For immunoblotting, membranes were blocked with 5% nonfat dry milk in saline buffer overnight at 4°C, and the following antibodies were used: anti-β-actin (sc-130657, Santa Cruz Biotechnology, CA, USA, 43 kDa) and anti-matrix metallopeptidase 9 (MMP9) (sc-6841, Santa Cruz Biotechnology, CA, USA, 92 kDa).