Deletion of the Type IV Secretion System Effector VceA Promotes Autophagy and Inhibits Apoptosis in Brucella-Infected Human Trophoblast Cells

A genome-wide CRISPR screen identified host genes essential for intracellular Brucella survival

Brucella is a zoonotic intracellular bacterium that poses threats to human health and economic security. Intracellular infection is a hallmark of the agent Brucella and a primary cause of distress, through which the bacterium regulates the host intracellular environment to promote its own colonization and replication, evading host immunity and pharmaceutical killing. Current studies of Brucella intracellular processes are typically premised on bacterial phenotype such as intracellular bacterial survival, followed by biochemical or molecular biological approaches to reveal detailed mechanisms. While such processes can deepen the understanding of Brucella-host interaction, the insights into host alterations in infection would be easily restricted to known pathways. In the current study, we applied CRISPR Cas9 screen to identify host genes that are most affected by Brucella infection on cell viability at the genomic level. As a result of CRISPR screening, we firstly identified that knockout of the negatively selected genes GOLGA6L6, DEFB103B, OR4F29, and ERCC6 attenuate the viability of both the host cells and intracellular Brucella, suggesting these genes to be potential therapeutic targets for Brucella control. In particular, knockout of DEFB103B diminished Brucella intracellular survival by altering host cell autophagy. Conversely, knockout of positive screening genes promoted intracellular proliferation of Brucella. In summary, we screened host genes at the genomic level throughout Brucella infection, identified host genes that are previously not recognized to be involved in Brucella infection, and provided targets for intracellular infection control.IMPORTANCEBrucella is a Gram-negative bacterium that infects common mammals causing arthritis, myalgia, neuritis, orchitis, or miscarriage and is difficult to cure with antibiotics due to its intracellular parasitism. Therefore, unraveling the mechanism of Brucella-host interactions will help controlling Brucella infections. CRISPR-Cas9 is a gene editing technology that directs knockout of individual target genes by guided RNA, from which genome-wide gene-knockout cell libraries can be constructed. Upon infection with Brucella, the cell library would show differences in viability as a result of the knockout and specific genes could be revealed by genomic DNA sequencing. As a result, genes affecting cell viability during Brucella infection were identified. Further testing of gene function may reveal the mechanisms of Brucella-host interactions, thereby contributing to clinical therapy.

Effector Proteins of Type IV Secretion System: Weapons of Brucella Used to Fight Against Host Immunity

Brucella is an intracellular bacterial pathogen capable of long-term persistence in the host, resulting in chronic infections in livestock and wildlife. The type IV secretion system (T4SS) is an important virulence factor of Brucella and is composed of 12 protein complexes encoded by the VirB operon. T4SS exerts its function through its secreted 15 effector proteins. The effector proteins act on important signaling pathways in host cells, inducing host immune responses and promoting the survival and replication of Brucella in host cells to promote persistent infection. In this article, we describe the intracellular circulation of Brucella-infected cells and survey the role of Brucella VirB T4SS in regulating inflammatory responses and suppressing host immune responses during infection. In addition, the important mechanisms of these 15 effector proteins in resisting the host immune response during Brucella infection are elucidated. For example, VceC and VceA assist in achieving sustained survival of Brucella in host cells by affecting autophagy and apoptosis. BtpB, together with BtpA, controls the activation of dendritic cells during infection, induces inflammatory responses, and controls host immunity. This article reviews the effector proteins secreted by Brucella T4SS and their involvement in immune responses, which can provide a reliable theoretical basis for the subsequent mechanism of hijacking the host cell signaling pathway by bacteria and contribute to the development of better vaccines to effectively treat Brucella bacterial infection.

Immune Responses Potentially Involved in the Gestational Complications of Brucella Infection

Infection by Brucella species in pregnant animals and humans is associated with an increased risk of abortion, preterm birth, and transmission of the infection to the offspring. The pathogen has a marked tropism for the placenta and the pregnant uterus and has the ability to invade and replicate within cells of the maternal-fetal unit, including trophoblasts and decidual cells. Placentitis is a common finding in infected pregnant animals. Several proinflammatory factors have been found to be increased in both the placenta of Brucella-infected animals and in trophoblasts or decidual cells infected in vitro. As normal pregnancies require an anti-inflammatory placental environment during most of the gestational period, Brucella-induced placentitis is thought to be associated with the obstetric complications of brucellosis. A few studies suggest that the blockade of proinflammatory factors may prevent abortion in these cases.

Alr Gene in Brucella suis S2: Its Role in Lipopolysaccharide Biosynthesis and Bacterial Virulence in RAW264.7

Brucella suis, the causative agent of brucellosis, poses a significant public health and animal husbandry threat. However, the role of the alanine racemase (alr) gene, which encodes alanine racemase in Brucella, remains unclear. Here, we analyzed an alr deletion mutant and a complemented strain of Brucella suis S2. The knockout strain displayed an unaltered, smooth phenotype in acriflavine agglutination tests but lacked the core polysaccharide portion of lipopolysaccharide (LPS). Genes involved in the LPS synthesis were significantly upregulated in the deletion mutant. The alr deletion strain exhibited reduced intracellular viability in the macrophages, increased macrophage-mediated killing, and upregulation of the apoptosis markers. Bcl2, an anti-apoptotic protein, was downregulated, while the pro-apoptotic proteins, Bax, Caspase-9, and Caspase-3, were upregulated in the macrophages infected with the deletion strain. The infected macrophages showed increased mitochondrial membrane permeability, Cytochrome C release, and reactive oxygen species, activating the mitochondrial apoptosis pathway. These findings revealed that alanine racemase was dispensable in B. suis S2 but influenced the strain's rough features and triggered the mitochondrial apoptosis pathway during macrophage invasion. The deletion of the alr gene reduced the intracellular survival and virulence. This study enhances our understanding of the molecular mechanism underlying Brucella's survival and virulence and, specifically, how alr gene affects host immune evasion by regulating bacterial LPS biosynthesis.

Brucella BtpB Manipulates Apoptosis and Autophagic Flux in RAW264.7 Cells

Brucella transfers effectors into host cells, manipulating cellular processes to its advantage; however, the mechanism by which effectors regulate cellular processes during infection is poorly understood. A growing number of studies have shown that apoptosis and autophagy are critical mechanisms for target cells to cope with pathogens and maintain cellular homeostasis. BtpB is a Brucella type IV secretion system effector with a complex mechanism for manipulating host infection. Here, we show that the ectopic expression of BtpB promoted DNA fragmentation. In contrast, an isogenic mutant strain, ΔbtpB, inhibited apoptosis compared to the wild-type strain B. suis S2 in RAW264.7 cells. In addition, BtpB inhibited autophagy, as determined by LC3-II protein levels, the number of LC3 puncta, and p62 degradation. We also found that BtpB reduced autophagolysosome formation and blocked the complete autophagic flux. Moreover, our results revealed that the autophagy inhibitor, chloroquine, reduces Brucella's intracellular survival. Overall, our data unveil new mechanisms of virulence implicating the effector BtpB in regulating host intracellular infection.

Inflammatory Mechanism of Brucella Infection in Placental Trophoblast Cells

Brucellosis is a severe zoonotic infectious disease caused by the infection of the Brucella, which is widespread and causes considerable economic losses in underdeveloped areas. Brucella is a facultative intracellular bacteria whose main target cells for infection are macrophages, placental trophoblast cells and dendritic cells. The main clinical signs of Brucella infection in livestock are reproductive disorders and abortion. At present, the pathogenesis of placentitis or abortion caused by Brucella in livestock is not fully understood, and further research on the effect of Brucella on placental development is still necessary. This review will mainly introduce the research progress of Brucella infection of placental trophoblast cells as well as the inflammatory response caused by it, explaining the molecular regulation mechanism of Brucella leading to reproductive system disorders and abortion, and also to provide the scientific basis for revealing the pathogenesis and infection mechanism of Brucella.

The pathological and therapeutic roles of mesenchymal stem cells in preeclampsia

Mesenchymal stem cells (MSCs) have made progress in the treatment of ischemic and inflammatory diseases. Preeclampsia (PE) is characterized by placenta ischemic and inflammatory injury. Our paper summarized the new role of MSCs in PE pathology and its potency in PE therapy and analyzed its current limitations. Intravenously administered MSCs dominantly distributed in perinatal tissues. There may be additional advantages to using MSCs-based therapies for reproductive disorders. It will provide new ideas for future research in this field.

Brucella melitensis outer membrane protein 25 interacts with ferritin heavy polypeptide 1 in human trophoblast cells

Outer membrane protein 25 (OMP25) is involved in Brucella virulence and serves an important role in Brucella pathogenesis during infection. However, the protein interacting with OMP25 in host cells remains to be elucidated. The present study constructed a cDNA library from Brucella melitensis 16M‑infected human placenta trophoblastic cells (HPT‑8) and identified and confirmed the interaction between Brucella OMP25 and ferritin heavy polypeptide 1 (FTH1) of HPT‑8 using yeast two‑hybrid and co‑immunoprecipitation technologies. The expression of Toll‑like receptor (TLR)4, myeloid differentiation primary response protein MyD88 (MyD88) mRNA and inflammatory factors was detected by RNA interference. The results showed that OMP25 interacted with FTH1. Subsequently, TLR4 and MyD88 mRNA expression levels and inflammatory factors, such as nitric oxide, lactate dehydrogenase and TNF‑α, significantly increased after inserting OMP25 into the HPT‑8 cells. Notably, a low dose of OMP25 resulted in immunological protection, whereas high dose of OMP25 resulted in a cytotoxic effect on the HPT‑8 cells. It is suggested that OMP25 and FTH1 serve important roles in intracellular parasitism of Brucella and inhibition of expression.

Lysine Acylation Modification Landscape of Brucella abortus Proteome and its Virulent Proteins

The myriad of posttranslational modifications (PTMs) of proteins that occur in all living cells are crucial to all kinds of biological processes. Brucella is an intracellular parasitic bacterium that can cause chronic diseases in both humans and livestock. To reveal the relationship between PTMs and the virulence and survival of Brucella, we described the first comprehensive multiple PTM-omics atlas of B. abortus 2308. Five PTMs involving lysine, namely 2-hydroxyisobutyrylation, succinylation, crotonylation, acetylation, and malonylation were identified. Nearly 2,000 modified proteins were observed, and these proteins took part in many biological processes, with a variety of molecular functions. In addition, we detected many significant virulence factors of Brucella among the modified proteins. 10 of the 15 T4SS effector proteins were detected with one or more PTMs. Moreover, abundant PTMs were detected in other typical virulence factors. Considering the role of PTMs in various biological processes of Brucella virulence and survival, we propose that the virulence of Brucella is associated with the PTMs of proteins. Taken together, this study provides the first global survey of PTMs in Brucella. This is a prospective starting point for further functional analysis of PTMs during the survival of Brucella in hosts, interpretation of the function of Brucella proteins, and elucidation of the pathogenic mechanism of Brucella.

Antibiogram Screening and Detection of Virulence-Associated Genes in Brucella Species Acquired from Cattle in South Africa's Eastern Cape Province

Brucellosis is a widespread zoonotic illness, and it poses serious public health and economic risks. The purpose of this investigation is to look at the antimicrobial susceptibility of unpasteurized milk, blood, and lymph node specimens from cattle, goats, and sheep, as well as to identify virulence-associated genes. In this investigation, a total of 123 isolates were examined. The activity of 15 antimicrobials against Brucella pathogens were assessed using the Kirby−Bauer disk diffusion technique. Nine virulence factors were detected with polymerase chain reaction analysis. Five antibiotics were 100% effective against Brucella isolates. A high level of resistance (100%) was documented with streptomycin, penicillin, and seven more antibiotics. Doxycycline resistance was found in 12% of goat isolates, and tetracycline resistance was found in 21% and 44% of goat and sheep isolates, respectively. Multiple antibiotic resistance (MAR) index >0.2 was found in 38.2% (47/123) of Brucella isolates. VecC and BetB, two B. abortus genes, were confirmed to be comparable. The findings of this study suggests that Brucella spp. are reservoirs of antibiotic resistance in the Eastern Cape Province. As such, they represent a potential pool of antibiotic genes that might be transferred to other pathogens in the community, and thus continue to pose a healthcare hazard.

The VirB System Plays a Crucial Role in Brucella Intracellular Infection

Brucellosis is a highly prevalent zoonotic disease caused by Brucella. Brucella spp. are gram-negative facultative intracellular parasitic bacteria. Its intracellular survival and replication depend on a functional virB system, an operon encoded by VirB1–VirB12. Type IV secretion system (T4SS) encoded by the virB operon is an important virulence factor of Brucella. It can subvert cellular pathway and induce host immune response by secreting effectors, which promotes Brucella replication in host cells and induce persistent infection. Therefore, this paper summarizes the function and significance of the VirB system, focusing on the structure of the VirB system where VirB T4SS mediates biogenesis of the endoplasmic reticulum (ER)-derived replicative Brucella-containing vacuole (rBCV), the effectors of T4SS and the cellular pathways it subverts, which will help better understand the pathogenic mechanism of Brucella and provide new ideas for clinical vaccine research and development.

Deletion of the type IV secretion system promoter VirB in Brucella abortus A19 strain attenuated the virulence of the bacteria and promotes autophagy

Brucella abortus is a Gram-negative intracellular parasite bacteria causing serious health hazards in humans and animals. The type IV secretion system (T4SS), encoded by the virB promoter, has been identified as an important virulence factor for Brucella abortus, but the impact on Brucella abortus A19 remains unclear. In this study, the T4SS of Brucella abortus A19 was inactivated by deleting the virB promoter, resulting in a mutant strain A19ΔvirB. Real-time PCR and Western-blotting analysis demonstrated that T4SS-related proteins were not expressed after virB promoter deletion. Moreover, the survival rate of A19 in high salt and strong acidic environments was decreased after virB promoter deletion. Compared to the parental strain A19, the A19ΔvirB mutant strain showed reduced growth rate in TSB, decreased invasion ability to macrophages and dendritic cells, and reduced virulence of the mutant strain in macrophages, dendritic cells and mice. In addition, the A19ΔvirB mutant strain showed enhanced autophagy on macrophages and dendritic cells compared with A19, and the A19ΔvirB mutant strain was able to upregulate IL-6 and downregulate IL-10 in macrophages. These data help us to better understand the T4SS of the A19 vaccine strain and contribute to our efforts to improve Brucella vaccines.

Chorionic villus-derived mesenchymal stem cell-mediated autophagy promotes the proliferation and invasiveness of trophoblasts under hypoxia by activating the JAK2/STAT3 signalling pathway

BACKGROUND

Trophoblast dysfunction during pregnancy is fundamentally involved in preeclampsia. Several studies have revealed that human chorionic villous mesenchymal stem cells (CV-MSCs) could regulate trophoblasts function.

RESULTS

To understand how human chorionic villous mesenchymal stem cells (CV-MSCs) regulate trophoblast function, we treated trophoblasts with CV-MSC supernatant under hypoxic conditions. Treatment markedly enhanced proliferation and invasion and augmented autophagy. Transcriptome and pathway analyses of trophoblasts before and after treatment revealed JAK2/STAT3 signalling as an upstream regulator. In addition, STAT3 mRNA and protein levels increased during CV-MSC treatment. Consistent with these findings, JAK2/STAT3 signalling inhibition reduced the autophagy, survival and invasion of trophoblasts, even in the presence of CV-MSCs, and blocking autophagy did not affect STAT3 activation in trophoblasts treated with CV-MSCs. Importantly, STAT3 overexpression increased autophagy levels in trophoblasts; thus, it positively regulated autophagy in hypoxic trophoblasts. Human placental explants also proved our findings by showing that STAT3 was activated and that LC3B-II levels were increased by CV-MSC treatment.

CONCLUSION

In summary, our data suggest that CV-MSC-dependent JAK2/STAT3 signalling activation is a prerequisite for autophagy upregulation in trophoblasts.

PADI4 mediates autophagy and participates in the role of ganoderic acid A monomers in delaying the senescence of Alzheimer's cells through the Akt/mTOR pathway

The effects of PADI4 and GAA on the senescence of Alzheimer's cells were explored in the present work. HT22 cells were treated with Aβ25-35 to establish an Alzheimer's model and were then treated with different concentrations of GAA and transfected with a siPADI4 lentiviral vector. GAA could reverse the effects of Aβ25-35 on inhibiting cell viability and promoting apoptosis and senescence. siPADI4 reduced Aβ25-35-induced cell viability and upregulated Aβ25-35-induced cell apoptosis and senescence, as well as partially reversed the effect of GAA on cells, and these results were confirmed by detecting the expressions of senescence- and apoptosis-related proteins. In addition, siPADI4 was found to promote the phosphorylation of Akt and mTOR, which was partially reversed by GAA. In conclusion, PADI4 mediates autophagy and participates in the role of GAA monomers in delaying the senescence of Alzheimer's cells through the Akt/mTOR pathway.

Pathophysiology of Preeclampsia: The Role of Exosomes

The pathogenesis of preeclampsia begins when a fertilized egg infiltrates the decidua, resulting in implantation failure (e.g., due to extravillous trophoblast infiltration disturbance and abnormal spiral artery remodeling). Thereafter, large amounts of serum factors (e.g., soluble fms-like tyrosine kinase 1 and soluble endoglin) are released into the blood from the hypoplastic placenta, and preeclampsia characterized by multiorgan disorder caused by vascular disorders develops. Successful implantation and placentation require immune tolerance to the fertilized egg as a semi-allograft and the stimulation of extravillous trophoblast infiltration. Recently, exosomes with diameters of 50-100 nm have been recognized to be involved in cell-cell communication. Exosomes affect cell functions in autocrine and paracrine manners via their encapsulating microRNA/DNA and membrane-bound proteins. The microRNA profiles of blood exosomes have been demonstrated to be useful for the evaluation of preeclampsia pathophysiology and prediction of the disease. In addition, exosomes derived from mesenchymal stem cells have been found to have cancer-suppressing effects. These exosomes may repair the pathophysiology of preeclampsia through the suppression of extravillous trophoblast apoptosis and promotion of these cells' invasive ability. Exosomes secreted by various cells have received much recent attention and may be involved in the maintenance of pregnancy and pathogenesis of preeclampsia.

Amnion-Derived Mesenchymal Stem Cell Exosomes-Mediated Autophagy Promotes the Survival of Trophoblasts Under Hypoxia Through mTOR Pathway by the Downregulation of EZH2

Human amnion-derived mesenchymal stem cells (AD-MSCs) have been reported as a promising effective treatment to repair tissue. Trophoblast dysfunction during pregnancy is significantly involved in the pathogenesis of preeclampsia (PE). To understand how AD-MSCs regulated trophoblast function, we treated trophoblasts with AD-MSC-derived exosomes under hypoxic conditions. The treatment markedly enhanced the trophoblast proliferation and autophagy. Furthermore, significant decrease of EZH2 levels and inactivation of mTOR signaling were observed in AD-MSC exosomes-treated trophoblasts. Consistent with these findings, overexpression of EZH2 activated the mTOR signaling in trophoblasts, and reduced the autophagy and survival of trophoblasts, even in the presence of AD-MSC-derived exosomes. In addition, EZH2 inhibition exhibited the same trophoblast autophagy-promoting effect as induced by AD-MSC-derived exosomes, also accompanied by the inactivation of mTOR signaling. Importantly, when EZH2 was overexpressed in trophoblasts treated with PQR620, a specific mTOR signaling inhibitor, the autophagy and proliferation in trophoblasts were decreased. Studies on human placental explants also confirmed our findings by showing that the expression levels of EZH2 and mTOR were decreased while the autophagy-associated protein level was increased by AD-MSC-derived exosome treatment. In summary, our results suggest that EZH2-dependent mTOR signaling inactivation mediated by AD-MSC-derived exosomes is a prerequisite for autophagy augmentation in hypoxic trophoblasts.

A Zinc-Dependent Metalloproteinase of Brucella abortus Is Required in the Intracellular Adaptation of Macrophages

Brucella abortus is a pathogen that survives in macrophages. Several virulence factors participate in this process, including the open reading frame (ORF) BAB1_0270 codifying for a zinc-dependent metalloproteinase (ZnMP). Here, its contribution in the intracellular adaptation of B. abortus was analyzed by infecting RAW264.7 macrophages with the mutant B. abortus Δ270 strain. Results showed that this ZnMP did not participated in either the adherence or the initial intracellular traffic of B. abortus in macrophages. Nevertheless, its deletion significantly increased the co-localization of B. abortus Δ270 with phagolysosomal cathepsin D and reduced its co-localization with calnexin present in endoplasmic reticulum (RE)-derived vesicles. Although B. abortus Δ270 showed an upregulated expression of genes involved in virulence (vjbR, hutC, bvrR, virB1), it was insufficient to reach a successful intracellular replication within macrophages. Furthermore, its attenuation favored in macrophages infected the production of high levels of cytokines (TNF-α and IL-6) and co-stimulatory proteins (CD80 and CD86), signals required in T cell activation. Finally, its deletion significantly reduced the ability of B. abortus Δ270 to adapt, grow and express several virulence factors under acidic conditions. Based on these results, and considering that this ZnMP has homology with ImmA/IrrE proteases, we discuss its role in the virulence of this pathogen, concluding that ZnMP is required in the intracellular adaptation of B. abortus 2308 during the infection of macrophages.

Bacterial Manipulation of Autophagic Responses in Infection and Inflammation

Eukaryotes have cell-autonomous defenses against environmental stress and pathogens. Autophagy is one of the main cellular defenses against intracellular bacteria. In turn, bacteria employ diverse mechanisms to interfere with autophagy initiation and progression to avoid elimination and even to subvert autophagy for their benefit. This review aims to discuss recent findings regarding the autophagic responses regulated by bacterial effectors. Effectors manipulate autophagy at different stages by using versatile strategies, such as interfering with autophagy-initiating signaling, preventing the recognition of autophagy-involved proteins, subverting autophagy component homeostasis, manipulating the autophagy process, and impacting other biological processes. We describe the barriers for intracellular bacteria in host cells and highlight the role of autophagy in the host-microbial interactions. Understanding the mechanisms through which bacterial effectors manipulate host responses will provide new insights into therapeutic approaches for prevention and treatment of chronic inflammation and infectious diseases.

Stenotrophomonas maltophilia Encodes a VirB/VirD4 Type IV Secretion System That Modulates Apoptosis in Human Cells and Promotes Competition against Heterologous Bacteria, Including Pseudomonas aeruginosa

Stenotrophomonas maltophilia is an emerging opportunistic and nosocomial pathogen. S. maltophilia is also a risk factor for lung exacerbations in cystic fibrosis patients. S. maltophilia attaches to various mammalian cells, and we recently documented that the bacterium encodes a type II secretion system which triggers detachment-induced apoptosis in lung epithelial cells. We have now confirmed that S. maltophilia also encodes a type IVA secretion system (VirB/VirD4 [VirB/D4] T4SS) that is highly conserved among S. maltophilia strains and, looking beyond the Stenotrophomonas genus, is most similar to the T4SS of Xanthomonas To define the role(s) of this T4SS, we constructed a mutant of strain K279a that is devoid of secretion activity due to loss of the VirB10 component. The mutant induced a higher level of apoptosis upon infection of human lung epithelial cells, indicating that a T4SS effector(s) has antiapoptotic activity. However, when we infected human macrophages, the mutant triggered a lower level of apoptosis, implying that the T4SS also elaborates a proapoptotic factor(s). Moreover, when we cocultured K279a with strains of Pseudomonas aeruginosa, the T4SS promoted the growth of S. maltophilia and reduced the numbers of heterologous bacteria, signaling that another effector(s) has antibacterial activity. In all cases, the effect of the T4SS required S. maltophilia contact with its target. Thus, S. maltophilia VirB/D4 T4SS appears to secrete multiple effectors capable of modulating death pathways. That a T4SS can have anti- and prokilling effects on different targets, including both human and bacterial cells, has, to our knowledge, not been seen before.