Thymic expression of insulin-related genes in an animal model of autoimmune type 1 diabetes

✍ Scribed by Ouafae Kecha-Kamoun; Imane Achour; Henri Martens; Julien Collette; Pierre J. Lefebvre; Dale L. Greiner; Vincent Geenen

• Publisher: John Wiley and Sons
• Year: 2001
• Tongue: English
• Weight: 327 KB
• Volume: 17
• Category: Article
• ISSN: 1520-7552
• DOI: 10.1002/dmrr.182

✦ Synopsis

Background Insulin and multiple other autoantigens have been implicated in the pathogenesis of autoimmune type 1 diabetes, but the origin of immunological self-reactivity specifically oriented against insulin-secreting islet b-cells remains obscure. The primary objective of the present study was to investigate the hypothesis that a defect in thymic central T-cell selftolerance of the insulin hormone family could contribute to the pathophysiology of type 1 diabetes. This hypothesis was investigated in a classic animal model of type 1 diabetes, the Bio-Breeding (BB) rat.

Methods

The expression of the mammalian insulin-related genes (Ins, Igf1 and Igf2) was analysed in the thymus of inbred Wistar Furth rats (WF), diabetes-resistant BB (BBDR) and diabetes-prone BB (BBDP) rats.

Results RT-PCR analyses of total RNA from WF, BBDP and BBDR thymi revealed that Igf1 and Ins mRNAs are present in 15/15 thymi from 2-day-old, 5-day-old and 5-week-old WF, BBDR and BBDP rats. In contrast, a complete absence of Igf2 mRNA was observed in more than 80% of BBDP thymi. The absence of detectable Igf2 transcripts in the thymus of BBDP rats is tissuespecific, since Igf2 mRNAs were detected in all BBDP brains and livers examined. Using a specific immunoradiometric assay, the concentration of thymic IGF-2 protein was significantly lower in BBDP than in BBDR rats ( p<0.01).

Conclusions The present study suggests an association between the emergence of autoimmune diabetes and a defect in Igf2 expression in the thymus of BBDP rats. This tissue-specific defect in gene expression could contribute both to the lymphopenia of these rats (by impaired T-cell development) and the absence of central T-cell self-tolerance of the insulin hormone family (by defective negative selection of self-reactive T-cells).