Eva Balada

DNA methylation and systemic lupus erythematosus.

Abstract:  Several studies have indicated the importance of DNA hypomethylation in the etiology of systemic lupus erythematosus (SLE). Different enzymes linked to the DNA methylation process have been described. The identification of all these enzymes means that cells have the capacity to modify their methylation patterns. Therefore, to obtain a deeper understanding of the role this epigenetic mechanism may have on SLE, the enzymes involved in the DNA methylation mechanism must be thoughtfully analyzed. In fact, studies of enzymes (other than DNMT1) in this autoimmune disease are still lacking. We have recently investigated the simultaneous gene expression of DNMT1, DNMT3A, DNMT3B, MBD2, and MBD4 in SLE patients. Here we review some of the studies that focus on the relationship between DNA methylation and SLE as well as we report our recent findings in this field. We suggest some alternative hypothesis that could help to understand the causes of the global DNA hypomethylation observed in the CD4+ T cells of these patients.

Molecular mechanisms mediated by human endogenous retroviruses (HERVs) in autoimmunity.

Eight per cent of the human genome is derived from the integration of retroviral sequences that were incorporated in our DNA more than 25 million years ago. Although some of these elements show mutations and deletions, some HERVs are transcriptionally active and produce functional proteins. Different mechanisms have been described which link HERVs to some chronic diseases such as several cancers, nervous system diseases and autoimmune rheumatic and connective tissue diseases. They could cause disease because of their capacity for being moved and inserted next to certain genes whose expression would be consequentially altered. Another way in which disease could potentially arise is when HERV‐encoded proteins are expressed. These proteins would be considered as [foreign] and they could trigger B‐cells to produce antibodies against them, which, in turn, might cross‐react with other proteins of our bodies. This mechanism could give rise to autoimmune diseases such as rheumatoid arthritis (RA), lupus erythematosus, Sjögrens syndrome (SJS), mixed connective tissue diseases and inflammatory neurological disease. Furthermore, it should be pointed out that HERV‐proteins may act as superantigens. Interestingly, some environmental agents seem to induce the expression of HERVs. Thus, ultraviolet light and several chemical agents could reactivate such sequences by altering their structure without modifying their nucleotide composition when the methylation pattern is changed. Therefore, the epigenetic changes observed in pathological conditions such as systemic lupus erythematosus (SLE) or cancer could be translated into an effect on the activation of some of the retroelements present in our genome which ultimately could have a direct or indirect role on the initiation and clinical evolution of certain chronic diseases. Copyright

DNase 1 and systemic lupus erythematosus.

Systemic lupus erythematosus (SLE) is an autoimmune disease of unknown aetiology with a complex genetic basis that includes many susceptibility genes on multiple chromosomes. As many complex human diseases, SLE involves multiple, interacting genetic and environmental determinants, and identifying genes and enzymes for complex traits is challenging and has had limited success so far. DNase1 has been implicated in the pathophysiology of SLE since the 1950s. The importance of DNase1 has grown up since the description that apoptotic cells can be the source of self-antigens in SLE. Many articles have focused in disturbed apoptosis and in the defects of the apoptotic cell debris as the origin of nucleosomes against which the immune response can be induced. The enzyme DNase1 plays a role in the clearance of apoptotic debris, and is therefore of capital interest in this process. In this review we highlight the current findings in the pathophysiology, genetics, and therapeutical role of DNase1 in SLE.

Transcript overexpression of the MBD2 and MBD4 genes in CD4+ T cells from systemic lupus erythematosus patients

Global DNA hypomethylation in CD4+ T cells has been detected in systemic lupus erythematosus (SLE), and it seems to be linked to its pathogenesis. We investigated the relationship between overall DNA methylation and the expression of two methyl CpG‐binding domain (MBD) proteins. DNA deoxymethylcytosine (dmC) content of purified CD4+ T cells from 29 SLE patients and 30 healthy controls was measured by means of an ELISA. Transcript levels of two methyl CpG‐binding proteins (MBD2 and MBD4) were quantified by real‐time RT‐PCR. Association studies were also carried out with several laboratory parameters, as well as with the patients’ clinical manifestations. SLE patients had significantly less CD4+ T cell DNA dmC content than controls (0.802±0.134 vs. 0.901±0.133; P=0.007). MBD2 and MBD4 mRNA levels were considerably higher in the patients’ group: 0.975 ± 0683 versus 0.604 ± 0.614 (P=0.004) and 0.359 ± 0.330 versus 0.092 ± 0.169, respectively (P<0.0005). It is interesting that SLE patients showed a negative correlation between methylation indices and MBD2 (r=–0.609, P<0.0005) and MBD4 (r=–0.395, P=0.034) transcript levels. MBD2 and MBD4 transcript overexpression and inverse correlations with DNA methylation indices indicate that both enzymes may really have a direct and active role on the genome‐wide DNA hypomethylation observed in CD4+ T cells from SLE patients.

Transcript levels of DNA methyltransferases DNMT1, DNMT3A and DNMT3B in CD4+ T cells from patients with systemic lupus erythematosus.

Global DNA hypomethylation in CD4+ T cells has been detected in systemic lupus erythematosus (SLE) and it seems to be linked to its pathogenesis. We investigated the relationship between overall DNA methylation and the expression of three DNA (cytosine‐5) methyltransferases involved in the DNA methylation process. The DNA deoxymethylcytosine (dmC) content of purified CD4+ T cells from 29 SLE patients and 30 healthy controls was measured by means of an enzyme‐linked immunosorbent assay (ELISA). The transcript levels of DNA cytosine‐5‐methyltransferase 1 (DNMT1), DNA cytosine‐5‐methyltransferase 3A (DNMT3A) and DNA cytosine‐5‐methyltransferase 3B (DNMT3B) were quantified by real‐time reverse transcription–polymerase chain reaction (RT‐PCR). Association studies were also carried out with several laboratory parameters, as well as with the patients’ clinical manifestations. SLE patients had a significantly lower CD4+ T‐cell DNA dmC content than controls (0·802 ± 0·134 versus 0·901 ± 0·133) (P = 0·007). No differences in transcript levels were observed for DNMT1, DNMT3A and DNMT3B between patients and controls. The simultaneous association of low complement counts with lymphopenia, high titres of anti‐double‐stranded DNA (anti‐dsDNA), or an SLE disease activity index (SLEDAI) of > 5, resulted in the increase of at least one of the three DNA methyltransferases. It is possible that patients were reacting indirectly to an underlying DNA hypomethylation status by increasing the mRNA levels of DNA methyltransferases when the disease was being definitely active.

Anti-MDA5 antibodies in a large Mediterranean population of adults with dermatomyositis.

A new myositis-specific autoantibody directed against melanoma differentiation-associated gene 5 (anti-MDA5) has been described in patients with dermatomyositis (DM). We report the clinical characteristics of patients with anti-MDA5 in a large Mediterranean cohort of DM patients from a single center, and analyze the feasibility of detecting this autoantibody in patient sera using new assays with commercially available recombinant MDA5. The study included 117 white adult patients with DM, 15 (13%) of them classified as clinically amyopathic dermatomyositis (CADM). Clinical manifestations were analyzed, with special focus on interstitial lung disease and its severity. Determination of anti-MDA5 antibodies was performed by a new ELISA and immunoblot technique. In sera, from 14 (12%) DM patients (8 CADM), MDA5 was recognized by ELISA, and confirmed by immunoblot. Eight of the 14 anti-MDA5-positive patients (57.14%) presented rapidly-progressive interstitial lung disease (RP-ILD) versus 3 of 103 anti-MDA5-negative patients (2.91%) (P < 0.05; OR: 44.4, 95% CI 9.3–212). The cumulative survival rate was significantly lower in anti-MDA5-positive patients than in the remainder of the series (P < 0.05). Patients with anti-MDA5-associated ILD presented significantly lower 70-month cumulative survival than antisynthetase-associated ILD patients. Among the cutaneous manifestations, only panniculitis was significantly associated with the presence of anti-MDA5 antibodies (P < 0.05; OR: 3.85, 95% CI 1.11–13.27). These findings support the reliability of using commercially available recombinant MDA5 for detecting anti-MDA5 antibodies and confirm the association of these antibodies with RP-ILD in a large series of Mediterranean patients with DM.

Implication of Human Endogenous Retroviruses in the Development of Autoimmune Diseases

Retroviruses can exist in an endogenous form, in which viral sequences are integrated into the human germ line and are vertically transmitted in a Mendelian fashion. Human endogenous retroviruses (HERVs), probably representing footprints of ancient germ-cell retroviral infections, occupy about 1% of the human genome. Some HERVs emerged in the genome over 25 million years ago, while others have appeared rather recently, at about the time of hominid and ape lineages divergence. Although some of these elements show mutations and deletions, some HERVs are transcriptionally active and produce functional proteins. Some medical conditions, such as cancer and autoimmune diseases, are linked to the transcription of some of the HERVs genes, to the expression of HERVs proteins (that may act as superantigens, for example), and/or to the development of antibodies against them that might cross-react with our own proteins. Their genetic sequences may also be, totally or partially, integrated into genes that regulate the immune response. These mechanisms could give rise to autoimmune diseases, such as lupus erythematosus, insulin-dependent diabetes mellitus, multiple sclerosis, Sjögrens syndrome, and rheumatoid arthritis, among others. This review is aimed at discussing evidence for a possible role of HERVs in the etiopathogenesis of different autoimmune diseases.

Opposed independent effects and epistasis in the complex association of IRF5 to SLE

Genetic variation in the interferon regulatory factor 5 (IRF5) gene affects systemic lupus erythematosus (SLE) susceptibility. However, association is complex and incompletely defined. We obtained fourteen European sample collections with a total of 1383 SLE patients and 1614 controls to better define the role of the different IRF5 variants. Eleven polymorphisms were studied, including nine tag single nucleotide polymorphisms (SNPs) and two extra functional polymorphisms. Two tag SNPs showed independent and opposed associations: susceptibility (rs10488631, P<10−17) and protection (rs729302, P<10−6). Haplotype analyses showed that the susceptibility haplotype, identified by the minor allele of rs10488631, can be due to epistasis between three IRF5 functional polymorphisms. These polymorphisms determine increased mRNA expression, a splice variant with a different exon 1 and a longer proline-rich region in exon 6. This result is striking as none of the three polymorphisms had an independent effect on their own. Protection was independent of these polymorphisms and seemed to reside in the 5′ side of the gene. In conclusion, our results help to understand the role of the IRF5 locus in SLE susceptibility by clearly separating protection from susceptibility as caused by independent polymorphisms. In addition, we have found evidence for epistasis between known functional polymorphisms for the susceptibility effect.

The complex immunogenetic basis of systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is a systemic autoimmune disease of unknown etiology with a complex genetic basis that includes many susceptibility genes on multiple chromosomes. As complex human diseases like SLE involve multiple, interacting genetic and environmental determinants, identifying genes for complex traits is challenging and has had limited success so far. Several key approaches that are necessary to identify disease susceptibility genes in common diseases such as SLE are now available. Collectively, these approaches will allow the prioritization of candidate genes based on available knowledge of map position and biologic relevance. They will also allow us to obtain the genomic structure of these genes as well as to study sequence variants that will facilitate the identification of genes that are important in the development and expression (severity) of lupus and associated phenotypes. Although it is still a labor-intensive and expensive project to identify susceptibility genes in common diseases such as SLE, the new techniques that are now being used will undoubtedly improve gene mapping in such a kind of diseases. In this review we highlight the current findings in the genetics of human SLE after using these approaches.

Antiphosphatidylethanolamine antibodies contribute to the diagnosis of antiphospholipid syndrome in patients with systemic lupus erythematosus

Objective: To evaluate the correlation between antiphosphatidylethanolamine antibodies (aPE) and some antiphospholipid antibodies (aPL)-related clinical manifestations in patients with systemic lupus erythematosus (SLE). Methods: Patients with SLE (n = 217) were tested for the presence of aPE, anticardiolipin antibodies (aCL), and lupus anticoagulant (LA). The prospective aPL-related clinical manifestations studied were: thrombosis, thrombocytopenia, recurrent fetal losses, heart valvulopathies, hemolytic anemia, livedo reticularis, and pulmonary hypertension. Results: A total of 109 SLE patients (50.23%) were IgG aPE-positive; 17.51% presented aPE as the sole autoantibody and had some clinical features of aPL-related clinical manifestations. IgG aPE were associated to the presence of heart valvulopathies (p = 0.002). A statistical difference was also found when considering high levels of IgG aPE (O.D.> 0.600) in patients with livedo reticularis (p = 0.008). Conclusion: The evaluation of IgG aPE may allow us to detect some more patients with aPL-related clinical manifestations in the SLE population. aPE correlated particularly with valvulopathies and livedo reticularis.OBJECTIVE To evaluate the correlation between antiphosphatidylethanolamine antibodies (aPE) and some antiphospholipid antibodies (aPL)-related clinical manifestations in patients with systemic lupus erythematosus (SLE). METHODS Patients with SLE (n=217) were tested for the presence of aPE, anticardiolipin antibodies (aCL), and lupus anticoagulant (LA). The prospective aPL-related clinical manifestations studied were: thrombosis, thrombocytopenia, recurrent fetal losses, heart valvulopathies, hemolytic anemia, livedo reticularis, and pulmonary hypertension. RESULTS A total of 109 SLE patients (50.23%) were IgG aPE-positive; 17.51% presented aPE as the sole autoantibody and had some clinical features of aPL-related clinical manifestations. IgG aPE were associated to the presence of heart valvulopathies (p=0.002). A statistical difference was also found when considering high levels of IgG aPE (O.D.>0.600) in patients with livedo reticularis (p=0.008). CONCLUSION The evaluation of IgG aPE may allow us to detect some more patients with aPL-related clinical manifestations in the SLE population, aPE correlated particularly with valvulopathies and livedo reticularis.