Thy-1 Expressing Mesenchymal Cells in Rat Nephrogenesis in Correlation with Cells Immunoreactive for α-Smooth Muscle Actin and Vimentin

Abstract

Thy-1 expression may influence myofibroblast development. Through the epithelial-mesenchymal transition (EMT), injured renal epithelial cells undergo regression to the metanephric mesenchymal phenotype and then acquire a myofibroblastic nature (expressing α-smooth muscle actin; α-SMA). Because the metanephric blastema differentiates into mesenchymal and renal epithelial cells, we investigated Thy-1 immunoexpression during nephrogenesis in F344 rats in correlation with vimentin and α-SMA expressions. Kidney samples were obtained from fetuses on gestation days 18 and 21, neonates on days 1-18 and adults at 6 weeks of age. Mesangial cells in S-shaped bodies and immature and mature glomeruli continuously expressed both Thy-1 and α-SMA during early nephrogenesis (fetuses and neonates on days 1-9). During early nephrogenesis, loosely-arranged blastemal cell-derived mesenchymal cells in the cortex and medulla also exhibited Thy-1 and α-SMA, although the α-SMA expression was weaker than that of Thy-1. Vimentin expression coincided with that of Thy-1. These findings indicate that the derivation of α-SMA-expressing myofibroblastic cells may be related to mesangial or blastemal cells expressing both Thy-1 and α-SMA. Interestingly, there was a difference in Thy-1 expression between cortical and medullary tubulointerstitial cells from late nephrogenesis (neonates on days 12-18) and those from adults in that the cortical cells reacted faintly or negatively to Thy-1, whereas the medullary cells reacted strongly to Thy-1; additionally, bundle-arranged mesenchymal cells that were only observed in the neonates on days 1-12 reacted strongly to α-SMA, but faintly to Thy-1. Blastemal cell-derived mesenchymal cells seem to alter the immunoexpressions of Thy-1 and α-SMA, depending on the conditions which they develop. Thy-1 immunoexpression would be useful for investigation of reverse embryogenesis, which might occur in fibrotic kidneys.

Keywords: Thy-1; blastemal cells; myofibroblasts; nephrogenesis; rat; α-smooth muscle actin.

Fig. 1

Cortical areas during rat nephrogenesis. Loosely-arranged mesenchymal cells are prominently seen among the developing renal tubules, and there are round-, comma- and S-shaped bodies (arrows) as well as immature glomeruli in the fetus on gestation day (GD) 18 (a). In conjunction with nephrogenesis, the mesenchymal cells are decreased in neonates on days 6 (b) and 18 (c). HE stain. Bar=50 μm.

Fig. 2

Medullary areas during nephrogenesis. Loosely-arranged mesenchymal cells are seen mainly around the branched epithelial ureteric tubules (arrows) in the fetus on gestation day 21 (a). Mesenchymal cells arranged parallel to each other and perpendicular to the developing renal tubules (arrows) are present in the cortico-medullary junction of the neonate on day 3 (b). Mature renal tubules and tubulointerstitial cells are seen in neonate on day 18 (c). HE stain. Bar=50 μm.

Fig. 3

Immunohistochemical findings in cortical areas for Thy-1 (a, c), α-smooth muscle actin (α-SMA) (b), and vimentin (d) on GD 18. Thy-1-positive cells are seen in S-shaped bodies (a, c; large arrows) and mesangial cell in immature glomeruli (a, c; small arrows); additionally, loosely-arranged mesenchymal cells in the cortex react to Thy-1 (a, c; arrowheads). In serial sections (a, b; small arrows), Thy-1-positive mesangial cells (a) also react to α-SMA (b); additionally, there are loosely-arranged mesenchymal cells faintly reacting to α-SMA in the cortex (b, arrowheads). In serial sections (c, d), the vimentin-positive mesangial cells seen in immature glomeruli (c, d; small arrows) and loosely-arranged mesenchymal cells in the cortex (c, d; arrowheads) correspond to Thy-1-positive cells. Immunohistochemistry, counterstained with hematoxylin. Bar=50 μm.

Fig. 4

Immunohistochemical findings in medullary areas for Thy-1 (a) and α-SMA (b) in serial sections (a, b) on GD 18. Loosely-arranged mesenchymal cells mainly around developing renal tubules react strongly to Thy-1 (a, arrows), whereas these cells show a faint reaction to α-SMA (b, arrows). Immunohistochemistry, counterstained with hematoxylin. Bar= 50 μm.

Fig. 5

Immunohistochemical findings in the cortico-medullary junction for Thy-1 (a, c), α-SMA (b) and vimentin (d) 3 days after birth (neonate). Thy-1-positive cells are seen around the developing renal tubules (a, small arrows); the positive cells correspond to cells reacting to α-SMA (b, serial section to a; small arrows) and vimentin (d, serial section to c, small arrows). Bundle-arranged mesenchymal cells seen in the cortico-medullary junction show a positive reaction for α-SMA (b; large arrow), whereas they show a faint reaction for Thy-1 (a, b; large arrows); in serial sections (a for Thy-1 and d for vimentin), bundle-arranged mesenchymal cells reacted faintly to Thy-1 (a; large arrow) and vimentin (d; large arrow), in contrast to the strong reaction for α-SMA in the mesenchymal cells (b; large arrow). Immunohistochemistry, counterstained with hematoxylin. Bar=50 μm.

Fig. 6

Immunohistochemical findings for Thy-1 (a, c) and α-SMA (b, d) in adults at 6 weeks of age. In serial sections (a, b) of the cortex, mesangial cells in mature glomeruli react strongly to Thy-1 (a) and faintly to α-SMA (b). Tubulointerstitial cells in the cortex do not react to Thy-1 (a), whereas interstitial cells in the medulla show a strong reaction to Thy-1 (c). In serial sections (c, d) of the medulla, Thy-1-positive tubulointerstitial cells (c) do not react to α-SMA (d); similarly, cortical tubulointerstitial cells are negative for α-SMA (b). Spindle-shaped cells (so-called pericytes) surrounding arteriolae show a positive reaction for Thy-1 (inset in a; arrow) and α-SMA (d; arrows). Immunohistochemistry, counterstained with hematoxylin. Bar=50 μm.