High glucose-induced altered basement membrane composition and structure increases trans-endothelial permeability: implications for diabetic retinopathy.

PURPOSE: The following study was designed to investigate early biosynthetic and ultrastructural changes that alter functional properties of the basement membrane (BM) and affect vascular permeability in diabetic retinopathy.

MATERIALS AND METHODS: To determine whether altered matrix synthesis affects cell monolayer permeability, rat retinal endothelial cells (RRECs) were grown for 4 days to confluency in normal (N, 5 mM) or high glucose (HG, 30 mM) medium on transwell inserts and subjected to an in vitro cell monolayer permeability assay. Inserts were cut out and viewed under a transmission electron microscope to assess extracellular matrix (ECM) accumulation and cell morphology. In parallel cell cultures, fibronectin and collagen IV protein expression were determined using Western Blot analysis.

RESULTS: Electron microscopic analysis of cells exposed to short-term HG showed no difference in inter-endothelial cell tight junctions (TJs) or in the number of vesicles or coated pits compared to those of normal cells. However, ECM accumulation underlying HG cells was significantly increased compared to that of cells grown in N medium (139 ± 7% of control, p = 0.04), with areas of focal thickening. Western blot analysis showed increased fibronectin and collagen IV expression (152 ± 24% of control, p = 0.01; 146 ± 16% of control, p = 0.02, respectively) in cells grown in HG compared to those grown in N medium. Cell monolayers grown in HG exhibited increased permeability to FITC-dextran compared to cells grown in N medium (134 ± 15% of control, p = 0.02).

CONCLUSIONS: High glucose-induced excess ECM accumulation and altered composition underlies structural and functional changes that allow increased permeability. This finding provides evidence for the first time that the thickened vascular basement membrane contributes to the development of excess permeability seen in diabetic retinopathy.