Cloning of a cDNA encoding a surface antigen of Schistosoma mansoni schistosomula recognized by sera of vaccinated mice

Triad of TDP43 control in neurodegeneration: autoregulation, localization and aggregation

Cytoplasmic aggregation of TAR DNA-binding protein 43 (TDP43; also known as TARDBP or TDP-43) is a key pathological feature of several neurodegenerative diseases, including amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). TDP43 typically resides in the nucleus but can shuttle between the nucleus and the cytoplasm to exert its multiple functions, which include regulation of the splicing, trafficking and stabilization of RNA. Cytoplasmic mislocalization and nuclear loss of TDP43 have both been associated with ALS and FTD, suggesting that calibrated levels and correct localization of TDP43 - achieved through an autoregulatory loop and tightly controlled nucleocytoplasmic transport - safeguard its normal function. Furthermore, TDP43 can undergo phase transitions, including its dispersion into liquid droplets and its accumulation into irreversible cytoplasmic aggregates. Thus, autoregulation, nucleocytoplasmic transport and phase transition are all part of an intrinsic control system regulating the physiological levels and localization of TDP43, and together are essential for the cellular homeostasis that is affected in neurodegenerative disease.

TDP-43 aggregation induced by oxidative stress causes global mitochondrial imbalance in ALS

Amyotrophic lateral sclerosis (ALS) was initially thought to be associated with oxidative stress when it was first linked to mutant superoxide dismutase 1 (SOD1). The subsequent discovery of ALS-linked genes functioning in RNA processing and proteostasis raised the question of how different biological pathways converge to cause the disease. Both familial and sporadic ALS are characterized by the aggregation of the essential DNA- and RNA-binding protein TDP-43, suggesting a central role in ALS etiology. Here we report that TDP-43 aggregation in neuronal cells of mouse and human origin causes sensitivity to oxidative stress. Aggregated TDP-43 sequesters specific microRNAs (miRNAs) and proteins, leading to increased levels of some proteins while functionally depleting others. Many of those functionally perturbed gene products are nuclear-genome-encoded mitochondrial proteins, and their dysregulation causes a global mitochondrial imbalance that augments oxidative stress. We propose that this stress-aggregation cycle may underlie ALS onset and progression.

Optogenetic modulation of TDP-43 oligomerization accelerates ALS-related pathologies in the spinal motor neurons

Cytoplasmic aggregation of TDP-43 characterizes degenerating neurons in most cases of amyotrophic lateral sclerosis (ALS). Here, we develop an optogenetic TDP-43 variant (opTDP-43), whose multimerization status can be modulated in vivo through external light illumination. Using the translucent zebrafish neuromuscular system, we demonstrate that short-term light stimulation reversibly induces cytoplasmic opTDP-43 mislocalization, but not aggregation, in the spinal motor neuron, leading to an axon outgrowth defect associated with myofiber denervation. In contrast, opTDP-43 forms pathological aggregates in the cytoplasm after longer-term illumination and seeds non-optogenetic TDP-43 aggregation. Furthermore, we find that an ALS-linked mutation in the intrinsically disordered region (IDR) exacerbates the light-dependent opTDP-43 toxicity on locomotor behavior. Together, our results propose that IDR-mediated TDP-43 oligomerization triggers both acute and long-term pathologies of motor neurons, which may be relevant to the pathogenesis and progression of ALS.

Optogenetic approaches for inducing TDP-43 aggregation have been described previously in cellular models. Here the authors develop an approach to optogenetically induce TDP-43 aggregation in vivo using zebrafish to model ALS pathologies.

Immunofluorescent Localization of Proteins in Schistosoma mansoni

Immunofluorescence allows the detection, visualization, and localization of proteins by using the ability of antibodies to firmly bind to specific antigens. Proteins must be accessible to thorough interaction with the specific antibodies. Different immune evasion mechanisms of parasites are directed to hamper or prevent access of antibodies to critical proteins or virulence factors. The blood fluke Schistosoma mansoni would not survive a day in the host blood capillaries if antibodies were able to readily bind to proteins located at the surface and mediate its attrition and demise by the complement system and/or the FcγR- or FcαR-bearing leukocytes. The worm surface is the area of parasite-host interaction and the route to critical nutrients, but is selectively permeable, allowing access of nutrient molecules but not host antibodies. Gentle procedures, which, however, are not commonly in use in vivo, are required to increase the permeability of the parasite outer membrane shield to just allow access of specific antibodies and identify and localize the proteins at the apical surface. Robust methods involving acetone, methanol, and Triton X-100 treatment lead to disintegration of the dual lipid bilayer cover with exposure of the proteins located in the tegument beneath. Internal proteins may not be accessed except following cryostat or paraffin sectioning. Accordingly, vaccine-induced specific antibodies to the apical surface or tegument proteins are unable to harm intact parasites. Specific antibodies to surface membrane proteins may only add to the action of administered or endo schistosomicides via acceleration of killing and interference with repair of severely and lightly impacted parasites, respectively. Therefore, careful immunofluorescent localization of S. mansoni proteins is important for devising the different control strategies against infection.

Why the radiation-attenuated cercarial immunization studies failed to guide the road for an effective schistosomiasis vaccine: A review

Schistosomiasis is a debilitating parasitic disease caused by platyhelminthes of the genus Schistosoma, notably Schistosoma mansoni, Schistosoma haematobium, and Schistosoma japonicum. Pioneer researchers used radiation-attenuated (RA) schistosome larvae to immunize laboratory rodent and non-human primate hosts. Significant and reproducible reduction in challenge worm burden varying from 30% to 90% was achieved, providing a sound proof that vaccination against this infection is feasible. Extensive histopathological, tissue mincing and incubation, autoradiographic tracking, parasitological, and immunological studies led to defining conditions and settings for achieving optimal protection and delineating the resistance underlying mechanisms. The present review aims to summarize these findings and draw the lessons that should have guided the development of an effective schistosomiasis vaccine.

Radiation-attenuated schistosome vaccination – a brief historical perspective

The high level of protection which can be induced by vaccination of a range of hosts, from rodents to primates, with live radiation-attenuated schistosome larvae offers great promise for development of a human schistosome vaccine. Studies of the irradiated vaccine models benefitted from significant funding during the 1970–90s and much was learned concerning the inducers, targets and mechanisms of immunity. Less progress was made in definition of the protective antigens involved. The application of new techniques for identifying membrane and secreted antigens has recently provided new vaccine candidates and a new impetus for schistosome vaccine development. This article is intended as an overview of some of the main lessons learned from the studies of the irradiated vaccines as a backdrop to renewed interest in schistosome vaccine development.

Proteome approach for identification of schistosomiasis japonica vaccine candidate antigen

Experimental vaccination with radiation-attenuated cercariae (RAC) confers possible practical levels of resistance to challenge infection by humoral and by cellular mechanism. Here, we aimed to identify possible vaccine antigens by using specific IgG antibody from RAC vaccinated miniature pig. Two milligrams of soluble egg antigen (SEA) or schistosomal worm antigen preparation (SWAP) was fractionated using two dimensional liquid chromatography (proteome PF 2D) consisted of high performance chromatofocusing (HPCF) and high resolution reversed phase chromatography (HPRP). Of the 42 HPCF fractions of SEA or SWAP, 26 (61.9%) or 15 (35.7%) showed positive dot blot reaction with RAC vaccinated serum respectively. The dot blot positive fractions were applied to the second HPRP column. One hundred and seven out of 26 x 96 of SEA fractions and 18 out of 15 x 96 SWAP fractions reacted with RAC vaccinated serum. From the positive fractions we chose 17 of SEA and 10 of SWAP that had no reactivity with normal cercariae infected (NCI) sera and had single peak of 214 nm; and automated N-terminal amino acid sequence based on in situ Edman Reaction was conducted. Four sequences were obtained and applied to the homology search in NCBI database. A total of eight candidate genes were listed up and their cDNA clones from schistosomula stage were obtained. Two of the recombinant proteins (AAW27472.1 and AXX25883.1) showed strong reactivity with the RAC vaccinated serum but marginal with NCI serum. This protocol using proteome PF 2D could be applicable in identifying immunoreactive proteins from crude extract for the development of vaccines or for diagnostics.

Blueprint for schistosomiasis vaccine development

A number of different schistosome antigens are capable of partially protecting experimental animals from challenge infection. More than 100 such antigens have been identified, about 15% of which are strongly protective and deemed promising though they do not reach the level close to sterile immunity seen after vaccination with irradiated cercariae. Studies of human correlate reactions, i.e. serological reactions and cytokine responses to schistosomiasis antigens, in individuals living in areas endemic for schistosomiasis have shown associations between certain antigen-specific immune responses and lack of re-infection over time. This approach was applied in Brazil and Egypt where it was possible to epidemiologically follow cohorts of individuals in endemic areas for extended periods of time correlating infection status with immune responses against a panel of well-researched, highly purified vaccine candidates. The immune correlates found were unique to each antigen and could be either positive or negative, i.e. associated with resistance or with susceptibility to re-infection. However, few antigens were clear-cut in this respect, i.e. the majority of them induced ambiguous responses. For example, a single antigen might have a significant positive correlation when antigen-driven interferon (INF)-gamma production is measured but also show a significant negative correlation with respect to the IgG1 titre induced. These observations suggest that there are desirable, antigen-specific immune responses that would be valuable in a vaccine but they also indicate that there are responses that must be avoided. The insights gained should be useful not only for antigen selection but also for vaccine formulation prior to Phase I/II trials in humans. It would be of great value if similar independent, long-term human correlate studies could also be undertaken in areas endemic for Schistosoma japonicum.

The guanine protein coupled receptor rhodopsin is developmentally regulated in the free-living stages of Schistosoma mansoni

Schistosoma mansoni parasites inhabit three distinct environments including water, intermediate molluscan hosts, and definitive vertebrate hosts. Determining how schistosomes interact with these environments may be one mechanism by which suitable vaccines or novel chemotherapeutic targets will be identified. Towards this end, we describe the identification of a 36-kDa S. mansoni protein that shares extensive sequence similarity to light absorbing rhodopsin guanine protein coupled receptors (GPCRs). This protein, S. mansoni rhodopsin (SmRHO), is the first molecularly characterized GPCR described in schistosomes. Sequence analysis reveals that SmRHO shares extensive phylogenetic conservation among rhodopsins/opsins expressed in water-dwelling invertebrates, possibly indicative of orthology. We demonstrate here that SmRHO is expressed in the free-living, light responsive miracidia and cercaria stages and is down-regulated in the adult, vertebrate residing forms. Moreover, we show that SmRHO is localized to sub-tegumental structures found towards the anterior end of cercariae. As SmRHO may be implicated in schistosome photoreception processes, we have begun a search for additional parasite encoded GPCR super-family members, which may be associated with chemoreception, chemotaxis, and olfaction. Identifying and characterizing new GPCRs may uncover hidden aspects of parasite biology useful towards the development of novel intervention strategies.

A Schistosoma mansoni 62-kDa band is identified as an irradiated vaccine T-cell antigen and characterized as calreticulin

The Schistosoma mansoni soluble adult worm antigen (SAWA) bands of 62/60 kDa were found to contain immunodominant T-cell immunogen(s) in irradiated cercariae-immunized Swiss and C57BL/6 mice. In the present study, spleen T cells of BALB/c mice immunized twice with ultraviolet light-irradiated cercariae proliferated and produced interleukin 4 in response to the 62/60-kDa SAWA bands in T-cell western assays. To characterize the 62/60-kDa bands, an adult S. mansoni worm cDNA expression library constructed in lambdagt11 was immunoscreened with serum of mice immunized with the 62/60-kDa antigens, and the immunoreactive cDNA inserts were sequenced. Purified 62- and 60-kDa proteins were used for amino acid microsequencing and for immunization studies in Swiss, C57BL/6, and BALB/c mice and rabbits. Taken together, the data indicated that the 60-kDa molecules are poorly immunogenic in mice and rabbits, whereas the 62-kDa species identified as S. mansoni calreticulin, is a good T- and B-cell antigen and represents a potential vaccine candidate.

Genetic immunization of mice with DNA encoding the 23 kDa transmembrane surface protein of Schistosoma japonicum (Sj23) induces antigen-specific immunoglobulin G antibodies

The 23 kDa transmembrane surface protein of schistosomes is of recognized interest in studies of immune responsiveness in schistosomiasis. To examine the immunogenicity of the 23 kDa antigen of Schistosoma japonicum, Sj23, when delivered by genetic immunization, mice were immunized using a DNA construct containing the Sj23 cDNA under the control of a CMV promotor. Serological analysis of peripheral blood from immunized mice demonstrated that this construct was able to induce the production of antigen-specific IgG antibodies that recognized a schistosome antigen of 23 kDa in Western blots. Despite inducing antigen-specific antibodies, the Sj23 DNA vaccine was unable to confer protection in immunized mice subjected to challenge with S.japonicum cercariae. Appropriate engineering of the unique structure of the Sj23 kDa transmembrane protein of schistosomes may provide a novel vehicle for expressing foreign epitopes from other infectious agents or, possibly, cancer antigens, anchored to the surface of transfected cells.

Murine model of IgE production with a predominant Th2-response by feeding protein antigen without adjuvants

Stimulation of systemic antigen-specific IgE production plays an important role in the mediation of food allergy; however, the mechanism of IgE production against food antigens is not fully understood. The development of relevant animal models may help to elucidate the pathogenesis of food allergy. We here show that DBA/2 mice receiving a casein diet without any adjuvant produced high levels of IgE specific for casein, accompanied by predominant Th2-like responses in liver lymphocytes, mesenteric lymph node cells and spleen cells. This model of IgE production produced by feeding protein antigen as a constituent of the diet can be applied to investigate the mechanism of IgE production and to develop reagents for controlling food allergy.

Molecular identification of a Schistosoma mansoni tegumental protein with similarity to cytoplasmic dynein light chains

The tegument of Schistosoma mansoni contains a number of proteins that presumably function in its maintenance and/or repair against damage incurred from host-mediated humoral immune responses. Here, we show that the schistosome antigen identified by monoclonal antibody 709A2/2 is a cytoplasmic dynein light chain. Dynein light chains are components of dynein, an enzyme complex involved in various aspects of microtubule-based motility. Monoclonal antibody 709A2/2 recognizes two polypeptides, one of 8.9 kDa and a second of 7.6 kDa, as determined by SDS-polyacrylamide gel electrophoresis. We find that expression of S. mansoni dynein light chain is developmentally regulated and localized to the tegument in the schistosomula, lung stage worms, and adult worms, but is not present in the cercariae or ciliated miracidia. By Northern blot analysis of adult worm RNA, S. mansoni dynein light chain is encoded by a single message of approximately 600 base pairs. A cDNA encoding this polypeptide contains an open reading frame of 89 amino acids with a deduced molecular mass of 10.4 kDa. Coprecipitation of an apparent 18.4-kDa antigen with S. mansoni dynein light chain by monoclonal antibody 709A2/2 illustrates that this molecule has an affinity for other proteins. Such interactions may play a role in S. mansoni dynein light chain participation in organelle trafficking in S. mansoni.

Schistosome vaccines

Schistosomiasis control currently relies primarily on chemotherapy which is both expensive and temporary. There is an urgent need for an effective vaccine. Studies in animal models and man have demonstrated the existence of protective immunity. Antibody-dependent cell-mediated cytotoxicity mechanisms involving eosinophils and macrophages have been implemented in destruction of the parasites. Antigens expressed on the surface of the schistosomulum are among the targets of protective immune responses. Vaccines comprising recombinant antigens are now being tested in vivo for their capacity to evoke protective responses. Live oral vaccines based on attenuated Salmonella expressing schistosomular surface antigens are being developed.

Schistosome vaccines: current progress and future prospects

Vaccination against human schistosomes in laboratory hosts is now a reality. A number of different parasite molecules have been shown to confer partial protective immunity against challenge infection with Schistosoma mansoni or Schistosoma japonicum in rodent or primate hosts. These antigens are unusually diverse in their structure and stage specificity. Interestingly, although all of the vaccine molecules characterized are situated in the tegument, their exposure on the parasite surface, in most instances, is transient and/or non-essential. The properties of four of these immunogens, glutathione-S-transferase (P26,28), paramyosin (Sm97), GP38, and GP18 are discussed. Despite the identification and recombinant synthesis of several promising protective antigens, vaccination of humans against schistosomiasis remains in the realm of fantasy. At the technical level, a major problem is the failure of any of the current vaccine immunogens and immunization protocols to induce levels of resistance sufficient for significant reduction of human infection or disease. Once this important hurdle is passed, human immunization trials should be attempted as the potential beneficial impact of a vaccine against schistosomiasis remains enormous.