TGFB1 and obesity due to melanocortin 4 receptor deficiency: Based on many results regarding aging-related pathology (Figure 2), the effects of TGF-β signaling can be generalized into two aspects: (1) The impairment of TGF-β signaling in certain cell types, exemplified by a loss of neuroprotective activities in AD and a loss of TGF-β-mediated growth inhibition in cancer, and (2) the chronic elevation of TGF-β signaling linked to tissue fibrosis, chronic inflammation, and decreased regeneration capacity, as well as metabolic malfunction observed in AD, muscle atrophy, obesity, and other diseases.