Several advances in 2013 have improved our understanding of how epigenetic mechanisms affect autoimmune disorders. Many new insights were made into the regulation of gene expression by DNA methylation in systemic lupus erythematosus. For rheumatoid arthritis, complex interrelationships between DNA methylation and microRNAs in regulating gene expression were described.
Lupus develops when genetically predisposed people encounter environmental agents, such as ultraviolet light, silica, infections, and cigarette smoke, that cause oxidative stress, but how oxidative damage modifies the immune system to cause lupus flares is unknown. We previously showed that inhibiting DNA methylation in CD4+ T cells by blocking ERK pathway signaling is sufficient to alter gene expression, and that the modified cells cause lupus-like autoimmunity in mice. We also reported that T cells from patients with active lupus have decreased ERK pathway signaling, have decreased DNA methylation, and overexpress genes normally suppressed by DNA methylation. This study was undertaken to test whether oxidizing agents decrease ERK pathway signaling in T cells, decrease DNA methyltransferase levels, and cause demethylation and overexpression of T cell genes similar to that found in T cells from patients with active lupus.
CD4+ T cells were treated with the oxidizers H2O2 or ONOO−. Effects on ERK pathway signaling were measured by immunoblotting, DNA methyltransferase 1 (DNMT-1) levels were measured by reverse transcriptase–polymerase chain reaction (RT-PCR), and the methylation and expression of T cell genes were measured using flow cytometry, RT-PCR, and bisulfite sequencing.
H2O2 and ONOO− inhibited ERK pathway signaling in T cells by inhibiting the upstream regulator protein kinase Cδ, decreased DNMT-1 levels, and caused demethylation and overexpression of genes previously shown to be suppressed by DNA methylation in T cells from patients with active lupus.
Our findings indicate that oxidative stress may contribute to human lupus flares by inhibiting ERK pathway signaling in T cells to decrease DNMT-1 and cause DNA demethylation.
Lupus develops when genetically predisposed people encounter environmental agents such as UV light, silica, infections and cigarette smoke that cause oxidative stress, but how oxidative damage modifies the immune system to cause lupus flares is unknown. We reported that inhibiting DNA methylation in CD4+ T cells by blocking ERK pathway signaling is sufficient to alter gene expression, and that the modified cells cause lupus-like autoimmunity in mice. We also reported that T cells from patients with active lupus have decreased ERK pathway signaling, decreased DNA methylation, and overexpress genes normally suppressed by DNA methylation. We therefore tested whether oxidizing agents decrease T cell ERK pathway signaling, decrease DNA methyltransferase levels, and cause demethylation and overexpression of T cell genes similar to that found in T cells from patients with active lupus.
CD4+ T cells were treated with the oxidizers H2O2 or ONOO−. Effects on ERK pathway signaling were measured by immunoblotting, Dnmt1 levels by RT-PCR, and the methylation and expression of T cell genes were measured using flow cytometry, RT-PCR and bisulfite sequencing.
H2O2 and ONOO− inhibited T cell ERK pathway signaling by inhibiting the upstream regulator PKCδ, decreased Dnmt1 levels, and caused demethylation and overexpression genes previously shown to suppressed by DNA methylation in T cells from patients with active lupus.
Oxidative stress may contribute to human lupus flares by inhibiting T cell ERK pathway signaling to decrease Dnmt1 and cause DNA demethylation.
Lupus flares when genetically predisposed people encounter appropriate environmental agents. Current evidence indicates that the environment contributes by inhibiting T cell DNA methylation, causing overexpression of normally silenced genes. DNA methylation depends on both dietary transmethylation micronutrients and Erk-regulated DNA methyltransferase 1 (Dnmt1) levels. We used transgenic mice to study interactions between diet, Dnmt1 levels and genetic predisposition on the development and severity of lupus.
A doxycycline-inducible Erk defect was bred into lupus-resistant (C57BL/6) or lupus-susceptible (C57BL/6xSJL) mouse strains. Doxycycline treated mice were fed a standard commercial diet for eighteen weeks then switched to diets supplemented(MS) or restricted(MR) intransmethylation micronutrients. Disease severity was assessed by anti-dsDNA antibodies, proteinuria, hematuria and histopathology of kidney tissues. Pyrosequencing was used to determine micronutrient effects on DNA methylation.
Doxycycline induced modest levels of anti-dsDNA antibodies in C57BL/6 mice and higher levels in C57BL/6xSJL mice. Doxycycline-treated C57BL/6xSJL mice developed hematuria and glomerulonephritis on the MR and standard but not the MS diet. In contrast C57BL/6 mice developed kidney disease only on the MR diet. Decreasing Erk signaling and methyl donors also caused demethylation and overexpression of the CD40lg gene in female mice, consistent with demethylation of the second X chromosome. Both the dietary methyl donor content and duration of treatment influenced methylation and expression of the CD40lg gene.
Dietary micronutrients that affect DNA methylation can exacerbate or ameliorate SLE disease in this transgenic murine lupus model, and contribute to lupus susceptibility and severity through genetic/epigenetic interactions.
Extracellular Receptor Kinase (Erk; Systemic Lupus Erythematosus (SLE; CD70; micronutrients; CD40L; KirL1
Numerous observations implicate interferon-α (IFNα) in the pathophysiology of systemic lupus erythematosus (SLE); however, the potential impact of endogenous anti-IFNα autoantibodies (AIAAs) on IFN-pathway and disease activity is unclear. The aim of this study was to characterize IFN-pathway activity and the serologic and clinical profiles of AIAA-positive patients with SLE.
Sera obtained from patients with SLE (n = 49), patients with rheumatoid arthritis (n = 25), and healthy control subjects (n = 25) were examined for the presence of AIAAs, using a biosensor immunoassay. Serum type I IFN bioactivity and the ability of AIAA-positive sera to neutralize IFNα activity were determined using U937 cells. Levels of IFN-regulated gene expression in peripheral blood were determined by microarray, and serum levels of BAFF, IFN-inducible chemokines, and other autoantibodies were measured using immunoassays.
AIAAs were detected in 27% of the serum samples from patients with SLE, using a biosensor immunoassay. Unsupervised hierarchical clustering analysis identified 2 subgroups of patients, IFNlow and IFNhigh, that differed in the levels of serum type I IFN bioactivity, IFN-regulated gene expression, BAFF, anti-ribosomal P, and anti-chromatin autoantibodies, and in AIAA status. The majority of AIAA-positive patients had significantly lower levels of serum type I IFN bioactivity, reduced downstream IFN-pathway activity, and lower disease activity compared with the IFNhigh patients. AIAA-positive sera were able to effectively neutralize type I IFN activity in vitro.
Patients with SLE commonly harbor AIAAs. AIAA-positive patients have lower levels of serum type I IFN bioactivity and evidence for reduced downstream IFN-pathway and disease activity. AIAAs may influence the clinical course in SLE by blunting the effects produced by IFNα.
CD4+ T cell DNA hypomethylation may contribute to the development of drug induced and idiopathic human lupus. Inhibiting DNA methylation in mature CD4+ T cells causes MHC-specific autoreactivity in vitro. The lupus-inducing drugs hydralazine and procainamide also inhibit T cell DNA methylation and induce autoreactivity, and T cells from patients with active lupus have hypomethylated DNA and a similarly autoreactive T cell subset. Further, T cells treated with DNA methylation inhibitors demethylate the same sequences that demethylate in T cells from patients with active lupus. The pathologic significance of the autoreactivity induced by inhibiting T cell DNA methylation has been tested by treating murine T cells in vitro with drugs which modify DNA methylation, then injecting the cells into syngeneic female mice. Mice receiving CD4+ T cells demethylated by a variety of agents including procainamide and hydralazine develop a lupus-like disease. Further, transgenic mice with an inducible T cell DNA methylation defect also develop lupus-like autoimmunity. This chapter describes the protocols for inducing autoreactivity in murine T cells in vitro, and inducing autoimmunity in vivo using an adoptive transfer approach or transgenic animal models.
Lupus; drug-induced lupus; DNA methylation; animal models; autoimmunity
Obesity, is a chronic, biological, preventable, and treatable disease. The accumulation of fat mass causes physical changes (adiposity), metabolic and hormonal changes due to adipose tissue dysfunction (adiposopathy), and psychological changes. Bariatric endocrinology was conceived from the need to address the neuro-endocrinological derangements that are associated with adiposopathy, and from the need to broaden the scope of the management of its complications. In addition to the well-established metabolic complications of overweight and obesity, adiposopathy leads to hyperinsulinemia, hyperleptinemia, hypoadiponectinemia, dysregulation of gut peptides including GLP-1 and ghrelin, the development of an inflammatory milieu, and the strong risk of vascular disease. Therapy for adiposopathy hinges on effectively lowering the ratio of orexigenic to anorexigenic signals reaching the the hypothalamus and other relevant brain regions, favoring a lower caloric intake. Adiposopathy, overweight and obesity should be treated indefinitely with the specific aims to reduce fat mass for the adiposity complications, and to normalize adipose tissue function for the adiposopathic complications. This paper defines the principles of medical practice in bariatric endocrinology—the treatment of overweight and obesity as means to treat adiposopathy and its accompanying metabolic and hormonal derangements.
Women develop lupus more frequently than men and the reason remains incompletely understood. Evidence that men with Klinefelter’s Syndrome (XXY) develop lupus at approximately the same rate as women suggests that a second X chromosome contributes. However, since the second X is normally inactivated, how it predisposes to lupus is unclear. DNA methylation contributes to the silencing of one X chromosome in women, and CD4+ T cell DNA demethylation contributes to the development of lupus-like autoimmunity. This suggests that demethylation of genes on the inactive X may predispose women to lupus, and this hypothesis is supported by a report that CD40LG, an immune gene encoded on the X chromosome, demethylates and is overexpressed in T cells from women but not men with lupus. Overexpression of other immune genes on the inactive X may also predispose women to this disease. We therefore compared mRNA and miRNA expression profiles in experimentally demethylated T cells from women and men as well as in T cells from women and men with lupus. T cells from healthy men and women were treated with the DNA methyltransferase inhibitor 5-azacytidine, then X-linked mRNAs were surveyed with oligonucleotide arrays, and X-linked miRNA’s surveyed with PCR arrays. CD40LG, CXCR3, OGT, miR-98, let-7f-2*, miR 188-3p, miR-421 and miR-503 were among the genes overexpressed in women relative to men. MiRNA target prediction analyses identified CBL, which downregulates T cell receptor signaling and is decreased in lupus T cells, as a gene targeted by miR-188-3p and miR-98. Transfection with miR-98 and miR-188-3p suppressed CBL expression. The same mRNA and miRNA transcripts were also demethylated and overexpressed in CD4+ T cells from women relative to men with active lupus. Together these results further support a role for X chromosome demethylation in the female predisposition to lupus.
Lupus; epigenetics; women’s health; X chromosome; gene expression; microRNA
Purpose of review
Epigenetic mechanisms regulate gene expression, and epigenetic gene dysregulation is implicated in the pathogenesis of a growing number of disorders. Of the autoimmune diseases, epigenetic mechanisms are most clearly involved in human systemic lupus erythematosus (SLE). Herein, we summarize earlier work on epigenetic mechanisms contributing to human SLE. We first focus on the roles of DNA demethylation and DNA methyltransferase enzyme dysregulation, and we then review recent and important advances in this field.
Many advances in the past year have been made. The importance of DNA demethylation in SLE was confirmed through twin studies. New T lymphocyte immune genes that are activated by DNA demethylation, and that may participate in autoreactivity, were identified. Finally, novel mechanisms contributing to DNA demethylation in SLE were discovered.
A comprehensive understanding of the epigenetic mechanisms contributing to SLE will likely enable development of new therapeutic agents and strategies that target the dysregulated genes or correct the aberrant epigenetic modifications. Although specific agents have not yet been tested in SLE, the studies reviewed hold promise that these approaches will be useful in the treatment of human lupus.
chromatin; DNA methylation; epigenetics; histone; lupus
CD4+ T cells from patients with active lupus have impaired ERK pathway signaling that decreases DNA methyltransferase expression, resulting in DNA demethylation, overexpression of immune genes and autoimmunity. The ERK pathway defect is due to impaired phosphorylation of T505 in the PKCδ activation loop. However, the mechanisms preventing PKCδ T505 phosphorylation in lupus T cells are unknown. Others have reported that oxidative modifications, and nitration in particular, of T cells as well as serum proteins correlate with lupus disease activity. We hypothesized that nitration inactivates PKCδ, contributing to impaired ERK pathway signaling in lupus T cells.
CD4+ T cells were purified from lupus patients and controls then stimulated with PMA. Signaling protein levels, nitration and phosphorylation were quantitated by immunoprecipitation and immunoblotting of T cell lysates. Transfections were performed by electroporation.
Treating CD4+ T cells with peroxynitrite nitrated PKCδ, preventing PKCδ T505 phosphorylation and inhibiting ERK pathway signaling similar to that observed in lupus T cells. Patients with active lupus had higher nitrated T cell PKCδ levels than controls which correlated directly with disease activity, and anti-nitrotyrosine immunoprecipitations demonstrated that nitrated PKCδ, but not unmodified PKCδ, was refractory to PMA stimulated T505 phosphorylation, similar to PKCδ in peroxynitrite treated cells.
Oxidative stress causes PKCδ nitration, which prevents its phosphorylation and contributes to the decreased ERK signaling in lupus T cells. These results identify PKCδ as a link between oxidative stress and the T cell epigenetic modifications in lupus.
Systemic lupus erythematosus; PKCδ; T cells; Signal transduction; Oxidative stress
Systemic lupus erythematosus is a chronic relapsing autoimmune disease that primarily
afflicts women, and both a genetic predisposition and appropriate environmental
exposures are required for lupus to develop and flare. The genetic requirement is
evidenced by an increased concordance in identical twins and by the validation of at
least 35 single-nucleotide polymorphisms predisposing patients to lupus. Genes alone,
though, are not enough. The concordance of lupus in identical twins is often
incomplete, and when concordant, the age of onset is usually different. Lupus is also
not present at birth, but once the disease develops, it typically follows a chronic
relapsing course. Thus, genes alone are insufficient to cause human lupus, and
additional factors encountered in the environment and over time are required to
initiate the disease and subsequent flares. The nature of the environmental
contribution, though, and the mechanisms by which environmental agents modify the
immune response to cause lupus onset and flares in genetically predisposed people
have been controversial. Reports that the lupus-inducing drugs procainamide and
hydralazine are epigenetic modifiers, that epigenetically modified T cells are
sufficient to cause lupus-like autoimmunity in animal models, and that patients with
active lupus have epigenetic changes similar to those caused by procainamide and
hydralazine have prompted a growing interest in how epigenetic alterations contribute
to this disease. Understanding how epigenetic mechanisms modify T cells to contribute
to lupus requires an understanding of how epigenetic mechanisms regulate gene
expression. The roles of DNA methylation, histone modifications, and microRNAs in
lupus pathogenesis will be reviewed here.
Systemic lupus erythematosus (SLE) is an autoimmune disease primarily afflicting women. The reason for the gender bias is unclear, but genetic susceptibility, estrogen and environmental agents appear to play significant roles in SLE pathogenesis. Environmental agents can contribute to lupus susceptibility through epigenetic mechanisms. We used (C57BL/6 × SJL)F1 mice transgenic for a dominant-negative MEK (dnMEK) that was previously shown to be inducibly and selectively expressed in T cells. In this model, induction of the dnMEK by doxycycline treatment suppresses T cell ERK signaling, decreasing DNA methyltransferase expression and resulting in DNA demethylation, overexpression of immune genes Itgal (CD11a) and Tnfsf7 (CD70), and anti-dsDNA antibody. To examine the role of gender and estrogen in this model, male and female transgenic mice were neutered and implanted with time-release pellets delivering placebo or estrogen. Doxycycline induced IgG anti-dsDNA antibodies in intact and neutered, placebo-treated control female but not male transgenic mice. Glomerular IgG deposits were also found in the kidneys of female but not male transgenic mice, and not in the absence of doxycycline. Estrogen enhanced anti-dsDNA IgG antibodies only in transgenic, ERK-impaired female mice. Decreased ERK activation also resulted in overexpression and demethylation of the X-linked methylation-sensitive gene CD40lg in female but not male mice, consistent with demethylation of the second X chromosome in the females. The results show that both estrogen and female gender contribute to the female predisposition in lupus susceptibility through hormonal and epigenetic X chromosome effects and through suppression of ERK signaling by environmental agents.
Extracellular Receptor Kinase (ERK); Systemic Lupus erythematosus (SLE); Mouse
Lupus is less common in men than women, and the reason is incompletely understood. Current evidence indicates that lupus flares when genetically predisposed individuals encounter environmental agents that trigger the disease, and that the environmental contribution is mediated at least in part by T cell DNA demethylation. We hypothesized that lupus disease activity is directly related to total genetic risk and inversely related to T cell DNA methylation levels in each patient. Since women are predisposed to lupus in part because of their second X chromosome, we also hypothesized that men would require a greater genetic risk, a greater degree of autosomal T cell DNA demethylation, or both, to achieve a lupus flare equal in severity to women. Genetic risk was determined by genotyping men and women with lupus across 32 confirmed lupus susceptibility loci. The methylation status of two T cell autosomal genes known to demethylate in proportion to disease activity, KIR2DL4 (KIR) and PRF1, was measured by bisulfite sequencing. Lupus disease activity was determined by the SLEDAI. Interactions between genetic score, T cell DNA demethylation, and the SLEDAI score were compared between the men and women by regression analysis. Combining the degree of DNA demethylation with the genetic risk score for each patient demonstrated that the (genetic risk)/(DNA methylation) ratio increased directly with disease activity in both men and women with lupus. Importantly, men required a greater (genetic risk)/(DNA methylation) ratio to achieve a SLEDAI score equivalent to women (p=0.010 for KIR and p=0.0054 for PRF1). This difference was not explained by a difference in the genetic risk or T cell DNA demethylation alone, suggesting a genetic-epigenetic interaction. These results suggest that genetic risk and T cell DNA demethylation interact in lupus patients to influence the severity of lupus flares, and that men require a higher genetic risk and/or greater degree of T cell DNA demethylation to achieve a lupus flare equal in severity to women.
Genetic risk; epigenetics; DNA methylation; lupus; genetic-epigenetic interaction; sex-disparity
Systemic lupus erythematosus (SLE) is a sexually dimorphic autoimmune disease which is more common in women, but affected men often experience a more severe disease. The genetic basis of sexual dimorphism in SLE is not clearly defined. A study was undertaken to examine sex-specific genetic effects among SLE susceptibility loci.
A total of 18 autosomal genetic susceptibility loci for SLE were genotyped in a large set of patients with SLE and controls of European descent, consisting of 5932 female and 1495 male samples. Sex-specific genetic association analyses were performed. The sex–gene interaction was further validated using parametric and nonparametric methods. Aggregate differences in sex-specific genetic risk were examined by calculating a cumulative genetic risk score for SLE in each individual and comparing the average genetic risk between male and female patients.
A significantly higher cumulative genetic risk for SLE was observed in men than in women. (P = 4.52×10−8) A significant sex–gene interaction was seen primarily in the human leucocyte antigen (HLA) region but also in IRF5, whereby men with SLE possess a significantly higher frequency of risk alleles than women. The genetic effect observed in KIAA1542 is specific to women with SLE and does not seem to have a role in men.
The data indicate that men require a higher cumulative genetic load than women to develop SLE. These observations suggest that sex bias in autoimmunity could be influenced by autosomal genetic susceptibility loci.
Several confirmed genetic susceptibility loci for lupus have been described. To date, no clear evidence for genetic epistasis is established in lupus. We test for gene-gene interactions in a number of known lupus susceptibility loci.
Eighteen SNPs tagging independent and confirmed lupus susceptibility loci were genotyped in a set of 4,248 lupus patients and 3,818 normal healthy controls of European descent. Epistasis was tested using a 2-step approach utilizing both parametric and non-parametric methods. The false discovery rate (FDR) method was used to correct for multiple testing.
We detected and confirmed gene-gene interactions between the HLA region and CTLA4, IRF5, and ITGAM, and between PDCD1 and IL21 in lupus patients. The most significant interaction detected by parametric analysis was between rs3131379 in the HLA region and rs231775 in CTLA4 (Interaction odds ratio=1.19, z-score= 3.95, P= 7.8×10−5 (FDR≤0.05), PMDR= 5.9×10−45). Importantly, our data suggest that in lupus patients the presence of the HLA lupus-risk alleles in rs1270942 and rs3131379 increases the odds of also carrying the lupus-risk allele in IRF5 (rs2070197) by 17% and 16%, respectively (P= 0.0028 and 0.0047).
We provide evidence for gene-gene epistasis in systemic lupus erythematosus. These findings support a role for genetic interaction contributing to the complexity of lupus heritability.
Candidate gene and genome-wide association studies have identified several disease susceptibility loci in lupus patients. These studies have been largely performed in European-derived and Asian lupus patients. In this study, we examine if some of these same susceptibility loci increase lupus risk in African-American individuals.
Single nucleotide polymorphisms tagging 15 independent lupus susceptibility loci were genotyped in a set of 1,724 lupus patients and 2,024 normal healthy controls of African-American descent. The loci examined included: PTPN22, FCGR2A, TNFSF4, STAT4, CTLA4, PDCD1, PXK, BANK1, MSH5 (HLA region), CFB (HLA region), C8orf13-BLK region, MBL2, KIAA1542, ITGAM, and MECP2/IRAK1.
We provide the first evidence for genetic association between lupus and five susceptibility loci in African-American patients (C8orf13-BLK, BANK1, TNFSF4, KIAA1542 andCTLA4; P values= 8.0 × 10−6, 1.9 × 10−5, 5.7 × 10−5, 0.00099, 0.0045, respectively). Further, we confirm the genetic association between lupus and five additional lupus susceptibility loci (ITGAM, MSH5, CFB, STAT4, and FCGR2A; P values= 7.5 × 10−11, 5.2 × 10−8, 8.7 × 10−7, 0.0058, and 0.0070, respectively), and provide evidence for a genome-wide significance for the association between ITGAM and MSH5 (HLA region) for the first time in African-American lupus patients.
These findings provide evidence for novel genetic susceptibility loci for lupus in African-Americans and demonstrate that the majority of lupus susceptibility loci examined confer lupus risk across multiple ethnicities.
Systemic lupus erythematosus (SLE; OMIM 152700) is a chronic autoimmune disease for which the aetiology includes genetic and environmental factors. ITGAM, integrin αΜ (complement component 3 receptor 3 subunit) encoding a ligand for intracellular adhesion molecule (ICAM) proteins, is an established SLE susceptibility locus. This study aimed to evaluate the independent and joint effects of genetic variations in the genes that encode ITGAM and ICAM.
The authors examined several markers in the ICAM1–ICAM4–ICAM5 locus on chromosome 19p13 and the single ITGAM polymorphism (rs1143679) using a large-scale case–control study of 17 481 unrelated participants from four ancestry populations. The single marker association and gene–gene interaction were analysed for each ancestry, and a meta-analysis across the four ancestries was performed.
The A-allele of ICAM1–ICAM4–ICAM5 rs3093030, associated with elevated plasma levels of soluble ICAM1, and the A-allele of ITGAM rs1143679 showed the strongest association with increased SLE susceptibility in each of the ancestry populations and the trans-ancestry meta-analysis (ORmeta=1.16, 95% CI 1.11 to 1.22; p=4.88×10−10 and ORmeta=1.67, 95% CI 1.55 to 1.79; p=3.32×10−46, respectively). The effect of the ICAM single-nucleotide polymorphisms (SNPs) was independent of the effect of the ITGAM SNP rs1143679, and carriers of both ICAM rs3093030-AA and ITGAM rs1143679-AA had an OR of 4.08 compared with those with no risk allele in either SNP (95% CI 2.09 to 7.98; p=3.91×10−5).
These findings are the first to suggest that an ICAM–integrin-mediated pathway contributes to susceptibility to SLE.
Systemic lupus erythematosus is a clinically heterogeneous autoimmune disease. A number of genetic loci that increase lupus susceptibility have been established. This study examines if these genetic loci also contribute to the clinical heterogeneity in lupus.
Materials and methods
4001 European-derived, 1547 Hispanic, 1590 African-American and 1191 Asian lupus patients were genotyped for 16 confirmed lupus susceptibility loci. Ancestry informative markers were genotyped to calculate and adjust for admixture. The association between the risk allele in each locus was determined and compared in patients with and without the various clinical manifestations included in the ACR criteria.
Renal disorder was significantly correlated with the lupus risk allele in ITGAM (p=5.0×10−6, OR 1.25, 95% CI 1.12 to 1.35) and in TNFSF4 (p=0.0013, OR 1.14, 95% CI 1.07 to 1.25). Other significant findings include the association between risk alleles in FCGR2A and malar rash (p=0.0031, OR 1.11, 95% CI 1.17 to 1.33), ITGAM and discoid rash (p=0.0020, OR 1.20, 95% CI 1.06 to 1.33), STAT4 and protection from oral ulcers (p=0.0027, OR 0.89, 95% CI 0.83 to 0.96) and IL21 and haematological disorder (p=0.0027, OR 1.13, 95% CI 1.04 to 1.22). All these associations are significant with a false discovery rate of <0.05 and pass the significance threshold using Bonferroni correction for multiple testing.
Significant associations were found between lupus clinical manifestations and the FCGR2A, ITGAM, STAT4, TNSF4 and IL21 genes. The findings suggest that genetic profiling might be a useful tool to predict disease manifestations in lupus patients in the future.
Systemic lupus erythematosus (SLE) is a chronic, multiorgan, autoimmune disease that affects people of all ages and ethnicities.
To explore the relationship between age at disease onset and many of the diverse manifestations of SLE. Additionally, to determine the relationship between age of disease onset and genetic risk in patients with SLE.
The relationship between the age at disease onset and SLE manifestations were explored in a multiracial cohort of 1317 patients. Patients with SLE were genotyped across 19 confirmed genetic susceptibility loci for SLE. Logistic regression was used to determine the relationships between the number of risk alleles present and age of disease onset.
Childhood-onset SLE had higher odds of proteinuria, malar rash, anti-dsDNA antibody, haemolytic anaemia, arthritis and leucopenia (OR=3.03, 2.13, 2.08, 2.50, 1.89, 1.53, respectively; p values <0.0001, 0.0004, 0.0005, 0.0024, 0.0114, 0.045, respectively). In female subjects, the odds of having cellular casts were 2.18 times higher in childhood-onset than in adult-onset SLE (p=0.0027). With age of onset ≥50, the odds of having proteinuria, cellular casts, anti-nRNP antibody, anti-Sm antibody, anti-dsDNA antibody and seizures were reduced. However, late adult-onset patients with SLE have higher odds of developing photosensitivity than early adult-onset patients. Each SLE-susceptibility risk allele carried within the genome of patients with SLE increased the odds of having a childhood-onset disease in a race-specific manner: by an average of 48% in Gullah and 25% in African-Americans, but this was not significant in Hispanic and European-American lupus patients.
The genetic contribution towards predicting early-onset disease in patients with SLE is quantified for the first time. A more severe SLE phenotype is found in patients with early-onset disease in a large multi-racial cohort, independent of gender, race and disease duration.
T cell DNA methylation levels decline with age, activating genes such as KIR and TNFSF7 (CD70), implicated in lupus-like autoimmunity and acute coronary syndromes. The mechanisms causing age-dependent DNA demethylation are unclear. Maintenance of DNA methylation depends on DNA methyltransferase 1 (Dnmt1) and intracellular S-adenosylmethionine levels, and is inhibited by S-adenosylhomocysteine (SAH). SAM levels depend on dietary micronutrients including folate and methionine. SAH levels depend on serum homocysteine concentrations. T cell Dnmt1 levels also decline with age. We hypothesized that age-dependent Dnmt1 decreases synergize with low folate, low methionine or high homocysteine levels to demethylate and activate methylation-sensitive genes. T cells from healthy adults ages 22-81, stimulated and cultured with low folate, low methionine, or high homocysteine concentrations showed demethylation and overexpression of KIR and CD70 beginning at age ~50 and increased further with age. The effects were reproduced by Dnmt1 knockdowns in T cells from young subjects. These results indicate that maintenance of T cell DNA methylation patterns is more sensitive to low folate and methionine levels in older than younger individuals, due to low Dnmt1 levels, and that homocysteine further increases aberrant gene expression. Thus, attention to proper nutrition may be particularly important in the elderly.
Aging; Epigenetics; DNA methylation; Senescence
Systemic lupus erythematosus is a poorly understood autoimmune disease, characterized by autoantibodies to nuclear antigens and immune complex deposition in organs like the kidney. Current evidence indicates that a pathologic CD4+T cell subset, characterized by impaired extracellular signal-regulated kinase (ERK) pathway signaling, DNA hypomethylation, and consequent aberrant gene expression contributes to disease pathogenesis. Hydralazine is a lupus-inducing drug that also decreases T cell DNA methylation by inhibiting the ERK signaling pathway, replicating the defect found in lupus T cells. These observations suggest that defective ERK pathway signaling alters gene expression in T cells by inhibiting DNA methylation, contributing to lupus pathogenesis. The signaling defect in hydralazine-treated and lupus T cells has now been mapped to protein kinase C δ. Understanding the mechanism causing decreased ERK pathway signaling in lupus may shed light on mechanisms contributing to disease development in genetically predisposed people.
Lupus T cells; epigenetics; DNA methylation; extracellular signal-regulated kinase pathway signaling; Protein Kinase δ
CD40 ligand (CD40LG), encoded on the X chromosome, has been reported to be overexpressed on lupus Tcells. Herein, we investigated the effect of DNA demethylation on Tcell CD40LG expression and the production of IgG by autologous B cells in lupus. We found normal human T cells transfected with CD40LG induced autologous B cell activation and plasma cell differentiation. Both female lupus CD4+ T cells and demethylating agents treated CD4+ T cells overexpressed CD40LG mRNA. Further, lupus T cells from both genders or demethylated CD4+ T cells from healthy women overstimulated autologous B cells, and this could be reversed with anti-CD40LG Ab in only females. We demonstrated that female lupus CD4+ T cells and demethylated CD4+ T cells express high level of CD40LG and overstimulate B cells to produce IgG. This is due to DNA demethylation and thereby reactivation of the inactive X chromosome in female.
CD40 ligand; DNA methylation; Immunoglobulin G; Systemic lupus; erythematosus
T cells from lupus patients have hypomethylated DNA and overexpress genes normally suppressed by DNA methylation that contribute to disease pathogenesis. We found that stimulatory and inhibitory killer cell immunoglobulin–like receptor (KIR3) genes are aberrantly overexpressed on experimentally demethylated T cells. We therefore asked if lupus T cells also overexpress KIR, and if the proteins are functional. T cells from lupus patients were found to overexpress KIR genes, and expression was proportional to disease activity. Antibodies to the stimulatory molecule KIR2DL4 triggered IFN-γ release by lupus T cells, and production was proportional to disease activity. Similarly, crosslinking the inhibitory molecule KIR3DL1 prevented the autoreactive macrophage killing that characterizes lupus T cells. These results indicate that aberrant T cell KIR expression may contribute to IFN overproduction and macrophage killing in human lupus, and suggest that antibodies to inhibitory KIR may be a treatment for this disease.
Lupus; KIR genes; T cells; DNA methylation; epigenetics
A senescent CD4+CD28− T cell subset develops with aging and in chronic inflammatory diseases like rheumatoid arthritis, and is implicated in plaque rupture and myocardial infarctions. This subset is pro-inflammatory, cytotoxic for endothelial cells, and aberrantly expresses genes like CD70, perforin and killer-cell immunoglobulin-like receptor (KIR) genes. Why CD4+CD28− cells overexpress these genes is unclear. We found that the CD70, perforin and KIR2DL4 promoters are demethylated in CD4+CD28− T cells, and that DNA methyltransferase 1 (Dnmt1) and Dnmt3a levels are decreased in this subset. siRNA “knockdown” of Dnmt1, but not Dnmt3a, in CD4+CD28+ T cells caused similar demethylation and overexpression of KIR2DL4, perforin and CD70, while simultaneous knockdown of Dnmt1 and Dnmt3a caused greater demethylation and overexpression of these genes than Dnmt1 alone. We conclude that decreased Dnmt1 and Dnmt3a causes demethylation and overexpression of these and perhaps other genes in CD4+CD28− cells, potentially contributing to pathologic functions by this subset.
T cell; DNA methylation; aging; rheumatoid arthritis; senescence
Self tolerance loss is fundamental to autoimmunity. While understanding of immune regulation is expanding rapidly, the mechanisms causing loss of tolerance in most autoimmune diseases remain elusive. Autoimmunity is believed to develop when genetically predisposed individuals encounter environmental agents that trigger the disease. Recent advances in the genetic and environmental contributions to autoimmunity suggest that interactions between genetic elements and epigenetic changes caused by environmental agents may be responsible for inducing autoimmune disease. Genetic loci predisposing to autoimmunity are being identified through multi-center consortiums, and the number of validated genes is growing rapidly. Recent reports also indicate that the environment can contribute to autoimmunity by modifying gene expression through epigenetic mechanisms. This article will review current understanding of the genetics and epigenetics of lupus, rheumatoid arthritis, multiple sclerosis and type 1 diabetes, using systemic lupus erythematosus as the primary example. Other autoimmune diseases may have a similar foundation.
Epigenetics; Genetics; Lupus; Multiple Sclerosis; Rheumatoid Arthritis