Hyperglycemia Regulates Hypoxia-Inducible Factor-1α Protein Stability and Function

Abstract

Hyperglycemia and hypoxia are suggested to play essential pathophysiological roles in the complications of diabetes, which may result from a defective response of the tissues to low oxygen tension. In this study, we show that in primary dermal fibroblasts and endothelial cells, hyperglycemia interferes with the function of hypoxiainducible factor-1 (HIF-1), a transcription factor that is essential for adaptive responses of the cell to hypoxia. Experiments using proteasomal and prolyl hydroxylases inhibitors indicate that hyperglycemia inhibits hypoxiainduced stabilization of HIF-1␣ protein levels against degradation and suggest that mechanisms in addition to proline hydroxylation may be involved. This effect of hyperglycemia was dose dependent and correlates with a lower transcription activation potency of HIF-1␣, as assessed by transient hypoxia-inducible reporter gene assay. Regulation of HIF-1␣ function by hyperglycemia could be mimicked by mannitol, suggesting hyperosmolarity as one critical parameter. The interference of hyperglycemia with hypoxia-dependent stabilization of HIF-1␣ protein levels was confirmed in vivo, where only very low levels of HIF-1␣ protein could be detected in diabetic wounds, as compared with chronic venous ulcers. In conclusion, our data demonstrate that hyperglycemia impairs hypoxia-dependent protection of HIF-1␣ against proteasomal degradation and suggest a mechanism by which diabetes interferes with cellular responses to hypoxia. Diabetes 53:3226 -3232, 2004 C hronic complications of diabetes are a major health problem, and it has become a priority to characterize further their pathophysiological mechanisms to develop novel, rational therapeutic strategies. Even though prolonged exposure of the tissues to hyperglycemia seems to be the primary causative factor, some other factors may play a role as far as intensive blood glucose control reduces chronic complications but does not prevent them altogether (1,2). It has become increasingly evident that hypoxia plays an important role in all diabetes complications (3). In addition to deficient blood supply as a consequence of micro-and macrovascular disease, it has been postulated that hyperglycemia induces a pseudohypoxia state. This theory is based on the finding that high glucose concentrations induce a high NADH ϩ /NAD ϩ ratio in cells even when the oxygen tension is normal (4).Adaptive responses of cells to hypoxia are mediated by the hypoxia-inducible factor-1 (HIF-1), which is a heterodimeric transcription factor composed of two subunits, HIF-1␣ and aryl hydrocarbon receptor nuclear translocator (ARNT), both constitutively expressed in mammalian cells. Regulation of HIF-1 activity is critically dependent on the degradation of the HIF-1␣ subunit in normoxia. The molecular basis of its degradation is the O 2 -dependent hydroxylation of at least one of the two proline residues (5,6) in the oxygen-dependent degradation domain of HIF-1␣ by specific prolyl 4-hydroxylases (PHDs) (7-9). In this form, HIF-1 ␣ binds to the von Hippel-Lind...

Diabetes impairs progenitor cell mobilisation after hindlimb ischaemia–reperfusion injury in rats

“…Enhanced production of reactive oxygen species simulates a hyperoxic state and may lead to HIF-1α ubiquitination and degradation after ischaemia in diabetes [26]. Moreover, hyperglycaemia itself has been shown to inhibit hypoxia-induced stabilisation of HIF-1α protein against degradation [27]. Therefore, we suggest that the weak angiogenic response to ischaemia in diabetes depends upon inability to mobilise the progenitor cells necessary for new vessel growth.…”

High glucose attenuates insulin-induced VEGF expression in bovine retinal microvascular endothelial cells

“…In similar studies, 30 mM is used as a high concentration for glucose. 27,28 In this study, we also used 30 mM as the highest concentration. Further, we found that, similar to high glucose, the PI3-K inhibitor also inhibited insulininduced VEGF expression, but inhibitors of PKC or P42/ p44 MAPK hardly showed any inhibitory effect against the insulin-induced VEGF expression.…”

Timing of Arteriovenous Fistula Placement

“…14 Via this enlightened analysis, the authors demonstrated that patients with PAD exhibited a significantly shallower slope in the bone formation-PTH relationship; this indicates a reduced bone anabolic response at prevailing PTH tone in those individuals with PAD ( Figure 1). Because PTH exerts important bone anabolic actions in part via the inhibition of osteoprogenitor apoptosis, 15 independent assessment of the PTH-osteoblast surface relationship also revealed a distinctly shallower slope in patients with PAD. 14 These relationships persisted after adjustment for C-reactive protein as an index of inflammation.…”