Ultrastructural Analyses of Acellular Glomerular Basement Membranes and Mesangial Matrix in a Spontaneously Diabetic Rhesus Monkey

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Abstract
Renal changes similar to those considered diagnostic for diabetes in humans are infrequently observed in spontaneous noninsulin-dependent (NID) diabetic monkeys. In the current study, renal cortical tissue blocks are rendered acellular to demonstrate glomerular basement membrane (GBM) and mesangial matrix (MM) changes in a naturally occurring NID diabetic rhesus monkey (Macaca mulatta). Transmission electron micrographs of these specimens show axial MM accumulations with numerous striated collagen fibrils that frequently extend onto internal (endothelial) surfaces of peripheral GBM. The outer (epithelial) component, although compact, appears bilaminar due to folded external surfaces not coinciding with similar irregularities on internal surfaces. By scanning electron microscopy, external surfaces of sclerotic GBMs are extensively wrinkled and, following cryofracture, show congestion and expanded MM. Afenestrated meshwork of MM, which appears less dense and compact than epithelial BM, extends from axial regions onto GBM internal surfaces. The true thickness of randomly sampled peripheral GBM thickness (∼ 400 nm) is approximately double that of normal rhesus GBM. Diabetic GBMs exhibit ruthenium red positivity for surface polyanions with linear site densities not significantly different from normal. These observations indicate that sclerotic GBMs in diabetic rhesus monkeys closely resemble those seen in human endsfage diabetic glomerulopathy and suggest that this nonhuman primate may offer an excellent model for studies of chronic diabetic BM disease.