Decreased Npc1 gene dosage in mice is associated with weight gain

A recent genome-wide association study has determined that the Niemann-Pick C1 (NPC1) gene is associated with early-onset and morbid adult obesity. However, what effects of the nonsynonymous variation in NPC1 on protein function result in weight gain remains unknown. The NPC1 heterozygous mouse model (Npc1(+/-)), which expresses one-half the normal amounts of functional Npc1 protein compared to the homozygous normal (Npc1(+/+)) mouse, was used to determine whether decreased Npc1 gene dosage was associated with weight gain when fed either a low-fat (10% kcal fat) or high-fat (45% kcal fat) diet beginning at 4 weeks of age until 20 weeks of age. The results indicated that Npc1(+/-) mice had significantly increased weight gain beginning at 13 weeks of age when fed a high-fat diet, but not when fed a low-fat diet, compared to the Npc1(+/+) mice fed the same diet. With respect to mice fed a high-fat diet, the Npc1(+/-) mice continued to have significantly increased weight gain to 30 weeks of age. At this age, the Npc1(+/-) mice were found to have increased liver and inguinal adipose weights compared to the Npc1(+/+) mice. Therefore, decreased Npc1 gene dosage resulting in decreased Npc1 protein function, promoted weight gain in mice fed a high-fat diet consistent with a gene-diet interaction.