Calponin expression in renal tubulointerstitial fibrosis induced in rats by Cisplatin

Abstract

Renal tubulointerstitial fibrosis is the common feature of chronic renal failure, regardless of its etiology. Myofibroblasts play important roles in progression of the fibrosis and are characterized by expressions of various cytoskeletons such as vimentin, desmin and α-smooth muscle actin (α-SMA). To pursue the characteristics of the cells, we immunohistochemically investigated the relationship between calponin (a marker of terminal smooth muscles) expression and myofibroblasts in cisplatin-induced rat renal tubulointerstitial fibrosis. Calponin-expressing interstitial cells increased with fibrosis and reacted simultaneously to vimentin or α-SMA (a marker of well-differentiated myofibroblasts) but not desmin or Thy-1 (a marker of myofibroblasts at the early stage). The present study shows that calponin may be expressed transiently in relatively well-developed myofibroblasts in rat renal fibrosis. Calponin could become a marker for myofibroblast development in chronic renal toxicity in rats.

Keywords: calponin; cisplatin; myofibroblasts; rat; tubulointerstitial fibrosis.

Fig. 1.

Immunohistochemical findings for calponin in the cortex (a) and medulla (b) of control kidneys. Calponin expression is specifically observed in the vascular smooth muscle cells. There are no interstitial cells reacting to calponin both in the cortex and the medulla. Bar = 50 μm. Immunohistochemistry, counterstained with hematoxylin.

Fig. 2.

Immunohistochemical findings for calponin in the affected cortico-medullary junction of CDDP-injected rats. On day 3 after CDDP injection, a calponin-positive cell is seen in the interstitium (a, arrow). On day 9, the dilated tubules are surrounded by calponin-positive, spindle-shaped myofibroblasts (b, arrows), and some regenerating cuboidal epithelial cells of the dilated renal tubules are positive for calponin (c, arrowhead). On day 20, calponin-positive myofibroblasts are seen surrounding the dilated renal tubules (d, arrows). On day 25, although calponin-positive interstitial cells are not seen, flattened epithelial cells rimming the dilated renal tubules react to calponin (e, arrowheads). On day 60, a calponin-positive reaction is also seen in flattened and cuboidal regenerating epithelial cells (f, arrowheads) in the dilated tubules and in a myofibroblast (f, arrow) in the scar tissue (f). Bar = 25 μm. Immunohistochemistry, counterstained with hematoxylin.

Fig. 3.

Double immunofluorescence for calponin and vimentin, desmin or α-smooth muscle actin (α-SMA) in the affected cortico-medullary junction on days 15. Calponin-positive cells react to vimentin (a) and α-SMA (c), but there are no cells reacting both to calponin and desmin (b). Bar = 50 μm. Green indicates calponin-positive cells (a, b, and c), and red indicates vimentin (a), desmin (b) and α-SMA (c). DAPI for nuclei (blue). Double-positive cells are shown in yellow (arrowheads).

Fig. 4.

Double immunofluorescence for calponin and Thy-1 in the cortico-medullary junction in the control or on day 15. In the control kidney, pericytes (large arrows) and some interstitial cells (arrowhead) show a positive reaction to Thy-1 in the cortex (a), whereas many interstitial cells in the medulla react to Thy-1 (b). In addition to vascular smooth muscles (a, small arrow), calponin expression is seen in regenerating epithelial cells of the dilated tubules (c, large arrows) and interstitial myofibroblasts (c, small arrows); there are no cells reacting simultaneously to calponin and Thy-1 (c). Bar = 50 μm. Red indicates calponin-positive cells (a, c), and green indicates Thy-1 reactivity (a, b, c). DAPI for nuclei (blue).