Kruppel-like factor 4 regulates neutrophil activation

Scalable identification of lineage-specific gene regulatory networks from metacells with NetID

The identification of gene regulatory networks (GRNs) is crucial for understanding cellular differentiation. Single-cell RNA sequencing data encode gene-level covariations at high resolution, yet data sparsity and high dimensionality hamper accurate and scalable GRN reconstruction. To overcome these challenges, we introduce NetID leveraging homogenous metacells while avoiding spurious gene-gene correlations. Benchmarking demonstrates superior performance of NetID compared to imputation-based methods. By incorporating cell fate probability information, NetID facilitates the prediction of lineage-specific GRNs and recovers known network motifs governing bone marrow hematopoiesis, making it a powerful toolkit for deciphering gene regulatory control of cellular differentiation from large-scale single-cell transcriptome data.

Neutrophils with low production of reactive oxygen species are activated during immune priming and promote development of arthritis

Rheumatoid arthritis (RA) is an inflammatory autoimmune disease mediated by immune cell dysfunction for which there is no universally effective prevention and treatment strategy. As primary effector cells, neutrophils are important in the inflammatory joint attack during the development of RA. Here, we used single-cell sequencing technology to thoroughly analyze the phenotypic characteristics of bone marrow-derived neutrophils in type II collagen (COL2)-induced arthritis (CIA) models, including mice primed and boosted with COL2. We identified a subpopulation of neutrophils with high expression of neutrophil cytoplasmic factor 1 (NCF1) in primed mice, accompanied by a characteristic reactive oxygen species (ROS) response, and a decrease in Ncf1 expression in boosted mice with the onset of arthritis. Furthermore, we found that after ROS reduction, arthritis occurred in primed mice but was attenuated in boosted mice. This bidirectional effect of ROS suggested a protective role of ROS during immune priming. Mechanistically, we combined functional assays and metabolomics identifying Ncf1-deficient neutrophils with enhanced migration, chemotactic receptor CXCR2 expression, inflammatory cytokine secretion, and Th1/Th17 differentiation. This alteration was mainly due to the metabolic reprogramming of Ncf1-deficient neutrophils from an energy supply pathway dominated by gluconeogenesis to an inflammatory immune pathway associated with the metabolism of histidine, glycine, serine, and threonine signaling, which in turn induced arthritis. In conclusion, we have systematically identified the functional and inflammatory phenotypic characteristics of neutrophils under ROS regulation, which provides a theoretical basis for understanding the pathogenesis of RA, to further improve prevention strategies and identify novel therapeutic targets.

Intestinal epithelial Krüppel-like factor 4 alleviates endotoxemia and atherosclerosis through improving NF-κB/miR-34a-mediated intestinal permeability

Maintenance of intestinal barrier function contributes to gastrointestinal homeostasis and therefore cardiovascular diseases. A number of studies show that intestinal permeability is affected by excessive inflammatory responses. Krüppel-like factor (KLF) 4 is one of the critical transcriptional factors, which controls multiple immune responses. In this study we investigated the role of KLF4 in regulating intestinal inflammation and permeability during the atherosclerotic process. Atherosclerotic model was established in ApoE-/- mice by feeding a high fat high cholesterol (HFHC) diet. We showed that colon expression levels of KLF4 and tight junction proteins were significantly decreased whereas inflammatory responses increased in atherosclerotic mice. Overexpression of colon epithelial Klf4 decreased atherosclerotic plaque formation and vascular inflammation in atherosclerotic mice, accompanied by remarkable suppression of intestinal NF-κB activation. We found that overexpression of epithelial Klf4 in atherosclerotic mice significantly increased intestinal tight junction expression and ameliorated endotoxemia, whereas replenishment of LPS abolished these benefits. Overexpression of Klf4 reversed LPS-induced permeability and downregulation of ZO-1 and Occludin in Caco-2 cells in vitro. HFHC diet stimulated the expression of epithelial microRNA-34a, whereas silence of epithelial Klf4 abolished the benefits of microRNA-34a sponge, a specific miR-34a inhibitor, on intestinal permeability and atherosclerotic development. A clinical cohort of 24 atherosclerotic patients supported colon KLF4/NF-κB/tight junction protein axis mediated intestine/cardiovascular interaction in patients with atherosclerosis. Taken together, intestinal epithelial KLF4 protects against intestinal inflammation and barrier dysfunction, ameliorating atherosclerotic plaque formation.

KLF4 loss in hepatocellular carcinoma: Improving prognostic prediction and correlating immune infiltrates

Introduction: Although the molecular mechanisms of Krüpple-like factor 4 (KLF4) as a tumor suppressor in HCC tumorigenesis have been thoroughly examined, its clinical application in terms of precise prognostication and its influence on tumor immune microenvironment in patients with HCC require further investigation. Methods: Bioinformatics and immunohistochemistry (IHC) were used to validate KLF4 expressions in a tissue microarray (TMA) containing HCC samples. Using Cox regression models, independent prognostic factors were identified and employed in the development of nomograms. Decision curve analysis (DCA) demonstrated the superiority of the nomograms. GO and KEGG pathway analyses were applied to the functional study of KLF4. The GSVA program explored the link between KLF4 expression and tumor-infiltrating immune cells, and CAMOIP was used to construct KLF4 expression immune scores. Changes in immune-related gene markers were also investigated in relation to KLF4 expression. The association between immune cell infiltration and KLF4 expression was validated by IHC in TMA. Results: HCC was reported to have a notable depletion of KLF4. The absence of KLF4 was associated with advanced clinicopathological characteristics of HCC and predicted a bad prognosis for patients. Nomograms constructed using KLF4 expression, tumor differentiation, and TNM stage provided a more accurate prognostic assessment of HCC patients than TNM stage alone. KLF4 expression was associated with immunological-related functions, infiltration of macrophages, CD8+ T cells, and other immune cells, and elevation of immune checkpoints. Higher levels of CD8+ T cells and macrophage infiltration are associated with increased KLF4 expression in HCC TMA. Conclusion: KLF4 loss in HCC is a prognostic biomarker that influences the tumor immune microenvironment (TIME).

KLF2 regulates neutrophil activation and thrombosis in cardiac hypertrophy and heart failure progression

It is widely recognized that inflammation plays a critical role in cardiac hypertrophy and heart failure. However, clinical trials targeting cytokines have shown equivocal effects, indicating the need for a deeper understanding of the precise role of inflammation and inflammatory cells in heart failure. Leukocytes from human subjects and a rodent model of heart failure were characterized by a marked reduction in expression of Klf2 mRNA. Using a mouse model of angiotensin II–induced nonischemic cardiac dysfunction, we showed that neutrophils played an essential role in the pathogenesis and progression of heart failure. Mechanistically, chronic angiotensin II infusion activated a neutrophil KLF2/NETosis pathway that triggered sporadic thrombosis in small myocardial vessels, leading to myocardial hypoxia, cell death, and hypertrophy. Conversely, targeting neutrophils, neutrophil extracellular traps (NETs), or thrombosis ameliorated these pathological changes and preserved cardiac dysfunction. KLF2 regulated neutrophil activation in response to angiotensin II at the molecular level, partly through crosstalk with HIF1 signaling. Taken together, our data implicate neutrophil-mediated immunothrombotic dysregulation as a critical pathogenic mechanism leading to cardiac hypertrophy and heart failure. This neutrophil KLF2-NETosis-thrombosis mechanism underlying chronic heart failure can be exploited for therapeutic gain by therapies targeting neutrophils, NETosis, or thrombosis.

Endogenous α7 nAChR Agonist SLURP1 Facilitates Escherichia coli K1 Crossing the Blood-Brain Barrier

Alpha 7 nicotinic acetylcholine receptor (α7 nAChR) is critical for the pathogenesis of Escherichia coli (E. coli) K1 meningitis, a severe central nervous system infection of the neonates. However, little is known about how E. coli K1 manipulates α7 nAChR signaling. Here, through employing immortalized cell lines, animal models, and human transcriptional analysis, we showed that E. coli K1 infection triggers releasing of secreted Ly6/Plaur domain containing 1 (SLURP1), an endogenous α7 nAChR ligand. Exogenous supplement of SLURP1, combined with SLURP1 knockdown or overexpression cell lines, showed that SLURP1 is required for E. coli K1 invasion and neutrophils migrating across the blood-brain barrier (BBB). Furthermore, we found that SLURP1 is required for E. coli K1-induced α7 nAChR activation. Finally, the promoting effects of SLURP1 on the pathogenesis of E. coli K1 meningitis was significantly abolished in the α7 nAChR knockout mice. These results reveal that E. coli K1 exploits SLURP1 to activate α7 nAChR and facilitate its pathogenesis, and blocking SLURP1-α7 nAChR interaction might represent a novel therapeutic strategy for E. coli K1 meningitis.

Krueppel-Like Factor 4 Expression in Phagocytes Regulates Early Inflammatory Response and Disease Severity in Pneumococcal Pneumonia

The transcription factor Krueppel-like factor (KLF) 4 fosters the pro-inflammatory immune response in macrophages and polymorphonuclear neutrophils (PMNs) when stimulated with Streptococcus pneumoniae, the main causative pathogen of community-acquired pneumonia (CAP). Here, we investigated the impact of KLF4 expression in myeloid cells such as macrophages and PMNs on inflammatory response and disease severity in a pneumococcal pneumonia mouse model and in patients admitted to hospital with CAP. We found that mice with a myeloid-specific knockout of KLF4 mount an insufficient early immune response with reduced levels of pro-inflammatory cytokines and increased levels of the anti-inflammatory cytokine interleukin (IL) 10 in bronchoalveolar lavage fluid and plasma and an impaired bacterial clearance from the lungs 24 hours after infection with S. pneumoniae. This results in higher rates of bacteremia, increased lung tissue damage, more severe symptoms of infection and reduced survival. Higher KLF4 gene expression levels in the peripheral blood of patients with CAP at hospital admission correlate with a favourable clinical presentation (lower sequential organ failure assessment (SOFA) score), lower serum levels of IL-10 at admission, shorter hospital stay and lower mortality or requirement of intensive care unit treatment within 28 days after admission. Thus, KLF4 in myeloid cells such as macrophages and PMNs is an important regulator of the early pro-inflammatory immune response and, therefore, a potentially interesting target for therapeutic interventions in pneumococcal pneumonia.

Induction of Krüppel-Like Factor 4 Mediates Polymorphonuclear Neutrophil Activation in Streptococcus pneumoniae Infection

The recruitment and activation of polymorphonuclear neutrophils (PMNs) are of central importance for the elimination of pathogens in bacterial infections. We investigated the Streptococcus pneumoniae-dependent induction of the transcription factor Krüppel-like factor (KLF) 4 in PMNs as a potential regulator of PMN activation. We found that KLF4 expression is induced in human blood-derived PMNs in a time- and dose-dependent manner by wild-type S. pneumoniae and capsule knockout mutants. Unencapsulated knockout mutants induced stronger KLF4 expression than encapsulated wild types. The presence of autolysin LytA-competent (thus viable) pneumococci and LytA-mediated bacterial autolysis were required for KLF4 induction in human and murine PMNs. LyzMcre-mediated knockdown of KLF4 in murine blood-derived PMNs revealed that KLF4 influences pneumococci killing and increases the release of the proinflammatory cytokines tumor necrosis factor α and keratinocyte chemoattractant and decreases the release of the anti-inflammatory cytokine interleukin-10. Thus, S. pneumoniae induces KLF4 expression in PMNs, which contributes to PMN activation in S. pneumoniae infection.

KLF4 down-regulation resulting from TLR4 promotion of ERK1/2 phosphorylation underpins inflammatory response in sepsis

Sepsis is a systemic inflammatory response to invading pathogens, leading to high mortality rates in intensive care units worldwide. Krüppel-like factor 4 (KLF4) is an important anti-inflammatory transcription factor. In this study, we investigate the anti-inflammatory role of KLF4 in caecal ligation and puncture (CLP)-induced septic mice and lipopolysaccharide (LPS)-induced RAW264.7 cells and its potential mechanism. We found that KLF4 was down-regulated in CLP-induced septic mice and in LPS-induced RAW264.7 cells, and that its overexpression led to increased survival rates of septic mice along with inhibited inflammatory response in vivo and in vitro. ITGA2B was up-regulated in the setting of sepsis and was inhibited by KLF4 overexpression. ITGA2B knock-down mimicked the effects of KLF4 overexpression on septic mice and LPS-induced RAW264.7 cells. TLR4 promoted the phosphorylation of ERK1/2 and then up-regulated the ubiquitination and the degradation of KLF4, thereby elevating the expression of ITGA2B. Moreover, TLR4 knock-down or treatment with PD98059 (a MEK inhibitor) inhibited inflammatory response in the setting of sepsis in vivo and in vitro. Furthermore, this effect of PD98059 treatment was lost upon KLF4 knock-down. Collectively, these results explain the down-regulation of KLF4 in sepsis, namely via TLR4 promotion of ERK1/2 phosphorylation, and identify ITGA2B as the downstream gene of KLF4, thus highlighting the anti-inflammatory role of KLF4 in sepsis.