The malate-aspartate NADH shuttle member Aralar1 determines glucose metabolic fate, mitochondrial activity, and insulin secretion in beta cells.
The NADH shuttle system, which transports reducing equivalents from the cytosol to the mitochondria, is essential for the coupling of glucose metabolism to insulin secretion in pancreatic beta cells. Aralar1 and citrin are two isoforms of the mitochondrial aspartate/glutamate carrier, one key constituent of the malate-aspartate NADH shuttle. Here, the effects of Aralar1 overexpression in INS-1E beta cells and isolated rat islets were investigated for the first time. We prepared a recombinant adenovirus encoding for human Aralar1 (AdCA-Aralar1), tagged with the small FLAG epitope. Transduction of INS-1E cells and isolated rat islets with AdCA-Aralar1 increased aralar1 protein levels and immunostaining revealed mitochondrial localization. Compared with control INS-1E cells, overexpression of Aralar1 potentiated metabolism secretion coupling stimulated by 15 mm glucose. In particular, there was an increase of NAD(P)H generation, of mitochondrial membrane hyperpolarization, ATP levels, glucose oxidation, and insulin secretion (+45%, p < 0.01). Remarkably, this was accompanied by reduced lactate production. Rat islets overexpressing Aralar1 secreted more insulin at 16.7 mm glucose (+65%, p < 0.05) compared with controls. These results show that aspartate-glutamate carrier capacity limits glucose-stimulated insulin secretion and that Aralar1 overexpression enhances mitochondrial metabolism.
Rubi
Blanca
B
Department of Cell Physiology and Metabolism, University Medical Centre, 1 rue Michel-Servet, CH-1211 Geneva 4, Switzerland.
del Arco
Araceli
A
Bartley
Clarissa
C
Satrustegui
Jorgina
J
Maechler
Pierre
P
D000255:Adenosine Triphosphate / Q000378:metabolism; D000256:Adenoviridae / Q000235:genetics; D000818:Animals; D001224:Aspartic Acid / Q000737:chemistry*; D002118:Calcium / Q000378:metabolism; D002460:Cell Line; D002469:Cell Separation; D002478:Cells, Cultured; D003600:Cytosol / Q000378:metabolism; D000939:Epitopes / Q000737:chemistry; D005434:Flow Cytometry; D005947:Glucose / Q000378:metabolism*; D018698:Glutamic Acid / Q000737:chemistry / Q000378:metabolism; D006019:Glycolysis; D006801:Humans; D015151:Immunoblotting; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D007515:Islets of Langerhans / Q000378:metabolism*; D007763:Lac Operon; D007773:Lactates / Q000378:metabolism; D008293:Malates / Q000737:chemistry*; D008564:Membrane Potentials; D026901:Membrane Transport Proteins / Q000737:chemistry* / Q000378:metabolism; D008928:Mitochondria / Q000378:metabolism*; D033681:Mitochondrial Membrane Transport Proteins; D024101:Mitochondrial Proteins / Q000737:chemistry* / Q000378:metabolism; D008954:Models, Biological; D009249:NADP / Q000378:metabolism; D010100:Oxygen / Q000378:metabolism; D020033:Protein Isoforms; D051381:Rats; D014018:Tissue Distribution
D000939:Epitopes; D007328:Insulin; D007773:Lactates; D008293:Malates; D026901:Membrane Transport Proteins; D033681:Mitochondrial Membrane Transport Proteins; D024101:Mitochondrial Proteins; D020033:Protein Isoforms; C114606:SLC25A12 protein, human; D001224:Aspartic Acid; D018698:Glutamic Acid; D009249:NADP; C030298:malic acid; D000255:Adenosine Triphosphate; D005947:Glucose; D010100:Oxygen; D002118:Calcium