Electronegative LDL impairs vascular endothelial cell integrity in diabetes by disrupting fibroblast growth factor 2 (FGF2) autoregulation.
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.


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.
Lu
Jonathan
J
Department of Medicine, Baylor College of Medicine, 6565 Fannin St., MS A-601, Houston, TX 77030, USA.
Jiang
Wei
W
Yang
Jun-Hai
JH
Chang
Po-Yuan
PY
Walterscheid
Jeffrey P
JP
Chen
Hsin-Hung
HH
Marcelli
Marco
M
Tang
Daming
D
Lee
Yuan-Teh
YT
Liao
Warren S L
WS
Yang
Chao-Yuh
CY
Chen
Chu-Huang
CH
D000818:Animals; D001011:Aorta; D017209:Apoptosis / Q000187:drug effects*; D002417:Cattle; D003924:Diabetes Mellitus, Type 2 / Q000473:pathology / Q000503:physiopathology*; D004730:Endothelium, Vascular / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D016222:Fibroblast Growth Factor 2 / Q000494:pharmacology*; D015870:Gene Expression / Q000187:drug effects; D006706:Homeostasis; D006801:Humans; D008077:Lipoproteins, LDL / Q000097:blood* / Q000302:isolation & purification / Q000494:pharmacology; D012016:Reference Values; D042461:Vascular Endothelial Growth Factor A / Q000494:pharmacology
D008077:Lipoproteins, LDL; D042461:Vascular Endothelial Growth Factor A; C099252:oxidized low density lipoprotein; D016222:Fibroblast Growth Factor 2