title: Complementary roles of IRS-1 and IRS-2 in the hepatic regulation of metabolism.
abstract: Hepatic insulin resistance is a critical component in the development of type 2 diabetes mellitus. In many cases, insulin resistance in liver is associated with reduced expression of both major insulin receptor substrate (IRS) proteins, IRS-1 and IRS-2. To investigate the specific functions of IRS-1 and IRS-2 in regulating liver function in vivo, we developed an adenovirus-mediated RNA interference technique in which short hairpin RNAs (shRNAs) are used to knock down IRS-1, IRS-2, or both, by 70-80% in livers of WT mice. The knockdown of IRS-1 resulted in an upregulation of the gluconeogenic enzymes glucose-6 phosphatase and phosphoenolpyruvate carboxykinase, as well as a marked increase in hepatic nuclear factor-4 alpha. Decreased IRS-1 was also associated with a decrease in glucokinase expression and a trend toward increased blood glucose, whereas knockdown of IRS-2 resulted in the upregulation of lipogenic enzymes SREBP-1c and fatty acid synthase, as well as increased hepatic lipid accumulation. The concomitant injection of IRS-1 and IRS-2 adenoviral shRNAs resulted in systemic insulin resistance, glucose intolerance, and hepatic steatosis. The alterations in the dual-knockdown mice were associated with defective Akt activation and Foxo1 phosphorylation. Taken together, our results demonstrate that hepatic IRS-1 and IRS-2 have complementary roles in the control of hepatic metabolism, with IRS-1 more closely linked to glucose homeostasis and IRS-2 more closely linked to lipid metabolism.
authors.affiliation: Research Division, Joslin Diabetes Center, Harvard Medical School, Boston, Massachusetts, USA.
authors.forename: Cullen M
authors.initials: CM
authors.lastname: Taniguchi
authors.forename: Kohjiro
authors.initials: K
authors.lastname: Ueki
authors.forename: Ronald
authors.initials: R
authors.lastname: Kahn
mesh_terms: D000256:Adenoviridae / Q000235:genetics / Q000378:metabolism; D017667:Adipocytes / Q000378:metabolism; D000818:Animals; D004789:Enzyme Activation; D005227:Fatty Acids / Q000378:metabolism; D005786:Gene Expression Regulation; D005943:Gluconeogenesis / Q000235:genetics / Q000502:physiology; D005947:Glucose / Q000378:metabolism; D006706:Homeostasis; D007328:Insulin / Q000378:metabolism; D055504:Insulin Receptor Substrate Proteins; D047908:Intracellular Signaling Peptides and Proteins; D020738:Leptin / Q000378:metabolism; D008099:Liver / Q000166:cytology / Q000378:metabolism* / Q000473:pathology / Q000502:physiology; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010750:Phosphoproteins / Q000235:genetics / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt; D034622:RNA Interference; D034741:RNA, Small Interfering / Q000737:chemistry / Q000235:genetics / Q000378:metabolism
chemical_list: D005227:Fatty Acids; D005947:Glucose; D007328:Insulin; D055504:Insulin Receptor Substrate Proteins; D047908:Intracellular Signaling Peptides and Proteins; D020738:Leptin; D019869:Phosphatidylinositol 3-Kinases; D010750:Phosphoproteins; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D034741:RNA, Small Interfering; C526295:Irs1 protein, mouse; C526298:Irs2 protein, mouse