TNFRSF9 and obesity due to melanocortin 4 receptor deficiency: We previously showed that 4-1BB deficiency attenuates obesity-induced adipose inflammation and metabolic complications such as insulin resistance in mice fed a high-fat diet (HFD) [16], and that in vitro stimulation of 4-1BB promoted free fatty acid-induced inflammatory response in muscle cells through NF-κB activation [3].