Roles of Mitogen-Activating Protein Kinase Kinase Kinase Kinase-3 (MAP4K3) in Preterm Skeletal Muscle Satellite Cell Myogenesis and Mammalian Target of Rapamycin Complex 1 (mTORC1) Activation Regulation.

BACKGROUND Preterm skeletal muscle genesis is a paradigm for myogenesis. The role of mitogen-activating protein kinase kinase kinase kinase-3 (MAP4K3) in preterm skeletal muscle satellite cells myogenesis or its relationship to mammalian target of rapamycin complex 1 (mTORC1) activity have not been previously elaborated. MATERIAL AND METHODS Small interfering RNA (siRNA) interference technology was used to inhibit MAP4K3 expression. Leucine stimulation experiments were performed following MAP4K3-siRNA interference. The differentiation of primary preterm skeletal muscle satellite cells was observed after siRNA-MAP4K3 interference. Western blot analysis was used to determine the expression of MAP4K3, MyHC, MyoD, myogenin, p-mTOR, and p-S6K1. The immunofluorescence fusion index of MyHC and myogenin were detected. MAP4K3 effects on preterm rat satellite cells differentiation and its relationship to mTORC1 activity are reported. RESULTS MAP4K3 siRNA knockdown inhibited myotube formation and both MyoD and myogenin expression in primary preterm rat skeletal muscle satellite cells, but MAP4K3 siRNA had no effect on the activity of mTORC1. In primary preterm rat skeletal muscle satellite cells, MAP4K3 knockdown resulted in significantly weaker, but not entirely blunted, leucine-induced mTORC1 signaling. CONCLUSIONS MAP4K3 positively regulates preterm skeletal muscle satellite cell myogenesis, but may not regulate mTORC1 activity. MAP4K3 may play a role in mTORC1 full activation in response to leucine.