title: Activation of Akt by advanced glycation end products (AGEs): involvement of IGF-1 receptor and caveolin-1.
abstract: Diabetes is characterized by chronic hyperglycemia, which in turn facilitates the formation of advanced glycation end products (AGEs). AGEs activate signaling proteins such as Src, Akt and ERK1/2. However, the mechanisms by which AGEs activate these kinases remain unclear. We examined the effect of AGEs on Akt activation in 3T3-L1 preadipocytes. Addition of AGEs to 3T3-L1 cells activated Akt in a dose- and time-dependent manner. The AGEs-stimulated Akt activation was blocked by a PI3-kinase inhibitor LY 294002, Src inhibitor PP2, an antioxidant NAC, superoxide scavenger Tiron, or nicotinamide adenine dinucleotide phosphate (NAD(P)H) oxidase inhibitor DPI, suggesting the involvement of Src and NAD(P)H oxidase in the activation of PI3-kinase-Akt pathway by AGEs. AGEs-stimulated Src tyrosine phosphorylation was inhibited by NAC, suggesting that Src is downstream of NAD(P)H oxidase. The AGEs-stimulated Akt activity was sensitive to Insulin-like growth factor 1 receptor (IGF-1R) kinase inhibitor AG1024. Furthermore, AGEs induced phosphorylation of IGF-1 receptorβsubunit (IGF-1Rβ) on Tyr1135/1136, which was sensitive to PP2, indicating that AGEs stimulate Akt activity by transactivating IGF-1 receptor. In addition, the AGEs-stimulated Akt activation was attenuated by β-methylcyclodextrin that abolishes the structure of caveolae, and by lowering caveolin-1 (Cav-1) levels with siRNAs. Furthermore, addition of AGEs enhanced the interaction of phospho-Cav-1 with IGF-1Rβ and transfection of 3T3-L1 cells with Cav-1 Y14F mutants inhibited the activation of Akt by AGEs. These results suggest that AGEs activate NAD(P)H oxidase and Src which in turn phosphorylates IGF-1 receptor and Cav-1 leading to activation of IGF-1 receptor and the downstream Akt in 3T3-L1 cells. AGEs treatment promoted the differentiation of 3T3-L1 preadipocytes and addition of AG1024, LY 294002 or Akt inhibitor attenuated the promoting effect of AGEs on adipogenesis, suggesting that IGF-1 receptor, PI3-Kinase and Akt are involved in the facilitation of adipogenesis by AGEs.
authors.affiliation: Department and Institute of Pharmacology, School of Medicine, National Yang-Ming University, Taipei, Taiwan, Republic of China.
authors.forename: Su-Jung
authors.initials: SJ
authors.lastname: Yang
authors.forename: Chen-Yu
authors.initials: CY
authors.lastname: Chen
authors.forename: Geen-Dong
authors.initials: GD
authors.lastname: Chang
authors.forename: Hui-Chin
authors.initials: HC
authors.lastname: Wen
authors.forename: Ching-Yu
authors.initials: CY
authors.lastname: Chen
authors.forename: Shi-Chuan
authors.initials: SC
authors.lastname: Chang
authors.forename: Jyh-Fei
authors.initials: JF
authors.lastname: Liao
authors.forename: Chung-Ho
authors.initials: CH
authors.lastname: Chang
mesh_terms: D016475:3T3 Cells; D017667:Adipocytes / Q000166:cytology; D000818:Animals; D000975:Antioxidants / Q000378:metabolism; D051242:Caveolin 1 / Q000378:metabolism*; D002867:Chromones / Q000494:pharmacology; D004789:Enzyme Activation; D017127:Glycation End Products, Advanced / Q000378:metabolism*; D005993:Glycerolphosphate Dehydrogenase / Q000378:metabolism; D051379:Mice; D009025:Morpholines / Q000494:pharmacology; D019255:NADPH Oxidases / Q000378:metabolism; D010766:Phosphorylation; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism*; D034741:RNA, Small Interfering / Q000378:metabolism; D017526:Receptor, IGF Type 1 / Q000378:metabolism*; D015398:Signal Transduction; D015533:Transcriptional Activation; D020032:Tyrphostins / Q000494:pharmacology; D019061:src-Family Kinases / Q000037:antagonists & inhibitors
chemical_list: D000975:Antioxidants; D051242:Caveolin 1; D002867:Chromones; D017127:Glycation End Products, Advanced; D009025:Morpholines; D034741:RNA, Small Interfering; D020032:Tyrphostins; C447031:tyrphostin AG 1024; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one; D005993:Glycerolphosphate Dehydrogenase; D019255:NADPH Oxidases; D017526:Receptor, IGF Type 1; D019061:src-Family Kinases; D051057:Proto-Oncogene Proteins c-akt