Abstract:

Objective To investigate the association of NOD-like receptor protein 3 (NLRP3) inflammasome activation with the extent of liver fibrosis in mice with Schistosoma japonicum infection. Methods Forty-eight SPF-grade female BALB/c mice at six to eight weeks of age were grouped as non-infection (n = 8), S. japonicum infection for 5, 6, 8 and 12 weeks (n = 10 in each). Each mouse in the infection group was infected with 20±3 cercariae through an abdominal transdermal patch. The liver tissues were collected for Sirius red staining to detect collagen deposition or liver fibrosis. SYBR Green quantitative PCR(qPCR) was performed to detect the relative mRNA expression of NOD-like receptor protein 3 (NLRP3), apoptosis associated speck-like protein containing a CARD domain (ASC), pro-caspase-1, pro-IL-1β and pro-IL-18. Immunohistochemical staining (IHC) and H-score were used to evaluate the protein levels of caspase-1 active fragment p10 and IL-1β. Results Sirius red staining revealed that in the S. japonicum infection group the collagen deposition area was the largest at 8 weeks post infection (29.66±1.07)%, followed by 6 weeks (21.69±1.24)%, 12 weeks (11.98±0.95)%, and 5 weeks (1.76±0.34)%. Compared with the non-infection group, qPCR results showed that at 5, 6, 8 and 12 weeks after infection, the relative mRNA expression of NLPR3 was 8.12±0.66 (P<0.01), 24.13±2.81 (P<0.01), 14.86±0.35 (P<0.01), and 6.74±0.67 (P<0.01), respectively; the relative mRNA expression of ASC was 0.82±0.14, 7.12±0.90, 3.08±0.87, and 4.13±0.93 (P<0.01); the relative mRNA expression of pro-caspase-1 was 1.14±0.72, 2.53±0.46 (P<0.05), 3.16±0.80 (P<0.01), and 2.19±0.87; and the relative mRNA expression of pro-IL-1β was 9.95±1.04, 117.76±10.01 (P<0.01), 36.98±11.73 (P<0.01), and 7.74±2.27. No significant changes were found for pro-IL-18 (2.42±0.36, 1.85±0.11, 1.74±0.10, and 1.69±0.15, respectively). The IHC H-scores of caspase-1 p10 at 5, 6, 8, and 12 weeks after infection were 2.80±0.12, 2.10±0.06, 8.57±1.00 (P<0.01), and 4.55±0.50 (P<0.01), while those of IL-1β were 0.13±0.13, 0.20±0.00, 3.30±0.59 (P<0.01), and 1.80±0.43, respectively. Conclusion S. japonicum infection for 8 weeks shows the most serious liver fibrosis. NLRP3 inflammasomes were significantly activated at weeks 6 and 8 post infection. NLRP3 inflammasome activation in the liver is positively correlated with the extent of hepatic fibrosis in infected mice.

Key words: Schistosoma japonicum, NOD-like receptor protein 3 inflammasome, Liver fibrosis