[Space flight/bedrest immobilization and bone. Development of inhibitors for atrophy caused by unloading stress].

Muscle atrophy caused by unloading stress is a serious problem in bed rest patients or astronauts. In our previous studies, we revealed that induction and activation of ubiquitin ligase Cbl-b played an important role in skeletal muscle atrophy caused by unloading stress. Under muscle atrophy conditions, Cbl-b interacted with and degraded IRS-1 (insulin receptor substrate 1) that is a central molecule in the IGF-1 signaling pathway. In addition, we developed a Cbl-b inhibitor (Cblin) that a pentapeptide mimetic of tyrosin608-phosphorylated IRS-1, DGpYMP. This Cblin peptide inhibited Cbl-b mediated IRS-1 ubiquitination and strongly decreased the Cbl-b-mediated induction of MAFbx/atrogin-1. We are further developing Cbl-b inhibitors that are more effective than an original Cblin peptide.