Oligonucleotide Microarray Analysis Reveals PDX1 as an Essential Regulator of Mitochondrial Metabolism in Rat Islets

Mutations in the transcription factor IPF1/PDX1 have been associated with type 2 diabetes. To elucidate β-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. Mutations in the transcription factor IPF1/PDX1 have been associated with type 2 diabetes. To elucidate β-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 β-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) 1The abbreviations used are: MODY, maturity onset diabetes of the young; PDX1, pancreatic duodenal homeobox 1; OXPHOS, oxidative phosphorylation; IBMX, isobutylmethylxanthine; RT, reverse transcriptase. 1The abbreviations used are: MODY, maturity onset diabetes of the young; PDX1, pancreatic duodenal homeobox 1; OXPHOS, oxidative phosphorylation; IBMX, isobutylmethylxanthine; RT, reverse transcriptase. as well as predisposing individuals to late onset type 2 diabetes (1Stoffers D.A. Stanojevic V. Habener J.F. J. Clin. Investig. 1998; 102: 232-241Google Scholar, 2Hani E.H. Stoffers D.A. Chevre J.C. Durand E. Stanojevic V. Dina C. Habener J.F. Froguel P. J. Clin. Investig. 1999; 104: R41-R48Google Scholar, 3Macfarlane W.M. Frayling T.M. Ellard S. Evans J.C. Allen L.I.S. Bulman M.P. Ayres S. Shepherd M. Clark P. Millward A. Demaine A. Wilkin T. Docherty K. Hattersley A.T. J. Clin. Investig. 1999; 104: 33-39Google Scholar, 4Clocquet A.R. Egan J.M. Stoffers D.A. Muller D.C. Wideman L. Chin G.A. Clarke W.L. Hanks J.B. Habener J.F. Elahi D. Diabetes. 2000; 49: 1856-1864Google Scholar, 5Hansen L. Urioste S. Petersen H.V. Jensen J.N. Eiberg H. Barbetti F. Serup P. Hansen T. Pedersen O. J. Clin. Endocrinol. Metab. 2000; 85: 1323-1326Google Scholar). 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 β-cell function (6Stoffers D.A. Zinkin N.T. Stanojevic V. Clarke W.L. Habener J.F. Nat. Genet. 1997; 15: 106-110Google Scholar, 7Schwitzgebel V.M. Mamin A. Brun T. Ritz-Laser B. Zaiko M. Maret A. Jornayvaz F.R. Theintz G.E. Michielin O. Melloul D. Philippe J. J. Clin. Endocrinol. Metab. 2003; 88: 4398-4406Google Scholar). As in humans, inactivation of both pdx1 alleles in murine models results in pancreas agenesis, whereas heterozygous mice or animals carrying a β-cell-specific deletion of the gene exhibit impaired glucose tolerance (8Jonsson J. Carlsson L. Edlund T. Edlund H. Nature. 1994; 371: 606-609Google Scholar, 9Lottmann H. Vanselow J. Hessabi B. Walther R. J. Mol. Med. 2001; 79: 321-328Google Scholar, 10Thomas M.K. Devon O.N. Lee J.H. Peter A. Schlosser D.A. Tenser M.S. Habener J.F. J. Clin. Investig. 2001; 108: 319-329Google Scholar, 11Offield M.F. Jetton T.L. Labosky P.A. Ray M. Stein R.W. Magnuson M.A. Hogan B.L. Wright C.V. Development (Camb.). 1996; 122: 983-995Google Scholar). Several of these models also develop overt diabetes with age indicating a progressive deterioration of β-cell function and/or mass. A recent study concluded that reduction in PDX1 expression impedes primarily β-cell function such as NAD(P)H generation, mitochondrial metabolism, and/or mobilization of intracellular calcium (12Brissova M. Shiota M. Nicholson W.E. Gannon M. Knobel S.M. Piston D.W. Wright C.V. Powers A.C. J. Biol. Chem. 2002; 277: 11225-11232Google Scholar) rather than β-cell mass. In contrast, another publication (13Johnson J.D. Ahmed N.T. Luciani D.S. Han Z. Tran H. Fujita J. Misler S. Edlund H. Polonsky K.S. J. Clin. Investig. 2003; 111: 1147-1160Google Scholar) demonstrates that the metabolism secretion coupling (glucose sensing, NADH formation, and calcium currents) was normal in Pdx1+/– β-cells. However, β-cells in aging mice were more susceptible to apoptosis, with reduced expression of anti-apoptotic genes such as BclXL and Bcl-2, as compared with control islets. This study concluded that decreased β-cell mass rather than function is the key mechanism whereby PDX1 deficiency leads to impaired blood glucose regulation and to progressive age-dependent development of diabetes (13Johnson J.D. Ahmed N.T. Luciani D.S. Han Z. Tran H. Fujita J. Misler S. Edlund H. Polonsky K.S. J. Clin. Investig. 2003; 111: 1147-1160Google Scholar). The two investigations highlight the profound regulatory complexity that PDX1 impinges on β-cell function and/or survival. The direct contribution of PDX1 on these two potential nonmutually exclusive physiological processes remains to be elucidated. Whereas PDX1 is clearly a central player in pancreas development and subsequent β-cell function, relatively few bona fide PDX1 target genes have been identified. Most interesting, although PDX1 was found to be one of the main transcription factors mediating the stimulatory effect of glucose on insulin gene expression, its impact on constitutive expression of the hormone in vivo remains controversial (12Brissova M. Shiota M. Nicholson W.E. Gannon M. Knobel S.M. Piston D.W. Wright C.V. Powers A.C. J. Biol. Chem. 2002; 277: 11225-11232Google Scholar, 14Melloul D. Marshak S. Cerasi E. Diabetologia. 2002; 45: 309-326Google Scholar). Similarly, conflicting results have been reported for the regulation of glucokinase gene expression by the transcription factor (12Brissova M. Shiota M. Nicholson W.E. Gannon M. Knobel S.M. Piston D.W. Wright C.V. Powers A.C. J. Biol. Chem. 2002; 277: 11225-11232Google Scholar, 15Watada H. Kajimoto Y. Miyagawa J.-I. Hanafusa T. Hamaguchi K. Matsuoka T.-A. Yamamoto K. Matsuzawa Y. Kawamori R. Yamasaki Y. Diabetes. 1996; 45: 1826-1831Google Scholar, 16Wang H. Maechler P. Ritz-Laser B. Hagenfeldt K.A. Ishihara H. Philippe J. J. Biol. Chem. 2001; Scholar). In contrast, PDX1 been to transcription of and in β-cells as well as in P. C. Mol. Endocrinol. 1996; Scholar, Habener J.F. J. 1994; Scholar, P. Jensen J. S. A. 1996; Scholar, A. Edlund H. Nature. 2000; Scholar). of genes in β-cells targets implicated in impaired insulin secretion and/or associated with the DNA microarray a to the complex altered in response to and this to study the impact of PDX1 on β-cell by gene of islets with a expressing a dominant negative of PDX1 to control islets. identified genes and that a than or in expression levels with Most interesting, expression of the mitochondrially encoded nd1 gene, a subunit of the respiratory complex I, NADH was decreased by through a there was expression of succinate dehydrogenase and ATP synthase and as well as genes in the total cellular ATP as well as a in ATP these the nuclear-encoded transcription factor TFAM, mitochondrial gene expression, was down-regulated by DN79PDX1. study a of PDX1 in mitochondrial metabolism through regulation of mitochondrial and were islets were by and in with and H. H. J. Clin. Investig. 1999; 104: Scholar). and the of PDX1 was by H. H. Maechler P. Ritz-Laser B. Hagenfeldt K.A. Ishihara H. Philippe J. J. Biol. Chem. 2001; Scholar). The the rat insulin and of was as S. M. Y. S. Y. K. C. S. A. 1996; Scholar). the was used as a control H. H. J. Clin. Investig. 1999; 104: Scholar). islets were with of and and for for and in for an and were or islets to the of E. P. Muller M. J. Scholar). A to the of the rat insulin was by in the the of DNA I in the of and the DNA were performed as V.M. Zaiko M. Mamin A. Ritz-Laser B. Philippe J. Mol. Endocrinol. 2002; Scholar). and were on a and to a The was with and in for and in the of a by H. a A to was for and were by by to for than and ATP were in 2 and for in the with insulin secretion islets was a of in the insulin was was detected by rat insulin as and an rat insulin insulin was as of total cellular insulin cellular ATP was of in glucose a to the in cytosolic ATP levels in response to glucose or IBMX, glucose were the adenoviral construct encoding the H. Maechler P. A. Nat. Biol. 2003; Scholar). were for in the of glucose and in ATP were a as by A. S. B. Maechler P. Scholar). glucose was the by 1998; Scholar). in was a and results were as of was or islets the of in of single and to caused by biological islets were for total one A total of and were and used to of was into a with a a to the were the transcript and with the of and was and to by an and rat and these only whereas the or However, is important to that this of the pancreas were on a and were The and or for of the in and control with a in both and islets were used for that were in control or islets were detected these To identify transcripts, were with of the of was compared with of the of in of of This is on the the of results by as well as the of of identified in gene expression E. W.M. R. 2002; Scholar, W.M. R. E. S. J. 2002; Scholar). for the in the a were to be This was used to the of A in of of were or was to identify potential genes were and into the was the and was into as B. M. R. 1999; Scholar). were the be was performed an and were the were performed in for and were to the of the mRNA as the of the was by and molecular on islets mice a gene have been by (13Johnson J.D. Ahmed N.T. Luciani D.S. Han Z. Tran H. Fujita J. Misler S. Edlund H. Polonsky K.S. J. Clin. Investig. 2003; 111: 1147-1160Google Scholar). rat islets with a adenoviral construct encoding a dominant negative of PDX1 the but an was to its dominant negative function by with PDX1 for to the in the rat insulin gene H. Maechler P. Ritz-Laser B. Hagenfeldt K.A. Ishihara H. Philippe J. J. Biol. Chem. 2001; Scholar). To of the adenoviral the was with and of or and mRNA levels for insulin as well a were by PDX1 target gene were decreased in levels of found in control H. Maechler P. Ritz-Laser B. Hagenfeldt K.A. Ishihara H. Philippe J. J. Biol. Chem. 2001; Scholar). The capacity of and comprising of to direct expression in β-cells was by analysis islets. PDX1 a of in islets with but with the control This was to that in the expressing the in a construct H. Maechler P. Ritz-Laser B. Hagenfeldt K.A. Ishihara H. Philippe J. J. Biol. Chem. 2001; Scholar). Most interesting, PDX1 was only detected by of To the of to with its were performed a rat insulin gene in the of the A single complex was detected with islets with but with A complex was also detected in with two to PDX1 and H. Maechler P. Hagenfeldt K.A. J. 1998; Scholar). The of with the was confirmed by the of the complex in the of a PDX1 these results that is and of with a in islets with the adenoviral construct in in the PDX1 gene, associated with or late onset have been to impaired insulin secretion in β-cells M.K. Devon O.N. Lee J.H. Peter A. Schlosser D.A. Tenser M.S. Habener J.F. J. Clin. Investig. 2001; 108: 319-329Google Scholar, M. Shiota M. Nicholson W.E. Gannon M. Knobel S.M. Piston D.W. Wright C.V. Powers A.C. J. Biol. Chem. 2002; 277: 11225-11232Google Scholar). have been in a study (13Johnson J.D. Ahmed N.T. Luciani D.S. Han Z. Tran H. Fujita J. Misler S. Edlund H. Polonsky K.S. J. Clin. Investig. 2003; 111: 1147-1160Google Scholar) that β-cell mass rather than β-cell function in a of To this the impact of dominant negative of PDX1 on insulin to glucose, leucine, and islets with were for and levels of the transduction glucose the the of and the late Diabetologia. 2000; Scholar). were in glucose for to the of the for glucose, as well as a and in insulin secretion in islets and Increasing of in a in both and insulin and inhibition for glucose and leucine, Most interesting, insulin secretion was in islets with of whereas blunted the cellular insulin was altered in or islets that reduced insulin secretion was of decreased Most interesting, the response to glucose in PDX1-deficient islets was restored in the of forskolin and This that the is To coupling, the of glucose by the of in islets expressing DN79PDX1. of was in both control and islets these results the that reduction in PDX1 mitochondrial insulin secretion glucose Furthermore, calcium also be in insulin as by the effect of arginine. of PDX1 in by into the molecular in impaired insulin secretion associated with altered PDX1 expression, performed microarray of rat islets with or with H. Y. R. B. M. T. J. Biol. Chem. 2001; only of were in islets. of expression and islets by more than of 70 genes or whereas 56 were down-regulated by more than A of genes to function with the analysis also in is to mRNA levels were suppressed in islets expressing DN79PDX1. In contrast, the insulin transcript was of genes encoding was altered the that coupling is impaired by PDX1 to the regulation and cellular impact of this of genes that were in islets as compared with control genes on genes or control and and and and and in a of known genes identified by microarray analysis as in islets control type I type and A factor and inhibitor 2 control and subunit response factor implicated in and a of the malate dehydrogenase also dehydrogenase subunit A mitochondrial synthase subunit synthase subunit synthase mitochondrial complex dehydrogenase A or and of DNA of DNA 2 of DNA factor a gene by in a pancreatic a transcription transcription factor direct expression of in the factor A response and for a or a and regulatory in factor in a PDX1 of both the and oxidative the of genes by expression of in islets of with the microarray confirmed that pyruvate cytosolic and mitochondrial malate succinate dehydrogenase as well as ATP synthase were up-regulated by in islets with as compared with control The malate the mitochondrial was also by Most interesting, by a for this mRNA as compared with the result by the microarray analysis a in mRNA levels of the subunit of NADH dehydrogenase I of the was in islets the of the and The associated with expression of that pyruvate is is of the This cellular to result the reduced capacity of complex I of the respiratory to succinate complex and is to for the of ATP be explaining the of ATP synthase in an to ATP To the physiological impact of these total cellular ATP levels in or islets in the of As gene ATP levels were in islets expressing as compared with control islets glucose was of cytosolic ATP levels in the H. Maechler P. A. Nat. Biol. 2003; Scholar). of glucose to islets in a of cytosolic ATP, was the of of the to the In contrast, cytosolic ATP was blunted in islets expressing of ATP levels in glucose as as islets in glucose indicating that ATP was than in control islets. this of the mitochondrial potential and ATP formation, in the inhibition of ATP in both control and islets. ATP by glucose was by the of forskolin and in control islets of Surprisingly, in islets glucose caused a in the of forskolin and of the cytosolic ATP glucose results that the of cAMP glucose to a in cytosolic cAMP and ATP to insulin secretion. used a known inhibitor of the mitochondrial complex I M. 1998; to the effect with on ATP have been to total ATP and glucose and insulin secretion M. D. J. M. J. Biol. Chem. Scholar). cytosolic ATP glucose of the The was to the one by islets with the that complex I is a target of the transcription TFAM by results that the β-cell associated with reduction in PDX1 expression is altered in ATP through of the subunit of complex the nd1 gene is mitochondrially whereas PDX1 gene The common these two exclusive genes the mitochondrial transcription factor TFAM J. H. A. P. M. D.A. Nat. Genet. 1998; Scholar). This factor is nuclear-encoded and to the mitochondrial gene transcription and be a PDX1 TFAM is on the performed on islets for 2 and with or TFAM mRNA levels were suppressed by and in 2 and as compared with control islets indicating that the transcription factor is a bona fide PDX1 target In the reduced respiratory caused by mitochondrial gene expression to susceptibility of β-cells to To this the gene expression of and was in islets 2 and a 50% in mRNA levels of the gene in islets with as compared with control islets However, mRNA levels were of control whereas the expression of the anti-apoptotic gene was decreased by results susceptibility of the β-cell to The molecular reduced PDX1 with β-cell dysfunction (12Brissova M. Shiota M. Nicholson W.E. Gannon M. Knobel S.M. Piston D.W. Wright C.V. Powers A.C. J. Biol. Chem. 2002; 277: 11225-11232Google Scholar, J.D. Ahmed N.T. Luciani D.S. Han Z. Tran H. Fujita J. Misler S. Edlund H. Polonsky K.S. J. Clin. Investig. 2003; 111: 1147-1160Google Scholar). a of and molecular have identified the as a target of PDX1 that of PDX1 through adenoviral expression of a dominant negative form of the transcription factor alters the of mitochondrial important in the coupling of glucose metabolism to insulin secretion. the of the is by results that forskolin and the effect of glucose on insulin secretion through of Most interesting, forskolin and in the of glucose a in cytosolic ATP in islets with levels as compared with control islets. This result an in mitochondrial intracellular of mitochondrial oxidative a mechanism was in to a hormone T. G.A. J. 2003; Scholar). of insulin secretion by forskolin and that the is normal in PDX1-deficient islets. that insulin secretion is impaired in PDX1-deficient islets this been to insulin secretion by the and to through P.A. H. B. P. J. 1997; Scholar). to the factor insulin and in response to the of a complex and the both and R. T. 2003; Scholar). were detected by gene in encoding R. T. 2003; of the and or calcium a impaired insulin secretion most results levels of cellular ATP in islets in exocytosis. This is by that insulin secretion is suppressed in rat islets with an inhibitor of the respiratory complex I caused a in total cellular ATP levels M. D. J. M. J. Biol. Chem. Scholar). with in islets PDX1 heterozygous mice (12Brissova M. Shiota M. Nicholson W.E. Gannon M. Knobel S.M. Piston D.W. Wright C.V. Powers A.C. J. Biol. Chem. 2002; 277: 11225-11232Google in insulin mRNA levels and were in β-cells expressing (12Brissova M. Shiota M. Nicholson W.E. Gannon M. Knobel S.M. Piston D.W. Wright C.V. Powers A.C. J. Biol. Chem. 2002; 277: 11225-11232Google Scholar, J.D. Ahmed N.T. Luciani D.S. Han Z. Tran H. Fujita J. Misler S. Edlund H. Polonsky K.S. J. Clin. Investig. 2003; 111: 1147-1160Google Scholar, J. L. K. Edlund H. 1998; Scholar). However, and of PDX1 by in vivo or expression of in reduced insulin levels H. Vanselow J. Hessabi B. Walther R. J. Mol. Med. 2001; 79: 321-328Google Scholar, 16Wang H. Maechler P. Ritz-Laser B. Hagenfeldt K.A. Ishihara H. Philippe J. J. Biol. Chem. 2001; Scholar). factors for reduction in PDX1 function, whereas severe insulin gene of that to in the mitochondrial and most of the ATP for survival. In the pancreatic ATP and mitochondrial factors also the coupling of glucose metabolism to insulin secretion Diabetologia. 2000; Scholar). found that expression of the nd1 gene, a subunit of the complex I, was reduced by in islets as compared with control I, also known as NADH dehydrogenase or is of the of NADH to Scholar). encoded by the mitochondrial and for S. S. K. V. 2003; Scholar). Mutations in these have been associated with a of most A. D.C. Scholar). mutations in the nd1 gene have also been associated with type 2 diabetes M. S. M. Y. L. A. M. K. S. Y. H. T. 1996; Scholar, A. A. K. H. M. C. H. Scholar, M. H. J. Med. Genet. 1999; Scholar, Y. K. T. T. M. T. Y. M. 2003; Scholar). PDX1-deficient islets a reduction in total cellular ATP and the in cytosolic ATP was an effect that was by with these a M. D. J. M. J. Biol. Chem. Scholar) that another inhibitor of complex I, insulin exocytosis. Most interesting, mitochondrial respiratory coupling been to H. L. Y. P. J. Biol. Chem. 2003; Scholar, D.A. 2003; Scholar). The in was up-regulated by in the the cellular to complex I coupling in the that reduced expression ATP and to in response to such as and results that in parallel there is a cellular to ATP, by the succinate dehydrogenase and ATP synthase mRNA Furthermore, the transcript levels for pyruvate mitochondrial malate and also be a of the reduced complex I of the is for the of ATP and coupling factors in the β-cell D. H. P. Jensen S. S. A. 2002; Scholar, S. V. B. M. Diabetes. 2000; 49: Scholar, Jetton T.L. J. Biol. Chem. 2002; 277: Scholar). be that this leads to of pyruvate to malate is to the the up-regulated The result be reduced and NADH formation, a reported by (12Brissova M. Shiota M. Nicholson W.E. Gannon M. Knobel S.M. Piston D.W. Wright C.V. Powers A.C. J. Biol. Chem. 2002; 277: 11225-11232Google Scholar) in islets PDX1 heterozygous the increases in the respiratory complex I and increases in the of the cytosolic ATP is by glucose an for the insulin secretion Most interesting, these in the of in glucose indicating a that with this pyruvate dehydrogenase in rat islets in of a in pyruvate carboxylase Jetton T.L. J. Biol. Chem. 2002; 277: Scholar). The that a subunit of the mitochondrially encoded NADH dehydrogenase is by of a transcription factor to that PDX1 expression of the mitochondrial transcription factor This was confirmed by a 50% reduction in TFAM mRNA TFAM with the of the mitochondrial two transcription as well as regulatory and the transcription of mitochondrial genes J. H. A. P. M. D.A. Nat. Genet. 1998; Scholar, 1999; Scholar). The central function of TFAM that genes also be in the of gene with and that of as well as encoding genes were also down-regulated by in islets. is that β-cell-specific inactivation of TFAM impaired insulin secretion by β-cell loss M. C. A. Magnuson M.A. Nat. Genet. 2000; Scholar). for the or rat TFAM PDX1 with the of the study clearly that the associated with impaired insulin secretion in β-cells with reduced PDX1 expression is to mitochondrial dysfunction in with on PDX1-deficient mice (12Brissova M. Shiota M. Nicholson W.E. Gannon M. Knobel S.M. Piston D.W. Wright C.V. Powers A.C. J. Biol. Chem. 2002; 277: 11225-11232Google Scholar). reduction in ATP only insulin secretion but also as in the TFAM null mice M. C. A. Magnuson M.A. Nat. Genet. 2000; Scholar). This is by decreased expression of the anti-apoptotic gene in islets with expression of genes such as and as well as the is of in the of insulin secretion, with β-cell apoptosis, as reported for another of PDX1 heterozygous mice (13Johnson J.D. Ahmed N.T. Luciani D.S. Han Z. Tran H. Fujita J. Misler S. Edlund H. Polonsky K.S. J. Clin. Investig. 2003; 111: 1147-1160Google Scholar). In conclusion, the that of PDX1 severe on β-cell The in that impaired mitochondrial function in as well as late onset type 2 diabetes to both insulin secretion and in β-cell mass. for in microarray