ADRB2 and obesity due to melanocortin 4 receptor deficiency: In this review, we focus on four key metabolic GPCRs—GPR40, GPR120, GLP-1R, and β-adrenergic receptors (ADRB1, ADRB2, and ADRB3)—with respect to their roles in metabolic physiology and significance in obesity and related metabolic diseases (Figure 1).