Previous report showed that angiotensin II accelerates osteoporosis, and recent clinical studies suggest that several antihypertensive drugs, especially angiotensin-converting enzyme inhibitors, reduced bone fractures. However, the underling mechanism by which angiotensin II induces bone dysfunction is largely unknown. Here in this study, we show that angiotensin II induces mitochondrial oxidative stress and mitochondrial DNA (mtDNA) damage. We find that the protein and RNA levels of mitochondrial catalase and manganese superoxide dismutase (MnSOD) are decreased in osteoblasts in the presence of angiotensin II. Further, we show that angiotensin II inhibits the protein level of SIRT1, but not SIRT3, which results in the hyperacetylation of the forkhead box O3a (FoxO3a) and inhibition of the expression of catalase and MnSOD. Finally, we show that SRT3025 (Sirt1 activator) and Mn (III) tetrakis (4-benzoic acid) porphyrin (MnTBAP, a MnSOD mimetics) can markedly reduce mitochondrial oxidative stress and mtDNA damage. In summary, we identify a novel SIRT1-FoxO3a-MnSOD axis in angiotensin II-induced mitochondrial oxidative stress and mtDNA damage in osteoblasts. (C) 2014 Elsevier Inc. All rights reserved.