Transcriptomic analysis reveal the responses of dendritic cells to VDBP

BACKGROUND

Vitamin D binding protein (VDBP) is an essential plasma carrier protein, which plays possible roles in reproductive health, disease and so on. However, the effects of VDBP on immunity have not been fully studied and the pertinent literatures remain very limited.

OBJECTIVE

In this study, we introduced the exogenous VDBP into DC2.4 and established a stable DC2.4/VDBP cell line to explore the role of this gene in immunity.

METHODS

Dendritic cells (DCs), as the most effective antigen presenting cells (APC) found so far, are directly involved in regulating some innate immunity. In order to evaluate the biological role of VDBP in DCs, we stably overexpressed VDBP in DCs, and conducted Cell Counting Kit‑8 (CCK-8 kit) and flow cytometry to detect changes in cell function. CCK-8 kit was used to monitor the viability of DCs after gene overexpression, and flow cytometry was used to detect changes in cell cycle distribution and apoptosis. Subsequently, in order to reveal the mechanism of VDBP regulating DCs, we adopted RNA sequencing (RNA-seq).

RESULTS

CCK-8 results revealed VDBP successfully inhibited viability of DCs. Besides, we found that overexpression of this gene greatly promoted apoptosis and obviously altered the cell cycle distribution of DCs in G1 and G2 phases. Moreover, RNA-seq was carried out and 151 differently expression genes (DEGs) were obtained. In addition, gene differential expression analysis showed that most of them were uniformly enriched in immunity-related pathways.

CONCLUSION

These results indicated that VDBP greatly repressed proliferation, facilitated apoptosis and changed cell cycle in DCs via altering the expression levels of gene associated with their cellular immunity.

Serum vitamin D status following pediatric cardiac surgery and association with clinical outcome

Our aim is to determine the prevalence of vitamin D deficiency in children with congenital heart disease (CHD). In addition, we demonstrated the effect of cardiopulmonary bypass (CPB) on vitamin D, parathyroid hormone (PTH), and calcium levels. The association between perioperative vitamin D levels and postoperative clinical outcomes has been explored. A prospective observational study was conducted from February 2018 to June 2019 on 69 children undergoing elective surgery for CHD under CPB. Blood samples were collected preoperatively, immediate postoperatively, and 24 h postoperatively. Vitamin D deficiency was present in 34 (49.3%) patients preoperatively and 63 (91.3%) patients immediately postoperative. We identified 42.03% decline of 25(OH)D immediately postoperative. Changes in ionized calcium (iCa) concentrations were accompanied by reciprocal alterations in PTH concentrations. Lower postoperative 25(OH)D was associated with higher maximum vasoactive inotropic score (VIS) in the first 24 h postoperative (r = - 0.259, p = 0.03).Conclusion: Vitamin D deficiency is common in children with CHD and the majority are vitamin D deficient following cardiac surgery with acute decline of serum 25(OH)D after CPB. Lower postoperative vitamin D levels in children undergoing cardiac surgery are associated with the need for increasing the inotropic support.What is Known:• Vitamin D is a pleiotropic hormone, important for calcium homeostasis.• Vitamin D deficiency might affect the outcome in critically ill patients.What is New:• Cardiopulmonary bypass causes acute decline of vitamin D in children.• Lower postoperative vitamin D is associated with higher inotropic support.

Vitamin D Binding Protein, Total and Free Vitamin D Levels in Different Physiological and Pathophysiological Conditions

This review focuses on the biologic importance of the vitamin D binding protein (DBP) with emphasis on its regulation of total and free vitamin D metabolite levels in various clinical conditions. Nearly all DBP is produced in the liver, where its regulation is influenced by estrogen, glucocorticoids and inflammatory cytokines but not by vitamin D itself. DBP is the most polymorphic protein known, and different DBP alleles can have substantial impact on its biologic functions. The three most common alleles-Gc1f, Gc1s, Gc2-differ in their affinity with the vitamin D metabolites and have been variably associated with a number of clinical conditions. Although DBP has a number of biologic functions independent of vitamin D, its major biologic function is that of regulating circulating free and total levels of vitamin D metabolites. 25 hydroxyvitamin D (25(OH)D) is the best studied form of vitamin D as it provides the best measure of vitamin D status. In a normal non-pregnant individual, approximately 0.03% of 25(OH)D is free; 85% is bound to DBP, 15% is bound to albumin. The free hormone hypothesis postulates that only free 25(OH)D can enter cells. This hypothesis is supported by the observation that mice lacking DBP, and therefore with essentially undetectable 25(OH)D levels, do not show signs of vitamin D deficiency unless put on a vitamin D deficient diet. Similar observations have recently been described in a family with a DBP mutation. This hypothesis also applies to other protein bound lipophilic hormones including glucocorticoids, sex steroids, and thyroid hormone. However, tissues expressing the megalin/cubilin complex, such as the kidney, have the capability of taking up 25(OH)D still bound to DBP, but most tissues rely on the free level. Attempts to calculate the free level using affinity constants generated in a normal individual along with measurement of DBP and total 25(OH)D have not accurately reflected directly measured free levels in a number of clinical conditions. In this review, we examine the impact of different clinical conditions as well as different DBP alleles on the relationship between total and free 25(OH)D, using only data in which the free 25(OH)D level was directly measured. The major conclusion is that a number of clinical conditions alter this relationship, raising the question whether measuring just total 25(OH)D might be misleading regarding the assessment of vitamin D status, and such assessment might be improved by measuring free 25(OH)D instead of or in addition to total 25(OH)D.

A monoclonal antibody sandwich ELISA for vitamin D-binding protein (VDBP) is unaffected by Gc-globulin phenotype peptides and actin and demonstrates reduced levels in sepsis and non-sepsis intensive care patients

The measurement of vitamin D-binding protein (VDBP) by immunoassay has been confounded by variable antibody recognition of the Gc1s, Gc1F and Gc2 phenotypes. This has led to spurious conclusions regarding vitamin D status in different ethnic groups. In order to overcome these problems there is a requirement for VDBP antibodies that are unaffected by phenotype status. Here we report the generation and testing of three monoclonal antibodies to VDBP which recognise linear epitopes and are unaffected by vast molar excesses of synthetic peptides spanning these phenotypic domains. These IgG1 kappa antibodies were purified and biotinylated to allow suitable pairings to develop a sandwich ELISA for circulating VDBP. The VDBP ELISA is unaffected by actin and confirms that VDBP levels are significantly reduced in sepsis patients and non-sepsis intensive care patients compared to normal healthy subjects. Levels of VDBP along with total 25OH vitamin D3 can be used to calculate free 25OH vitamin D3 levels and these compare well with consensus values determined independently. The VDBP ELISA meets acceptable performance criteria and as such can be used in conjunction with total 25OH vitamin D3 to determine the free 25OH vitamin D3 status in various cohorts.

Behind the scenes of vitamin D binding protein: more than vitamin D binding

Although being discovered in 1959, the number of published papers in recent years reveals that vitamin D binding protein (DBP), a member of the albuminoid superfamily, is a hot research topic. Besides the three major phenotypes (DBP1F, DBP1S and DBP2), more than 120 unique variants have been described of this polymorphic protein. The presence of DBP has been demonstrated in different body fluids (serum, urine, breast milk, ascitic fluid, cerebrospinal fluid, saliva and seminal fluid) and organs (brain, heart, lungs, kidneys, placenta, spleen, testes and uterus). Although the major function is binding, solubilization and transport of vitamin D and its metabolites, the name of this glycoprotein hides numerous other important biological functions. In this review, we will focus on the analytical aspects of the determination of DBP and discuss in detail the multifunctional capacity [actin scavenging, binding of fatty acids, chemotaxis, binding of endotoxins, influence on T cell response and influence of vitamin D binding protein-macrophage activating factor (DBP-MAF) on bone metabolism and cancer] of this abundant plasma protein.

Vitamin D deficiency in surgical congenital heart disease: prevalence and relevance

Vitamin D is a pleiotropic hormone important for the proper functioning of multiple organ systems. An emerging body of adult and pediatric critical care literature strongly suggests that vitamin D deficiency contributes to secondary organ pathophysiology, prolongs ICU stay, and worsens outcome in critically ill populations. Recent clinical studies suggest that a significant number of children with congenital heart disease (CHD) have post-operative vitamin D deficiency which appears to be associated with greater cardiovascular dysfunction. Altogether the cumulative body of literature suggests that peri-operative optimization of vitamin D status has the potential to speed recovery and/or improve outcome. This review describes the epidemiological and basic science research linking vitamin D deficiency to post-operative organ dysfunction. Furthermore, the available supplementation approaches are reviewed in the context of prevention of post-operative vitamin D deficiency and avoidance of toxicity in the majority of CHD patients. Finally, knowledge gaps regarding vitamin D supplementation are identified and the next stages for research are outlined.