Leptin impairs myogenesis in C2C12 cells through JAK/STAT and MEK signaling pathways

► Leptin (100 ng/mL) stimulates mitogenesis and raise T202/Y204P-ERK1/2 protein expression. ► Leptin impairs cell viability and muscle fiber formation. ► Both JAK/STAT3 and MEK/MAPK but not PI3-K/AKT/GSK-3β signaling pathways were activated by leptin. ► Insulin surpasses leptin effect through PI3-K/AKT-dependent inhibition of GSK-3beta. ► STAT3 (Y705P-STAT3) and MEK (T202/Y204P-ERK1/2) mediate leptin-dependent effects.