Factor Xa protects cultured hippocampal neurons from glutamate toxicity

Activated protein C prevents glutamate- and thrombin-induced activation of nuclear factor-kappaB in cultured hippocampal neurons

Brain injury is associated with neuroinflammation, neurodegeneration, and also blood coagulation with thrombin formation and generation of activated protein C (APC). We have previously shown that APC, a serine protease of hemostasis, at very low concentrations has protective effects in rat hippocampal and cortical neurons at glutamate-induced excitotoxicity through protease-activated receptor-1 (PAR-1) or endothelial receptor of protein C (EPCR)/PAR-1. The transcription factor nuclear factor kappaB (NF-kappaB) takes part in regulating neuronal survival in several pathological conditions. To elucidate the impact of NF-kappaB in APC-mediated cell survival, we investigated nuclear translocation of NF-kappaB p65 at glutamate- or thrombin-induced toxicity in hippocampal neurons. We used immunoassay and immunostaining with confocal microscopy with anti-NF-kappaBp65 antibody. We show that APC at concentrations as low as 1-2 nM inhibits translocation of NF-kappaB p65 into the nucleus of cultured rat hippocampal neurons, induced by 100 muM glutamate or 50 nM thrombin (but not 10 nM). The blocking effect of APC on NF-kappaB p65 translocation was observed at 1 and 4 h after treatment of neurons with glutamate, when the NF-kappaBp 65 level in the nucleus was significantly above the basal level. Then we investigated whether the binding of APC to EPCR/PAR-1 is required to control NF-kappaB activation. Antibodies blocking PAR-1 (ATAP2) or EPCR (P-20) abolished the APC-induced decrease of nuclear level of NF-kappaB p65 at glutamate-induced toxicity, whereas control antibodies to PAR-1 (S-19) and EPCR (IgG) exerted no effect. Thus, we suggest that the activation of NF-kappaB in rat hippocampal neurons mediates the glutamate- and thrombin-activated cell death program, which is reduced by exposure of cells to APC. APC induces the reduction of the nuclear level of NF-kappaB p65 in hippocampal neurons at glutamate-induced excitotoxicity via binding to EPCR and subsequent PAR-1 activation and signaling.

Activated protein C via PAR1 receptor regulates survival of neurons under conditions of glutamate excitotoxicity

The effect of an anticoagulant and cytoprotector blood serine proteinase--activated protein C (APC)--on survival of cultured hippocampal and cortical neurons under conditions of glutamate-induced excitotoxicity has been studied. Low concentrations of APC (0.01-10 nM) did not cause neuron death, but in the narrow range of low concentrations APC twofold and stronger decreased cell death caused by glutamate toxicity. High concentrations of APC (>50 nM) induced the death of hippocampal neurons similarly to the toxic action of glutamate. The neuroprotective effect of APC on the neurons was mediated by type 1 proteinase-activated receptor (PAR1), because the inactivation of the enzyme with phenylmethylsulfonyl fluoride or PAR1 blockade by a PAR1 peptide antagonist ((Tyr1)-TRAP-7) prevented the protective effect of APC. Moreover, APC inhibited the proapoptotic effect of 10 nM thrombin on the neurons. Geldanamycin, a specific inhibitor of heat shock protein Hsp90, completely abolished the antiapoptotic effect of 0.1 nM APC on glutamate-induced cytotoxicity in the hippocampal neurons. Thus, APC at low concentrations, activating PAR1, prevents the death of hippocampal and cortical neurons under conditions of glutamate excitotoxicity.

Modulation of hippocampal neuron survival by thrombin and factor Xa

Effects of thrombin, factor Xa (FXa), and protease-activated receptor 1 and 2 agonist peptides (PAR1-AP and PAR2-AP) on survival and intracellular Ca2+ homeostasis in hippocampal neuron cultures treated with cytotoxic doses of glutamate were investigated. It is shown that at low concentrations (<or=10 nM) thrombin and FXa protect neurons from glutamate-induced excitotoxicity. Inactivation of the proteases blocked the neuroprotective effect. Using PAR1-AP, PAR2-AP, and PAR1 antagonist, we have demonstrated that the neuroprotective effect of thrombin is mediated through activation of PAR1, whereas the effect of FXa may involve novel subtype(s) of PARs. Unlike FXa, thrombin induced transient intracellular calcium signal in hippocampal neurons, which was mainly mediated via IP(3) receptors of the endoplasmic reticulum. Both of the serine proteases improved the recovery of neuronal Ca2+ homeostasis after glutamate treatment.