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

Trichinella spiralis (T. spiralis) is a widely distributed pathogenic microorganism that causes trichinellosis, a disease that has the potential of causing severe harm to their host. Numerous studies have demonstrated that autophagy can be triggered by microbial infection, such as bacteria, viruses, protozoa, and parasitic helminths. However, it’s still unknown whether autophagy can facilitate host resistance to T. spiralis infection. The present study examined the role of autophagy in striated muscle cell transformation following infection with T. spiralis in BALB/c mice. Transmission electron microscopy (TEM) was used to detect the production of the host diaphragm autophagosome after T. spiralis infection, and changes in the protein and transcriptional levels of autophagic marker proteins were also detected. The significance of autophagy in T. spiralis infection, namely inhibition of T. spiralis growth, was preliminarily evaluated by conducting in vivo experiments using autophagy inhibitors. Besides, we studied the effect of excretory-secretory products (ES) of T. spiralis on autophagy of C2C12 myoblasts. The changes in protein and gene expression levels in autophagy-related pathways in vitro and in vivo were measured as further evidence. The results showed that T. spiralis infection induced autophagy in the host muscle cells. Meanwhile, ES inhibited autophagy of myoblasts in vitro, but this did not affect the cell viability. The upregulation and downregulation of autophagy-related factors in skeletal muscle cells may indicate an adaptive mechanism providing a comfortable niche for the parasite.

Autophagy, a intracellular degradation system, is a kind of unique phenomenon in eukaryotic cells. The commonly referred autophagy is the process of forming autophagosomes by wrapping the cytoplasmic components with double-membrane structure, and then fusing with lysosomes to degrade the internal substances of the cell. Autophagy can be induced by various pathogens including parasites. When the body is infected with intracellular parasites, the host cell can remove the parasites by autophagy. However, parasites have also evolved defence mechanisms that use autophagy in host cells to promote growth. These can be seen in some intracellular parasitic infections such as Toxoplasma gondii and Plasmodium. Although the role of autophagy in other parasitic infections has been revealed, it remains unclear whether autophagy is involved in the invasion process by Trichinella. We investigated the role of Trichinella infection on host muscle cells autophagy and the effect of autophagosome formation on the survival of T. spiralis. Understanding the role of autophagy in the interaction between parasitic infection and host cell is of great significance for the prevention and treatment of Trichinella infection and the development of anti-parasite drugs.

Acquired Protective Immunity in Atlantic Salmon Salmo salar against the Myxozoan Kudoa thyrsites Involves Induction of MHIIβ+ CD83+ Antigen-Presenting Cells

The histozoic myxozoan parasite Kudoa thyrsites causes postmortem myoliquefaction and is responsible for economic losses to salmon aquaculture in the Pacific Northwest. Despite its importance, little is known about the host-parasite relationship, including the host response to infection. The present work sought to characterize the immune response in Atlantic salmon during infection, recovery, and reexposure to K. thyrsites After exposure to infective seawater, infected and uninfected smolts were sampled three times over 4,275 degree-days. Histological analysis revealed infection severity decreased over time in exposed fish, while in controls there was no evidence of infection. Following a secondary exposure of all fish, severity of infection in the controls was similar to that measured in exposed fish at the first sampling time but was significantly reduced in reexposed fish, suggesting the acquisition of protective immunity. Using immunohistochemistry, we detected a population of MHIIβ+ cells in infected muscle that followed a pattern of abundance concordant with parasite prevalence. Infiltration of these cells into infected myocytes preceded destruction of the plasmodium and dissemination of myxospores. Dual labeling indicated a majority of these cells were CD83+/MHIIβ+ Using reverse transcription-quantitative PCR, we detected significant induction of cellular effectors, including macrophage/dendritic cells (mhii/cd83/mcsf), B cells (igm/igt), and cytotoxic T cells (cd8/nkl), in the musculature of infected fish. These data support a role for cellular effectors such as antigen-presenting cells (monocyte/macrophage and dendritic cells) along with B and T cells in the acquired protective immune response of Atlantic salmon against K. thyrsites.

Trypanosoma cruzi: biological characterization of a isolate from an endemic area and its susceptibility to conventional drugs

We describe some biological and molecular characteristics of a Trypanosoma cruzi isolate derived from a Triatomine captured in Nicaragua. PCR based typification showed that this isolate, named Nicaragua, belonged to the lineage Tc I. Nicaragua infected culture cells were treated with allopurinol, showing different behavior according to the cellular compartment, being cardiomyocyte primary cultures more resistant to this drug. The course of the infection in a mice experimental model and its susceptibility to benznidazole and allopurinol was analyzed. In benznidazole treatment, mice reverted the high lethal effect of parasites during the acute infection, however, a few parasites were detected in the heart of 88% of mice 1 year post-infection. Since T. cruzi is a heterogeneous species population it is important to study and characterize different parasites actually circulating in humans in endemic areas. In this work we show that T. cruzi Nicaragua isolate, is sensitive to early benznidazole treatment.

Perspectives on Trypanosoma cruzi-induced heart disease (Chagas disease)

Chagas disease is caused by the parasite Trypanosoma cruzi. It is a common cause of heart disease in endemic areas of Latin America. The year 2009 marks the 100th anniversary of the discovery of T cruzi infection and Chagas disease by the Brazilian physician Carlos Chagas. Chagasic cardiomyopathy develops in from 10% to 30% of persons who are chronically infected with this parasite. Echocardiography and magnetic resonance imaging (MRI) are important modalities in the evaluation and prognostication of individuals with chagasic heart disease. The etiology of chagasic heart disease likely is multifactorial. Parasite persistence, autoimmunity, and microvascular abnormalities have been studied extensively as possible pathogenic mechanisms. Experimental studies suggest that alterations in cardiac gap junctions may be etiologic in the pathogenesis of conduction abnormalities. The diagnosis of chronic Chagas disease is made by serology. The treatment of this infection has shortcomings that need to be addressed. Cardiac transplantation and bone marrow stem cell therapy for persons with Chagas disease have received increasing research attention in recent years.

Involvement of the c-Ski oncoprotein in cell cycle arrest and transformation during nurse cell formation after Trichinella spiralis infection

The role of c-Ski, an oncoprotein encoded by the oncogene, c-ski, in Trichinella spiralis-infected muscle tissues during nurse cell formation, was investigated by following the expression kinetics and distribution of c-Ski (both protein and mRNA) in the infected muscle cell, as well as the expression kinetics of the transforming growth factor beta (TGF-beta) signaling pathway factor genes (TGF-beta, Smad2 and Smad4) which cooperate with c-Ski. Immunohistochemical analysis using an anti-c-Ski antibody indicated that in the early stages of infection (13 and 18 days post-infection (p.i.)) the increased expression of the c-Ski protein was limited to the eosinophilic cytoplasm and not the enlarged nuclei or basophilic cytoplasm. At a later stage of infection (23 and 28 days p.i.) the c-Ski protein was limited to the enlarged nuclei in the basophilic cytoplasm, rather than the eosinophilic cytoplasm. At 48 days p.i., the c-Ski protein was barely detectable. Real-time PCR analysis showed that expression of the c-ski gene increased from 13 days p.i., reached a peak at 23-28 days p.i. and then decreased to a low level by 48 days p.i. Expression kinetics for the TGF-beta signaling pathway factor genes (TGF-beta, Smad2 and Smad4) were similar to that of c-ski. These findings provide evidence that the c-Ski protein is involved in nurse cell formation through the TGF-beta signaling pathway process in the host cell nucleus.

Activation of transforming growth factor β by Trypanosoma cruzi

The anti-inflammatory cytokine, transforming growth factor beta (TGFbeta), plays an important role in Chagas disease, which is caused by the protozoan parasite Trypanosoma cruzi. In the current study, we show that the addition of an anti-TGFbeta antibody inhibited T. cruzi infection of cardiomyocytes, demonstrating the requirement for active endogenous TGFbeta. As TGFbeta is synthesized as a biologically inactive precursor, which is proteolytically processed to yield a mature, active homodimer, we hypothesized that T. cruzi could activate latent TGFbeta. To test this, we added recombinant latent TGFbeta to a TGFbeta-responsive reporter cell line in the presence of T. cruzi. We observed that T. cruzi was able to activate latent recombinant TGFbeta in this cellular model. We then investigated the ability of T. cruzi to activate latent TGFbetain vitro. We found that live T. cruzi, or cytosolic extracts of T. cruzi, activated latent TGFbeta in a dose- and temperature-dependent manner. The agent involved in TGFbeta activation was shown to be thermolabile and hydrophobic. Taken together, our studies demonstrate that T. cruzi directly activates latent TGFbeta. This activation is required for parasite entry into the mammalian cells and is likely to play an important role in modulating the outcome of T. cruzi infection.

Responses of adipose and muscle lipoprotein lipase to chronic infection and subsequent acute lipopolysaccharide challenge

Infection of male Swiss Webster mice with Toxoplasma gondii or Neospora caninum leads to long-term alterations in energy balance. Following an initial 20 to 30% weight loss in all T. gondii-infected mice, half of the animals regain most of the lost weight (gainers), whereas the others maintain their low body weight (nongainers). Infection with N. caninum does not elicit weight loss. Lipoprotein lipase (LPL), the enzyme responsible for plasma triglyceride (TG) clearance and partitioning among tissues, is under tissue-specific modulation associated with energy balance. It is also a major determinant of infection-induced hypertriglyceridemia. This study aimed to assess the long-term modulation of adipose and muscle LPL activity in mice infected with T. gondii or N. caninum, to evaluate the effects of subsequent acute lipopolysaccharide (LPS) administration, and to relate LPL modulation in these conditions with infection-related changes in body weight gain. Twenty-eight days after infection, LPL activity in muscle of both gainer and nongainer T. gondii-infected mice was reduced by 40 to 50% compared with the levels in controls and N. caninum-infected mice, whereas LPL activity in adipose depots remained unchanged in all infected groups compared to the level in controls. LPS (from Escherichia coli, 100 ng/kg) injection induced a global reduction in adipose LPL in all groups, as assessed 90 min later. In both T. gondii-infected subgroups, muscle LPL was not further reduced by LPS treatment, whereas it was decreased by 40 to 50% in muscles of control and N. caninum-infected mice. Pre-LPS TG levels in plasma were similar in all groups. LPS greatly increased TG levels in plasma in both control and N. caninum-infected animals, whereas it did not alter those of T. gondii-infected gainer or nongainer animals. These results show that (i) independently of the extent of postinfection weight gain, long-term infection with T. gondii chronically reduces muscle LPL, which becomes unresponsive to acute endotoxemia; (ii) modulation of tissue LPL activity during chronic T. gondii infection favors TG partitioning towards adipose tissue; and (iii) skeletal muscle LPL is a key determinant of the acute response of triglyceridemia to LPS.