biology and pharmacology open new exciting opportunities in chemoprevention and treatment of skin cancers.

An active and selective molecular mechanism mediating the uptake of sex steroids by prostate cancer cells

Steroid hormones play important roles in normal physiological functions and diseases. Sex steroids hormones are important in the biology and treatment of sex hormone-related cancer such as prostate cancer and breast cancer. Cells may take up steroids using multiple mechanisms. The conventionally accepted hypothesis that steroids cross cell membrane through passive diffusion has not been tested rigorously. Experimental data suggested that cells may take up sex steroid using an active uptake mechanism. ³H-testosterone uptake by prostate cancer cells showed typical transporter-mediated uptake kinetic. Cells retained testosterone taken up from the medium. The uptake of testosterone was selective for certain steroid hormones but not others. Data also indicated that the active and selective uptake mechanism resided in cholesterol-rich membrane domains, and may involve ATP and membrane transporters. In summary, the present study provided strong evidence to support the existence of an active and selective molecular mechanism for sex steroid uptake.

Antiproliferative Activity of Non-Calcemic Vitamin D Analogs on Human Melanoma Lines in Relation to VDR and PDIA3 Receptors

Vitamin D is a precursor for secosteroidal hormones, which demonstrate pleiotropic biological activities, including the regulation of growth and the differentiation of normal and malignant cells. Our previous studies have indicated that the inhibition of melanoma proliferation by a short side-chain, low calcemic analog of vitamin D—21(OH)pD is not fully dependent on the expression of vitamin D receptor (VDR). We have examined the effects of classic vitamin D metabolites, 1,25(OH)₂D₃ and 25(OH)D₃, and two low calcemic vitamin D analogs, (21(OH)pD and calcipotriol), on proliferation, mRNA expression and vitamin D receptor (VDR) translocation in three human melanoma cell lines: WM98, A375 and SK-MEL-188b (subline b of SK-MEL-188, which lost responsiveness to 1,25(OH)₂D₃ and became VDR^−/−CYP27B1^−/−). All tested compounds efficiently inhibited the proliferation of WM98 and A375 melanoma cells except SK-MEL-188b, in which only the short side-chain vitamin D analog—21(OH)pD was effective. Overall, 21(OH)pD was the most potent compound in all three melanoma cell lines in the study. The lack of responsiveness of SK-MEL-188b to 1,25(OH)₂D₃, 25(OH)D₃ and calcipotriol is explained by a lack of characteristic transcripts for the VDR, its splicing variants as well as for vitamin D-activating enzyme CYP27B1. On the other hand, the expression of VDR and its splicing variants and other vitamin D related genes (RXR, PDIA3, CYP3A4, CYP2R1, CYP27B1, CYP24A1 and CYP11A1) was detected in WM98 and A375 melanomas with the transcript levels being modulated by vitamin D analogs. The expression of VDR isoforms in WM98 cells was stimulated strongly by calcipotriol. The antiproliferative activities of 21(OH)pD appear not to require VDR translocation to the nucleus, which explains the high efficacy of this noncalcemic pregnacalciferol analog in SK-MEL-188b melanoma, that is, VDR^−/−. Therefore, we propose that 21(OH)pD is a good candidate for melanoma therapy, although the mechanism of its action remains to be defined.

Vitamin D and VDR in cancer cachexia and muscle regeneration

Low circulating levels of vitamin D were associated with decreased muscle strength and physical performance. Along this line, the present study was aimed to investigate: i) the therapeutic potential of vitamin D in cancer-induced muscle wasting; ii) the mechanisms by which vitamin D affects muscle phenotype in tumor-bearing animals.

Rats bearing the AH130 hepatoma showed decreased circulating vitamin D compared to control rats, while muscle vitamin D receptor (VDR) mRNA was up-regulated. Both circulating vitamin D and muscle VDR expression increased after vitamin D administration, without exerting appreciable effects on body weight and muscle mass.

The effects of vitamin D on muscle cells were studied in C2C12 myocytes. Vitamin D-treated myoblasts did not differentiate properly, fusing only partially and forming multinucleated structures with aberrant shape and low myosin heavy chain content. Vitamin D treatment resulted in VDR overexpression and myogenin down-regulation. Silencing VDR expression in C2C12 cultures abrogated the inhibition of differentiation exerted by vitamin D treatment.

These data suggest that VDR overexpression in tumor-bearing animals contributes to muscle wasting by impairing muscle regenerative program. In this regard, attention should be paid when considering vitamin D supplementation to patients affected by chronic pathologies where muscle regeneration may be involved.

Vitamin D and its effects on cardiovascular diseases: a comprehensive review

Vitamin D is a molecule that is actively involved in multiple metabolic pathways. It is mostly known for its implications related to calcium metabolism. It has also been determined that it actively participates in the cardiovascular system, influencing blood pressure, coronary artery disease and other vascular diseases, such as heart failure and atrial fibrillation. Furthermore, it has been established that this vitamin is extensively involved in the regulation of both the renin angiotensin aldosterone system and the immune system. In this review, we present the different vitamin D metabolic pathways associated with the cardiovascular pathophysiology, and we include studies in animal and human models, as well as some of the controversies found in the literature. This review also incorporates an overview of the implications in the molecular biology and public health fields.

Targeting caveolin-3 for the treatment of diabetic cardiomyopathy

Diabetes is a global health problem with more than 550 million people predicted to be diabetic by 2030. A major complication of diabetes is cardiovascular disease, which accounts for over two-thirds of mortality and morbidity in diabetic patients. This increased risk has led to the definition of a diabetic cardiomyopathy phenotype characterised by early left ventricular dysfunction with normal ejection fraction. Here we review the aetiology of diabetic cardiomyopathy and explore the involvement of the protein caveolin-3 (Cav3). Cav3 forms part of a complex mechanism regulating insulin signalling and glucose uptake, processes that are impaired in diabetes. Further, Cav3 is key for stabilisation and trafficking of cardiac ion channels to the plasma membrane and so contributes to the cardiac action potential shape and duration. In addition, Cav3 has direct and indirect interactions with proteins involved in excitation-contraction coupling and so has the potential to influence cardiac contractility. Significantly, both impaired contractility and rhythm disturbances are hallmarks of diabetic cardiomyopathy. We review here how changes to Cav3 expression levels and altered relationships with interacting partners may be contributory factors to several of the pathological features identified in diabetic cardiomyopathy. Finally, the review concludes by considering ways in which levels of Cav3 may be manipulated in order to develop novel therapeutic approaches for treating diabetic cardiomyopathy.

Vitamin D and cardiovascular disease: is the evidence solid?

Vitamin D deficiency, prevalent in 30-50% of adults in developed countries, is largely due to inadequate cutaneous production that results from decreased exposure to sunlight, and to a lesser degree from low dietary intake of vitamin D. Serum levels of 25-hydroxyvitamin D (25-OH D) <20 ng/mL indicate vitamin D deficiency and levels >30 ng/mL are considered optimal. While the endocrine functions of vitamin D related to bone metabolism and mineral ion homoeostasis have been extensively studied, robust epidemiological evidence also suggests a close association between vitamin D deficiency and cardiovascular morbidity and mortality. Experimental studies have demonstrated novel actions of vitamin D metabolites on cardiomyocytes, and endothelial and vascular smooth muscle cells. Low 25-OH D levels are associated with left ventricular hypertrophy, vascular dysfunction, and renin-angiotensin system activation. Despite a large body of experimental, cross-sectional, and prospective evidence implicating vitamin D deficiency in the pathogenesis of cardiovascular disease, a causal relationship remains to be established. Moreover, the cardiovascular benefits of normalizing 25-OH D levels in those without renal disease or hyperparathyroidism have not been established, and questions of an epiphenomenon where vitamin D status merely reflects a classic risk burden have been raised. Randomized trials of vitamin D replacement employing cardiovascular endpoints will provide much needed evidence for determining its role in cardiovascular protection.

Gastric acid, calcium absorption, and their impact on bone health

Calcium balance is essential for a multitude of physiological processes, ranging from cell signaling to maintenance of bone health. Adequate intestinal absorption of calcium is a major factor for maintaining systemic calcium homeostasis. Recent observations indicate that a reduction of gastric acidity may impair effective calcium uptake through the intestine. This article reviews the physiology of gastric acid secretion, intestinal calcium absorption, and their respective neuroendocrine regulation and explores the physiological basis of a potential link between these individual systems.

Small-molecule hormones: molecular mechanisms of action

Small-molecule hormones play crucial roles in the development and in the maintenance of an adult mammalian organism. On the molecular level, they regulate a plethora of biological pathways. Part of their actions depends on their transcription-regulating properties, exerted by highly specific nuclear receptors which are hormone-dependent transcription factors. Nuclear hormone receptors interact with coactivators, corepressors, basal transcription factors, and other transcription factors in order to modulate the activity of target genes in a manner that is dependent on tissue, age and developmental and pathophysiological states. The biological effect of this mechanism becomes apparent not earlier than 30-60 minutes after hormonal stimulus. In addition, small-molecule hormones modify the function of the cell by a number of nongenomic mechanisms, involving interaction with proteins localized in the plasma membrane, in the cytoplasm, as well as with proteins localized in other cellular membranes and in nonnuclear cellular compartments. The identity of such proteins is still under investigation; however, it seems that extranuclear fractions of nuclear hormone receptors commonly serve this function. A direct interaction of small-molecule hormones with membrane phospholipids and with mRNA is also postulated. In these mechanisms, the reaction to hormonal stimulus appears within seconds or minutes.

Discovery of novel vitamin D receptor interacting proteins that modulate 1,25-dihydroxyvitamin D3 signaling

The nuclear vitamin D receptor (VDR) modulates gene transcription in 1,25-dihydroxyvitamin D(3) (1,25D) target tissues such as kidney, intestine, and bone. VDR is also expressed in heart, and 1,25D deficiency may play a role in the acceleration of cardiovascular disease. Employing a yeast two-hybrid system and a human heart library, using both a 1,25D-independent and 1,25D-dependent screen, we discovered six candidate VDR interacting proteins (VIPs). These novel VIPs include CXXC5, FASTK, NR4A1, TPM2, MYL3 and XIRP1. Mammalian two-hybrid assays as well as GST pull-downs were used to confirm VIP-VDR interaction, and the combination of these two assays reveals that CXXC5, XIRP1, FASTK and NR4A1 interactions with VDR may be modulated by 1,25D. The functional effects of these VIPs on 1,25D-mediated gene expression were explored in transcriptional assays employing three separate and distinct 1,25D-responsive element (VDRE)-driven luciferase reporter genes in transfected Caco-2 and HEK-293 cells, and in a C2C12 myoblast line. FASTK and TPM2 activated expression in all cell line and promoter contexts, while CXXC5 and XIRP1 exhibited differing effects depending on the cell line and promoter employed, suggesting promoter and cell-specific effects of these unique VIPs on VDR signaling. Further evaluation of the interaction between CXXC5 and VDR revealed that CXXC5 acts in a dose-dependent manner to stimulate VDR-mediated transcription on select VDREs. Identification of novel heart VIPs and their influence on VDR activity may increase our understanding of how vitamin D impacts cardiac physiology and may facilitate development of VDR/VIP drug analogs to combat heart disease.

Vitamin D metabolism, functions and needs: from science to health claims

BACKGROUND

Vitamin D is a nutrient long considered as essential for skeletal health but is now attracting interest from medical and nutritional communities as knowledge emerges of its biological function and its association with decreased risk of many chronic diseases.

RESULTS

A question emerges: How much more vitamin D do we need for these new functions of vitamin D? This review discusses vitamin D physiology and hypovitaminosis D and presents two vitamin D dietary policies: that according to regulatory authorities and that of nutrition scientists. Scientific evidence suggests that 25(OH)D serum levels should be over 75 nmol/L; otherwise, there is no beneficial effect of vitamin D on long-latency diseases. Current regulatory authority recommendations are insufficient to reach this level of adequacy. Observational and some prospective data show that vitamin D has a role in the prevention of cancer as well as immunity, diabetes and cardiovascular and muscle disorders, which supports the actions of 1α,25(OH)2D at cellular and molecular levels. The recent assessments done by the European Food Safety Authority should lead to new health claims.

CONCLUSIONS

Vitamin D, through food fortification and supplementation, is a promising new health strategy and thus provides opportunities for food industry and nutrition researchers to work together towards determining how to achieve this potential health benefit.

Identification of novel immunoregulatory molecules in human thymic regulatory CD4+CD25+ T cells by phage display

Thymic CD4+CD25+ cells play an important role in immune regulation and are continuously developed in the thymus as an independent lineage. How these cells are generated, what are their multiple pathways of suppressive activity and which are their specific markers are questions that remain unanswered. To identify molecules involved in the function and development of human CD4+CD25+ T regulatory cells we targeted thymic CD4+CD25+ cells by peptide phage display. A phage library containing random peptides was screened ex vivo for binding to human thymic CD4+CD25+ T cells. After four rounds of selection on CD4+CD25+ enriched populations of thymocytes, we sequenced several phage displayed peptides and selected one with identity to the Vitamin D Receptor (VDR). We confirmed the binding of the VDR phage to active Vitamin D in vitro, as well as the higher expression of VDR in CD4+CD25+ cells. We suggest that differential expression of VDR on natural Tregs may be related to the relevance of Vitamin D in function and ontogeny of these cells.

Vitamin D receptor (VDR) regulation of voltage-gated chloride channels by ligands preferring a VDR-alternative pocket (VDR-AP)

We have postulated that the vitamin D receptor (VDR) contains two overlapping ligand binding sites, a genomic pocket and an alternative pocket (AP), that mediate regulation of gene transcription and rapid responses, respectively. Flexible VDR + ligand docking calculations predict that the major blood metabolite, 25(OH)-vitamin D(3) (25D3), and curcumin (CM) bind more selectively to the VDR-AP when compared with the seco-steroid hormone 1α,25(OH)(2)-vitamin D(3) (1,25D3). In VDR wild-type-transfected COS-1 cells and TM4 Sertoli cells, 1,25D3, 25D3, and CM each trigger voltage-gated, outwardly rectifying chloride channel (ORCC) currents that can be blocked by the VDR antagonist 1β,25(OH)(2)-vitamin D(3) and the chloride channel antagonist (4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid). VDR mutational analysis in transfected COS-1 cells demonstrate the DNA-binding domain is not, but the ligand binding and hinge domains of the VDR are, required for 1,25D3 and 25D3 to activate the ORCC. Dose-response studies demonstrate that 25D3 and 1,25D3 are approximately equipotent in stimulating ORCC rapid responses, whereas 1 nm 1,25D3 was 1000-fold more potent than 25D3 and CM in stimulating gene expression. The VDR-AP agonist effects of 1,25D3, 25D3, and low-dose CM are lost after pretreatment of TM4 cells with VDR small interfering RNA. Collectively, these results are consistent with an essential role for the VDR-AP in initiating the signaling required for rapid opening of ORCC. The fact that 25D3 is equipotent to 1,25D3 in opening ORCC suggests that reconsideration of the ability of 25D3 to generate biological responses in vivo may be in order.