Marie-Victoire Guillot-Sestier

Ferulic acid is a nutraceutical β-secretase modulator that improves behavioral impairment and alzheimer-like pathology in transgenic mice.

Amyloid precursor protein (APP) proteolysis is required for production of amyloid-β (Aβ) peptides that comprise β-amyloid plaques in brains of Alzheimer’s disease (AD) patients. Recent AD therapeutic interest has been directed toward a group of anti-amyloidogenic compounds extracted from plants. We orally administered the brain penetrant, small molecule phenolic compound ferulic acid (FA) to the transgenic PSAPP mouse model of cerebral amyloidosis (bearing mutant human APP and presenilin-1 transgenes) and evaluated behavioral impairment and AD-like pathology. Oral FA treatment for 6 months reversed transgene-associated behavioral deficits including defective: hyperactivity, object recognition, and spatial working and reference memory, but did not alter wild-type mouse behavior. Furthermore, brain parenchymal and cerebral vascular β-amyloid deposits as well as abundance of various Aβ species including oligomers were decreased in FA-treated PSAPP mice. These effects occurred with decreased cleavage of the β-carboxyl-terminal APP fragment, reduced β-site APP cleaving enzyme 1 protein stability and activity, attenuated neuroinflammation, and stabilized oxidative stress. As in vitro validation, we treated well-characterized mutant human APP-overexpressing murine neuron-like cells with FA and found significantly decreased Aβ production and reduced amyloidogenic APP proteolysis. Collectively, these results highlight that FA is a β-secretase modulator with therapeutic potential against AD.

Brain injury, neuroinflammation and Alzheimer's disease

With as many as 300,000 United States troops in Iraq and Afghanistan having suffered head injuries (Miller, 2012), traumatic brain injury (TBI) has garnered much recent attention. While the cause and severity of these injuries is variable, severe cases can lead to lifelong disability or even death. While aging is the greatest risk factor for Alzheimers disease (AD), it is now becoming clear that a history of TBI predisposes the individual to AD later in life (Sivanandam and Thakur, 2012). In this review article, we begin by defining hallmark pathological features of AD and the various forms of TBI. Putative mechanisms underlying the risk relationship between these two neurological disorders are then critically considered. Such mechanisms include precipitation and ‘spreading’ of cerebral amyloid pathology and the role of neuroinflammation. The combined problems of TBI and AD represent significant burdens to public health. A thorough, mechanistic understanding of the precise relationship between TBI and AD is of utmost importance in order to illuminate new therapeutic targets. Mechanistic investigations and the development of preclinical therapeutics are reliant upon a clearer understanding of these human diseases and accurate modeling of pathological hallmarks in animal systems.

Innate Immunity in Alzheimer’s Disease: A Complex Affair

Alzheimers disease (AD) is characterized by three major histopathological hallmarks: β-amyloid deposits, neurofibrillary tangles and gliosis. While neglected for decades, the neuroinflammatory processes coordinated by microglia are now accepted as etiologic events in AD evolution. Microglial cells are found in close vicinity to amyloid plaques and display various activation phenotypes determined by the expression of a wide range of cytokines, chemokines, and innate immune surface receptors. During the development of AD pathology, microglia fail to restrict amyloid plaques and may contribute to neurotoxicity and cognitive deficit. Nevertheless, under specific activation states, microglia can participate in cerebral amyloid clearance. This review focuses on the complex relationship between microglia and Aβ pathology, and highlights both deleterious and beneficial roles of microglial activation states in the context of AD. A deeper understanding of microglial biology will hopefully pave the way for next-generation AD therapeutic approaches aimed at harnessing these enigmatic innate immune cells of the central nervous system.

Innate Immunity Fights Alzheimer's Disease

Alzheimers disease (AD) is the most common age-related dementia. Pathognomonic accumulation of cerebral β-amyloid plaques likely results from imbalanced production and removal of amyloid-β (Aβ) peptides. In AD, innate immune cells lose their ability to restrict cerebral Aβ accumulation. At least in principle, mononuclear phagocytes can be enlisted to clear Aβ/β-amyloid from the brain. While the classical focus has been on dampening neuroinflammation in the context of AD, we hypothesize that rebalancing cerebral innate immunity by inhibiting actions of key anti-inflammatory cytokines returns the brain to a physiological state. Recent experiments demonstrating beneficial effects of blocking anti-inflammatory cytokine signaling in preclinical mouse models provide supportive evidence. This concept represents an important step toward innate immune-targeted therapy to combat AD.

The role of the immune system in neurodegenerative disorders: Adaptive or maladaptive?

Neurodegenerative diseases share common features, including catastrophic neuronal loss that leads to cognitive or motor dysfunction. Neuronal injury occurs in an inflammatory milieu that is populated by resident and sometimes, infiltrating, immune cells - all of which participate in a complex interplay between secreted inflammatory modulators and activated immune cell surface receptors. The importance of these immunomodulators is highlighted by the number of immune factors that have been associated with increased risk of neurodegeneration in recent genome-wide association studies. One of the more difficult tasks for designing therapeutic strategies for immune modulation against neurodegenerative diseases is teasing apart beneficial from harmful signals. In this regard, learning more about the immune components of these diseases has yielded common themes. These unifying concepts should eventually enable immune-based therapeutics for treatment of Alzheimer׳s and Parkinson׳s diseases and amyotrophic lateral sclerosis. Targeted immune modulation should be possible to temper maladaptive factors, enabling beneficial immune responses in the context of neurodegenerative diseases. This article is part of a Special Issue entitled SI: Neuroimmunology in Health And Disease.

STAT3 SIGNALING REFEREES MICROGLIAL AMYLOID CLEARANCE IN ALZHEIMER’S DISEASE

tion in the Golgi and also shows greatly impaired cell surface expression. Surprisingly, we find that these mutants appear to be exported from the endoplasmic reticulum (ER) without defect. The results suggest the existence of an efficient protein recycling pathway that returns mutant TREM2 to the ER after export. Intriguingly, we find that all mutants that fail to undergo maturation also display a propensity to form a stable homodimer that is not dissociated by SDS, urea, reducing agents or heating. Because all mutations producing this effect localize to the extracellular, Ig-like domain, the results suggest an important role for this domain in regulating the biochemical characteristics of TREM2. Conclusions: Our findings suggest that disease-causing TREM2 mutations may result in early-onset neurodegeneration via loss of cell surface expression, and imply that a common biochemical abnormality is induced by pathogenic mutations within the Ig-like domain.

PHYSICAL INTERACTION OF TREM2 AND C1Q IN ALZHEIMER’S DISEASE

mice were analyzed for tau pathology. Results:TREM2-targeted ASO treatment in APP/PS1 mice substantially decreased TREM2 mRNA compared to control ASO treatment across multiple brain regions (p<0.01). When evaluated for Ab, ASO-mediated TREM2 knockdown significantly reduced Ab plaque deposition (p<0.001) and attenuated microglial association around plaque deposits (p<0.001). Treatment of TauP301S mice with TREM2-targeted ASO robustly decreased TREM2mRNA (p<0.001) and was associated with significantly less phosphorylated tau reactivity within the hippocampus (p<0.05). Conclusions: These results confirm a role for TREM2 in mediating plaque deposition and tau phosphorylation and suggest that TREM2 lowering reduces pathological markers of neurodegeneration. While these data are seemingly contradictory to the presumption that TREM2 genetic variants confer a loss of function, we believe an ASO approach allows us to understand the timing of TREM2 action throughout disease progression, which may involve a timeor location-dependent role for TREM2. Overall, ASOs that target TREM2 will be highly informative on TREM2-mediated AD pathogenesis and may be effective at modulating disease.

T CELL TGF-BETA SIGNALING CONTROL OF THE IMMUNE RESPONSE TO CEREBRAL AB

Background: Metabolism of the essential amino acid tryptophan (TRP) by the kynureninepathway (KP)gives rise toneuroactive compounds including quinolinic acid. While the KP is thought to lead to neurodegeneration by excitatory transmission, the KP also serves as the sole source for biosynthetic de novo NAD+. In macrophages and microglia, the rate-limiting enzyme of the KP is indoleamine-2,3-dioxygenase 1 (IDO1). Recent studies implicate maladaptive microglial immune responses in AD, so we investigated the function of immune IDO1 inAD.Methods: IDO1-/-mousemacrophages andmicroglia as well as human monocyte-derived macrophages (huMDMs) treated with 1MT (200mM, 20h) were treated with Ab42 (1mM, 20h) and underwent seahorse, electron microscopy, blue native gel electrophoresis (BN-PAGE), untargeted and targeted metabolomics, to examine changes in immunometabolism andmitochondrial dynamics. LC/MS was conducted on CSF from n1⁄4119 AD, n1⁄4120 MCI, and n1⁄4148normal patients for kynurenine andNAD+metabolites.Results: To our surprise, we found that IDO1-/macrophages and microglia as well as huMDMs that lack de novo NAD+ synthesis exhibited decreased basal respiration, oxygen consumption, NAD+ levels, and ATP production. Electron microscopy revealed mitochondria from IDO1-/-macrophage andmicroglia exhibited grossmorphological abnormalities and BN-PAGE revealed a decrease in CI activity in the ETC. Untargeted metabolomics on human macrophages and microglia treated with IDO1 inhibitors and those from IDO-/mice revealed an increase in glycolytic metabolism and accumulation of pro-inflammatory fatty acids as well as a decrease in amino acidmetabolism, and subsequent anaplerosis. Overexpression of de novo NAD+ synthesis proteins rescuedmetabolic and inflammatory deficits, reprogramming immune cells from proto anti-inflammatory phenotypes. Interestingly, LC-MS analysis from AD patients indicated decreased levels of KYN, KYN/TRP ratio, and downstream KP metabolites. Mass-labeling studies demonstrated decreased de novo NAD+ synthesis within microglia and macrophages in AD. Finally, IDO1 deletion in APPSwe-PS1DE9 mice aggravated inflammation and increased amyloid deposition.Conclusions: This is the first study to implicate functional de novo NAD+ synthesis within tissue and its role in AD pathology. Taken together, our findings suggest that IDO1-driven immune KP activity is beneficial in models of AD through metabolic and anti-inflammatory effects driven by de novo NAD+ synthesis.

Quantitative 3D In Silico Modeling (q3DISM) of Cerebral Amyloid-beta Phagocytosis in Rodent Models of Alzheimer's Disease.

Neuroinflammation is now recognized as a major etiological factor in neurodegenerative disease. Mononuclear phagocytes are innate immune cells responsible for phagocytosis and clearance of debris and detritus. These cells include CNS-resident macrophages known as microglia, and mononuclear phagocytes infiltrating from the periphery. Light microscopy has generally been used to visualize phagocytosis in rodent or human brain specimens. However, qualitative methods have not provided definitive evidence of in vivo phagocytosis. Here, we describe quantitative 3D in silico modeling (q3DISM), a robust method allowing for true 3D quantitation of amyloid-β (Aβ) phagocytosis by mononuclear phagocytes in rodent Alzheimers Disease (AD) models. The method involves fluorescently visualizing Aβ encapsulated within phagolysosomes in rodent brain sections. Large z-dimensional confocal datasets are then 3D reconstructed for quantitation of Aβ spatially colocalized within the phagolysosome. We demonstrate the successful application of q3DISM to mouse and rat brains, but this methodology can be extended to virtually any phagocytic event in any tissue.

Il10 deficiency licenses innate immunity to fight against cerebral amyloidosis

alpha-synuclein fibrils, rAAVmediated expression of IL-10, a master anti-inflammatory cytokine, suppresses proinflammatory chemokine, cytokine and other innate immune factor gene induction. Based on this data that IL-10, an anti-inflammatory cytokine, markedly dampens innate immune activation in vitro, we postulated that IL-10 based therapies may have beneficial outcome in aS mouse models. Methods:We have tested the effect of spinal cord targeted delivery of rAAV-IL-10 in the homozygous M83 mice expressing the A53Tmutant alpha synuclein. An additional ‘seeded’ model using the peripheral to central propagation of aS pathology in hemizygous M83 mice was also used (See, Sacino et al, Proc Natl