Impact of the loss of caveolin-1 on lung mass and cholesterol metabolism in mice with and without the lysosomal cholesterol transporter, Niemann-Pick type C1

Abstract

Caveolin-1 (Cav-1) is a major structural protein in caveolae in the plasma membranes of many cell types, particularly endothelial cells and adipocytes. Loss of Cav-1 function has been implicated in multiple diseases affecting the cardiopulmonary and central nervous systems, as well as in specific aspects of sterol and lipid metabolism in the liver and intestine. Lungs contain an exceptionally high level of Cav-1. Parameters of cholesterol metabolism in the lung were measured, initially in Cav-1-deficient mice (Cav-1(-/-)), and subsequently in Cav-1(-/-) mice that also lacked the lysosomal cholesterol transporter Niemann-Pick C1 (Npc1) (Cav-1(-/-):Npc1(-/-)). In 50-day-old Cav-1(-/-) mice fed a low- or high-cholesterol chow diet, the total cholesterol concentration (mg/g) in the lungs was marginally lower than in the Cav-1(+/+) controls, but due to an expansion in their lung mass exceeding 30%, whole-lung cholesterol content (mg/organ) was moderately elevated. Lung mass (g) in the Cav-1(-/-):Npc1(-/-) mice (0.356±0.022) markedly exceeded that in their Cav-1(+/+):Npc1(+/+) controls (0.137±0.009), as well as in their Cav-1(-/-):Npc1(+/+) (0.191±0.013) and Cav-1(+/+):Npc1(-/-) (0.213±0.022) littermates. The corresponding lung total cholesterol contents (mg/organ) in mice of these genotypes were 6.74±0.17, 0.71±0.05, 0.96±0.05 and 3.12±0.43, respectively, with the extra cholesterol in the Cav-1(-/-):Npc1(-/-) and Cav-1(+/+):Npc1(-/-) mice being nearly all unesterified (UC). The exacerbation of the Npc1 lung phenotype and increase in the UC level in the Cav-1(-/-):Npc1(-/-) mice imply a regulatory role of Cav-1 in pulmonary cholesterol metabolism when lysosomal sterol transport is disrupted.

Keywords: Cellular cholesterol trafficking; Cholesterol feeding; Cholesterol synthesis; Pulmonary dysfunction; Relative organ weight.

Fig. 1

Absolute and relative lung weight, and lung cholesterol concentration and content, each as a function of age, in Cav-1^−/− and Cav-1^+/+ mice. Absolute lung weight (A) was expressed relative to body weight (B). Lung total cholesterol concentration (C) was multiplied by absolute lung weight to determine lung cholesterol content (D). The 100-day-old mice were all females, like those at 50 days. At 24 days, there were female and male mice of each Cav-1 genotype. Values represent the mean ± 1 SEM of data from 3-7 mice in each group. Different letters (a-d) denote statistically different values (p < 0.05) as determined by 2-way ANOVA with age and genotype as variables.

Fig. 2

Effect of feeding a high-cholesterol diet on lung weight and cholesterol content in Cav-1^−/− and Cav-1^+/+ mice at 50 days of age. Male Cav-1^−/− and Cav-1^+/+ mice were fed either the basal diet alone or the same diet with added cholesterol (0.5% wt/wt) for 3 weeks starting at 28 or 29 days of age. Plasma total cholesterol concentration (A), relative lung weight (B) and lung total cholesterol concentration (C) and content (D) were measured. Values represent the mean ± 1 SEM of data from 5-7 mice in each group. Different letters (a-c) denote statistically different values (p < 0.05) as determined by 2-way ANOVA with genotype and dietary cholesterol level as variables.

Fig. 3

Body and lung weights, and lung cholesterol concentration and content in mice deficient in either Caveolin-1 or Niemann-Pick C1, or both of these proteins. These mice were generated as described in Materials and Methods, and were fed a basal rodent chow diet from weaning until studied at 50 days of age. The number of mice for each genotype was 4 Cav-1^+/+:Npc1^+/+, 8 Cav-1^−/−:Npc1^+/+, 6 Cav-1^+/+:Npc1^−/− and 5 Cav-1^−/−:Npc1^−/−, with approximately equal numbers of males and females in each group. Values are the mean ± 1 SEM of data from the specified number of animals. Different letters (a-c) denote statistically different values (p < 0.05) as determined by 1-way ANOVA with genotype as the variable.

Fig. 4

Relative mRNA expression levels in the lungs of mice deficient in either Caveolin-1, Niemann-Pick C1, or both of these proteins. These mice were generated as described in Materials and Methods and were fed a basal chow diet until studied at 50 days of age. The lungs were used for the mRNA analyses shown here, as well as for measurement of the tissue content of unesterified and esterified cholesterol (Table 3). The gene names and primer sequences are given in Table 1. The amount of mRNA found was expressed relative to that obtained for the Cav-1^+/+:Npc1^+/+ mice, which in each case was arbitrarily set at 1.0. Values are the mean ± 1 SEM of data from the same numbers of mice for each genotype as given in Fig. 3 and Table 3. Different letters (a-c) denote statistically different values (p < 0.05) as determined by 1-way ANOVA with genotype as the variable.