Lucian Ghitescu

Correlated Endothelial Caveolin Overexpression and Increased Transcytosis in Experimental Diabetes

We investigated the mechanism by which diabetes renders the capillary endothelium more permeable to macromolecules in the lungs of short-term diabetic rats. We used quantitative immunocytochemistry (ICC) to comparatively assess the permeability of alveolar capillaries to serum albumin in diabetic and normoglycemic animals. The effect of diabetes on the population of endothelial caveolae was evaluated by morphometry and by ICC and immunochemical quantification of the amount of caveolin in the whole cell or associated with the purified endothelial plasma membrane. A net increase in the amount of serum albumin taken up by the plasmalemmal vesicles of alveolar endothelial cells and transported to the interstitium was documented in diabetic animals. Interendothelial junctions were not permeated by albumin molecules. The alveolar endothelial cells of hyperglycemic rats contain more caveolae (1.3-fold), accounting for a larger (1.5-fold) fraction of the endothelial volume than those of normal animals. The hypertrophy of the caveolar compartment is accompanied by overexpression of endothelial caveolin 1. Although the aggregated thickness of the endothelial and alveolar epithelium basement membranes increases in diabetes (1.3-fold), the porosity of this structure appears to be unchanged. Capillary hyperpermeability to plasma macromolecules recorded in the early phase of diabetes is explained by an intensification of transendothelial vesicular transport and not by the destabilization of the interendothelial junctions.

Alterations of the Rat Mesentery Vasculature in Experimental Diabetes

The alteration induced by diabetes on vascular permeability to serum albumin was investigated in the mesentery of streptozotocin-induced hyperglycemic rats. Double-tagged (125I and dinitrophenol-haptenated) heterologous albumin was intravenously administered in normal and hyperglycemic animals, and the extravasation of the tracer was evaluated by radioactivity measurements and by morphometry at the ultrastructural level using quantitative protein A-colloidal gold immunocytochemistry. The results demonstrate that diabetes induces a significant increase in the permeability of the mesentery vessels to albumin. This increase is due to a more efficient transport of macromolecules by endothelial plasmalemmal vesicles and not to leakier interendothelial junctions. Passage across the endothelial basement membranes did not appear to be restricted in either the control or diabetic condition. However, in diabetes, the mesothelial basement membrane appeared to become modified and to restrain the passage of albumin toward the peritoneal cavity. After 3 months of diabetes, the rats presented a net increase in the average diameter of the blood vessels localized in the mesentery arcada (macrovascular hyperplasy) and a notable angiogenesis, manifested at the level of the microvasculature in the mesenteric windows.

Glomerular CD34 Expression in Short- and Long-term Diabetes

Aging and diabetes are associated with exacerbated expression of adhesion molecules. Given their importance in endothelial dysfunction and their possible involvement in the alteration of glomerular permeability occurring in diabetes, we have evaluated expression of the sialomucin-type adhesion molecule CD34 in renal glomerular cells of normal and diabetic animals at two different ages by colloidal gold immunocytochemistry and immunoblotting. CD34 labeling was mostly assigned to the plasma membranes of glomerular endothelium and mesangial processes. Podocyte membranes were also labeled, but to a lesser degree. Short- and long-term diabetes triggers a substantial increase in immunogold labeling for CD34 in renal tissues compared with young normoglycemic animals. However, the level of labeling in old diabetic and healthy control rats is similar, suggesting that the effect of diabetes and aging on CD34 expression is similar but not synergistic. Western blotting of isolated glomerular fractions corroborated immunocytochemical results. Increased expression of CD34 may reflect its involvement in the pathogenesis of glomerular alterations related to age and diabetes. Alterations present in early diabetes, resembling those occurring with age, strengthen the concept that diabetes is an accelerated form of aging.