Sialylation regulates neutrophil transepithelial migration, CD11b/CD18 activation, and intestinal mucosal inflammatory function

Neutrophils and NETs in kidney disease

Neutrophils, conventionally regarded as a homogeneous immune cell population, have emerged as a heterogeneous group of cells with distinct gene profiles and immune properties. Activated neutrophils release a spectrum of bioactive substances, including cytokines, chemokines, proteolytic enzymes, reactive oxygen species and neutrophil extracellular traps (NETs), which are composed of decondensed DNA and antimicrobial proteins. NETs have a pivotal role in innate immunity, including in preventing the ascent of uropathogenic bacteria into the kidneys, as they efficiently trap pathogenic microorganisms. However, although indispensable for defence against pathogens, NETs also pose risks of self-damage owing to their cytotoxicity, thrombogenicity and autoantigenicity. Accordingly, neutrophils and NETs have been implicated in the pathogenesis of various disorders that affect the kidneys, including acute kidney injury, vasculitis, systemic lupus erythematosus, thrombotic microangiopathy and in various aetiologies of chronic kidney disease. Pathological alterations in the glomerular vascular wall can promote the infiltration of neutrophils, which can cause tissue damage and inflammation through their interactions with kidney-resident cells, including mesangial cells and podocytes, leading to local cell death. Targeting neutrophil activation and NET formation might therefore represent a new therapeutic strategy for these conditions.

From Ulcerative Colitis to Metastatic Colorectal Cancer: The Neutrophil Contribution

Ulcerative colitis (UC) is an inflammatory colon and rectum disease affecting approximately 5 million people worldwide. There is no cure for UC, and approximately 8% of patients with UC develop colorectal cancer (CRC) by gradual acquisition of mutations driving the formation of adenomas and their progression to adenocarcinomas and metastatic disease. CRC constitutes 10% of total cancer cases worldwide and 9% of cancer deaths. Both UC and CRC have an increasing incidence worldwide. Although the epithelium has been well studied in UC and CRC, the contribution of neutrophils is less clear. Neutrophils are rapidly recruited in excessive amounts from peripheral blood to the colon during UC, and their overactivation in the proinflammatory UC tissue environment contributes to tissue damage. In CRC, the role of neutrophils is controversial, but emerging evidence suggests that their role depends on the evolution and context of the disease. The role of neutrophils in the transition from UC to CRC is even less clear. However, recent studies propose neutrophils as therapeutic targets for better clinical management of both diseases. This review summarizes the current knowledge on the roles of neutrophils in UC and CRC.

SIAE-Mediated Loss of Sialic Acid Acetylation Contributes to Ulcerative Colitis

Background

Ulcerative colitis (UC) disrupts the colon's protective mucus layer, exposing the epithelium to bacteria and triggering inflammation. This barrier, crucial for intestinal health, depends on complex glycosylation, notably sialic acid modifications. However, the precise role of sialic acid acetylation and the enzyme SIAE (sialic acid acetylesterase) in UC pathogenesis remains unclear. This study investigates the role of glycosylation changes, specifically sialic acid de-acetylation, in UC progression.

Methods

Tissue samples were obtained from patients with ulcerative colitis (UC) and colorectal cancer at the Second Affiliated Hospital of Soochow University. HT-29 cells were utilized to investigate the molecular mechanisms of SIAE in UC pathogenesis. Mass spectrometry was performed to analyze differences in protein and glycoprotein expression. Western blot (WB) and immunohistochemistry (IHC) were used to examine SIAE protein expression changes during inflammation. Furthermore, polymerase chain reaction (PCR) and immunofluorescence were employed to determine the effects of SIAE on sialic acid levels and mucosal immunity.

Results

In this study, we characterized proteins and glycoproteins from patient tissues with UC, finding that sialic acid acetylesterase (SIAE) is upregulated in UC. HT-29 cells exposed to TNF-α induced an inflammatory response with a 5-fold increased expression of SIAE and NEU1 when TNF-α was at a concentration of 100 ng/mL. Mass spectrometry analysis revealed a reduction in acetylation on glycans and glycoproteins, while confocal microscopy confirmed a decrease in sialic acid on the cell surface. Gene expression analysis showed that CDH1, CTNND1, and ITGA8 were significantly downregulated in HT-29 cells stimulated by TNF-α, suggesting a reduction in cell-cell adhesion. SNA lectin-confocal microscopy revealed a reduction of sialic acid on HT-29 cells in TNF-α-induced UC cell models.

Conclusion

This study demonstrates that SIAE is significantly upregulated in ulcerative colitis (UC) tissues and TNF-α-stimulated HT-29 cells, leading to a marked reduction in sialic acid acetylation and cell surface sialic acid levels. These changes correlate with decreased expression of cell adhesion molecules, suggesting a disruption of the mucosal barrier integrity. Consequently, SIAE-mediated sialic acid de-acetylation emerges as a critical factor in UC pathogenesis, potentially serving as both a valuable biomarker and a promising therapeutic target.

Sialylation in the gut: From mucosal protection to disease pathogenesis

Sialylation, a crucial post-translational modification of glycoconjugates, entails the attachment of sialic acid (SA) to the terminal glycans of glycoproteins and glycolipids through a tightly regulated enzymatic process involving various enzymes. This review offers a comprehensive exploration of sialylation within the gut, encompassing its involvement in mucosal protection and its impact on disease progression. The sialylation of mucins and epithelial glycoproteins contributes to the integrity of the intestinal mucosal barrier. Furthermore, sialylation regulates immune responses in the gut, shaping interactions among immune cells, as well as their activation and tolerance. Additionally, the gut microbiota and gut-brain axis communication are involved in the role of sialylation in intestinal health. Altered sialylation patterns have been implicated in various intestinal diseases, including inflammatory bowel disease (IBD), colorectal cancer (CRC), and other intestinal disorders. Emerging research underscores sialylation as a promising avenue for diagnostic, prognostic, and therapeutic interventions in intestinal diseases. Potential strategies such as sialic acid supplementation, inhibition of sialidases, immunotherapy targeting sialylated antigens, and modulation of sialyltransferases have been utilized in the treatment of intestinal diseases. Future research directions will focus on elucidating the molecular mechanisms underlying sialylation alterations, identifying sialylation-based biomarkers, and developing targeted interventions for precision medicine approaches.

Dual role of CD177 + neutrophils in inflammatory bowel disease: a review

Inflammatory bowel disease (IBD) represents a group of recurrent chronic inflammatory disorders associated with autoimmune dysregulation, typically characterized by neutrophil infiltration and mucosal inflammatory lesions. Neutrophils, as the earliest immune cells to arrive at inflamed tissues, play a dual role in the onset and progression of mucosal inflammation in IBD. Most of these cells specifically express CD177, a molecule increasingly recognized for its critical role in the pathogenesis of IBD. Under IBD-related inflammatory stimuli, CD177 is highly expressed on neutrophils and promotes their migration. CD177 + neutrophils activate bactericidal and barrier-protective functions at IBD mucosal inflammation sites and regulate the release of inflammatory mediators highly correlated with the severity of inflammation in IBD patients, thus playing a dual role. However, mitigating the detrimental effects of neutrophils in inflammatory bowel disease remains a challenge. Based on these data, we have summarized recent articles on the role of neutrophils in intestinal inflammation, with a particular emphasis on CD177, which mediates the recruitment, transepithelial migration, and activation of neutrophils, as well as their functional consequences. A better understanding of CD177 + neutrophils may contribute to the development of novel therapeutic targets to selectively modulate the protective role of this class of cells in IBD.

Cellular translocation and secretion of sialidases

Sialidases (or neuraminidases) catalyze the hydrolysis of sialic acid (Sia)-containing molecules, mostly the removal of the terminal Sia on glycans (desialylation) of either glycoproteins or glycolipids. Therefore, sialidases can modulate the functionality of the target glycoprotein or glycolipid and are involved in various biological pathways in health and disease. In mammalian cells, there are four kinds of sialidase, which are Neu1, Neu2, Neu3, and Neu4, based on their subcellular locations and substrate specificities. Neu1 is the lysosomal sialidase, Neu2 is the cytosolic sialidase, Neu3 is the plasma membrane-associated sialidase, and Neu4 is found in the lysosome, mitochondria, and endoplasmic reticulum. In addition to specific subcellular locations, sialidases can translocate to different subcellular localizations within particular cell conditions and stimuli, thereby participating in different cellular functions depending on their loci. Lysosomal sialidase Neu1 can translocate to the cell surface upon cell activation in several cell types, including immune cells, platelets, endothelial cells, and epithelial cells, where it desialylates receptors and thus impacts receptor activation and signaling. On the other hand, cells secrete sialidases upon activation. Secreted sialidases can serve as extracellular sialidases and cause the desialylation of both extracellular glycoproteins or glycolipids and cell surface glycoproteins or glycolipids on their own and other cells, thus playing roles in various biological pathways as well. This review discusses the recent advances and understanding of sialidase translocation in different cells and secretion from different cells under different conditions and their involvement in physiological and pathological pathways.

SIGLEC-5/14 Inhibits CD11b/CD18 Integrin Activation and Neutrophil-Mediated Tumor Cell Cytotoxicity

Since the successful introduction of checkpoint inhibitors targeting the adaptive immune system, monoclonal antibodies inhibiting CD47-SIRPα interaction have shown promise in enhancing anti-tumor treatment efficacy. Apart from SIRPα, neutrophils express a broad repertoire of inhibitory receptors, including several members of the sialic acid-binding receptor (SIGLEC) family. Here, we demonstrate that interaction between tumor cell-expressed sialic acids and SIGLEC-5/14 on neutrophils inhibits antibody-dependent cellular cytotoxicity (ADCC). We observed that conjugate formation and trogocytosis, both essential processes for neutrophil ADCC, were limited by the sialic acid-SIGLEC-5/14 interaction. During neutrophil-tumor cell conjugate formation, we found that inhibition of the interaction between tumor-expressed sialic acids and SIGLEC-5/14 on neutrophils increased the CD11b/CD18 high affinity conformation. By dynamic acoustic force measurement, the binding between tumor cells and neutrophils was assessed. The interaction between SIGLEC-5/14 and the sialic acids was shown to inhibit the CD11b/CD18-regulated binding between neutrophils and antibody-opsonized tumor cells. Moreover, the interaction between sialic acids and SIGLEC-5/14-consequently hindered trogocytosis and tumor cell killing. In summary, our results provide evidence that the sialic acid-SIGLEC-5/14 interaction is an additional target for innate checkpoint blockade in the tumor microenvironment.

Targeting adrenergic receptors to mitigate invariant natural killer T cells-induced acute liver injury

Invariant Natural Killer T (iNKT) cell activation by α-galactosylceramide (αGC) potentiates cytotoxic immune responses against tumors. However, αGC-induced liver injury is a limiting factor for iNKT-based immunotherapy. Although adrenergic receptor stimulation is an important immunosuppressive signal that curbs tissue damage induced by inflammation, its effect on the antitumor activity of invariant Natural Killer T (iNKT) cells remains unclear. We use mouse models and pharmacological tools to show that the stimulation of the sympathetic nervous system (SNS) inhibits αGC-induced liver injury without impairing iNKT cells' antitumoral functions. Mechanistically, SNS stimulation prevents the collateral effect of TNF-α production by iNKT cells and neutrophil accumulation in hepatic parenchyma. Our results suggest that the modulation of the adrenergic signaling can be a complementary approach to αGC-based immunotherapy to mitigate iNKT-induced liver injury without compromising its antitumoral activity.

Interactions between Siglec-8 and endogenous sialylated cis ligands restrain cell death induction in human eosinophils and mast cells

Sialic acid-binding immunoglobulin-like lectin (Siglec)-8 is a sialoside-binding receptor expressed by eosinophils and mast cells that exhibits priming status- and cell type-dependent inhibitory activity. On eosinophils that have been primed with IL-5, GM-CSF, or IL-33, antibody ligation of Siglec-8 induces cell death through a pathway involving the β2 integrin-dependent generation of reactive oxygen species (ROS) via NADPH oxidase. In contrast, Siglec-8 engagement on mast cells inhibits cellular activation and mediator release but reportedly does not impact cell viability. The differences in responses between cytokine-primed and unprimed eosinophils, and between eosinophils and mast cells, to Siglec-8 ligation are not understood. We previously found that Siglec-8 binds to sialylated ligands present on the surface of the same cell (so-called cis ligands), preventing Siglec-8 ligand binding in trans. However, the functional relevance of these cis ligands has not been elucidated. We therefore explored the potential influence of cis ligands of Siglec-8 on both eosinophils and mast cells. De-sialylation using exogenous sialidase profoundly altered the consequences of Siglec-8 antibody engagement on both cell types, eliminating the need for cytokine priming of eosinophils to facilitate cell death and enabling Siglec-8-dependent mast cell death without impacting anti-Siglec-8 antibody binding. The cell death process licensed by de-sialylation resembled that characterized in IL-5-primed eosinophils, including CD11b upregulation, ROS production, and the activities of Syk, PI3K, and PLC. These results implicate cis ligands in restraining Siglec-8 function on eosinophils and mast cells and reveal a promising approach to the selective depletion of mast cells in patients with mast cell-mediated diseases.

Immune profiling of experimental murine mastitis reveals conserved response to mammary pathogenic Escherichia coli, Mycoplasma bovis, and Streptococcus uberis

Mastitis is one of the most prevalent and economically important diseases of dairy animals. The disease is caused by ascending bacterial infection through the teat canal. Among the most common mastitis-causing bacteria are Gram-negative coliforms, Gram-positive streptococci and staphylococci, and mycoplasma. The most prominent cellular hallmark of acute mammary infection is a massive recruitment of blood neutrophils into the tubular and alveolar milk spaces. The complex biological processes of leukocyte recruitment, activation, adhesion, and migration in the mammary gland remain largely elusive to date. While field research of mastitis in dairy animals contributed a lot to the development of mitigation, control, and even eradication programs, little progress was made toward understanding the molecular mechanisms underlying the pathogenesis of the disease. We report here experimental mastitis model systems in lactating mice challenged with field strains of common udder pathogens in dairy cows. We used these model systems to apply recently developed multiplex gene expression technology (Nanostring nCounter), which enabled us to study the expression of over 700 immune genes. Our analysis revealed a core of 100 genes that are similarly regulated and functionally or physically interacting in E. coli, M. bovis, and Strep uberis murine mastitis. Common significantly enriched gene sets include TNFɑ signaling via NFkB, Interferon gamma and alpha response, and IL6-JAK-STAT3 signaling. In addition, we show a significantly enriched expression of genes associated with neutrophil extracellular traps (NET) in glands challenged by the three pathogens. Ligand-receptor analysis revealed interactions shared by the three pathogens, including the interaction of the cytokines IL1β, IL1ɑ, and TNFɑ with their receptors, and proteins involved in immune cell recruitment such as complement C3 and ICAM1 (with CD11b), chemokines CCL3 and CCL4 (with CCR1), and CSF3 (with CSF3R). Taken together, our results show that mammary infection with E. coli, M. bovis, and Strep uberis culminated in the activation of a conserved core of immune genes and pathways including NET formation.