β-Cell-specific pyruvate dehydrogenase deficiency impairs glucose-stimulated insulin secretion

Abstract

Glucose-stimulated insulin secretion (GSIS) by ␤-cells requires the generation of ATP from oxidation of pyruvate as well as generation of coupling factors involving three different pyruvate cycling shuttles. The roles of several key enzymes involved in pyruvate cycling in ␤-cells have been documented using isolated islets and ␤-cell clonal lines. To investigate the role of the pyruvate dehydrogenase (PDH) complex (PDC) in GSIS, a murine model of ␤-cell-specific PDH deficiency (␤-PDHKO) was created. Pancreatic insulin content was decreased in 1-day-old ␤-PDHKO male pups and adult male mice. The plasma insulin levels were decreased and blood glucose levels increased in ␤-PDHKO male mice from neonatal life onward. GSIS was reduced in isolated islets from ␤-PDHKO male mice with about 50% reduction in PDC activity. Impairment in a glucose tolerance test and in vivo insulin secretion during hyperglycemic clamp was evident in ␤-PDHKO adults. No change in the number or size of islets was found in pancreata from 4-wk-old ␤-PDHKO male mice. However, an increase in the mean size of individual ␤-cells in islets of these mice was observed. These findings show a key role of PDC in GSIS by pyruvate oxidation. This ␤-PDHKO mouse model represents the first mouse model in which a mitochondrial oxidative enzyme deletion by gene knockout has been employed to demonstrate an altered GSIS by ␤-cells. pyruvate cycling; ␤-cell hypertrophy INSULIN SECRETION by pancreatic islet ␤-cells is influenced by a variety of effectors, with glucose being the primary and most important stimulus. Insulin secretion requires metabolism of glucose in the ␤-cell with an associated increase in total intracellular ATP and an increase in the cytosolic ATP/ADP ratio (7,18,36). Increases in the cytosolic ATP concentration result in the sequential closure of K ATP channels, depolarization of the plasma membrane, opening of voltage-sensitive L-type Ca 2ϩ channels, Ca 2ϩ influx, and insulin secretion (15, 34). The uptake of glucose and its phosphorylation to glucose 6-phosphate are catalyzed by high Km glucose transporter 2 and the rate-limiting high Km glucokinase, respectively. These "glucosensors" ensure an increase in glucose phosphorylation, since blood glucose concentrations rise after a carbohydraterich meal. Pyruvate derived from glucose is channeled predominantly into its mitochondrial metabolism because of low levels of lactate dehydrogenase activity and of the monocarboxylate transporter-1 for lactate in the plasma membrane of islets (23,24,26,34). Another link between the cytosolic and mitochondrial metabolism of glucose is the transfer of NADH via the glycerol 3-phosphate shuttle and the malate-aspartate shuttle for ATP production (8,22).Evidence shows that metabolites derived from mitochondrial metabolism of pyruvate generated primarily from glucose and to a limited extent from other nutrients (such as amino acids) play a critical role in metabolism-secretion coupling of insulin secretion by ␤-cells (24, 26). Pyruvate is converted to acetyl-CoA and...

Lack of mitochondria-generated acetyl-CoA by pyruvate dehydrogenase complex downregulates gene expression in the hepatic de novo lipogenic pathway

“…Mice used in the present study had a B6 genetic background, whereas mice used in our previously reported paper (6) had a mixed (129J/B6) genetic background. Earlier, we also reported some differences for ␤-cell structure and function between two pancreatic ␤-cellspecific PDCKO mouse strains (30,39). So it is not surprising that we have observed some variations in the levels of serum insulin and blood glucose of L-PDCKO mice (B6 genetic background) in the present study compared with that of the L-PDCKO mice (129J/B6 mixed genetic background), as reported previously (6).…”

“…Generation of the systemic null mutation in male mice proved to be lethal at an early embryonic stage. However, tissue-specific (except the brain) deletion of the Pdha1 gene permitted both pre-and postnatal development and growth of male mice for metabolic studies (6,30,38,39). Earlier, we generated liver-specific deletion of the Pdha1 gene in male mice (L-PDCKO) to investigate its impact on lipid biosynthesis from glucose in the liver (6).…”

Glucagon-Like Peptide-1 Protects Human Islets against Cytokine-Mediated β-Cell Dysfunction and Death: A Proteomic Study of the Pathways Involved

“…52 This might be counteracted by the GLP-1-induced expression and activation of the mitochondrial pyruvate dehydrogenase E1 component subunit beta, which functions, in its complex, as the primary link between glycolysis and the Krebs cycle and thereby positively affects GSIS. 53 These data correspond with the findings of Sparre and colleagues, 39 who showed a reduced energy production in rat islets upon IL-1β exposure. Furthermore, we also observed a clear effect on REG1A and REG1B, which are acinar cell-derived proliferation factors shown to be involved in β-cell proliferation.…”

The Pancreatic β-Cell: A Bioenergetic Perspective

“…120). Not surprisingly, ␤-cell specific knockout of the pyruvate dehydrogenase subunit dramatically inhibits GSIS (492). There are conflicting reports on the ability of PDH to regulate ␤-cell bioenergetics.…”