A mutation in human CMP-sialic acid hydroxylase occurred after the Homo-Pan divergence

Serum Antibodies to N-Glycolylneuraminic Acid Are Elevated in Duchenne Muscular Dystrophy and Correlate with Increased Disease Pathology in Cmah-/-mdx Mice

Humans cannot synthesize the common mammalian sialic acid N-glycolylneuraminic acid (Neu5Gc) because of an inactivating deletion in the cytidine-5'-monophospho-(CMP)-N-acetylneuraminic acid hydroxylase (CMAH) gene responsible for its synthesis. Human Neu5Gc deficiency can lead to development of anti-Neu5Gc serum antibodies, the levels of which can be affected by Neu5Gc-containing diets and by disease. Metabolic incorporation of dietary Neu5Gc into human tissues in the face of circulating antibodies against Neu5Gc-bearing glycans is thought to exacerbate inflammation-driven diseases like cancer and atherosclerosis. Probing of sera with sialoglycan arrays indicated that patients with Duchenne muscular dystrophy (DMD) had a threefold increase in overall anti-Neu5Gc antibody titer compared with age-matched controls. These antibodies recognized a broad spectrum of Neu5Gc-containing glycans. Human-like inactivation of the Cmah gene in mice is known to modulate severity in a variety of mouse models of human disease, including the X chromosome-linked muscular dystrophy (mdx) model for DMD. Cmah^-/-mdx mice can be induced to develop anti-Neu5Gc-glycan antibodies as humans do. The presence of anti-Neu5Gc antibodies, in concert with induced Neu5Gc expression, correlated with increased severity of disease pathology in Cmah^-/-mdx mice, including increased muscle fibrosis, expression of inflammatory markers in the heart, and decreased survival. These studies suggest that patients with DMD who harbor anti-Neu5Gc serum antibodies might exacerbate disease severity when they ingest Neu5Gc-rich foods, like red meats.

Sialic acid O-acetylation: From biosynthesis to roles in health and disease

Sialic acids are nine-carbon sugars that frequently cap glycans at the cell surface in cells of vertebrates as well as cells of certain types of invertebrates and bacteria. The nine-carbon backbone of sialic acids can undergo extensive enzymatic modification in nature and O-acetylation at the C-4/7/8/9 position in particular is widely observed. In recent years, the detection and analysis of O-acetylated sialic acids have advanced, and sialic acid-specific O-acetyltransferases (SOATs) and O-acetylesterases (SIAEs) that add and remove O-acetyl groups, respectively, have been identified and characterized in mammalian cells, invertebrates, bacteria, and viruses. These advances now allow us to draw a more complete picture of the biosynthetic pathway of the diverse O-acetylated sialic acids to drive the generation of genetically and biochemically engineered model cell lines and organisms with altered expression of O-acetylated sialic acids for dissection of their roles in glycoprotein stability, development, and immune recognition, as well as discovery of novel functions. Furthermore, a growing number of studies associate sialic acid O-acetylation with cancer, autoimmunity, and infection, providing rationale for the development of selective probes and inhibitors of SOATs and SIAEs. Here, we discuss the current insights into the biosynthesis and biological functions of O-acetylated sialic acids and review the evidence linking this modification to disease. Furthermore, we discuss emerging strategies for the design, synthesis, and potential application of unnatural O-acetylated sialic acids and inhibitors of SOATs and SIAEs that may enable therapeutic targeting of this versatile sialic acid modification.

Ape Origins of Human Malaria

African apes harbor at least twelve Plasmodium species, some of which have been a source of human infection. It is now well established that Plasmodium falciparum emerged following the transmission of a gorilla parasite, perhaps within the last 10,000 years, while Plasmodium vivax emerged earlier from a parasite lineage that infected humans and apes in Africa before the Duffy-negative mutation eliminated the parasite from humans there. Compared to their ape relatives, both human parasites have greatly reduced genetic diversity and an excess of nonsynonymous mutations, consistent with severe genetic bottlenecks followed by rapid population expansion. A putative new Plasmodium species widespread in chimpanzees, gorillas, and bonobos places the origin of Plasmodium malariae in Africa. Here, we review what is known about the origins and evolutionary history of all human-infective Plasmodium species, the time and circumstances of their emergence, and the diversity, host specificity, and zoonotic potential of their ape counterparts.

Unveiling the Sugary Secrets of Plasmodium Parasites

Plasmodium parasites cause malaria disease, one of the leading global health burdens for humanity, infecting hundreds of millions of people each year. Different glycans on the parasite and the host cell surface play significant roles in both malaria pathogenesis and host defense mechanisms. So far, only small, truncated N- and O-glycans have been identified in Plasmodium species. In contrast, complex glycosylphosphatidylinositol (GPI) glycolipids are highly abundant on the parasite’s cell membrane and are essential for its survival. Moreover, the parasites express lectins that bind and exploit the host cell surface glycans for different aspects of the parasite life cycle, such as adherence, invasion, and evasion of the host immune system. In parallel, the host cell glycocalyx and lectin expression serve as the first line of defense against Plasmodium parasites and directly dictate susceptibility to Plasmodium infection. This review provides an overview of the glycobiology involved in Plasmodium-host interactions and its contribution to malaria pathogenesis. Recent findings are presented and evaluated in the context of potential therapeutic exploitation.

Multiple Genomic Events Altering Hominin SIGLEC Biology and Innate Immunity Predated the Common Ancestor of Humans and Archaic Hominins

Human-specific pseudogenization of the CMAH gene eliminated the mammalian sialic acid (Sia) Neu5Gc (generating an excess of its precursor Neu5Ac), thus changing ubiquitous cell surface “self-associated molecular patterns” that modulate innate immunity via engagement of CD33-related-Siglec receptors. The Alu-fusion-mediated loss-of-function of CMAH fixed ∼2–3 Ma, possibly contributing to the origins of the genus Homo. The mutation likely altered human self-associated molecular patterns, triggering multiple events, including emergence of human-adapted pathogens with strong preference for Neu5Ac recognition and/or presenting Neu5Ac-containing molecular mimics of human glycans, which can suppress immune responses via CD33-related-Siglec engagement. Human-specific alterations reported in some gene-encoding Sia-sensing proteins suggested a “hotspot” in hominin evolution. The availability of more hominid genomes including those of two extinct hominins now allows full reanalysis and evolutionary timing. Functional changes occur in 8/13 members of the human genomic cluster encoding CD33-related Siglecs, all predating the human common ancestor. Comparisons with great ape genomes indicate that these changes are unique to hominins. We found no evidence for strong selection after the Human–Neanderthal/Denisovan common ancestor, and these extinct hominin genomes include almost all major changes found in humans, indicating that these changes in hominin sialobiology predate the Neanderthal–human divergence ∼0.6 Ma. Multiple changes in this genomic cluster may also explain human-specific expression of CD33rSiglecs in unexpected locations such as amnion, placental trophoblast, pancreatic islets, ovarian fibroblasts, microglia, Natural Killer(NK) cells, and epithelia. Taken together, our data suggest that innate immune interactions with pathogens markedly altered hominin Siglec biology between 0.6 and 2 Ma, potentially affecting human evolution.

Sialic Acids as Receptors for Pathogens

Carbohydrates have long been known to mediate intracellular interactions, whether within one organism or between different organisms. Sialic acids (Sias) are carbohydrates that usually occupy the terminal positions in longer carbohydrate chains, which makes them common recognition targets mediating these interactions. In this review, we summarize the knowledge about animal disease-causing agents such as viruses, bacteria and protozoa (including the malaria parasite Plasmodium falciparum) in which Sias play a role in infection biology. While Sias may promote binding of, e.g., influenza viruses and SV40, they act as decoys for betacoronaviruses. The presence of two common forms of Sias, Neu5Ac and Neu5Gc, is species-specific, and in humans, the enzyme converting Neu5Ac to Neu5Gc (CMAH, CMP-Neu5Ac hydroxylase) is lost, most likely due to adaptation to pathogen regimes; we discuss the research about the influence of malaria on this trait. In addition, we present data suggesting the CMAH gene was probably present in the ancestor of animals, shedding light on its glycobiology. We predict that a better understanding of the role of Sias in disease vectors would lead to more effective clinical interventions.

A mobile technology-based cooperative learning platform for undergraduate biology courses in common college classrooms

As a high-impact educational practice, cooperative learning uses a structured group study to promote students' active learning. Currently, it lacks economical yet effective tools to facilitate the interactive nature of structured cooperative learning in regular classrooms. Here, we have established a mobile technology-based cooperative learning (MBCL) platform that comprises the 2018 iPad, Apple Pencil, LiveBoard, Google Forms, and Google Drive. We tested the MBCL platform in multiple undergraduate biology courses. During semester-long MBCL studies, the students engaged in cooperative learning to discuss a real-life issue or chapter-based contents. With the MBCL platform, the students' group study processes were shown on shared, visible electronic whiteboards that were updated in real-time, generating visible thinking and instant, interactive communication. The instructor was able to guide the students promptly to conduct knowledge integration and knowledge synthesis using tables and diagrams. The deep learning outcome was evident in the examples and quantitative analyses of students' whiteboard study results and team presentations. Thus, integrating innovative mobile technologies into high-impact teaching practices, exemplified by the MBCL platform, promotes deep learning in higher education.

The sialyl-O-acetylesterase NanS of Tannerella forsythia encompasses two catalytic modules with different regiospecificity for O7 and O9 of sialic acid

The periodontal pathogen Tannerella forsythia utilizes host sialic acids as a nutrient source. To also make O-acetylated sialyl residues susceptible to the action of its sialidase and sialic acid up-take system, Tannerella produces NanS, an O-acetylesterase with two putative catalytic domains. Here, we analyzed NanS by homology modeling, predicted a catalytic serine-histidine-aspartate triad for each catalytic domain and performed individual domain inactivation by single alanine exchanges of the triad nucleophiles S32 and S311. Subsequent functional analyses revealed that both domains possess sialyl-O-acetylesterase activity, but differ in their regioselectivity with respect to position O9 and O7 of sialic acid. The 7-O-acetylesterase activity inherent to the C-terminal domain of NanS is unique among sialyl-O-acetylesterases and fills the current gap in tools targeting 7-O-acetylation. Application of the O7-specific variant NanS-S32A allowed us to evidence the presence of cellular 7,9-di-O-acetylated sialoglycans by monitoring the gain in 9-O-acetylation upon selective removal of acetyl groups from O7. Moreover, we established de-7,9-O-acetylation by wild-type NanS as an easy and efficient method to validate the specific binding of three viral lectins commonly used for the recognition of (7),9-O-acetylated sialoglycans. Their binding critically depends on an acetyl group in O9, yet de-7,9-O-acetylation proved advantageous over de-9-O-acetylation as the additional removal of the 7-O-acetyl group eliminated ligand formation by 7,9-ester migration. Together, our data show that NanS gained dual functionality through recruitment of two esterase modules with complementary activities. This enables Tannerella to scavenge 7,9-di-O-acetylated sialyl residues and provides a novel, O7-specific tool for studying sialic acid O-acetylation.

Origin and evolution of nonulosonic acid synthases and their relationship with bacterial pathogenicity revealed by a large-scale phylogenetic analysis

Nonulosonic acids (NulOs) are a group of nine-carbon monosaccharides with different functions in nature. N-acetylneuraminic acid (Neu5Ac) is the most common NulO. It covers the membrane surface of all human cells and is a central molecule in the process of self-recognition via SIGLECS receptors. Some pathogenic bacteria escape the immune system by copying the sialylation of the host cell membrane. Neu5Ac production in these bacteria is catalysed by the enzyme NeuB. Some bacteria can also produce other NulOs named pseudaminic and legionaminic acids, through the NeuB homologues PseI and LegI, respectively. In Opisthokonta eukaryotes, the biosynthesis of Neu5Ac is catalysed by the enzyme NanS. In this study, we used publicly available data of sequences of NulOs synthases to investigate its distribution within the three domains of life and its relationship with pathogenic bacteria. We mined the KEGG database and found 425 NeuB sequences. Most NeuB sequences (58.74 %) from the KEGG orthology database were classified as from environmental bacteria; however, sequences from pathogenic bacteria showed higher conservation and prevalence of a specific domain named SAF. Using the HMM profile we identified 13 941 NulO synthase sequences in UniProt. Phylogenetic analysis of these sequences showed that the synthases were divided into three main groups that can be related to the lifestyle of these bacteria: (I) predominantly environmental, (II) intermediate and (III) predominantly pathogenic. NeuB was widely distributed in the groups. However, LegI and PseI were more concentrated in groups II and III, respectively. We also found that PseI appeared later in the evolutionary process, derived from NeuB. We use this same methodology to retrieve sialic acid synthase sequences from Archaea and Eukarya. A large-scale phylogenetic analysis showed that while the Archaea sequences are spread across the tree, the eukaryotic NanS sequences were grouped in a specific branch in group II. None of the bacterial NanS sequences grouped with the eukaryotic branch. The analysis of conserved residues showed that the synthases of Archaea and Eukarya present a mutation in one of the three catalytic residues, an E134D change, related to a Neisseria meningitidis reference sequence. We also found that the conservation profile is higher between NeuB of pathogenic bacteria and NanS of eukaryotes than between NeuB of environmental bacteria and NanS of eukaryotes. Our large-scale analysis brings new perspectives on the evolution of NulOs synthases, suggesting their presence in the last common universal ancestor.

Virus-Induced Changes of the Respiratory Tract Environment Promote Secondary Infections With Streptococcus pneumoniae

Secondary bacterial infections enhance the disease burden of influenza infections substantially. Streptococcus pneumoniae (the pneumococcus) plays a major role in the synergism between bacterial and viral pathogens, which is based on complex interactions between the pathogen and the host immune response. Here, we discuss mechanisms that drive the pathogenesis of a secondary pneumococcal infection after an influenza infection with a focus on how pneumococci senses and adapts to the influenza-modified environment. We briefly summarize what is known regarding secondary bacterial infection in relation to COVID-19 and highlight the need to improve our current strategies to prevent and treat viral bacterial coinfections.

One-Step Generation of Multiple Gene-Edited Pigs by Electroporation of the CRISPR/Cas9 System into Zygotes to Reduce Xenoantigen Biosynthesis

Xenoantigens cause hyperacute rejection and limit the success of interspecific xenografts. Therefore, genes involved in xenoantigen biosynthesis, such as GGTA1, CMAH, and B4GALNT2, are key targets to improve the outcomes of xenotransplantation. In this study, we introduced a CRISPR/Cas9 system simultaneously targeting GGTA1, CMAH, and B4GALNT2 into in vitro-fertilized zygotes using electroporation for the one-step generation of multiple gene-edited pigs without xenoantigens. First, we optimized the combination of guide RNAs (gRNAs) targeting GGTA1 and CMAH with respect to gene editing efficiency in zygotes, and transferred electroporated embryos with the optimized gRNAs and Cas9 into recipient gilts. Next, we optimized the Cas9 protein concentration with respect to the gene editing efficiency when GGTA1, CMAH, and B4GALNT2 were targeted simultaneously, and generated gene-edited pigs using the optimized conditions. We achieved the one-step generation of GGTA1/CMAH double-edited pigs and GGTA1/CMAH/B4GALNT2 triple-edited pigs. Immunohistological analyses demonstrated the downregulation of xenoantigens; however, these multiple gene-edited pigs were genetic mosaics that failed to knock out some xenoantigens. Although mosaicism should be resolved, the electroporation technique could become a primary method for the one-step generation of multiple gene modifications in pigs aimed at improving pig-to-human xenotransplantation.

Current Perspective of Sialylated Milk Oligosaccharides in Mammalian Milk: Implications for Brain and Gut Health of Newborns

Human milk oligosaccharides (HMOs) are the third most abundant solid component after lactose and lipids of breast milk. All mammal milk contains soluble oligosaccharides, including neutral milk oligosaccharides (NMOs) without sialic acid (Sia) moieties and acidic oligosaccharides or sialylated milk oligosaccharides (SMOs) with Sia residues at the end of sugar chains. The structural, biological diversity, and concentration of milk oligosaccharides in mammalian milk are significantly different among species. HMOs have multiple health benefits for newborns, including development of immune system, modification of the intestinal microbiota, anti-adhesive effect against pathogens, and brain development. Most infant formulas lack oligosaccharides which resemble HMOs. Formula-fed infants perform poorly across physical and psychological wellbeing measures and suffer health disadvantages compared to breast-fed infants due to the differences in the nutritional composition of breast milk and infant formula. Of these milk oligosaccharides, SMOs are coming to the forefront of research due to the beneficial nature of Sia. This review aims to critically discuss the current state of knowledge of the biology and role of SMOs in human milk, infant formula milks, and milk from several other species on gut and brain health of human and animal offspring.

Glycans in Immunologic Health and Disease

The surfaces of all living organisms and most secreted proteins share a common feature: They are glycosylated. As the outermost-facing molecules, glycans participate in nearly all immunological processes, including driving host-pathogen interactions, immunological recognition and activation, and differentiation between self and nonself through a complex array of pathways and mechanisms. These fundamental immunologic roles are further cast into sharp relief in inflammatory, autoimmune, and cancer disease states in which immune regulation goes awry. Here, we review the broad impact of glycans on the immune system and discuss the changes and clinical opportunities associated with the onset of immunologic disease.

Identification of chicken-derived scFv against N-glycolylneuraminic acid retrieved from an immune library by phage display

N- glycolylneuraminic acid (Neu5Gc) is a type of sialic acid, it can be synthesized by a range of mammals except chickens and healthy human. After entering human body, Neu5Gc in foods such as red meat and milk can cause chronic inflammation, thus promoting the development of cancer and related diseases. In this study, we identified a gene sequence of Neu5Gc-specific single-chain variable fragment (ScFv) by phage display from a primary chicken antibodies library. Then the gene sequence was used to express a 29 kDa anti-Neu5Gc ScFv protein as detection probe in competitive inhibition ELISA (IC-ELISA). The linear regression equation of the IC-ELISA was y = 23.12x+33.19 (R = 0.980), and the half-maximal inhibitory concentration (IC50) and the limit of detection (LOD) was 5.333 and 0.66 μg/mL. The mean recovery of the spiked samples was 83.04%, and the intra-assay and inter-assay coefficients of variation (CVs) were both 5.59%. The results suggested that the specific anti-Neu5Gc ScFv is a promising probe for the development of IC-ELISA and test strip in order to detect the presence of Neu5Gc in red meat, milk, and tumor tissues.

Immunotherapy approaches targeting neuroblastoma

PURPOSE OF REVIEW

In the era of immune-oncology, a breakthrough in the field of pediatric solid tumor research has been the demonstration that immunotherapy for patients with high-risk neuroblastoma improves the event-free and overall survival. Immunotherapeutic approaches including a monoclonal antibody targeting the cell surface glycosphingolipid disialoganglioside and cytokines successfully eliminate minimal residual disease.

RECENT FINDINGS

Since this seminal discovery, clinical trials evaluating immunotherapy in combination with chemotherapy and cellular therapies have begun to demonstrate effectiveness in treatment of bulky disease. Broader knowledge has also been gained regarding immunotherapy-limiting side-effects. Furthermore, biologic studies in actively treated patients have contributed to our growing understanding of the underlying immunologic processes and mechanisms of tumor response and immune evasion.

SUMMARY

The example of neuroblastoma is beginning to demonstrate that various immunotherapies combined with more conventional anticancer treatments can be synergistic. These advancements pose new challenges to both clinical researchers and medical provider and herald a new era in pediatric cancer therapy.

Sialic Acids and Their Influence on Human NK Cell Function

Sialic acids are sugars with a nine-carbon backbone, present on the surface of all cells in humans, including immune cells and their target cells, with various functions. Natural Killer (NK) cells are cells of the innate immune system, capable of killing virus-infected and tumor cells. Sialic acids can influence the interaction of NK cells with potential targets in several ways. Different NK cell receptors can bind sialic acids, leading to NK cell inhibition or activation. Moreover, NK cells have sialic acids on their surface, which can regulate receptor abundance and activity. This review is focused on how sialic acids on NK cells and their target cells are involved in NK cell function.

Exploring the Impact of Ketodeoxynonulosonic Acid in Host-Pathogen Interactions Using Uptake and Surface Display by Nontypeable Haemophilus influenzae

All cells in vertebrates are coated with a dense array of glycans often capped with sugars called sialic acids. Sialic acids have many functions, including serving as a signal for recognition of “self” cells by the immune system, thereby guiding an appropriate immune response against foreign “nonself” and/or damaged cells.

Surface expression of the common vertebrate sialic acid (Sia) N-acetylneuraminic acid (Neu5Ac) by commensal and pathogenic microbes appears structurally to represent “molecular mimicry” of host sialoglycans, facilitating multiple mechanisms of host immune evasion. In contrast, ketodeoxynonulosonic acid (Kdn) is a more ancestral Sia also present in prokaryotic glycoconjugates that are structurally quite distinct from vertebrate sialoglycans. We detected human antibodies against Kdn-terminated glycans, and sialoglycan microarray studies found these anti-Kdn antibodies to be directed against Kdn-sialoglycans structurally similar to those on human cell surface Neu5Ac-sialoglycans. Anti-Kdn-glycan antibodies appear during infancy in a pattern similar to those generated following incorporation of the nonhuman Sia N-glycolylneuraminic acid (Neu5Gc) onto the surface of nontypeable Haemophilus influenzae (NTHi), a human commensal and opportunistic pathogen. NTHi grown in the presence of free Kdn took up and incorporated the Sia into its lipooligosaccharide (LOS). Surface display of the Kdn within NTHi LOS blunted several virulence attributes of the pathogen, including Neu5Ac-mediated resistance to complement and whole blood killing, complement C3 deposition, IgM binding, and engagement of Siglec-9. Upper airway administration of Kdn reduced NTHi infection in human-like Cmah null (Neu5Gc-deficient) mice that express a Neu5Ac-rich sialome. We propose a mechanism for the induction of anti-Kdn antibodies in humans, suggesting that Kdn could be a natural and/or therapeutic “Trojan horse” that impairs colonization and virulence phenotypes of free Neu5Ac-assimilating human pathogens.

The influence of evolutionary history on human health and disease

Nearly all genetic variants that influence disease risk have human-specific origins; however, the systems they influence have ancient roots that often trace back to evolutionary events long before the origin of humans. Here, we review how advances in our understanding of the genetic architectures of diseases, recent human evolution and deep evolutionary history can help explain how and why humans in modern environments become ill. Human populations exhibit differences in the prevalence of many common and rare genetic diseases. These differences are largely the result of the diverse environmental, cultural, demographic and genetic histories of modern human populations. Synthesizing our growing knowledge of evolutionary history with genetic medicine, while accounting for environmental and social factors, will help to achieve the promise of personalized genomics and realize the potential hidden in an individual's DNA sequence to guide clinical decisions. In short, precision medicine is fundamentally evolutionary medicine, and integration of evolutionary perspectives into the clinic will support the realization of its full potential.

Porcine genome engineering for xenotransplantation

The extreme shortage of human donor organs for treatment of patients with end-stage organ failures is well known. Xenotransplantation, which might provide unlimited organ supply, is a most promising strategy to solve this problem. Domestic pigs are regarded as ideal organ-source animals owing to similarity in anatomy, physiology and organ size to humans as well as high reproductive capacity and low maintenance cost. However, several barriers, which include immune rejection, inflammation and coagulative dysfunctions, as well as the cross-species transmission risk of porcine endogenous retrovirus, blocked the pig-to-human xenotransplantation. With the rapid development of genome engineering technologies and the potent immunosuppressive medications in recent years, these barriers could be eliminated through genetic modification of pig genome together with the administration of effective immunosuppressants. A number of candidate genes involved in the regulation of immune response, inflammation and coagulation have been explored to optimize porcine xenograft survival in non-human primate recipients. PERV inactivation in pigs has also been accomplished to firmly address the safety issue in pig-to-human xenotransplantation. Many encouraging preclinical milestones have been achieved with some organs surviving for years. Therefore, the clinical trials of some promising organs, such as islet, kidney and heart, are aimed to be launched in the near future.

Effects of Dietary 5'-CMP on Neu5Gc Contents in the Muscle and Viscera of Xiang Pigs

ABSTRACT

In order to reduce the health risks associated with red meat as listed by the World Health Organization, the work presented in this article aimed to elucidate the interaction between 5'-CMP-supplemented feed and N-glycolylneuraminic acid (Neu5Gc) in experimental animals in vivo. 5'-CMP was added to the diet of 90-, 180-, and 270-day-old Xiang pigs, and after 30 days, the Neu5Gc contents, physicochemical parameters, and free amino acid contents of muscle and internal viscera were measured by high-performance liquid chromatography coupled with fluorescence detection. The mechanism by which 5'-CMP affects Neu5Gc contents was investigated using molecular docking. Results show that 5'-CMP significantly decreased the Neu5Gc content in 180-day-old Xiang pigs (P < 0.05) but had no effect on the Neu5Gc contents in 90- and 270-day-old Xiang pigs. Umami amino acids were significantly increased in 180-day-old Xiang pigs. In the 90- and 270-day-old pigs, histidine increased by 10.38 and 17.87%, respectively. The other free amino acids were either reduced or not affected. Moreover, the 5'-CMP-supplemented diet did not affect the physicochemical parameters of the longissimus muscle in the Xiang pigs. 5'-CMP could occupy almost all the sialyltransferase active-site residues but not His302 and showed inhibition of the sialyltransferase activity. The results provided an experimental basis for the subsequent reduction of Neu5Gc in red meat before slaughter.

HIGHLIGHTS

Human-specific polymorphic pseudogenization of SIGLEC12 protects against advanced cancer progression

Compared with our closest living evolutionary cousins, humans appear unusually prone to develop carcinomas (cancers arising from epithelia). The SIGLEC12 gene, which encodes the Siglec-XII protein expressed on epithelial cells, has several uniquely human features: a fixed homozygous missense mutation inactivating its natural ligand recognition property; a polymorphic frameshift mutation eliminating full-length protein expression in ~60%-70% of worldwide human populations; and, genomic features suggesting a negative selective sweep favoring the pseudogene state. Despite the loss of canonical sialic acid binding, Siglec-XII still recruits Shp2 and accelerates tumor growth in a mouse model. We hypothesized that dysfunctional Siglec-XII facilitates human carcinoma progression, correlating with known tumorigenic signatures of Shp2-dependent cancers. Immunohistochemistry was used to detect Siglec-XII expression on tissue microarrays. PC-3 prostate cancer cells were transfected with Siglec-XII and transcription of genes enriched with Siglec-XII was determined. Genomic SIGLEC12 status was determined for four different cancer cohorts. Finally, a dot blot analysis of human urinary epithelial cells was established to determine the Siglec-XII expressors versus non-expressors. Forced expression in a SIGLEC12 null carcinoma cell line enriched transcription of genes associated with cancer progression. While Siglec-XII was detected as expected in ~30%-40% of normal epithelia, ~80% of advanced carcinomas showed strong expression. Notably, >80% of late-stage colorectal cancers had a functional SIGLEC12 allele, correlating with overall increased mortality. Thus, advanced carcinomas are much more likely to occur in individuals whose genomes have an intact SIGLEC12 gene, likely because the encoded Siglec-XII protein recruits Shp2-related oncogenic pathways. The finding has prognostic, diagnostic, and therapeutic implications.

The non-human glycan, N-glycolylneuraminic acid (Neu5Gc), is not expressed in all organs and skeletal muscles of nine animal species

Red meat-derived sialic acid (Sia), N-glycolylneuraminic acid (Neu5Gc), promotes the risk of carcinoma and inflammation. Expression in skeletal muscle and organs across animal species remains unknown. We measured Neu5Gc in skeletal muscle and organ tissues from nine species using UHPLC and found that: (1) neu5Gc concentration in skeletal muscle was highest in goats (166 ± 48.7 µg/g protein), followed by cattle, pig, sheep, horse, cat and deer: >75% was conjugated. No Neu5Gc was detected in kangaroo and dog muscles; (2) total Neu5Gc in organ meats was generally about 2-54% higher than in muscle. Surprisingly Neu5Gc was absent in seven organs of female deer; (3) nine commercial ovine meat cuts contained similar Neu5Gc levels. Thus, red meat Neu5Gc concentration is tissue and species-specific and absent in muscle and organ tissue of some species. Our study provides guidelines for animal meat preferences for consumers and sheds light on the functionality of Neu5Gc.

Global view of human protein glycosylation pathways and functions

Glycosylation is the most abundant and diverse form of post-translational modification of proteins that is common to all eukaryotic cells. Enzymatic glycosylation of proteins involves a complex metabolic network and different types of glycosylation pathways that orchestrate enormous amplification of the proteome in producing diversity of proteoforms and its biological functions. The tremendous structural diversity of glycans attached to proteins poses analytical challenges that limit exploration of specific functions of glycosylation. Major advances in quantitative transcriptomics, proteomics and nuclease-based gene editing are now opening new global ways to explore protein glycosylation through analysing and targeting enzymes involved in glycosylation processes. In silico models predicting cellular glycosylation capacities and glycosylation outcomes are emerging, and refined maps of the glycosylation pathways facilitate genetic approaches to address functions of the vast glycoproteome. These approaches apply commonly available cell biology tools, and we predict that use of (single-cell) transcriptomics, genetic screens, genetic engineering of cellular glycosylation capacities and custom design of glycoprotein therapeutics are advancements that will ignite wider integration of glycosylation in general cell biology.

Influenza D virus

Influenza D is the only type of influenza virus that mainly affects cattle with frequent spillover to other species. Since the initial description of influenza D virus (IDV) in 2011, the virus has been found to circulate among cattle and swine populations worldwide. Research conducted during the past several years has led to an increased understanding of this novel influenza virus with bovines as a reservoir. In this review, we describe the current knowledge of epidemiology and host range of IDV followed by discussion of infection biology and animal model development for IDV. Finally, we review progress towards understanding of the pathogenesis and host response of IDV as well as developing preventive vaccines for IDV.

Host Synthesized Carbohydrate Antigens on Viral Glycoproteins as "Achilles' Heel" of Viruses Contributing to Anti-Viral Immune Protection

The glycans on enveloped viruses are synthesized by host-cell machinery. Some of these glycans on zoonotic viruses of mammalian reservoirs are recognized by human natural antibodies that may protect against such viruses. These antibodies are produced mostly against carbohydrate antigens on gastrointestinal bacteria and fortuitously, they bind to carbohydrate antigens synthesized in other mammals, neutralize and destroy viruses presenting these antigens. Two such antibodies are: anti-Gal binding to α-gal epitopes synthesized in non-primate mammals, lemurs, and New World monkeys, and anti-N-glycolyl neuraminic acid (anti-Neu5Gc) binding to N-glycolyl-neuraminic acid (Neu5Gc) synthesized in apes, Old World monkeys, and many non-primate mammals. Anti-Gal appeared in Old World primates following accidental inactivation of the α1,3galactosyltransferase gene 20–30 million years ago. Anti-Neu5Gc appeared in hominins following the inactivation of the cytidine-monophosphate-N-acetyl-neuraminic acid hydroxylase gene, which led to the loss of Neu5Gc <6 million-years-ago. It is suggested that an epidemic of a lethal virus eliminated ancestral Old World-primates synthesizing α-gal epitopes, whereas few mutated offspring lacking α-gal epitopes and producing anti-Gal survived because anti-Gal destroyed viruses presenting α-gal epitopes, following replication in parental populations. Similarly, anti-Neu5Gc protected few mutated hominins lacking Neu5Gc in lethal virus epidemics that eliminated parental hominins synthesizing Neu5Gc. Since α-gal epitopes are presented on many zoonotic viruses it is suggested that vaccines elevating anti-Gal titers may be of protective significance in areas endemic for such zoonotic viruses. This protection would be during the non-primate mammal to human virus transmission, but not in subsequent human to human transmission where the virus presents human glycans. In addition, production of viral vaccines presenting multiple α-gal epitopes increases their immunogenicity because of effective anti-Gal-mediated targeting of vaccines to antigen presenting cells for extensive uptake of the vaccine by these cells.

Therapeutic Monosaccharides: Looking Back, Moving Forward

In this review, we focus on the metabolism of mammalian glycan-associated monosaccharides, where the vast majority of our current knowledge comes from research done during the 1960s and 1970s. Most monosaccharides enter the cell using distinct, often tissue specific transporters from the SLC2A family. If not catabolized, these monosaccharides can be activated to donor nucleotide sugars and used for glycan synthesis. Apart from exogenous and dietary sources, all monosaccharides and their associated nucleotide sugars can be synthesized de novo, using mostly glucose to produce all nine nucleotide sugars present in human cells. Today, monosaccharides are used as treatment options for a small number of rare genetic disorders and even some common conditions. Here, we cover therapeutic applications of these sugars and highlight biochemical gaps that must be revisited as we go forward.

N-glycolyl chondroitin synthesis using metabolically engineered E. coli

N-glycolyl chondroitin (Gc-CN) is a metabolite of N-glycolylneuraminic acid (Neu5Gc), a sialic acid that is commonly found in mammals, but not humans. Humans can incorporate exogenous Neu5Gc into their tissues from eating red meat. Neu5Gc cannot be biosynthesized by humans due to an evolutionary mutation and has been implicated in causing inflammation causing human diseases, such as cancer. The study Neu5Gc is important in evolutionary biology and the development of potential cancer biomarkers. Unfortunately, there are several limitations to detecting Neu5Gc. The elimination of Neu5Gc involves a degradative pathway leading to the incorporation of N-glycolyl groups into glycosaminoglycans (GAGs), such as Gc-CN. Gc-CN has been found in humans and in animals including mice, lamb and chimpanzees. Here, we present the biosynthesis of Gc-CN in bacteria by feeding chemically synthesized N-glycolylglucosamine to Escherichia coli. A metabolically engineered strain of E. coli K4, fed with glucose supplemented with GlcNGc, converted it to N-glycolylgalactosamine (GalNGc) that could then be utilized as a substrate in the chondroitin biosynthetic pathway. The final product, Gc-CN was converted to disaccharides using chondroitin lyase ABC and analyzed by liquid chromatography-tandem mass spectrometry with multiple reaction monitoring detection. This analysis showed the incorporation of GalNGc into the backbone of the chondroitin oligosaccharide.

Comprehensive structural glycomic characterization of the glycocalyxes of cells and tissues

The glycocalyx comprises glycosylated proteins and lipids and fcorms the outermost layer of cells. It is involved in fundamental inter- and intracellular processes, including non-self-cell and self-cell recognition, cell signaling, cellular structure maintenance, and immune protection. Characterization of the glycocalyx is thus essential to understanding cell physiology and elucidating its role in promoting health and disease. This protocol describes how to comprehensively characterize the glycocalyx N-glycans and O-glycans of glycoproteins, as well as intact glycolipids in parallel, using the same enriched membrane fraction. Profiling of the glycans and the glycolipids is performed using nanoflow liquid chromatography-mass spectrometry (nanoLC-MS). Sample preparation, quantitative LC-tandem MS (LC-MS/MS) analysis, and data processing methods are provided. In addition, we discuss glycoproteomic analysis that yields the site-specific glycosylation of membrane proteins. To reduce the amount of sample needed, N-glycan, O-glycan, and glycolipid analyses are performed on the same enriched fraction, whereas glycoproteomic analysis is performed on a separate enriched fraction. The sample preparation process takes 2-3 d, whereas the time spent on instrumental and data analyses could vary from 1 to 5 d for different sample sizes. This workflow is applicable to both cell and tissue samples. Systematic changes in the glycocalyx associated with specific glycoforms and glycoconjugates can be monitored with quantitation using this protocol. The ability to quantitate individual glycoforms and glycoconjugates will find utility in a broad range of fundamental and applied clinical studies, including glycan-based biomarker discovery and therapeutics.

Amino Acids Bearing Aromatic or Heteroaromatic Substituents as a New Class of Ligands for the Lysosomal Sialic Acid Transporter Sialin

Sialin, encoded by the SLC17A5 gene, is a lysosomal sialic acid transporter defective in Salla disease, a rare inherited leukodystrophy. It also enables metabolic incorporation of exogenous sialic acids, leading to autoantibodies against N-glycolylneuraminic acid in humans. Here, we identified a novel class of human sialin ligands by virtual screening and structure-activity relationship studies. The ligand scaffold is characterized by an amino acid backbone with a free carboxylate, an N-linked aromatic or heteroaromatic substituent, and a hydrophobic side chain. The most potent compound, 45 (LSP12-3129), inhibited N-acetylneuraminic acid 1 (Neu5Ac) transport in a non-competitive manner with IC₅₀ ≈ 2.5 μM, a value 400-fold lower than the K_M for Neu5Ac. In vitro and molecular docking studies attributed the non-competitive character to selective inhibitor binding to the Neu5Ac site in a cytosol-facing conformation. Moreover, compound 45 rescued the trafficking defect of the pathogenic mutant (R39C) causing Salla disease. This new class of cell-permeant inhibitors provides tools to investigate the physiological roles of sialin and help develop pharmacological chaperones for Salla disease.

GBA3: a polymorphic pseudogene in humans that experienced repeated gene loss during mammalian evolution

The gene encoding the cytosolic β-glucosidase GBA3 shows pseudogenization due to a truncated allele (rs358231) that is polymorphic in humans. Since this enzyme is involved in the transformation of many plant β-glycosides, this particular case of gene loss may have been influenced by dietary adaptations during evolution. In humans, apart from the inactivating allele, we found that GBA3 accumulated additional damaging mutations, implying an extensive GBA3 loss. The allelic distribution of loss-of-function alleles revealed significant differences between human populations which can be partially related with their staple diet. The analysis of mammalian orthologs disclosed that GBA3 underwent at least nine pseudogenization events. Most events of pseudogenization occurred in carnivorous lineages, suggesting a possible link to a β-glycoside poor diet. However, GBA3 was also lost in omnivorous and herbivorous species, hinting that the physiological role of GBA3 is not fully understood and other unknown causes may underlie GBA3 pseudogenization. Such possibility relies upon a putative role in sialic acid biology, where GBA3 participates in a cellular network involving NEU2 and CMAH. Overall, our data shows that the recurrent loss of GBA3 in mammals is likely to represent an evolutionary endpoint of the relaxation of selective constraints triggered by diet-related factors.

Gram-Negative Bacterial Endotoxin LPS Induces NeuGc Loss through Ets1-Dependent Downregulation of Intestine-Specific pcmah Transcript in Porcine Intestinal Cells

N-glycolylneuraminic acid (NeuGc), a non-human sialic acid derivative synthesized by cytidine-5′-monophospho-N-acetylneuraminic acid hydroxylase (CMAH), plays a crucial role in mediating infections by certain pathogens. Although it has been postulated that NeuGc biosynthesis and CMAH expression are downregulated during microbial infection, the underlying mechanisms remain unclear. The present study showed that exposure to lipopolysaccharide (LPS), a Gram-negative bacterial endotoxin, leads to loss of NeuGc biosynthesis in pig small intestinal I2I-2I cells. This LPS-induced NeuGc loss was accompanied by decreased CMAH transcript levels, especially intestine-specific 5′pcmah-1. Furthermore, LPS suppressed the activity of the Pi promoter responsible for 5′pcmah-1 by inhibiting DNA binding of Est1. These findings provide insight into the regulatory mechanisms of Neu5Gc biosynthesis during pathogenic infectious events, which may represent a host defense mechanism that protects the self against pathogenic bacterial infections even in non-sanitary environments.

Human Natural Antibodies to Mammalian Carbohydrate Antigens as Unsung Heroes Protecting against Past, Present, and Future Viral Infections

Human natural antibodies to mammalian carbohydrate antigens (MCA) bind to carbohydrate-antigens synthesized in other mammalian species and protect against zoonotic virus infections. Three such anti-MCA antibodies are: (1) anti-Gal, also produced in Old-World monkeys and apes, binds to α-gal epitopes synthesized in non-primate mammals, lemurs, and New-World monkeys; (2) anti-Neu5Gc binds to Neu5Gc (N-glycolyl-neuraminic acid) synthesized in apes, Old-World monkeys, and many non-primate mammals; and (3) anti-Forssman binds to Forssman-antigen synthesized in various mammals. Anti-viral protection by anti-MCA antibodies is feasible because carbohydrate chains of virus envelopes are synthesized by host glycosylation machinery and thus are similar to those of their mammalian hosts. Analysis of MCA glycosyltransferase genes suggests that anti-Gal appeared in ancestral Old-World primates following catastrophic selection processes in which parental populations synthesizing α-gal epitopes were eliminated in enveloped virus epidemics. However, few mutated offspring in which the α1,3galactosyltransferase gene was accidentally inactivated produced natural anti-Gal that destroyed viruses presenting α-gal epitopes, thereby preventing extinction of mutated offspring. Similarly, few mutated hominin offspring that ceased to synthesize Neu5Gc produced anti-Neu5Gc, which destroyed viruses presenting Neu5Gc synthesized in parental hominin populations. A present-day example for few humans having mutations that prevent synthesis of a common carbohydrate antigen (produced in >99.99% of humans) is blood-group Bombay individuals with mutations inactivating H-transferase; thus, they cannot synthesize blood-group O (H-antigen) but produce anti-H antibody. Anti-MCA antibodies prevented past extinctions mediated by enveloped virus epidemics, presently protect against zoonotic-viruses, and may protect in future epidemics. Travelers to regions with endemic zoonotic viruses may benefit from vaccinations elevating protective anti-MCA antibody titers.

Sialylation and Galectin-3 in Microglia-Mediated Neuroinflammation and Neurodegeneration

Microglia are brain macrophages that mediate neuroinflammation and contribute to and protect against neurodegeneration. The terminal sugar residue of all glycoproteins and glycolipids on the surface of mammalian cells is normally sialic acid, and addition of this negatively charged residue is known as “sialylation,” whereas removal by sialidases is known as “desialylation.” High sialylation of the neuronal cell surface inhibits microglial phagocytosis of such neurons, via: (i) activating sialic acid receptors (Siglecs) on microglia that inhibit phagocytosis and (ii) inhibiting binding of opsonins C1q, C3, and galectin-3. Microglial sialylation inhibits inflammatory activation of microglia via: (i) activating Siglec receptors CD22 and CD33 on microglia that inhibit phagocytosis and (ii) inhibiting Toll-like receptor 4 (TLR4), complement receptor 3 (CR3), and other microglial receptors. When activated, microglia release a sialidase activity that desialylates both microglia and neurons, activating the microglia and rendering the neurons susceptible to phagocytosis. Activated microglia also release galectin-3 (Gal-3), which: (i) further activates microglia via binding to TLR4 and TREM2, (ii) binds to desialylated neurons opsonizing them for phagocytosis via Mer tyrosine kinase, and (iii) promotes Aβ aggregation and toxicity in vivo. Gal-3 and desialylation may increase in a variety of brain pathologies. Thus, Gal-3 and sialidases are potential treatment targets to prevent neuroinflammation and neurodegeneration.

The Possible Role of Anti-Neu5Gc as an Obstacle in Xenotransplantation

Seventy to ninety percentage of preformed xenoreactive antibodies in human serum bind to the galactose-α(1,3)-galactose Gal epitope, and the creation of Gal knockout (KO) pigs has eliminated hyperacute rejection as a barrier to xenotransplantation. Now other glycan antigens are barriers to move ahead with xenotransplantation, and the N-glycolyl neuraminic acid, Neu5Gc (or Hanganutziu-Deicher antigen), is also a major pig xenoantigen. Humans have anti-Neu5Gc antibodies. Several data indicate a strong immunogenicity of Neu5Gc in humans that may contribute to an important part in antibody-dependent injury to pig xenografts. Pig islets express Neu5Gc, which reacted with diet-derived human antibodies and mice deleted for Neu5Gc reject pancreatic islets from wild-type counterpart. However, Neu5Gc positive heart were not rejected in Neu5Gc KO mice indicating that the role of Neu5Gc-specific antibodies has to be nuanced and depend of the graft situation parameters (organ/tissue, recipient, implication of other glycan antigens). Recently generated Gal/Neu5Gc KO pigs eliminate the expression of Gal and Neu5Gc, and improve the crossmatch of humans with the pig. This review summarizes the current and recent experimental and (pre)clinical data on the Neu5Gc immunogenicity and emphasize of the potential impact of anti-Neu5Gc antibodies in limiting xenotransplantation in humans.

Glycan diversity in the course of vertebrate evolution

Vertebrates are estimated to have arisen over 500 million years ago in the Cambrian Period. Species that survived the Big Five extinction events at a global scale underwent repeated adaptive radiations along with habitat expansions from the sea to the land and sky. The development of the endoskeleton and neural tube enabled more complex body shapes. At the same time, vertebrates became suitable for the invasion and proliferation of foreign organisms. Adaptive immune systems were acquired for responses to a wide variety of pathogens, and more sophisticated systems developed during the evolution of mammals and birds. Vertebrate glycans consist of common core structures and various elongated structures, such as Neu5Gc, Galα1-3Gal, Galα1-4Gal, and Galβ1-4Gal epitopes, depending on the species. During species diversification, complex glycan structures were generated, maintained or lost. Whole-genome sequencing has revealed that vertebrates harbor numerous and even redundant glycosyltransferase genes. The production of various glycan structures is controlled at the genetic level in a species-specific manner. Because cell surface glycans are often targets of bacterial and viral infections, glycan structural diversity is presumed to be protective against infections. However, the maintenance of apparently redundant glycosyltransferase genes and investment in species-specific glycan structures, even in higher vertebrates with highly developed immune systems, are not well explained. This fact suggests that glycans play important roles in unknown biological processes.

GM1 Ganglioside Is A Key Factor in Maintaining the Mammalian Neuronal Functions Avoiding Neurodegeneration

Many species of ganglioside GM1, differing for the sialic acid and ceramide content, have been characterized and their physico-chemical properties have been studied in detail since 1963. Scientists were immediately attracted to the GM1 molecule and have carried on an ever-increasing number of studies to understand its binding properties and its neurotrophic and neuroprotective role. GM1 displays a well balanced amphiphilic behavior that allows to establish strong both hydrophobic and hydrophilic interactions. The peculiar structure of GM1 reduces the fluidity of the plasma membrane which implies a retention and enrichment of the ganglioside in specific membrane domains called lipid rafts. The dynamism of the GM1 oligosaccharide head allows it to assume different conformations and, in this way, to interact through hydrogen or ionic bonds with a wide range of membrane receptors as well as with extracellular ligands. After more than 60 years of studies, it is a milestone that GM1 is one of the main actors in determining the neuronal functions that allows humans to have an intellectual life. The progressive reduction of its biosynthesis along the lifespan is being considered as one of the causes underlying neuronal loss in aged people and severe neuronal decline in neurodegenerative diseases. In this review, we report on the main knowledge on ganglioside GM1, with an emphasis on the recent discoveries about its bioactive component.

Glycosylated Biotherapeutics: Immunological Effects of N-Glycolylneuraminic Acid

The emerging field of biotherapeutics provides successful treatments for various diseases, yet immunogenicity and limited efficacy remain major concerns for many products. Glycosylation is a key factor determining the pharmacological properties of biotherapeutics, including their stability, solubility, bioavailability, pharmacokinetics, and immunogenicity. Hence, an increased attention is directed at optimizing the glycosylation properties of biotherapeutics. Currently, most biotherapeutics are produced in non-human mammalian cells in light of their ability to produce human-like glycosylation. However, most mammals produce the sialic acid N-glycolylneuraminic acid (Neu5Gc), while humans cannot due to a specific genetic defect. Humans consume Neu5Gc in their diet from mammalian derived foods (red meat and dairy) and produce polyclonal antibodies against diverse Neu5Gc-glycans. Moreover, Neu5Gc can metabolically incorporate into human cells and become presented on surface or secreted glycans, glycoproteins, and glycolipids. Several studies in mice suggested that the combination of Neu5Gc-containing epitopes and anti-Neu5Gc antibodies could contribute to exacerbation of chronic inflammation-mediated diseases (e.g., cancer, cardiovascular diseases, and autoimmunity). This could potentially become complicated with exposure to Neu5Gc-containing biotherapeutics, bio-devices or xenografts. Indeed, Neu5Gc can be found on various approved and marketed biotherapeutics. Here, we provide a perspective review on the possible consequences of Neu5Gc glycosylation of therapeutic protein drugs due to the limited published evidence of Neu5Gc glycosylation on marketed biotherapeutics and studies on their putative effects on immunogenicity, drug efficacy, and safety.

Biological Functions and Analytical Strategies of Sialic Acids in Tumor

Sialic acids, a subset of nine carbon acidic sugars, often exist as the terminal sugars of glycans on either glycoproteins or glycolipids on the cell surface. Sialic acids play important roles in many physiological and pathological processes via carbohydrate-protein interactions, including cell-cell communication, bacterial and viral infections. In particular, hypersialylation in tumors, as well as their roles in tumor growth and metastasis, have been widely described. Recent studies have indicated that the aberrant sialylation is a vital way for tumor cells to escape immune surveillance and keep malignance. In this article, we outline the present state of knowledge on the metabolic pathway of human sialic acids, the function of hypersialylation in tumors, as well as the recent labeling and analytical techniques for sialic acids. It is expected to offer a brief introduction of sialic acid metabolism and provide advanced analytical strategies in sialic acid studies.

A comparison of the bone and growth phenotype of mdx, mdx:Cmah-/- and mdx:Utrn +/- murine models with the C57BL/10 wild-type mouse

The muscular dystrophy X-linked (mdx) mouse is commonly used as a mouse model of Duchenne muscular dystrophy (DMD). Its phenotype is, however, mild, and other mouse models have been explored. The mdx:Cmah^−/− mouse carries a human-like mutation in the Cmah gene and has a severe muscle phenotype, but its growth and bone development are unknown. In this study, we compared male mdx, mdx:Utrn^+/−, mdx:Cmah^−/− and wild-type (WT) mice at 3, 5 and 7 weeks of age to determine the suitability of the mdx:Cmah^−/− mouse as a model for assessing growth and skeletal development in DMD. The mdx:Cmah^−/− mice were lighter than WT mice at 3 weeks, but heavier at 7 weeks, and showed an increased growth rate at 5 weeks. Cortical bone fraction as assessed by micro-computed tomography was greater in both mdx and mdx:Cmah^−/− mice versus WT mice at 7 weeks. Tissue mineral density was also higher in mdx:Cmah^−/− mice at 3 and 7 weeks. Gene profiling of mdx:Cmah^−/− bone identified increased expression of Igf1, Igf1r and Vegfa. Both the mdx and mdx:Cmah^−/− mice showed an increased proportion of regulated bone marrow adipose tissue (BMAT) but a reduction in constitutive BMAT. The mdx:Cmah^−/− mice show evidence of catch-up growth and more rapid bone development. This pattern does not mimic the typical DMD growth trajectory and therefore the utility of the mdx:Cmah^−/− mouse for studying growth and skeletal development in DMD is limited. Further studies of this model may, however, shed light on the phenomenon of catch-up growth.

This article has an associated First Person interview with the first author of the paper.

Summary: Unlike boys with DMD, the mdx:Cmah^−/− mouse shows increased weight gain and more rapid bone development; therefore, its utility for studying growth and skeletal development in DMD is limited.

Sialic acid and biology of life: An introduction

Sialic acids are important molecule with high structural diversity. They are known to occur in higher animals such as Echinoderms, Hemichordata, Cephalochorda, and Vertebrata and also in other animals such as Platyhelminthes, Cephalopoda, and Crustaceae. Plants are known to lack sialic acid. But they are reported to occur in viruses, bacteria, protozoa, and fungi. Deaminated neuraminic acid although occurs in vertebrates and bacteria, is reported to occur in abundance in the lower vertebrates. Sialic acids are mostly located in terminal ends of glycoproteins and glycolipids, capsular and tissue polysialic acids, bacterial lipooligosaccharides/polysaccharides, and in different forms that dictate their role in biology. Sialic acid play important roles in human physiology of cell-cell interaction, communication, cell-cell signaling, carbohydrate-protein interactions, cellular aggregation, development processes, immune reactions, reproduction, and in neurobiology and human diseases in enabling the infection process by bacteria and virus, tumor growth and metastasis, microbiome biology, and pathology. It enables molecular mimicry in pathogens that allows them to escape host immune responses. Recently sialic acid has found role in therapeutics. In this chapter we have highlighted the (i) diversity of sialic acid, (ii) their occurrence in the diverse life forms, (iii) sialylation and disease, and (iv) sialic acid and therapeutics.

Molecular characterization of cytidine monophospho-N-acetylneuraminic acid hydroxylase (CMAH) associated with the erythrocyte antigens in dogs

Background

N-glycolylneuraminic acid (Neu5Gc) is synthesized from its precursor N-acetylneuraminic acid (Neu5Ac) by cytidine-5′-monophospho-N acetylneuraminic acid hydroxylase (CMAH), which is encoded by the CMAH gene. Most mammals have both Neu5Gc and Neu5Ac, but humans and ferrets have only Neu5Ac because of loss-of-function mutations. Dogs and cats are polymorphic for Neu5Gc and Neu5Ac expression like cats, in which the CMAH gene is responsible for the AB Blood group system. Although the CMAH gene has been characterized in many species, not much is known about it in dogs. In this study, we cloned the dog CMAH cDNA, and performed mRNA expression analysis of this gene in several organs. We also identified single nucleotide polymorphisms (SNPs) in the CMAH gene.

Results

We cloned the 1737-bp open reading frame of the dog CMAH gene. This gene consists of at least 14 coding exons and codes for a polypeptide of 578 amino acids and is located on chromosome 35. The amino acid identities of dog CMAH with the corresponding sequences from cat, pig, chimpanzee, mouse, and rat were high (89 to 93%). RT-PCR analysis showed that the dog CMAH cDNA was expressed in various tissues. We identified four exonic SNPs (three synonymous and one non-synonymous), 11 intronic SNPs, and an indel in 11 dog breeds by analyzing the nucleotide sequences of the 14 exons, including the coding region of CMAH. In the genotype of the non-synonymous SNP, c.554 A > G (p.Lys185Arg), in a total of 285 dogs of seven different breeds, the allele G was widely distributed, and the allele A was the most frequent in the Shiba dogs. The dogs expressing Neu5Ac did not carry the loss-of-function deletion of CMAH found in humans and ferrets, and it remains unclear whether the point mutations influence the expression of Neu5Ac.

Conclusions

We characterized the canine CMAH gene at the molecular level for the first time. The results obtained in this study provide essential information that will help in understanding the molecular roles of the CMAH gene in canine erythrocyte antigens.

rAAVrh74.MCK.GALGT2 Demonstrates Safety and Widespread Muscle Glycosylation after Intravenous Delivery in C57BL/6J Mice

rAAVrh74.MCK.GALGT2 is a surrogate gene therapy that inhibits muscular dystrophy in multiple animal models. Here, we report on a dose-response study of functional muscle GALGT2 expression as well as toxicity and biodistribution studies after systemic intravenous (i.v.) delivery of rAAVrh74.MCK.GALGT2. A dose of 4.3 × 10¹⁴vg/kg (measured with linear DNA standard) resulted in GALGT2-induced glycosylation in the majority of skeletal myofibers throughout the body and in almost all cardiomyocytes, while several lower doses also showed significant muscle glycosylation. No adverse clinical signs or treatment-dependent changes in tissue or organ pathology were noted at 1 or 3 months post-treatment. Blood cell and serum enzyme chemistry measures in treated mice were all within the normal range except for alkaline phosphatase (ALP) activity, which was elevated in serum but not in tissues. Some anti-rAAVrh74 capsid T cell responses were noted at 4 weeks post-treatment, but all such responses were not present at 12 weeks. Using intramuscular delivery, GALGT2-induced muscle glycosylation was increased in Cmah-deficient mice, which have a humanized sialoglycome, relative to wild-type mice, suggesting that use of mice may underestimate GALGT2 activity in human muscle. These data demonstrate safety and high transduction of muscles throughout the body plan with i.v. delivery of rAAVrh74.MCK.GALGT2.

N-Glycolylneuraminic Acid (Neu5Gc) Null Large Animals by Targeting the CMP-Neu5Gc Hydroxylase (CMAH)

The two major sialic acids described in mammalian cells are the N-glycolylneuraminic acid (Neu5Gc) and the N-acetylneuraminic acid (Neu5Ac). Neu5Gc synthesis starts from the N-acetylneuraminic acid (Neu5Ac) precursor modified by an hydroxylic group addition catalyzed by CMP-Neu5Ac hydroxylase enzyme (CMAH). In humans, CMAH was inactivated by a 92 bp deletion occurred 2-3 million years ago. Few other mammals do not synthetize Neu5Gc, however livestock species used for food production and as a source of biological materials for medical applications carry Neu5Gc. Trace amounts of Neu5Gc are up taken through the diet and incorporated into various tissues including epithelia and endothelia cells. Humans carry "natural," diet-induced Anti-Neu5Gc antibodies and when undertaking medical treatments or receiving transplants or devices that contain animal derived products they can cause immunological reaction affecting pharmacology, immune tolerance, and severe side effect like serum sickness disease (SSD). Neu5Gc null mice have been the main experimental model to study such phenotype. With the recent advances in genome editing, pigs and cattle KO for Neu5Gc have been generated always in association with the αGal KO. These large animals are normal and fertile and provide additional experimental models to study such mutation. Moreover, they will be the base for the development of new therapeutic applications like polyclonal IgG immunotherapy, Bioprosthetic Heart Valves, cells and tissues replacement.

Adaptation of Plasmodium falciparum to humans involved the loss of an ape-specific erythrocyte invasion ligand

Plasmodium species are frequently host-specific, but little is currently known about the molecular factors restricting host switching. This is particularly relevant for P. falciparum, the only known human-infective species of the Laverania sub-genus, all other members of which infect African apes. Here we show that all tested P. falciparum isolates contain an inactivating mutation in an erythrocyte invasion associated gene, PfEBA165, the homologues of which are intact in all ape-infective Laverania species. Recombinant EBA165 proteins only bind ape, not human, erythrocytes, and this specificity is due to differences in erythrocyte surface sialic acids. Correction of PfEBA165 inactivating mutations by genome editing yields viable parasites, but is associated with down regulation of both PfEBA165 and an adjacent invasion ligand, which suggests that PfEBA165 expression is incompatible with parasite growth in human erythrocytes. Pseudogenization of PfEBA165 may represent a key step in the emergence and evolution of P. falciparum.

Here, Proto et al. show that human infective Plasmodium falciparum isolates contain an inactivating mutation in the erythrocyte invasion associated gene PfEBA165, while homologues of ape-infective Laverania species are intact, and that expression of intact PfEBA165 is incompatible with parasite growth in human erythrocytes.

Coordinated roles for glycans in regulating the inhibitory function of CD22 on B cells

CD22 is an inhibitory B cell co-receptor that recognizes sialic acid-containing glycoconjugates as ligands. Interactions with its glycan ligands are key to regulating the ability of CD22 to modulate B cell function, the most widely explored of which is antagonizing B cell receptor (BCR) signaling. Most importantly, interactions of CD22 with ligands on the same cell (cis) control the organization of CD22 on the cell surface, which minimizes co-localization with the BCR. In contrast with the modest ability of CD22 to intrinsically dampen BCR signaling, glycan ligands presented on another cell (trans) along with an antigen drawn CD22 and the BCR together within an immunological synapse, strongly inhibiting BCR signaling. New concepts are emerging for how CD22 controls B cell function, such as changes in glycosylation at different stages of B cell differentiation, specifically on GC B cells. Related to these changes, new players, such galectin-9, have been discovered that regulate cell surface nanoclusters of CD22. Roles of glycan ligands in controlling CD22 are the primary focus of this review as we highlight the ability of CD22 to modulate B cell function.

Synthesis of N-Glycolylneuraminic Acid (Neu5Gc) and Its Glycosides

Sialic acids constitute a family of negatively charged structurally diverse monosaccharides that are commonly presented on the termini of glycans in higher animals and some microorganisms. In addition to N-acetylneuraminic acid (Neu5Ac), N-glycolyl neuraminic acid (Neu5Gc) is among the most common sialic acid forms in nature. Nevertheless, unlike most animals, human cells loss the ability to synthesize Neu5Gc although Neu5Gc-containing glycoconjugates have been found on human cancer cells and in various human tissues due to dietary incorporation of Neu5Gc. Some pathogenic bacteria also produce Neu5Ac and the corresponding glycoconjugates but Neu5Gc-producing bacteria have yet to be found. In addition to Neu5Gc, more than 20 Neu5Gc derivatives have been found in non-human vertebrates. To explore the biological roles of Neu5Gc and its naturally occurring derivatives as well as the corresponding glycans and glycoconjugates, various chemical and enzymatic synthetic methods have been developed to obtain a vast array of glycosides containing Neu5Gc and/or its derivatives. Here we provide an overview on various synthetic methods that have been developed. Among these, the application of highly efficient one-pot multienzyme (OPME) sialylation systems in synthesizing compounds containing Neu5Gc and derivatives has been proven as a powerful strategy.

Human species-specific loss of CMP-N-acetylneuraminic acid hydroxylase enhances atherosclerosis via intrinsic and extrinsic mechanisms

Cardiovascular disease (CVD) events due to atherosclerosis cause one-third of worldwide deaths and risk factors include physical inactivity, age, dyslipidemia, hypertension, diabetes, obesity, smoking, and red meat consumption. However, ∼15% of first-time events occur without such factors. In contrast, coronary events are extremely rare even in closely related chimpanzees in captivity, despite human-like CVD-risk-prone blood lipid profiles, hypertension, and mild atherosclerosis. Similarly, red meat-associated enhancement of CVD event risk does not seem to occur in other carnivorous mammals. Thus, heightened CVD risk may be intrinsic to humans, and genetic changes during our evolution need consideration. Humans exhibit a species-specific deficiency of the sialic acid N-glycolylneuraminic acid (Neu5Gc), due to pseudogenization of cytidine monophosphate-N-acetylneuraminic acid (Neu5Ac) hydroxylase (CMAH), which occurred in hominin ancestors ∼2 to 3 Mya. Ldlr ^-/- mice with human-like Cmah deficiency fed a sialic acids (Sias)-free high-fat diet (HFD) showed ∼1.9-fold increased atherogenesis over Cmah wild-type Ldlr ^-/- mice, associated with elevated macrophage cytokine expression and enhanced hyperglycemia. Human consumption of Neu5Gc (from red meat) acts as a "xeno-autoantigen" via metabolic incorporation into endogenous glycoconjugates, as interactions with circulating anti-Neu5Gc "xeno-autoantibodies" potentiate chronic inflammation ("xenosialitis"). Cmah ^-/- Ldlr ^-/- mice immunized with Neu5Gc-bearing antigens to generate human-like anti-Neu5Gc antibodies suffered a ∼2.4-fold increased atherosclerosis on a Neu5Gc-rich HFD, compared with Neu5Ac-rich or Sias-free HFD. Lesions in Neu5Gc-immunized and Neu5Gc-rich HFD-fed Cmah ^-/- Ldlr ^-/- mice were more advanced but unexplained by lipoprotein or glucose changes. Human evolutionary loss of CMAH likely contributes to atherosclerosis predisposition via multiple intrinsic and extrinsic mechanisms, and future studies could consider this more human-like model.

Antitumor effects of the GM3(Neu5Gc) ganglioside-specific humanized antibody 14F7hT against Cmah-transfected cancer cells

The GM3(Neu5Gc) ganglioside represents a tumor-specific antigen that is considered a promising target for cancer immunotherapy. We previously demonstrated that the humanized antibody 14F7hT, specific for this ganglioside, exhibited significant antitumor effects in preclinical hematological tumor models. As this antibody recognizes human tumor tissues from several origins, we addressed its potential effect on different tumor types. The use of cell lines for testing GM3(Neu5Gc)-targeting strategies, in particular for human malignancies, is complicated by the absence in humans of functional cytidine monophospho-N-acetyl-neuraminic acid hydroxylase (CMAH), the enzyme required for Neu5Gc sialic acid biosynthesis. Quantitative flow cytometry revealed the absence of surface GM3(Neu5Gc) in several human but also mouse cell lines, in the last case due to low expression of the enzyme. Hypoxia-induced expression of this ganglioside on human SKOV3 cells was observed upon culture in Neu5Gc-containing medium without evidence for CMAH-independent biosynthesis. However, only transfection of the mouse Cmah gene into human SKOV3 and mouse 3LL cells induced a stable expression of GM3(Neu5Gc) on the cancer cell surface, resulting in effective models to evaluate the antitumor responses by 14F7hT in vitro and in vivo. This antibody exerted antibody-dependent cell-mediated cytotoxicity (ADCC) and in vivo antitumor effects on these Cmah-transfected non-hematological tumors from both mouse and human origin. These results contribute to validate GM3(Neu5Gc) as a relevant target for cancer immunotherapy and reinforces the value of 14F7hT as a novel anti-cancer drug.

Rationale and Design for a Phase 1 Study of N-Acetylmannosamine for Primary Glomerular Diseases

Introduction

Sialic acids are important contributors to the polyanionic component of the glomerular filtration barrier, which regulates permeability selectivity. Pathologic glomerular hyposialylation, associated with podocyte effacement, has been implicated in human and mouse glomerulopathies. Oral treatment with N-acetylmannosamine (ManNAc), the uncharged precursor of sialic acid, ameliorates glomerular pathology in different models of glomerular disease.

Methods

Here we explore the sialylation status of kidney biopsies obtained from 27 subjects with various glomerular diseases using lectin histochemistry.

Results

We identified severe glomerular hyposialylation in 26% of the biopsies. These preliminary findings suggest that this condition may occur relatively frequently and may be a novel target for therapy. We describe the background, rationale, and design of a phase 1 study to test safety, tolerability, and pharmacokinetics of ManNAc in subjects with primary podocyte diseases.

Conclusion

We recently demonstrated that ManNAc was safe and well tolerated in a first-in-human phase 1 study in subjects with UDP-N-acetylglucosamine (GlcNAc) 2-epimerase/ManNAc kinase (GNE) myopathy, a disorder of impaired sialic acid synthesis. Using previous preclinical and clinical data, we propose to test ManNAc therapy for subjects with primary glomerular diseases. Even though the exact mechanisms, affected cell types, and pathologic consequences of glomerular hyposialylation need further study, treatment with this physiological monosaccharide could potentially replace or supplement existing glomerular diseases therapies.