Aberrant sialylation of serum IgA1 was associated with prognosis of patients with IgA nephropathy

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.

O-glycoforms of polymeric IgA1 in the plasma of patients with IgA nephropathy are associated with pathological phenotypes

BACKGROUND

IgA1 O-glycosylation plays an important role in the pathogenesis of IgA nephropathy (IgAN). However, variations in IgA1 O-glycoforms have not been explored. We aimed to investigate the IgA1 O-glycoforms in the hinge region (HR) of polymeric IgA1 and then evaluate the association between IgA1 O-glycoforms and crescent formation in IgAN.

METHODS

The discovery cohort (cohort 1) comprised 11 crescentic IgAN patients, 10 noncrescentic IgAN patients and 10 healthy controls, and the validation cohort (cohort 2) comprised 11 crescentic IgAN patients, 9 noncrescentic IgAN patients, and 9 healthy controls. A total of 143 IgAN patients with different crescent percentages (cohort 3) were also included. Polymeric IgA1 was purified from the plasma of the participants. The variation in O-glycoforms was evaluated by estimating the molecular weights of IgA1 hinge glycopeptides using reversed-phase liquid chromatography (LC) and tandem mass spectrometry under electron-transfer/higher-energy collision dissociation (EThcD) fragmentation mode.

RESULTS

In discovery cohort (cohort 1), the numbers of GalNAc bound to one HR were lower in IgAN patients. The proportions of GalNAc3 (defined as O-glycans bound to one HR at 3 sites) and GalNAc4 were highest in crescentic IgAN patients followed by noncrescentic IgAN patients and were lowest in healthy controls (GalNAc 3: 9.92%±3.37% vs 6.65%±1.53% vs 4.05%±1.24%; P < 0.001; GalNAc4: 45.91%±4.75% vs 41.13%±2.95% vs 40.98%±2.95%; P = 0.004). The proportions of GalNAc5 and GalNAc6 were lowest in crescentic IgAN patients followed by noncrescentic IgAN patients and were highest in healthy controls (GalNAc5: 50.15%±4.27% vs 47.92%±4.09% vs 45.87%±3.79%, P = 0.028; GalNAc6: 6.58%±2.53% vs 6.04%±1.35% vs 4.65%±2.27%; P = 0.034). These results were consistent in the validation cohort (cohort 2); In another cohort with 143 patients with different crescents percentage (cohort 3), the numbers of GalNAc in polymeric IgA1 decreased with increasing percentage of crescents.

CONCLUSIONS

The numbers of GalNAc in IgA1 HRs were lower in IgAN patients, especially in crescentic IgAN patients, and may be associated with a severe IgAN phenotype.

Immunoglobulin E sialylation regulates allergic responses

Shade et al. demonstrate that people with peanut allergies produce IgE antibodies that are enriched for sialic acid-containing glycoforms. The sialylated IgE triggered significantly more degranulation by basophils and mast cells, suggesting intrinsic functional differences between IgEs from allergic and nonallergic subjects.

Sialylation of immunoglobulin E is a determinant of allergic pathogenicity

Approximately one-third of the world's population suffers from allergies¹. Exposure to allergens crosslinks immunoglobulin E (IgE) antibodies that are bound to mast cells and basophils, triggering the release of inflammatory mediators, including histamine². Although IgE is absolutely required for allergies, it is not understood why total and allergen-specific IgE concentrations do not reproducibly correlate with allergic disease^3-5. It is well-established that glycosylation of IgG dictates its effector function and has disease-specific patterns. However, whether IgE glycans differ in disease states or affect biological activity is completely unknown⁶. Here we perform an unbiased examination of glycosylation patterns of total IgE from individuals with a peanut allergy and from non-atopic individuals without allergies. Our analysis reveals an increase in sialic acid content on total IgE from individuals with a peanut allergy compared with non-atopic individuals. Removal of sialic acid from IgE attenuates effector-cell degranulation and anaphylaxis in several functional models of allergic disease. Therapeutic interventions-including removing sialic acid from cell-bound IgE with a neuraminidase enzyme targeted towards the IgE receptor FcεRI, and administering asialylated IgE-markedly reduce anaphylaxis. Together, these results establish IgE glycosylation, and specifically sialylation, as an important regulator of allergic disease.

Circulating CD89-IgA complex does not predict deterioration of kidney function in Korean patients with IgA nephropathy

Background:

Soluble CD89 (sCD89)-IgA complex plays a key role in the pathogenesis of IgA nephropathy (IgAN). However, there is a lack of evidence supporting this complex as a good biomarker for disease progression. This study aimed to evaluate the usefulness of sCD89-IgA complex for risk stratification of IgAN.

Methods:

A total of 326 patients with biopsy-proven IgAN were included. sCD89-IgA complex was measured by sandwich-enzyme-linked immunosorbent assay. The study endpoints were a 30% decline in estimated glomerular filtration rate (eGFR).

Results:

sCD89-IgA complex levels were inversely and weakly associated with eGFR at the time of biopsy (r=−0.12, p=0.03). However, the significance between the two factors was lost in the multivariate linear regression after adjustment of clinical factors (β=0.35, p=0.75). In a multivariate Cox model, the highest (hazard ratio [HR], 0.75; 95% confidence interval [CI], 0.35–1.61; p=0.45) and middle (HR, 0.93; 95% CI, 0.46–1.89; p=0.84) tertiles of sCD89-IgA complex levels were not associated with an increased risk of developing a 30% decrease in eGFR. Furthermore, the decline rates in eGFR did not differ between groups and C-statistics revealed that the sCD89-IgA complex were not superior to clinical factors in predicting disease progression.

Conclusions:

This study found no association between sCD89-IgA complex levels and disease progression in IgAN. Although sCD89 can contribute to the formation of immune complexes, our findings suggest that the sCD89-IgA level is not a good predictor of adverse outcomes and has limited clinical utility as a biomarker for risk stratification in IgAN.

Histone deacetylase inhibitors attenuate P-aIgA1-induced cell proliferation and extracellular matrix synthesis in human renal mesangial cells in vitro

AIM

Aberrantly glycosylated IgA1 is a key factor in the pathogenesis of IgA nephropathy (IgAN). In this study we investigated the effects of aggregated IgA1 derived from IgAN patients (P-aIgA1) on human renal mesangial cells (HMCs) and the anti-proliferative and antifibrotic effects of histone deacetylase (HDAC) inhibitors in vitro.

METHODS

Three types of IgA1 were prepared, ie, N-IgA1 (IgA1 from healthy volunteers), P-IgA1 (IgA1 from IgAN patients), and P-aIgA1 (aggregated IgA1 from IgAN patients). The isolated IgA1 was heated for thermal polymerization. The proliferation of human renal mesangial cells (HMCs) were assessed using MTT assay. The expression levels of relevant proteins were examined using immunoblotting assays or immunohistochemistry.

RESULTS

P-aIgA1 (25-250 μg/mL) dose-dependently promoted the proliferation of HMCs, and markedly increased the protein levels of type I histone deacetylase (HDAC1, HDAC2 and HDAC8) in the cells. Both P-IgA1 and N-IgA1 were much weaker in stimulating cell proliferation and HDAC expression. P-aIgA1 (50 μg/mL) markedly increased the protein levels of Col1a1 and PAI-1, as well as pSmad2/3 and pStat3 in the cells. Pretreatment with the HDAC inhibitor trichostatin A (TSA, 250 nmol/L) or valproic acid (VPA, 400 μg/mL) partially reversed P-aIgA1-induced cell proliferation and extracellular matrix synthesis in HMCs.

CONCLUSION

P-aIgA1 produces pro-proliferative and profibrotic actions in HMCs via upregulating the expression of HDACs, and subsequently activating TGF-β/Smad2/3 and Jak2/Stat3 signaling pathways. Both VPA and TSA attenuate P-aIgA1-induced cell proliferation and fibrosis in HMCs.

Study of correlation between polymorphism of ST6GALNAC2 and susceptibility to IgA nephropathy

The aim of the present study was to explore the correlation between single nucleotide polymorphisms (SNPs) rs3840858 and rs2304921 in a specific α-2,6 sialyltransferase gene, ST6GALNAC2, and the susceptibility to immunoglobulin (IgA) nephropathy (IgAN). The distributions of genotypes of SNPs rs3840858 and rs2304921 in ST6GALNAC2 were detected by direct sequencing. The distributions of the genotype and allele frequencies of rs3840858 in patients with IgAN were significantly different from those in the control group (genotypes, P=0.001; alleles, P=0.001). The DI genotype ratio (17.8%) in the IgAN group was higher than that in the control group (5.6%) and the I allele frequency (8.9%) in the IgAN group was higher than that in the control group (2.8%). Univariate logistic regression analysis indicated that rs3840858 polymorphism is a risk factor of IgAN (P=0.001). The risk of developing IgAN in individuals who carried the DI genotype was 3-fold higher than that in individuals who carried the DD genotype [odds ratio (OR)=3.676, 95% confidence interval (CI)=1.284-10.519], and the risk of developing IgAN in individuals who carried the I allele was higher than that in individuals who carried the D allele (OR=3.415, 95% CI=1.223-9.531). The distributions of the genotype (AA, AG and GG) and allele (A and G) frequencies of rs2304921 did not have a statistically significant difference between patients with IgAN and those without (P>0.05). The SNP rs3840858 in the ST6GALNAC2 gene may be associated with the risk of developing IgAN in the population studied; however, polymorphism of rs2304921 appears to be irrelevant to the risk of developing IgAN in this population.

Phyllodes tumor of the breast: role of Axl and ST6GalNAcII in the development of mammary phyllodes tumors

Phyllodes tumor exhibits an aggressive growth. The expression of many biological markers has been explored to discriminate between different grades of phyllodes tumor and to predict their behavior. The purpose of this study was to evaluate the implications of Axl and ST6GalNAcII in phyllodes tumors. Real-time PCR, Western blot, and immunohistochemical were used to analyze differential expression of ST6GalNAcII and Axl in phyllodes tumor (PT) cell lines and tissue specimens. RNAi assay, ECM invasion assay, and tumorigenicity assay were used to analyze the altered expression of ST6GalNAcII gene effects on the expression of Axl and invasive ability of phyllodes tumor cells in vitro and in vivo. Compared to benign tumors, borderline and malignant ones showed a remarkable increase in mRNA levels of Axl and ST6GalNAcII gene, and it was higher in malignant tumor cells than in borderline tumor cells. When ST6GalNAcII was silenced, compared to the control, the expression level of Axl was significantly reduced in malignant tumor cell transfectants and knockdown of ST6GalNAcII gene significantly inhibited invasive activity in malignant tumor cells. The high expression of ST6GalNAcII and Axl was significantly correlated with tumor grade and distance metastasis by immunohistochemical analysis. Axl and ST6GalNAcII expression increases with increasing tumor grade in mammary phyllodes tumors. ST6GalNAc II might be participated in the glycosylation of Axl, and this Axl glycosylation may mediate the tumorigenicity, invasion, and distant metastasis of PT cells.

Enzymatic sialylation of IgA1 O-glycans: implications for studies of IgA nephropathy

Patients with IgA nephropathy (IgAN) have elevated circulating levels of IgA1 with some O-glycans consisting of galactose (Gal)-deficient N-acetylgalactosamine (GalNAc) with or without N-acetylneuraminic acid (NeuAc). We have analyzed O-glycosylation heterogeneity of naturally asialo-IgA1 (Ale) myeloma protein that mimics Gal-deficient IgA1 (Gd-IgA1) of patients with IgAN, except that IgA1 O-glycans of IgAN patients are frequently sialylated. Specifically, serum IgA1 of healthy controls has more α2,3-sialylated O-glycans (NeuAc attached to Gal) than α2,6-sialylated O-glycans (NeuAc attached to GalNAc). As IgA1-producing cells from IgAN patients have an increased activity of α2,6-sialyltransferase (ST6GalNAc), we hypothesize that such activity may promote premature sialylation of GalNAc and, thus, production of Gd-IgA1, as sialylation of GalNAc prevents subsequent Gal attachment. Distribution of NeuAc in IgA1 O-glycans may play an important role in the pathogenesis of IgAN. To better understand biological functions of NeuAc in IgA1, we established protocols for enzymatic sialylation leading to α2,3- or α2,6-sialylation of IgA1 O-glycans. Sialylation of Gal-deficient asialo-IgA1 (Ale) myeloma protein by an ST6GalNAc enzyme generated sialylated IgA1 that mimics the Gal-deficient IgA1 glycoforms in patients with IgAN, characterized by α2,6-sialylated Gal-deficient GalNAc. In contrast, sialylation of the same myeloma protein by an α2,3-sialyltransferase yielded IgA1 typical for healthy controls, characterized by α2,3-sialylated Gal. The GalNAc-specific lectin from Helix aspersa (HAA) is used to measure levels of Gd-IgA1. We assessed HAA binding to IgA1 sialylated at Gal or GalNAc. As expected, α2,6-sialylation of IgA1 markedly decreased reactivity with HAA. Notably, α2,3-sialylation also decreased reactivity with HAA. Neuraminidase treatment recovered the original HAA reactivity in both instances. These results suggest that binding of a GalNAc-specific lectin is modulated by sialylation of GalNAc as well as Gal in the clustered IgA1 O-glycans. Thus, enzymatic sialylation offers a useful model to test the role of NeuAc in reactivities of the clustered O-glycans with lectins.

Qufeng Tongluo Prescription () inhibits mesangial cell proliferation and promotes apoptosis through regulating cell cycle progression

OBJECTIVE

To study the effects and possible underlying mechanism of Qufeng Tongluo Prescription (, QFTL) on the regulation of mesangial cells (MCs) proliferation and apoptosis.

METHODS

The MCs used in this experiment have undergone five passages induced by lipopolysaccharide (LPS). Changes in the proliferation, apoptosis, cell cycle regulatory proteins and mRNA expression levels of the MCs after administration of Benazepril or QFTL were measured by methyl thiazolyl tetrazolium (MTT) reduction assay, flow cytometry, Western blot and quantitative real-time polymerase chain reaction (qRT-PCR), respectively.

RESULTS

The addition of Benazepril or QFTL serum inhibited LPS-induced MC proliferation after treatment for 24, 48 and 72 h, respectively (P<0.05 or P<0.01). Moreover, the inhibitory effect is more significant in the QFTL group at 48 h (P<0.05). Compared with the control group, LPS-induced cell proliferation decreased the number of cells in G1 phase versus cells in S and G2/M phases, while the addition of QFTL and Benazepril serum increased the ratio of cells at G1 phase (P<0.05 or P<0.01) to cells at S phase (P<0.01), implicating the cell cycle inhibition effect exerted by QFTL. LPS decreased the level of MC apoptosis, compared with the control group (P<0.05), while QFTL and Benazepril serum increased the level of MC apoptosis (P<0.01). Moreover, the difference between the QFTL group and the Benazepril group was statistically significant (P<0.01). Compared with the control group, the protein and mRNA expression levels of cylinD1, cyclin dependent kinase 2 (CDK2) and p21 were significantly increased (P<0.05 or P<0.01), p27 was decreased but with no statistical significance (P>0.05); After being treated with QFTL and Benazepril serum, the protein and mRNA expression levels of cylinD1, CDK2, p21 were decreased and p27 increased significantly (P<0.05 or P<0.01); Compared with the Benazepril group, QFTL show better effects on protein and mRNA expression levels of cylinD1, CDK2 (P<0.05 or P<0.01) and p21 protein expression (P<0.05).

CONCLUSION

QFTL inhibits MCs proliferation, promotes MCs apoptosis through an underlying mechanism of down-regulating the protein and mRNA expression levels of cylinD1, CDK2, p21 and up-regulation of the expression level of p27.

N-acetylgalactosamine exposure of serum IgA1 was associated with glomerulosclerosis and tubular atrophy/interstitial fibrosis of IgA nephropathy patients

AIM

Immunoglobulin A nephropathy (IgAN) is the most common glomerulonephritis with various histological and clinical phenotypes. N-acetylgalactosamine (GalNAc) exposure plays a pivotal role in the pathogenesis of IgAN. The aim of the current study is to investigate whether GalNAc exposure of serum IgA1 was associated with clinical and pathological manifestation of IgAN.

METHODS

Sera from 199 patients with biopsy proved IgAN were collected. Clinical and pathological manifestations were collected. Biotinylated Helix aspersa were used in ELISA to examine GalNAc exposure on IgA1 molecules. Patients were divided into two groups according to the GalNAc exposure rate less or more than 0.4.

RESULTS

Age, gender, and serum creatinine were comparable between the two groups. Univariate analysis showed that significantly higher urinary protein excretion rate but less severe glomerular sclerosis and tubularinterstitial fibrosis were observed in the lower GalNAc exposure group. Multivariate regression analysis demonstrated that adjusted by age and gender, the GalNAc exposure rate more than 0.4 was a risk factor of glomerular sclerosis and tubularinterstitial fibrosis, OR*(95% CI) were 2.76 (1.19-6.37) and 2.49 (1.18-5.25), respectively.

CONCLUSION

Immunoglobulin A nephropathy patients with lower proteinuria had higher GalNAc exposure rates. The GalNAc exposure rate more than 0.4 was a risk factor of severe chronic renal tissue change.

Suppression of adiponectin by aberrantly glycosylated IgA1 in glomerular mesangial cells in vitro and in vivo

The pathogenesis of IgA nephropathy (IgAN) may be associated with the mesangial deposition of aberrantly glycosylated IgA1. To identify mediators affected by aberrantly glycosylated IgA1 in cultured human mesangial cells (HMCs), we generated enzymatically modified desialylated and degalactosylated (deSial/deGal) IgA1. The state of deglycosylated IgA1 was confirmed by lectin binding to Helix aspersa (HAA) and Sambucus nigra (SNA). In the cytokine array analysis, 52 proteins were upregulated and 34 were downregulated in HMCs after stimulation with deSial/deGal IgA1. Among them, the secretion of adiponectin was suppressed in HMCs after stimulation with deSial/deGal IgA1. HMCs expressed mRNAs for adiponectin and its type 1 receptor, but not the type 2 receptor. Moreover, we revealed a downregulation of adiponectin expression in the glomeruli of renal biopsy specimens from patients with IgAN compared to those with lupus nephritis. We also demonstrated that aberrantly glycosylated IgA1 was deposited in the mesangium of patients with IgAN by dual staining of HAA and IgA. Moreover, the urinary HAA/SNA ratio of lectin binding was significantly higher in IgAN compared to other kidney diseases. Since adiponectin has anti-inflammatory effects, including the inhibition of adhesion molecules and cytokines, these data suggest that the local suppression of this adipokine by aberrantly glycosylated IgA1 could be involved in the regulation of glomerular inflammation and sclerosis in IgAN.

Mesangial cells stimulated by immunoglobin A1 from IgA nephropathy upregulates transforming growth factor-beta1 synthesis in podocytes via renin-angiotensin system activation

BACKGROUND AND AIMS

We undertook this study to investigate the effect of mesangial cells stimulated by immunoglobin A1 from IgAN on transforming growth factor-beta1 synthesis in podocytes.

METHODS

Jacalin affinity chromatography and Sephacryl S-200 molecular sieve chromatography were used to isolate IgA1 from blood of IgAN patients, which was then used as aggregated IgA1 (aIgA1). Podocytes were incubated with special mesangial medium. Real-time polymerase chain reaction (PCR) and enzyme-linked immunosorbent assay (ELISA) were used, respectively, to measure TGF-beta1 mRNA expression and its protein concentration in medium.

RESULTS

TGF-beta1 mRNA and its protein concentration in the medium of podocytes increased when exposed to the medium of mesangial cells, which were stimulated by IgA1 from IgAN patients. Angiotensinogen and angiotensin-converting enzyme (ACE) mRNAs, as well as angiotensin II, were also increased by the medium (p <0.05). Enalaprilat and valsartan partly lowered overproduction of TGF-beta1 mRNA and excreted protein of podocytes, whereas enalaprilat plus valsartan completely restored them to the level as control.

CONCLUSIONS

These data suggest that mesangial cells stimulated by IgA1 from IgAN patients may excrete some material to facilitate TGF-beta1 synthesis in podocytes through activating renin-angiotensin system by cross-talk.

Differential expression of glycogenes in tonsillar B lymphocytes in association with proteinuria and renal dysfunction in IgA nephropathy

Aberrant O-glycosylation of serum and tonsillar IgA1 is one of the main pathogeneses of IgA nephropathy (IgAN). However, the synthesis of underglycosylated IgA1 in tonsils has not yet been characterized. This study examined tonsillar B lymphocytes of IgAN (n=34) using tonsils derived from patients with chronic tonsillitis (n=24) and sleep apnea syndrome (n=14) as a control. Gene expression of beta1,3-galactosyltransferase (beta3GalT), and the core 1 beta3GalT-specific molecular chaperone, Cosmc, UDP-N-acetyl-alpha-D-galactosamine: polypeptide N-acetylgalactosaminyl-transferase 2, were significantly decreased in tonsillar CD19-positive B lymphocytes from IgAN patients compared to control tonsillar tissues as determined by real-time RT-PCR. Tonsillar B cell beta3GalT gene expression significantly correlated with estimated GFR and negatively correlated with proteinuria and histological injury score. Western blotting showed the protein expression of beta3GalT in the tonsils to significantly decrease in IgAN in comparison to the controls. These data suggest the downregulation of beta3GalT in tonsillar B lymphocytes to be closely associated with the clinical characteristics of IgAN.

Mesangial medium with IgA1 from IgA nephropathy inhibits nephrin expression in mouse podocytes

BACKGROUND

IgA nephropathy (IgAN) is characterized by mesangial deposition of polymeric IgA1, and podocyte injury plays an important role in glomerulosclerosis of the disease. Our previous study indicated that medium of mesangial cells co-incubated with aggregated IgA1 (aIgA1), isolated from IgAN patients, down-regulated nephrin expression. Yet the mechanism remains unclear.

MATERIALS AND METHODS

Podocytes were incubated with a medium of mesangial cells co-incubated with aIgA1, which was isolated from IgAN patients, and enalaprilat (10(-5) M), valsartan (10(-5) M) and anti-mouse tumour necrosis factor-alpha antibody (50 ng mL(-1)) separately. Nephrin expression in podocytes was measured by real-time polymerase chain reaction and Western blot analysis.

RESULTS

The level of angiotensinogen and angiotensin-converting enzyme mRNAs in podocytes, as well as angiotensin, was also increased by a medium of mesangial cells co-incubated with aIgA1 from IgAN patients (P<0.05). Enalaprilat or valsartan partly improved nephrin expression when compared with that by podocytes exposed to the mesangial medium (P<0.05), while the nephrin expression of podocytes with enalaprilat or valsartan was lower than that of podocytes exposed to medium of mesangial cells stimulated by aIgA1 from healthy control (P<0.05). However, anti-mouse tumour necrosis factor-alpha antibody did not show any improvement in nephrin expression.

CONCLUSION

Our findings implicate that local renin angiotensin system activation in podocytes is partly involved in down-regulation of nephrin by mesangial medium in IgA nephropathy.

Effect of aggregated immunoglobulin A1 from immunoglobulin A nephropathy patients on nephrin expression in podocytes

AIM

Abnormal immunoglobulin (Ig)A1 is considered to play a pivotal role in IgA nephropathy. We used mouse podocytes as the experimental model to investigate the effect of aggregated IgA1 (aIgA1) isolated from IgA nephropathy (IgAN) patients on nephrin expression in podocytes through direct and indirect pathways.

METHODS

Jacalin affinity chromatography and Sephacryl S-200 molecular sieve chromatography were used to isolate IgA1 from blood of IgAN patients which was therefore became aIgA1. Podocytes were incubated with aIgA1 or special mesangial medium. Nephrin expression in podocytes was measured by real-time polymerase chain reaction and western blot analysis.

RESULTS

Aggregated IgA1 from IgAN patients and healthy controls reduced nephrin expression in podocytes at mRNA and protein levels when compared with podocytes incubated with control medium (RPMI-1640 with 0.5% foetal bovine serum) (P<0.05). While medium from mesangial cells incubated with aIgA1 from IgAN inhibited nephrin expression in podocytes at mRNA and protein levels when compared with podocytes incubated with medium from mesangial cells with aIgA1 from healthy controls (P<0.05).

CONCLUSION

Our findings implicate that aIgA1 from IgAN patients could inhibit nephrin expression through direct and indirect pathways, although these mechanisms remain to be clarified.

Aberrant galactosylation of IgA1 is involved in the genetic susceptibility of Chinese patients with IgA nephropathy

BACKGROUND

Immunoglobulin A nephropathy (IgAN) is associated with genetic and environmental factors, and undergalactosylation of IgA1 in the serum is considered to be a contributor to pathogenesis of IgAN. The present study was conducted to detect the galactose- (Gal) deficient IgA1 level in Chinese IgAN patients and their family members.

METHODS

Sixty-three IgAN patients were enrolled, where 32 first-degree relatives of 19 patients and 44 spouses of 44 patients were recruited. Healthy blood donors (n = 39) were used as normal controls. Biotinylated HAA (Helix aspersa) was utilized to detect the Gal-deficient IgA1 in enzyme-linked immunosorbent assay (ELISA). All the results were corrected by serum IgA1 concentration.

RESULTS

Compared with normal controls, the sera IgA1 of patients and their first-degree relatives demonstrated increased Gal-deficient IgAl level (0.17 +/- 0.09 versus 0.10 +/- 0.04, P = 0.001; 0.14 +/- 0.07 versus 0.10 +/- 0.04, P = 0.028); no significant difference between patients and their first-degree relatives was detected (0.17 +/- 0.09 versus 0.14 +/- 0.07, P = 0.127). In contrast, serum Gal-deficient IgA1 level of IgAN patients was higher than their counterpart spouses and normal controls (0.18 +/- 0.13 versus 0.14 +/- 0.09, P = 0.009; 0.18 +/- 0.13 versus 0.10 +/- 0.04, P = 0.001), while that of patients' spouses was comparable with normal controls (0.14 +/- 0.09 versus 0.10 +/- 0.04, P = 0.075). There was no correlation between clinicopathological data and serum Gal-deficient IgA1 level.

CONCLUSION

The patients with IgAN and their first relatives showed significant higher Gal-deficient IgA1 level than healthy controls, whereas patients' spouses were the same as healthy controls. It can be suggested that the Gal-deficient IgA1 might be inherited in Chinese patients with IgAN.

Activity of alpha2,6-sialyltransferase and its gene expression in peripheral B lymphocytes in patients with IgA nephropathy

It is known that aberrant sialylation of IgA1 is involved in the pathogenesis of IgA nephropathy (IgAN). We hypothesize that aberrant sialylation of serum IgA1 may result from changes in the activity of alpha2,6-sialyltransferase (alpha2,6-ST) or expression of its coding gene ST6GALNAC2 in peripheral B lymphocytes. Sixty patients with IgAN and 20 healthy controls were enrolled. Peripheral B lymphocytes were isolated by CD-19-positive magnetic beads. The expression level of ST6GALNAC2 was quantitatively analysed by real-time reverse-transcriptase polymerase chain reaction (PCR). Serum IgA1 and sialylation levels were detected by enzyme-linked immunosorbent assay (ELISA) and specific lectin-binding ELISA. Activity of alpha2,6-ST was measured by specific lectin-binding ELISA. Expression of ST6GALNAC2 in B peripheral lymphocytes was significantly lower in patients with IgAN than that in normal controls (3.7 +/- 2.2 versus 6.3 +/- 2.3, P = 0.016); alpha2,6-ST activity in B lymphocytes was correlated positively with the level of alpha2,6-sialic acid in serum IgA1 in patients (n = 42) and controls (n = 12) (r = 0.37, P = 0.007). However, alpha2,6-ST activity did not differ between patients with IgAN and controls (1.19 +/- 1.43 versus 1.06 +/- 1.17, P > 0.05). These data suggested that reduced sialylation of serum IgA1 may result from decreased expression of ST6GALNAC2. The factors affecting activity of alpha2,6-ST in the sialylation of IgA1 need to be further investigated.