High-Resolution Ultrastructural Study of the Rat Glomerular Basement Membrane in Long-Term Experimental Diabetes

Abstract

The ultrastructure of the glomerular basement membrane of the long-term diabetic and age-matched control rats was studied with the application of advanced high-resolution microscopy. By using the freeze substitution method for the preparation of the renal tissue, it was possible to observe that the glomerular basement membrane in control and diabetic animals is composed on only a single lamina densa without the presence of a lamina lucida interna or externa. High-resolution electron microscopy of the diabetic glomerular basement membrane showed significant alterations in its morphology and ultrastructure. First, the basement membrane in diabetic condition appeared to be split into two halves, endothelial and epithelial. In the epithelial half of the membrane, the network of distinct strands referred to as cords, which were clearly present in the glomerular basement membrane of age-matched control animals, became less distinct and showed a diffused appearance being evenly replaced by thin filaments. The openings of the network were filled with a granular material. In the endothelial half of the membrane, on the other hand, the cord network was variably lost in diabetic condition and, within the resulting vacant spaces, bundles of fibrils 12 nm in width, identified as basotubules, were deposited. Immunolabeling for type IV collagen was found to be enriched in the endothelial half of the basement membrane being associated with the bundles of basotubules. The ultrastructural changes reported by high-resolution microscopy could be related to the molecular alterations of the basement membrane components and to the loss in permselectivity occurring during diabetes.

Basement membrane abnormalities in human eyes with diabetic retinopathy.

“…A distinct layering observed by electron microscopy in at least some diabetic BMs (gsterby, 1990) suggests that the accumulated components are properly assembled. Diabetic nephropathy brings about a decrease in heparan sulfate proteoglycan and an increase in a BM chondroitin sulfate proteoglycan, Type IV collagen, and advanced glycation endproducts in glomerular capillary BMs (Gugliucci and Bendayan, 1995;Inoue and Bendayan, 1995;Kasinath et al, 1994;McCarthy et al, 1994;Williamson et al, 1988). Similar information on ocular BM changes in diabetes, and especially in DR, is rather scarce.…”

Extracellular Vesicles as Signaling Mediators and Disease Biomarkers across Biological Barriers

“…Trans-renal EV passage is facilitated under pathological conditions. In diabetic nephropathy, for example, the meshwork structure of the glomerular basement membrane is loosened, which results in the formation of pores and tunnels with diameters up to 10-80 nm or even larger [256]. These pores allow the passage of EVs released from glomerular endothelial cells, which thus reach the podocytes.…”

Alterations in the expression of the a 3 b 1 integrin in certain membrane domains of the glomerular epithelial cells (podocytes) in diabetes mellitus

“…Indeed, in 1 is able to mediate adhesion of cultured podocytes to collagen molecules, laminin and fibronectin [24], and, with the exception of type I collagen, rat GBM does contain all these ECM components [39,40]. Thus, the reduced expression of a 3 on podocyte plasma membrane facing the GBM could be related to the asymmetrical distribution of type IV collagen on the subendothelial side of the glomerular wall established during diabetic glomerulosclerosis [29][30][31]. To test such hypothetical correlation, we examined the expression of a 3 in tissues of 1-month hyperglycaemic rats which do not yet show any morphological modification of their GBM.…”

“…[Diabetologia (1997) In long-term diabetes a progressive alteration of the glomerular extracellular matrix (ECM) compartments leads to an expansion of the glomerular basement membrane (GBM) [27,28]. During diabetes the GBM not only thickens but the spatial distribution of some of its components (i. e. type IV collagen) is markedly altered [29][30][31]. Since long-term diabetes is associated with significant alterations of the ECM and since integrins appear to be the key proteins mediating cell-ECM relationships, it is important to understand the role of integrins in the onset of diabetic nephropathy.…”