Actin and annexins I and II are among the main endothelial plasmalemma-associated proteins forming early glucose adducts in experimental diabetes.

An immunochemical and biochemical study was performed to reveal which of the endothelial plasma membrane proteins become glycated during the early phases of diabetes. The blood front of the lung microvascular endothelial plasmalemma was purified by the cationic colloidal silica method from normal and diabetic (streptozotocin-induced) rats and comparatively analyzed by two-dimensional electrophoresis. No major qualitative differences in the general spectrum of endothelial plasmalemmal proteins were recorded between normoglycemic and hyperglycemic animals. By probing with anti-glucitollysine antibodies, we found that at 1 month after the onset of diabetes, several endothelial membrane polypeptides contained glucose covalently linked to their lysyl residues. Ten days of insulin treatment restored euglycemia in the diabetic animals and completely abolished the membrane nonenzymatic glycosylation. All the glycated polypeptides of the endothelial plasma membrane belong to the peripheral type and are associated with its cytoplasmic face (cell cortex). They were solubilized by buffers of high pH and were not detected in the lung cytosolic fraction (100,000 g). By microsequencing, the major proteins labeled by the anti-glucitollysine have been identified as being actin, annexin I, annexin II, the p34 subunit of the Arp2/3 complex, and the Ras suppressor protein-1. Conversely, the intrinsic endothelial membrane proteins do not seem to be affected by hyperglycemia. This defines the internal face of the endothelial plasma membrane, particularly the cortical cytoskeleton, as a preferential target for nonenzymatic glycosylation in diabetes, with possible consequences on the fluidity of the endothelial plasmalemma and impairment of the endothelial mechanotransducing ability.