It is estimated that one billion people around the world are vitamin D deficient. Vitamin D deficiency has been linked to various inflammatory diseases. However, the mechanism by which vitamin D reduces inflammation remains poorly understood. In this study, we investigated the inhibitory effects of physiologic levels of vitamin D on lipopolysaccharide (LPS)-stimulated inflammatory response in human blood monocytes, and explored potential mechanisms of vitamin D action. We observed that two forms of the vitamin D, 1,25(OH)2D3, and 25(OH)D3, dose dependently inhibited LPS-induced p38 phosphorylation at physiologic concentrations, IL-6 and TNF-α production by human monocytes. Upon vitamin D treatment, the expression of mitogen-activated protein kinase phosphatase-1 (MKP-1) was significantly upregulated in human monocytes and murine bone marrow-derived macrophages (BMM). Increased binding of the vitamin D receptor and increased histone H4 acetylation at the identified vitamin D response element of the murine and human MKP-1 promoters were demonstrated. Moreover, in BMM from MKP1−/− mice, the inhibition of LPS-induced p38 phosphorylation by vitamin D was completely abolished. Vitamin D inhibition of LPS-induced IL-6 and TNF-α production by BMM from MKP-1−/− mice was significantly reduced as compared to wild type mice. In conclusion, this study identified the upregulation of MKP-1 by vitamin D as a novel pathway by which vitamin D inhibits LPS-induced p38 activation and cytokine production in monocytes/macrophages.

Skin barrier dysfunction has been reported in both atopic dermatitis (AD) and food allergy (FA). However, only one-third of patients with AD have FA. The purpose of this study was to use a minimally invasive skin tape strip sampling method and a multiomics approach to determine whether children with AD and FA (AD FA+) have stratum corneum (SC) abnormalities that distinguish them from AD without FA (AD FA−) and nonatopic (NA) controls. Transepidermal water loss was found to be increased in AD FA+. Filaggrin and the proportion of ω-hydroxy fatty acid sphingosine ceramide content in nonlesional skin of children with AD FA+ were substantially lower than in AD FA− and NA skin. These abnormalities correlated with morphologic changes in epidermal lamellar bilayer architecture responsible for barrier homeostasis. Shotgun metagenomic studies revealed that the nonlesional skin of AD FA+ had increased abundance of Staphylococcus aureus compared to NA. Increased expression of keratins 5, 14, and 16 indicative of hyperproliferative keratinocytes was observed in the SC of AD FA+. The skin transcriptome of AD FA+ had increased gene expression for dendritic cells and type 2 immune pathways. A network analysis revealed keratins 5, 14, and 16 were positively correlated with AD FA+, whereas filaggrin breakdown products were negatively correlated with AD FA+. These data suggest that the most superficial compartment of nonlesional skin in AD FA+ has unique properties associated with an immature skin barrier and type 2 immune activation.

Lipids in the stratum corneum of atopic dermatitis (AD) patients differ substantially in composition from healthy subjects. We hypothesized that hyperactivated type 2 immune response alters AD skin lipid metabolism. We have analyzed stratum corneum lipids from nonlesional and lesional skin of AD subjects and IL-13 skin-specific Tg mice. We also directly examined the effects of IL-4/IL-13 on human keratinocytes in vitro. Mass spectrometric analysis of lesional stratum corneum from AD subjects and IL-13 Tg mice revealed an increased proportion of short-chain (N-14:0 to N-24:0) NS ceramides, sphingomyelins, and 14:0-22:0 lysophosphatidylcholines (14:0-22:0 LPC) with a simultaneous decline in the proportion of corresponding long-chain species (N-26:0 to N-32:0 sphingolipids and 24:0-30:0 LPC) when compared with healthy controls. An increase in short-chain LPC species was also observed in nonlesional AD skin. Similar changes were observed in IL-4/IL-13-driven responses in Ca2+-differentiated human keratinocytes in vitro, all being blocked by STAT6 silencing with siRNA. RNA sequencing analysis performed on stratum corneum of AD as compared with healthy subjects identified decreased expression of fatty acid elongases ELOVL3 and ELOVL6 that contributed to observed changes in atopic skin lipids. IL-4/IL-13 also inhibited ELOVL3 and ELOVL6 expression in keratinocyte cultures in a STAT6-dependent manner. Downregulation of ELOVL3/ELOVL6 expression in keratinocytes by siRNA decreased the proportion of long-chain fatty acids globally and in sphingolipids. Thus, our data strongly support the pathogenic role of type 2 immune activation in AD skin lipid metabolism.

Minimally invasive expression profiling of nonlesional skin reveals stratification in AD molecular pathology by type 2 inflammation that correlates with disease severity.

Background the effects of serum vitamin D status on atopy, steroid requirement and functional responsiveness to corticosteroids in children vs. adults with asthma have not been studied systematically. Objective to explore age-specific effects of vitamin D in asthma. Methods serum vitamin D levels were examined in a prospective study of adults and children (102 normal controls and 103 asthmatics). Peripheral blood mononuclear cells (PBMC) were cultured for 3h +/−100nM dexamethasone (DEX) and the expression of corticosteroid-regulated genes was detected by real time PCR. Serum IgE levels were measured; information about asthmatics’ steroid requirement was collected. Results 47.6% of asthmatics and 56.8% normal control subjects had deficient serum vitamin D levels (<20ng/ml) with mean ± SD of 20.7±9.8ng/ml and 19.2±7.7ng/ml, respectively. In multivariate regression models, a significant positive correlation between serum vitamin D and the expression of vitamin D regulated targets - cyp24a by PBMC (p=0.0084, pediatric asthma group only) and serum LL-37 levels (p=0.0006, pediatric; but p=0.0067 in adult asthma groups) was found. An inverse association between vitamin D and serum IgE levels was observed in the pediatric (p=0.006) asthma group. Serum vitamin D (p=0.05) as well as PBMC cyp24a expression (p=0.0312) demonstrated significant inverse relationship with daily ICS dose in the pediatric asthma group only. Cyp24a expression in PBMC correlated positively with in vitro suppression of TNFα (p=0.05) and IL-13 (p=0.0094) in PBMC by DEX only in the pediatric asthma group. Conclusions this study demonstrated significant associations between serum vitamin D status and steroid requirement and in vitro responsiveness to corticosteroids in the pediatric but not the adult asthma group. Vitamin D was also related to IgE levels in children but not in adults. Clinical Implication The results of this study suggest that vitamin D supplementation in children may enhance corticosteroid responses, control atopy and could thereby improve asthma control.