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To investigate the changes in cell autophagy and the molecular mechanism of rapamycin affecting the fracture healing.Sprague-Dawley (SD) rats were used to establish the right femoral shaft fracture models, and then underwent immunofluorescence assay to detect the autophagy level in bone tissues. After model establishment, SD rats were divided into two groups, the control group and the rapamycin group (1 mg/kg/d). Respectively, at the 2nd, 4th, and 6th week, rats were randomly selected from each group for X-ray and Micro-computed tomography (Micro-CT) examinations to determine callus growth, immunofluorescence assay to detect the protein expression of light chain 3 II (LC3 II), immunohistochemistry to evaluate the autophagy level through detecting the expression of Beclin1 in rats, Western blotting assay to detect cell apoptosis in tissues, hematoxylin and eosin staining (HE staining) to evaluate the osteoblastic activity through count of osteoblast in bone tissue at the end of fracture, and measure the expression of vascular endothelial growth factors (VEGF).Significant increases were seen in protein expression of cells in bone tissues at the end of fracture. In rapamycin group, callus formation and calcification level in rats were all higher than those in control group; compared with control group, for rats in rapamycin group, cell autophagy was significantly elevated in bone tissues, while cell apoptosis at the end of fracture was reduced with a significant increase in osteoblastic activity. The expression of VEGF in rapamycin group was higher than that in control group.Rapamycin can facilitate fracture healing through inducing cell apoptosis and suppressing cell apoptosis in bone tissues.

The current study was to explore the effect of melatonin on osteoporosis and relevant mechanisms.We performed micro-CT to detect bone microstructure and ELISA to detect the contents of osteocalcin (OCN) and bone alkaline phosphatase (BAP) in serum. Double fluorescence labeling of calcein and tetracycline and toluidine blue staining were used to determine morphological indexes of bone tissues. Alizarin red staining and Oil Red O staining were performed to recognize bone cells and adipocytes. RT-PCR was performed to determine the expression of osteoblast differentiation related genes.In the current study, data from micro-CT indicated that melatonin significantly increased the bone mass density (BMD), bone volume/tissue volume (BV/TV), trabecular number (Tb.N) and trabecular thickness (Tb.Th), and decreased the Structure Model Index (SMI) and trabecular Separation/Spacing (Tb.Sp) in elderly rats. Melatonin reduced calcium and phosphorus losses in urine and increased BAP and OCN levels in serum in elderly rats and increased bone formation rate (BFR) and bone mineralization rate (MAR) in elderly rats. Melatonin increased the number of osteoblasts in bone marrow and reduced the number of adipocytes in elderly rats. Melatonin also promoted the expression of osteogenic differentiation genes and suppressed the expression of adipogenic differentiation genes.WE suggest that melatonin could alleviate osteoporosis in aged rats' models probably by promoting osteoblast differentiation.