Renal tubular differentiation in mouse and mouse metanephric culture. I. Ultrastructural studies

Renal tubular dysgenesis in twin-twin transfusion syndrome

In twin-twin transfusion syndrome (TTTS), the disparity in circulation is reflected in discordant fetal growth, urine output, and amniotic fluid accumulation. The effect of uneven shunting of the growth factor and nutrient-rich vasculature on development and differentiation of the kidney has not been well studied. We analyzed renal tubular growth and differentiation in 25 fetal autopsies with TTTS (13 donors and 12 recipients, including 9 sibling pairs) between 18 and 33 weeks gestation. Immunohistochemical markers for fumarylacetoacetate hydrolase (FAH), Leu-M1, and Lotus tetragonolobus (LTA) were used to identify proximal convoluted tubules, and epithelial membrane antigen (EMA) was used to demonstrate distal convoluted and collecting tubules. FAH appeared to be more specific and reliable than either Leu-M1 or LTA in the identification of proximal tubules. Donors tended to demonstrate a paucity of proximal tubules with crowding of glomeruli characteristic of renal tubular dysgenesis (RTD). The degree of dysgenesis was greater in later gestations and associated with more severe growth restriction. Donors in TTTS are at risk for the development of RTD. Several authors suggest ischemia as the underlying cause of "acquired" RTD. However, in this setting there is no evidence of cell death or necrosis, and we suggest that hypoperfusion leading to decreased glomerular filtration is the underlying etiology, with the severity of RTD related to the degree of shunting.

Glucocorticoid teratogenesis in the developing nephron

Although the induction of polycystic kidney disease by neonatal glucocorticoid treatment has been extensively documented, there are no data on induction of polycystic kidney disease with fetal exposure to glucocorticoids. We injected groups of pregnant Swiss Webster albino mice subcutaneously with 250 mg/kg of hydrocortisone acetate on individual days from days 1 to 19 of gestation. A control group received an equal volume of saline. Histologic analysis of 1,522 kidneys from the offspring of these animals revealed no evidence of polycystic kidneys in the control group or in offspring of animals injected before day 11 of pregnancy. A bimodal distribution of cystic kidney disease was noted in the remaining animals, with highest prevalence after injection on day 12 (50.8%) and day 17 (34.3%). We conclude that 250 mg/kg of glucocorticoids may induce polycystic kidney disease in utero, but possibly only during critical periods of metanephric development.

Freeze-fracture observations on human fetal kidney in serum-free organ culture

The current study was undertaken to examine and characterize junctional complexes, through freeze-fracture, in developing human fetal kidney and in cultured renal explants maturing in vitro. Tissue specimens were cultured for 7 days in Leibovitz's L-15 medium in the absence of serum or hormones. In uncultured explants, cells in the different nephron segments were joined by zonulae occludentes which consisted of ridges on the P-face and grooves on the E-face of lateral membranes. Tight junction composition was heterogeneous and complexity increased from proximal to collecting tubules. Proximal tubule cells were also characterized by the presence of gap junctions and a brush border. Podocytes were joined by macular junctions, while zipper-like junctions were observed between collecting duct cells. Intercalated cells were decorated with rod-shaped intramembrane particles on lateral and apical membranes, instead of the usual spherical particles present in other cells. All these structures could be observed at various intervals during tissue culture, indicating the preservation of ultrastructural integrity of the explants. These observations extend and support previous studies made at the light and electron microscopic levels. Thence, the present culture model constitutes a valuable tool to study the direct effect of growth factors on nephrogenesis.

Fetal mouse kidney maturation in vitro: coordinated influences of epidermal growth factor, transferrin and hydrocortisone

We have investigated the individual and combined actions of epidermal growth factor (EGF), transferrin and hydrocortisone on the maturation of whole fetal mouse metanephroi maintained in serum-free conditions for up to 5 days. The presence of EGF (100 ng/ml) resulted in elevated levels of [3H]-thymidine incorporation when compared to controls; autoradiograms showed that the proliferation of mesenchymal cells in the nephrogenic zone is particularly enhanced as verified by cell counting. Brush border hydrolase activities (alkaline phosphatase and gamma-glutamyltransferase), on the other hand, were significantly diminished. Transferrin (5 micrograms/ml) slightly stimulated DNA synthesis and potentiated EGF mitogenic action. The activation of DNA replication by the growth factor seems to be mediated through the protein kinase C pathway. When added alone, hydrocortisone (10(-6) M) strongly inhibited DNA synthesis, stimulated hydrolase activities and exerted a positive effect on brush border differentiation. When combined with EGF or to EGF + transferrin, hydrocortisone counteracted the effects of these latter peptides on DNA synthesis and enzyme activities. Considering the earlier observation of a reciprocal relation between proliferation and differentiation during the neotubulogenic phase of kidney development, the results described in the current study suggest that synergistic and synarchic actions of these heterologous factors are involved in the regulation of tubulogenesis.

Expression of differentiation molecules is preserved in human fetal kidneys during culture

A model has been developed in our laboratory to culture human fetal kidney (Brière 1987). This system is original because it is realized in serum-free Leibovitz's L-15 medium unsupplemented with hormones. Since the culture conditions are minimal for growth and differentiation, many parameters had to be analysed to verify the validity of the system. It was shown that the overall architecture of the explants was preserved during the culture period as well as other morphological and biochemical characteristics. Cells in different populations of the cultured explants keep synthesizing DNA although at a decreased rate. The aim of the current work was to further evaluate the model by studying the expression of some renal cell differentiation antigens (CD24, CD9, CALLA/CD10) in the fetal kidneys during culture. The 4 selected monoclonal antibodies (OKB2, IOB2, IOT5a, IOB3) detected the corresponding surface antigens in various developing renal structures present in uncultured explants. It was observed that these antigens were well preserved during culture and were still expressed on the same structures after 5 d. The present culture model appears as a valuable tool to assess kidney development, and the above mentioned cell surface antigens might be used as markers to study nephrogenesis or the differentiation of membrane specializations.

Renal tubular differentiation in mouse and mouse metanephric culture. II. Na-K-ATPase activity

Sodium-potassium adenosine triphosphatase (Na-K-ATPase) activity was measured by microassay, and the surface density of basolateral membranes was measured morphometrically in postglomerular segments of single tubules isolated from normally developing, intact mouse kidneys and from transfilter metanephric cultures. Proximal tubule Na-K-ATPase activity was 1092 +/- 480 pmol/mm per hour in newborn mice, increasing to 2462 +/- 258 in 1-week-old and 3470 +/- 578 pmol/mm per hour in adult mice. The Na-K-ATPase activity in newborn mice was approximately one-third of the activity in adult mice. Tubular Na-K-ATPase in transfilter metanephric culture was 972 +/- 536 pmol/mm per hour, a mean value almost identical to that in newborn mice. The surface density of basolateral cell membranes was 1.36 +/- 0.60 microns2/microns3 in newborn mice and 1.34 +/- 0.45 microns2/microns3 in 1-week-old mice, increasing to 2.70 +/- 0.98 microns2/microns3 in 4-week-old mice and 2.89 +/- 0.51 microns2/microns3 in adult mice. The surface density of tubular basolateral cell membranes in transfilter metanephric culture was 1.13 +/- 0.51 microns2/microns3, not significantly different from the surface density in newborn mice. The calculated mean surface area of basolateral membranes per unit tubular length was greater in cultures than in newborns, however, because total epithelial volume per unit length was significantly larger in the cultured tubules. Membrane surface area in intact mice increased with age, the surface area per unit length of tubule in adults being 4.6 times the area in newborn animals.(ABSTRACT TRUNCATED AT 250 WORDS)