Molecular mechanisms of nutrient mediated regulation of hypoxia inducible factor -1a(HIF-1a) in endothelial cells.

Abstract

Poorly-controlled diabetes mellitus is associated with the development of chronic vascular complications, which cause morbidity and premature mortality. Many studies have highlighted that maintenance of normal blood glucose levels in all people with diabetes is 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-alpha (HIF-1alpha). In an animal model of diabetes, HIF-1alpha protein expression was seen to increase in the vasculature surrounding the sciatic nerve at ten- and twenty-four weeks of diabetes duration, which was seen to be reversed at twenty-four weeks in response to treatment with the antioxidant alpha-lipoic acid. In vitro, exposure of HUVEC to 20mM glucose for twenty-four hours induced perinuclear expression of HIF-1alpha protein, as opposed to nuclear expression evident under hypoxic conditions. Furthermore, at twenty-four hours in 20mM glucose, the detected HIF-1alpha mRNA level was significantly higher than that seen in all other conditions (p < 0.001). The increase in HIF-1alpha 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 alpha-lipoic acid treatment reversed the stability of HIF-1alpha mRNA. The effect of high glucose on HIF-1alpha mRNA level was not seen in response to partially/non-metabolisable glucose analogues, indicating glucose metabolism to be central to the stabilisation of HIF-1alpha mRNA. In conclusion, using the metabolism of high concentrations of glucose to regulate HIF-1alpha at the level of mRNA and protein 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.