GRP78 expression inhibits insulin and ER stress-induced SREBP-1c activation and reduces hepatic steatosis in mice.
Hepatic steatosis is present in insulin-resistant obese rodents and is concomitant with active lipogenesis. Hepatic lipogenesis depends on the insulin-induced activation of the transcription factor SREBP-1c. Despite prevailing insulin resistance, SREBP-1c is activated in the livers of genetically and diet-induced obese rodents. Recent studies have reported the presence of an ER stress response in the livers of obese ob/ob mice. To assess whether ER stress promotes SREBP-1c activation and thus contributes to lipogenesis, we overexpressed the chaperone glucose-regulated protein 78 (GRP78) in the livers of ob/ob mice using an adenoviral vector. GRP78 overexpression reduced ER stress markers and inhibited SREBP-1c cleavage and the expression of SREBP-1c and SREBP-2 target genes. Furthermore, hepatic triglyceride and cholesterol contents were reduced, and insulin sensitivity improved, in GRP78-injected mice. These metabolic improvements were likely mediated by restoration of IRS-2 expression and tyrosine phosphorylation. Interestingly, GRP78 overexpression also inhibited insulin-induced SREBP-1c cleavage in cultured primary hepatocytes. These findings demonstrate that GRP78 inhibits both insulin-dependent and ER stress-dependent SREBP-1c proteolytic cleavage and explain the role of ER stress in hepatic steatosis in obese rodents.
Kammoun
Hélène L
HL
INSERM, UMR-S, Centre de Recherche des Cordeliers, Paris, France.
Chabanon
Hervé
H
Hainault
Isabelle
I
Luquet
Serge
S
Magnan
Christophe
C
Koike
Tatsuro
T
Ferré
Pascal
P
Foufelle
Fabienne
F
D000818:Animals; D051778:Basic Helix-Loop-Helix Leucine Zipper Transcription Factors; D004721:Endoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism*; D000091342:Endoplasmic Reticulum Chaperone BiP; D005234:Fatty Liver / Q000378:metabolism / Q000473:pathology / Q000628:therapy*; D015870:Gene Expression / Q000187:drug effects / Q000235:genetics; D005947:Glucose / Q000378:metabolism; D006360:Heat-Shock Proteins / Q000235:genetics* / Q000378:metabolism; D022781:Hepatocytes / Q000187:drug effects / Q000378:metabolism; D007328:Insulin / Q000494:pharmacology*; D055504:Insulin Receptor Substrate Proteins / Q000378:metabolism; D007333:Insulin Resistance / Q000502:physiology; D050356:Lipid Metabolism / Q000235:genetics; D008099:Liver / Q000378:metabolism; D008297:Male; D051379:Mice; D008820:Mice, Obese; D008954:Models, Biological; D018832:Molecular Chaperones / Q000235:genetics* / Q000378:metabolism; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism; D009765:Obesity / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D011924:Rats, Zucker; D015398:Signal Transduction / Q000235:genetics; D051780:Sterol Regulatory Element Binding Protein 1 / Q000235:genetics / Q000378:metabolism*; D051782:Sterol Regulatory Element Binding Protein 2 / Q000378:metabolism; D019284:Thapsigargin / Q000494:pharmacology; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism
D051778:Basic Helix-Loop-Helix Leucine Zipper Transcription Factors; D000091342:Endoplasmic Reticulum Chaperone BiP; D006360:Heat-Shock Proteins; C000717248:Hspa5 protein, mouse; D007328:Insulin; D055504:Insulin Receptor Substrate Proteins; C506001:Mlxipl protein, mouse; D018832:Molecular Chaperones; D009687:Nuclear Proteins; D051780:Sterol Regulatory Element Binding Protein 1; D051782:Sterol Regulatory Element Binding Protein 2; D014157:Transcription Factors; D019284:Thapsigargin; D005947:Glucose