Involvement of the 5‐lipoxygenase pathway in the neurotoxicity of the prion peptide PrP106‐126

Abstract

Transmissible spongiform encephalopathies are characterised by the transformation of the normal cellular prion protein (PrP(C)) into an abnormal isoform (PrP(TSE)). Previous studies have shown that N-methyl-D-aspartate (NMDA) receptor antagonists can inhibit glutathione depletion and neurotoxicity induced by PrP(TSE) and a toxic prion protein peptide, PrP106-126, in vitro. NMDA receptor activation is known to increase intracellular accumulation of Ca(2+), resulting in up-regulation of arachidonic acid (AA) metabolism. This can stimulate the lipoxygenase pathways that may generate a number of potentially neurotoxic metabolites. Because of the putative relationship between AA breakdown and PrP106-126 neurotoxicity, we investigated AA metabolism in primary cerebellar granule neuron cultures treated with PrP106-126. Our studies revealed that PrP106-126 exposure for 30 min significantly up-regulated AA release from cerebellar granule neurons. PrP106-126 neurotoxicity was mediated through the 5-lipoxygenase (5-LOX) pathway, as shown by abrogation of neuronal death with the 5-LOX inhibitors quinacrine, nordihydroguaiaretic acid, and caffeic acid. These inhibitors also prevented PrP106-126-induced caspase 3 activation and annexin V binding, indicating a central role for the 5-LOX pathway in PrP106-126-mediated proapoptosis. Interestingly, inhibitors of the 12-lipoxygenase pathway had no effect on PrP106-126 neurotoxicity or proapoptosis. These studies clearly demonstrate that AA metabolism through the 5-LOX pathway is an important early event in PrP106-126 neurotoxicity and consequently may have a critical role in PrP(TSE)-mediated cell loss in vivo. If this is so, therapeutic intervention with 5-LOX inhibitors may prove beneficial in the treatment of prion disorders.

Blockade of 12-lipoxygenase expression protects cortical neurons from apoptosis induced by β-amyloid peptide

“…As illustrated in Figure 1b, a 24-h treatment of cortical cells with 25 mM Ab [25][26][27][28][29][30][31][32][33][34][35] increased the percentage of apoptotic cells, as assessed by 4 0 ,6-diamidino-2-phenylindole (DAPI) staining. This proapoptotic effect of Ab was totally suppressed by a 48-h pretreatment of the cells with the 12-LOX antisense oligonucleotide, whereas the sense or the scramble 12-LOX oligonucleotide did not show any protective action (Figure 1b).…”

“…Previous studies indicated that 5-LOX could play a critical role in neuronal cell death, mediating, for instance, kainic acidinduced excitotoxicity 27 and apoptosis generated by prion peptide. 28 We recently reported that the 5-LOX inhibitor, caffeic acid, did not counteract apoptosis induced by Ab in cortical neurons, suggesting that 5-LOX was not involved in this degeneration process. 33 In the present study, we further evaluated this hypothesis through the same strategy as that used for 12-LOX.…”

“…For instance, 5-LOX was shown to mediate kainic acid-induced excitotoxicity 27 and apoptosis generated by prion peptide. 28 With regard to 12-LOX, this enzyme was previously shown to mediate both oxidative glutamate toxicity and BSO-induced apoptosis. 23 In a recent study, 33 we showed that baicalein, a 12-LOX inhibitor, protected cortical neurons from Ab-induced apoptosis, suggesting a role for 12-LOX in the apoptotic process triggered by Ab in these cells.…”

“…Cortical neurons were harvested following a 24-h treatment with 25 mM Ab [25][26][27][28][29][30][31][32][33][34][35] . To measure caspase activity, cells were washed once with ice-cold PBS, and 250 ml ice-cold extraction buffer was added directly to the cultures.…”

“…22,23 LOXs represent important regulators of cell proliferation and death in different cell types. [24][25][26] Moreover, a few studies suggested the involvement of 5-or 12-LOX in pathways leading to neuronal death, such as kainic acid excitotoxicity, 27 apoptosis induced by prion peptide 28 and oxidative glutamate toxicity. 23 In this work, we show that blockade of 12-LOX expression protects cortical neurons from Ab-induced apoptosis, through disruption of a c-Jun-dependent apoptosis pathway.…”