SEM and TEM analyses of isolated human retinal microvessel basement membranes in diabetic retinopathy

Abstract

Human retinas from persons with diabetic retinopathy and age-matched controls were rendered acellular by sequential detergent treatment. The resulting network of microvascular extracellular matrix (ECM) materials, including basement membranes (BMs), was compared by TEM and, following cryofracture, by SEM. Our study demonstrates that in diabetics, retinal capillary BM complexes are generally thickened and that their ECM subcomponents, including BM leaflets and BM-like pericytic matrix (PCM), are differentially altered. Two diabetic microvessel types were identified. In type A vessels, ECM expansion is manifested by loosely arranged combinations of concentric PCM layers and collagen fibrils with thickened subendothelial (EBM) and pericyte (PBM) BM leaflets. Type B vessels show densely compact central PCM masses and poorly recognizable EBMs and PBMs. In both types, Müller cell BMs (MBMs) are relatively unaffected. High-resolution SEM shows tissue-specific features in normal EBM and MBM surfaces, but disease-related topographic changes are not evident. It is possible that the ECM arrangements identified in our study relate to different microvessel domains and that their specific morphological features may play important roles in the pathogenesis of diabetic retinopathy including capillary closure and neovascularization.

Scanning and transmission electron microscopic studies of normal and diabetic acellular glomerular and retinal microvessel basement membranes

“…Nevertheless, our studies from a large number of sections indicate that the entire acellular walls of diabetic retinal microvessels ranges from 1,200 to 3,000 nm in thickness compared with 750 to 900 nm for similar vessels from normal individuals (Carlson and Bjork, 1990). Interestingly, regardless of the vessel type, the majority of the increase in extracellular matrix could be accounted for by concentric or masses (nodular) accumulations of pericytic matrix.…”

Increased expression of basement membrane collagen in human diabetic retinopathy.

“…In situ hybridization studies in mice have shown that the postnatal retina contains collagen IV mRNA only at the level ofblood vessels ( 18). Even ifglial cells contributed to the collagen IV mRNA measured by the more sensitive method of RT-PCR, their role in the increased expression observed in diabetic patients is likely to be minor since the Muller cell basement membranes appear much less affected than the subendothelial and pericytic basement membranes in diabetic retinal microvessels ( 15). Insofar as the in vitro biosynthetic profile of retinal endothelial cells and pericytes indicates that only the endothelial cells synthesize substantial amounts ofcollagen IV (32), it may be extrapolated that our observations reflect increased synthesis ofcollagen IV by vascular endothelial cells in diabetic patients.…”

“…We performed the experiments in human retinas because thickening of basement membranes is well documented in diabetic retinal vessels (2,15) and intact RNA can be extracted from these vessels up to 36 h postmortem ( 16). Having determined that Northern analysis is insufficiently sensitive for detection of the collagen IV transcript, which is rare in the adult retina ( 17,18) Table I.…”

Aminoguanidine does not inhibit the initial phase of experimental diabetic retinopathy in rats

“…Photomicrographs of ten randomly-selected capillaries of the inner nuclear layer were taken at a magnification of 14 500 x. The width of the retinal capillary basement membrane thickness was measured according to the method of Siperstein, using an image analysing system (Video Plan, Kontron, Miinchen, Germany) [13]. Basement membrane proportions in the external circumference of pericytes and between pericytes and endothelial cells were excluded from the examination.…”