Electron microscopic study of capillary in the human renal cell carcinoma

Abstract

In this study, we investigated the ultrastructure of the microvasculature in human renal cell carcinoma (RCC) specimens. RCC specimens from 30 patients were studied by light microscopy after hematoxylin and eosin staining and alpha-smooth muscle actin staining, and by electron microscopy after uranyl acetate lead nitrate staining or periodic acid thiosemicarbazide gelatin methenamine silver staining. In the light microscopy, the capillaries located adjacent to the renal medullary tubules in normal renal tissue specimen were in an orderly manner, while capillaries in the RCC specimens were found to be densely or sparsely distributed unconventionally. The pericytes encircling the capillary endothelial cells were positive for alpha-smooth muscle actin and formed aggregates in many of the RCC specimens, but did not form aggregates in the normal tissue specimens. In the electron microscopy, capillary endothelial cells in the normal renal tissue specimens were found to form well-developed membranous structure such as characterized by fenestrations and tight junctions. However, few pericytes were detected. On the other hand, the capillary endothelial cells in RCC specimens were found to be immature with poorly developed junctional complexes. Capillary pericytes with numerous cytoplasmic processes were found in many of the RCC specimens. In addition, the basement membranes of the capillary walls were structurally abnormal in that it was being multilayered. Based on the results of analysis of a total of 324 capillaries observed in all RCC specimens, capillaries could be classified as type I capillaries, associated with well-developed pericytes with numerous processes, or type II capillaries, associated with few pericytes with few processes. Type I capillaries predominated in cases which an angiographically hypervascularity was detected. Whereas, type II capillaries predominated in cases in which angiographically hypovascular pattern were detected. The fine structure of the pericytes seems to reflect the qualitative difference in capillary structure between normal renal tissue and RCC specimens. Therefore, the present findings may contribute to the recognition of intratumoral hemodynamics.