Thioredoxin-Interacting Protein Is Stimulated by Glucose through a Carbohydrate Response Element and Induces β-Cell Apoptosis

Recently, we identified thioredoxin-interacting protein (TXNIP) as the most dramatically glucose-induced gene in our human islet microarray study. TXNIP is a regulator of the cellular redox state, but its role in pancreatic beta-cells and the mechanism of its regulation by glucose remain unknown. We therefore generated a stable transfected beta-cell line (INS-1) overexpressing human TXNIP and found that TXNIP overexpression induced apoptosis as assessed by Bax, Bcl2, caspase-3, and cleaved caspase-9 as well as Hoechst staining. Interestingly, islets of insulin-resistant/diabetic mice (AZIP-F1, BTBRob/ob) demonstrated elevated TXNIP expression, suggesting that TXNIP may play a role in glucotoxicity and the beta-cell loss observed under these conditions. Furthermore, we found that glucose-induced TXNIP transcription is not dependent on glucose metabolism and is mediated by a distinct carbohydrate response element (ChoRE) in the human TXNIP promoter consisting of a perfect nonpalindromic repeat of two E-boxes. Transfection studies demonstrated that this ChoRE was necessary and sufficient to confer glucose responsiveness. Thus, TXNIP is a novel proapoptotic beta-cell gene elevated in insulin resistance/diabetes and up-regulated by glucose through a unique ChoRE and may link glucotoxicity and beta-cell apoptosis.