Abstract:

Objective To investigate the dynamic effects of chronic Schistosoma japonicum infection on renal fibrosis in mice and its molecular mechanism, thereby providing experimental evidence for elucidating the pathogenesis of schistosomiasis-associated kidney injury. Methods A chronic Schistosoma japonicum infection model was established in C57BL/6J mice (n=15), and an uninfected group (n=15) was set up simultaneously. Kidney tissues were collected at 12, 14, and 16 weeks post-infection (n=5 per group: infected and uninfected control) for subsequent analysis. The mRNA expression levels of fibrosis markers (α-SMA, CTGF, Col-1, and Col-4) in kidney tissues were detected by quantitative real-time PCR (qRT-PCR), and protein expression of CTGF, Col-1, P-Smad2/3 and Smad7 was analyzed by Western blot. Smad7 protein expression abundance and cellular localization were assessed by immunohistochemistry. Mouse glomerular mesangial cells (MES-13) were stimulated in vitro with soluble adult worm antigen (SWA) and transforming growth factor-β (TGF-β) from Schistosoma japonicum. The mRNA expression levels of fibrosis markers, Smad3, and Smad7 were measured by qRT-PCR, and the expression of Col-1 and α-SMA proteins in cells was observed via immunofluorescence. Results qRT-PCR results showed that, compared with the uninfected group, the mRNA expression of α-SMA, CTGF, Col-1, and Col-4 in the kidneys of mice infected for 12, 14, and 16 weeks was significantly up-regulated (t=4.61, 6.64, 3.52; t=3.29, 5.07, 7.22; t=3.66, 4.74, 3.10; t=3.24, 5.92, 2.67, all P<0.05). Western blot analysis revealed that the protein expression levels of CTGF and Col-1 were markedly increased at all time points in the infected groups compared to the uninfected group (t=4.07, 7.39, 8.84; t=3.08, 4.21, 4.85, all P<0.05). The expression of P-Smad2/3 protein in kidney tissues of the 14-week infection group was higher than that in the uninfected group (t=3.61, P<0.05), whereas the expression of Smad7 protein was lower than that in the uninfected group (t=7.96, P<0.05). In vitro experiments showed that after the intervention of SWA and TGF-β1, the mRNA expressions of α-SMA, CTGF, Col-1, Col-4 and Smad3 in MES-13 cells were all higher than those in the non-intervention group, while the mRNA expression of Smad7 was lower than that in the non-intervention group, There were statistically significant differences in mRNA expression among the three groups (F=62.26, 112.70, 7.64, 127.20, 10.78, 6.75, all P<0.05). Immunofluorescence confirmed enhanced expression of α-SMA and Col-1 proteins in the SWA group. Conclusion Chronic Schistosoma japonicum infection induces a sustained state of renal fibrosis in mouse models. The direct activation of the TGF-β signaling pathway by SWA may play an important role in the pathogenesis of fibrosis.

Key words: Schistosoma japonicum, Chronic infection, Soluble worm antigen (SWA), Renal fibrosis, TGF-β/Smad signaling pathway