Mutations in the transcription factor IPF1/PDX1 have been associated with type 2 diabetes. To elucidate -cell dysfunction, PDX1 was suppressed by transduction of rat islets with an adenoviral construct encoding a dominant negative form of PDX1. After 2 days, there was a marked inhibition of insulin secretion in response to glucose, leucine, and arginine. Increasing cAMP levels with forskolin and isobutylmethylxanthine restored glucose-stimulated insulin secretion, indicating normal capacity for exocytosis. To identify molecular targets implicated in the altered metabolism secretion coupling, DNA microarray analysis was performed on PDX1-deficient and control islets. Of the 2640 detected transcripts, 70 were up-regulated and 56 were down-regulated. Transcripts were subdivided into 12 clusters; the most prevalent were associated with metabolism. Quantitative reverse transcriptase-PCR confirmed increases in succinate dehydrogenase and ATP synthase mRNAs as well as pyruvate carboxylase and the transcript for the malate shuttle. In parallel there was a 50% reduction in mRNA levels for the mitochondrially encoded nd1 gene, a subunit of the NADH dehydrogenase comprising complex I of the mitochondrial respiratory chain. As a consequence, total cellular ATP concentration was drastically decreased by 75%, and glucose failed to augment cytosolic ATP, explaining the blunted glucose-stimulated insulin secretion. Rotenone, an inhibitor of complex I, mimicked this effect. Surprisingly, TFAM, a nuclear-encoded transcription factor important for sustaining expression of mitochondrial genes, was down-regulated in islets expressing DN79PDX1. In conclusion, loss of PDX1 function alters expression of mitochondrially encoded genes through regulation of TFAM leading to impaired insulin secretion.Type 2 diabetes mellitus is a common severe disease of intermediary metabolism usually caused by both -cell dysfunction and resistance to the biological actions of insulin on its main target tissues (liver, muscle, and fat). The susceptibility for type 2 diabetes is inherited, but single diabetes genes have only been identified in about 5% of cases. Mutations in one of these genes, the homeodomain transcription factor ipf1 (also known as, pdx1, idx1, or stf1), have been associated with a rare form of maturity onset diabetes of the young (MODY4) 1 as well as predisposing individuals to late onset type 2 diabetes (1-5). Furthermore, homozygous null mutations in the ipf1 gene result in pancreas agenesis indicating that this transcription factor is indispensable for both pancreas development and subsequent -cell function (6, 7).As in humans, inactivation of both pdx1 alleles in murine models results in pancreas agenesis, whereas heterozygous mice or animals carrying a -cell-specific deletion of the gene exhibit impaired glucose tolerance (8 -11). Several of these models also develop overt diabetes with age indicating a progressive deterioration of -cell function and/or mass. A recent study concluded that reduction in PDX1 expression impedes p...
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