Regulation of phagocytosis in macrophages by neuraminidase 1

Neuraminidase 1 regulates the cellular state of microglia by modulating the sialylation of Trem2

Neuraminidase 1 (Neu1) cleaves terminal sialic acids from sialoglycoproteins in endolysosomes and at the plasma membrane. As such, Neu1 regulates immune cells, primarily those of the monocytic lineage. Here we examined how Neu1 influences microglia by modulating the sialylation of full-length Trem2 (Trem2-FL), a multifunctional receptor that regulates microglial survival, phagocytosis, and cytokine production. When Neu1 was deficient/downregulated, Trem2-FL remained sialylated, accumulated intracellularly, and was excessively cleaved into a C-terminal fragment (Trem2-CTF) and an extracellular soluble domain (sTrem2), enhancing their signaling capacities. Sialylated Trem2-FL (Sia-Trem2-FL) did not hinder Trem2-FL-DAP12-Syk complex assembly but impaired signal transduction through Syk, ultimately abolishing Trem2-dependent phagocytosis. Concurrently, Trem2-CTF-DAP12 complexes dampened NFκB signaling, while sTrem2 propagated Akt-dependent cell survival and NFAT1-mediated production of TNFα and CCL3. Because Neu1 and Trem2 are implicated in neurodegenerative/neuroinflammatory diseases, including Alzheimer disease (AD) and sialidosis, modulating Neu1 activity represents a therapeutic approach to broadly regulate microglia-mediated neuroinflammation.

The Exploitation of the Glycosylation Pattern in Asthma: How We Alter Ancestral Pathways to Develop New Treatments

Asthma has reached epidemic levels, yet progress in developing specific therapies is slow. One of the main reasons for this is the fact that asthma is an umbrella term for various distinct subsets. Due to its high heterogeneity, it is difficult to establish biomarkers for each subset of asthma and to propose endotype-specific treatments. This review focuses on protein glycosylation as a process activated in asthma and ways to utilize it to develop novel biomarkers and treatments. We discuss known and relevant glycoproteins whose functions control disease development. The key role of glycoproteins in processes integral to asthma, such as inflammation, tissue remodeling, and repair, justifies our interest and research in the field of glycobiology. Altering the glycosylation states of proteins contributing to asthma can change the pathological processes that we previously failed to inhibit. Special emphasis is placed on chitotriosidase 1 (CHIT1), an enzyme capable of modifying LacNAc- and LacdiNAc-containing glycans. The expression and activity of CHIT1 are induced in human diseased lungs, and its pathological role has been demonstrated by both genetic and pharmacological approaches. We propose that studying the glycosylation pattern and enzymes involved in glycosylation in asthma can help in patient stratification and in developing personalized treatment.

Metabolism-driven glycosylation represents therapeutic opportunities in interstitial lung diseases

Metabolic changes are coupled with alteration in protein glycosylation. In this review, we will focus on macrophages that are pivotal in the pathogenesis of pulmonary fibrosis and sarcoidosis and thanks to their adaptable metabolism are an attractive therapeutic target. Examples presented in this review demonstrate that protein glycosylation regulates metabolism-driven immune responses in macrophages, with implications for fibrotic processes and granuloma formation. Targeting proteins that regulate glycosylation, such as fucosyltransferases, neuraminidase 1 and chitinase 1 could effectively block immunometabolic changes driving inflammation and fibrosis, providing novel avenues for therapeutic interventions.

Desialylation of ATG5 by sialidase (NEU1) promotes macrophages autophagy and exacerbates inflammation under hypoxia

During the process of atherosclerosis (AS), hypoxia induces plaque macrophage inflammation, promoting lipid accumulation. Autophagy is a cell homeostasis process that increases tolerance to stressors like oxidative stress and hypoxia. However, the specific mechanism by which hypoxia initiates autophagy and the inflammation of macrophages remains to be elucidated. Here, we found that hypoxia-induced macrophage inflammation was mediated by autophagy. Then, the effect of hypoxia on autophagy was investigated in terms of post-translational modifications of proteins. The results showed that desialylation of the autophagy protein ATG5 under hypoxic conditions enhanced protein stability by affecting its charge effect and promoted the formation of the ATG5-ATG12-ATG16L complex, further increasing autophagosome formation. And NEU1, a key enzyme in sialic acid metabolism, was significantly up-regulated under hypoxic conditions and was identified as an interacting protein of ATG5, affecting the sialylation of ATG5. In addition, the knockdown or inhibition of NEU1 reversed hypoxia-induced autophagy and inflammatory responses. In conclusion, our data reveal a key mechanism of autophagy regulation under hypoxia involving ATG5 sialylation and NEU1, suggesting that NEU1 may be a potential target for the prevention and treatment of atherosclerosis.

Sialic-Acid-Related Enzymes of B Cells and Monocytes as Novel Markers to Discriminate Improvement Categories and to Fulfill Two Remission Definitions in Rheumatoid Arthritis

The enzymes α-2,6-sialyltransferase 1 (ST6Gal1), neuraminidase 1 (Neu1), α-2,3-sialyltransferase 1 (ST3Gal1), and neuraminidase 3 (Neu3) are known to affect immune cell function. However, it is not known whether the levels of these enzymes relate to remission definitions or differentiate American College of Rheumatology (ACR), European League Against Rheumatism (EULAR), and Simplified Disease Activity Index (SDAI) responses in patients with rheumatoid arthritis (RA). We measured the ST6Gal1, Neu1, ST3Gal1, and Neu3 levels of B cells and monocytes in RA patients and correlated the cells' enzyme levels/ratios with the improvement in the ACR, EULAR and SDAI responses and with the two remission definitions. The difference in the B-cell Neu1 levels differed between the ACR 70% improvement and non-improvement groups (p = 0.043), between the EULAR good major response (improvement) and non-good response groups (p = 0.014), and also between the SDAI 50% or 70% improvement and non-improvement groups (p = 0.001 and 0.018, respectively). The same held true when the RA patients were classified by positive rheumatoid factor or the use of biologics. The B-cell Neu1 levels significantly indicated 2005 modified American Rheumatism Association and 2011 ACR/EULAR remission definitions (area under the curve (AUC) = 0.674 with p = 0.001, and AUC = 0.682 with p < 0.001, respectively) in contrast to the CRP and ESR (all AUCs < 0.420). We suggest that B-cell Neu1 is superior for discriminating ACR, EULAR, and SDAI improvement and is good for predicting two kinds of remission definitions.

Non-steroidal anti-inflammatory drug target gene associations with major depressive disorders: a Mendelian randomisation study integrating GWAS, eQTL and mQTL Data

Previous observational studies reported associations between non-steroidal anti-inflammatory drugs (NSAIDs) and major depressive disorder (MDD), however, these associations are often inconsistent and underlying biological mechanisms are still poorly understood. We conducted a two-sample Mendelian randomisation (MR) study to examine relationships between genetic variants and NSAID target gene expression or DNA methylation (DNAm) using publicly available expression, methylation quantitative trait loci (eQTL or mQTL) data and genetic variant-disease associations from genome-wide association studies (GWAS of MDD). We also assessed drug exposure using gene expression and DNAm levels of NSAID targets as proxies. Genetic variants were robustly adjusted for multiple comparisons related to gene expression, DNAm was used as MR instrumental variables and GWAS statistics of MDD as the outcome. A 1-standard deviation (SD) lower expression of NEU1 in blood was related to lower C-reactive protein (CRP) levels of -0.215 mg/L (95% confidence interval (CI): 0.128-0.426) and a decreased risk of MDD (odds ratio [OR] = 0.806; 95% CI: 0.735-0.885; p = 5.36 × 10^-6). A concordant direction of association was also observed for NEU1 DNAm levels in blood and a risk of MDD (OR = 0.886; 95% CI: 0.836-0.939; p = 4.71 × 10^-5). Further, the genetic variants associated with MDD were mediated by NEU1 expression via DNAm (β = -0.519; 95% CI: -0.717 to -0.320256; p = 3.16 × 10^-7). We did not observe causal relationships between inflammatory genetic marker estimations and MDD risk. Yet, we identified a concordant association of NEU1 messenger RNA and an adverse direction of association of higher NEU1 DNAm with MDD risk. These results warrant increased pharmacovigilance and further in vivo or in vitro studies to investigate NEU1 inhibitors or supplements for MDD.

N-acetylneuraminic acid links immune exhaustion and accelerated memory deficit in diet-induced obese Alzheimer's disease mouse model

Systemic immunity supports lifelong brain function. Obesity posits a chronic burden on systemic immunity. Independently, obesity was shown as a risk factor for Alzheimer's disease (AD). Here we show that high-fat obesogenic diet accelerated recognition-memory impairment in an AD mouse model (5xFAD). In obese 5xFAD mice, hippocampal cells displayed only minor diet-related transcriptional changes, whereas the splenic immune landscape exhibited aging-like CD4+ T-cell deregulation. Following plasma metabolite profiling, we identified free N-acetylneuraminic acid (NANA), the predominant sialic acid, as the metabolite linking recognition-memory impairment to increased splenic immune-suppressive cells in mice. Single-nucleus RNA-sequencing revealed mouse visceral adipose macrophages as a potential source of NANA. In vitro, NANA reduced CD4+ T-cell proliferation, tested in both mouse and human. In vivo, NANA administration to standard diet-fed mice recapitulated high-fat diet effects on CD4+ T cells and accelerated recognition-memory impairment in 5xFAD mice. We suggest that obesity accelerates disease manifestation in a mouse model of AD via systemic immune exhaustion.

Sialidase Inhibitors with Different Mechanisms

Sialidases, or neuraminidases, are enzymes that catalyze the hydrolysis of sialic acid (Sia)-containing molecules, mostly removal of the terminal Sia (desialylation). By desialylation, sialidase can modulate the functionality of the target compound and is thus often involved in biological pathways. Inhibition of sialidases with inhibitors is an important approach for understanding sialidase function and the underlying mechanisms and could serve as a therapeutic approach as well. Transition-state analogues, such as anti-influenza drugs oseltamivir and zanamivir, are major sialidase inhibitors. In addition, difluoro-sialic acids were developed as mechanism-based sialidase inhibitors. Further, fluorinated quinone methide-based suicide substrates were reported. Sialidase product analogue inhibitors were also explored. Finally, natural products have shown competitive inhibiton against viral, bacterial, and human sialidases. This Perspective describes sialidase inhibitors with different mechanisms and their activities and future potential, which include transition-state analogue inhibitors, mechanism-based inhibitors, suicide substrate inhibitors, product analogue inhibitors, and natural product inhibitors.

Immune disguise: the mechanisms of Neu5Gc inducing autoimmune and transplant rejection

Organ (stem cell) transplantation is the most effective treatment for advanced organ failure. Neu5Gc (N-hydroxyacetylneuraminic acid) is a pathogenic non-human sialic acid, which is very similar to the molecular structure of Neu5Ac (N-acetylneuraminic acid) in human body. Neu5Gc has the function of "immune disguise", which is the main obstacle to transplantation. Gene knockout such as cytidine monophosphate-N-acetylneuraminidase (CMAH) reduces donor antigenicity, making xenotransplantation from fiction to reality. Exploring the immune disguise event in this emerging field has become a hot topic in the research of transplantation immune tolerance mechanism.

Neuraminidases-Key Players in the Inflammatory Response after Pathophysiological Cardiac Stress and Potential New Therapeutic Targets in Cardiac Disease

Glycoproteins and glycolipids on the cell surfaces of vertebrates and higher invertebrates contain α-keto acid sugars called sialic acids, terminally attached to their glycan structures. The actual level of sialylation, regulated through enzymatic removal of the latter ones by NEU enzymes, highly affects protein-protein, cell-matrix and cell-cell interactions. Thus, their regulatory features affect a large number of different cell types, including those of the immune system. Research regarding NEUs within heart and vessels provides new insights of their involvement in the development of cardiovascular pathologies and identifies mechanisms on how inhibiting NEU enzymes can have a beneficial effect on cardiac remodelling and on a number of different cardiac diseases including CMs and atherosclerosis. In this regard, a multitude of clinical studies demonstrated the potential of N-acetylneuraminic acid (Neu5Ac) to serve as a biomarker following cardiac diseases. Anti-influenza drugs i.e., zanamivir and oseltamivir are viral NEU inhibitors, thus, they block the enzymatic activity of NEUs. When considering the improvement in cardiac function in several different cardiac disease animal models, which results from NEU reduction, the inhibition of NEU enzymes provides a new potential therapeutic treatment strategy to treat cardiac inflammatory pathologies, and thus, administrate cardioprotection.

Single-cell multiomics analysis reveals regulatory programs in clear cell renal cell carcinoma

The clear cell renal cell carcinoma (ccRCC) microenvironment consists of many different cell types and structural components that play critical roles in cancer progression and drug resistance, but the cellular architecture and underlying gene regulatory features of ccRCC have not been fully characterized. Here, we applied single-cell RNA sequencing (scRNA-seq) and single-cell assay for transposase-accessible chromatin sequencing (scATAC-seq) to generate transcriptional and epigenomic landscapes of ccRCC. We identified tumor cell-specific regulatory programs mediated by four key transcription factors (TFs) (HOXC5, VENTX, ISL1, and OTP), and these TFs have prognostic significance in The Cancer Genome Atlas (TCGA) database. Targeting these TFs via short hairpin RNAs (shRNAs) or small molecule inhibitors decreased tumor cell proliferation. We next performed an integrative analysis of chromatin accessibility and gene expression for CD8⁺ T cells and macrophages to reveal the different regulatory elements in their subgroups. Furthermore, we delineated the intercellular communications mediated by ligand–receptor interactions within the tumor microenvironment. Taken together, our multiomics approach further clarifies the cellular heterogeneity of ccRCC and identifies potential therapeutic targets.

NEU1—A Unique Therapeutic Target for Alzheimer’s Disease

Neuraminidase 1 (NEU1) is considered to be the most abundant and ubiquitous mammalian enzyme, with a broad tissue distribution. It plays a crucial role in a variety of cellular mechanisms. The deficiency of NEU1 has been implicated in various pathological manifestations of sialidosis and neurodegeneration. Thus, it is a novel therapeutic target for neurodegenerative changes in the Alzheimer’s brain. However, to manipulate NEU1 as a therapeutic target, it is imperative to understand that, although NEU1 is commonly known for its lysosomal catabolic function, it is also involved in other pathways. NEU1 is involved in immune response modulation, elastic fiber assembly modulation, insulin signaling, and cell proliferation. In recent years, our knowledge of NEU1 has continued to grow, yet, at the present moment, current data is still limited. In addition, the unique biochemical properties of NEU1 make it challenging to target it as an effective therapeutic option for sialidosis, which is a rare disease but has an enormous patient burden. However, the fact that NEU1 has been linked to the pathology of Alzheimer’s disease, which is rapidly growing worldwide, makes it more relevant to be studied and explored. In the present study, the authors have discussed various cellular mechanisms involving NEU1 and how they are relevant to sialidosis and Alzheimer’s disease.

N-Glycosylation and Inflammation; the Not-So-Sweet Relation

Chronic inflammation is the main feature of many long-term inflammatory diseases such as autoimmune diseases, metabolic disorders, and cancer. There is a growing number of studies in which alterations of N-glycosylation have been observed in many pathophysiological conditions, yet studies of the underlying mechanisms that precede N-glycome changes are still sparse. Proinflammatory cytokines have been shown to alter the substrate synthesis pathways as well as the expression of glycosyltransferases required for the biosynthesis of N-glycans. The resulting N-glycosylation changes can further contribute to disease pathogenesis through modulation of various aspects of immune cell processes, including those relevant to pathogen recognition and fine-tuning the inflammatory response. This review summarizes our current knowledge of inflammation-induced N-glycosylation changes, with a particular focus on specific subsets of immune cells of innate and adaptive immunity and how these changes affect their effector functions, cell interactions, and signal transduction.

α-2,6-sialic acid/IgG anti-dsDNA ratios correlate with human lupus disease activity and possible mechanisms: A pilot study

Objective

To study the association of α2,6-sialic acid (SIA) content in serum IgG anti-dsDNA with human systemic lupus erythematosus disease activity index (SLEDAI) and the effect of sialylated and desialylated (deSIA) IgG anti-dsDNA on lupus B cells.

Methods

Blood from lupus patients was collected to determine the ratio of SIA in isolated IgG anti-dsDNA over serum IgG anti-dsDNA (SIA/IgG anti-dsDNA) ratios, which were plotted against SLEDAI using a receiver-operating-characteristics curve. Lupus B cells were cultured in vitro with chimeric sialylated IgG anti-dsDNA and its deSIA form. Culture supernatants were assayed for anti-inflammatory IL-10 and SIA/IgG anti-dsDNA ratios, which were compared among different pre-treatment groups using t-tests.

Results

The area-under-the-curve (AUC) for anti-dsDNA levels against SLEDAI was 0.791 positively (95% confidence interval [C.I.]: 0.699–0.884) and SIA/IgG anti-dsDNA ratios against SLEDAI yielded an AUC of 0.705 inversely (95% C.I: 0.601–0.809): not significantly different. SIA/IgG anti-dsDNA ratios discriminated significantly between patients without and patients with proteinuria ( p = .046). SIA/IgG anti-dsDNA ratios correlated significantly and positively with serum C3c and C4 levels. Pre-treatment with IgG anti-dsDNA and its immune complexes (dsDNA/IgG anti-dsDNA IC) induced higher IL-10 from lupus B cells than medium pre-treatment (most p < .01 from day 2 to day 5 culture). DeSIA IgG anti-dsDNA IC induced lower IL-10 ( p < .05) and lower SIA/IgG anti-dsDNA ratios ( p < .001) from lupus B cells than medium and dsDNA pre-treatment.

Conclusion

α2,6-SIA/IgG anti-dsDNA ratios inversely forecasted SLEDAI scores. Possible mechanisms may be due to the different effects of sialylated and deSIA IgG anti-dsDNA on lupus B cells in terms of IL-10 secretion and SIA/IgG anti-dsDNA ratios.

Mammalian Neuraminidases in Immune-Mediated Diseases: Mucins and Beyond

Mammalian neuraminidases (NEUs), also known as sialidases, are enzymes that cleave off the terminal neuraminic, or sialic, acid resides from the carbohydrate moieties of glycolipids and glycoproteins. A rapidly growing body of literature indicates that in addition to their metabolic functions, NEUs also regulate the activity of their glycoprotein targets. The simple post-translational modification of NEU protein targets-removal of the highly electronegative sialic acid-affects protein folding, alters protein interactions with their ligands, and exposes or covers proteolytic sites. Through such effects, NEUs regulate the downstream processes in which their glycoprotein targets participate. A major target of desialylation by NEUs are mucins (MUCs), and such post-translational modification contributes to regulation of disease processes. In this review, we focus on the regulatory roles of NEU-modified MUCs as coordinators of disease pathogenesis in fibrotic, inflammatory, infectious, and autoimmune diseases. Special attention is placed on the most abundant and best studied NEU1, and its recently discovered important target, mucin-1 (MUC1). The role of the NEU1 - MUC1 axis in disease pathogenesis is discussed, along with regulatory contributions from other MUCs and other pathophysiologically important NEU targets.

The Janus-like role of neuraminidase isoenzymes in inflammation

The processes of activation, extravasation, and migration of immune cells to a site are early and essential steps in the induction of an acute inflammatory response. These events are an essential part of the inflammatory cascade, which involves multiple regulatory steps. Using a murine air pouch model of inflammation with LPS as an inflammation inducer, we demonstrate that isoenzymes of the neuraminidase family (NEU1, 3, and 4) play essential roles in these processes by acting as positive or negative regulators of leukocyte infiltration. In genetically knocked‐out (KO) mice for different NEU genes (Neu1 KO, Neu3 KO, Neu4 KO, and Neu3/4 double KO mice) with LPS‐induced air pouch inflammation, leukocytes at the site of inflammation were counted, and the inflamed tissue was analyzed using immunohistochemistry. Our data show that leukocyte recruitment was decreased in NEU1‐ and NEU3‐deficient mice, while it was increased in NEU4‐deficient animals. Consistent with these results, systemic as well as pouch exudate levels of pro‐inflammatory cytokines were reduced in Neu1 and increased in Neu4 KO mice. Pharmacological inhibitors specific for NEU1, NEU3, and NEU4 isoforms also affected leukocyte recruitment. Together our data demonstrate that NEU isoenzymes have distinct—and even opposing—effects on leukocyte recruitment, and therefore warrant further investigation to determine their mechanisms and importance as regulators of the inflammatory cascade.

Four Immune-Related Genes (FN1, UGCG, CHPF2 and THBS2) as Potential Diagnostic and Prognostic Biomarkers for Carbon Nanotube-Induced Mesothelioma

Background

Malignant pleural mesothelioma (MPM), a highly aggressive cancer, was mainly attributed to asbestos exposure. Carbon nanotubes (CNTs) share similar negative features to asbestos, provoking concerns about their contribution to MPM. This study was used to identify genes associated with CNT-induced MPM.

Methods

Microarray datasets were available in the Gene Expression Omnibus database. The limma method was used to identify differentially expressed genes (DEGs) in CNT-exposed MeT5A cells (GSE48855) or mice (GSE51636). Weighted correlation network analysis (WGCNA) and protein–protein interaction (PPI) network construction were conducted to screen hub DEGs. The mRNA expression levels of hub DEGs were validated on MPM samples of GSE51024, GSE2549 and GSE42977 datasets, and their diagnostic efficacy was determined by receiver operating characteristic curve analysis. The prognostic values of hub DEGs were assessed using online tools based on The Cancer Genome Atlas data. Their functions were annotated by Database for Annotation, Visualization and Integrated Discovery (DAVID) enrichment and correlation with immune cells and markers.

Results

WGCNA identified that two modules were associated with disease status. Thirty-one common DEGs in the GSE48855 and GSE51636 datasets were overlapped with the genes in these two modules. Twenty of them had a high degree centrality (≥4) in the PPI network. Four DEGs (FN1, fibronectin 1; UGCG, UDP-glucose ceramide glucosyltransferase; CHPF2, chondroitin polymerizing factor 2; and THBS2, thrombospondin 2) could predict the overall survival, and they were confirmed to be upregulated in MPM samples compared with controls. Also, they could effectively predict the MPM risk, with an overall accuracy of >0.9. DAVID analysis revealed FN1, CHPF2 and THBS2 functioned in cell-ECM interactions; UGCG influenced glycosphingolipid metabolism. All genes were positively associated with infiltrating levels of immune cells (macrophages or dendritic cells) and the expression of the dendritic cell marker (NRP1, neuropilin 1).

Conclusion

These four immune-related genes represent potential biomarkers for monitoring CNT-induced MPM and predicting the prognosis.

Neuraminidase 1 is a driver of experimental cardiac hypertrophy

AIMS 

Despite considerable therapeutic advances, there is still a dearth of evidence on the molecular determinants of cardiac hypertrophy that culminate in heart failure. Neuraminidases are a family of enzymes that catalyze the cleavage of terminal sialic acids from glycoproteins or glycolipids. This study sought to characterize the role of neuraminidases in pathological cardiac hypertrophy and identify pharmacological inhibitors targeting mammalian neuraminidases.

METHODS AND RESULTS 

Neuraminidase 1 (NEU1) was highly expressed in hypertrophic hearts of mice and rats, and this elevation was confirmed in patients with hypertrophic cardiomyopathy (n = 7) compared with healthy controls (n = 7). The increased NEU1 was mainly localized in cardiomyocytes by co-localization with cardiac troponin T. Cardiomyocyte-specific NEU1 deficiency alleviated hypertrophic phenotypes in response to transverse aortic constriction or isoproterenol hydrochloride infusion, while NEU1 overexpression exacerbated the development of cardiac hypertrophy. Mechanistically, co-immunoprecipitation coupled with mass spectrometry, chromatin immunoprecipitation, and luciferase assays demonstrated that NEU1 translocated into the nucleus and interacted with GATA4, leading to Foetal gene (Nppa and Nppb) expression. Virtual screening and experimental validation identified a novel compound C-09 from millions of compounds that showed favourable binding affinity to human NEU1 (KD = 0.38 μM) and effectively prevented the development of cardiac remodelling in cellular and animal models. Interestingly, anti-influenza drugs zanamivir and oseltamivir effectively inhibited mammalian NEU1 and showed new indications of cardio-protection.

CONCLUSIONS 

This work identifies NEU1 as a critical driver of cardiac hypertrophy and inhibition of NEU1 opens up an entirely new field of treatment for cardiovascular diseases.

Integrative genomics of the mammalian alveolar macrophage response to intracellular mycobacteria

Background

Bovine TB (bTB), caused by infection with Mycobacterium bovis, is a major endemic disease affecting global cattle production. The key innate immune cell that first encounters the pathogen is the alveolar macrophage, previously shown to be substantially reprogrammed during intracellular infection by the pathogen. Here we use differential expression, and correlation- and interaction-based network approaches to analyse the host response to infection with M. bovis at the transcriptome level to identify core infection response pathways and gene modules. These outputs were then integrated with genome-wide association study (GWAS) data sets to enhance detection of genomic variants for susceptibility/resistance to M. bovis infection.

Results

The host gene expression data consisted of RNA-seq data from bovine alveolar macrophages (bAM) infected with M. bovis at 24 and 48 h post-infection (hpi) compared to non-infected control bAM. These RNA-seq data were analysed using three distinct computational pipelines to produce six separate gene sets: 1) DE genes filtered using stringent fold-change and P-value thresholds (DEG-24: 378 genes, DEG-48: 390 genes); 2) genes obtained from expression correlation networks (CON-24: 460 genes, CON-48: 416 genes); and 3) genes obtained from differential expression networks (DEN-24: 339 genes, DEN-48: 495 genes). These six gene sets were integrated with three bTB breed GWAS data sets by employing a new genomics data integration tool—gwinteR. Using GWAS summary statistics, this methodology enabled detection of 36, 102 and 921 prioritised SNPs for Charolais, Limousin and Holstein-Friesian, respectively.

Conclusions

The results from the three parallel analyses showed that the three computational approaches could identify genes significantly enriched for SNPs associated with susceptibility/resistance to M. bovis infection. Results indicate distinct and significant overlap in SNP discovery, demonstrating that network-based integration of biologically relevant transcriptomics data can leverage substantial additional information from GWAS data sets. These analyses also demonstrated significant differences among breeds, with the Holstein-Friesian breed GWAS proving most useful for prioritising SNPS through data integration. Because the functional genomics data were generated using bAM from this population, this suggests that the genomic architecture of bTB resilience traits may be more breed-specific than previously assumed.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-021-07643-w.

Neuraminidase 1 and its Inhibitors from Chinese Herbal Medicines: An Emerging Role for Cardiovascular Diseases

Neuraminidase, also known as sialidase, is ubiquitous in animals and microorganisms. It is predominantly distributed in the cell membrane, cytoplasmic vesicles, and lysosomes. Neuraminidase generally recognizes the sialic acid glycosidic bonds at the ends of glycoproteins or glycolipids and enzymatically removes sialic acid. There are four types of neuraminidases, named as Neu1, Neu2, Neu3, and Neu4. Among them, Neu1 is the most abundant in mammals. Recent studies have revealed the involvement of Neu1 in several diseases, including cardiovascular diseases, diabetes, cancers, and neurological disorders. In this review, we center the attention to the role of Neu1 in cardiovascular diseases, including atherosclerosis, ischemic myocardial injury, cerebrovascular disease, congenital heart disease, and pulmonary embolism. We also summarize inhibitors from Chinese herbal medicines (CHMs) in inhibiting virus neuraminidase or human Neu1. Many Chinese herbs and Chinese herb preparations, such as Lonicerae Japonicae Flos, Scutellariae Radix, Yupingfeng San, and Huanglian Jiedu Decoction, have neuraminidase inhibitory activity. We hope to highlight the emerging role of Neu1 in humans and potentially titillate interest for further studies in this area.

NEU1 is more abundant in uveitic retina with concomitant desialylation of retinal cells

Desialylation of cell surface glycoproteins carried out by sialidases affects various immunological processes. However, the role of neuraminidase 1 (NEU1), one of four mammalian sialidases, in inflammation and autoimmune disease is not completely unraveled to date. In this study, we analyzed retinal expression of NEU1 in equine recurrent uveitis (ERU), a spontaneous animal model for autoimmune uveitis. Mass spectrometry revealed significantly higher abundance of NEU1 in retinal Müller glial cells (RMG) of ERU-diseased horses compared to healthy controls. Immunohistochemistry uncovered NEU1 expression along the whole Müller cell body in healthy and uveitic state and confirmed higher abundance in inflamed retina. Müller glial cells are the principal macroglial cells of the retina and play a crucial role in uveitis pathogenesis. To determine whether higher expression levels of NEU1 in uveitic RMG correlate with desialylation of retinal cells, we performed lectin binding assays with sialic acid-specific lectins. Through these experiments we could demonstrate a profound loss of both α2-3- and α2-6-linked terminal sialic acids in uveitis. Hence, we hypothesize that higher abundance of NEU1 in uveitic RMG plays an important role in the pathogenesis of uveitis by desialylation of retinal cells. As RMG become activated in the course of uveitis and actively promote inflammation, we propose that NEU1 might represent a novel activation marker for inflammatory RMG. Our data provide novel insights in the expression and implication of NEU1 in inflammation and autoimmune disease.

Neuraminidases 1 and 3 Trigger Atherosclerosis by Desialylating Low-Density Lipoproteins and Increasing Their Uptake by Macrophages

Background Chronic vascular disease atherosclerosis starts with an uptake of atherogenic modified low-density lipoproteins (LDLs) by resident macrophages, resulting in formation of arterial fatty streaks and eventually atheromatous plaques. Increased plasma sialic acid levels, increased neuraminidase activity, and reduced sialic acid LDL content have been previously associated with atherosclerosis and coronary artery disease in human patients, but the mechanism underlying this association has not been explored. Methods and Results We tested the hypothesis that neuraminidases contribute to development of atherosclerosis by removing sialic acid residues from glycan chains of the LDL glycoprotein and glycolipids. Atherosclerosis progression was investigated in apolipoprotein E and LDL receptor knockout mice with genetic deficiency of neuraminidases 1, 3, and 4 or those treated with specific neuraminidase inhibitors. We show that desialylation of the LDL glycoprotein, apolipoprotein B 100, by human neuraminidases 1 and 3 increases the uptake of human LDL by human cultured macrophages and by macrophages in aortic root lesions in Apoe^-/- mice via asialoglycoprotein receptor 1. Genetic inactivation or pharmacological inhibition of neuraminidases 1 and 3 significantly delays formation of fatty streaks in the aortic root without affecting the plasma cholesterol and LDL levels in Apoe^-/- and Ldlr^-/- mouse models of atherosclerosis. Conclusions Together, our results suggest that neuraminidases 1 and 3 trigger the initial phase of atherosclerosis and formation of aortic fatty streaks by desialylating LDL and increasing their uptake by resident macrophages.

An iPSC-based neural model of sialidosis uncovers glycolytic impairment-causing presynaptic dysfunction and deregulation of Ca2+ dynamics

Sialidosis is a neuropathic lysosomal storage disease caused by a deficiency in the NEU1 gene-encoding lysosomal neuraminidase and characterized by abnormal accumulation of undigested sialyl-oligoconjugates in systemic organs including brain. Although patients exhibit neurological symptoms, the underlying neuropathological mechanism remains unclear. Here, we generated induced pluripotent stem cells (iPSCs) from skin fibroblasts with sialidosis and induced the differentiation into neural progenitor cells (NPCs) and neurons. Sialidosis NPCs and neurons mimicked the disease-like phenotypes including reduced neuraminidase activity, accumulation of sialyl-oligoconjugates and lysosomal expansions. Functional analysis also revealed that sialidosis neurons displayed two distinct abnormalities, defective exocytotic glutamate release and augmented α-amino-3-hydroxyl-5-methyl-4-isoxazole-propionate receptor (AMPAR)-mediated Ca²⁺ influx. These abnormalities were restored by overexpression of the wild-type NEU1 gene, demonstrating causative role of neuraminidase deficiency in functional impairments of disease neurons. Comprehensive proteomics analysis revealed the significant reduction of SNARE proteins and glycolytic enzymes in synaptosomal fraction, with downregulation of ATP production. Bypassing the glycolysis by treatment of pyruvate, which is final metabolite of glycolysis pathway, improved both the synaptsomal ATP production and the exocytotic function. We also found that upregulation of AMPAR and L-type voltage dependent Ca²⁺ channel (VDCC) subunits in disease neurons, with the restoration of AMPAR-mediated Ca²⁺ over-load by treatment of antagonists for the AMPAR and L-type VDCC. Our present study provides new insights into both the neuronal pathophysiology and potential therapeutic strategy for sialidosis.

Therapeutic Potential of Neu1 in Alzheimer's Disease Via the Immune System

Alzheimer's Disease (AD) is pathologically characterized by the accumulation of soluble oligomers causing extracellular beta-amyloid deposits in form of neuritic plaques and tau-containing intraneuronal neurofibrillary tangles in brain. One proposed mechanism explaining the formation of these proteins is impaired phagocytosis by microglia/macrophages resulting in defective clearance of soluble oligomers of beta-amyloid stimulating aggregation of amyloid plaques subsequently causing AD. However, research indicates that activating macrophages in M2 state may reduce toxic oligomers. NEU1 mutation is associated with a rare disease, sialidosis. NEU1 deficiency may also cause AD-like amyloidogenic process. Amyloid plaques have successfully been reduced using NEU1.Thus, NEU1 is suggested to have therapeutic potential for AD, with lysosomal exocytosis being suggested as underlying mechanism. Studies however demonstrate that NEU1 may activate macrophages in M2 state, which as noted earlier, is crucial to reducing toxic oligomers. In this review, authors discuss the potential therapeutic role of NEU1 in AD via immune system.

Activated microglia desialylate their surface, stimulating complement receptor 3-mediated phagocytosis of neurons

The glycoproteins and glycolipids of the cell surface have sugar chains that normally terminate in a sialic acid residue, but inflammatory activation of myeloid cells can cause sialidase enzymes to remove these residues, resulting in desialylation and altered activity of surface receptors, such as the phagocytic complement receptor 3 (CR3). We found that activation of microglia with lipopolysaccharide (LPS), fibrillar amyloid beta (Aβ), Tau or phorbol myristate acetate resulted in increased surface sialidase activity and desialylation of the microglial surface. Desialylation of microglia by adding sialidase, stimulated microglial phagocytosis of beads, but this was prevented by siRNA knockdown of CD11b or a blocking antibody to CD11b (a component of CR3). Desialylation of microglia by a sialyl-transferase inhibitor (3FAx-peracetyl-Neu5Ac) also stimulated microglial phagocytosis of beads. Desialylation of primary glial-neuronal co-cultures by adding sialidase or the sialyl-transferase inhibitor resulted in neuronal loss that was prevented by inhibiting phagocytosis with cytochalasin D or the blocking antibody to CD11b. Adding desialylated microglia to glial-neuronal cultures, in the absence of neuronal desialylation, also caused neuronal loss prevented by CD11b blocking antibody. Adding LPS or Aβ to primary glial-neuronal co-cultures caused neuronal loss, and this was prevented by inhibiting endogenous sialidase activity with N-acetyl-2,3-dehydro-2-deoxyneuraminic acid or blockage of CD11b. Thus, activated microglia release a sialidase activity that desialylates the cell surface, stimulating CR3-mediated phagocytosis of neurons, making extracellular sialidase and CR3 potential treatment targets to prevent inflammatory loss of neurons.

α-2,3-Sialyltransferase 1 and neuraminidase-3 from monocytes in patients with rheumatoid arthritis correlate with disease activity measures: A pilot study

BACKGROUND

We decided to study the association of monocyte α-2,3-sialyltransferase 1 (ST3Gal-1), neuraminidase-3 (Neu3), α-2,6-sialyltransferase 1 (ST6Gal-1), and neuraminidase-1 (Neu1) levels with disease activity score 28 (DAS28) in human rheumatoid arthritis (RA), considering that mouse monocytes' sialic acid (SIA) levels relate to their phagocytosis and IgG binding ability.

METHODS

ST3Gal-1, Neu3, ST6Gal-1, Neu1, α-2,3-SIA, and α-2,6-SIA levels on RA peripheral blood monocytes, T cells, and polymorphonuclear cells were determined by using fluorochrome-conjugated anti-cell-specific marker antibodies and fluorochrome-conjugated anti-enzyme antibodies. Simple correlation and linear regression were used to correlate enzyme levels with DAS28.

RESULTS

RA monocyte ST3Gal-1 and Neu3 levels correlated with DAS28 in patients having DAS28 >5.1 (r = 0.469, p = 0.002; r = 0.410, p = 0.006, respectively). When multivariable analysis was performed for erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), and SIA-related enzyme levels in different cell types as independent variables with DAS28 as a dependent variable, monocyte ST3Gal-1 levels correlated with DAS28 (p = 0.009) but not ESR and CRP in patients having DAS28 >5.1 (both p ≥ 0.292). RA monocyte ST3Gal-1 levels correlated with DAS28 (p = 0.010) and with ESR (p < 0.001) at month 0 when applied to all RA patients including both remission and nonremission groups in multivariable analysis. The latter findings persisted longitudinally at month 3.

CONCLUSION

Monocyte ST3Gal-1 and Neu3 levels correlated longitudinally with DAS28 by two different methods suggest that monocyte ST3Gal-1 and Neu3 levels may be used as biomarkers to monitor RA disease activity.

Identification of CD36 as a new interaction partner of membrane NEU1: potential implication in the pro-atherogenic effects of the elastin receptor complex

In addition to its critical role in lysosomes for catabolism of sialoglycoconjugates, NEU1 is expressed at the plasma membrane and regulates a myriad of receptors by desialylation, playing a key role in many pathophysiological processes. Here, we developed a proteomic approach dedicated to the purification and identification by LC-MS/MS of plasma membrane NEU1 interaction partners in human macrophages. Already known interaction partners were identified as well as several new candidates such as the class B scavenger receptor CD36. Interaction between NEU1 and CD36 was confirmed by complementary approaches. We showed that elastin-derived peptides (EDP) desialylate CD36 and that this effect was blocked by the V14 peptide, which blocks the interaction between bioactive EDP and the elastin receptor complex (ERC). Importantly, EDP also increased the uptake of oxidized LDL by macrophages that is blocked by both the V14 peptide and the sialidase inhibitor 2-deoxy-2,3-didehydro-N-acetylneuraminic acid (DANA). These results demonstrate, for the first time, that binding of EDP to the ERC indirectly modulates CD36 sialylation level and regulates oxidized LDL uptake through this sialidase. These effects could contribute to the previously reported proatherogenic role of EDP and add a new dimension in the regulation of biological processes through NEU1.

Neuraminidase activity mediates IL-6 production by activated lupus-prone mesangial cells

The development of nephritis is a leading cause of morbidity and mortality in lupus patients. Although the general pathophysiological progression of lupus nephritis is known, the molecular mediators and mechanisms are incompletely understood. Previously, we demonstrated that the glycosphingolipid (GSL) catabolic pathway is elevated in the kidneys of MRL/lpr lupus mice and human lupus patients with nephritis. Specifically, the activity of neuraminidase (NEU) and expression of Neu1, an enzyme in the GSL catabolic pathway is significantly increased. To better understand the role and mechanisms by which this pathway contributes to the progression of LN, we analyzed the expression and effects of NEU activity on the function of MRL/lpr lupus-prone mesangial cells (MCs). We demonstrate that NEU1 and NEU3 promote IL-6 production in MES13 MCs. Neu1 expression, NEU activity, and IL-6 production are significantly increased in stimulated primary MRL/lpr lupus-prone MCs, and blocking NEU activity inhibits IL-6 production. NEU1 and NEU3 expression overlaps IgG deposits in MCs in vitro and in renal sections from nephritic MRL/lpr mice. Together, our results suggest that NEU activity mediates IL-6 production in lupus-prone MCs possibly through an IgG-receptor complex signaling pathway.

Platelet microparticles reprogram macrophage gene expression and function

Platelet microparticles (MPs) represent the most abundant MPs subtype in the circulation, and can mediate intercellular communication through delivery of bioactives molecules, such as cytokines, proteins, lipids and RNAs. Here, we show that platelet MPs can be internalised by primary human macrophages and deliver functional miR-126–3p. The increase in macrophage miR-126–3p levels was not prevented by actinomycin D, suggesting that it was not due to de novo gene transcription. Platelet MPs dose-dependently downregulated expression of four predicted mRNA targets of miR-126–3p, two of which were confirmed also at the protein level. The mRNA downregulatory effects of platelet MPs were abrogated by expression of a neutralising miR-126–3p sponge, implying the involvement of miR-126–3p. Transcriptome-wide, microarray analyses revealed that as many as 66 microRNAs and 653 additional RNAs were significantly and differentially expressed in macrophages upon exposure to platelet MPs. More specifically, platelet MPs induced an upregulation of 34 microRNAs and a concomitant downregulation of 367 RNAs, including mRNAs encoding for cytokines/chemokines CCL4, CSF1 and TNF. These changes were associated with reduced CCL4, CSF1 and TNF cytokine/chemokine release by macrophages, and accompanied by a marked increase in their phagocytic capacity. These findings demonstrate that platelet MPs can modify the transcriptome of macrophages, and reprogram their function towards a phagocytic phenotype.

Supplementary Material to this article is available online at www.thrombosis-online.com.

Quantitative label-free proteomic analysis of human urine to identify novel candidate protein biomarkers for schistosomiasis

BACKGROUND

Schistosomiasis is a chronic neglected tropical disease that is characterized by continued inflammatory challenges to the exposed population and it has been established as a possible risk factor in the aetiology of bladder cancer. Improved diagnosis of schistosomiasis and its associated pathology is possible through mass spectrometry to identify biomarkers among the infected population, which will influence early detection of the disease and its subtle morbidity.

METHODOLOGY

A high-throughput proteomic approach was used to analyse human urine samples for 49 volunteers from Eggua, a schistosomiasis endemic community in South-West, Nigeria. The individuals were previously screened for Schistosoma haematobium and structural bladder pathologies via microscopy and ultrasonography respectively. Samples were categorised into schistosomiasis, schistosomiasis with bladder pathology, bladder pathology, and a normal healthy control group. These samples were analysed to identify potential protein biomarkers.

RESULTS

A total of 1306 proteins and 9701 unique peptides were observed in this study (FDR = 0.01). Fifty-four human proteins were found to be potential biomarkers for schistosomiasis and bladder pathologies due to schistosomiasis by label-free quantitative comparison between groups. Thirty-six (36) parasite-derived potential biomarkers were also identified, which include some existing putative schistosomiasis biomarkers that have been previously reported. Some of these proteins include Elongation factor 1 alpha, phosphopyruvate hydratase, histone H4 and heat shock proteins (HSP 60, HSP 70).

CONCLUSION

These findings provide an in-depth analysis of potential schistosoma and human host protein biomarkers for diagnosis of chronic schistosomiasis caused by Schistosoma haematobium and its pathogenesis.

Biochemical, Cellular, Physiological, and Pathological Consequences of Human Loss of N-Glycolylneuraminic Acid

About 2-3 million years ago, Alu-mediated deletion of a critical exon in the CMAH gene became fixed in the hominin lineage ancestral to humans, possibly through a stepwise process of selection by pathogen targeting of the CMAH product (the sialic acid Neu5Gc), followed by reproductive isolation through female anti-Neu5Gc antibodies. Loss of CMAH has occurred independently in some other lineages, but is functionally intact in Old World primates, including our closest relatives, the chimpanzee. Although the biophysical and biochemical ramifications of losing tens of millions of Neu5Gc hydroxy groups at most cell surfaces remains poorly understood, we do know that there are multiscale effects functionally relevant to both sides of the host-pathogen interface. Hominin CMAH loss might also contribute to understanding human evolution, at the time when our ancestors were starting to use stone tools, increasing their consumption of meat, and possibly hunting. Comparisons with chimpanzees within ethical and practical limitations have revealed some consequences of human CMAH loss, but more has been learned by using a mouse model with a human-like Cmah inactivation. For example, such mice can develop antibodies against Neu5Gc that could affect inflammatory processes like cancer progression in the face of Neu5Gc metabolic incorporation from red meats, display a hyper-reactive immune system, a human-like tendency for delayed wound healing, late-onset hearing loss, insulin resistance, susceptibility to muscular dystrophy pathologies, and increased sensitivity to multiple human-adapted pathogens involving sialic acids. Further studies in such mice could provide a model for other human-specific processes and pathologies involving sialic acid biology that have yet to be explored.

A novel multi-network approach reveals tissue-specific cellular modulators of fibrosis in systemic sclerosis

Background

Systemic sclerosis (SSc) is a multi-organ autoimmune disease characterized by skin fibrosis. Internal organ involvement is heterogeneous. It is unknown whether disease mechanisms are common across all involved affected tissues or if each manifestation has a distinct underlying pathology.

Methods

We used consensus clustering to compare gene expression profiles of biopsies from four SSc-affected tissues (skin, lung, esophagus, and peripheral blood) from patients with SSc, and the related conditions pulmonary fibrosis (PF) and pulmonary arterial hypertension, and derived a consensus disease-associate signature across all tissues. We used this signature to query tissue-specific functional genomic networks. We performed novel network analyses to contrast the skin and lung microenvironments and to assess the functional role of the inflammatory and fibrotic genes in each organ. Lastly, we tested the expression of macrophage activation state-associated gene sets for enrichment in skin and lung using a Wilcoxon rank sum test.

Results

We identified a common pathogenic gene expression signature—an immune–fibrotic axis—indicative of pro-fibrotic macrophages (MØs) in multiple tissues (skin, lung, esophagus, and peripheral blood mononuclear cells) affected by SSc. While the co-expression of these genes is common to all tissues, the functional consequences of this upregulation differ by organ. We used this disease-associated signature to query tissue-specific functional genomic networks to identify common and tissue-specific pathologies of SSc and related conditions. In contrast to skin, in the lung-specific functional network we identify a distinct lung-resident MØ signature associated with lipid stimulation and alternative activation. In keeping with our network results, we find distinct MØ alternative activation transcriptional programs in SSc-associated PF lung and in the skin of patients with an “inflammatory” SSc gene expression signature.

Conclusions

Our results suggest that the innate immune system is central to SSc disease processes but that subtle distinctions exist between tissues. Our approach provides a framework for examining molecular signatures of disease in fibrosis and autoimmune diseases and for leveraging publicly available data to understand common and tissue-specific disease processes in complex human diseases.

Electronic supplementary material

The online version of this article (doi:10.1186/s13073-017-0417-1) contains supplementary material, which is available to authorized users.

The NEU1-selective sialidase inhibitor, C9-butyl-amide-DANA, blocks sialidase activity and NEU1-mediated bioactivities in human lung in vitro and murine lung in vivo

Neuraminidase-1 (NEU1) is the predominant sialidase expressed in human airway epithelia and lung microvascular endothelia where it mediates multiple biological processes. We tested whether the NEU1-selective sialidase inhibitor, C9-butyl-amide-2-deoxy-2,3-dehydro-N-acetylneuraminic acid (C9-BA-DANA), inhibits one or more established NEU1-mediated bioactivities in human lung cells. We established the IC50 values of C9-BA-DANA for total sialidase activity in human airway epithelia, lung microvascular endothelia and lung fibroblasts to be 3.74 µM, 13.0 µM and 4.82 µM, respectively. In human airway epithelia, C9-BA-DANA dose-dependently inhibited flagellin-induced, NEU1-mediated mucin-1 ectodomain desialylation, adhesiveness for Pseudomonas aeruginosa and shedding. In lung microvascular endothelia, C9-BA-DANA reversed NEU1-driven restraint of cell migration into a wound and disruption of capillary-like tube formation. NEU1 and its chaperone/transport protein, protective protein/cathepsin A (PPCA), were differentially expressed in these same cells. Normalized NEU1 protein expression correlated with total sialidase activity whereas PPCA expression did not. In contrast to eukaryotic sialidases, C9-BA-DANA exerted far less inhibitory activity for three selected bacterial neuraminidases (IC50 > 800 µM). Structural modeling of the four human sialidases and three bacterial neuraminidases revealed a loop between the seventh and eighth strands of the β-propeller fold, that in NEU1, was substantially shorter than that seen in the six other enzymes. Predicted steric hindrance between this loop and C9-BA-DANA could explain its selectivity for NEU1. Finally, pretreatment of mice with C9-BA-DANA completely protected against flagellin-induced increases in lung sialidase activity. Our combined data indicate that C9-BA-DANA inhibits endogenous and ectopically expressed sialidase activity and established NEU1-mediated bioactivities in human airway epithelia, lung microvascular endothelia, and fibroblasts in vitro and murine lungs in vivo.

Sialyltransferase and Neuraminidase Levels/Ratios and Sialic Acid Levels in Peripheral Blood B Cells Correlate with Measures of Disease Activity in Patients with Systemic Lupus Erythematosus and Rheumatoid Arthritis: A Pilot Study

Objective

We attempted to determine whether the level of enzymes sialyltransferase (ST) and neuraminidase (Neu) and sialic acid (SIA) in patients with systemic lupus erythematosus (SLE) correlates with the SLE Disease Activity Index (SLEDAI) and in patients with rheumatoid arthritis (RA) correlates with the Disease Activity Score28 (DAS28).

Methods

We examined cell-surface levels of ST6Gal-1, Neu1, ST3Gal-1, Neu3, α-2,6-SIA, and α-2,3-SIA by using fluorescent anti-enzyme antibodies, fluorescent-conjugated Sambucus nigra lectin, and fluorescent-conjugated Maackia amurensis lectin on blood cells in SLE and RA patients and assessed correlations of these levels with SLEDAI and with DAS28. Areas under the curve (AUC) were calculated for different variables against SLEDAI.

Results

The B-cell ST3Gal-1/Neu3 ratio positively correlated with SLEDAI scores (ρ = 0.409 and P = 0.002, statistically significant after Bonferroni’ correction for multiple analyses.). It was supported by the inverse correlation of B-cell Neu3 levels with SLEDAI scores (ρ = −0.264, P = 0.048). The B-cell ST3Gal-1/Neu3 ratio against SLEDAI yielded an AUC of 0.689, which was comparable to that of anti-dsDNA levels at 0.635. In contrast, both ST3Gal-1 and Neu3 levels of RA B cells (r = 0.376, P = 0.013; r = 0.425, P = 0.005, respectively) correlated positively with high disease-activity DAS28 scores.

Conclusion

B-cell ST3Gal-1/Neu3 ratios in SLE and B-cell ST3Gal-1 and Neu3 levels in RA with high disease-activity DAS28 scores correlated with disease activity measures and may be useful in monitoring disease activities.

Sialylation of neurites inhibits complement-mediated macrophage removal in a human macrophage-neuron Co-Culture System

The complement system has been implicated in the removal of dysfunctional synapses and neurites during development and in disease processes in the mouse, but it is unclear how far the mouse data can be transferred to humans. Here, we co-cultured macrophages derived from human THP1 monocytes and neurons derived from human induced pluripotent stem cells, to study the role of the complement system in a human model. Components of the complement system were expressed by the human macrophages and human neuronal culture, while receptors of the complement cascade were expressed by human macrophages as shown via gene transcript analysis and flow cytometry. We mimicked pathological conditions leading to an altered glycocalyx by treatment of human neurons with sialidases. Desialylated human neurites were opsonized by the complement component C1q. Furthermore, human neurites with an intact sialic acid cap remained untouched, while desialylated human neurites were removed and ingested by human macrophages. While blockage of the complement receptor 1 (CD35) had no effect, blockage of CD11b as part of the complement receptor 3 (CR3) reversed the effect on macrophage phagocytosis of desialylated human neurites. Data demonstrate that in the human system sialylation of the neuronal glycocalyx serves as an inhibitory flag for complement binding and CR3-mediated phagocytosis by macrophages.

Desialylation is a mechanism of Fc-independent platelet clearance and a therapeutic target in immune thrombocytopenia

Immune thrombocytopenia (ITP) is a common bleeding disorder caused primarily by autoantibodies against platelet GPIIbIIIa and/or the GPIb complex. Current theory suggests that antibody-mediated platelet destruction occurs in the spleen, via macrophages through Fc-FcγR interactions. However, we and others have demonstrated that anti-GPIbα (but not GPIIbIIIa)-mediated ITP is often refractory to therapies targeting FcγR pathways. Here, we generate mouse anti-mouse monoclonal antibodies (mAbs) that recognize GPIbα and GPIIbIIIa of different species. Utilizing these unique mAbs and human ITP plasma, we find that anti-GPIbα, but not anti-GPIIbIIIa antibodies, induces Fc-independent platelet activation, sialidase neuraminidase-1 translocation and desialylation. This leads to platelet clearance in the liver via hepatocyte Ashwell-Morell receptors, which is fundamentally different from the classical Fc-FcγR-dependent macrophage phagocytosis. Importantly, sialidase inhibitors ameliorate anti-GPIbα-mediated thrombocytopenia in mice. These findings shed light on Fc-independent cytopenias, designating desialylation as a potential diagnostic biomarker and therapeutic target in the treatment of refractory ITP.

Neuraminidase-1 mediates skeletal muscle regeneration

Neuraminidase-1 (NEU1) is the sialidase responsible for the catabolism of sialoglycoconjugates in lysosomes. Congenital NEU1 deficiency causes sialidosis, a severe lysosomal storage disease associated with a broad spectrum of clinical manifestations, which also include skeletal deformities, skeletal muscle hypotonia and weakness. Neu1(-/-) mice, a model of sialidosis, develop an atypical form of muscle degeneration caused by progressive expansion of the connective tissue that infiltrates the muscle bed, leading to fiber degeneration and atrophy. Here we investigated the role of Neu1 in the myogenic process that ensues during muscle regeneration after cardiotoxin-induced injury of limb muscles. A comparative analysis of cardiotoxin-treated muscles from Neu1(-/-) mice and Neu1(+/+) mice showed increased inflammatory and proliferative responses in the absence of Neu1 during the early stages of muscle regeneration. This was accompanied by significant and sequential upregulation of Pax7, MyoD, and myogenin mRNAs. The levels of both MyoD and myogenin proteins decreased during the late stages of regeneration, which most likely reflected an increased rate of degradation of the myogenic factors in the Neu1(-/-) muscle. We also observed a delay in muscle cell differentiation, which was characterized by prolonged expression of embryonic myosin heavy chain, as well as reduced myofiber cross-sectional area. At the end of the regenerative process, collagen type III deposition was increased compared to wild-type muscles and internal controls, indicating the initiation of fibrosis. Overall, these results point to a role of Neu1 throughout muscle regeneration.

Autophagy is decreased in triple-negative breast carcinoma involving likely the MUC1-EGFR-NEU1 signalling pathway

Triple-negative breast carcinoma (TN) is a heterogeneous cancer type expressing EGFR in 75% of cases. MUC1 is a large type I sialylated glycoprotein comprising two subunits (α and β chains, also called respectively MUC1-VNTR and MUC1-CT), which was found to regulate EGFR activity through endocytic internalisation. Endocytosis and autophagy use the lysosome pathway involving NEU1. Recently, a molecular EGFR-MUC1-NEU1 complex was suggested to play a role in EGFR pathway. In the aim to understand the relationship between EGFR-MUC1-NEU1 complex and autophagy in breast carcinoma, we compared triple negative (TN) showing a high-EGFR expression with luminal (LUM) presenting low-EGFR level. We studied the expression of MUC1-VNTR, MUC1-CT and NEU1 in comparison with those of two molecular actors of autophagy, PI3K (p110β) and Beclin1. A total of 87 breast cancers were split in two groups following the immunohistochemical classification of breast carcinoma: 48 TN and 39 LUM. Our results showed that TN presented a high expression of EGFR and a low expression of MUC1-VNTR, MUC1-CT, NEU1, Beclin-1 and PI3Kp110β. Moreover, in TN, a positive statistical correlation was observed between Beclin-1 or PI3Kp110β and MUC1-VNTR or NEU1, but not with EGFR. In conclusion, our data suggest that autophagy is reduced in TN leading likely to the deregulation of EGFR-MUC1-NEU1 complex and its associated cellular pathways.

Pathogenesis, Emerging therapeutic targets and Treatment in Sialidosis

INTRODUCTION

Sialidosis is a neurosomatic, lysosomal storage disease (LSD) caused by mutations in the NEU1 gene, encoding the lysosomal sialidase NEU1. Deficient enzyme activity results in impaired processing/degradation of sialo-glycoproteins, and accumulation of oversialylated metabolites. Sialidosis is considered an orphan disorder for which no therapy is currently available.

AREAS COVERED

The review describes the clinical forms of sialidosis and the NEU1 mutations so far identified; NEU1 requirement to complex with the protective protein/cathepsin A for stability and activation; and the pathogenic effects of NEU1 deficiency. Studies of the molecular mechanisms of pathogenesis in animal models uncovered basic cellular pathways downstream of NEU1 and its substrates, which may be implicated in more common adult (neurodegenerative) diseases. The development of a Phase I/II clinical trial for patients with galactosialidosis may prove suitable for sialidosis patients with the attenuated form of the disease.

EXPERT OPINION

Recently, there has been a renewed interest in the development of therapies for orphan LSDs, like sialidosis. Given the small number of potentially eligible patients, the way to treat sialidosis would be through the coordinated effort of clinical centers, which provide diagnosis and care for these patients, and the basic research labs that work towards understanding the disease pathogenesis.

Sensing the neuronal glycocalyx by glial sialic acid binding immunoglobulin-like lectins

Sialic acid binding immunoglobulin-like lectins (Siglecs) are cell surface receptors of microglia and oligodendrocytes that recognize the sialic acid cap of healthy neurons and neighboring glial cells. Upon ligand binding, Siglecs typically signal through an immunoreceptor tyrosine-based inhibition motif (ITIM) to keep the cell in a homeostatic status and support healthy neighboring cells. Siglecs can be divided into two groups; the first, being conserved among different species. The conserved Siglec-4/myelin-associated glycoprotein is expressed on oligodendrocytes and Schwann cells. Siglec-4 protects neurons from acute toxicity via interaction with sialic acids bound to neuronal gangliosides. The second group of Siglecs, named CD33-related Siglecs, is almost exclusively expressed on immune cells and is highly variable among different species. Microglial expression of Siglec-11 is human lineage-specific and prevents neurotoxicity via interaction with α2.8-linked sialic acid oligomers exposed on the neuronal glycocalyx. Microglial Siglec-E is a mouse CD33-related Siglec member that prevents microglial phagocytosis and the associated oxidative burst. Mouse Siglec-E of microglia binds to α2.8- and α2.3-linked sialic acid residues of the healthy glycocalyx of neuronal and glial cells. Recently, polymorphisms of the human Siglec-3/CD33 were linked to late onset Alzheimer's disease by genome-wide association studies. Human Siglec-3 is expressed on microglia and produces inhibitory signaling that decreases uptake of particular molecules such as amyloid-β aggregates. Thus, glial ITIM-signaling Siglecs recognize the intact glycocalyx of neurons and are involved in the modulation of neuron-glia interaction in healthy and diseased brain.

Changes in polysialic acid expression on myeloid cells during differentiation and recruitment to sites of inflammation: role in phagocytosis

Polysialic acid (polySia) is a unique linear homopolymer of α2,8-linked sialic acid that has been studied extensively as a posttranslational modification of neural cell adhesion molecule in the central nervous system. Only two proteins are known to be polysialylated in cells of the immune system: CD56 on human natural killer cells and murine bone marrow (BM) leukocytes, and neuropilin-2 (NRP-2) on dendritic cells (DCs). We tested the hypothesis that polySia expression is regulated during maturation and migration of leukocytes and plays a role in functional activity. Using wild-type and NCAM(-/-) mice, we show that BM neutrophils express only polysialylated CD56, whereas a subset of BM monocytes expresses polysialylated CD56 and/or another polysialylated protein(s). We demonstrate that polysialylated CD56 expression is progressively down-regulated in wild-type monocytes and monocyte-derived cells during migration from BM through peripheral blood to pulmonary and peritoneal sites of inflammation. Freshly isolated monocyte-derived peritoneal macrophages are devoid of polySia yet re-express polySia on NRP-2 and an additional protein(s) after maintenance in culture. Removal of polySia from these cells enhances phagocytosis of Klebsiella pneumoniae, suggesting that down-regulation of polySia on macrophages facilitates bacterial clearance. Using wild-type and NRP-2(-/-) mice, we demonstrate that NRP-2 and an additional protein(s) are polysialylated by ST8 SiaIV in BM-derived DCs. We conclude that polySia expression in monocyte-derived cells is dynamically regulated by ST8 SiaIV activity and by expression of carrier proteins during recruitment to sites of inflammation and influences cellular interactions with microbes, contributing to innate and adaptive immune responses.

Desialylation of surface receptors as a new dimension in cell signaling

Terminal sialic acid residues are found in abundance in glycan chains of glycoproteins and glycolipids on the surface of all live cells forming an outer layer of the cell originally known as glycocalyx. Their presence affects the molecular properties and structure of glycoconjugates, modifying their function and interactions with other molecules. Consequently, the sialylation state of glycoproteins and glycolipids has been recognized as a critical factor modulating molecular recognitions inside the cell, between the cells, between the cells and the extracellular matrix, and between the cells and certain exogenous pathogens. Until recently sialyltransferases that catalyze transfer of sialic acid residues to the glycan chains in the process of their biosynthesis were thought to be mainly responsible for the creation and maintenance of a temporal and spatial diversity of sialylated moieties. However, the growing evidence suggests that in mammalian cells, at least equally important roles belong to sialidases/neuraminidases, which are located on the cell surface and in intracellular compartments, and may either initiate the catabolism of sialoglycoconjugates or just cleave their sialic acid residues, and thereby contribute to temporal changes in their structure and functions. The current review summarizes emerging data demonstrating that mammalian neuraminidase 1, well known for its lysosomal catabolic function, is also targeted to the cell surface and assumes the previously unrecognized role as a structural and functional modulator of cellular receptors.

Dendritic cells: a spot on sialic Acid

Glycans decorating cell surface and secreted proteins and lipids occupy the juncture where critical host–host and host-pathogen interactions occur. The role of glycan epitopes in cell–cell and cell-pathogen adhesive events is already well-established, and cell surface glycan structures change rapidly in response to stimulus and inflammatory cues. Despite the wide acceptance that glycans are centrally implicated in immunity, exactly how glycans and their changes contribute to the overall immune response remains poorly defined. Sialic acids are unique sugars that usually occupy the terminal position of the glycan chains and may be modified by external factors, such as pathogens, or upon specific physiological cellular events. At cell surface, sialic acid-modified structures form the key fundamental determinants for a number of receptors with known involvement in cellular adhesiveness and cell trafficking, such as the Selectins and the Siglec families of carbohydrate recognizing receptors. Dendritic cells (DCs) preside over the transition from innate to the adaptive immune repertoires, and no other cell has such relevant role in antigen screening, uptake, and its presentation to lymphocytes, ultimately triggering the adaptive immune response. Interestingly, sialic acid-modified structures are involved in all DC functions, such as antigen uptake, DC migration, and capacity to prime T cell responses. Sialic acid content changes along DC differentiation and activation and, while, not yet fully understood, these changes have important implications in DC functions. This review focuses on the developmental regulation of DC surface sialic acids and how manipulation of DC surface sialic acids can affect immune-critical DC functions by altering antigen endocytosis, pathogen and tumor cell recognition, cell recruitment, and capacity for T cell priming. The existing evidence points to a potential of DC surface sialylation as a therapeutic target to improve and diversify DC-based therapies.

Elastin-derived peptides potentiate atherosclerosis through the immune Neu1-PI3Kγ pathway

AIMS

Elastin is degraded during vascular ageing and its products, elastin-derived peptides (EP), are present in the human blood circulation. EP binds to the elastin receptor complex (ERC) at the cell surface, composed of elastin-binding protein (EBP), a cathepsin A and a neuraminidase 1. Some in vitro functions have clearly been attributed to this binding, but the in vivo implications for arterial diseases have never been clearly investigated.

METHODS AND RESULTS

Here, we demonstrate that chronic doses of EP injected into mouse models of atherosclerosis increase atherosclerotic plaque size formation. Similar effects were observed following an injection of a VGVAPG peptide, suggesting that the ERC mediates these effects. The absence of phosphoinositide 3-kinase γ (PI3Kγ) in bone marrow-derived cells prevented EP-induced atherosclerosis development, demonstrating that PI3Kγ drive EP-induced arterial lesions. Accordingly, in vitro studies showed that PI3Kγ was required for EP-induced monocyte migration and ROS production and that this effect was dependent upon neuraminidase activity. Finally, we showed that degradation of elastic lamellae in LDLR(-/-) mice fed an atherogenic diet correlated with atherosclerotic plaque formation. At the same time, the absence of the cathepsin A-neuraminidase 1 complex in cells of the haematopoietic lineage abolished atheroma plaque size progression and decreased leucocytes infiltration, clearly demonstrating the role of this complex in atherogenesis and suggesting the involvement of endogenous EP.

CONCLUSION

Altogether, this work identifies EP as an enhancer of atherogenesis and defines the Neuraminidase 1/PI3Kγ signalling pathway as a key mediator of this function in vitro and in vivo.

Positive regulation of insulin signaling by neuraminidase 1

Neuraminidases (sialidases) catalyze the removal of sialic acid residues from sialylated glycoconjugates. We now report that mammalian neuraminidase 1 (Neu1), in addition to its catabolic function in lysosomes, is transported to the cell surface where it is involved in the regulation of insulin signaling. Insulin binding to its receptor rapidly induces interaction of the receptor with Neu1, which hydrolyzes sialic acid residues in the glycan chains of the receptor and, consequently, induces its activation. Cells from sialidosis patients with a genetic deficiency of Neu1 show impairment of insulin-induced phosphorylation of downstream protein kinase AKT, and treatment of these cells with purified Neu1 restores signaling. Genetically modified mice with ∼10% of the normal Neu1 activity exposed to a high-fat diet develop hyperglycemia and insulin resistance twice as fast as their wild-type counterparts. Together, these studies identify Neu1 as a novel component of the signaling pathways of energy metabolism and glucose uptake.