Development of immunoglobulin A nephropathy- like disease in beta-1,4-galactosyltransferase-I-deficient mice

Lactobacillus casei Cell Wall Extract and Production of Galactose-Deficient IgA1 in a Humanized IGHA1 Mouse Model

Key Points

We generated a transgenic mouse model expressing the human IgA1 heavy chain, which has a hinge region with rich O -linked glycosylation. After inflammatory stimulation, the mouse model showed elevated galactose-deficient IgA1 levels in the serum. Coupled with complement H factor mutant, the mice model exhibited glomerular lesions, associated with hematuria and albuminuria like IgA nephropathy.

Background

IgA nephropathy is the most common primary glomerulonephritis worldwide, and there is emerging evidence linking galactose-deficient IgA1 (Gd-IgA1) to the pathogenesis of the disease. However, mouse models that can be used to study Gd-IgA1's origin of production, biochemical characteristics, and immune reactivity are lacking.

Methods

We generated a humanized IgA1 mouse model with transgenic expression of the human IGHA1 gene from the mouse chromosomal locus of IgA heavy chain. The IGHA1 +/+ mice were crossed with complement factor H heterozygous mutant (FHW/R) to generate IGHA1 +/+FHW/R mice. IGHA1 +/+ mice were exposed to different levels of environmental pathogens in the first 4 months, as housed in germ-free, specific pathogen–free, or conventional environments. In addition, wild-type C57BL/6J mice, IGHA1 +/+ mice, and IGHA1 +/+FHW/R mice were inoculated with Lactobacillus casei cell wall extract (LCWE) mixed with complete Freund's adjuvant (CFA) at 2 months of age to develop a mouse model of IgA nephropathy.

Results

Elevated levels of human IgA1 in blood circulation and mucosal sites were observed in IGHA1 +/+ mice from exposure to pathogens. Compared with buffer-treated control mice, LCWE plus CFA-treated mice had moderately elevated levels of circulating human IgA1 (by one-fold) and human IgA1 immune complexes (by two-fold). Serum Gd-IgA1 levels increased four-fold after LCWE treatments. Analyses of the O -glycopeptides of the IgA1 hinge region confirmed hypogalactosylation of IgA1, with the variety of the glycoforms matching those seen in clinical samples. Furthermore, LCWE induced persistent IgA1 and C3 deposition in the glomerular mesangial areas in association with mesangial expansion and hypercellularity, which are frequently observed in IgA nephropathy biopsies. The IGHA1+/+FHW/R mice stimulated with LCWE and CFA developed albuminuria and hematuria.

Conclusions

We observed elevated plasma Gd-IgA1 levels with kidney deposition of IgA1 in the IGHA1 +/+ mice after LCWE and CFA. In conjunction with factor H mutation, the mice exhibited severe glomerular alterations, associated with hematuria and albuminuria in resemblance of clinical IgA nephropathy.

Lessons from IgA Nephropathy Models

IgA nephropathy (IgAN) is the most common type of primary glomerulonephritis worldwide; however, the underlying mechanisms of this disease are not fully understood. This review explores several animal models that provide insights into IgAN pathogenesis, emphasizing the roles of aberrant IgA1 glycosylation and immune complex formation. It discusses spontaneous, immunization, and transgenic models illustrating unique aspects of IgAN development and progression. The animal models, represented by the grouped ddY (gddY) mouse, have provided guidance concerning the multi-hit pathogenesis of IgAN. In this paradigm, genetic and environmental factors, including the dysregulation of the mucosal immune system, lead to increased levels of aberrantly glycosylated IgA, nephritogenic immune complex formation, and subsequent glomerular deposition, followed by mesangial cell activation and injury. Additionally, this review considers the implications of clinical trials targeting molecular pathways influenced by IgAN (e.g., a proliferation-inducing ligand [APRIL]). Collectively, these animal models have expanded the understanding of IgAN pathogenesis while facilitating the development of therapeutic strategies that are currently under clinical investigation. Animal-model-based studies have the potential to facilitate the development of targeted therapies with reduced side effects for IgAN patients.

Intestinal epithelium dysfunctions cause IgA deposition in the kidney glomeruli of intestine-specific Ap1m2-deficient mice

BACKGROUND

Intestinal epithelial cells (IECs) serve as robust barriers against potentially hostile luminal antigens and commensal microbiota. Epithelial barrier dysfunction enhances intestinal permeability, leading to leaky gut syndrome (LGS) associated with autoimmune and chronic inflammatory disorders. However, a causal relationship between LGS and systemic disorders remains unclear. Ap1m2 encodes clathrin adaptor protein complex 1 subunit mu 2, which facilitates polarized protein trafficking toward the basolateral membrane and contributes to the establishment of epithelial barrier functions.

METHODS

We generated IEC-specific Ap1m2-deficient (Ap1m2ΔIEC) mice with low intestinal barrier integrity as an LSG model and examined the systemic impact.

FINDINGS

Ap1m2ΔIEC mice spontaneously developed IgA nephropathy (IgAN)-like features characterized by the deposition of IgA-IgG immune complexes and complement factors in the kidney glomeruli. Ap1m2 deficiency markedly enhanced aberrantly glycosylated IgA in the serum owing to downregulation and mis-sorting of polymeric immunoglobulin receptors in IECs. Furthermore, Ap1m2 deficiency caused intestinal dysbiosis by attenuating IL-22-STAT3 signaling. Intestinal dysbiosis contributed to the pathogenesis of IgAN because antibiotic treatment reduced aberrantly glycosylated IgA production and renal IgA deposition in Ap1m2ΔIEC mice.

INTERPRETATION

IEC barrier dysfunction and subsequent dysbiosis by AP-1B deficiency provoke IgA deposition in the mouse kidney. Our findings provide experimental evidence of a pathological link between LGS and IgAN.

FUNDING

AMED, AMED-CREST, JSPS Grants-in-Aid for Scientific Research, JST CREST, Fuji Foundation for Protein Research, and Keio University Program for the Advancement of Next Generation Research Projects.

Oral bacteria induce IgA autoantibodies against a mesangial protein in IgA nephropathy model mice

IgA nephropathy (IgAN) is caused by deposition of IgA in the glomerular mesangium. The mechanism of selective deposition and production of IgA is unclear; however, we recently identified the involvement of IgA autoantibodies. Here, we show that CBX3 is another self-antigen for IgA in gddY mice, a spontaneous IgAN model, and in IgAN patients. A recombinant antibody derived from gddY mice bound to CBX3 expressed on the mesangial cell surface in vitro and to glomeruli in vivo. An elemental diet and antibiotic treatment decreased the levels of autoantibodies and IgAN symptoms in gddY mice. Serum IgA and the recombinant antibody from gddY mice also bound to oral bacteria of the mice and binding was competed with CBX3. One species of oral bacteria was markedly decreased in elemental diet-fed gddY mice and induced anti-CBX3 antibody in normal mice upon immunization. These data suggest that particular oral bacteria generate immune responses to produce IgA that cross-reacts with mesangial cells to initiate IgAN.

Yi-shen-hua-shi granules modulate immune and inflammatory damage via the ALG3/PPARγ/NF-κB pathway in the treatment of immunoglobulin a nephropathy

ETHNOPHARMACOLOGICAL RELEVANCE

Controversy persists regarding the treatment of immunoglobulin A nephropathy (IgAN), thereby highlighting the demand for safer more effective therapeutic drugs. Although supplementary treatment using Yi-Shen-Hua-Shi (YSHS) granules has distinct advantages with respect to improving renal function in IgAN, a lack of clarity regarding the underlying mechanisms limits their clinical application.

AIM OF THE STUDY

In this study, we aimed to elucidate the therapeutic mechanisms underlying the efficacy of YSHS granules in the treatment of IgAN.

MATERIALS AND METHODS

A rat model of IgAN was established based on lipopolysaccharide, carbon tetrachloride, and bovine serum albumin induction. In order to evaluate the effects of YSHS granules, we performed a range of techniques, including immunofluorescence assays, hematoxylin and eosin staining, and flow cytometry, to assess inflammation, immunity, and other relevant factors. Direct data-independent acquisition-mass spectrometry (DIA-MS) analysis and parallel reaction monitoring (PRM) were used for functional characterization and quantitative validation of differentially expressed proteins (DEPs), and Western blot analysis is used to identify downstream proteins associated with DEPs.

RESULTS

Compared with the model group, the levels of proteinuria, urine red blood cells, serum creatinine, blood urea nitrogen, low-density lipoprotein-cholesterol, triglycerides, and pathological kidney damage were reduced in the YSHS group. A high dose of YSHS granules was found to raise the levels of CD8 T cells and reduce the CD4/CD8 ratio in the peripheral serum. To examine the mechanisms underlying the therapeutic effects YSHS granules, we performed direct DIA-MS analysis to identify proteins that were differentially expressed among the model, YSHS, and control groups. A total of 29 proteins were identified as being commonly expressed in all three groups. Further KEGG and protein-protein interaction (PPI) network analysis revealed that YSHS granules can contribute to the regulation of N-glycosylation-associated proteins, such as ALG3 and STT3A, in rats with IgAN. Detected changes in the expression of ALG3 and STT3A were consistent with the PRM results. We also established that the administration of YSHS granules can contribute to regulation of the ALG3-associated PPAR-γ/NF-κB signaling pathway.

CONCLUSIONS

Our findings in this study provide evidence to indicate the efficacy of YSHS granules in the treatment of IgAN, the putative underlying mechanisms of which involve the modulation of N-glycosylation, mediated via the PPAR-γ/NF-κB pathway.

N-Glycosylation and Inflammation; the Not-So-Sweet Relation

Chronic inflammation is the main feature of many long-term inflammatory diseases such as autoimmune diseases, metabolic disorders, and cancer. There is a growing number of studies in which alterations of N-glycosylation have been observed in many pathophysiological conditions, yet studies of the underlying mechanisms that precede N-glycome changes are still sparse. Proinflammatory cytokines have been shown to alter the substrate synthesis pathways as well as the expression of glycosyltransferases required for the biosynthesis of N-glycans. The resulting N-glycosylation changes can further contribute to disease pathogenesis through modulation of various aspects of immune cell processes, including those relevant to pathogen recognition and fine-tuning the inflammatory response. This review summarizes our current knowledge of inflammation-induced N-glycosylation changes, with a particular focus on specific subsets of immune cells of innate and adaptive immunity and how these changes affect their effector functions, cell interactions, and signal transduction.

N-glycosylation, a leading role in viral infection and immunity development

N-linked protein glycosylation is an essential co-and posttranslational protein modification that occurs in all three domains of life; the assembly of N-glycans follows a complex sequence of events spanning the (Endoplasmic Reticulum) ER and the Golgi apparatus. It has a significant impact on both physicochemical properties and biological functions. It plays a significant role in protein folding and quality control, glycoprotein interaction, signal transduction, viral attachment, and immune response to infection. Glycoengineering of protein employed for improving protein properties and plays a vital role in the production of recombinant glycoproteins and struggles to humanize recombinant therapeutic proteins. It considers an alternative platform for biopharmaceuticals production. Many immune proteins and antibodies are glycosylated. Pathogen’s glycoproteins play vital roles during the infection cycle and their expression of specific oligosaccharides via the N-glycosylation pathway to evade detection by the host immune system. This review focuses on the aspects of N-glycosylation processing, glycoengineering approaches, their role in viral attachment, and immune responses to infection.

O- and N-Glycosylation of Serum Immunoglobulin A is Associated with IgA Nephropathy and Glomerular Function

BACKGROUND

IgA nephropathy (IgAN) is the most common primary glomerular disease worldwide and is a leading cause of renal failure. The disease mechanisms are not completely understood, but a higher abundance of galactose-deficient IgA is recognized to play a crucial role in IgAN pathogenesis. Although both types of human IgA (IgA1 and IgA2) have several N-glycans as post-translational modification, only IgA1 features extensive hinge-region O-glycosylation. IgA1 galactose deficiency on the O-glycans is commonly detected by a lectin-based method. To date, limited detail is known about IgA O- and N-glycosylation in IgAN.

METHODS

To gain insights into the complex O- and N-glycosylation of serum IgA1 and IgA2 in IgAN, we used liquid chromatography-mass spectrometry (LC-MS) for the analysis of tryptic glycopeptides of serum IgA from 83 patients with IgAN and 244 age- and sex-matched healthy controls.

RESULTS

Multiple structural features of N-glycosylation of IgA1 and IgA2 were associated with IgAN and glomerular function in our cross-sectional study. These features included differences in galactosylation, sialylation, bisection, fucosylation, and N-glycan complexity. Moreover, IgA1 O-glycan sialylation was associated with both the disease and glomerular function. Finally, glycopeptides were a better predictor of IgAN and glomerular function than galactose-deficient IgA1 levels measured by lectin-based ELISA.

CONCLUSIONS

Our high-resolution data suggest that IgA O- and N-glycopeptides are promising targets for future investigations on the pathophysiology of IgAN and as potential noninvasive biomarkers for disease prediction and deteriorating kidney function.

Is complement the main accomplice in IgA nephropathy? From initial observations to potential complement-targeted therapies

IgA Nephropathy (IgAN) is the main cause of primary glomerulonephritis, globally. This disease is associated with a wide range of clinical presentations, variable prognosis and a spectrum of histological findings. More than fifty years after its first description, this heterogeneity continues to complicate efforts to understand the pathogenesis. Nevertheless, involvement of the complement system in IgAN was identified early on. Dysfunction of the immunoglobulin A (IgA) system, the principal offender in this disease, including modification of isoforms and glycoforms of IgA1, the nature of immune complexes and autoantibodies to galactose deficient IgA1 might all be responsible for complement activation in IgAN. However, the specific mechanisms engaging complement are still under examination. Research in this domain should allow for identification of patients that may benefit from complement-targeted therapy, in the foreseeable future.

History of IgA Nephropathy Mouse Models

IgA nephropathy (IgAN) is the most common primary glomerulonephritis in the world. It was first described in 1968 by Jean Berger and Nicole Hinglais as the presence of intercapillary deposits of IgA. Despite this simple description, patients with IgAN may present very broad clinical features ranging from the isolated presence of IgA in the mesangium without clinical or biological manifestations to rapidly progressive kidney failure. These features are associated with a variety of histological lesions, from the discrete thickening of the mesangial matrix to diffuse cell proliferation. Immunofluorescence on IgAN kidney specimens shows the isolated presence of IgA or its inconsistent association with IgG and complement components. This clinical heterogeneity of IgAN clearly echoes its complex and multifactorial pathophysiology in humans, inviting further analyses of its various aspects through the use of experimental models. Small-animal models of IgAN provide the most pertinent strategies for studying the multifactorial aspects of IgAN pathogenesis and progression. Although only primates have the IgA1 subclass, several murine models have been developed in which various aspects of immune responses are deregulated and which are useful in the understanding of IgAN physiopathology as well as in the assessment of IgAN therapeutic approaches. In this manuscript, we review all murine IgAN models developed since 1968 and discuss their remarkable contribution to understanding the disease.

Are there animal models of IgA nephropathy?

Immunoglobulin A (IgA) nephropathy (IgAN) is the most common primary glomerulonephritis worldwide. Up to 40% of IgAN patients develop end-stage kidney disease after 15-20 years. Despite the poor prognosis associated with this multifactorial disease, no clear treatment strategy has been identified, primarily due to the lack of understanding of its pathogenesis. Clinical observations indicate that aberrant IgAN immune systems, rather than intrinsic renal abnormalities, may be involved in its pathogenesis. Moreover, nephritogenic IgA and its related immune complexes are considered to be produced not only in the mucosa, but also in systemic immune sites, such as the bone marrow; however, there are numerous challenges to understanding this dynamic and complex immune axis in humans. Thus, several investigators have used experimental animal models. Although there are inter-strain differences in IgA molecules and immune responses between humans and rodents, animal models remain a powerful tool for investigating IgAN's pathogenesis, and the subsequent development of effective treatments. Here, we introduced some classical models of IgAN with or without genetic manipulation and recent translational approaches with some promising models. This includes humanized mouse models expressing human IgA1 and human IgA Fc receptor (CD89) that develops spontaneously the disease. Pre-clinical studies targeting IgA1 are discussed. Together, animal models are very useful tools to study pathophysiology and to validate new therapeutic approaches for IgAN.

The glyco-redox interplay: Principles and consequences on the role of reactive oxygen species during protein glycosylation

Reactive oxygen species (ROS) carry out prime physiological roles as intracellular signaling agents, yet pathologically high concentrations of ROS cause irreversible damage to biomolecules, alter cellular programs and contribute to various diseases. While decades of intensive research have identified redox-related patterns and signaling pathways, very few addressed how the glycosylation machinery senses and responds to oxidative stress. A common trait among ROS and glycans residing on glycoconjugates is that they are both highly dynamic, as they are quickly fine-tuned in response to stressors such as inflammation, cancer and infectious diseases. On this account, the delicate balance of the redox potential, which is tightly regulated by dozens of enzymes including NOXs, and the mitochondrial electron transport chain as well as the fluidity of glycan biosynthesis resulting from the cooperation of glycosyltransferases, glycosidases, and nucleotide sugar transporters, is paramount to cell survival. Here, we review the broad spectrum of the interplay between redox changes and glycosylation with respect to their principle consequences on human physiology.

Novel urinary glycan profiling by lectin array serves as the biomarkers for predicting renal prognosis in patients with IgA nephropathy

In IgA nephropathy (IgAN), IgA1 molecules are characterized by galactose deficiency in O-glycans. Here, we investigated the association between urinary glycosylation profile measured by 45 lectins at baseline and renal prognosis in 142 patients with IgAN. The primary outcome was estimated glomerular filtration rate (eGFR) decline (> 4 mL/min/1.73 m²/year), or eGFR ≥ 30% decline from baseline, or initiation of renal replacement therapies within 3 years. During follow-up (3.4 years, median), 26 patients reached the renal outcome (Group P), while 116 patients were with good renal outcome (Group G). Multivariate logistic regression analyses revealed that lectin binding signals of Erythrina cristagalli lectin (ECA) (odds ratio [OR] 2.84, 95% confidence interval [CI] 1.11–7.28) and Narcissus pseudonarcissus lectin (NPA) (OR 2.32, 95% CI 1.11–4.85) adjusted by age, sex, eGFR, and urinary protein were significantly associated with the outcome, and they recognize Gal(β1-4)GlcNAc and high-mannose including Man(α1-6)Man, respectively. The addition of two lectin-binding glycan signals to the interstitial fibrosis/tubular atrophy score further improved the model fitness (Akaike’s information criterion) and incremental predictive abilities (c-index, net reclassification improvement, and integrated discrimination improvement). Urinary N-glycan profiling by lectin array is useful in the prediction of IgAN prognosis, since ECA and NPA recognize the intermediate glycans during N-glycosylation of various glycoproteins.

Various biological functions of carbohydrate chains learned from glycosyltransferase-deficient mice

Carbohydrate chains are attached to various proteins and lipids and modify their functions. The complex structures of carbohydrate chains, which have various biological functions, are involved not only in regulating protein conformation, transport, and stability but also in cell-cell and cell-matrix interactions. These functional carbohydrate structures are designated as "glyco-codes." Carbohydrate chains are constructed through complex reactions of glycosyltransferases, glycosidases, nucleotide sugars, and protein and lipid substrates in a cell. To elucidate the functions of carbohydrate chains, I and my colleagues generated and characterized knockout (KO) mice of galactosyltransferase family genes. In this review, I introduce our studies about galactosyltransferase family genes together with related studies performed by other researchers, which I presented in my award lecture for the Ando-Tajima Prize of the Japanese Association for Laboratory Animal Science (JALAS) in 2019.

B4GALT1-congenital disorders of glycosylation: Expansion of the phenotypic and molecular spectrum and review of the literature

A congenital disorder of glycosylation due to biallelic mutations in B4GALT1 has been previously reported in only three patients with two different mutations. Through homozygosity mapping followed by segregation analysis in an extended pedigree, we identified three additional patients homozygous for a novel mutation in B4GALT1, expanding the phenotypic spectrum of the disease. The patients showed a uniform clinical presentation with intellectual disability, marked pancytopenia requiring chronic management, and novel features including pulmonary hypertension and nephrotic syndrome. Notably, affected individuals exhibited a moderate elevation of Man3GlcNAc4Fuc1 on serum N-glycan analysis, yet two of the patients had a normal pattern of transferrin glycosylation in repeated analysis. The novel mutation is the third disease-causing variant described in B4GALT1, and the first one within its transmembrane domain.

TLR9 activation induces aberrant IgA glycosylation via APRIL- and IL-6-mediated pathways in IgA nephropathy

Galactose-deficient IgA1 (Gd-IgA1) plays a crucial role in the development of IgA nephropathy (IgAN). However, the pathogenic mechanisms driving Gd-IgA1 production have not been fully elucidated. Innate-immune activation via Toll-like receptor 9 (TLR9) is known to be involved in Gd-IgA1 production. A proliferation inducing ligand (APRIL) and IL-6 are also known to enhance Gd-IgA1 synthesis in IgAN. With this as background, we investigated how TLR9 activation in IgA secreting cells results in overproduction of nephritogenic IgA in the IgAN-prone ddY mouse and in human IgA1-secreting cells. Injection of the TLR9 ligand CpG-oligonucleotides increased production of aberrantly glycosylated IgA and IgG-IgA immune complexes in ddY mice that, in turn, exacerbated kidney injury. CpG-oligonucleotide-stimulated mice had elevated serum levels of APRIL that correlated with those of aberrantly glycosylated IgA and IgG-IgA immune complexes. In vitro, TLR9 activation enhanced production of the nephritogenic IgA as well as APRIL and IL-6 in splenocytes of ddY mice and in human IgA1-secreting cells. However, siRNA knock-down of APRIL completely suppressed overproduction of Gd-IgA1 induced by IL-6. Neutralization of IL-6 decreased CpG-oligonucleotide-induced overproduction of Gd-IgA1. Furthermore, APRIL and IL-6 pathways each independently mediated TLR9-induced overproduction of Gd-IgA1. Thus, TLR9 activation enhanced synthesis of aberrantly glycosylated IgA that, in a mouse model of IgAN, further enhanced kidney injury. Hence, APRIL and IL-6 synergistically, as well as independently, enhance synthesis of Gd-IgA1.

Roles for Golgi Glycans in Oogenesis and Spermatogenesis

Glycosylation of proteins by N- and O-glycans or glycosaminoglycans (GAGs) mostly begins in the endoplasmic reticulum and is further orchestrated in the Golgi compartment via the action of >100 glycosyltransferases that reside in this complex organelle. The synthesis of glycolipids occurs in the Golgi, also by resident glycosyltransferases. A defect in the glycosylation machinery may impair the functions of glycoproteins and other glycosylated molecules, and lead to a congenital disorder of glycosylation (CDG). Spermatogenesis in the male and oogenesis in the female are tightly regulated differentiation events leading to the production of functional gametes. Insights into roles for glycans in gamete production have been obtained from mutant mice following deletion or inactivation of genes that encode a glycosylation activity. In this review, we will summarize the effects of altering the synthesis of N-glycans, O-glycans, proteoglycans, glycophosphatidylinositol (GPI) anchored proteins, and glycolipids during gametogenesis in the mouse. Glycosylation genes whose deletion causes embryonic lethality have been investigated following conditional deletion using various Cre recombinase transgenes with a cell-type specific promoter. The potential effects of mutations in corresponding glycosylation genes of humans will be discussed in relation to consequences to fertility and potential for use in contraception.

Murine Models of Human IgA Nephropathy

IgA nephropathy (IgAN) is the most common form of primary glomerulonephritis in the world. IgAN is characterized by mesangial deposits of IgA1-containing immune complexes. IgA1 usually co-deposits with complement C3 and variable IgG and/or IgM. Exactly 50 years have passed since IgAN was described, however, the pathogenesis of disease onset and progression have not been fully clarified. Animal models can re-create the complex immunologic microenvironments that foster human autoimmunity and nephritis and provide access to tissue compartments not readily examined in patients. Thus, multiple models that may be helpful in studies of specific aspects of IgAN have been developed. A unique spontaneous animal model of IgAN, the ddY mouse, was reported in 1985. These mice show mild proteinuria and glomerular IgA deposits, with a highly variable incidence and degree of glomerular injury owing to a heterogeneous genetic background. Thus, we intercrossed an early onset group of ddY mice in which the development of IgAN resulted in the establishment of a novel 100% early onset-grouped ddY mouse model with increased levels of aberrantly glycosylated IgA and immune complexes. Although the molecular features of human IgA1 are different from rodent IgA, human IgA1 knock-in (α1KI)-CD89 transgenic mice, which express both human IgA1 and CD89, show circulating and mesangial deposits of IgA1-soluble CD89 complexes that result in kidney inflammation, hematuria, and proteinuria. In this review, we introduce several murine models of IgAN that can be useful tools for the analysis of multiple aspects of the pathogenesis of IgAN, which may aid in the assessment of approaches for the treatment of IgAN.

Glycopatterns of Urinary Protein as New Potential Diagnosis Indicators for Diabetic Nephropathy

Diabetic nephropathy is a major cause of chronic kidney disease and end-stage kidney disease. However, so little is known about alterations of the glycopatterns in urine with the development of diabetic nephropathy. Presently, we interrogated glycopatterns in urine specimens using a lectin microarray. The results showed that expression levels of Siaα2-6Gal/GalNAc recognized by SNA exhibited significantly increased tendency with the development of diabetic nephropathy; moreover, SNA blotting indicated glycoproteins (90 kDa, 70 kDa, and 40 kDa) in urine may contribute to this alteration. Furthermore, the glycopatterns of (GlcNAc)2-4 recognized by STL exhibited difference between diabetic and nondiabetic nephropathy. The results of urinary protein microarray fabricated by another 48 urine specimens also indicated (GlcNAc)2-4 is a potential indictor to differentiate the patients with diabetic nephropathy from nondiabetic nephropathy. Furtherly, STL blotting showed that the 50 kDa glycoproteins were correlated with this alteration. In conclusion, our data provide pivotal information to monitor the development of diabetic nephropathy and distinguish between diabetic nephropathy and nondiabetic renal disease based on precise alterations of glycopatterns in urinary proteins, but further studies are needed in this regard.

The Origin and Activities of IgA1-Containing Immune Complexes in IgA Nephropathy

IgA nephropathy (IgAN) is the most common primary glomerulonephritis, frequently leading to end-stage renal disease, as there is no disease-specific therapy. IgAN is diagnosed from pathological assessment of a renal biopsy specimen based on predominant or codominant IgA-containing immunodeposits, usually with complement C3 co-deposits and with variable presence of IgG and/or IgM. The IgA in these renal deposits is galactose-deficient IgA1, with less than a full complement of galactose residues on the O-glycans in the hinge region of the heavy chains. Research from the past decade led to the definition of IgAN as an autoimmune disease with a multi-hit pathogenetic process with contributing genetic and environmental components. In this process, circulating galactose-deficient IgA1 (autoantigen) is bound by antiglycan IgG or IgA (autoantibodies) to form immune complexes. Some of these circulating complexes deposit in glomeruli, and thereby activate mesangial cells and induce renal injury through cellular proliferation and overproduction of extracellular matrix components and cytokines/chemokines. Glycosylation pathways associated with production of the autoantigen and the unique characteristics of the corresponding autoantibodies in patients with IgAN have been uncovered. Complement likely plays a significant role in the formation and the nephritogenic activities of these complexes. Complement activation is mediated through the alternative and lectin pathways and probably occurs systemically on IgA1-containing circulating immune complexes as well as locally in glomeruli. Incidence of IgAN varies greatly by geographical location; the disease is rare in central Africa but accounts for up to 40% of native-kidney biopsies in eastern Asia. Some of this variation may be explained by genetically determined influences on the pathogenesis of the disease. Genome-wide association studies to date have identified several loci associated with IgAN. Some of these loci are associated with the increased prevalence of IgAN, whereas others, such as deletion of complement factor H-related genes 1 and 3, are protective against the disease. Understanding the molecular mechanisms and genetic and biochemical factors involved in formation and activities of pathogenic IgA1-containing immune complexes will enable the development of future disease-specific therapies as well as identification of non-invasive disease-specific biomarkers.

The kinetics of glomerular deposition of nephritogenic IgA

Whether IgA nephropathy is attributable to mesangial IgA is unclear as there is no correlation between intensity of deposits and extent of glomerular injury and no clear mechanism explaining how these mesangial deposits induce hematuria and subsequent proteinuria. This hinders the development of a specific therapy. Thus, precise events during deposition still remain clinical challenge to clarify. Since no study assessed induction of IgA nephropathy by nephritogenic IgA, we analyzed sequential events involving nephritogenic IgA from IgA nephropathy-prone mice by real-time imaging systems. Immunofluorescence and electron microscopy showed that serum IgA from susceptible mice had strong affinity to mesangial, subepithelial, and subendothelial lesions, with effacement/actin aggregation in podocytes and arcade formation in endothelial cells. The deposits disappeared 24-h after single IgA injection. The data were supported by a fluorescence molecular tomography system and real-time and 3D in vivo imaging. In vivo imaging showed that IgA from the susceptible mice began depositing along the glomerular capillary from 1 min and accumulated until 2-h on the first stick in a focal and segmental manner. The findings indicate that glomerular IgA depositions in IgAN may be expressed under the balance between deposition and clearance. Since nephritogenic IgA showed mesangial as well as focal and segmental deposition along the capillary with acute cellular activation, all glomerular cellular elements are a plausible target for injury such as hematuria.

Uncoupling of glomerular IgA deposition and disease progression in alymphoplasia mice with IgA nephropathy

Previous clinical and experimental studies have indicated that cells responsible for IgA nephropathy (IgAN), at least in part, are localized in bone marrow (BM). Indeed, we have demonstrated that murine IgAN can be experimentally reconstituted by bone marrow transplantation (BMT) from IgAN prone mice in not only normal mice, but also in alymphoplasia mice (aly/aly) independent of IgA⁺ cells homing to mucosa or secondary lymphoid tissues. The objective of the present study was to further assess whether secondary lymph nodes (LN) contribute to the progression of this disease. BM cells from the several lines of IgAN prone mice were transplanted into aly/aly and wild-type mice (B6). Although the transplanted aly/aly showed the same degree of mesangial IgA and IgG deposition and the same serum elevation levels of IgA and IgA-IgG immune-complexes (IC) as B6, even in extent, the progression of glomerular injury was observed only in B6. This uncoupling in aly/aly was associated with a lack of CD4⁺ T cells and macrophage infiltration, although phlogogenic capacity to nephritogenic IC of renal resident cells was identical between both recipients. It is suggested that secondary LN may be required for the full progression of IgAN after nephritogenic IgA and IgA/IgG IC deposition.

Changes in nephritogenic serum galactose-deficient IgA1 in IgA nephropathy following tonsillectomy and steroid therapy

Background

Recent studies have shown that galactose-deficient IgA1 (GdIgA1) has an important role in the pathogenesis of IgA nephropathy (IgAN). Although emerging data suggest that serum GdIgA1 can be a useful non-invasive IgAN biomarker, the localization of nephritogenic GdIgA1-producing B cells remains unclear. Recent clinical and experimental studies indicate that immune activation tonsillar toll-like receptor (TLR) 9 may be involved in the pathogenesis of IgAN. Here we assessed the possibility of GdIgA1 production in the palatine tonsils in IgAN patients.

Methods

We assessed changes in serum GdIgA1 levels in IgAN patients with clinical remission of hematuria and proteinuria following combined tonsillectomy and steroid pulse therapy. Further, the association between clinical outcome and tonsillar TLR9 expression was evaluated.

Results

Patients (n = 37) were divided into two groups according to therapy response. In one group, serum GdIgA1 levels decreased after tonsillectomy (59%) alone, whereas in the other group most levels only decreased after the addition of steroid pulse therapy to tonsillectomy (41%). The former group showed significantly higher tonsillar TLR9 expression and better improvement in hematuria immediately after tonsillectomy than the latter group.

Conclusions

The present study indicates that the palatine tonsils are probably a major sites of GdIgA1-producing cells. However, in some patients these cells may propagate to other lymphoid organs, which may partially explain the different responses observed to tonsillectomy alone. These findings help to clarify some of the clinical observations in the management of IgAN, and may highlight future directions for research.

O-linked glycosylation determines the nephritogenic potential of IgA rheumatoid factor

Deficient glycosylation of O-linked glycans in the IgA1 hinge region is associated with IgA nephropathy in humans, but the pathogenic contribution of the underlying structural aberrations remains incompletely understood. We previously showed that mice implanted with cells secreting the class-switch variant 6-19 IgA anti-IgG2a rheumatoid factor, but not 46-42 IgA anti-IgG2a rheumatoid factor, develop glomerular lesions resembling IgA nephropathy. Because the levels of O-linked glycosylation in the hinge region and the structures of N-linked glycans in the CH1 domain differ in 6-19 IgA and 46-42 IgA, we determined the respective contributions of O- and N-linked glycans to the nephritogenic potential of the 6-19 IgA rheumatoid factor in mice. Wild-type 6-19 IgA secreted by implanted cells induced significant formation of glomerular lesions, whereas poorly O-glycosylated 6-19 IgA glycovariants or a 6-19 IgA hinge mutant lacking O-linked glycans did not. However, we observed no apparent heterogeneity in the structure of N-linked glycans attached to three different sites of the Fc regions of nephritogenic and non-nephritogenic 6-19 IgAs. Collectively, our data suggest a critical role of O-linked glycans attached to the hinge region in the development of IgA nephropathy-like GN induced by 6-19 IgA rheumatoid factor in mice.

Development of Animal Models of Human IgA Nephropathy

IgA nephropathy (IgAN) is the most common form of primary glomerulonephritis in the world. IgAN is characterized by the mesangial accumulation of immune complexes containing IgA1, usually with co-deposits of complement C3 and variable IgG and/or IgM. Although more than 40 years have passed since IgAN was first described, the mechanisms underlying the disease development are not fully understood. Small-animal experimental models of IgAN can be very helpful in studies of IgAN, but development of these models has been hindered by the fact that only humans and hominoid primates have IgA1 subclass. Thus, multiple models have been developed, that may be helpful in studies of some specific aspects of IgAN. These models include a spontaneous animal model of IgAN, the ddY mouse first reported in 1985. These mice show mild proteinuria without hematuria, and glomerular IgA deposits, with a highly variable incidence and degree of glomerular injury, due to the heterogeneous genetic background. To obtain a murine line consistently developing IgAN, we intercrossed an earlyonset group of ddY mice, in which the development of IgAN includes mesangial IgA deposits and glomerular injury. After selective intercrossing for >20 generations, we established a novel 100% early-onset grouped ddY murine model. All grouped ddY mice develop proteinuria within eight weeks of age. The grouped ddY mouse model can be a useful tool for analysis of multiple aspects of the pathogenesis of IgAN and may aid in assessment of some approaches for the treatment of IgAN.

Disruption of Smad4 expression in T cells leads to IgA nephropathy-like manifestations

The link between glomerular IgA nephropathy (IgAN) and T helper 2 (Th2) response has been implicated, however, the mechanisms are poorly defined because of the lack of an appropriate model. Here we report a novel murine model characterized by lineage-restricted deletion of the gene encoding MAD homologue 4 (Smad4) in T cells (Smad4(co/co;Lck-cre) ). Loss of Smad4 expression in T cells results in overproduction of Th2 cytokines and high serum IgA levels. We found that Smad4(co/co;Lck-cre) mice exhibited massive glomerular IgA deposition, increased albumin creatinine ratio, aberrant glycosylated IgA, IgA complexed with IgG1 and IgG2a, and polymeric IgA, all known features of IgAN in humans. Furthermore, we examined the β1, 4-galactosyltransferases (β4GalT) enzyme which is involved in the synthesis of glycosylated murine IgA, and we found reduced β4GalT2 and β4GalT4 mRNA levels in B cells. These findings indicate that Smad4(co/co;Lck-cre) mice could be a useful model for studying the mechanisms between IgAN and Th2 response, and further, disruption of Smad4-dependent signaling in T cells may play an important role in the pathogenesis of human IgAN and contributing to a Th2 T cell phenotype.

Large-scale identification of target proteins of a glycosyltransferase isozyme by Lectin-IGOT-LC/MS, an LC/MS-based glycoproteomic approach

Model organisms containing deletion or mutation in a glycosyltransferase-gene exhibit various physiological abnormalities, suggesting that specific glycan motifs on certain proteins play important roles in vivo. Identification of the target proteins of glycosyltransferase isozymes is the key to understand the roles of glycans. Here, we demonstrated the proteome-scale identification of the target proteins specific for a glycosyltransferase isozyme, β1,4-galactosyltransferase-I (β4GalT-I). Although β4GalT-I is the most characterized glycosyltransferase, its distinctive contribution to β1,4-galactosylation has been hardly described so far. We identified a large number of candidates for the target proteins specific to β4GalT-I by comparative analysis of β4GalT-I-deleted and wild-type mice using the LC/MS-based technique with the isotope-coded glycosylation site-specific tagging (IGOT) of lectin-captured N-glycopeptides. Our approach to identify the target proteins in a proteome-scale offers common features and trends in the target proteins, which facilitate understanding of the mechanism that controls assembly of a particular glycan motif on specific proteins.

Determination of severity of murine IgA nephropathy by glomerular complement activation by aberrantly glycosylated IgA and immune complexes

The pathogenic roles of glomerular deposition of components of the complement cascade in IgA nephropathy (IgAN) are not completely clarified. To investigate the pathologic role of complement pathways in IgAN, two IgAN-prone mouse models were examined. Grouped ddY (gddY) mice showed significant high proteinuria, severe glomerular lesions, and extracellular matrix expansion compared with high serum IgA (HIGA) mice but with similar intensity of glomerular IgA deposition. Glomerular activation of the classical, lectin, and alternative pathways was demonstrated by significantly stronger staining for complement (C)3, C5b-9, C1q, C4, mannose-binding lectin (MBL)-A/C, MBL-associated serine protease-2, and factor B and properdin in gddY mice than in HIGA mice. Similarly, the serum levels of IgA-IgG2a/IgM and IgA-MBL-A/C immune complexes and polymeric IgA were significantly higher in gddY mice than in HIGA mice. Moreover, the serum levels of aberrantly glycosylated IgA characterized by the binding of Sambucus nigra bark lectin and Ricinus communis agglutinin I were significantly higher in gddY mice than in HIGA mice. This aberrancy in glycosylation was confirmed by monosaccharide compositional analysis of purified IgA using gas-liquid chromatography. This study is the first to demonstrate that aberrantly glycosylated IgA may influence the formation of macromolecular IgA including IgA-IgG immune complexes and subsequent complement activation, leading to full progression of IgAN.

Autoimmunity in wiskott-Aldrich syndrome: an unsolved enigma

Wiskott-Aldrich Syndrome (WAS) is a severe X-linked Primary Immunodeficiency that affects 1-10 out of 1 million male individuals. WAS is caused by mutations in the WAS Protein (WASP) expressing gene that leads to the absent or reduced expression of the protein. WASP is a cytoplasmic protein that regulates the formation of actin filaments in hematopoietic cells. WASP deficiency causes many immune cell defects both in humans and in the WAS murine model, the Was(-/-) mouse. Both cellular and humoral immune defects in WAS patients contribute to the onset of severe clinical manifestations, in particular microthrombocytopenia, eczema, recurrent infections, and a high susceptibility to develop autoimmunity and malignancies. Autoimmune diseases affect from 22 to 72% of WAS patients and the most common manifestation is autoimmune hemolytic anemia, followed by vasculitis, arthritis, neutropenia, inflammatory bowel disease, and IgA nephropathy. Many groups have widely explored immune cell functionality in WAS partially explaining how cellular defects may lead to pathology. However, the mechanisms underlying the occurrence of autoimmune manifestations have not been clearly described yet. In the present review, we report the most recent progresses in the study of immune cell function in WAS that have started to unveil the mechanisms contributing to autoimmune complications in WAS patients.

Development of a model of early-onset IgA nephropathy

ddY mice spontaneously develop IgA nephropathy (IgAN) with a variable age of disease onset. Establishing a model with early-onset IgAN could aid the investigation of mechanisms that underlie the pathogenesis of this disease. On the basis of histologic grading in serial biopsies, we previously classified ddY mice into early-onset, late-onset, and quiescent groups. Here, we selectively mated mice with the early-onset phenotype for >20 generations and established "grouped ddY" mice that develop IgAN within 8 weeks of age. Similar to human IgAN, the prognosis was worse for male mice than females. These mice homogeneously retained genotypes of four marker loci previously associated with the early-onset phenotype, confirming a close association of these loci with early-onset IgAN in ddY mice. Grouped ddY mice comprised two sublines, however, which had distinct genotypes at a susceptibility locus for high serum IgA levels, which maps within the Ig heavy-chain gene complex. The subline bearing the Igh-2(a) IgA allotype had a more rapid course of fatal disease and lower oligosaccharide content, suggesting that aberrant IgA glycosylation may promote the progression of murine IgAN. Taken together, these data indicate that grouped ddY mice may be a useful model for the identification of susceptibility genes and the underlying molecular mechanisms involved in the pathogenesis of human IgAN.

Analysis of carbohydrates and glycoconjugates by matrix-assisted laser desorption/ionization mass spectrometry: an update for 2007-2008

This review is the fifth update of the original review, published in 1999, on the application of MALDI mass spectrometry to the analysis of carbohydrates and glycoconjugates and brings coverage of the literature to the end of 2008. The first section of the review covers fundamental studies, fragmentation of carbohydrate ions, use of derivatives and new software developments for analysis of carbohydrate spectra. Among newer areas of method development are glycan arrays, MALDI imaging and the use of ion mobility spectrometry. The second section of the review discusses applications of MALDI MS to the analysis of different types of carbohydrate. Specific compound classes that are covered include carbohydrate polymers from plants, N- and O-linked glycans from glycoproteins, biopharmaceuticals, glycated proteins, glycolipids, glycosides and various other natural products. There is a short section on the use of MALDI mass spectrometry for the study of enzymes involved in glycan processing and a section on the use of MALDI MS to monitor products of the chemical synthesis of carbohydrates with emphasis on carbohydrate-protein complexes and glycodendrimers. Corresponding analyses by electrospray ionization now appear to outnumber those performed by MALDI and the amount of literature makes a comprehensive review on this technique impractical. However, most of the work relating to sample preparation and glycan synthesis is equally relevant to electrospray and, consequently, those proposing analyses by electrospray should also find material in this review of interest.

Glycoprotein hyposialylation gives rise to a nephrotic-like syndrome that is prevented by sialic acid administration in GNE V572L point-mutant mice

Mutations in the key enzyme of sialic acid biosynthesis, UDP-N-acetylglucosamine 2-epimerase/N-acetyl-mannosamine kinase, result in distal myopathy with rimmed vacuoles (DMRV)/hereditary inclusion body myopathy (HIBM) in humans. Sialic acid is an acidic monosaccharide that modifies non-reducing terminal carbohydrate chains on glycoproteins and glycolipids, and it plays an important role in cellular adhesions and interactions. In this study, we generated mice with a V572L point mutation in the GNE kinase domain. Unexpectedly, these mutant mice had no apparent myopathies or motor dysfunctions. However, they had a short lifespan and exhibited renal impairment with massive albuminuria. Histological analysis showed enlarged glomeruli with mesangial matrix deposition, leading to glomerulosclerosis and abnormal podocyte foot process morphologies in the kidneys. Glycan analysis using several lectins revealed glomerular epithelial cell hyposialylation, particularly the hyposialylation of podocalyxin, which is one of important molecules for the glomerular filtration barrier. Administering Neu5Ac to the mutant mice from embryonic stages significantly suppressed the albuminuria and renal pathology, and partially recovered the glomerular glycoprotein sialylation. These findings suggest that the nephrotic-like syndrome observed in these mutant mice resulted from impaired glomerular filtration due to the hyposialylation of podocyte glycoproteins, including podocalyxin. Furthermore, it was possible to prevent the nephrotic-like disease in these mice by beginning Neu5Ac treatment during gestation.

O-glycosylated IgA rheumatoid factor induces IgA deposits and glomerulonephritis

Structural aberrations of O-linked glycans present in the IgA1 hinge region are associated with IgA nephropathy, but their contribution to its pathogenesis remains incompletely understood. In this study, mice implanted with hybridoma secreting 6-19 IgA anti-IgG2a rheumatoid factor, but not 46-42 IgA rheumatoid factor bearing the same IgA allotype, developed mesangial deposits consisting of IgA, IgG2a, and C3. Studies in immunoglobulin- and C3-deficient mice revealed that the development of these glomerular lesions required the formation of IgA-IgG2a immune complexes and subsequent activation of complement. The proportion of polymeric and monomeric forms, the IgG2a-binding affinity, and the serum levels of IgA-IgG2a immune complexes were similar between 6-19 IgA- and 46-42 IgA-injected mice. In contrast, the analysis of oligosaccharide structures revealed highly galactosylated O-linked glycans in the hinge region of 6-19 IgA and poorly O-glycosylated in the hinge region of 46-42 IgA. Furthermore, the structure of N-linked glycans in the CH1 domain was the complex type in 6-19 IgA and the hybrid type in 46-42 IgA. In summary, this study demonstrates the presence of O-linked glycans in the hinge region of mouse IgA and suggests that 6-19 IgA rheumatoid factor-induced GN could serve as an experimental model for IgA nephropathy.

Development of IgA nephropathy-like glomerulonephritis associated with Wiskott-Aldrich syndrome protein deficiency

Wiskott-Aldrich syndrome (WAS) is a rare X-linked disorder caused by mutations in the WAS gene. Glomerulonephritis is a frequent complication, however, histopathological data from affected patients is scarce because the thrombocytopenia that affects most patients is a contraindication to renal biopsies. We found that WASp-deficient mice develop proliferative glomerulonephritis reminiscent of human IgA nephropathy (IgAN). We examined whether increased aberrant IgA production is associated with the development of glomerulonephritis in WASp-deficient mice. Serum IgA and IgA production by splenic B cells was increased in WASp-deficient mice compared to wild-type (WT) mice. A lectin-binding study revealed a reduced ratio of sialylated and galactosylated IgA in the sera from old WASp-deficient mice. Circulating IgA-containing immune complexes showed significantly higher titers in WASp-deficient mice compared to WT mice. These results indicate that the increased IgA production and aberrant glycosylation of IgA may be critically involved in the pathogenesis of glomerulonephritis in WAS.

Mice overexpressing BAFF develop a commensal flora-dependent, IgA-associated nephropathy

B cell activation factor of the TNF family (BAFF) is a potent B cell survival factor. BAFF overexpressing transgenic mice (BAFF-Tg mice) exhibit features of autoimmune disease, including B cell hyperplasia and hypergammaglobulinemia, and develop fatal nephritis with age. However, basal serum IgA levels are also elevated, suggesting that the pathology in these mice may be more complex than initially appreciated. Consistent with this, we demonstrate here that BAFF-Tg mice have mesangial deposits of IgA along with high circulating levels of polymeric IgA that is aberrantly glycosylated. Renal disease in BAFF-Tg mice was associated with IgA, because serum IgA was highly elevated in nephritic mice and BAFF-Tg mice with genetic deletion of IgA exhibited less renal pathology. The presence of commensal flora was essential for the elevated serum IgA phenotype, and, unexpectedly, commensal bacteria-reactive IgA antibodies were found in the blood. These data illustrate how excess B cell survival signaling perturbs the normal balance with the microbiota, leading to a breach in the normal mucosal-peripheral compartmentalization. Such breaches may predispose the nonmucosal system to certain immune diseases. Indeed, we found that a subset of patients with IgA nephropathy had elevated serum levels of a proliferation inducing ligand (APRIL), a cytokine related to BAFF. These parallels between BAFF-Tg mice and human IgA nephropathy may provide a new framework to explore connections between mucosal environments and renal pathology.

Pathological role of tonsillar B cells in IgA nephropathy

Although impaired immune regulation along the mucosa-bone marrow axis has been postulated to play an important role, the pathogenesis of IgA nephropathy (IgAN) is unknown; thus, no disease-specific therapy for this disease exists. The therapeutic efficacy of tonsillectomy or tonsillectomy in combination with steroid pulse therapy for IgAN has been discussed. Although randomized control trials for these therapies are ongoing in Japan, the scientific rationale for these therapies remains obscure. It is now widely accepted that abnormally glycosylated IgA1 and its related immune complex (IC) are probably key molecules for the pathogenesis, and are thus considered possible noninvasive biomarkers for this disease. Emerging evidence indicates that B cells in mucosal infections, particularly in tonsillitis, may produce the nephritogenic IgA. In this paper, we briefly summarize characteristics of the nephritogenic IgA/IgA IC, responsible B cells, and underlying mechanisms. This clinical and experimental information may provide important clues for a therapeutic rationale.

Different pathological roles of toll-like receptor 9 on mucosal B cells and dendritic cells in murine IgA nephropathy

Although pathogenesis of IgA nephropathy (IgAN) is still obscure, pathological contribution of mucosal immunity including production of nephritogenic IgA and IgA immune complex (IC) has been discussed. We have reported that mucosal toll-like receptor (TLR)-9 is involved in the pathogenesis of human and murine IgAN. However, cell-type expressing TLR9 in mucosa remains unclear. To address this, we nasally challenged cell-specific CpG DNA ((i): dendritic cell: (DC), (ii): B cell, (iii): both), known as ligand for TLR9, to IgAN prone mice and analyzed disease phenotype of each group. After 8 times of the weekly administration, every group showed deterioration of glomerular damage. However, CpG-A-group showed clear extension of mesangial proliferative lesions with increase of serum IgA-IgG2a IC and its glomerular depositions, while CpG-B-group showed extent of glomerular sclerotic lesions with increase of serum and glomerular IgA and M2 macrophage infiltration. Present results indicate that mucosal TLR9 on B cells and DC may differently contribute to the progression of this disease via induction of nephritogenic IgA or IgA-IgG IC, respectively. This picture is suggestive for the pathological difference between child and adult IgAN.

Beta4-galactosyltransferase-5 is a lactosylceramide synthase essential for mouse extra-embryonic development

Glycosphingolipids (GSLs) are important for various biological functions in the nervous system, the immune system, embryogenesis and in other tissues and processes. Lactosylceramide (LacCer), which is synthesized from glucosylceramide (GlcCer) by LacCer synthase, is a core structure of GSLs, including gangliosides. LacCer synthase was reported to be synthesized by the beta4-galactosyltransferase-6 (beta4GalT-6) gene in the rat brain. However, the existence of another LacCer synthase gene was shown in cultured cells lacking beta4GalT-6. Here, we report that LacCer synthase is mainly synthesized by the beta4GalT-5 gene during early mouse embryogenesis, and its disruption is embryonic lethal. beta4GalT-5-deficient embryos showed developmental retardation from E7.5 and died by E10.5 as reported previously. LacCer synthase activity was significantly reduced in beta4GalT-5-deficient embryos and extra-embryonic endoderm (XEN) cells derived from blastocysts, and it was recovered when beta4GalT-5 cDNA was introduced into beta4GalT-5-deficient XEN cells. The amounts of LacCer and GM3 ganglioside were drastically reduced, while GlcCer accumulated in the beta4GalT-5-deficient XEN cells. Hematoma and ectopically accumulated trophoblast giant cells were observed in the anti-mesometrial pole of the extra-embryonic tissues, although all three embryonic layers formed. beta4GalT-5-deficient embryos developed until E12.5 as chimeras with wild-type tetraploid cells, which formed the extra-embryonic membranes, indicating that extra-embryonic defects caused the early embryonic lethality. Our results suggest that beta4GalT-5 is essential for extra-embryonic development during early mouse embryogenesis.

Renal involvement of monoclonal immunoglobulin deposition disease associated with an unusual monoclonal immunoglobulin A glycan profile

A 38-year-old man was admitted to the hospital for the evaluation of proteinuria, microscopic hematuria, and monoclonal IgA-kappa gammopathy. The initial renal pathological findings showed mesangial proliferative glomerulonephritis with endocapillary proliferation, a necrotizing lesion, and cellular crescent formation accompanied by IgA1-kappa deposition in the mesangium. Neither typical immune-complex deposits nor organized-structure deposits were detected. We diagnosed the patient with monoclonal immunoglobulin deposition disease (MIDD) associated with monoclonal IgA (mIgA). After the initiation of a monthly treatment with melphalan and predonisolone (MP therapy), the patient's serum IgA levels declined, and clinical remission was ultimately achieved. The follow-up renal biopsy showed reduced IgA-kappa staining, and both the endocapillary proliferation and the necrotizing lesion had disappeared. To elucidate the mechanism of IgA deposition, we investigated the glycan profile of the patient's serum mIgA using a mass spectrometry technique. The results revealed an unusual N-glycan profile compared to that of another patient with circulating mIgA lacking renal involvement and that of a healthy control. mIgA deposition in the mesangial area is a rare disease, and the glycan profiling of MIDD with renal involvement has not been reported previously. Thus, the present case suggests that any variation in Ig glycosylation may be a step in the pathogenesis of MIDD with renal involvement and/or contribute to some cases of IgA nephropathy.

beta-1,4-Galactosyltransferase-I participates in lipopolysaccharide induced reactive microgliosis

beta-1,4-Galactosyltransferase-I (beta-1,4-GalT-I) is one of the best studied glycosyltransferases. Previous studies demonstrated that beta-1,4-GalT-I was a major galactosyltransferase responsible for selectin-ligand biosynthesis and that inflammatory responses of beta-1,4-GalT-I deficient mice were impaired. Our previous study suggest that beta-1,4-GalT-I may play an important role in regulating immune cell migration into the inflammatory site. In this study, we investigate beta-1,4-GalT-I may play an important role in mediating microgliosis. The results of this study demonstrated that beta-1,4-GalT-I was strongly induced in the ventral midbrain by intranigral injection of LPS. Most galactose-containing glycans and beta-1,4-GalT-I were expressed in microglia. Moreover, an Ab against beta-1,4-GalT-I attenuated both LPS-induced microglial activation and phagocytosis. We therefore suggest that beta-1,4-GalT-I may play an important role in regulating immune cell migration into the inflammatory site and mediating microgliosis.

Learning/memory impairment and reduced expression of the HNK-1 carbohydrate in beta4-galactosyltransferase-II-deficient mice

The glycosylation of glycoproteins and glycolipids is important for central nervous system development and function. Although the roles of several carbohydrate epitopes in the central nervous system, including polysialic acid, the human natural killer-1 (HNK-1) carbohydrate, alpha2,3-sialic acid, and oligomannosides, have been investigated, those of the glycan backbone structures, such as Galbeta1-4GlcNAc and Galbeta1-3GlcNAc, are not fully examined. Here we report the generation of mice deficient in beta4-galactosyltransferase-II (beta4GalT-II). This galactosyltransferase transfers Gal from UDP-Gal to a nonreducing terminal GlcNAc to synthesize the Gal beta1-4GlcNAc structure, and it is strongly expressed in the central nervous system. In behavioral tests, the beta4GalT-II(-/-) mice showed normal spontaneous activity in a novel environment, but impaired spatial learning/memory and motor coordination/learning. Immunohistochemistry showed that the amount of HNK-1 carbohydrate was markedly decreased in the brain of beta4GalT-II(-/-) mice, whereas the expression of polysialic acid was not affected. Furthermore, mice deficient in glucuronyltransferase (GlcAT-P), which is responsible for the biosynthesis of the HNK-1 carbohydrate, also showed impaired spatial learning/memory as described in our previous report, although their motor coordination/learning was normal as shown in this study. Histological examination showed abnormal alignment and reduced number of Purkinje cells in the cerebellum of beta4GalT-II(-/-) mice. These results suggest that the Galbeta1-4GlcNAc structure in the HNK-1 carbohydrate is mainly synthesized by beta4GalT-II and that the glycans synthesized by beta4GalT-II have essential roles in higher brain functions, including some that are HNK-1-dependent and some that are not.

Mass spectrometry in the characterization of human genetic N-glycosylation defects

Human genetic diseases that affect N-glycosylation result from the defective synthesis of the N-linked sugar moiety (glycan) of glycoproteins. The role of glycans for proper protein folding and biological functions is illustrated in the variety and severity of clinical manifestations shared by congenital disorders of glycosylation (CDG). This family of inherited metabolic disorders includes defects in the assembly of the oligosaccharide precursor that lead to an under-occupancy of N-glycosylation sites (CDG-I), and defects of glycan remodeling (CDG-II). Mass spectrometry constitutes a key tool for characterization of CDG-I defects by mass resolution of native protein glycoforms that differ for glycosylation-site occupancy. Glycan MS analyses in CDG-II is mandatory to detect whenever possible a repertoire of structures to pinpoint candidate enzymes and genes responsible for the abnormal N-glycan synthesis. In this manuscript, we review the MS applications in the area of CDG and related disorders with a special emphasis on those techniques that have been already applied or might become functional for diagnosis, characterization, and treatment monitoring in some specific conditions.

Mammalian glycosylation in immunity

Glycosylation produces a diverse and abundant repertoire of glycans, which are collectively known as the glycome. Glycans are one of the four fundamental macromolecular components of all cells, and are highly regulated in the immune system. Their diversity reflects their multiple biological functions that encompass ligands for proteinaceous receptors known as lectins. Since the discovery that selectins and their glycan ligands are important for the regulation of leukocyte trafficking, it has been shown that additional features of the vertebrate immune system are also controlled by endogenous cellular glycosylation. This Review focuses on the emerging immunological roles of the mammalian glycome.

Porcine beta1,4-galactosyltransferase-I sequence and expression

Beta1,4-galactosyltransferase-I (B4GALT1), one of seven beta1,4-galactosyltransferases, is an enzyme commonly found in the trans-Golgi complex that adds galactose to oligosaccharides. In the three mammals studied to date, the B4GALT1 gene directs production of B4GALT1 protein using either of two transcription start sites. The product of the smaller transcript serves the traditional biosynthetic role in the Golgi. This form also complexes with alpha-lactalbumin, a mammary-specific protein, to form lactose synthase. In addition to a biosynthetic role, the protein translated from the longer transcript appears on the plasma membranes of some cells where it serves as a signalling receptor in cell-matrix interactions such as sperm-egg binding. The objective of this study was to sequence the protein-coding region of porcine B4GALT1 and examine the sequence for relationships to the bovine, human, murine and chicken B4GALT1 genes. The sequence for the 1203 base pair protein-coding region of porcine B4GALT1 was obtained. Analysis of the deduced protein sequences revealed that the transmembrane region displayed the highest identity between the four mammals. The catalytic domain was 84-88% identical between the porcine sequence and those of the bovine, human and mouse. The porcine protein had the lowest overall homology to the chicken amino acid sequence, 58% identity. Conservation of both transcription start sites in the porcine gene supports the existence of two isoforms. When compared to the other mammalian B4GALT1 genes, the porcine coding sequence contained a single threonine codon inserted into the region encoding the cytoplasmic domain. Two putative phosphorylation sites in the mouse cytoplasmic domain were conserved in the porcine sequence. Northern blots revealed a widely expressed 4.4 kb transcript that was more abundant in the mammary gland during lactation. These results are important for studies of the function of this unusual and important glycosyltransferase during glycoprotein biosynthesis, lactation and fertilization.