Etiopathogenesis Of Systemic Lupus Erythematosus Research Articles

Hormones and B-cell development in health and autoimmunity.

The development of B cells into antibody-secreting plasma cells is central to the adaptive immune system as they induce protective and specific antibody responses against invading pathogens. Various studies have shown that, during this process, hormones can play important roles in the lymphopoiesis, activation, proliferation, and differentiation of B cells, and depending on the signal given by the receptor of each hormone, they can have a positive or negative effect. In autoimmune diseases, hormonal deregulation has been reported to be related to the survival, activation and/or differentiation of autoreactive clones of B cells, thus promoting the development of autoimmunity. Clinical manifestations of autoimmune diseases have been associated with estrogens, prolactin (PRL), and growth hormone (GH) levels. However, androgens, such as testosterone and progesterone (P4), could have a protective effect. The objective of this review is to highlight the links between different hormones and the immune response mediated by B cells in the etiopathogenesis of systemic lupus erythematosus (SLE), rheumatoid arthritis (RA), and multiple sclerosis (MS). The data collected provide insights into the role of hormones in the cellular, molecular and/or epigenetic mechanisms that modulate the B-cell response in health and disease.

Disturbed gut virome with potent interferonogenic property in systemic lupus erythematosus

Accumulating evidence suggests an essential role of disturbed gut microbiota in the etiopathogenesis of systemic lupus erythematosus (SLE), but it remains unclear as to gut virome. In this study, fecal virus-like particles (VLPs) isolated from 76 non-treated SLE patients and 75 healthy controls were subjected to gut virome profiling. The proportion of bacteriophages was significantly elevated in the SLE gut, and the altered viral taxa were correlated with clinical parameters. Gut virome and bacteriome were closely associated with each other in SLE patients. The combination of gut viral and bacterial markers displayed better performance in distinguishing SLE patients from healthy controls. Further, VLPs from non-treated SLE patients promoted interferon-α production in an epithelial cell line and human immune cells. Intriguingly, the interferon-stimulatory capacity diminished in VLPs from post-treated SLE patients. Our findings may shed novel insights into SLE pathogenesis. Further in-depth understanding of gut virome might help develop future biomarkers and therapeutics for SLE patients.

The effect of prolactin on immune cell subsets involved in SLE pathogenesis.

The higher frequency of autoimmune diseases in the female population compared to males suggests that certain hormones, such as prolactin (PRL), play a role in determining the prevalence of autoimmunity in women, particularly during childbearing age. PRL can act not only as a hormone but also as a cytokine, being able to modulate immune responses. Hyperprolactinemia has been implicated in the pathogenesis of various autoimmune diseases where it may affect disease activity. One of the conditions where PRL has such a role is systemic lupus erythematosus (SLE). PRL regulates the proliferation and survival of both lymphoid and myeloid cells. It also affects the selection of T-cell repertoires by influencing the thymic microenvironment. In autoimmune conditions, PRL interferes with the activity of regulatory T cells. It also influences B cell tolerance by lowering the activation threshold of anergic B cells. The production of CD40L and cytokines, such as interleukin IL-6, are also promoted by PRL. This, in turn, leads to the production of autoantibodies, one of the hallmarks of SLE. PRL increases the cytotoxic activity of T lymphocytes and the secretion of proinflammatory cytokines. The production of proinflammatory cytokines, particularly those belonging to the type 1 interferon (IFN) family, is part of the SLE characteristic genetic signature. PRL also participates in the maturation and differentiation of dendritic cells, promoting the presentation of autoantigens and high IFNα secretion. It also affects neutrophil function and the production of neutrophil traps. Macrophages and dendritic cells can also be affected by PRL, linking this molecule to the abnormal behavior of both innate and adaptive immune responses.This review aimed to highlight the importance of PRL and its actions on the cells of innate and adaptive immune responses. Additionally, by elucidating the role of PRL in SLE etiopathogenesis, this work will contribute to a better understanding of the factors involved in SLE development and regulation.

Distinct Microbiomes of Gut and Saliva in Patients With Systemic Lupus Erythematous and Clinical Associations.

Alterations in the microbiome of the gut and oral cavity are involved in the etiopathogenesis of systemic lupus erythematosus (SLE). We aimed to assess whether both microbiome compositions in feces and saliva were specific in patients with SLE. A total of 35 patients with SLE, as well as sex- and age-matched asymptomatic subjects as healthy control (HC) group were recruited. Fecal swabs and saliva samples were collected from the participants. 16S ribosomal RNA gene sequencing was performed on the samples. Compared with the HC group, reduced bacterial richness and diversity were detected in the feces of patients with SLE, and increased bacterial diversity in their saliva. Both feces and saliva samples explained the cohort variation. The feces were characterized by enrichment of Lactobacillus, and depletion of an unclassified bacterium in the Ruminococcaceae family and Bifidobacterium. Lack of Bifidobacterium was observed in patients with arthritis. Akkermansia and Ruminococcus negatively correlated with the serum levels of C3. In saliva, Veillonella, Streptococcus, and Prevotella were dominant, and Bacteroides was negatively associated with disease activity. These findings can assist us to comprehensively understand the bacterial profiles of different body niches in SLE patients.

Hsa_circ_0010957 level is increased and sponges microRNA‑125b in CD4+ Tcells of patients with systemic lupus erythematosus.

Systemic lupus erythematosus (SLE) is a severe autoimmune disorder, the pathogenesis of which remains largely unknown. The present study aimed to investigate the role and mechanism of circular RNAs in the etiopathogenesis of SLE. CD4+ T cells in patients with SLE expressed higher levels of hsa_circ_0010957 compared with healthy individuals and was a good differentiator of the active from inactive SLE disease. It was also determined that hsa_circ_0010957 mediated microRNA (miR)-125b/STAT3 signaling and subsequent secretion of inflammatory cytokines interleukin (IL)-18, IL-6 and IL-17, which are important factors in the process of SLE. Hsa_circ_0010957 abrogated the proinflammatory effect of IL-6 via the blockade of STAT3 signaling. In conclusion, increased hsa_circ_0010957 may be involved in SLE pathogenesis via miR-125b/STAT3 signaling. Hsa_circ_0010957 promises to be a potential biomarker and therapeutic target for SLE.

Modern considerations on the predisposing factors in the etiopathogenesis of systemic lupus erythematosus

Lupus erythematosus is an autoimmune disease with severe skin involvement and/or multisystemic implications characterized by the development of autoantibodies and immune complexes that, in turn, cause inflammation, tissue damage and a variety of clinical manifestations. The etiopathogeny of lupus erythematosus is very complex and still incompletely discovered. The onset of this disease or the episodes of exacerbation involves various factors: genetic, immune, hormonal, environmental but many more are still under research. There is strong evidence to back up the theory of an autoimmune disease, even though the precise mechanism is yet to be discovered. Apart from a preexisting background predisposing to lupus, certain triggers are required to act in a synergic way to determine the onset of the clinical signs. Studies show that it is 10-15 times more common in women of childbearing age than men, with a higher incidence amongst Afro-American population compared to Caucasians. The aim of this article is to shed some light on the most important determining and trigger factors involved in systemic lupus erythematosus by reviewing the most recent published data.

Bite of the wolf: innate immune responses propagate autoimmunity in lupus.

The etiopathogenesis of systemic lupus erythematosus (SLE), a clinically heterogeneous multisystemic syndrome that derives its name from the initial characterization of facial lesions that resemble the bite of a wolf, is considered a complex, multifactorial interplay between underlying genetic susceptibility factors and the environment. Prominent pathogenic factors include the induction of aberrant cell death pathways coupled with defective cell death clearance mechanisms that promote excessive externalization of modified cellular and nuclear debris with subsequent loss of tolerance to a wide variety of autoantigens and innate and adaptive immune dysregulation. While abnormalities in adaptive immunity are well recognized and are key to the pathogenesis of SLE, recent findings have emphasized fundamental roles of the innate immune system in the initiation and propagation of autoimmunity and the development of organ damage in this disease. This Review focuses on recent discoveries regarding the role of components of the innate immune system, specifically neutrophils and interferons, in promoting various aspects of lupus pathogenesis, with potential implications for novel therapeutic strategies.

The immunomodulatory effects of mesenchymal stromal cell-based therapy in human and animal models of systemic lupus erythematosus.

Systemic lupus erythematosus (SLE) is a chronic systemic autoimmune inflammatory disease with no absolute cure. Although the exact etiopathogenesis of SLE is still enigmatic, it has been well demonstrated that a combination of genetic predisposition and environmental factors trigger a disturbance in immune responses and thereby participate in the development of this condition. Almost all available therapeutic strategies in SLE are primarily based on the administration of immunosuppressive drugs and are not curative. Mesenchymal stromal cells (MSCs) are a subset of non-hematopoietic adult stem cells that can be isolated from many adult tissues and are increasingly recognized as immune response modulating agents. MSC-mediated inhibition of immune responses is a complex mechanism that involves almost every aspect of the immune response. MSCs suppress the maturation of antigen-presenting cells (DC and MQ), proliferation of T cells (Th1, T17, and Th2), proliferation and immunoglobulin production of B cells, the cytotoxic activity of CTL and NK cells in addition to increasing regulatory cytokines (TGF-β and IL10), and decreasing inflammatory cytokines (IL17, INF-ϒ, TNF-α, and IL12) levels. MSCs have shown encouraging results in the treatment of several autoimmune diseases, in particular SLE. This report aims to review the beneficial and therapeutic properties of MSCs; it also focuses on the results of animal model studies, preclinical studies, and clinical trials of MSC therapy in SLE from the immunoregulatory aspect.

Towards a pro-resolving concept in systemic lupus erythematosus.

Systemic lupus erythematosus (SLE) is a prototypic autoimmune disease with prominent chronic inflammatory aspects. SLE most often affects women (9:1) in childbearing age. The multifactorial nature of the etiopathogenesis of SLE involves a deficient clearance of dead and dying cells. This is supported by the occurrence of autoantibodies directed against autoantigens modified in dying and dead cells (dsDNA, high mobility group box 1 protein, apoptosis-associated chromatin modifications, e.g., histones H3-K27-me3; H2A/H4 AcK8,12,16; and H2B-AcK12) that are deposited in various tissues, including skin, kidneys, joints, muscles, and brain. The subsequent hyperinflammatory response often leads to irreparable tissue damage and organ destruction. In healthy individuals, dead and dying cells are rapidly removed by macrophages in an anti-inflammatory manner, referred to as efferocytosis. In SLE, extensive and prolonged cell death (apoptosis, necrosis, neutrophil extracellular trap (NET) formation) leads to autoantigens leaking out of the not cleared cell debris. These neo-epitopes are subsequently presented to B cells by follicular dendritic cells in the germinal centers of secondary lymphoid tissues conditioning the break of self-tolerance. Activation of autoreactive B cells and subsequent production of autoantibodies facilitate the formation of immune complexes (ICs) fueling the inflammatory response and leading to further tissue damage. ICs may also be ingested by phagocytes, which then produce further pro-inflammatory cytokines. These processes establish a vicious circle that leads to sustained inflammation. This review highlights the cell death-related events in SLE, the protagonists involved in SLE pathogenesis, the resolution of inflammation in various tissues affected in SLE, and explores strategies for intervention to restore hemostasis in a hyperinflammatory state.

Systemic Lupus Erythematosus and DNA Degradation and Elimination Defects.

Introduction: Systemic lupus erythematosus (SLE) is a chronic autoimmune disease that is characterized by the production of autoantibodies specific for components of the cell nucleus and that causes damage to body tissues and organs. The pathogenesis of SLE remains unclear, with numerous studies pointing to a combination of genetic and environmental factors. A critical stage in SLE development is cell necrosis, in which undegraded chromatin and nucleoproteins are released into the blood, resulting in circulating cell-free DNA and serum nucleoproteins that trigger anti-dsDNA autoantibody production. This systematic literature review aimed to examine whether SLE stems from a DNA degradation and elimination defect.Materials and Methods: An advanced literature search was conducted in PubMed using the following keywords: [(“SLE” OR “Systemic Lupus Erythematosus” OR “Lupus”)] AND [(“DNA” OR “DNA Degradation”)] AND [(“Defect Elimination”)]. More articles were obtained from the references of the identified articles and basic Google searches. Twenty-five peer-reviewed articles published within the past 10 years (2007–2018) were included for review.Results: The findings of each study are summarized in Tables 1, 2.Discussion and Conclusion: The etiopathogenesis of SLE remains controversial, which limits therapeutic inventions for this disease. However, SLE is a DNA degradation and elimination disorder caused by uncleared histones and nuclear material that leak into the extracellular space and form cell-free DNA, triggering an immune response that destroys tissues and organs. Under normal conditions, apoptosis allows DNA and other nuclear material to be efficiently cleared through degradation and additional complex mechanisms such that this material does not trigger the immune system to produce nuclear autoantibodies.

Functional mannose binding lectin levels in patients with pediatric onset systemic lupus erythematosus in remission.

Complement system plays a crucial role in the pathogenesis of systemic lupus erythematosus (SLE). Excessive activation of complement causes tissue injury and SLE occurrence is typically associated with congenital deficiencies of the early components of the classical complement pathway. Mannose-binding lectin (MBL) is recognized as important causative factor in the etio-pathogenesis of SLE and MBL-2 gene has evolved as a candidate gene for SLE susceptibility. This study was done to assess the functional MBL (fMBL) level in SLE patients in remission and its co-relation with disease severity and outcome. Functional MBL levels were compared with age and sex matched healthy controls and were correlated with duration of illness,complement levels and anti-double- stranded DNA antibody levels. Mean fMBL level in patients was found to be 696.19±408.98U/mL and 579.52±393.87U/mL in the control group. Four children had very low fMBL levels (<40U/mL). Functional MBL levels were higher in patients with SLE even when the disease was in remission as compared to healthy controls, although not statistically significant. Large variation exists in fMBL levels in patients with SLE even when in remission. Very low fMBL levels were found in some children with younger age of onset of SLE, multisystem involvement and severe course of the disease. Positive correlation of MBL levels with anti-ds DNA titers suggest that its values vary with activity and could be a potential biomarker of the disease.

Organ-specific biomarkers in lupus.

Systemic lupus erythematosus (SLE) is a complex and highly heterogeneous disease, which affects multiple organs, including joints, skin, kidneys, heart, hematopoietic system, and nerve system. While the etiopathogenesis of SLE still remains unclear, genetic susceptibilities and aberrant epigenetic modifications are believed to be involved. For precision therapy, it is necessary to assess accurately and objectively organ involvements and disease activity, which is difficult by current clinical laboratory tests. Biomarkers, which are a biologic, genetic, epigenetic or a chemical characteristic and conveniently detectable, serve as measures of disease diagnosis, activity, prognosis, and manifestation prediction, thereby providing instruction for individualized therapy. In addition, biomarkers differ according to different manifestations, since the disease activity index and treatments vary significantly. For example, unlike other non-renal SLE, lupus nephritis requires significant immunosuppressive drugs. Over the past decades, the research on biomarkers in lupus has been strengthened and numerous promising biomarkers have been identified at levels of genomics, transcriptomics and proteomics. In this review, we summarize the conventional and novel biomarkers in the tissue-specific manner, and discuss their roles in specific organ diagnosis, future manifestation prediction, disease activity assessment and their correlation with histology results. By doing so, it aims to shed a light on individualized treatment.

Confirmation of five novel susceptibility loci for systemic lupus erythematosus (SLE) and integrated network analysis of 82 SLE susceptibility loci.

We recently identified ten novel SLE susceptibility loci in Asians and uncovered several additional suggestive loci requiring further validation. This study aimed to replicate five of these suggestive loci in a Han Chinese cohort from Hong Kong, followed by meta-analysis (11,656 cases and 23,968 controls) on previously reported Asian and European populations, and to perform bioinformatic analyses on all 82 reported SLE loci to identify shared regulatory signatures. We performed a battery of analyses for these five loci, as well as joint analyses on all 82 SLE loci. All five loci passed genome-wide significance: MYNN (rs10936599, Pmeta = 1.92 × 10-13, OR = 1.14), ATG16L2 (rs11235604, Pmeta = 8.87 × 10 -12, OR = 0.78), CCL22 (rs223881, Pmeta = 5.87 × 10-16, OR = 0.87), ANKS1A (rs2762340, Pmeta = 4.93 × 10-15, OR = 0.87) and RNASEH2C (rs1308020, Pmeta = 2.96 × 10-19, OR = 0.84) and co-located with annotated gene regulatory elements. The novel loci share genetic signatures with other reported SLE loci, including effects on gene expression, transcription factor binding, and epigenetic characteristics. Most (56%) of the correlated (r2 > 0.8) SNPs from the 82 SLE loci were implicated in differential expression (9.81 × 10-198 < P < 5 × 10-3) of cis-genes. Transcription factor binding sites for p53, MEF2A and E2F1 were significantly (P < 0.05) over-represented in SLE loci, consistent with apoptosis playing a critical role in SLE. Enrichment analysis revealed common pathways, gene ontology, protein domains, and cell type-specific expression. In summary, we provide evidence of five novel SLE susceptibility loci. Integrated bioinformatics using all 82 loci revealed that SLE susceptibility loci share many gene regulatory features, suggestive of conserved mechanisms of SLE etiopathogenesis.

Inflammatory etiopathogenesis of systemic lupus erythematosus: an update.

The immune system struggles every day between responding to foreign antigens and tolerating self-antigens to delicately maintain tissue homeostasis. If self-tolerance is broken, the development of autoimmunity can be the consequence, as it is in the case of the chronic inflammatory autoimmune disease systemic lupus erythematosus (SLE). SLE is considered to be a multifactorial disease comprising various processes and cell types that act abnormally and in a harmful way. Oxidative stress, infections, or, in general, tissue injury are accompanied by massive cellular demise. Several processes such as apoptosis, necrosis, or NETosis (formation of Neutrophil Extracellular Traps [NETs]) may occur alone or in combination. If clearance of dead cells is insufficient, cellular debris may accumulate and trigger inflammation and leakage of cytoplasmic and nuclear autoantigens like ribonucleoproteins, DNA, or histones. Inadequate removal of cellular remnants in the germinal centers of secondary lymphoid organs may result in the presentation of autoantigens by follicular dendritic cells to autoreactive B cells that had been generated by chance during the process of somatic hypermutation (loss of peripheral tolerance). The improper exposure of nuclear autoantigens in this delicate location is consequently prone to break self-tolerance to nuclear autoantigens. Indeed, the germline variants of autoantibodies often do not show autoreactivity. The subsequent production of autoantibodies plays a critical role in the development of the complex immunological disorder fostering SLE. Immune complexes composed of cell-derived autoantigens and autoantibodies are formed and get deposited in various tissues, such as the kidney, leading to severe organ damage. Alternatively, they may also be formed in situ by binding to planted antigens of circulating autoantibodies. Here, we review current knowledge about the etiopathogenesis of SLE including the involvement of different types of cell death, serving as the potential source of autoantigens, and impaired clearance of cell remnants, causing accumulation of cellular debris.

AN OVERVIEW OF THE VI EULAR SCIENTIFIC EDUCATIONAL COURSE DEDICATED TO SYSTEMIC LUPUS ERYTHEMATOSUS (PISA, ITALY, SEPTEMBER 1–6, 2013)

The article presents an overview of the lectures and workshops of the VI scientific educational course by the European League against Rheumatism (EULAR) dedicated to systemic lupus erythematosus (SLE), which was held in Pisa, Italy, in early September 2013. The course aims were to train young practicing rheumatologists to make early diagnosis and provide timely and adequate treatment with allowance for the current concepts of SLE etiopathogenesis; the use of the EULAR recommendations and classification criteria; and analysis of complex clinical cases. The main issues of this course included lesion of the nervous system in SLE, lupus nephritis, therapy with traditional and biological response modifiers, management of pregnancy in SLE patients, the need for standardization of the methods for the diagnosis and treatment of these conditions.

Infections and systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is a chronic autoimmune disease that presents a protean spectrum of clinical manifestations, and may affect any organ. The typical course of SLE is insidious, slow, and progressive, with potential exacerbations and remissions, and even dramatically acute and rapidly fatal outcomes. Recently, infections have been shown to be highly associated with the onset and/or exacerbations of SLE, and their possible causative and/or protective role has been largely emphasized in the medical literature. However, the etiopathogenesis of SLE is still obscure and far from being completely elucidated. Among infections, particularly Epstein-Barr virus (EBV), parvovirus B19, retrovirus, and cytomegalovirus (CMV) infections might play a pivotal pathogenetic role. The multifaceted interactions between infections and autoimmunity reveal many possibilities for either causative or protective associations. Indeed, some infections, primarily protozoan infections, might confer protection from autoimmune processes, depending on the unique interaction between the microorganism and host. Further studies are needed in order to demonstrate that infectious agents might, indeed, be causative of SLE, and to address the potential clinical sequelae of infections in the field of autoimmunity.

Interplay of Infections, Autoimmunity, and Immunosuppression in Systemic Lupus Erythematosus

Infectious agents are considered to be crucial environmental factor in the etiopathogenesis of systemic lupus erythematosus (SLE). Infections may serve as initial trigger to the development of autoimmunity and carry an overall greater risk of morbidity and mortality than the general population. Initial presentation of SLE can mimic infections, and in turn infections can mimic disease flares in established SLE. Infections due to predisposition by commonly used immunosuppressive therapies are a significant cause of morbidity and mortality. In this review, viral, bacterial, fungal, and parasitic infections that contribute to the etiology of SLE, potentially mimic or precipitate flares, create diagnostic dilemmas, complicate treatment, or protect against disease, are discussed. Infection risks of current immunosuppressive therapies used in the treatment of SLE are outlined. Strategies to prevent infection, including vaccines, prophylactic antibiotic therapies, toll-like receptor antagonism, and antioxidant treatment that may decrease disease burden and improve quality of life in lupus patients will be discussed.

Molecular Insights into Systemic Lupus Erythematosus Pathogenesis

Systemic lupus erythematosus (SLE) is a complex, heterogeneous, and chronic autoimmune disorder of an unknown origin. Its clinical symptoms range from a benign skin disorder to severe, life-threatening conditions.1 Immune effector dysfunctions are hall marks of SLE disease.2 The etiopathogenesis of the altered immune response in SLE remains unknown. SLE is characterized by the presence of auto-antibodies (AutoAbs) for a wide variety of self antigens and circulating immune complexes.1,2 The onset of lupus is variable and may affect all stages of life. The disease predominantly affiicts females in the child-bearing years about 6- to 10-fold more frequently than males. We have not had a new drug in 50 years, because of the unknown etiology of the abnormal immune response. The current lupus therapies are non-specific, symptomatic, and cause significant side effects. In this editorial, I have made an attempt to describe multistep immune alterations that pave the way for the inception and sustaining of SLE pathogenesis, and postulated molecular mechanisms involved in SLE disease onset. Such information will help in better understanding SLE etiopathogenesis and in developing effective and safer strategies to combat SLE as well as other autoimmune diseases.

Studies on peroxynitrite-modified H1 histone: Implications in systemic lupus erythematosus

Peroxynitrite is a powerful nitrating and oxidizing molecule and capable of modifying proteins' structure. Hyper-nitration of tyrosine residues has been seen in various pathological states, including autoimmune disorders like systemic lupus erythematosus (SLE) and rheumatoid arthritis. SLE, a chronic autoimmune disease, is primarily characterized by increased levels of autoantibodies, predominantly against ds-DNA. However, the initial antigenic stimulus for the disease etiopathogenesis has remained elusive. Carbonyl and nitrotyrosine have been extensively used as a biomarker of oxidative and nitrosative stress. In this study, commercially available H1 histone was exposed to increasing concentrations of peroxynitrite for 30 min. The peroxynitrite-mediated structural changes in histone were studied by ultraviolet & fluorescence spectroscopy, CD, HPLC, 1-anilinonaphthalene-8-sulfonic acid binding and polyacrylamide gel electrophoresis. Analysis of results revealed that carbonyl and nitrotyrosine contents were significantly increased in peroxynitrite-modified H1 compared to native H1. In experimental animal, peroxynitrite-modified H1 induced high titre antibodies as compared to native H1, and the immunogenicity was found to be directly proportional to nitrotyrosine content. Further, the induced antibodies showed specificity for the immunogen and appreciable cross-reactions with tyrosine rich nitrated proteins. Formation of high molecular weight immune complex with retarded mobility further supports the specificity of induced anti-peroxynitrite-modified H1 antibodies for the immunogen. Binding of SLE anti-DNA autoantibodies with peroxynitrite-modified H1 was analyzed by direct binding and competition ELISA. The data show preferential binding of SLE autoantibodies to peroxynitrite-modified H1 as compared to native H1 histone and native DNA. The results point towards the possible role of peroxynitrite-modified H1 histone in SLE etiopathogenesis.

Physicochemical and immunological studies on mitochondrial DNA modified by peroxynitrite: implications of neo-epitopes of mitochondrial DNA in the etiopathogenesis of systemic lupus erythematosus

Recent evidence has demonstrated that mitochondria possess their own nitric oxide synthase (mtNOS) and can produce endogenous reactive-nitrogen-species (RNS) including peroxynitrite (ONOO(-)). This study was undertaken to investigate the role of mitochondrial DNA (mtDNA) damage by ONOO(-) in systemic lupus erythematosus (SLE) autoimmunity. MtDNA was isolated from fresh goat liver and modified by ONOO(-), generated by synergistic action of nitric oxide (NO) and superoxide (O (-) 2) donors. Modifications occurring in mtDNA were characterized by physicochemical techniques. SLE patients (n = 50) with varying disease activity according to the SLE Disease Activity Index (SLEDAI) and healthy controls (n = 34) were evaluated for antibodies to native and ONOO(-)-modified mtDNA by immunoassays. Gel retardation assays were performed to cross-examine the immunoassay results using affinity-purified SLE immunoglobulin G (IgG). Nitrosative stress in SLE patients was studied by measuring nitrotyrosine and inducible NO synthase (iNOS). The ONOO(-) caused extensive damage to mtDNA as evident by ultraviolet (UV) hyperchromicity and loss of florescence intensity. Thermal melting studies, agarose gel electrophoresis and nuclease S1 digestibility clearly indicate structural perturbation in mtDNA by ONOO(-). Quenching studies with specific NO or O (-) 2 quenchers confirmed that the damaging agent was ONOO(-). SLE autoantibodies exhibited enhanced binding with ONOO(-)-mtDNA as compared to their native analog. Interestingly, not only was there an increased number of subjects positive for ONOO(-) -mtDNA, but also the levels of anti-ONOO(-) -mtDNA antibodies were statistically significantly higher among SLE patients whose SLEDAI scores were ≥ 20 as compared with SLE patients with lower SLEDAI scores (SLEDAI < 20). Normal healthy controls showed negligible binding with either antigen. Furthermore, SLE patients had higher levels of nitrotyrosine and iNOS compared with their respective healthy controls. Our novel results provide an important insight into the immunological basis of anti-DNA autoantibody generation in SLE. Our data conclude that modification of mtDNA by ONOO(-) causes structural perturbations, resulting in the generation of neo-epitopes, and making it a potential immunogen in SLE. The mtDNA modified by ONOO(-) may be useful in evaluating the progression of SLE and in elucidating the mechanisms of disease pathogenesis.