Overexpression of SIRT1 prevents hypoxia-induced apoptosis in osteoblast cells

Hypoxic-ischemic injury of the bone results in osteonecrosis. Nicotinamide adenosine dinucleotide (NAD)-dependent deacetylase sirtuin-1 (SIRT1), a type of NAD-dependent deacetylase, is involved in multiple biological functions, particularly in anti-apoptosis. However, the effects of SIRT1 in osteoblasts remain unclear and whether SIRT1 protects osteoblasts in hypoxic conditions remains to be elucidated. In the present study, the role of SIRT1 in the osteoblast cells under hypoxia and the underlying mechanism of the anti-apoptotic activity of SIRT1 were investigated. MC3T3-E1 osteoblast cells were used for the present study and oxygen-absorbing packs were used to induce cell hypoxia and apoptosis. MC3T3-E1 cells were overexpressed SIRT1 by transfection with a SIRT1 adenovirus. The small interfering RNA of SIRT1 to was used to transfect cells to decrease the protein level. An MTT assay was used to estimate cell viability. Apoptosis was examined with the APOPercentage apoptosis assay kit and the activity of caspases was measured by a caspase 3 and 7 activity kit. Co-immunoprecipitation was used to investigate protein binding ability. The mRNA and protein expression levels were quantified with reverse transcription-quantitative polymerase chain reaction and immunoblotting. It was demonstrated that the expression of SIRT1 mRNA and protein were elevated, and peaked at 12 h under hypoxic conditions. The data demonstrated that SIRT1 overexpression in cells significantly increased cell viability and markedly decreased the percentage of apoptosis compared with the control and knockdown groups. Furthermore, overexpression of SIRT1 significantly activated anti-apoptotic effects by deacetylating lysine residue binding to protein kinase B and decreasing the activity of caspases 3, 9 and subsequent pathways. The results from the present study suggested that SIRT1 may serve a protective function in hypoxia-induced apoptosis in MC3T3-E1 cells, and that SIRT1 intervention may potentially aid in the treatment of ischemic bone disease.