Vitamin D and malabsorptive gastrointestinal conditions: A bidirectional relationship?

This paper is one of the outcomes of the 5th International Conference "Controversies in Vitamin D" held in Stresa, Italy from 15 to 18 September 2021 as part of a series of annual meetings which was started in 2017. The scope of these meetings is to discuss controversial issues about vitamin D. Publication of the outcomes of the meeting in international journals allows a wide sharing of the most recent data with the medical and academic community. Vitamin D and malabsorptive gastrointestinal conditions was one of the topics discussed at the meeting and focus of this paper. Participants to the meeting were invited to review available literature on selected issues related to vitamin D and gastrointestinal system and to present their topic to all participants with the aim to initiate a discussion on the main outcomes of which are reported in this document. The presentations were focused on the possible bidirectional relationship between vitamin D and gastrointestinal malabsorptive conditions such as celiac disease, inflammatory bowel diseases (IBDs) and bariatric surgery. In fact, on one hand the impact of these conditions on vitamin D status was examined and on the other hand the possible role of hypovitaminosis D on pathophysiology and clinical course of these conditions was also evaluated. All examined malabsorptive conditions severely impair vitamin D status. Since vitamin D has known positive effects on bone this in turn may contribute to negative skeletal outcomes including reduced bone mineral density, and increased risk of fracture which may be mitigated by vitamin D supplementation. Due to the immune and metabolic extra-skeletal effects there is the possibility that low levels of vitamin D may negatively impact on the underlying gastrointestinal conditions worsening its clinical course or counteracting the effect of treatment. Therefore, vitamin D status assessment and supplementation should be routinely considered in all patients affected by these conditions. This concept is strengthened by the existence of a possible bidirectional relationship through which poor vitamin D status may negatively impact on clinical course of underlying disease. Sufficient elements are available to estimate the desired threshold vitamin D level above which a favourable impact on the skeleton in these conditions may be obtained. On the other hand, ad hoc controlled clinical trials are needed to better define this threshold for obtaining a positive effect of vitamin D supplementation on occurrence and clinical course of malabsorptive gastrointestinal diseases.

Vitamin D regulation of immune function during covid-19.

Covid-19 has to date infected a confirmed 275 million people with 5.4 million, now dead, with the count rising every day. Although the virus, SARS-CoV2, causing Covid-19 infects many cells in the body, its infection of the upper and lower respiratory tract (upper airway epithelia and pulmonary alveolar pneumocytes and macrophages) causing what is now called a cytokine storm in the lungs is the major cause of morbidity and mortality. This results from a dysregulation of the innate immune system with an outpouring of proinflammatory cytokines and chemokines leading to abnormal activation of the adaptive immune pathway. Airway epithelia constitutively expresses CYP27B1, the enzyme producing the active vitamin D metabolite, 1,25(OH)2D, and the vitamin D receptor (VDR) for which 1,25(OH)2D is the ligand. Pulmonary alveolar macrophages, on the other hand, are induced to express both CYP27B1 and VDR by various pathogens including viruses and cytokines released from infected epithelia and other immune cells. Although not demonstrated for corona viruses like SARS-CoV2, for other viruses and other respiratory pathogens activation of innate immunity leading to increased local 1,25(OH)2D production has been shown to enhance viral neutralization and clearance while modulating the subsequent proinflammatory response. Whether such will be the case for SARS-CoV2 remains to be seen, but is currently being proposed and investigated. This mini review will discuss some of the mechanisms by which vitamin D may help reduce morbidity and mortality in this devastating pandemic.

Association of Vitamin D Status and COVID-19-Related Hospitalization and Mortality.

BACKGROUND: The relationship between vitamin D status and COVID-19-related clinical outcomes is controversial. Prior studies have been conducted in smaller, single-site, or homogeneous populations limiting adjustments for social determinants of health (race/ethnicity and poverty) common to both vitamin D deficiency and COVID-19 outcomes. OBJECTIVE: To evaluate the dose-response relationship between continuous 25(OH)D and risk for COVID-19-related hospitalization and mortality after adjusting for covariates associated with both vitamin D deficiency and COVID-19 outcomes. DESIGN: Retrospective cohort study. PATIENTS: Veteran patients receiving care in US Department of Veteran Affairs (VA) health care facilities with a positive severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) test and a blood 25(OH)D test between February 20, 2020, and November 8, 2020, followed for up to 60 days. MAIN MEASURES: Exposure was blood 25(OH)D concentration ascertained closest to and within 15 to 90 days preceding an index positive SARS-CoV-2 test. Co-primary study outcomes were COVID-19-related inpatient hospitalization requiring airborne, droplet, contact, or other isolation and mortality ascertained within 60 days of an index positive SARS-CoV-2 test. KEY RESULTS: Of 4,599 veterans with a positive SARS-CoV-2 test, vitamin D deficiency (< 20 ng/mL) was identified in 665 (14.5%); 964 (21.0%) were hospitalized; and 340 (7.4%) died. After adjusting for all covariates, including race/ethnicity and poverty, there was a significant independent inverse dose-response relationship between increasing continuous 25(OH)D concentrations (from 15 to 60 ng/mL) and decreasing probability of COVID-19-related hospitalization (from 24.1 to 18.7%, p=0.009) and mortality (from 10.4 to 5.7%, p=0.001). In modeling 25(OH)D as a log-transformed continuous variable, the greatest risk for hospitalization and death was observed at lower 25(OH)D concentrations. CONCLUSIONS: Continuous blood 25(OH)D concentrations are independently associated with COVID-19-related hospitalization and mortality in an inverse dose-response relationship in this large racially and ethnically diverse cohort of VA patients. Randomized controlled trials are needed to evaluate the impact of vitamin D supplementation on COVID-19-related outcomes.

Vitamin D Regulation of Immune Function.

PURPOSE OF REVIEW: To review the mechanisms by which vitamin D and its metabolites regulate the immune system to facilitate the ability of the body to prevent and/or treat SARS-CoV2 and other respiratory infections and encourage further research into the role that vitamin D supplementation plays in preventing/treating such infections. RECENT FINDINGS: Vitamin D deficiency is associated with an increased risk of SARS-CoV2 and other respiratory infections. Clinical trials in general demonstrate that correction of vitamin D deficiency reduces the risk of hospitalization, ICU admission, and death from SARS-CoV2 infection. The airway epithelium and alveolar macrophages express the enzyme, CYP27B1, that produces the active metabolite of vitamin D, 1,25(OH)2D, and the vitamin D receptor, VDR. Vitamin D and its metabolites promote the innate immune response, which provides the first line of defense against viral and bacterial infections while restricting the adaptive immune response, which if unchecked promotes the inflammatory response leading to the acute respiratory distress syndrome and death. The rationale for treating vitamin D deficiency to reduce the risk of SARS-CoV2 infection and supplementing patients with vitamin D early in the course of SARS-CoV2 infection rests primarily on the ability of vitamin D metabolites to promote an effective immune response to the infection.

p120-catenin suppresses proliferation and tumor growth of oral squamous cell carcinoma via inhibiting nuclear phospholipase C-γ1 signaling.

p120-catenin (p120) serves as a stabilizer of the calcium-dependent cadherin-catenin complex and loss of p120 expression has been observed in several types of human cancers. The p120-dependent E-cadherin-ß-catenin complex has been shown to mediate calcium-induced keratinocyte differentiation via inducing activation of plasma membrane phospholipase C-γ1 (PLC-γ1). On the other hand, PLC-γ1 has been shown to interact with phosphatidylinositol 3-kinase enhancer in the nucleus and plays a critical role in epidermal growth factor-induced proliferation of oral squamous cell carcinoma (OSCC) cells. To determine whether p120 suppresses OSCC proliferation and tumor growth via inhibiting PLC-γ1, we examined effects of p120 knockdown or p120 and PLC-γ1 double knockdown on proliferation of cultured OSCC cells and tumor growth in xenograft OSCC in mice. The results showed that knockdown of p120 reduced levels of PLC-γ1 in the plasma membrane and increased levels of PLC-γ1 and its signaling in the nucleus in OSCC cells and OSCC cell proliferation as well as xenograft OSCC tumor growth. However, double knockdown of p120 and PLC-γ1 or knockdown of PLC-γ1 alone did not have any effect. Immunohistochemical analysis of OSCC tissue from patients showed a lower expression level of p120 and a higher expression level of PLC-γ1 compared with that of adjacent noncancerous tissue. These data indicate that p120 suppresses OSCC cell proliferation and tumor growth by inhibiting signaling mediated by nuclear PLC-γ1.

The Vitamin D Receptor as Tumor Suppressor in Skin.

Cutaneous malignancies including melanomas and keratinocyte carcinomas (KC) are the most common types of cancer, occurring at a rate of over one million per year in the United States. KC, which include both basal cell carcinomas and squamous cell carcinomas, are substantially more common than melanomas and form the subject of this chapter. Ultraviolet radiation (UVR), both UVB and UVA, as occurs with sunlight exposure is generally regarded as causal for these malignancies, but UVB is also required for vitamin D synthesis in the skin. Keratinocytes are the major cell in the epidermis. These cells not only produce vitamin D but contain the enzymatic machinery to metabolize vitamin D to its active metabolite, 1,25(OH)2D, and express the receptor for this metabolite, the vitamin D receptor (VDR). This allows the cell to respond to the 1,25(OH)2D that it produces. Based on our own data and that reported in the literature, we conclude that vitamin D signaling in the skin suppresses UVR-induced epidermal tumor formation. In this chapter we focus on four mechanisms by which vitamin D signaling suppresses tumor formation. They are inhibition of proliferation/stimulation of differentiation with discussion of the roles of hedgehog, Wnt/ß-catenin, and hyaluronan/CD44 pathways in mediating vitamin D regulation of proliferation/differentiation, regulation of the balance between oncogenic and tumor suppressor long noncoding RNAs, immune regulation, and promotion of DNA damage repair (DDR).

Transcriptional Regulation of Dental Epithelial Cell Fate.

Dental enamel is hardest tissue in the body and is produced by dental epithelial cells residing in the tooth. Their cell fates are tightly controlled by transcriptional programs that are facilitated by fate determining transcription factors and chromatin regulators. Understanding the transcriptional program controlling dental cell fate is critical for our efforts to build and repair teeth. In this review, we describe the current understanding of these regulators essential for regeneration of dental epithelial stem cells and progeny, which are identified through transgenic mouse models. We first describe the development and morphogenesis of mouse dental epithelium in which different subpopulations of epithelia such as ameloblasts contribute to enamel formation. Then, we describe the function of critical factors in stem cells or progeny to drive enamel lineages. We also show that gene mutations of these factors are associated with dental anomalies in craniofacial diseases in humans. We also describe the function of the master regulators to govern dental lineages, in which the genetic removal of each factor switches dental cell fate to that generating hair. The distinct and related mechanisms responsible for the lineage plasticity are discussed. This knowledge will lead us to develop a potential tool for bioengineering new teeth.

Mediator 1 contributes to enamel mineralization as a coactivator for Notch1 signaling and stimulates transcription of the alkaline phosphatase gene.

Tooth enamel is mineralized through the differentiation of multiple dental epithelia including ameloblasts and the stratum intermedium (SI), and this differentiation is controlled by several signaling pathways. Previously, we demonstrated that the transcriptional coactivator Mediator 1 (MED1) plays a critical role in enamel formation. For instance, conditional ablation of Med1 in dental epithelia causes functional changes in incisor-specific dental epithelial stem cells, resulting in mineralization defects in the adult incisors. However, the molecular mechanism by which Med1 deficiency causes these abnormalities is not clear. Here, we demonstrated that Med1 ablation causes early SI differentiation defects resulting in enamel hypoplasia of the Med1-deficient molars. Med1 deletion prevented Notch1-mediated differentiation of the SI cells resulting in decreased alkaline phosphatase (ALPL), which is essential for mineralization. However, it does not affect the ability of ameloblasts to produce enamel matrix proteins. Using the dental epithelial SF2 cell line, we demonstrated that MED1 directly activates transcription of the Alpl gene through the stimulation of Notch1 signaling by forming a complex with cleaved Notch1-RBP-Jk on the Alpl promoter. These results suggest that MED1 may be essential for enamel matrix mineralization by serving as a coactivator for Notch1 signaling regulating transcription of the Alpl gene.

p120-catenin is required for regulating epidermal proliferation, differentiation, and barrier function.

p120-catenin (p120) is an important regulator in the function and stability of E-cadherin. However, the role of p120 in the epidermis is unclear. Previous studies have shown that globally knockout of p120 caused increased epidermal proliferation but little changes in epidermal differentiation and permeability. In the present study, we generated a conditional knockout mouse model and examined epidermal proliferation, differentiation and permeability. The results showed that conditional knockout of p120 in the epidermis caused not only increased epidermal proliferation but also decreased epidermal differentiation and increased permeability. These data suggest that p120 is required for suppressing epidermal proliferation, promoting epidermal differentiation and maintaining permeability barrier function of the epidermis.

Vitamin D assays and the definition of hypovitaminosis D: results from the First International Conference on Controversies in Vitamin D.

The First International Conference on Controversies in Vitamin D was held in Pisa, Italy, 14-16 June 2017. The meeting's purpose was to address controversies in vitamin D research, review the data available, to help resolve them, and suggest a research agenda to clarify areas of uncertainty. The serum 25-hydroxyvitamin D [25(OH)D] concentration [i.e. the sum of 25(OH)D3 and 25(OH)D2 ] remains the critical measurement for defining vitamin D status. Assay variation for 25(OH)D has contributed to the current chaos surrounding efforts to define hypovitaminosis D. An essential requirement to develop a consensus on vitamin D status is that measurement of 25(OH)D and, in the future, other potential vitamin D biomarkers [e.g. 1α,25(OH)2 D3 , 3-epi-25(OH)D, 24,25(OH)2 D3, vitamin D-binding protein, free/bioavailable 25(OH)D and parathyroid hormone] be standardized/harmonized, to allow pooling of research data. Vitamin D Standardization Program tools are described and recommended for standardizing 25(OH)D measurement in research. In the future, similar methodology, based on National Institute for Standards and Technology standard reference materials, must be developed for other candidate markers of vitamin D status. Failure to standardize/harmonize vitamin D metabolite measurements is destined to promulgate continued chaos. At this time, 25(OH)D values below 12 ng ml-1 (30 nmol l-1 ) should be considered to be associated with an increased risk of rickets/osteomalacia, whereas 25(OH)D concentrations between 20 ng ml-1 and 50 ng ml-1 (50-125 nmol l-1 ) appear to be safe and sufficient in the general population for skeletal health. In an effort to bridge knowledge gaps in defining hypovitaminosis D, an international study on rickets as a multifactorial disease is proposed.

Regulation of Ligand and Shear Stress-induced Insulin-like Growth Factor 1 (IGF1) Signaling by the Integrin Pathway.

Mechanical loading of the skeleton, as achieved during daily movement and exercise, preserves bone mass and stimulates bone formation, whereas skeletal unloading from prolonged immobilization leads to bone loss. A functional interplay between the insulin-like growth factor 1 receptor (IGF1R), a major player in skeletal development, and integrins, mechanosensors, is thought to regulate the anabolic response of osteogenic cells to mechanical load. The mechanistic basis for this cross-talk is unclear. Here we report that integrin signaling regulates activation of IGF1R and downstream targets in response to both IGF1 and a mechanical stimulus. In addition, integrins potentiate responsiveness of IGF1R to IGF1 and mechanical forces. We demonstrate that integrin-associated kinases, Rous sarcoma oncogene (SRC) and focal adhesion kinase (FAK), display distinct actions on IGF1 signaling; FAK regulates IGF1R activation and its downstream effectors, AKT and ERK, whereas SRC controls signaling downstream of IGF1R. These findings linked to our observation that IGF1 assembles the formation of a heterocomplex between IGF1R and integrin ß3 subunit indicate that the regulation of IGF1 signaling by integrins proceeds by direct receptor-receptor interaction as a possible means to translate biomechanical forces into osteoanabolic signals.

Osteogenic Differentiation of Periosteal Cells During Fracture Healing.

Five to ten percent of fractures fail to heal normally leading to additional surgery, morbidity, and altered quality of life. Fracture healing involves the coordinated action of stem cells primarily coming from the periosteum which differentiate into the chondrocytes and osteoblasts, forming first the soft (cartilage) callus followed by the hard (bone) callus. These stem cells are accompanied by a vascular invasion that appears critical for the differentiation process and which may enable the entry of osteoclasts necessary for the remodeling of the callus into mature bone. However, more research is needed to clarify the signaling events that activate the osteochondroprogenitor cells of periosteum and stimulate their differentiation into chondrocytes and osteoblasts. Ultimately a thorough understanding of the mechanisms for differential regulation of these osteochondroprogenitors will aid in the treatment of bone healing and the prevention of delayed union and nonunion of fractures. In this review, evidence supporting the concept that the periosteal cells are the major cell sources of skeletal progenitors for the fracture callus will be discussed. The osteogenic differentiation of periosteal cells manipulated by Wnt/ß-catenin, TGF/BMP, Ihh/PTHrP, and IGF-1/PI3K-Akt signaling in fracture repair will be examined. The effect of physical (hypoxia and hyperoxia) and chemical factors (reactive oxygen species) as well as the potential coordinated regulatory mechanisms in the periosteal progenitor cells promoting osteogenic differentiation will also be discussed. Understanding the regulation of periosteal osteochondroprogenitors during fracture healing could provide insight into possible therapeutic targets and thereby help to enhance future fracture healing and bone tissue engineering approaches. J. Cell. Physiol. 232: 913-921, 2017. © 2016 Wiley Periodicals, Inc.

p120-Catenin Is Required for Dietary Calcium Suppression of Oral Carcinogenesis in Mice.

Previous studies have shown that dietary calcium suppresses oral carcinogenesis, but the mechanism is unclear. p120-catenin (p120) is a cytoplasmic protein closely associated with E-cadherin to form the E-cadherin-ß-catenin complex and may function as a tumor suppressor in the oral epithelium. To determine whether p120 is involved in the mechanism by which dietary calcium suppresses oral carcinogenesis, The normal, low, or high calcium diet was fed control mice (designated as floxed p120 mice) or mice in which p120 was specifically deleted in the oral squamous epithelium during the adult stage (designated as p120cKO mice). All mice were exposed to a low dose of oral cancer carcinogen 4-nitroquinoline 1-oxide and rates of oral squamous cell carcinoma (OSCC) and proliferation and differentiation in the cancerous and non-cancerous oral epithelium of these mice were examined. The results showed that the low calcium diet increased rates of OSCC and proliferation of the non-cancerous oral epithelium and decreased differentiation of the non-cancerous oral epithelium, but had no effect on cancerous oral epithelium. In contrast, the high calcium diet had opposite effects. However, the effect of the dietary calcium on the rates of OSCC, proliferation, and differentiation of the non-cancerous epithelium were not seen in p120cKO mice. Based on these results, we conclude that p120 is required for dietary calcium suppression of oral carcinogenesis and oral epithelial proliferation and dietary calcium induction of oral epithelial differentiation. J. Cell. Physiol. 232: 1360-1367, 2017. © 2016 Wiley Periodicals, Inc.

UVB induces epidermal 11ß-hydroxysteroid dehydrogenase type 1 activity in vivo.

Detrimental consequences of ultraviolet radiation (UVR) in skin include photoageing, immunosuppression and photocarcinogenesis, processes also significantly regulated by local glucocorticoid (GC) availability. In man, the enzyme 11ß-hydroxysteroid dehydrogenase type 1 (11ß-HSD1) generates the active GC cortisol from cortisone (or corticosterone from 11-dehydrocorticosterone in rodents). 11ß-HSD1 oxo-reductase activity requires the cofactor NADPH, generated by hexose-6-phosphate dehydrogenase. We previously demonstrated increased 11ß-HSD1 levels in skin obtained from photoexposed versus photoprotected anatomical regions. However, the direct effect of UVR on 11ß-HSD1 expression remains to be elucidated. To investigate the cutaneous regulation of 11ß-HSD1 following UVR in vivo, the dorsal skin of female SKH1 mice was irradiated with 50, 100, 200 and 400 mJ/cm(2) UVB. Measurement of transepidermal water loss, 11ß-HSD1 activity, mRNA/protein expression and histological studies was taken at 1, 3 and 7 days postexposure. 11ß-HSD1 and hexose-6-phosphate dehydrogenase mRNA expression peaked 1 day postexposure to 400 mJ/cm(2) UVB before subsequently declining (days 3 and 7). Corresponding increases in 11ß-HSD1 protein and enzyme activity were observed 3 days postexposure coinciding with reduced GC receptor mRNA expression. Immunofluorescence studies revealed 11ß-HSD1 localization to hyperproliferative epidermal keratinocytes in UVB-exposed skin. 11ß-HSD1 expression and activity were also induced by 200 and 100 (but not 50) mJ/cm(2) UVB and correlated with increased transepidermal water loss (indicative of barrier disruption). UVB-induced 11ß-HSD1 activation represents a novel mechanism that may contribute to the regulation of cutaneous responses to UVR exposure.

Total 25(OH) vitamin D, free 25(OH) vitamin D and markers of bone turnover in cirrhotics with and without synthetic dysfunction.

BACKGROUND & AIMS: Current clinical assays for total 25-hydroxy (OH) vitamin D measure vitamin D bound to vitamin D-binding protein (DBP) and albumin plus unbound ('free') D. We investigated the relationship between total and free 25(OH)D with bone metabolism markers in normal (>3.5 g/dl) vs. low (≤3.5 g/dl) albumin cirrhotics. METHODS: Eighty-two cirrhotics underwent measurement of free and total 25(OH)D by immunoassay, DBP and markers of bone metabolism [intact parathyroid hormone (iPTH), C-telopeptide (CTX), bone-specific alkaline phosphatase (BSAP), osteocalcin, amino-terminal pro-peptide of type 1-collagen (P1NP)]. Pearson's coefficients assessed relevant associations. RESULTS: Cirrhotics with low (n = 54) vs. normal (n = 28) albumin had lower total 25(OH)D (12.1 vs. 21.7 ng/ml), free 25(OH)D (6.2vs.8.6 pg/ml) and DBP(91.4 vs. 140.3 µg/ml) [P < 0.01 for each]. iPTH was similar in low and normal albumin groups (33 vs. 28 pg/ml; P = 0.38), although serum CTX(0.46vs.0.28 ng/ml) and BSAP(31.7 vs. 24.8 µg/L) were increased (P < 0.01). An inverse relationship was observed between total 25(OH)D and iPTH in normal (r = -0.47, P = 0.01) but not low albumin cirrhotics (r = 0.07, P = 0.62). Similar associations were seen between free 25(OH)D and iPTH(Normal: r = -0.46, P = 0.01; Low: r = -0.03, P = 0.84). BSAP, osteocalcin and P1NP were elevated above the normal range in all cirrhotics but not consistently associated with total or free 25(OH)D. CONCLUSIONS: Cirrhotics with low vs. normal albumin have lower levels of DBP, total and free 25(OH)D. The expected relationship between total or free 25(OH)D with iPTH was observed in normal but not in low albumin cirrhotics, demonstrating that total 25(OH)D is not an accurate marker of bioactive vitamin D status in cirrhotics with synthetic dysfunction. Additional investigation into the role of vitamin D supplementation and its impact on bone mineral homoeostasis in this population is needed.

Vitamin D receptor, a tumor suppressor in skin.

Vitamin D and calcium are well-established regulators of keratinocyte proliferation and differentiation. Therefore, it was not a great surprise that deletion of the vitamin D receptor (VDR) should predispose the skin to tumor formation, and that the combination of deleting both the VDR and calcium sensing receptor (CaSR) should be especially pro-oncogenic. In this review I have examined 4 mechanisms that appear to underlie the means by which VDR acts as a tumor suppressor in skin. First, DNA damage repair is curtailed in the absence of the VDR, allowing mutations in DNA to accumulate. Second and third involve the increased activation of the hedgehog and ß-catenin pathways in the epidermis in the absence of the VDR, leading to poorly regulated proliferation with reduced differentiation. Finally, VDR deletion leads to a shift in the expression of long noncoding RNAs toward a more oncogenic profile. How these different mechanisms interact and their relative importance in the predisposition of the VDR null epidermis to tumor formation remain under active investigation.

LncRNA: a new player in 1α, 25(OH)(2) vitamin D(3) /VDR protection against skin cancer formation.

Sunlight, vitamin D and skin cancer form a controversial brew. While too much sunlight exposure causes skin cancer, it is the major source of vitamin D from skin. We propose that these processes can be balanced. Vitamin D signalling (VDS) protects against skin cancer as demonstrated by the susceptibility of the skin to tumor formation in VDR null mice and protection from UVB-induced mutations when VDR agonists are administered. The question is how is protection afforded. Previously, we have focused on the Wnt/ß-catenin/hedgehog and DNA damage repair (DDR) pathways. As VDR regulates hundreds of genes with thousands of VDR response elements (VDRE) throughout the genome, and many VDREs are in non-coding regions, we decided to explore long non-coding RNAs (lncRNA). LncRNAs are mRNA-like transcripts ranging from 200 bases ~100 kb lacking significant open reading frames. They are aberrantly expressed in human cancers and involved in a spectrum of tumorigenic/metastatic processes (cell proliferation/apoptosis/angiogenesis). We discovered that VDS regulated the expression of certain lncRNAs in a manner consistent with VDS protection against skin cancer. Given the huge variation in genes actively regulated by 1,25(OH)2 D from different cell types, it is conceivable that our results could apply to personalized medicine based on the distinctive lncRNA profiles. These lncRNAs could also serve as skin cancer biomarkers secreted into the blood or urine via exosomes as demonstrated in other cancer types (breast, prostate). Modulation of lncRNA profile by VDS may also provide insight into regulating pathways such as Wnt/ß-catenin and hedgehog.

The vitamin D receptor: a tumor suppressor in skin.

Cutaneous malignancies including melanomas and non melanoma skin cancers (NMSC) are the most common types of cancer, occurring at a rate of over 1 million per year in the United States. The major cell in the epidermis, the keratinocyte, not only produces vitamin D but contains the enzymatic machinery to metabolize vitamin D to its active metabolite, 1,25(OH)2D, and expresses the receptor for this metabolite, the vitamin D receptor (VDR), allowing the cell to respond to the 1,25(OH)2D that it produces. In vitro, 1,25(OH)2D stimulates the differentiation and inhibits the proliferation of these cells and so would be expected to be tumor suppressive. However, epidemiologic evidence demonstrating a negative relationship between circulating levels of the substrate for CYP27B1, 25OHD, and the incidence of these malignancies is mixed, raising the question whether vitamin D is protective in the in vivo setting. UV radiation (UV), both UVB and UVA, as occurs with sunlight exposure is generally regarded as causal for these malignancies, but UVB is also required for vitamin D synthesis in the skin. This complicates conclusions reached from epidemiologic studies in that UVB is associated with higher 25OHD levels as well as increased incidence of cutaneous malignancies. Based on our own data and that reported in the literature we hypothesize that vitamin D signaling in the skin suppresses UVR induced epidermal tumor formation. In this chapter we will first discuss recent data regarding potential mechanisms by which vitamin D signaling suppresses tumor formation, then focus on three general mechanisms that mediate tumor suppression by VDR in the skin: inhibition of proliferation and stimulation of differentiation, immune regulation, and stimulation of DNA damage repair (DDR).

Vitamin D for the Prevention of Disease: An Endocrine Society Clinical Practice Guideline.

BACKGROUND: Numerous studies demonstrate associations between serum concentrations of 25-hydroxyvitamin D (25[OH]D) and a variety of common disorders, including musculoskeletal, metabolic, cardiovascular, malignant, autoimmune, and infectious diseases. Although a causal link between serum 25(OH)D concentrations and many disorders has not been clearly established, these associations have led to widespread supplementation with vitamin D and increased laboratory testing for 25(OH)D in the general population. The benefit-risk ratio of this increase in vitamin D use is not clear, and the optimal vitamin D intake and the role of testing for 25(OH)D for disease prevention remain uncertain. OBJECTIVE: To develop clinical guidelines for the use of vitamin D (cholecalciferol [vitamin D3] or ergocalciferol [vitamin D2]) to lower the risk of disease in individuals without established indications for vitamin D treatment or 25(OH)D testing. METHODS: A multidisciplinary panel of clinical experts, along with experts in guideline methodology and systematic literature review, identified and prioritized 14 clinically relevant questions related to the use of vitamin D and 25(OH)D testing to lower the risk of disease. The panel prioritized randomized placebo-controlled trials in general populations (without an established indication for vitamin D treatment or 25[OH]D testing), evaluating the effects of empiric vitamin D administration throughout the lifespan, as well as in select conditions (pregnancy and prediabetes). The panel defined "empiric supplementation" as vitamin D intake that (a) exceeds the Dietary Reference Intakes (DRI) and (b) is implemented without testing for 25(OH)D. Systematic reviews queried electronic databases for publications related to these 14 clinical questions. The Grading of Recommendations, Assessment, Development, and Evaluation (GRADE) methodology was used to assess the certainty of evidence and guide recommendations. The approach incorporated perspectives from a patient representative and considered patient values, costs and resources required, acceptability and feasibility, and impact on health equity of the proposed recommendations. The process to develop this clinical guideline did not use a risk assessment framework and was not designed to replace current DRI for vitamin D. RESULTS: The panel suggests empiric vitamin D supplementation for children and adolescents aged 1 to 18 years to prevent nutritional rickets and because of its potential to lower the risk of respiratory tract infections; for those aged 75 years and older because of its potential to lower the risk of mortality; for those who are pregnant because of its potential to lower the risk of preeclampsia, intra-uterine mortality, preterm birth, small-for-gestational-age birth, and neonatal mortality; and for those with high-risk prediabetes because of its potential to reduce progression to diabetes. Because the vitamin D doses in the included clinical trials varied considerably and many trial participants were allowed to continue their own vitamin D-containing supplements, the optimal doses for empiric vitamin D supplementation remain unclear for the populations considered. For nonpregnant people older than 50 years for whom vitamin D is indicated, the panel suggests supplementation via daily administration of vitamin D, rather than intermittent use of high doses. The panel suggests against empiric vitamin D supplementation above the current DRI to lower the risk of disease in healthy adults younger than 75 years. No clinical trial evidence was found to support routine screening for 25(OH)D in the general population, nor in those with obesity or dark complexion, and there was no clear evidence defining the optimal target level of 25(OH)D required for disease prevention in the populations considered; thus, the panel suggests against routine 25(OH)D testing in all populations considered. The panel judged that, in most situations, empiric vitamin D supplementation is inexpensive, feasible, acceptable to both healthy individuals and health care professionals, and has no negative effect on health equity. CONCLUSION: The panel suggests empiric vitamin D for those aged 1 to 18 years and adults over 75 years of age, those who are pregnant, and those with high-risk prediabetes. Due to the scarcity of natural food sources rich in vitamin D, empiric supplementation can be achieved through a combination of fortified foods and supplements that contain vitamin D. Based on the absence of supportive clinical trial evidence, the panel suggests against routine 25(OH)D testing in the absence of established indications. These recommendations are not meant to replace the current DRIs for vitamin D, nor do they apply to people with established indications for vitamin D treatment or 25(OH)D testing. Further research is needed to determine optimal 25(OH)D levels for specific health benefits.