Constitutive immune activity promotes JNK- and FoxO-dependent remodeling of Drosophila airways.

Extensive remodeling of the airways is a major characteristic of chronic inflammatory lung diseases such as asthma or chronic obstructive pulmonary disease (COPD). To elucidate the importance of a deregulated immune response in the airways for remodeling processes, we established a matching Drosophila model. Here, triggering the Imd (immune deficiency) pathway in tracheal cells induced organ-wide remodeling. This structural remodeling comprises disorganization of epithelial structures and comprehensive epithelial thickening. We show that these structural changes do not depend on the Imd pathway's canonical branch terminating on nuclear factor κB (NF-κB) activation. Instead, activation of a different segment of the Imd pathway that branches off downstream of Tak1 and comprises activation of c-Jun N-terminal kinase (JNK) and forkhead transcription factor of the O subgroup (FoxO) signaling is necessary and sufficient to mediate the observed structural changes of the airways. Our findings imply that targeting JNK and FoxO signaling in the airways could be a promising strategy to interfere with disease-associated airway remodeling processes.

A Drosophila asthma model - what the fly tells us about inflammatory diseases of the lung.

Asthma and COPD are the most relevant inflammatory diseases of the airways. In western countries they show a steeply increasing prevalence, making them to a severe burden for health systems around the world. Although these diseases are typically complex ones, they have an important genetic component. Genome-wide association studies have provided us with a relatively small but comprehensive list of asthma susceptibility genes that will be extended and presumably completed in the near future. To identify the role of these genes in the physiology and pathophysiology of the lung, genetically tractable model organisms are indispensable and murine models were the only ones that have been extensively used. An urgent demand for complementary models is present that provide specific advantages lacking in murine models, especially regarding speed and flexibility. Among the model organisms available, only the fruit fly Drosophila melanogaster shares a comparable organ composition and at least a lung equivalent. It has to be acknowledged that the fruit fly Drosophila has almost completely been ignored as a model organism for lung diseases, simply because it is devoid of lungs. Nevertheless, its airway system shows striking similarities with the one of mammals regarding its physiology and reaction towards pathogens, which holds the potential to function as a versatile model in asthma-related diseases.

Protist-type lysozymes of the nematode Caenorhabditis elegans contribute to resistance against pathogenic Bacillus thuringiensis.

Pathogens represent a universal threat to other living organisms. Most organisms express antimicrobial proteins and peptides, such as lysozymes, as a protection against these challenges. The nematode Caenorhabditis elegans harbours 15 phylogenetically diverse lysozyme genes, belonging to two distinct types, the protist- or Entamoeba-type (lys genes) and the invertebrate-type (ilys genes) lysozymes. In the present study we characterized the role of several protist-type lysozyme genes in defence against a nematocidal strain of the Gram-positive bacterium Bacillus thuringiensis. Based on microarray and subsequent qRT-PCR gene expression analysis, we identified protist-type lysozyme genes as one of the differentially transcribed gene classes after infection. A functional genetic analysis was performed for three of these genes, each belonging to a distinct evolutionary lineage within the protist-type lysozymes (lys-2, lys-5, and lys-7). Their knock-out led to decreased pathogen resistance in all three cases, while an increase in resistance was observed when two out of three tested genes were overexpressed in transgenic lines (lys-5, lys-7, but not lys-2). We conclude that the lysozyme genes lys-5, lys-7, and possibly lys-2 contribute to resistance against B. thuringiensis, thus highlighting the particular role of lysozymes in the nematode's defence against pathogens.

Drosophila in asthma research.

Genetic research has revealed a number of asthma-susceptibility genes. In addition, with the development of genome-wide association studies, which has gained unprecedented momentum, the roles of many more candidate genes in asthma will be uncovered. In parallel with such genetic insight, a detailed understanding of the function of susceptibility genes in asthma is required, a task best suited for genetically tractable model organisms. The inherent limitations of models like the mouse necessitate finding complementary systems for study. Although the fruit fly Drosophila has not been used previously in asthma-related research, it might prove to be extremely helpful in relating genetic processes to biological function. We discuss the usefulness of the Drosophila model by analyzing potential homologs of known asthma-susceptibility genes in the fly. Except for those associated with adaptive immunity, we and others found unequivocal orthologs for all of them. Most asthma-related genes are indeed expressed in the airway epithelium. In addition, some are regulated upon airway infection of the Drosophila airway epithelium, pointing to an important role in airway immunity and development of asthma-like phenotypes in the fruit fly. Finally, high throughput functional analyses are needed to complete genome-wide comparison studies in complex diseases such as asthma. Because such studies are most readily performed in the fruit fly, it may be a particularly useful asthma model system.

Infection induces a survival program and local remodeling in the airway epithelium of the fly.

Although the prevalence of inflammatory airway diseases is steadily growing, our knowledge regarding the underlying molecular and cellular mechanisms is fragmentary. The striking simplicity of the fruit fly's airway epithelium, which is composed of epithelial cells only, justifies its use as a model to study general features and response characteristics of airway epithelia in general. Infection with the gram-negative pathogen Erwinia carotovora induces an immune response in all epithelial cells via activation of the immune deficiency (IMD) pathway, but the transcriptional profile differs significantly from that observed after ectopic activation of this signaling pathway. After strong infections, genes controlling central aspects of tracheal development are reactivated, a response that is not seen after ectopic IMD pathway activation. Presumably to counteract infection-induced cell death-promoting signals, a survival response is launched, characterized by the concurrent expression and activation of the longevity genes dfoxo and dthor. Regions of the airways featuring the strongest immune reactions show substantial remodeling, which is characterized by a significant thickening of the epithelial cells. In conclusion, features related to those observed in inflammatory diseases of the human airways are apparently part of the normal response repertoire of airway epithelia to infection.

Molecular architecture of the fruit fly's airway epithelial immune system.

BACKGROUND: Airway epithelial cells not only constitute a physical barrier, but also the first line of defence against airborne pathogens. At the same time, they are constantly exposed to reactive oxygen species. Therefore, airway epithelia cells have to possess a sophisticated innate immune system and a molecular armamentarium to detoxify reactive oxygen species. It has become apparent that deregulation of epithelial innate immunity is a major reason for the development of chronic inflammatory lung diseases. To elucidate the molecular architecture of the innate immune system of airway epithelial cells, we choose the fruit fly Drosophila melanogaster as a model, because it has the simplest type of airways, consisting of epithelial cells only. Elucidating the structure of the innate immune system of this "airway epithelial cell culture" might enable us to understand why deregulatory processes in innate immune signalling cascades lead to long lasting inflammatory events. RESULTS: All airway epithelial cells of the fruit fly are able to launch an immune response. They contain only one functional signal transduction pathway that converges onto NF-kappaB factors, namely the IMD-pathway, which is homologous to the TNF-alpha receptor pathway. Although vital parts of the Toll-pathway are missing, dorsal and dif, the NF-kappaB factors dedicated to this signalling system, are present. Other pathways involved in immune regulation, such as the JNK- and the JAK/STAT-pathway, are completely functional in these cells. In addition, most peptidoglycan recognition proteins, representing the almost complete collection of pattern recognition receptors, are part of the epithelial cells equipment. Potential effector molecules are different antimicrobial peptides and lysozymes, but also transferrin that can inhibit bacterial growth through iron-depletion. Reactive oxygen species can be inactivated through the almost complete armamentarium of enzymatic antioxidants that has the fly to its disposal. CONCLUSION: The innate immune system of the fly's airway epithelium has a very peculiar organization. A great variety of pattern recognition receptors as well as of potential effector molecules are conspicuous, whereas signalling presumably occurs through a single NF-kappaB activating pathway. This architecture will allow reacting if confronted with different bacterial or fungal elicitors by activation of a multitude of effectors.

Expression of a mitochondrial peroxiredoxin prevents programmed cell death in Leishmania donovani.

Leishmania promastigote cells transmitted by the insect vector get phagocytosed by macrophages and convert into the amastigote form. During development and transformation, the parasites are exposed to various concentrations of reactive oxygen species, which can induce programmed cell death (PCD). We show that a mitochondrial peroxiredoxin (LdmPrx) protects Leishmania donovani from PCD. Whereas this peroxiredoxin is restricted to the kinetoplast area in promastigotes, it covers the entire mitochondrion in amastigotes, accompanied by dramatically increased expression. A similar change in the expression pattern was observed during the growth of Leishmania from the early to the late logarithmic phase. Recombinant LdmPrx shows typical peroxiredoxin-like enzyme activity. It is able to detoxify organic and inorganic peroxides and prevents DNA from hydroxyl radical-induced damage. Most notably, Leishmania parasites overexpressing this peroxiredoxin are protected from hydrogen peroxide-induced PCD. This protection is also seen in promastigotes grown to the late logarithmic phase, also characterized by high expression of this peroxiredoxin. Apparently, the physiological role of this peroxiredoxin is stabilization of the mitochondrial membrane potential and, as a consequence, inhibition of PCD through removal of peroxides.

A peroxiredoxin specifically expressed in two types of pharyngeal neurons is required for normal growth and egg production in Caenorhabditis elegans.

A family of antioxidant proteins, the peroxiredoxins, serve two purposes, detoxification of reactive oxygen species and cellular signaling. Among the three peroxiredoxins of Caenorhabditis elegans (CePrx1-3), CePrx2 was found to have a very unusual expression pattern, restricted to only two types of pharyngeal neurons; namely, the single pharyngeal interneuron I4 and the sensory interneuron I2. CePrx1 and CePrx3-depleted worms showed no obvious phenotypic alterations, whereas worms devoid of CePrx2 were retarded developmentally and had a significantly reduced brood size. Other features, such as lifespan, pharyngeal activity or defecation rates were indistinguishable from those of wild-type worms. Recombinant CePrx2 revealed antioxidant activity, as it was able to detoxify hydrogen peroxide and butylhydroperoxide (t-BOOH), and to protect glutamine synthetase from inactivation by thiol-dependent metal-catalyzed oxidation. In addition, the molecule was able to act as a terminal peroxidase in the thioredoxin system. Expression of ceprx2 in C.elegans was induced after short-term exposure of worms to t-BOOH but survival of ceprx2 knockout mutants in the presence of reactive oxygen or nitrogen species was not impaired. Thus, CePrx2 may protect specifically the two types of neurons from oxidative damage or, more likely, plays a critical role in peroxide signaling in this nematode.