Overexpression of 5-Lipoxygenase Increases the Neuronal Vulnerability of PC12 Cells to Aβ₄₂

Abstract

5-Lipoxygenase (5-LOX), which is believed to be a major source of oxidative stress, participates in somatostatinreceptor transmembrane signaling in the central nervous system. We used the Tet-On inducible expression system in PC12 cells to obtain cell lines with reproducible, stable 5-LOX expression levels to study its function. Cell apoptosis rates induced by Ab 42 were determined using an apo-BrdDU kit. Lipid peroxide, antioxidant enzyme, and caspase-3 activities were evaluated with respective commercial kits. The expression of 5-LOX, bcl-2, and bax were detected by immunoblotting. A subclone of PC18 with Tet-On inducible expression of 5-LOX was selected from PC12 transfectants. Expression of 5-LOX had no signiˆcant inhibitory eŠect on the cell viability of the PC18 clone. In contrast, compared with the control group, the cell viability of clone PC18 was signiˆcantly reduced after the induction of 5-LOX during Ab exposure. The diŠerences in cell viability before and after the induction of 5-LOX during Ab insult were signiˆcantly oŠset by AA861. Overexpression of 5-LOX only slightly improved the activities of superoxide dismutase (SOD). The levels of intracellular peroxides, SOD and caspase-3 activity, and Bax expression were signiˆcantly upregulated, and the levels of glutathione peroxidase and catalase were downregulated correspondingly in clone PC18 during Ab exposure. These results indicate that constitutive expression of 5-LOX is not detrimental per se, but overexpression of 5-LOX may become problematic during Ab exposure.

Amyloid β-42 induces neuronal apoptosis by targeting mitochondria

“…Oligomeric and fibrillar Aβ-42 also induces mitochondrial dysfunctions in cortical neurons, including a reduction in mitochondrial membrane potential, state 3 respiration, respiratory control ratio and uncoupled respiration ( 38 ). Consistent with a previous study ( 39 ), the present study demonstrated that Aβ-42 induced significant neuronal apoptosis, and activated the Caspase pathway. Ca 2+ is an active second messenger, and is involved in many cellular processes.…”

“…In conclusion, the present study demonstrated that Aβ-42 treatment activated the Caspase signaling pathway, and induced obvious neuronal apoptosis. Although the role of Aβ-42 in neuronal survival has been described ( 14 , 39 ), to the best of our knowledge, these data demonstrated for the first time that Aβ-42 increases mitochondrial fission by changing the expression of mitochondrial fission and fusion proteins. Inhibition of Drp1-dependent mitochondrial fission efficiently suppressed Aβ-42-induced intracellular ROS production and loss of mitochondrial membrane potential in neurons.…”

Effect of aging on 5-hydroxymethylcytosine in the mouse hippocampus

“…Previous reports found that 5-LOX expression in the brain increases during aging (Chinnici et al, 2007; Uz et al, 1998) and in Alzheimer’s disease (Firuzi et al, 2008; Ikonomovic et al, 2008; Wang et al, 2011), but the aging-affected methylation status of the mouse 5-LOX gene has not been consistently related with the rate of 5-LOX transcription (Dzitoyeva et al, 2009). It has been noticed that global 5hmC changes do not necessary reflect the same type of 5hmC changes in individual gene sequences.…”

Regulation of gamma-secretase activating protein by the 5Lipoxygenase: in vitro and in vivo evidence

“…Thus, ApoEˉ/ˉ mice lacking 5LO have reduced caspase-3 activity23, while overexpression of 5LO significantly enhanced caspase-3 activation in PC12 cells24, and 5LO pharmacological inhibition significantly down-regulated caspase-3 activation in the brains of rats undergoing middle cerebral artery occlusion25.…”