Ontogenic changes in lung cholesterol metabolism, lipid content, and histology in mice with Niemann–Pick type C disease

• NPC1-deficient mice have increased lung mass starting during neonatal development.
• Lung content of cholesterol and phospholipid in Npc1−/− mice increases with age.
• Lungs of Npc1−/− mice show increase in synthesis of cholesterol but not fatty acids.
• Lungs of Npc1−/− mice show an increase in lipid-laden macrophages in the alveoli.
• Effects of NPC2 deficiency on lung lipid metabolism resemble those in Npc1−/− mice.

Niemann–Pick Type C (NPC) disease is caused by a deficiency of either NPC1 or NPC2. Loss of function of either protein results in the progressive accumulation of unesterified cholesterol in every tissue leading to cell death and organ damage. Most literature on NPC disease focuses on neurological and liver manifestations. Pulmonary dysfunction is less well described. The present studies investigated how Npc1 deficiency impacts the absolute weight, lipid composition and histology of the lungs of Npc1−/− mice (Npc1nih) at different stages of the disease, and also quantitated changes in the rates of cholesterol and fatty acid synthesis in the lung over this same time span (8 to 70 days of age). Similar measurements were made in Npc2−/− mice at 70 days. All mice were of the BALB/c strain and were fed a basal rodent chow diet. Well before weaning, the lung weight, cholesterol and phospholipid (PL) content, and cholesterol synthesis rate were all elevated in the Npc1−/− mice and remained so at 70 days of age. In contrast, lung triacylglycerol content was reduced while there was no change in lung fatty acid synthesis. Despite the elevated PL content, the composition of PL in the lungs of the Npc1−/− mice was unchanged. H&E staining revealed an age-related increase in the presence of lipid-laden macrophages in the alveoli of the lungs of the Npc1−/− mice starting as early as 28 days. Similar metabolic and histologic changes were evident in the lungs of the Npc2−/− mice. Together these findings demonstrate an intrinsic lung pathology in NPC disease that is of early onset and worsens over time.