No abstract

BackgroundThe 5-lipoxygenase (5LO) enzymatic pathway is widely distributed within the central nervous system. Previous works showed that this protein is up-regulated in Alzheimer's disease (AD), and that its genetic absence results in a reduction of Amyloid beta (Aβ) levels in the Tg2576 mice.Here by employing an adeno-associated viral (AAV) vector system to over-express 5LO in the same mouse model, we examined its contribution to their cognitive impairments and brain AD-like amyloid pathology.ResultsOur results showed that compared with controls, 5LO-targeted gene brain over-expression in Tg2576 mice results in significant memory deficits. On the other hand, brain tissues had a significant elevation in the levels of Aβ peptides and deposition, no change in the steady state levels of amyloid-β precursor protein (APP), BACE-1 or ADAM-10, but a significant increase in PS1, nicastrin, and Pen-2, three major components of the γ-secretase complex. Additional data indicate that the transcription factor CREB was elevated and so were the mRNA levels for PS1, nicastrin and Pen-2.ConclusionsThese data demonstrate that neuronal 5LO plays a functional role in the pathogenesis of AD-like amyloidotic phenotype by modulating the γ-secretase pathway. They support the hypothesis that this enzyme is a novel therapeutic target for the treatment and prevention of AD.

Objective High level of homocysteine (Hcy) is a recognized risk factor for developing Alzheimer disease (AD). However, the mechanisms involved are unknown. Previously, it was shown that high Hcy increases brain b-amyloid (Ab) levels in amyloid precursor protein transgenic mice, but no data are available on the effect that it may have on the other main pathologic features of AD such as tau. Methods 3xTg mice with diet-induced high Hcy were compared with mice having normal Hcy. Neuronal cells were incubated with and without Hcy. Results Diet-induced high Hcy resulted in an exacerbation of the entire AD-like phenotype of the 3xTg mice. In particular, we found that compared with controls, mice with high Hcy developed significant memory and learning deficits, and had elevated Ab levels and deposition, which was mediated by an activation of the γ-secretase pathway. In addition, the same mice had a significant increase in the insoluble fraction of tau and its phosphorylation at specific epitopes, which was mediated by the cdk5 pathway. In vitro studies confirmed these observations and provided evidence that the effects of Hcy on Ab and tau are independent from each other. Interpretation Taken together, our findings demonstrate that a dietary condition that leads to an elevation of Hcy levels results in an exacerbation of all 3 major pathological features of the AD phenotype: memory deficits, and Ab and tau neuropathology. They support the concept that this dietary lifestyle can act as a risk factor and actively contribute to the development of the disease.

Objective The 5-lipoxygenase (5LO) enzyme is up-regulated in Alzheimer’s disease (AD), and its genetic absence reduces Aβ levels in APP mice. However, its functional role in modulating tau neuropathology remains to be elucidated. Methods To this end, we generated triple transgenic mice (3xTg-AD) over-expressing neuronal 5LO and investigated their phenotype. Results Compared with controls, 3xTg-AD mice over-expressing 5LO manifested an exacerbation of memory deficits, plaques and tangles pathologies. The elevation in Aβ was secondary to an up-regulation of γ-secretase pathway, whereas tau hyperphosphorylation resulted from an activation of the Cdk5 kinase. In vitro study confirmed the involvement of this kinase in the 5-LO-dependent tau phosphorylation, which was independent of the effect on Aβ. Interpretation Our findings highlight the novel functional role that neuronal 5LO plays in exacerbating AD-related tau pathologies. They provide critical preclinical evidence to justify testing selective 5LO inhibitors for AD treatment.

Objective The 5-lipoxygenase (5-LO) enzymatic pathway is widely distributed within the central nervous system, and is up-regulated in Alzheimer's disease. However, the mechanism whereby it may influence the disease pathogenesis remains elusive. Methods We evaluated the molecular mechanism by which 5-LO regulates Amyloid β (Aβ) formation in vitro and in vivo by pharmacological and genetic approaches. Results Here we show that 5-LO regulates the formation of Aβ by activating the cAMP-response element binding protein (CREB), which in turn increases transcription of the γ-secretase complex. Preventing CREB activation by pharmacologic inhibition or dominant negative mutants blocks the 5-LO-dependent elevation of Aβ formation and the increase of γ-secretase mRNA and protein levels. Moreover, 5-LO targeted gene disruption or its in vivo selective pharmacological inhibition results in a significant reduction of Aβ, CREB and γ-secretase levels. Interpretation These data establish a novel functional role for 5-LO in regulating endogenous formation of Aβ levels in the central nervous system. Thus, 5-LO pharmacological inhibition may be beneficial in the treatment and prevention of Alzheimer's disease.