The melanocortin 3 receptor (MC3R) is a key regulator of energy homeostasis and feeding behavior. Global Mc3r knockout mice exhibit greater fat mass and reduced lean mass. Our previous research has found that Mc3r transcripts can be detected in liver and the MC3R deficiency phenotype is partially reversed in liver-specific MC3R recovery mice on a chow diet, in both male and female mice, and high fat diet, in females only. To further examine the role of hepatic MC3R, we produced a liver-specific Mc3r knockout model by crossing mice expressing albumin-Cre recombinase (Alb-Cre+/+) to mice with a floxed Mc3r gene (LoxP+/+), and placed them on a 45 kcal% energy from fat diet for 12 weeks. Female liver-specific Mc3r-deficient mice with diet-induced obesity displayed nonsignificant trends towards worsened glucose tolerance during a glucose tolerance test (glucose AUC Lox+/+, Alb-Cre+/+: n=10, 24036±1644; Alb-Cre+/+: n=10, 19745±1364; BL/6: n=11, 21072±1152 min*mg/dL, p=0.059) and insulin resistance during a glucose tolerance test (glucose AUC LoxP+/+, Alb-Cre+/+: n=10, 14938±812.2;Alb-Cre+/+: n=14, 13062±850; BL/6: n=11, 11725±1024 min*mg/dL, p=0.12), but no differences in morning serum C-peptide (LoxP+/+, Alb-Cre+/+: n=8, 0.74±0.07; Alb-Cre+/+: n=4, 0.55±0.15; BL/6: n=8, 0.29±0.05 ng/mL, p=0.32). Similar patterns were observed for total food consumption (LoxP+/+, Alb-Cre+/+: n=10, 37.2±1.2; Alb-Cre+/+: n=15, 34.5±0.7; BL/6: n=10, 35.7±1.4 g/15 days, p=0.082), with no differences in feeding efficiency (LoxP+/+, Alb-Cre+/+: n=10, 0.027±0.008; Alb-Cre+/+: n=15, 0.009±0.011; BL/6: n=10, 0.017±0.025 g/kcal, p=0.19). No notable trends were observed in male mice. These data suggest that hepatic Mc3r deficiency alone is at most a minor contributor to the obesity phenotypes associated with HFD-treated Mc3r-deficient mice. Additional analysis of tissue samples from these mice and future studies examining Mc3r function in the liver will further elucidate the role of hepatic MC3R.


J.Chen: None. J.K.Elmquist: Research Support; Regeneron Pharmaceuticals Inc. J.A.Yanovski: Research Support; Hikma Pharmaceuticals, Rhythm Pharmaceuticals, Inc., Soleno Therapeutics, Inc., Versanis Bio Inc. T.P.Patel: None. A.Jain: None. D.Elizondo: None. E.K.Altman: None. N.Tugarinov: None. M.Hollis: None. R.Roberson: None. A.Caron: None.

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