Sialylation of Thomsen-Friedenreich antigen is a noninvasive blood-based biomarker for GNE myopathy

Chemoenzymatic synthesis and immunological evaluation of sialyl-Thomsen-Friedenreich (sTF) antigen conjugate to CRM197

sTF (sialyl-Thomsen-Friedenreich) is a type of tumor-associated carbohydrate antigens (TACAs) and is highly expressed in various human malignancies. To validate if sTF could be a valuable molecular target for future cancer vaccine development, in this work the sTF antigen was prepared by adopting a strategy combining chemical and enzymatic methods, and then was covalently conjugated to a carrier protein, CRM197. The preliminary immunological evaluation, performed on BALB/c mice, revealed that the sTF-CRM197 conjugate elicited high titers of specific IgG antibodies. FACS experiments showed that the antisera induced by sTF-CRM197 conjugate could specifically recognize and bind to sTF-positive cancer cells T-47D. Furthermore, the conjugate mediated effective and specific antibody-mediated complement-dependent cytotoxicity (CDC).

GNE myopathy: History, etiology, and treatment trials

GNE myopathy is an ultrarare muscle disease characterized by slowly progressive muscle weakness. Symptoms typically start in early adulthood, with weakness and atrophy in the tibialis anterior muscles and with slow progression over time, which largely spares the quadriceps muscles. Muscle biopsy shows atrophic fibers and rimmed vacuoles without inflammation. Inherited in an autosomal recessive manner, patients with GNE myopathy carry mutations in the GNE gene which affect the sialic acid synthesis pathway. Here, we look at the history and clinical aspects of GNE myopathy, as well as focus on prior treatment trials and challenges and unmet needs related to this disorder.

The role of amyloid β in the pathological mechanism of GNE myopathy

GNE myopathy is a hereditary muscle disorder characterized by muscle atrophy and weakness initially involving the lower distal extremities. The treatment of GNE myopathy mainly focuses on a sialic acid deficiency caused by a mutation in the GNE gene, but it has not achieved the expected effect. The main pathological features of GNE myopathy are myofiber atrophy and rimmed vacuoles, including accumulation of amyloid β, which is mainly found in atrophic muscle fibers. Although the role of amyloid β and other misfolded proteins on the nervous system has been widely recognized, the cause and process of the formation of amyloid β in the pathological process of GNE myopathy are unclear. In addition, amyloid β has been reported to be linked to quality control mechanisms of proteins, such as molecular chaperones, the ubiquitin–proteasome system, and the autophagy-lysosome system. Herein, we summarize the possible reasons for amyloid β deposition and illustrate amyloid β-mediated events in the cells and their role in muscle atrophy in GNE myopathy. This review represents an overview of amyloid β and GNE myopathy that could help identify a potential mechanism and thereby a plausible therapeutic for the disease.

Inherited Neuromuscular Disorders: Which Role for Serum Biomarkers?

Inherited neuromuscular disorders (INMD) are a heterogeneous group of rare diseases that involve muscles, motor neurons, peripheral nerves or the neuromuscular junction. Several different lab abnormalities have been linked to INMD: sometimes they are typical of the disorder, but they usually appear to be less specific. Sometimes serum biomarkers can point out abnormalities in presymtomatic or otherwise asymptomatic patients (e.g., carriers). More often a biomarker of INMD is evaluated by multiple clinicians other than expert in NMD before the diagnosis, because of the multisystemic involvement in INMD. The authors performed a literature search on biomarkers in inherited neuromuscular disorders to provide a practical approach to the diagnosis and the correct management of INMD. A considerable number of biomarkers have been reported that support the diagnosis of INMD, but the role of an expert clinician is crucial. Hence, the complete knowledge of such abnormalities can accelerate the diagnostic workup supporting the referral to specialists in neuromuscular disorders.

Krebs von den Lungen 6 decreased in the serum and muscle of GNE myopathy patients

UDP‐N‐acetylglucosamine 2‐epimerase/N‐acetylmannosamine kinase (GNE) is necessary for sialic acid biosynthesis. GNE myopathy is caused by a defect in GNE, and hyposialylation is a key factor in the pathomechanism of GNE myopathy. Although candidates for evaluating hyposialylation have been reported, it is difficult to measure them in routine clinical practice. Sialylation is necessary for synthesis of various glycoproteins, including Krebs von den Lungen‐6 (KL‐6)/mucin 1 (MUC1). Here we report that KL‐6/MUC1 is decreased in GNE myopathy. We observed that KL‐6 levels were decreased in the serum of patients with GNE myopathy, and that KL‐6 and MUC1‐C were also decreased in muscle biopsy specimens from these patients. An immunofluorescent study revealed that KL‐6 and MUC1‐C were not present in the sarcolemma but were, instead, localized in rimmed vacuoles in specimens from patients with GNE myopathy. KL‐6 is already used to detect lung diseases in clinical practice, and this glycoprotein may be a novel candidate for evaluating hyposialylation in GNE myopathy.

Efficient chemoenzymatic synthesis of fluorinated sialyl Thomsen-Friedenreich antigens and investigation of their characteristics

A set of fluorinated sialyl-T derivatives were efficiently synthesized using one-pot multi-enzyme (OPME) chemoenzymatic approach. The P. multocida α2-3-sialyltransferase (PmST1) involved in the synthesis showed extremely flexible donor and acceptor substrate specificities. These sialosides have been successfully investigated with stability towards Clostridium perfringens sialidase substrate specificity assay using ¹H NMR spectroscopy. Hydrolysis studies monitored by ¹H NMR clearly demonstrated that the fluorine substitution obviously reduced hydrolysis rate of Clostridium perfringens sialidase. To further investigate the fluorine influence, structure-dependent variation of sialoside-lectin binding was observed for MAL and different sialoside-immobilized surfaces. Subtle changes on the ligand of carbohydrate-binding protein were distinguished by SPR. These fluorinated sialyl-T derivatives obtained are valuable probes for further biological studies or antitumor drug design.

The Potential Action of Thomsen-Friedenreich Monoclonal Antibody (A78-G/A7) in Thyroid Cancer

Background

Thomsen–Friedenreich antibody (TF-Ab) is a specific antibody against the Thomsen–Friedenreich antigen (TF-Ag). At present, studies on a number of other tumors have shown that TF-Ab can effectively inhibit metastasis and induce apoptosis in tumor cells. However, the role of TF-Ab in thyroid cancer (TC) remains unclear.

Materials and Methods

Normal subjects and patients with primary papillary TC with or without lymph node metastasis were tested for TF-Ab expression by enzyme-linked immunosorbent assays (ELISAs). Immunofluorescence was used to assess the expression of TF-Ag in thyroid papillary carcinoma with or without lymph node metastasis and undifferentiated cancer tissues. To evaluate the role of TF-Ab in TC, the effects of TF monoclonal antibody (mAb A78-G/A7) on cell biological function were investigated by MTT assays, flow cytometry, adhesion assays and transwell experiments.

Results

Compared with normal individuals, TF-Ab levels in patients with TC were decreased, but no changes were observed with respect to lymph node metastasis. The expression of TF-Ag in TC tissues was relatively higher than that detected in adjacent tissues, but it was not affected by the presence or absence of lymph node metastasis. Upon treatment mAb A78-G/A7 treating, TC cell cycles were affected, meanwhile the abilities to adhere, invade and migrate were also significantly reduced.

Conclusion

The results of the present study showed that mAb A78-G/A7 could affect the invasion and migration of all assayed TC cell lines. The effects of mAb A78-G/A7 on the cell cycle, adhesion, invasion and migration of TC cells were more significant than those observed for proliferation and apoptosis.

GNE Myopathy: Etiology, Diagnosis, and Therapeutic Challenges

GNE myopathy, previously known as hereditary inclusion body myopathy (HIBM), or Nonaka myopathy, is a rare autosomal recessive muscle disease characterized by progressive skeletal muscle atrophy. It has an estimated prevalence of 1 to 9:1,000,000. GNE myopathy is caused by mutations in the GNE gene which encodes the rate-limiting enzyme of sialic acid biosynthesis. The pathophysiology of the disease is not entirely understood, but hyposialylation of muscle glycans is thought to play an essential role. The typical presentation is bilateral foot drop caused by weakness of the anterior tibialis muscles with onset in early adulthood. The disease slowly progresses over the next decades to involve skeletal muscles throughout the body, with relative sparing of the quadriceps until late stages of the disease. The diagnosis of GNE myopathy should be considered in young adults presenting with bilateral foot drop. Histopathologic findings on muscle biopsies include fiber size variation, atrophic fibers, lack of inflammation, and the characteristic "rimmed" vacuoles on modified Gomori trichome staining. The diagnosis is confirmed by the presence of pathogenic (mostly missense) mutations in both alleles of the GNE gene. Although there is no approved therapy for this disease, preclinical and clinical studies of several potential therapies are underway, including substrate replacement and gene therapy-based strategies. However, developing therapies for GNE myopathy is complicated by several factors, including the rare incidence of disease, limited preclinical models, lack of reliable biomarkers, and slow disease progression.

Analysis of carbohydrates and glycoconjugates by matrix-assisted laser desorption/ionization mass spectrometry: An update for 2013-2014

This review is the eighth update of the original article published in 1999 on the application of Matrix-assisted laser desorption/ionization mass spectrometry (MALDI) mass spectrometry to the analysis of carbohydrates and glycoconjugates and brings coverage of the literature to the end of 2014. Topics covered in the first part of the review include general aspects such as theory of the MALDI process, matrices, derivatization, MALDI imaging, fragmentation, and arrays. The second part of the review is devoted to applications to various structural types such as oligo- and poly- saccharides, glycoproteins, glycolipids, glycosides, and biopharmaceuticals. Much of this material is presented in tabular form. The third part of the review covers medical and industrial applications of the technique, studies of enzyme reactions, and applications to chemical synthesis. © 2018 Wiley Periodicals, Inc. Mass Spec Rev 37:353-491, 2018.

GNE myopathy: from clinics and genetics to pathology and research strategies

GNE myopathy is an ultra-rare autosomal recessive disease, which starts as a distal muscle weakness and ultimately leads to a wheelchair bound state. Molecular research and animal modelling significantly moved forward understanding of GNE myopathy mechanisms and suggested therapeutic interventions to alleviate the symptoms. Multiple therapeutic attempts are being made to supplement sialic acid depleted in GNE myopathy muscle cells. Translational research field provided valuable knowledge through natural history studies, patient registries and clinical trial, which significantly contributed to bringing forward an era of GNE myopathy treatment. In this review, we are summarising current GNE myopathy, scientific trends and open questions, which would be of significant interest for a wide neuromuscular diseases community.

CDG Therapies: From Bench to Bedside

Congenital disorders of glycosylation (CDG) are a group of genetic disorders that affect protein and lipid glycosylation and glycosylphosphatidylinositol synthesis. More than 100 different disorders have been reported and the number is rapidly increasing. Since glycosylation is an essential post-translational process, patients present a large range of symptoms and variable phenotypes, from very mild to extremely severe. Only for few CDG, potentially curative therapies are being used, including dietary supplementation (e.g., galactose for PGM1-CDG, fucose for SLC35C1-CDG, Mn²⁺ for TMEM165-CDG or mannose for MPI-CDG) and organ transplantation (e.g., liver for MPI-CDG and heart for DOLK-CDG). However, for the majority of patients, only symptomatic and preventive treatments are in use. This constitutes a burden for patients, care-givers and ultimately the healthcare system. Innovative diagnostic approaches, in vitro and in vivo models and novel biomarkers have been developed that can lead to novel therapeutic avenues aiming to ameliorate the patients’ symptoms and lives. This review summarizes the advances in therapeutic approaches for CDG.

A One-Step Chemoenzymatic Labeling Strategy for Probing Sialylated Thomsen-Friedenreich Antigen

Abnormal expression of sialylated Thomsen-Friedenreich antigen (Neu5Acα2-3Galβ1-3GalNAcα-O-Ser/Thr, sialyl-T) has a strong relationship with various types of human cancers and many other diseases. However, the size and structural complexity, and relatively lower abundance of sialyl-T have posed a significant challenge to its detection. Therefore, details about the role of sialyl-T in a variety of physiological and pathological processes are still poorly understood. Here, a one-step chemoenzymatic labeling strategy to probe sialyl-T is described. This approach enables the sensitive, selective, and rapid detection of sialyl-T, and global profiling and identification of unknown sialyl-T-attached glycoproteins, which are potential therapeutic targets or biomarkers. The use of one-step labeling strategy not only has a higher sensitivity than a typical two-step reporter strategy but also avoids undergoing an additional chemical reaction step to introduce a reporter group after the labeling reaction, making it particularly useful for detecting low-abundance glycan epitopes on living cells.

Quantification of lectin fluorescence in GNE myopathy muscle biopsies

INTRODUCTION

GNE myopathy is an adult-onset muscle disorder characterized by impaired sialylation of (muscle) glycans, detectable by lectin histochemistry. We describe a standardized method to quantify (lectin-) fluorescence in muscle sections, applicable for diagnosis and response to therapy for GNE myopathy.

METHODS

Muscle sections were fluorescently labeled with the sialic acid-binding Sambucus nigra agglutinin (SNA) lectin and antibodies to sarcolemma residence protein caveolin-3 (CAV-3). Entire tissue sections were imaged in tiles and fluorescence was quantified.

RESULTS

SNA fluorescence co-localizing with CAV-3 was ∼50% decreased in GNE myopathy biopsies compared with muscle-matched controls, confirming previous qualitative results.

DISCUSSION

This quantitative fluorescence method can accurately determine sialylation status of GNE myopathy muscle biopsies. This method is adaptable for expression of other membrane-associated muscle proteins, and may be of benefit for disorders in which therapeutic changes in expression are subtle and difficult to assess by other methods. Muscle Nerve 58: 286-292, 2018.

Substantial deficiency of free sialic acid in muscles of patients with GNE myopathy and in a mouse model

GNE myopathy (GNEM), also known as hereditary inclusion body myopathy (HIBM), is a late- onset, progressive myopathy caused by mutations in the GNE gene encoding the enzyme responsible for the first regulated step in the biosynthesis of sialic acid (SA). The disease is characterized by distal muscle weakness in both the lower and upper extremities, with the quadriceps muscle relatively spared until the late stages of disease. To explore the role of SA synthesis in the disease, we conducted a comprehensive and systematic analysis of both free and total SA levels in a large cohort of GNEM patients and a mouse model. A sensitive LC/MS/MS assay was developed to quantify SA in serum and muscle homogenates. Mean serum free SA level was 0.166 μg/mL in patients and 18% lower (p<0.001) than that of age-matched control samples (0.203 μg/mL). In biopsies obtained from patients, mean free SA levels of different muscles ranged from 0.046–0.075 μg/μmol Cr and were markedly lower by 72–85% (p<0.001) than free SA from normal controls. Free SA was shown to constitute a small fraction (3–7%) of the total SA pool in muscle tissue. Differences in mean total SA levels in muscle from patients compared with normal controls were less distinct and more variable between different muscles, suggesting a small subset of sialylation targets could be responsible for the pathogenesis of GNEM. Normal quadriceps had significantly lower levels of free SA (reduced by 39%) and total SA (reduced by 53%) compared to normal gastrocnemius. A lower SA requirement for quadriceps may be linked to the reported quadriceps sparing in GNEM. Analysis of SA levels in Gne^M743T/M743T mutant mice corroborated the human study results. These results show that serum and muscle free SA is severely reduced in GNEM, which is consistent with the biochemical defect in SA synthesis associated with GNE mutations. These results therefore support the approach of reversing SA depletion as a potential treatment for GNEM patients.

Genetic defects in the hexosamine and sialic acid biosynthesis pathway

BACKGROUND

Congenital disorders of glycosylation are caused by defects in the glycosylation of proteins and lipids. Classically, gene defects with multisystem disease have been identified in the ubiquitously expressed glycosyltransferases required for protein N-glycosylation. An increasing number of defects are being described in sugar supply pathways for protein glycosylation with tissue-restricted clinical symptoms.

SCOPE OF REVIEW

In this review, we address the hexosamine and sialic acid biosynthesis pathways in sugar metabolism. GFPT1, PGM3 and GNE are essential for synthesis of nucleotide sugars uridine diphosphate N-acetylglucosamine (UDP-GlcNAc) and cytidine-5'-monophospho-N-acetylneuraminic acid (CMP-sialic acid) as precursors for various glycosylation pathways. Defects in these enzymes result in contrasting clinical phenotypes of congenital myasthenia, immunodeficiency or adult-onset myopathy, respectively. We therefore discuss the biochemical mechanisms of known genetic defects in the hexosamine and CMP-sialic acid synthesis pathway in relation to the clinical phenotypes.

MAJOR CONCLUSIONS

Both UDP-GlcNAc and CMP-sialic acid are important precursors for diverse protein glycosylation reactions and for conversion into other nucleotide-sugars. Defects in the synthesis of these nucleotide sugars might affect a wide range of protein glycosylation reactions. Involvement of multiple glycosylation pathways might contribute to disease phenotype, but the currently available biochemical information on sugar metabolism is insufficient to understand why defects in these pathways present with tissue-specific phenotypes.

GENERAL SIGNIFICANCE

Future research on the interplay between sugar metabolism and different glycosylation pathways in a tissue- and cell-specific manner will contribute to elucidation of disease mechanisms and will create new opportunities for therapeutic intervention. This article is part of a Special Issue entitled "Glycans in personalised medicine" Guest Editor: Professor Gordan Lauc.

Glycosylation Analysis for Congenital Disorders of Glycosylation

Congenital disorders of glycosylation (CDG) are a group of diseases with highly variable phenotypes and inconsistent clinical features. Since the first description of a CDG in 1980, approximately 100 disorders have been identified. Most of these are defects in protein glycosylation, although an increasing number are defects of glycolipid or proteoglycan biosynthesis. A group of biochemical markers has been used to characterize protein glycosylation abnormalities in CDG. This unit describes three protocols that can be used to measure plasma or serum carbohydrate deficient transferrin (CDT) profile, N-glycan profile, and O-glycan profile by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) or liquid chromatography-electrospray ionization-tandem mass spectrometry (LC-ESI-MS). The quantification of particular biomarkers, such as T antigens or sialylated T antigens, could also be achieved by liquid chromatography-tandem mass spectrometry (LC-MS/MS). These techniques can be used to identify a majority of patients with defects in protein glycosylation, although different techniques, such as flow cytometry with immunostaining, are necessary to detect defects in glycolipid or proteoglycan biosynthesis which is not included in this unit.