TNF and obesity due to melanocortin 4 receptor deficiency: Not surprisingly, we have found that obese db/db mice lacking TNFα function developed early onset and severe obesity compared with db/db mice; compared with TNFα−/− mice, db/db mice showed that key molecules in Wnt/β-catenin signaling were down-regulated both in mRNA and protein levels from adolescent age, while adipogenic markers were up-regulated.