Normal Food Intake and Body Weight in Mice Lacking the G Protein-Coupled Receptor GPR39

It has been recently proposed that obestatin, a peptide encoded by the ghrelin gene, reduces food intake by activating the orphan G protein-coupled receptor GPR39. To gain further insights into the role of GPR39 in body weight homeostasis, we characterized the phenotype of mice with targeted disruption of the GPR39 gene. Body weight, adiposity, and food intake were found to be similar between GPR39(+/+) and GPR39(-/-) mice. Furthermore, fasting glucose and insulin levels were similar between both genotypes. Injection of obestatin peptide (1 micromol/kg, ip) obtained from multiple sources did not consistently inhibit food intake in wild-type mice after an overnight fast, and no difference in food intake was observed between wild-type and GPR39 knockout mice after injection of the peptide. Finally, ectopic expression of GPR39 in HEK293T cells revealed a constitutive activation of the receptor that was unaffected by stimulation with obestatin. Our phenotypic characterization suggests that GPR39 is not a major modulator of food intake in mice, although a more subtle role cannot be excluded. The role of GPR39 in normal physiology requires further study and should be conducted independently of the function of obestatin.