Involvement of Bmal1 and Clock in Bromobenzene Metabolite-Induced Diurnal Renal Toxicity.

Circadian rhythms are endogenous oscillators that regulate 24 h behavioral and physiological processes. Our previous investigation demonstrated that bromobenzene metabolite (4-bromocatechol: 4-BrCA) exhibited chronotoxicity (i.e., the nephrotoxicity induced by 4-BrCA was observed during the dark phase, while not observed at light phase in mice). However, the molecular mechanism is still unknown. The aim of the present study is to investigate the cellular molecule(s) involved in the 4-BrCA-induced nephrotoxicity using mouse renal cortex tubular cell lines (MuRTE61 cells). We found that 4-BrCA showed dose dependent (0.01-1 mM) cell proliferation defect in MuRTE61 cells. By treating with 0.03 mM 4-BrCA, we demonstrated that major clock genes (Bmal1, Clock, Cry1, Cry2, Per1, and Per2) were significantly downregulated. Interestingly, the expression levels of two genes, Bmal1 and Clock, continued to decrease after 3 h of treatment with 4-BrCA, while Cry1, Per1, and Per2 were unchanged until 24 h of treatment. Moreover, BMAL1 and CLOCK levels are higher at light phase. We speculated that BMAL1 and CLOCK might function defensively against 4-BrCA-induced nephrotoxicity since the expression levels of Bmal1 and Clock were rapidly decreased. Finally, overexpression of Bmal1 and Clock restored 4-BrCA-induced cell proliferation defect in MuRTE61 cells. Taken together, our results suggest that Bmal1 and Clock have protective roles against 4-BrCA-induced nephrotoxicity.

Mucin-type O-glycosylation controls pluripotency in mouse embryonic stem cells via Wnt receptor endocytosis.

Mouse embryonic stem cells (ESCs) can differentiate into a range of cell types during development, and this pluripotency is regulated by various extrinsic and intrinsic factors. Mucin-type O-glycosylation has been suggested to be a potential factor in the control of ESC pluripotency, and is characterized by the addition of N-acetylgalactosamine (GalNAc) to serine or threonine residues of membrane-anchored proteins and secreted proteins. To date, the relationship between mucin-type O-glycosylation and signaling in ESCs remains undefined. Here, we identify the elongation pathway via C1GalT1 that synthesizes T antigen (Galß1-3GalNAc) as the most prominent among mucin-type O-glycosylation modifications in ESCs. Moreover, we show that mucin-type O-glycosylation on the Wnt signaling receptor frizzled-5 (Fzd5) regulates its endocytosis via galectin-3 binding to T antigen, and that reduction of T antigen results in the exit of the ESCs from pluripotency via canonical Wnt signaling activation. Our findings reveal a novel regulatory mechanism that modulates Wnt signaling and, consequently, ESC pluripotency.This article has an associated First Person interview with the first author of the paper.

Toolbox Accelerating Glycomics (TAG): Improving Large-Scale Serum Glycomics and Refinement to Identify SALSA-Modified and Rare Glycans.

Glycans are involved in many fundamental cellular processes such as growth, differentiation, and morphogenesis. However, their broad structural diversity makes analysis difficult. Glycomics via mass spectrometry has focused on the composition of glycans, but informatics analysis has not kept pace with the development of instrumentation and measurement techniques. We developed Toolbox Accelerating Glycomics (TAG), in which glycans can be added manually to the glycan list that can be freely designed with labels and sialic acid modifications, and fast processing is possible. In the present work, we improved TAG for large-scale analysis such as cohort analysis of serum samples. The sialic acid linkage-specific alkylamidation (SALSA) method converts differences in linkages such as α2,3- and α2,6-linkages of sialic acids into differences in mass. Glycans modified by SALSA and several structures discovered in recent years were added to the glycan list. A routine to generate calibration curves has been implemented to explore quantitation. These improvements are based on redefinitions of residues and glycans in the TAG List to incorporate information on glycans that could not be attributed because it was not assumed in the previous version of TAG. These functions were verified through analysis of purchased sera and 74 spectra with linearity at the level of R2 > 0.8 with 81 estimated glycan structures obtained including some candidate of rare glycans such as those with the N,N'-diacetyllactosediamine structure, suggesting they can be applied to large-scale analyses.

Comprehensive Glycomic Approach Reveals Novel Low-Molecular-Weight Blood Group-Specific Glycans in Serum and Cerebrospinal Fluid.

ABO blood antigens on the human red blood cell membrane as well as different cells in various human tissues have been thoroughly studied. Anti-A and -B antibodies of IgM are present in serum/plasma, but blood group-specific glyco-antigens have not been extensively described. In this study, we performed comprehensive and quantitative serum glycomic analyses of various glycoconjugates and free oligosaccharides in all blood groups. Our comprehensive glycomic approach revealed that blood group-specific antigens in serum/plasma are predominantly present on glycosphingolipids on lipoproteins rather than glycoproteins. Expression of the ABO antigens on glycosphingolipids depends not only on blood type but also on secretor status. Blood group-specific glycans in serum/plasma were classified as type I, whereas those on RBCs had different structures including hexose and hexosamine residues. Analysis of free oligosaccharides revealed that low-molecular-weight blood group-specific glycans, commonly containing lacto-N-difucotetraose, were expressed in serum/plasma according to blood group. Furthermore, comprehensive glycomic analysis in human cerebrospinal fluid showed that many kinds of free oligosaccharides were highly expressed, and low-molecular-weight blood group-specific glycans, which existed in plasma from the same individuals, were present. Our findings provide the first evidence for low-molecular-weight blood group-specific glycans in both serum/plasma and cerebrospinal fluid.

Different Renal Chronotoxicity of Bromobenzene and Its Intermediate Metabolites in Mice.

Bromobenzene (BB) is known to pose a serious threat to human health. We previously demonstrated that BB showed chronotoxicity, that is, daily fluctuations in the severity of hepatotoxicity induced in mice. Although BB showed mild nephrotoxicity, a daily fluctuation was not observed in this toxicity. This might be attributed to the fact that BB-induced chronotoxicity is observed only in the liver and not in the kidneys and that the damage caused by BB is prominent in the liver, masking the daily fluctuation in nephrotoxicity. To confirm these two possibilities, we examined the daily fluctuations in nephrotoxicity due to BB intermediate metabolites that target the kidneys: 3-bromophenol, bromohydroquinone, and 4-bromocatechol. Mice were injected with 3-bromophenol, bromohydroquinone, or 4-bromocatechol intraperitoneally at six different time points in a day (zeitgeber time (ZT): ZT2, ZT6, ZT10, ZT14, ZT18, or ZT22). Mortality was monitored for 7 d post-injection. Mice were more sensitive to the acute toxicity of these metabolites around at ZT14 (dark-phase) exposure than around at ZT2 (light-phase) exposure. Furthermore, mice administered with a non-lethal dose of 4-bromocatechol showed significant increases in the levels of plasma blood urea nitrogen and renal malondialdehyde at ZT14 exposure. Moreover, glutathione peroxidase-4, a ferroptosis indicator, was attenuated at ZT14 exposure. These results indicate the toxicity of BB metabolites was higher during the dark-phase exposure, and demonstrate the reason why the diurnal variation of nephrotoxicity by BB was not observed in our previous report is that renal damage was masked due to severe hepatic damage.

Chronotoxicity of Streptomycin-Induced Renal Injury in Mice.

The aim of the present study was to investigate the "chronotoxicity" of streptomycin (SM) in relation to its circadian periodicity. Male ICR mice were injected intraperitoneally with SM (780 mg/kg, one shot) one of six time points throughout the day. Mortality was monitored until 14 d after the injection and clearly differed depending on the timing of the injection (i.e., mice were more sensitive to injection during the dark phase). Moreover, when mice were administered with non-lethal doses of SM (550 mg/kg, every 24 h for 3 d, in the light phase or dark phase), the levels of nephrotoxicity indicators (blood urea nitrogen and renal levels of malondialdehyde and cyclooxygenase-2) were significantly increased by the injection in the dark phase, but not in the light phase. These results suggested that SM showed clear chronotoxicity. Our current data indicated that chronotoxicology may provide valuable information on the importance of injection timings for evaluations of toxicity and undesirable side effects.

Quantifying Protein-Specific N-Glycome Profiles by Focused Protein and Immunoprecipitation Glycomics.

Serum N-glycans have been reported to be potential diagnostic and therapeutic biomarkers for many diseases and conditions, such as inflammation, fibrosis, and cancer progression. We previously described the focused protein glycomic analysis (FPG) from gel-separated serum proteins. With this methodology, we sought novel glycan biomarkers for nonalcoholic steatohepatitis (NASH) and successfully identified some N-glycans that were significantly elevated in NASH patients compared to nonalcoholic fatty liver patients. Among them, trisialylated monofucosylated triantennary glycan (A3F) of alpha-1 antitrypsin showed the most dynamic change. For rapid identification of N-glycans on the focused proteins, we constructed a simplified method called immunoprecipitation glycomics (IPG), where the target proteins were immunoprecipitated with affinity beads and subsequently subjected to glycomic analysis by MALDI-TOF MS. Focusing on alpha-1 antitrypsin and ceruloplasmin as the target proteins, we compared the values of N-glycans determined by FPG and IPG. The quantified values of each N-glycan by these two methods showed a statistically significant correlation, indicating that high throughput and quantitative N-glycomics of targeted proteins can be achieved by the simplified IPG method. Thus, an analytical strategy combining FPG and IPG can be adapted to general biomarker discovery and validation in appropriate disease areas.

Identification of unique glycoisoforms of vitamin D-binding protein and haptoglobin as biomarker candidates in hepatocarcinogenesis of STAM mice.

Hepatocellular carcinoma (HCC) is the major subtype of primary liver cancer, and is typically diagnosed late in its course. Considering the limitations and the reluctance of patients to undergo a liver biopsy, a reliable, noninvasive diagnostic marker that predicts and assesses the treatment and prognosis of HCC is needed. With recent technological advances of mass spectrometry, glycomics is gathering momentum and holds substantial potential to discover new glycan markers in cancer research. Here, to discover specific glycan markers for the early diagnosis of HCC, we analyzed the glycan profiles of gel-separated serum proteins of progressive liver disease model mice. By focused protein glycomics of 12 gel-separated glycoproteins using sera from the mouse models, we revealed the entire profile of glycans in each major serum protein. We found that the levels of trisialylated triantennary glycans of haptoglobin and vitamin D-binding protein increased significantly as the disease progressed, while the alteration in these protein levels were modest. Furthermore, these glycan increases were not observed in age-matched control mice. In conclusion, our approach has identified specific glycan marker candidates for the early diagnosis of HCC.

Impact of the Niemann-Pick c1 Gene Mutation on the Total Cellular Glycomics of CHO Cells.

Niemann-Pick disease type C (NPC) is an autosomal recessive lipid storage disorder, and the majority of cases are caused by mutations in the NPC1 gene. In this study, we clarified how a single gene mutation in the NPC1 gene impacts the cellular glycome by analyzing the total glycomic expression profile of Chinese hamster ovary cell mutants defective in the Npc1 gene (Npc1 KO CHO cells). A number of glycomic alterations were identified, including increased expression of lactosylceramide, GM1, GM2, GD1, various neolacto-series glycosphingolipids, and sialyl-T (O-glycan), which was found to be the major sialylated protein-bound glycan, as well as various N-glycans, which were commonly both fucosylated and sialylated. We also observed significant increases in the total amounts of free oligosaccharides (fOSs), especially in the unique complex- and hybrid-type fOSs. Treatment of Npc1 KO CHO cells with 2-hydroxypropyl-ß-cyclodextrin (HPBCD), which can reduce cholesterol and glycosphingolipid (GSL) storage, did not affect the glycomic alterations observed in the GSL-, N-, and O-glycans of Npc1 KO CHO cells. However, HPBCD treatment corrected the glycomic alterations observed in fOSs to levels observed in wild-type cells.

Glycomics of human embryonic stem cells and human induced pluripotent stem cells.

Most cells are coated by a dense glycocalyx composed of glycoconjugates such as glycosphingolipids, glycoproteins, and proteoglycans. The overall glycomic profile is believed to be crucial for the diverse roles of glycans, which are mediated by specific interactions that regulate cell-cell adhesion, the immune response, microbial pathogenesis, and other cellular events. Many cell surface markers were discovered and identified as glycoconjugates such as stage-specific embryonic antigen, Tra-1-60/81 and various other cell surface molecules (e.g., cluster of differentiation). Recent progress in the development of analytical methodologies and strategies has begun to clarify the cellular glycomics of various cells including human embryonic stem cells (hESCs) and human induced pluripotent stem cells (hiPSCs). The glycomic profiles of these cells are highly cell type-specific and reflect cellular alterations, such as development, differentiation and cancerous change. In this mini review, we briefly summarize the glycosylation spectra specific to hESCs and hiPSCs, which cover glycans of all major glycoconjugates (i.e., glycosphingolipids, N- and O-glycans of glycoproteins, and glycosaminoglycans) and free oligosaccharides.

Quantitative analysis of total serum glycome in human and mouse.

Model mice are frequently used in drug discovery research. Knowledge of similarities and differences between the mouse and human glycomes is critical when model mice are used for the discovery of glycan-related biomarkers and targets for therapeutic intervention. Since few comparative glycomic studies between human and mouse have been conducted, we performed a comprehensive comparison of the major classes of glycans in human and mouse sera using mass spectrometric and liquid chromatographic analyses. Up to 131 serum glycans, including N-glycans, free oligosaccharides (fOSs), glycosaminoglycans, O-glycans, and glycosphingolipid (GSL)-glycans, were quantified. In both serum samples, N-glycans were the most abundant in the total serum glycome, while fOSs were the least abundant. As expected, the diversity of sialic acid (i.e. Neu5Ac vs. Neu5Gc) was the major species difference between human and mouse in terms of N- and O-glycosylation, while GSL-glycomic profiles were completely different, even when the sialic acid diversity was taken into consideration. Furthermore, total serum glycomics of STAM mouse were unveiled as an initial step to identify novel biomarkers of liver diseases, with which we could identify several glycans with expression significantly increased or decreased expression.

Glycomics of human embryonic stem cells and human induced pluripotent stem cells.

Most cells are coated by a dense glycocalyx composed of glycoconjugates such as glycosphingolipids, glycoproteins, and proteoglycans. The overall glycomic profile is believed to be crucial for the diverse roles of glycans, which are mediated by specific interactions that regulate cell-cell adhesion, the immune response, microbial pathogenesis, and other cellular events. Many cell surface markers were discovered and identified as glycoconjugates such as stage-specific embryonic antigen, Tra-1-60/81 and various other cell surface molecules (e.g., cluster of differentiation). Recent progress in the development of analytical methodologies and strategies has begun to clarify the cellular glycomics of various cells including human embryonic stem cells (hESCs) and human induced pluripotent stem cells (hiPSCs). The glycomic profiles of these cells are highly cell type-specific and reflect cellular alterations, such as development, differentiation and cancerous change. In this mini review, we briefly summarize the glycosylation spectra specific to hESCs and hiPSCs, which cover glycans of all major glycoconjugates (i.e., glycosphingolipids, N- and O-glycans of glycoproteins, and glycosaminoglycans) and free oligosaccharides.

Lack of galactosylation enhances the pathogenic activity of IgG1 but Not IgG2a anti-erythrocyte autoantibodies.

IgG bears asparagine-linked oligosaccharide side chains in the Fc region. Variations in their extent of galactosylation and sialylation could modulate IgG Fc-dependent effector functions, and hence Ab activity. However, it has not yet been clarified whether the pathogenic potential of IgG autoantibodies is consistently enhanced by the absence of galactose residues per se or the lack of terminal sialylation, which is dependent on galactosylation. Moreover, it remains to be defined whether the increased pathogenicity of agalactosylated IgG is related to activation of the complement pathway by mannose-binding lectin, as suggested by in vitro studies. Using a murine model of autoimmune hemolytic anemia, we defined the contribution of galactosylation or sialylation to the pathogenic activity of IgG1 and IgG2a anti-erythrocyte class-switch variants of 34-3C monoclonal autoantibody. We generated their degalactosylated or highly sialylated glycovariants and compared their pathogenic effects with those of highly galactosylated or desialylated counterparts. Our results demonstrated that lack of galactosylation, but not sialylation, enhanced the pathogenic activity of 34-3C IgG1, but not IgG2a autoantibodies. Moreover, analysis of in vivo complement activation and of the pathogenic activity in mice deficient in C3 or IgG FcRs excluded the implication of mannose-binding lectin-mediated complement activation in the enhanced pathogenic effect of agalactosylated IgG1 anti-erythrocyte autoantibodies.

Total cellular glycomics allows characterizing cells and streamlining the discovery process for cellular biomarkers.

Although many of the frequently used pluripotency biomarkers are glycoconjugates, a glycoconjugate-based exploration of novel cellular biomarkers has proven difficult due to technical difficulties. This study reports a unique approach for the systematic overview of all major classes of oligosaccharides in the cellular glycome. The proposed method enabled mass spectrometry-based structurally intensive analyses, both qualitatively and quantitatively, of cellular N- and O-linked glycans derived from glycoproteins, glycosaminoglycans, and glycosphingolipids, as well as free oligosaccharides of human embryonic stem cells (hESCs), induced pluripotent stem cells (hiPSCs), and various human cells derived from normal and carcinoma cells. Cellular total glycomes were found to be highly cell specific, demonstrating their utility as unique cellular descriptors. Structures of glycans of all classes specifically observed in hESCs and hiPSCs tended to be immature in general, suggesting the presence of stem cell-specific glycosylation spectra. The current analysis revealed the high similarity of the total cellular glycome between hESCs and hiPSCs, although it was suggested that hESCs are more homogeneous than hiPSCs from a glycomic standpoint. Notably, this study enabled a priori identification of known pluripotency biomarkers such as SSEA-3, -4, and -5 and Tra-1-60/81, as well as a panel of glycans specifically expressed by hESCs and hiPSCs.

Quantitative GSL-glycome analysis of human whole serum based on an EGCase digestion and glycoblotting method.

Glycosphingolipids (GSLs) are lipid molecules linked to carbohydrate units that form the plasma membrane lipid raft, which is clustered with sphingolipids, sterols, and specific proteins, and thereby contributes to membrane physical properties and specific recognition sites for various biological events. These bioactive GSL molecules consequently affect the pathophysiology and pathogenesis of various diseases. Thus, altered expression of GSLs in various diseases may be of importance for disease-related biomarker discovery. However, analysis of GSLs in blood is particularly challenging because GSLs are present at extremely low concentrations in serum/plasma. In this study, we established absolute GSL-glycan analysis of human serum based on endoglycoceramidase digestion and glycoblotting purification. We established two sample preparation protocols, one with and the other without GSL extraction using chloroform/methanol. Similar amounts of GSL-glycans were recovered with the two protocols. Both protocols permitted absolute quantitation of GSL-glycans using as little as 20 µl of serum. Using 10 healthy human serum samples, up to 42 signals corresponding to GSL-glycan compositions could be quantitatively detected, and the total serum GSL-glycan concentration was calculated to be 12.1-21.4 µM. We further applied this method to TLC-prefractionated serum samples. These findings will assist the discovery of disease-related biomarkers by serum GSL-glycomics.

Decreased amyloid-ß pathologies by intracerebral loading of glycosphingolipid-enriched exosomes in Alzheimer model mice.

Elevated levels of amyloid-ß peptide (Aß) in the human brain are linked to the pathogenesis of Alzheimer disease. Recent in vitro studies have demonstrated that extracellular Aß can bind to exosomes, which are cell-secreted nanovesicles with lipid membranes that are known to transport their cargos intercellularly. Such findings suggest that the exosomes are involved in Aß metabolism in brain. Here, we found that neuroblastoma-derived exosomes exogenously injected into mouse brains trapped Aß and with the associated Aß were internalized into brain-resident phagocyte microglia. Accordingly, continuous intracerebral administration of the exosomes into amyloid-ß precursor protein transgenic mice resulted in marked reductions in Aß levels, amyloid depositions, and Aß-mediated synaptotoxicity in the hippocampus. In addition, we determined that glycosphingolipids (GSLs), a group of membrane glycolipids, are highly abundant in the exosomes, and the enriched glycans of the GSLs are essential for Aß binding and assembly on the exosomes both in vitro and in vivo. Our data demonstrate that intracerebrally administered exosomes can act as potent scavengers for Aß by carrying it on the exosome surface GSLs and suggest a role of exosomes in Aß clearance in the central nervous system. Improving Aß clearance by exosome administration would provide a novel therapeutic intervention for Alzheimer disease.

Quantitative O-Glycomics by Microwave-Assisted ß-Elimination in the Presence of Pyrazolone Analogues.

O-Linked glycosylation of serine/threonine residues is a posttranslational modification of proteins and is essential for protein recognition and lipid functions on cell surfaces and within cells. The characterization of differently structured O-linked glycans (O-glycans) is particularly challenging because there is no known endoglycosidase for such groups. Therefore, chemical digestion approaches have been widely used; however, it is sometimes difficult to suppress unwanted side reactions. Recently, we reported a novel O-glycomics procedure using ß-elimination in the presence of pyrazolone analogues (BEP). In the present study, we describe a microwave (MW)-assisted BEP procedure for rapid and quantitative O-glycomic analysis. Following optimization of the reaction conditions, the MW-assisted BEP reaction substantially improved the recovery of total O-glycans from model glycoproteins (PSM) and the reaction time was reduced from 16 to 2 h. Combined with sequential solid-phase extractions, this MW-assisted BEP procedure enabled O-glycomic analyses of various biological samples.

POMGNT1 Is Glycosylated by Mucin-Type O-Glycans.

Protein O-linked mannose ß1,2-N-acetylglucosaminyltransferase 1 (POMGNT1) is a Golgi glycosyltransferase that catalyzes the formation of the N-acetylglucosamine (GlcNAc) ß1→2Man linkage of O-mannosyl glycan. POMGNT1 is not modified by N-glycans because there are no potential N-glycosylation sites; however, it is not clear whether POMGNT1 is modified by O-glycans. To determine whether POMGNT1 is O-glycosylated, we prepared recombinant human POMGNT1 from HEK293T cells. The recombinant POMGNT1 was recognized by Sambucus sieboldiana lectin (SSA), and sialidase digestion of POMGNT1 decreased SSA reactivity and enhanced the reactivity of Arachis hypogaea lectin (PNA). These results suggest that POMGNT1 is modified by a sialylated core-1 O-glycan. Next, we analyzed the structures of the O-glycans on POMGNT1 by ß-elimination and pyrazolone-labeling methods in combination with mass spectrometry. We identified several mucin-type O-glycans containing (NeuAc)1(Hex)1(HexNAc)1, (NeuAc)2(Hex)1(HexNAc)1, and (NeuAc)2(Hex)2(HexNAc)2. To examine whether the O-glycans affect the functions and properties of POMGNT1, we compared glycosylated and non-glycosylated forms of recombinant sPOMGNT1 for their activity and surface hydrophobicity using the hydrophobic probe 1-anilino-8-naphthalene sulfonate (ANS). POMGNT1 activity and surface hydrophobicity were not affected by the presence or absence of O-glycans.

Theoretical Studies on the Reaction Mechanism of Schiff Base Formation from Hexoses.

The Maillard reaction is one of the nonenzymatic post-translational modifications of proteins. Products of this reaction are considered to be related to aging diseases and the sensation of taste. In the initial stage of the Maillard reaction, Schiff base formation first occurs by the nucleophilic attack of amine nitrogen in proteins, and then, the reaction proceeds through the formation of 1,2-eminal and Amadori compounds. In this study, we computationally investigated the reaction pathway of Schiff base formation from hexoses. The optimized geometries of energy minima and transition states were calculated by using the density functional theory with the CAM-B3LYP/6-311+G(2d,2p) level of theory. The Schiff base formation progressed through three steps: two steps of carbinolamine formation and one step of dehydration. The dehydration is considered to be the rate-determining step in all hexoses because the activation barrier of the dehydration was higher than that of the carbinolamine formation. Furthermore, the steric configuration of the OH group at positions 2 and 3 affected the activation barrier.

Sialic acid-dependent attachment of mucins from three mouse strains to Entamoeba histolytica.

Mouse strain-specific differences in the carbohydrate composition of intestinal mucins were hypothesized to account for strain-dependent susceptibility to Entamoeba histolytica. To test this hypothesis, intestinal mucins from susceptible and resistant inbred strains of mice were analyzed for their O-glycan content and for their ability to inhibit amoebic adherence to (GalNAc)12-27-HSA neo-glycoproteins. The results showed that the colorectal mucin O-glycan of susceptible CBA mice was lower in sialic acid content than that of resistant C57BL/6 and BALB/c mice. Mucins from CBA mice were more potent inhibitors of E. histolytica adherence to neo-glycoproteins than were mucins from C57BL/6 or BALB/c mice. Consistent with the role of terminal Gal/GalNAc as a receptor for amoebic adherence, sialidase treatment of C57BL/6 and BALB/c colorectal mucins increased their ability to inhibit E. histolytica adherence to the neo-glycoproteins. These results provide evidence of mouse strain-specific differences in the sialic acids content of mucin O-glycans. These dissimilarities likely contribute to the differential susceptibility of the three mouse strains to E. histolytica infection.