Impaired membrane resealing and autoimmune myositis in synaptotagmin VII-deficient mice.

Members of the synaptotagmin family have been proposed to function as Ca2+ sensors in membrane fusion. Syt VII is a ubiquitously expressed synaptotagmin previously implicated in plasma membrane repair and Trypanosoma cruzi invasion, events which are mediated by the Ca2+-regulated exocytosis of lysosomes. Here, we show that embryonic fibroblasts from Syt VII-deficient mice are less susceptible to trypanosome invasion, and defective in lysosomal exocytosis and resealing after wounding. Examination of mutant mouse tissues revealed extensive fibrosis in the skin and skeletal muscle. Inflammatory myopathy, with muscle fiber invasion by leukocytes and endomysial collagen deposition, was associated with elevated creatine kinase release and progressive muscle weakness. Interestingly, similar to what is observed in human polymyositis/dermatomyositis, the mice developed a strong antinuclear antibody response, characteristic of autoimmune disorders. Thus, defective plasma membrane repair in tissues under mechanical stress may favor the development of inflammatory autoimmune disease.

A common nonsynonymous single nucleotide polymorphism in the SLC30A8 gene determines ZnT8 autoantibody specificity in type 1 diabetes.

OBJECTIVE: 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. RESEARCH DESIGN AND METHODS: 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. CONCLUSIONS: 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.

Expression and function of synaptotagmin VII in CTLs.

The Ca(2+) sensor synaptotagmin (Syt) VII regulates the exocytosis of conventional lysosomes in several cell types. In CTLs, the Ca(2+)-regulated exocytosis of lytic granules/secretory lysosomes is responsible for the perforin/granzyme-mediated lysis of target cells. To investigate the role of Syt VII in CTL effector function, the expression and function of Syt VII were examined in wild-type and Syt VII-deficient mice. In comparison with Syt VII(+/+) controls, Syt VII(-/-) animals were impaired in their ability to clear an infection with the intracellular pathogen Listeria monocytogenes. When isolated CTLs were examined, we found that Syt VII is expressed upon CTL activation and localizes to granzyme A-containing lytic granules. Syt VII-deficient CTLs have no defects in proliferation and cytokine production, and their lytic granules contain normal amounts of perforin and granzyme A and polarize normally at the immunological synapse. However, despite normal conjugate formation with target cells, CTLs from Syt VII(-/-) mice exhibit reduced effector activity, when compared with controls. Treatment of Syt VII(+/+) or Syt VII(-/-) CTLs with an inhibitor of the perforin-mediated lytic pathway resulted in comparable levels of cytotoxic activity, suggesting that Syt VII regulates perforin-mediated cytolytic CTL responses.