Screening for novel lead compounds increasing insulin expression in medullary thymic epithelial cells

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Insulin expression in the thymus has been implicated in regulating the negative selection of autoreactive T cells and in mediating the central immune tolerance to pancreatic beta-cells. Thymic insulin expression modulation might be an important drug target for preventing type 1 diabetes. We performed a high-throughput screening to identify compounds with such activity. A reporter plasmid was constructed with the human insulin promoter sequence including a short allele of the upstream variable number tandem repeat (VNTR) sequence (32 repeats), subcloned into the pGL4.17 vector. The plasmid was stably transfected into an insulin-transcribing medullary thymic epithelial cell (mTEC) line. Primary high-throughput screening assays were carried out by stimulating with candidate compounds for 24h, and the activity of luciferase was measured. Positive compounds were further validated by real-time PCR. Of 19,707 compounds, we identified one compound that could enhance mTEC insulin expression, as confirmed by real-time PCR. We also observed that transfection with the autoimmune regulator (AIRE) increased endogenous AIRE expression in mTECs. Our insulin-VNTRI-promoter reporter system is consistent with the insulin expression regulation in mTECs, and one compound that was identified could increase insulin expression in mTECs. A positive feedback effect of AIRE in mTECS was observed. Whether these efforts in murine thymus cells apply to humans remains to be determined.