Correlation between autophagy of osteoblasts and oxidative stress of osteoporosis rats

The proliferation, apoptosis and autophagy of osteoblast are correlated with osteoporosis (OP), during which oxidative stress is involved. Oxidative stress can induce cell autophagy injury. This study established an OP rat model, in which osteoblast autophagy was investigated along with oxidative stress. Female SD rats (6 weeks old) were randomly assigned into sham, model and estrogen (E2) groups (N=20). OP model was established by bilateral ovariectomy, followed by E2 (10 mu g/kg/d) for 6 weeks. Rats were sacrificed to test micro-structure and volume of bone tissues. HE staining and transmission electron microscopy were used to observe morphology and autophagosome. ELISA was used to quantify serum level of osteocalcin (OCN), type I collagen carboxyl terminal peptide (CTX), E2, superoxide dismutase (SOD), reactive oxygen species (ROS) and catalase (CAT). Western blot was used to quantify Beclin-1, light chain 3 of microtubule related protein (LC3-II), mammalian target of rapamycin (mTOR), and phosphatidyl inositol-3-hydroxykinase (PI3K), in order to analyze the relationship between autophagy and oxidative stress. OP model had elevated autophagosome number, OCN, CTX, ROS, Beclin-1 and LC3-II expression, plus depressed E2, CAT, SOD, mTOR and PI3K (P<0.05). E2 treatment improved OP disease, decreased autophagosome number, OCN, CTX, ROS Beclin-1 and LC3-II, and elevated E2, CAT, SOD, mTOR and PI3K levels (P<0.05). Autophagy of osteoblast was negatively correlated with bone volume and anti-oxidative enzyme, and was positively correlated with bone trabecular distance. Autophagy of osteoblast is correlated with bone microstructure, volume and oxidative stress, and it plays a role in OP pathology.