Abstract
Schistosomiasis japonica is a serious tropical parasitic disease in humans, which causes inflammation and fibrosis of the liver. Hepatic stellate cells (HSCs) are known to play an important role in schistosome-induced fibrosis, but their role in schistosome-induced inflammation is still largely unknown. Here, we use a murine model of schistosomiasis japonica to investigate the role that nuclear factor kappa B (NF-κB), a critical mediator of inflammatory responses, plays in schistosome-induced inflammation. We revealed that NF-κB was significantly activated in HSCs at the early stage of infection, but not at later stages. We also show that the expression levels of several chemokines regulated by NF-κB signaling (Ccl2, Ccl3 and Ccl5) were similarly elevated at early infection. TLR4 signaling, one of the strongest known inducers of NF-κB activation, seemed not activated in HSCs post-infection. Importantly, we found that levels of miR-146 (a known negative regulator of NF-κB signaling) in HSCs opposed those of NF-κB signaling, elevating at later stage of infection. These results indicate that HSCs might play an important role in the progression of hepatic schistosomiasis japonica by linking liver inflammation to fibrosis via NF-κB signaling. Moreover, our work suggests that miR-146 appeared to regulate this process. These findings are significant and imply that manipulating the function of HSCs by targeting either NF-κB signaling or miR-146 expression may provide a novel method of treating hepatic schistosomiasis japonica.
Highlights
Schistosomiasis is a serious, yet neglected, tropical parasitic disease that affects more than 200 million people worldwide [1]
We report that Hepatic stellate cells (HSCs) appear to play an important role in linking the process of hepatic granulomatous to hepatic fibrosis via nuclear factor kappa B (NF-kB) signaling, with miR-146 potentially modulating this process by targeting TRAF6, a key adapter molecules in the TLR4/NF-kB pathway
The results of liver section staining showed that eggs began to lodge in the liver with only minimal cellular infiltration on day 32 post-infection, while by 6 weeks postinfection, eggs were surrounded by a dense population of immune cells, leading to the formation of a mature granuloma with mild extracellular matrix (ECM) deposition (Fig. 1A)
Summary
Schistosomiasis is a serious, yet neglected, tropical parasitic disease that affects more than 200 million people worldwide [1]. Studies have shown that the activation of hepatic stellate cells (HSCs) is central to the development of liver fibrosis from other means (including via viral infection, autoimmune deficiencies, and dietary or chemical causes) [2]. Quiescent HSCs store vitamin A in normal liver tissue, but are activated to become proliferative, contractile, and fibrogenic myofibroblasts during liver fibrosis [2,3]. Accumulating evidence from both murine and human schistosomiasis reveals that HSCs function in the granulomatous, fibrotic process induced by schistosome eggs [3,7]. It is intriguing that a recent study showed that Schistosoma japonicum (S. japonicum) eggs induced a pro-inflammatory but anti-fibrogenic phenotype in a human HSC cell line (LX-2) [8]
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