Molecular characterization of SjBIRP, another apoptosis inhibitor, from Schistosoma japonicum

Molecular and Functional Characterization of Inhibitor of Apoptosis Proteins (IAP, BIRP) in Echinococcus granulosus

The larval stage of Echinococcus granulosus sensu lato, resulting in cystic echinococcosis, a parasitic zoonosis, causes huge economic losses to the livestock industry and poses a threat to public health. Inhibitor of apoptosis proteins (IAPs) is a class of endogenous anti-apoptotic family, which plays a significant functional role in the regulation of organism’s development. Herein, to explore potential functions of IAPs in E. granulosus, two members of IAPs from E. granulosus (Eg-IAP and Eg-BIRP) were cloned, expressed, and molecularly characterized. Eg-IAP and Eg-BIRP encoded putative 331 and 168 residue proteins, respectively. Bioinformatic analysis showed that both proteins contained a type II BIR domain-the essential functional domain of IAPs. Fluorescence immunohistochemistry revealed that both proteins were ubiquitously localized in all life-cycle stages of E. granulosus. Our fluorescent quantitative PCR (RT-qPCR) results revealed relatively higher transcription levels of two Eg-IAPs in protoscoleces (PSCs) compared to the 18-day strobilated worms. We further used different concentrations of LCL161, a Smac-mimetic pan-IAPs inhibitor, to induce the apoptosis in PSCs in vitro, and revealed that the survival rate of PSCs and transcription levels of both genes were negatively correlated with the concentration of LCL161. While the results of light microscopy, transmission electron microscopy (TEM), and terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay also showed a higher apoptotic rate in PSCs with the increasing concentrations of LCL161. Taken together, our findings provide the reasonable evidence that both Eg-IAP and Eg-BIRP have potential implication in critical anti-apoptotic roles during the development of E. granulosus.

Schistosoma japonicum IAP and Teg20 safeguard tegumental integrity by inhibiting cellular apoptosis

Schistosomes are causative agents of human schistosomiasis, which is endemic in tropical and subtropical areas of the world. Adult schistosomes can survive in their final hosts for several decades, and they have evolved various strategies to overcome the host immune response. Consequently, understanding the mechanisms that regulate parasitic cell survival will open avenues for developing novel strategies against schistosomiasis. Our previous study suggested that an inhibitor of apoptosis protein in Schistosoma japonicum (SjIAP) may play important roles in parasitic survival and development. Here, we demonstrated that SjIAP can negatively regulate cellular apoptosis in S. japonicum by suppressing caspase activity. Immunohistochemistry analysis indicated that SjIAP ubiquitously expressed within the worm body including the tegument. Silencing of SjIAP expression via small interfering RNA led to destruction of the tegument integrity in schistosomes. We further used co-immunoprecipitation to identify interaction partners of SjIAP and revealed the tegument protein SjTeg-20 as a putative interacting partner of SjIAP. The interaction between SjIAP and SjTeg-20 was confirmed by a yeast two-hybrid (Y2H) assay. Moreover, results of a TUNEL assay, RNA interference, scanning and transmission electron microscopy, caspase assays, transcript profiling, and protein localization of both interacting molecules provided first evidence for an essential role of SjIAP and SjTeg-20 to maintain the structural integrity of the tegument by negatively regulating apoptosis. Taken together, our findings suggest that the cooperative activities of SjIAP and SjTeg-20 belong to the strategic inventory of S. japonicum ensuring survival in the hostile environment within the vasculature of the final host.

Schistosomiasis is a worldwide public health concern particularly in developing countries. The causative agents, schistosomes, can survive within the vascular system of their final hosts for several decades despite facing the host’s immune response. Therefore, elucidating the mechanism of cell survival will contribute to the understanding of host-parasite interaction and may lead to the identification of suitable targets for developing novel strategies against schistosomiasis. Inhibitor of apoptosis proteins are highly conserved proteins functioning as endogenous inhibitors of apoptotic cell death. Here, we demonstrated that an inhibitor of apoptosis protein of Schistosoma japonicum (SjIAP) governs the integrity of the tegument of schistosomes by inhibiting cellular apoptosis of the parasite. Further studies revealed that SjTeg-20, an S. japonicum tegumental protein, cooperates with SjIAP to inhibit apoptosis in schistosomes. Our findings provide new insights into the role of SjIAP and SjTeg-20 in maintaining the integrity of the worm tegument by negatively regulating apoptosis.

Protease Inhibitors of Parasitic Flukes: Emerging Roles in Parasite Survival and Immune Defence

Protease inhibitors play crucial roles in parasite development and survival, counteracting the potentially damaging immune responses of their vertebrate hosts. However, limited information is currently available on protease inhibitors from schistosomes and food-borne trematodes. Future characterization of these molecules is important not only to expand knowledge on parasitic fluke biology but also to determine whether they represent novel vaccine and/or drug targets. Moreover, protease inhibitors from flukes may represent lead compounds for the development of a new range of therapeutic agents against inflammatory disorders and cancer. This review discusses already identified protease inhibitors of fluke origin, emphasizing their biological function and their possible future development as new intervention targets.

AST IV inhibits H₂O₂-induced human umbilical vein endothelial cell apoptosis by suppressing Nox4 expression through the TGF-β1/Smad2 pathway

Endothelial cell apoptosis plays an important role in the pathophysiological mechanisms of vascular complications in diabetes mellitus (DM). NADPH oxidase 4 (Nox4)-dependent reactive oxygen species (ROS) aggregation is the main cause of vascular endothelial cell apoptosis. The transforming growth factor-β1 (TGF-β1)/Smad2 signaling pathway is involved in the apoptosis of several types of cells. However, the association between vascular endothelial cell apoptosis and Nox4, and the involvement of the TGF-β1/Smad2 signaling pathway in vascular endothelial cell apoptosis remain unclear. In the present study, we aimed to investigate the role of Nox4-dependent ROS production and to determine the involvement of the TGF-β1/Smad2 signaling pathway in endothelial cell apoptosis induced by oxidative stress which causes vascular injury in DM. We demonstrated that hydrogen peroxide (H2O2) increased Nox4-dependent-ROS aggregation, as well as the expression of TGF-β1, Smad2, Bax and caspase-3, decreased Bcl-2 expression and increased the apoptosis of human umbilical vein endothelial cells (HUVECs). Treatment with diphenyliodonium (DPI), a specific inhibitor of Nox4 or astragaloside IV (AST IV), a monomer located in an extract of astragaloside, decreased Nox4 expression and the levels of ROS, decreased TGF-β1 and Smad2 expression, altered the expression of apoptosis-related genes and decreased the apoptosis of HUVECs. Treatment with LY2109761, a selective inhibitor of the TGF-β1/Smad2 pathway, produced results similar to those of DPI; however, LY2109761 had no effect on Nox4 expression and ROS levels. Taken together, the findings of the present study suggest that H2O2 contributes to HUVEC apoptosis by inducing Nox4-dependent ROS aggregation and activating the TGF-β1/Smad2 signaling pathway. Our data indicate that the protective effects of AST IV against vascular endothelial cell apoptosis in DM are mainly associated with the decrease in Nox4 expression through the TGF-β1/Smad2 signaling pathway. Furthermore, the inhibition of the activation of the TGF-β1/Smad2 signaling pathway may be another potential therapeutic strategy in the treatment of DM.