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Genetic absence of ALOX5 protects from homocysteine-induced memory impairment, tau phosphorylation and synaptic pathology.

ABSTRACT: Elevated level of homocysteine (Hcy) is considered a risk factor for neurodegenerative diseases, but the mechanisms remain to be established. Because high Hcy is associated with an up-regulation of the ALOX5 gene product, the 5Lipoxygenase (5LO), herein we investigated whether this activation is responsible for the Hcy effect on neurodegeneration or is a secondary event. To reach this goal, wild type mice and mice genetically deficient for 5LO were assessed after being exposed to a diet known to significantly increase brain levels of Hcy. Confirming compliance with the dietary regimen, we found that by the end of the study brain levels of Hcy were significantly increase in both groups. However, diet-induced high Hcy resulted in a significant increase in A?, tau phosphorylation, neuroinflammation, synaptic pathology and memory impairment in control mice, but not in mice lacking ALOX5.Taken together our findings demonstrate that the up-regulation of the ALOX5 gene pathway is responsible for the development of the biochemical and behavioral sequelae of high Hcy brain levels in the context of a neurodegenerative phenotype. They provide critical support that this gene and its expressed protein are viable therapeutic targets to prevent the onset, or delay neurodegenerative events in subjects exposed to this risk factor.

SUBMITTER: Li JG

PROVIDER: S-EPMC6075360 | biostudies-literature | 2017 May

REPOSITORIES: biostudies-literature

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Genetic absence of ALOX5 protects from homocysteine-induced memory impairment, tau phosphorylation and synaptic pathology.

Li Jian-Guo JG Barrero Carlos C Merali Salim S Praticò Domenico D

Human molecular genetics 20170501 10

Elevated level of homocysteine (Hcy) is considered a risk factor for neurodegenerative diseases, but the mechanisms remain to be established. Because high Hcy is associated with an up-regulation of the ALOX5 gene product, the 5Lipoxygenase (5LO), herein we investigated whether this activation is responsible for the Hcy effect on neurodegeneration or is a secondary event. To reach this goal, wild type mice and mice genetically deficient for 5LO were assessed after being exposed to a diet known to ...[more]

PMID: 28334897

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Project description:Alzheimer's disease (AD) is defined by the presence of intraneuronal neurofibrillary tangles (NFTs) composed of hyperphosphorylated tau aggregates as well as extracellular amyloid-beta plaques. The presence and spread of tau pathology through the brain is classified by Braak stages and thought to correlate with the progression of AD. Several in vitro and in vivo studies have examined the ability of tau pathology to move from one neuron to the next, suggesting a "prion-like" spread of tau aggregates may be an underlying cause of Braak tau staging in AD. Using the HEK293 TauRD-P301S-CFP/YFP expressing biosensor cells as a highly sensitive and specific tool to identify the presence of seed competent aggregated tau in brain lysate-i.e., tau aggregates that are capable of recruiting and misfolding monomeric tau-, we detected substantial tau seeding levels in the entorhinal cortex from human cases with only very rare NFTs, suggesting that soluble tau aggregates can exist prior to the development of overt tau pathology. We next looked at tau seeding levels in human brains of varying Braak stages along six regions of the Braak Tau Pathway. Tau seeding levels were detected not only in the brain regions impacted by pathology, but also in the subsequent non-pathology containing region along the Braak pathway. These data imply that pathogenic tau aggregates precede overt tau pathology in a manner that is consistent with transneuronal spread of tau aggregates. We then detected tau seeding in frontal white matter tracts and the optic nerve, two brain regions comprised of axons that contain little to no neuronal cell bodies, implying that tau aggregates can indeed traverse along axons. Finally, we isolated cytosolic and synaptosome fractions along the Braak Tau Pathway from brains of varying Braak stages. Phosphorylated and seed competent tau was significantly enriched in the synaptic fraction of brain regions that did not have extensive cellular tau pathology, further suggesting that aggregated tau seeds move through the human brain along synaptically connected neurons. Together, these data provide further evidence that the spread of tau aggregates through the human brain along synaptically connected networks results in the pathogenesis of human Alzheimer's disease.

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Genetic absence of ALOX5 protects from homocysteine-induced memory impairment, tau phosphorylation and synaptic pathology.

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Genetic absence of ALOX5 protects from homocysteine-induced memory impairment, tau phosphorylation and synaptic pathology.

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