The involvement of apoptotic factors, growth factors and intermediate filament proteins in early human kidney development
The spatial and temporal patterns of appearance of proteins Ki-67, bcl-2, caspase-3, p53, cytokeratins, vimentin, EGF, TGF-., FGF-8, FGF-10, BMP-2/4 subfamily, BMP-7 and VEGF were investigated in the mesonephros and metanephros of 5-9 –weeks old human conceptuses using immunohistochemical methods.
Between the 5th and 7th developmental weeks, Ki-67 and caspase-3 positive cells characterized all mesonephric structures indicating importance of cell proliferation in the growth of the mesonephros, and role of apoptosis in the nephrogenesis. From the 7th week on, p53 and bcl-2 positive cells appeared in the mesonephros as well.
Regressive changes in the mesonephros could be regulated by activation of p53, while bcl-2 could contribute to selective survival of some tubules giving rise to adult structures.
In the early human metanephros (5-7-weeks), Ki-67 positive cells characterized all metanephric structures, indicating a role of cell proliferation in branching of the ureteric bud and in nephron formation.
During the same period, bcl-2 and caspase-3 reacting cells were found only in the metanephric mesenchyme and nephrons.
Bcl-2 protein probably protected nephrons from apoptosis, while caspase-3 protein controlled cell death in the mesenchyme.
At later stages (7-9-weeks), appearance of p53 positive cells could participate in further morphogenesis of the metanephric collecting system.
Vimentin was found in all mesonephric structures, while cytokeratins were seen only in the mesonephric tubules.
In the 5-6-week metanephros, vimentin immunoreactivity was found in all structures and later increased in the collecting system
and interstitium. In the 5th week, cytokeratins 8 and 19 appeared in the ureteric bud and ampullae, and later showed increasing immunoreactivity in the collecting system and nephrons.
The coexpression of intermediate filament proteins in metanephric development is a temporary feature and might be associated with mesenchymal to epithelial transformation of developing nephrons. In adult kidneys, such coexpression is associated with fibrogenesis or carcinomatous changes.
EGF and TGF-. were detected early in all mesonephric structures, and immunoreactivity to both factors decreased in later stages. At early stages, immunoreactivity to EGF and TGF-. was detected in all metanephric structures and from the 7th week onward, it decreased in differentiating nephrons.
EGF and TGF patterns of appearance indicate their role in induction, proliferation and growth of metanephric structures.
In the mesonephros, cells positive to both FGF’s and BMP’s were found in all structures and their immunoreactivity slightly decreased in the early fetal period.
VEGF positivity appeared in all mesonephric structures, and increased in the fetal period coincidently with formation of the mesonephric blood vessel network.
In the metanephros, FGF-8 first appeared only in the metanephric mesenchyme, but from the 7th week on, its reactivity increased and spread to other metanephric structures.
FGF-10 positive cells appeared in all metanephric structures already in the 5th week, and slightly intensified with progression of development.
Cell survival and nephrogenesis in the permanent kidney might be associated with the appearance of both growth factors.
Both BMP-2/4 and BMP-7 displayed a similar pattern of reactivity in all metanephric structures, which intensified with advancing development, indicating their involvement in cell survival and ureteric bud branching.
Already in the earliest developmental stages, VEGF protein appeared in all metanephric structures. At later stages, VEGF showed more intense reaction in the collecting system than in the differentiating nephrons and interstitium.
The presence of this growth factor might be associated with the influence of metanephric struct