Change of transferrin sialylation differs between mild sepsis and severe sepsis and septic shock

RCL glycosylation of serum corticosteroid-binding globulin: implications in cortisol delivery and septic shock

Corticosteroid-binding globulin (CBG) is a serum glycoprotein that binds and delivers anti-inflammatory cortisol to inflammatory sites through neutrophil elastase-mediated proteolysis of an exposed reactive centre loop (RCL) on CBG. Timely and tissue-specific delivery of cortisol is critical to alleviate inflammation including in life-threatening septic shock conditions. Herein, we firstly summarise our recently published report of functional RCL O- and N-glycosylation events of serum CBG (Chernykh, J Biol Chem, 2023). A key finding of that published work was the LC-MS/MS-based discovery of RCL O-glycans at Thr342 and Thr345 of serum CBG and their inhibitory roles in neutrophil elastase-mediated RCL proteolysis. While these observations are of significance as they implicate RCL O-glycosylation as a potential regulator of cortisol delivery, the link to septic shock remains unexplored. To this end, we used a similar LC-MS/MS approach to profile the RCL O-glycosylation of CBG purified from serum of twelve septic shock patients. Serum CBG from all patients exhibited RCL O-glycosylation comprising (di)sialyl T (NeuAc1-2Gal1GalNAc1) core 1-type O-glycan structures decorating exclusively the Thr342 site. Importantly, relative to less severe cases, individuals presenting with the most severe illness displayed elevated RCL O-glycosylation upon ICU admission, suggesting a previously unknown link to septic shock severity. Overall, we have elucidated the coordinated RCL N- and O-glycosylation events of serum CBG, which improve our understanding of molecular mechanisms governing the timely and tissue-specific delivery of cortisol to inflammatory sites. This work provides clues to molecular aberrations and disease mechanisms underpinning septic shock.

Impact of different pathogen classes on the serum N-glycome in septic shock

The morbidity and mortality of sepsis remain high. Clinicians lack effective markers to rapidly diagnose sepsis and identify the underlying pathogen infection particularly for patients with candidaemia or cases of culture-negative sepsis where culture-based diagnostics are inadequate. In our search for new lines of potential sepsis biomarkers, we here explore the impact of various classes of infectious agents on the serum N-glycome in a septic shock cohort. Comparative N-glycomics was performed on sera collected from 49 septic shock patients infected with viral (n = 9), bacterial (n = 37) or fungal (n = 3) pathogens using an established PGC-LC-MS/MS method. Aberrant serum N-glycosylation features were observed in patients with fungal infection relative to the other infection sub-groups including i) altered expression of prominent α2,6-sialylated biantennary N-glycan isomers, ii) elevated levels of IgG-type N-glycosylation and iii) a global shift in the serum N-glycome involving altered glycan type distribution and considerable changes in core fucosylation and α2,6-sialylation. Septic shock patients infected with bacterial and viral pathogens exhibited similar global serum N-glycome features and therefore could not be stratified based on their serum N-glycosylation. Subtle and less consistent serum N-glycome differences were observed between septic shock patients infected with different bacterial pathogens. In conclusion, our study has tested the impact of different pathogen classes on the serum N-glycome in a septic shock cohort, and reports that fungal infection impacts the host serum N-glycome differently compared to bacterial or viral infections thus potentially opening avenues for glycan-based biomarkers to better diagnose patients with candidaemia.

Protein sialylation affects the pH-dependent binding of ferric ion to human serum transferrin

Physiological or pathophysiological changes lead to posttranslational changes in the sialic acid content of human serum transferrin (hTf), an essential mediator of iron transport in the human body, resulting in a significantly increased concentration of desialylated hTf. The intrinsic fluorescence quenching upon binding of iron to hTf was successfully modeled using the binding polynomial for two iron-binding sites, allowing measurements in a high-throughput format. Removal of sialic acid residues resulted in a 3-fold increase in iron binding affinity for both sites of hTf at pH 7.4. The pH-dependence of iron binding showed significant differences in equilibrium constants, resulting in a 10-fold increase in binding affinity for desialylated hTf at pH 5.9. The changes in hTf sialylation apparently result in tuning of the stability of the conformational state, which in turn contributes to the stability of the diferric hTf. The observed differences in the conditional thermodynamic equilibrium constants suggest that the desialylated protein has a higher preference for diferric hTf over monoferric hTf species down to pH 6.5, which may also influence the interaction with transferrin receptors that preferentially bind to diferric hTf. The results suggest a link between changes in hTf glycan structure and alterations in iron binding equilibrium associated with tissue acidosis.

Cardiac-specific overexpression of catalase attenuates lipopolysaccharide-induced cardiac anomalies through reconciliation of autophagy and ferroptosis

Lipopolysaccharide (LPS) from Gram-negative bacteria is a major contributor to cardiovascular failure, but the signaling mechanisms underlying its stress response are not fully understood. This study aimed to investigate the effect of the antioxidant enzyme catalase on LPS-induced cardiac abnormalities and the mechanisms involved, with particular focus on the interplay between autophagy, ferroptosis, and apoptosis. Cardiac-specific catalase (CAT) overexpression and wild-type (WT) mice were stimulated with LPS (6 mg/kg, intravenous injection), and cardiac morphology and function were evaluated. Oxidative stress, ferroptosis, apoptosis, and mitochondrial status were monitored, and survival curves were plotted based on the results of LPS stimulation. The results showed that, compared with WT mice, mice overexpressing catalase had a higher survival rate under LPS stimulation. Ultrasound echocardiography, cardiomyocyte characteristics, and Masson's trichrome staining showed that LPS inhibited cardiac function and caused cardiac fibrosis, while catalase alleviated these adverse effects. LPS increased apoptosis (TUNEL, caspase-3 activation, cleaved caspase-3), increased O₂^·- production, induced inflammation (TNF-α), autophagy, iron toxicity, and carbonyl damage, and significantly damaged mitochondria (mitochondrial membrane potential, mitochondrial proteins, and ultrastructure). These effects were significantly alleviated by catalase. Interestingly, the antioxidant N-acetylcysteine, autophagy inhibitor 3-methyladenine, and ferroptosis inhibitor lipostatin-1 all eliminated the LPS-induced contraction dysfunction and ferroptosis (using lipid peroxidation). Induction of ferroptosis could eliminate the cardioprotective effect of NAC. In conclusion, catalase rescues LPS-induced cardiac dysfunction by regulating oxidative stress, autophagy, ferroptosis, apoptosis, and mitochondrial damage in cardiomyocytes.

Glycoproteomics meets thermodynamics: A calorimetric study of the effect of sialylation and synergistic anion on the binding of iron to human serum transferrin

The thermodynamic parameters for the binding of ferric ions to human serum transferrin (hTf) as the major mediator of iron transport in blood plasma were determined by isothermal titration calorimetry in the presence of carbonate and oxalate as synergistic anions at pH 7.4. The results indicate that the binding of ferric ions to the two binding sites of hTf is driven both enthalpically and entropically in a lobe-dependent manner: binding to the C-site is mainly enthalpically driven, whereas binding to the N-site is mainly entropically driven. Lower sialic acid content of hTf leads to more exothermic apparent binding enthalpies for both lobes, while the increased apparent binding constants for both sites were found in the presence of carbonate. Sialylation also unequally affected the heat change rates for both sites only in the presence of carbonate, but not in the presence of oxalate. Overall, the results suggest that the desialylated hTf has a higher iron sequestering ability, which may have implications for iron metabolism.

Comparative analysis of transferrin and IgG N-glycosylation in two human populations

Human plasma transferrin (Tf) N-glycosylation has been mostly studied as a marker for congenital disorders of glycosylation, alcohol abuse, and hepatocellular carcinoma. However, inter-individual variability of Tf N-glycosylation is not known, mainly due to technical limitations of Tf isolation in large-scale studies. Here, we present a highly specific robust high-throughput approach for Tf purification from human blood plasma and detailed characterization of Tf N-glycosylation on the level of released glycans by ultra-high-performance liquid chromatography based on hydrophilic interactions and fluorescence detection (HILIC-UHPLC-FLD), exoglycosidase sequencing, and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS). We perform a large-scale comparative study of Tf and immunoglobulin G (IgG) N-glycosylation analysis in two human populations and demonstrate that Tf N-glycosylation is associated with age and sex, along with multiple biochemical and physiological traits. Observed association patterns differ compared to the IgG N-glycome corroborating tissue-specific N-glycosylation and specific N-glycans' role in their distinct physiological functions.

Structural and functional diversity of neutrophil glycosylation in innate immunity and related disorders

The granulated neutrophils are abundant innate immune cells that utilize bioactive glycoproteins packed in cytosolic granules to fight pathogenic infections, but the neutrophil glycobiology remains poorly understood. Facilitated by technological advances in glycoimmunology, systems glycobiology and glycoanalytics, a considerable body of literature reporting on novel aspects of neutrophil glycosylation has accumulated. Herein, we summarize the building knowledge of the structural and functional diversity displayed by N- and O-linked glycoproteins spatiotemporally expressed and sequentially brought-into-action across the diverse neutrophil life stages during bone marrow maturation, movements to, from and within the blood circulation and microbicidal processes at the inflammatory sites in peripheral tissues. It transpires that neutrophils abundantly decorate their granule glycoproteins including neutrophil elastase, myeloperoxidase and cathepsin G with peculiar glyco-signatures not commonly reported in other areas of human glycobiology such as hyper-truncated chitobiose core- and paucimannosidic-type N-glycans and monoantennary complex-type N-glycans. Sialyl Lewis^x, Lewis^x, poly-N-acetyllactosamine extensions and core 1-/2-type O-glycans are also common neutrophil glyco-signatures. Granule-specific glycosylation is another fascinating yet not fully understood feature of neutrophils. Recent literature suggests that unconventional biosynthetic pathways and functions underpin these prominent neutrophil-associated glyco-phenotypes. The impact of glycosylation on key neutrophil effector functions including extravasation, degranulation, phagocytosis and formation of neutrophil extracellular traps during normal physiological conditions and in innate immune-related diseases is discussed. We also highlight new technologies that are expected to further advance neutrophil glycobiology and briefly discuss the untapped diagnostic and therapeutic potential of neutrophil glycosylation that could open avenues to combat the increasingly prevalent innate immune disorders.

PPARα contributes to protection against metabolic and inflammatory derangements associated with acute kidney injury in experimental sepsis

Sepsis-associated acute kidney injury (AKI) is a significant problem in critically ill children and adults resulting in increased morbidity and mortality. Fundamental mechanisms contributing to sepsis-associated AKI are poorly understood. Previous research has demonstrated that peroxisome proliferator-activated receptor α (PPARα) expression is associated with reduced organ system failure in sepsis. Using an experimental model of polymicrobial sepsis, we demonstrate that mice deficient in PPARα have worse kidney function, which is likely related to reduced fatty acid oxidation and increased inflammation. Ultrastructural evaluation with electron microscopy reveals that the proximal convoluted tubule is specifically injured in septic PPARα deficient mice. In this experimental group, serum metabolomic analysis reveals unanticipated metabolic derangements in tryptophan-kynurenine-NAD+ and pantothenate pathways. We also show that a subgroup of children with sepsis whose genome-wide expression profiles are characterized by repression of the PPARα signaling pathway has increased incidence of severe AKI. These findings point toward interesting associations between sepsis-associated AKI and PPARα-driven fatty acid metabolism that merit further investigation.

Itraq-Based Quantitative Proteomic Analysis of Lungs in Murine Polymicrobial Sepsis with Hydrogen Gas Treatment

Sepsis-associated acute lung injury (ALI), which carries a high morbidity and mortality in patients, has no effective therapeutic strategies to date. Our group has already reported that hydrogen gas (H2) exerts a protective effect against sepsis in mice. However, the molecular mechanisms underlying H2 treatment are not fully understood. This study investigated the effects of H2 on lung injuries in septic mice through the isobaric tags for relative and absolute quantitation (iTRAQ)-based quantitative proteomic analysis. Male ICR mice used in this study were subjected to cecal ligation and puncture (CLP) or sham operation. And 2% H2 was inhaled for 1 h beginning at 1 and 6 h after sham or CLP operation. The iTRAQ-based liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis was preformed to investigate lung proteomics. Sepsis-challenged animals had decreased survival rate, as well as had increased bacterial burden in blood, peritoneal lavage, and lung sample, which were significantly ameliorated by H2 treatment. Moreover, a total of 4,472 proteins were quantified, and 192 differentially expressed proteins were related to the protective mechanism of H2 against sepsis. Functional enrichment analysis showed that H2-related differential proteins could be related to muscle contraction, oxygen transport, protein synthesis, collagen barrier membranes, cell adhesion, and coagulation function. These proteins were significantly enriched in four signaling pathways, and two of which are associated with coagulation. In addition, H2 alleviates ALI in septic mice through downregulating the expression of Sema 7A, OTULIN, and MAP3K1 as well as upregulating the expression of Transferrin. Thus, our findings provide an insight into the mechanism of H2 treatment in sepsis by proteomic approach, which may be helpful to the clinic application of H2 in patients with sepsis.

Differential protein expression in patients with urosepsis

PURPOSE

Urosepsis in adults comprises approximately 25% of all sepsis cases, and is due to complicated urinary tract infections in most cases. However, its mechanism is not fully clarified. Urosepsis is a very complicated disease with no effective strategy for early diagnosis and treatment. This study aimed to identify possible target-related proteins involved in urosepsis using proteomics and establish possible networks using bioinformatics.

METHODS

Fifty patients admitted to the Urology Unit of Lanzhou General PLA (Lanzhou, China), from October 2012 to October 2015, were enrolled in this study. The patients were further divided into shock and matched-pair non-shock groups. 2-DE technique, mass spectrometry and database search were used to detect differentially expressed proteins in serum from the two groups.

RESULTS

Six proteins were found at higher levels in the shock group compared with non-shock individuals, including serum amyloid A-1 protein (SAA1), apolipoprotein L1 (APOL1), ceruloplasmin (CP), haptoglobin (HP), antithrombin-III (SERPINC1) and prothrombin (F2), while three proteins showed lower levels, including serotransferrin (TF), transthyretin (TTR) and alpha-2-macroglobulin (A2M).

CONCLUSION

Nine proteins were differentially expressed between uroseptic patients (non-shock groups) and severe uroseptic patients (shock groups), compared with non-shock groups, serum SAA1, APOL1,CP, HP, SERPINC1and F2 at higher levels, while TF, TTR and A2M at lower levels in shock groups.these proteins were mainly involved in platelet activation, signaling and aggregation, acute phase protein pathway, lipid homeostasis, and iron ion transport, deserve further research as potential candidates for early diagnosis and treatment. (The conclusion seems too simple and vague, please re-write it. You may focus at what proteins have been expressed and introduce more detail about its significance.).

Acute phase inflammation is characterized by rapid changes in plasma/peritoneal fluid N-glycosylation in mice

Murine zymosan-induced peritonitis is a widely used model for studying the molecular and cellular events responsible for the initiation, persistence and/or resolution of inflammation. Among these events, it is becoming increasingly evident that changes in glycosylation of proteins, especially in the plasma and at the site of inflammation, play an important role in the inflammatory response. Using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS)-based glycosylation profiling, we investigated the qualitative and quantitative effect of zymosan-induced peritonitis on N-glycosylation in mouse plasma and peritoneal fluid. Our results show that both N-glycomes exhibit highly similar glycosylation patterns, consisting mainly of diantennary and triantennary complex type N-glycans with high levels (>95 %) of galactosylation and sialylation (mostly NeuGc) and a medium degree of core fucosylation (30 %). Moreover, MS/MS structural analysis, assisted by linkage-specific derivatization of sialic acids, revealed the presence of O-acetylated sialic acids as well as disialylated antennae (“branching sialylation”) characterized by the presence of α2-6-linked NeuGc on the GlcNAc of the NeuGcα2-3-Galβ1-3-GlcNAc terminal motif. A significant decrease of (core) fucosylation together with an increase of both α2-3-linked NeuGc and “branching sialylation” were observed in N-glycomes of mice challenged with zymosan, but not in control mice injected with PBS. Importantly, substantial changes in glycosylation were already observed 12 h after induction of peritonitis, thereby demonstrating an unexpected velocity of the biological mechanisms involved.

Clinical diagnostics and therapy monitoring in the congenital disorders of glycosylation

Abnormal protein glycosylation is observed in many common disorders like cancer, inflammation, Alzheimer’s disease and diabetes. However, the actual use of this information in clinical diagnostics is still very limited. Information is usually derived from analysis of total serum N-glycan profiling methods, whereas the current use of glycoprotein biomarkers in the clinical setting is commonly based on protein levels. It can be envisioned that combining protein levels and their glycan isoforms would increase specificity for early diagnosis and therapy monitoring. To establish diagnostic assays, based on the mass spectrometric analysis of protein-specific glycosylation abnormalities, still many technical improvements have to be made. In addition, clinical validation is equally important as well as an understanding of the genetic and environmental factors that determine the protein-specific glycosylation abnormalities. Important lessons can be learned from the group of monogenic disorders in the glycosylation pathway, the Congenital Disorders of Glycosylation (CDG). Now that more and more genetic defects are being unraveled, we start to learn how genetic factors influence glycomics profiles of individual and total serum proteins. Although only in its initial stages, such studies suggest the importance to establish diagnostic assays for protein-specific glycosylation profiling, and the need to look beyond the single glycoprotein diagnostic test. Here, we review progress in and lessons from genetic disease, and review the increasing opportunities of mass spectrometry to analyze protein glycosylation in the clinical diagnostic setting. Furthermore, we will discuss the possibilities to expand current CDG diagnostics and how this can be used to approach glycoprotein biomarkers for more common diseases.

Changes in IgG and total plasma protein glycomes in acute systemic inflammation

Recovery after cardiac surgery is a complex process that has to compensate for both individual variability and extensive tissue damage in the context of systemic inflammation. Protein glycosylation is essential in many steps of the inflammatory cascade, but due to technological limitations the role of individual variation in glycosylation in systemic inflammation has not been addressed until now. We analysed composition of the total plasma and IgG N-glycomes in 107 patients undergoing cardiac surgery. In nearly all individuals plasma N-glycome underwent the same pattern of changes in the first 72 h, revealing a general mechanism of glycosylation changes. To the contrary, changes in the IgG glycome were very individualized. Bi-clustering analysis revealed the existence of four distinct patterns of changes. One of them, characterized by a rapid increase in galactosylated glycoforms, was associated with nearly double mortality risk measured by EuroSCORE II. Our results indicate that individual variation in IgG glycosylation changes during acute systemic inflammation associates with increased mortality risk and indicates new avenues for the development of personalized diagnostic and therapeutic approach.

The analysis of the human plasma N-glycome in endometriosis patients

OBJECTIVE

Analysis of the plasma N-glycome in endometriosis patients compared with controls.

STUDY DESIGN

In a case-control study, blood samples were collected from patients who underwent either diagnostic or operative laparoscopy between 2008 and 2011 in the Semmelweis University, Budapest, I. Department of Obstetrics and Gynaecology. From these patients, 92 with endometriosis (30 stage I-II and 62 stage III-IV, including altogether 18 deep infiltrating cases) and 62 controls were selected for glycan analysis. After release, plasma N-glycans were subjected to hydrophilic interaction high performance liquid chromatography, which resulted in 19 chromatographic glycan peaks (GP). The abundances of the GPs were compared between the study groups. For statistical analysis a non-parametric test, the Mann-Whitney-U test, was used.

RESULTS

We found a statistically significant decrease of GP1 and increase of GP14, GP17 and GP18 in endometriosis patients. The latter peaks consist of glycans which play a role in inflammatory processes and malignancy. We also found significant differences in GP2, GP4, GP6, and GP9 between controls and the different endometriosis stage groups. The observed alterations in GP2, GP4 and GP6 may be related to altered glycosylation and remodelling of the glycan branches of the IgG molecule. The alterations of GP9 are presumably associated with changes of transferrin glycosylation. Furthermore we detected a highly significant decrease of GP1 in patients with deep infiltrating endometriosis compared with controls.

CONCLUSIONS

This is the first analysis of the plasma N-glycome in endometriosis. The observed changes in GP14, GP17 and GP18 and in GP2, GP4, GP6 and GP9 provide new aspects to the pathophysiology of the disease and the alterations of the GP1 may serve as a new potential marker in the future.

Alternative glycosylation modulates function of IgG and other proteins - implications on evolution and disease

BACKGROUND

Nearly all membrane and secreted proteins, as well as numerous intracellular proteins are glycosylated. However, contrary to proteins which are defined by their individual genetic templates, glycans are encoded in a complex dynamic network of hundreds of genes which participate in the complex biosynthetic pathway of protein glycosylation.

SCOPE OF REVIEW

This review summarizes present knowledge about the importance of alternative glycosylation of IgG and other proteins.

MAJOR CONCLUSIONS

Numerous proteins depend on correct glycosylation for proper function. Very good example for this is the alternative glycosylation of IgG whose effector functions can be completely changed by the addition or removal of a single monosaccharide residue from its glycans.

GENERAL SIGNIFICANCE

The change in the structure of a protein requires mutations in DNA and subsequent selection in the next generation, while even slight alterations in activity or intracellular localization of one or more biosynthetic enzymes are sufficient for the creation of novel glycan structures, which can then perform new functions. Glycome composition varies significantly between individuals, which makes them slightly or even significantly different in their ability to execute specific molecular pathways with numerous implications for development and progression of various diseases. This article is part of a Special Issue entitled Glycoproteomics.