Erratum to "Mitogen activated protein kinases (MAPK) and protein phosphatases are involved in Aspergillus fumigatus adhesion and biofilm formation" [Cell Surf. 1 (2018) 43-56]

[This corrects the article DOI: 10.1016/j.tcsw.2018.03.002.].

Green propolis increases myeloid suppressor cells and CD4+Foxp3+ cells and reduces Th2 inflammation in the lungs after allergen exposure

ETHNOPHARMACOLOGICAL RELEVANCE

Propolis is a natural product produced by honeybees used as a medicine at least to 300 BC. In the last decades, several studies showed biological and pharmacological properties of propolis, witch scientifically explains the empirical use for centuries. The anti-inflammatory activity of propolis with the purpose to reduce Th2 inflammation has been evaluated in allergic asthma. However, it remains to be determined how propolis negatively regulates the immune response after allergen re-exposure.

AIM OF THE STUDY

We hypothesized that the anti-inflammatory activity of propolis is dependent on the induction of myeloid derived suppressor cells (MDSC) and regulatory T cells.

MATERIALS AND METHODS

To assess this hypothesis, we used an ovalbumin-induced asthma model to evaluate the effect of EPP-AF® dry extract from Brazilian green propolis.

RESULTS

Propolis treatment decreased pulmonary inflammation and mucus production as well as eosinophils and IL-5 in the broncoalveolar lavage. Propolis enhanced also in vitro differentiation and in vivo frequency of lung MDSC and CD4⁺Foxp3⁺ regulatory T cells.

CONCLUSIONS

Together these results confirm the immunomodulatory potential of propolis during sensitization and challenge with allergen. In addition, the collecting findings show, for the first time, that propolis increases the frequency of MDSC and CD4⁺Foxp3⁺ regulatory T cells in the lungs, and suggest that it could be use as target for development of new immunotherapy or adjuvant immunotherapy for asthma.

Mitogen activated protein kinases (MAPK) and protein phosphatases are involved in Aspergillus fumigatus adhesion and biofilm formation

The main characteristic of biofilm formation is extracellular matrix (ECM) production. The cells within the biofilm are surrounded by ECM which provides structural integrity and protection. During an infection, this protection is mainly against cells of the immune system and antifungal drugs. A. fumigatus forms biofilms during static growth on a solid substratum and in chronic aspergillosis infections. It is important to understand how, and which, A. fumigatus signal transduction pathways are important for the adhesion and biofilm formation in a host during infection. Here we investigated the role of MAP kinases and protein phosphatases in biofilm formation. The loss of the MAP kinases MpkA, MpkC and SakA had an impact on the cell surface and the ECM during biofilm formation and reduced the adherence of A. fumigatus to polystyrene and fibronectin-coated plates. The phosphatase null mutants ΔsitA and ΔptcB, involved in regulation of MpkA and SakA phosphorylation, influenced cell wall carbohydrate exposure. Moreover, we characterized the A. fumigatus protein phosphatase PphA. The ΔpphA strain was more sensitive to cell wall-damaging agents, had increased β-(1,3)-glucan and reduced chitin, decreased conidia phagocytosis by Dictyostelium discoideum and reduced adhesion and biofilm formation. Finally, ΔpphA strain was avirulent in a murine model of invasive pulmonary aspergillosis and increased the released of tumor necrosis factor alpha (TNF-α) from bone marrow derived macrophages (BMDMs). These results show that MAP kinases and phosphatases play an important role in signaling pathways that regulate the composition of the cell wall, extracellular matrix production as well as adhesion and biofilm formation in A. fumigatus.

Mitogen activated protein kinases SakA(HOG1) and MpkC collaborate for Aspergillus fumigatus virulence

Here, we investigated which stress responses were influenced by the MpkC and SakA mitogen-activated protein kinases of the high-osmolarity glycerol (HOG) pathway in the fungal pathogen Aspergillus fumigatus. The ΔsakA and the double ΔmpkC ΔsakA mutants were more sensitive to osmotic and oxidative stresses, and to cell wall damaging agents. Both MpkC::GFP and SakA::GFP translocated to the nucleus upon osmotic stress and cell wall damage, with SakA::GFP showing a quicker response. The phosphorylation state of MpkA was determined post exposure to high concentrations of congo red and Sorbitol. In the wild-type strain, MpkA phosphorylation levels progressively increased in both treatments. In contrast, the ΔsakA mutant had reduced MpkA phosphorylation, and surprisingly, the double ΔmpkC ΔsakA had no detectable MpkA phosphorylation. A. fumigatus ΔsakA and ΔmpkC were virulent in mouse survival experiments, but they had a 40% reduction in fungal burden. In contrast, the ΔmpkC ΔsakA double mutant showed highly attenuated virulence, with approximately 50% mice surviving and a 75% reduction in fungal burden. We propose that both cell wall integrity (CWI) and HOG pathways collaborate, and that MpkC could act by modulating SakA activity upon exposure to several types of stresses and during CW biosynthesis.

Opposing roles of LTB4 and PGE2 in regulating the inflammasome-dependent scorpion venom-induced mortality

Tityus serrulatus sting causes thousands of deaths annually worldwide. T. serrulatus-envenomed victims exhibit local or systemic reaction that culminates in pulmonary oedema, potentially leading to death. However, the molecular mechanisms underlying T. serrulatus venom (TsV) activity remain unknown. Here we show that TsV triggers NLRP3 inflammasome activation via K(+) efflux. Mechanistically, TsV triggers lung-resident cells to release PGE2, which induces IL-1β production via E prostanoid receptor 2/4-cAMP-PKA-NFκB-dependent mechanisms. IL-1β/IL-1R actions account for oedema and neutrophil recruitment to the lungs, leading to TsV-induced mortality. Inflammasome activation triggers LTB4 production and further PGE2 via IL-1β/IL-1R signalling. Activation of LTB4-BLT1/2 pathway decreases cAMP generation, controlling TsV-induced inflammation. Exogenous administration confirms LTB4 anti-inflammatory activity and abrogates TsV-induced mortality. These results suggest that the balance between LTB4 and PGE2 determines the amount of IL-1β inflammasome-dependent release and the outcome of envenomation. We suggest COX1/2 inhibition as an effective therapeutic intervention for scorpion envenomation.

Physicochemical characterization by AFM, FT-IR and DSC and biological assays of a promising antileishmania delivery system loaded with a natural Brazilian product

The control and treatment of Leishmaniasis, a neglected and infectious disease affecting approximately 12 million people worldwide, are challenging. Leishmania parasites multiply intracellularly within macrophages located in deep skin and in visceral tissues, and the currently employed treatments for this disease are subject to significant drawbacks, such as resistance and toxicity. Thus, the search for new Leishmaniasis treatments is compulsory, and Ocotea duckei Vattimo, a plant-derived product from the biodiverse Brazilian flora, may be a promising new treatment for this disease. In this regard, the aim of this work was to develop and characterize a delivery system based on solid lipid nanoparticles (SLN) that contain the liposoluble lignan fraction (LF) of Ocotea duckei Vattimo, which targets the Leishmania phagolysosome of infected macrophages. LF-loaded SLNs were obtained via the hot microemulsion method, and their physical and chemical properties were comprehensively assessed using PCS, AFM, SEM, FT-IR, DSC, HPLC, kinetic drug release studies, and biological assays. The size of the developed delivery system was 218.85±14.2 nm, its zeta potential was -30 mV and its entrapment efficiency (EE%) was high (the EEs% of YAN [yangambin] and EPI-YAN [epi-yangambin] markers were 94.21±0.40% and 94.20±0.00%, respectively). Microscopy, FT-IR and DSC assays confirmed that the delivery system was nanosized and indicated a core-shell encapsulation model, which corroborated the measured kinetics of drug release. The total in vitro release rates of YAN and EPI-YAN in buffer (with sink conditions attained) were 29.6±8.3% and 34.3±8.9%, respectively, via diffusion through the cellulose acetate membrane of the SLN over a period of 4 h. After 24 h, the release rates of both markers reached approximately 45%, suggesting a sustained pattern of release. Mathematical modeling indicated that both markers, YAN and EPI-YAN, followed matrix diffusion-based release kinetics (Higuchi's model) with an estimated diffusion coefficient (D) of 1.3.10(-6) cm(2)/s. The LF-loaded SLNs were non-toxic to murine macrophages (20-80 μg mL(-1) range) and exerted a prominent anti-leishmanial effect (20 μg mL(-1)). These data suggest this new and well-characterized lipid nanoparticle delivery system safely and effectively kills Leishmania and warrants further clinical investigation.

Interleukin 1 receptor-driven neutrophil recruitment accounts to MyD88-dependent pulmonary clearance of legionella pneumophila infection in vivo

Legionella pneumophila, the etiological agent of Legionnaires' disease, triggers activation of multiple innate immune pathways that lead to the restriction of bacterial replication in vivo. Despite the critical role for MyD88 in infection clearance, the receptors and mechanisms responsible for MyD88-mediated pulmonary bacterial clearance are still unclear. Here, we used flagellin mutants of L. pneumophila, which bypass the NAIP5/NLRC4-mediated restriction of bacterial replication, to assess the receptors involved in MyD88-mediated pulmonary bacterial clearance. By systematically comparing pulmonary clearance of L. pneumophila in C57BL/6 MyD88(-/-), TLR2(-/-), TLR3(-/-), TLR4(-/-), TLR9(-/-), IL-1R(-/-), and IL-18(-/-) mice, we found that, while the knockout of a single Toll-like receptor or interleukin 18 resulted only in minor impairment of bacterial clearance, deficiency in the interleukin 1 (IL-1) receptor led to a significant impairment. IL-1/MyD88-mediated pulmonary bacterial clearance occurs via processes involving the recruitment of neutrophils. Collectively, our data contribute to the understanding of the effector mechanisms involved in MyD88-mediated pulmonary bacterial clearance.

Identification and functional characterization of K(+) transporters encoded by Legionella pneumophila kup genes

Legionnaires' disease is an emerging, severe, pneumonia-like illness caused by the Gram-negative intracellular bacteria Legionella pneumophila, which are able to infect and replicate intracellularly in macrophages. Little is known regarding the mechanisms used by intracellular L. pneumophila for the acquisition of specific nutrients that are essential for bacterial replication. Here, we investigate three L. pneumophila genes with high similarity to the Escherichia coli K(+) transporters. These three genes were expressed by L. pneumophila and have been designated kupA, kupB and kupC. Investigation using the L. pneumophila kup mutants revealed that kupA is involved in K(+) acquisition during axenic growth. The kupA mutants replicated efficiently in rich axenic media, but poorly in a chemically defined medium. The kupA mutants were defective in the recruitment of polyubiquitinated proteins to the Legionella-containing vacuole that is formed in macrophages and displayed an intracellular multiplication defect during the replication in Acanthamoeba castellanii and in mouse macrophages. We found that bafilomycin treatment of macrophages was able to rescue the growth defects of kupA mutants, but itdid not influence the replication of wild-type bacteria. The defects identified in kupA mutants of L. pneumophila were complemented by the expression E. coli trkD/Kup gene in trans, a bona fide K(+) transporter encoded by E. coli. Collectively, our data indicate that KupA is a functional K(+) transporter expressed by L. pneumophila that facilitates the bacterial replication intracellularly and in nutrient-limited conditions.

The mouse as a model for pulmonary legionella infection

Legionella pneumophila is an intracellular bacterium that was evolutionarily selected to survive in freshwater environments by infecting free-living unicellular protozoa. Once humans inhale contaminated water droplets, the bacteria reach the pulmonary alveoli where they are phagocytized by resident alveolar macrophages. Depending on host immunity and bacterial virulence genes, the infection may progress to an acute pneumonia called Legionnaires' disease, which can be fatal. Of note, an effective immune response is critical to the outcome of the human infection. These clinical observations highlight the importance of animal models of pulmonary infection for in vivo investigation of bacterial pathogenesis and host responses. In this chapter we provide detailed protocols for intranasal infection of mouse with L. pneumophila.

Activation of NLRC4 by flagellated bacteria triggers caspase-1-dependent and -independent responses to restrict Legionella pneumophila replication in macrophages and in vivo

Although NLRC4/IPAF activation by flagellin has been extensively investigated, the downstream signaling pathways and the mechanisms responsible for infection clearance remain unclear. In this study, we used mice deficient for the inflammasome components in addition to wild-type (WT) Legionella pneumophila or bacteria deficient for flagellin (flaA) or motility (fliI) to assess the pathways responsible for NLRC4-dependent growth restriction in vivo and ex vivo. By comparing infections with WT L. pneumophila, fliI, and flaA, we found that flagellin and motility are important for the colonization of the protozoan host Acanthamoeba castellanii. However, in macrophages and mammalian lungs, flagellin expression abrogated bacterial replication. The flagellin-mediated growth restriction was dependent on NLRC4, and although it was recently demonstrated that NLRC4 is able to recognize bacteria independent of flagellin, we found that the NLRC4-dependent restriction of L. pneumophila multiplication was fully dependent on flagellin. By examining infected caspase-1(-/-) mice and macrophages with flaA, fliI, and WT L. pneumophila, we could detect greater replication of flaA, which suggests that caspase-1 only partially accounted for flagellin-dependent growth restriction. Conversely, WT L. pneumophila multiplied better in macrophages and mice deficient for NLRC4 compared with that in macrophages and mice deficient for caspase-1, supporting the existence of a novel caspase-1-independent response downstream of NLRC4. This response operated early after macrophage infection and accounted for the restriction of bacterial replication within bacteria-containing vacuoles. Collectively, our data indicate that flagellin is required for NLRC4-dependent responses to L. pneumophila and that NLRC4 triggers caspase-1-dependent and -independent responses for bacterial growth restriction in macrophages and in vivo.

The pattern recognition receptors Nod1 and Nod2 account for neutrophil recruitment to the lungs of mice infected with Legionella pneumophila

The intracellular bacterium Legionella pneumophila induces a severe form of pneumonia called Legionnaires diseases, which is characterized by a strong neutrophil (NE) infiltrate to the lungs of infected individuals. Although the participation of pattern recognition receptors, such as Toll-like receptors, was recently demonstrated, there is no information on the role of nod-like receptors (NLRs) for bacterial recognition in vivo and for NE recruitment to the lungs. Here, we employed a murine model of Legionnaires disease to evaluate host and bacterial factors involved in NE recruitment to the mice lungs. We found that L. pneumophila type four secretion system, known as Dot/Icm, was required for NE recruitment as dot/icm mutants fail to trigger NE recruitment in a process independent of bacterial multiplication. By using mice deficient for Nod1, Nod2, and Rip2, we found that these receptors accounted for NE recruitment to the lungs of infected mice. In addition, Rip2-dependent responses were important for cytokine production and bacterial clearance. Collectively, these studies show that Nod1, Nod2, and Rip2 account for generation of innate immune responses in vivo, which are important for NE recruitment and bacterial clearance in a murine model of Legionnaires diseases.