The Role of Vitamin D in Neuroprotection in Multiple Sclerosis: An Update.

Multiple sclerosis (MS) is a complex neurological condition that involves both inflammatory demyelinating and neurodegenerative components. MS research and treatments have traditionally focused on immunomodulation, with less investigation of neuroprotection, and this holds true for the role of vitamin D in MS. Researchers have already established that vitamin D plays an anti-inflammatory role in modulating the immune system in MS. More recently, researchers have begun investigating the potential neuroprotective role of vitamin D in MS. The active form of vitamin D, 1,25(OH)2D3, has a range of neuroprotective properties, which may be important in remyelination and/or the prevention of demyelination. The most notable finding relevant to MS is that 1,25(OH)2D3 promotes stem cell proliferation and drives the differentiation of neural stem cells into oligodendrocytes, which carry out remyelination. In addition, 1,25(OH)2D3 counteracts neurodegeneration and oxidative stress by suppressing the activation of reactive astrocytes and M1 microglia. 1,25(OH)2D3 also promotes the expression of various neuroprotective factors, including neurotrophins and antioxidant enzymes. 1,25(OH)2D3 decreases blood-brain barrier permeability, reducing leukocyte recruitment into the central nervous system. These neuroprotective effects, stimulated by 1,25(OH)2D3, all enhance neuronal survival. This review summarizes and connects the current evidence supporting the vitamin D-mediated mechanisms of action for neuroprotection in MS.

Vitamin D metabolic pathway genes and risk of multiple sclerosis in Canadians.

BACKGROUND: Multiple sclerosis (MS) is determined by interactions between genes and environment and the influence of vitamin D adequacy has been proposed. Previous studies have shown that serum 25-hydroxyvitamin D (25(OH)D) levels are genetically influenced. Polymorphisms in vitamin D pathway genes are candidates for association with MS susceptibility. METHODS: MS patients (n=1364) and their unaffected first-degree relatives (n=1661) were ascertained through the Canadian Collaborative study. Seventy-one SNPs, across four genes [vitamin D receptor (VDR), 1-alpha-hydroxylase (CYP27B1) enzyme, vitamin D binding protein (DBP), 24-hydroxylase (CYP24)], were genotyped and tested for association with MS susceptibility using TDT in PLINK. Secondary analyses included stratification for HLA-DRB1*15 and parent of origin transmission effects. RESULTS: We found no significant association of vitamin D pathway genes with MS susceptibility after correction for multiple comparisons. However, the VDR Fok1 variant (rs2228570), selected for previously positive associations with MS susceptibility and 25(OH)D levels in MS patients showed marginally distorted transmission in DRB15-negative patients (p=0.03). There was no evidence for differential maternal versus paternal allele transmission. CONCLUSIONS: The findings fail to directly connect vitamin D metabolism genes to MS susceptibility, despite a large sample size and comprehensive gene coverage.

Congenital abnormalities and multiple sclerosis.

BACKGROUND: There is a strong maternal parent-of-origin effect in determining susceptibility to multiple sclerosis (MS). One hypothesis is that an abnormal intrauterine milieu leading to impaired fetal development could plausibly also result in increased susceptibility to MS. A possible marker for this intrauterine insult is the presence of a non-fatal congenital anomaly. METHODS: We investigated whether or not congenital anomalies are associated with MS in a population-based cohort. We identified 7063 MS index cases and 2655 spousal controls with congenital anomaly information from the Canadian Collaborative Project on Genetic Susceptibility to MS (CCPGSMS). RESULTS: The frequency of congenital anomalies were compared between index cases and controls. No significant differences were found. CONCLUSIONS: Congenital anomalies thus do not appear to be associated with MS. However, we did not have complete data on types and severity of congenital anomalies or on maternal birth history and thus this study should be regarded as preliminary.

A ChIP-seq defined genome-wide map of vitamin D receptor binding: associations with disease and evolution.

Initially thought to play a restricted role in calcium homeostasis, the pleiotropic actions of vitamin D in biology and their clinical significance are only now becoming apparent. However, the mode of action of vitamin D, through its cognate nuclear vitamin D receptor (VDR), and its contribution to diverse disorders, remain poorly understood. We determined VDR binding throughout the human genome using chromatin immunoprecipitation followed by massively parallel DNA sequencing (ChIP-seq). After calcitriol stimulation, we identified 2776 genomic positions occupied by the VDR and 229 genes with significant changes in expression in response to vitamin D. VDR binding sites were significantly enriched near autoimmune and cancer associated genes identified from genome-wide association (GWA) studies. Notable genes with VDR binding included IRF8, associated with MS, and PTPN2 associated with Crohn's disease and T1D. Furthermore, a number of single nucleotide polymorphism associations from GWA were located directly within VDR binding intervals, for example, rs13385731 associated with SLE and rs947474 associated with T1D. We also observed significant enrichment of VDR intervals within regions of positive selection among individuals of Asian and European descent. ChIP-seq determination of transcription factor binding, in combination with GWA data, provides a powerful approach to further understanding the molecular bases of complex diseases.

Childhood cow's milk allergy and the risk of multiple sclerosis: a population based study.

Autoimmune mechanisms are thought to have a major role in the pathogenesis of multiple sclerosis (MS) and vitamin D is hypothesised to contribute to disease susceptibility. Cow's milk allergy (CMA) is a common childhood allergy arising from an immune system imbalance and can also lead to vitamin D deficiency due to dairy food avoidance. Here, we investigated whether or not CMA influences the subsequent risk to develop MS in a population-based cohort. We identified 6638 MS index cases and 2509 spousal controls with CMA information from the Canadian Collaborative Project on Genetic Susceptibility to MS (CCPGSMS). Frequency of CMA was compared between index cases and controls. No significant differences were found. Childhood CMA thus does not appear to be a risk factor for MS.

Epistasis among HLA-DRB1, HLA-DQA1, and HLA-DQB1 loci determines multiple sclerosis susceptibility.

Multiple sclerosis (MS), a common central nervous system inflammatory disease, has a major heritable component. Susceptibility is associated with the MHC class II region, especially HLA-DRB5*0101-HLA-DRB1*1501-HLA-DQA1*0102-HLA-DQB1*0602 haplotypes(hereafter DR2), which dominate genetic contribution to MS risk. Marked linkage disequilibrium (LD) among these loci makes identification of a specific locus difficult. The once-leading candidate, HLA-DRB1*15, localizes to risk, neutral, and protective haplotypes. HLA-DRB1*15 and HLA-DQB1*0602, nearly always located together on a small ancestral chromosome segment, are strongly MS-associated. One intervening allele on this haplotype, viz. HLA-DQA1*0102, shows no primary MS association. Two Canadian cohorts (n = 830 and n = 438 trios) genotyped for HLA-DRB1, HLA-DQA1 and HLA-DQB1 alleles were tested for association using TDT. To evaluate epistasis involving HLA-DRB1*15, transmissions from HLA-DRB1*15-negative parents were stratified by the presence/absence of HLA-DRB1*15 in affected offspring. All 3 alleles contribute to MS susceptibility through novel epistatic interactions. HLA-DQA1*0102 increased disease risk when combined with HLA-DRB1*1501 in trans, thereby unambiguously implicating HLA-DQ in MS susceptibility. Three-locus haplotypes demonstrated that HLA-DRB1*1501 and HLA-DQB1*0602 each influence risk. Transmissions of rare morcellated DR2 haplotypes showed no interaction with HLA-DQA1*0102. Incomplete haplotypes bearing only HLA-DRB1*1501 or HLA-DQB1*0602 did not predispose to MS. Balanced reciprocal transmission distortion can mask epistatic allelic association. These findings implicate epistasis among HLA class II alleles in human immune responses generally, provide partial explanation for intense linkage disequilibrium in the MHC, have relevance to animal models, and demonstrate key roles for DR2-specific interactions in MS susceptibility. MHC disease associations may be more generally haplotypic or diplotypic.

Expression of the multiple sclerosis-associated MHC class II Allele HLA-DRB1*1501 is regulated by vitamin D.

Multiple sclerosis (MS) is a complex trait in which allelic variation in the MHC class II region exerts the single strongest effect on genetic risk. Epidemiological data in MS provide strong evidence that environmental factors act at a population level to influence the unusual geographical distribution of this disease. Growing evidence implicates sunlight or vitamin D as a key environmental factor in aetiology. We hypothesised that this environmental candidate might interact with inherited factors and sought responsive regulatory elements in the MHC class II region. Sequence analysis localised a single MHC vitamin D response element (VDRE) to the promoter region of HLA-DRB1. Sequencing of this promoter in greater than 1,000 chromosomes from HLA-DRB1 homozygotes showed absolute conservation of this putative VDRE on HLA-DRB1*15 haplotypes. In contrast, there was striking variation among non-MS-associated haplotypes. Electrophoretic mobility shift assays showed specific recruitment of vitamin D receptor to the VDRE in the HLA-DRB1*15 promoter, confirmed by chromatin immunoprecipitation experiments using lymphoblastoid cells homozygous for HLA-DRB1*15. Transient transfection using a luciferase reporter assay showed a functional role for this VDRE. B cells transiently transfected with the HLA-DRB1*15 gene promoter showed increased expression on stimulation with 1,25-dihydroxyvitamin D3 (P = 0.002) that was lost both on deletion of the VDRE or with the homologous "VDRE" sequence found in non-MS-associated HLA-DRB1 haplotypes. Flow cytometric analysis showed a specific increase in the cell surface expression of HLA-DRB1 upon addition of vitamin D only in HLA-DRB1*15 bearing lymphoblastoid cells. This study further implicates vitamin D as a strong environmental candidate in MS by demonstrating direct functional interaction with the major locus determining genetic susceptibility. These findings support a connection between the main epidemiological and genetic features of this disease with major practical implications for studies of disease mechanism and prevention.

No effect of birth weight on the risk of multiple sclerosis. A population-based study.

BACKGROUND: Genetic and environmental factors have important roles in multiple sclerosis (MS) susceptibility. A clear maternal effect has been shown in several population-based studies. This parent-of-origin effect could result from factors operating during gestation. It has been shown that a low birth weight increases the risk of several adult-onset diseases. In a population-based Canadian cohort, we investigated whether there is any difference in birth weight for MS index cases compared to spousal controls. METHODS: Using the longitudinal Canadian database, we identified 6,188 MS index cases and 1,640 spousal controls with birth weight information. Additionally, data were available on 164 discordant MS twins. The birth weight was compared between index cases and controls as well as for twin pairs. RESULTS: When stratifying by sex, no significant difference in birth weight was found (average female index case birth weight = 7.23 pounds, average female control birth weight = 7.19 pounds, p = 0.48; average male index case birth weight = 7.56 pounds, average male control birth weight = 7.55 pounds, p = 0.92). Furthermore, there was no difference in birth weight between affected and unaffected twins (average affected twin weight = 5.46 pounds, average unaffected twin weight = 5.44 pounds, p =0.85). CONCLUSIONS: The maternal effect in MS aetiology does not appear to act through a route that has an influence on birth weight. As birth weight is a relatively poor marker of fetal development, other factors involved in fetal and early development need to be explored to elucidate the mechanism of the increased MS risk conferred maternally.

No effect of preterm birth on the risk of multiple sclerosis: a population based study.

BACKGROUND: Genetic and environmental factors have important roles in multiple sclerosis (MS) susceptibility. A clear parent of origin effect has been shown in several populations, perhaps resulting from factors operating during gestation. Preterm birth (birth at less than 37 weeks gestational age) has been shown to result in long-term health problems, including impaired neurological development. Here, in a population-based cohort, we investigate whether preterm birth increases the risk to subsequently develop MS. METHODS: We identified 6585 MS index cases and 2509 spousal controls with preterm birth information from the Canadian Collaborative Project on Genetic Susceptibility to MS. Rates of individuals born preterm were compared for index cases and controls. RESULTS: There were no significant differences between cases and controls with respect to preterm births. 370 (5.6%) MS index cases and 130 (5.2%) spousal controls were born preterm, p = 0.41. CONCLUSION: Preterm birth does not appear to contribute to MS aetiology. Other factors involved in foetal and early development need to be explored to elucidate the mechanism of the increased risk conferred by the apparent maternal effect.

Evidence for genetic regulation of vitamin D status in twins with multiple sclerosis.

BACKGROUND: Multiple sclerosis (MS) risk is determined by both genes and environment. One of the most striking features of MS is its geographic distribution, particularly the pattern of high MS frequency in areas with low sunlight exposure, the main inducer of vitamin D synthesis. Recent epidemiologic, experimental, and clinical evidence support an effect for low environmental supplies of vitamin D in mediating an increased susceptibility to MS. OBJECTIVES: We 1) examined the association of serum 25-hydroxy-vitaminD [25(OH)D] concentrations and MS status and 2) assessed the genetic contribution to serum 25(OH)D concentrations and tested for its association with genetic variants in 2 candidate genes [vitamin D receptor and 1-alpha-hydroxylase (CYP27B1)]. DESIGN: We used a twin study approach, comprising adult pairs identified from the longitudinal population-based Canadian Collaborative Project on Genetic Susceptibility to MS. Monozygotic (MZ; n = 40) and dizygotic (DZ; n = 59) pairs, both concordant and discordant for MS, were studied. End-of-winter serum 25(OH)D concentrations were measured by radioimmunoassay, and genotypes were assessed by single nucleotide polymorphism (SNP) assay. RESULTS: Serum concentrations of 25(OH)D were highly correlated in MS-concordant pairs (r = 0.83, P < 0.001), but they were not significantly associated with having the disease (P = 0.4) when analyzed by logistic regression. Intraclass correlation for 25(OH)D concentration was significantly greater in MZ pairs (MZ, r: 0.71 > DZ r: 0.32, P = 0.006). Significant associations of 2 CYP27B1 SNP variants and 25(OH)D concentrations were observed. CONCLUSION: The findings indicate important genetic influences on regulation of seasonal circulating 25(OH)D concentrations in MS twins.

Analysis of 45 candidate genes for disease modifying activity in multiple sclerosis.

Multiple sclerosis (MS) is a common inflammatory disease of the central nervous system unsurpassed for its variability in disease outcome. As little is conclusively known about MS disease mechanisms, we have selected a variety of candidate genes that may influence the prognosis of the disease based on their function. A cohort of sporadic MS cases, taken from opposite extremes of the putative distribution of long-term outcome using the most stringent clinical criteria to date, was used to determine the role of on MS disease severity. The MS cases selected represent the prognostic best 5 % (benign MS) and worst 5 % (malignant MS) of cases in terms of clinical outcome assessed by the EDSS. Genotyping the two sets of MS patients (112 benign and 51 malignant) and a replication cohort from Sardinia provided no evidence to suggest that the genes selected have any outcome modifying activity, although small effects of these genes cannot be ruled out.

Sex ratio of multiple sclerosis in Canada: a longitudinal study.

BACKGROUND: Incidence of multiple sclerosis is thought to be increasing, but this notion has been difficult to substantiate. In a longitudinal population-based dataset of patients with multiple sclerosis obtained over more than three decades, we did not show a difference in time to diagnosis by sex. We reasoned that if a sex-specific change in incidence was occurring, the female to male sex ratio would serve as a surrogate of incidence change. METHODS: Since environmental risk factors seem to act early in life, we calculated sex ratios by birth year in 27 074 Canadian patients with multiple sclerosis identified as part of a longitudinal population-based dataset. FINDINGS: The female to male sex ratio by year of birth has been increasing for at least 50 years and now exceeds 3.2:1 in Canada. Year of birth was a significant predictor for sex ratio (p<0.0001, chi(2)=124.4; rank correlation r=0.84). INTERPRETATION: The substantial increase in the female to male sex ratio in Canada seems to result from a disproportional increase in incidence of multiple sclerosis in women. This rapid change must have environmental origins even if it is associated with a gene-environment interaction, and implies that a large proportion of multiple sclerosis cases may be preventable in situ. Although the reasons why incidence of the disease is increasing are unknown, there are major implications for health-care provision because lifetime costs of multiple sclerosis exceed pound1 million per case in the UK.