The three-dimensional ultrastructure of diabetic glomeruli revealed by the quick-freezing and deep-etching method

The three-dimensional ultrastructure of the glomerular basement membrane (GBM) and mesangial matrix (MM) in streptozotocin (STZ)-induced diabetic rats and in one case of a human diabetic nephropathy were examined using the quick-freezing and deep-etching method. In the diabetic rats, the GBM inner layer was diffusely enlarged, and the meshwork structures in the GBM middle layer and the MM were markedly irregular due to the rupturing of fine fibrils. These irregularities and enlargements of the mesh pores in the diabetic rats developed during the experimental period and were significantly different from those in the control rats. Insulin treatment after STZ injection significantly prevented ultrastructural changes in the GBM and MM. The human diabetic case was a 69-year-old male who had been suffering from non-insulin dependent diabetes mellitus for 29 years. He had a background diabetic retinopathy, microalbuminuria and a decrease in lower limb tendon reflexes. Conventional electron microscopy revealed electron-lucent areas in enlarged subendothelial spaces and mesangium. By the quick-freezing and deep-etching method, the GBM inner layer was diffusely enlarged, and the meshwork structure of the GBM middle layer and the MM showed marked irregularity due to the rupturing of fine fibrils. These findings suggest that the initial morphological changes in diabetic nephropathy include structural abnormalities of fine fibrils in the GBM and MM, which may correspond to the subendothelial and mesangial electron-lucent areas as observed in conventional ultrathin sections.