Functional characterization of peroxisomes and pathological consequences of peroxisomal dysfunction in the lung
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Only sparse information is available from the literature on the molecular consequences and pathological alterations of the peroxisomal compartment and its enzyme composition in mouse and human lungs. Neither were any studies performed on the molecular consequences of peroxisome deficiency on the lung in knockout mouse models nor on the alterations of the peroxisomal compartment in human lung diseases. Therefore, in this dissertation the peroxisomal compartment and its related gene expression were characterized in different cell types of mouse (C57Bl/6J) and human lungs, using a variety of light-, fluorescence- and electron microscopic as well as biochemical and molecular biological techniques. Furthermore, the molecular consequences and pathological alterations in the lung of PEX11beta knockout mice with deficient peroxisome proliferation were characterized and the changes of the peroxisomal compartment in epithelial cells in the lung of IPF patients described. In contrast to the literature, the results obtained in this dissertation reveal for the first time the presence of peroxisomes in all distinct cell types in the lung and describe significant differences in their cell type-specific numerical abundance, structure and enzyme composition. In this respect, Pex14p proved to be the marker of choice for identification of the whole peroxisomal population, independent of the specific cell type. In contrast, catalase, an enzyme used in many morphological studies to identify these organelles, was only present in high amounts in AECII and Clara cells. Furthermore, peroxisomes of the alveolar and bronchiolar epithelium, as well as alveolar macrophages were rich in the lipid transporter ABCD3 and beta-oxidation enzymes, suggesting their involvement in the modification and recycling of surfactant lipids and in the control of pro-inflammatory lipid mediators and ligands for nuclear receptors of the PPAR family. Prior to this dissertation, no information was available on the peroxisomal compartment during the transdifferentiation process of alveolar epithelial cells (AECII to AECI) and the effect of KGF on peroxisomal markers in this process. The results in this dissertation revealed that some peroxisomal proteins and corresponding mRNAs were tremendously downregulated during AECII transition in the absence of KGF, whereas KGF application conserved the AECII phenotype and led to an increase of catalase and ether lipid synthesizing enzymes. These results correspond to the significant differences observed in the peroxisomal compartment between AECII and AECI in situ in lung sections. The results suggest that KGF might influence differentiation pathways in AECII, regulating peroxisome abundance and corresponding gene transcription. Additional results show that the peroxisomal numerical abundance is extremely high in AECII at birth, suggestive for a pivotal role of peroxisomal lipid metabolism during this period. Thereafter, with the concomitant increase of AECI number during alveolarization, the peroxisomal compartment is downregulated and is only prominent in AECII and alveolar macrophages in the mature adult lung.Furthermore, the molecular consequences of peroxisomal deficiency for regular lung structure and function were analyzed by the use of a knockout mouse model with a peroxisomal biogenesis defect, in which peroxisomal proliferation is disrupted (PEX11beta-/-). These mice showed severe alterations in the abundance of ROS metabolizing enzymes and significant differences in cell type-specific markers, involved in different maturation or signal transduction pathways in the lung. With the help of PEX11beta-/- mice, we could demonstrate that peroxisome deficiency influences lung morphogenesis and maturation, as indicated by severe alterations of the alveolarization process and the differences in the expression levels of mRNAs for components of signal transduction pathways, involved in distal morphogenesis (Wnt5a) and differentiation of individual lung cell types (PPARs). The severe alterations of antioxidant enzymes and pro-inflammatory proteins in PEX11beta-/- lungs are suggestive for disturbed antioxidant and pro-inflammatory response in PEX11beta-/- animals and suggest an essential role for peroxisomal metabolism in maintaining regular airway homeostasis.Finally, preliminary results reveal alterations of the peroxisomal compartment in the lung tissue of patients with idiopathic pulmonary fibrosis (IPF), a devastating human lung disease. The exact role and the molecular consequences of these peroxisomal alterations in IPF, however, have to be investigated in future studies. Taken together, the results of this dissertation suggest an important role of peroxisomes for regular lung development and adult lung homeostasis functions and indicate that this intracellular organelle compartment might be influenced as well in human lung diseases.Verknüpfung zu Publikationen oder weiteren Datensätzen
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Giessen : VVB Laufersweiler 2009