OBJECTIVE-In diabetes, glucose toxicity affects different organ systems, including pancreatic islets where it leads to β-Cell apoptosis, but the mechanisms are not fully understood. Recently, we identified thioredoxin-interacting protein (TXNIP) as a proapoptotic β-Cell factor that is induced by glucose, raising the possibility that TXNIP may play a role in β-Cell glucose toxicity. RESEARCH DESIGN AND METHODS-To assess the effects of glucose on TXNIP expression and apoptosis and define the role of TXNIP, we used INS-1 β-cells; primary mouse islets; obese, diabetic BTBR.ob mice; and a unique mouse model of TXNIP deficiency (HcB-19) that harbors a natural nonsense mutation in the TXNIP gene. RESULTS-Incubation of INS-1 cells at 25 mmol/l glucose for 24 h led to an 18-ffold increase in TXNIP protein, as assessed by immunoblotting. This was accompanied by increased apoptosis, as demonstrated by a 12-fold induction of cleaved caspase-3. Overexpression of TXNIP revealed that TXNIP induces the intrinsic mitochondrial pathway of apoptosis. Islets of diabetic BTBR.ob mice also demonstrated increased TXNIP and apoptosis as did isolated wild-type islets incubated at high glucose. In contrast, TXNIP-deficient HcB-19 islets were protected against glucose-induced apoptosis as measured by terminal deoxynu-cleotidyl transfferase-mediated dUTP nick-end labeling and caspase-3, indicating that TXNIP is a required causal link between glucose toxicity and β-Cell death. CONCLUSIONS-These findings shed new light onto the molecular mechanisms of β-Cell glucose toxicity and apoptosis, demonstrate that TXNIP induction plays a critical role in this vicious cycle, and suggest that inhibition of TXNIP may represent a novel approach to reduce glucotoxic β-Cell loss. © 2008 by the American Diabetes Association.