Activation of RIG-I signaling in the early stage of Paragonimus proliferus infection causes lung injury via type I immune response in rat

Paragonimiasis is a common zoonotic parasitic disease. The retinoic acid-inducible gene I (RIG-I) signaling is very important for the host to recognize invading pathogens (especially viruses and bacteria). However, the role of RIG-I signaling in the early stages of P. proliferus infection remains unclear. Therefore, in this study, Sprague-Dawley (SD) rat models with lung damage caused by P. proliferus were established. Experimental methods including Enzyme-linked Immuno Sorbent Assay (ELISA), real-time fluorescent quantitative polymerase chain reaction (PCR), western blotting, and hematoxylin and eosin (HE) staining were used to explore the mechanisms of lung injury caused by P. proliferus. As a result, the expression of the mRNA and proteins of RIG-I signal-related key target molecules, including RIG-I, tumor necrosis factor (TNF) receptor associated factor 6 (TRAF6), interferon regulatory Factor 7 (IRF7), IPS-1, and downstream C-X-C chemokine ligand 10 (CXCL10), were significantly up-regulated immediately after infection, peaked at 3 or 7 days, and showed a downward trend on after 14 days. The levels of pro-inflammatory cytokines interleukin-1 (IL-1), interferon (IFN)-α, -β, and -γ, which represent type 1 immune response, gradually increased and reached a peak by 14 days, which was consistent with the changes in the degree of inflammatory damage observed under HE staining of lung tissues. In conclusion, RIG-I signaling is activated in the early stage (before 14 days) of P. proliferus infection, it is inferred that the lung injury of the host may be related to the activation of RIG-I like signaling to induce type I immune response.

Differences in microbiome of healthy Sprague Dawley rats with Paragonimus proliferus infection and potential pathogenic role of microbes in paragonimiasis

Paragonimiasis, which is caused by Paragonimus, is considered to be a neglected tropical disease by the World Health Organization. The pathogenicity of Paragonimus mainly manifests as mechanical damage and immunotoxicity caused by adult worms and larvae. However, microbiota associated with Paragonimus and potential disturbance of host microbiota after infection are unknown. Paragonimus proliferus is a rare species, and its successful infection rate in experimental rats is 100%. In the current study, we compared the microbial community in lung tissues, small intestine contents, and fecal samples from Sprague Dawley (SD) rats with and without P. proliferus infection. To determine the impact of P. proliferus on the microbial community in rats, we identified the microbiota in adult worms of P. proliferus via high-throughput sequencing. Results showed dramatic differences in the composition of microbiota in lung tissues between infected and uninfected rats. Paragonimus metacercariae introduced both environmental and gut microbes into the lung tissues of rats. Many potentially pathogenic microbes were also found in the lung of infected rats. Paragonimus infection increased the chances of potentially pathogenic microbiota invading and colonizing the lungs. However, for the purpose of long-term parasitism, there might be a complex interrelationship between Paragonimus and microorganisms. Our study might shed lights on the understanding of the pathogenicity of Paragonimus.

Dynamic transcriptome landscape of pulmonary tissues of rats infected with Paragonimus proliferus

Paragonimiasis (pulmonary fluke disease) is a foodborne parasitic disease caused by trematode infections. Paragonimus proliferus is a characteristic Paragonimus species that was first identified in Yunnan Province of China. No direct evidence has yet proven that P. proliferus can infect humans. However, we previously found that P. proliferus infects and damages rat lung tissues via an unclear mechanism. Here, we infected Sprague Dawley rats with P. proliferus and sequenced their lung transcriptomes at various intervals thereafter. We detected P. proliferus on the surface of rat lung tissues at 7 days post infection. It colonized by attaching and secreting dsRNA and utilized nutrients from the lung tissues for mitosis and meiosis and the dynein arm of lung tissues to develop symmetrical organs. The rats generated different types of immune responses that differed according to the stage of infection. We then analyzed P. proliferus responses to these immune strategies and the genes expressed during each stage of infection. Our findings provide a foundation for developing medical treatments for P. proliferus infection.

Dynamic transcriptome landscape of Paragonimus proliferus developmental stages in the rat lungs

Paragonimus proliferus, a lung fluke of the genus Paragonimus, was first reported in Yunnan province, China. P. proliferus can infect Sprague-Dawley (SD) rats and cause lung damage, but there is still no direct evidence of human infection. Until now, there has been a lack of studies on P. proliferus parasitism and development in mammalian lung tissue. The aim of this study was to perform transcriptomic profiling of P. proliferus at different developmental stages. SD rats were infected with P. proliferus metacercariae obtained from crabs; worms isolated from the lungs at different time points as well as metacercariae were subjected to whole transcriptome sequencing. Overall, 34,403 transcripts with the total length of 33,223,828 bp, average length of 965 bp, and N50 of 1833 bp were assembled. Comparative analysis indicated that P. proliferus, similar to other Paragonimus spp., expressed genes related to catabolism, whereas P. proliferus-specific transcripts were related to the maintenance of cellular redox homeostasis, sensitivity to bacteria, and immune response. Transcriptional dynamics analysis revealed that genes involved in the regulation of catabolism and apoptosis had stable expression over the P. proliferus life cycle, whereas those involved in development and immune response showed time-dependent changes. High expression of genes associated with immune response corresponded to that of genes regulating the sensitivity to bacteria and immune protection. We constructed a P. proliferus developmental model, including the development of the body, suckers, blood cells, reproductive and tracheal systems, lymph, skin, cartilage, and other tissues and organs, and an immune response model, which mainly involved T cells and macrophages. Our study provides a foundation for further research into the molecular biology and infection mechanism of P. proliferus.

Differentially Expressed Homologous Genes Reveal Interspecies Differences of Paragonimus Proliferus based on Transcriptome Analysis

Paragonimus proliferus (P. proliferus), one of 46 Paragonimus species registered in the National Center for Biotechnology Information database, may be much more widely distributed in Southeast Asia than previously thought, as its reported natural foci have increased in the past decades. However, very little is known about its molecular biology, especially at the transcriptome level. For the first time, the transcriptome of this species was sequenced and compared with four other common Paragonimus species, namely Paragonimus skrjabini, Paragonimus kellicotti, Paragonimus miyazakii, and Paragonimus westermani, to predict homologous genes and differentially expressed homologous genes to explore interspecies differences of Paragonimus proliferus. A total of 7393 genes were found to be significantly differentially expressed. Of these, 49 were considered to be core genes because they were differentially expressed in all four comparison groups. Annotations revealed that these genes were related mainly to "duplication, transcription, or translation", energy or nutrient metabolism, and parasitic growth, proliferation, motility, invasion, adaptation to the host, or virulence. Interestingly, a majority (5601/7393) of the identified genes, and in particular the core genes (48/49), were expressed at lower levels in P. proliferus. The identified genes may play essential roles in the biological differences between Paragonimus species. This work provides fundamental background information for further research into the molecular biology of P. proliferus.