Inflammasome activation restrains the intracellular Neospora caninum proliferation in bovine macrophages

Cytokine production by bovine adipose tissue stromal vascular fraction cells upon Neospora caninum stimulation

In bovines few studies addressed the contribution of adipose tissue to the host immune response to infection. Here we evaluated the in vitro response of bovine adipose tissue stromal vascular fraction (SVF) cells to the protozoan parasite Neospora caninum, using live and freeze-killed tachyzoites. Live N. caninum induced the production of IL-6, IL-1β and IL-10 by SVF cells isolated from subcutaneous adipose tissue (SAT), while in mesenteric adipose tissue (MAT) SVF cell cultures only IL-1β and IL-10 production was increased, showing slight distinct responses between adipose tissue depots. Whereas a clear IL-8 increase was detected in peripheral blood leucocytes (PBL) culture supernatants in response to live N. caninum, no such increase was observed in SAT or MAT SVF cell cultures. Nevertheless, in response to LPS, increased IL-8 levels were detected in all cell cultures. IL-10 levels were always increased in response to stimulation (live, freeze-killed N. caninum and LPS). Overall, our results show that bovine adipose tissue SVF cells produce cytokines in response to N. caninum and can therefore be putative contributors to the host immune response against this parasite.

RNA sequencing reveals dynamic expression of lncRNAs and mRNAs in caprine endometrial epithelial cells induced by Neospora caninum infection

Background

The effective transmission mode of Neospora caninum, with infection leading to reproductive failure in ruminants, is vertical transmission. The uterus is an important reproductive organ that forms the maternal–fetal interface. Neospora caninum can successfully invade and proliferate in the uterus, but the molecular mechanisms underlying epithelial-pathogen interactions remain unclear. Accumulating evidence suggests that host long noncoding RNAs (lncRNAs) play important roles in cellular molecular regulatory networks, with reports that these RNA molecules are closely related to the pathogenesis of apicomplexan parasites. However, the expression profiles of host lncRNAs during N. caninum infection has not been reported.

Methods

RNA sequencing (RNA-seq) analysis was used to investigate the expression profiles of messenger RNAs (mRNAs) and lncRNAs in caprine endometrial epithelial cells (EECs) infected with N. caninum for 24 h (TZ_24h) and 48 h (TZ_48 h), and the potential functions of differentially expressed (DE) lncRNAs were predicted by using Gene Ontology (GO) enrichment and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis of their mRNA targets.

Results

RNA-seq analysis identified 1280.15 M clean reads in 12 RNA samples, including six samples infected with N. caninum for 24 h (TZ1_24h-TZ3_24h) and 48 h (TZ1_48h-TZ3_48h), and six corresponding control samples (C1_24h-C3_24h and C1_48h-C3_48h). Within the categories TZ_24h-vs-C_24h, TZ_48h-vs-C_48h and TZ_48h-vs-TZ_24h, there were 934 (665 upregulated and 269 downregulated), 1238 (785 upregulated and 453 downregulated) and 489 (252 upregulated and 237 downregulated) DEmRNAs, respectively. GO enrichment and KEGG analysis revealed that these DEmRNAs were mainly involved in the regulation of host immune response (e.g. TNF signaling pathway, MAPK signaling pathway, transforming growth factor beta signaling pathway, AMPK signaling pathway, Toll-like receptor signaling pathway, NOD-like receptor signaling pathway), signaling molecules and interaction (e.g. cytokine-cytokine receptor interaction, cell adhesion molecules and ECM-receptor interaction). A total of 88 (59 upregulated and 29 downregulated), 129 (80 upregulated and 49 downregulated) and 32 (20 upregulated and 12 downregulated) DElncRNAs were found within the categories TZ_24h-vs-C_24h, TZ_48h-vs-C_48h and TZ_48h-vs-TZ_24h, respectively. Functional prediction indicated that these DElncRNAs would be involved in signal transduction (e.g. MAPK signaling pathway, PPAR signaling pathway, ErbB signaling pathway, calcium signaling pathway), neural transmission (e.g. GABAergic synapse, serotonergic synapse, cholinergic synapse), metabolism processes (e.g. glycosphingolipid biosynthesis-lacto and neolacto series, glycosaminoglycan biosynthesis-heparan sulfate/heparin) and signaling molecules and interaction (e.g. cytokine-cytokine receptor interaction, cell adhesion molecules and ECM-receptor interaction).

Conclusions

This is the first investigation of global gene expression profiles of lncRNAs during N. caninum infection. The results provide valuable information for further studies of the roles of lncRNAs during N. caninum infection.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13071-022-05405-5.

Neurological Infection, Kynurenine Pathway, and Parasitic Infection by Neospora caninum

Neuroinflammation is one of the most frequently studied topics of neurosciences as it is a common feature in almost all neurological disorders. Although the primary function of neuroinflammation is to protect the nervous system from an insult, the complex and sequential response of activated glial cells can lead to neurological damage. Depending on the type of insults and the time post-insult, the inflammatory response can be neuroprotective, neurotoxic, or, depending on the glial cell types, both. There are multiple pathways activated and many bioactive intermediates are released during neuroinflammation. One of the most common one is the kynurenine pathway, catabolizing tryptophan, which is involved in immune regulation, neuroprotection, and neurotoxicity. Different models have been used to study the kynurenine pathway metabolites to understand their involvements in the development and maintenance of the inflammatory processes triggered by infections. Among them, the parasitic infection Neospora caninum could be used as a relevant model to study the role of the kynurenine pathway in the neuroinflammatory response and the subset of cells involved.

Aeromonas sobria regulates proinflammatory immune response in mouse macrophages via activating the MAPK, AKT, and NF-κB pathways

Aeromonas sobria, a Gram-negative bacterium that can colonize both humans and animals, is found in a variety of environments, including water, seafood, meat, and vegetables (Cahill, 1990; Galindo et al., 2004; Song et al., 2019). Aeromonas spp. are conditionally pathogenic bacteria in aquaculture, which can rapidly proliferate, causing disease and even death in fish, especially when the environment is degraded (Neamat-Allah et al., 2020, 2021a, 2021b). In developing countries, Aeromonas spp. have been associated with a wide spectrum of infections in humans, including gastroenteritis, wound infections, septicemia, and lung infections (San Joaquin and Pickett, 1988; Wang et al., 2009; Su et al., 2013). Infections caused by Aeromonas spp. are usually more severe in immunocompromised individuals (Miyamoto et al., 2017). The presence of a plasmid encoding a β‍-lactamase in A. sobria that confers resistance to β-lactam antibiotics poses a huge challenge to the treatment of diseases caused by this microorganism (Lim and Hong, 2020). Consequently, an in-depth understanding of the interaction between A. sobria and its hosts is urgently required to enable the development of effective strategies for the treatment of A. sobria infections.

Host defense against Neospora caninum infection via IL-12p40 production through TLR2/TLR3-AKT-ERK signaling pathway in C57BL/6 mice

Neospora caninum is an intracellular parasite which can cause neosporosis and significant economic losses in both dairy and beef industries worldwide. A better understanding of the immune response by host cells against N. caninum could help to design better strategies for the prevention and treatment of neosporosis. Although previous studies have shown TLR2/TLR3 were involved in controlling N. caninum infection in mice, the precise mechanisms of the AKT and MAPK pathways controlled by TLR2/TLR3 to regulate N. caninum-induced IL-12p40 production and the role of TLR2/TLR3 in anti-N. caninum infection in bovine macrophages remain unclear. In the present study, TLR2^-/- mice displayed more parasite burden and lower level of IL-12p40 production compared to TLR3^-/- mice. N. caninum could activate AKT and ERK signaling pathways in WT mouse macrophages, which were inhibited in TLR2^-/- and TLR3^-/- mouse macrophages. In N. caninum-infected WT mouse macrophages, AKT inhibitor or AKT siRNA could decrease the phosphorylation of ERK. AKT or ERK inhibitors reduced the production of IL-12p40 and increased the number of parasites. The productions of ROS, NO, and GBP2 were significantly reduced in TLR2^-/- and TLR3^-/- mouse macrophages. Supplementation of rIL-12p40 inhibited N. caninum proliferation and rescued the productions of IFN-γ, NO, and GBP2 in WT, TLR2^-/-, and TLR3^-/- mouse macrophages. In bovine macrophages, the expressions of TLR2, TLR3, and IL-12p40 mRNA were significantly enhanced by N. caninum, and N. caninum proliferation was inhibited by TLR2/TLR3 agonists. Taken together, the proliferation of N. caninum in mouse macrophages was controlled by the TLR2/TLR3-AKT-ERK signal pathway via increased IL-12p40 production, which in turn lead to the productions of NO, GBP2, and IFN-γ during N. caninum infection. And in bovine macrophages, TLR2 and TLR3 contributed to inhibiting N. caninum proliferation via increased IL-12p40 production.

Porphyromonas gingivalis survival skills: Immune evasion

Periodontitis is a chronic inflammatory condition that destroys the tooth-supporting tissues and eventually leads to tooth loss. As one of the most prevalent oral conditions, periodontitis endangers the oral health of 70% of people throughout the world. Periodontitis is also related to various systemic diseases, such as diabetes mellitus, atherosclerosis, and rheumatoid arthritis, which not only has a great impact on population health status and the quality of life but also increases the social burden. Porphyromonas gingivalis (P. gingivalis) is a gram-negative oral anaerobic bacterium that plays a key role in the pathogenesis of periodontitis. Porphyromonas gingivalis can express various of virulence factors to overturn innate and adaptive immunities, which makes P. gingivalis survive and propagate in the host, destroy periodontal tissues, and have connection to systemic diseases. Porphyromonas gingivalis can invade into and survive in host tissues by destructing the gingival epithelial barrier, internalizing into the epithelial cells, and enhancing autophagy in epithelial cells. Deregulation of complement system, degradation of antibacterial peptides, and destruction of phagocyte functions facilitate the evasion of P. gingivalis. Porphyromonas gingivalis can also suppress adaptive immunity, which allows P. gingivalis to exist in the host tissues and cause the inflammatory response persistently. Here, we review studies devoted to understanding the strategies utilized by P. gingivalis to escape host immunity. Methods for impairing P. gingivalis immune evasion are also mentioned.

Giardia duodenalis extracellular vesicles regulate the proinflammatory immune response in mouse macrophages in vitro via the MAPK, AKT and NF-κB pathways

Background

Giardia duodenalis is an extracellular protozoan parasite that causes giardiasis in mammals. The presentation of giardiasis ranges from asymptomatic to severe diarrhea, and the World Health Organization lists it in the Neglected Diseases Initiative. Extracellular vesicles (EVs) are a key mediator of intracellular communication. Although previous studies have shown that G. intestinalis can regulate a host’s innate immune response, the role of G. intestinalis EVs (GEVs) in triggering a G. intestinalis-induced innate immune response remains to be further explored.

Methods

In this study, GEVs, G. intestinalis and GEVs + G. intestinalis were inoculated into macrophages, respectively. The transcription and secretion levels of proinflammatory cytokines, including interleukin (IL)-1β, IL-6 and tumor necrosis factor alpha (TNF-α), were measured using real-time quantitative PCR (qPCR) and enzyme-linked immunosorbent assays (ELISAs). The phosphorylation levels of the MAPK, AKT and NF-κB signaling pathways in GEV-stimulated mouse macrophages were examined using western blotting and immunofluorescence methods. The roles of activated pathways in the GEV-triggered inflammatory response were determined using inhibition assays, western blotting and ELISAs.

Results

The results showed that pretreatment with GEVs enhanced with G. intestinalis (GEVs + G. intestinalis) induced IL-1β, IL-6 and TNF-α transcription and secretion from mouse macrophages compared to stimulation with either GEVs or G. intestinalis alone. Inoculation of mouse macrophages with GEVs upregulated the phosphorylation levels of the p38 MAPK, p44/42 MAPK (Erk1/2), AKT and NF-κB signaling pathways and led to the nuclear translocation of NF-κB p65. Blocking the activated p38, Erk and NF-κB signaling pathways significantly downregulated the secretion of proinflammatory cytokines, and blocking the activated AKT signaling pathway demonstrated reverse effects.

Conclusions

The results of this study reveal that GEVs can enhance G. intestinalis-induced inflammatory response levels in mouse macrophages through activation of the p38, ERK and NF-κB signaling pathways. The role of GEVs in regulating host cell immune responses may provide insights into exploring the underlying mechanisms in G. intestinalis–host interactions.

Graphical abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13071-021-04865-5.

Activation of ChTLR15/ChNF-κB-ChNLRP3/ChIL-1β signaling transduction pathway mediated inflammatory responses to E. tenella infection

Avian coccidiosis caused by Eimeria leads to severe economic losses in the global poultry industry. Although chicken Toll-like receptor 15 (ChTLR15) was reported to be involved in Eimeria infection, the detailed mechanism underlying its role in the inflammatory response remains to be discovered. The present study demonstrated that the mRNA expression levels of ChTLR15, ChMyD88, ChNF-κB, ChNLRP3, ChCaspase-1, ChIL-18 and ChIL-1β and the protein levels of ChTLR15 and ChNLRP3 in cecal tissues of Eimeria-infected chickens were significantly elevated at 4, 12, and 24 h compared with those in noninfected control chickens (p < 0.01). Moreover, the mRNA levels of molecules in the ChTLR15/ChNF-κB and ChNLRP3/ChIL-1β pathways and the protein levels of ChTLR15 and ChNLRP3 in chicken embryo fibroblast cells (DF-1) stimulated by E. tenella sporozoites were consistent with those in Eimeria-infected chickens. Furthermore, overexpression of ChTLR15 in DF1 cells augmented activation of the ChTLR15/ChNF-κB and ChNLRP3/ChIL-1β pathways when stimulated with E. tenella sporozoites, while knockdown of ChTLR15 in DF1 cells showed inverse effects. Taken together, the present study provides evidence that E. tenella sporozoites specifically activate ChTLR15 and then trigger activation of the ChNLRP3/ChIL-1β pathway, which partially mediates inflammatory responses to Eimeria infection.

Interplays between inflammasomes and viruses, bacteria (pathogenic and probiotic), yeasts and parasites

In recent years, scientists studying the molecular mechanisms of inflammation have discovered an amazing phenomenon - the inflammasome - a component of the innate immune system that can regulate the functional activity of effector cells during inflammation. At present, it is known that inflammasomes are multimolecular complexes (cytosolic multiprotein oligomers of the innate immune system) that contain many copies of receptors recognizing the molecular structures of cell-damaging factors and pathogenic agents. Inflammasomes are mainly formed in myeloid cells, and their main function is participation in the cleavage of the pro-IL-1β and pro-IL-18 cytokines into their biologically active forms (IL-1β, IL-18). Each type of microorganism influences particular inflammasome activation, and long-term exposure of the organism to viruses, bacteria, yeasts or parasites, among others, can induce uncontrolled inflammation and autoinflammatory diseases. Therefore, this review aims to present the most current scientific data on the molecular interplay between inflammasomes and particular microorganisms. Knowledge about the mechanisms responsible for the interaction between the host and certain types of microorganisms could contribute to the individuation of innovative strategies for the treatment of uncontrolled inflammation targeting a specific type of inflammasome activated by a specific type of pathogen.

Pyroptosis executioner gasdermin D contributes to host defense and promotes Th 1 immune response during Neospora caninum infection

Neospora caninum (N. caninum) is an intracellular parasite and is the causative agent of neosporosis, which leads to reproductive failure in cattle. Pyroptosis is a recently discovered form of programmed cell death executed by gasdermin D (GSDMD). This cell death mechanism is an important host defense against intracellular pathogens. However, pyroptosis induced by N. caninum is poorly understood. The aim of this study was to explore the roles of GSDMD-mediated pyroptosis during N. caninum infection in vivo. N. caninum-infected wild type mice and GSDMD-deficient mice were used to evaluate host resistance and its ability to affect immune response against this parasite. The results showed that GSDMD deficiency significantly reduced survival and impaired the host's abilities to clear parasite loads in tissues, monocytes/macrophages and neutrophils. Additionally, GSDMD was essential for circulating IL-18 and IFN-γ production induced by N. caninum infection, indicating that GSDMD can mediate the Th 1 immune response against N. caninum infection. Additional data revealed that treatment with exogenous recombinant IL-18 in N. caninum-infected Gsdmd^-/- mice rescues the reduction of circulating IFN-γ production to help eliminate the parasite. Taken together, our data indicate that GSDMD-mediated pyroptosis plays a vital role in maintaining host resistance to N. caninum and is essential for clearing the parasite. This form of programmed cell death promotes the Th 1 immune response by controlling IL-18 release and is considered a host defense against N. caninum. This study expands our understanding of interactions between host immune response/defense and N. caninum infection.

ROS-mediated NLRP3 inflammasome activation participates in the response against Neospora caninum infection

Background

Neospora caninum is an obligate intracellular protozoan that causes neosporosis, N. caninum infection is a major cause of abortion in cattle worldwide. Currently, specific treatment for neosporosis is not available. The NOD-like receptor family pyrin domain containing 3 (NLRP3) inflammasome is a cytoplasmic protein complex that plays an important role in host defense against N. caninum infection, but the underlying mechanisms are poorly understood.

Methods

The reactive oxygen species (ROS) inhibitor and the ROS inducer, wild-type (WT) and NLRP3-deficient peritoneal macrophages or mice were used to investigate the role of ROS in NLRP3 inflammasome activation and controlling parasite burdens. ROS production, cell death and cell viability, production of inflammasome-mediated IL-1β or IL-18, cleavage of caspase-1 and NLRP3 expression, as well as parasite burdens were detected.

Results

In vitro, N. caninum induced ROS generation in a dose-dependent manner in peritoneal macrophages. The pretreatment of ROS inhibitor N-acetyl-l-cysteine (NAC) significantly attenuated N. caninum-induced ROS production, LDH release, IL-1β secretion and NLRP3 expression, whereas N. caninum proliferation was notably increased. In contrary, the ROS inducer pyrogallol (PG) significantly enhanced ROS production and NLRP3 inflammasome activity and decreased the parasite burden in N. caninum-infected peritoneal macrophages. NADPH-dependent ROS-mediated NLRP3 inflammasome activation induced by N. caninum can also be confirmed by using the NADPH oxidase inhibitor diphenyleneiodonium chloride (DPI). However, the NAC or DPI pre-treatment or PG treatment did not significantly alter N. caninum-induced inflammasome activities and parasite proliferation in Nlrp3^−/− peritoneal macrophages. In vivo, IL-18 releases in serum and parasite burdens in peritoneal exudate cells were significantly increased in PG-treated WT mice after infection with N. caninum; however, IL-18 productions and parasite burdens were not changed in PG-treated Nlrp3^−/− mice. Furthermore, PG treatment in WT mice infected with N. caninum significantly decreased the mortality, weight loss and parasite burdens in tissues and histopathological lesions.

Conclusions

Neospora caninum-induced NADPH-dependent ROS generation plays an important role in NLRP3 inflammasome activation and controlling parasites. The ROS inducer PG can control N. caninum infection mainly by promoting NLRP3 inflammasome activation. ROS-mediated NLRP3 inflammasome axis can be a potential therapeutic target for neosporosis.

Interplay Between Reactive Oxygen Species and the Inflammasome Are Crucial for Restriction of Neospora caninum Replication

Neospora caninum poses as a considerable threat to animal health and generates significant economic impact in livestock production worldwide. Here, we have investigated the mechanism that underlies the participation of the inflammasome complex and Reactive Oxygen Species (ROS) in the regulation of immune responses during N. caninum infection. For that purpose, we used in vitro (bone marrow derived macrophages) and in vivo mouse models of infection. Our results show that NLRP3 and NLRC4 receptors, alongside with ASC and Caspase-1, are required for proper activation of the inflammasome during N. caninum infection. As expected, the engagement of these pathways is crucial for IL-1α, IL-1β, and IL-18 production, as well as the induction of pyroptosis. Our results also show that N. caninum induces ROS production dependent of the inflammasome assembly, which in its turn also depends on MyD88/NF-κB-induced ROS to maintain its activation and, ultimately, lead to restriction of parasite replication.

From Signaling Pathways to Distinct Immune Responses: Key Factors for Establishing or Combating Neospora caninum Infection in Different Susceptible Hosts

: Neospora caninum is an intracellular protozoan parasite affecting numerous animal species. It induces significant economic losses because of abortion and neonatal abnormalities in cattle. In case of infection, the parasite secretes numerous arsenals to establish a successful infection in the host cell. In the same context but for a different purpose, the host resorts to different strategies to eliminate the invading parasite. During this battle, numerous key factors from both parasite and host sides are produced and interact for the maintaining and vanishing of the infection, respectively. Although several reviews have highlighted the role of different compartments of the immune system against N. caninum infection, each one of them has mostly targeted specific points related to the immune component and animal host. Thus, in the current review, we will focus on effector molecules derived from the host cell or the parasite using a comprehensive survey method from previous reports. According to our knowledge, this is the first review that highlights and discusses immune response at the host cell-parasite molecular interface against N. caninum infection in different susceptible hosts.

Inflammasome Activation in Bovine Peripheral Blood-Derived Macrophages Is Associated with Actin Rearrangement

Simple Summary

In the early stage of infection, the innate immune system produces a rapid inflammatory response that blocks the growth and spread of the infectious agent. In this study, we explored the role of the actin cellular cytoskeleton in the inflammatory response due to stimulation of the bovine macrophages with Salmonella typhimurium flagellin. We found that actin was rearranged to form filopodia, which in the early stage of inflammation are important for macrophage motility. As inflammation progressed, actin polymerized at the same site as inflammasome complexes formed. Ultimately the macrophage died, which will attract more inflammatory cells to the infection site to help block the infection.

Abstract

Inflammation is critical for infection control and acts as an arsenal defense mechanism against invading microbes through activation of the host immune system. It works via its inflammasome components to sense the dangerous invading microorganism and send messages to the immune system to destroy them. To date, the function of bovine macrophage inflammasome and its relationship with actin has not been identified. This study aimed to investigate the activation of bovine inflammasome by phase one flagellin from Salmonella typhimurium and its interaction with actin. Bovine monocyte-derived macrophages were prepared and challenged with S. typhimurium SL1344 phase one flagellin. The results demonstrated the relationship between the flagellin-based activation of inflammasome and actin rearrangement. The flagellin-based activation of inflammasome promoted the activation and co-localization of F-actin and the inflammasome complex. Actin was remodeled to different degrees according to the stage of inflammasome activation. The actin redistribution varied from polymerization to filopodia, while at the stage of pyroptotic cell death, actin was broken down and interacted with activated inflammasome complexes. In conclusion, flagellin-dependent inflammasome activation and actin localization to the inflammasome at the stage of pyroptotic cell death may be of importance for appropriate immune responses, pending further studies to explore the exact cross-linking between the inflammasome complex and actin.