The vitamin D receptor is present in caveolae-enriched plasma membranes and binds 1 alpha,25(OH)2-vitamin D3 in vivo and in vitro

Potent 19-norvitamin D analogs for prostate and liver cancer therapy

The active form of vitamin D(3), 1α,25(OH)(2)D(3) or calcitriol, is known to inhibit the proliferation and invasiveness of many types of cancer cells, including prostate and liver cancer cells. These findings support the use of 1α,25(OH)(2)D(3) for prostate and liver cancer therapy. However, 1α,25(OH)(2)D(3) can cause hypercalcemia, thus, analogs of 1α,25(OH)(2)D(3) that are less calcemic but exhibit potent antiproliferative activity would be attractive as therapeutic agents. We have developed 2α-functional group substituted 19-norvitamin D(3) analogs with and without 14-epimerization. Among them, 2α- and 2β-(3-hydroxypropyl)-1α,25-dihydroxy-19-norvitamin D(3) (MART-10 and -11, respectively) and 14-epi-2α- and 14-epi-2β-(3-hydroxypropyl)-1α,25-dihydroxy-19-norvitamin D(3) (14-epi-MART-10 and 14-epi-MART-11, respectively) were found to be the most promising. In this review, we discuss the synthesis of this unique class of vitamin D analogs, the molecular mechanism of anticancer actions of vitamin D, and the biological evaluation of these analogs for potential application to the prevention and treatment of prostate and liver cancer.

Vitamin D in human reproduction: a narrative review

BACKGROUND

Special attention has been given to the effect of vitamin D supplementation on fertility outcomes in both sexes.

AIMS

The purpose of this narrative review was to elucidate the role of vitamin D in male and female reproduction, providing current evidence from both animal and human studies.

MATERIALS AND METHODS

Using PubMed and Medline, we searched for publications during the last 30 years regarding the role of vitamin D in human reproduction.

RESULTS

Accumulating evidence from animal and human studies suggests that vitamin D is involved in many functions of the reproductive system in both genders. In women, vitamin D status has been associated with in vitro fertilization (IVF) outcome, features of polycystic ovarian syndrome (PCOS) and endometriosis. Although several data converge towards a beneficial effect of vitamin D supplementation in metabolic disturbances in women with PCOS, a significant knowledge gap precludes the establishment of a clear cause-effect relationship. In men, vitamin D status has been associated with semen quality and sperm count, motility and morphology. There is evidence for a favourable effect of vitamin D supplementation on semen quality, testosterone concentrations and fertility outcomes.

DISCUSSION

Studies with superior methodological characteristics are needed in order to establish a role for vitamin D on the treatment of female and male infertility.

CONCLUSIONS

Recent data on vitamin D provide new insights in the complex pathogenesis and treatment of infertility.

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.

The roles of vitamin D in skeletal muscle: form, function, and metabolism

Beyond its established role in bone and mineral homeostasis, there is emerging evidence that vitamin D exerts a range of effects in skeletal muscle. Reports of profound muscle weakness and changes in the muscle morphology of adults with vitamin D deficiency have long been described. These reports have been supplemented by numerous trials assessing the impact of vitamin D on muscle strength and mass and falls in predominantly elderly and deficient populations. At a basic level, animal models have confirmed that vitamin D deficiency and congenital aberrations in the vitamin D endocrine system may result in muscle weakness. To explain these effects, some molecular mechanisms by which vitamin D impacts on muscle cell differentiation, intracellular calcium handling, and genomic activity have been elucidated. There are also suggestions that vitamin D alters muscle metabolism, specifically its sensitivity to insulin, which is a pertinent feature in the pathophysiology of insulin resistance and type 2 diabetes. We will review the range of human clinical, animal, and cell studies that address the impact of vitamin D in skeletal muscle, and discuss the controversial issues. This is a vibrant field of research and one that continues to extend the frontiers of knowledge of vitamin D's broad functional repertoire.

The world pandemic of vitamin D deficiency could possibly be explained by cellular inflammatory response activity induced by the renin-angiotensin system

This review attempts to show that there may be a relationship between inflammatory processes induced by chronic overstimulation of the renin-angiotensin system (RAS) and the worldwide deficiency of vitamin D (VitD) and that both disorders are probably associated with environmental factors. Low VitD levels represent a risk factor for several apparently different diseases, such as infectious, autoimmune, neurodegenerative, and cardiovascular diseases, as well as diabetes, osteoporosis, and cancer. Moreover, VitD insufficiency seems to predispose to hypertension, metabolic syndrome, left ventricular hypertrophy, heart failure, and chronic vascular inflammation. On the other hand, inappropriate stimulation of the RAS has also been associated with the pathogenesis of hypertension, heart attack, stroke, and hypertrophy of the left ventricle and vascular smooth muscle cells. Because VitD receptors (VDRs) and RAS receptors are almost distributed in the same tissues, a possible link between VitD and the RAS is even more plausible. Furthermore, from an evolutionary point of view, both systems were developed simultaneously, actively participating in the regulation of inflammatory and immunological mechanisms. Changes in RAS activity and activation of the VDR seem to be inversely related; thus any changes in one of these systems would have a completely opposite effect on the other, making it possible to speculate that the two systems could have a feedback relationship. In fact, the pandemic of VitD deficiency could be the other face of increased RAS activity, which probably causes lower activity or lower levels of VitD. Finally, from a therapeutic point of view, the combination of RAS blockade and VDR stimulation appears to be more effective than either RAS blockade or VDR stimulation individually.

Mitochondrial translocation of vitamin D receptor is mediated by the permeability transition pore in human keratinocyte cell line

Background

Vitamin D receptor (VDR) is a well known transcriptional regulator, active as heterodimer in association with coactivators and corepressors. In addition it has been described the extranuclear distribution of the receptor and in particular the recently reported mitochondrial localization in platelets and megakaryocytes is intriguing because it appears to be a common feature of steroid receptors. Whereas for other members of the steroid receptor family the mitochondrial function has been explored, up to now nothing is known about a mitochondrial form of VDR in human proliferating cells.

Methodology/Principal Findings

In this study we characterized for the first time the mitochondrial localization of VDR in the human keratinocyte cell line HaCaT. In proliferating HaCaT cells VDR was abundantly expressed in mitochondria in association with its binding partner RXRα and the import was ligand-independent. By immunoprecipitation studies we demonstrated the interaction of VDR with proteins of the permeability transition pore (PTP), VDAC and StAR. We then adopted different pharmacological and silencing approaches with the aim of hampering PTP function, either affecting PTP opening or abating the expression of the complex member StAR. By all means the impairment of pore function led to a reduction of mitochondrial levels of VDR.

Conclusions

The results reported here demonstrate a ligand-independent mitochondrial import of VDR through the permeability transition pore, and open interesting new perspectives on PTP function as transporter and on VDR role in mitochondria.

Age-related changes in the response of intestinal cells to 1α,25(OH)2-vitamin D3

The hormonally active form of vitamin D(3), 1α,25(OH)(2)-vitamin D(3), acts in intestine, its major target tissue, where its actions are of regulatory and developmental importance: regulation of intracellular calcium through modulation of second messengers and activation of mitogenic cascades leading to cell proliferation. Several causes have been postulated to modify the hormone response in intestinal cells with ageing, among them, alterations of vitamin D receptor (VDR) levels and binding sites, reduced expression of G-proteins and hormone signal transduction changes. The current review summarizes the actual knowledge regarding the molecular and biochemical basis of age-impaired 1α,25(OH)(2)-vitamin D(3) receptor-mediated signaling in intestinal cells. A fundamental understanding why the hormone functions are impaired with age will enhance our knowledge of its importance in intestinal cell physiology.

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.

Novel vitamin D compounds and skin cancer prevention

As skin cancer is one of the most costly health issues in many countries, particularly in Australia, the possibility that vitamin D compounds might contribute to prevention of this disease is becoming increasingly more attractive to researchers and health communities. In this article, important epidemiologic, mechanistic and experimental data supporting the chemopreventive potential of several vitamin D-related compounds are explored. Evidence of photoprotection by the active hormone, 1α,25dihydroxyvitamin D3, as well as a derivative of an over-irradiation product, lumisterol, a fluorinated analog and bufalin, a potential vitamin D-like compound, are provided. The aim of this article is to understand how vitamin D compounds contribute to UV adaptation and potentially, skin cancer prevention.

Vitamin D: an overview of its role in skeletal muscle physiology in children and adolescents

Many children may have insufficient serum concentrations of vitamin D, which could prevent optimal muscle development and function. Vitamin D deficiency in animal models results in negative effects on muscle fiber structure and calcium/phosphorus handling, suggesting an integral role of vitamin D in skeletal muscle function. While there is a dearth of data in humans, the available evidence demonstrates a positive association between vitamin D status and muscle function. This review focuses on the important role of vitamin D in muscle function in children and adolescents who live in North American regions where exposure to ultraviolet B radiation is limited and who are thus at increased risk for vitamin D insufficiency. The effects of vitamin D on muscle cell proliferation and differentiation, muscle fiber structure, and calcium and phosphorus handling are discussed. Moreover, the roles of vitamin D and the vitamin D receptor and their genomic and nongenomic actions in muscle function are explored in depth. Future research should aim to establish a vitamin D status consistent with optimal musculoskeletal development and function in young children.

Evaluation of 25-hydroxy-vitamin D and parathyroid hormone in Callithrix penicillata primates living in their natural habitat in Brazil

BACKGROUND

Vitamin D is a secosteroid hormone with important roles in the control of bone and mineral metabolism of vertebrates and in the maintenance of systemic homeostasis. This study aimed (i) to evaluate the serum concentrations of 25-hydroxy-vitamin D levels [25(OH)D], parathyroid hormone (PTH) and ionized calcium (iCa) of wild Callithrix penicillata (black-tufted marmosets) and (ii) to propose reference ranges for those analytes for free-living marmosets.

METHODS

Blood samples were collected from 15 wild animals and analyzed for 25(OH)D, PTH and iCa. Reference values were calculated following standard analytical criteria.

RESULTS

The observed mean serum levels (±standard deviation) were 25(OH)D, 61.7 (±20.8) ng/ml; PTH, 275.2 (±34.1) pg/ml; iCai 4.0 (±0.6) mg/dl.

CONCLUSIONS

For free-living marmosets, the proposed physiological range for 25(OH)D is 20.1-103.3 ng/ml and for PTH is 207.0-343.3 pg/dl, with a confidence interval of 95%.

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.

Phospholipase A2 activating protein is required for 1α,25-dihydroxyvitamin D3 dependent rapid activation of protein kinase C via Pdia3

1α,25-Dihydroxyvitamin D(3) (1,25D3) regulates musculoskeletal cells via two different mechanisms: vitamin D receptor (VDR)-dependent gene transcription and rapid membrane-signaling via VDR as well as protein disulfide isomerase, family A, member 3 (Pdia3). In chondrocytes from the costochondral cartilage growth zone (GC), ligand binding to Pdia3 causes a rapid increase in phospholipase A(2) (PLA(2)) activity leading to release of arachidonic acid and formation of lysophospholipid (LPL). LPL activates phospholipase C (PLC), and resulting inositol trisphosphate (IP(3)) and diacylglycerol contribute to PKCα activation and downstream activation of ERK1/2. PLA(2) activating protein (PLAA) is increased in the growth zone of rat growth plates suggesting that it mediates the 1,25D3-dependent pathway. This study examined the role of PLAA in mediating 1,25D3-dependent PKC activation using GC cells and MC3T3-E1 wild-type and PLAA-silenced osteoblasts as models. PLAA, Pdia3, and caveolin-1 (Cav-1) were detected in plasma membranes and caveolae of GC and MC3T3-E1 cells. Pdia3-immunoprecipitated samples were positive for PLAA only after 1,25D3 treatment. Cav-1 was detected when immunoprecipitated with anti-Pdia3 and anti-PLAA in both vehicle and 1,25D3 treated cells. These observations were confirmed by immunohistochemistry. 1,25D3 failed to activate PLA(2) and PKC or cause PGE(2) release in PLAA-silenced cells. PLAA-antibody successfully blocked the PLAA protein and consequently suppressed PKC activity in GC and MC3T3-E1 cells. Crosslinking studies confirmed the localization of PLAA on the extracellular face on the plasma membrane in untreated MC3T3-E1 cells. Taken together, our results suggest that PLAA is an important mediator of 1α,25(OH)(2)D(3) rapid membrane mediated signaling. 1α,25(OH)(2)D(3) likely causes conformational changes bringing Pdia3 into proximity with PLAA, and aiding in transducing the signal from caveolae to the plasma membrane.

The ever-changing brain: cellular and molecular mechanisms for the effects of stressful experiences

The adult brain is capable of considerable structural and functional plasticity and the study of hormone actions in brain has contributed to our understanding of this important phenomenon. In particular, stress and stress-related hormones such as glucocorticoids and mineralocorticoids play a key role in the ability of acute and chronic stress to cause reversible remodeling of neuronal connections in the hippocampus, prefrontal cortex, and amygdala. To produce this plasticity, these hormones act by both genomic and non-genomic mechanisms together with ongoing, experience-driven neural activity mediated by excitatory amino acid neurotransmitters, neurotrophic factors such as brain derived neurotrophic factor, extracellular molecules such as neural cell adhesion molecule, neuropeptides such as corticotrophin releasing factor, and endocannabinoids. The result is a dynamic brain architecture that can be modified by experience. Under this view, the role of pharmaceutical agents, such as antidepressants, is to facilitate such plasticity that must also be guided by experiences.

Vitamin D in exercise: physiologic and analytical concerns

Despite a wide number of studies performed on the general population, little is known about the Vitamin D status of athletes. A particular influence of many factors, including skin pigmentation, early- or late-day training, indoor training, geographic location and extensive sunscreen use, has been observed in this specific population. The need of supplementation with Vitamin D in athletes is not defined or, when supplementation is needed, even the optimal amount of Vitamin D to be used is not specified. The periodic measurement of Vitamin D is the only procedure capable to define athletes' status. Although various methods for the measurement of Vitamin D are routinely used, they often give discordant and poorly reproducible results; thus, it is necessary to standardize the various methods, in order to have comparable results. In conclusion, current available data indicate both that little is known about the Vitamin D status of athletes and that is still unclear if supplementation could be desirable. Finally, it must be pointed out that all the papers about Vitamin D status should indicate in detail the method used for really allowing a correct interpretation of data.

How vitamin D works on bone

Vitamin D is important for the normal development and maintenance of bone. The elucidation of the vitamin D activation pathway and the cloning of the vitamin D receptor have advanced our understanding of the actions of vitamin D on bone. The preponderance of evidence indicates that 1,25(OH)₂D₃ enhances bone mineralization through its effects to promote calcium and phosphate absorption. Although 1,25(OH)₂D₃ stimulates bone resorption in vitro, treatment in vivo can prevent bone loss and fracture through several potential mechanisms. The development of vitamin D analogues has provided new therapeutic options for increasing bone mineral density and reducing fractures.

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.

[The vitamin D endocrine system]

The vitamin D endocrine system comprises a group of 7-dehydrocholesterol-derived secosteroid molecules, including its active metabolite 1,25-dihydroxy-vitamin D (1,25(OH)(2)D), its precursors and other metabolites, its binding protein (DBP) and nuclear receptor (VDR), as well as cytochrome P450 complex enzymes participating in activation and inactivation pathways of those molecules. The biologic effects of 1,25(OH)(2)D are mediated by VDR, a ligand-activated transcription factor which is a member of the nuclear receptors family, spread in almost all human cells. In addition to its classic role in the regulation of calcium metabolism and bone health, evidence suggests that 1,25(OH)(2)D directly or indirectly modulates about 3% of the human genome, participating in the regulation of chief functions of systemic homeostasis, such as cell growth, differentiation and apoptosis, regulation of immune, cardiovascular and musculoskeletal systems, and insulin metabolism. Given the critical influence of the vitamin D endocrine system in many processes of systemic metabolic equilibrium, the laboratory assays available for the evaluation of this system have to present high accuracy and reproducibility, enabling the establishment of cutoff points that, beyond being consensually accepted, reliably express the vitamin D status of the organism, and the respective clinical-metabolic impacts on the global health of the individual.

Mechanism of Pdia3-dependent 1α,25-dihydroxy vitamin D3 signaling in musculoskeletal cells

1α,25-Dihydroxy vitamin D3 [1,25(OH)2D3] acts on cells through traditional steroid hormone receptor-mediated gene transcription and by initiating rapid membrane-associated signaling pathways. Two receptors have been implicated in rapid signaling by 1,25(OH)2D3, the classical nuclear vitamin D receptor (VDR) and the more recently identified protein disulfide isomerase, family A, member 3 (Pdia3). Our lab along with other groups has established various tools to investigate the role of these two receptors, including gene knock-out, conditional knock-out, silencing, and over-expression in various model systems (growth plate chondrocytes, osteoblastic cells, chick intestinal epithelial cells, mouse embryoid bodies, extracellular matrix vesicles and isolated cell membranes). The data demonstrate the requirement for Pdia3 in 1,25(OH)2D3 induced phospholipase A2 (PLA2) and protein kinase C (PKC) activation and downstream responses. Pdia3+/- heterozygote mice also exhibit both cartilage and bone defects. VDR is present on the plasma membrane and one VDR-/- mouse strain lacks transcaltachia, although 1,25(OH)2D3 induced PKC activation and transcaltachia are not affected in another VDR-/- mouse strain. In the context of osteoblast differentiation, both receptors are expressed during osteogenic commitment of embryoid bodies and silencing of each causes a more mature osteoblast phenotype in MC3T3-E1 pre-osteoblasts. Pdia3 exists in caveolae, where it interacts with PLA2 activating protein (PLAA) and caveolin-1 to initiate rapid signaling via PLA2, phospholipase C (PLC), PKC, and ultimately the ERK1/2 family of mitogen activated protein kinases (MAPK). Using the growth plate chondrocyte and matrix vesicle models, we have demonstrated that Pdia3-dependent signaling in response to 1,25(OH)2D3 regulates growth plate physiology.

Estrogen effects on the brain: actions beyond the hypothalamus via novel mechanisms

From its origins in how the brain controls the endocrine system via the hypothalamus and pituitary gland, neuroendocrinology has evolved into a science that now includes hormone action on many aspects of brain function. These actions involve the whole central nervous system and not just the hypothalamus. Advances in our understanding of cellular and molecular actions of steroid hormones have gone beyond the important cell nuclear actions of steroid hormone receptors to include signaling pathways that intersect with other mediators such as neurotransmitters and neuromodulators. This has, in turn, broadened the search for and identification of steroid receptors to include nonnuclear sites in synapses, dendrites, mitochondria, and glial cells, as well as cell nuclei. The study of estrogen receptors and estrogen actions on processes related to cognition, mood, autonomic regulation, pain, and neuroprotection, among other functions, has led the way in this new view of hormone actions on the brain. In this review, we summarize past and current work in our laboratory on this topic. This exciting and growing field involving many laboratories continues to reshape our ideas and approaches to neuroendocrinology both at the bench and the bedside.

Vitamin D and the mammary gland: a review on its role in normal development and breast cancer

Breast cancer is a heterogeneous disease associated with diverse biological behaviours and clinical outcome. Although some molecular subgroups of breast cancer have a targeted therapy, the most aggressive tumours still lack a molecular target. Despite vitamin D being classically associated with the physiological role of calcium regulation and phosphate transport in bone metabolism, several studies have demonstrated a wide range of functions for this hormone, which are particularly important in the field of cancer. The mechanisms underlying the protective actions of vitamin D in cancer development are only sparsely understood, but evidence shows that vitamin D participates in cell growth regulation, apoptosis and cell differentiation. In addition, it has been implicated in the suppression of cancer cell invasion, angiogenesis and metastasis. Most of vitamin D biological actions are mediated by the vitamin D receptor and the synthesis and catabolism of this hormone are regulated by the enzymes CYP27B1 and CYP24A1. In the present review we highlight research data concerning the function of this hormone in the mammary gland, with a special focus on breast carcinogenesis. Hence, and although the available data are controversial, we consider not only updated information on the epidemiology of vitamin D in breast cancer and its potential value as a therapeutic agent or prophylactic (with an emphasis on molecular mechanisms and effectors of vitamin D action), but include data on its role in other stages of breast cancer progression as well. Accordingly, we review data on the influence of vitamin D in the development of normal breast and the expression of vitamin D-related proteins (VDR, CYP27B1 and CYP24A21) in benign mammary lesions and ductal carcinomas in situ.

Vitamin D and diabetes

There is no doubt that vitamin D deficiency is the cause of several metabolic bone diseases, but vitamin D status is also linked to many major human diseases including immune disorders. Mounting data strengthen the link between vitamin D and diabetes, in particular T1D and T2D. Despite some inconsistencies between studies that associate serum 25(OH)D levels with the risk of developing T1D or T2D, there seems to be an overall trend for an inverse correlation between levels of 25(OH)D and both disorders. There is also compelling evidence that 1,25(OH)2D regulates b-cell function by different mechanisms, such as influencing insulin secretion by regulating intracellular levels of Ca2+, increasing β-cell resistance to apoptosis, and perhaps also increasing β-cell replication. The capacity of vitamin D, more specifically 1,25(OH)2D, to modulate immune responses is of particular interest for both the therapy and prevention of diabetes. In the case of T1D, vitamin D supplementation in prediabetic individuals could help prevent or reduce the initiation of autoimmune processes possibly by regulating thymic selection of the T-cell repertoire, decreasing the numbers of autoreactive T cells, and inducing Treg cells. Although immune modulation is generally discussed for the treatment of T1D, it is also relevant for T2D. Indeed, recent studies have shown that T2D patients have increased systemic inflammation and that this state can induce β-cell dysfunction and death. Supplementation trials with regular vitamin D for the protection against the development of T1D and T2D have generated some contradictory data, but many weaknesses can be identified in these trials as most were underpowered or open-labeled. However, the overwhelming strength of preclinical data and of the observational studies make vitamin D or its analogues strong candidates for the prevention or treatment of diabetes or its complications. However, proof of causality needs well-designed clinical trials and if positive, adequate dosing, regimen, and compound studies are needed to define the contribution of vitamin D status and therapy in the global diabetes problem. There are many confounding factors that need to be taken into consideration when translating successful vitamin D therapies in animal models into humans, for example, gender, age, lifestyle, and genetic background. To come to solid conclusions on the potential of vitamin D or its analogues in the prevention of or therapy for all forms of diabetes, it is clear that large prospective trials with carefully selected populations and end points will be needed, but should also receive high priority.

The role of the vitamin D receptor and ERp57 in photoprotection by 1α,25-dihydroxyvitamin D3

UV radiation (UVR) is essential for formation of vitamin D(3), which can be hydroxylated locally in the skin to 1α,25-dihydroxyvitamin D(3) [1,25-(OH)(2)D(3)]. Recent studies implicate 1,25-(OH)(2)D(3) in reduction of UVR-induced DNA damage, particularly thymine dimers. There is evidence that photoprotection occurs through the steroid nongenomic pathway for 1,25-(OH)(2)D(3) action. In the current study, we tested the involvement of the classical vitamin D receptor (VDR) and the endoplasmic reticulum stress protein 57 (ERp57), in the mechanisms of photoprotection. The protective effects of 1,25-(OH)(2)D(3) against thymine dimers were abolished in fibroblasts from patients with hereditary vitamin D-resistant rickets that expressed no VDR protein, indicating that the VDR is essential for photoprotection. Photoprotection remained in hereditary vitamin D-resistant rickets fibroblasts expressing a VDR with a defective DNA-binding domain or a mutation in helix H1 of the classical ligand-binding domain, both defects resulting in a failure to mediate genomic responses, implicating nongenomic responses for photoprotection. Ab099, a neutralizing antibody to ERp57, and ERp57 small interfering RNA completely blocked protection against thymine dimers in normal fibroblasts. Co-IP studies showed that the VDR and ERp57 interact in nonnuclear extracts of fibroblasts. 1,25-(OH)(2)D(3) up-regulated expression of the tumor suppressor p53 in normal fibroblasts. This up-regulation of p53, however, was observed in all mutant fibroblasts, including those with no VDR, and with Ab099; therefore, VDR and ERp57 are not essential for p53 regulation. The data implicate the VDR and ERp57 as critical components for actions of 1,25-(OH)(2)D(3) against DNA damage, but the VDR does not require normal DNA binding or classical ligand binding to mediate photoprotection.

VDR activation of intracellular signaling pathways in skeletal muscle

The purpose of this article is to review the activation of signal transduction pathways in skeletal muscle cells by the hormone 1α,25(OH)(2)-vitamin D(3) [1α,25(OH)(2)D(3)], focusing on the role of the vitamin D receptor (VDR). The hormone induces fast, non transcriptional responses, involving stimulation of the transmembrane second messenger systems adenylyl cyclase/cAMP/PKA, PLC/DAG+IP(3)/PKC, Ca(2+) messenger system and MAPK cascades. Short treatment with 1α,25(OH)(2)D(3) induces reverse translocation of the VDR from the nucleus to plasma membranes. Accordingly, a complex is formed in the caveolae between the VDR and TRCP3, integral protein of capacitative Ca(2+) entry (CCE), suggesting an association between both proteins and a functional role of the VDR in 1α,25(OH)(2)D(3) activation of CCE. Stimulation of tyrosine phosphorylation cascades by 1α,25(OH)(2)D(3) have demonstrated the formation of complexes between Src and the VDR. Through these mechanisms, 1α,25(OH)(2)D(3) plays an important function in contractility and myogenesis.

A retinoic acid receptor RARα pool present in membrane lipid rafts forms complexes with G protein αQ to activate p38MAPK

Retinoic acid (RA) regulates several gene programs by nuclear RA receptors (RARs) that are ligand-dependent transcriptional transregulators. The basic mechanism for switching on transcription of cognate-target genes involves RAR binding at specific response elements and a network of interactions with coregulatory protein complexes. In addition to these classical genomic effects, we recently demonstrated that RA also induces the rapid activation of the p38MAPK/MSK1 pathway, with characteristic downstream consequences on the phosphorylation of RARs and the expression of their target genes. Here, we aimed at deciphering the underlying mechanism of the rapid non-genomic effects of RA. We highlighted a novel paradigm in which a fraction of the cellular RARα pool is present in membrane lipid rafts, where it forms complexes with G protein alpha Q (Gαq) in response to RA. This rapid RA-induced formation of RARα/Gαq complexes in lipid rafts is required for the activation of p38MAPK that occurs in response to RA. Accordingly, in RA-resistant cancer cells, characterized by the absence of p38MAPK activation, RARα present in membrane lipid rafts does not associate with Gαq, pointing out the essential contribution of RARα/Gαq complexes in RA signaling.

Hepatocellular carcinoma and vitamin D: a review

The non-classical actions of vitamin D, namely antiproliferation, pro-differentiation, pro-apoptosis, anti-inflammation, and immune regulation, have received great attention during the past decade. Increasing evidence from epidemiological studies showing the inverse association between vitamin D status and incidence of many forms of cancer as well as biochemical studies has suggested that vitamin D deficiency may play a role in the cause and progression of these types of cancer. Recently, vitamin D and its analogs have been deemed as potential regimen to treat a variety of cancers alone or in combination with other drugs. Although, the epidemiologic evidence regarding the association of vitamin D and hepatocellular carcinoma (HCC) is still inconclusive, biochemical evidence clearly indicates that HCC cells are responsive to the inhibitory effect of vitamin D and its analogs. In this review, we discuss the current status of HCC and its treatment, the source, metabolism, functions, and the mechanism of actions of vitamin D, and the biochemical studies of vitamin D analogs and their implications in the prevention and treatment of HCC.

The anti-cancer and anti-inflammatory actions of 1,25(OH)₂D₃

Various epidemiological studies have shown an aetiological link between vitamin D deficiency and cancer incidence. The active metabolite of vitamin D, 1,25-dihydroxyvitamin D₃ [1,25(OH)₂D₃], has potent anti-cancer activities both in vitro and in vivo. These anti-cancer effects are attained by regulating the transcription of numerous genes that are involved in different pathways to reduce tumorigenesis and are dependent on the cancer cell type. Besides reducing cell growth and inducing apoptosis, 1,25(OH)₂D₃ also inhibits angiogenesis and metastasis. Moreover, its potency to inhibit inflammation also contributes to its anti-tumoral activity. Here, we report the different ways in which 1,25(OH)₂D₃ interferes with the malignant processes that are activated in cancer cells.

Vitamin D receptor (VDR)-mediated actions of 1α,25(OH)₂vitamin D₃: genomic and non-genomic mechanisms

The conformationally flexible secosteroid, 1α,25(OH)₂vitamin D₃ (1α,25(OH)₂D₃) initiates biological responses via binding to the vitamin D receptor (VDR). The VDR contains two overlapping ligand binding sites, a genomic pocket (VDR-GP) and an alternative pocket (VDR-AP), that respectively bind a bowl-like ligand configuration (gene transcription) or a planar-like ligand shape (rapid responses). When occupied by 1α,25(OH)₂D₃, the VDR-GP interacts with the retinoid X receptor to form a heterodimer that binds to vitamin D responsive elements in the region of genes directly controlled by 1α,25(OH)₂D₃. By recruiting complexes of either coactivators or corepressors, activated VDR modulates the transcription of genes encoding proteins that promulgate the traditional genomic functions of vitamin D, including signaling intestinal calcium and phosphate absorption to effect skeletal and calcium homeostasis. 1α,25(OH)₂D₃/VDR control of gene expression and rapid responses also delays chronic diseases of aging such as osteoporosis, cancer, type-1 and -2 diabetes, arteriosclerosis, vascular disease, and infection.

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.

Nuclear lipid microdomains regulate nuclear vitamin D3 uptake and influence embryonic hippocampal cell differentiation

Despite recent advances in the understanding of the role of 1,25-dihydroxyvitamin D(3) (1,25-(OH)(2)D(3)) in the CNS, the mechanism of action remains obscure. We demonstrate that some 1,25-(OH)(2)D(3) receptor (VDR) is localized in the cell nucleus in specialized microdomains enriched in sphingomyelin and cholesterol; the integrity of these microdomains is necessary for embryonic hippocampal cell differentiation. Sphingomyelinase (SMase) treatment reduces both VDR and labeled 1,25-(OH)(2)D(3) content in nuclear microdomains. We have previously shown that HN9.10e embryonic hippocampal cells differentiate when incubated with 100 nM 1,25-(OH)(2)D(3) in the presence of 10% fetal calf serum, while serum deprivation induces cell death. In this study, we have investigated whether conditions that alter lipid content of nuclear microdomains modify 1,25-(OH)(2)D(3)-induced differentiation. Serum deprivation activates SMase and modifies the composition of nuclear microdomains, which lose the 1,25-(OH)(2) vitamin D(3) receptor. The incubation of serum-deprived cells with 100 nM 1,25-(OH)(2)D(3) prevents differentiation. However, treatment with 400 nM 1,25-(OH)(2)D(3) during serum withdrawal increases the lipid content of the nuclear microdomains, allows the interaction of 1,25-(OH)(2)D(3) with its receptor, and results in differentiation. These results suggest the presence of VDR in nuclear microdomains is necessary for 1,25-(OH)(2)D(3)-induced differentiation in embryonic hippocampal cells.

1α,25(OH)₂-vitamin D and a nongenomic vitamin D analogue inhibit ultraviolet radiation-induced skin carcinogenesis

Exposure to ultraviolet radiation (UVR) can lead to a range of deleterious responses in the skin. An important form of damage is the DNA photolesion cyclobutane pyrimidine dimer (CPD). CPDs can be highly mutagenic if not repaired prior to cell division and can lead to UV-induced immunosuppression, making them potentially carcinogenic. UVR exposure also produces vitamin D, a prehormone. Different shapes of the steroid hormone 1α,25-dihydroxyvitamin D₃ [1,25(OH)₂D₃] can produce biological responses through binding either to its cognate nuclear receptor (VDR) to regulate gene transcription or to the VDR associated with plasma membrane caveolae to produce, via signal transduction, nongenomic physiologic responses. Here, we show that both 1,25(OH)₂D₃ and 1α,25(OH)₂-lumisterol (JN), a conformationally restricted analogue that can generate only nongenomic responses, are effective inhibitors of UV damage in an immunocompetent mouse (Skh:hr1) model susceptible to UV-induced tumors. Both 1,25(OH)₂D₃ and JN significantly reduced UVR-induced CPD, apoptotic sunburn cells, and immunosuppression. Furthermore, these compounds inhibited skin tumor development, both papillomas and squamous cell carcinomas, in these mice. The observed reduction of these UV-induced effects by 1,25(OH)₂D₃ and JN suggests a role for these compounds in prevention against skin carcinogenesis. To the best of our knowledge, this is the first comprehensive report of an in vivo long-term biological response generated by chronic dosing with a nongenomic-selective vitamin D steroid.

1α,25-dihydroxycholecalciferol induces nitric oxide production in cultured endothelial cells

BACKGROUND

Recently, 1α,25-dihydroxycholecalciferol (vitD) has received increasing interest for its effects on many tissues and organs other than bone. A number of experimental studies have shown that vitD may have an important role in modifying risk for cardiovascular disease.

AIMS

This study was planned to test the effects of vitD on endothelial nitric oxide (NO) production and to study the intracellular pathways leading to NO release.

METHODS

In human umbilical vein endothelial cells (HUVEC) cultures the effects of vitD on NO production and p38, Akt, ERK and eNOS phosphorylations were examined in absence or in presence of the NO synthase inhibitor L-NAME and protein kinases specific inhibitors SB203580, wortmannin and UO126.

RESULTS

VitD caused a concentration-dependent increase in NO production. The maximum effect was observed at a concentration of 1 nM and the optimal time of stimulation was 1 min. Effects induced by vitD were abolished by L-NAME and by pre-treatment with protein kinases inhibitors. To verify the effective involvement of vitD receptor (VDR) in the action mechanism of vitD, experiments were repeated in presence of the specific VDR ligands ZK159222 and ZK191784.

CONCLUSIONS

The results of this study demonstrate that vitD can induce a significant increase in endothelial NO production. VitD interaction with VDR caused the phosphorylation of p38, AKT and ERK leading to eNOS activation.

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.

Vitamin D and the vitamin D receptor in liver pathophysiology

Vitamin D through the vitamin D nuclear receptor (VDR) plays a key role in mineral ion homeostasis. The liver is central in vitamin D synthesis, however the direct involvement of the vitamin D-VDR axis on the liver remains to be evaluated. In this review, we will describe vitamin D metabolism and the mechanisms of homeostatic control. We will also address the associations between the vitamin D-VDR axis and pathological liver entities, such as non-alcoholic fatty liver disease, autoimmune liver disease, viral hepatitis and liver cancer. The link between liver diseases and the vitamin D-VDR axis will be discussed in light of evidences arising from in vitro and in vivo studies. Finally, we will consider the therapeutic potential of the vitamin D-VDR axis in liver diseases.

Molecular mechanisms for regulation of intestinal calcium absorption by vitamin D and other factors

Optimal intestinal calcium (Ca) absorption is necessary for the protection of bone and the prevention of osteoporosis. Ca absorption can be represented as the sum of a saturable pathway and a non-saturable pathway that is primarily dependent upon luminal Ca concentration. While models have been proposed to describe these transport components, significant gaps still exist in our understanding of these processes. Habitual low intake of Ca up-regulates the saturable transport pathway, a process mediated by increased renal production of 1,25 dihydroxyvitamin D (1,25(OH)(2)D). Consistent with this, low vitamin D status as well as deletion/mutation of the vitamin D receptor (VDR) or 25 hydroxyvitamin D-1α hydroxylase (CYP27B1) genes limit Ca absorption by reducing the saturable pathway. There is some evidence that non-saturable Ca absorption in the ileum is also regulated by vitamin D status, but the mechanism is unclear. Treatment with a number of hormones can regulate Ca absorption in vivo (e.g. parathyroid hormone (PTH), thyroid hormone, growth hormone (GH)/insulin-like growth factor I (IGF-1), estrogen, testosterone). However, some of these actions are indirect (i.e. mediated through the regulation of vitamin D metabolism or signaling), whereas only a few (e.g. estrogen, IGF-1) have been shown to persist in the absence of vitamin D signaling.

The biology and pathology of vitamin D control in bone

Vitamin D is a steroid pro-hormone, whose active metabolite binds the vitamin D receptor (VDR) which, in turn, binds to DNA sequences on target genes as a heterodimer with the retinoid-X receptor, resulting in regulation of gene expression. The vitamin D pro-hormone can be synthesized in the skin, in response to ultraviolet radiation; however, dietary sources have become increasingly important as a result of cultural changes over the past few centuries. Based on its initial discovery as an anti-rachitic factor, studies of the role of vitamin D and its receptor have largely focused on the skeleton. Investigations into the pathophysiologic basis and therapeutic responses of skeletal disorders associated with impaired vitamin D action have led to the identification of the molecular pathways involved in hormone activation and regulation of gene expression by the liganded VDR. These studies have also demonstrated that the skeletal actions of the VDR and its ligand are largely redundant if normal mineral ion homeostasis can be maintained by other means. However, investigations in animal models with tissue-specific ablation of the VDR or the enzyme required for hormone activation have demonstrated novel actions in skeletal tissues. The active vitamin D metabolite has been shown to have both paracrine and endocrine actions in other tissues as well.

The role of caveolae in endothelial cell dysfunction with a focus on nutrition and environmental toxicants

Complications of vascular diseases, including atherosclerosis, are the number one cause of death in Western societies. Dysfunction of endothelial cells is a critical underlying cause of the pathology of atherosclerosis. Lipid rafts, and especially caveolae, are enriched in endothelial cells, and down-regulation of the caveolin-1 gene may provide protection against the development of atherosclerosis. There is substantial evidence that exposure to environmental pollution is linked to cardiovascular mortality, and that persistent organic pollutants can markedly contribute to endothelial cell dysfunction and an increase in vascular inflammation. Nutrition can modulate the toxicity of environmental pollutants, and evidence suggests that these affect health and disease outcome associated with chemical insults. Because caveolae can provide a regulatory platform for pro-inflammatory signalling associated with vascular diseases such as atherosclerosis, we suggest a link between atherogenic risk and functional changes of caveolae by environmental factors such as dietary lipids and organic pollutants. For example, we have evidence that endothelial caveolae play a role in uptake of persistent organic pollutants, an event associated with subsequent production of inflammatory mediators. Functional properties of caveolae can be modulated by nutrition, such as dietary lipids (e.g. fatty acids) and plant-derived polyphenols (e.g. flavonoids), which change activation of caveolae-associated signalling proteins. The following review will focus on caveolae providing a platform for pro-inflammatory signalling, and the role of caveolae in endothelial cell functional changes associated with environmental mediators such as nutrients and toxicants, which are known to modulate the pathology of vascular diseases.

Epigenetics meets endocrinology

Although genetics determines endocrine phenotypes, it cannot fully explain the great variability and reversibility of the system in response to environmental changes. Evidence now suggests that epigenetics, i.e. heritable but reversible changes in gene function without changes in nucleotide sequence, links genetics and environment in shaping endocrine function. Epigenetic mechanisms, including DNA methylation, histone modification, and microRNA, partition the genome into active and inactive domains based on endogenous and exogenous environmental changes and developmental stages, creating phenotype plasticity that can explain interindividual and population endocrine variability. We will review the current understanding of epigenetics in endocrinology, specifically, the regulation by epigenetics of the three levels of hormone action (synthesis and release, circulating and target tissue levels, and target-organ responsiveness) and the epigenetic action of endocrine disruptors. We will also discuss the impacts of hormones on epigenetics. We propose a three-dimensional model (genetics, environment, and developmental stage) to explain the phenomena related to progressive changes in endocrine functions with age, the early origin of endocrine disorders, phenotype discordance between monozygotic twins, rapid shifts in disease patterns among populations experiencing major lifestyle changes such as immigration, and the many endocrine disruptions in contemporary life. We emphasize that the key for understanding epigenetics in endocrinology is the identification, through advanced high-throughput screening technologies, of plasticity genes or loci that respond directly to a specific environmental stimulus. Investigations to determine whether epigenetic changes induced by today's lifestyles or environmental 'exposures' can be inherited and are reversible should open doors for applying epigenetics to the prevention and treatment of endocrine disorders.

Vitamin D deficiency and toxicity in chronic kidney disease: in search of the therapeutic window

Both vitamin D deficiency and vitamin D toxicity are associated with cardiovascular complications in chronic kidney disease (CKD). Clinical and experiment data indicate that the association of vitamin D levels with cardiovascular disease is best illustrated as a biphasic, or U-shaped, curve. Children and adolescents with CKD need vitamin D due to the demands of a growing skeleton, to prevent renal rickets. However, this therapy carries the risk of severe side effects and chronic toxicity. Observational studies show that vitamin D deficiency and toxicity are frequently present in patients with CKD. In view of the importance of cardiovascular complications for the long-term survival of young patients, these findings demand a judicious use of vitamin D preparations. In clinical practice, the therapeutic window is rather small, presenting a therapeutic challenge to avoid both vitamin D deficiency and toxicity.

Vitamin D supplementation: a pharmacologic perspective

PURPOSE OF REVIEW

Vitamin D supplementation is expected to increase as clinicians try to optimize their patients' vitamin D status. This review integrates newer information into a perspective on vitamin D disposition and effect.

RECENT FINDINGS

Vitamin D is being considered for indications beyond bone health. The limited dose-response data vary by indication, but generally target a goal serum 25(OH)D concentration of 80-120 nmol/l. Although oral vitamin D is adequately absorbed, distributed, metabolized, and utilized before being excreted, these factors may vary with baseline vitamin D status, genetic polymorphism, and the form of vitamin D being administered. Additionally, the responses to vitamin D can be tissue-specific and are not always well described.

SUMMARY

There is still a need to better characterize the disposition and effect of vitamin D supplementation. Data will need to be more specific to the therapeutic indication and demonstrate health outcomes. Long-term effects of high-dose supplementation at the tissue level will be especially important to describe.

Vitamin D receptor and enzyme expression in dorsal root ganglia of adult female rats: modulation by ovarian hormones

Vitamin D insufficiency impacts sensory processes including pain and proprioception, but little is known regarding vitamin D signaling in adult sensory neurons. We analyzed female rat dorsal root ganglia (DRG) for vitamin receptor (VDR) and the vitamin D metabolizing enzymes CYP27B1 and CYP24. Western blots and immunofluorescence revealed the presence of these proteins in sensory neurons. Nuclear VDR immunoreactivity was present within nearly all neurons, while cytoplasmic VDR was found preferentially in unmyelinated calcitonin gene-related peptide (CGRP)-positive neurons, colocalizing with CYP27B1 and CYP24. These data suggest that 1,25(OH)(2)D3 may affect sensory neurons through nuclear or extranuclear signaling pathways. In addition, local vitamin D metabolite concentrations in unmyelinated sensory neurons may be controlled through expression of CYP27B1 and CYP24. Because vitamin D deficiency appears to exacerbate some peri-menopausal pain syndromes, we assessed the effect of ovariectomy on vitamin D-related proteins. Two weeks following ovariectomy, total VDR expression in DRG dropped significantly, owing to a slight decrease in the percentage of total neurons expressing nuclear VDR and a large drop in unmyelinated CGRP-positive neurons expressing cytoplasmic VDR. Total CYP27B1 expression dropped significantly, predominantly due to decreased expression within unmyelinated CGRP-positive neurons. CYP24 expression remained unchanged. Therefore, unmyelinated CGRP-positive neurons appear to have a distinct vitamin D phenotype with hormonally-regulated ligand and receptor levels. These findings imply that vitamin D signaling may play a specialized role in a neural cell population that is primarily nociceptive.

Vitamin D effects on pregnancy and the placenta

Vitamin D is a pleiotropic secosteroid hormone important for health and disease prevention. The actions of vitamin D are mediated by the vitamin D receptor that binds the active form of vitamin D [1,25(OH)(2)D] to induce both transcriptional and non-genomic responses. Vitamin D has well known classical functions in calcium uptake and bone metabolism, but more recent work highlights the importance of the nonclassical actions of vitamin D in a variety of cell types. These actions include modulation of the innate and adaptive immune systems and regulation of cell proliferation. Adequate vitamin D intake is essential for maternal and fetal health during pregnancy, and epidemiological data indicate that many pregnant women have sub-optimal vitamin D levels. Notably, vitamin D deficiency correlates with preeclampsia, gestational diabetes mellitus, and bacterial vaginosis, and an increased risk for C-section delivery. Recent work emphasizes the importance of nonclassical roles of vitamin D in pregnancy and the placenta. The placenta produces and responds to vitamin D where vitamin D functions as a modulator of implantation, cytokine production and the immune response to infection. We describe vitamin D metabolism and the cellular responses to vitamin D, and then summarize the role of vitamin D in placental trophoblast, pregnancy and the fetus.