MC4R and obesity due to melanocortin 4 receptor deficiency: In addition, different studies demonstrated the anti-obesity effect of celastrol was independent on melanocortin 4 receptor (MC4R), and lipocalin 2 (Lcn2) (Feng et al., 2019a; Saito et al., 2019), because the deletion of these genes did not weaken the weight-loss and liver-protecting effect of celastrol in mice.