Drug pipeline in neurodegeneration based on transgenic mice models of Alzheimer's disease

Plasma membrane abundance dictates phagocytic capacity and functional cross-talk in myeloid cells

Professional phagocytes like neutrophils and macrophages tightly control what they consume, how much they consume, and when they move after cargo uptake. We show that plasma membrane abundance is a key arbiter of these cellular behaviors. Neutrophils and macrophages lacking the G protein subunit Gβ4 exhibited profound plasma membrane expansion, accompanied by marked reduction in plasma membrane tension. These biophysical changes promoted the phagocytosis of bacteria, fungus, apoptotic corpses, and cancer cells. We also found that Gβ4-deficient neutrophils are defective in the normal inhibition of migration following cargo uptake. Sphingolipid synthesis played a central role in these phenotypes by driving plasma membrane accumulation in cells lacking Gβ4. In Gβ4 knockout mice, neutrophils not only exhibited enhanced phagocytosis of inhaled fungal conidia in the lung but also increased trafficking of engulfed pathogens to other organs. Together, these results reveal an unexpected, biophysical control mechanism central to myeloid functional decision-making.

Effect and Mechanism of Rapamycin on Cognitive Deficits in Animal Models of Alzheimer's Disease: A Systematic Review and Meta-analysis of Preclinical Studies

Background

Alzheimer's disease (AD), the most common form of dementia, remains long-term and challenging to diagnose. Furthermore, there is currently no medication to completely cure AD patients. Rapamycin has been clinically demonstrated to postpone the aging process in mice and improve learning and memory abilities in animal models of AD. Therefore, rapamycin has the potential to be significant in the discovery and development of drugs for AD patients.

Objective

The main objective of this systematic review and meta-analysis was to investigate the effects and mechanisms of rapamycin on animal models of AD by examining behavioral indicators and pathological features.

Methods

Six databases were searched and 4,277 articles were retrieved. In conclusion, 13 studies were included according to predefined criteria. Three authors independently judged the selected literature and methodological quality. Use of subgroup analyses to explore potential mechanistic effects of rapamycin interventions: animal models of AD, specific types of transgenic animal models, dosage, and periodicity of administration.

Results

The results of Morris Water Maze (MWM) behavioral test showed that escape latency was shortened by 15.60 seconds with rapamycin therapy, indicating that learning ability was enhanced in AD mice; and the number of traversed platforms was increased by 1.53 times, indicating that the improved memory ability significantly corrected the memory deficits.

CONCLUSIONS

Rapamycin therapy reduced age-related plaque deposition by decreasing AβPP production and down-regulating β-secretase and γ-secretase activities, furthermore increased amyloid-β clearance by promoting autophagy, as well as reduced tau hyperphosphorylation by up-regulating insulin-degrading enzyme levels.

Retinal Changes in Transgenic Mouse Models of Alzheimer's Disease

Alzheimer's disease (AD) is a neurodegenerative disorder, the most common form of dementia. AD is characterised by amyloid-β (Aβ) plaques and neurofibrillary tangles (NFT) in the brain, in association with neuronal loss and synaptic failure, causing cognitive deficits. Accurate and early diagnosis is currently unavailable in lifespan, hampering early intervention of potential new treatments. Visual deficits have been well documented in AD patients, and the pathological changes identified in the brain are also believed to be found in the retina, an integral part of the central nervous system. Retinal changes can be detected by real-time non-invasive imaging, due to the transparent nature of the ocular media, potentially allowing an earlier diagnosis as well as monitoring disease progression and treatment outcome. Animal models are essential for AD research, and this review has a focus on retinal changes in various transgenic AD mouse models with retinal imaging and immunohistochemical analysis as well as therapeutic effects in those models. We also discuss the limitations of transgenic AD models in clinical translations.

A New Approach to Model Sporadic Alzheimer's Disease by Intracerebroventricular Streptozotocin Injection in APP/PS1 Mice

Alzheimer's disease (AD) is the most common cause of dementia among elderly people. Majority of AD cases are sporadic (SAD) with unknown cause. Transgenic animal models closely reflect the familial (genetic) aspect of the disease but not the sporadic type. However, most new drug candidates which are tested positive in transgenic animal models failed in clinical studies so far. Herein, we aim to develop an AD animal model that combines most of the neuropathological features seen in sporadic AD in humans with amyloid plaques observed in transgenic mice. Four-month-old wild-type and APP/PS1 AD mice were given a single intracerebroventricular (ICV) injection of 3 mg/kg streptozotocin (STZ), a diabetogenic agent. Three weeks later, their cognitive behavior was assessed, and their brain tissues were collected for biochemical and histological analysis. STZ produced cognitive deficits in both non-transgenic mice and AD mice. Biochemical analysis showed a severe decline in synaptic proteins, increase in tau phosphorylation, oxidative stress, disturbed brain insulin signaling with extensive neuroinflammation, and cell death. Significant increase was also observed in the level of the soluble beta amyloid precursor protein (APP) fragments and robust accumulation of amyloid plaques in AD mice compared to the control. These results suggest that STZ ICV treatment causes disturbance in multiple metabolic and cell signaling pathways in the brain that facilitated amyloid plaque accumulation and tau phosphorylation. Therefore, this animal model can be used to evaluate new AD therapeutic agents for clinical translation.

Alzheimer-related genes show accelerated evolution

Alzheimer's disease (AD) is a neurodegenerative disorder of unknown cause with complex genetic and environmental traits. While AD is extremely prevalent in human elderly, it hardly occurs in non-primate mammals and even non-human-primates develop only an incomplete form of the disease. This specificity of AD to human clearly implies a phylogenetic aspect. Still, the evolutionary dimension of AD pathomechanism remains difficult to prove and has not been established so far. To analyze the evolutionary age and dynamics of AD-associated-genes, we established the AD-associated genome-wide RNA-profile comprising both protein-coding and non-protein-coding transcripts. We than applied a systematic analysis on the conservation of splice-sites as a measure of gene-structure based on multiple alignments across vertebrates of homologs of AD-associated-genes. Here, we show that nearly all AD-associated-genes are evolutionarily old and did not originate later in evolution than not-AD-associated-genes. However, the gene-structures of loci, that exhibit AD-associated changes in their expression, evolve faster than the genome at large. While protein-coding-loci exhibit an enhanced rate of small changes in gene structure, non-coding loci show even much larger changes. The accelerated evolution of AD-associated-genes indicates a more rapid functional adaptation of these genes. In particular AD-associated non-coding-genes play an important, as yet largely unexplored, role in AD. This phylogenetic trait indicates that recent adaptive evolution of human brain is causally involved in basic principles of neurodegeneration. It highlights the necessity for a paradigmatic change of our disease-concepts and to reconsider the appropriateness of current animal-models to develop disease-modifying strategies that can be translated to human.

Sowing the Seeds of Discovery: Tau-Propagation Models of Alzheimer's Disease

The propagation of pathological proteins throughout the brain is the primary physiological hallmark of the progression of Alzheimer's Disease (AD). A growing body of evidence indicates that hyperphosphorylated Tau proteins are spread transcellularly between neurons in a prionlike fashion, inducing misfolding and aggregation into neurofibrillary tangles which accumulate along specific connectivity pathways. Earlier transgenic rodent AD models did not capture this disease-relevant spread, and therefore, seeded Tau-propagation models have been developed. Here, mutant human Tau (as isolated protein or packaged into an adeno-associated virus (AAV) viral vector) is stereotaxically injected into select brain regions and its histopathological propagation to downstream neurons quantified. These models offer a faster and more direct mechanism to evaluate genetic components and therapeutic approaches which attenuate Tau spreading in vivo. Recently, these Tau-seeding models have revealed several new targets for AD drug discovery, including nSMase2, SIRT1, p300/CBP, LRP1, and TYROBP, as well as the potential therapeutics based on melatonin and chondroitinase ABC. Importantly, these Tau-propagation rodent models more closely phenocopy the progression of AD in humans and are therefore likely to improve preclinical studies and derisk future moves into clinical trials.

Persistent Neurovascular Unit Dysfunction: Pathophysiological Substrate and Trigger for Late-Onset Neurodegeneration After Traumatic Brain Injury

Traumatic brain injury (TBI) represents one of the major causes of death worldwide and leads to persisting neurological deficits in many of the survivors. One of the most significant long-term sequelae deriving from TBI is neurodegenerative disease, which is a group of incurable diseases that impose a heavy socio-economic burden. However, mechanisms underlying the increased susceptibility of TBI to neurodegenerative disease remain elusive. The neurovascular unit (NVU) is a functional unit composed of neurons, neuroglia, vascular cells, and the basal lamina matrix. The key role of NVU dysfunction in many central nervous system diseases has been revealed. Studies have proved the presence of prolonged structural and functional abnormalities of the NVU after TBI. Moreover, growing evidence suggests impaired NVU function is also implicated in neurodegenerative diseases. Therefore, we propose the Neurovascular Unit Dysfunction (NVUD) Hypothesis, in which the persistent NVU dysfunction is thought to underlie the development of post-TBI neurodegeneration. We deduce NVUD Hypothesis through relational inference and supporting evidence, and suggest continued NVU abnormalities following TBI serve as the pathophysiological substrate and trigger yielding chronic neuroinflammation, proteinopathies and oxidative stress, consequently leading to the progression of neurodegenerative diseases. The NVUD Hypothesis may provide potential treatment and prevention strategies for TBI and late-onset neurodegenerative diseases.

Amyloid-β, tau, and the cholinergic system in Alzheimer's disease: seeking direction in a tangle of clues

The link between histopathological hallmarks of Alzheimer's disease (AD), i.e. amyloid plaques, and neurofibrillary tangles, and AD-associated cognitive impairment, has long been established. However, the introduction of interactions between amyloid-beta (Aβ) as well as hyperphosphorylated tau, and the cholinergic system to the territory of descriptive neuropathology has drastically changed this field by adding the theory of synaptic neurotransmission to the toxic pas de deux in AD. Accumulating data show that a multitarget approach involving all amyloid, tau, and cholinergic hypotheses could better explain the evolution of events happening in AD. Various species of both Aβ and tau could be traced in cholinergic neurons of the basal forebrain system early in the course of the disease. These molecules induce degeneration in the neurons of this system. Reciprocally, aberrant cholinergic system modulation promotes changes in amyloid precursor protein (APP) metabolism and tau phosphorylation, resulting in neurotoxicity, neuroinflammation, and neuronal death. Altogether, these changes may better correlate with the clinical findings and cognitive impairment detected in AD patients. Failure of several of Aβ- and tau-related therapies further highlights the need for special attention to molecules that target all of these mentioned pathologic changes. Another noteworthy fact here is that none of the popular hypotheses of AD such as amyloidopathy or tauopathy seem to be responsible for the changes observed in AD alone. Thus, the main culprit should be sought higher in the stream somewhere in APP metabolism or Wnt signaling in the cholinergic system of the basal forebrain. Future studies should target these pathological events.

A positive allosteric modulator of mGluR5 promotes neuroprotective effects in mouse models of Alzheimer's disease

Alzheimer's Disease (AD) is the most prevalent neurodegenerative disorder. Despite advances in the understanding of its pathophysiology, none of the available therapies prevents disease progression. Excess glutamate plays an important role in excitotoxicity by activating ionotropic receptors. However, the mechanisms modulating neuronal cell survival/death via metabotropic glutamate receptors (mGluRs) are not completely understood. Recent data indicates that CDPPB, a positive allosteric modulator of mGluR5, has neuroprotective effects. Thus, this work aimed to investigate CDPPB treatment effects on amyloid-β (Aβ) induced pathological alterations in vitro and in vivo and in a transgenic mouse model of AD (T41 mice). Aβ induced cell death in primary cultures of hippocampal neurons, which was prevented by CDPPB. Male C57BL/6 mice underwent stereotaxic surgery for unilateral intra-hippocampal Aβ injection, which induced memory deficits, neurodegeneration, neuronal viability reduction and decrease of doublecortin-positive cells, a marker of immature neurons and neuronal proliferation. Treatment with CDPPB for 8 days reversed neurodegeneration and doublecortin-positive cells loss and recovered memory function. Fourteen months old T41 mice presented cognitive deficits, neuronal viability reduction, gliosis and Aβ accumulation. Treatment with CDPPB for 28 days increased neuronal viability (32.2% increase in NeuN⁺ cells) and reduced gliosis in CA1 region (Iba-1⁺ area by 31.3% and GFAP⁺ area by 37.5%) in transgenic animals, without inducing hepatotoxicity. However, it did not reverse cognitive deficit. Despite a four-week treatment did not prevent memory loss in aged transgenic mice, CDPPB is protective against Aβ stimulus. Therefore, this drug represents a potential candidate for further investigations as AD treatment.

Computer-aided identification of protein targets of four polyphenols in Alzheimer's disease (AD) and validation in a mouse AD model

Natural polyphenols are a large class of phytochemicals with neuroprotective effects. Four polyphenolic compounds: hesperidin, icariin, dihydromyricetin and baicalin were selected to evaluate their effects on Alzheimer’s disease (AD). We analyzed by an inverse docking procedure (INVDOCK) the potential protein targets of these polyphenols within the KEGG AD pathway. Consequently, their therapeutic effects were evaluated and compared in a transgenic APP/PS1 mouse model of AD. These polyphenols were docked to several targets, including APP, BACE, PSEN, IDE, CASP, calpain and TNF-α, suggesting potential in vivo activities. Five month old transgenic mice were treated with these polyphenols. Icariin and hesperidin restored behavioral deficits and ameliorated Aβ deposits in both the cortex and hippocampus while baicalin and dihydromyricetin showed no substantial effects. Our findings suggest that hesperidin and icariin could be considered potential therapeutic candidates of human AD.

Amelioration of Alzheimer's disease pathology and cognitive deficits by immunomodulatory agents in animal models of Alzheimer's disease

The most common age-related neurodegenerative disease is Alzheimer’s disease (AD) characterized by aggregated amyloid-β (Aβ) peptides in extracellular plaques and aggregated hyperphosphorylated tau protein in intraneuronal neurofibrillary tangles, together with loss of cholinergic neurons, synaptic alterations, and chronic inflammation within the brain. These lead to progressive impairment of cognitive function. There is evidence of innate immune activation in AD with microgliosis. Classically-activated microglia (M1 state) secrete inflammatory and neurotoxic mediators, and peripheral immune cells are recruited to inflammation sites in the brain. The few drugs approved by the US FDA for the treatment of AD improve symptoms but do not change the course of disease progression and may cause some undesirable effects. Translation of active and passive immunotherapy targeting Aβ in AD animal model trials had limited success in clinical trials. Treatment with immunomodulatory/anti-inflammatory agents early in the disease process, while not preventive, is able to inhibit the inflammatory consequences of both Aβ and tau aggregation. The studies described in this review have identified several agents with immunomodulatory properties that alleviated AD pathology and cognitive impairment in animal models of AD. The majority of the animal studies reviewed had used transgenic models of early-onset AD. More effort needs to be given to creat models of late-onset AD. The effects of a combinational therapy involving two or more of the tested pharmaceutical agents, or one of these agents given in conjunction with one of the cell-based therapies, in an aged animal model of AD would warrant investigation.

Evaluation of Animal Models by Comparison with Human Late-Onset Alzheimer's Disease

Despite many efforts to alleviate the pathological conditions of Alzheimer's disease (AD), effective therapeutic drugs have not been developed, mainly because of the lack of molecular information about AD and animal models. We observed the reciprocal regulation of AD-associated genes (AD genes) and their related functions. Upregulated AD genes were positioned in central regions in the protein-protein interaction network and were involved in inflammation and DNA repair pathways. Downregulated AD genes positioned in the periphery of the network were associated with metabolic pathways. Using these features of AD genes, we found that 5×FAD, amyloid β-injected mice, and rats in the initial phases after bilateral common carotid artery occlusion (BCCAO) exhibited patterns that were most similar to those of AD. In contrast, using differentially expressed genes from animal models, we observed that 3×Tg and animals in late phases of BCCAO were positioned close to AD genes.

Principles for central nervous system inflammation research: A call for a consortium approach

INTRODUCTION

Neuroinflammation is now considered to be of pathophysiologic significance in Alzheimer's disease and other neurodegenerative conditions. Nonetheless, there is no consensus as to what inflammatory mechanisms need to be combated (or facilitated), how therapies for them should be applied, or when they might be efficacious.

METHODS

This article seeks to put forward cornerstone facts about neuroinflammation, with suggestions for future directions.

RESULTS

Multiple scientific points about neuroinflammation still remain unaddressed. The main issue, however, is political. An expert body is needed that can sort through the myriad findings and provide consensus advice to agencies that fund basic and clinical research.

DISCUSSION

Consortium approaches have shown immense value in other Alzheimer's disease research areas and are badly needed in neuroinflammation research. Lacking a consensus, neuroinflammation is just a very large number of isolated articles clamoring for attention.

The CNS in inbred transgenic models of 4-repeat Tauopathy develops consistent tau seeding capacity yet focal and diverse patterns of protein deposition

BACKGROUND

MAPT mutations cause neurodegenerative diseases such as frontotemporal dementia but, strikingly, patients with the same mutation may have different clinical phenotypes.

METHODS

Given heterogeneities observed in a transgenic (Tg) mouse line expressing low levels of human (2 N, 4R) P301L Tau, we backcrossed founder stocks of mice to C57BL/6Tac, 129/SvEvTac and FVB/NJ inbred backgrounds to discern the role of genetic versus environmental effects on disease-related phenotypes.

RESULTS

Three inbred derivatives of a TgTau^P301L founder line had similar quality and steady-state quantity of Tau production, accumulation of abnormally phosphorylated 64-68 kDa Tau species from 90 days of age onwards and neuronal loss in aged Tg mice. Variegation was not seen in the pattern of transgene expression and seeding properties in a fluorescence-based cellular assay indicated a single "strain" of misfolded Tau. However, in other regards, the aged Tg mice were heterogeneous; there was incomplete penetrance for Tau deposition despite maintained transgene expression in aged animals and, for animals with Tau deposits, distinctions were noted even within each subline. Three classes of rostral deposition in the cortex, hippocampus and striatum accounted for 75% of pathology-positive mice yet the mean ages of mice scored as class I, II or III were not significantly different and, hence, did not fit with a predictable progression from one class to another defined by chronological age. Two other patterns of Tau deposition designated as classes IV and V, occurred in caudal structures. Other pathology-positive Tg mice of similar age not falling within classes I-V presented with focal accumulations in additional caudal neuroanatomical areas including the locus coeruleus. Electron microscopy revealed that brains of Classes I, II and IV animals all exhibit straight filaments, but with coiled filaments and occasional twisted filaments apparent in Class I. Most strikingly, Class I, II and IV animals presented with distinct western blot signatures after trypsin digestion of sarkosyl-insoluble Tau.

CONCLUSIONS

Qualitative variations in the neuroanatomy of Tau deposition in genetically constrained slow models of primary Tauopathy establish that non-synchronous, focal events contribute to the pathogenic process. Phenotypic diversity in these models suggests a potential parallel to the phenotypic variation seen in P301L patients.

A Toxic Conformer of Aβ42 with a Turn at 22-23 is a Novel Therapeutic Target for Alzheimer's Disease

Immunotherapy targeting Aβ42 is drawing attention as a possible therapeutic approach for Alzheimer’s disease (AD). Considering the significance of reported oligomerized Aβ42 species, selective targeting of the oligomer will increase the therapeutic efficacy. However, what kinds of oligomers are suitable targets for immunotherapy remains unclear. We previously identified a toxic conformer of Aβ42, which has a turn structure at 22–23 (“toxic turn”), among Aβ42 conformations. This toxic conformer of Aβ42 has been reported to show rapid oligomerization and to exhibit strong neurotoxicity and synaptotoxicity. We recently developed a monoclonal antibody against the toxic conformer (24B3), which demonstrated the increase of the toxic conformer in the cerebrospinal fluid of AD patients, indicating its accumulation in AD patients’ brains. In this study, we evaluated the therapeutic efficacy of 24B3 targeting the toxic conformer in AD model mice. The intraperitoneal administration of 24B3 for 3 months improved cognitive impairment and reduced the toxic conformer levels. Notably, this treatment did not reduce the number of senile plaques. Furthermore, the single intravenous administration of 24B3 suppressed the memory deficit in AD mice. These results suggest that the toxic conformer of Aβ42 with a turn at 22–23 represents one of the promising therapeutic targets.

Health-promoting effects of the citrus flavanone hesperidin

Hesperidin, a member of the flavanone group of flavonoids, can be isolated in large amounts from the rinds of some citrus species. Considering the wide range of pharmacological activities and widespread application of hesperidin, this paper reviews preclinical and clinical trials of hesperidin and its related compounds, including their occurrence, pharmacokinetics, and some marketed products available. Preclinical studies and clinical trials demonstrated therapeutical effects of hesperidin and its aglycone hesperetin in various diseases, such as neurological disorders, psychiatric disorders, and cardiovascular diseases and others, due to its anti-inflammatory, antioxidant, lipid-lowering, and insulin-sensitizing properties.

The Amyloid Cascade Hypothesis in Alzheimer's Disease: It's Time to Change Our Mind

Since its discovery in 1984, the beta amyloid peptide has treaded the boards of neurosciences as the star molecule in Alzheimer's disease pathogenesis. In the last decade, however, this vision has been challenged by evidence-based medicine showing the almost complete failure of clinical trials that experimented anti-amyloid therapies with great hopes. Moreover, data have accumulated which clearly indicate that this small peptide plays a key role in the physiological processes of memory formation. In the present review, we will discuss the different aspects of the amyloid cascade hypothesis, highlighting its pros and cons, and we will analyse the results of the therapeutic approaches attempted to date that should change the direction of Alzheimer's disease research in the future.

Molecular Signaling Mechanisms of Natural and Synthetic Retinoids for Inhibition of Pathogenesis in Alzheimer's Disease

Retinoids, which are vitamin A derivatives, interact through retinoic acid receptors (RARs) and retinoid X receptors (RXRs) and have profound effects on several physiological and pathological processes in the brain. The presence of retinoic acid signaling is extensively detected in the adult central nervous system, including the amygdala, cortex, hypothalamus, hippocampus, and other brain areas. Retinoids are primarily involved in neural patterning, differentiation, and axon outgrowth. Retinoids also play a key role in the preservation of the differentiated state of adult neurons. Impairment in retinoic acid signaling can result in neurodegeneration and progression of Alzheimer's disease (AD). Recent studies demonstrated severe deficiencies in spatial learning and memory in mice during retinoic acid (vitamin A) deprivation indicating its significance in preserving memory function. Defective cholinergic neurotransmission plays an important role in cognitive deficits in AD. All-trans retinoic acid is known to enhance the expression and activity of choline acetyltransferase in neuronal cell lines. Activation of RAR and RXR is also known to impede the pathogenesis of AD in mice by inhibiting accumulation of amyloids. In addition, retinoids have been shown to inhibit the expression of chemokines and pro-inflammatory cytokines in microglia and astrocytes, which are activated in AD. In this review article, we have described the chemistry and molecular signaling mechanisms of natural and synthetic retinoids and current understandings of their therapeutic potentials in prevention of AD pathology.

Intracerebroventricular Streptozotocin Injections as a Model of Alzheimer's Disease: in Search of a Relevant Mechanism

Streptozotocin (STZ), a glucosamine-nitrosourea compound derived from soil bacteria and originally developed as an anticancer agent, in 1963 has been found to induce diabetes in experimental animals. Since then, systemic application of STZ became the most frequently studied experimental model of insulin-dependent (type 1) diabetes. The compound is selectively toxic toward insulin-producing pancreatic beta cells, which is explained as the result of its cellular uptake by the low-affinity glucose transporter 2 (GLUT2) protein located in their cell membranes. STZ cytotoxicity is mainly due to DNA alkylation which results in cellular necrosis. Besides pancreatic beta cells, STZ applied systemically damages also other organs expressing GLUT2, such as kidney and liver, whereas brain is not affected directly because blood-brain barrier lacks this transporter protein. However, single or double intracerebroventricular (icv) STZ injection(s) chronically decrease cerebral glucose uptake and produce multiple other effects that resemble molecular, pathological, and behavioral features of Alzheimer's disease (AD). Taking into consideration that glucose hypometabolism is an early and persistent sign of AD and that Alzheimer's brains present features of impaired insulin signaling, icv STZ injections are exploited by some investigators as a non-transgenic model of this disease and used for preclinical testing of pharmacological therapies for AD. While it has been assumed that icv STZ produces cerebral glucose hypometabolism and other effects directly through desensitizing brain insulin receptors, the evidence for such mechanism is poor. On the other hand, early data on insulin immunoreactivity showed intense insulin expression in the rodent brain, and the possibility of local production of insulin in the mammalian brain has never been conclusively excluded. Also, there are GLUT2-expressing cells in the brain, in particular in the circumventricular organs and hypothalamus; some of these cells may be involved in glucose sensing. Thus, icv STZ may damage brain glucose insulin producing cells and/or brain glucose sensors. Mechanistic explanation of the mode of action of icv STZ, which is currently lacking, would provide a valuable contribution to the field of animal models of Alzheimer's disease.

tau protein, ischemic injury and vascular dementia

Clinical, neuroimaging and neuropathological studies have confirmed overlap between Alzheimer's disease (AD) and vascular dementia (VaD). Classical neuropathological changes of AD (plaques and tangles) can be present in VaD. We review neuroimaging, biochemical and animal studies to consider the role of tau protein in ischemic injury and VaD pathogenesis. The evidence comes largely from transgenic animal studies that confirm that tau transgenes influence cerebral vasculature. Clinicobiochemical studies in the cerebrospinal fluid (CSF) have, similarly, confirmed alterations in both total and phosphorylated tau protein in VaD. These data suggest that tau protein not only serves as a potential diagnostic tool for differential diagnosis of VaD from other types of dementia, but may also be a therapeutic target in ischemic stroke.

Successful arrest of photoreceptor and vision loss expands the therapeutic window of retinal gene therapy to later stages of disease

Inherited retinal degenerations cause progressive loss of photoreceptor neurons with eventual blindness. Corrective or neuroprotective gene therapies under development could be delivered at a predegeneration stage to prevent the onset of disease, as well as at intermediate-degeneration stages to slow the rate of progression. Most preclinical gene therapy successes to date have been as predegeneration interventions. In many animal models, as well as in human studies, to date, retinal gene therapy administered well after the onset of degeneration was not able to modify the rate of progression even when successfully reversing dysfunction. We evaluated consequences of gene therapy delivered at intermediate stages of disease in a canine model of X-linked retinitis pigmentosa (XLRP) caused by a mutation in the Retinitis Pigmentosa GTPase Regulator (RPGR) gene. Spatiotemporal natural history of disease was defined and therapeutic dose selected based on predegeneration results. Then interventions were timed at earlier and later phases of intermediate-stage disease, and photoreceptor degeneration monitored with noninvasive imaging, electrophysiological function, and visual behavior for more than 2 y. All parameters showed substantial and significant arrest of the progressive time course of disease with treatment, which resulted in long-term improved retinal function and visual behavior compared with control eyes. Histology confirmed that the human RPGR transgene was stably expressed in photoreceptors and associated with improved structural preservation of rods, cones, and ON bipolar cells together with correction of opsin mislocalization. These findings in a clinically relevant large animal model demonstrate the long-term efficacy of RPGR gene augmentation and substantially broaden the therapeutic window for intervention in patients with RPGR-XLRP.

Alzheimer's in 3D culture: challenges and perspectives

Alzheimer's disease (AD) is the most common cause of dementia, and there is currently no cure. The "β-amyloid cascade hypothesis" of AD is the basis of current understanding of AD pathogenesis and drug discovery. However, no AD models have fully validated this hypothesis. We recently developed a human stem cell culture model of AD by cultivating genetically modified human neural stem cells in a three-dimensional (3D) cell culture system. These cells were able to recapitulate key events of AD pathology including β-amyloid plaques and neurofibrillary tangles. In this review, we will discuss the progress and current limitations of AD mouse models and human stem cell models as well as explore the breakthroughs of 3D cell culture systems. We will also share our perspective on the potential of dish models of neurodegenerative diseases for studying pathogenic cascades and therapeutic drug discovery.

Neuroinflammatory signals in Alzheimer disease and APP/PS1 transgenic mice: correlations with plaques, tangles, and oligomeric species

To understand neuroinflammation-related gene regulation during normal aging and in sporadic Alzheimer disease (sAD), we performed functional genomics analysis and analyzed messenger RNA (mRNA) expression by quantitative reverse transcription-polymerase chain reaction of 22 genes involved in neuroinflammation-like responses in the cerebral cortex of wild-type and APP/PS1 transgenic mice. For direct comparisons, mRNA expression of 18 of the same genes was then analyzed in the entorhinal cortex, orbitofrontal cortex, and frontal cortex area 8 of middle-aged human subjects lacking Alzheimer disease-related pathology and in older subjects with sAD pathology covering Stages I-II/0(A), III-IV/A-B, and V-VI/C of Braak and Braak classification. Modifications of cytokine and immune mediator mRNA expression were found with normal aging in wild-type mice and in middle-aged individuals and patients with early stages of sAD-related pathology; these were accompanied by increased protein expression of certain mediators in ramified microglia. In APP/PS1 mice, inflammatory changes coincided with β-amyloid (Aβ) deposition; increased levels of soluble oligomers paralleled the modified mRNA expression of cytokines and mediators in wild-type mice. In patients with sAD, regulation was stage- and region-dependent and not merely acceleration and exacerbation of mRNA regulation with aging. Gene regulation at first stages of AD was not related to hyperphosphorylated tau deposition in neurofibrillary tangles, Aβ plaque burden, concentration of Aβ1-40 (Aβ40) and Aβ1-42 (Aβ42), or fibrillar Aβ linked to membranes but rather to increased levels of soluble oligomers. Thus, species differences and region- and stage-dependent inflammatory responses in sAD, particularly at the initial stages, indicate the need to identify new anti-inflammatory compounds with specific molecular therapeutic targets.

Computational discovery and experimental verification of tyrosine kinase inhibitor pazopanib for the reversal of memory and cognitive deficits in rat model neurodegeneration

Pazopanib, a tyrosine kinase inhibitor marketed for cancer treatment, abrogates the course of neurodegeneration.

Cognition and memory impairment are hallmarks of the pathological cascade of various neurodegenerative disorders. Herein, we developed a novel computational strategy with two-dimensional virtual screening for not only affinity but also specificity. We integrated the two-dimensional virtual screening with ligand screening for 3D shape, electrostatic similarity and local binding site similarity to find existing drugs that may reduce the signs of cognitive deficits. For the first time, we found that pazopanib, a tyrosine kinase inhibitor marketed for cancer treatment, inhibits acetylcholinesterase (AchE) activities at sub-micromolar concentration. We evaluated and compared the effects of intragastrically-administered pazopanib with donepezil, a marketed AchE inhibitor, in cognitive and behavioral assays including the novel object recognition test, Y maze and Morris water maze test. Surprisingly, we found that pazopanib can restore memory loss and cognitive dysfunction to a similar extent as donepezil in a dosage of 15 mg kg^–1, only one fifth of the equivalent clinical dosage for cancer treatment. Furthermore, we demonstrated that pazopanib dramatically enhances the hippocampal Ach levels and increases the expression of the synaptic marker SYP. These findings suggest that pazopanib may become a viable treatment option for memory and cognitive deficits with a good safety profile in humans.

Moving beyond anti-amyloid therapy for the prevention and treatment of Alzheimer's disease

Background

High-profile Phase 3 clinical trials of bapineuzumab and solanezumab, antibodies targeted at amyloid-beta (Aβ) removal, have failed to meet their primary endpoints. Neither drug improves clinical outcomes in patients with late onset AD, joining a long list of unsuccessful attempts to treat AD with anti-amyloid therapies.

Discussion

These therapies are based on the assumption that Aβ accumulation is the primary pathogenic trigger of AD. Current evidence suggests that Aβ may actually accumulate as part of an adaptive response to long-term chronic brain stress stimuli that would make more suitable candidates for therapeutic intervention.

Summary

At this juncture it is no longer unreasonable to suggest that further iterations of anti-Aβ therapies should be halted. Clinicians and researchers should instead direct their attention toward greater understanding of the biological function of Aβ both in healthy and demented brains, as well as the involvement of long-term chronic exposure to stress in the etiology of AD.

How dependent is synaptic plasticity on microglial phenotype?

Microglia are particularly plastic cells which can be shifted from their resting state by numerous factors and adopt distinct phenotypes. The cells are multifunctional, though their main role is probably maintenance of homoeostasis. Resting cells are responsible for surveillance, whereas activation induces the cells to adopt neuroprotective or neurodetrimental roles, which are anti-inflammatory or pro-inflammatory respectively. The evidence indicates that activated cells with a pro-inflammatory phenotype predominate in neurodegenerative diseases and models of neurodegeneration and that this may significantly contribute to the deteriorating neuronal function. This question is considered in this review, in particular in the context of animal models of Alzheimer's disease (AD). This article is part of a Special Issue entitled 'Neuroimmunology and Synaptic Function'.

Alzheimer's disease drug-development pipeline: few candidates, frequent failures

INTRODUCTION

Alzheimer's disease (AD) is increasing in frequency as the global population ages. Five drugs are approved for treatment of AD, including four cholinesterase inhibitors and an N-methyl-D-aspartate (NMDA)-receptor antagonist. We have an urgent need to find new therapies for AD.

METHODS

We examined Clinicaltrials.gov, a public website that records ongoing clinical trials. We examined the decade of 2002 to 2012, to better understand AD-drug development. We reviewed trials by sponsor, sites, drug mechanism of action, duration, number of patients required, and rate of success in terms of advancement from one phase to the next. We also reviewed the current AD therapy pipeline.

RESULTS

During the 2002 to 2012 observation period, 413 AD trials were performed: 124 Phase 1 trials, 206 Phase 2 trials, and 83 Phase 3 trials. Seventy-eight percent were sponsored by pharmaceutical companies. The United States of America (U.S.) remains the single world region with the greatest number of trials; cumulatively, more non-U.S. than U.S. trials are performed. The largest number of registered trials addressed symptomatic agents aimed at improving cognition (36.6%), followed by trials of disease-modifying small molecules (35.1%) and trials of disease-modifying immunotherapies (18%). The mean length of trials increases from Phase 2 to Phase 3, and the number of participants in trials increases between Phase 2 and Phase 3. Trials of disease-modifying agents are larger and longer than those for symptomatic agents. A very high attrition rate was found, with an overall success rate during the 2002 to 2012 period of 0.4% (99.6% failure).

CONCLUSIONS

The Clinicaltrials.gov database demonstrates that relatively few clinical trials are undertaken for AD therapeutics, considering the magnitude of the problem. The success rate for advancing from one phase to another is low, and the number of compounds progressing to regulatory review is among the lowest found in any therapeutic area. The AD drug-development ecosystem requires support.

Neuroinflammation and related neuropathologies in APPSL mice: further value of this in vivo model of Alzheimer's disease

BACKGROUND

Beyond cognitive decline, Alzheimer's disease (AD) is characterized by numerous neuropathological changes in the brain. Although animal models generally do not fully reflect the broad spectrum of disease-specific alterations, the APPSL mouse model is well known to display early plaque formation and to exhibit spatial learning and memory deficits. However, important neuropathological features, such as neuroinflammation and lipid peroxidation, and their progression over age, have not yet been described in this AD mouse model.

METHODS

Hippocampal and neocortical tissues of APPSL mice at different ages were evaluated. One hemisphere from each mouse was examined for micro- and astrogliosis as well as concomitant plaque load. The other hemisphere was evaluated for lipid peroxidation (quantified by a thiobarbituric acid reactive substances (TBARS) assay), changes in Aβ abundance (Aβ38, Aβ40 and Aβ42 analyses), as well as determination of aggregated Aβ content (Amorfix A4 assay). Finally, correlation analyses were performed to illustrate the time-dependent correlation between neuroinflammation and Aβ load (soluble, insoluble, fibrils), or lipid peroxidation, respectively.

RESULTS

As is consistent with previous findings, neuroinflammation starts early and shows strong progression over age in the APPSL mouse model. An analyses of concomitant Aβ load and plaque deposition revealed a similar progression, and high correlations between neuroinflammation markers and soluble or insoluble Aβ or fibrillar amyloid plaque loads were observed. Lipid peroxidation, as measured by TBARS levels, correlates well with neuroinflammation in the neocortex but not the hippocampus. The hippocampal lipid peroxidation correlated strongly with the increase of LOC positive fiber load, whereas neocortical TBARS levels were unrelated to amyloidosis.

CONCLUSIONS

These data illustrate for the first time the progression of major AD related neuropathological features other than plaque load in the APPSL mouse model. Specifically, we demonstrate that microgliosis and astrocytosis are prominent aspects of this AD mouse model. The strong correlation of neuroinflammation with amyloid burden and lipid peroxidation underlines the importance of these pathological factors for the development of AD. The new finding of a different relation of lipid peroxidation in the hippocampus and neocortical regions show that the model might contribute to the understanding of complex pathological mechanisms and their interplay in AD.

The behavioral, pathological and therapeutic features of the senescence-accelerated mouse prone 8 strain as an Alzheimer's disease animal model

Alzheimer's disease (AD) is a widespread and devastating progressive neurodegenerative disease. Disease-modifying treatments remain beyond reach, and the etiology of the disease is uncertain. Animal model are essential for identifying disease mechanisms and developing effective therapeutic strategies. Research on AD is currently being carried out in rodent models. The most common transgenic mouse model mimics familial AD, which accounts for a small percentage of cases. The senescence-accelerated mouse prone 8 (SAMP8) strain is a spontaneous animal model of accelerated aging. Many studies indicate that SAMP8 mice harbor the behavioral and histopathological signatures of AD, namely AD-like cognitive and behavioral alterations, neuropathological phenotypes (neuron and dendrite spine loss, spongiosis, gliosis and cholinergic deficits in the forebrain), β-amyloid deposits resembling senile plaques, and aberrant hyperphosphorylation of Tau-like neurofibrillary tangles. SAMP8 mice are useful in the development of novel therapies, and many pharmacological agents and approaches are effective in SAMP8 mice. SAMP8 mice are considered a robust model for exploring the etiopathogenesis of sporadic AD and a plausible experimental model for developing preventative and therapeutic treatments for late-onset/age-related AD, which accounts for the vast majority of cases.