[Expression of Smad proteins in the process of liver fibrosis in mice infected with Schistosoma japonicum].

OBJECTIVE

To study the expression of Smads proteins involved in TGF-beta1 signal transduction during the process of liver fibrosis in BALB/c mice infected with Schistosoma japonicum.

METHODS

Thirty-four BALB/c mice were each infected with (20 +/- 1) S. japonicum cercariae. The mice were sacrificed at 8, 12, 16 and 24 weeks postinfection. Ten healthy BALB/c mice served as normal control group. The liver tissues were fixed in 10% formaldehyde for histology and immunohistochemistry assay. The single-egg granuloma area was measured in hematoxylin-eosin stain section. The degree of liver fibrosis was determined by Sirius red staining. Immunohistochemistry was used to observe the expression of Smad protein.

RESULTS

The area of single-egg granuloma peaked at 8th week post-infection [(533 +/- 1.03) mm2], and with time passing, the area diminished, and the area of granuloma reduced to (2.94 +/- 1.69) mm2 at 24 weeks post-infection. The difference was significant among the 4 periods after infection in single-egg granuloma area (P < 0.05). Collagen fibers appeared around granulomas at 8 weeks (2.03 +/- 0.52) and increased gradually. At 24 weeks post-infection, the degree of liver fibrosis reached a peak (6.90 +/- 1.57), and the liver fibrosis degree was significantly different among infection groups (P < 0.05). Immunohistochemistry showed low expression level of Smad2/3 and Smad7 and inconspicuous level of Smad4 in livers of the normal mice. The expression of Smad2/3 was found mostly in the cytoplasm and nucleus of cells around granulomas at 8th week post-infection, and the positive area of Smad2/3 was (7.24 +/- 1.64)% by semi-quantity. At 12 weeks post-infection, the Smad2/3 protein expression level around granulomas and liver sinus reached the peak [(10.01 +/- l.07)%], and there was significant difference between infection groups and the control [(2.13 +/- 0.32)%]. A significant difference in the Smad2/3 protein expression level was found between 12 weeks post-infection group and 8 weeks or 16 weeks post-infection groups. The expression level of Smad4 was (8.81 +/- 1.13)% at 8th week post-infection, higher than that in the control [(4.83 +/- 1.15)%] (P < 0.05). There was no difference among the infected mice at different periods in the level of Smad4 (P > 0.05). After 8 weeks post infection, Smad7 protein sparsely appeared around the granuloma [(4.15 +/- 1.26)%] while it disappeared around liver sinus. At 12 weeks post-infection, the level of Smad7 protein was higher [(6.34 +/- 1.5)%], but with prolonged infection time, no significant difference was revealed (P > 0.05). The level of Smad7 in infected mice was higher than that in the control (P < 0.05).

CONCLUSION

Resylts show high expression for Smad2/3 and Smad7 and low expression level of Smad4 during the process of liver fibrosis in BALB/c mice infected with Schistosoma japonicum.