Vitamin D receptor levels and binding are reduced in aged rat intestinal subcellular fractions

In vitro studies revealed a downregulation of Wnt/β-catenin cascade by active vitamin D and TX 527 analog in a Kaposi's sarcoma cellular model

The Kaposi's sarcoma-associated herpesvirus G-protein-coupled receptor (vGPCR) is a key molecule in the pathogenesis of Kaposi's sarcoma. We have previously demonstrated that 1α,25(OH)₂D₃ or its less calcemic analog TX 527 exerts antiproliferative effects in endothelial cells stable expressing vGPCR. Since it is well documented that vGPCR activates the canonical Wnt/β-catenin signaling pathway, the aim of this study was to evaluate if Wnt/β-catenin cascade is target of 1α,25(OH)₂D₃ or TX 527 as part of their antineoplastic mechanism. Firstly, Western blot studies showed an increase in β-catenin protein levels in a dose and time dependent manner; and when VDR was knockdown, β-catenin protein levels were significantly decreased. Secondly, β-catenin localization, investigated by immunofluorescence and subcellular fractionation techniques, was found increased in the nucleus and plasma membrane after 1α,25(OH)₂D₃ treatment. VE-cadherin protein levels were also increased in the plasma membrane fraction. Furthermore, β-catenin interaction with VDR was observed by co-immunoprecipitation and mRNA expression of β-catenin target genes was found decreased. Finally, DKK-1, the extracellular inhibitor of Wnt/β-catenin pathway, showed an initial upregulation of mRNA expression. Altogether, the results obtained by different techniques revealed a downregulation of Wnt/β-catenin cascade after 1α,25(OH)₂D₃ or TX 527 treatment, showing the foundation for a potential chemotherapeutic agent.

VDR agonists down regulate PI3K/Akt/mTOR axis and trigger autophagy in Kaposi's sarcoma cells

The Kaposi's sarcoma-associated herpesvirus G protein-coupled receptor (KSHV/vGPCR) is a key molecule in the pathogenesis of Kaposi's sarcoma. We have previously shown that 1α,25(OH)2D3 or its less-calcemic analog TX 527 inhibits the proliferation of endothelial cells expressing vGPCR, NF-κB activity and induces apoptosis in a VDR dependent manner. In this work, we further explored whether 1α,25(OH)2D3 or TX 527 regulates PI3K/Akt/mTOR axis and induces autophagy as part of its antineoplastic mechanism of action. Proliferation assays indicated that vGPCR cell number decreased in presence of LY294002 (PI3K/Akt inhibitor) likewise 1α,25(OH)2D3 or TX 527 (10 nM, 48 h). Also, Akt phosphorylation was found decreased in dose (0.1-100 nM) and time response studies (12-72 h) after both compounds treatments. In addition, decreased phosphorylated Akt was significantly observed in the nucleus. Moreover, regulation of Akt phosphorylation was NF-κB and VDR dependent. TNFAIP3/A20, an ubiquitin-editing enzyme, a direct NF-κB target gene and a negative regulator of Beclin-1, was down-regulated whereas Beclin-1 was up-regulated after 10 nM of 1α,25(OH)2D3 or TX 527 treatment. Decrement in Akt phosphorylation was accompanied by a reduced mTOR phosphorylation and an increase in the autophagy marker LC3-II. Since increment in autophagosomes not always indicates increment in autophagy activity, we used Chloroquine (CQ, 1 μM), an inhibitor of autophagy flow, to confirm autophagy after both VDR agonists treatment. In conclusion, VDR agonists, 1α,25(OH)2D3 or TX 527, inhibited PI3K/Akt/mTOR axis and induced autophagy in endothelial cells expressing vGPCR by a VDR-dependent mechanism.

Low 25-hydroxyvitamin D levels and the risk of frailty syndrome: a systematic review and dose-response meta-analysis

Background

Vitamin D deficiency and frailty are common with aging. Previous studies examining vitamin D status and frailty have produced mixed results, and in particular, the shape of the association has not been well established. We examined the association between 25-hydroxyvitamin D (25OHD) serum levels and frailty by performing a systematic review and dose-response meta-analysis.

Methods

We searched the PubMed, EMBASE and Cochrane Library databases of Elsevier through February 2017. Cross-sectional and cohort studies that reported adjusted risk ratios with 95% confidence intervals (CI) for frailty with ≥3 categories of 25OHD serum levels were selected. Data extraction was performed independently by two authors. The reported risk estimates for 25OHD categories were recalculated, employing a comprehensive trend estimation from summarized dose-response data.

Results

The pooled risk estimate of frailty syndrome per 25 nmol/L increment in serum 25OHD concentration was 0.88 (95% CI = 0.82–0.95, I² = 86.8%) in the 6 cross-sectional studies and 0.89 (95% CI = 0.85–0.94, I² = 0.0%) in the 4 prospective cohort studies. Based on the Akaike information criteria (AIC), a linear model was selected (AIC for the nonlinear model: − 5.4, AIC for the linear model: − 6.8 in the prospective cohort studies; AIC for the linear model: − 13.6, AIC for the nonlinear model: − 1.77 in the cross-sectional studies).

Conclusions

This dose-response meta-analysis indicates that serum 25OHD levels are significantly and directly associated with the risk of frailty. Further studies should address the underlying mechanisms to explain this relationship and to determine whether vitamin D supplementation is effective for preventing frailty syndrome.

Electronic supplementary material

The online version of this article (10.1186/s12877-018-0904-2) contains supplementary material, which is available to authorized users.

The role of the intraplaque vitamin d system in atherogenesis

Vitamin D has been shown to play critical activities in several physiological pathways not involving the calcium/phosphorus homeostasis. The ubiquitous distribution of the vitamin D receptor that is expressed in a variety of human and mouse tissues has strongly supported research on these "nonclassical" activities of vitamin D. On the other hand, the recent discovery of the expression also for vitamin D-related enzymes (such as 25-hydroxyvitamin D-1 α -hydroxylase and the catabolic enzyme 1,25-dihydroxyvitamin D-24-hydroxylase) in several tissues suggested that the vitamin D system is more complex than previously shown and it may act within tissues through autocrine and paracrine pathways. This updated model of vitamin D axis within peripheral tissues has been particularly investigated in atherosclerotic pathophysiology. This review aims at updating the role of the local vitamin D within atherosclerotic plaques, providing an overview of both intracellular mechanisms and cell-to-cell interactions. In addition, clinical findings about the potential causal relationship between vitamin D deficiency and atherogenesis will be analysed and discussed.

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.

NFκB pathway is down-regulated by 1α,25(OH)(2)-vitamin D(3) in endothelial cells transformed by Kaposi sarcoma-associated herpes virus G protein coupled receptor

We have previously demonstrated that 1α,25 dihydroxy-vitamin D(3) (1α,25(OH)(2)D(3)) has antiproliferative effects on the growth of endothelial cells transformed by the viral G protein-coupled receptor associated to Kaposi sarcoma (vGPCR). In this work, we have investigated whether 1α,25(OH)(2)D(3) exerts its growth inhibitory effects by inhibiting the Nuclear Factor κ B (NFκB) pathway which is highly activated by vGPCR. Cell proliferation studies demonstrated that 1α,25(OH)(2)D(3), similarly to bortezomib, a proteosome inhibitor that suppresses the activation of NFκB, reduced the proliferation of endothelial cells transformed by vGPCR (SVEC-vGPCR). The activity of NFκB in these cells decreased by 70% upon 1α,25(OH)(2)D(3) treatment. Furthermore, time and dose response studies showed that the hormone significantly decreased NFκB and increased IκBα mRNA and protein levels in SVEC-vGPCR cells, whereas in SVEC only IκBα increased significantly. Moreover, NFκB translocation to the nucleus was inhibited and occurred by a mechanism independent of NFκB association with vitamin D(3) receptor (VDR). 1α,25(OH)(2)D(3)-induced increase in IκBα required de novo protein synthesis, and was independent of MAPK and PI3K/Akt pathways. Altogether, these results suggest that down-regulation of the NFκB pathway is part of the mechanism involved in the antiproliferative effects of 1α,25(OH)(2)D(3) on endothelial cells transformed by vGPCR.

Relevance of vitamin D in muscle health

This review will summarize the impact of vitamin D deficiency on muscle health. Mechanistic evidence regarding the presence of the specific vitamin D receptor in muscle tissue and muscle biopsy abnormalities observed with deficiency will be reviewed, as well as molecular and non-molecular effects of vitamin D in muscle tissue. At the clinical level, the evidence from randomized controlled trials of vitamin D supplementation on functional improvement and fall reduction will be summarized. Further, the manuscript will discuss whether vitamin D effects on fall prevention modulate in part its benefit on fracture prevention and why fall prevention is essential in fracture prevention at higher age. Finally, trial and epidemiological data will be reviewed to assess desirable serum 25-hydroxyvitamin D levels for optimal muscle health.

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.

Mitochondrial localization of vitamin D receptor in human platelets and differentiated megakaryocytes

BACKGROUND

Like other steroid hormones, vitamin D elicits both transcriptional events and rapid non genomic effects. Vitamin D receptor (VDR) localization and mechanisms of VDR-triggered non genomic responses are still controversial. Although anticoagulant effects of vitamin D have been reported and VDR signalling has been characterized in monocytes and vascular cells, nothing is known about VDR expression and functions in human platelets, anucleated fragments of megakaryocytes which are known targets of other steroids.

METHODOLOGY/PRINCIPAL FINDINGS

In this study we characterized the expression and cellular localization of VDR in human platelets and in a megakaryocyte lineage. Human platelets and their TPA-differentiated precursors expressed a classical 50 kDa VDR protein, which increased with megakaryocytes maturation. By biochemical fractionation studies we demonstrated the presence of the receptor in the soluble and mitochondrial compartment of human platelets, and the observation was confirmed by immunoelectron microscopy analysis. Similar localization was found in mature megakaryocytes, where besides its classical nuclear localization the receptor was evident as soluble and mitochondria resident protein.

CONCLUSIONS

The results reported here suggest that megakaryocytopoiesis and platelet activation, which are calcium-dependent events, might be modulated by a mitochondrial non genomic activity of VDR. These data open challenging future studies on VDR physiological role in platelets and more generally in mitochondria.

The Evolution of Cell Communication: The Road not Taken

In the post-genomic era the complex problem of evolutionary biology can be tackled from the top-down, the bottom-up, or from the middle-out. Given the emergent and contingent nature of this process, we have chosen to take the latter approach, both as a mechanistic link to developmental biology and as a rational means of identifying signaling mechanisms based on their functional genomic significance. Using this approach, we have been able to configure a working model for lung evolution by reverse-engineering lung surfactant from the mammalian lung to the swim bladder of fish. Based on this archetypal cell-molecular model, we have reduced evolutionary biology to cell communication, starting with unicellular organisms communicating with the environment, followed by cell-cell communication to generate metazoa, culminating in the communication of genetic information between generations, i.e. reproduction. This model predicts the evolution of physiologic systems-including development, homeostasis, disease, regeneration/repair, and aging- as a logical consequence of biology reducing entropy. This approach provides a novel and robust way of formulating refutable, testable hypotheses to determine the ultimate origins and first principles of physiology, providing candidate genes for phenotypes hypothesized to have mediated evolutionary changes in structure and/or function. Ultimately, it will form the basis for predictive medicine and molecular bioethics, rather than merely showing associations between genes and pathology, which is an unequivocal Just So Story. In this new age of genomics, our reach must exceed our grasp.

Ageing and vitamin D deficiency: effects on calcium homeostasis and considerations for vitamin D supplementation

Vitamin D is a fat-soluble, seco-steroid hormone. In man, the vitamin D receptor is expressed in almost all tissues, enabling effects in multiple systems of the human body. These effects can be endocrine, paracrine and autocrine. The present review summarises the effects of ageing on the vitamin D endocrine system and on Ca homeostasis. Furthermore, consequences for vitamin D supplementation are discussed.