Cytosolic NADP+-dependent isocitrate dehydrogenase plays a key role in lipid metabolism.
NADPH is an essential cofactor for many enzymatic reactions including glutathione metabolism and fat and cholesterol biosynthesis. We have reported recently an important role for mitochondrial NADP(+)-dependent isocitrate dehydrogenase in cellular defense against oxidative damage by providing NADPH needed for the regeneration of reduced glutathione. However, the role of cytosolic NADP(+)-dependent isocitrate dehydrogenase (IDPc) is still unclear. We report here for the first time that IDPc plays a critical role in fat and cholesterol biosynthesis. During differentiation of 3T3-L1 adipocytes, both IDPc enzyme activity and its protein content were increased in parallel in a time-dependent manner. Increased expression of IDPc by stable transfection of IDPc cDNA positively correlated with adipogenesis of 3T3-L1 cells, whereas decreased IDPc expression by an antisense IDPc vector retarded adipogenesis. Furthermore, transgenic mice with overexpressed IDPc exhibited fatty liver, hyperlipidemia, and obesity. In the epididymal fat pads of the transgenic mice, the expressions of adipocyte-specific genes including peroxisome proliferator-activated receptor gamma were markedly elevated. The hepatic and epididymal fat pad contents of acetyl-CoA and malonyl-CoA in the transgenic mice were significantly lower, whereas the total triglyceride and cholesterol contents were markedly higher in the liver and serum of transgenic mice compared with those measured in wild type mice, suggesting that the consumption rate of those lipogenic precursors needed for fat biosynthesis must be increased by elevated IDPc activity. Taken together, our findings strongly indicate that IDPc would be a major NADPH producer required for fat and cholesterol synthesis.
Koh
Ho-Jin
HJ
Department of Genetic Engineering, Kyungpook National University, Daegu 702-701, Korea.
Lee
Su-Min
SM
Son
Byung-Gap
BG
Lee
Soh-Hyun
SH
Ryoo
Zae Young
ZY
Chang
Kyu-Tae
KT
Park
Jeen-Woo
JW
Park
Dong-Chan
DC
Song
Byoung J
BJ
Veech
Richard L
RL
Song
Hebok
H
Huh
Tae-Lin
TL
D041721:3T3-L1 Cells; D017667:Adipocytes / Q000166:cytology / Q000201:enzymology*; D000818:Animals; D002455:Cell Division / Q000502:physiology; D002784:Cholesterol / Q000096:biosynthesis / Q000378:metabolism*; D003600:Cytosol / Q000201:enzymology; D005234:Fatty Liver / Q000378:metabolism / Q000503:physiopathology; D015971:Gene Expression Regulation, Enzymologic; D006949:Hyperlipidemias / Q000378:metabolism / Q000503:physiopathology*; D007521:Isocitrate Dehydrogenase / Q000235:genetics / Q000378:metabolism*; D050356:Lipid Metabolism; D051379:Mice; D008822:Mice, Transgenic; D009249:NADP / Q000378:metabolism*; D009765:Obesity / Q000378:metabolism / Q000503:physiopathology; D010641:Phenotype; D018160:Receptors, Cytoplasmic and Nuclear / Q000378:metabolism; D014157:Transcription Factors / Q000378:metabolism
D018160:Receptors, Cytoplasmic and Nuclear; D014157:Transcription Factors; D009249:NADP; D002784:Cholesterol; D007521:Isocitrate Dehydrogenase; C039355:isocitrate dehydrogenase (NADP+)