Dataset Information

N-acetylgalactosaminide ?2,6-sialyltransferase II is a candidate enzyme for sialylation of galactose-deficient IgA1, the key autoantigen in IgA nephropathy.

ABSTRACT:

Background

Galactose-deficient O-glycans in the hinge region (HR) of immunoglobulin A1 (IgA1) play a key role in the pathogenesis of IgA nephropathy (IgAN). O-Glycans of circulatory IgA1 consist of N-acetylgalactosamine (GalNAc) with a ?1,3-linked galactose; both sugars may be sialylated. In patients with IgAN, ?2,6-sialylated GalNAc is a frequent form of the galactose-deficient O-glycans. Prior analyses of IgA1-producing cells had indicated that ?2,6-sialyltransferase II (ST6GalNAc-II) is likely responsible for sialylation of GalNAc of galactose-deficient IgA1, but direct evidence is missing.

Methods

We produced a secreted variant of recombinant human ST6GalNAc-II and an IgA1 fragment comprised of C?1-HR-C?2. This IgA1 fragment and a synthetic HR peptide with enzymatically attached GalNAc residues served as acceptors. ST6GalNAc-II activity was assessed in vitro and the attachment of sialic acid to these acceptors was detected by lectin blot and mass spectrometry.

Results

ST6GalNAc-II was active with both acceptors. High-resolution mass spectrometry analysis revealed that up to three sialic acid residues were added to the GalNAc residues of the HR glycopeptide.

Conclusions

Our data provide direct evidence that ST6GalNAc-II can sialylate GalNAc of galactose-deficient IgA1. As serum levels of galactose-deficient IgA1 with sialylated glycoforms are increased in IgAN patients, our data explain the corresponding part of the biosynthetic pathway.

SUBMITTER: Stuchlova Horynova M

PROVIDER: S-EPMC4309194 | biostudies-literature | 2015 Feb

REPOSITORIES: biostudies-literature

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Publications

N-acetylgalactosaminide α2,6-sialyltransferase II is a candidate enzyme for sialylation of galactose-deficient IgA1, the key autoantigen in IgA nephropathy.

Stuchlova Horynova Milada M Vrablikova Alena A Stewart Tyler J TJ Takahashi Kazuo K Czernekova Lydie L Yamada Koshi K Suzuki Hitoshi H Julian Bruce A BA Renfrow Matthew B MB Novak Jan J Raska Milan M

Nephrology, dialysis, transplantation : official publication of the European Dialysis and Transplant Association - European Renal Association 20141003 2

<h4>Background</h4>Galactose-deficient O-glycans in the hinge region (HR) of immunoglobulin A1 (IgA1) play a key role in the pathogenesis of IgA nephropathy (IgAN). O-Glycans of circulatory IgA1 consist of N-acetylgalactosamine (GalNAc) with a β1,3-linked galactose; both sugars may be sialylated. In patients with IgAN, α2,6-sialylated GalNAc is a frequent form of the galactose-deficient O-glycans. Prior analyses of IgA1-producing cells had indicated that α2,6-sialyltransferase II (ST6GalNAc-II) ...[more]

PMID: 25281698

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Project description:Background and objectivesIncreased circulating galactose-deficient IgA1 and subsequently complement activation both play important roles in the pathophysiology of IgA nephropathy. However, their relationship to disease severity and progression remains unclear.Design, setting, participants, & measurementsWe assessed 1210 participants in a cohort study of biopsy-proven IgA nephropathy at Peking University First Hospital. Plasma concentrations of galactose-deficient IgA1 and complement component C3 were measured at the time of biopsy. We tested associations of galactose-deficient IgA1 and galactose-deficient IgA1/C3 ratio with CKD progression event, defined as ESKD or 50% decline in eGFR, using Cox proportional hazards models and restricted cubic splines.ResultsAfter a median follow-up of 43 months (interquartile range, 24-76 months), 172 (14%) participants reached the CKD progression event. The association of galactose-deficient IgA1 levels and CKD progression event showed a nonlinear relationship. The risk of CKD progression events was greater with higher plasma galactose-deficient IgA1 levels but reached a plateau when galactose-deficient IgA1>325 U/ml, whereas the risk of CKD progression events monotonically increased with higher galactose-deficient IgA1/C3 ratio. After adjustment for traditional risk factors (demographics, eGFR, proteinuria, hypertension, Oxford pathologic score, and corticosteroids/immunosuppressive therapy), higher levels of galactose-deficient IgA1/C3 ratio were independently associated with CKD progression event (per natural log-transformed [galactose-deficient IgA1/C3], hazard ratio, 2.03; 95% confidence interval [95% CI], 1.25 to 3.29; P=0.004). In reference to the first quartile of the galactose-deficient IgA1/C3 ratio, hazard ratios were 1.71 (95% CI, 1.01 to 2.89) for the second quartile, 1.55 (95% CI, 0.91 to 2.63) for the third quartile, and 2.17 (95% CI, 1.33 to 3.56) for the fourth quartile.ConclusionsIn IgA nephropathy, plasma galactose-deficient IgA1/C3 ratio was associated with CKD progression event independent of clinical and biopsy characteristics.