Fig. 1Mechanism of pancreatic β-cell glucolipotoxicity. Normal laboratory ranges of glucose and fatty acids are not toxic to β-cells. The problems arise when β-cells experience prolonged exposure of sustained elevation of hyperglycemia together with elevated hyperlipidemia. Chronic high glucose levels exert a significant effect on β-cell lipid metabolism via altered enzyme activity and expression of key transcription factors. The consequent change in cellular energy metabolism results in glucolipotoxicity, which induces β-cell apoptotic cell death and promotes type 2 diabetes. FFA, free fatty acid; LCFACoA, long-chain fatty acyl-CoA; DAG, diacylglycerol; TG, triglyceride; PL, phospholipid.
Fig. 2Progression from the normal state to severe diabetes. This panel shows the changes that occur in β-cells during the three-stage progression from the normal state to severe diabetes. GSIS, glucose-stimulated insulin secretion; GLUT2, glucose transporter2; GK, glucokinase; IAPP, islet amyloid polypeptide; ER, endoplasmic reticulum.
Fig. 3Working hypothesis in glucolipotoxicity-induced β-cell dysfunction. PGC-1α inhibits insulin and BETA2/NeuroD transcription levels, and attenuating PGC-1α overexpression protects against glucolipotoxicity-induced β-cell dysfunction [13].
Fig. 4β-cell dysfunction by glucolipotoxicity. Under glucolipotoxic conditions, oxidative stress is induced and the JNK pathway is activated. PDX-1 is translocated pathogenically from the nucleus to the cytoplasm by JNK activation and finally induces suppression of insulin secretion [41].