PLATELET ACTIVATION BY HISTOPHILUS SOMNI AND ITS LIPOOLIGOSACCHARIDE INDUCES ENDOTHELIAL CELL PROINFLAMMATORY RESPONSES AND PLATELET INTERNALIZATION

Characterization of Histophilus somni sialic acid uptake mutant (ΔnanP-ΔnanU) using a mouse septicemia and mortality model

Histophilus somni is an important pathogen of the bovine respiratory disease complex, yet the mechanisms underlying its virulence remain poorly understood. It is known that H. somni can incorporate sialic acid into lipooligosaccharide (LOS), and sialylated H. somni is more resistant to phagocytosis and complement-mediated killing by serum compared to non-sialylated bacteria in vitro. However, the virulence of non-sialylated H. somni has not been evaluated in vivo using an animal model. In this study, we investigated the contribution of sialic acid to virulence by constructing an H. somni sialic acid uptake mutant (ΔnanP-ΔnanU) and comparing the parent and mutant strains in a mouse septicemia and mortality model. Intraperitoneal challenge of mice with wildtype H. somni (1 × 108 colony forming units/mouse, CFU) was lethal to all animals. Mice challenged with three different doses (1, 2, or 5 × 108 CFU/mouse) of an H. somni ΔnanP-ΔnanU sialic acid uptake mutant exhibited survival rates of 90 %, 60 %, and 0 % respectively. High-performance anion exchange chromatography analyses revealed that LOS prepared from both parent and the ΔnanP-ΔnanU mutant strains of H. somni were sialylated. These findings suggest the presence of de novo sialic acid synthesis pathway, although the genes associated with de novo sialic acid synthesis (neuB and neuC) were not identified by genomic analysis. The lower attenuation in mice is most likely attributed to the sialylated LOS of H. somni nanPU mutant.

Upregulation of girdin delays endothelial cell apoptosis via promoting engulfment of platelets

BACKGROUND

Endothelial cells are crucial in maintaining the homeostasis of the blood-brain barrier. Girders of actin filament (Girdin) and phosphor (p)-Girdin are essential for the engulfment of human brain microvascular endothelial cells (HBMECs) into platelets (PLTs), but the potential mechanism remains unclear and requires further study.

METHODS

Following PLT and cytochalasin D treatment, Hoechst 33,342 detected apoptosis. The transfection efficiency of the short hairpin RNA targeting Girdin (sh-Girdin) or overexpressing Girdin (OE-Girdin) was determined using western blotting. Sh-Girdin, OE-Girdin, mutated Girdin (m-Girdin), and microfilament binding region deleted Girdin (Del-Girdin) were transfected into HBMECs under PLT conditions. Subsequently, the engulfment of HBMECs by PLTs was detected by flow cytometry and transmission electron microscopy. Girdin and phosphorylated (p)-Girdin levels were quantified by western blot. The positive expression of Girdin was measured by immunohistochemistry (IHC). The localization of PLT, Girdin, and p-Girdin and the engulfment of HBMECs in PLTs were analyzed by confocal microscopy.

RESULT

Cytochalasin D overturned the inhibitory effect of PLT on cell apoptosis. OE-Girdin enhanced the fluorescent intensity of PLT-labelling and the engulfment of HBMECs by PLTs, while sh-Girdin, m-Girdin, and Del-Girdin ran reversely. OE-Girdin elevated the Girdin and p-Girdin levels, while sh-Girdin and Del-Girdin were the opposite, but m-Girdin did not affect the p-Girdin and Girdin levels.

CONCLUSION

Girdin and p-Girdin were co-located with PLTs in HBMECs. The over-expression of Girdin was identified as being associated with the increasing engulfment of PTLs. Girdin may be an effective target to alleviate endothelial cell apoptosis.

Transcript Characteristics on the Susceptibility Difference of Bovine Respiratory Disease

Bovine respiratory disease (BRD) is one of the major health issues in the cattle industry, resulting in significant financial crises globally. There is currently no good treatment, and cattle are made resistant to pneumonia through disease-resistant breeding. The serial blood samples from six Xinjiang brown (XJB) calves were collected for the RNA sequencing (RNA-seq). The obtained six samples were grouped into two groups, in each group as infected with BRD and healthy calves, respectively. In our study, the differential expression mRNAs were detected by using RNA-seq and constructed a protein-protein interaction (PPI) network related to the immunity in cattle. The key genes were identified by protein interaction network analysis, and the results from RNA-seq were verified using reverse transcription-quantitative polymerase chain reaction (RT-qPCR). A total of 488 differentially expressed (DE) mRNAs were identified. Importantly, the enrichment analysis of these identified DEGs classified them as mainly enriched in the regulation and immune response processes. The 16 hub genes were found to be related to immune pathways categorized by PPIs analysis. Results revealed that many hub genes were related to the immune response to respiratory disease. These results will provide the basis for a better understanding of the molecular mechanism of bovine resistance to BRD.

Histophilus somni stimulates bovine monocyte-derived macrophages to release microparticles that increase fibrin clot formation in vitro

Histophilus somni is a Gram-negative coccobacillus that causes diffuse vasculitis and intravascular thrombosis that can lead to multiple organ failure in cattle. Macrophages are important cellular mediators of fibrin deposition and removal at sites of inflammation. It has become evident that macrophages and other cells release microparticles (MPs) that have an array of biological activities, including pro-coagulant activity. We sought to determine whether monocyte-derived macrophages exposed to H. somni in vitro release MPs that activate the clotting cascade in a manner that could lead to thrombus formation. Bovine monocyte-derived macrophages were incubated with H. somni (at a 10:1 ratio) in RPMI with 10% heat inactivated fetal bovine serum for 6 h at 37 °C with 5 % CO₂. Membrane-shed MPs were isolated from the conditioned media, washed twice with Ca²⁺ and Mg²⁺ free HBSS, and pro-coagulant activity assessed by a one-step plasma clotting assay. We observed greater pro-coagulant activity for MPs from H. somni stimulated macrophages than from unstimulated controls. Microparticle pro-coagulant activity was inhibited by addition of an anti-tissue factor antibody. We also observed co-localization of fluorescein-labeled H. somni cells and annexin V staining as evaluated by confocal microscopy. These results demonstrate that exposure to H. somni cells causes bovine monocyte-derived macrophages to release MPs that contain tissue factor, the first such report for bovine macrophages. We infer that if similar events occur in vivo they could amplify thrombus formation in bovine histophilosis.

Procoagulant activity of bovine neutrophils incubated with conditioned media or extracellular vesicles from Histophilus somni stimulated bovine brain endothelial cells

Histophilus somni is a Gram negative coccobacillus that causes respiratory, reproductive and central nervous system disease in cattle. The hallmark of H. somni infection is diffuse vasculitis and intravascular thrombosis that can lead to an acute central nervous system disease known as thrombotic meningoencephalitis (TME). Because neutrophils are major players in the pathophysiology of septic meningitis, we sought to determine their role in H. somni-induced fibrin clot formation in vitro. Bovine brain endothelial cells (TBBE cells) were exposed to H. somni cells at a 1:25 ratio, respectively. Conditioned media (CM) were collected after a 6 h incubation at 37 °C with 5% CO₂, and then incubated with bovine peripheral blood polymorphonuclear neutrophils (PMNs). Following incubation, fibrin clot formation and tissue factor activity were assessed by a re-calcified plasma clotting assay. We found greater tissue factor activity in cell lysates and CM from H. somni-stimulated TBBE cells than unstimulated control TBBE cells. In addition, PMNs exposed to CM or extracellular vesicles from H. somni-stimulated TBBE cells expressed von Willenbrand factor, exhibited increased fibrin clot formation, and displayed greater tissue factor activity than PMNs exposed to CM or extracellular vesicles from unstimulated control TBBE cells. These results suggest that bovine PMNs might acquire extracellular vesicles from endothelial cells that leads to thrombus formation in bovine brain microvasculature and contribute to the process that characterizes TME.

Gene set enrichment analysis of SNP data in dairy and beef cattle with bovine respiratory disease

Bovine respiratory disease (BRD) is a complex disease that is associated with infection by bacterial and viral pathogens when cattle fail to adequately respond to stress. The objective of this study was to use gene set enrichment analysis of SNP data (GSEA-SNP) and a network analysis (ingenuity pathway analysis) to identify gene sets, genes within gene sets (leading-edge genes) and upstream regulators associated with BRD in pre-weaned dairy calves and beef feedlot cattle. BRD cases and controls were diagnosed using the McGuirk health scoring system. Holstein calves were sampled from commercial calf-raising facilities in California (1003 cases and 1011 controls) and New Mexico (376 cases and 372 controls). Commercial feedlot cattle were sampled from Colorado (500 cases and 499 controls) and Washington (504 cases and 497 controls). There were 102 and 237 unique leading-edge genes identified in the dairy calf and beef cattle populations respectively. Six leading-edge genes (ADIPOQ, HTR2A, MIF, PDE6G, PRDX3 and SNCA) were associated with BRD in both dairy and beef cattle. Network analysis identified glucose as the most influential upstream regulator in dairy cattle, whereas in beef cattle, TNF was the most influential upstream regulator. The genes, gene sets and upstream regulators associated with BRD have common functions associated with immunity, inflammation and pulmonary disease and provide insights into the mechanisms that are critical to BRD susceptibility in cattle.

A Predominant Clonal Thromboembolic Meningoencephalitis Group of Histophilus somni Assigned by Major Outer Membrane Protein Gene Sequencing and Pulsed-Field Gel Electrophoresis

Histophilus somni, a member of the family Pasteurellaceae, causes a variety of diseases, including thromboembolic meningoencephalitis (TEME) and respiratory diseases, which result in considerable economic losses to the cattle and sheep industries. In this study, 132 chronologically diverse isolates from cattle in Japan and 68 isolates from other countries comprising 49 from cattle and 19 from sheep were characterized using major outer membrane protein (MOMP) gene sequence and pulsed-field gel electrophoresis (PFGE) analyses. The H. somni isolates formed nine MOMP genetic clades (clade Ia, Ib, and II-VIII) and 10 PFGE clusters (HS1-HS10). Except for two (1.0%), all isolates fell into one of the nine MOMP genetic clades, while 62 (31.0%) isolates belonged to no PFGE cluster. MOMP genetic clade Ia and PFGE cluster HS1 were the major groups, and all HS1 isolates possessed the clade Ia MOMP gene. Isolates from TEME cases were significantly associated with these major groups (chi-square test, p < 0.0001), as 88.2% of the TEME isolates belonged to MOMP genetic clade Ia and PFGE cluster HS1, which formed the most predominant clonal group. After an inactivated vaccine using an HS1 strain with the clade Ia MOMP gene was introduced in Japan in late 1989, the number of TEME cases and isolates assigned into the clonal group decreased simultaneously. However, the proportions of clade Ia and cluster HS1 isolates from TEME cases remained high after 1990. These results suggest a close association of TEME with PFGE cluster HS1 and MOMP genetic clade Ia, and imply the presence of factors or characteristics commonly possessed by those strains that contribute to the development of TEME.

Engulfment of platelets delays endothelial cell aging via girdin and its phosphorylation

Endothelial cells are critical in angiogenesis and maintain the homeostasis of the blood‑brain barrier (BBB). Platelets (PLTs) are essential in vascular biology, including angiogenesis. The present study aimed to investigate the effect of PLTs on the aging of endothelial cells. Human brain microvascular endothelial cells (HBMECs) and human astrocytes were co‑cultured to mimic the BBB. Transmission electron microscopy was used to observe the engulfment of PLTs. Confocal microscopy was used to observe the co‑localization of PLTs, girders of actin filament (girdin) and phosphorylated (p‑)girdin. Senescence‑associated β‑galactosidase (β‑gal) staining, 3‑(4,5‑dimethylthiazol‑2‑yl)‑2,5‑diphenyltetrazolium bromide and flow cytometry were performed to examine the cell senescence, viability and apoptosis, respectively. Transwell assays were performed to examine cell invasion and migration. Western blot analysis was performed to detect the expression of girdin, AKT and p‑AKT. PLTs delayed senescence, and promoted the viability and resistance to apoptosis of the HBMECs. Cell invasion and migration were enhanced by PLTs. In addition, girdin and p‑girdin were essential to the engulfment of HBMECs to PLTs. Mechanically, the inhibition of AKT signals reversed the effect of PLTs on HBMECs by increasing the activity of β‑gal, decreasing the cell viability, and inhibiting the invasion and migration of the HBMECs. The engulfment of PLTs assisted in delaying the aging of endothelial cells via girdin and p‑girdin, in which the AKT signal was involved. The present study indicated a potential strategy for delaying endothelial cell aging in the treatment of central nervous system diseases.

Effect of Histophilus somni on Heart and Brain Microvascular Endothelial Cells

Histophilus somni is a pathogenic gram-negative bacterium responsible for pneumonia and septicemia in cattle. Sequelae include infectious thrombotic meningoencephalitis (ITME), myocarditis, arthritis, and abortion. These syndromes are associated with widespread vasculitis and thrombosis, implicating a role for endothelium in pathogenesis. Histopathologic and immunohistochemical investigation of 10 natural cases of bovine H. somni myocarditis and 1 case of ITME revealed intravascular H. somni in large biofilm-like aggregates adherent to the luminal surface of microvascular endothelium. Ultrastructurally, bacterial communities were extracellular and closely associated with degenerating or contracted endothelial cells. Histophilus somni was identified by bacterial culture and/or immunohistochemistry. Western blots of the bacterial isolates revealed that they expressed the immunodominant protective 40 kDa OMP and immunoglobulin-binding protein A (IbpA) antigens. The latter is a large surface antigen and shed fibrillar antigen with multiple domains. The cytotoxic DR2Fic domain of IbpA was conserved as demonstrated by polymerase chain reaction. Treatment of endothelial cells in vitro with IbpA in crude culture supernatants or purified recombinant GST-IbpA DR2Fic (rDR2) cytotoxin induced retraction of cultured bovine brain microvascular endothelial cells. By contrast, no retraction of bovine endothelium was induced by mutant rDR2H/A with an inactive Fic motif or by a GST control, indicating that the cytotoxic DR2Fic motif plays an important role in endothelial cell retraction in vasculitis. The formation of biofilm-like aggregates by H. somni on bovine microvascular endothelium may be fundamental to its pathogenesis in heart and brain.

Evolving views on bovine respiratory disease: An appraisal of selected key pathogens - Part 1

Bovine respiratory disease (BRD) is one of the most commonly diagnosed causes of morbidity and mortality in cattle and interactions of factors associated with the animal, the pathogen and the environment are central to its pathogenesis. Emerging knowledge of a role for pathogens traditionally assumed to be minor players in the pathogenesis of BRD reflects an increasingly complex situation that will necessitate regular reappraisal of BRD pathogenesis and control. This review appraises the role of selected key pathogens implicated in BRD pathogenesis to assess how our understanding of their role has evolved in recent years.

Phagocytosis of platelets enhances endothelial cell survival under serum deprivation

Platelets are key players in fundamental processes of vascular biology, such as angiogenesis, tissue regeneration, and tumor metastasis. However, the underlying mechanisms remain unclear. In this study, some tumor vascular endothelial cells were positively stained by antiplatelet antibodies. Further investigation revealed that platelets were taken up by endothelial cells in vitro and in vivo. Human umbilical vascular endothelial cells were rendered apoptotic under conditions of serum deprivation. However, endothelial apoptosis was suppressed and cell viability was enhanced when platelets were added to the cultures. Endothelial survival was paralleled by an upregulation of phosphorylated Akt and p70 S6K. In conclusion, this study demonstrated that platelets can be phagocytosed by endothelial cells, and the phagocytosed platelets could suppress endothelial apoptosis and promote cell viability level. The mechanism underlying this process involves the activation of Akt signaling.

Histophilus somni causes extracellular trap formation by bovine neutrophils and macrophages

Histophilus somni (formerly Haemophilus somnus) is a Gram-negative pleomorphic coccobacillus that causes respiratory, reproductive, cardiac and neuronal diseases in cattle. H. somni is a member of the bovine respiratory disease complex that causes severe bronchopneumonia in cattle. Previously, it has been reported that bovine neutrophils and macrophages have limited ability to phagocytose and kill H. somni. Recently, it was discovered that bovine neutrophils and macrophages produce extracellular traps in response to Mannheimia haemolytica, another member of the bovine respiratory disease complex. In this study, we demonstrate that H. somni also causes extracellular trap production by bovine neutrophils in a dose- and time-dependent manner, which did not coincide with the release of lactate dehydrogenase, a marker for necrosis. Neutrophil extracellular traps were produced in response to outer membrane vesicles, but not lipooligosacchride alone. Using scanning electron microscopy and confocal microscopy, we observed H. somni cells trapped within a web-like structure. Further analyses demonstrated that bovine neutrophils trapped and killed H. somni in a DNA-dependent manner. Treatment of DNA extracellular traps with DNase I freed H. somni cells and diminished bacterial death. Treatment of bovine monocyte-derived macrophages with H. somni cells also caused macrophage extracellular trap formation. These findings suggest that extracellular traps may play a role in the host response to H. somni infection in cattle.

Two outer membrane lipoproteins from Histophilus somni are immunogenic in rabbits and sheep and induce protection against bacterial challenge in mice

Histophilus somni is an economically important pathogen of cattle and other ruminants and is considered one of the key components of the bovine respiratory disease (BRD) complex, the leading cause of economic loss in the livestock industry. BRD is a multifactorial syndrome, in which a triad of agents, including bacteria, viruses, and predisposing factors or "stressors," combines to induce disease. Although vaccines against H. somni have been used for many decades, traditional bacterins have failed to demonstrate effective protection in vaccinated animals. Hence, the BRD complex continues to produce strong adverse effects on the health and well-being of stock and feeder cattle. The generation of recombinant proteins may facilitate the development of more effective vaccines against H. somni, which could confer better protection against BRD. In the present study, primers were designed to amplify, clone, express, and purify two recombinant lipoproteins from H. somni, p31 (Plp4) and p40 (LppB), which are structural proteins of the outer bacterial membrane. The results presented here demonstrate, to our knowledge for the first time, that when formulated, an experimental vaccine enriched with these two recombinant lipoproteins generates high antibody titers in rabbits and sheep and exerts a protective effect in mice against septicemia induced by H. somni bacterial challenge.

Platelets and the innate immune system: mechanisms of bacterial-induced platelet activation

It has become clear that platelets are not simply cell fragments that plug the leak in a damaged blood vessel; they are, in fact, also key components in the innate immune system, which is supported by the presence of Toll-like receptors (TLRs) on platelets. As the cells that respond first to a site of injury, they are well placed to direct the immune response to deal with any resulting exposure to pathogens. The response is triggered by bacteria binding to platelets, which usually triggers platelet activation and the secretion of antimicrobial peptides. The main platelet receptors that mediate these interactions are glycoprotein (GP)IIb-IIIa, GPIbα, FcγRIIa, complement receptors, and TLRs. This process may involve direct interactions between bacterial proteins and the receptors, or can be mediated by plasma proteins such as fibrinogen, von Willebrand factor, complement, and IgG. Here, we review the variety of interactions between platelets and bacteria, and look at the potential for inhibiting these interactions in diseases such as infective endocarditis and sepsis.

Platelets and innate immunity

Although platelets are best known as primary mediators of hemostasis, this function intimately associates them with inflammatory processes, and it has been increasingly recognized that platelets play an active role in both innate and adaptive immunity. For example, platelet adhesive interactions with leukocytes and endothelial cells via P-selectin can lead to several pro-inflammatory events, including leukocyte rolling and activation, production of cytokine cascades, and recruitment of the leukocytes to sites of tissue damage. Superimposed on this, platelets express immunologically-related molecules such as CD40L and Toll-like receptors that have been shown to functionally modulate innate immunity. Furthermore, platelets themselves can interact with microorganisms, and several viruses have been shown to cross-react immunologically with platelet antigens. This review discusses the central role that platelets play in inflammation, linking them with varied pathological conditions, such as atherosclerosis, sepsis, and immune thrombocytopenic purpura, and suggests that platelets also act as primary mediators of our innate defences.

Host response to bovine respiratory pathogens

Bovine respiratory disease (BRD) involves complex interactions amongst viral and bacterial pathogens that can lead to intense pulmonary inflammation (fibrinous pleuropneumonia). Viral infection greatly increases the susceptibility of cattle to secondary infection of the lung with bacterial pathogens likeMannheimia haemolyticaandHistophilus somni. The underlying reason for this viral/bacterial synergism, and the manner in which cattle respond to the virulence strategies of the bacterial pathogens, is incompletely understood. Bovine herpesvirus type 1 (BHV-1) infection of bronchial epithelial cellsin vitroenhances the binding ofM. haemolyticaand triggers release of inflammatory mediators that attract and enhance binding of neutrophils. An exotoxin (leukotoxin) released fromM. haemolyticafurther stimulates release of inflammatory mediators and causes leukocyte death. Cattle infected withH. somnifrequently display vasculitis. Exposure of bovine endothelial cells toH. somniior its lipooligosaccharide (LOS) increases endothelium permeability, and makes the surface of the endothelial cells pro-coagulant. These processes are amplified in the presence of platelets. The above findings demonstrate that bovine respiratory pathogens (BHV-1,M. haemolyticaandH. somni) interact with leukocytes and other cells (epithelial and endothelial cells) leading to the inflammation that characterizes BRD.

Visualization of the ultrastructural interface of cells with the outer and inner-surface of coral skeletons

Crystalline, porous biomaterials, such as marine invertebrate skeletons, have been widely used for functional reconstruction of human tissues like bone and dental implants. Since in such an abrasive microenvironment adequate cell-material interactions are crucial for a successful treatment, it is of great importance to improve the means to examine these interactions. We developed a method that reveals the ultrastructure of the interface between coral skeletons and cultured neural cells to a higher quality than do traditional methods as it does not include damaging procedures like decalcification or sectioning non-decalcified skeletons. It is rather based on generating two electron opacity distinct Araldite masks, of the skeleton and its surrounding, by polymerizing them to different durations. The contrast created at the border of the two masks outlined the fine and fragile crystals of the coral skeleton's outer and inner surfaces and their contact sites with the cells. The skeleton's internal structure contains a mesh of narrow (few microns wide) and large channel-shaped gaps interrupted by irregular-shaped crystalline material. Neural cells grew on the skeleton surface by stretching between crystal tips, with occasional rearrangements of cytoskeletal fibers located near the anchorage focal adherence points. Cell processes infiltrated the skeleton interior by stretching between inter-surface crystals and by adjusting their volume to the space of the conduits they grew into. The technique advances the study of coral biology and of neural cells-hard biomaterial interaction; it can be applied to other biomaterials and cell types and open new ways for studying tissue development and engineering.