Autophagy activation facilitates mechanical stimulation-promoted osteoblast differentiation and ameliorates hindlimb unloading-induced bone loss

Autophagy has been indicated to be involved in regulating bone metabolism. However, little is known about the role of autophagy in mechanical stimulation-influenced osteoblast differentiation and bone formation. In the present study, we first demonstrated that autophagy activation was essential for cyclic mechanical stretching-promoted osteoblast differentiation of bone marrow mesenchymal stem cells. To explore the in vivo role of autophagy in osteoblast differentiation, the hindlimb unloading-induced disuse osteoporosis model was used. Compared to the normal controls, hindlimb unloading led to abundant bone loss as well as lessened autophagy activation of osteoblasts. However, the activation of autophagy by ULK1 overexpression or in the presence of rapamycin significantly increased osteoblast differentiation activity and restored the bone volume. The findings implicate autophagy as a novel mechanosensitive pathway that regulates osteoblast differentiation. The pharmacological activation of autophagy may be an interesting approach for the prevention and treatment of disuse osteoporosis.