Abstract
The Hermansky Pudlak syndromes (HPS) constitute a family of disorders characterized by oculocutaneous albinism and bleeding diathesis, often associated with lethal lung fibrosis. HPS results from mutations in genes of membrane trafficking complexes that facilitate delivery of cargo to lysosome-related organelles. Among the affected lysosome-related organelles are lamellar bodies (LB) within alveolar type 2 cells (AT2) in which surfactant components are assembled, modified, and stored. AT2 from HPS patients and mouse models of HPS exhibit enlarged LB with increased phospholipid content, but the mechanism underlying these defects is unknown. We now show that AT2 in the pearl mouse model of HPS type 2 lacking the adaptor protein 3 complex (AP-3) fails to accumulate the soluble enzyme peroxiredoxin 6 (PRDX6) in LB. This defect reflects impaired AP-3-dependent trafficking of PRDX6 to LB, because pearl mouse AT2 cells harbor a normal total PRDX6 content. AP-3-dependent targeting of PRDX6 to LB requires the transmembrane protein LIMP-2/SCARB2, a known AP-3-dependent cargo protein that functions as a carrier for lysosomal proteins in other cell types. Depletion of LB PRDX6 in AP-3- or LIMP-2/SCARB2-deficient mice correlates with phospholipid accumulation in lamellar bodies and with defective intraluminal degradation of LB disaturated phosphatidylcholine. Furthermore, AP-3-dependent LB targeting is facilitated by protein/protein interaction between LIMP-2/SCARB2 and PRDX6 in vitro and in vivo Our data provide the first evidence for an AP-3-dependent cargo protein required for the maturation of LB in AT2 and suggest that the loss of PRDX6 activity contributes to the pathogenic changes in LB phospholipid homeostasis found HPS2 patients.
Highlights
8414 JOURNAL OF BIOLOGICAL CHEMISTRY dent cargo protein required for the maturation of lamellar body fractions (LB) in alveolar type 2 (AT2) and suggest that the loss of Peroxiredoxin 6 (PRDX6) activity contributes to the pathogenic changes in LB phospholipid homeostasis found HPS2 patients
Peroxiredoxin 6 Is Significantly Reduced in the Lamellar Bodies of pearl Mice—The pearl mouse lacks expression of adaptor protein 3 (AP-3) in most cell types due to inactivation of the Ap3b1 gene encoding the ubiquitously expressed 3A subunit [35]. pearl mice display a pulmonary phenotype in which total phospholipid content in lung tissue is increased and lamellar bodies in AT2 cells are enlarged, suggestive of intracellular pulmonary surfactant retention [22,23,24]
It is generally thought that the changes in lamellar body size and phospholipid content lead to AT2 cell injury, downstream inflammation, and fibrosis, it has not been clear how specific protein trafficking defects, like those observed in Hermansky Pudlak syndromes (HPS) model melanocytes during melanosome biogenesis, might cause these morphological and content changes in lamellar bodies
Summary
Wild type (WT) C57BL/6J, mutant Ap3b1pe/Ap3b1pe (pearl), and transgenic pearl mice in which the Ap3b1 gene product was expressed in alveolar epithelial cells under the direction of the human SP-C promoter (3.7 kb; line HPS2mt Tg A) [25] were bred and maintained at the Laboratory Animal Facility at the Children’s Hospital of Philadelphia or at Vanderbilt University as described previously [24]. All animal protocols were reviewed and approved by the Institutional Animal Care and Use Committees of The Children’s Hospital Research Institute, the University of Pennsylvania School of Medicine, and the Vanderbilt University School of Medicine, and adhered to the principles of the National Institutes of Health Guide for the Care and Use of Laboratory Animals. Unless specified, both male and female mice were used between 8 and 10 weeks of age
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
