Search

Connexins (Cxs) are membrane-spanning proteins which enable flow of information important for kidney homeostasis. Changes in their spatiotemporal patterning characterize blood vessel abnormalities and chronic kidney diseases (CKD). We analysed spatiotemporal expression of Cx37, Cx40, Cx43 and Cx45 in nephron and glomerular cells of developing, postnatal kidneys, and nephrotic syndrome of the Finnish type (CNF) by using immunohistochemistry, statistical methods and electron microscopy. During kidney development, strong Cx45 expression in proximal tubules and decreasing expression in glomeruli was observed. In developing distal nephron, Cx37 and Cx40 showed moderate-to-strong expression, while weak Cx43 expression gradually increased. Cx45/Cx40 co-localized in mesangial and granular cells. Cx43 /Cx45 co-localized in podocytes, mesangial and parietal epithelial cells, and with podocyte markers (synaptopodin, nephrin). Different Cxs co-expressed with endothelial (CD31) and VSMC (α –SMA) markers in vascular walls. Peak signalling of Cx37, Cx43 and Cx40 accompanied kidney nephrogenesis, while strongest Cx45 signalling paralleled nephron maturation. Spatiotemporal Cxs patterning indicate participation of Cx45 in differentiation of proximal tubules, and Cx43, Cx37 and Cx40 in distal tubules differentiation. CNF characterized disorganized Cx45 expression in proximal tubules, increased Cx43 expression in distal tubules and overall elevation of Cx40 and Cx37, while Cx40 co-localized with increased number of interstitial myofibroblasts. [ABSTRACT FROM AUTHOR]

Differentiation of human podocytes starts with mesenchymal-to-epithelial transition (MET) of the metanephric mesenchyme into the S-shaped nephrons. During further development, differentiating podocytes regain mesenchyme-like cell characteristics by epithelial-to-mesenchymal transition (EMT), leading to formation of the terminally differentiated, non-dividing cell. Both MET and EMT processes involve changes in content and organization of cytoskeletal and actin filaments, accompanied by the increased glomerular vascularization. Here, we analyze and compare normal human developing, postnatal and nephrotic podocytes and glomeruli, using immunohistochemical and double immunofluorescent methods for detection of markers of cytoskeletal filaments (nestin, cytokeratin 10-CK10, vimentin and α-SMA), vasculogenesis (CD31 and VEGF) and podocyte function (receptor for advanced glycation end products, RAGE). In addition, electron microscopy is used to detect ultrastructural changes of the podocytes. Early metanephric cup mesenchyme expresses all investigated markers except α-SMA, which characterizes only surface mesenchymal cells. In differentiating podocytes and cells of Bowman's capsule (parietal podocytes) nestin decreases, vimentin increases, while CK10 gradually disappears. Increase in α-SMA is associated with blood vessels development, appearance of podocyte pedicles and slit diaphragm and loss of intercellular connections (zonulae adherentes). Increase in CD31 characterizes vascular glomerular tufts development, while decrease in RAGE expression accompanies normal podocyte differentiation. In congenital nephrotic syndrome of the Finnish type, dedifferentiated podocytes display changes in cytoskeletal filaments and depletion of podocyte pedicles, while glomerular vascular supply is diminished. Our data also suggest high potential of metanephric mesenchyme and parietal podocytes in possible regeneration of the damaged podocytes. [ABSTRACT FROM AUTHOR]

Ciliogenesis in developing and post-natal human kidneys appears to influence cell proliferation and differentiation, apico-basal cell polarity, and tubular lumen formation. We have analyzed the appearance of primary cilia and differentiation of kidney cells in ten human conceptuses aged 6-22 weeks and in one 5-year-old kidney, using a double immunofluorescence labeling technique for α-tubulin, γ-tubulin, Oct-4, and Ki-67 and by electron microscopy. Immature forms of nephrons and ampullae were characterized by intense cell proliferation, which subsequently decreased during development. Primary cilia appeared on the surfaces of non-proliferating cells in developing nephrons, gradually increasing in length from 0.59 μm in renal vesicles to 0.81 μm in the S-forms of nephrons, ultimately reaching 3.04 μm in length in mature fetal and post-natal nephrons. Ciliary length increased from 0.59 μm in ampullae to 1.28 μm in post-natal collecting tubules. Mesenchymal to epithelial transformation of kidney cells coincided with the appearance of apico-basal polarity, both gap and tight junctions, and lumen formation. Up-regulation of Oct-4 expression correlated with the onset of kidney cell differentiation. Our results demonstrate the importance of proper primary cilia lengthening and Oct-4 expression for the normal development of fetal and post-natal kidneys and of apico-basal polarity for normal tubular lumen formation. Disturbances in these processes are associated with ciliopathies. [ABSTRACT FROM AUTHOR]

The spatial and temporal expression patterns of cytokeratins, vimentin, epithelial growth factor (EGF) and transforming growth factor alpha (TGF-α), were investigated in the 5–9-week old human mesonephros and metanephros. Vimentin was found in all mesonephric structures, while cytokeratins were seen only in the mesonephric tubules. EGF and TGF-α were detected early in all mesonephric structures, and immunoreactivity to both factors decreased in later stages. 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 fibrosis or carcinomatous changes. At early stages, immunoreactivity to EGF and TGF-α was detected in all metanephric structures and from the 7th week onward, it decreased in differentiating nephrons. EGF and TGF-α patterns of appearance indicate their role in induction, proliferation and growth of metanephric structures. Disturbances in that pattern might cause reduction in kidney growth. [ABSTRACT FROM AUTHOR]

The expression pattern of mitotic Ki-67 and anti-apoptotic bcl-2 proteins, as well as apoptotic caspase-3 and p53 proteins, were investigated in the human mesonephros and metanephros of 5–9 week-old human conceptuses. Apoptotic cells were additionally detected using the terminal deoxynucleotidyl transferase (TdT) nick-end labelling (TUNEL) method. Between the 5th and 7th developmental weeks Ki-67, caspase-3 and TUNEL-positive cells characterized all mesonephric structures, indicating importance of cell proliferation in the growth of the mesonephros and role of apoptosis in 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, caspase-3 and TUNEL-positive 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-expressing cells could participate in further morphogenesis of the metanephric collecting system. The factors investigated had a spatially and temporally restricted pattern of appearance in developing kidneys. Changes in that pattern might lead to serious disturbances of kidney formation and function in early childhood. [ABSTRACT FROM AUTHOR]

Normal and anencephalic human conceptuses were analysed histologically to investigate the role of differentiation of the intracranial notochord and its relation to the formation of the basichondrocranium. We have examined 16 normal embryos and fetuses and 4 anencephalic fetuses. Each developmental stage of formation of the normal basichondrocranium presented specific morphological changes during the course of notochord depletion. In contrast with normal specimens, anencephalic fetuses presented malformations of the basichondrocranium which were always related to an abnormal position of the notochord. Macroscopical differences between craniorachischisis and cranioschisis in fetuses with anencephaly correlated with the existence of two histologically different degrees of malformation. In fetuses with craniorachischisis we found severe disturbances in the shape, position and ossification of the basichondrocranium and in the course of the intracranial notochord. In fetuses with cranioschisis the described disturbances of the basichondrocranium and intracranial notochord were mild. In addition, marked differences in affection of the central nervous system and the hypophysis were observed. These findings suggest different periods of dysmorphogenesis. Our results underline the importance of the chordal mesoderm in the differentiation for the formation of cephalic structures in Man. [ABSTRACT FROM AUTHOR]