title: Pulmonary surfactant transport in alveolar type II cells.
abstract: Pulmonary surfactant (PS) is a mixture of several lipids (mainly phosphatidylcholine; PC) and four apoproteins (A, B, C and D). The classical hypothesis of PS transport suggests that PS is synthesized in the endoplasmic reticulum and transported to the lamellar body (LB) via the Golgi apparatus. However, recent studies have raised questions regarding this single route. This study examined, independently, the intracellular trafficking route of three different components of PS, that is, PC, SP-A and SP-B. Alveolar type II cells were isolated from Sprague-Dawley rats or Japanese white rabbits. The cells were cultured with either [3H]choline or [35S]methionine/cysteine with or without brefeldin A, which disassembles the Golgi apparatus. LB was purified from disintegrated cells with sucrose density gradient centrifugation. [3H]PC was extracted from radiolabeled media, cells, and the LB fraction with Bligh-Dyer's method. [35S]SP-A or [35S]SP-B was immunoprecipitated from each sample with a specific antibody. [3H]PC was transported and stored to the LB via a Golgi-independent pathway. [35S]SP-A was transported to the Golgi apparatus, underwent glycosylation, and was then constitutively secreted. The secreted [35S]SP-A was re-uptaken into the LB. [35S]SP-B was transported and stored to the LB via the Golgi-dependent pathway. These results indicate that, rather than a single route, surfactant components take different pathways to reside in the LB. These different pathways may reflect the different nature and role of each surfactant component such as surface tension-lowering activity and innate host defense.
authors.affiliation: Department of Respiratory Medicine, Kanazawa Medical University, Ishikawa, Japan. k-osanai@kanazawa-med.ac.jp
authors.forename: Kazuhiro
authors.initials: K
authors.lastname: Osanai
authors.forename: Chiharu
authors.initials: C
authors.lastname: Tsuchihara
authors.forename: Rieko
authors.initials: R
authors.lastname: Hatta
authors.forename: Taku
authors.initials: T
authors.lastname: Oikawa
authors.forename: Katsuma
authors.initials: K
authors.lastname: Tsuchihara
authors.forename: Masaharu
authors.initials: M
authors.lastname: Iguchi
authors.forename: Toshimitsu
authors.initials: T
authors.lastname: Seki
authors.forename: Masakatsu
authors.initials: M
authors.lastname: Takahashi
authors.forename: Jyongsu
authors.initials: J
authors.lastname: Huang
authors.forename: Hirohisa
authors.initials: H
authors.lastname: Toga
mesh_terms: D000818:Animals; D001692:Biological Transport; D020126:Brefeldin A; D002478:Cells, Cultured; D004847:Epithelial Cells / Q000378:metabolism*; D006056:Golgi Apparatus / Q000378:metabolism; D010713:Phosphatidylcholines / Q000378:metabolism; D011650:Pulmonary Alveoli / Q000166:cytology / Q000378:metabolism*; D037662:Pulmonary Surfactant-Associated Protein A / Q000378:metabolism; D037701:Pulmonary Surfactant-Associated Protein B / Q000378:metabolism; D011663:Pulmonary Surfactants / Q000378:metabolism*; D011817:Rabbits; D051381:Rats; D017207:Rats, Sprague-Dawley; D022142:Secretory Vesicles
chemical_list: D010713:Phosphatidylcholines; D037662:Pulmonary Surfactant-Associated Protein A; D037701:Pulmonary Surfactant-Associated Protein B; D011663:Pulmonary Surfactants; D020126:Brefeldin A