The significant role of ATG5 in the maintenance of normal functions of Mc3T3-E1 osteoblast.

OBJECTIVE: To observe the effects of autophagy-related gene 5 (ATG5) on the proliferation, differentiation, and apoptosis of Mc3T3-E1 osteoblast as well as the effects of ATG5 on apoptosis of osteoblasts under the conditions of non-oxidative stress and oxidative stress.

MATERIALS AND METHODS: ATG5 overexpressing and silencing cell lines were established in this experiment with lentiviral vector and transcription activator-like effect or nuclease (Talen) technique, respectively, using Mc3T3-E1 cells. Cell counting kit-8 (CCK-8) was used to detect the proliferation rate of osteoblasts, and flow cytometry was applied to detect the impacts of overexpressed and silenced ATG5 on the cell cycle. Alizarin red staining was used to detect the mineralization capacity of osteoblasts after 4-week osteoinduction differentiation. Quantitative Real-time polymerase chain reaction (qRT-PCR) and Western blot methods were adopted to detect the levels of gene and protein expressions of runt-related transcription factor 2 (Runx2), osteocalcin (OCN) and collagen I (COL-I) correlated with osteoblast differentiation after 48 h of osteoinduction differentiation. The staining with Annexin V-phycoerythrin/7-amino-actinomycin D (Annexin V-PE/7AAD) and flow cytometry were performed to detect the influence of ATG5 on osteoblast apoptosis.

RESULTS: Stable ATG5 overexpressing and silencing Mc3T3-E1 cell lines were established successfully. CCK-8 test results showed that ATG5 silence inhibited cell proliferation, but the overexpression of ATG5 did not result in an obvious change in cell proliferation. Cell cycle did not change when ATG5 was overexpressed, while was stagnated in S-phase when silenced. The number of mineralized nodules of cells was reduced notably when ATG5 was silenced, while the overexpression of ATG5 did not have an impact on mineralization capacity of the cell after 4-week of osteoinduction differentiation. The test results of qRT-PCR and Western blotting suggested that ATG5 silence inhibited the gene and protein expressions of Runx2, OCN, and COL-I, while the influence of overexpressed ATG5 on the expressions of genes related to osteoblastic differentiation was not obvious after 48 h of osteoinduction differentiation. ATG5 silence made the cells easier to be damaged by hydrogen peroxide, which resulted in the rise of apoptosis rate of osteoblasts, while the overexpressed ATG5 inhibited osteoblast apoptosis after treatment with hydrogen peroxide for 12 h.

CONCLUSIONS: ATG5 silence can lead to inhibition of osteoblast proliferation and differentiation. Moreover, it makes the cells easier to be damaged by oxidative stress, and it causes an increase in apoptosis. However, the overexpression of ATG5 strengthens the anti-oxidative capacity of osteoblasts and reduces apoptosis. ATG5 may be an effective target of anti-oxidative therapy for osteoporosis, which brings a new direction for the treatment of osteoporosis.