Effects of Trichinella spiralis and its excretory/secretory products on autophagy of host muscle cells in vivo and in vitro

Potential role of host autophagy in Clonorchis sinensis infection

An in vivo mouse model of Clonorchis sinensis (C. sinensis) infection with or without the administration of autophagy inhibitor chloroquine (CQ) stimulation was established to assess the possible involvement of autophagic response during C. sinensis infection. Abnormal liver function was observed at 4, 6, and 8 weeks post-infection, as indicated by elevated levels of ALT/GPT, AST/GOT, TBIL, and α-SMA in the infected groups. These findings indicated that C. sinensis infection activated autophagy, as shown by a decreased LC3II/I ratio and accumulated P62 expression in infected mice. Interestingly, CQ administration exhibited dual and opposing effects during the infection. In the early stage of infection, the engagement of CQ appeared to mitigate symptoms by reducing inflammation and fibrotic responses. However, in the later stage of infection, CQ might contribute to parasite survival by evading autophagic targeting, thereby exacerbating hepatic impairment and worsening liver fibrosis. Autophagy in liver was suppressed throughout the infection. These observations attested that C. sinensis infection triggered autophagy, and highlighted a complex role for CQ, with both protective and detrimental effects, in the in vivo process of C. sinensis infection.

Plancitoxin-1 mediates extracellular trap evasion by the parasitic helminth Trichinella spiralis

BACKGROUND

Trichinella spiralis (T. spiralis) is a parasitic helminth that causes a globally prevalent neglected zoonotic disease, and worms at different developmental stages (muscle larvae, adult worms, newborn larvae) induce immune attack at different infection sites, causing serious harm to host health. Several innate immune cells release extracellular traps (ETs) to entrap and kill most pathogens that invade the body. In response, some unicellular pathogens have evolved a strategy to escape capture by ETs through the secretion of nucleases, but few related studies have investigated multicellular helminths.

RESULTS

In the present study, we observed that ETs from neutrophils capture adult worms of T. spiralis, while ETs from macrophages trap muscle larvae and newborn larvae, and ETs had a killing effect on parasites in vitro. To defend against this immune attack, T. spiralis secretes plancitoxin-1, a DNase II-like protein, to degrade ETs and escape capture, which is essential for the survival of T. spiralis in the host.

CONCLUSIONS

In summary, these findings demonstrate that T. spiralis escapes ET-mediated capture by secreting deoxyribonuclease as a potential conserved immune evasion mechanism, and plancitoxin-1 could be used as a potential vaccine candidate.

Trichinella spiralis inhibits myoblast differentiation by targeting SQSTM1/p62 with a secreted E3 ubiquitin ligase

Trichinella spiralis infection is associated with the formation of cysts within host skeletal muscle cells, thereby enabling immune evasion and subsequent growth and development; however, the pathogenic factors involved in this process and their mechanisms remain elusive. Here, we found that Ts-RNF secreted by T. spiralis is required for its growth and development in host cells. Further study revealed that Ts-RNF functions as an E3 ubiquitin ligase that targets the UBA domain of SQSTM1/p62 by forming K63-type ubiquitin chains. This modification interferes with autophagic flux, leading to impaired mitochondrial clearance and abnormal myotube differentiation and fusion. Our results established that T. spiralis increases its escape by interfering with host autophagy via the secretion of an E3 ubiquitin ligase.

Effects of Trichinella spiralis and its serine protease inhibitors on autophagy of host small intestinal cells

In eukaryotes, autophagy is induced as an innate defense mechanism against pathogenic microorganisms by self-degradation. Although trichinellosis is a foodborne zoonotic disease, there are few reports on the interplay between Trichinella spiralissurvival strategies and autophagy-mediated host defense. Therefore, this study focused on the association between T. spiralis and autophagy of host small intestinal cells. In this study, the autophagy-related indexes of host small intestinal cells after T. spiralis infection were detected using transmission electron microscopy, hematoxylin and eosin staining, immunohistochemistry, quantitative real-time polymerase chain reaction, and Western blotting. The results showed that autophagosomes and autolysosomes were formed in small intestinal cells, intestinal villi appeared edema, epithelial compactness was decreased, microtubule-associated protein 1A/1B-light chain 3B (LC3B) was expressed in lamina propria stromal cells of small intestine, and the expression of autophagy-related genes and proteins was changed significantly, indicating that T. spiralis induced autophagy of host small intestinal cells. Then, the effect of T. spiralis on autophagy-related pathways was explored by Western blotting. The results showed that the expression of autophagy-related pathway proteins was changed, indicating that T. spiralis regulated autophagy by affecting autophagy-related pathways. Finally, the roles of T. spiralis serine protease inhibitors (TsSPIs), such as T. spiralis Kazal-type SPI (TsKaSPI) and T. spiralis Serpin-type SPI (TsAdSPI), were further discussed in vitro and in vivo experiments. The results revealed that TsSPIs induced autophagy by influencing autophagy-related pathways, and TsAdSPI has more advantages. Overall, our results indicated that T. spiralis induced autophagy of host small intestinal cells, and its TsSPIs play an important role in enhancing autophagy flux by affecting autophagy-related pathways. These findings lay a foundation for further exploring the pathogenesis of intestinal dysfunction of host after T. spiralis infection, and also provide some experimental and theoretical basis for the prevention and treatment of trichinellosis.

ROS-AMPK/mTOR-dependent enterocyte autophagy is involved in the regulation of Giardia infection-related tight junction protein and nitric oxide levels

Giardia duodenalis, a cosmopolitan noninvasive protozoan parasite of zoonotic concern and public health importance, infects the upper portions of the small intestine and causes one of the most common gastrointestinal diseases globally termed giardiasis, especially in situations lacking safe drinking water and adequate sanitation services. The pathogenesis of giardiasis is complex and involves multiple factors from the interaction of Giardia and intestinal epithelial cells (IECs). Autophagy is an evolutionarily conserved catabolic pathway that involves multiple pathological conditions including infection. Thus far, it remains uncertain if autophagy occurs in Giardia-infected IECs and if autophagic process is associated with the pathogenic factors of giardiasis, such as tight junction (TJ) barrier defects and nitric oxide (NO) release of IECs. Here Giardia-in vitro exposed IECs showed upregulation of a series of autophagy-related molecules, such as LC3, Beclin1, Atg7, Atg16L1, and ULK1, and downregulation of p62 protein. IEC autophagy induced by Giardia was further assessed by using autophagy flux inhibitor, chloroquine (CQ), with the ratio of LC3-II/LC3-I significantly increased and downregulated p62 significantly reversed. Inhibition of autophagy by 3-methyladenine (3-MA) rather than CQ could markedly reverse Giardia-induced downregulation of TJ proteins (claudin-1, claudin-4, occludin, and ZO-1; also known as epithelial cell markers) and NO release, implying the involvement of early-stage autophagy in TJ/NO regulation. We subsequently confirmed the role of ROS-mediated AMPK/mTOR signaling in modulating Giardia-induced autophagy, TJ protein expression, and NO release. In turn, impairment of early-stage autophagy by 3-MA and late-stage autophagy by CQ both exhibited an exacerbated effect on ROS accumulation in IECs. Collectively, we present the first attempt to link the occurrence of IEC autophagy with Giardia infection in vitro, and provides novel insights into the contribution of ROS-AMPK/mTOR-dependent autophagy to Giardia infection-related downregulation of TJ protein and NO levels.

Autophagy of hepatic stellate cell induced by Clonorchis sinensis

BACKGROUND

Clonorchis sinensis was a food-borne zoonotic parasite in the worldwide and also an important risk factor of hepatic fibrosis. Excretory/secretion products of C. sinensis (CsESPs) are involved in parasite-host interactions and contribute to the development of hepatic damage. The aim of the present study was to investigate whether CsESPs and CsTP (adult protein) could induce autophagy of hepatic stellate cells (HSCs) and further activate HSCs so as to participate in the pathogenesis of hepatic fibrosis.

METHODS AND RESULTS

The human hepatic stellate cell line LX-2 was stimulated by CsESPs and CsTP. CsESPs showed the effect on cell proliferation in methyl thiazolyl tetrazolium (MTT) assay while CsTP failed. Autophagosomes and autolysosomes were observed after the transmission mRFP-EGFP-LC3 plasmid into the LX-2 cells. CsESPs had more powerful to induce the accumulation of autophagosomes and autolysosomes to enhance autophagic flux compared with CsTP. Western-blotting analysis confirmed that the ratio of LC3-II/I in LX-2 cells was up-regulated after CsESPs treatment for 6 h, which further proved that CsESPs could induce autophagy in LX-2 cells. Meanwhile, q-PCR results showed that the mRNA levels of collagen I, collagen III and α-SMA decreased in LX-2 cells after treatment with autophagy inhibitor chloroquine, whereas they increased when combination with CsESPs.

CONCLUSIONS

These results suggested that CsESPs-induced autophagy might be involved in the activation of HSCs, and consequently participate in the pathogenesis of hepatic fibrosis caused by C. sinensis infection.