gw-3965 and Alzheimer-Disease

The liver X receptor agonist, GW3965, improves cognition in Alzheimer's disease (AD) mouse models. Here, we determined if short-term GW3965 treatment induces changes in the DNA methylation state of the hippocampus, which are associated with cognitive improvement. Twenty-four-month-old triple-transgenic AD (3xTg-AD) mice were treated with GW3965 (50 mg/kg/day for 6 days). DNA methylation state was examined by modified bisulfite conversion and hybridization on Illumina Infinium Methylation BeadChip 450 k arrays. The Morris water maze was used for behavioral analysis. Our results show in addition to improvement in cognition methylation changes in 39 of 13,715 interrogated probes in treated 3xTg-AD mice compared with untreated 3xTg-AD mice. These changes in methylation probes include 29 gene loci. Importantly, changes in methylation status were mainly from synapse-related genes (SYP, SYN1, and DLG3) and neurogenesis-associated genes (HMGB3 and RBBP7). Thus, our results indicate that liver X receptors (LXR) agonist treatment induces rapid changes in DNA methylation, particularly in loci associated with genes involved in neurogenesis and synaptic function. Our results suggest a new potential mechanism to explain the beneficial effect of GW3965.

Topics: Alzheimer Disease; Animals; Benzoates; Benzylamines; DNA Methylation; Female; HMGB3 Protein; Liver X Receptors; Mice; Neurogenesis; Orphan Nuclear Receptors; Qa-SNARE Proteins; Retinoblastoma-Binding Protein 7; Synapses; Synaptophysin

The vascular hypothesis of Alzheimer's disease postulates that disruption of the brain microvasculature is important for the accumulation of amyloid beta and increased neuroinflammation. Liver X Receptor agonist, GW3965, has been demonstrated to successfully modulate neuroinflammation and lipid metabolism in murine models of AD. This is partially due to increased expression of ApoE levels and increased mobility of endothelial progenitor cells. This paper analyzes changes in the neurovascular unit and in astrocytes and microglia markers following oral administration of GW3965 in a very old triple transgenic AD mice (3xTg-AD mice). We found that astrogliosis, but not activation of microglia, decreased in very old (24 months) 3xTg-AD mice treated with GW965. In addition, GW3965 increased LRP1 levels in neuron-like cells and partially restored microvascular morphology by decreasing tortuosity and increasing length as shown by Lectin immunostaining. Interestingly, these changes were associated with decreased Aβ in blood vessels. In conclusion, short-term treatment of 3xTg-AD mice with GW3965 restored microvascular architecture which may be important in the cognitive improvement previously shown.

Topics: Aging; Alzheimer Disease; Amyloid beta-Peptides; Animals; Astrocytes; Benzoates; Benzylamines; Biomarkers; Glial Fibrillary Acidic Protein; Hippocampus; Liver X Receptors; Mice; Mice, Transgenic; Microglia; Microvessels; Neurons

Alzheimer's disease (AD) is characterized by a robust inflammatory response elicited by the accumulation and subsequent deposition of amyloid (Aβ) within the brain. The brain's immune cells migrate to and invest their processes within Aβ plaques but are unable to efficiently phagocytose and clear plaques from the brain. Previous studies have shown that treatment of myeloid cells with nuclear receptor agonists increases expression of phagocytosis-related genes. In this study, we elucidate a novel mechanism by which nuclear receptors act to enhance phagocytosis in the AD brain. Treatment of murine models of AD with agonists of the nuclear receptors PPARγ, PPARδ, LXR, and RXR stimulated microglial phagocytosis in vitro and rapidly induced the expression of the phagocytic receptors Axl and MerTK. In murine models of AD, we found that plaque-associated macrophages expressed Axl and MerTK and treatment of the cells with an RXR agonist further induced their expression, coincident with the rapid reduction in plaque burden. Further characterization of MerTK(+)/Axl(+) macrophages revealed that they also expressed the phagocytic receptor TREM2 and high levels of CD45, consistent with a peripheral origin of these cells. Importantly, in an ex vivo slice assay, nuclear receptor agonist treatment reversed the AD-related suppression of phagocytosis through a MerTK-dependent mechanism. Thus, nuclear receptor agonists increase MerTK and Axl expression on plaque-associated immune cells, consequently licensing their phagocytic activity and promoting plaque clearance.

Topics: Alzheimer Disease; Animals; Axl Receptor Tyrosine Kinase; Benzoates; Benzylamines; Bexarotene; c-Mer Tyrosine Kinase; Cells, Cultured; Disease Models, Animal; Gene Expression Regulation; Leukocyte Common Antigens; Macrophages; Male; Membrane Glycoproteins; Mice; Microglia; Myeloid Cells; Phagocytosis; Pioglitazone; Plaque, Amyloid; Proto-Oncogene Proteins; Receptor Protein-Tyrosine Kinases; Receptors, Cytoplasmic and Nuclear; Receptors, Immunologic; Tetrahydronaphthalenes; Thiazoles; Thiazolidinediones

Alzheimer disease (AD) is characterized by the extracellular accumulation of amyloid β (Aβ), which is accompanied by a robust inflammatory response in the brain. Both of these pathogenic processes are regulated by nuclear receptors, including the liver X receptors (LXRs) and peroxisome-proliferator receptor γ (PPARγ). Agonists of LXRs have been demonstrated previously to reduce Aβ levels and improve cognitive deficits in AD mouse models by inducing the transcription and lipidation of apolipoprotein E (apoE). Agonists targeting PPARγ reduce the microglial expression of proinflammatory genes and have also been shown to modulate apoE expression. Here we investigate whether a combination therapy with both LXR and PPARγ agonists results in increased benefits in an AD mouse model. We found that the LXR agonist GW3965 and the PPARγ agonist pioglitazone were individually able to increase the levels of apoE and related genes, decrease the expression of proinflammatory genes, and facilitate Aβ decreases in the hippocampus. Combined treatment with both agonists provoked a further increase in the expression of apoE and a decrease in the soluble and deposited forms of Aβ. The decrease in plaques was associated with increased colocalization between microglia and plaques. In addition, the PPARγ agonist in the combined treatment paradigm was able to counteract the elevation in plasma triglycerides that is a side effect of LXR agonist treatment. These results suggest that combined LXR/PPARγ agonist treatment merits further investigation for the treatment of AD.

Topics: Alzheimer Disease; Amyloid beta-Protein Precursor; Animals; Apolipoproteins E; Behavior, Animal; Benzoates; Benzylamines; Biomarkers; Cognition Disorders; Disease Models, Animal; Gene Expression Regulation; Humans; Inflammation Mediators; Liver X Receptors; Male; Mice, Transgenic; Microglia; Orphan Nuclear Receptors; Particle Size; Pioglitazone; Plaque, Amyloid; PPAR gamma; Presenilin-1; Proteolysis; Thiazolidinediones; Transcription, Genetic; Triglycerides

Alzheimer's disease (AD) is the major cause of dementia worldwide. The pharmacological activation of nuclear receptors (Liver X receptors: LXRs or Retinoid X receptors: RXR) has been shown to induce overexpression of the ATP-Binding Cassette A1 (ABCA1) and Apolipoprotein E (ApoE), changes that are associated with improvement in cognition and reduction of amyloid beta pathology in amyloidogenic AD mouse models (i.e. APP, PS1: 2tg-AD). Here we investigated whether treatment with a specific LXR agonist has a measurable impact on the cognitive impairment in an amyloid and Tau AD mouse model (3xTg-AD: 12-months-old; three months treatment). The data suggests that the LXR agonist GW3965 is associated with increased expression of ApoE and ABCA1 in the hippocampus and cerebral cortex without a detectable reduction of the amyloid load. We also report that most cells overexpressing ApoE (86±12%) are neurons localized in the granular cell layer of the hippocampus and entorhinal cortex. In the GW3965 treated 3xTg-AD mice we also observed reduction in astrogliosis and increased number of stem and proliferating cells in the subgranular zone of the dentate gyrus. Additionally, we show that GW3965 rescued hippocampus long term synaptic plasticity, which had been disrupted by oligomeric amyloid beta peptides. The effect of GW3965 on synaptic function was protein synthesis dependent. Our findings identify alternative functional/molecular mechanisms by which LXR agonists may exert their potential benefits as a therapeutic strategy against AD.

Topics: Alzheimer Disease; Amyloid beta-Peptides; Animals; Apolipoproteins E; ATP Binding Cassette Transporter 1; Benzoates; Benzylamines; Biomarkers; Cell Proliferation; Cerebral Cortex; Cognition Disorders; Dentate Gyrus; DNA-Binding Proteins; Excitatory Postsynaptic Potentials; Female; Fluorescent Antibody Technique; Gliosis; Hippocampus; Liver X Receptors; Long-Term Potentiation; Male; Mice, Transgenic; Nerve Tissue Proteins; Nestin; Neural Stem Cells; Nuclear Proteins; Orphan Nuclear Receptors; Protein Biosynthesis; tau Proteins; Up-Regulation

The unique vulnerability of the olfactory system to Alzheimer's disease (AD) provides a quintessential translational tool for understanding mechanisms of synaptic dysfunction and pathological progression in the disease. Using the Tg2576 mouse model of β-amyloidosis, we show that aberrant, hyperactive olfactory network activity begins early in life, before detectable behavioral impairments or comparable hippocampal dysfunction and at a time when amyloid-β (Aβ) deposition is restricted to the olfactory bulb (OB). Hyperactive odor-evoked activity in the piriform cortex (PCX) and increased OB-PCX functional connectivity emerged at a time coinciding with olfactory behavior impairments. This hyperactive activity persisted until later in life when the network converted to a hyporesponsive state. This conversion was Aβ-dependent, because liver-X receptor agonist treatment to promote Aβ degradation rescued the hyporesponsive state and olfactory behavior. These data lend evidence to a novel working model of olfactory dysfunction in AD and, complimentary to other recent works, suggest that disease-relevant network dysfunction is highly dynamic and region specific, yet with lasting effects on cognition and behavior.

Topics: Alzheimer Disease; Amyloid beta-Peptides; Amyloid beta-Protein Precursor; Amyloidosis; Animals; Behavioral Symptoms; Benzoates; Benzothiazoles; Benzylamines; Brain Waves; Cerebral Cortex; Disease Models, Animal; Electroencephalography; Enzyme-Linked Immunosorbent Assay; Fourier Analysis; Habituation, Psychophysiologic; Humans; Mice; Mice, Transgenic; Odorants; Olfactory Pathways; Sensation Disorders; Smell; Thiazoles

Apolipoprotein E is associated with age-related risk for Alzheimer's disease and plays critical roles in Abeta homeostasis. We report that ApoE plays a role in facilitating the proteolytic clearance of soluble Abeta from the brain. The endolytic degradation of Abeta peptides within microglia by neprilysin and related enzymes is dramatically enhanced by ApoE. Similarly, Abeta degradation extracellularly by insulin-degrading enzyme is facilitated by ApoE. The capacity of ApoE to promote Abeta degradation is dependent upon the ApoE isoform and its lipidation status. The enhanced expression of lipidated ApoE, through the activation of liver X receptors, stimulates Abeta degradation. Indeed, aged Tg2576 mice treated with the LXR agonist GW3965 exhibited a dramatic reduction in brain Abeta load. GW3965 treatment also reversed contextual memory deficits. These data demonstrate a mechanism through which ApoE facilitates the clearance of Abeta from the brain and suggest that LXR agonists may represent a novel therapy for AD.

Topics: Aging; Alzheimer Disease; Amyloid beta-Peptides; Animals; Animals, Newborn; Apolipoproteins E; ATP Binding Cassette Transporter 1; ATP-Binding Cassette Transporters; Behavior, Animal; Benzoates; Benzylamines; Brain; Cells, Cultured; Disease Models, Animal; DNA-Binding Proteins; Dose-Response Relationship, Drug; Enzyme-Linked Immunosorbent Assay; Liver X Receptors; Memory; Mice; Mice, Inbred C57BL; Mice, Transgenic; Microglia; Orphan Nuclear Receptors; Peptide Fragments; Plaque, Amyloid; Receptors, Cytoplasmic and Nuclear; Time Factors