A Novel Role for the Nuclear Receptor, NR4A1, in Klebsiella pneumoniae Lung Infection

ABSTRACTKlebsiella pneumoniae is a Gram-negative bacterial pathogen and common cause of pneumonia and bacteremia. Increasingly, K. pneumoniae has become a public health concern due to its rate of nosocomial infection and emerging, broad-spectrum antibiotic resistance. The nuclear receptor NR4A1 exhibits functionality in a multitude of organ systems and is implicated as having a role in the immune response to bacterial infection, though its role in K. pneumoniae infection is unknown. To determine if Nr4a1 functions in response to K. pneumoniae pulmonary disease, we infected wild-type and Nr4a1−/− mice with K. pneumoniae and assessed bacterial growth, immune cell recruitment and function, and cytokine production. We found that Nr4a1−/− mice had increased bacterial burden in the lungs and spleen, though no differences in cell recruitment. Pro-inflammatory cytokines, Il1β and Il6, as well as chemokine, Cxcl2, were significantly decreased in the BAL fluid cells of Nr4a1−/− mice 5 hours post-infection. Additionally, Nr4a1−/− mice had reduced IL-1β and myeloperoxidase protein production. We then examined the bactericidal function of macrophages and neutrophils from WT and Nr4a1−/− mice. We identified that Nr4a1−/− neutrophils had decreased bactericidal function compared to wild-type neutrophils, which was associated with reduced expression of Il1β, Lcn2, Mpo, and Lyz2. These data suggest Nr4a1 plays a novel and essential role in neutrophil function during the host immune response to K. pneumoniae pulmonary infection.

Hyptis brevipes AND Paullinia pinnata EXTRACTS AND THEIR FRACTIONS PRESENTING ACTIVITY AGAINST Mycobacterium abscessus subsp. massiliense

Medicinal plants are of great interest for the discovery of new biomolecules with diversified effects. Over the last decade different outbreaks caused by Mycobacterium abscessus subsp. massiliense have been reported, evidencing it as an important emerging pathogen in underdeveloped countries. This study investigated the antimycobacterial activity of six Brazilian medicinal plant extracts and their fractions. Hyptis brevipes, Tocoyena formosa, Randia armata, Paullinia pinnata, Lafoensia pacari and Anadenanthera colubrina were evaluated against M. a. massiliense. Total extracts from the medicinal plants H. brevipes, T. formosa, P. pinnata and L. pacari presented a minimal bactericidal concentration of 1 mg/mL. After fractioning, the ethanolic fractions from H. brevipes and P. pinnata presented bactericidal activity, and the ethyl acetate fraction from H. brevipes and T. formosa presented antimycobacterial action. The best bactericidal function of all plant fractions was the ethanolic, which contained rutin and rosmarinic acid that were shown to have microbicidal activity. KEY WORDS: Mycobacterium abscessus; medicinal plants; Brazilian medicinal plants; HPLCand biodiversity.

The Impact of Hypoxia on the Host-Pathogen Interaction between Neutrophils and Staphylococcus aureus

Neutrophils are key to host defence, and impaired neutrophil function predisposes to infection with an array of pathogens, with Staphylococcus aureus a common and sometimes life-threatening problem in this setting. Both infiltrating immune cells and replicating bacteria consume oxygen, contributing to the profound tissue hypoxia that characterises sites of infection. Hypoxia in turn has a dramatic effect on both neutrophil bactericidal function and the properties of S. aureus, including the production of virulence factors. Hypoxia thereby shapes the host–pathogen interaction and the progression of infection, for example promoting intracellular bacterial persistence, enabling local tissue destruction with the formation of an encaging abscess capsule, and facilitating the establishment and propagation of bacterial biofilms which block the access of host immune cells. Elucidating the molecular mechanisms underlying host–pathogen interactions in the setting of hypoxia will enable better understanding of persistent and recalcitrant infections due to S. aureus and may uncover novel therapeutic targets and strategies.

M1 macrophage dependent-p53 regulates the intracellular survival of mycobacteria

Tumor suppressor p53 is not only affects immune responses but also contributes to antibacterial activity. However, its bactericidal function during mycobacterial infection remains unclear. In this study, we found that the p53-deficient macrophages failed to control Mycobacterium tuberculosis (Mtb), manifested as a lower apoptotic cell death rate and enhanced intracellular survival. The expression levels of p53 during Mtb infection were stronger in M1 macrophages than in M2 macrophages. The TLR2/JNK signaling pathway plays an essential role in the modulation of M1 macrophage polarization upon Mtb infection. It facilitates p53-mediated apoptosis through the production of reactive oxygen species, nitric oxide and inflammatory cytokines in Mtb-infected M1 macrophages. In addition, nutlin-3 effectively abrogated the intracellular survival of mycobacteria in both TB patients and healthy controls after H37Ra infection for 24 h, indicating that the enhancement of p53 production effectively suppressed the intracellular survival of Mtb in hosts. These results suggest that p53 can be a new therapeutic target for TB therapy.

Drosophila macrophages switch to aerobic glycolysis to mount effective antibacterial defense

Macrophage-mediated phagocytosis and cytokine production represent the front lines of resistance to bacterial invaders. A key feature of this pro-inflammatory response in mammals is the complex remodeling of cellular metabolism towards aerobic glycolysis. Although the function of bactericidal macrophages is highly conserved, the metabolic remodeling of insect macrophages remains poorly understood. Here, we used adults of the fruit fly Drosophila melanogaster to investigate the metabolic changes that occur in macrophages during the acute and resolution phases of Streptococcus-induced sepsis. Our studies revealed that orthologs of Hypoxia inducible factor 1α (HIF1α) and Lactate dehydrogenase (LDH) are required for macrophage activation, their bactericidal function, and resistance to infection, thus documenting the conservation of this cellular response between insects and mammals. Further, we show that macrophages employing aerobic glycolysis induce changes in systemic metabolism that are necessary to meet the biosynthetic and energetic demands of their function and resistance to bacterial infection.

Tailored antimicrobial activity and long-term cytocompatibility of plasma polymer silver nanocomposites

The deposition of coatings enabling antibacterial properties in combination with cytocompatibility remains a challenge for biomaterial applications, such as in medical devices. Silver is one of the most utilized antibacterial surface components, due to its efficacy and extensive applicability. In this work, silver-containing plasma polymer nanocomposites (single layer and multilayers) were developed and tested, with a focus on cytotoxicity and bactericidal function, on the NIH3T3 mammalian cell line as well as Gram-negative ( Pseudomonas aeruginosa) and Gram-positive ( Staphylococcus aureus) bacterial strains. The data demonstrate that a tuneable Ag+ release is required, allowing sufficient antimicrobial activity while retaining appropriate cytocompatibility over the entire testing period of up to eight days.

Ablation of the leptin receptor in myeloid cells impairs pulmonary clearance ofStreptococcus pneumoniaeand alveolar macrophage bactericidal function

Leptin is a pleiotropic hormone produced by white adipose tissue that regulates appetite and many physiological functions, including the immune response to infection. Genetic leptin deficiency in humans and mice impairs host defenses against respiratory tract infections. Since leptin deficiency is associated with obesity and other metabolic abnormalities, we generated mice that lack the leptin receptor (LepRb) in cells of the myeloid linage (LysM-LepRb-KO) to evaluate its impact in lean metabolically normal mice in a murine model of pneumococcal pneumonia. We observed higher lung and spleen bacterial burdens in LysM-LepRb-KO mice following an intratracheal challenge with Streptococcus pneumoniae. Although numbers of leukocytes recovered from bronchoalveolar lavage fluid did not differ between groups, we did observe higher levels of pulmonary IL-13 and TNFα in LysM-LepRb-KO mice 48 h post infection. Phagocytosis and killing of ingested S. pneumoniae were also impaired in alveolar macrophages (AMs) from LysM-LepRb-KO mice in vitro and were associated with reduced LTB4and enhanced PGE2synthesis in vitro. Pretreatment of AMs with LTB4and the cyclooxygenase inhibitor, indomethacin, restored phagocytosis but not bacterial killing in vitro. These results confirm our previous observations in leptin-deficient ( ob/ob) and fasted mice and demonstrate that decreased leptin action, as opposed to metabolic irregularities associated with obesity or starvation, is responsible for the defective host defense against pneumococcal pneumonia. They also provide novel targets for therapeutic intervention in humans with bacterial pneumonia.