Spontaneous and induced apoptosis in systemic lupus erythematosus: multiple assays fail to reveal consistent abnormalities

Investigation of Genes Associated With Atherosclerosis in Patients With Systemic Lupus Erythematosus

Objectives

In this study, we aimed to identify patients with systemic lupus erythematosus (SLE) who are genetically at risk for developing atherosclerosis.

Patients and methods

Between November 2014 and May 2016, a total of 38 patients with SLE (36 females, 2 males; mean age: 37.6 years; range, 18 to 71 years) and 32 healthy females (mean age: 31.5 years; range, 19 to 54 years) were included in the study. Carotid intima-media thickness (CIMT) was measured using high-resolution B-mode ultrasonography. SurePrint G3 Human Gene Expression 8x60K Microarray kit was used in our study. Genes showing differences in expression between the groups were identified by using GeneSpring GX 10.0 program. Pathway analyses of gene expressions were performed using Ingenuity Pathways Analysis (IPA). Gene ontology analyses were performed using the Protein Analysis Through Evolutionary Relationships (PANTHER).

Results

Clinical findings of SLE patients were mainly photosensitivity (71.1%), arthritis (63.2%), lupus nephritis (55.3%), thrombocytopenia (26.3%), and autoimmune hemolytic anemia (21.1%). A total of 155 genes showing expression level difference were detected between SLE patients and healthy controls. In molecular network analysis, 28.2% of all genes were found to be directly or indirectly associated with atherosclerosis and cardiovascular disease.

Conclusion

In SLE patients, many genes are expressed differently from healthy individuals. Expression of these genes is important in the pathogenesis of SLE. Genes identified differently in gene expression analysis can help us to identify SLE patients at risk for atherosclerosis in the Turkish population.

Evaluation of polymorphic variants in apoptotic genes and their role in susceptibility and clinical progression to systemic lupus erythematosus

Background Systemic lupus erythematosus (SLE) is an autoimmune disease marked by the disruption of the immune homeostasis. Patients exhibit a wide range of clinical manifestations, and environmental and genetic factors are involved in SLE pathogenesis. Evidence suggests that abnormalities in the cellular and molecular events that coordinate apoptosis may favour the generation of autoantigens involved in autoimmunity. In this way, the apoptotic deregulation may be affected by polymorphic variants in apoptotic-related genes. Methods We analyzed FAS, FASL, BCL-2 and BAX polymorphisms in order to correlate to SLE susceptibility and clinical features. A total of 427 SLE patients from the Hospital de Clínicas de Porto Alegre and 543 controls from southern Brazil were evaluated. Results We observed higher frequencies of the FASL -844CC genotype and -844C allele, as well as of the FASL-844C/IVS2nt-124A haplotype in African-derived SLE patients when compared to controls ( P < 0.001). FASL -844C, which is related to high FasL expression, could contribute to increased apoptosis and to the breakdown of immunological tolerance, favouring autoantibody production and inflammation. On the other hand, the BAX -248GA genotype and the -248A allele , related to low protein expression, were observed as a protective factor against SLE in this same population. The rate of apoptosis and cell death was evaluated in peripheral lymphocytes, and SLE patients presented a higher percentage of dead lymphocytes (CD3⁺Annexin V⁺ 7-AAD⁺) compared to the control group. Conclusion Our data support a role for apoptosis in SLE susceptibility.

The association among leukocyte apoptosis, autoantibodies and disease severity in systemic lupus erythematosus

Background

Both apoptosis and autoantibodies are important factors associated with disease activity in the pathogenesis of systemic lupus erythematosus (SLE). This study tested the hypothesis that increased leukocyte apoptosis is associated with elevated levels of autoantibodies and the disease activity of SLE.

Methods

Leukocyte apoptosis was determined by flow cytometry, including annexin V, APO2.7, and 7-amino-actinomycin D (7-AAD) on each subtype of leukocyte in 23 patients with SLE. Leukocyte apoptosis was also evaluated in nine patients with Sjogren’s syndrome (SJS) and in 20 volunteer subjects. Titers of common autoantibodies and the disease activity index (SLEDAI-2 k) of the SLE patients were also determined.

Results

Except for annexin V and APO 2.7 of monocytes and late apoptosis (annexin V + 7-ADD) of lymphocytes, apoptosis in the total and in subsets of leukocytes were significantly higher in SLE patients than in controls (all p < 0.05, post hoc analysis). The mean percentage of late apoptosis of leukocytes (annexin V + 7-AAD) positively correlated with levels of anti-Ro52/60 (r = 0.513, p < 0.01), anti-La (r = 0.439, p = 0.04), and anti-Mi-2 (r = 0.492, p = 0.02), and inversely correlated with both C3 and C4 levels, although not statistically significant. The percentage of APO2.7 of CD19+ cells positively correlated with SLEDAI-2 K score (p = 0.01).

Conclusions

Leukocyte apoptosis is significantly higher in patients with SLE and correlates well with the levels of several autoantibodies. The APO2.7 of B-lymphocyte (CD19+) cells positively correlates with the disease activity of SLE.

Nitric oxide, mitochondrial hyperpolarization, and T cell activation

T lymphocyte activation is associated with nitric oxide (NO) production, which plays an essential role in multiple T cell functions. NO acts as a messenger, activating soluble guanyl cyclase and participating in the transduction signaling pathways involving cyclic GMP. NO modulates mitochondrial events that are involved in apoptosis and regulates mitochondrial membrane potential and mitochondrial biogenesis in many cell types, including lymphocytes. Mitochondrial hyperpolarization (MHP), an early and reversible event during both activation and apoptosis of Tlymphocytes, is regulated by NO. Here, we discuss recent evidence that NO-induced MHP represents a molecular switch in multiple T cell signaling pathways. Overproduction of NO in systemic lupus erythematosus induces mitochondrial biogenesis and alters Ca(2+) signaling. Thus, whereas NO plays a physiological role in lymphocyte cell signaling, its overproduction may disturb normal T cell function, contributing to the pathogenesis of autoimmunity.

Apoptotic cell death and lupus

Programmed cell death and the disposal of cell corpses by phagocytic cells are highly regulated ongoing processes essential for the survival and well-being of higher organisms. Abnormalities in the susceptibility of certain cells to receptor-induced death are known to lead to certain human diseases (e.g., autoimmune lymphoproliferative syndrome) and may contribute to the pathogenesis of systemic lupus erythematosus. Impaired clearance of apoptotic cells is also likely to be an important factor in lupus pathogenesis, though the biological basis of such a defect remains elusive. Finally, the process of apoptosis has been shown to contribute to lupus disease effector mechanisms. A better understanding of the role of apoptosis in lupus very likely will lead to improved diagnosis and therapy.

The role of nitric oxide in abnormal T cell signal transduction in systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is a chronic autoimmune disease characterized by production of antinuclear autoantibodies and diverse array of clinical manifestations. T cells from patients with SLE have been shown to be activated in vivo and provide help to autoreactive B cells. Lupus T cells exhibit enhanced spontaneous and diminished activation-induced apoptosis and predisposition to necrosis. Persistent mitochondrial hyperpolarization and ATP depletion - associated with significantly increased mitochondrial mass - characterize T lymphocyte dysfunction in SLE. In addition to cell death abnormalities, mitochondrial dysfunction is associated with altered signal transduction through the T cell receptor and Ca2+ fluxing. Exposure of normal T cell to nitric oxide induces mitochondrial hyperpolarization and biogenesis and regenerates the Ca2+ signaling profile of lupus T cells. This article reviews a novel understanding of the role of nitric oxide in signal transduction and cell death abnormalities in SLE.

Anaemia in systemic lupus erythematosus: from pathophysiology to clinical assessment

Haematological abnormalities are common in systemic lupus erythematosus. Anaemia is found in about 50% of patients, with anaemia of chronic disease being the most common form. Impaired erythropoietin response and presence of antibodies against erythropoietin may contribute to the pathogenesis of this type of anaemia. Patients with autoimmune haemolytic anaemia usually belong to a distinct category, which is associated with anticardiolipin antibodies, thrombosis, thrombocytopenia, and renal disease, often in the context of secondary antiphospholipid syndrome. Autoantibodies, T lymphocytes, and deregulation of the cytokine network can affect bone marrow erythropoiesis, leading to anaemia.

Apoptosis: the link between autoantibodies and leuko-/lymphocytopenia in patients with lupus erythematosus

OBJECTIVE

To analyse the relation between serum autoantibodies and leuko-/lymphocytopenia in patients with lupus erythematosus (LE).

METHODS

Laboratory routine analyses (white blood cell counts, autoantibody detection), and flow cytometry (annexin V, CD3, CD4, CD8, CD95, F(ab)2 anti-human IgG) have been performed in LE-patients versus healthy controls. In vitro, the influence of pooled serum containing anti-dsDNA antibodies has been analysed on the CD95 expression.

RESULTS

Leukocytes, lymphocytes, CD3+, CD3+ CD4+, and CD3+ CD8+ cells from LE-patients were significantly reduced compared with controls. Patients with autoantibodies had significantly lower absolute cell counts than those without. Apoptosis was increased in LE versus controls (p < 0.04). The percentage of CD95+ T-cells was increased, and the absolute number of CD95+ cells was reduced in LE. In vitro up-regulation of CD95 could be detected on T-cells of healthy donors. Induction of CD95 seems to be donor-dependent.

CONCLUSION

The data suggest that autoantibodies may be associated with blood cytopenias. CD95 seems to play a central role in this signalling cascade. The underlying mechanism is unclear, but seems to be autoantibody-related apoptosis induction.

Genetic models for the clearance of apoptotic cells

The immunogenic potential of nuclear antigens exposed during apoptosis, together with considerable animal data suggesting that impaired apoptotic clearance can result in systemic lupus erythematosus (SLE)-like autoimmunity, has lent support to the idea that self-immunization with apoptotic debris is a key driving mechanism in lupus. The multiple roles of complement receptors, diverse scavenger receptors, and intermediate proteins that bind to and opsonize apoptotic cells indicate a complex web of interactions leading to the clearance of apoptotic debris. Disturbances in parts of this system may lead to lupus or to lupus exacerbations. Therapy directed toward augmenting clearance and decreasing concomitant inflammation may lead to improved management of SLE.

Ultraviolet B radiation-induced cell death: critical role of ultraviolet dose in inflammation and lupus autoantigen redistribution

The nuclear self-Ags targeted in systemic lupus erythematosus translocate to the cell membrane of UV-irradiated apoptotic keratinocytes and may represent an important source of self-immunization. It is hard to understand how the noninflammatory milieu accompanying most apoptosis might provoke an immunogenic response leading to autoantibodies. We have found that the precise amount of keratinocyte UV exposure is crucial in determining the rate of apoptosis, the amount of inflammatory cytokine production, and the degree of autoantigen translocation. Low doses of UVB (</=15 mJ/cm(2)) promptly induced a normal, caspase-dependent apoptosis, while intermediate doses of UV-B (35 mJ/cm(2)) caused apoptosis with altered morphology, slower DNA fragmentation, and poly(ADP-ribose) polymerase degradation accompanied by increased Bcl-2. High doses of UVB (80 mJ/cm(2)) induced instead necrosis. We observed IL-1 production upon intermediate and high UVB doses. Nuclear Ag redistribution was also markedly UV dose dependent: at low doses, Sm, Ku, and DNA translocated to the surfaces of early apoptotic cells. At intermediate doses, these Ags concentrated on the cell membrane when the nucleus was still visible. At high doses, these autoantigens diffused into the cytoplasm and were released into the supernatant. Taken together, the results show that low-dose UVB induces prompt noninflammatory apoptosis. In contrast, intermediate and high doses of UVB induce proinflammatory apoptosis and necrosis, where the production of inflammatory cytokines is accompanied by exposure and release of autoantigens. The key importance of the UV dose on the fate of apoptotic keratinocytes and on their potential immunogenicity should help clarify the role of UVB in inducing systemic lupus erythematosus autoimmunity.

Association of a four-amino acid residue insertion polymorphism of the HS1 gene with systemic lupus erythematosus: Molecular and functional analysis

OBJECTIVE

To investigate whether polymorphism(s) or mutation(s) in the hematopoietic cell-specific Lyn substrate 1 (HS1) gene are involved in the pathogenesis of systemic lupus erythematosus (SLE).

METHODS

The entire coding region of the HS1 gene was analyzed by reverse transcriptase-polymerase chain reaction/single-strand conformational polymorphism analysis. HS1-transfected WEHI-231 cells or B lymphocytes from patients with SLE were studied for apoptosis, activation, and proliferation by flow cytometric analysis and MTT assay.

RESULTS

We identified a glutamic acid-proline-glutamic acid-proline insertion between codons 366 and 367 (EPEP366-367ins) and 2 amino acid substitutions (A235T and E361K). The genotype frequency among individuals homozygous for the EPEP+ allele was 0.184 in 201 patients with SLE but only 0.098 in 184 healthy individuals (P = 0.016). The allele frequency of EPEP366-367ins was 0.408 in patients with SLE; this frequency was significantly higher than that in healthy controls (0.312) (P = 0.006). WEHI-231 cells transfected with EPEP+ HS1 were 100-fold more sensitive to B cell receptor (BCR)-mediated apoptosis than were those transfected with HS1 without EPEP. B lymphocytes from SLE patients with the EPEP+ allele were significantly more apoptotic without BCR stimulation and less activated after BCR stimulation than were those from SLE patients without the EPEP allele.

CONCLUSION

These results suggest that HS1 with the EPEP insertion polymorphism transmits accelerated signals from BCR and is involved in the pathogenesis of SLE.

Altered Bax expression and decreased apoptosis in bone marrow cells of lupus-susceptible NZB/W mice

Estrogen is believed to contribute to the development of the autoimmune disorder systemic lupus erythematosus (SLE) (lupus) in women. We hypothesized that estrogen might promote the development of lupus by altering apoptosis of bone marrow cells, perhaps through regulation of the apoptotic proteins Bax and Bcl-2. We compared the effects of estrogen (E2) and thrombopoietin (TPO) on the expression of Bax or Bcl-2 in bone marrow cells isolated from female non-lupus (NZW or NZB parental strains) or lupus-prone (NZB and NZW cross; NZB/W) mice. We report that the basal level of Bax in parental bone marrow cells was significantly greater than that of cells from NZB/W animals. Treatment of NZB or NZW marrow cells with E2 resulted in a significant decrease in Bax expression, which was completely reversed upon co-treatment with TPO. Bax expression was not significantly altered by E2 and/or TPO in NZB/W cells. Bcl-2 levels did not differ between murine strains under basal or hormone-treated conditions. Lower basal expression of Bax protein was associated with significantly less apoptosis for NZB/W marrow cells. In addition, there were significantly greater numbers of cells in bone marrow of lupus-susceptible animals. Our results indicate that bone marrow cells of NZB/W animals differ physiologically from those of NZW or NZB mice, and suggest that decreased expression of Bax in bone marrow precursors may lead to decreased apoptosis of mature blood cells in lupus-susceptible mice.

Mitochondrial hyperpolarization and ATP depletion in patients with systemic lupus erythematosus

OBJECTIVE

Peripheral blood lymphocytes (PBLs) from systemic lupus erythematosus (SLE) patients exhibit increased spontaneous and diminished activation-induced apoptosis. We tested the hypothesis that key biochemical checkpoints, the mitochondrial transmembrane potential (deltapsim) and production of reactive oxygen intermediates (ROIs), mediate the imbalance of apoptosis in SLE.

METHODS

We assessed the deltapsim with potentiometric dyes, measured ROI production with oxidation-sensitive fluorochromes, and monitored cell death by annexin V and propidium iodide staining of lymphocytes, using flow cytometry. Intracellular glutathione levels were measured by high-performance liquid chromatography, while ATP and ADP levels were assessed by the luciferin-luciferase assay.

RESULTS

Both deltapsim and ROI production were elevated in the 25 SLE patients compared with the 25 healthy subjects and the 10 rheumatoid arthritis patients. Intracellular glutathione contents were diminished, suggesting increased utilization of reducing equivalents in SLE. H2O2, a precursor of ROIs, increased deltapsim and caused apoptosis in normal PBLs. In contrast, H2O2-induced apoptosis and deltapsim elevation were diminished, particularly in T cells, and the rate of necrotic cell death was increased in patients with SLE. The intracellular ATP content and the ATP:ADP ratio were reduced and correlated with the deltapsim elevation in lupus. CD3:CD28 costimulation led to transient elevation of the deltapsim, followed by ATP depletion, and sensitization of normal PBLs to H2O2-induced necrosis. Depletion of ATP by oligomycin, an inhibitor of F0F1-ATPase, had similar effects.

CONCLUSION

T cell activation and apoptosis are mediated by deltapsim elevation and increased ROI production. Mitochondrial hyperpolarization and the resultant ATP depletion sensitize T cells for necrosis, which may significantly contribute to inflammation in patients with SLE.

Increased frequency of pre-germinal center B cells and plasma cell precursors in the blood of children with systemic lupus erythematosus

We have analyzed the blood B cell subpopulations of children with systemic lupus erythematosus (SLE) and healthy controls. We found that the normal recirculating mature B cell pool is composed of four subsets: conventional naive and memory B cells, a novel B cell subset with pregerminal center phenotype (IgD(+)CD38(+)centerin(+)), and a plasma cell precursor subset (CD20(-)CD19(+/low)CD27(+/++) CD38(++)). In SLE patients, naive and memory B cells (CD20(+)CD38(-)) are approximately 90% reduced, whereas oligoclonal plasma cell precursors are 3-fold expanded, independently of disease activity and modality of therapy. Pregerminal center cells in SLE are decreased to a lesser extent than conventional B cells, and therefore represent the predominant blood B cell subset in a number of patients. Thus, SLE is associated with major blood B cell subset alterations.

Heavy chain revision in MRL mice: a potential mechanism for the development of autoreactive B cell precursors

Abs reactive to DNA and DNA/histone complexes are distinguished by the presence of positively charged amino acids, such as arginine, in the heavy chain complementarity-determining region 3. The presence of these amino acids partly results from atypical V(H)-D-J(H) rearrangements such as D-D fusions and D inversions. Previous results in our laboratory demonstrated that newborn autoimmune MRL/MpJ-+/+ mice undergo these unusual recombinations more frequently when compared with normal C3H/HeJ controls. In addition, the heavy chain junctions in newborn MRL mice demonstrated a preferred usage of V(H)-proximal D genes and distal J(H) genes suggestive of secondary gene rearrangements. In this study we explore the possibility that adult MRL B220(+)IgM(-) pre B cells, which have not yet undergone Ag selection, exhibit similar rearrangement patterns. Indeed, MRL pre-B cells possessed more atypical rearrangements (D-D fusions) than those of C3H/HeJ mice. However, the biased use of upstream D genes and downstream J(H) genes observed in the newborn MRL mice was not present in the pre-B cell library. These results suggest that the heavy chain rearrangement process persists later during B cell life in lupus-prone mice and lead us to propose a model of heavy chain receptor revision in the periphery of autoimmune mice.