br lipoxygenase pathway in brain aging and

5-lipoxygenase pathway in Auranofin aging and alzheimer’s disease 5LO is found throughout the central nervous system, in both neuron and glia cells (Farias et al., 2007). However, its expression levels are highest in the cortex and hippocampus areas, two regions that are particularly vulnerable to neurodegenerative insults (Lammers et al., 1996, Chinnici et al., 2007). Interestingly, it has been shown by different groups that in the brain 5LO and its metabolites manifest an age-dependent increase (Chinnici et al., 2007, Di Francesco et al., 2013, Uz et al., 1998). Since aging is one of the strongest risk factors for developing AD, initially it was proposed that this pathway could potentially be involved in brain aging and events germaine to the pathogenesis of AD (Chu and Praticò, 2009). Post-mortem studies have shown that compared with healthy controls, AD brains had higher 5LO protein levels in cortex and hippocampus. By contrast, no significant differences were detected between the two groups when the cerebellum, an area typically devoid of AD pathology, was assayed (Firuzi et al., 2008, Ikonomovic et al., 2008). A small pilot study in humans has linked 5LO gene polymorphisms to early- and late-onset AD, although large-scale population studies are yet to confirm these findings (Qu et al., 2001). Recently, it was reported that CysLT1 receptor is involved in Aβ1-42-induced neurotoxicity, and that its pharmacological blockade by a receptor antagonist could ameliorate Aβ1-42 induced impairments of cognitive function and hippocampal LTP (Tang et al., 2014a, Tang et al., 2014b, Lai et al., 2014).
5-lipoxygenase as a modulator of Aβ formation: in vivo and in vitro evidence To address this question we utilized Tg2576 mice, a transgenic mouse model that expresses the K670N/M671L APP mutation found in a Swedish family with early-onset AD, which develop age-dependent brain amyloidosis. We crossed the Tg2576 with mice genetically deficient for 5LO (i.e., homozygous knockout of 5LO) and compared them with regular Tg2576 animals to see how brain amyloidosis was affected when 5LO was not genetically available. We found that both soluble and insoluble Aβ peptides were significantly reduced in the brains of Tg2576 animals lacking 5LO, and that this reduction was even more apparent as the animals aged from middle- to late-life. On immunohistochemical analyses, this reduction in Aβ peptides translated to fewer amyloids β plaques and reduced total amyloid burden (Firuzi et al., 2008). What was singular about this initial work was that Aβ reduction caused by 5LO knockout did not seem to change steady state levels of APP or increase several proteins thought to participate in Aβ clearance in the brain. Genetic and pharmacological methods were used next to further support the concept that 5LO may act as an endogenous modulator of Aβ formation in vivo and in vitro. In N2A (neuro-2A neuroblastoma) cells stably expressing Swedish mutant of human APP (APP swe), over-expression of 5LO resulted in an elevation of Aβ formation, which associated with increased protein levels of the four components of the γ-secretase complex PS1, nicastrin, APH-1, and Pen-2 (Chu and Praticò, 2011a). The regulation of 5LO on Aβ formation was modulated by the activation of the cAMP-response element binding protein (CREB), which in turn increased transcription of the four components of the γ-secretase complex. Neuronal cells exposed to the main 5LO metabolic product, 5-HETE, produced more Aβ, had an elevation of the γ-secretase complex, and CREB levels and activity. The effect was prevented by blocking CREB activation via a pharmacologic inhibition or dominant negative mutants (Chu and Praticò, 2011a). In vivo experiments confirmed these observations. An adeno-associated viral (AAV)-mediated 5LO gene transfer in the central nervous system of Tg2576 resulted in 5LO over-expression and a significant increase in the amount of Aβ formed and deposited in their brains. Biochemical analysis in the same tissues showed a significant increase in the levels of the transcription factor CREB, and a significant elevation of the mRNA and protein levels of the γ-secretase complex (Chu et al., 2012a).