Interaction of glycated protein and DFO mimicked hypoxia in cellular responses of HUVECs

Abstract

The accelerated non-enzymatic modification of proteins by Maillard reaction during prolonged hyperglycemia is a key player in the diabetes associated pathology. In addition, hypoxia has been implicated in the recent past as a modulating factor. Therefore we have examined the interaction of glycation modified human serum albumin (AGE-HSA) and deferoxamine (DFO) mimicked hypoxia on the expression of hypoxia inducible factor 1α (HIF-1α), and the role of RAGE (receptor for AGE) signaling in up-regulation of HIF-1α. Expression of VEGF (a downstream target of HIF-1α) and sICAM-1 (inflammatory marker) was also detected. When HUVEC were subjected to hypoxia, highest expression of HIF-1α was observed. When treated with AGE-HSA at two concentrations, higher expression was found vis-a-vis control, with 0.2 mg ml⁻¹ than 2.0 mg ml⁻¹ which was mediated in part by RAGE as determined by RAGE silencing. However, when the cells were exposed to a combination treatment of hypoxia and AGE-HSA, a biphasic effect at the two different concentrations was observed as compared to the individual treatments. VEGF was synergistically up-regulated by hypoxia and AGE-HSA. On the other hand sICAM-1 was up-regulated by AGE-HSA but down-regulated by hypoxia. These results show that AGE-HSA functions as a non-hypoxic factor which modulates the expression of HIF-1α in a concentration dependent manner in the range studied. It can be concluded that glycated serum proteins may activate HIF-1α independently in diabetes. Further, when both glycated proteins and hypoxic conditions are present, they act in opposition in regulation of HIF-1α.