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Electronegative LDL Impairs Vascular Endothelial Cell Integrity in Diabetes by Disrupting Fibroblast Growth Factor 2 (FGF2) Autoregulation

¹ Department of Medicine, Baylor College of Medicine, Houston, Texas
² Department of Cancer Prevention and Lymphoma/Myeloma, University of Texas M. D. Anderson Cancer Center, Houston, Texas
³ Department of Internal Medicine, National Taiwan University Hospital, Taipei, Taiwan
⁴ Department of Biochemistry and Molecular Biology, University of Texas M. D. Anderson Cancer Center, Houston, Texas

Address correspondence and reprint requests to Dr. Chu-Huang Chen, Department of Medicine, Baylor College of Medicine, 6565 Fannin St., MS A-601, Houston, TX 77030. E-mail: cchen{at}bcm.tmc.edu

Key Words: Akt-CA, constitutively active Akt • Akt-DN, dominant-negative Akt • BAEC, bovine aortic endothelial cell • EC, endothelial cell • FGF, fibroblast growth factor • PAF, platelet-activating factor • oxLDL, copper-oxidized LDL • PI3K, phosphatidylinositol 3-kinase • VEGF, vascular endothelial growth factor

OBJECTIVE—L5, a circulating electronegative LDL identified in patients with hypercholesterolemia or type 2 diabetes, induces endothelial cell (EC) apoptosis by suppressing fibroblast growth factor (FGF)2 expression. FGF2 plays a pivotal role in endothelial regeneration and compensatory arteriogenesis. It is likely that vasculopathy and poor collateralization in diabetes is a result of FGF2 dysregulation.

RESEARCH DESIGN AND METHODS—To investigate this mechanism, we isolated L5 from type 2 diabetic patients. In cultured bovine aortic ECs (BAECs), L5 inhibited FGF2 transcription and induced apoptosis. Because FGF2 stimulates the phosphatidylinositol 3-kinase (PI3K)-Akt pathway, we examined whether FGF2 transcription is regulated by Akt through a feedback mechanism.

RESULTS—Diabetic L5 reduced FGF2 release to the medium but enhanced caspase-3 activity, with resultant apoptosis. Inhibition of PI3K with wortmannin or suppression of Akt activation with dominant-negative Akt inhibited FGF2 expression. Transfection of BAECs with FGF2 antisense cDNA depleted endogenous FGF2 protein. In these cells, not only was Akt phosphorylation inhibited, but FGF2 transcription was also critically impaired. In contrast, transfecting BAECs with FGF2 sense cDNA augmented Akt phosphorylation. Treatment with constitutively active Akt enhanced FGF2 expression. Augmentation of either FGF2 transcription or Akt phosphorylation rendered BAECs resistant to L5.

CONCLUSIONS—These findings suggest that FGF2 is the primary initiator of its own expression, which is autoregulated through a novel FGF2-PI3K-Akt loop. Thus, by disrupting FGF2 autoregulation in vascular ECs, L5 may impair reendothelialization and collateralization in diabetes.

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