Peculiarities of the extracellular matrix in the interstitium of the renal stem/progenitor cell niche

Abstract

The development of the nephron is piloted by interactions between epithelial and surrounding mesenchymal stem/progenitor cells. Data show that an astonishingly wide interstitial space separates both kinds of stem/progenitor cells. A simple contrasting procedure was applied to visualize features that keep renal epithelial and mesenchymal stem/progenitor cells in distance. The kidney of neonatal rabbits was fixed in solutions containing glutaraldehyde (GA) in combination with alcian blue, lanthanum, ruthenium red, or tannic acid. To obtain a comparable view to the renal stem/progenitor cell niche, the tissue was exactly orientated along the axis of collecting ducts. Fixation with GA or in combination with alcian blue or lanthanum revealed an inconspicuous interstitial space. In contrast, fixation with GA containing ruthenium red exhibits strands of extracellular matrix lining from epithelial stem/progenitor cells through the interstitium up to the surface of mesenchymal stem/progenitor cells. Fixation with GA containing tannic acid shows that the basal lamina of epithelial stem/progenitor cells, the adjacent interstitial space and also the surface of mesenchymal stem/progenitor cells are connected over a net of extracellular matrix. The applied technique appears to be a suitable method to illuminate the interstitium in stem/progenitor cell niches of specialized tissues, the microenvironment of tumors and extension of degeneration.

Illustration of extensive extracellular matrix at the epithelial-mesenchymal interface within the renal stem/progenitor cell niche

“…Finally the specimens were embedded in Epon (Fluka), which was polymerized at 60°C for 48 h. Semithin and ultrathin sections were performed with a diamond knife on an ultramicrotome EM UC6 (Leica GmbH, Wetzlar, Germany). Sections were collected onto grids (200 mesh) and contrasted using 2% uranyl acetate and lead citrate as earlier described [31]. Sections were examined at 80 kV using an EM 902 transmission electron microscope (Zeiss, Oberkochen, Germany).…”

“…Immunohistochemical and morphological data have shown that around the tip of each CD ampulla an unique basal lamina and an interstitial space is established keeping nephrogenic mesenchymal cells in an astonishingly wide distance to neighboring epithelial stem/progenitor cells [28-30]. Light and electron microscopic analyses further show that after conventional fixation in glutaraldehyde the bright interstitial space does not exhibit recognizable extracellular matrix [31]. Furtheron, the striking interstitial space is not restricted to a single species, but was shown in developing rabbit [28,32], mouse [33-36], rat [37,38] and human [29,39] kidney.…”

Cell Projections and Extracellular Matrix Cross the Interstitial Interface within the Renal Stem/Progenitor Cell Niche: Accidental, Structural or Functional Cues?

“…Most interestingly, between cell projections of mesenchymal and epithelial cells, numerous parallel lining TNT were detected each exhibiting an average diameter between 3.5 and 4.1 nm. Regarding the exclusive occurrence at the interstitial interface [16], focusing on the presented results (fig. 6) or reflecting earlier findings made by Lehtonen [26], it appears most probable that illustrated mesenchymal cell projections are involved in the transmission of morphogenetic signals during nephron induction via TNT.…”

“…Actual data further demonstrate that epithelial and mesenchymal stem/progenitor cells are separated by a wide but individually composed interstitial interface [16]. However, cellular communication and transmission of morphogenetic signals across this interface remains widely unknown.…”

Recent progress in histochemistry and cell biology

“…Epithelial and mesenchymal stem/progenitor cells are separated by a wide interstitial space. As this site may harbor an unknown individual environment supporting recruitment and development of stem/progenitor cells necessary for nephron development, Minuth et al (2011) performed transmission electron microscopy to rabbit renal embryonic parenchyma to analyze the morphological peculiarities of this interstitium within the stem/progenitor cell niche, applying conventional glutaraldehyde fixation in the absence/presence of lanthanum, alcian blue, ruthenium red or tannic acid. The authors could show that conspicuous strands of extracellular matrix are lining through the particular interstitium and that this newly detected arrangement of extracellular matrix plays a role in the positioning of respective stem/progenitor cells.…”