Pulmonary abnormalities due to ABCA1 deficiency in mice

Abstract

Ϫ/Ϫ ) have been shown to have low-serum high-density lipoprotein and abnormal lung morphology. We examined alterations in the structure and function of lungs from Ϫ/Ϫ mice (DBA1/J). Electron microscopy of the diseased mouse lung revealed areas of focal disease confirming previous results (47). Lipid analysis of the lung tissue of Ϫ/Ϫ mice showed a 1.2-and 1.4-fold elevation in total phospholipid (PL) and saturated phosphatidylcholine, respectively, and a marked 50% enrichment in total cholesterol content predominately due to a 17.5-fold increase in cholesteryl ester compared with wild type (WT). Lung surfactant in the Ϫ/Ϫ mice was characterized by alveolar proteinosis (161%), a slight increase in total PL (124%), and a marked increase in free cholesterol (155%) compared with WT. Alveolar macrophages were enriched in cholesterol (4.8-fold) due to elevations in free cholesterol (2.4-fold) and in cholesteryl ester (14.8-fold) compared with WT macrophages. More PL mass was cleared from the alveolar space of Ϫ/Ϫ mice lungs, measured using intratracheal installation of 3 H-PL liposomes. Compared with WT mice, the Abca1 Ϫ/Ϫ mice demonstrated respiratory distress with rapid, shallow breathing. Thus the lungs of mice lacking ABCA1 protein demonstrated abnormal morphology and physiology, with alveolar proteinosis and cholesterol enrichment of tissue, surfactant, and macrophages. The results indicate that the activity of ABCA1 is important for the maintenance of normal lung lipid composition, structure, and function. lung; surfactant; type II cells; alveolar macrophages; cholesterol MAINTENANCE OF APPROPRIATE surface tension in the lung is the primary function of pulmonary surfactant, the lipid-protein mixture that lines the alveoli (for review, Ref. 33). Surfactant proteins (SP) are divided into two groups, the hydrophilic SP-A and SP-D and the hydrophobic SP-C and SP-B (for review, Ref. 64). The lipid moiety of surfactant is predominantly phospholipid with 10% cholesterol by weight (34); cholesterol represents 58% of the neutral lipid fraction (26). The relative distribution of cholesterol differs between the various subfractions of alveolar surfactant (24). In rat surfactant, cholesterol represents 18% of the total lipid in the large aggregate heavy subfraction that pellets after centrifugation at 60,000 g but is a major component (60% of total lipid) of the small aggregate light subfraction isolated at 100,000 g (24). The large aggregate is the most surface-active fraction of surfactant and contains most of the SPs (22). Although the lung is capable of de novo synthesis of cholesterol, the bulk of pulmonary cholesterol is provided by serum lipoproteins. Radiolabeled cholesterol from very low-density (VLDL), lowdensity (LDL), and high-density (HDL) lipoproteins is taken up promptly by the perfused rat lung and, subsequently, recovered from the surfactant fraction (26, 51, 56). Type II cells, known to be responsible for the synthesis and secretion of surfactant, bind and incorporate gold-conjugated VLDL, LDL, and HDL as ...

Deletion of the Transmembrane Transporter ABCG1 Results in Progressive Pulmonary Lipidosis

“…These include GM-CSF, SP-B, SP-C, SP-D, ABCA3, ABCA1, and LAL (11)(12)(13)(14)(15)(16)(17)(18). Together, these reports illustrate the important roles of pulmonary macrophages and pneumocytes type 2 in regulating lipid, and especially surfactant, metabolism.…”

“…Nonetheless, we conclude that Abcg1 Ϫ/Ϫ type 2 cells retain the capacity to secrete surfactant since surfactant levels (recovered after BAL) increased ϳ5-fold and tubular myelin is present in the alveolar hypophase of Abcg1 Ϫ/Ϫ mice. Recent studies have linked mutations in ABCA3 (13) or ABCA1 (17) to respiratory distress syndrome and altered surfactant secretion in humans and mice, respectively. Thus, the decrease in Abca3 that occurs in the lungs of Abcg1 Ϫ/Ϫ mice (Fig.…”

A Critical Role for ABCG1 in Macrophage Inflammation and Lung Homeostasis

“…Recently, a role for ABCG1 in pulmonary function was discovered (24). The lung phenotype of older (8 mo of age) Abcg1 Ϫ/Ϫ mice is similar to that observed for Abca1 Ϫ/Ϫ mice (25). The deletion of ABCG1 or ABCA1 leads to progressive lipid accumulation and cellular accumulation in the lung (24).…”

Loss of ABCG1 Results in Chronic Pulmonary Inflammation

“…Taken together, these studies identified pivotal roles for ABCG1 in controlling pulmonary homeostasis in vivo (20,22). Interestingly, based on gene deletion in mice and/or natural mutations in humans, other members of the ABC family of transporters, ABCA1, ABCA3, and ABCC7, have also been shown to play important roles in pulmonary physiology (23)(24)(25)(26)(27).…”