Molecular Mechanisms for Regulation of Neutrophil Apoptosis under Normal and Pathological Conditions

Drug repurposing of cyclin-dependent kinase inhibitors for neutrophilic acute respiratory distress syndrome and psoriasis

BACKGROUND

Neutrophilic inflammation, characterized by dysregulated neutrophil activation, triggers a variety of inflammatory responses such as chemotactic infiltration, oxidative bursts, degranulation, neutrophil extracellular traps (NETs) formation, and delayed turnover. This type of inflammation is pivotal in the pathogenesis of acute respiratory distress syndrome (ARDS) and psoriasis. Despite current treatments, managing neutrophil-associated inflammatory symptoms remains a significant challenge.

AIM OF REVIEW

This review emphasizes the role of cyclin-dependent kinases (CDKs) in neutrophil activation and inflammation. It aims to highlight the therapeutic potential of repurposing CDK inhibitors to manage neutrophilic inflammation, particularly in ARDS and psoriasis. Additionally, it discusses the necessary precautions for the clinical application of these inhibitors due to potential off-target effects and the need for dose optimization.

KEY SCIENTIFIC CONCEPTS OF REVIEW

CDKs regulate key neutrophilic functions, including chemotactic responses, degranulation, NET formation, and apoptosis. Repurposing CDK inhibitors, originally developed for cancer treatment, shows promise in controlling neutrophilic inflammation. Clinical anticancer drugs, palbociclib and ribociclib, have demonstrated efficacy in treating neutrophilic ARDS and psoriasis by targeting off-label pathways, phosphoinositide 3-kinase (PI3K) and phosphodiesterase 4 (PDE4), respectively. While CDK inhibitors offer promising therapeutic benefits, their clinical repurposing requires careful consideration of off-target effects and dose optimization. Further exploration and clinical trials are necessary to ensure their safety and efficacy in treating inflammatory conditions.

Whole blood RNA sequencing identifies transcriptional differences between primary sclerosing cholangitis and ulcerative colitis

Background & Aims

Genetic and microbiome studies across patients with primary sclerosing cholangitis (PSC) and ulcerative colitis (UC) have indicated that UC in PSC is a separate disease entity to primary UC, but expression studies for PSC are lacking.

Methods

We conducted whole blood RNA sequencing experiments for 495 patients with UC, 220 patients with PSC (including 177 with UC), and 320 healthy controls from Germany and Norway. Differential expression analyses, gene ontology and coexpression analyses and random forest machine learning were performed to identify genes, ontologies and transcriptional features that discriminate diagnoses.

Results

The blood transcriptome in UC and PSC is dominated by neutrophil activation genes (e.g. S100A12). In UC, but not in PSC (neither PSC alone nor patients with an additional diagnosis of UC [PSC/UC]), ribosomal, mitochondrial, and energy metabolism genes are upregulated in conjunction with antibody transcript expression (MZB1, IGJ). In PSC, there is an increase in modules related to apoptosis and expression of genes of interferon-I-related ontologies. Random forest analysis could poorly discriminate PSC alone from PSC/UC (AUROC 0.56), but could discriminate PSC, UC, and controls with high accuracy (AUROC UC vs. controls 0.95, PSC vs. controls 0.88, UC vs. PSC 0.986). The main coexpression modules relevant for distinguishing PSC, UC, and controls are enriched in neutrophil degranulation and antibody production genes.

Conclusions

Supported by machine learning results, PSC and UC appear to be separate entities on a molecular level, while PSC/UC and PSC are indistinguishable.

Impact and implications

Clinical and genetic studies suggest that the colitis-like symptoms in primary sclerosing cholangitis (PSC) represent a different disease entity from primary ulcerative colitis (UC). The present study supports this assumption with transcriptomic data from whole blood and describes notable differences in gene expression between primary UC and PSC, providing insights into the still unclear pathophysiology of both diseases. These findings are of interest to scientists seeking to decipher the molecular pathophysiology of both diseases and provide evidence that a redefinition of the PSC-UC phenotype should be considered. The study practically supports future molecular research by providing a large transcriptomic whole blood reference cohort.

A variety of death modes of neutrophils and their role in the etiology of autoimmune diseases

Neutrophils are important in the context of innate immunity and actively contribute to the progression of diverse autoimmune disorders. Distinct death mechanisms of neutrophils may exhibit specific and pivotal roles in autoimmune diseases and disease pathogenesis through the orchestration of immune homeostasis, the facilitation of autoantibody production, the induction of tissue and organ damage, and the incitement of pathological alterations. In recent years, more studies have provided in-depth examination of various neutrophil death modes, revealing nuances that challenge conventional understanding and underscoring their potential clinical utility in diagnosis and treatment. This review explores the multifaceted processes and characteristics of neutrophil death, with a focus on tailored investigations within various autoimmune diseases. It also highlights the potential interplay between neutrophil death and the landscape of autoimmune disorders. The review encapsulates the pertinent pathways implicated in various neutrophil death mechanisms across diverse autoimmune diseases while also charts possible avenues for future research.

Molecular and functional changes in neutrophilic granulocytes induced by nicotine: a systematic review and critical evaluation

Background

Over 1.1 billion people smoke worldwide. The alkaloid nicotine is a prominent and addictive component of tobacco. In addition to tumors and cardiovascular disorders, tobacco consumption is associated with a variety of chronic-inflammatory diseases. Although neutrophilic granulocytes (neutrophils) play a role in the pathogenesis of many of these diseases, the impact of nicotine on neutrophils has not been systematically reviewed so far.

Objectives

The aim of this systematic review was to evaluate the direct influence of nicotine on human neutrophil functions, specifically on cell death/damage, apoptosis, chemotaxis, general motility, adhesion molecule expression, eicosanoid synthesis, cytokine/chemokine expression, formation of neutrophil extracellular traps (NETs), phagocytosis, generation of reactive oxygen species (ROS), net antimicrobial activity, and enzyme release.

Material and methods

This review was conducted according to the PRISMA guidelines. A literature search was performed in the databases NCBI Pubmed® and Web of Science™ in February 2023. Inclusion criteria comprised English written research articles, showing in vitro studies on the direct impact of nicotine on specified human neutrophil functions.

Results

Of the 532 originally identified articles, data from 34 articles were finally compiled after several evaluation steps. The considered studies highly varied in methodological aspects. While at high concentrations (>3 mmol/l) nicotine started to be cytotoxic to neutrophils, concentrations typically achieved in blood of smokers (in the nmol/l range) applied for long exposure times (24-72h) supported the survival of neutrophils. Smoking-relevant nicotine concentrations also increased the chemotaxis of neutrophils towards several chemoattractants, elevated their production of elastase, lipocalin-2, CXCL8, leukotriene B4 and prostaglandin E2, and reduced their integrin expression. Moreover, while nicotine impaired the neutrophil phagocytotic and anti-microbial activity, a range of studies demonstrated increased NET formation. However, conflicting effects were found on ROS generation, selectin expression and release of β-glucuronidase and myeloperoxidase.

Conclusion

Nicotine seems to support the presence in the tissue and the inflammatory and selected tissue-damaging activity of neutrophils and reduces their antimicrobial functions, suggesting a direct contribution of nicotine to the pathogenesis of chronic-inflammatory diseases via influencing the neutrophil biology.

Regulated cell death in neutrophils: From apoptosis to NETosis and pyroptosis

Neutrophils are among the most abundant immune cells, representing about 50%- 70% of all circulating leukocytes in humans. Neutrophils rapidly infiltrate inflamed tissues and play an essential role in host defense against infections. They exert microbicidal activity through a variety of specialized effector mechanisms, including phagocytosis, production of reactive oxygen species, degranulation and release of secretory vesicles containing broad-spectrum antimicrobial factors. In addition to their homeostatic turnover by apoptosis, recent studies have revealed the mechanisms by which neutrophils undergo various forms of regulated cell death. In this review, we will discuss the different modes of regulated cell death that have been described in neutrophils, with a particular emphasis on the current understanding of neutrophil pyroptosis and its role in infections and autoinflammation.

Neutrophils and the Systemic Inflammatory Response Syndrome (SIRS)

We are not entirely able to understand, assess, and modulate the functioning of the immune system in clinical situations that lead to a systemic inflammatory response. In the search for diagnostic and treatment strategies (which are still far from perfect), it became very important to study the pathogenesis and participation of endogenous inflammation mediators. This study attempts to more precisely establish the role of neutrophils in individual phenomena occurring during an inflammatory and anti-inflammatory reaction, taking into account their cidal, immunoregulatory, and reparative abilities. Pro- and anticoagulatory properties of endothelium in systemic inflammatory response syndrome (SIRS) are emphasised, along with the resulting clinical implications (the application of immunotherapy using mesenchymal stem/stromal cells (MSCs) or IL-6 antagonists in sepsis and COVID-19 treatment, among others). Special attention is paid to reactive oxygen species (ROS), produced by neutrophils activated during "respiratory burst" in the course of SIRS; the protective and pathogenic role of these endogenous mediators is highlighted. Moreover, clinically useful biomarkers of SIRS (neutrophil extracellular traps, cell-free DNA, DAMP, TREMs, NGAL, miRNA, selected cytokines, ROS, and recognised markers of endothelial damage from the group of adhesins by means of immunohistochemical techniques) related to the neutrophils are presented, and their role in the diagnosing and forecasting of sepsis, burn disease, and COVID-19 is emphasised. Finally, examples of immunomodulation of sepsis and antioxidative thermal injury therapy are presented.

Impaired response of blood neutrophils to cell-death stimulus differentiates AQP4-IgG-seropositive NMOSD from MOGAD

BACKGROUND

In neuromyelitis optica spectrum disorders (NMOSD) and myelin oligodendrocyte glycoprotein antibody-associated disease (MOGAD), neutrophils are found in CNS lesions. We previously demonstrated that NMOSD neutrophils show functional deficiencies. Thus, we hypothesized that neutrophil accumulation in the CNS may be facilitated by impairments affecting mechanisms of neutrophil death.

OBJECTIVE

To evaluate cell death in blood neutrophils from aquaporin-4 (AQP4)-IgG-seropositive NMOSD and MOGAD patients as well as matched healthy controls (HC) using in vitro assays.

METHODS

Twenty-eight AQP4 + NMOSD and 19 MOGAD patients in stable disease phase as well as 45 age- and sex-matched HC were prospectively recruited. To induce cell death, isolated neutrophils were cultured with/without phorbol 12-myristate 13-acetate (PMA). Spontaneous and PMA-induced NETosis and apoptosis were analyzed using 7-AAD and annexin-V by flow cytometry. Caspase-3 was assessed by western blot. Myeloperoxidase-DNA complexes (MPO-DNA), MPO and elastase were evaluated by ELISA, and cell-free DNA (cfDNA) by a fluorescence-based assay. Reactive oxygen species (ROS) were evaluated by a dihydrorhodamine 123-based cytometric assay. Serum GM-CSF, IL-6, IL-8, IL-15, TNF-ɑ and IL-10 were evaluated by multiplex assays, and neurofilament light chain (NfL) by single-molecule array assay.

RESULTS

In response to PMA, neutrophils from AQP4 + NMOSD but not from MOGAD patients showed an increased survival, and subsequent reduced cell death (29.6% annexin V⁺ 7-AAD⁺) when compared to HC (44.7%, p = 0.0006). However, AQP4 + NMOSD also showed a mild increase in annexin V⁺ 7-AAD^- early apoptotic neutrophils (24.5%) compared to HC (20.8%, p = 0.048). PMA-induced reduction of caspase-3 activation was more pronounced in HC (p = 0.020) than in AQP4 + NMOSD neutrophils (p = 0.052). No differences were observed in neutrophil-derived MPO-DNA or serum levels of MPO, elastase, IL-6, IL-8 and TNF-ɑ. IL-15 levels were increased in both groups of patients. In AQP4 + NMOSD, an increase in cfDNA, GM-CSF and IL-10 was found in serum. A positive correlation among cfDNA and NfL was found in AQP4 + NMOSD.

CONCLUSIONS

AQP4 + NMOSD neutrophils showed an increased survival capacity in response to PMA when compared to matched HC neutrophils. Although the data indicate that the apoptotic but not the NETotic response is altered in these neutrophils, additional evaluations are required to validate this observation.

Molecular Basis for Paradoxical Activities of Polymorphonuclear Neutrophils in Inflammation/Anti-Inflammation, Bactericide/Autoimmunity, Pro-Cancer/Anticancer, and Antiviral Infection/SARS-CoV-II-Induced Immunothrombotic Dysregulation

Polymorphonuclear neutrophils (PMNs) are the most abundant white blood cells in the circulation. These cells act as the fast and powerful defenders against environmental pathogenic microbes to protect the body. In addition, these innate inflammatory cells can produce a number of cytokines/chemokines/growth factors for actively participating in the immune network and immune homeostasis. Many novel biological functions including mitogen-induced cell-mediated cytotoxicity (MICC) and antibody-dependent cell-mediated cytotoxicity (ADCC), exocytosis of microvesicles (ectosomes and exosomes), trogocytosis (plasma membrane exchange) and release of neutrophil extracellular traps (NETs) have been successively discovered. Furthermore, recent investigations unveiled that PMNs act as a double-edged sword to exhibit paradoxical activities on pro-inflammation/anti-inflammation, antibacteria/autoimmunity, pro-cancer/anticancer, antiviral infection/COVID-19-induced immunothrombotic dysregulation. The NETs released from PMNs are believed to play a pivotal role in these paradoxical activities, especially in the cytokine storm and immunothrombotic dysregulation in the recent SARS-CoV-2 pandemic. In this review, we would like to discuss in detail the molecular basis for these strange activities of PMNs.