Tau and neuroinflammation: What impact for Alzheimer's Disease and Tauopathies?

In Silico Approach for Designing Potent Neuroprotective Hexapeptide

Alzheimer's disease (AD) is a constantly recurring neurodegenerative disease that deteriorates over a period of time. In this pathology, connections between neurons become extremely damaged due to the deposition of senile plaques in the membrane region, which results in abnormal signal transduction processes. Also, the intracellular microtubule networks are disrupted in the hyperphosphorylated tau cascade of AD. Therefore, design and development of potent neuroprotective molecules that can instantaneously target multiple facets of AD pathogenesis are greatly needed to tackle this unmet medical need. Here, we have implemented a pharmacophore based in silico analysis of various neuroprotective peptides known for neurotherapeutic application in AD. Fascinatingly, we have identified an active core of these peptides and designed a library of hexapeptides. We observed that peptide "LETVNQ" (LE6) has shown significant protection ability against degeneration of neurons. Experimental evidence suggests that this peptide immensely reduced the aggregation rate of amyloid-β (Aβ) and helped in microtubule polymerization. Intriguingly, this newly designed peptide does not have any cytotoxicity toward differentiated PC12 neurons; rather it helps in neurite outgrowth. Further, LE6 helps to maintain the complex microtubule network in cells by promoting the polymerization rate of intracellular microtubules and mediates excellent protection of neurons even after removal of nerve growth factor (NGF). Finally, we observed that this LE6 peptide has substantial stability under physiological conditions and helps to retain healthy morphology of primary rat cortical neurons. This excellent piece of work identifies a potent hexapeptide, which has exceptional ability to protect neurons as well as microtubule from degeneration and may become potent therapeutics against AD pathogenesis in the future.

Polysaccharide of Schisandra Chinensis Fructus ameliorates cognitive decline in a mouse model of Alzheimer's disease

ETHNOPHARMACOLOGICAL RELEVANCE

Polysaccharides is an important ingredient of Schisandra Chinensis Fructus which often appears in ancient prescriptions for forgetfulness or dementia.

AIM OF THE STUDY

The purpose of our study is to investigate the effects of polysaccharides of Schisandra Chinensis Fructus (SCP) on animal model of Alzheimer's disease (AD), which is a common disease of dementia, to elucidate the traditional medical theories with modern pharmacological methods and provide a reference for further clarifying its active mechanisms.

MATERIALS AND METHODS

Hydrolysates of SCP were analyzed by HPLC. Y-maze, Morris water maze (MWM) were used for evaluating cognition processes of mice. Immunohistochemistry (IHC) was used to detect the deposition of Aβ. The levels of cytokine expression including Tumor Necrosis Factor α (TNF-α), interleukin-1β (IL-1β) and interleukin-6 (IL-6) in the hippocampus were detected by ELISA kits. Activation of astrocytes and microglia was assessed by immunofluorescence labeling GFAP and Iba-1. The phosphorylated state of various mitogen-activated protein kinase (MAPKs) signaling molecules (p38 MAPK, ERK 1/2, and JNK) and activation of nuclear factor κB (NF-κB) was studied by western blot. Histopathological changes were observed by H.E. straining.

RESULTS

SCP could significantly improve the cognition and histopathological changes of AD mice, reduce the deposition of Aβ, downregulate the expression of pro-inflammatory cytokines and the activation of glial cells in the hippocampus. Further, SCP decreased nuclear displacement of NF-κB and MAPKs phosphorylation.

CONCLUSIONS

SCP could improve the cognition of mice, and it may play an anti-AD role by activating the NF-κB/MAPK pathway to alleviate neuroinflammation.

Tau binding protein CAPON induces tau aggregation and neurodegeneration

To understand the molecular processes that link Aβ amyloidosis, tauopathy and neurodegeneration, we screened for tau-interacting proteins by immunoprecipitation/LC-MS. We identified the carboxy-terminal PDZ ligand of nNOS (CAPON) as a novel tau-binding protein. CAPON is an adaptor protein of neuronal nitric oxide synthase (nNOS), and activated by the N-methyl-D-aspartate receptor. We observed accumulation of CAPON in the hippocampal pyramidal cell layer in the App^NL-G-F -knock-in (KI) brain. To investigate the effect of CAPON accumulation on Alzheimer’s disease (AD) pathogenesis, CAPON was overexpressed in the brain of App^NL-G-F mice crossbred with MAPT (human tau)-KI mice. This produced significant hippocampal atrophy and caspase3-dependent neuronal cell death in the CAPON-expressing hippocampus, suggesting that CAPON accumulation increases neurodegeneration. CAPON expression also induced significantly higher levels of phosphorylated, oligomerized and insoluble tau. In contrast, CAPON deficiency ameliorated the AD-related pathological phenotypes in tauopathy model. These findings suggest that CAPON could be a druggable AD target.

To understand the molecular processes that link Aβ amyloidosis, tauopathy and neurodegeneration, the authors screened for tau-interacting proteins. They demonstrated that a novel tau binding protein CAPON accelerates tau pathology and neuronal cell death in an Alzheimer’s disease mouse model.

Animal models of closed-skull, repetitive mild traumatic brain injury

The underlying mechanisms that result in neurophysiological changes and cognitive sequelae in the context of repetitive mild traumatic brain injury (rmTBI) remain poorly understood. Animal models provide a unique opportunity to examine cellular and molecular responses using histological assessment, which can give important insights on the neurophysiological changes associated with the evolution of brain injury. To better understand the potential cumulative effects of multiple concussions, the focus of animal models is shifting from single to repetitive head impacts. With a growing body of literature on this subject, a review and discussion of current findings is valuable to better understand the neuropathology associated with rmTBI, to evaluate the current state of the field, and to guide future research efforts. Despite variability in experimental settings, existing animal models of rmTBI have contributed to our understanding of the underlying mechanisms following repeat concussion. However, how to reconcile the various impact methods remains one of the major challenges in the field today.

NF-κB-mediated inflammatory damage is differentially affected in SH-SY5Y and C6 cells treated with 27-hydroxycholesterol

Previous studies have demonstrated that 27-hydroxycholesterol (27-OHC), a cholesterol metabolite, was involved in the inflammatory process of Alzheimer's disease (AD). The present study aimed to investigate the 27-OHC-induced inflammatory damage to neurons and astrocytes and the underlying mechanism(s) accounting for this damage. Human neuroblastoma cells (SH-SY5Y cells) and rat glioma cells (C6 cells) were treated with vehicle or 27-OHC (5, 10, or 20 μM) for 24 hr. The levels of secreted interleukin-1β (IL-1β), interleukin-10 (IL-10), tumor necrosis factor alpha (TNF-α), and inducible nitric oxide synthase (iNOS) were determined by using an enzyme-linked immunosorbent assay (ELISA). Immunofluorescence staining was used to determine the cellular expression of toll-like receptor 4 (TLR4) and transforming growth factor-β (TGF-β). The mRNA and protein expression levels of nuclear factor-κB p65 (NF-κB p65), nuclear factor-κB p50 (NF-κB p50) and cyclooxygenase-2 (COX-2) in both SH-SY5Y and C6 cells were also detected by real-time PCR and Western blot, respectively. The results of this study showed that 27-OHC treatment increased secretion of TNF-α and iNOS and decreased secretion of IL-10, upregulated expression of TGF-β, NF-κB p65 and p50, and downregulated expression of COX-2 in SH-SY5Y cells. In C6 cells, treatment with 27-OHC resulted in decreased secretion of IL-1β, IL-10, TNF-α, and iNOS, and increased expression of TLR4 and TGF-β. These results suggest that 27-OHC may cause inflammatory damage to neurons by activating the TGF-β/NF-κB signaling pathway and to astrocytes by activating the TLR4/TGF-β signaling, which results in the subsequent release of inflammatory cytokines.

Perivascular space fluid contributes to diffusion tensor imaging changes in white matter

Diffusion tensor imaging (DTI) has been extensively used to map changes in brain tissue related to neurological disorders. Among the most widespread DTI findings are increased mean diffusivity and decreased fractional anisotropy of white matter tissue in neurodegenerative diseases. Here we utilize multi-shell diffusion imaging to separate diffusion signal of the brain parenchyma from non-parenchymal fluid within the white matter. We show that unincorporated anisotropic water in perivascular space (PVS) significantly, and systematically, biases DTI measures, casting new light on the biological validity of many previously reported findings. Despite the challenge this poses for interpreting these past findings, our results suggest that multi-shell diffusion MRI provides a new opportunity for incorporating the PVS contribution, ultimately strengthening the clinical and scientific value of diffusion MRI.

CX3CR1-deficient microglia shows impaired signalling of the transcription factor NRF2: Implications in tauopathies

TAU protein aggregation is the main characteristic of neurodegenerative diseases known as tauopathies. Low-grade chronic inflammation is also another hallmark that indicates crosstalk between damaged neurons and glial cells. Previously, we have demonstrated that neurons overexpressing TAU^P301L release CX3CL1, which activates the transcription factor NRF2 signalling to limit over-activation in microglial cells in vitro and in vivo. However, the connection between CX3CL1/CX3CR1 and NRF2 system and its functional implications in microglia are poorly described. We evaluated CX3CR1/NRF2 axis in the context of tauopathies and its implication in neuroinflammation. Regarding the molecular mechanisms that connect CX3CL1/CX3CR1 and NRF2 systems, we observed that in primary microglia from Cx3cr1^-/- mice the mRNA levels of Nrf2 and its related genes were significantly decreased, establishing a direct linking between both systems. To determine functional relevance of CX3CR1, migration and phagocytosis assays were evaluated. CX3CR1-deficient microglia showed impaired cell migration and deficiency of phagocytosis, as previously described for NRF2-deficient microglia, reinforcing the idea of the relevance of the CX3CL1/CX3CR1 axis in these events. The importance of these findings was evident in a tauopathy mouse model where the effects of sulforaphane (SFN), an NRF2 inducer, were examined on neuroinflammation in Cx3cr1^+/+ and Cx3cr1^-/- mice. Interestingly, the treatment with SFN was able to modulate astrogliosis but failed to reduce microgliosis in Cx3cr1^-/- mice. These findings suggest an essential role of the CX3CR1/NRF2 axis in microglial function and in tauopathies. Therefore, polymorphisms with loss of function in CX3CR1 or NRF2 have to be taken into account for the development of therapeutic strategies.

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CX3CR1-deficient primary microglial cells present impaired expression of the transcription factor NRF2 signature.

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TAM receptors expression is decreased in CX3CR1-deficient microglia.

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AXL receptor is a NRF2-dependent gene.

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Loss of CX3CR1 expression led to impaired phagocytosis and migration of microglia.

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Sulforaphane treatment did not reverse rAAV-TAU^P301L induced microgliosis in CX3CR1-deficient mice.

The Link Between Tau and Insulin Signaling: Implications for Alzheimer's Disease and Other Tauopathies

The microtubule-associated protein tau (MAPT) is mainly identified as a tubulin binding protein essential for microtubule dynamics and assembly and for neurite outgrowth. However, several other possible functions for Tau remains to be investigated. Insulin signaling is important for synaptic plasticity and memory formation and therefore is essential for proper brain function. Tau has recently been characterized as an important regulator of insulin signaling, with evidence linking Tau to brain and peripheral insulin resistance and beta cell dysfunction. In line with this notion, the hypothesis of Tau pathology as a key trigger of impaired insulin sensitivity and secretion has emerged. Conversely, insulin resistance can also favor Tau dysfunction, resulting in a vicious cycle of these events. In this review article, we discuss recent evidence linking Tau pathology, insulin resistance and insulin deficiency. We further highlight the deleterious consequences of Tau pathology-induced insulin resistance to the brain and/or peripheral tissues, suggesting that these are key events mediating cognitive decline in Alzheimer’s disease (AD) and other tauopathies.

Recent Expansions on Cellular Models to Uncover the Scientific Barriers Towards Drug Development for Alzheimer's Disease

Globally, the central nervous system (CNS) disorders appear as the most critical pathological threat with no proper cure. Alzheimer's disease (AD) is one such condition frequently observed with the aged population and sometimes in youth too. Most of the research utilizes different animal models for in vivo study of AD pathophysiology and to investigate the potency of the newly developed therapy. These in vivo models undoubtably provide a powerful investigation tool to study human brain. Although, it sometime fails to mimic the exact environment and responses as the human brain owing to the distinctive genetic and anatomical features of human and rodent brain. In such condition, the in vitro cell model derived from patient specific cell or human cell lines can recapitulate the human brain environment. In addition, the frequent use of animals in research increases the cost of study and creates various ethical issues. Instead, the use of in vitro cellular models along with animal models can enhance the translational values of in vivo models and represent a better and effective mean to investigate the potency of therapeutics. This strategy also limits the excessive use of laboratory animal during the drug development process. Generally, the in vitro cell lines are cultured from AD rat brain endothelial cells, the rodent models, human astrocytes, human brain capillary endothelial cells, patient derived iPSCs (induced pluripotent stem cells) and also from the non-neuronal cells. During the literature review process, we observed that there are very few reviews available which describe the significance and characteristics of in vitro cell lines, for AD investigation. Thus, in the present review article, we have compiled the various in vitro cell lines used in AD investigation including HBMEC, BCECs, SHSY-5Y, hCMEC/D3, PC-2 cell line, bEND3 cells, HEK293, hNPCs, RBE4 cells, SK-N-MC, BMVECs, CALU-3, 7W CHO, iPSCs and cerebral organoids cell lines and different types of culture media such as SCM, EMEM, DMEM/F12, RPMI, EBM and 3D-cell culture.

Cellular Senescence as the Key Intermediate in Tau-Mediated Neurodegeneration

Neuroinflammation is thought to play a key role in the progression of neurodegenerative disease such as Alzheimer's disease (AD). Given the apparent nexus of inflammatory disease with the secretory-associated senescence phenotype (SASP) of cellular senescence, two reports found that tau-mediated neurodegeneration involves induction of senescence in astrocytes, microglia, and possibly even neurons. Elimination of senescent cells by pharmacologically induced genetic ablation or by senolytic drugs blocks progression of mutant human tau-mediated neurodegeneration in mice. This work suggests a working hypothesis through which tau activation leads to senescence and then tau propagation throughout the brain is supported by, and neurotoxicity is caused by, SASP, forming a pathological positive feedback loop. Although preliminary, these data suggest that the development of senolytics for AD and other tauopathies, especially early disease, and possibly senomodulatory drugs for later stage neurodegenerative disease may prove fruitful.

Angiotensin IV suppresses inflammation in the brains of rats with chronic cerebral hypoperfusion

INTRODUCTION

This study aimed to evaluate the influence of central angiotensin IV (Ang IV) infusion on chronic cerebral hypoperfusion (CCH)-related neuropathological changes including amyloid-β (Aβ), hyperphosphorylated tau (p-tau) and the inflammatory response.

MATERIALS AND METHODS

Rats with CCH received central infusion of Ang IV, its receptor AT₄R antagonist divalinal-Ang IV or artificial cerebrospinal fluid for six weeks. During this procedure, the systolic blood pressure (SBP) was monitored, and the levels of Aβ₄₂, p-tau and pro-inflammatory cytokines in the brain were detected.

RESULTS

Rats with CCH exhibited higher levels of Aβ₄₂, p-tau and pro-inflammatory cytokines in the brain when compared with controls. Infusion of Ang IV significantly reduced the expression of pro-inflammatory cytokines in the brains of rats with CCH. Meanwhile, the reduction of pro-inflammatory cytokines levels caused by Ang IV was reversed by divalinal-Ang IV. During the treatment, the SBP in rats was not significantly altered.

CONCLUSION

This study demonstrates for the first time that Ang IV dose-dependently suppresses inflammation through AT₄R in the brains of rats with CCH, which is independent from SBP. These findings suggest that Ang IV/AT₄R may represent a potential therapeutic target for CCH-related neurological diseases.

Pathogenic Feed-Forward Mechanisms in Alzheimer's and Parkinson's Disease Converge on GSK-3

Alzheimer's disease (AD) and Parkinson's disease (PD) share many commonalities ranging from signaling deficits such as altered cholinergic activity, neurotrophin and insulin signaling to cell stress cascades that result in proteinopathy, mitochondrial dysfunction and neuronal cell death. These pathological processes are not unidirectional, but are intertwined, resulting in a series of feed-forward loops that worsen symptoms and advance disease progression. At the center of these loops is glycogen synthase kinase-3 (GSK-3), a keystone protein involved in many of the multidirectional biological processes that contribute to AD and PD neuropathology. Here, a unified overview of the involvement of GSK-3 in the major processes involved in these diseases will be presented. The mechanisms by which these processes are linked will be discussed and the feed-forward pathways identified. In this regard, this review will put forth the notion that combination therapy, targeting these multiple facets of AD or PD neuropathology is a necessary next step in the search for effective therapies.

Tau protein aggregation is associated with cellular senescence in the brain

Tau protein accumulation is the most common pathology among degenerative brain diseases, including Alzheimer's disease (AD), progressive supranuclear palsy (PSP), traumatic brain injury (TBI), and over twenty others. Tau-containing neurofibrillary tangle (NFT) accumulation is the closest correlate with cognitive decline and cell loss (Arriagada, Growdon, Hedley-Whyte, & Hyman, ), yet mechanisms mediating tau toxicity are poorly understood. NFT formation does not induce apoptosis (de Calignon, Spires-Jones, Pitstick, Carlson, & Hyman, 2009), which suggests that secondary mechanisms are driving toxicity. Transcriptomic analyses of NFT-containing neurons microdissected from postmortem AD brain revealed an expression profile consistent with cellular senescence. This complex stress response induces aberrant cell cycle activity, adaptations to maintain survival, cellular remodeling, and metabolic dysfunction. Using four AD transgenic mouse models, we found that NFTs, but not Aβ plaques, display a senescence-like phenotype. Cdkn2a transcript level, a hallmark measure of senescence, directly correlated with brain atrophy and NFT burden in mice. This relationship extended to postmortem brain tissue from humans with PSP to indicate a phenomenon common to tau toxicity. Tau transgenic mice with late-stage pathology were treated with senolytics to remove senescent cells. Despite the advanced age and disease progression, MRI brain imaging and histopathological analyses indicated a reduction in total NFT density, neuron loss, and ventricular enlargement. Collectively, these findings indicate a strong association between the presence of NFTs and cellular senescence in the brain, which contributes to neurodegeneration. Given the prevalence of tau protein deposition among neurodegenerative diseases, these findings have broad implications for understanding, and potentially treating, dozens of brain diseases.

Distinct Microglial Responses in Two Transgenic Murine Models of TAU Pathology

Microglial cells are crucial players in the pathological process of neurodegenerative diseases, such as Alzheimer’s disease (AD). Microglial response in AD has been principally studied in relation to amyloid-beta pathology but, comparatively, little is known about inflammatory processes associated to tau pathology. In the hippocampus of AD patients, where tau pathology is more prominent than amyloid-beta pathology, a microglial degenerative process has been reported. In this work, we have directly compared the microglial response in two different transgenic tau mouse models: ThyTau22 and P301S. Surprisingly, these two models showed important differences in the microglial profile and tau pathology. Where ThyTau22 hippocampus manifested mild microglial activation, P301S mice exhibited a strong microglial response in parallel with high phospho-tau accumulation. This differential phospho-tau expression could account for the different microglial response in these two tau strains. However, soluble (S1) fractions from ThyTau22 hippocampus presented relatively high content of soluble phospho-tau (AT8-positive) and were highly toxic for microglial cells in vitro, whereas the correspondent S1 fractions from P301S mice displayed low soluble phospho-tau levels and were not toxic for microglial cells. Therefore, not only the expression levels but the aggregation of phospho-tau should differ between both models. In fact, most of tau forms in the P301S mice were aggregated and, in consequence, forming insoluble tau species. We conclude that different factors as tau mutations, accumulation, phosphorylation, and/or aggregation could account for the distinct microglial responses observed in these two tau models. For this reason, deciphering the molecular nature of toxic tau species for microglial cells might be a promising therapeutic approach in order to restore the deficient immunological protection observed in AD hippocampus.

Liraglutide and a lipidized analog of prolactin-releasing peptide show neuroprotective effects in a mouse model of β-amyloid pathology

Obesity and type 2 diabetes mellitus (T2DM) are important risk factors for Alzheimer's disease (AD). Drugs originally developed for T2DM treatment, e.g., analog of glucagon-like peptide 1 liraglutide, have shown neuroprotective effects in mouse models of AD. We previously examined the neuroprotective properties of palm¹¹-PrRP31, an anorexigenic and glucose-lowering analog of prolactin-releasing peptide, in a mouse model of AD-like Tau pathology, THY-Tau22 mice. Here, we demonstrate the neuroprotective effects of palm¹¹-PrRP31 in double transgenic APP/PS1 mice, a model of AD-like β-amyloid (Aβ) pathology. The 7-8-month-old APP/PS1 male mice were subcutaneously injected with liraglutide or palm¹¹-PrRP31 for 2 months. Both the liraglutide and palm¹¹-PrRP31 treatments reduced the Aβ plaque load in the hippocampus. Palm¹¹-PrRP31 also significantly reduced hippocampal microgliosis, consistent with our observations of a reduced Aβ plaque load, and reduced cortical astrocytosis, similar to the treatment with liraglutide. Palm¹¹-PrRP31 also tended to increase neurogenesis, as indicated by the number of doublecortin-positive cells in the hippocampus. After the treatment with both anorexigenic compounds, we observed a significant decrease in Tau phosphorylation at Thr231, one of the first epitopes phosphorylated in AD. This effect was probably caused by elevated activity of protein phosphatase 2A subunit C, the main Tau phosphatase. Both liraglutide and palm¹¹-PrRP31 reduced the levels of caspase 3, which has multiple roles in the pathogenesis of AD. Palm¹¹-PrRP31 increased protein levels of the pre-synaptic marker synaptophysin, suggesting that palm¹¹-PrRP31 might help preserve synapses. These results indicate that palm¹¹-PrRP31 has promising potential for the treatment of neurodegenerative diseases.

First-in-class DAPK1/CSF1R dual inhibitors: Discovery of 3,5-dimethoxy-N-(4-(4-methoxyphenoxy)-2-((6-morpholinopyridin-3-yl)amino)pyrimidin-5-yl)benzamide as a potential anti-tauopathies agent

Kinase irregularity has been correlated with several complex neurodegenerative tauopathies. Development of selective inhibitors of these kinases might afford promising anti-tauopathy therapies. While DAPK1 inhibitors halt the formation of tau aggregates and counteract neuronal death, CSF1R inhibitors could alleviate the tauopathies-associated neuroinflammation. Herein, we report the design, synthesis, biological evaluation, mechanistic study, and molecular docking study of novel CSF1R/DAPK1 dual inhibitors as multifunctional molecules inhibiting the formation of tau aggregates and neuroinflammation. Compound 3l, the most potent DAPK1 inhibitor in the in vitro kinase assay (IC₅₀ = 1.25 μM) was the most effective tau aggregates formation inhibitor in the cellular assay (IC₅₀ = 5.0 μM). Also, compound 3l elicited potent inhibition of CSF1R in the in vitro kinase assay (IC₅₀ = 0.15 μM) and promising inhibition of nitric oxide production in LPS-induced BV-2 cells (55% inhibition at 10 μM concentration). Kinase profiling and hERG binding assay anticipated the absence of off-target toxicities while the PAMPA-BBB assay predicted potentially high BBB permeability. The mechanistic study and selectivity profile suggest compound 3l as a non-ATP-competitive DAPK1 inhibitor and an ATP-competitive CSF1R inhibitor while the in silico calculations illustrated binding of compound 3l to the substrate-binding site of DAPK1. Hence, compound 3l might act as a protein-protein interaction inhibitor by hindering DAPK1 kinase reaction through preventing the binding of DAPK1 substrates.

An outline for the pharmacological effect of icariin in the nervous system

Icariin is a major active component of the traditional herb Epimedium, also known as Horny Goat Weed. It has been extensively studied throughout the past several years and is known to exert anti-oxidative, anti-neuroinflammatory, and anti-apoptotic effects. It is now being considered as a potential therapeutic agent for a wide variety of disorders, ranging from neoplasm to cardiovascular disease. More recent studies have shown that icariin exhibits potential preventive and/or therapeutic effects in the nervous system. For example, icariin can prevent the production of amyloid β (1-42) and inhibit the expression of amyloid precursor protein (APP) and β-site APP cleaving enzyme 1 (BACE-1) in animal models of Alzheimer's disease (AD). Icariin has been shown to mitigate pro-inflammatory responses of microglia in culture and in animal models of cerebral ischemia, depression, Parkinson's disease (PD), and multiple sclerosis (MS). Icariin also prevents the neurotoxicity induced by hydrogen peroxide (H₂O₂), endoplasmic reticulum (ER) stress, ibotenic acid, and homocysteine. In addition, icariin is implicated in facilitating learning and memory in both normal aging animals and disease models. To date, we still have no consolidated source of knowledge about the pharmacological effects of icariin in the nervous system, though its roles in other tissues have been reviewed in recent years. Here, we summarize the pharmacological development of icariin as well as its possible mechanisms in prevention and/or therapy of disorders afflicting the nervous system in hope of expanding the knowledge about the preventive and/or therapeutic effect of icariin in brain disorders.

Neuroinflammation in mouse models of Alzheimer's disease

Alzheimer's disease (AD) is the most common type of neurocognitive disorder. Although both amyloid β peptide deposition and neurofibrillary tangle formation in the AD brain have been established as pathological hallmarks of the disease, many other factors contribute in a complex manner to the pathogenesis of AD before clinical symptoms of the disease become apparent. Longitudinal pathophysiological processes cause patients' brains to exist in a state of chronic neuroinflammation, with glial cells acting as key regulators of the neuroinflammatory state. However, the detailed molecular and cellular mechanisms of glial function underlying AD pathogenesis remain elusive. Furthermore, recent studies have shown that peripheral inflammatory conditions affect glial cells in the brain through a process of neuroimmune communication. Such disease complexities make it difficult for the pathogenesis of AD to be understood, and impede the development of effective therapeutic strategies to combat the disease. Relevant AD animal models are thus likely to serve as a key resource to overcome many of these issues. Furthermore, as the pathogenesis of AD might be linked to conditions both within the brain as well as peripherally, it might become necessary for AD to be studied as a whole-body disorder. The present review aimed to summarize insights regarding current AD research, and share perspectives for understanding glial function in the context of the pathogenesis of AD.

Targeting neurodegeneration to prevent post-traumatic epilepsy

In the quest for developing new therapeutic targets for post-traumatic epilepsies (PTE), identifying mechanisms relevant to development and progression of disease is critical. A growing body of literature suggests involvement of neurodegenerative mechanisms in the pathophysiology of acquired epilepsies, including following traumatic brain injury (TBI). In this review, we discuss the potential of some of these mechanisms to be targets for the development of a therapy against PTE.

The Adenosinergic Signaling: A Complex but Promising Therapeutic Target for Alzheimer's Disease

Alzheimer’s disease (AD) is the most common neurodegenerative disorder in elderly people. AD is characterized by a progressive cognitive decline and it is neuropathologically defined by two hallmarks: extracellular deposits of aggregated β-amyloid (Aβ) peptides and intraneuronal fibrillar aggregates of hyper- and abnormally phosphorylated Tau proteins. AD results from multiple genetic and environmental risk factors. Epidemiological studies reported beneficial effects of caffeine, a non-selective adenosine receptors antagonist. In the present review, we discuss the impact of caffeine and of adenosinergic system modulation on AD, in terms of pathology and therapeutics.

Beneficial Effect of a Selective Adenosine A2A Receptor Antagonist in the APPswe/PS1dE9 Mouse Model of Alzheimer's Disease

Consumption of caffeine, a non-selective adenosine A_2A receptor (A_2AR) antagonist, reduces the risk of developing Alzheimer’s disease (AD) and mitigates both amyloid and Tau lesions in transgenic mouse models of the disease. While short-term treatment with A_2AR antagonists have been shown to alleviate cognitive deficits in mouse models of amyloidogenesis, impact of a chronic and long-term treatment on the development of amyloid burden, associated neuroinflammation and memory deficits has never been assessed. In the present study, we have evaluated the effect of a 6-month treatment of APPsw/PS1dE9 mice with the potent and selective A_2AR antagonist MSX-3 from 3 to 9-10 months of age. At completion of the treatment, we found that the MSX-3 treatment prevented the development of memory deficits in APP/PS1dE9 mice, without significantly altering hippocampal and cortical gene expressions. Interestingly, MSX-3 treatment led to a significant decrease of Aβ1-42 levels in the cortex of APP/PS1dE9 animals, while Aβ1-40 increased, thereby strongly affecting the Aβ1-42/Aβ1-40 ratio. Together, these data support the idea that A_2AR blockade is of therapeutic value for AD.

Emerging Roles of Astrocytes in Neuro-Vascular Unit and the Tripartite Synapse With Emphasis on Reactive Gliosis in the Context of Alzheimer's Disease

Astrocytes, which are five-fold more numerous than neurons in the central nervous system (CNS), are traditionally viewed to provide simple structural and nutritional supports for neurons and to participate in the composition of the blood brain barrier (BBB). In recent years, the active roles of astrocytes in regulating cerebral blood flow (CBF) and in maintaining the homeostasis of the tripartite synapse have attracted increasing attention. More importantly, astrocytes have been associated with the pathogenesis of Alzheimer's disease (AD), a major cause of dementia in the elderly. Although microglia-induced inflammation is considered important in the development and progression of AD, inflammation attributable to astrogliosis may also play crucial roles. A1 reactive astrocytes induced by inflammatory stimuli might be harmful by up-regulating several classical complement cascade genes thereby leading to chronic inflammation, while A2 induced by ischemia might be protective by up-regulating several neurotrophic factors. Here we provide a concise review of the emerging roles of astrocytes in the homeostasis maintenance of the neuro-vascular unit (NVU) and the tripartite synapse with emphasis on reactive astrogliosis in the context of AD, so as to pave the way for further research in this area, and to search for potential therapeutic targets of AD.

For better or worse: Immune system involvement in Alzheimer's Disease

In this issue of the Biomedical Journal, we explore the key role of the immune system in the development of Alzheimer's disease. We also learn more about the link between two disorders related to metabolic imbalances, with findings that could help to inform future screening programs. Finally, we would like to highlight some big news for our journal: the Biomedical Journal will be indexed in the Science Citation Index and receive its first official impact factor from this year.