Trx4, a novel thioredoxin protein, is important for Toxoplasma gondii fitness.

BACKGROUND: To successfully replicate within the host cell, Toxoplasma gondii employs several mechanisms to overcome the host cell defenses and mitigate the harmful effects of the free radicals resulting from its own metabolic processes using effectors such as thioredoxin proteins. In this study, we characterize the location and functions of a newly identified thioredoxin in T. gondii, which was named Trx4. METHODS: We characterized the functional role of Trx4 in T. gondii Type I RH and Type II Pru strains by gene knockout and studied its subcellular localization by endogenous protein HA tagging using CRISPR-Cas9 gene editing. The enzyme-catalyzed proximity labeling technique, the TurboID system, was employed to identify the proteins in proximity to Trx4. RESULTS: Trx4 was identified as a dense granule protein of T. gondii predominantly expressed in the parasitophorous vacuole (PV) and was partially co-localized with GRA1 and GRA5. Functional analysis showed that deletion of trx4 markedly influenced the parasite lytic cycle, resulting in impaired host cell invasion capacity in both RH and Pru strains. Mutation of Trx domains in Trx4 in RH strain revealed that two Trx domains were important for the parasite invasion. By utilizing the TurboID system to biotinylate proteins in proximity to Trx4, we identified a substantial number of proteins, some of which are novel, and others are previously characterized, predominantly distributed in the dense granules. In addition, we uncovered three novel proteins co-localized with Trx4. Intriguingly, deletion of trx4 did not affect the localization of these three proteins. Finally, a virulence assay demonstrated that knockout of trx4 resulted in a significant attenuation of virulence and a significant reduction in brain cyst loads in mice. CONCLUSIONS: Trx4 plays an important role in T. gondii invasion and virulence in Type I RH strain and Type II Pru strain. Combining the TurboID system with CRISPR-Cas9 technique revealed many PV-localized proximity proteins associated with Trx4. These findings suggest a versatile role of Trx4 in mediating the processes that occur in this distinctive intracellular membrane-bound vacuolar compartment.

2023: A year of accomplishments for the 13 Science Citation Index Expanded- and Emerging Sources Citation Index-indexed Baishideng journals.

In 2023, Baishideng Publishing Group (Baishideng) routinely published 47 open-access journals, including 46 English-language journals and 1 Chinese-language journal. Our successes were accomplished through the collective dedicated efforts of Baishideng staffs, Editorial Board Members, and Peer Reviewers. Among these 47 Baishideng journals, 7 are included in the Science Citation Index Expanded (SCIE) and 6 in the Emerging Sources Citation Index (ESCI). With the support of Baishideng authors, company staffs, Editorial Board Members, and Peer Reviewers, the publication work of 2023 is about to be successfully completed. This editorial summarizes the 2023 activities and accomplishments of the 13 SCIE- and ESCI-indexed Baishideng journals, outlines the Baishideng publishing policy changes and additions made this year, and highlights the unique advantages of Baishideng journals.

The transcription factor AP2XI-2 is a key negative regulator of Toxoplasma gondii merogony.

Sexual development in Toxoplasma gondii is a multistep process that culminates in the production of oocysts, constituting approximately 50% of human infections. However, the molecular mechanisms governing sexual commitment in this parasite remain poorly understood. Here, we demonstrate that the transcription factors AP2XI-2 and AP2XII-1 act as negative regulators, suppressing merozoite-primed pre-sexual commitment during asexual development. Depletion of AP2XI-2 in type II Pru strain induces merogony and production of mature merozoites in an alkaline medium but not in a neutral medium. In contrast, AP2XII-1-depleted Pru strain undergoes several rounds of merogony and produces merozoites in a neutral medium, with more pronounced effects observed under alkaline conditions. Additionally, we identified two additional AP2XI-2-interacting proteins involved in repressing merozoite programming. These findings underscore the intricate regulation of pre-sexual commitment by a network of factors and suggest that AP2XI-2 or AP2XII-1-depleted Pru parasites can serve as a model for studying merogony in vitro.

A newly characterized dense granule protein (GRA76) is important for the growth and virulence of Toxoplasma gondii.

Pathogenicity of the zoonotic pathogen Toxoplasma gondii largely depends on the secretion of effector proteins into the extracellular milieu and host cell cytosol, including the dense granule proteins (GRAs). The protein-encoding gene TGME49_299780 was previously identified as a contributor to parasite fitness. However, its involvement in parasite growth, virulence and infectivity in vitro and in vivo remains unknown. Here, we comprehensively examined the role of this new protein, termed GRA76, in parasite pathogenicity. Subcellular localization revealed high expression of GRA76 in tachyzoites inside the parasitophorous vacuole (PV). However, its expression was significantly decreased in bradyzoites. A CRISPR-Cas9 approach was used to knock out the gra76 gene in the T. gondii type I RH strain and type II Pru strain. The in vitro plaque assays and intracellular replication showed the involvement of GRA76 in replication of RH and Pru strains. Deletion of the gra76 gene significantly decreased parasite virulence, and reduced the brain cyst burden in mice. Using RNA sequencing, we detected a significant increase in the expression of bradyzoite-associated genes such as BAG1 and LDH2 in the PruΔgra76 strain compared with the wild-type Pru strain. Using an in vitro bradyzoite differentiation assay, we showed that loss of GRA76 significantly increased the propensity for parasites to form bradyzoites. Immunization with PruΔgra76 conferred partial protection against acute and chronic infection in mice. These findings show the important role of GRA76 in the pathogenesis of T. gondii and highlight the potential of PruΔgra76 as a candidate for a live-attenuated vaccine.

The Toxoplasma protein phosphatase 6 catalytic subunit (TgPP6C) is essential for cell cycle progression and virulence.

Protein phosphatases are post-translational regulators of Toxoplasma gondii proliferation, tachyzoite-bradyzoite differentiation and pathogenesis. Here, we identify the putative protein phosphatase 6 (TgPP6) subunits of T. gondii and elucidate their role in the parasite lytic cycle. The putative catalytic subunit TgPP6C and regulatory subunit TgPP6R likely form a complex whereas the predicted structural subunit TgPP6S, with low homology to the human PP6 structural subunit, does not coassemble with TgPP6C and TgPP6R. Functional studies showed that TgPP6C and TgPP6R are essential for parasite growth and replication. The ablation of TgPP6C significantly reduced the synchronous division of the parasite's daughter cells during endodyogeny, resulting in disordered rosettes. Moreover, the six conserved motifs of TgPP6C were required for efficient endodyogeny. Phosphoproteomic analysis revealed that ablation of TgPP6C predominately altered the phosphorylation status of proteins involved in the regulation of the parasite cell cycle. Deletion of TgPP6C significantly attenuated the parasite virulence in mice. Immunization of mice with TgPP6C-deficient type I RH strain induced protective immunity against challenge with a lethal dose of RH or PYS tachyzoites and Pru cysts. Taken together, the results show that TgPP6C contributes to the cell division, replication and pathogenicity in T. gondii.

Role of SNAP25 on the occurrence and development of eosinophilic gastritis.

Eosinophilic gastritis is characterized by gastrointestinal symptoms accompanied by peripheral eosinophilia. This study aims to explore the association between eosinophilic gastritis and Synaptosome Associated Protein 25 (SNAP25), and provide a new direction for the diagnosis and treatment of eosinophilic gastritis. GSE54043 was downloaded from the gene expression omnibus database. Differentially expressed genes (DEGs) were screened. The functions of common DEGs were annotated by Database for Annotation, Visualization and Integrated Discovery and Metascape. The protein-protein interaction network of common DEGs was obtained by Search Tool for the Retrieval of Interacting Genes and visualized by Cytoscape. Significant modules were identified from the protein-protein interaction network. A total of 186 patients with eosinophilic gastritis were recruited. The clinical data were recorded and the expression levels of CPE, SST, PCSK2, SNAP25, and SYT4 were detected. Pearson chi-square test and Spearman correlation coefficient were used to analyze the relationship between eosinophilic gastritis and related parameters. Univariate and multivariate Logistic regression were used for further analysis. 353 DEGs were presented. The top 10 genes screened by cytoHubb were shown, and Veen diagram figured out 5 mutual genes. Pearson's chi-square test showed that SNAP25 (P < .001) was significantly associated with eosinophilic gastritis. Spearman correlation coefficient showed a significant correlation between eosinophilic gastritis and SNAP25 (ρ = -0.569, P < .001). Univariate logistic regression analysis showed that SNAP25 (OR = 0.046, 95% CI: 0.018-0.116, P < .001) was significantly associated with eosinophilic gastritis. Multivariate logistic regression analysis showed that SNAP25 (OR = 0.024, 95% CI: 0.007-0.075, P < .001) was significantly associated with eosinophilic gastritis. The low expression of SNAP25 gene in eosinophilic gastritis is associated with a higher risk of eosinophilic gastritis.

The antioxidant protein glutaredoxin 1 is essential for oxidative stress response and pathogenicity of Toxoplasma gondii.

Glutaredoxins (Grxs) are ubiquitous antioxidant proteins involved in many molecular processes to protect cells against oxidative damage. Here, we study the roles of Grxs in the pathogenicity of Toxoplasma gondii. We show that Grxs are localized in the mitochondria (Grx1), cytoplasm (Grx2), and apicoplast (Grx3, Grx4), while Grx5 had an undetectable level of expression. We generated Δgrx1-5 mutants of T. gondii type I RH and type II Pru strains using CRISPR-Cas9 system. No significant differences in the infectivity were detected between four Δgrx (grx2-grx5) strains and their respective wild-type (WT) strains in vitro or in vivo. Additionally, no differences were detected in the production of reactive oxygen species, total antioxidant capacity, superoxide dismutase activity, and sensitivity to external oxidative stimuli. Interestingly, RHΔgrx1 or PruΔgrx1 exhibited significant differences in all the investigated aspects compared to the other grx2-grx5 mutant and WT strains. Transcriptome analysis suggests that deletion of grx1 altered the expression of genes involved in transport and metabolic pathways, signal transduction, translation, and obsolete oxidation-reduction process. The data support the conclusion that grx1 supports T. gondii resistance to oxidative killing and is essential for the parasite growth in cultured cells and pathogenicity in mice and that the active site CGFS motif was necessary for Grx1 activity.

Functional Characterization of 15 Novel Dense Granule Proteins in Toxoplasma gondii Using the CRISPR-Cas9 System.

The analysis of the subcellular localization and function of dense granule proteins (GRAs) is of central importance for the understanding of host-parasite interaction and pathogenesis of Toxoplasma gondii infection. Here, we identified 15 novel GRAs and used C-terminal endogenous gene tagging to determine their localization at the intravacuolar network (IVN), parasitophorous vacuole (PV), or PV membrane (PVM) in the tachyzoites and at the periphery of the bradyzoites-containing cysts. The functions of the 15 gra genes were examined in type I RH strain and 5 of these gra genes were also evaluated in the cyst-forming type II Pru strain. The 15 novel gra genes were successfully disrupted by using CRISPR-Cas9 mediated homologous recombination and the results showed that 13 gra genes were not individually essential for T. gondii replication in vitro or virulence in mice during acute and chronic infection. Intriguingly, deletion of TGME49_266410 and TGME49_315910 in both RH and Pru strains decreased the parasite replication in vitro and attenuated its virulence, and also reduced the cyst-forming ability of the Pru strain in mice during chronic infection. Comparison of the transcriptomic profiles of the 15 gra genes suggests that they may play roles in other life cycle stages and genotypes of T. gondii. Taken together, our findings improve the understanding of T. gondii pathogenesis and demonstrate the involvement of two novel GRAs, TGME49_266410 and TGME49_315910, in the parasite replication and virulence. IMPORTANCE Dense granule proteins (GRAs) play important roles in Toxoplasma gondii pathogenicity. However, the functions of many putative GRAs have not been elucidated. Here, we found that 15 novel GRAs are secreted into intravacuolar network (IVN), parasitophorous vacuole (PV), or PV membrane (PVM) in tachyzoites and are located at the periphery of the bradyzoite-containing cysts. TGME49_266410 and TGME49_315910 were crucial to the growth of RH and Pru strains in vitro. Deletion of TGME49_266410 and TGME49_315910 attenuated the parasite virulence in mice. However, disruption of other 13 gra genes did not have a significant impact on the proliferation and pathogenicity of T. gondii in vitro or in vivo. The marked effects of the two novel GRAs (TGME49_266410 and TGME49_315910) on the in vitro growth and virulence of T. gondii are notable and warrant further elucidation of the temporal and spatial dynamics of translocation of these two novel GRAs and how do they interfere with host cell functions.

Effect of deleting four Toxoplasma gondii calcium-binding EGF domain-containing proteins on parasite replication and virulence.

Several calcium-binding proteins including calcium-dependent protein kinases play important roles in several facets of the intracellular infection cycle of the apicomplexan protozoan parasite Toxoplasma gondii. However, the role of the calcium-binding epidermal growth factor (EGF) domain-containing proteins (CBDPs) remains poorly understood. In this study, we examined the functions of four CBDP genes in T. gondii RH strain of type I by generating knock-out strains using CRISPR-Cas9 system. We investigated the ability of mutant strains deficient in CBDP1, CBDP2, CBDP3, or CBDP4 to form plaques, replicate intracellularly, and egress from the host cells. The results showed that no definite differences between any of these four CBDP mutant strains and the wild-type strain in terms of their ability to form plaques, intracellular replication, and egress. Additionally, CBDP mutants did not exhibit any significant attenuated virulence compared to the wild-type strain in mice. The expression profiles of CBDP2-4 genes were conserved among T. gondii strains of different genotypes, life cycle stages, and developmental forms. Whether other CBDP genes play any roles in the pathogenicity of T. gondii strains of different genotypes remains to be elucidated.

The protein phosphatase 2A holoenzyme is a key regulator of starch metabolism and bradyzoite differentiation in Toxoplasma gondii.

Phenotypic switching between tachyzoite and bradyzoite is the fundamental mechanism underpinning the pathogenicity and adaptability of the protozoan parasite Toxoplasma gondii. Although accumulation of cytoplasmic starch granules is a hallmark of the quiescent bradyzoite stage, the regulatory factors and mechanisms contributing to amylopectin storage in bradyzoites are incompletely known. Here, we show that T. gondii protein phosphatase 2A (PP2A) holoenzyme is composed of a catalytic subunit PP2A-C, a scaffold subunit PP2A-A and a regulatory subunit PP2A-B. Disruption of any of these subunits increased starch accumulation and blocked the tachyzoite-to-bradyzoite differentiation. PP2A contributes to the regulation of amylopectin metabolism via dephosphorylation of calcium-dependent protein kinase 2 at S679. Phosphoproteomics identified several putative PP2A holoenzyme substrates that are involved in bradyzoite differentiation. Our findings provide novel insight into the role of PP2A as a key regulator of starch metabolism and bradyzoite differentiation in T. gondii.

Integrity of the editing and publishing process is the basis for improving an academic journal's Impact Factor.

BACKGROUND: Journal Impact Factor™ (JIF) is often used to evaluate the relative reputation and quality of academic journals in their respective fields, and can greatly influence the quality and scope of subsequent manuscript submissions. Therefore, many if not all academic journals are interested in increasing their JIF, to improve their academic impact. AIM: To determine the importance of the integrity of the editorial and publication process in improving the academic influence of academic journals and the JIF of academic journals. METHODS: In this paper, we describe our statistical analysis of bibliometric factors - including the 2021 JIFs released in the Journal Citation Report™ 2022, discipline rankings, received and published articles in 2019-2021, and webpage visits and downloads - for seven journals published by Baishideng Publishing Group (Baishideng) and indexed in Science Citation Index Expanded™; ultimately, we introduce and discuss the editing and publishing processes of Baishideng's journals in their entirety, as they form the basis for our objective of safeguarding and bolstering integrity in academic publication. RESULTS: For the seven journals assessed, their 2021 JIFs were basically unchanged from 2020, with the current metric ranging from 5.374 for World Journal of Gastroenterology (WJG) to 1.534 for World Journal of Clinical Cases (WJCC). Further assessments of the journals' bibliometrics from 2019 to 2020, showed that World Journal of Stem Cells has the highest self-citation rate (1.43%) and World Journal of Gastrointestinal Surgery has the lowest (0.21%). Additionally, the total 3012 articles published during this period were cited by more than 20000 articles in approximately 8000 academic journals. Of note, the 1102 articles published in WJG were cited by articles in 3059 journals, among which 171 journals have a JIF of > 10, including internationally renowned academic journals such as CA-A Cancer Journal for Clinicians (2021 JIF 286.130, record count: 1), Lancet (2021 JIF 202.731, record count: 4), Nature Reviews Immunology (2021 JIF 108.555, record count: 2), Nature Reviews Gastroenterology & Hepatology (2021 JIF 73.082, record count: 9), Lancet Gastroenterology & Hepatology (2021 JIF 45.042, record count: 8), Gastroenterology (2021 JIF 33.883, record count: 19), and Gut (2021 JIF 31.793, record count: 21). This suggests that Baishideng's journals have been widely recognized for their academic quality. In the Reference Citation Analysis (RCA) database, all seven Baishideng-published journals obtained a 2022 Journal Article Influence Index (JAII). For example, WJG has a 2022 JAII of 22.048, ranking 18th out of 102 journals in the field of gastroenterology & hepatology in the RCA, with 469909 total citations (6/102) and 21313 total articles (5/102). The numbers of manuscripts received and published in 2021 were both higher than those in 2019-2020. For example, WJCC received a total of 3650 manuscripts in 2021, which is 91.1% higher than those in 2019-2020 (average: 1910 papers/year). In 2021, WJCC published 1296 articles, representing an increase of 105.1% compared to those in 2019-2020 (average: 632 articles/year). The numbers of webpage visits and downloads received by the seven journals have increased year by year. For example, the number of total visits received by WJG in 2019-2021 was 1974052 in 2019, 2317835 in 2020 (increased by 17.4% compared with that in 2019), and 2652555 in 2021 (increased by 4.4% compared with that in 2020). The visitors were from more than 220 countries and regions worldwide, such as the United States, China, and the United Kingdom. Open access (OA) plays a vital role in improving the quality, efficiency, transparency, and integrity of academic journal publishing. From 2019 to 2021, a total of 5543 OA articles were published in the seven journals, of which 2083 (37.6%) were invited and published free-of-charge. During the same period, 1683 articles were published in WJG, and the authors were from more than 70 countries and regions. For the total 5543 articles published in the seven journals from 2019 to 2021, 3903 article quality tracking reports were received after the online publication of these articles. The quality of the articles was further evaluated through the Baishideng's article quality and author evaluation tracking system, with 4655 articles (84.0%) having received author evaluation and feedback, which contributes to tracking metrics for authors' satisfaction with the collective publication processes. From March 25, 2021 to June 28, 2022, the seven journals received a total of 424 reader evaluations and 229 letters from readers; this subsequent reader engagement demonstrates that the popularity of the published articles and the volume of their readership audience were improved through the reader evaluation system. CONCLUSION: Ultimately, the findings from our bibliometric assessments indicate that establishing, promoting and actively practicing processes that safeguard and bolster the integrity of the editing and publication process also help to improve the academic influence of academic journals, which itself is the cornerstone for improving JIF.

Baishideng's Reference Citation Analysis database announces the first Article Influence Index of multidisciplinary scholars.

After three rounds of rigorous evaluation of registered scholars conducted by the Reference Citation Analysis (RCA) editorial team of Baishideng Publishing Group (Baishideng), the RCA database of Baishideng officially released the 2022 Article Influence Index (2022 AII) of 632 scholars from 74 countries/territories in 98 research categories, for the first time. The list of 632 scholars can be found at: https://www.referencecitationanalysis.com/searchscholar. Among them, the highest 2022 AII is 348.211, the highest number of total citations is 42830, and the highest number of total articles is 901. The category with the largest number of RCA scholars is Gastroenterology & Hepatology, with a total of 100 (15.8%), and the second is Surgery, with a total of 46 (7.3%). This article summarizes the RCA scholars and describes the mission of RCA, the openness and transparency of RCA evaluation, the calculation method for the 2022 AII, and the evaluation process of RCA scholars. The RCA scholar list will effectively serve as a useful Find-a-Scholar tool. Any interested scholar is welcome to register and join this RCA scholar list.

Baishideng's Reference Citation Analysis database announces the first Journal Article Influence Index of 104 core journals and a list of high-quality academic journals in orthopedics.

After three rounds of rigorous evaluation of core journals in orthopedics conducted by the Reference Citation Analysis (RCA) editorial team of Baishideng Publishing Group (Baishideng), the RCA database of Baishideng officially released the 2022 Journal Article Influence Index (2022 JAII) of 104 core journals and a list of high-quality academic journals in orthopedics, for the first time on August 9, 2022. The list of 104 core journals can be found at: https://www.referencecitationanalysis.com/SearchJournal. Among them, the highest 2022 JAII is 55.015 and the lowest is 3.076. This article introduces the 21 high-quality academic journals and describes the calculation method for the 2022 JAII, the evaluation process, and the inclusion principles for journals in the RCA. These steps are the underpinning of the RCA's empirical journal academic evaluation service by which the digital platform addresses the needs of authors to select reliable journals for submission, readers to select high-quality literature for reading, and editors to track their own journal citation performance. As such, the RCA core journal list will serve as a useful Find-a-Journal tool. Any interested party is welcome to use this journal list and recommend it to their peers.

Baishideng's Reference Citation Analysis database announces the first Journal Article Influence Index of 101 core journals and a list of high-quality academic journals in gastroenterology and hepatology.

After three rounds of rigorous evaluation of core journals in gastroenterology and hepatology conducted by the Reference Citation Analysis (RCA) editorial team of Baishideng Publishing Group (Baishideng), the RCA database of Baishideng officially released the 2022 Journal Article Influence Index (2022 JAII) of 101 core journals in gastroenterology and hepatology, for the first time. The list of 101 core journals can be found at: https://www.referencecitationanalysis.com/SearchJournal. Among them, the highest 2022 JAII is 48.014 and the lowest is 3.900. This article highlights the top 20 journals, describes the calculation method for the 2022 JAII, the evaluation process, and the inclusion principles for journals in the RCA. These steps are the underpinning of the RCA's empirical journal academic evaluation service by which the digital platform addresses the needs of authors to select reliable journals for submission, readers to select high-quality literature for reading, and editors to track their own journal citation performance. As such, the RCA core journal list will serve as a useful Find-a-Journal tool. Any interested party is welcome to use this journal list and recommend it to their peers.

New Year's greeting and overview of World Journal of Orthopedics in 2021.

On behalf of the Editorial Office of World Journal of Orthopedics (WJO), we extend our sincere gratitude to our authors, subscribers, readers, Editorial Board members, and peer reviewers, thanking each and every one for their contributions to WJO in 2020 and with wishes for a Happy New Year. It was the support of all our Editorial Board members and peer reviewers that allowed the Baishideng Publishing Group Inc to successfully carry out the complete peer review, editing and publishing processes for WJO in 2020. We have analyzed the data of WJO's manuscript submissions and article publications in 2020, the invited manuscripts for 2021, manuscript peer review, composition of Editorial Board, and citation of WJO's articles, and present the findings here. We expect to be even more productive and to further raise the academic rank of WJO in 2021.

Meeting report of the chief editorial board meeting for World Journal of Diabetes 2021.

The 2021 online editorial board meeting of the World Journal of Diabetes (WJD) was held on November 9, 2021. Jin-Lei Wang, General Manager on behalf of the Baishideng Publishing Group, and Professor Islam, one of the Editors-in-Chiefs (EiCs) of the WJD, organized the meeting. Three EiCs and 18 Baishideng Publishing Group staff attended the meeting. The meeting goal was to brief the EiCs on the journal's performance, discuss the issues of concern of the EiCs, and gather ideas for the journal's development in 2022. As of November 8, the WJD had received 287 manuscripts since the year's start, among which 122 met the criteria for publication. These numbers represent an increase of 117.4% for submissions and 110.3% for publications compared to those in 2020. However, how to effectively control the academic quality of manuscripts and attract high-quality original article submissions remain a challenge. The EiCs provided feedback and suggestions centered on three topics: (1) Who should and how to control the academic quality of the manuscripts; (2) How the EiCs perform their responsibilities; and (3) The distinctive and shared responsibilities of the publisher and the EiCs.

Functional Characterization of 17 Protein Serine/Threonine Phosphatases in Toxoplasma gondii Using CRISPR-Cas9 System.

Protein serine/threonine phosphatases (PSPs), found in various plants and protozoa, are involved in the regulation of various biological processes. However, very little is known about the role of PSPs in the pathogenicity of the apicomplexan protozoan Toxoplasma gondii. Herein, the subcellular localization of 17 PSPs (PP5, PP7, EFPP, SLP, PPM3F, PPM4, PPM5A, PPM5B, PPM6, PPM8, PPM9, PPM12, PPM14, PPM18, CTD1, CTD2, and CTD3) was examined by 6× HA tagging of endogenous genes in C-terminal. The PSPs were detected in the cytoplasm (PP5, EFPP, PPM8, and CTD2), dense granules (SLP), nucleus (PPM4 and PPM9), inner membrane complex (PPM12), basal complex (CTD3), and apical pole (PP7). The remaining PSPs exhibited low or undetectable level of expression. To characterize the contribution of these genes to the infectivity of T. gondii, knock-out (KO) strains of type I RH strain deficient in the 17 psp genes and KO type II Pru strain deficient in pp7 and slp genes were constructed. The pathogenicity of individual RHΔpsp mutants was characterized in vitro using plaque, egress, and intracellular replication assays, and mouse infection, while pathogenicity of PruΔpp7 and PruΔslp mutant strains was evaluated by examining the parasite lytic cycle in vitro and assessment of brain cyst burden in mice. No significant differences were observed between 16 RHΔpsp strains and wild-type (WT) RH strain. However, RHΔpp7 exhibited significantly lower invasion efficiency and parasitophorous vacuole formation in vitro, and less virulence in mice compared with other RHΔpsp and WT strains. In addition, PruΔpp7 exhibited marked attenuation of virulence and significant reduction in the brain cyst burden in mice compared with PruΔslp and WT strains, suggesting the key role of PP7 in the virulence of T. gondii. Comparative transcriptomic profiling of the 17 psp genes showed that they may play different roles in the pathogenesis of different genotypes or life cycle stages of T. gondii. These findings provide new insight into the role of PSPs in the pathogenesis of T. gondii.

Effect of deletion of gra17 and gra23 genes on the growth, virulence, and immunogenicity of type II Toxoplasma gondii.

The protozoan parasite Toxoplasma gondii secretes a number of dense granule proteins (GRAs) from the dense granule organelle to manipulate the host cell. Two of these effector proteins (GRA17 and GRA23) are involved in the trafficking of molecules between the parasitophorous vacuole (PV) and the host cell cytoplasm. However, their roles in establishing chronic infection remain obscured. In this study, CRISPR-Cas9 was used to delete gra17 or gra23 gene in T. gondii Pru strain (type II). The growth, the virulence, the ability to establish chronic infection, and the immunogenicity of the constructed mutant strains were investigated in Kunming mice. Pru:Δgra17 and Pru:Δgra23 mutants developed PVs with abnormal morphology and exhibited reduced growth rate, compared with the wild-type Pru strain. Deletion of gra17 abrogated acute infection and blocked cyst formation. Although the deletion of gra23 caused slight attenuation of the parasite virulence in mice, it caused a significant reduction in cyst formation. Immunization with Pru:Δgra17 induced high levels of IgG (IgG1 and IgG2a) antibodies and cytokines (interleukin-2 [IL-2], IL-10, IL-12, and interferon gamma [IFN-γ]), which conferred significant protection in mice challenged with virulent type I (RH), ToxoDB#9 (PYS) strains, or less virulent type II (Pru) strain of T. gondii. These findings show that GRA17 and GRA23 play important roles in T. gondii chronic infection and that irreversible deletion of gra17 in T. gondii type II Pru strain can be a viable option for stimulating protective immunity to T. gondii infection.

Immunostimulatory efficacy and protective potential of putative TgERK7 protein in mice experimentally infected by Toxoplasma gondii.

The extracellular signal-regulated kinases (ERKs) serve as important determinants of cellular signal transduction pathways, and hence may play important roles during infections. Previous work suggested that putative ERK7 of Toxoplasma gondii is required for efficient intracellular replication of the parasite. However, the antigenic and immunostimulatory properties of TgERK7 protein remain unknown. The objective of this study was to produce a recombinant TgERK7 protein in vitro and to evaluate its effect on the induction of humoral and T cell-mediated immune responses against T. gondii infection in BALB/c mice. Immunization using TgERK7 mixed with Freund's adjuvants significantly increased the ratio of CD3e+CD4+ T/CD3e+CD8a+ T lymphocytes in spleen and elevated serum cytokines (IFN-γ, IL-2, IL-4, IL-10, IL-12p70, IL-23, MCP-1, and TNF-α) in immunized mice compared to control mice. On the contrary, immunization did not induce high levels of serum IgG antibodies. Five predicted peptides of TgERK7 were synthesized and conjugated with KLH and used to analyze the antibody specificity in the sera of immunized mice. We detected a progressive increase in the antibody level only against TgERK7 peptide A (DEVDKHVLRKYD). Antibody raised against this peptide significantly decreased intracellular proliferation of T. gondii in vitro, suggesting that peptide A can potentially induce a protective antibody response. We also showed that immunization improved the survival rate of mice challenged with a virulent strain and significantly reduced the parasite cyst burden within the brains of chronically infected mice. Our data show that TgERK7-based immunization induced TgERK7 peptide A-specific immune responses that can impart protective immunity against T. gondii infection. The therapeutic potential of targeting ERK7 signaling pathway for future toxoplasmosis treatment is warranted.

iTRAQ-based Quantitative Proteomics Analysis Identifies Host Pathways Modulated during Toxoplasma gondii Infection in Swine.

Toxoplasma gondii is a leading cause of foodborne illness and consumption of undercooked pig meat is a major risk factor for acquiring toxoplasmosis, which causes a substantial burden on society. Here, we used isobaric tags for relative and absolute quantification (iTRAQ) labelling coupled with liquid chromatography-tandem mass spectrometry (LC-MS/MS) to identify cellular proteins and pathways altered during T. gondii infection in pigs. We also used parallel reaction monitoring-based LC-MS/MS to verify the levels of protein expression of infected spleens and mesenteric lymph nodes (MLNs). At 6 days post-infection (dpi), 156, 391, 170, 292, and 200 differentially expressed proteins (DEPs) were detected in the brain, liver, lung, MLNs and spleen, respectively. At 18 dpi, 339, 351, 483, 388, and 303 DEPs were detected in the brain, liver, lung, MLNs and spleen, respectively. Although proteins involved in immune responses were upregulated in all infected tissues, protein expression signature in infected livers was dominated by downregulation of the metabolic processes. By weighted gene co-expression network analysis, we could further show that all proteins were clustered into 25 co-expression modules and that the pink module significantly correlated with the infection status. We also identified 163 potential anti-T. gondii proteins (PATPs) and provided evidence that two PATPs (HSP70.2 and PDIA3) can reduce T. gondii burden in porcine macrophages in vitro. This comprehensive proteomics analysis reveals new facets in the pathogenesis of T. gondii infection and identifies key proteins that may contribute to the pig's defense against this infection.