Glucose-Regulated Gene Expression Maintaining the Glucose-Responsive State of β-Cells

The mammalian beta-cell has particular properties that synthesize, store, and secrete insulin in quantities that are matched to the physiological demands of the organism. To achieve this task, beta-cells are regulated both acutely and chronically by the extracellular glucose concentration. Several in vivo and in vitro studies indicate that preservation of the glucose-responsive state of beta-cells is lost when the extracellular glucose concentration chronically deviates from the normal physiological condition. Experiments with the protein synthesis inhibitor cycloheximide suggest that the maintenance of the functional state of beta-cells depends on protein(s) with rapid turnover. Analysis of newly synthesized proteins via two-dimensional gel electrophoresis and high-density gene expression microarrays demonstrates that the glucose-dependent preservation of beta-cell function is correlated with glucose regulation of a large number of beta-cell genes. Two different microarray analyses of glucose regulation of the mRNA profile in beta-cells show that the sugar influences expression of multiple genes involved in energy metabolism, the regulated insulin biosynthetic/secretory pathway, membrane transport, intracellular signaling, gene transcription, and protein synthesis/degradation. Functional analysis of some of these regulated gene clusters has provided new evidence for the concept that cataplerosis, the conversion of mitochondrial metabolites into lipid intermediates, is a major metabolic pathway that allows beta-cell activation independently of closure of ATP-sensitive potassium channels.