Dorsal switch protein 1 as a damage signal in insect gut immunity to activate dual oxidase via an eicosanoid, PGE2

The Lrp transcriptional factor of an entomopathogenic bacterium, Xenorhabdus hominickii, activates non-ribosomal peptide synthetases to suppress insect immunity

Two bacterial genera, Xenorhabdus and Photorhabdus, are mutually symbiotic to the entomopathogenic nematodes, Steinernema and Heterorhabditis, respectively. The infective juveniles deliver the symbiotic bacteria to the hemocoel of target insects, in which the bacteria proliferate and help the development of the host nematode. The successful parasitism of the nematode-bacterial complex depends on host immunosuppression by the bacteria via their secondary metabolites. Leucine-responsive regulatory protein (Lrp) is a global bacterial transcriptional factor that plays a crucial role in parasitism. However, its regulatory targets to suppress insect immunity are not clearly understood. This study investigated the bacterial genes regulated by Lrp and the subsequent production of secondary metabolites in Xenorhabdus hominickii. Lrp expression occurred at the early infection stage of the bacteria in a target insect, Spodoptera exigua. A preliminary in silico screening indicated that 3.7% genes among 4075 predicted genes encoded in X. hominickii had the Lrp-response element on their promoters, including two non-ribosomal peptide synthetases (NRPSs). Eight NRPS (NRPS1-NRPS8) genes were predicted in the bacterial genome, in which six NRPS (NRPS3-NRPS8) expressions were positively correlated with Lrp expression in the infected larvae of S. exigua. Exchange of the Lrp promoter with an inducible promoter altered the production of the secondary metabolites and the NRPS expression levels. The immunosuppressive activities of X. hominickii were dependent on the Lrp expression level. The metabolites produced by Lrp expression included the eicosanoid-biosynthesis inhibitors and hemolytic factors. A cyclic dipeptide (=cPF) was produced by the bacteria at high Lrp expression and inhibited the phospholipase A2 activity of S. exigua in a competitive inhibitory manner. These results suggest that Lrp is a global transcriptional factor of X. hominickii and plays a crucial role in insect immunosuppression by modulating NRPS expression.

Alveolar macrophage-derived gVPLA2 promotes ventilator-induced lung injury via the cPLA2/PGE2 pathway

BACKGROUND

Ventilator-induced lung injury (VILI) is a clinical complication of mechanical ventilation observed in patients with acute respiratory distress syndrome. It is characterized by inflammation mediated by inflammatory cells and their secreted mediators.

METHODS

To investigate the mechanisms underlying VILI, a C57BL/6J mouse model was induced using high tidal volume (HTV) mechanical ventilation. Mice were pretreated with Clodronate liposomes to deplete alveolar macrophages or administered normal bone marrow-derived macrophages or Group V phospholipase A2 (gVPLA2) intratracheally to inhibit bone marrow-derived macrophages. Lung tissue and bronchoalveolar lavage fluid (BALF) were collected to assess lung injury and measure Ca2 + concentration, gVPLA2, downstream phosphorylated cytoplasmic phospholipase A2 (p-cPLA2), prostaglandin E2 (PGE2), protein expression related to mitochondrial dynamics and mitochondrial damage. Cellular experiments were performed to complement the animal studies.

RESULTS

Depletion of alveolar macrophages attenuated HTV-induced lung injury and reduced gVPLA2 levels in alveolar lavage fluid. Similarly, inhibition of alveolar macrophage-derived gVPLA2 had a similar effect. Activation of the cPLA2/PGE2/Ca2 + pathway in alveolar epithelial cells by gVPLA2 derived from alveolar macrophages led to disturbances in mitochondrial dynamics and mitochondrial dysfunction. The findings from cellular experiments were consistent with those of animal experiments.

CONCLUSIONS

HTV mechanical ventilation induces the secretion of gVPLA2 by alveolar macrophages, which activates the cPLA2/PGE2/Ca2 + pathway, resulting in mitochondrial dysfunction. These findings provide insights into the pathogenesis of VILI and may contribute to the development of therapeutic strategies for preventing or treating VILI.

Cellulose microcrystalline: A promising ecofriendly approach to control Culex quinquefasciatus larvae

The growing use of synthetic chemical compounds/substances in vector control of mosquitoes, associated with their adverse effects on the environment and non-target organisms, has demanded the development of eco-friendly alternatives. In this context, this study aimed to evaluate the larvicidal action of different cellulose microcrystalline (CMs) concentrations and investigate their toxicity mechanisms in Culex quinquefasciatus fourth instar larvae as a model species. Probit analysis revealed that the median lethal concentrations (LC50) for 24 h and 36 h exposure were 100 and 58.29 mg/L, respectively. We also showed that such concentrations induced a redox imbalance in the larvae, marked by an increase in the production of reactive oxygen species (ROS) and thiobarbituric acid reactive substances (TBARS), as well as a reduction in the activity of superoxide dismutase (SOD) and catalase (CAT). Furthermore, different alterations in the external morphology of the larvae were associated with the ingestion of CMs. On the other hand, exposure of adult zebrafish (Danio rerio) to LC5024h and LC5036h for seven days did not induce any behavioral changes or alterations mutagenic, genotoxic, biochemical, or in the production of cytokines IFN-γ and IL-10. Thus, taken together, our study demonstrates for the first time that the use of CMs can constitute a promising strategy in the control of C. quinquefasciatus larvae, combining insecticidal efficiency with an "eco-friendly" approach in the fight against an important mosquito vector of several human diseases.

Metabolic changes and potential biomarkers in "Candidatus Liberibacter solanacearum"-infected potato psyllids: implications for psyllid-pathogen interactions

Psyllid yellows, vein-greening (VG), and zebra chip (ZC) diseases, which are primarily transmitted by potato psyllid (PoP) carrying Candidatus Liberibacter solanacearum (CLso), have caused significant losses in solanaceous crop production worldwide. Pathogens interact with their vectors at the organic and cellular levels, while the potential changes that may occur at the biochemical level are less well reported. In this study, the impact of CLso on the metabolism of PoP and the identification of biomarkers from infected psyllids were examined. Using ultra-performance liquid chromatography tandem mass spectrometry (UPLC-MS/MS) analysis, metabolomic changes in CLso-infected psyllids were compared to uninfected ones. A total of 34 metabolites were identified as potential biomarkers of CLso infection, which were primarily related to amino acid, carbohydrate, and lipid metabolism. The significant increase in glycerophospholipids is thought to be associated with CLso evading the insect vector's immune defense. Matrix-assisted Laser Desorption Ionization Mass Spectrometry Imaging (MALDI-MSI) was used to map the spatial distribution of these biomarkers, revealing that 15-keto-Prostaglandin E2 and alpha-D-Glucose were highly expressed in the abdomen of uninfected psyllids but down-regulated in infected psyllids. It is speculated that this down-regulation may be due to CLso evading surveillance by immune suppression in the PoP midgut. Overall, valuable biochemical information was provided, a theoretical basis for a better understanding of psyllid-pathogen interactions was offered, and the findings may aid in breaking the transmission cycle of these diseases.

Immune functions of pattern recognition receptors in Lepidoptera

Pattern recognition receptors (PRRs), as the "sensors" in the immune response, play a prominent role in recognizing pathogen-associated molecular patterns (PAMPs) and initiating an effective defense response to pathogens in Lepidoptera. It is becoming increasingly clear that damage-associated molecular patterns (DAMPs) normally play a physiological role within cells; however, when exposed to extracellular, they may become "part-time" critical signals of the immune response. Based on research in recent years, we review herein typical PRRs of Lepidoptera, including peptidoglycan recognition protein (PGRP), gram-negative binding protein (GNBP), β-1,3-glucan recognition protein (βGRP), C-type lectin (CTL), and scavenger receptor (SR). We also outline the ways in which DAMPs participate in the immune response and the correlation between PRRs and immune escape. Taken together, these findings suggest that the role of PRRs in insect innate immunity may be much greater than expected and that it is possible to recognize a broader range of signaling molecules.