Sialic acid is a critical fetal defense against maternal complement attack

Placental glycosylation senses the anti-angiogenic milieu induced by human sFLT1 during pregnancy

Abnormal placental angiogenesis during gestation resulting from high levels of anti-angiogenic factors, soluble fms-like tyrosine kinase-1 (sFLT1) and soluble endoglin, has been implicated in the progression of preeclampsia (PE). This heterogeneous syndrome (defined by hypertension with or without proteinuria after 20 weeks of pregnancy) remains a major global health burden with long-term consequences for both mothers and child. Previously, we showed that in vivo systemic human (hsFLT1) overexpression led to reduced placental efficiency and PE-like syndrome in mice. Galectins (gal-1, -3 and -9) are critical determinants of vascular adaptation to pregnancy and dysregulation of the galectin-glycan circuits is associated with the development of this life-threatening disease. In this study, we assessed the galectin-glycan networks at the maternal-fetal interface associated with the hsFLT1-induced PE in mice. We observed an increase on the maternal gal-1 expression in the decidua and junctional zone layers of the placenta derived from hs FLT1high pregnancies. In contrast, placental gal-3 and gal-9 expression were not sensitive to the hsFLT1 overexpression. In addition, O- and N-linked glycan expression, poly-LacNAc sequences and terminal sialylation were down-regulated in hsFLT1 high placentas. Thus, the gal-1-glycan axis appear to play an important role counteracting the anti-angiogenic status caused by sFLT1, becoming critical for vascular adaptation at the maternal-fetal interface.

Sialic acids on T cells are crucial for their maintenance and survival

Sialic acids are found as terminal sugars on glycan structures on cellular surfaces. T cells carry these sialoglycans abundantly, and they are thought to serve multiple functions in cell adhesion, cell migration, and protection from complement attack. We studied the role of sialoglycans on T cells in a mouse model with a T cell-specific deletion of cytidine monophosphate-sialic acid synthase (CMAS), the enzyme that is crucial for the synthesis of sialoglycans. These mice showed a T-cell deficiency in peripheral lymphoid organs. Many T cells with an undeleted Cmas allele were found in the periphery, suggesting that they escaped the Cre-mediated deletion. The remaining peripheral T cells of T cell-specific Cmas KO mice had a memory-like phenotype. Additional depletion of the complement factor C3 could not rescue the phenotype, showing that the T-cell defect was not caused by a host complement activity. Cmas-deficient T cells showed a high level of activated caspase 3, indicating an ongoing apoptosis. In bone marrow chimeric cellular transfer experiments, we observed a strong competitive disadvantage of Cmas-deficient T cells compared to wild-type T cells. These results show that sialoglycans on the surface of T cells are crucial for T-cell survival and maintenance. This function has not been recognized before and is similar to the function of sialoglycans on B cells.

Angiogenic factors and the lectin pathway of complement in women with secondary recurrent pregnancy loss

The poor remodeling of placental spiral arteries seen in preeclampsia is also discussed to contribute to recurrent pregnancy loss (RPL) preceded by abnormal angiogenesis and excessive complement activation. Low levels of Mannose-binding-lectin (MBL), a pattern recognition molecule (PRM) of the lectin pathway, have been found in women with RPL. We propose that pregnancy loss is connected to defective angiogenesis with reperfusion damage in the placenta and decreased levels of PRM in the lectin pathway in women with RPL. In this cohort study, we investigate the angiogenic factors and the lectin complement pathway in early pregnancy and their time-dependent relationship with pregnancy outcomes in 76 women with secondary RPL (sRPL) who have at least four prior pregnancy losses and a live birth. We evaluated levels of Angiopoietin-1 (Ang-1), Angiopoietin-2 (Ang-2), Vascular Endothelial Growth Factor (VEGF), soluble fms-like tyrosine kinase-1 (sFlt-1), and the PRMs, MBL, ficolin-1, -2, -3 and an additional soluble PRM, Pentraxin-3, during the 5th, 6th, and 7th gestational weeks. Our results showed that, compared to live births, pregnancies that ended in loss were associated with elevated VEGF levels and decreased levels of the Ang-2/Ang-1 ratio. Also, increasing levels of ficolin-2 were significantly associated with pregnancy loss, with MBL showing no association. Our research suggests that women with sRPL may have inadequate placentation with impaired angiogenesis in pregnancies ending in a loss.

Evolutionarily conserved ovarian fluid proteins are responsible for extending egg viability in salmonid fish

In contrast to most fishes, salmonids exhibit the unique ability to hold their eggs for several days after ovulation without significant loss of viability. During this period, eggs are held in the body cavity in a biological fluid, the coelomic fluid (CF) that is responsible for preserving egg viability. To identify CF proteins responsible for preserving egg viability, a proteomic comparison was performed using 3 salmonid species and 3 non-salmonid species to identify salmonid-specific highly abundant proteins. In parallel, rainbow trout CF fractions were purified and used in a biological test to estimate their egg viability preservation potential. The most biologically active CF fractions were then subjected to mass spectrometry analysis. We identified 50 proteins overabundant in salmonids and present in analytical fractions with high egg viability preservation potential. The identity of these proteins illuminates the biological processes participating in egg viability preservation. Among identified proteins of interest, the ovarian-specific expression and abundance in CF at ovulation of N-acetylneuraminic acid synthase a (Nansa) suggest a previously unsuspected role. We show that salmonid CF is a complex biological fluid containing a diversity of proteins related to immunity, calcium binding, lipid metabolism, proteolysis, extracellular matrix and sialic acid metabolic pathway that are collectively responsible for preserving egg viability.

The functional roles of protein glycosylation in human maternal-fetal crosstalk

BACKGROUND

The establishment of maternal-fetal crosstalk is vital to a successful pregnancy. Glycosylation is a post-translational modification in which glycans (monosaccharide chains) are attached to an organic molecule. Glycans are involved in many physiological and pathological processes. Human endometrial epithelium, endometrial gland secretions, decidual immune cells, and trophoblasts are highly enriched with glycoconjugates and glycan-binding molecules important for a healthy pregnancy. Aberrant glycosylation in the placenta and uterus has been linked to repeated implantation failure and various pregnancy complications, but there is no recent review summarizing the functional roles of glycosylation at the maternal-fetal interface and their associations with pathological processes.

OBJECTIVE AND RATIONALE

This review aims to summarize recent findings on glycosylation, glycosyltransferases, and glycan-binding receptors at the maternal-fetal interface, and their involvement in regulating the biology and pathological conditions associated with endometrial receptivity, placentation and maternal-fetal immunotolerance. Current knowledge limitations and future insights into the study of glycobiology in reproduction are discussed.

SEARCH METHODS

A comprehensive PubMed search was conducted using the following keywords: glycosylation, glycosyltransferases, glycan-binding proteins, endometrium, trophoblasts, maternal-fetal immunotolerance, siglec, selectin, galectin, repeated implantation failure, early pregnancy loss, recurrent pregnancy loss, preeclampsia, and fetal growth restriction. Relevant reports published between 1980 and 2023 and studies related to these reports were retrieved and reviewed. Only publications written in English were included.

OUTCOMES

The application of ultrasensitive mass spectrometry tools and lectin-based glycan profiling has enabled characterization of glycans present at the maternal-fetal interface and in maternal serum. The endometrial luminal epithelium is covered with highly glycosylated mucin that regulates blastocyst adhesion during implantation. In the placenta, fucose and sialic acid residues are abundantly presented on the villous membrane and are essential for proper placentation and establishment of maternal-fetal immunotolerance. Glycan-binding receptors, including selectins, sialic-acid-binding immunoglobulin-like lectins (siglecs) and galectins, also modulate implantation, trophoblast functions and maternal-fetal immunotolerance. Aberrant glycosylation is associated with repeated implantation failure, early pregnancy loss and various pregnancy complications. The current limitation in the field is that most glycobiological research relies on association studies, with few studies revealing the specific functions of glycans. Technological advancements in analytic, synthetic and functional glycobiology have laid the groundwork for further exploration of glycans in reproductive biology under both physiological and pathological conditions.

WIDER IMPLICATIONS

A deep understanding of the functions of glycan structures would provide insights into the molecular mechanisms underlying their involvement in the physiological and pathological regulation of early pregnancy. Glycans may also potentially serve as novel early predictive markers and therapeutic targets for repeated implantation failure, pregnancy loss, and other pregnancy complications.

Insights into the Structure, Metabolism, Biological Functions and Molecular Mechanisms of Sialic Acid: A Review

Sialic acid (SA) is a kind of functional monosaccharide which exists widely in edible bird's nest (EBN), milk, meat, mucous membrane surface, etc. SA is an important functional component in promoting brain development, anti-oxidation, anti-inflammation, anti-virus, anti-tumor and immune regulation. The intestinal mucosa covers the microbial community that has a significant impact on health. In the gut, SA can also regulate gut microbiota and metabolites, participating in different biological functions. The structure, source and physiological functions of SA were reviewed in this paper. The biological functions of SA through regulating key signaling pathways and target genes were discussed. In summary, SA can modulate gut microbiota and metabolites, which affect gene expressions and exert its biological activities. It is helpful to provide scientific reference for the further investigation of SA in the functional foods.

Neurodevelopmental defects in human cortical organoids with N-acetylneuraminic acid synthase mutation

Biallelic genetic variants in N-acetylneuraminic acid synthase (NANS), a critical enzyme in endogenous sialic acid biosynthesis, are clinically associated with neurodevelopmental disorders. However, the mechanism underlying the neuropathological consequences has remained elusive. Here, we found that NANS mutation resulted in the absence of both sialic acid and protein polysialylation in the cortical organoids and notably reduced the proliferation and expansion of neural progenitors. NANS mutation dysregulated neural migration and differentiation, disturbed synapse formation, and weakened neuronal activity. Single-cell RNA sequencing revealed that NANS loss of function markedly altered transcriptional programs involved in neuronal differentiation and ribosomal biogenesis in various neuronal cell types. Similarly, Nans heterozygous mice exhibited impaired cortical neurogenesis and neurobehavioral deficits. Collectively, our findings reveal a crucial role of NANS-mediated endogenous sialic acid biosynthesis in regulating multiple features of human cortical development, thus linking NANS mutation with its clinically relevant neurodevelopmental disorders.

The monosialoganglioside GM1a protects against complement attack

The complement system is a part of the innate immune system in the fluid phase and efficiently eliminates pathogens. However, its activation requires tight regulation on the host cell surface in order not to compromise cellular viability. Previously, we showed that loss of placental cell surface sialylation in mice in vivo leads to a maternal complement attack at the fetal-maternal interface, ultimately resulting in loss of pregnancy. To gain insight into the regulatory function of sialylation in complement activation, we here generated trophoblast stem cells (TSC) devoid of sialylation, which also revealed complement sensitivity and cell death in vitro. Glycolipid-analysis by multiplexed capillary gel electrophoresis coupled to laser-induced fluorescence detection (xCGE-LIF) allowed us to identify the monosialoganglioside GM1a as a key element of cell surface complement regulation. Exogenously administered GM1a integrated into the plasma membrane of trophoblasts, substantially increased binding of complement factor H (FH) and was sufficient to protect the cells from complement attack and cell death. GM1a treatment also rescued human endothelial cells and erythrocytes from complement attack in a concentration dependent manner. Furthermore, GM1a significantly reduced complement mediated hemolysis of erythrocytes from a patient with Paroxysmal nocturnal hemoglobinuria (PNH). This study demonstrates the complement regulatory potential of exogenously administered gangliosides and paves the way for sialoglycotherapeutics as a novel substance class for membrane-targeted complement regulators.

The vertebrate sialylation machinery: structure-function and molecular evolution of GT-29 sialyltransferases

Every eukaryotic cell is covered with a thick layer of complex carbohydrates with essential roles in their social life. In Deuterostoma, sialic acids present at the outermost positions of glycans of glycoconjugates are known to be key players in cellular interactions including host-pathogen interactions. Their negative charge and hydrophilic properties enable their roles in various normal and pathological states and their expression is altered in many diseases including cancers. Sialylation of glycoproteins and glycolipids is orchestrated by the regulated expression of twenty sialyltransferases in human tissues with distinct enzymatic characteristics and preferences for substrates and linkages formed. However, still very little is known on the functional organization of sialyltransferases in the Golgi apparatus and how the sialylation machinery is finely regulated to provide the ad hoc sialome to the cell. This review summarizes current knowledge on sialyltransferases, their structure-function relationships, molecular evolution, and their implications in human biology.

Control of lupus activity during pregnancy via the engagement of IgG sialylation: novel crosstalk between IgG sialylation and pDC functions

Immunoglobulin (IgG) glycosylation affects the effector functions of IgG in a myriad of biological processes and has been closely associated with numerous autoimmune diseases, including systemic lupus erythematosus (SLE), thus underlining the pathogenic role of glycosylation aberration in autoimmunity. This study aims to explore the relationship between IgG sialylation patterns and lupus pregnancy. Relative to that in serum samples from the control cohort, IgG sialylation level was aberrantly downregulated in serum samples from the SLE cohort at four stages (from preconception to the third trimester of pregnancy) and was significantly associated with lupus activity and fetal loss during lupus pregnancy. The type I interferon signature of pregnant patients with SLE was negatively correlated with the level of IgG sialylation. The lack of sialylation dampened the ability of IgG to suppress the functions of plasmacytoid dendritic cells (pDCs). RNA-seq analysis further revealed that the expression of genes associated with the spleen tyrosine kinase (SYK) signaling pathway significantly differed between IgG- and deSia-IgG-treated pDCs. This finding was confirmed by the attenuation of the ability to phosphorylate SYK and BLNK in deSia-IgG. Finally, the coculture of pDCs isolated from pregnant patients with SLE with IgG/deSia-IgG demonstrated the sialylation-dependent anti-inflammatory function of IgG. Our findings suggested that IgG influences lupus activity through regulating pDCs function via the modulation of the SYK pathway in a sialic acid-dependent manner.

DNA methylation abnormalities induced by advanced maternal age in villi prime a high-risk state for spontaneous abortion

BACKGROUND

Advanced maternal age (AMA) has increased in many high-income countries in recent decades. AMA is generally associated with a higher risk of various pregnancy complications, and the underlying molecular mechanisms are largely unknown. In the current study, we profiled the DNA methylome of 24 human chorionic villi samples (CVSs) from early pregnancies in AMA and young maternal age (YMA), 11 CVSs from early spontaneous abortion (SA) cases using reduced representation bisulfite sequencing (RRBS), and the transcriptome of 10 CVSs from AMA and YMA pregnancies with mRNA sequencing(mRNA-seq). Single-cell villous transcriptional atlas presented expression patterns of targeted AMA-/SA-related genes. Trophoblast cellular impairment was investigated through the knockdown of GNE expression in HTR8-S/Vneo cells.

RESULTS

AMA-induced local DNA methylation changes, defined as AMA-related differentially methylated regions (DMRs), may be derived from the abnormal expression of genes involved in DNA demethylation, such as GADD45B. These DNA methylation changes were significantly enriched in the processes involved in NOTCH signaling and extracellular matrix organization and were reflected in the transcriptional alterations in the corresponding biological processes and specific genes. Furthermore, the DNA methylation level of special AMA-related DMRs not only significantly changed in AMA but also showed more excessive defects in CVS from spontaneous abortion (SA), including four AMA-related DMRs whose nearby genes overlapped with AMA-related differentially expressed genes (DEGs) (CDK11A, C19orf71, COL5A1, and GNE). The decreased DNA methylation level of DMR near GNE was positively correlated with the downregulated expression of GNE in AMA. Single-cell atlas further revealed comparatively high expression of GNE in the trophoblast lineage, and knockdown of GNE in HTR8-S/Vneo cells significantly impaired cellular proliferation and migration.

CONCLUSION

Our study provides valuable resources for investigating AMA-induced epigenetic abnormalities and provides new insights for explaining the increased risks of pregnancy complications in AMA pregnancies.

Placental glycotype of the caviomorph rodent Lagostomus maximus and its evolution within Eutheria

The main evolutionary milestone in the oviparity-viviparity transition is placentation. The placenta is an organ with great morphological diversity among eutherians. The expression of different glycosidic residues (Gr) in the near-term placenta constitutes its glycotype. In this study, the expression of different Gr was determined by lectin histochemistry in early, midterm, and near-term placentas of the plains viscacha (Lagostomus maximus), a caviomorph rodent with the highest poliovulatory rate and embryonic resorption rate among eutherians. Besides, a matrix with the expression of each Gr in the exchange trophoblast of viscacha and other eutherians was constructed to map and infer phylogenetic and evolutionary relationships. Between early, midterm, and near-term placentas, variations in the pattern expression of Gr were observed. The glycotype of the near-term placenta is composed of a high diversity of Gr. Reconstruction of the ancestral state for each Gr present in the near-term placenta showed a diverse scenario: some sugars were common to the species of Placentalia included in this study. In the analyzed species with synepitheliochorial and epitheliochorial placentas, no differential glycosylation patterns between them were observed. In species with invasive placentas, such as the endotheliochorial placentas of Carnivora, some common Gr were detected among them, while others were species-specific. In species with hemochorial placenta, the same Gr are shared. Particularly, in the viscacha greater differences with species of the Hominidae and even Muridae families were observed. Nevertheless, greater similarities with other caviomorph rodents were detected. Placental glycotype of each species constitutes an excellent tool to achieve phylogenetic and evolutionary inferences among eutherians.

Alternative pathway activation in pregnancy, a measured amount "complements" a successful pregnancy, too much results in adverse events

During pregnancy, the maternal host must adapt in order to enable growth of the fetus. These changes affect all organ systems and are designed both to protect the fetus and to minimize risk to the mother. One of the most prominent adaptations involves the immune system. The semi-allogenic fetoplacental unit has non-self components and must be protected against attack from the host. This requires both attenuation of adaptive immunity and protection from innate immune defense mechanisms. One of the key innate immune players is complement, and it is important that the fetoplacental unit is not identified as non-self and subjected to complement attack. Adaptation of the complement response must, however, be managed in such a way that maternal protection against infection is not compromised. As the complement system also plays a significant facilitating role in many of the stages of a normal pregnancy, it is also important that any necessary adaptation to accommodate the semi-allogenic aspects of the fetoplacental unit does not compromise this. In this review, both the physiological role of the alternative pathway of complement in facilitating a normal pregnancy, and its detrimental participation in pregnancy-specific disorders, are discussed.

Generation and characterization of a novel gne Knockout Model in Zebrafish

GNE Myopathy is a rare, recessively inherited neuromuscular worldwide disorder, caused by a spectrum of bi-allelic mutations in the human GNE gene. GNE encodes a bi-functional enzyme responsible for the rate-limiting step of sialic acid biosynthesis pathway. However, the process in which GNE mutations lead to the development of a muscle pathology is not clear yet. Cellular and mouse models for GNE Myopathy established to date have not been informative. Further, additional GNE functions in muscle have been hypothesized. In these studies, we aimed to investigate gne functions using zebrafish genetic and transgenic models, and characterized them using macroscopic, microscopic, and molecular approaches. We first established transgenic zebrafish lineages expressing the human GNE cDNA carrying the M743T mutation, driven by the zebrafish gne promoter. These fish developed entirely normally. Then, we generated a gne knocked-out (KO) fish using the CRISPR/Cas9 methodology. These fish died 8–10 days post-fertilization (dpf), but a phenotype appeared less than 24 h before death and included progressive body axis curving, deflation of the swim bladder and decreasing movement and heart rate. However, muscle histology uncovered severe defects, already at 5 dpf, with compromised fiber organization. Sialic acid supplementation did not rescue the larvae from this phenotype nor prolonged their lifespan. To have deeper insights into the potential functions of gne in zebrafish, RNA sequencing was performed at 3 time points (3, 5, and 7 dpf). Genotype clustering was progressive, with only 5 genes differentially expressed in gne KO compared to gne WT siblings at 3 dpf. Enrichment analyses of the primary processes affected by the lack of gne also at 5 and 7 dpf point to the involvement of cell cycle and DNA damage/repair processes in the gne KO zebrafish. Thus, we have established a gne KO zebrafish lineage and obtained new insights into gne functions. This is the only model where GNE can be related to clear muscle defects, thus the only animal model relevant to GNE Myopathy to date. Further elucidation of gne precise mechanism-of-action in these processes could be relevant to GNE Myopathy and allow the identification of novel therapeutic targets.

N-glycosylation of cervicovaginal fluid reflects microbial community, immune activity, and pregnancy status

Human cervicovaginal fluid (CVF) is a complex, functionally important and glycan rich biological fluid, fundamental in mediating physiological events associated with reproductive health. Using a comprehensive glycomic strategy we reveal an extremely rich and complex N-glycome in CVF of pregnant and non-pregnant women, abundant in paucimannose and high mannose glycans, complex glycans with 2-4 N-Acetyllactosamine (LacNAc) antennae, and Poly-LacNAc glycans decorated with fucosylation and sialylation. N-glycosylation profiles were observed to differ in relation to pregnancy status, microbial composition, immune activation, and pregnancy outcome. Compared to CVF from women experiencing term birth, CVF from women who subsequently experienced preterm birth showed lower sialylation, which correlated to the presence of a diverse microbiome, and higher fucosylation, which correlated positively to pro-inflammatory cytokine concentration. This study is the first step towards better understanding the role of cervicovaginal glycans in reproductive health, their contribution to the mechanism of microbial driven preterm birth, and their potential for preventative therapy.

Maternal Serum and Placental Metabolomes in Association with Prenatal Phthalate Exposure and Neurodevelopmental Outcomes in the MARBLES Cohort

Prenatal exposure to phthalates, a family of endocrine-disrupting plasticizers, is associated with disruption of maternal metabolism and impaired neurodevelopment. We investigated associations between prenatal phthalate exposure and alterations of both the maternal third trimester serum metabolome and the placental metabolome at birth, and associations of these with child neurodevelopmental outcomes using data and samples from the Markers of Autism Risk in Babies Learning Early Signs (MARBLES) cohort. The third trimester serum (n = 106) and placental (n = 132) metabolomes were investigated using 1H nuclear magnetic resonance spectroscopy. Children were assessed clinically for autism spectrum disorder (ASD) and cognitive development. Although none of the urinary phthalate metabolite concentrations were associated with maternal serum metabolites after adjustment for covariates, mixture analysis using quantile g-computation revealed alterations in placental metabolites with increasing concentrations of phthalate metabolites that included reduced concentrations of 2-hydoxybutyrate, carnitine, O-acetylcarnitine, glucitol, and N-acetylneuraminate. Child neurodevelopmental outcome was not associated with the third trimester serum metabolome, but it was correlated with the placental metabolome in male children only. Maternal phthalate exposure during pregnancy is associated with differences in the placental metabolome at delivery, and the placental metabolome is associated with neurodevelopmental outcomes in males in a cohort with high familial ASD risk.

Sulfation of sialic acid is ubiquitous and essential for vertebrate development

Glycosylation of proteins and lipids occurs in vertebrates, usually terminating with sialylation, which regulates the physicochemical and biological properties of these glycoconjugates. Although less commonly known, sialic acid residues also undergo various modifications, such as acetylation, methylation, and sulfation. However, except for acetylation, the enzymes or functions of the other modification processes are unknown. To the best of our knowledge, this study is the first to demonstrate the ubiquitous occurrence of sulfated sialic acids and two genes encoding the sialate: O-sulfotransferases 1 and 2 in vertebrates. These two enzymes showed about 50% amino acid sequence identity, and appeared to be complementary to each other in acceptor substrate preferences. Gene targeting experiments showed that the deficiency of these genes was lethal for medaka fish during young fry development and accompanied by different phenotypes. Thus, the sulfation of sialic acids is essential for the vertebrate development.

Sialic acids on B cells are crucial for their survival and provide protection against apoptosis

Sialic acids (Sias) on the B cell membrane are involved in cell migration, in the control of the complement system and, as sialic acid-binding immunoglobulin-like lectin (Siglec) ligands, in the regulation of cellular signaling. We studied the role of sialoglycans on B cells in a mouse model with B cell-specific deletion of cytidine monophosphate sialic acid synthase (CMAS), the enzyme essential for the synthesis of sialoglycans. Surprisingly, these mice showed a severe B cell deficiency in secondary lymphoid organs. Additional depletion of the complement factor C3 rescued the phenotype only marginally, demonstrating a complement-independent mechanism. The B cell survival receptor BAFF receptor was not up-regulated, and levels of activated caspase 3 and processed caspase 8 were high in B cells of Cmas-deficient mice, indicating ongoing apoptosis. Overexpressed Bcl-2 could not rescue this phenotype, pointing to extrinsic apoptosis. These results show that sialoglycans on the B cell surface are crucial for B cell survival by counteracting several death-inducing pathways.

Low molecular weight polysialic acid binds to properdin and reduces the activity of the alternative complement pathway

Sialic acids as the terminal caps of the cellular glycocalyx play an essential role in self-recognition and were shown to modulate complement processes via interaction between α2,3-linked sialic acids and complement factor H. Previously, it was suggested that low molecular weight α2,8-linked polysialic acid (polySia avDP20) interferes with complement activation, but the exact molecular mechanism is still unclear. Here, we show that soluble polySia avDP20 (molecular weight of ~ 6 kDa) reduced the binding of serum-derived alternative pathway complement activator properdin to the cell surface of lesioned Hepa-1c1c7 and PC-12 neuroblastoma cells. Furthermore, polySia avDP20 added to human serum blocked the alternative complement pathway triggered by plate-bound lipopolysaccharides. Interestingly, no inhibitory effect was observed with monosialic acid or oligosialic acid with a chain length of DP3 and DP5. In addition, polySia avDP20 directly bound properdin, but not complement factor H. These data show that soluble polySia avDP20 binds properdin and reduces the alternative complement pathway activity. Results strengthen the previously described concept of self-recognition of sialylation as check-point control of complement activation in innate immunity.

Establishment of fetomaternal tolerance through glycan-mediated B cell suppression

Discrimination of self from non-self is fundamental to a wide range of immunological processes1. During pregnancy, the mother does not recognize the placenta as immunologically foreign because antigens expressed by trophoblasts, the placental cells that interface with the maternal immune system, do not activate maternal T cells2. Currently, these activation defects are thought to reflect suppression by regulatory T cells3. By contrast, mechanisms of B cell tolerance to trophoblast antigens have not been identified. Here we provide evidence that glycan-mediated B cell suppression has a key role in establishing fetomaternal tolerance in mice. B cells specific for a model trophoblast antigen are strongly suppressed through CD22-LYN inhibitory signalling, which in turn implicates the sialylated glycans of the antigen as key suppressive determinants. Moreover, B cells mediate the MHC-class-II-restricted presentation of antigens to CD4+ T cells, which leads to T cell suppression, and trophoblast-derived sialoglycoproteins are released into the maternal circulation during pregnancy in mice and humans. How protein glycosylation promotes non-immunogenic placental self-recognition may have relevance to immune-mediated pregnancy complications and to tumour immune evasion. We also anticipate that our findings will bolster efforts to harness glycan biology to control antigen-specific immune responses in autoimmune disease.

Regulation of the innate immune cells during pregnancy: An immune checkpoint perspective

The foetus can be regarded as a half‐allograft implanted into the maternal body. In a successful pregnancy, the mother does not reject the foetus because of the immune tolerance mechanism at the maternal‐foetal interface. The innate immune cells are a large part of the decidual leukocytes contributing significantly to a successful pregnancy. Although the contributions have been recognized, their role in human pregnancy has not been completely elucidated. Additionally, the accumulated evidence demonstrates that the immune checkpoint molecules expressed on the immune cells are co‐inhibitory receptors regulating their activation and biological function. Therefore, it is critical to understand the immune microenvironment and explore the function of the innate immune cells during pregnancy. This review summarizes the classic immune checkpoints such as PD‐1, CTLA‐4 and some novel molecules recently identified, including TIM‐3, CD200, TIGIT and the Siglecs family on the decidual and peripheral innate immune cells during pregnancy. Furthermore, it emphasizes the role of the immune checkpoint molecules in pregnancy‐associated complications and reproductive immunotherapy.

Congenital Transmission of Apicomplexan Parasites: A Review

Apicomplexans are a group of pathogenic protists that cause various diseases in humans and animals that cause economic losses worldwide. These unicellular eukaryotes are characterized by having a complex life cycle and the ability to evade the immune system of their host organism. Infections caused by some of these parasites affect millions of pregnant women worldwide, leading to various adverse maternal and fetal/placental effects. Unfortunately, the exact pathogenesis of congenital apicomplexan diseases is far from being understood, including the mechanisms of how they cross the placental barrier. In this review, we highlight important aspects of the diseases caused by species of Plasmodium, Babesia, Toxoplasma, and Neospora, their infection during pregnancy, emphasizing the possible role played by the placenta in the host-pathogen interaction.

The expression and role of glycans at the feto-maternal interface in humans

During pregnancy, both the maternal endometrium and the blastocyst have highly glycosylated proteins with glycosylations controlled in a specific manner. Carbohydrates play a fundamental role in cell-cell and cell-matrix recognition and are involved in defining the structure and integrity of tissues. The uterus' secretions, which are rich in glycoproteins and glycogen and the presence of a functional glycocalyx on the uterine epithelium, establish a favourable milieu, which is essential for the correct implantation and subsequent development of the blastocyst. Likewise, carbohydrate residues such as fucose and sialic acid present at the placental level are determinant in creating an immuno-environment, which supports the mother's tolerance towards the fetal antigens. In this review, we explore the literature concerning the role of important glycan-epitopes at the feto-maternal interface in the human species. Moreover, we also show some unpublished interesting results on changes of glycan residues in human placenta tissues from the first trimester of pregnancy.

Gne deletion in mice leads to lethal intracerebral hemorrhage during embryonic development

Among the enzymes of the biosynthesis of sialoglycoconjugates, UDP-N-acetylglucosamine-2-epimerase/N-acetylmannosamine kinase (GNE), catalyzing the first essential step of the sialic acid (Sia) de novo biosynthesis, and CMP-Sia synthase (CMAS), activating Sia to CMP-Sia, are particularly important. The knockout of either of these enzymes in mice is embryonically lethal. While the lethality of Cmas-/- mice has been attributed to a maternal complement attack against asialo fetal placental cells, the cause of lethality in Gne-deficient embryos has remained elusive. Here, we advanced the significance of sialylation for embryonic development through detailed histological analyses of Gne-/- embryos and placentae. We found that Gne-/- embryonic and extraembryonic tissues are hyposialylated, rather than completely deficient of sialoglycans which holds true for Cmas-/- embryos. Residual sialylation of Gne-/- cells can be explained by scavenging free Sia from sialylated maternal serum glycoconjugates via the lysosomal salvage pathway. The placental architecture of Gne-/- mice was unaffected, but severe hemorrhages in the neuroepithelium with extensive bleeding into the cephalic ventricles were present at E12.5 in the mutants. At E13.5, the vast majority of Gne-/- embryos were asystolic. This phenotype persisted when Gne-/- mice were backcrossed to a complement component 3-deficient background, confirming distinct pathomechanisms of Cmas-/- and Gne-/- mice. We conclude that the low level of sialylation observed in Gne-/- mice is sufficient, both for immune homeostasis at the fetal-maternal interface and for embryonic development until E12.5. However, formation of the neural microvasculature is the first critical process depending on a higher degree of sialylation during development of the embryo proper.

Control of intestinal inflammation by glycosylation-dependent lectin-driven immunoregulatory circuits

Diverse immunoregulatory circuits operate to preserve intestinal homeostasis and prevent inflammation. Galectin-1 (Gal1), a β-galactoside-binding protein, promotes homeostasis by reprogramming innate and adaptive immunity. Here, we identify a glycosylation-dependent "on-off" circuit driven by Gal1 and its glycosylated ligands that controls intestinal immunopathology by targeting activated CD8⁺ T cells and shaping the cytokine profile. In patients with inflammatory bowel disease (IBD), augmented Gal1 was associated with dysregulated expression of core 2 β6-N-acetylglucosaminyltransferase 1 (C2GNT1) and α(2,6)-sialyltransferase 1 (ST6GAL1), glycosyltransferases responsible for creating or masking Gal1 ligands. Mice lacking Gal1 exhibited exacerbated colitis and augmented mucosal CD8⁺ T cell activation in response to 2,4,6-trinitrobenzenesulfonic acid; this phenotype was partially ameliorated by treatment with recombinant Gal1. While C2gnt1^-/- mice exhibited aggravated colitis, St6gal1^-/- mice showed attenuated inflammation. These effects were associated with intrinsic T cell glycosylation. Thus, Gal1 and its glycosylated ligands act to preserve intestinal homeostasis by recalibrating T cell immunity.

The C-Mannosylome of Human Induced Pluripotent Stem Cells Implies a Role for ADAMTS16 C-Mannosylation in Eye Development

C-mannosylation is a modification of tryptophan residues with a single mannose and can affect protein folding, secretion, and/or function. To date, only a few proteins have been demonstrated to be C-mannosylated, and studies that globally assess protein C-mannosylation are scarce. To interrogate the C-mannosylome of human induced pluripotent stem cells, we compared the secretomes of CRISPR–Cas9 mutants lacking either the C-mannosyltransferase DPY19L1 or DPY19L3 to WT human induced pluripotent stem cells using MS-based quantitative proteomics. The secretion of numerous proteins was reduced in these mutants, including that of A Disintegrin And Metalloproteinase with ThromboSpondin Motifs 16 (ADAMTS16), an extracellular protease that was previously reported to be essential for optic fissure fusion in zebrafish eye development. To test the functional relevance of this observation, we targeted dpy19l1 or dpy19l3 in embryos of the Japanese rice fish medaka (Oryzias latipes) by CRISPR–Cas9. We observed that targeting of dpy19l3 partially caused defects in optic fissure fusion, called coloboma. We further showed in a cellular model that DPY19L1 and DPY19L3 mediate C-mannosylation of a recombinantly expressed thrombospondin type 1 repeat of ADAMTS16 and thereby support its secretion. Taken together, our findings imply that DPY19L3-mediated C-mannosylation is involved in eye development by assisting secretion of the extracellular protease ADAMTS16.

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TSR1 of ADAMTS16 can be C-mannosylated.

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Deletion of DPY19L1 or DPY19L3 in hiPSCs caused reduced secretion of ADAMTS16.

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Targeting of dpy19l3 in medaka occasionally led to coloboma.

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.

Placental Glycoredox Dysregulation Associated with Disease Progression in an Animal Model of Superimposed Preeclampsia

Pregnancies carried by women with chronic hypertension are at increased risk of superimposed preeclampsia, but the placental pathways involved in disease progression remain poorly understood. In this study, we used the stroke-prone spontaneously hypertensive rat (SHRSP) model to investigate the placental mechanisms promoting superimposed preeclampsia, with focus on cellular stress and its influence on galectin-glycan circuits. Our analysis revealed that SHRSP placentas are characterized by a sustained activation of the cellular stress response, displaying significantly increased levels of markers of lipid peroxidation (i.e., thiobarbituric acid reactive substances (TBARS)) and protein nitration and defective antioxidant enzyme expression as early as gestation day 14 (which marks disease onset). Further, lectin profiling showed that such redox imbalance was associated with marked alterations of the placental glycocode, including a prominent decrease of core 1 O-glycan expression in trophoblasts and increased decidual levels of sialylation in SHRSP placentas. We also observed significant changes in the expression of galectins 1, 3 and 9 with pregnancy progression, highlighting the important role of the galectin signature as dynamic interpreters of placental microenvironmental challenges. Collectively, our findings uncover a new role for the glycoredox balance in the pathogenesis of superimposed preeclampsia representing a promising target for interventions in hypertensive disorders of pregnancy.

Spatial N-glycomics of the human aortic valve in development and pediatric endstage congenital aortic valve stenosis

Congenital aortic valve stenosis (AS) progresses as an obstructive narrowing of the aortic orifice due to deregulated extracellular matrix (ECM) production by aortic valve (AV) leaflets and leads to heart failure with no effective therapies. Changes in glycoprotein and proteoglycan distribution are a hallmark of AS, yet valvular carbohydrate content remains virtually uncharacterized at the molecular level. While almost all glycoproteins clinically linked to stenotic valvular modeling contain multiple sites for N-glycosylation, there are very few reports aimed at understanding how N-glycosylation contributes to the valve structure in disease. Here, we tested for spatial localization of N-glycan structures within pediatric congenital aortic valve stenosis. The study was done on valvular tissues 0-17 years of age with de-identified clinical data reporting pre-operative valve function spanning normal development, aortic valve insufficiency (AVI), and pediatric endstage AS. High mass accuracy imaging mass spectrometry (IMS) was used to localize N-glycan profiles in the AV structure. RNA-Seq was used to identify regulation of N-glycan related enzymes. The N-glycome was found to be spatially localized in the normal aortic valve, aligning with fibrosa, spongiosa or ventricularis. In AVI diagnosed tissue, N-glycans localized to hypertrophic commissures with increases in pauci-mannose structures. In all valve types, sialic acid (N-acetylneuraminic acid) N-glycans were the most abundant N-glycan group. Three sialylated N-glycans showed common elevation in AS independent of age. On-tissue chemical methods optimized for valvular tissue determined that aortic valve tissue sialylation shows both α2,6 and α2,3 linkages. Specialized enzymatic strategies demonstrated that core fucosylation is the primary fucose configuration and localizes to the normal fibrosa with disparate patterning in AS. This study identifies that the human aortic valve structure is spatially defined by N-glycomic signaling and may generate new research directions for the treatment of human aortic valve disease.

Sweet turning bitter: Carbohydrate sensing of complement in host defence and disease

The complement system plays a major role in threat recognition and in orchestrating responses to microbial intruders and accumulating debris. This immune surveillance is largely driven by lectins that sense carbohydrate signatures on foreign, diseased and healthy host cells and act as complement activators, regulators or receptors to shape appropriate immune responses. While carbohydrate sensing protects our bodies, misguided or impaired recognition can contribute to disease. Moreover, pathogenic microbes have evolved to evade complement by mimicking host signatures. While complement is recognized as a disease factor, we only slowly start to appreciate the role of carbohydrate interactions in the underlying processes. A better understanding of complement's sweet side will contribute to a better description of disease mechanisms and enhanced diagnostic and therapeutic options. This review introduces the key components in complement-mediated carbohydrate sensing, discusses their role in health and disease, and touches on the potential effects of carbohydrate-related disease intervention. LINKED ARTICLES: This article is part of a themed issue on Canonical and non-canonical functions of the complement system in health and disease. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v178.14/issuetoc.

Sialylation acts as a checkpoint for innate immune responses in the central nervous system

Sialic acids are monosaccharides that normally terminate the glycan chains of cell surface glyco-proteins and -lipids in mammals, and are highly enriched in the central nervous tissue. Sialic acids are conjugated to proteins and lipids (termed "sialylation") by specific sialyltransferases, and are removed ("desialylation") by neuraminidases. Cell surface sialic acids are sensed by complement factor H (FH) to inhibit complement activation or by sialic acid-binding immunoglobulin-like lectin (SIGLEC) receptors to inhibit microglial activation, phagocytosis, and oxidative burst. In contrast, desialylation of cells enables binding of the opsonins C1, calreticulin, galectin-3, and collectins, stimulating phagocytosis of such cells. Hypersialylation is used by bacteria and cancers as camouflage to escape immune recognition, while polysialylation of neurons protects synapses and neurogenesis. Insufficient lysosomal cleavage of sialylated molecules can lead to lysosomal accumulation of lipids and aggregated proteins, which if excessive may be expelled into the extracellular space. On the other hand, desialylation of immune receptors can activate them or trigger removal of proteins. Loss of inhibitory SIGLECs or FH triggers reduced clearance of aggregates, oxidative brain damage and complement-mediated retinal damage. Thus, cell surface sialylation recognized by FH, SIGLEC, and other immune-related receptors acts as a major checkpoint inhibitor of innate immune responses in the central nervous system, while excessive cleavage of sialic acid residues and consequently removing this checkpoint inhibitor may trigger lipid accumulation, protein aggregation, inflammation, and neurodegeneration.

Glycobiology and schizophrenia: a biological hypothesis emerging from genomic research

Advances in genomics are opening new windows into the biology of schizophrenia. Though common variants individually have small effects on disease risk, GWAS provide a powerful opportunity to explore pathways and mechanisms contributing to pathophysiology. Here, we highlight an underappreciated biological theme emerging from GWAS: the role of glycosylation in schizophrenia. The strongest coding variant in schizophrenia GWAS is a missense mutation in the manganese transporter SLC39A8, which is associated with altered glycosylation patterns in humans. Furthermore, variants near several genes encoding glycosylation enzymes are unambiguously associated with schizophrenia: FUT9, MAN2A1, TMTC1, GALNT10, and B3GAT1. Here, we summarize the known biological functions, target substrates, and expression patterns of these enzymes as a primer for future studies. We also highlight a subset of schizophrenia-associated proteins critically modified by glycosylation including glutamate receptors, voltage-gated calcium channels, the dopamine D2 receptor, and complement glycoproteins. We hypothesize that common genetic variants alter brain glycosylation and play a fundamental role in the development of schizophrenia. Leveraging these findings will advance our mechanistic understanding of disease and may provide novel avenues for treatment development.

A comprehensive review of edible bird's nest

Edible bird's nest (EBN) is built by seven species of Aerodramus and Collocalia (Apodidae), using salivary gland secretion mixed with feathers or grass during the breeding. Its rich nutritional values such as anti-aging activity, immunomodulatory and antioxidant activity make consumers flock to it. Consumers' pursuit, on the one hand, aroused the arrogance of counterfeiters, which eventually leads to food safety problems. On the other hand, it promotes the in-depth studies of EBN in all aspects, such as compositions, biological activities, authenticity identification, quality control, and so on. This paper presented the origins and classifications of EBN and the current situation of EBN industry in detail; reviewed the nutritional compositions, pharmacological actions, identification, inspection and content determination of EBN comprehensively; and prospected the future research directions to provide suggestions for the further study.

Essential Role of Complement in Pregnancy: From Implantation to Parturition and Beyond

The complement cascade was identified over 100 years ago, yet investigation of its role in pregnancy remains an area of intense research. Complement inhibitors at the maternal-fetal interface prevent inappropriate complement activation to protect the fetus. However, this versatile proteolytic cascade also favorably influences numerous stages of pregnancy, including implantation, fetal development, and labor. Inappropriate complement activation in pregnancy can have adverse lifelong sequelae for both mother and child. This review summarizes the current understanding of complement activation during all stages of pregnancy. In addition, consequences of complement dysregulation during adverse pregnancy outcomes from miscarriage, preeclampsia, and pre-term birth are examined. Finally, future research directions into complement activation during pregnancy are considered.

Control of Innate Immunity by Sialic Acids in the Nervous Tissue

Sialic acids (Sias) are the most abundant terminal sugar residues of glycoproteins and glycolipids on the surface of mammalian cells. The nervous tissue is the organ with the highest expression level of Sias. The ‘sialylation’ of glycoconjugates is performed via sialyltransferases, whereas ‘desialylation’ is done by sialidases or is a possible consequence of oxidative damage. Sialic acid residues on the neural cell surfaces inhibit complement and microglial activation, as well as phagocytosis of the underlying structures, via binding to (i) complement factor H (CFH) or (ii) sialic acid-binding immunoglobulin-like lectin (SIGLEC) receptors. In contrast, activated microglial cells show sialidase activity that desialylates both microglia and neurons, and further stimulates innate immunity via microglia and complement activation. The desialylation conveys neurons to become susceptible to phagocytosis, as well as triggers a microglial phagocytosis-associated oxidative burst and inflammation. Dysfunctions of the ‘Sia–SIGLEC’ and/or ‘Sia–complement’ axes often lead to neurological diseases. Thus, Sias on glycoconjugates of the intact glycocalyx and its desialylation are major regulators of neuroinflammation.

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.

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.

Reduced sialylation triggers homeostatic synapse and neuronal loss in middle-aged mice

Sialic acid-binding Ig-like lectin (Siglec) receptors are linked to neurodegenerative processes, but the role of sialic acids in physiological aging is still not fully understood. We investigated the impact of reduced sialylation in the brain of mice heterozygous for the enzyme glucosamine-2-epimerase/N-acetylmannosamine kinase (GNE+/-) that is essential for sialic acid biosynthesis. We demonstrate that GNE+/- mice have hyposialylation in different brain regions, less synapses in the hippocampus and reduced microglial arborization already at 6 months followed by increased loss of neurons at 12 months. A transcriptomic analysis revealed no pro-inflammatory changes indicating an innate homeostatic immune process leading to the removal of synapses and neurons in GNE+/- mice during aging. Crossbreeding with complement C3-deficient mice rescued the earlier onset of neuronal and synaptic loss as well as the changes in microglial arborization. Thus, sialic acids of the glycocalyx contribute to brain homeostasis and act as a recognition system for the innate immune system in the brain.

Podocyte-Specific Sialylation-Deficient Mice Serve as a Model for Human FSGS

BACKGROUND

The etiology of steroid-resistant nephrotic syndrome, which manifests as FSGS, is not completely understood. Aberrant glycosylation is an often underestimated factor for pathologic processes, and structural changes in the glomerular endothelial glycocalyx have been correlated with models of nephrotic syndrome. Glycans are frequently capped by sialic acid (Sia), and sialylation's crucial role for kidney function is well known. Human podocytes are highly sialylated; however, sialylation's role in podocyte homeostasis remains unclear.

METHODS

We generated a podocyte-specific sialylation-deficient mouse model (PCmas^-/- ) by targeting CMP-Sia synthetase, and used histologic and ultrastructural analysis to decipher the phenotype. We applied CRISPR/Cas9 technology to generate immortalized sialylation-deficient podocytes (asialo-podocytes) for functional studies.

RESULTS

Progressive loss of sialylation in PCmas^-/- mice resulted in onset of proteinuria around postnatal day 28, accompanied by foot process effacement and loss of slit diaphragms. Podocyte injury led to severe glomerular defects, including expanded capillary lumen, mesangial hypercellularity, synechiae formation, and podocyte loss. In vivo, loss of sialylation resulted in mislocalization of slit diaphragm components, whereas podocalyxin localization was preserved. In vitro, asialo-podocytes were viable, able to proliferate and differentiate, but showed impaired adhesion to collagen IV.

CONCLUSIONS

Loss of cell-surface sialylation in mice resulted in disturbance of podocyte homeostasis and FSGS development. Impaired podocyte adhesion to the glomerular basement membrane most likely contributed to disease development. Our data support the notion that loss of sialylation might be part of the complex process causing FSGS. Sialylation, such as through a Sia supplementation therapy, might provide a new therapeutic strategy to cure or delay FSGS and potentially other glomerulopathies.