Cyclooxygenase inhibition targets neurons to prevent early behavioural decline in Alzheimer's disease model mice.

Identifying preventive targets for Alzheimer's disease is a central challenge of modern medicine. Non-steroidal anti-inflammatory drugs, which inhibit the cyclooxygenase enzymes COX-1 and COX-2, reduce the risk of developing Alzheimer's disease in normal ageing populations. This preventive effect coincides with an extended preclinical phase that spans years to decades before onset of cognitive decline. In the brain, COX-2 is induced in neurons in response to excitatory synaptic activity and in glial cells in response to inflammation. To identify mechanisms underlying prevention of cognitive decline by anti-inflammatory drugs, we first identified an early object memory deficit in APPSwe-PS1ΔE9 mice that preceded previously identified spatial memory deficits in this model. We modelled prevention of this memory deficit with ibuprofen, and found that ibuprofen prevented memory impairment without producing any measurable changes in amyloid-ß accumulation or glial inflammation. Instead, ibuprofen modulated hippocampal gene expression in pathways involved in neuronal plasticity and increased levels of norepinephrine and dopamine. The gene most highly downregulated by ibuprofen was neuronal tryptophan 2,3-dioxygenase (Tdo2), which encodes an enzyme that metabolizes tryptophan to kynurenine. TDO2 expression was increased by neuronal COX-2 activity, and overexpression of hippocampal TDO2 produced behavioural deficits. Moreover, pharmacological TDO2 inhibition prevented behavioural deficits in APPSwe-PS1ΔE9 mice. Taken together, these data demonstrate broad effects of cyclooxygenase inhibition on multiple neuronal pathways that counteract the neurotoxic effects of early accumulating amyloid-ß oligomers.

Suppression of inflammation with conditional deletion of the prostaglandin E2 EP2 receptor in macrophages and brain microglia.

Prostaglandin E2 (PGE2), a potent lipid signaling molecule, modulates inflammatory responses through activation of downstream G-protein coupled EP(1-4) receptors. Here, we investigated the cell-specific in vivo function of PGE2 signaling through its E-prostanoid 2 (EP2) receptor in murine innate immune responses systemically and in the CNS. In vivo, systemic administration of lipopolysaccharide (LPS) resulted in a broad induction of cytokines and chemokines in plasma that was significantly attenuated in EP2-deficient mice. Ex vivo stimulation of peritoneal macrophages with LPS elicited proinflammatory responses that were dependent on EP2 signaling and that overlapped with in vivo plasma findings, suggesting that myeloid-lineage EP2 signaling is a major effector of innate immune responses. Conditional deletion of the EP2 receptor in myeloid lineage cells in Cd11bCre;EP2(lox/lox) mice attenuated plasma inflammatory responses and transmission of systemic inflammation to the brain was inhibited, with decreased hippocampal inflammatory gene expression and cerebral cortical levels of IL-6. Conditional deletion of EP2 significantly blunted microglial and astrocytic inflammatory responses to the neurotoxin MPTP and reduced striatal dopamine turnover. Suppression of microglial EP2 signaling also increased numbers of dopaminergic (DA) neurons in the substantia nigra independent of MPTP treatment, suggesting that microglial EP2 may influence development or survival of DA neurons. Unbiased microarray analysis of microglia isolated from adult Cd11bCre;EP2(lox/lox) and control mice demonstrated a broad downregulation of inflammatory pathways with ablation of microglial EP2 receptor. Together, these data identify a cell-specific proinflammatory role for macrophage/microglial EP2 signaling in innate immune responses systemically and in brain.

Neuroinflammation and α-synuclein accumulation in response to glucocerebrosidase deficiency are accompanied by synaptic dysfunction.

Clinical, epidemiological and experimental studies confirm a connection between the common degenerative movement disorder Parkinson's disease (PD) that affects over 1 million individuals, and Gaucher disease, the most prevalent lysosomal storage disorder. Recently, human imaging studies have implicated impaired striatal dopaminergic neurotransmission in early PD pathogenesis in the context of Gaucher disease mutations, but the underlying mechanisms have yet to be characterized. In this report we describe and characterize two novel long-lived transgenic mouse models of Gba deficiency, along with a subchronic conduritol-ß-epoxide (CBE) exposure paradigm. All three murine models revealed striking glial activation within nigrostriatal pathways, accompanied by abnormal α-synuclein accumulation. Importantly, the CBE-induced, pharmacological Gaucher mouse model replicated this change in dopamine neurotransmission, revealing a markedly reduced evoked striatal dopamine release (approximately 2-fold) that indicates synaptic dysfunction. Other changes in synaptic plasticity markers, including microRNA profile and a 24.9% reduction in post-synaptic density size, were concomitant with diminished evoked dopamine release following CBE exposure. These studies afford new insights into the mechanisms underlying the Parkinson's-Gaucher disease connection, and into the physiological impact of related abnormal α-synuclein accumulation and neuroinflammation on nigrostriatal dopaminergic neurotransmission.

Human and rodent amyloid-beta peptides differentially bind heme: relevance to the human susceptibility to Alzheimer's disease.

Amyloid-beta (Abeta) peptides are implicated in the neurodegeneration of Alzheimer's disease (AD). We previously investigated the mechanism of neurotoxicity of Abeta and found that human Abeta (huAbeta) binds and depletes heme, forming an Abeta-heme complex with peroxidase activity. Rodent Abeta (roAbeta) is identical to huAbeta, except for three amino acids within the proposed heme-binding motif (Site-H). We studied and compared heme-binding between roAbeta and huAbeta. Unlike roAbeta, huAbeta binds heme tightly (K(d)=140+/-60 nM) and forms a peroxidase. The plot of bound (huAbeta-heme) vs. unbound heme fits best to a two site binding hyperbola, suggesting huAbeta possesses two heme-binding sites. Consistently, a second high affinity heme-binding site was identified in the lipophilic region (site-L) of huAbeta (K(d)=210+/-80 nM). The plot of (roAbeta-heme) vs. unbound heme, on the other hand, was different as it fits best to a sigmoidal binding curve, indicating different binding and lower affinity of roAbeta for heme (K(d)=1 microM). The effect of heme-binding to site-H on heme-binding to site-L in roAbeta and huAbeta is discussed. While both roAbeta and huAbeta form aggregates equally, rodents lack AD-like neuropathology. High huAbeta/heme ratio increases the peroxidase activity. These findings suggest that depletion of regulatory heme and formation of Abeta-heme peroxidase contribute to huAbeta's neurotoxicity in the early stages of AD. Phylogenic variations in the amino acid sequence of Abeta explain tight heme-binding to huAbeta and likely contribute to the increased human susceptibility to AD.

Gene-environment interaction models to unmask susceptibility mechanisms in Parkinson's disease.

Lipoxygenase (LOX) activity has been implicated in neurodegenerative disorders such as Alzheimer's disease, but its effects in Parkinson's disease (PD) pathogenesis are less understood. Gene-environment interaction models have utility in unmasking the impact of specific cellular pathways in toxicity that may not be observed using a solely genetic or toxicant disease model alone. To evaluate if distinct LOX isozymes selectively contribute to PD-related neurodegeneration, transgenic (i.e. 5-LOX and 12/15-LOX deficient) mice can be challenged with a toxin that mimics cell injury and death in the disorder. Here we describe the use of a neurotoxin, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), which produces a nigrostriatal lesion to elucidate the distinct contributions of LOX isozymes to neurodegeneration related to PD. The use of MPTP in mouse, and nonhuman primate, is well-established to recapitulate the nigrostriatal damage in PD. The extent of MPTP-induced lesioning is measured by HPLC analysis of dopamine and its metabolites and semi-quantitative Western blot analysis of striatum for tyrosine hydroxylase (TH), the rate-limiting enzyme for the synthesis of dopamine. To assess inflammatory markers, which may demonstrate LOX isozyme-selective sensitivity, glial fibrillary acidic protein (GFAP) and Iba-1 immunohistochemistry are performed on brain sections containing substantia nigra, and GFAP Western blot analysis is performed on striatal homogenates. This experimental approach can provide novel insights into gene-environment interactions underlying nigrostriatal degeneration and PD.