OBJECTIVE
Vascular smooth muscle cell (VSMC) dysfunction plays a role in diabetic macrovasculopathy. This dysfunction may be caused or exacerbated by expression of many of genes potently activated by the transcriptional factor nuclear factor kappaB (NF-kappaB). We have examined whether culture of VSMCs under high glucose conditions to stimulate the diabetic state can lead to the activation of NF-kappaB.
METHODS
NF-kappaB activation was assessed in VSMCs stably transfected with a cis-reporter plasmid containing the NF-kappaB binding sites.
RESULTS
Within 3-h incubation, high glucose (27.5 or 55 mmol/l) alone induced an increase in NF-kappaB activity in VSMCs; this increase was mimicked by mannitol given to deliver the same osmolar stress to the cells. High glucose or mannitol also enhanced TNFalpha-stimulated NF-kappaB activity. Incubation with high glucose for 48 h followed by stimulation with TNFalpha led to a marked potentiation of NF-kappaB activation compared with normoglycemic (5.5 mmol/l) VSMCs exposed to TNFalpha, while mannitol attenuated this effect. A 48-h incubation with high glucose substantially reduced glutathione (GSH) levels compared with normoglycemic VSMCs, whereas mannitol significantly increased GSH levels. An antioxidant N-acetyl-L-cysteine and a selective protein kinase C (PKC) inhibitor GF109203X significantly suppressed the TNFalpha-induced NF-kappaB activation, and abrogated potentiation of TNFalpha-induced NF-kappaB activity caused by high glucose (27.5 mmol/l).
CONCLUSION
These results suggest that acutely high glucose causes alterations in osmolarity leading to activation of NF-kappaB, but that exposure to high glucose for more prolonged times causes changes in antioxidant defences and activation of PKC, which potentiates cytokine activation of NF-kappaB. Further definition of these pathways will help to delineate important signals mediating the aberrant behavior of VSMCs under hyperglycemic/diabetic conditions.