Glucose-induced Akt1 activation mediates fibronectin synthesis in endothelial cells.
OBJECTIVE
Increased expression and decreased degradation of extracellular matrix (ECM) proteins are key features of chronic diabetic complications. Fibronectin, a predominant ECM protein, has been shown to be overexpressed in all target organs of diabetic complications and in endothelial cells cultured in high levels of glucose. The present study was designed to elucidate the role of protein kinase B (Akt/PKB) in glucose-induced fibronectin mRNA expression and protein production in vascular endothelial cells.


METHODS
Human umbilical vein endothelial cells were cultured in the presence of high glucose to study Akt/PKB activation. The upstream and downstream mediators in the Akt/PKB pathway were also investigated using dominant negative transfections and specific inhibitors of signalling pathways. Cells were subjected to real time RT-PCR, western blotting, and confocal microscopy to assess Akt1/PKBalpha activation and fibronectin mRNA expression and protein production. To detect transcription factor activation, electrophoretic mobility shift assay was carried out.


RESULTS
Our data demonstrate that fibronectin mRNA expression and protein production that are induced by high glucose are mediated via activation of Akt/PKB, which is modulated by mitogen-activated protein kinase, phosphatidylinositol 3-kinase, and protein kinase C. Glucose-induced fibronectin mRNA expression and protein production are also mediated by Akt1/PKBalpha-dependent activation of the transcription factors nuclear factor-kappaB and activating protein-1.


CONCLUSIONS
Our study provides insight into the mechanical basis of glucose-induced increases in fibronectin mRNA expression and protein production. High levels of glucose may increase fibronectin mRNA expression and protein production by activating Akt/PKB.
Xin
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Department of Pathology, University of Western Ontario, London, ON, Canada.
Khan
Z A
ZA
Chen
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Chakrabarti
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D002470:Cell Survival / Q000187:drug effects; D002478:Cells, Cultured; D042783:Endothelial Cells / Q000187:drug effects / Q000378:metabolism; D004730:Endothelium, Vascular / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D004789:Enzyme Activation / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005353:Fibronectins / Q000096:biosynthesis* / Q000187:drug effects / Q000235:genetics; D005947:Glucose / Q000378:metabolism* / Q000494:pharmacology; D006801:Humans; D016328:NF-kappa B / Q000187:drug effects / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt / Q000037:antagonists & inhibitors / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D012333:RNA, Messenger / Q000187:drug effects / Q000378:metabolism; D018808:Transcription Factor AP-1 / Q000187:drug effects / Q000378:metabolism; D015854:Up-Regulation
D004791:Enzyme Inhibitors; D005353:Fibronectins; D016328:NF-kappa B; D012333:RNA, Messenger; D018808:Transcription Factor AP-1; C494918:AKT1 protein, human; D051057:Proto-Oncogene Proteins c-akt; D005947:Glucose