Mechanisms of Igf2 inhibition in thymic epithelial cells infected by coxsackievirus CV-B4

Epidemiological studies have evidenced a link between type 1 diabetes (T1D) and infections by enteroviruses, especially with coxsackievirus B4 (CV-B4). CV-B4 is able to infect human and murine thymic epithelial cells (TECs) and, in a murine TEC line, we have shown that the diabetogenic strain CV-B4 E2 decreases transcription of insulin-like growth factor 2 gene (Igf2), coding for the self-peptide of the insulin family. Here we show that in CV-B4 infection of mice alters Igf2 transcripts isoforms in TECs, followed by a decrease of pro-IGF2 precursor in the thymus. CV-B4 infection of a murine TEC line decreases Igf2 P3 promoter activity by targeting the region -68 to -22 upstream of the transcription start site (TSS) whereas Igf2 transcripts stability is not affected, pointing towards a regulation of Igf2 transcription. Our data also show that CV-B4 decreases IL-6/STAT3 signaling in vitro. This study provides new knowledge about the regulation of intrathymic Igf2 transcription by CV-B4 and reinforces the hypothesis that CV-B4 infection of the thymus could break central self-tolerance of the insulin family by decreasing Igf2 transcription and IGF2 presentation in thymus epithelium. IMPORTANCECoxsackievirus B4 represents one of the most important environmental factors associated to type 1 diabetes, autoimmune disease for which no curative treatment exist. The diabetogenic strain Coxsackievirus B4 E2 was previously shown to decrease Igf2 expression, important player for central tolerance towards insulin, in a thymic epithelial cell line. The understanding of Igf2 regulation mechanisms during coxsackievirus B4 infection represents an interest for the understanding of central tolerance development but also for Igf2 transcriptional regulation itself, still poorly understood. Here we demonstrate that, some transcripts isoforms of Igf2 are also decreased in thymic epithelial cells in vivo. Moreover, we show that this decrease is induced by an alteration of specific regions of Igf2 P3 promoter and may be linked by a decrease of STAT3 signaling. In fine we hope that this work could lead to future therapies leading to reprogramming central tolerance towards {beta} cells antigens via Igf2 expression.