Figure 6.

p21 mediates the neuroprotective effect of tissue-type plasminogen activator (tPA). (A) Mean fold increase in p21 mRNA expression in wild-type (Wt) and tumor necrosis factor-α deficient (TNF-α^−/−) neurons incubated with either active tPA 5 nmol/L or inactive tPA (itPA) 5 nmol/L or plasmin 10 nmol/L or TNF-α 20 ng/ml. Values represent mean±s.d; n=8 per group. ^*P<0.01 compared with p21 mRNA expression in neurons treated with itPA. (B) Mean fold increase in p21 mRNA expression in wild-type (Wt) and tPA-deficient (tPA^−/−) neurons exposed to 5 minutes of oxygen–glucose deprivation (OGD) conditions. A subgroup of Wt neurons was incubated with anti-TNF-α antibodies 40 ng/ml. ^*P<0.01 versus Wt neurons incubated with anti-TNF-α antibodies and tPA^−/− neurons; n=8 per group. Values represent mean±s.d. (C) Mean cell survival in Wt neurons infected with a lentiviral vector encoding a scrambled short hairpin RNA (shRNA) sequence that does not lead to the specific degradation of any known cellular mRNA or with a silencing p21 shRNA and treated with tPA 5 nmol/L followed 5 minutes later by exposure to 55 minutes of OGD conditions (lethal hypoxia). ^*P<0.01 versus non-preconditioned neurons; n=10 observations. Values represent mean±s.d. (D) Mean cell survival in Wt neurons infected with a lentiviral vector encoding a scrambled shRNA sequence or a silencing p21 shRNA and exposed to OGD conditions for 5 minutes (hypoxic preconditioning, HP), followed 5 minutes later by exposure to 55 minutes of OGD conditions (lethal hypoxia). ^*P<0.01 versus non-preconditioned neurons; n=12 observations. Values represent mean±s.d. Ns, nonsignificant