Plasmin activity in the porcine airways is enhanced during experimental infection with Mycoplasma hyopneumoniae, is positively correlated with proinflammatory cytokine levels and is ameliorated by vaccination

Mycoplasma invasion into host cells: An integrated model of infection strategy

Mycoplasma belong to the genus Mollicutes and are notable for their small genome sizes (500-1300 kb) and limited biosynthetic capabilities. They exhibit pathogenicity by invading various cell types to survive as intracellular pathogens. Adhesion is a crucial prerequisite for successful invasion and is orchestrated by the interplay between mycoplasma surface adhesins and specific receptors on the host cell membrane. Invasion relies heavily on clathrin- and caveolae-mediated internalization, accompanied by multiple activated kinases, cytoskeletal rearrangement, and a myriad of morphological alterations, such as membrane invagination, nuclear hypertrophy and aggregation, cytoplasmic edema, and vacuolization. Once mycoplasma successfully invade host cells, they establish resilient sanctuaries in vesicles, cytoplasm, perinuclear regions, and the nucleus, wherein specific environmental conditions favor long-term survival. Although lysosomal degradation and autophagy can eliminate most invading mycoplasmas, some viable bacteria can be released into the extracellular environment via exocytosis, a crucial factor in the prolonging infection persistence. This review explores the intricate mechanisms by which mycoplasma invades host cells and perpetuates their elusive survival, with the aim of highlighting the challenge of eradicating this enigmatic bacterium.

Hijacking of Host Plasminogen by Mesomycoplasma (Mycoplasma) hyopneumoniae via GAPDH: an Important Virulence Mechanism To Promote Adhesion and Extracellular Matrix Degradation

Mesomycoplasma hyopneumoniae is the etiological agent of mycoplasmal pneumonia of swine (MPS), which causes substantial economic losses to the world's swine industry. Moonlighting proteins are increasingly being shown to play a role in the pathogenic process of M. hyopneumoniae. Glyceraldehyde-3-phosphate dehydrogenase (GAPDH), a key enzyme in glycolysis, displayed a higher abundance in a highly virulent strain of M. hyopneumoniae than in an attenuated strain, suggesting that it may have a role in virulence. The mechanism by which GAPDH exerts its function was explored. Flow cytometry and colony blot analysis showed that GAPDH was partly displayed on the surface of M. hyopneumoniae. Recombinant GAPDH (rGAPDH) was able to bind PK15 cells, while the adherence of a mycoplasma strain to PK15 was significantly blocked by anti-rGAPDH antibody pretreatment. In addition, rGAPDH could interact with plasminogen. The rGAPDH-bound plasminogen was demonstrated to be activated to plasmin, as proven by using a chromogenic substrate, and to further degrade the extracellular matrix (ECM). The critical site for GAPDH binding to plasminogen was K336, as demonstrated by amino acid mutation. The affinity of plasminogen for the rGAPDH C-terminal mutant (K336A) was significantly decreased according to surface plasmon resonance analysis. Collectively, our data suggested that GAPDH might be an important virulence factor that facilitates the dissemination of M. hyopneumoniae by hijacking host plasminogen to degrade the tissue ECM barrier. IMPORTANCE Mesomycoplasma hyopneumoniae is a specific pathogen of pigs that is the etiological agent of mycoplasmal pneumonia of swine (MPS), which is responsible for substantial economic losses to the swine industry worldwide. The pathogenicity mechanism and possible particular virulence determinants of M. hyopneumoniae are not yet completely elucidated. Our data suggest that GAPDH might be an important virulence factor in M. hyopneumoniae that facilitates the dissemination of M. hyopneumoniae by hijacking host plasminogen to degrade the extracellular matrix (ECM) barrier. These findings will provide theoretical support and new ideas for the research and development of live-attenuated or subunit vaccines against M. hyopneumoniae.

Oral Immunization with Attenuated Salmonella Choleraesuis Expressing the P42 and P97 Antigens Protects Mice against Mycoplasma hyopneumoniae Challenge

Mycoplasma hyopneumoniae (M. hyopneumoniae, Mhp) is the etiological agent of swine enzootic pneumonia (EP), which has been associated with considerable economic losses due to reduced daily weight gain and feed efficiency. Adhesion to the cilia is important for Mhp to colonize the respiratory epithelium. Therefore, a successful vaccine must induce broad Mhp-specific immune responses at the mucosal surface. Recombinant attenuated Salmonella strains are believed to act as powerful live vaccine vectors that are able to elicit mucosal immune responses against various pathogens. To develop efficacious and inexpensive vaccines against Mhp, the immune responses and protection induced by recombinant attenuated Salmonella vaccines based on the P42 and P97 antigens of Mhp were evaluated. In general, the oral inoculation of recombinant rSC0016(pS-P42) or rSC0016(pS-P97) resulted in strong mucosal immunity, cell-mediated immunity, and humoral immunity, which was a mixed Th1/Th2-type response. In addition, the levels of specific IL-4 and IFN-γ in the immunized mice were increased, and the proliferation of lymphocytes was also enhanced, confirming the production of a good cellular immune response. Finally, both vaccine candidate strains were able to improve the weight loss of mice after a challenge and reduce clinical symptoms, lung pathological damage, and the inflammatory cell infiltration. These results suggest that the delivery of protective antigens with recombinant attenuated Salmonella vectors may be an effective means by which to combat Mhp infection. IMPORTANCE Mhp is the main pathogen of porcine enzootic pneumonia, a highly infectious and economically significant respiratory disease that affects pigs of all ages. As the target tissue of Mhp infections are the mucosal sites of the respiratory tract, the induction of protective immunity at the mucosal tissues is the most efficient strategy by which to block disease transmission. Because the stimulation of mucosal immune responses is efficient, Salmonella-vector oral vaccines are expected to be especially useful against mucosal-invading pathogens. In this study, we expressed the immunogenic proteins of P42 and P97 with the attenuated Salmonella Choleraesuis vector rSC0016, thereby generating a low-cost and more effective vaccine candidate against Mhp by inducing significant mucosal, humoral and cellular immunity. Furthermore, rSC0016(pS-P42) effectively prevents Mhp-induced weight loss and the pulmonary inflammation of mice. Because of the effectiveness of rSC0016(pS-P42) against Mhp infection in mice, this novel vaccine candidate strain shows great potential for its use in the pig breeding industry.

Reannotation of Mycoplasma hyopneumoniae hypothetical proteins revealed novel potential virulence factors

Mycoplasma hyopneumoniae is a bacterium that inhabits the swine respiratory tract, causing porcine enzootic pneumonia, which generates significant economic losses to the swine industry worldwide. The knowledge on M. hyopneumoniae biology and virulence have been significantly increased by genomics studies. However, around 30% of the predicted proteins remained of unknown function so far. According to the original annotation, the genome of M. hyopneumoniae 7448, a Brazilian pathogenic strain, had 693 coding DNA sequences, 244 of which were annotated as coding for hypothetical or uncharacterized proteins. Among them, there may be still several genes coding for unknown virulence factors. Therefore, this study aimed to functionally reannotate the whole set of 244 M. hyopneumoniae 7448 proteins of unknown function based on currently available database and bioinformatic tools, in order to predict novel potential virulence factors. Predictions of physicochemical properties, subcellular localization, function, overall association to virulence and antigenicity are provided. With that, 159 out of the set of 244 proteins of unknown function had a putative function associated to them, allowing identification of novel enzymes, membrane transporters, lipoproteins, DNA-binding proteins and adhesins. Furthermore, 139 proteins were generally associated to virulence, 14 of which had a function assigned and were differentially expressed between pathogenic and non-pathogenic strains of M. hyopneumoniae. Moreover, all extracellular or cytoplasmic membrane predicted proteins had putative epitopes identified. Overall, these analyses improved the functional annotation of M. hyopneumoniae 7448 genome from 65% to 87% and allowed the identification of new potential virulence factors.

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.

Genomic Variability and Post-translational Protein Processing Enhance the Immune Evasion of Mycoplasma hyopneumoniae and Its Interaction With the Porcine Immune System

Mycoplasma hyopneumoniae (M. hyopneumoniae, Mhp) is a geographically widespread and economically devastating pathogen that colonizes ciliated epithelium; the infection of Mhp can damnify the mucociliary functions as well as leading to Mycoplasma pneumonia of swine (MPS). MPS is a chronic respiratory infectious disease with high infectivity, and the mortality can be increased by secondary infections as the host immunity gets down-regulated during Mhp infection. The host immune responses are regarded as the main driving force for the disease development, while MPS is prone to attack repeatedly in farms even with vaccination or other treatments. As one of the smallest microorganisms with limited genome scale and metabolic pathways, Mhp can use several mechanisms to achieve immune evasion effect and derive enough nutrients from its host, indicating that there is a strong interaction between Mhp and porcine organism. In this review, we summarized the immune evasion mechanisms from genomic variability and post-translational protein processing. Besides, Mhp can induce the immune cells apoptosis by reactive oxygen species production, excessive nitric oxide (NO) release and caspase activation, and stimulate the release of cytokines to regulate inflammation. This article seeks to provide some new points to reveal the complicated interaction between the pathogen and host immune system with Mhp as a typical example, further providing some new strategies for the vaccine development against Mhp infection.

Elevated Plasmin(ogen) as a Common Risk Factor for COVID-19 Susceptibility

Patients with hypertension, diabetes, coronary heart disease, cerebrovascular illness, chronic obstructive pulmonary disease, and kidney dysfunction have worse clinical outcomes when infected with SARS-CoV-2, for unknown reasons. The purpose of this review is to summarize the evidence for the existence of elevated plasmin(ogen) in COVID-19 patients with these comorbid conditions. Plasmin, and other proteases, may cleave a newly inserted furin site in the S protein of SARS-CoV-2, extracellularly, which increases its infectivity and virulence. Hyperfibrinolysis associated with plasmin leads to elevated D-dimer in severe patients. The plasmin(ogen) system may prove a promising therapeutic target for combating COVID-19.

Zinc oxide nanoparticles from Corydalis yanhusuo attenuated the mycoplasmal pneumonia in mice through inhibiting the MAPKs signaling pathway

BACKGROUND

The Mycoplasma pneumoniae (M.pneumoniae) was accounted to 3-10% of total pneumonia incidences. In recent decades, metallic nanoparticles were extensively examined as nano-antibiotics.

OBJECTIVE

In this investigation, we intended to inspect the therapeutic potential of Zinc oxide nanoparticles (ZnONPs) from (Corydalis yanhusuo) C. yanhusuo against the mycoplasma infected pneumonia in mice.

METHODOLOGY

The ZnONPs were formulated via green route technique and characterized by UV-vis spectroscopy, transmission electron microscopy, Fourier transform infrared technique, and atomic force microscopy. The antimicrobial activity of formulated ZnONPs was tested by well diffusion method. The total protein, interleukin-1 (IL-1), interleukin-6 (IL-6), interleukin-8 (IL-8), tumor necrosis factor alpha (TNF-α) and transforming growth factor (TGF) status in the BALF of M. pneumonia infected animals were investigated via kit method. The expressions of ERK1/2, JNK1/2, and NF-κB were examined through the Western blotting. The Histopathological analysis of lung tissues of experimental animals was done.

RESULTS

The UV-vis spectroscopy and TEM examinations were proved the existence of CY-ZnONPs. The formulated CY-ZnONPs were displayed the potential antimicrobial activity. The supplementation of CY-ZnONPs were noticeably diminished the total protein and IL-6, IL-8, and TNF-α levels in the BALF of pneumonia mice. The ERK1/2, JNK1/2, and NF-κB expressions were appreciably diminished in the CY-ZnONPs supplemented mice. It also reduced the inflammatory cells penetration, and exhibited normal tissue arrangements in the lung tissues of pneumonia mice.

CONCLUSION

The findings of this investigation were proved that the synthesized CY-ZnONPs has the potential to ameliorate the M. pneumoniae infected pneumonia in investigational mice.

Identification of a novel TLR5 agonist derived from the P97 protein of Mycoplasma hyopneumoniae

By modulating specific immune responses against antigens, adjuvants are used in many vaccine preparations to enhance protective immunity. The C-terminal domain of the protein P97 (P97c) of Mycoplasma hyopneumoniae, which is the etiologic agent of porcine enzootic pneumonia, has been shown to increase the specific humoral response against an antigen when this antigen is merged with P97c and delivered by adenovectors. However, the immunostimulating mechanism of this protein remains unknown. In the present study, recombinantly expressed P97c triggered a concentration-dependent TLR5 activation and stimulates the production of interleukin-8 from HEK-Blue mTLR5 cells. Circular dichroism spectroscopy and prediction of 3-dimensional conformation exposed a relevant secondary and tertiary structural homology between P97c and flagellin, the known potent TLR5 agonist. P97c adjuvanticity was evaluated by fusing the conserved epitope of the ectodomain matrix 2 protein (M2e) of the influenza A virus to the protein. Mice immunized with P97c-3M2e revealed a high antibody titer against the M2e epitope associated with a mixed Th1/Th2 immune response. Overall, this study identifies a novel agonist of the pattern recognition receptor TLR5 and reveals that P97c is a potential adjuvant through the activation of the innate immune system.

Differential responses to stress of two Mycoplasma hyopneumoniae strains

Mycoplasma hyopneumoniae is a respiratory pathogen, causing porcine enzootic pneumonia. To survive in the porcine respiratory tract, M. hyopneumoniae must cope with both oxidative and heat stress imposed by the host. To get insights into M. hyopneumoniae stress responses and pathogenicity mechanisms, the protein profiles of two M. hyopneumoniae strains, pathogenic 7448 strain and non-pathogenic strain J, were surveyed under oxidative (OS) or heat (HS) stress. M. hyopneumoniae strains were submitted to OS (0.5% hydrogen peroxide) or HS (temperature shifts to 42 °C) conditions and protein profiling was carried out by LC-MS/MS and label-free quantitative analyses. Data are available via ProteomeXchange with identifier PXD012742. Qualitative and quantitative differences involving 40-60 M. hyopneumoniae proteins were observed for both strains when comparing bacteria exposed to OS or HS to non-treated controls. However, no differences in abundance were found in proteins classically related to stress responses, as peroxidases and chaperones, suggesting that these proteins would be constitutively present in both strains in the tested conditions. Interestingly, under stress conditions, more virulence-related proteins were detected in M. hyopneumoniae 7448 differentially represented proteins than in M. hyopneumoniae J, suggesting that stress may trigger a differential response of the corresponding genes, shared by both strains.

Mycoplasma hyopneumoniae resides intracellularly within porcine epithelial cells

Enzootic pneumonia incurs major economic losses to pork production globally. The primary pathogen and causative agent, Mycoplasma hyopneumoniae, colonises ciliated epithelium and disrupts mucociliary function predisposing the upper respiratory tract to secondary pathogens. Alleviation of disease is reliant on antibiotics, vaccination, and sound animal husbandry, but none are effective at eliminating M. hyopneumoniae from large production systems. Sustainable pork production systems strive to lower reliance on antibiotics but lack of a detailed understanding of the pathobiology of M. hyopneumoniae has curtailed efforts to develop effective mitigation strategies. M. hyopneumoniae is considered an extracellular pathogen. Here we show that M. hyopneumoniae associates with integrin β1 on the surface of epithelial cells via interactions with surface-bound fibronectin and initiates signalling events that stimulate pathogen uptake into clathrin-coated vesicles (CCVs) and caveosomes. These early events allow M. hyopneumoniae to exploit an intracellular lifestyle by commandeering the endosomal pathway. Specifically, we show: (i) using a modified gentamicin protection assay that approximately 8% of M. hyopneumoniae cells reside intracellularly; (ii) integrin β1 expression specifically co-localises with the deposition of fibronectin precisely where M. hyopneumoniae cells assemble extracellularly; (iii) anti-integrin β1 antibodies block entry of M. hyopneumoniae into porcine cells; and (iv) M. hyopneumoniae survives phagolysosomal fusion, and resides within recycling endosomes that are trafficked to the cell membrane. Our data creates a paradigm shift by challenging the long-held view that M. hyopneumoniae is a strict extracellular pathogen and calls for in vivo studies to determine if M. hyopneumoniae can traffic to extrapulmonary sites in commercially-reared pigs.

Surface proteins mhp390 (P68) contributes to cilium adherence and mediates inflammation and apoptosis in Mycoplasma hyopneumoniae

Mycoplasma hyopneumoniae is the causative agent of porcine enzootic pneumonia (EP) and responsible for major economic losses in global swine industry. After colonization of the respiratory epithelium, M. hyopneumoniae elicits a general mucociliary clearance loss, prolonged inflammatory response, host immunosuppression and secondary infections. Until now, the pathogenesis of M. hyopneumoniae is not completely elucidated. This present study explores the pathogenicity of mhp390 (P68, a membrane-associated lipoprotein) by elucidating its multiple functions. Microtitrer plate adherence assay demonstrated that mhp390 is a new cilia adhesin that plays an important role in binding to swine tracheal cilia. Notably, mhp390 could induce significant apoptosis of lymphocytes and monocytes from peripheral blood mononuclear cells (PBMCs), as well as primary alveolar macrophages (PAMs), which might weaken the host immune response. In addition, mhp390 contributes to the production of proinflammatory cytokines, at least partially, via the release of IL-1β and TNF-α. To the best of our knowledge, this is the first report of the multiple functions of M. hyopneumoniae mhp390, which may supplement known virulence genes and further develop our understanding of the pathogenicity of M. hyopneumoniae.

The immune mechanism of Mycoplasma hyopneumoniae 168 vaccine strain through dendritic cells

Background

Mycoplasma hyopneumoniae (Mhp) causes porcine enzootic pneumonia, a disease that cause major economic losses in the pig industry. Dendritic cells (DCs), the most effective antigen-presenting cells, are widely distributed beneath respiratory epithelium, DCs uptake and present antigens to T cells, to initiate protective immune responses in different infections. In this study, we investigated the role of porcine DCs in vaccine Mhp-168 exposure.

Results

The antigen presenting ability of DCs were improved by vaccine Mhp-168 exposure. DCs could activate T-cell proliferation by up-regulating the antigen presenting molecule MHCII expression and co-stimulatory molecule CD80/86. However, the up-regulation of IL-10 and accompany with down-regulation of IFN-γ gene level may account for the limitation of attenuated Mhp-168 strain use as vaccine alone.

Conclusion

These findings are benefit for exploring the protection mechanisms and the possible limitations of this attenuated Mhp-168 vaccine.

Update on Mycoplasma hyopneumoniae infections in pigs: Knowledge gaps for improved disease control

Mycoplasma hyopneumoniae (M. hyopneumoniae) is the primary pathogen of enzootic pneumonia, a chronic respiratory disease in pigs. Infections occur worldwide and cause major economic losses to the pig industry. The present paper reviews the current knowledge on M. hyopneumoniae infections, with emphasis on identification and analysis of knowledge gaps for optimizing control of the disease. Close contact between infected and susceptible pigs is the main route of M. hyopneumoniae transmission. Management and housing conditions predisposing for infection or disease are known, but further research is needed to better understand M. hyopneumoniae transmission patterns in modern pig production systems, and to assess the importance of the breeding population for downstream disease control. The organism is primarily found on the mucosal surface of the trachea, bronchi and bronchioles. Different adhesins and lipoproteins are involved in the adherence process. However, a clear picture of the virulence and pathogenicity of M. hyopneumoniae is still missing. The role of glycerol metabolism, myoinositol metabolism and the Mycoplasma Ig binding protein-Mycoplasma Ig protease system should be further investigated for their contribution to virulence. The destruction of the mucociliary apparatus, together with modulating the immune response, enhances the susceptibility of infected pigs to secondary pathogens. Clinical signs and severity of lesions depend on different factors, such as management, environmental conditions and likely also M. hyopneumoniae strain. The potential impact of strain variability on disease severity is not well defined. Diagnostics could be improved by developing tests that may detect virulent strains, by improving sampling in live animals and by designing ELISAs allowing discrimination between infected and vaccinated pigs. The currently available vaccines are often cost-efficient, but the ongoing research on developing new vaccines that confer protective immunity and reduce transmission should be continued, as well as optimization of protocols to eliminate M. hyopneumoniae from pig herds.

Effects of Mycoplasma hyopneumoniae on porcine nasal cavity dendritic cells

Mycoplasma hyopneumoniae (Mhp) is the primary etiological agent responsible for swine enzootic pneumonia (EP), a disease that cause tremendous economic losses all over the swine industry. Dendritic cells (DCs), the most effective antigen-presenting cells, are widely distributed beneath respiratory epithelium. DCs uptake and present antigens to T cells, to initiate protective immune responses or generate immune-mediated pathology in different infections. In this study, we investigated the changes in the different DCs subpopulations, T cells and SIgA positive cells counts in porcine nasal cavity after long time Mhp infection. We further evaluated the role of porcine DCs in Mhp exposure. Our results showed that the number of SLA-II-DR⁺SWC3a⁺DCs, SLA-II-DR⁺CD11b⁺ DCs, T cells, SIgA positive cells in nasal cavity were decreased after Mhp 28 days infection in vivo experiment. The antigen presenting ability of DCs were inhibited by Mhp exposure. DCs couldn't activate T-cell proliferation by down-regulating the antigen presenting molecule CD1a expression and promoting high level of IL-10 production. Further more, the expression levels of IL-12 and IFN-γ in DCs were decreased, suggesting that DCs favour for Th2 immune response development after Mhp exposure in vitro. Taken together, Mhp infection impairs the immune function which allows the persistence of Mhp and cause predispose pigs to secondary infections. The decline of DCs presentation ability is the reason why dysfunction and persistence in Mhp infection. These findings are benefit for exploring the pathogenic mechanisms of Mhp in pigs.

Induction of mycoplasmal pneumonia in experimentally infected pigs by means of different inoculation routes

The purpose of this study was to assess the effect of three different inoculation routes into mycoplasmal pneumonia (MP) in pigs challenged with Mycoplasma hyopneumoniae (M. hyopneumoniae). Thirty six-week-old M. hyopneumoniae seronegative piglets were randomly assigned to four groups: three challenged groups with experimentally inoculated pigs by either the endotracheal (ET; n = 8), intranasal (IN; n = 8) or aerosol (AE; n = 8) routes and one uninfected group (Control; n = 6). Blood samples were collected 1 day before challenge and at necropsy, 28 days post-inoculation (dpi), to assess seroconversion. Laryngeal swabs were collected at −1, 7, 14, 21 and 28 dpi in order to evaluate colonization. At necropsy, lung lesions were scored and lung tissue was collected for histopathological studies and M. hyopneumoniae DNA detection. Broncho-alveolar lavage fluid (BALF) was also obtained to detect M. hyopneumoniae DNA, specific IgA antibodies and cytokines. MP was observed in all inoculated groups, but the ET group displayed a significantly higher number of animals affected by MP as well as a higher mean lung lesion score. These results were paralleled with an earlier seroconversion and upper respiratory tract colonization of M. hyopneumoniae. Additionally, in the ET group, higher levels of pro-inflammatory cytokines and specific IgA antibodies in BALF were found. Under the conditions of the present study, MP was reproduced by the three evaluated inoculation routes. Obtained results suggest that the ET route is the most effective in order to induce MP in pigs experimentally challenged with M. hyopneumoniae.

MHJ_0461 is a multifunctional leucine aminopeptidase on the surface of Mycoplasma hyopneumoniae

Aminopeptidases are part of the arsenal of virulence factors produced by bacterial pathogens that inactivate host immune peptides. Mycoplasma hyopneumoniae is a genome-reduced pathogen of swine that lacks the genetic repertoire to synthesize amino acids and relies on the host for availability of amino acids for growth. M. hyopneumoniae recruits plasmin(ogen) onto its cell surface via the P97 and P102 adhesins and the glutamyl aminopeptidase MHJ_0125. Plasmin plays an important role in regulating the inflammatory response in the lungs of pigs infected with M. hyopneumoniae. We show that recombinant MHJ_0461 (rMHJ_0461) functions as a leucine aminopeptidase (LAP) with broad substrate specificity for leucine, alanine, phenylalanine, methionine and arginine and that MHJ_0461 resides on the surface of M. hyopneumoniae. rMHJ_0461 also binds heparin, plasminogen and foreign DNA. Plasminogen bound to rMHJ_0461 was readily converted to plasmin in the presence of tPA. Computational modelling identified putative DNA and heparin-binding motifs on solvent-exposed sites around a large pore on the LAP hexamer. We conclude that MHJ_0461 is a LAP that moonlights as a multifunctional adhesin on the cell surface of M. hyopneumoniae.

Exploitation of plasmin(ogen) by bacterial pathogens of veterinary significance

The plasminogen (Plg) system plays an important homeostatic role in the degradation of fibrin clots, extracellular matrices and tissue barriers important for cellular migration, as well as the promotion of neurotransmitter release. Plg circulates in plasma at physiologically high concentrations (150-200μg ml(-1)) as an inactive proenzyme. Proteins enriched in lysine and other positively charged residues (histidine and arginine) as well as glycosaminoglycans and gangliosides bind Plg. The binding interaction initiates a structural adjustment to the bound Plg that facilitates cleavage by proteases (plasminogen activators tPA and uPA) that activate Plg to the active serine protease plasmin. Both pathogenic and commensal bacteria capture Plg onto their cell surface and promote its conversion to plasmin. Many microbial Plg-binding proteins have been described underpinning the importance this process plays in how bacteria interact with their hosts. Bacteria exploit the proteolytic capabilities of plasmin by (i) targeting the mammalian fibrinolytic system and degrading fibrin clots, (ii) remodeling the extracellular matrix and generating bioactive cleavage fragments of the ECM that influence signaling pathways, (iii) activating matrix metalloproteinases that assist in the destruction of tissue barriers and promote microbial metastasis and (iv) destroying immune effector molecules. There has been little focus on the exploitation of the fibrinolytic system by veterinary pathogens. Here we describe several pathogens of veterinary significance that possess adhesins that bind plasmin(ogen) onto their cell surface and promote its activation to plasmin. Cumulative data suggests that these attributes provide pathogenic and commensal bacteria with a means to colonize and persist within the host environment.

Proteolytic processing of the cilium adhesin MHJ_0194 (P123J ) in Mycoplasma hyopneumoniae generates a functionally diverse array of cleavage fragments that bind multiple host molecules

Mycoplasma hyopneumoniae, the aetiological agent of porcine enzootic pneumonia, regulates the presentation of proteins on its cell surface via endoproteolysis, including those of the cilial adhesin P123 (MHJ_0194). These proteolytic cleavage events create functional adhesins that bind to proteoglycans and glycoproteins on the surface of ciliated and non-ciliated epithelial cells and to the circulatory host molecule plasminogen. Two dominant cleavage events of the P123 preprotein have been previously characterized; however, immunoblotting studies suggest that more complex processing events occur. These extensive processing events are characterized here. The functional significance of the P97 cleavage fragments is also poorly understood. Affinity chromatography using heparin, fibronectin and plasminogen as bait and peptide arrays were used to expand our knowledge of the adhesive capabilities of P123 cleavage fragments and characterize a novel binding motif in the C-terminus of P123. Further, we use immunohistochemistry to examine in vivo, the biological significance of interactions between M. hyopneumoniae and fibronectin and show that M. hyopneumoniae induces fibronectin deposition at the site of infection on the ciliated epithelium. Our data supports the hypothesis that M. hyopneumoniae possesses the molecular machinery to influence key molecular communication pathways in host cells.

Mycoplasma hyopneumoniae-derived lipid-associated membrane proteins induce inflammation and apoptosis in porcine peripheral blood mononuclear cells in vitro

Mycoplasma hyopneumoniae is the causative agent of swine enzootic pneumonia (EP), a disease that causes considerable economic losss in swine industry. Lipid-associated membrane proteins (LAMPs) of mycoplasma play important roles in causing mycoplasma diseases. The present study explores the pathogenic mechanisms of M. hyopneumoniae LAMPs by elucidating their role in modulating the inflammation, apoptosis, and relevant signaling pathways of peripheral blood mononuclear cells (PBMCs) of pig. LAMP treatment inhibited the growth of PBMCs. Up-regulation of cytokines, such as IL-6 and IL-1β, as well as increased production of nitric oxide (NO) and superoxide anion were all detected in the supernatant of LAMPs-treated PBMCs. Furthermore, flow cytometric analysis using dual staining with annexin-V-FITC and propidium iodide (PI) showed that LAMPs of M. hyopneumoniae induced a time-dependent apoptosis in lymphocyts and monocytes from PBMCs, which was blocked by NOS inhibitor or antioxidant. In addition, LAMPs induced the phosphorylation of p38, the ratio of pro-apoptotic Bax protein to anti-apoptotic Bcl-2, activation of caspase-3 and caspase-8, and poly ADP-ribose polymerase (PARP) cleavage in PBMCs. These findings demonstrated that M. hyopneumoniae LAMPs induced the production of proinflammatory cytokines, NO and reactive oxygen species (ROS), and apoptosis of PBMCs in vitro through p38 MAPK and Bax/Bcl-2 signaling pathways, as well as caspase activation.

Evaluation of recombinant Mycoplasma hyopneumoniae P97/P102 paralogs formulated with selected adjuvants as vaccines against mycoplasmal pneumonia in pigs

Pig responses to recombinant subunit vaccines containing fragments of eight multifunctional adhesins of the Mycoplasma hyopneumoniae (Mhp) P97/P102 paralog family formulated with Alhydrogel(®) or Montanide™ Gel01 were compared with a commercial bacterin following experimental challenge. Pigs, vaccinated intramuscularly at 9, 12 and 15 weeks of age with either of the recombinant formulations (n=10 per group) or Suvaxyn(®) M. hyo (n=12), were challenged with Mhp strain Hillcrest at 17 weeks of age. Unvaccinated, challenged pigs (n=12) served as a control group. Coughing was assessed daily. Antigen-specific antibody responses were monitored by ELISA in serum and tracheobronchial lavage fluid (TBLF), while TBLF was also assayed for cytokine responses (ELISA) and bacterial load (qPCR). At slaughter, gross and histopathology of lungs were quantified and damage to epithelial cilia in the porcine trachea was evaluated by scanning electron microscopy. Suvaxyn(®) M. hyo administration induced significant serological responses against Mhp strain 232 whole cell lysates (wcl) and recombinant antigen F3P216, but not against the remaining vaccine subunit antigens. Alhydrogel(®) and Montanide™ Gel01-adjuvanted antigen induced significant antigen-specific IgG responses, with the latter adjuvant eliciting comparable Mhp strain 232 wcl specific IgG responses to Suvaxyn(®) M. hyo. No significant post-vaccination antigen-specific mucosal responses were detected with the recombinant vaccinates. Suvaxyn(®) M. hyo was superior in reducing clinical signs, lung lesion severity and bacterial load but the recombinant formulations offered comparable protection against cilial damage. Lower IL-1β, TNF-α and IL-6 responses after challenge were associated with reduced lung lesion severity in Suvaxyn(®) M. hyo vaccinates, while elevated pathology scores in recombinant vaccinates corresponded to cytokine levels that were similarly elevated as in unvaccinated pigs. This study highlights the need for continued research into protective antigens and vaccination strategies that will prevent Mhp colonisation and establishment of infection.

MHJ_0125 is an M42 glutamyl aminopeptidase that moonlights as a multifunctional adhesin on the surface of Mycoplasma hyopneumoniae

Bacterial aminopeptidases play important roles in pathogenesis by providing a source of amino acids from exogenous proteins, destroying host immunological effector peptides and executing posttranslational modification of bacterial and host proteins. We show that MHJ_0125 from the swine respiratory pathogen Mycoplasma hyopneumoniae represents a new member of the M42 class of bacterial aminopeptidases. Despite lacking a recognizable signal sequence, MHJ_0125 is detectable on the cell surface by fluorescence microscopy and LC-MS/MS of (i) biotinylated surface proteins captured by avidin chromatography and (ii) peptides released by mild trypsin shaving. Furthermore, surface-associated glutamyl aminopeptidase activity was detected by incubation of live M. hyopneumoniae cells with the diagnostic substrate H-Glu-AMC. MHJ_0125 moonlights as a multifunctional adhesin, binding to both heparin and plasminogen. Native proteomics and comparative modelling studies suggest MHJ_0125 forms a dodecameric, homopolymeric structure and provide insight into the positions of key residues that are predicted to interact with heparin and plasminogen. MHJ_0125 is the first aminopeptidase shown to both bind plasminogen and facilitate its activation by tissue plasminogen activator. Plasmin cleaves host extracellular matrix proteins and activates matrix metalloproteases, generating peptide substrates for MHJ_0125 and a source of amino acids for growth of M. hyopneumoniae. This unique interaction represents a new paradigm in microbial pathogenesis.