C22-bronchial and T7-alveolar epithelial cell lines of the immortomouse are excellent murine cell culture model systems to study pulmonary peroxisome biology and metabolism

Direct Stochastic Optical Reconstruction Microscopy (dSTORM) of Peroxisomes

Peroxisomes are central metabolic organelles whose maturation and function depend on efficient and accurate targeting of peroxisomal membrane proteins (PMPs). Ultrastructural imaging of the PMPs is a quite difficult task as it requires high spatial and temporal resolution. Further, the spatial resolution of conventional light microscopy is limited due to the diffraction of light. However, recent methodological developments in super resolution microscopy showed us to access the nanoscale regimes spatially allowing to elucidate the membrane structures of cell organelles. In this chapter, we present protocols used in our laboratory for the super-resolution imaging of the peroxisomal membrane protein 14 (PEX14p) by direct stochastic optical reconstruction microscopy (dSTORM).

PPARα-mediated peroxisome induction compensates PPARγ-deficiency in bronchiolar club cells

Despite the important functions of PPARγ in various cell types of the lung, PPARγ-deficiency in club cells induces only mild emphysema. Peroxisomes are distributed in a similar way as PPARγ in the lung and are mainly enriched in club and AECII cells. To date, the effects of PPARγ-deficiency on the overall peroxisomal compartment and its metabolic alterations in pulmonary club cells are unknown. Therefore, we characterized wild-type and club cell-specific PPARγ knockout-mice lungs and used C22 cells to investigate the peroxisomal compartment and its metabolic roles in the distal airway epithelium by means of 1) double-immunofluorescence labelling for peroxisomal proteins, 2) laser-assisted microdissection of the bronchiolar epithelium and subsequent qRT-PCR, 3) siRNA-transfection of PPARγand PPRE dual-luciferase reporter activity in C22 cells, 4) PPARg inhibition by GW9662, 5) GC-MS based lipid analysis. Our results reveal elevated levels of fatty acids, increased expression of PPARα and PPRE activity, a strong overall upregulation of the peroxisomal compartment and its associated gene expression (biogenesis, α-oxidation, β-oxidation, and plasmalogens) in PPARγ-deficient club cells. Interestingly, catalase was significantly increased and mistargeted into the cytoplasm, suggestive for oxidative stress by the PPARγ-deficiency in club cells. Taken together, PPARα-mediated metabolic induction and proliferation of peroxisomes via a PPRE-dependent mechanism could compensate PPARγ-deficiency in club cells.