The initial goal of our project was to identify autoantigens in type 1 diabetes. Several years ago we succeeded in cloning two novel proteins, IA-2 and IA-2 beta, from a beta cell subtraction library. These proteins were found to be enzymatically inactive members of the protein tyrosine phosphatase family, widely distributed in neuroendocrine cells throughout the body and integral transmembrane components of dense core secretory vesicles. Further studies showed they belonged to an ancient gene family going back 500 million years with homologs in Drosophila and C elegans.? ? Examination of sera from patients with type 1 diabetes revealed that IA-2 and IA-2 beta were major autoantigens and that autoantibodies to these proteins appeared years before the development of clinical diseases. As a result, autoantibodies to IA-2 and IA-2 beta have become predictive markers for identifying individuals at high risk of developing diabetes and are being widely used to select pre-diabetics for entry into therapeutic intervention trials. Type 1 diabetes is now serving as a model for other autoimmune diseases where intensive searches for predictive autoantibodies are underway.? ? Over the last couple of years emphasis has been on determining the function of IA-2 and IA-2 beta. By knocking out these genes in mice we have shown that they are involved in the secretion of insulin and that their deletion results in impaired insulin release and elevated glucose tolerance tests. Similar findings were observed upon knocking down IA-2 by small interfering RNA in cultured beta cells. From these and other studies we conclude that IA-2 is a modulator of both regulated and basal insulin secretion and acts by stabilizing dense core secretory vesicles. ? ? Since IA-2 and IA-2 beta are present in many neuroendocrine cells throughout the body we are beginning to find other changes in our knockout mice. One is female infertility which we found is due to impaired secretion of luteinizing hormones (LH). This is the first demonstration that alterations in structural proteins of dense core vesicles can result in female infertility. ? ? Studies are now being carried out to determine the molecular basis by which IA-2 and IA-2 beta function and how IA-2 stabilizes dense core secretory vesicles. The role of signal transduction pathways also is being explored. Using a proteomic approach attempts are being made to identify new autoantigens in type 1 diabetes and in addition, other autoimmune diseases (e.g., Sjogren?s Syndrome). Once identified the predictive value of these autoantibodies will be determined.
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