Increased metabolic rate and insulin sensitivity in male mice lacking the carcino-embryonic antigen-related cell adhesion molecule 2

The carcino-embryonic antigen-related cell adhesion molecule (CEACAM)2 is produced in many feeding control centres in the brain, but not in peripheral insulin-targeted tissues. Global Ceacam2 null mutation causes insulin resistance and obesity resulting from hyperphagia and hypometabolism in female Ceacam2 homozygous null mutant mice (Cc2 [also known as Ceacam2](-/-)) mice. Because male mice are not obese, the current study examined their metabolic phenotype. The phenotype of male Cc2 (-/-) mice was characterised by body fat composition, indirect calorimetry, hyperinsulinaemic-euglycaemic clamp analysis and direct recording of sympathetic nerve activity. Despite hyperphagia, total fat mass was reduced, owing to the hypermetabolic state in male Cc2 (-/-) mice. In contrast to females, male mice also exhibited insulin sensitivity with elevated beta-oxidation in skeletal muscle, which is likely to offset the effects of increased food intake. Males and females had increased brown adipogenesis. However, only males had increased activation of sympathetic tone regulation of adipose tissue and increased spontaneous activity. The mechanisms underlying sexual dimorphism in energy balance with the loss of Ceacam2 remain unknown. These studies identified a novel role for CEACAM2 in the regulation of metabolic rate and insulin sensitivity via effects on brown adipogenesis, sympathetic nervous outflow to brown adipose tissue, spontaneous activity and energy expenditure in skeletal muscle.