Molecular mechanisms of nutrient mediated regulation of hypoxia inducible factor -1a(HIF-1a) in endothelial cells.
Hector, Emma E.
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Poorly controlled diabetes mellitus is associated with the development of chronic vascular complications which cause morbidity and premature mortality. Many studies have highlighted maintenance of normal blood glucose levels in all people with diabetes as the most effective way in which chronic complications can be reduced and prevented . Presently, the underlying mechanisms associated with the manifestation and progression of vascular complications are poorly defined. Therefore, this study considered how the increased oxidative demand placed upon cells by high glucose concentration would result in a state of pseudo hypoxia, and potentially the expression of hypoxia inducible factor-a (HIF-1a). In an animal model of diabetes, HIF-1a protein expression was seen to increase in the vasculature surrounding the sciatic nerve at 10 and 24 weeks diabetes duration, which was seen to be reversed at 24 weeks in response to treatment with the antioxidant a-lipoic acid. In vitro, exposure of HUVEC to 20mM glucose for 24h induced perinuclear expression of HIF-1a protein, as opposed to nuclear expression evident under hypoxic conditions. Furthermore, at 24h in 20mM glucose, HIF-1a mRNA level detected was significantly higher than that seen in all other conditions (p<O.OOI). The increase in HIF-1a mRNA detected was seen to be dependent upon mRNA stability, and potentially its association with RNA-binding proteins and/or the natural antisense, aHIF. Pi3K and to a lesser extent p42/44 MAPK signalling pathways were also implicated, and a-lipoic acid treatment reversed the stability of HIF-1a mRNA. The effect of high glucose on HIF-1a mRNA level was not seen in response to partially/non-metabolisable glucose analogues, indicating glucose metabolism to be central to the stabilisation of HIF-1a mRNA. In conclusion, regulation of HIF-1a at the level of mRNA and protein by the metabolism of high concentrations of glucose, may contribute to the generation of chronic vascular disease associated with diabetes, and should be further explored as a potential mechanism by which such complications may be prevented.