Decreased levels of metabolic enzymes in pancreatic islets of patients with type 2 diabetes.
OBJECTIVE
Glucose-stimulated insulin secretion is defective in patients with type 2 diabetes. We sought to acquire new information about enzymes of glucose metabolism, with an emphasis on mitochondrial enzymes, by comparing pancreatic islets of type 2 diabetes patients with those of non-diabetic controls.


METHODS
Expression of genes encoding 13 metabolic enzymes was estimated with microarrays and activities of up to nine metabolic enzymes were measured.


RESULTS
The activities of the mitochondrial enzymes, glycerol phosphate dehydrogenase, pyruvate carboxylase (PC) and succinyl-CoA:3-ketoacid-CoA transferase (SCOT) were decreased by 73%, 65% and 92%, respectively, in the diabetic compared with the non-diabetic islets. ATP citrate lyase, a cytosolic enzyme of the mitochondrial citrate pyruvate shuttle, was decreased 57%. Activities of propionyl-CoA carboxylase, NADP-isocitrate dehydrogenase, cytosolic malic enzyme, aspartate aminotransferase and malate dehydrogenase were not significantly different from those of the control. The low activities of PC and SCOT were confirmed with western blots, which showed that their protein levels were low. The correlation of relative mRNA signals with enzyme activities was good in four instances, moderate in four instances and poor in one instance. In diabetic islets, the mRNA signal of the islet cell-enriched transcription factor musculoaponeurotic fibrosarcoma oncogene homologue A, which regulates expression of islet genes, including the PC gene, was decreased to 54% of the control level. PC activity and protein levels in the non-diabetic islets were significantly lower than in islets from non-diabetic rodents.


CONCLUSIONS
Low levels of certain islet metabolic enzymes, especially mitochondrial enzymes, are associated with human type 2 diabetes.
MacDonald
M J
MJ
Children's Diabetes Center, University of Wisconsin School of Medicine and Public Health, Madison, WI 53706, USA. mjmacdon@wisc.edu
Longacre
M J
MJ
Langberg
E-C
EC
Tibell
A
A
Kendrick
M A
MA
Fukao
T
T
Ostenson
C-G
CG
D001275:ATP Citrate (pro-S)-Lyase / Q000235:genetics / Q000378:metabolism; D000328:Adult; D000368:Aged; D001219:Aspartate Aminotransferases / Q000235:genetics / Q000378:metabolism; D015153:Blotting, Western; D015256:Coenzyme A-Transferases / Q000235:genetics / Q000378:metabolism; D003924:Diabetes Mellitus, Type 2 / Q000201:enzymology*; D005260:Female; D005993:Glycerolphosphate Dehydrogenase / Q000235:genetics / Q000378:metabolism; D006801:Humans; D007521:Isocitrate Dehydrogenase / Q000235:genetics / Q000378:metabolism; D008291:Malate Dehydrogenase / Q000235:genetics / Q000378:metabolism; D008297:Male; D043586:Methylmalonyl-CoA Decarboxylase / Q000235:genetics / Q000378:metabolism; D008875:Middle Aged; D016133:Polymerase Chain Reaction; D011766:Pyruvate Carboxylase / Q000235:genetics / Q000378:metabolism
D005993:Glycerolphosphate Dehydrogenase; D008291:Malate Dehydrogenase; D007521:Isocitrate Dehydrogenase; C039355:isocitrate dehydrogenase (NADP+); D001275:ATP Citrate (pro-S)-Lyase; D001219:Aspartate Aminotransferases; D015256:Coenzyme A-Transferases; C021460:3-ketoacid CoA-transferase; D011766:Pyruvate Carboxylase; D043586:Methylmalonyl-CoA Decarboxylase