Jin Chu

5-lipoxygenase as an endogenous modulator of amyloid beta formation in vivo

The 5‐lipoxygenase (5‐LO) enzymatic pathway is widely distributed within the central nervous system, and is upregulated in Alzheimers disease. However, the mechanism whereby it may influence the disease pathogenesis remains elusive.

Pharmacologic Blockade of 5-Lipoxygenase Improves the Amyloidotic Phenotype of an Alzheimer's Disease Transgenic Mouse Model: Involvement of γ-Secretase

The 5-lipoxygenase (5-LO) enzyme is widely distributed within the central nervous system. Previous works showed that this protein is up-regulated in Alzheimers disease (AD) and that its genetic absence results in a reduction of amyloid β (Aβ) levels in Tg2576 mice. In the present study, we examined the effect of 5-LO pharmacological inhibition on the amyloidotic phenotype of these mice. Aβ deposition in the brains of mice receiving zileuton, a selective and specific 5-LO inhibitor, was significantly reduced when compared with control Tg2576 mice receiving vehicle. This reduction was associated with a similar decrease in brain Aβ peptides levels. Zileuton treatment did not induce any change in the steady state levels of amyloid-β precursor protein (APP), BACE1 or ADAM10. By contrast, it resulted in a significant reduction of presenilin 1 (PSEN1, alias PS1), nicastrin (NCSTN) , presenilin enhancer 2 homolog (PSNEN, alias, Pen-2), and anterior pharynx defective 1 (APH-1), the four components of the γ-secretase complex-at the protein and message level. Furthermore, in vitro studies confirmed that zileuton prevents Aβ formation by modulating γ-secretase complex levels without affecting Notch signaling. These data establish a functional role for 5-LO in the pathogenesis of AD-like amyloidosis, whereby it modulates the γ-secretase pathway. They suggest that pharmacological inhibition of 5-LO could provide a novel therapeutic opportunity for AD.

5-Lipoxygenase gene transfer worsens memory, amyloid, and tau brain pathologies in a mouse model of alzheimer disease

The 5‐lipoxygenase (5LO) enzyme is upregulated in Alzheimer disease (AD), and its genetic absence reduces Aβ levels in APP mice. However, its functional role in modulating tau neuropathology remains to be elucidated.

Homocysteine Exacerbates β-Amyloid Pathology, Tau Pathology, and Cognitive Deficit in a Mouse Model of Alzheimer Disease with Plaques and Tangles

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 β‐amyloid (Aβ) 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.

Amelioration of the Alzheimer's Disease Phenotype by Absence of 12/15-Lipoxygenase

BACKGROUND Alzheimers disease (AD) is a chronic neurodegenerative disorder whose initiating events are not known. Increasing evidence suggests that oxidative stress and inflammation play a role in its pathogenesis. 12/15 Lipoxygenase (12/15LO) by oxidizing polyunsaturated fatty acids forms hydroperoxyacids, which are potent pro-oxidants and inflammatory mediators. Previously, we reported that this metabolic pathway is increased in AD. METHODS Here we explore the effect of genetic deletion of 12/15LO on the AD-like phenotype of the tg2576 transgenic mice. RESULTS Genetic absence of this enzyme results in a significant reduction in amyloid-β (Aβ) production and deposition and an improvement of cognitive deficits. In vivo and in vitro studies show that the effect of this enzymatic pathway on amyloidosis is mediated by modulation of Aβ precursor protein processing via the β secretase (BACE) proteolytic cascade, which ultimately results in altered formation of Aβ peptides. CONCLUSIONS Our findings support the novel hypothesis that blockade of 12/15LO in the central nervous system by modulating BACE proteolytic pathway could be an effective therapy for prevention or treatment of AD.

Gene knockout of 5-lipoxygenase rescues synaptic dysfunction and improves memory in the triple-transgenic model of Alzheimer's disease

5-Lipoxygenase (5LO) is upregulated in Alzheimer’s disease (AD) and in vivo modulates the amyloidotic phenotype of amyloid precursor protein transgenic mice. However, no data are available on the effects that 5LO has on synaptic function, integrity and cognition. To address this issue, we used a genetic and a pharmacological approach by generating 3 × Tg mice deficient for 5LO and administering 3 × Tg mice with a 5LO inhibitor. Compared with controls, we found that even before the development of overt neuropathology, both animals manifested significant memory improvement, rescue of their synaptic dysfunction and amelioration of synaptic integrity. In addition, later in life, these mice had a significant reduction of Aβ and tau pathology. Our findings support a novel functional role for 5LO in regulating synaptic plasticity and memory. They establish this protein as a pleiotropic contributor to the development of the full spectrum of the AD phenotype, making it a valid therapeutic target for the treatment of AD.

Adeno-associated virus-mediated brain delivery of 5-lipoxygenase modulates the AD-like phenotype of APP mice

BackgroundThe 5-lipoxygenase (5LO) enzymatic pathway is widely distributed within the central nervous system. Previous works showed that this protein is up-regulated in Alzheimers 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.

Stress hormone leads to memory deficits and altered tau phosphorylation in a model of Alzheimer's disease.

Several studies have linked stress with Alzheimers disease (AD) vulnerability; however, the mechanism remains to be fully elucidated. In the current paper, we investigated the role of glucocortitcoids on the AD-like phenotype. We administered the glucocorticoid dexamethasone to Tg2576 mice for 4 weeks and then investigated its effect on memory, amyloid-β and tau levels, and metabolism. At the end of the treatment period, we observed that mice receiving dexamethasone had a significant impairment in the fear conditioning paradigm compared with controls. Dexamethasone-treated animals showed a significant increase in the amount of brain soluble Aβ40 levels, but no alteration in the steady state levels of its precursor protein, AβPP, or in the major protease enzymes involved in its metabolism (i.e., ADAM-10, BACE-1, or γ-secretase complex). While total tau protein levels were unaltered between the two groups, we found that dexamethasone significantly reduced tau phosphorylation at specific sites that were mediated by decreases in glycogen synthase kinase-3β protein level activity. Finally, we observed a direct correlation between memory impairments and tau phosphorylation levels. Our study highlights the significant role that glucocorticoids play in exacerbating AD-like cognitive impairments via alteration of tau protein phosphorylation state.

Transcriptional regulation of βsecretase‐1 by 12/15‐lipoxygenase results in enhanced amyloidogenesis and cognitive impairments

12/15‐Lipoxygenase (12/15‐LO) is an enzyme widely distributed in the central nervous system, and it has been involved in the neurobiology of Alzheimer disease (AD). However, the mechanism involved remains elusive.

Involvement of 5-lipoxygenase activating protein in the amyloidotic phenotype of an Alzheimer’s disease mouse model

BackgroundThe 5-lipoxygenase enzyme is widely distributed within the central nervous system and its activity is regulated by the presence and availability of another protein, called 5-lipoxygenase activating protein. While previous works have shown that 5-lipoxygenase is involved in the pathogenesis of Alzheimer’s disease, no data are available on the role that 5-lipoxygenase activating protein plays in Alzheimer’s disease.MethodsIn the present paper, we studied the effect of pharmacologic inhibition of 5-lipoxygenase activating protein on the amyloidotic phenotype of Tg2576 mice.ResultsAmyloid β peptide (Aβ) deposition in the brains of mice receiving MK-591, a selective and specific 5-lipoxygenase activating protein inhibitor, was significantly reduced when compared with controls. This reduction was associated with a similar decrease in brain Aβ peptides levels. MK-591 treatment did not induce any change in the steady-state levels of amyloid-β precursor protein, β-site amyloid precursor protein cleaving enzyme 1 or disintegrin and metalloproteinase domain-containing protein 10. By contrast, it resulted in a significant reduction of the γ-secretase complex, at the protein and message level. Furthermore, in vitro studies confirmed that MK-591 prevents Aβ formation by modulating γ-secretase complex levels without affecting Notch signaling.ConclusionsThese data establish a novel functional role for 5-lipoxygenase activating protein in the pathogenesis of Alzheimer’s disease-like amyloidosis, and suggest that its pharmacological inhibition could provide a novel therapeutic opportunity for Alzheimer’s disease.