Occurrence of fenestral diaphragms and knots in renal glomerular endothelia of diabetic mutant MafA-/-MafK+ mice as revealed in embedment-free transmission electron microscopy.

Using the advantages (high contrast and transparency and efficient 3D viewing) of embedment-free section transmission electron microscopy (TEM), the occurrence of numerous fenestral diaphragms was clearly shown in 3D en-face viewing of the renal glomerular capillary endothelium of severe overt diabetes mellitus mice, which were generally MafA-deficient and simultaneously MafK-overexpressed specifically in pancreatic β-cells. This presents another example of nephritis-induced diaphragmed fenestrae in the renal glomerular endothelium. In addition, knot-/umbilicus-like structures discrete from and larger than the central knots of regular diaphragms of fenestrated endothelium were clearly demonstrated to occur randomly in the renal glomerular endothelial fenestrae of mutant mice and wild ones. The knot-structures were revealed to be protrusions of underlining basement lamina in conventional TEM by section-tilting observation.