JAK2 and obesity due to melanocortin 4 receptor deficiency: In recent years, protein tyrosine phosphatase 1B (PTP1B) has attracted attention as a potential therapeutic target for developing new drugs, especially for treating T2D and obesity.[13, 14, 15, 16] Since it is a negative regulator of the insulin signaling pathway, also PTP1B has been shown to play an important role in metabolic signaling (especially obesity and T2D) through interaction with the IR and JAK2 downstream of the leptin receptor.