Upregulation of SIRT 1 inhibits H 2 O 2 ‐ induced osteoblast apoptosis via FoxO 1 / β ‐ catenin pathway

Osteoporosis is a disease that significantly influences life expectancy and quality in humans. Oxidative stress may stimulate bone marrow osteoclast differentiation and inhibit osteoblast (OB) differentiation. OB proliferation and differentiation are affected by the forkhead box O (FoxO)1/ β‐catenin signaling pathway. The osteogenic differentiation of mesenchymal stem cells (MSCs) may be promoted by silent information regulator type‐1 [sirtuin (SIRT)1]. However, the molecular mechanism of SIRT1 regulation of osteogenic differentiation of MSCs remains unclear, and further elucidation is needed. The present study investigated the role of SIRT1 in the FoxO1/β‐catenin signaling pathway in oxidative stress and its mechanism in the osteoblastic progenitor cell line (MC3T3‐E1). The results demonstrated that OB apoptosis and elevated oxidative stress in cells were simulated by H2O2, which was inhibited by moderate SIRT1 overexpression through reducing the oxidative stress. Further studies revealed that FOXO1 and β‐catenin pathway activity was downregulated by SIRT1 and eventually resulted in inhibition of target genes, including the proapoptotic gene B cell lymphoma‐2 interacting mediator of cell death, DNA repair gene growth arrest and DNA damage inducible protein 45 and the OB differentiation suppressor gene peroxisome proliferator activated receptor (PPAR)‐γ. Furthermore, β‐catenin and PPAR‐γ were inhibited by SIRT1. Overall, the results of the present study suggest that moderate overexpression of SIRT1 (~3‐fold of normal level) may directly or indirectly inhibit apoptosis of OBs via the FOXO1 and β‐catenin signaling pathway. Introduction Osteoporosis (OP) is a disease characterized by structural deteriorationist, low bone mass, and porous bone associated with higher fracture risk, significantly influencing expectancy and quality of life in humans. Osteoblasts (OB) play pivotal roles in mediation of formation, resorption and remodeling of bones (1). OB and osteoclast (OC) are units of bone remodeling and healthy of bone is dependent on balance and interaction between them (1). The imbalance caused by reduction of OB differentiation and increased differentiation of OC were the major reasons of OP (1). OP was increased year by year with aging population and per‐capita life expectancy, especially for postmenopausal womenfolk (2). In the past decades, researches showed that estrogen deficiency and immune and inflammatory responses are the main factors inducing OP (3,4). However, recent investigations indicated that oxidative stress can stimulate bone marrow OC differentiation and inhibit OB differentiation, thereby promoting the development of OP (5,6). Therefore, as a risk factor for the development of OP, oxidative stress has received more attention (6,7). And the focus of pathologic mechanism of OP was gradually shifted from estrogen‐centric to aging and oxidative stress (8). Oxidative stress is a highly reactive molecule in living organisms, such as reactive nitrogen radicals (RNS) and reactive oxygen species (ROS) (9,10). High production of them would lead to oxidative damage to bimolecular, which further induces tissues and organs damaged (10). ROS is closely related with biomedical and pathogenic bases of variety diseases and pathological processes. Oxidative stress levels in the body depend on the balance between ROS and antioxidant defense system in vivo (10). Investigations showed that oxidative stress can inhibit bone marrow stromal cell line (M2‐1 OB4) and OB progenitor cell line (MC3T3‐E1) differentiation into OB, and inhibit OB mineralization and induce its apoptosis (11). Studies revealed that H2O2 in human bone marrow stromal cells (HBMSCs) increased level of ROS through activation of c‐Jun N‐terminal kinase (JNK) and nuclear factor κB (NF‐κB) Pathway, which result in reduction of glutathione, activation of caspases 3, 9 and 8, and finally inducing apoptosis of HBMSCs (12). Upregulation of SIRT1 inhibits H2O2‐induced osteoblast apoptosis via FoxO1/β‐catenin pathway HANLIN YAO1, ZHEN YAO2, SHAOCHENG ZHANG3, WENJUN ZHANG4 and WEN ZHOU5 1Department of Orthopaedic, The Second Affiliated Hospital of Kunming Medical University, Kunming, Yunnan 650000; 2Department of Orthopaedic, Xinchang Hospital Affiliated to Wenzhou Medical University, Hangzhou, Zhejiang 312500; 3Department of Orthopaedic, Changhai Hospital Affiliated to Second Military Medical University, Shanghai 200433; 4Department of Orthopaedic, Qingpu People's Hospital of Zhujiajue, Shanghai 201713; 5Department of Sports Science, Shanghai University of Sports, Shanghai 200433, P.R. China Received March 22, 2017; Accepted October 18, 2017 DOI: 10.3892/mmr.2018. 8657 Correspondence to: Dr Shaocheng Zhang, Department of Orthopaedic, Changhai Hospital Affiliated to Second Military Medical University, 168 Changhai Road, Shanghai 200433,