Poly(ADP-ribose) polymerase activity in systemic lupus erythematosus and systemic sclerosis

The PP2A regulatory subunit PPP2R2A controls NAD+ biosynthesis to regulate T cell subset differentiation in systemic autoimmunity

The protein phosphatase 2A (PP2A) regulatory subunit PPP2R2A is involved in the regulation of immune response. We report that lupus-prone mice with T cells deficient in PPP2R2A display less autoimmunity and nephritis. PPP2R2A deficiency promotes NAD+ biosynthesis through the nicotinamide riboside (NR)-directed salvage pathway in T cells. NR inhibits murine Th17 and promotes Treg cell differentiation, in vitro, by PΑRylating histone H1.2 and causing its reduced occupancy in the Foxp3 loci and increased occupancy in the Il17a loci, leading to increased Foxp3 and decreased Il17a transcription. NR treatment suppresses disease in MRL.lpr mice and restores NAD+-dependent poly [ADP-ribose] polymerase 1 (PARP1) activity in CD4 T cells from patients with systemic lupus erythematosus (SLE), while reducing interferon (IFN)-γ and interleukin (IL)-17 production. We conclude that PPP2R2A controls the level of NAD+ through the NR-directed salvage pathway and promotes systemic autoimmunity. Translationally, NR suppresses lupus nephritis in mice and limits the production of proinflammatory cytokines by SLE T cells.

DNA double-strand break repair and nucleic acid-related immunity

DNA damage repair and innate immunity are two conserved mechanisms that both function in cellular stress responses. Recently, an increasing amount of evidence has uncovered the close relationship between these two ancient biological processes. Here, we review the classical function of factors involved in DNA repair, and especially double-strand break repair, in innate immunity; more importantly, we discuss the novel roles of DNA repair factors in regulating innate immunity and vice versa. In addition, we also review the roles of DNA repair, innate immunity and their crosstalk in human diseases, which suggest that these two pathways may be compelling targets for disease prevention and treatment.

DNA Damage Response and Oxidative Stress in Systemic Autoimmunity

The DNA damage response and repair (DDR/R) network, a sum of hierarchically structured signaling pathways that recognize and repair DNA damage, and the immune response to endogenous and/or exogenous threats, act synergistically to enhance cellular defense. On the other hand, a deregulated interplay between these systems underlines inflammatory diseases including malignancies and chronic systemic autoimmune diseases, such as systemic lupus erythematosus, systemic sclerosis, and rheumatoid arthritis. Patients with these diseases are characterized by aberrant immune response to self-antigens with widespread production of autoantibodies and multiple-tissue injury, as well as by the presence of increased oxidative stress. Recent data demonstrate accumulation of endogenous DNA damage in peripheral blood mononuclear cells from these patients, which is related to (a) augmented DNA damage formation, at least partly due to the induction of oxidative stress, and (b) epigenetically regulated functional abnormalities of fundamental DNA repair mechanisms. Because endogenous DNA damage accumulation has serious consequences for cellular health, including genomic instability and enhancement of an aberrant immune response, these results can be exploited for understanding pathogenesis and progression of systemic autoimmune diseases, as well as for the development of new treatments.

Poly(ADP-Ribose) Polymerases in Host-Pathogen Interactions, Inflammation, and Immunity

The literature review presented here details recent research involving members of the poly(ADP-ribose) polymerase (PARP) family of proteins. Among the 17 recognized members of the family, the human enzyme PARP1 is the most extensively studied, resulting in a number of known biological and metabolic roles. This review is focused on the roles played by PARP enzymes in host-pathogen interactions and in diseases with an associated inflammatory response. In mammalian cells, several PARPs have specific roles in the antiviral response; this is perhaps best illustrated by PARP13, also termed the zinc finger antiviral protein (ZAP). Plant stress responses and immunity are also regulated by poly(ADP-ribosyl)ation. PARPs promote inflammatory responses by stimulating proinflammatory signal transduction pathways that lead to the expression of cytokines and cell adhesion molecules. Hence, PARP inhibitors show promise in the treatment of inflammatory disorders and conditions with an inflammatory component, such as diabetes, arthritis, and stroke. These functions are correlated with the biophysical characteristics of PARP family enzymes. This work is important in providing a comprehensive understanding of the molecular basis of pathogenesis and host responses, as well as in the identification of inhibitors. This is important because the identification of inhibitors has been shown to be effective in arresting the progression of disease.

DNA Damage and Deficiencies in the Mechanisms of Its Repair: Implications in the Pathogenesis of Systemic Lupus Erythematosus

Systemic lupus erythematosus (SLE) is a perplexing and potentially severe disease, the pathogenesis of which is yet to be understood. SLE is considered to be a multifactorial disease, in which genetic factors, immune dysregulation, and environmental factors, such as ultraviolet radiation, are involved. Recently, the description of novel genes conferring susceptibility to develop SLE even in their own (monogenic lupus) has raised the interest in DNA dynamics since many of these genes are linked to DNA repair. Damage to DNA induces an inflammatory response and eventually triggers an immune response, including those targeting self-antigens. We review the evidence that indicates that patients with SLE present higher levels of DNA damage than normal subjects do and that several proteins involved in the preservation of the genomic stability show polymorphisms, some of which increase the risk for SLE development. Also, the experience from animal models reinforces the connection between DNA damage and defective repair in the development of SLE-like disease including characteristic features such as anti-DNA antibodies and nephritis. Defining the role of DNA damage response in SLE pathogenesis might be strategic in the quest for novel therapies.

The roles and applications of autoantibodies in progression, diagnosis, treatment and prognosis of human malignant tumours

The existence of autoantibodies towards an individual's own proteins or nucleic acids has been established for more than 100years, and for a long period, these autoantibodies have been believed to be closely associated with autoimmune diseases. However, in recent years, researchers have become more interested in the role and application of autoantibodies in progression, diagnosis, treatment and prognosis of human malignant tumours. Over the past few decades, numerous epidemiological studies have shown that the risk of certain cancers is significantly altered (increased or decreased) in patients with autoimmune diseases, which suggests that autoantibodies may play either promoting or suppressing roles in cancer progression. The idea that autoantibodies are directly involved in tumour progression gains special support by the findings that some antibodies secreted by a variety of cancer cells can promote their proliferation and metastasis. Because the cancer cells generate cell antigenic changes (neoantigens), which trigger the immune system to produce autoantibodies, serum autoantibodies against tumour-associated antigens have been established as a novel type of cancer biomarkers and have been extensively studied in different types of cancer. The autoantibodies as biomarkers in cancer diagnosis are not only more sensitive and specific than antigens, but also could appear before clinical evidences of the tumours, thus disclosing them. The observations that cancer risk is lower in patients with some autoimmune diseases suggest that certain autoantibodies may be protective from certain cancers. Moreover, the presence of autoantibodies in healthy individuals implies that it could be safe to employ autoantibodies to treat cancer. Of note, an autoantibodies derived from lupus murine model received much attention due to their selective cytotoxicity for malignant tumour cell without harming normal ones. These studies showed the therapeutic value of autoantibodies in cancer. In this review, we revisited the pathological or protective role of autoantibodies in cancer progression, summarize the application of autoantibodies in cancer diagnosis and prognosis, and discuss the value of autoantibodies in cancer therapy. The studies established to date suggest that autoantibodies not only regulate cancer progression but also promise to be valuable instruments in oncological diagnosis and therapy.

Regulated necrosis-related molecule mRNA expression in humans and mice and in murine acute tissue injury and systemic autoimmunity leading to progressive organ damage, and progressive fibrosis

The species-specific, as well as organ-specific expression of regulated necrosis (RN)-related molecules, is not known. We determined the expression levels of tumour necrosis factor receptor-1 (TNFR1), receptor activated protein kinase (RIPK)1, RIPK3, mixed lineage kinase domain-like (MLKL), CASP8, Fas-associated protein with death domain (FADD), cellular inhibitor of apoptosis protein (CIAP)1, CIAP2, glutathione peroxidase-4 (GPX4), cyclophilin D (CYPD), CASP1, NLRP3 and poly(ADP-ribose) polymerase-1 (PARP1) in human and mouse solid organs. We observed significant differences in expression of these molecules between human and mice. In addition, we characterized their expression profiles in acute as well as persistent tissue injury and chronic tissue remodelling using acute and chronic kidney injury models. We observed that the degree and pattern of induction of RN-related molecules were highly dependent on the trigger and disease pathogenesis. Furthermore, we studied their expression patterns in mice with lupus-like systemic autoimmunity, which revealed that the expression of MLKL, GPX4 and PARP1 significantly increased in the spleen along disease progression and CASP1, RIPK1, RIPK3 and CYPD were higher at the earlier stages but were significantly decreased in the later stages. In contrast, in the kidney, the expression of genes involved in pyroptosis, e.g. NLRP3 and CASP1 were significantly increased and TNFR1, RIPK1, RIPK3, CIAP1/2 and GPX4 were significantly decreased along the progression of lupus nephritis (LN). Thus, the organ- and species-specific expression of RN-related molecules should be considered during designing experiments, interpreting the results as well as extrapolating the conclusions from one species or organ to another species or organ respectively.

DNA-damaging autoantibodies and cancer: the lupus butterfly theory

Autoantibodies reactive against host DNA are detectable in the circulation of most people with systemic lupus erythematosus (SLE). The long-held view that antibodies cannot penetrate live cells has been disproved. A subset of lupus autoantibodies penetrate cells, translocate to nuclei, and inhibit DNA repair or directly damages DNA. The result of these effects depends on the microenvironment and genetic traits of the cell. Some DNA-damaging antibodies alone have little impact on normal cells, but in the presence of other conditions, such as pre-existing DNA-repair defects, can become highly toxic. These findings raise new questions about autoimmunity and DNA damage, and reveal opportunities for new targeted therapies against malignancies particularly vulnerable to DNA damage. In this Perspectives article, we review the known associations between SLE, DNA damage and cancer, and propose a theory for the effects of DNA-damaging autoantibodies on SLE pathophysiology and cancer risk.

Increased ERK and JNK activation and decreased ERK/JNK ratio are associated with long-term organ damage in patients with systemic lupus erythematosus

OBJECTIVE

The activities of two mitogen-activated protein kinases (MAPKs), extracellular signal-regulated kinase (ERK) and c-Jun N-terminal kinase (JNK), correlate with disease severity in SLE patients. Whether they are also associated with long-term organ damage is unknown. The aim of the present work was to determine whether impaired expression and activity of ERK and JNK correlate with long-term damage in SLE.

METHODS

The expression of ERK and JNK and their phosphorylated active forms was determined by western blot analysis four times during the first year of follow-up in peripheral blood mononuclear cells from 36 SLE patients. A correlation analysis was performed between ERK and JNK expression and longterm organ damage estimated by the SLICC/ARC Damage Index (SDI) 4 years later.

RESULTS

Mean levels of ERK and JNK activities during the first year correlated with long-term organ damage severity (r = 0.38 and r = 0.35, respectively; P = 0.05). Overall JNK expression increased with the severity of chronic damage (P = 0.01; P = 0.05 for SDI score 2 and 3, respectively). In contrast, overall ERK expression significantly decreased in patients with maximal organ damage (SDI score 3) compared with patients with an SDI score of 2 (P = 0.03). The ERK/JNK ratio decreased by approximately 40% and 30% in patients with an SDI score of 3 as compared with patients without organ damage and healthy controls, respectively.

CONCLUSION

These results demonstrate that early activation of ERK and JNK along with decreased overall ERK expression and reduced ERK/JNK ratio may predict the severity of long-term organ damage in SLE patients.

Constitutive abnormal expression of RasGRP-1 isoforms and low expression of PARP-1 in patients with systemic lupus erythematosus

OBJECTIVE

Defective expression of Ras guanil releasing protein-1 (RasGRP-1) and increased apoptosis have been reported in lymphocytes from SLE patients. Whether these aberrations are correlated and linked to disease activity has not been elucidated.

METHODS

Expression of normal 90 kDa RasGRP-1, its most prevalent 86 kDa isoform and full PARP-1 116 kDa and its cleavage fragment 84 kDa were determined in whole protein lysates of peripheral blood mononuclear cells (PBMC) in correlation with mitogen activated protein kinase (MAPK) activity and SLE clinical status in a large group of SLE patients during 1 year follow-up.

RESULTS

Expression of normal 90 kDa RasGRP-1 was comparable in patients and controls. However, SLE patients demonstrated a constitutively increased 86 kDa/90 kDA ratio (p < 0.01) and decreased full poly (ADP-ribose) polymerase protein-1 (PARP-1) expression (p < 0.002) compared with controls who were disease-independent. A remission in disease activity was associated with decreased RasGRP-1 expression. Expression of 84 kDa PARP-1 cleavage fragment was found in 15% of patients but in none of the controls. In addition, expression of PARP-1 correlated positively with normal 90 kDa RasGRP-1 expression and negatively with the RasGRP-1 86 kDa/90 kDA ratio.

CONCLUSIONS

These data suggest that constitutive aberrant expression of PARP-1 and RasGRP-1 ratio may act in concert to impair survival of lymphocytes in SLE patients.