Energy homeostasis in apolipoprotein AIV and cholecystokinin-deficient mice

Apolipoprotein AIV (ApoAIV) and cholecystokinin (CCK) are well-known satiating signals that are stimulated by fat consumption. Peripheral ApoAIV and CCK interact to prolong satiating signals. In the present study, we hypothesized that ApoAIV and CCK control energy homeostasis in response to high-fat diet feeding. To test this hypothesis, energy homeostasis in ApoAIV and CCK double knockout (ApoAIV/CCK-KO), ApoAIV knockout (ApoAIV-KO), and CCK knockout (CCK-KO) mice were monitored. When animals were maintained on a low-fat diet, ApoAIV/CCK-KO, ApoAIV-KO, and CCK-KO mice had comparable energy intake and expenditure, body weight, fat mass, fat absorption, and plasma parameters relative to the controls. In contrast, these KO mice exhibited impaired lipid transport to epididymal fat pads in response to intraduodenal infusion of dietary lipids. Furthermore, ApoAIV-KO mice had upregulated levels of CCK receptor 2 (CCK2R) in the small intestine while ApoAIV/CCK-KO mice had upregulated levels of CCK2R in the brown adipose tissue. After 20 wk of a high-fat diet, ApoAIV-KO and CCK-KO mice had comparable body weight and fat mass, as well as lower energy expenditure at some time points. However, ApoAIV/CCK-KO mice exhibited reduced body weight and adiposity relative to wild-type mice, despite having normal food intake. Furthermore, ApoAIV/CCK-KO mice displayed normal fat absorption and locomotor activity, as well as enhanced energy expenditure. These observations suggest that mice lacking ApoAIV and CCK have reduced body weight and adiposity, possibly due to impaired lipid transport and elevated energy expenditure.