Trichinella: Differential expression of angiogenic factors in macrophages stimulated with antigens from encapsulated and non-encapsulated species

Effect of somatic antigens of Dirofilaria repens adult worms on angiogenesis, cell proliferation and migration and pseudo-capillary formation in human endothelial cells

BACKGROUND

Angiogenesis is defined as the formation of new vessels by sprouting of endothelial cells from pre-existing vessels in response to stimuli, such as hypoxia or inflammation. Subcutaneous dirofilariasis, caused by Dirofilaria repens, is a zoonotic disease characterized by the formation of subcutaneous nodules with the presence of at least one encapsulated worm, showing perivascular vascularization around it. The aim of this study is to analyze whether the somatic antigen of adult D. repens worms interacts with and modulates the angiogenic mechanism, cell proliferation and migration, and formation of pseudo-capillaries.

METHODS

The expression of VEGF-A, VEGFR-1/sFlt, VEGFR-2, mEnd and sEnd in cultures of human vascular endothelial cells stimulated with somatic antigen of adult worms of D. repens (DrSA), vascular endothelial growth factor (VEGF) and DrSA + VEGF were evaluated by using ELISA commercial kits. Cellular viability was analyzed by live cell count, cytotoxicity assays by using a commercial kit, cell proliferation by MTT-based assay, cell migration by wound-healing assay carried out by scratching wounds and capacity of formation of pseudo-capillaries analyzing cell connections and cell groups in Matrigel cell cultures. In all cases unstimulated cultures were used as controls.

RESULTS

DrSA + VEGF significantly increased the expression of VEGF-A, VEGFR-2 and mEndoglin compared to other groups and unstimulated cultures. Moreover, DrSA + VEGF produced cell proliferation and migration and increased the formation of pseudo-capillaries.

CONCLUSIONS

Somatic antigen of adult D. repens worms activated the proangiogenic mechanism, cell proliferation and cell migration as well as formation of pseudo-capillaries in this in vitro human endothelial cell model. These processes could be related to the survival of adult D. repens in subcutaneous nodules in infected hosts.

Niosomal versus nano-crystalline ivermectin against different stages of Trichinella spiralis infection in mice

Ivermectin (IVM) is one of the competitive treatments used for trichinellosis. However, several studies linked its efficacy with early diagnosis and administration to tackle the intestinal phase with limited activity being recorded against encysted larvae. The aim of this study was to employ niosomes for enhancing effectiveness of oral IVM against different stages of Trichinella spiralis (T. spiralis) infection with reference to nano-crystalline IVM. Mice were randomized into four groups: group Ι, 15 uninfected controls; group ΙΙ, 30 infected untreated controls; group ΙΙΙ, 30 infected nano-crystalline IVM treated, and group ΙV, 30 infected niosomal IVM treated. All groups were equally subdivided into 3 subgroups; (a) treated on the 1^st day post infection (dpi), (b) treated on the 10^th dpi, and (c) treated on the 30^th dpi. Assessment was done by counting adult worms and larvae plus histopathological examination of jejunum and diaphragm. Biochemical assessment of oxidant/antioxidant status, angiogenic, and inflammatory biomarkers in intestinal and muscle tissues was also performed. Both niosomes and nano-crystals resulted in significant reduction in adult and larval counts compared to the infected untreated control with superior activity of niosomal IVM. The superiority of niosomes was expressed further by reduction of inflammation in both jejunal and muscle homogenates. Biochemical parameters showed highly significant differences in all treated mice compared to infected untreated control at different stages with highly significant effect of niosomal IVM. In conclusion, niosomal IVM efficacy exceeded the nano-crystalline IVM in treatment of different phases of trichinellosis.

Identification of a host collagen inducing factor from the excretory secretory proteins of Trichinella spiralis

Background

In a previous study, we found that Trichinella spiralis muscle larva excretory and secretory proteins (ES-P) most likely activate collagen synthesis via TGF-β/Smad signaling, and this event could influence collagen capsule formation.

Methodology/Principal findings

In order to identify the specific collagen inducing factor, ES-P was fractionated by a Superdex 200 10/300 GL column. We obtained three large fractions, F1, F2, and F3, but only F3 had collagen gene inducing ability. After immunoscreening, 10 collagen inducing factor candidates were identified. Among them, TS 15–1 and TS 15–2 were identical to the putative trypsin of T. spiralis. The deduced TS 15–1 (M.W. = 72 kDa) had two conserved catalytic motifs, an N-terminal Tryp_SPc domain (TS 15-1n) and a C-terminal Tryp_SPc domain (TS 15-1c). To determine their collagen inducing ability, recombinant proteins (rTS 15-1n and rTS 15-1c) were produced using the pET-28a expression system. TS 15–1 is highly expressed during the muscle larval stage and has strong antigenicity. We determined that rTS 15-1c could elevate collagen I via activation of the TGF-β1 signaling pathway in vitro and in vivo.

Conclusion/Significance

In conclusion, we identified a host collagen inducing factor from T. spiralis ES-P using immunoscreening and demonstrated its molecular characteristics and functions.

Trichinella spiralis can make collagen capsules in host muscle cells during its life cycle, which encapsulates muscle stage larvae. Many investigators have tried to reveal the complex mechanism behind this collagen capsule architecture, and it has been suggested that several serine proteases in excretory-secretory proteins of the parasite are potential collagen capsule inducing factors. In addition, collagen synthesis is activated through the TGF-β/Smad signaling pathway and these events are closely related with protease activated receptor 2 which was activated by various serine proteases. In this study, we isolated and characterized a collagen gene expression inducer from T. spiralis ES-P using immunoscreening and investigated the candidate protein for its usefulness as a wound healing therapeutic agent.

The roles of supernatant of macrophage treated by excretory-secretory products from muscle larvae of Trichinella spiralis on the differentiation of C2C12 myoblasts

The excretory-secretory products (ESPs) released by the muscle-larvae (ML) stage of Trichinella spiralis have been suggested to be involved in nurse cell formation. However, the molecular mechanisms by which ML-ESPs modulate nurse cell formation remain unclear. Macrophages exert either beneficial or deleterious effects on tissue repair, depending on their activation/polarization state. They are crucial for skeletal muscle repair, notably, via their actions on myogenic precursor cells. However, these interactions during T. spiralis infection have not been characterized. In the present study, the ability of conditioned medium (CM) from J774A.1 macrophages treated with ML-ESPs to influence the differentiation of murine myoblasts, and the mechanisms of this influence, were investigated in vitro. The results showed that the expression of Myogenic Regulatory Factors (MRFs) MyoD and myogenin, myosin heavy chain (MyHC), and the p21 cyclin-dependent kinase inhibitor were reduced in CM treated cells compared to their expression in the control group. These findings indicated that CM inhibited myoblast differentiation. Conversely, CM promoted myoblast proliferation and increased cyclin D1 levels. Taken together, results of our study suggested that CM can indirectly influence myoblast differentiation and proliferation, which provides a new method for the elucidation of the complex mechanisms involved in cell-parasite and cell-cell interactions during T. spiralis infection.

Evaluation of the role of angiogenic factors in the pathogenesis of schistosomiasis

Schistosomiasis is one disease produced by helminths, which affect many people in tropical areas. Granuloma formation is the main mechanism involved in the pathogenesis of this disease. Experimental studies have demonstrated angiogenesis (blood vessels formation from pre-existing vessels) in the initial phase of granuloma formation. In the present work, VEGF (vascular endothelial growth factor) levels were analyzed in sera from people diagnosed with different helminthic infections. Patients with schistosomiasis and filariasis had significantly high VEGF levels in compared with healthy people and patients diagnosed with hookworms. In addition, the effects of angiogenesis inhibition using anti-angiogenic factors (endostatin) were evaluated in a schistosomiasis murine model. A lesion decrease was observed in mice infected with Schistosoma mansoni and treated with endostatin. Finally, mechanisms of angiogenesis induction were studied and observed that cercariae antigens stimulated the angiogenic factors by host alveolar macrophages.

Angiogenesis and parasitic helminth-associated neovascularization

Successful metazoan parasitism, among many other factors, requires a supply of nutrients and the removal of waste products. There is a prerequisite for a parasite-defined vasculature. The angiogenic mechanism(s) involved presumably depend on the characteristics of the tissue- and vascular system-dwelling, parasitic helminths. Simplistically, 2 possibilities or a combination of both have been considered in this review. The multifactorial induction of parasitic helminth-associated neovascularization could arise through, either a host-, a parasite- or a host-/parasite-dependent, angiogenic switch. Most studies appear to support the first and third hypotheses, but evidence exists for the intrahepatic cestodeEchinococcus multilocularis, the free-living nematodeCaenorhabditis elegansand the intravascular trematodeSchistosoma mansonifor the second inference. In contrast, the nematode anti-coagulant protein NAPc2 from adultAncylostoma caninumis also an anti-angiogenic factor.

Role of angiogenic factors in acute experimental Strongyloides venezuelensis infection

This study aims to investigate the role of angiogenic factors in the pathogenesis of experimental strongyloidiasis. Two complementary approaches were used: Firstly, CD1 mice were treated with endostatin, an angiogenesis inhibitor, and infected with Strongyloides venezuelensis. Also, the mechanisms involved in this process were studied. Parasitological examination revealed a significant decrease in egg per gram of faeces, number of collected larvae from lung tissue and number of collected adult females in mice treated with endostatin. Direct mechanisms with diminution of angiogenesis factors and an indirect mechanism with increase of eosinophil perhaps produced their effect. Secondly, the effect of the antigens responsible for stimulation of angiogenic factors [vascular endothelial growth factor (VEGF) and fibroblast growth factor 2 (FGF2)] from alveolar macrophages and the mechanisms involved in their production were investigated. Alveolar macrophage cells obtained by bronchoalveolar lavage were incubated at different concentrations of somatic and excretory/secretory antigens of S. venezuelensis. Also, mRNA levels of VEGF and FGF2 in macrophage cells were detected by RT-PCR. L3-PBS larvae antigens induced angiogenic factors. The relationship between angiogenesis factors and nitric oxide has been observed using nitric oxide synthase inhibitors.