A Common Nonsynonymous Single Nucleotide Polymorphism in the SLC30A8 Gene Determines ZnT8 Autoantibody Specificity in Type 1 Diabetes

Barbara Davis Center for Childhood Diabetes, University of Colorado Denver, Aurora, Colorado, USA.
Diabetes (Impact Factor: 8.1). 07/2008; 57(10):2693-7. DOI: 10.2337/db08-0522
Source: PubMed


Zinc transporter eight (SLC30A8) is a major target of autoimmunity in human type 1A diabetes and is implicated in type 2 diabetes in genome-wide association studies. The type 2 diabetes nonsynonymous single nucleotide polymorphism (SNP) affecting aa(325) lies within the region of highest ZnT8 autoantibody (ZnT8A) binding, prompting an investigation of its relationship to type 1 diabetes.
ZnT8A radioimmunoprecipitation assays were performed in 421 new-onset type 1 diabetic Caucasians using COOH-terminal constructs incorporating the known human aa(325) variants (Trp, Arg, and Gln). Genotypes were determined by PCR-based SNP analysis. RESULTS-Sera from 224 subjects (53%) were reactive to Arg(325) probes, from 185 (44%) to Trp(325)probes, and from 142 (34%) to Gln(325)probes. Sixty subjects reacted only with Arg(325) constructs, 31 with Trp(325) only, and 1 with Gln(325) only. The restriction to either Arg(325) or Trp(325) corresponded with inheritance of the respective C- or T-alleles. A strong gene dosage effect was also evident because both Arg- and Trp-restricted ZnT8As were less prevalent in heterozygous than homozygous individuals. The SLC30A8 SNP allele frequency (75% C and 25% T) varied little with age of type 1 diabetes onset or the presence of other autoantibodies.
The finding that diabetes autoimmunity can be defined by a single polymorphic residue has not previously been documented. It argues against ZnT8 autoimmunity arising from molecular mimicry and suggests a mechanistic link between the two major forms of diabetes. It has implications for antigen-based therapeutic interventions because the response to ZnT8 administration could be protective or immunogenic depending on an individual's genotype.

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    • "Differential expression of ZnT8R and ZnT8W could affect major histocompatibility complex class I presentation of these antigens to CD8 T cells in the thymus or in the periphery (8). The C-allele (encoding ZnT8-325R) confers a minor risk of type 2 diabetes and has been associated with reduced insulin secretion (3), but no direct evidence that this polymorphism alters ZnT8 expression is available. Alternatively, the polymorphism at position 325 could alter the T-cell epitope repertoire (8), thereby modifying the influence of HLA-A*24 on humoral autoimmunity (24), but so far, no association has been found between the breadth of the ZnT8 CD4 T-cell responses in patients and ZnT8A (25). "
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    ABSTRACT: The HLA-A*24 allele has shown negative associations with autoantibodies to islet antigen-2 (IA 2) and zinc transporter 8 (ZnT8) in patients with established type 1 diabetes. Understanding how this HLA class I allele affects humoral islet autoimmunity gives new insights into disease pathogenesis. We therefore investigated the epitope specificity of associations between HLA-A*24 and islet autoantibodies at disease onset. HLA-A*24 genotype and autoantibody responses to insulin (IAA), glutamate decarboxylase (GADA), IA-2, IA-2β and ZnT8 were analysed in samples collected from patients with recent-onset type 1 diabetes. After correction for age, gender, and HLA class II genotype, HLA-A*24 was shown to be a negative determinant of both IA-2A and ZnT8A. These effects were epitopespecific. Antibodies targeting the protein tyrosine phosphatase domains of IA-2 and IA-2β, but not the IA-2 juxta-membrane region were less common in patients carrying HLA-A*24 alleles. The prevalence of ZnT8A specific or cross-reactive with the ZnT8 tryptophan-325 polymorphic residue, but not those specific to arginine-325 was reduced in HLA*A24 positive patients. No associations were found between HLA-A*24 and IAA or GADA. Association of an HLA class I susceptibility allele with altered islet autoantibody phenotype at diagnosis suggests CD8 T-cell and/or natural killer cell mediated killing modulate humoral autoimmune responses.
    Full-text · Article · Feb 2013 · Diabetes
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    • "Interest in the role of zinc in the pathogenesis of DM was re-erupted with the discovery of the association between T2DM and a genetic polymorphism in the SLC30A8 gene [14], [15]. This polymorphism, which is caused by the minor allele of the single-nucleotide polymorphism rs1226634 (C/T transition; Arg {325}–Trp 273 {325}) [16], was subsequently shown to be associated with the presence of altered glucose homeostasis, pancreatic β cell dysfunction, or overt T2DM in many [17], [18] but not all [19], [20] study populations. Furthermore, the insulin producing pancreatic β cells contain some of the highest levels of Zn++ in the body. "
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    • "Based on our initial results with the DASP 2009 cohort demonstrating marked heterogeneity against three β-cell targets and ATP4B, autoantibodies against a more extensive panel of islet, organ-specific, and other potential autoantigens was determined in a second, independent sample set representing the coded DASP 2010 cohort. For these tests, 6 different β-cell targets were examined including GAD65, IA2, IA2-β and 3 different ZnT8 subtypes [34]. Based on the literature, autoantibodies were also tested against six potential organ–specific antigens implicated in T1D and/or other autoimmune conditions including ATP4B, TGM2, TPO, KCNRG, AQP-4, and GFAP. "
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