Human obesity and type 2 diabetes are associated with alterations in SREBP1 isoform expression that are reproduced ex vivo by tumor necrosis factor-alpha.
Sterol regulatory element binding protein (SREBP)-1 is a transcription factor with important roles in the control of fatty acid metabolism and adipogenesis. Little information is available regarding the expression of this molecule in human health or disease. Exposure of isolated human adipocytes to insulin enhanced SREBP1 gene expression and promoted its proteolytic cleavage to the active form. Furthermore, 3 h of in vivo hyperinsulinemia also significantly increased SREBP1 gene expression in human skeletal muscle. Transcript levels of SREBP1c, the most abundant isoform in adipose tissue, were significantly decreased in the subcutaneous adipose tissue of obese normoglycemic and type 2 diabetic subjects compared with that of nonobese normoglycemic control subjects. In skeletal muscle, SREBP1 expression was significantly reduced in type 2 diabetic subjects but not in obese subjects. Within the diabetic group, the extent of SREBP1 suppression was inversely related to metabolic control and was normalized by 3 h of in vivo hyperinsulinemia. Exposure of isolated human adipocytes to tumor necrosis factor-alpha (TNF-alpha) produced a marked and specific decrease in the mRNA encoding the SREBP1c isoform and completely blocked the insulin-induced cleavage of SREBP1 protein. Thus, both the expression and proteolytic maturation of human SREBP1 are positively modulated by insulin. The specific reduction in the SREBP1c isoform seen in the adipose tissue of obese and type 2 diabetic subjects can be recapitulated ex vivo by TNF-alpha, suggesting a possible mechanism for this association.
Sewter
Ciaran
C
Department of Clinical Biochemistry and Medicine, University of Cambridge, Addenbrooke's Hospital, Cambridge, UK.
Berger
Dirk
D
Considine
Robert V
RV
Medina
Gema
G
Rochford
Justin
J
Ciaraldi
Theodore
T
Henry
Robert
R
Dohm
Lynis
L
Flier
Jeffrey S
JS
O'Rahilly
Stephen
S
Vidal-Puig
Antonio J
AJ
D017667:Adipocytes / Q000378:metabolism*; D000328:Adult; D022762:CCAAT-Enhancer-Binding Proteins / Q000235:genetics*; D004268:DNA-Binding Proteins / Q000235:genetics*; D003920:Diabetes Mellitus / Q000235:genetics*; D003924:Diabetes Mellitus, Type 2 / Q000235:genetics*; D005260:Female; D005786:Gene Expression Regulation / Q000187:drug effects*; D006801:Humans; D008297:Male; D009765:Obesity / Q000235:genetics*; D009767:Obesity, Morbid / Q000235:genetics; D020033:Protein Isoforms / Q000235:genetics; D012333:RNA, Messenger / Q000235:genetics; D012016:Reference Values; D051780:Sterol Regulatory Element Binding Protein 1; D014157:Transcription Factors; D014158:Transcription, Genetic; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology*
D022762:CCAAT-Enhancer-Binding Proteins; D004268:DNA-Binding Proteins; D020033:Protein Isoforms; D012333:RNA, Messenger; C497387:SREBF1 protein, human; D051780:Sterol Regulatory Element Binding Protein 1; D014157:Transcription Factors; D014409:Tumor Necrosis Factor-alpha