['During orthodontic tooth movement, activation of the vascular system in the compressed periodontal ligament (PDL), which becomes hypoxic, is essential for periodontal tissue remodelling. PERIOSTIN, an extracellular matrix protein, is expressed in PDL and its concentration is increased on the compressive side during orthodontic tooth movement. PERIOSTIN promotes angiogenesis through upregulation of matrix metalloproteinase (MMP)-2, which has been shown to be expressed via αvβ3 integrin/extracellular signal-related kinase (ERK) signalling pathway and vascular endothelial growth factor (VEGF). Therefore, we hypothesized that hypoxia-induced PERIOSTIN promotes MMP-2 expression via αvβ3 integrin/ERK signalling and VEGF in PDL cells.', 'Human PDL cells were cultured in condition medium containing desferrioxamine (DFO) to mimic hypoxia. The total RNA, cell lysates or supernatant were collected, and MMP2 and VEGF expression, PERIOSTIN expression and ERK phosphorylation, and MMP-2 activity were analysed by real-time RT-PCR, western blot analysis, and zymography, respectively. A recombinant human PERIOSTIN or PERIOSTIN siRNA was applied to the cells, then the total RNA was extracted to measure MMP-2 and VEGF expression. The cells were treated with αvβ3 integrin-blocking antibody or ERK inhibitor followed by PERIOSTIN stimulation. MMP-2 expression was measured by real-time RT-PCR.', 'PERIOSTIN was upregulated in a time-dependent manner in human PDL cells treated with DFO, a chemical hypoxia mimic. MMP-2 and VEGF expression, and MMP-2 activity were increased by DFO or PERIOSTIN treatment, and decreased by PERIOSTIN silencing. PERIOSTIN treatment also induced ERK phosphorylation, and PERIOSTIN-induced MMP-2 was reduced by αvβ3 integrin-blocking antibody or ERK inhibitor.'] Does pERIOSTIN regulate MMP-2 expression via the αvβ3 integrin/ERK pathway in human periodontal ligament cells?