Mycoplasma hyopneumoniae Inhibits Porcine Beta-Defensin 2 Production by Blocking the Unfolded Protein Response To Facilitate Epithelial Adhesion and Infection

Mycoplasma hyopneumoniae nuclease Mhp597 negatively regulates TBK1-IRF3-IFN-I pathway by targeting vimentin to facilitate infection

Infection with Mycoplasma hyopneumoniae (M. hyopneumoniae) leads to chronic infectious pneumonia in pigs, resulting in significant distress and economic losses in the global pig industry. The pathogen secretes various proteins, including toxins, adhesins, and virulence-related enzymes, which facilitate adhesion, invasion, and immune evasion processes between bacteria and the host. However, the effector proteins of M. hyopneumoniae are predominantly uncharacterized. In this study, we demonstrate that the nuclease Mhp597 functions as a potential effector protein of M. hyopneumoniae, and we elucidate its mechanism of action in facilitating immune evasion. Our findings indicate that Mhp597 exhibits high expression efficiency in host cells and significantly inhibits IFN-α and IFN-β protein expression. Using yeast two-hybrid and co-immunoprecipitation experiments, we established that Mhp597 interacts with porcine alveolar macrophage vimentin (Vim) via specific amino acid residues (Arg 232, Lys 256, Phe 263, and Lys 317). Further analysis revealed that Mhp597 inhibited the phosphorylation of TBK1 and IRF3 via Vim, thereby suppressing type I interferon (IFN-I) production and promoting the proliferation of M. hyopneumoniae within host cells. In conclusion, this study provides the first detailed account of the molecular mechanism by which Mhp597 negatively regulates the TBK1-IRF3-IFN-I signaling pathway through Vim, thus facilitating immune evasion and proliferation of M. hyopneumoniae within host cells. These findings enhance our understanding of the pathogenic mechanisms of M. hyopneumoniae and suggest potential molecular targets for the development of novel therapeutic strategies.

Mycoplasma ovipnuemoniae impairs the immune response of sheep and suppresses neutrophil function by inhibiting S100A9

Mycoplasma pneumonia is a chronic respiratory disease that seriously affects the health of sheep. To date, little information is available about the damage caused by Mycoplasma ovipneumoniae (MO) pneumonia to host lungs. Here, after sheep were infected with MO for 28 days, severe inflammatory reactions and pathological damage occurred. By using single-cell RNA sequencing (scRNA-seq), all the transcriptome changes in 11 cell types in sheep lung tissue were systematically analyzed, and the key biological processes regulating inflammation and immunity were identified. Moreover, we constructed both intercellular communication models and differential expression maps of key regulatory genes for each cell subgroup. We also specifically focused on the response of T cell subpopulations and neutrophils to MO infection. Long-term infection may affect an organism's immune response, inhibit intercellular communication, and highlight the important role of the cyclophilin A (CypA) and macrophage migration inhibitory factor (MIF) pathways in intercellular communication. Notably, MO infection decreased the toxicity of CD8 effector T cells and depleted regulatory T cells, thus inhibiting normal cell function. Subsequently, emphasis was placed on the important role of the neutrophil marker gene S100A9 in promoting neutrophil clearance of MO through activation of the ERK signaling pathway and reactive oxygen species (ROS) burst in vitro. These results contribute to understanding the progression of MO infection in the lungs and provide a rich database on the molecular basis of the response to different cell types in MO infection.

Mycoplasma hyopneumoniae inhibits the unfolded protein response to prevent host macrophage apoptosis and M2 polarization

Enzootic pneumonia caused by Mycoplasma hyopneumoniae (M. hyopneumoniae) has inflicted substantial economic losses on the global pig industry. The progression of M. hyopneumoniae induced-pneumonia is associated with lung immune cell infiltration and extensive proinflammatory cytokine secretion. Our previous study established that M. hyopneumoniae disrupts the host unfolded protein response (UPR), a process vital for the survival and immune function of macrophages. In this study, we demonstrated that M. hyopneumoniae targets the UPR- and caspase-12-mediated endoplasmic reticulum (ER)-associated classical intrinsic apoptotic pathway to interfere with host cell apoptosis signaling, thereby preserving the survival of host tracheal epithelial cells (PTECs) and alveolar macrophages (PAMs) during the early stages of infection. Even in the presence of apoptosis inducers, host cells infected with M. hyopneumoniae exhibited an anti-apoptotic potential. Further analyses revealed that M. hyopneumoniae suppresses the three UPR branches and their induced apoptosis. Interestingly, while UPR activation typically drives host macrophages toward an M2 polarization phenotype, M. hyopneumoniae specifically obstructs this process to maintain a proinflammatory phenotype in the host macrophages. Overall, our findings propose that M. hyopneumoniae inhibits the host UPR to sustain macrophage survival and a proinflammatory phenotype, which may be implicated in its pathogenesis in inducing host pneumonia.

Research Progress on Immune Evasion of Mycoplasma hyopneumoniae

As the main pathogen associated with enzootic pneumonia (EP), Mycoplasma hyopneumoniae (Mhp) is globally prevalent and inflicts huge financial losses on the worldwide swine industry each year. However, the pathogenicity of Mhp has not been fully explained to date. Mhp invasion usually leads to long-term chronic infection and persistent lung colonization, suggesting that Mhp has developed effective immune evasion strategies. In this review, we offer more detailed information than was previously available about its immune evasion mechanisms through a systematic summary of the extant findings. Genetic mutation and post-translational protein processing confer Mhp the ability to alter its surface antigens. With the help of adhesins, Mhp can achieve cell invasion. And Mhp can modulate the host immune system through the induction of inflammation, incomplete autophagy, apoptosis, and the suppression of immune cell or immune effector activity. Furthermore, we offer the latest views on how we may treat Mhp infections and develop novel vaccines.

Bacterial effector restricts liquid-liquid phase separation of ZPR1 to antagonize host UPRER

How pathogens manipulate host UPR^ER to mediate immune evasion is largely unknown. Here, we identify the host zinc finger protein ZPR1 as an interacting partner of the enteropathogenic E. coli (EPEC) effector NleE using proximity-enabled protein crosslinking. We show that ZPR1 assembles via liquid-liquid phase separation (LLPS) in vitro and regulates CHOP-mediated UPR^ER at the transcriptional level. Interestingly, in vitro studies show that the ZPR1 binding ability with K63-ubiquitin chains, which promotes LLPS of ZPR1, is disrupted by NleE. Further analyses indicate that EPEC restricts host UPR^ER pathways at the transcription level in a NleE-ZPR1 cascade-dependent manner. Together, our study reveals the mechanism by which EPEC interferes with CHOP-UPR^ER via regulating ZPR1 to help pathogens escape host defense.

Baicalin ameliorates Mycoplasma gallisepticum-induced inflammatory injury via inhibiting STIM1-regulated ceramide accumulation in DF-1 cells

Mycoplasma gallisepticum (MG) is dependent on its host for many nutrients due to the loss of many important metabolic pathways. Ceramide is a sphingolipid that regulates multiple cellular processes in eukaryotic cell. Several studies highlighted the crucial role of ceramide on the pathogenesis of various pathogens. This study aimed to determine whether ceramide plays a crucial role in the pathogenesis of MG. Based on an MG infection model in DF-1 cells, the results revealed that MG infection induced ceramide accumulation in DF-1 cells. Inhibiting the de novo synthesis of ceramide significantly inhibited MG proliferation and inflammatory injury caused by MG in DF-1 cells. Meanwhile, MG infection led to endoplasmic reticulum stress, and pharmacologic inhibition of endoplasmic reticulum stress prevented ceramide accumulation and MG proliferation in DF-1 cells, alleviating the inflammatory injury caused by MG. In addition, MG infection significantly promoted expression level of stromal interaction molecule 1 (STIM1), thus induced calcium overload and oxidative stress. Furthermore, inhibition of STIM1 expression partially restored calcium homeostasis and mitigated oxidative stress, thus alleviated endoplasmic reticulum stress. Importantly, the inflammatory injury caused by MG were partially ameliorated by baicalin treatment (20 µg/mL) through downregulating STIM1 expression. In summary, these results suggests that ceramide accumulation through the de novo pathway plays an important role to promote MG proliferation and baicalin can alleviate MG infection induced inflammatory injury via regulating STIM1-related oxidative stress, endoplasmic reticulum stress and ceramide accumulation in DF-1 cells.

Stress granules: potential therapeutic targets for infectious and inflammatory diseases

Eukaryotic cells are stimulated by external pressure such as that derived from heat shock, oxidative stress, nutrient deficiencies, or infections, which induce the formation of stress granules (SGs) that facilitates cellular adaptation to environmental pressures. As aggregated products of the translation initiation complex in the cytoplasm, SGs play important roles in cell gene expression and homeostasis. Infection induces SGs formation. Specifically, a pathogen that invades a host cell leverages the host cell translation machinery to complete the pathogen life cycle. In response, the host cell suspends translation, which leads to SGs formation, to resist pathogen invasion. This article reviews the production and function of SGs, the interaction between SGs and pathogens, and the relationship between SGs and pathogen-induced innate immunity to provide directions for further research into anti-infection and anti-inflammatory disease strategies.

The attenuated Mycoplasma bovis strain promotes apoptosis of bovine macrophages by upregulation of CHOP expression

Mycoplasma bovis (M. bovis) is one of the major pathogens in the bovine respiratory disease complex, which includes pneumonia, mastitis, and arthritis and causes a great economic loss in the cattle industry. In China, a live-attenuated vaccine strain M. bovis P150 was obtained by a continuous culture of the wild-type strain M. bovis HB0801 (P1) in vitro for 150 passages. Using the infected bovine macrophage cell line BoMac, this work attempted to investigate the mechanism of P150 attenuation and protective immune response. To begin, we show that M. bovis P150 effectively triggered cytotoxicity and apoptosis in BoMac, although with lower intracellular survival than P1. The transcriptomes of BoMac after infection with M. bovis strains P1 and P150 were sequenced, and bioinformatic analysis identified 233 differentially expressed genes (DEGs), with 185 upregulated and 48 downregulated. Further Gene Ontology (GO) and Kyoto encyclopedia of genes and genomes (KEGG) pathway enrichment analyses revealed that the majority of the DEGs were linked to CHOP complex, MAP kinase phosphatase activity and were involved in the IL-17 signaling pathway in immune response, MAPK signaling pathway in signal transduction, and p53 signaling pathway in cell growth and death. Among them, the level of C/EBP homologous protein (CHOP) was significantly upregulated in P150-infected BoMac compared to P1-infected cells at different time points, along with its upstream and downstream genes phosphorylated-PERK, phosphorylated-EIF2α, ATF4, and GADD45A increased in the PERK-dependent ER stress response. The role of CHOP in apoptosis was further verified by M. bovis-induced siCHOP knockdown in BoMac cells. The results showed that CHOP knockdown enhanced P150-induced apoptosis and dramatically increased the M. bovis P1 and P150 intracellular survival, particularly for P150. These data suggest that P150 infection upregulates CHOP expression, which can increase apoptosis and mediate a crosstalk between ER stress and apoptosis during infection, and hence, contribute to high cytotoxicity and low intracellular survival.

Mycoplasma hyopneumoniae membrane protein Mhp271 interacts with host UPR protein GRP78 to facilitate infection

The unfolded protein response (UPR) plays a crucial role in Mycoplasma hyopneumoniae (M. hyopneumoniae) pathogenesis. We previously demonstrated that M. hyopneumoniae interferes with the host UPR to foster bacterial adhesion and infection. However, the underlying molecular mechanism of this UPR modulation is unclear. Here, we report that M. hyopneumoniae membrane protein Mhp271 interacts with host GRP78, a master regulator of UPR localized to the porcine tracheal epithelial cells (PTECs) surface. The interaction of Mhp271 with GRP78 reduces the porcine beta‐defensin 2 (PBD‐2) production, thereby facilitating M. hyopneumoniae adherence and infection. Furthermore, the R1‐2 repeat region of Mhp271 is crucial for GRP78 binding and the regulation of PBD‐2 expression. Intriguingly, a coimmunoprecipitation (Co‐IP) assay and molecular docking prediction indicated that the ATP, rather than the substrate‐binding domain of GRP78, is targeted by Mhp271 R1‐2. Overall, our findings identify host GRP78 as a target for M. hyopneumoniae Mhp271 modulating the host UPR to facilitate M. hyopneumoniae adherence and infection.

Pathogenicity & virulence of Mycoplasma hyopneumoniae

Mycoplasma hyopneumoniae: is the etiological agent of porcine enzootic pneumonia (EP), a disease that impacts the swine industry worldwide. Pathogen-induced damage, as well as the elicited host-response, contribute to disease. Here, we provide an overview of EP epidemiology, control and prevention, and a more in-depth review of M. hyopneumoniae pathogenicity determinants, highlighting some molecular mechanisms of pathogen-host interactions relevant for pathogenesis. Based on recent functional, immunological, and comparative “omics” results, we discuss the roles of many known or putative M. hyopneumoniae virulence factors, along with host molecules involved in EP. Moreover, the known molecular bases of pathogenicity mechanisms, including M. hyopneumoniae adhesion to host respiratory epithelium, protein secretion, cell damage, host microbicidal response and its modulation, and maintenance of M. hyopneumoniae homeostasis during infection are described. Recent findings regarding M. hyopneumoniae pathogenicity determinants also contribute to the development of novel diagnostic tests, vaccines, and treatments for EP.

Hiding in Plain Sight: Formation and Function of Stress Granules During Microbial Infection of Mammalian Cells

Stress granule (SG) formation is a host cell response to stress-induced translational repression. SGs assemble with RNA-binding proteins and translationally silent mRNA. SGs have been demonstrated to be both inhibitory to viruses, as well as being subverted for viral roles. In contrast, the function of SGs during non-viral microbial infections remains largely unexplored. A handful of microbial infections have been shown to result in host SG assembly. Nevertheless, a large body of evidence suggests SG formation in hosts is a widespread response to microbial infection. Diverse stresses caused by microbes and their products can activate the integrated stress response in order to inhibit translation initiation through phosphorylation of the eukaryotic translation initiation factor 2α (eIF2α). This translational response in other contexts results in SG assembly, suggesting that SG assembly can be a general phenomenon during microbial infection. This review explores evidence for host SG formation in response to bacterial, fungal, and protozoan infection and potential functions of SGs in the host and for adaptations of the pathogen.