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Detection of mixture effects is a major challenge in current experimental and regulatory toxicology. Robust markers are needed that are easy to quantify and responsive to chemical stressors in a broad dose range. Several hepatic enzymes and proteins related to drug metabolism like cytochrome-P-450 (CYP) enzymes and transporters have been shown to be responsive to pesticide active substances in a broad dose range and are therefore good candidates to be used as markers for mixture toxicity. Even though they can be well quantified at the mRNA level, quantification on the protein level is challenging because most of these proteins are membrane bound. Here we report the development of mass spectrometry-based assays using triple-x-proteomics (TXP) antibodies in combination with targeted selected ion monitoring (tSIM) to quantify changes of protein levels due to exposure to mixtures of pesticide active substances. Our results indicate that changes on the protein level of CYP1A1, ABCB2, ABCC3 are in line with observations on the mRNA and enzyme activity level and are indicative of mixture effects. Therefore, the tests are promising to reveal effects by chemical mixture effects in toxicological studies in rats., EXCLI Journal;Vol. 19 2020

Streptococcus pneumoniae is the most frequent cause of community-acquired pneumonia. Endogenous host defense molecules such as peptidoglycan recognition protein 4 (PGLYRP4) might influence the course of this disease. To the best of our knowledge, there are no reports on the relevance of PGLYRP4 in pneumonia. Therefore, wild type (WT) and PGLYRP4-deficient (PGLYRP4KO) mice were analyzed in an in vivo and in vitro experimental setting to examine the influence of PGLYRP4 on the course of pneumococcal pneumonia. Furthermore, caecal 16S rRNA microbiome analysis was performed, and microbiota were transferred to germfree WT mice to assess the influence of microbiotal communities on the bacterial burden. Mice lacking PGLYRP4 displayed an enhanced bacterial clearance in the lungs, and fewer mice developed bacteremia. In addition, an increased recruitment of immune cells to the site of infection, and an enhanced bacterial killing by stronger activation of phagocytes could be shown. This may depend partly on the detected higher expression of complement factors, interferon-associated genes, and the higher pro-inflammatory cytokine response in isolated primary PGLYRP4KO vs. WT cells. This phenotype is underlined by changes in the complexity and composition of the caecal microbiota of PGLYRP4KO compared to WT mice. Strikingly, we provided evidence, by cohousing and stable transfer of the respective WT or PGLYRP4KO mice microbiota into germfree WT mice, that the changes of the microbiota are responsible for the improved clearance of S. pneumoniae lung infection. In conclusion, the deficiency of PGLYRP4, a known antibacterial protein, leads to changes in the gut microbiota. Thus, alterations in the microbiota can change the susceptibility to S. pneumoniae lung infection independently of the host genotype.

Infektionen der unteren Atemwege zählen zu den häufigsten Todesursachen weltweit und betreffen jährlich mehr als 3 Millionen Menschen. Davon ist ein Großteil jünger als 5 oder älter als 65 Jahre alt. Der häufigste Erreger ist mit 1,5-2 Mio. Todesfällen pro Jahr S. pneumoniae. Ein grampositives, kokkoides Bakterium, das zwar allgemein gut antibiotisch behandelbar, jedoch schon lange für seine Resistenzen gegenüber u. a. β-Lactam- und Makrolidantibiotika bekannt ist. In gesunden Individuen mit einem intakten und potenten Immunsystem, die nicht ins Krankenhaus eingeliefert werden müssen, ist die Sterblichkeit mit ca. 0,1% relativ gering. Das Immunsystem verfügt offensichtlich über effektive Abwehrmechanismen. Des Weiteren sorgen kommensale Mikrobiota durch verschiedene Mechanismen dafür, dass es Pathogenen schwerfällt, sich im Wirt zu etablieren. Dies kann u. a. durch Konkurrenz um Nährstoffe, Belegung der Körpernischen oder durch die Ausschüttung von immunmodulatorischen und antibakteriellen Metaboliten geschehen. Körpereigene Immun-Abwehrproteine können durch direkte antibakterielle oder indirekte immunmodulatorische Wirkungen gegen eindringende Pathogene wirken und sorgen ebenso für ein sogenanntes gesundes Mikrobiom [67,68]. Diese Funktionen sind ebenfalls für die PGLYRP bekannt. Bislang sind jedoch keine Studien zur Wirksamkeit der PGLYRP gegenüber S. pneumoniae veröffentlicht. Um diese Lücke zu schließen wurde in dieser Arbeit der Einfluss der Proteine PGLYRP2 und PGLYRP4 auf eine S. pneumoniae-induzierte Pneumonie untersucht. Hierfür wurden WT und PGLYRP KO Mäusen transnasal infiziert und Auswirkungen auf das angeborene Immunsystem und das Mikrobiom analysiert. PGLYRP2 KO Mäuse zeigten gegenüber den WT Mäusen eine Verschlechterung des klinischen Verlaufs der Pneumokokken-induzierten Pneumonie. Insbesondere wiesen sie mehr Bakterien in Milz und tendenziell auch im Blut 48 hpi auf. Interessanterweise weist das PGLYRP2 keinen direkten, antibakteriellen Effekt gegenüber S. pneumoniae auf und es konnten ebenfalls keine Veränderungen des Darmmikrobioms festgestellt werden. Vielmehr wurden die Effekte durch eine Verringerung an proinflammatorischen Zytokinen und folglich einer geringeren Rekrutierung an PMN in die Lunge der PGLYRP2-KO Mäuse verursacht. Infolgedessen zeigten die PGLYRP2-KO Tiere einen beschleunigten Krankheitsverlauf. Im Gegensatz zu den PGLYRP2-KO Mäusen, wiesen die PGLYRP4-KO Mäuse einen verbesserten klinischen Verlauf gegenüber WT Mäusen auf. Diese Verbesserung war mit einer signifikant geringeren Bakterienlast sowohl in den Lungen, als auch im Blut der infizierten Tiere verbunden. Die bessere Eliminierung der Pneumokokken in PGLYRP4-KO gegenüber WT Mäusen wurde von einer stärkeren inflammatorischen Immunantwort, mit einer Infiltration von PMN, T und B Zellen in die Lunge, sowie einer stärkeren Aktivierung von PMN durch lösliche Faktoren von AEC ausgelöst. Zusätzlich wurde eine stärkere alveoläre Barriere festgestellt, die eine Dissemination der Bakterien in die Peripherie vermutlich reduziert. Des Weiteren konnte gezeigt werden, dass die PGLYRP4-KO Mäuse über ein vermehrt proinflammatorisches Mikrobiom im Darm verfügen. Durch Übertragung dieser Mikrobiota auf keimfreie WT Mäuse konnte belegt werden, dass die Veränderungen im Mikrobiom keine Folge des proinflammatorischen Phänotyps, sondern ursächlich für den Schutz der PGLYRP4 KO Mäuse vor einer Pneumokokken-induzierten Pneumonie sind. Zusammenfassend konnte der Einfluss von zwei PGLYRP auf die S. pneumoniae-induzierte Pneumonie belegt werden. Dabei nimmt PGLYRP2 in diesem Modell eine proinflammatorische Rolle und PGLYRP4 eine anti-inflammatorische und Mikrobiom-modulierende Rolle ein. Fortführende Arbeiten könnten, durch die Aufklärung der genauen Mechanismen und beteiligten Bakterien, möglicherweise neue Behandlungsstrategien für Infektionserkrankungen, insbesondere der Pneumonie, ermöglichen., Infections of the lower respiratory tract are one of the major burdens of life worldwide. Every year more than three million people, mostly below the age of five or above the age of 65, die on LRTIs. The most causative pathogen for LRTIs is S. pneumoniae. This Gram-positive, coccoid bacterium kills up to two million people every year even though antibacterial agents are often effective. Nevertheless, there are known resistances against β-lactam and macrolide antibiotics. Young and healthy patients, which do not need to be hospitalized and have a functional immune system generally have a low mortality of approx. 0.1%. Therefore, there are some effective, intrinsic host defense mechanisms, which protect against this pathogen. One of these mechanisms are hosts microbiota. They protect the host by e. g. colonizing body niches, using the same nutrition like invading pathogens and secreting immunomodulatory or antibacterial metabolites and proteins. Furthermore, there are host’s own defense proteins which can have direct antibacterial or indirect immunomodulatory functions, which can either directly target pathogens or indirectly support a healthy microbiome. These functions are also known for PGLYRPs. However, up to date, there are no studies, which show an effect of these PGLYRPs against S. pneumoniae. Therefore, this work aimed in analyzing the influences of PGLYRP2 and PGLYRP4 in S. pneumoniae-induced pneumonia. Hence, WT and PGLYRP-KO mice were transnasally infected with S. pneumoniae and effects by these KOs on the innate immunity and microbiota were analyzed. PGLYRP2-KO mice showed a worsened progression of the infection with slightly elevated bacterial load in the blood and significant higher bacterial load in the spleen 48 hpi compared to the WT mice. Interestingly, this effect was not due to a direct antibacterial effect, as indicated by an in vitro antibacterial assay, and there were no effects on the gut-microbiota as published by Saha et al. Instead, PGLYRP2-KO mice had lower levels of proinflammatory cytokines in the lung and recruited less PMN to clear the bacterial infection than WT mice. Thus, these mice had higher clinical scores in early time point and needed to be sacrificed earlier than the corresponding WT mice. Contrary, PGLYRP4-KO mice did better than WT mice in the pneumococcal infection and they had lower bacterial load in the lungs, as well as in the blood 48 hpi. The PGLYRP4-KO mice cleared the bacteria better due to a higher proinflammatory immune response accompanied by a higher infiltration of PMNs, T and B cells into the lungs. Furthermore, soluble factors of AECs from PGLYRP4-KO mice supported PMNs for better bacterial killing. Additionally, PGLYRP4-KO mice had a tighter alveolar barrier by up-regulation of tight junction proteins and had a more proinflammatory gut-microbiota. By cohousing and transfer of the microbiota from WT and PGLYRP4-KO mice to germfree WT mice, it could be proven, that the better bacterial clearance of S. pneumoniae in PGLYRP4-KO mice was triggered by the altered microbiota. In summary, this work showed the influence of two PGLYRPs on S. pneumoniae-induced pneumonia, whereas PGLYRP2 has a proinflammatory and PGLYRP4 has an anti-inflammatory and microbiota-modulating function. By elucidation of the mechanisms and involved bacteria, additional work could lead to new strategies in treatment of infectious diseases like pneumonia.

Peptidoglycan (PGN) recognition proteins (PGLYRPs) are a highly conserved group of host defense proteins in insects and mammals that sense bacterial cell wall PGN and act bactericidally or cleave PGN by amidase function. Streptococcus (S.) pneumoniae is one of the top five killers worldwide and causes, e.g., pneumonia, endocarditis, meningitis and sepsis. S. pneumoniae accounts for approximately 1.5–2 million deaths every year. The risk of antibiotic resistance and a general poor prognosis in young children and elderly people have led to the need for new treatment approaches. To the best of our knowledge, there is no report on the relevance of PGLYRP2 in lung infections. Therefore, we infected mice deficient for PGLYRP2 transnasally with S. pneumoniae and examined the innate immune response in comparison to WT animals. As expected, PGLYRP2-KO animals had to be sacrificed earlier than their WT counterparts, and this was due to higher bacteremia. The higher bacterial load in the PGLYRP2-KO mice was accomplished with lower amounts of proinflammatory cytokines in the lungs. This led to an abolished recruitment of neutrophils into the lungs, the spread of bacteria and the subsequent aggravated course of the disease and early mortality of the PGLYRP2-KO mice. These data suggest a substantial role of PGLYRP2 in the early defense against S. pneumoniae infection, and PGLYRP2 might also affect other infections in the lungs.