TIMP-1 promotes hypermigration of Toxoplasma-infected primary dendritic cells via CD63-ITGB1-FAK signaling

TIMP1 secretion induced by Toxoplasma effector GRA24 via p38 MAPK signaling promotes non-disruptive parasite translocation across polarized brain endothelial monolayers

The protozoan Toxoplasma gondii first crosses the intestinal wall and then the blood-brain barrier (BBB) to establish chronic, latent infections in humans and other warm-blooded vertebrates. However, the molecular mechanisms underlying this stealthy colonization remain poorly understood. In this study, we investigated the passage of T. gondii tachyzoites across polarized monolayers of murine brain endothelial cells (bEnd.3) and human intestinal cells (Caco-2). We found that exposure to live T. gondii tachyzoites, but not to tachyzoite lysate or lipopolysaccharide, induced elevated transcription and secretion of tissue inhibitor of metalloproteinases 1 (TIMP1), a pleiotropic protein linked to BBB maintenance. Recombinant TIMP1 consistently increased T. gondii transmigration across monolayers, while pharmacological inhibition of matrix metalloproteinases (MMPs) non-significantly impacted transmigration. Through a combined approach of pharmacological inhibition and mutant T. gondii lines, we identified the MYR translocon-associated effector GRA24 and host cell p38 mitogen-activated protein kinase (MAPK) signaling as key mediators of Timp1 induction. Moreover, despite T. gondii transmigration, cell polarization and barrier integrity were preserved, suggesting a non-disruptive passage of tachyzoites with minimal or transient barrier dysregulation. These findings reveal a role for GRA24-p38 MAPK signalling and TIMP1's MMP-independent effects in facilitating the translocation of T. gondii across restrictive biological barriers.IMPORTANCEThe parasite Toxoplasma gondii, which is globally widespread, colonizes the brains of humans and other warm-blooded animals. To do so, it first crosses the gut wall before entering the brain via the bloodstream. However, the mechanisms by which Toxoplasma overcomes the body's restrictive biological barriers remain largely unknown. In this study, we used cellular models of the gut and brain barriers to investigate how the parasite passes through. We found that Toxoplasma induces cells to secrete TIMP1, a multifunctional protein that reduces inflammation and is linked to blood-brain barrier protection. Surprisingly, TIMP1 also facilitated Toxoplasma's passage across cellular barriers. This elevated TIMP1 production and secretion by host cells was triggered by a secreted Toxoplasma effector protein (GRA24) and mediated through host cell signaling pathways (p38 MAPK). These findings suggest that Toxoplasma manipulates host cells to produce factors that aid its colonization while suppressing inflammation.

Extracellular Silica Nanomatrices Promote In Vitro Maturation of Anti-tumor Dendritic Cells via Activation of Focal Adhesion Kinase

The efficacy of dendritic cell (DC)-based cancer vaccines is critically determined by the functionalities of in vitro maturated DCs. The maturation of DCs typically relies on chemicals that are cytotoxic or hinder the ability of DCs to efficiently activate the antigen-specific cytotoxic T-lymphocytes (CTLs) against tumors. Herein, the maturation chemicals are replaced with extracellular silica nanomatrices, fabricated by glancing angle deposition, to promote in vitro maturation of murine bone marrow-derived DCs (mBMDCs). The extracellular nanomatrices composed of silica nanozigzags (NZs) enable the generation of mature mBMDCs with upregulated levels of co-stimulatory molecules, C-C chemokine receptor type-7, X-C motif chemokine recetpor-1, DC-specific ICAM-3 grabbing nonintegrin, and enhanced endocytic capacity. The in vitro maturation is partially governed by focal adhesion kinase (FAK) that is mechanically activated in the curved cell adhesions formed at the DC-NZ interfaces. The NZ-maturated mBMDCs can prime the antigen-specific CTLs into programmed cell death protein-1 (PD-1)lowCD44high memory phenotypes in vitro and suppress the growth of tumors in vivo. Meanwhile, the NZ-mediated beneficial effects are also observed in human monocyte-derived DCs. This work demonstrates that the silica NZs promote the anti-tumor capacity of in vitro maturated DCs via the mechanoactivation of FAK, supporting the potential of silica NZs being a promising biomaterial for cancer immunotherapy.

The integrin adhesome and control of anti-tumour immunity

It is widely regarded that the anti-tumour immune response drives clearance of tumours and leads to prolonged survival in patients. However, tumours are adept at reprogramming the surrounding microenvironment to an immunosuppressive milieu to prevent successful immune directed killing. Adhesion of cells to the extracellular matrix is essential for regulating cellular processes such as survival, proliferation and migration. This adhesion is largely conducted via integrins and their related intracellular signalling networks. Adhesion proteins such as focal adhesion kinase (FAK) are expressed in both tumour cells and cells of the surrounding microenvironment, and are often dysregulated in cancers. Recent work has demonstrated that adhesion proteins are contributing to regulation of the immunosuppressive microenvironment within tumours, and could provide a new avenue to target in combination with immunotherapies. Here, we provide an overview of the effort being made to elucidate the roles adhesion proteins play in modulating anti-tumour responses within a variety of cancer settings. In particular we focus on the multifaceted role of FAK within the tumour immune microenvironment. Finally, we summarise the data in clinical trials, where targeting FAK is being exploited to prime the tumour microenvironment and create potent responses when combined with immunotherapies.

Hypermigration of macrophages through the concerted action of GRA effectors on NF-κB/p38 signaling and host chromatin accessibility potentiates Toxoplasma dissemination

Mononuclear phagocytes facilitate the dissemination of the obligate intracellular parasite Toxoplasma gondii. Here, we report how a set of secreted parasite effector proteins from dense granule organelles (GRA) orchestrates dendritic cell-like chemotactic and pro-inflammatory activation of parasitized macrophages. These effects enabled efficient dissemination of the type II T. gondii lineage, a highly prevalent genotype in humans. We identify novel functions for effectors GRA15 and GRA24 in promoting CCR7-mediated macrophage chemotaxis by acting on NF-κB and p38 mitogen-activated protein kinase signaling pathways, respectively, with contributions by GRA16/18 and counter-regulation by effector TEEGR. Furthermore, GRA28 boosted chromatin accessibility and GRA15/24/NF-κB-dependent transcription at the Ccr7 gene locus in primary macrophages. In vivo, adoptively transferred macrophages infected with wild-type T. gondii outcompeted macrophages infected with a GRA15/24 double mutant in migrating to secondary organs in mice. The data show that T. gondii, rather than being passively shuttled, actively promotes its dissemination by inducing a finely regulated pro-migratory state in parasitized human and murine phagocytes via co-operating polymorphic GRA effectors.

IMPORTANCE

Intracellular pathogens can hijack the cellular functions of infected host cells to their advantage, for example, for intracellular survival and dissemination. However, how microbes orchestrate the hijacking of complex cellular processes, such as host cell migration, remains poorly understood. As such, the common parasite Toxoplasma gondii actively invades the immune cells of humans and other vertebrates and modifies their migratory properties. Here, we show that the concerted action of a number of secreted effector proteins from the parasite, principally GRA15 and GRA24, acts on host cell signaling pathways to activate chemotaxis. Furthermore, the protein effector GRA28 selectively acted on chromatin accessibility in the host cell nucleus to selectively boost host gene expression. The joint activities of GRA effectors culminated in pro-migratory signaling within the infected phagocyte. We provide a molecular framework delineating how T. gondii can orchestrate a complex biological phenotype, such as the migratory activation of phagocytes to boost dissemination.

Integrating single-nucleus RNA sequencing and spatial transcriptomics to elucidate a specialized subpopulation of astrocytes, microglia and vascular cells in brains of mouse model of lipopolysaccharide-induced sepsis-associated encephalopathy

BACKGROUND

Understanding the mechanism behind sepsis-associated encephalopathy (SAE) remains a formidable task. This study endeavors to shed light on the complex cellular and molecular alterations that occur in the brains of a mouse model with SAE, ultimately unraveling the underlying mechanisms of this condition.

METHODS

We established a murine model using intraperitoneal injection of lipopolysaccharide (LPS) in wild type and Anxa1-/- mice and collected brain tissues for analysis at 0-hour, 12-hour, 24-hour, and 72-hour post-injection. Utilizing advanced techniques such as single-nucleus RNA sequencing (snRNA-seq) and Stereo-seq, we conducted a comprehensive characterization of the cellular responses and molecular patterns within the brain.

RESULTS

Our study uncovered notable temporal differences in the response to LPS challenge between Anxa1-/- (annexin A1 knockout) and wild type mice, specifically at the 12-hour and 24-hour time points following injection. We observed a significant increase in the proportion of Astro-2 and Micro-2 cells in these mice. These cells exhibited a colocalization pattern with the vascular subtype Vas-1, forming a distinct region known as V1A2M2, where Astro-2 and Micro-2 cells surrounded Vas-1. Moreover, through further analysis, we discovered significant upregulation of ligands and receptors such as Timp1-Cd63, Timp1-Itgb1, Timp1-Lrp1, as well as Ccl2-Ackr1 and Cxcl2-Ackr1 within this region. In addition, we observed a notable increase in the expression of Cd14-Itgb1, Cd14-Tlr2, and Cd14-C3ar1 in regions enriched with Micro-2 cells. Additionally, Cxcl10-Sdc4 showed broad upregulation in brain regions containing both Micro-2 and Astro-2 cells. Notably, upon LPS challenge, there was an observed increase in Anxa1 expression in the mouse brain. Furthermore, our study revealed a noteworthy increase in mortality rates following Anxa1 knockdown. However, we did not observe substantial differences in the types, numbers, or distribution of other brain cells between Anxa1-/- and wildtype mice over time. Nevertheless, when comparing the 24-hour post LPS injection time point, we observed a significant decrease in the proportion and distribution of Micro-2 and Astro-2 cells in the vicinity of blood vessels in Anxa1-/- mice. Additionally, we noted reduced expression levels of several ligand-receptor pairs including Cd14-Tlr2, Cd14-C3ar1, Cd14-Itgb1, Cxcl10-Sdc4, Ccl2-Ackr1, and Cxcl2-Ackr1.

CONCLUSIONS

By combining snRNA-seq and Stereo-seq techniques, our study successfully identified a distinctive cellular colocalization, referred to as a special pathological niche, comprising Astro-2, Micro-2, and Vas-1 cells. Furthermore, we observed an upregulation of ligand-receptor pairs within this niche. These findings suggest a potential association between this cellular arrangement and the underlying mechanisms contributing to SAE or the increased mortality observed in Anxa1 knockdown mice.

TIMP-1 is an activator of MHC-I expression in myeloid dendritic cells with implications for tumor immunogenicity

Immune checkpoint therapies (ICT) for advanced solid tumors mark a new milestone in cancer therapy. Yet their efficacy is often limited by poor immunogenicity, attributed to inadequate priming and generation of antitumor T cells by dendritic cells (DCs). Identifying biomarkers to enhance DC functions in such tumors is thus crucial. Tissue Inhibitor of Metalloproteinases-1 (TIMP-1), recognized for its influence on immune cells, has an underexplored relationship with DCs. Our research reveals a correlation between high TIMP1 levels in metastatic melanoma and increased CD8 + T cell infiltration and survival. Network studies indicate a functional connection with HLA genes. Spatial transcriptomic analysis of a national melanoma cohort revealed that TIMP1 expression in immune compartments associates with an HLA-A/MHC-I peptide loading signature in lymph nodes. Primary human and bone-marrow-derived DCs secrete TIMP-1, which notably increases MHC-I expression in classical type 1 dendritic cells (cDC1), especially under melanoma antigen exposure. TIMP-1 affects the immunoproteasome/TAP complex, as seen by upregulated PSMB8 and TAP-1 levels of myeloid DCs. This study uncovers the role of TIMP-1 in DC-mediated immunogenicity with insights into CD8 + T cell activation, providing a foundation for mechanistic exploration and highlighting its potential as a new target for combinatorial immunotherapy to enhance ICT effectiveness.

Hypermigration of macrophages through the concerted action of GRA effectors on NF-κB/p38 signaling and host chromatin accessibility potentiates Toxoplasma dissemination

Mononuclear phagocytes facilitate the dissemination of the obligate intracellular parasite Toxoplasma gondii. Here, we report how a set of secreted parasite effector proteins from dense granule organelles (GRA) orchestrates dendritic cell-like chemotactic and pro-inflammatory activation of parasitized macrophages. These effects enabled efficient dissemination of the type II T. gondii lineage, a highly prevalent genotype in humans. We identify novel functions for effectors GRA15 and GRA24 in promoting CCR7-mediated macrophage chemotaxis by acting on NF-κB and p38 MAPK signaling pathways, respectively, with contributions of GRA16/18 and counter-regulation by effector TEEGR. Further, GRA28 boosted chromatin accessibility and GRA15/24/NF-κB-dependent transcription at the Ccr7 gene locus in primary macrophages. In vivo, adoptively transferred macrophages infected with wild-type T. gondii outcompeted macrophages infected with a GRA15/24 double mutant in migrating to secondary organs in mice. The data show that T. gondii, rather than being passively shuttled, actively promotes its dissemination by inducing a finely regulated pro-migratory state in parasitized human and murine phagocytes via co-operating polymorphic GRA effectors.

Tissue Inhibitor of Metalloproteinases-1 Interacts with CD74 to Promote AKT Signaling, Monocyte Recruitment Responses, and Vascular Smooth Muscle Cell Proliferation

Tissue inhibitor of metalloproteinases-1 (TIMP-1), an important regulator of matrix metalloproteinases (MMPs), has recently been shown to interact with CD74, a receptor for macrophage migration inhibitory factor (MIF). However, the biological effects mediated by TIMP-1 through CD74 remain largely unexplored. Using sequence alignment and in silico protein-protein docking analysis, we demonstrated that TIMP-1 shares residues with both MIF and MIF-2, crucial for CD74 binding, but not for CXCR4. Subcellular colocalization, immunoprecipitation, and internalization experiments supported these findings, demonstrating that TIMP-1 interacts with surface-expressed CD74, resulting in its internalization in a dose-dependent manner, as well as with a soluble CD74 ectodomain fragment (sCD74). This prompted us to study the effects of the TIMP-1-CD74 axis on monocytes and vascular smooth muscle cells (VSCMs) to assess its impact on vascular inflammation. A phospho-kinase array revealed the activation of serine/threonine kinases by TIMP-1 in THP-1 pre-monocytes, in particular AKT. Similarly, TIMP-1 dose-dependently triggered the phosphorylation of AKT and ERK1/2 in primary human monocytes. Importantly, Transwell migration, 3D-based Chemotaxis, and flow adhesion assays demonstrated that TIMP-1 engagement of CD74 strongly promotes the recruitment response of primary human monocytes, while live cell imaging studies revealed a profound activating effect on VSMC proliferation. Finally, re-analysis of scRNA-seq data highlighted the expression patterns of TIMP-1 and CD74 in human atherosclerotic lesions, thus, together with our experimental data, indicating a role for the TIMP-1-CD74 axis in vascular inflammation and atherosclerosis.

The Toxoplasma effector GRA28 promotes parasite dissemination by inducing dendritic cell-like migratory properties in infected macrophages

Upon pathogen detection, macrophages normally stay sessile in tissues while dendritic cells (DCs) migrate to secondary lymphoid tissues. The obligate intracellular protozoan Toxoplasma gondii exploits the trafficking of mononuclear phagocytes for dissemination via unclear mechanisms. We report that, upon T. gondii infection, macrophages initiate the expression of transcription factors normally attributed to DCs, upregulate CCR7 expression with a chemotactic response, and perform systemic migration when adoptively transferred into mice. We show that parasite effector GRA28, released by the MYR1 secretory pathway, cooperates with host chromatin remodelers in the host cell nucleus to drive the chemotactic migration of parasitized macrophages. During in vivo challenge studies, bone marrow-derived macrophages infected with wild-type T. gondii outcompeted those challenged with MYR1- or GRA28-deficient strains in migrating and reaching secondary organs. This work reveals how an intracellular parasite hijacks chemotaxis in phagocytes and highlights a remarkable migratory plasticity in differentiated cells of the mononuclear phagocyte system.

Cut loose TIMP-1: an emerging cytokine in inflammation

Appreciation of the entire biological impact of an individual protein can be hampered by its original naming based on one function only. Tissue inhibitor of metalloproteinases-1 (TIMP-1), mostly known for its eponymous function to inhibit metalloproteinases, exhibits only a fraction of its cellular effects via this feature. Recently, TIMP-1 emerged as a potent cytokine acting via various cell-surface receptors, explaining a so-far under-appreciated role of TIMP-1-mediated signaling on immune cells. This, at least partly, resolved why elevated blood levels of TIMP-1 correlate with progression of numerous inflammatory diseases. Here, we emphasize the necessity of unbiased name-independent recognition of structure-function relationships to properly appreciate the biological potential of TIMP-1 and other cytokines in complex physiological processes such as inflammation.

Toxoplasma effector-induced ICAM-1 expression by infected dendritic cells potentiates transmigration across polarised endothelium

The obligate intracellular parasite Toxoplasma gondii makes use of infected leukocytes for systemic dissemination. Yet, how infection impacts the processes of leukocyte diapedesis has remained unresolved. Here, we addressed the effects of T. gondii infection on the trans-endothelial migration (TEM) of dendritic cells (DCs) across polarised brain endothelial monolayers. We report that upregulated expression of leukocyte ICAM-1 is a feature of the enhanced TEM of parasitised DCs. The secreted parasite effector GRA15 induced an elevated expression of ICAM-1 in infected DCs that was associated with enhanced cell adhesion and TEM. Consequently, gene silencing of Icam-1 in primary DCs or deletion of parasite GRA15 reduced TEM. Further, the parasite effector TgWIP, which impacts the regulation of host actin dynamics, facilitated TEM across polarised endothelium. The data highlight that the concerted action of the secreted effectors GRA15 and TgWIP modulate the leukocyte-endothelial interactions of TEM in a parasite genotype-related fashion to promote dissemination. In addition to the canonical roles of endothelial ICAM-1, this study identifies a previously unappreciated role for leukocyte ICAM-1 in infection-related TEM.

Impact of Plant-Based Foods and Nutraceuticals on Toxoplasma gondii Cysts: Nutritional Therapy as a Viable Approach for Managing Chronic Brain Toxoplasmosis

Toxoplasma gondii is an obligate intracellular parasite that mainly infects warm-blooded animals including humans. T. gondii can encyst and persist chronically in the brain, leading to a broad spectrum of neurological sequelae. Despite the associated health threats, no clinical drug is currently available to eliminate T. gondii cysts. In a continuous effort to uncover novel therapeutic agents for these cysts, the potential of nutritional products has been explored. Herein, we describe findings from in vitro and in vivo studies that support the efficacy of plant-based foods and nutraceuticals against brain cyst burden and cerebral pathologies associated with chronic toxoplasmosis. Finally, we discuss strategies to increase the translatability of preclinical studies and nutritional products to address whether nutritional therapy can be beneficial for coping with chronic T. gondii infections in humans.

Regulation of Tumor Metabolism and Extracellular Acidosis by the TIMP-10-CD63 Axis in Breast Carcinoma

A hallmark of malignant solid tumor is extracellular acidification coupled with metabolic switch to aerobic glycolysis. Using the human MCF10A progression model of breast cancer, we show that glycolytic switch and extracellular acidosis in aggressive cancer cells correlate with increased expression of tissue inhibitor of metalloproteinase-1 (TIMP-1), known to induce intracellular signal transduction through the interaction with its cell surface receptor CD63, independent of its metalloproteinase inhibitory function. We found that, in aggressive breast carcinoma, the TIMP-1–CD63 signaling axis induced a metabolic switch by upregulating the rate of aerobic glycolysis, lowering mitochondrial respiration, preventing intracellular acidification, and inducing extracellular acidosis. Carbonic anhydrase IX (CAIX), a regulator of cellular pH through the hydration of metabolically released pericellular CO₂, was identified as a downstream mediator of the TIMP-1–CD63 signaling axis responsible for extracellular acidosis. Consistently with our previous study, the TIMP-1–CD63 signaling promoted survival of breast cancer cells. Interestingly, breast carcinoma cell survival was drastically reduced upon shRNA-mediated knockdown of CAIX expression, demonstrating the significance of CAIX-regulated pH in the TIMP-1–CD63-mediated cancer cell survival. Taken together, the present study demonstrates the functional significance of TIMP-1–CD63–CAXI signaling axis in the regulation of tumor metabolism, extracellular acidosis, and survival of breast carcinoma. We propose that this axis may serve as a novel therapeutic target.

GABAergic signaling by cells of the immune system: more the rule than the exception

Gamma-aminobutyric acid (GABA) is best known as an essential neurotransmitter in the evolved central nervous system (CNS) of vertebrates. However, GABA antedates the development of the CNS as a bioactive molecule in metabolism and stress-coupled responses of prokaryotes, invertebrates and plants. Here, we focus on the emerging findings of GABA signaling in the mammalian immune system. Recent reports show that mononuclear phagocytes and lymphocytes, for instance dendritic cells, microglia, T cells and NK cells, express a GABAergic signaling machinery. Mounting evidence shows that GABA receptor signaling impacts central immune functions, such as cell migration, cytokine secretion, immune cell activation and cytotoxic responses. Furthermore, the GABAergic signaling machinery of leukocytes is implicated in responses to microbial infection and is co-opted by protozoan parasites for colonization of the host. Peripheral GABA signaling is also implicated in inflammatory conditions and diseases, such as type 1 diabetes, rheumatoid arthritis and cancer cell metastasis. Adding to its role in neurotransmission, growing evidence shows that the non-proteinogenic amino acid GABA acts as an intercellular signaling molecule in the immune system and, as an interspecies signaling molecule in host–microbe interactions. Altogether, the data raise the assumption of conserved GABA signaling in a broad range of mammalian cells and diversification of function in the immune system.

Integrin-dependent migratory switches regulate the translocation of Toxoplasma-infected dendritic cells across brain endothelial monolayers

Multiple cellular processes, such as immune responses and cancer cell metastasis, crucially depend on interconvertible migration modes. However, knowledge is scarce on how infectious agents impact the processes of cell adhesion and migration at restrictive biological barriers. In extracellular matrix, dendritic cells (DCs) infected by the obligate intracellular protozoan Toxoplasma gondii undergo mesenchymal-to-amoeboid transition (MAT) for rapid integrin-independent migration. Here, in a cellular model of the blood–brain barrier, we report that parasitised DCs adhere to polarised endothelium and shift to integrin-dependent motility, accompanied by elevated transendothelial migration (TEM). Upon contact with endothelium, parasitised DCs dramatically reduced velocities and adhered under both static and shear stress conditions, thereby obliterating the infection-induced amoeboid motility displayed in collagen matrix. The motility of adherent parasitised DCs on endothelial monolayers was restored by blockade of β1 and β2 integrins or ICAM-1, which conversely reduced motility on collagen-coated surfaces. Moreover, parasitised DCs exhibited enhanced translocation across highly polarised primary murine brain endothelial cell monolayers. Blockade of β1, β2 integrins, ICAM-1 and PECAM-1 reduced TEM frequencies. Finally, gene silencing of the pan-integrin-cytoskeleton linker talin (Tln1) or of β1 integrin (Itgb1) in primary DCs resulted in increased motility on endothelium and decreased TEM. Adding to the paradigms of leukocyte diapedesis, the findings provide novel insights in how an intracellular pathogen impacts the migratory plasticity of leukocytes in response to the cellular environment, to promote infection-related dissemination.

Epidemiology, Pathophysiology, Diagnosis, and Management of Cerebral Toxoplasmosis

Toxoplasma gondii is known to infect a considerable number of mammalian and avian species and a substantial proportion of the world's human population. The parasite has an impressive ability to disseminate within the host's body and employs various tactics to overcome the highly regulatory blood-brain barrier and reside in the brain. In healthy individuals, T. gondii infection is largely tolerated without any obvious ill effects. However, primary infection in immunosuppressed patients can result in acute cerebral or systemic disease, and reactivation of latent tissue cysts can lead to a deadly outcome. It is imperative that treatment of life-threatening toxoplasmic encephalitis is timely and effective. Several therapeutic and prophylactic regimens have been used in clinical practice. Current approaches can control infection caused by the invasive and highly proliferative tachyzoites but cannot eliminate the dormant tissue cysts. Adverse events and other limitations are associated with the standard pyrimethamine-based therapy, and effective vaccines are unavailable. In this review, the epidemiology, economic impact, pathophysiology, diagnosis, and management of cerebral toxoplasmosis are discussed, and critical areas for future research are highlighted.

A motogenic GABAergic system of mononuclear phagocytes facilitates dissemination of coccidian parasites

Gamma-aminobutyric acid (GABA) serves diverse biological functions in prokaryotes and eukaryotes, including neurotransmission in vertebrates. Yet, the role of GABA in the immune system has remained elusive. Here, a comprehensive characterization of human and murine myeloid mononuclear phagocytes revealed the presence of a conserved and tightly regulated GABAergic machinery with expression of GABA metabolic enzymes and transporters, GABA-A receptors and regulators, and voltage-dependent calcium channels. Infection challenge with the common coccidian parasites Toxoplasma gondii and Neospora caninum activated GABAergic signaling in phagocytes. Using gene silencing and pharmacological modulators in vitro and in vivo in mice, we identify the functional determinants of GABAergic signaling in parasitized phagocytes and demonstrate a link to calcium responses and migratory activation. The findings reveal a regulatory role for a GABAergic signaling machinery in the host-pathogen interplay between phagocytes and invasive coccidian parasites. The co-option of GABA underlies colonization of the host by a Trojan horse mechanism.

Toxoplasma gondii Co-opts the Unfolded Protein Response To Enhance Migration and Dissemination of Infected Host Cells

Toxoplasma gondii is an intracellular parasite that reconfigures its host cell to promote pathogenesis. One consequence of Toxoplasma parasitism is increased migratory activity of host cells, which facilitates dissemination. Here, we show that Toxoplasma triggers the unfolded protein response (UPR) in host cells through calcium release from the endoplasmic reticulum (ER). We further identify a novel role for the host ER stress sensor protein IRE1 in Toxoplasma pathogenesis. Upon infection, Toxoplasma activates IRE1, engaging its noncanonical role in actin remodeling through the binding of filamin A. By inducing cytoskeletal remodeling via IRE1 oligomerization in host cells, Toxoplasma enhances host cell migration in vitro and dissemination of the parasite to host organs in vivo Our study has identified novel mechanisms used by Toxoplasma to induce dissemination of infected cells, providing new insights into strategies for treatment of toxoplasmosis.IMPORTANCE Cells that are infected with the parasite Toxoplasma gondii exhibit heightened migratory activity, which facilitates dissemination of the infection throughout the body. In this report, we identify a new mechanism used by Toxoplasma to hijack its host cell and increase its mobility. We further show that the ability of Toxoplasma to increase host cell migration involves not the enzymatic activity of IRE1 but rather IRE1 engagement with actin cytoskeletal remodeling. Depletion of IRE1 from infected host cells reduces their migration in vitro and significantly hinders dissemination of Toxoplasma in vivo Our findings reveal a new mechanism underlying host-pathogen interactions, demonstrating how host cells are co-opted to spread a persistent infection around the body.

The molecular biology and immune control of chronic Toxoplasma gondii infection

Toxoplasma gondii is an incredibly successful parasite owing in part to its ability to persist within cells for the life of the host. Remarkably, at least 350 host species of T. gondii have been described to date, and it is estimated that 30% of the global human population is chronically infected. The importance of T. gondii in human health was made clear with the first reports of congenital toxoplasmosis in the 1940s. However, the AIDS crisis in the 1980s revealed the prevalence of chronic infection, as patients presented with reactivated chronic toxoplasmosis, underscoring the importance of an intact immune system for parasite control. In the last 40 years, there has been tremendous progress toward understanding the biology of T. gondii infection using rodent models, human cell experimental systems, and clinical data. However, there are still major holes in our understanding of T. gondii biology, including the genes controlling parasite development, the mechanisms of cell-intrinsic immunity to T. gondii in the brain and muscle, and the long-term effects of infection on host homeostasis. The need to better understand the biology of chronic infection is underscored by the recent rise in ocular disease associated with emerging haplotypes of T. gondii and our lack of effective treatments to sterilize chronic infection. This Review discusses the cell types and molecular mediators, both host and parasite, that facilitate persistent T. gondii infection. We highlight the consequences of chronic infection for tissue-specific pathology and identify open questions in this area of host-Toxoplasma interactions.

Convergent Met and voltage-gated Ca2+ channel signaling drives hypermigration of Toxoplasma-infected dendritic cells

Ras-Erk MAPK signaling controls many of the principal pathways involved in metazoan cell motility, drives metastasis of multiple cancer types and is targeted in chemotherapy. However, its putative roles in immune cell functions or in infections have remained elusive. Here, using primary dendritic cells (DCs) in an infection model with the protozoan Toxoplasma gondii, we show that two pathways activated by infection converge on Ras-Erk MAPK signaling to promote migration of parasitized DCs. We report that signaling through the receptor tyrosine kinase Met (also known as HGF receptor) contributes to T. gondii-induced DC hypermotility. Furthermore, voltage-gated Ca2+ channel (VGCC, subtype CaV1.3) signaling impacted the migratory activation of DCs via calmodulin-calmodulin kinase II. We show that convergent VGCC signaling and Met signaling activate the GTPase Ras to drive Erk1 and Erk2 (also known as MAPK3 and MAPK1, respectively) phosphorylation and hypermotility of T. gondii-infected DCs. The data provide a molecular basis for the hypermigratory mesenchymal-to-amoeboid transition (MAT) of parasitized DCs. This emerging concept suggests that parasitized DCs acquire metastasis-like migratory properties that promote infection-related dissemination.

In Vivo CRISPR Screen Identifies TgWIP as a Toxoplasma Modulator of Dendritic Cell Migration

Toxoplasma can reach distant organs, especially the brain, leading to a lifelong chronic phase. However, genes involved in related in vivo processes are currently unknown. Here, we use focused CRISPR libraries to identify Toxoplasma genes that affect in vivo fitness. We focus on TgWIP, whose deletion affects Toxoplasma dissemination to distant organs. We show that TgWIP is secreted into the host cell upon invasion and interacts with the host WAVE regulatory complex and SHP2 phosphatase, both of which regulate actin dynamics. TgWIP affects the morphology of dendritic cells and mediates the dissolution of podosomes, which dendritic cells use to adhere to extracellular matrix. TgWIP enhances the motility and transmigration of parasitized dendritic cells, likely explaining its effect on in vivo fitness. Our results provide a framework for systemic identification of Toxoplasma genes with in vivo effects at the site of infection or on dissemination to distant organs, including the brain.

Toxoplasma gondii Dysregulates Barrier Function and Mechanotransduction Signaling in Human Endothelial Cells

Toxoplasma gondii can infect and replicate in vascular endothelial cells prior to entering host tissues. However, little is known about the molecular interactions at the parasite-endothelial cell interface. We demonstrate that T. gondii infection of primary human umbilical vein endothelial cells (HUVEC) altered cell morphology and dysregulated barrier function, increasing permeability to low-molecular-weight polymers. T. gondii disrupted vascular endothelial cadherin (VE-cadherin) and β-catenin localization to the cell periphery and reduced VE-cadherin protein expression. Notably, T. gondii infection led to reorganization of the host cytoskeleton by reducing filamentous actin (F-actin) stress fiber abundance under static and microfluidic shear stress conditions and by reducing planar cell polarity. RNA sequencing (RNA-Seq) comparing genome-wide transcriptional profiles of infected to uninfected endothelial cells revealed changes in gene expression associated with cell-cell adhesion, extracellular matrix reorganization, and cytokine-mediated signaling. In particular, genes downstream of Hippo signaling and the biomechanical sensor and transcriptional coactivator Yes-associated protein (YAP) were downregulated in infected endothelial cells. Interestingly, T. gondii infection activated Hippo signaling by increasing phosphorylation of LATS1, leading to cytoplasmic retention of YAP, and reducing YAP target gene expression. These findings suggest that T. gondii infection triggers Hippo signaling and YAP nuclear export, leading to an altered transcriptional profile of infected endothelial cells.IMPORTANCE Toxoplasma gondii is a foodborne parasite that infects virtually all warm-blooded animals and can cause severe disease in individuals with compromised or weakened immune systems. During dissemination in its infected hosts, T. gondii breaches endothelial barriers to enter tissues and establish the chronic infections underlying the most severe manifestations of toxoplasmosis. The research presented here examines how T. gondii infection of primary human endothelial cells induces changes in cell morphology, barrier function, gene expression, and mechanotransduction signaling under static conditions and under the physiological conditions of shear stress found in the bloodstream. Understanding the molecular interactions occurring at the interface between endothelial cells and T. gondii may provide insights into processes linked to parasite dissemination and pathogenesis.

Sustained Egr-1 Response via p38 MAP Kinase Signaling Modulates Early Immune Responses of Dendritic Cells Parasitized by Toxoplasma gondii

As a response to a diverse array of external stimuli, early growth response protein 1 (Egr-1) plays important roles in the transcriptional regulation of inflammation and the cellular immune response. However, a number of intracellular pathogens colonize immune cells and the implication of Egr-1 in the host-pathogen interplay has remained elusive. Here, we have characterized the Egr-1 responses of primary murine and human dendritic cells (DCs) upon challenge with the obligate intracellular parasite Toxoplasma gondii. We report that live intracellular parasites induce a sustained high expression of Egr-1 in DCs, different from the immediate-early Egr-1 response to parasite lysates, inactivated parasites or LPS. Moreover, a distinct nuclear localization of elevated amounts of Egr-1 protein was detected in infected DCs, but not in by-stander DCs. The ERK1/2 MAPK signaling pathway mediated the canonical immediate-early Egr-1 response to soluble antigens in a MyD88/TLR-dependent fashion. In contrast, a non-canonical extended Egr-1 response that relied primarily on p38 MAPK signaling was induced by intracellular parasites and was exhibited similarly by MyD88-deficient and wildtype DCs. The extended phase Egr-1 response was dramatically reduced upon challenge of DCs with T. gondii parasites deficient in GRA24, a secreted p38-interacting protein. Further, Egr-1-silenced primary DCs maintained their migratory responses upon T. gondii challenge. Importantly, Egr-1 silencing led to elevated expression of co-stimulatory molecules (CD40, CD80) in Toxoplasma-infected DCs and in LPS-challenged immature DCs, indicating that Egr-1 responses suppressed maturation of DCs. Moreover, the IL-12 and IL-2 responses of Toxoplasma-challenged DCs were modulated in a GRA24-dependent fashion. Jointly, the data show that the Egr-1 responses of DCs to microbial external stimuli and intracellular stimuli can be selectively mediated by ERK1/2 or p38 MAPK signaling, and that Egr-1 can act as an intrinsic negative modulator of maturation in primary DCs.

Differential Responses of Bovine Monocyte-Derived Macrophages to Infection by Neospora caninum Isolates of High and Low Virulence

Neospora caninum, a protozoan parasite closely related to Toxoplasma gondii, represents one of the main causes of abortion in cattle. Macrophages (MØs) are mediators of the innate immune response against infection and likely one of the first cells encountered by the parasite during the host infection process. In this study, we investigated in vitro how high or low virulent isolates of N. caninum (Nc-Spain7 and Nc-Spain1H, respectively) interact with bovine monocyte-derived MØs and the influence of the isolate virulence on the subsequent cellular response. Both isolates actively invaded, survived and replicated in the MØs. However, Nc-Spain7 showed a higher invasion rate and a replication significantly faster, following an exponential growth model, whereas Nc-Spain1H presented a delayed replication and a lower growth rate without an exponential pattern. N. caninum infection induced a hypermigratory phenotype in bovine MØs that was characterized by enhanced motility and transmigration in vitro and was accompanied by morphological changes and abrogated extracellular matrix degradation. A significantly higher hypermotility was observed with the highly virulent isolate Nc-Spain7. Nc-Spain1H-infected MØs showed elevated reactive oxygen species (ROS) production and IL12p40 expression, which also resulted in increased IFN-γ release by lymphocytes, compared to cells infected with Nc-Spain7. Furthermore, IL-10 was upregulated in MØs infected with both isolates. Infected MØs exhibited lower expression of MHC Class II, CD86, and CD1b molecules than uninfected MØs, with non-significant differences between isolates. This work characterizes for the first time N. caninum replication in bovine monocyte-derived MØs and details isolate-dependent differences in host cell responses to the parasite.

Advances and Challenges in Understanding Cerebral Toxoplasmosis

Toxoplasma gondii is a widespread parasitic pathogen that infects over one third of the global human population. The parasite invades and chronically persists in the central nervous system (CNS) of the infected host. Parasite spread and persistence is intimately linked to an ensuing immune response, which does not only limit parasite-induced damage but also may facilitate dissemination and induce parasite-associated immunopathology. Here, we discuss various aspects of toxoplasmosis where knowledge is scarce or controversial and, the recent advances in the understanding of the delicate interplay of T. gondii with the immune system in experimental and clinical settings. This includes mechanisms for parasite passage from the circulation into the brain parenchyma across the blood-brain barrier during primary acute infection. Later, as chronic latent infection sets in with control of the parasite in the brain parenchyma, the roles of the inflammatory response and of immune cell responses in this phase of the disease are discussed. Additionally, the function of brain resident cell populations is delineated, i.e., how neurons, astrocytes and microglia serve both as target cells for the parasite but also actively contribute to the immune response. As the infection can reactivate in the CNS of immune-compromised individuals, we bring up the immunopathogenesis of reactivated toxoplasmosis, including the special case of congenital CNS manifestations. The relevance, advantages and limitations of rodent infection models for the understanding of human cerebral toxoplasmosis are discussed. Finally, this review pinpoints questions that may represent challenges to experimental and clinical science with respect to improved diagnostics, pharmacological treatments and immunotherapies.