ABCA3 Is Critical for Lamellar Body Biogenesis in Vivo

Naeun Cheong,Huayan Zhang,Muniswamy Madesh,Ming Zhao,Kevin Yu,Chandra Dodia,Aron B Fisher,Rashmin C Savani,Henry Shuman

doi:10.1074/jbc.m703927200

Abstract

Mutations in ATP-binding cassette transporter A3 (human ABCA3) protein are associated with fatal respiratory distress syndrome in newborns. We therefore characterized mice with targeted disruption of the ABCA3 gene. Homozygous Abca3-/- knock-out mice died soon after birth, whereas most of the wild type, Abca3+/+, and heterozygous, Abca3+/-, neonates survived. The lungs from E18.5 and E19.5 Abca3-/- mice were less mature than wild type. Alveolar type 2 cells from Abca3-/- embryos contained no lamellar bodies, and expression of mature SP-B protein was disrupted when compared with the normal lung surfactant system of wild type embryos. Small structural and functional differences in the surfactant system were seen in adult Abca3+/- compared with Abca3+/+ mice. The heterozygotes had fewer lamellar bodies, and the incorporation of radiolabeled substrates into newly synthesized disaturated phosphatidylcholine, phosphatidylglycerol, phosphatidylethanolamine, and phosphatidylserine in both lamellar bodies and surfactant was lower than in Abca3+/+ mouse lungs. In addition, since the fraction of near term Abca3-/- embryos was significantly lower than expected from Mendelian inheritance ABCA3 probably plays roles in development unrelated to surfactant. Collectively, these findings strongly suggest that ABCA3 is necessary for lamellar body biogenesis, surfactant protein-B processing, and lung development late in gestation.

Highlights

One of the striking abnormalities observed in hereditary SP-B deficiency, which is characterized by deficiencies of surfactant quantity and function, is derangement of lamellar body morphology [12], abnormalities that are replicated in the SP-B knock-out mouse [13, 14]
The Abca3 knock-out mouse phenotype was similar to the clinical findings in patients with the most severe forms of surfactant deficiency associated with ATP-binding cassette protein A3 gene (ABCA3) mutations
Heterozygous Abca3ϩ/Ϫ mice were indistinguishable from wild type mice, developing and growing normally

Summary

Introduction

Decreased expression of ABCA3 in both isolated AT2 cells and in lungs alters the expression, localization, and processing of SP-B protein [16, 17, 19] Together, these findings are suggestive that ABCA3 is responsible for converting lysosomes or similar vesicular bodies into phospholipid storage organelles, which are transformed into lamellar bodies by the subsequent trafficking and processing of SP-B and SP-C. Lung architecture, AT2 cell morphology, surfactant protein-B processing, and lipid synthesis were all disrupted Both the Abca3Ϫ/Ϫ and Abca3ϩ/Ϫ mice will be useful models for providing insights into surfactant metabolism in normal and disease states

Methods

Results

Conclusion