Localization of Misprocessed Pulmonary Surfactant Protein C in Tubular Myelin Enriched Fractions By Cryo Immunogold Labeling

Abstract

Pulmonary surfactant is secreted by alveolar type II cells and reduces the surface tension at the air-liquid interface of alveoli. After pulmonary surfactant is secreted into the alveolar space, it transforms into tubular myelin, a highly ordered 3-dimensional lattice-like structure. Pulmonary surfactant protein C (SP-C), one of four pulmonary surfactant associated proteins, is synthesized as a proprotein which is processed to biologically active 35 amino acid mature peptide by proteolytic cleavage of N- and C-terminal peptides from the SP-C propeptide (Weaver, 1998). Processing of SP-C is linked to the expression of pulmonary surfactant protein B (SP-B): In SP-B deficient mice, SP-C is misprocessed and present in the bronchoalveolar lavage (BAL; Vorbroker et. al., 1995a). Although the intracellular localization of SP-C is well established (Vorbroker et. al., 1995b), there is no ultrastructure study available regarding the localization of misprocessed SP-C in the airway. In this study, we used transgenic mice expressing a truncated human SP-B propeptide (hSP-BΔC+/+) bred into the murine granulocyte macrophage colony stimulating factor (GMCSF) and SP-B double knockout background (hSP-BΔC+/+: GMCSF-/-: mSP-B-/-) as a model to localize the misprocessed SP-C by cryoimmunogold labeling.