Absence of sterol regulatory element-binding protein-1 (SREBP-1) ameliorates fatty livers but not obesity or insulin resistance in Lep(ob)/Lep(ob) mice.
Obesity is a common nutritional problem often associated with diabetes, insulin resistance, and fatty liver (excess fat deposition in liver). Leptin-deficient Lep(ob)/Lep(ob) mice develop obesity and those obesity-related syndromes. Increased lipogenesis in both liver and adipose tissue of these mice has been suggested. We have previously shown that the transcription factor sterol regulatory element-binding protein-1 (SREBP-1) plays a crucial role in the regulation of lipogenesis in vivo. To explore the possible involvement of SREBP-1 in the pathogenesis of obesity and its related syndromes, we generated mice deficient in both leptin and SREBP-1. In doubly mutant Lep(ob/ob) x Srebp-1(-/-) mice, fatty livers were markedly attenuated, but obesity and insulin resistance remained persistent. The mRNA levels of lipogenic enzymes such as fatty acid synthase were proportional to triglyceride accumulation in liver. In contrast, the mRNA abundance of SREBP-1 and lipogenic enzymes in the adipose tissue of Lep(ob)/Lep(ob) mice was profoundly decreased despite sustained fat, which could explain why the SREBP-1 disruption had little effect on obesity. In conclusion, SREBP-1 regulation of lipogenesis is highly involved in the development of fatty livers but does not seem to be a determinant of obesity in Lep(ob)/Lep(ob) mice.
Yahagi
Naoya
N
Department of Internal Medicine, University of Tokyo Graduate School of Medicine, Tokyo 113-8655, Japan.
Shimano
Hitoshi
H
Hasty
Alyssa H
AH
Matsuzaka
Takashi
T
Ide
Tomohiro
T
Yoshikawa
Tomohiro
T
Amemiya-Kudo
Michiyo
M
Tomita
Sachiko
S
Okazaki
Hiroaki
H
Tamura
Yoshiaki
Y
Iizuka
Yoko
Y
Ohashi
Ken
K
Osuga
Jun-Ichi
J
Harada
Kenji
K
Gotoda
Takanari
T
Nagai
Ryozo
R
Ishibashi
Shun
S
Yamada
Nobuhiro
N
D000273:Adipose Tissue / Q000378:metabolism; D000818:Animals; D015152:Blotting, Northern; D022762:CCAAT-Enhancer-Binding Proteins / Q000235:genetics* / Q000502:physiology*; D003433:Crosses, Genetic; D004268:DNA-Binding Proteins / Q000235:genetics* / Q000502:physiology*; D005234:Fatty Liver / Q000628:therapy*; D005838:Genotype; D007333:Insulin Resistance / Q000235:genetics*; D020738:Leptin / Q000096:biosynthesis; D050356:Lipid Metabolism; D008071:Lipoprotein Lipase / Q000096:biosynthesis; D008099:Liver / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D009765:Obesity / Q000235:genetics*; D010641:Phenotype; D012333:RNA, Messenger / Q000378:metabolism; D051780:Sterol Regulatory Element Binding Protein 1; D014157:Transcription Factors; D014280:Triglycerides / Q000378:metabolism
D022762:CCAAT-Enhancer-Binding Proteins; D004268:DNA-Binding Proteins; D020738:Leptin; D012333:RNA, Messenger; C497388:Srebf1 protein, mouse; D051780:Sterol Regulatory Element Binding Protein 1; D014157:Transcription Factors; D014280:Triglycerides; D008071:Lipoprotein Lipase