MafA is a transcription factor that binds to the promoter in the insulin gene and has been postulated to regulate insulin transcription in response to serum glucose levels, but there is no current in vivo evidence to support this hypothesis. To analyze the role of MafA in insulin transcription and glucose homeostasis in vivo, we generated MafA-deficient mice. Here we report that MafA mutant mice display intolerance to glucose and develop diabetes mellitus. Detailed analyses revealed that glucose-, arginine-, or KCl-stimulated insulin secretion from pancreatic ␤ cells is severely impaired, although insulin content per se is not significantly affected. MafA-deficient mice also display age-dependent pancreatic islet abnormalities. Further analysis revealed that insulin 1, insulin 2, Pdx1, Beta2, and Glut-2 transcripts are diminished in MafA-deficient mice. These results show that MafA is a key regulator of glucose-stimulated insulin secretion in vivo.Insulin is the only polypeptide hormone that is essential for the regulation of blood glucose levels and is synthesized exclusively in ␤ cells of the islets of Langerhans in the pancreas. The molecular mechanisms that control ␤-cell-specific insulin gene transcription are well characterized. Three conserved cis-regulatory elements within the promoter, E1, A3, and RIPE3b/ C1, respectively, appear to be indispensable for proper insulin gene regulation (22,25). Islet-restricted transcription factors Beta2/NeuroD and Pdx1 bind to the E1 and A3 elements in vitro. Gene disruption experiments in mice have revealed that both Beta2 and Pdx1 play critical roles in insulin gene regulation as well as in islet development and function (1,8,21). Furthermore, mutations in both the Beta2 and Pdx1 genes have been identified within populations of patients with type II diabetes (18,29,30).The third regulatory element, RIPE3b/C1, has also been shown to play a critical role in ␤-cell-specific insulin gene transcription as well as in glucose-regulated expression. Previous studies identified a pancreatic ␤-cell-restricted factor, called the RIPE3b1 activator, that is enriched in response to glucose in pancreatic ␤-cell nuclear extracts. Very recently, four groups reported that the RIPE3b1 activator is a member of the Maf family of transcription factors, MafA (10,12,20,26). The large Maf proteins, MafA/L-Maf/SMaf1 (2, 9, 24), MafB (11), c-Maf (23), and Nrl (31), each contain a basic motif followed by a leucine zipper, and all four family members harbor acidic domains that act as transcriptional activation domains. Although a role for MafA in insulin gene regulation was hypothesized, in vivo tests of the hypothesis have not been reported. To elucidate MafA function in insulin gene regulation, we generated MafA-deficient mice. MATERIALS AND METHODSTargeted disruption of the mafA gene. mafA genomic clones were isolated from a 129/SvJ genomic library (Stratagene) using a partial mouse MafA cDNA as a probe. The targeting vector was constructed with the bacterial lacZ gene containing a nuclear loca...

A Wnt coreceptor low-density lipoprotein receptor-related protein 5 (LRP5) plays an essential role in bone accrual and eye development. Here, we show that LRP5 is also required for normal cholesterol and glucose metabolism. The production of mice lacking LRP5 revealed that LRP5 deficiency led to increased plasma cholesterol levels in mice fed a high-fat diet, because of the decreased hepatic clearance of chylomicron remnants. In addition, when fed a normal diet, LRP5-deficient mice showed a markedly impaired glucose tolerance. The LRP5-deficient islets had a marked reduction in the levels of intracellular ATP and Ca 2؉ in response to glucose, and thereby glucoseinduced insulin secretion was decreased. The intracellular inositol 1,4,5-trisphosphate (IP3) production in response to glucose was also reduced in LRP5؊͞؊ islets. Real-time PCR analysis revealed a marked reduction of various transcripts for genes involved in glucose sensing in LRP5؊͞؊ islets. Furthermore, exposure of LRP5؉͞؉ islets to Wnt-3a and Wnt-5a stimulates glucose-induced insulin secretion and this stimulation was blocked by the addition of a soluble form of Wnt receptor, secreted Frizzled-related protein-1. In contrast, LRP5-deficient islets lacked the Wnt-3a-stimulated insulin secretion. These data suggest that Wnt͞LRP5 signaling contributes to the glucose-induced insulin secretion in the islets.and LRP6 are coreceptors involved in the Wnt signaling pathway (1-6). The Wnt signaling pathway plays a pivotal role in embryonic development (7,8) and oncogenesis (9) through various signaling molecules including Frizzled receptors (10), recently characterized LRP5 and LRP6 (1-6), and Dickkopf proteins (4, 6). In addition, the Wnt signaling is also involved in adipogenesis by negatively regulating adipogenic transcription factors (Tcfs) (11). Although Wnt signaling has been characterized in both developmental and oncogenic processes, little is known about its function in the normal adult.Recent studies have revealed that loss of function mutations in the LRP5 gene cause the autosomal recessive disorder osteoporosis-pseudoglioma syndrome (12). LRP5 is expressed in osteoblasts and transduces Wnt signaling via the canonical pathway, thereby modulating bone accrual development (12, 13). A point mutation in a ''propeller'' motif in LRP5 causes a dominant-positive high bone density by impairing the action of a normal antagonist of the Wnt pathway, Dickkopf, thereby increasing Wnt signaling (14,15). In addition, the human LRP5 gene is mapped within the region (IDDM4) linked to type 1 diabetes on chromosome 11q13 (16).In previous studies, we and others showed that LRP5 is highly expressed in many tissues, including hepatocytes and pancreatic beta cells (17,18). We also showed that LRP5 can bind apolipoprotein E (apoE) (18). This finding raises the possibility that LRP5 plays a role in the hepatic clearance of apoE-containing chylomicron remnants, a major plasma lipoprotein carrying diet-derived cholesterol.To evaluate the in vivo roles of LRP5, we generated LRP...

To promote their pathology, CD4 T-cells from patients with rheumatoid arthritis (RA) have to clonally expand and differentiate into cytokine-producing effector cells. In contrast to healthy T-cells, naïve RA T-cells have a defect in glycolytic flux due to upregulation of glucose-6-phosphate dehydrogenase (G6PD). Excess G6PD shunts glucose into the pentose phosphate pathway (PPP), resulting in NADPH accumulation and ROS consumption. With surplus reductive equivalents, RA T-cells insufficiently activate the redox-sensitive kinase ATM; bypass the G2/M cell cycle checkpoint and hyperproliferate. Insufficient ATM activation biases T-cell differentiation towards the Th1 and Th17 lineages, imposing a hyper-inflammatory phenotype. We have identified several interventions that replenishing intracellular ROS, correct the abnormal proliferative behavior of RA T-cells and successfully suppress synovial inflammation. Rebalancing glucose utilization and restoring oxidant signaling may provide a novel therapeutic strategy to prevent autoimmunity in RA.