Neutrophil Dysregulation in the Pathogenesis of Systemic Lupus Erythematosus

Neutrophil response to Porphyromonas gingivalis is modulated by low-level laser application

OBJECTIVES

Neutrophil response is critical in inflammatory regulation and immune response to bacterial infections. During periodontal disease, pathogenic bacteria lead to exaggerated neutrophil responses. We hypothesized that low-level laser application (LLLT), therapeutic strategy for dampening inflammatory processes, will regulate neutrophil activity in response to periodontopathogens.

MATERIALS AND METHODS

The impact of LLLT on neutrophil responses was measured by light delivered at wavelength of 850 nm. The direct effect of LLLT on P. gingivalis A7436 was determined by flow cytometry using LIVE/DEADTM Cell Vitality kit. The phagocytosis of P. gingivalis A7436 by human neutrophils was measured using flow cytometry. Superoxide generation was measured by cytochrome-C-reduction in the presence of N-formyl-L-methionyl-L-leucyl-L-phenylalanine (fMLP; 1 mM). Cytokine release by neutrophils was measured by multiplex immunoassay.

RESULTS

The phagocytosis of P. gingivalis by primary human neutrophils was significantly reduced in response to LLLT (p < 0.05). While LLLT led to increased superoxide production in neutrophils that were not challenged by P. gingivalis, it dampened the increased superoxide and IL-6 release by the neutrophils in response to P. gingivalis. LLLT did not directly affect the viability of P. gingivalis.

CONCLUSION

These results suggested that LLLT can provide therapeutic strategy in periodontal disease, regulating the neutrophil response to P. gingivalis.

Exploring the Role of Neutrophil Extracellular Traps in Systemic Lupus Erythematosus: A Clinical Case Study and Comprehensive Review

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Increased Urine Excretion of Neutrophil Granule Cargo in Active Proliferative Lupus Nephritis

Key Points

Neutrophil degranulation participates in glomerular injury in proliferative lupus nephritis. Urine excretion of neutrophil granule proteins is a potential diagnostic for proliferative lupus nephritis.

Background

Lupus nephritis (LN) occurs in more than half of patients with systemic lupus erythematosus, but the cellular and molecular events that contribute to LN are not clearly defined. We reported previously that neutrophil degranulation participates in glomerular injury in mouse models of acute LN. This study tests the hypothesis that glomerular recruitment and subsequent activation of neutrophils result in urine excretion of neutrophil granule constituents that are predictive of glomerular inflammation in proliferative LN.

Methods

Urine and serum levels of 11 neutrophil granule proteins were measured by antibody-based array in patients with proliferative LN and healthy donors (HDs), and the results were confirmed by ELISA. Glomerular neutrophil accumulation was assessed in biopsies of patients with LN who contributed urine for granule cargo quantitation and normal kidney tissue by microscopy. Degranulation was measured by flow cytometry in neutrophils isolated from patients with LN and HD controls by cell surface granule markers CD63 (azurophilic), CC66b (specific), and CD35 (secretory). Nonparametric statistical analyses were performed and corrected for multiple comparisons.

Results

Eight granule proteins (myeloperoxidase, neutrophil elastase, azurocidin, olfactomedin-4, lactoferrin, alpha-1-acid glycoprotein 1, matrix metalloproteinase 9, and cathelicidin) were significantly elevated in urine from patients with active proliferative LN by array and/or ELISA, whereas only neutrophil elastase was increased in LN serum. Urine excretion of alpha-1-acid glycoprotein 1 declined in patients who achieved remission. The majority of LN glomeruli contained ≥3 neutrophils. Basal levels of specific granule markers were increased in neutrophils from patients with LN compared with HD controls. Serum from patients with active LN stimulated specific and secretory, but not azurophilic granule, release by HD neutrophils.

Conclusions

Circulating neutrophils in patients with LN are primed for enhanced degranulation. Glomerular recruitment of those primed neutrophils leads to release and urine excretion of neutrophil granule cargo that serves as a urine marker of active glomerular inflammation in proliferative LN.

Taxifolin inhibits NETosis through activation of Nrf2 and provides protective effects in models of lupus and antiphospholipid syndrome

OBJECTIVES

Taxifolin (dihydroquercetin) is a bioactive plant flavonoid that exhibits anti-inflammatory and anti-oxidative properties. We hypothesized that taxifolin might be an effective dietary supplement to ameliorate symptoms arising from thrombo-inflammatory diseases such as lupus and APS.

METHODS

We used in vitro assays and a mouse model to determine mechanisms by which taxifolin inhibits neutrophil extracellular trap (NET) formation (i.e. NETosis) and venous thrombosis in lupus and APS.

RESULTS

At doses ranging from 0.1 to 1 µg/ml, taxifolin inhibited NETosis from control neutrophils stimulated with autoantibodies isolated from lupus and APS patients, and its suppressive effects were mitigated by blocking the antioxidant transcription factor Nrf2 (nuclear factor erythroid 2-related factor 2). Furthermore, taxifolin at a dose as low as 20 mg/kg/day reduced in vivo NETosis in thrombo-inflammatory mouse models of lupus and APS while also significantly attenuating autoantibody formation, inflammatory cytokine production and large-vein thrombosis.

CONCLUSION

Our study is the first to demonstrate the protective effects of taxifolin in the context of lupus and APS. Importantly, our study also suggests a therapeutic potential to neutralize neutrophil hyperactivity and NETosis that could have relevance to a variety of thrombo-inflammatory diseases.

Macrophage extracellular traps promote tumor-like biologic behaviors of fibroblast-like synoviocytes through cGAS-mediated PI3K/Akt signaling pathway in patients with rheumatoid arthritis

Rheumatoid arthritis is an autoimmune disease characterized by synovium hyperplasia and bone destruction. Macrophage extracellular traps are released from macrophages under various stimuli and may generate stable autoantigen-DNA complexes, as well as aggravate autoantibody generation and autoimmune responses. We aimed to investigate the role of macrophage extracellular traps on the biologic behaviors of rheumatoid arthritis fibroblast-like synoviocytes. Synovial tissues and fibroblast-like synoviocytes were obtained from patients with rheumatoid arthritis. Extracellular traps in synovium and synovial fluids were detected by immunofluorescence, immunohistochemistry, and SYTOX Green staining. Cell viability, migration, invasion, and cytokine expression of rheumatoid arthritis fibroblast-like synoviocytes were assessed by CCK-8, wound-healing assay, Transwell assays, and quantitative real-time polymerase chain reaction, respectively. RNA sequencing analysis was performed to explore the underlying mechanism, and Western blot was used to validate the active signaling pathways. We found that extracellular trap formation was abundant in rheumatoid arthritis and positively correlated to anti-CCP. Rheumatoid arthritis fibroblast-like synoviocytes stimulated with purified macrophage extracellular traps demonstrated the obvious promotion in tumor-like biologic behaviors. The DNA sensor cGAS in rheumatoid arthritis fibroblast-like synoviocytes was activated after macrophage extracellular trap stimuli. RNA sequencing revealed that differential genes were significantly enriched in the PI3K/Akt signaling pathway, and cGAS inhibitor RU.521 effectively reversed the promotion of tumor-like biologic behaviors in macrophage extracellular trap-treated rheumatoid arthritis fibroblast-like synoviocytes and downregulated the PI3K/Akt activation. In summary, our study demonstrates that macrophage extracellular traps promote the pathogenically biological behaviors of rheumatoid arthritis fibroblast-like synoviocytes through cGAS-mediated activation of the PI3K/Akt signaling pathway. These findings provide a novel insight into the pathogenesis of rheumatoid arthritis and the mechanisms of macrophages in modulating rheumatoid arthritis fibroblast-like synoviocyte tumor-like behaviors.

Neutrophils in Inflammatory Diseases: Unraveling the Impact of Their Derived Molecules and Heterogeneity

Inflammatory diseases involve numerous disorders and medical conditions defined by an insufficient level of self-tolerance. These diseases evolve over the course of a multi-step process through which environmental variables play a crucial role in the emergence of aberrant innate and adaptive immunological responses. According to experimental data accumulated over the past decade, neutrophils play a significant role as effector cells in innate immunity. However, neutrophils are also involved in the progression of numerous diseases through participation in the onset and maintenance of immune-mediated dysregulation by releasing neutrophil-derived molecules and forming neutrophil extracellular traps, ultimately causing destruction of tissues. Additionally, neutrophils have a wide variety of functional heterogeneity with adverse effects on inflammatory diseases. However, the complicated role of neutrophil biology and its heterogeneity in inflammatory diseases remains unclear. Moreover, neutrophils are considered an intriguing target of interventional therapies due to their multifaceted role in a number of diseases. Several approaches have been developed to therapeutically target neutrophils, involving strategies to improve neutrophil function, with various compounds and inhibitors currently undergoing clinical trials, although challenges and contradictions in the field persist. This review outlines the current literature on roles of neutrophils, neutrophil-derived molecules, and neutrophil heterogeneity in the pathogenesis of autoimmune and inflammatory diseases with potential future therapeutic strategies.

From systemic lupus erythematosus to lupus nephritis: The evolving road to targeted therapies

Systemic lupus erythematosus is a chronic autoimmune disease characterized by loss of tolerance against nuclear and cytoplasmic self-antigens, induction of immunity and tissue inflammation. Lupus nephritis (LN), the most important predictor of morbidity in SLE, develops in almost 30% of SLE patients at disease onset and in up to 50-60% within the first 10 years. Firstly, in this review, we put the pathogenic mechanisms of the disease into a conceptual frame, giving emphasis to the role of the innate immune system in this loss of self-tolerance and the induction of the adaptive immune response. In this aspect, many mechanisms have been described such as dysregulation and acceleration of cell-death pathways, an aberrant clearance and overload of immunogenic acid-nucleic-containing debris and IC, and the involvement of antigen-presenting cells and other innate immune cells in the induction of this adaptive immune response. This result in a clonal expansion of autoreactive lymphocytes with generation of effector T-cells, memory B-cells and plasma cells that produce autoantibodies that will cause kidney damage. Secondly, we review the immunological pathways of damage in the kidney parenchyma, initiated by autoantibody binding and immune complex deposition, and followed by complement-mediated microvascular injury, activation of kidney stromal cells and the recruitment of leukocytes. Finally, we summarize the rationale for the treatment of LN, from conventional to new targeted therapies, focusing on their systemic immunologic effects and the minimization of podocytary damage.

Ginger intake suppresses neutrophil extracellular trap formation in autoimmune mice and healthy humans

We previously reported that treatment of mice with 6-gingerol, the most abundant phytochemical in ginger root, leads to phosphodiesterase inhibition that counteracts neutrophil hyperactivity in models of antiphospholipid syndrome (APS) and lupus. Here, we explored the extent to which oral intake of a whole-ginger extract would similarly impact neutrophils in both autoimmune mice and healthy humans. In vitro, a solubilized ginger extract was able to attenuate neutrophil extracellular trap formation (NETosis) by human neutrophils through a mechanism that was dependent upon the cyclic AMP-dependent kinase, protein kinase A. When mice with features of either APS or lupus were administered a ginger extract orally, they demonstrated reduced circulating NETs, as well as the tempering of other disease outcomes, such as large-vein thrombosis (APS) and autoantibody production (lupus). In a pilot clinical trial, which was validated in a second cohort, daily intake of a ginger supplement for 7 days by healthy volunteers boosted neutrophil cAMP, inhibited NETosis in response to disease-relevant stimuli, and reduced circulating plasma NET levels. In summary, this work demonstrates that ginger intake restrains neutrophil hyperactivity in autoimmune mouse models and that ginger consumption by healthy individuals makes their neutrophils more resistant to NETosis.

Systemic lupus erythematosus: latest insight into etiopathogenesis

Systemic lupus erythematosus (SLE) is a complex autoimmune disorder of unknown etiology. Multifactorial interaction among various susceptible factors such as environmental, hormonal, and genetic factors makes it more heterogeneous and complex. Genetic and epigenetic modifications have been realized to regulate the immunobiology of lupus through environmental modifications such as diet and nutrition. Although these interactions may vary from population to population, the understanding of these risk factors can enhance the perception of the mechanistic basis of lupus etiology. To recognize the recent advances in lupus, an electronic search was conducted among search engines such as Google Scholar and PubMed, where we found about 30.4% publications of total studies related to genetics and epigenetics, 33.5% publications related to immunobiology and 34% related to environmental factors. These outcomes suggested that management of diet and lifestyle have a direct relationship with the severity of lupus that influence via modulating the complex interaction among genetics and immunobiology. The present review emphasizes the knowledge about the multifactorial interactions between various susceptible factors based on recent advances that will further update the understanding of mechanisms involved in disease pathoetiology. Knowledge of these mechanisms will further assist in the creation of novel diagnostic and therapeutic options.

The neutrophil: A key resourceful agent in immune‐mediated vasculitis

The term "vasculitis" refers to a group of rare immune-mediated diseases characterized by the dysregulated immune system attacking blood vessels located in any organ of the body, including the skin, lungs, and kidneys. Vasculitides are classified according to the size of the vessel that is affected. Although this observation is not specific to small-, medium-, or large-vessel vasculitides, patients show a high circulating neutrophil-to-lymphocyte ratio, suggesting the direct or indirect involvement of neutrophils in these diseases. As first responders to infection or inflammation, neutrophils release cytotoxic mediators, including reactive oxygen species, proteases, and neutrophil extracellular traps. If not controlled, this dangerous arsenal can injure the vascular system, which acts as the main transport route for neutrophils, thereby amplifying the initial inflammatory stimulus and the recruitment of immune cells. This review highlights the ability of neutrophils to "set the tone" for immune cells and other cells in the vessel wall. Considering both their long-established and newly described roles, we extend their functions far beyond their direct host-damaging potential. We also review the roles of neutrophils in various types of primary vasculitis, including immune complex vasculitis, anti-neutrophil cytoplasmic antibody-associated vasculitis, polyarteritis nodosa, Kawasaki disease, giant cell arteritis, Takayasu arteritis, and Behçet's disease.

Pathological mechanisms and crosstalk among different forms of cell death in systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is a systemic autoimmune disorder characterized by a profound immune dysregulation and the presence of a variety of autoantibodies. Aberrant activation of programmed cell death (PCD) signaling and accelerated cell death is critical in the immunopathogenesis of SLE. Accumulating cellular components from the dead cells and ineffective clearance of the dead cell debris, in particular the nucleic acids and nucleic acids-protein complexes, provide a stable source of self-antigens, which potently activate auto-reactive B cells and promote IFN-I responses in SLE. Different cell types display distinct susceptibility and characteristics to a certain type of cell death, while different PCDs in various cells have mutual and intricate connections to promote immune dysregulation and contribute to the development of SLE. In this review, we discuss the role of various cell death pathways and their interactions in the pathogenesis of SLE. An in depth understanding of the interconnections among various forms cell death in SLE will lead to a better understanding of disease pathogenesis, shedding light on the development of novel therapeutic targets.

Mechanistic insight into premature atherosclerosis and cardiovascular complications in systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is associated with a significant risk of cardiovascular disease (CVD), which substantially increases disease mortality and morbidity. The overall mechanisms associated with the development of premature atherosclerosis and CVD in SLE remain unclear, but has been considered as a result of an intricate interplay between the profound immune dysregulation and traditional CVD risk factors. Aberrant systemic inflammation in SLE may lead to an abnormal lipid profile and dysfunction, which can further fuel the pro-atherosclerotic environment. The existence of a strong imbalance between endothelial damage and vascular repair/angiogenesis promotes vascular injury, which is the early step in the progression of atherosclerotic CVD. Profound innate and adaptive immune dysregulation, characterized by excessive type I interferon burden, aberrant macrophage, platelet and complements activation, neutrophil dysregulation and neutrophil extracellular traps formation, uncontrolled T cell activation, and excessive autoantibody production and immune complex formation, have been proposed to promote accelerated CVD in SLE. While designing targeted therapies to correct the dysregulated immune activation may be beneficial in the treatment of SLE-related CVD, much additional work is needed to determine how to translate these findings into clinical practice. Additionally, a number of biomarkers display diagnostic potentials in improving CVD risk stratification in SLE, further prospective studies will help understand which biomarker(s) will be the most impactful one(s) in assessing SLE-linked CVD. Continued efforts to identify novel mechanisms and to establish criteria for assessing CVD risk as well as predicting CVD progression are in great need to improve CVD outcomes in SLE.

The metamorphosis of neutrophil transcriptional program during Leishmania infection

The role of neutrophils in the course of Leishmania infection remains controversial, displaying tremendous variability depending on the species of parasite, stage of infection, host genetic background, and methodological discrepancies among studies. Although neutrophils have long been categorized as short-lived cells with limited capacity to express proteins de novo, recent advances have revealed significant plasticity in neutrophil transcriptional programs and intrapopulation heterogeneity, which can be regulated by both intrinsic and extrinsic factors that together determine the profile of neutrophil effector response. In this review, we focus on the current understanding of neutrophil transcriptional plasticity, neutrotime, evidence of Leishmania-mediated alterations in neutrophil transcriptome leading to the rise of subpopulations, and finally, functional implications of those findings to the course of Leishmania infection.

Single Cell RNA Sequencing in Autoimmune Inflammatory Rheumatic Diseases: Current Applications, Challenges and a Step Toward Precision Medicine

Single cell RNA sequencing (scRNA-seq) represents a new large scale and high throughput technique allowing analysis of the whole transcriptome at the resolution of an individual cell. It has emerged as an imperative method in life science research, uncovering complex cellular networks and providing indices that will eventually lead to the development of more targeted and personalized therapies. The importance of scRNA-seq has been particularly highlighted through the analysis of complex biological systems, in which cellular heterogeneity is a key aspect, such as the immune system. Autoimmune inflammatory rheumatic diseases represent a group of disorders, associated with a dysregulated immune system and high patient heterogeneity in both pathophysiological and clinical aspects. This complicates the complete understanding of underlying pathological mechanisms, associated with limited therapeutic options available and their long-term inefficiency and even toxicity. There is an unmet need to investigate, in depth, the cellular and molecular mechanisms driving the pathogenesis of rheumatic diseases and drug resistance, identify novel therapeutic targets, as well as make a step forward in using stratified and informed therapeutic decisions, which could now be achieved with the use of single cell approaches. This review summarizes the current use of scRNA-seq in studying different rheumatic diseases, based on recent findings from published in vitro, in vivo, and clinical studies, as well as discusses the potential implementation of scRNA-seq in the development of precision medicine in rheumatology.

Macrophage Extracellular Traps: Current Opinions and the State of Research regarding Various Diseases

Macrophages are an important component of the human immune system and play a key role in the immune response, which can protect the body against infection and regulate the development of tissue inflammation. Some studies found that macrophages can produce extracellular traps (ETs) under various conditions of stimulation. ETs are web-like structures that consist of proteins and DNA. ETs are thought to immobilize and kill microorganisms, as well as play an important role in tissue damage, inflammatory progression, and autoimmune diseases. In this review, the structure, identification, mechanism, and research progress of macrophage extracellular traps (METs) in related diseases are reviewed.