The gut microbiome regulates astrocyte reaction to Aß amyloidosis through microglial dependent and independent mechanisms.

BACKGROUND: Previous studies show that antibiotic-mediated (abx) alteration of the gut microbiome (GMB) results in a reduction of amyloid beta (Aß) plaques and proinflammatory microglial phenotype in male APPPS1-21 mice. However, the effect of GMB perturbation on astrocyte phenotypes and microglial-astrocyte communication in the context of amyloidosis has not been examined. METHODS: To study whether the GMB modulates astrocyte phenotype in the context of amyloidosis, APPPS1-21 male and female mice were treated with broad-spectrum abx leading to GMB perturbation. GFAP + astrocytes, plaque-associated astrocytes (PAA), PAA morphological parameters, and astrocyte complement component C3 levels were quantified using a combination of immunohistochemistry, immunoblotting, widefield microscopy, and confocal microscopy. Furthermore, these same astrocyte phenotypes were assessed in abx-treated APPPS1-21 male mice that received either fecal matter transplant (FMT) from untreated APPPS1-21 male donors to restore their microbiome or vehicle control. To assess complete absence of the GMB on astrocyte phenotypes, the same astrocyte phenotypes were quantified in APPPS1-21 male mice raised in germ-free (GF) or specific-pathogen free conditions (SPF). Lastly, we assessed whether microglia are necessary for abx-induced astrocyte phenotypes by depleting microglia in APPPS1-21 male mice via treatment with a colony-stimulating factor 1 receptor (CSF1R) inhibitor (PLX5622) and vehicle control or PLX5622 and abx. RESULTS: Herein, we demonstrate that postnatal treatment of male APPPS1-21 mice with broad-spectrum abx leading to GMB perturbation reduces GFAP + reactive astrocytes and PAAs, suggesting that the GMB plays a role in regulating reactive astrocyte induction and recruitment to Aß plaques. Additionally, we show that compared to controls, PAAs in abx-treated male APPPS1-21 mice exhibit an altered morphology with increased number and length of processes and reduced astrocytic complement C3, consistent with a homeostatic phenotype. GFAP + astrocyte reduction, PAA reduction, astrocyte morphological changes, and C3 levels are restored when abx-treated mice are subject to FMT from untreated APPPS1-21 male donor mice. Next, we found that APPPS1-21 male mice raised in GF conditions have similar astrocyte phenotypes as abx-treated male APPPS1-21 male mice. Correlational analysis revealed that pathogenic bacteria depleted by abx correlate with GFAP + astrocytosis, PAAs, and astrocyte morphological changes. Finally, we determined that abx-mediated reduction in GFAP + astrocytosis, PAAs, and astrocytic C3 expression is independent of microglia. However, abx-induced astrocyte morphological alterations are dependent on the presence of microglia, suggesting that there is both microglial independent and dependent GMB control of reactive astrocyte phenotypes. CONCLUSIONS: We show for the first time, in the context of amyloidosis, that the GMB plays an important role in controlling reactive astrocyte induction, morphology, and astrocyte recruitment to Aß plaques. GMB regulation of these astrocytic phenotypes is both independent and dependent on microglia.

Poloxamer-188 Exacerbates Brain Amyloidosis, Presynaptic Dystrophies, and Pathogenic Microglial Activation in 5XFAD Mice.

BACKGROUND: Alzheimer's disease (AD) is initiated by aberrant accumulation of amyloid beta (Aß) protein in the brain parenchyma. The microenvironment surrounding amyloid plaques is characterized by the swelling of presynaptic terminals (dystrophic neurites) associated with lysosomal dysfunction, microtubule disruption, and impaired axonal transport. Aß-induced plasma membrane damage and calcium influx could be potential mechanisms underlying dystrophic neurite formation. OBJECTIVE: We tested whether promoting membrane integrity by brain administration of a safe FDA approved surfactant molecule poloxamer-188 (P188) could attenuate AD pathology in vivo. METHODS: Three-month-old 5XFAD male mice were administered several concentrations of P188 in the brain for 42 days with mini-osmotic pumps. After 42 days, mice were euthanized and assessed for amyloid pathology, dystrophic neurites, pathogenic microglia activation, tau phosphorylation, and lysosomal / vesicular trafficking markers in the brain. RESULTS: P188 was lethal at the highest concentration of 10mM. Lower concentrations of P188 (1.2, 12, and 120µM) were well tolerated. P188 increased brain Aß burden, potentially through activation of the γ-secretase pathway. Dystrophic neurite pathology was exacerbated in P188 treated mice as indicated by increased LAMP1 accumulation around Aß deposits. Pathogenic microglial activation was increased by P188. Total tau levels were decreased by P188. Lysosomal enzyme cathepsin D and calciumdependent vesicular trafficking regulator synaptotagmin-7 (SYT7) were dysregulated upon P188 administration. CONCLUSION: P188 brain delivery exacerbated amyloid pathology, dystrophic neurites, and pathogenic microglial activation in 5XFAD mice. These effects correlated with lysosomal dysfunction and dysregulation of plasma membrane vesicular trafficking. P188 is not a promising therapeutic strategy against AD pathogenesis.

Early detection and personalized medicine: Future strategies against Alzheimer's disease.

Alzheimer's disease (AD) is the leading cause of dementia and sixth cause of death in elderly adults. AD poses a huge economic burden on society and constitutes an unprecedented challenge for caregivers and families affected. Aging of the population is projected to drastically aggravate the situation in the near future. To date, no therapy is available to prevent or ameliorate the disease. Moreover, several clinical trials for promising therapeutic agents have failed. Lack of supporting biomarker data for pre-symptomatic enrollment and inaccurate stratification of patients based on genetic heterogeneity appear to be contributing factors to this lack of success. Recently, the treatment of cancer has seen enormous advances based on the personalized genetics and biomarkers of the individual patient, forming the foundation of precision medicine for cancer. Likewise, technological progress in AD biomarker research promises the availability of reliable assays for pathology staging on a routine basis relatively soon. Moreover, tremendous achievements in AD genetics and high-throughput genotyping technology allow identification of predisposing risk alleles accurately and on a large scale. Finally, availability of electronic health records (EHR) promises the opportunity to integrate biomarker, genomic and clinical data efficiently. Together, these advances will form the basis of precision medicine for AD.

Gestational high fat diet protects 3xTg offspring from memory impairments, synaptic dysfunction, and brain pathology.

Maternal history for sporadic Alzheimer's disease (AD) predisposes the offspring to the disease later in life. However, the mechanisms behind this phenomenon are still unknown. Lifestyle and nutrition can directly modulate susceptibility to AD. Herein we investigated whether gestational high fat diet influences the offspring susceptibility to AD later in life. Triple transgenic dams were administered high fat diet or regular chow throughout 3 weeks gestation. Offspring were fed regular chow throughout their life and tested for spatial learning and memory, brain amyloidosis, tau pathology, and synaptic function. Gestational high fat diet attenuated memory decline, synaptic dysfunction, amyloid-ß and tau neuropathology in the offspring by transcriptional regulation of BACE-1, CDK5, and tau gene expression via the upregulation of FOXP2 repressor. Gestational high fat diet protects offspring against the development of the AD phenotype. In utero dietary intervention could be implemented as preventative strategy against AD.

Autophagy Dysfunction in Alzheimer's Disease: Mechanistic Insights and New Therapeutic Opportunities.

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by progressive memory loss due to aberrant accumulation of misfolded proteins inside and outside neurons and glial cells, leading to a loss of cellular protein homeostasis. Today, no therapy is available to block or slow down AD progression, and the mechanisms of the disease are not fully understood. Autophagy is an intracellular degradation pathway crucial to maintaining cellular homeostasis by clearing damaged organelles, pathogens, and unwanted protein aggregates. In recent years, autophagy dysfunction has gained considerable attention in AD and other neurodegenerative diseases because it has been linked to the accumulation of misfolded proteins that ultimately causes neuronal death in many of these disorders. Interestingly, autophagy-activating compounds have also shown some promising results in both clinical trials and preclinical studies. This review aims at summarizing the current knowledge on autophagy dysfunction in the context of AD pathophysiology, providing recent mechanistic insights on AD-mediated autophagic flux disruption and highlighting potential and novel therapeutic opportunities that target this system for AD therapy.

Early-life exposure to high-fat diet influences brain health in aging mice.

Epidemiological studies have suggested a link between exposure to environmental factors early in life and susceptibility to neurodegenerative diseases in adulthood. In the short term, maternal diet is important for the growth and development of the fetus; however, it may also have long-term effects on the health status of the offspring. Here, we investigate the effect that maternal high-fat diet during gestation has on brain health of the offspring later in life. B6129SF2/J dams were fed a high-fat diet during the 3 weeks' gestation, then switched to standard chow diet after delivery. Offspring were always fed regular diet for the entire study and assessed in learning, memory, and brain pathology when 18 months old. Compared with offspring from control mothers, the ones from mothers exposed to high-fat diet had significant better performance in learning and memory tests, which associated with an amelioration of synaptic integrity. Additionally, they had a significant reduction in total tau, a decrease in its pathological conformational changes and lower levels of caspase-3-cleaved isoforms. Our findings demonstrate that in utero exposure to high-fat diet plays a protective role for offspring brain health later in life. They support the novel hypothesis that targeted dietary intervention specifically restricted to the gestation period could be implemented as preventative strategy for the age-dependent decline in brain health.

Impaired mitochondrial calcium efflux contributes to disease progression in models of Alzheimer's disease.

Impairments in neuronal intracellular calcium (iCa2+) handling may contribute to Alzheimer's disease (AD) development. Metabolic dysfunction and progressive neuronal loss are associated with AD progression, and mitochondrial calcium (mCa2+) signaling is a key regulator of both of these processes. Here, we report remodeling of the mCa2+ exchange machinery in the prefrontal cortex of individuals with AD. In the 3xTg-AD mouse model impaired mCa2+ efflux capacity precedes neuropathology. Neuronal deletion of the mitochondrial Na+/Ca2+ exchanger (NCLX, Slc8b1 gene) accelerated memory decline and increased amyloidosis and tau pathology. Further, genetic rescue of neuronal NCLX in 3xTg-AD mice is sufficient to impede AD-associated pathology and memory loss. We show that mCa2+ overload contributes to AD progression by promoting superoxide generation, metabolic dysfunction and neuronal cell death. These results provide a link between the calcium dysregulation and metabolic dysfunction hypotheses of AD and suggest mCa2+ exchange as potential therapeutic target in AD.

Elevated levels of brain homocysteine directly modulate the pathological phenotype of a mouse model of tauopathy.

A high circulating level of homocysteine (Hcy), also known as hyperhomocysteinemia, is a risk factor for Alzheimer's disease (AD). Previous studies show that elevated Hcy promotes brain amyloidosis and behavioral deficits in mouse models of AD. However, whether it directly modulates the development of tau neuropathology independently of amyloid beta in vivo is unknown. Herein, we investigate the effect of diet-induced elevated levels of brain Hcy on the phenotype of a relevant mouse model of human tauopathy. Compared with controls, tau mice fed with low folate and B vitamins diet had a significant increase in brain Hcy levels and worsening of behavioral deficits. The same mice had a significant elevation of tau phosphorylation, synaptic pathology, and astrocytes activation. In vitro studies demonstrated that Hcy effect on tau phosphorylation was mediated by an upregulation of 5-lipoxygenase via cdk5 kinase pathway activation. Our findings support the novel concept that high Hcy level in the central nervous system is a metabolic risk factor for neurodegenerative diseases, specifically characterized by the progressive accumulation of tau pathology, namely tauopathies.

Dissecting the Role of 5-Lipoxygenase in the Homocysteine-Induced Alzheimer's Disease Pathology.

Alzheimer's disease (AD) affects over 40 million patients around the world and poses a huge economic burden on society since no effective therapy is available yet. While the cause(s) for the most common sporadic form of the disease are still obscure, lifestyle and different environmental factors have emerged as modulators of AD susceptibility. Hyperhomocysteinemia (HHCY), a condition of high circulating levels of homocysteine, is an independent but modifiable risk factor for AD. Studies in AD mouse models have linked HHCY with memory impairment, amyloidosis, tau pathology, synaptic dysfunction, and neuroinflammation. However, the exact mechanism by which HHCY affects AD pathogenesis is unclear. The 5-lipoxygenase (5LO) is a protein upregulated in postmortem AD brains and plays a functional role in AD pathogenesis. Recently, in vitro and in vivo studies showed that HHCY effects on amyloid-ß and tau pathology, synapse and memory impairments are dependent on the activation of the 5LO enzymatic pathway, since its genetic absence or pharmacological inhibition prevents them. HHCY induces 5LO gene upregulation by lowering the methylation of its promoter, which results in increased translation and transcription of its mRNA. Based on these findings, we propose that epigenetic modification of 5LO represents the missing biological link between HHCY and AD pathogenesis, and for this reason it represents a viable therapeutic target to prevent AD development in individuals bearing this risk factor.

12/15-Lipoxygenase Inhibition Reverses Cognitive Impairment, Brain Amyloidosis, and Tau Pathology by Stimulating Autophagy in Aged Triple Transgenic Mice.

BACKGROUND: The 12/15-lipoxygenase (12/15-LO) enzyme is upregulated in the brains of patients with Alzheimer's disease (AD), and its expression levels influence the onset of the AD-like phenotype in mouse models. However, whether targeting this pathway after the neuropathology and behavioral impairments have been established remains to be investigated. METHODS: Triple transgenic (3xTg) mice received either PD146176-a selective and specific pharmacological inhibitor of 12/15-LO-or placebo starting at 12 months of age for 12 weeks. They were then assessed for the effect of the treatment on neuropathologies and behavioral impairments. RESULTS: At the end of the study, mice in the control group showed a worsening of memory and learning abilities, whereas mice receiving PD146176 were undistinguishable from wild-type mice. The same group also had significantly lower amyloid beta levels and deposition, less tau neuropathology, increased synaptic integrity, and autophagy activation. Ex vivo and in vitro genetic and pharmacological studies found that the mechanism involved in these effects was the activation of neuronal autophagy. CONCLUSIONS: Our findings provide new insights into the disease-modifying action of 12/15-LO pharmacological inhibition and establish it as a viable therapeutic approach for patients with AD.

MicroRNAs as Therapeutic Targets for Alzheimer's Disease.

Alzheimer's disease (AD) is the most common cause of dementia in the elderly. With increasing longevity and the absence of a cure, AD has become not only a major health problem but also a heavy social and economic burden worldwide. Given this public health challenge, and that the current approved therapy for AD is limited to symptomatic treatment (i.e., cholinesterase inhibitors and NMDA receptor antagonists), exploration of new molecular pathways as novel therapeutic targets remains an attractive option for disease modifying drug development. microRNAs (miRNAs) are short non-coding RNA that control gene expression at the post-translational level by inhibiting translation of specific mRNAs or degrading them. Dysregulation of several miRNAs has been described in AD brains. Interestingly, their molecular targets are pathways that are well-established functional players in the onset and development of AD pathogenesis. Today several molecular tools have been developed to modulate miRNA levels in vitro and in vivo. These scientific advancements are affording us for the first time with the real possibility of targeting in vivo these dysregulated miRNAs as a novel therapeutic approach against AD.

Modulation of AD neuropathology and memory impairments by the isoprostane F2α is mediated by the thromboxane receptor.

Beside amyloid-ß plaques and neurofibrillary tangles, brain oxidative damage has been constantly implicated in Alzheimer's disease (AD) pathogenesis. Numerous studies demonstrated that F2-isoprostanes, markers of in vivo lipid peroxidation, are elevated in AD patients and mouse models of the disease. Previously, we showed that the 8-isoprostaneF2α, (8ISO) increases brain amyloid-ß levels and deposition in the Tg2576 mice. However, no data are available on its effects on behavior and tau metabolism. To this end, we characterize the behavioral, biochemical, and neuropathologic effects of 8ISO in the triple transgenic mouse model. Compared with controls, mice receiving 8ISO showed significant memory deficits, increase in tau phosphorylation, activation of the cyclin kinase 5 pathway, and neuroinflammation. All these effects were blocked by pharmacologic blockade of the thromboxane receptor. Our findings establish the novel functional role that oxidative stress via the formation of this isoprostane plays in the development of cognitive impairments and AD-related tau neuropathology. It provides important preclinical support to the neurobiological importance of the thromboxane receptor as an active player in the pathogenesis of AD.

Zileuton restores memory impairments and reverses amyloid and tau pathology in aged Alzheimer's disease mice.

The enzyme 5-lipoxygenase (5LO) is upregulated in Alzheimer's disease (AD), and its pharmacologic blockade with zileuton slows down the development of the AD-like phenotype in young AD mice. However, its efficacy after the AD pathology is established is unknown. To this end, starting at 12 months of age triple transgenic mice (3xTg) received zileuton, a selective 5LO inhibitor, or placebo for 3 months, and then the effect of this treatment on behavior, amyloid, and tau pathology assessed. Although mice on placebo showed worsening of their memory, treated mice performed even better than at baseline. Compared with placebo, treated mice had significantly less Aß deposits and tau phosphorylation secondary to reduced γ-secretase and CDK-5 activation, respectively. Our data provide novel insights into the disease-modifying action of pharmacologically inhibiting 5LO as a viable AD therapeutic approach. They represent the successful completion of preclinical studies for the development of this class of drug as clinically applicable therapy for the disease.

Sleep deprivation impairs memory, tau metabolism, and synaptic integrity of a mouse model of Alzheimer's disease with plaques and tangles.

Several studies have highlighted the frequency of sleep disturbances in Alzheimer's disease (AD). However, whether they are secondary to the disease or per se increase its risk remains to be fully investigated. The aim of the current investigation was to study the effect of sleep deprivation (SD) on the development of AD phenotype in a transgenic mouse model with plaques and tangles, the 3xTg mice. We evaluated the functional and biological consequences on 3xTg mice that underwent 4 hours sleep restrain per day for 8 weeks. Compared with controls, behavioral assessment showed that SD-treated mice had a significant decline in their learning and memory. Although no differences were detected in the levels of soluble amyloid-ß peptides, the same animals displayed a decrease in tau phosphorylation, which associated with a significant increase in its insoluble fraction. In addition, we observed that SD resulted in lower levels of postsynaptic density protein 95 and increased glial fibrillary acidic protein levels. Finally, although total levels of the transcription factor cellular response element binding protein were unchanged, its phosphorylated form was significantly diminished in brains of sleep-deprived mice when compared with controls. Our study underlines the importance of SD as a chronic stressor, which by modulating biochemical processes influences the development of memory impairments and AD neuropathologies. Correction of SD could be a viable therapeutic strategy to prevent the onset or slow the progression of AD in individuals bearing this risk factor.

Modulation of amyloid-ß production by leukotriene B4 via the γ-secretase pathway.

Inflammatory mechanisms have been implicated in Alzheimer's disease (AD) pathogenesis, and among them, the pro-inflammatory 5-lipoxygenase (5LO) enzyme. While previous work has shown that 5LO modulates the amyloidotic phenotype of AD, the exact metabolic product responsible for this biological action remains unknown. In this study, we challenged neuronal cells with leukotriene B4 (LTB4), a major 5LO product, and found that it increased amyloid-ß formation whereby elevating the steady-state levels of the γ-secretase proteins, suggesting that LTB4 is the mediator of the 5LO effect. Therapies that by blocking 5LO activation suppress the formation of LTB4 or its action represent novel AD therapeutic opportunities.

Overexpression of 12/15-lipoxygenase increases anxiety behavior in female mice.

The 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's disease. However, whether this pathway is also involved in neuropsychiatry disorders including anxiety remain to be investigated. In this study we investigated whether genetic over-expression of 12/15-LO (H12/15-LO) modulates some elevated plus maze and Y-maze behaviors. While we observed that H12/15LO mice at the age of 12 months did not differ from wild type in the elevated plus maze paradigm, when they reached the age of 15 months, they manifested an increased anxiety-like behavior compared with controls. By contrast, no differences between the 2 groups at both ages when they were tested for working memory in the Y-maze paradigm. Additionally, we found that the change in anxiety was associated with a reduction in phosphorylation of the transcription factor CREB (cAMP response element-binding protein), and a significant increase in the synaptic protein synaptophysin. Taken together our findings suggest a novel role for 12/15-LO in the pathogenesis of anxiety-like behavior.

Intravenous transfer of apoptotic cell-treated dendritic cells leads to immune tolerance by blocking Th17 cell activity.

Apoptotic cell-induced tolerogenic dendritic cells (DCs) play an important role in induction of peripheral tolerance in vivo; however, the mechanisms of immune tolerance induced by these DCs are poorly understood. Here we show that treatment of apoptotic cells modulates expression of inflammation- and tolerance-associated molecules including Gr-1, B220, CD205 and galectin-1 on bone marrow-derived DCs. In addition, apoptotic cell-treated DCs suppress secretion of cytokines produced by Th17 cells. Our data also demonstrate that i.v. transfer of apoptotic cell-treated DCs blocks EAE development and down-regulates production of inflammatory cytokines such as IL-17A and IL-17F in CD4+ T cells. These results suggest that apoptotic cell-treated DCs may inhibit activity of Th17 cells via down-regulation of inflammatory cytokine production, thereby affecting EAE development in vivo. Our results reveal a potential mechanism of immune tolerance mediated by apoptotic cell-treated DCs and the possible use of apoptotic cell-treated DCs to treat autoimmune diseases such as MS/EAE.