Natural non-trasgenic animal models for research in Alzheimer's disease

Identification and Analysis of Axolotl Homologs for Proteins Implicated in Human Neurodegenerative Proteinopathies

Neurodegenerative proteinopathies such as Alzheimer's Disease are characterized by abnormal protein aggregation and neurodegeneration. Neuroresilience or regenerative strategies to prevent neurodegeneration, preserve function, or restore lost neurons may have the potential to combat human proteinopathies; however, the adult human brain possesses a limited capacity to replace lost neurons. In contrast, axolotls (Ambystoma mexicanum) show robust brain regeneration. To determine whether axolotls may help identify potential neuroresilience or regenerative strategies in humans, we first interrogated whether axolotls express putative proteins homologous to human proteins associated with neurodegenerative diseases. We compared the homology between human and axolotl proteins implicated in human proteinopathies and found that axolotls encode proteins highly similar to human microtubule-binding protein tau (tau), amyloid precursor protein (APP), and β-secretase 1 (BACE1), which are critically involved in human proteinopathies like Alzheimer's Disease. We then tested monoclonal Tau and BACE1 antibodies previously used in human and rodent neurodegenerative disease studies using immunohistochemistry and western blotting to validate the homology for these proteins. These studies suggest that axolotls may prove useful in studying the role of these proteins in disease within the context of neuroresilience and repair.

Insights on the Use of Transgenic Mice Models in Alzheimer's Disease Research

Alzheimer's disease (AD), the leading cause of dementia, presents a significant global health challenge with no known cure to date. Central to our understanding of AD pathogenesis is the β-amyloid cascade hypothesis, which underlies drug research and discovery efforts. Despite extensive studies, no animal models of AD have completely validated this hypothesis. Effective AD models are essential for accurately replicating key pathological features of the disease, notably the formation of β-amyloid plaques and neurofibrillary tangles. These pathological markers are primarily driven by mutations in the amyloid precursor protein (APP) and presenilin 1 (PS1) genes in familial AD (FAD) and by tau protein mutations for the tangle pathology. Transgenic mice models have been instrumental in AD research, heavily relying on the overexpression of mutated APP genes to simulate disease conditions. However, these models do not entirely replicate the human condition of AD. This review aims to provide a comprehensive evaluation of the historical and ongoing research efforts in AD, particularly through the use of transgenic mice models. It is focused on the benefits gathered from these transgenic mice models in understanding β-amyloid toxicity and the broader biological underpinnings of AD. Additionally, the review critically assesses the application of these models in the preclinical testing of new therapeutic interventions, highlighting the gap between animal models and human clinical realities. This analysis underscores the need for refinement in AD research methodologies to bridge this gap and enhance the translational value of preclinical studies.

Emerging concepts towards a translational framework in Alzheimer's disease

Over the past decades, significant efforts have been made to understand the precise mechanisms underlying the pathogenesis of Alzheimer's disease (AD), the most common cause of dementia. However, clinical trials targeting AD pathological hallmarks have consistently failed. Refinement of AD conceptualization, modeling, and assessment is key to developing successful therapies. Here, we review critical findings and discuss emerging ideas to integrate molecular mechanisms and clinical approaches in AD. We further propose a refined workflow for animal studies incorporating multimodal biomarkers used in clinical studies - delineating critical paths for drug discovery and translation. Addressing unresolved questions with the proposed conceptual and experimental framework may accelerate the development of effective disease-modifying strategies for AD.

Freshwater Cyanobacterial Toxins, Cyanopeptides and Neurodegenerative Diseases

Cyanobacteria produce a wide range of structurally diverse cyanotoxins and bioactive cyanopeptides in freshwater, marine, and terrestrial ecosystems. The health significance of these metabolites, which include genotoxic- and neurotoxic agents, is confirmed by continued associations between the occurrence of animal and human acute toxic events and, in the long term, by associations between cyanobacteria and neurodegenerative diseases. Major mechanisms related to the neurotoxicity of cyanobacteria compounds include (1) blocking of key proteins and channels; (2) inhibition of essential enzymes in mammalian cells such as protein phosphatases and phosphoprotein phosphatases as well as new molecular targets such as toll-like receptors 4 and 8. One of the widely discussed implicated mechanisms includes a misincorporation of cyanobacterial non-proteogenic amino acids. Recent research provides evidence that non-proteinogenic amino acid BMAA produced by cyanobacteria have multiple effects on translation process and bypasses the proof-reading ability of the aminoacyl-tRNA-synthetase. Aberrant proteins generated by non-canonical translation may be a factor in neuronal death and neurodegeneration. We hypothesize that the production of cyanopeptides and non-canonical amino acids is a more general mechanism, leading to mistranslation, affecting protein homeostasis, and targeting mitochondria in eukaryotic cells. It can be evolutionarily ancient and initially developed to control phytoplankton communities during algal blooms. Outcompeting gut symbiotic microorganisms may lead to dysbiosis, increased gut permeability, a shift in blood-brain-barrier functionality, and eventually, mitochondrial dysfunction in high-energy demanding neurons. A better understanding of the interaction between cyanopeptides metabolism and the nervous system will be crucial to target or to prevent neurodegenerative diseases.

T Lymphocytes in the Pathogenesis and Progression of Alzheimer's Disease: Pursuing Direct Neuropathological Evidence

Multiple studies have proposed important roles of T cells in the pathogenesis of Alzheimer's disease. Given the successful application of immune-based therapy for cancer and a variety of diseases, T cell-modifying therapy becomes an attractive way to develop new therapies for Alzheimer's disease and perhaps neurodegenerative diseases in general. However, most of these studies address peripheral T cell responses, while direct pathological evidence documenting T cell infiltration relative to Alzheimer's disease pathological markers (i.e., amyloid plaque and neurofibrillary tangle) is sparse and at best, very preliminary in both human subjects and relevant animal models. Here, we concisely summarize the available pathological data that directly corresponds to T cell infiltration, critically analyze the current knowledge gaps, and thoughtfully propose several key recommendations for future research.

Preclinical Models for Alzheimer's Disease: Past, Present, and Future Approaches

A robust preclinical disease model is a primary requirement to understand the underlying mechanisms, signaling pathways, and drug screening for human diseases. Although various preclinical models are available for several diseases, clinical models for Alzheimer's disease (AD) remain underdeveloped and inaccurate. The pathophysiology of AD mainly includes the presence of amyloid plaques and neurofibrillary tangles (NFT). Furthermore, neuroinflammation and free radical generation also contribute to AD. Currently, there is a wide gap in scientific approaches to preventing AD progression. Most of the available drugs are limited to symptomatic relief and improve deteriorating cognitive functions. To mimic the pathogenesis of human AD, animal models like 3XTg-AD and 5XFAD are the primarily used mice models in AD therapeutics. Animal models for AD include intracerebroventricular-streptozotocin (ICV-STZ), amyloid beta-induced, colchicine-induced, etc., focusing on parameters such as cognitive decline and dementia. Unfortunately, the translational rate of the potential drug candidates in clinical trials is poor due to limitations in imitating human AD pathology in animal models. Therefore, the available preclinical models possess a gap in AD modeling. This paper presents an outline that critically assesses the applicability and limitations of the current approaches in disease modeling for AD. Also, we attempted to provide key suggestions for the best-fit model to evaluate potential therapies, which might improve therapy translation from preclinical studies to patients with AD.

Inflammation context in Alzheimer's disease, a relationship intricate to define

Alzheimer's disease (AD), the most common form of dementia, is characterized by the accumulation of amyloid β (Aβ) and hyperphosphorylated tau protein aggregates. Importantly, Aβ and tau species are able to activate astrocytes and microglia, which release several proinflammatory cytokines, such as tumor necrosis factor α (TNF-α) and interleukin 1β (IL-1β), together with reactive oxygen (ROS) and nitrogen species (RNS), triggering neuroinflammation. However, this inflammatory response has a dual function: it can play a protective role by increasing Aβ degradation and clearance, but it can also contribute to Aβ and tau overproduction and induce neurodegeneration and synaptic loss. Due to the significant role of inflammation in the pathogenesis of AD, several inflammatory mediators have been proposed as AD markers, such as TNF-α, IL-1β, Iba-1, GFAP, NF-κB, TLR2, and MHCII. Importantly, the use of anti-inflammatory drugs such as NSAIDs has emerged as a potential treatment against AD. Moreover, diseases related to systemic or local inflammation, including infections, cerebrovascular accidents, and obesity, have been proposed as risk factors for the development of AD. In the following review, we focus on key inflammatory processes associated with AD pathogenesis.

Characterization of microtubule-associated protein tau isoforms and Alzheimer's disease-like pathology in normal sheep (Ovis aries): relevance to their potential as a model of Alzheimer's disease

Alzheimer's disease is a chronic neurodegenerative disease that accounts for up to 80% of all dementias. Characterised by deteriorations of memory and cognitive function, the key neuropathological features are accumulations of β-amyloid and hyperphosphorylated tau, as 'plaques' and 'tangles', respectively. Despite extensive study, however, the exact mechanism underlying aggregate formation in Alzheimer's disease remains elusive, as does the contribution of these aggregates to disease progression. Importantly, a recent evaluation of current Alzheimer's disease animal models suggested that rodent models are not able to fully recapitulate the pathological intricacies of the disease as it occurs in humans. Therefore, increasing attention is being paid to species that might make good alternatives to rodents for studying the molecular pathology of Alzheimer's disease. The sheep (Ovis aries) is one such species, although to date, there have been few molecular studies relating to Alzheimer's disease in sheep. Here, we investigated the Alzheimer's disease relevant histopathological characteristics of 22 sheep, using anti-β-amyloid (Abcam 12267 and mOC64) and phosphorylation specific anti-tau (AT8 and S396) antibodies. We identified numerous intraneuronal aggregates of both β-amyloid and tau that are consistent with early Alzheimer's disease-like pathology. We confirmed the expression of two 3-repeat (1N3R, 2N3R) and two 4-repeat (1N4R, 2N4R) tau isoforms in the ovine brain, which result from the alternative splicing of two tau exons. Finally, we investigated the phosphorylation status of the serine396 residue in 30 sheep, and report that the phosphorylation of this residue begins in sheep aged as young as 2 years. Together, these data show that sheep exhibit naturally occurring β-amyloid and tau pathologies, that reflect those that occur in the early stages of Alzheimer's disease. This is an important step towards the validation of the sheep as a feasible large animal species in which to model Alzheimer's disease.

Optimized protocol for obtaining and characterizing primary neuron-enriched cultures from embryonic chicken brains

We present here an optimized protocol to obtain primary neuron-enriched cultures from embryonic chicken brains with no need for an animal facility. The protocol details the steps to isolate a neuron-enriched cell fraction from chicken embryos, followed by characterization of the chicken neurons with mass spectrometry proteomics and cell staining. Because of the high homology between chicken and human amyloid precursor protein processing machinery, these chicken neurons can be used as an alternative to rodent models for studying Alzheimer disease.

Toothed Whales Have Black Neurons in the Blue Spot

Simple Summary

Neuromelanin is a dark pigment that is present in several types of neurons of the brain. The role of human neuromelanin is a matter of controversy and, over the past few years, has been attributed to having a dual nature, either in a protective role to shield neurons from toxic compounds, or as a trigger of neuroinflammation. This pigment has been researched mainly in the human brain, but it has also been found in the neurons of monkeys, horses, giraffes, cattle, sheep, goats, dogs, rats, and even in frogs and tadpoles. Even so, neuromelanin in humans and primates presents unique features that are not shown in other animals. A study on the morphology of the locus ceruleus (a key brain structure) of the family Delphinidae highlighted the presence of a large amount of neuromelanin within this brain area. In an attempt to better define the ultrastructure of neuromelanin in toothed whales, two brain specimens of the suborder Odontoceti were investigated. The two toothed whales that were examined presented melanin granules associated with lipid droplets and membranes that bore a striking resemblance with human neuromelanin. Its accumulation takes place over the entire life span, and appears to contain the story of one’s life exposure to several endogenous and environmental metals and/or compounds.

Abstract

Neuromelanin (NM) is a dark polymer pigment that is located mostly in the human substantia nigra, and in the locus ceruleus, referred to as “the blue spot”. NM increases linearly with age, and has been described mainly in the human brain; however, it also occurs in the neurons of monkeys, horses, giraffes, cattle, sheep, goats, dogs, rats, and even in frogs. While in most of these mammals NM shows the histochemical and ultrastructural features typical of lipofuscins, human NM is confined within cytoplasmic organelles that are surrounded by a double membrane, suggesting an autophagic origin. In a study on the morphology of the locus ceruleus of the family Delphinidae, the presence of a variable quantity of NM in the interior of locus ceruleus neurons was observed for the first time; meanwhile, nothing is known about its ultrastructure and composition. Transmission electron microscopy demonstrated in two toothed whales—an Atlantic spotted dolphin (Stenella frontalis; family Delphinidae) and a Blainville’s beaked whale (Mesoplodon densirostris; family Ziphiidae)—the presence of melanin granules associated with lipid droplets and membranes that were very similar to that of human NM. The relationship between NM and neuronal vulnerability must be studied in depth, and cetaceans may offer a new natural-spontaneous comparative model for the study of NM and its implication in neurodegenerative diseases.

Circadian control of heparan sulfate levels times phagocytosis of amyloid beta aggregates

Alzheimer's Disease (AD) is a neuroinflammatory disease characterized partly by the inability to clear, and subsequent build-up, of amyloid-beta (Aβ). AD has a bi-directional relationship with circadian disruption (CD) with sleep disturbances starting years before disease onset. However, the molecular mechanism underlying the relationship of CD and AD has not been elucidated. Myeloid-based phagocytosis, a key component in the metabolism of Aβ, is circadianly-regulated, presenting a potential link between CD and AD. In this work, we revealed that the phagocytosis of Aβ42 undergoes a daily circadian oscillation. We found the circadian timing of global heparan sulfate proteoglycan (HSPG) biosynthesis was the molecular timer for the clock-controlled phagocytosis of Aβ and that both HSPG binding and aggregation may play a role in this oscillation. These data highlight that circadian regulation in immune cells may play a role in the intricate relationship between the circadian clock and AD.

Methodology and Neuromarkers for Cetaceans’ Brains

Cetacean brain sampling may be an arduous task due to the difficulty of collecting and histologically preparing such rare and large specimens. Thus, one of the main challenges of working with cetaceans’ brains is to establish a valid methodology for an optimal manipulation and fixation of the brain tissue, which allows the samples to be viable for neuroanatomical and neuropathological studies. With this in view, we validated a methodology in order to preserve the quality of such large brains (neuroanatomy/neuropathology) and at the same time to obtain fresh brain samples for toxicological, virological, and microbiological analysis (neuropathology). A fixation protocol adapted to brains, of equal or even three times the size of human brains, was studied and tested. Finally, we investigated the usefulness of a panel of 20 antibodies (neuromarkers) associated with the normal structure and function of the brain, pathogens, age-related, and/or functional variations. The sampling protocol and some of the 20 neuromarkers have been thought to explore neurodegenerative diseases in these long-lived animals. To conclude, many of the typical measures used to evaluate neuropathological changes do not tell us if meaningful cellular changes have occurred. Having a wide panel of antibodies and histochemical techniques available allows for delving into the specific behavior of the neuronal population of the brain nuclei and to get a “fingerprint” of their real status.

Neuronal Deposition of Amyloid-β Oligomers and Hyperphosphorylated Tau Is Closely Connected with Cognitive Dysfunction in Aged Dogs

Background

Canine cognitive dysfunction (CCD) is a progressive syndrome recognized in mature to aged dogs with a variety of neuropathological changes similar to human Alzheimer's disease (AD), for which it is thought to be a good natural model. However, the presence of hyperphosphorylated tau protein (p-Tau) in dogs with CCD has only been demonstrated infrequently.

Objective

The aim of the present study was to investigate the presence of p-Tau and amyloid-β oligomer (Aβo) in cerebral cortex and hippocampus of dogs with CCD, with focus on an epitope retrieval protocol to unmask p-Tau.

Methods

Immunohistochemical and immunofluorescence analysis of the cortical and hippocampal regions of five CCD-affected and two nondemented aged dogs using 4G8 anti-Aβp, anti-Aβ_1 - 42 nanobody (PrioAD13) and AT8 anti-p-Tau (Ser202, Thr205) antibody were used to demonstrate the presence of Aβ plaques (Aβp) and Aβ_1 - 42 oligomers and p-Tau deposits, respectively.

Results

The extracellular Aβ senile plaques were of the diffuse type which lack the dense core normally seen in human AD. While p-Tau deposits displayed a widespread pattern and closely resembled the typical human neuropathology, they did not co-localize with the Aβp. Of considerable interest, however, widespread intraneuronal deposition of Aβ_1 - 42 oligomers were exhibited in the frontal cortex and hippocampal region that co-localized with p-Tau.

Conclusion

Taken together, these findings reveal further shared neuropathologic features of AD and CCD, supporting the case that aged dogs afflicted with CCD offer a relevant model for investigating human AD.

Gut Microbiota in Canine Idiopathic Epilepsy: Effects of Disease and Treatment

Simple Summary

There is evidence that supports the existence of a gut-brain axis system through which bi-directional communication occurs between gut bacteria and the brain. Epilepsy is one of the most common neurological disorders in humans and dogs. The role of microbiota in epilepsy remains unknown but it has been suggested that it is a possible influence of gut bacteria in controlling seizures. The aim of this study was to investigate the changes in gut microbiota from dogs with idiopathic epilepsy and the possible effect of antiepileptic drugs on the modulation of the composition of this microbiota. In comparison with control dogs, drug-naive epileptic individuals showed a significantly reduced abundance of GABA and SCFAs-producing bacteria, as well as bacteria associated with reduced risk for brain disease. Moreover, the use of phenobarbital or imepitoin monotherapy during one month in epileptic dogs did not modify the gut microbiota composition. These results open up the possibility of studying probiotic interventions in epilepsy. Considering the phylogenetic and metabolic similarities in intestinal microbiome between humans and dogs, this study contributes to the understanding of epilepsy both in human and veterinary medicine.

Abstract

Epilepsy is one of the most common neurological disorders in humans and dogs. The structure and composition of gut microbiome associated to this disorder has not yet been analyzed in depth but there is evidence that suggests a possible influence of gut bacteria in controlling seizures. The aim of this study was to investigate the changes in gut microbiota associated to canine idiopathic epilepsy (IE) and the possible influence of antiepileptic drugs (AEDs) on the modulation of this microbiota. Faecal microbiota composition was analyzed using sequencing of bacterial 16S rRNA gene in a group of healthy controls (n = 12) and a group of epileptic dogs both before (n = 10) and after a 30-day single treatment with phenobarbital or imepitoin (n = 9). Epileptic dogs showed significantly reduced abundance of GABA (Pseudomonadales, Pseudomonadaceae, Pseudomonas and Pseudomona_graminis) and SCFAs-producing bacteria (Peptococcaceae, Ruminococcaceae and Anaerotruncus) as well as bacteria associated with reduced risk for brain disease (Prevotellaceae) than control dogs. The administration of AEDs during 30 days did not modify the gut microbiota composition. These results are expected to contribute to the understanding of canine idiopathic epilepsy and open up the possibility of studying new therapeutic approaches for this disorder, including probiotic intervention to restore gut microbiota in epileptic individuals.

BMAA, Methylmercury, and Mechanisms of Neurodegeneration in Dolphins: A Natural Model of Toxin Exposure

Dolphins are well-regarded sentinels for toxin exposure and can bioaccumulate a cyanotoxin called β-N-methylamino-l-alanine (BMAA) that has been linked to human neurodegenerative disease. The same dolphins also possessed hallmarks of Alzheimer’s disease (AD), suggesting a possible association between toxin exposure and neuropathology. However, the mechanisms of neurodegeneration in dolphins and the impact cyanotoxins have on these processes are unknown. Here, we evaluate BMAA exposure by investigating transcription signatures using PCR for dolphin genes homologous to those implicated in AD and related dementias: APP, PSEN1, PSEN2, MAPT, GRN, TARDBP, and C9orf72. Immunohistochemistry and Sevier Münger silver staining were used to validate neuropathology. Methylmercury (MeHg), a synergistic neurotoxicant with BMAA, was also measured using PT-GC-AFS. We report that dolphins have up to a three-fold increase in gene transcription related to Aβ⁺ plaques, neurofibrillary tangles, neuritic plaques, and TDP-43⁺ intracytoplasmic inclusions. The upregulation of gene transcription in our dolphin cohort paralleled increasing BMAA concentration. In addition, dolphins with BMAA exposures equivalent to those reported in AD patients displayed up to a 14-fold increase in AD-type neuropathology. MeHg was detected (0.16–0.41 μg/g) and toxicity associated with exposure was also observed in the brain. These results demonstrate that dolphins develop neuropathology associated with AD and exposure to BMAA and MeHg may augment these processes.

Tacrolimus Protects against Age-Associated Microstructural Changes in the Beagle Brain

The overexpression of calcineurin leads to astrocyte hyperactivation, neuronal death, and inflammation, which are characteristics often associated with pathologic aging and Alzheimer's disease. In this study, we tested the hypothesis that tacrolimus, a calcineurin inhibitor, prevents age-associated microstructural atrophy, which we measured using higher-order diffusion MRI, in the middle-aged beagle brain (n = 30, male and female). We find that tacrolimus reduces hippocampal (p = 0.001) and parahippocampal (p = 0.002) neurite density index, as well as protects against an age-associated increase in the parahippocampal (p = 0.007) orientation dispersion index. Tacrolimus also protects against an age-related decrease in fractional anisotropy in the prefrontal cortex (p < 0.0001). We also show that these microstructural alterations precede cognitive decline and gross atrophy. These results support the idea that calcineurin inhibitors may have the potential to prevent aging-related pathology if administered at middle age.SIGNIFICANCE STATEMENT Hyperactive calcineurin signaling causes neuroinflammation and other neurobiological changes often associated with pathologic aging and Alzheimer's disease (AD). Controlling the expression of calcineurin before gross cognitive deficits are observable might serve as a promising avenue for preventing AD pathology. In this study, we show that the administration of the calcineurin inhibitor, tacrolimus, over 1 year prevents age- and AD-associated microstructural changes in the hippocampus, parahippocampal cortex, and prefrontal cortex of the middle-aged beagle brain, with no noticeable adverse effects. Tacrolimus is already approved by the Food and Drug Administration for use in humans to prevent solid organ transplant rejection, and our results bolster the promise of this drug to prevent AD and aging-related pathology.

Genetic Insights into Alzheimer's Disease

Alzheimer's disease (AD) is a pervasive, relentlessly progressive neurodegenerative disorder that includes both hereditary and sporadic forms linked by common underlying neuropathologic changes and neuropsychological manifestations. While a clinical diagnosis is often made on the basis of initial memory dysfunction that progresses to involve multiple cognitive domains, definitive diagnosis requires autopsy examination of the brain to identify amyloid plaques and neurofibrillary degeneration. Over the past 100 years, there has been remarkable progress in our understanding of the underlying pathophysiologic processes, pathologic changes, and clinical phenotypes of AD, largely because genetic pathways that include but expand beyond amyloid processing have been uncovered. This review discusses the current state of understanding of the genetics of AD with a focus on how these advances are both shaping our understanding of the disease and informing novel avenues and approaches for development of potential therapeutic targets.

Amyloid-beta peptide and phosphorylated tau in the frontopolar cerebral cortex and in the cerebellum of toothed whales: aging versus hypoxia

Hypoxia could be a possible risk factor for neurodegenerative alterations in cetaceans' brain. Among toothed whales, the beaked whales are particularly cryptic and routinely dive deeper than 1000 m for about 1 h in order to hunt squids and fishes. Samples of frontal cerebral and cerebellar cortex were collected from nine animals, representing six different species of the suborder Odontoceti. Immunohistochemical analysis employed anti-β-amyloid (Aβ) and anti-neurofibrillary tangle (NFT) antibodies. Six of nine (67%) animals showed positive immunolabeling for Aβ and/or NFT. The most striking findings were intranuclear Aβ immunopositivity in cerebral cortical neurons and NFT immunopositivity in cerebellar Purkinje neurons with granulovacuolar degeneration. Aβ plaques were also observed in one elderly animal. Herein, we present immunohistopathological findings classic of Alzheimer's and other neurodegenerative diseases in humans. Our findings could be linked to hypoxic phenomena, as they were more extensive in beaked whales. Despite their adaptations, cetaceans could be vulnerable to sustained and repetitive brain hypoxia.

A microfiber scaffold-based 3D in vitro human neuronal culture model of Alzheimer's disease

Increasing evidence indicates superiority of three-dimensional (3D) in vitro cell culture systems over conventional two-dimensional (2D) monolayer cultures in mimicking native in vivo microenvironments. Tissue-engineered 3D culture models combined with stem cell technologies have advanced Alzheimer's disease (AD) pathogenesis studies. However, existing 3D neuronal models of AD overexpress mutant genes or have heterogeneities in composition, biological properties and cell differentiation stages. Here, we encapsulate patient induced pluripotent stem cell (iPSC) derived neural progenitor cells (NPC) in poly(lactic-co-glycolic acid) (PLGA) microtopographic scaffolds fabricated via wet electrospinning to develop a novel 3D culture model of AD. First, we enhanced cellular infiltration and distribution inside the scaffold by optimizing various process parameters such as fiber diameter, pore size, porosity and hydrophilicity. Next, we compared key neural stem cell features including viability, proliferation and differentiation in 3D culture with 2D monolayer controls. The 3D microfibrous substrate reduces cell proliferation and significantly accelerates neuronal differentiation within seven days of culture. Furthermore, 3D culture spontaneously enhanced pathogenic amyloid-beta 42 (Aβ42) and phospho-tau levels in differentiated neurons carrying familial AD (FAD) mutations, compared with age-matched healthy controls. Overall, our tunable scaffold-based 3D neuronal culture platform serves as a suitable in vitro model that robustly recapitulates and accelerates the pathogenic characteristics of FAD-iPSC derived neurons.

Microglia in Alzheimer Disease: Well-Known Targets and New Opportunities

Microglia are the resident macrophages of the central nervous system. They play key roles in brain development, and physiology during life and aging. Equipped with a variety of molecular sensors and through the various functions they can fulfill, they are critically involved in maintaining the brain’s homeostasis. In Alzheimer disease (AD), microglia reaction was initially thought to be incidental and triggered by amyloid deposits and dystrophic neurites. However, recent genome-wide association studies have established that the majority of AD risk loci are found in or near genes that are highly and sometimes uniquely expressed in microglia. This leads to the concept of microglia being critically involved in the early steps of the disease and identified them as important potential therapeutic targets. Whether microglia reaction is beneficial, detrimental or both to AD progression is still unclear and the subject of intense debate. In this review, we are presenting a state-of-knowledge report intended to highlight the variety of microglial functions and pathways shown to be critically involved in AD progression. We first address both the acquisition of new functions and the alteration of their homeostatic roles by reactive microglia. Second, we propose a summary of new important parameters currently emerging in the field that need to be considered to identify relevant microglial targets. Finally, we discuss the many obstacles in designing efficient therapeutic strategies for AD and present innovative technologies that may foster our understanding of microglia roles in the pathology. Ultimately, this work aims to fly over various microglial functions to make a general and reliable report of the current knowledge regarding microglia’s involvement in AD and of the new research opportunities in the field.

A cross-species approach to disorders affecting brain and behaviour

Structural and functional elements of biological systems are highly conserved across vertebrates. Many neurological and psychiatric conditions affect both humans and animals. A cross-species approach to the study of brain and behaviour can advance our understanding of human disorders via the identification of unrecognized natural models of spontaneous disorders, thus revealing novel factors that increase vulnerability or resilience, and via the assessment of potential therapies. Moreover, diagnostic and therapeutic advances in human neurology and psychiatry can often be adapted for veterinary patients. However, clinical and research collaborations between physicians and veterinarians remain limited, leaving this wealth of comparative information largely untapped. Here, we review pain, cognitive decline syndromes, epilepsy, anxiety and compulsions, autoimmune and infectious encephalitides and mismatch disorders across a range of animal species, looking for novel insights with translational potential. This comparative perspective can help generate novel hypotheses, expand and improve clinical trials and identify natural animal models of disease resistance and vulnerability.

Functional genomics applications and therapeutic implications in sarcopenia

The human genome contains around 20,000-25,000 genes coding for 30,000 proteins. Some proteins and genes represent therapeutic targets for human diseases. RNA and protein expression profiling tools allow the study of the molecular basis of aging and drug discovery validation. Throughout the life, there is an age-related and disease-related muscle decline. Sarcopenia is defined as a loss of muscle mass and a decrease in functional properties such as muscle strength and physical performance. Yet, there is still no consensus on the evaluation methods of sarcopenia prognosis. The main challenge of this complex biological phenomena is its multifactorial etiology. Thus, functional genomics methods attempt to shape the related scientific approaches via an innovative in-depth view on sarcopenia. Gene and drug high throughput screening combined with functional genomics allow the generation and the interpretation of a large amount of data related to sarcopenia and therapeutic progress. This review focuses on the application of selected functional genomics techniques such as RNA interference, RNA silencing, proteomics, transgenic mice, metabolomics, genomics, and epigenomics to better understand sarcopenia mechanisms.

Canine Cognitive Dysfunction and Alzheimer's Disease - Two Facets of the Same Disease?

Neurodegenerative diseases present a major and increasing burden in the societies worldwide. With aging populations, the prevalence of neurodegenerative diseases is increasing, yet there are no effective cures and very few treatment options are available. Alzheimer's disease is one of the most prevalent neurodegenerative conditions and although the pathology is well studied, the pathogenesis of this debilitating illness is still poorly understood. This is, among other reasons, also due to the lack of good animal models as laboratory rodents do not develop spontaneous neurodegenerative diseases and human Alzheimer's disease is only partially mimicked by transgenic rodent models. On the other hand, older dogs commonly develop canine cognitive dysfunction, a disease that is similar to Alzheimer's disease in many aspects. Dogs show cognitive deficits that could be paralleled to human symptoms such as disorientation, memory loss, changes in behavior, and in their brains, beta amyloid plaques are commonly detected both in extracellular space as senile plaques and around the blood vessels. Dogs could be therefore potentially a very good model for studying pathological process and novel treatment options for Alzheimer's disease. In the present article, we will review the current knowledge about the pathogenesis of canine cognitive dysfunction, its similarities and dissimilarities with Alzheimer's disease, and developments of novel treatments for these two diseases with a focus on canine cognitive dysfunction.

Cyanobacterial neurotoxin BMAA and brain pathology in stranded dolphins

Dolphin stranding events occur frequently in Florida and Massachusetts. Dolphins are an excellent sentinel species for toxin exposures in the marine environment. In this report we examine whether cyanobacterial neurotoxin, β-methylamino-L-alanine (BMAA), is present in stranded dolphins. BMAA has been shown to bioaccumulate in the marine food web, including in the muscles and fins of sharks. Dietary exposure to BMAA is associated with the occurrence of neurofibrillary tangles and β-amyloid plaques in nonhuman primates. The findings of protein-bound BMAA in brain tissues from patients with Alzheimer’s disease has advanced the hypothesis that BMAA may be linked to dementia. Since dolphins are apex predators and consume prey containing high amounts of BMAA, we examined necropsy specimens to determine if dietary and environmental exposures may result in the accumulation of BMAA in the brains of dolphins. To test this hypothesis, we measured BMAA in a series of brains collected from dolphins stranded in Florida and Massachusetts using two orthogonal analytical methods: 1) high performance liquid chromatography, and 2) ultra-performance liquid chromatography with tandem mass spectrometry. We detected high levels of BMAA (20–748 μg/g) in the brains of 13 of 14 dolphins. To correlate neuropathological changes with toxin exposure, gross and microscopic examinations were performed on cortical brain regions responsible for acoustico-motor navigation. We observed increased numbers of β-amyloid⁺ plaques and dystrophic neurites in the auditory cortex compared to the visual cortex and brainstem. The presence of BMAA and neuropathological changes in the stranded dolphin brain may help to further our understanding of cyanotoxin exposure and its potential impact on human health.

Does the Genetic Feature of the Chinese Tree Shrew (Tupaia belangeri chinensis) Support Its Potential as a Viable Model for Alzheimer's Disease Research?

Alzheimer's disease (AD) is a neurodegenerative disease with increasing incidence across the world and no cure at the present time. An ideal animal model would facilitate the understanding of the pathogenesis of AD and discovery of potential therapeutic targets. The Chinese tree shrew (Tupaia belangeri chinensis) has a closer genetic affinity to primates relative to rodents, and can attain ages of 8 years or older, which represents another advantage for the study of neurodegenerative diseases such as AD compared to primates. Here, we analyzed 131 AD-related genes in the Chinese tree shrew brain tissues based on protein sequence identity, positive selection, mRNA, and protein expression by comparing with those of human, rhesus monkey, and mouse. In particular, we focused on the Aβ and neurofibrillary tangles formation pathways, which are crucial to AD pathogenesis. The Chinese tree shrew had a generally higher sequence identity with human than that of mouse versus human for the AD pathway genes. There was no apparent selection on the tree shrew lineage for the AD-related genes. Moreover, expression pattern of the Aβ and neurofibrillary tangle formation pathway genes in tree shrew brain tissues resembled that of human brain tissues, with a similar aging-dependent effect. Our results provided an essential genetic basis for future AD research using the tree shrew as a viable model.

Modelling Alzheimer's disease: Insights from in vivo to in vitro three-dimensional culture platforms

Alzheimer's disease (AD) is the most common form of dementia and is characterized by progressive memory loss, impairment of other cognitive functions, and inability to perform activities of daily life. The key to understanding AD aetiology lies in the development of effective disease models, which should ideally recapitulate all aspects pertaining to the disease. A plethora of techniques including in vivo, in vitro, and in silico platforms have been utilized in developing disease models of AD over the years. Each of these approaches has revealed certain essential characteristics of AD; however, none have managed to fully mimic the pathological hallmarks observed in the AD human brain. In this review, we will provide details into the genesis, evolution, and significance of the principal methods currently employed in modelling AD, the advantages and limitations faced in their application, including the headways made by each approach. This review will focus primarily on two-dimensional and three-dimensional in vitro modelling of AD, which during the last few years has made significant breakthroughs in the areas of AD pathology and therapeutic screening. In addition, a glimpse into state-of-the-art neural tissue engineering techniques incorporating biomaterials and microfluidics technologies is provided, which could pave the way for the development of more accurate and comprehensive AD models in the future.

Lack of human-like extracellular sortilin neuropathology in transgenic Alzheimer's disease model mice and macaques

BACKGROUND

Alzheimer's disease (AD) is a devastating neurodegenerative disorder bearing multiple pathological hallmarks suggestive of complex cellular/molecular interplay during pathogenesis. Transgenic mice and nonhuman primates are used as disease models for mechanistic and translational research into AD; the extent to which these animal models recapitulate AD-type neuropathology is an issue of importance. Putative C-terminal fragments from sortilin, a member of the vacuolar protein sorting 10 protein (Vps10p) family, have recently been shown to deposit in the neuritic β-amyloid (Aβ) plaques in the human brain.

METHODS

We set out to explore if extracellular sortilin neuropathology exists in AD-related transgenic mice and nonhuman primates. Brains from different transgenic strains and ages developed overt cerebral Aβ deposition, including the β-amyloid precursor protein and presenilin 1 double-transgenic (APP/PS1) mice at ~ 14 months of age, the five familial Alzheimer's disease mutations transgenic (5×FAD) mice at ~ 8 months, the triple-transgenic Alzheimer's disease (3×Tg-AD) mice at ~ 22 months, and aged monkeys (Macaca mulatta and Macaca fascicularis) were examined. Brain samples from young transgenic mice, middle-aged/aged monkeys, and AD humans were used as negative and positive pathological controls.

RESULTS

The C-terminal sortilin antibody, which labeled senile plaques in the AD human cerebral sections, did not display extracellular immunolabeling in the transgenic mouse or aged monkey brain sections with Aβ deposition. In Western blot analysis, sortilin fragments ~ 15 kDa were not detectable in transgenic mouse cortical lysates, but they occurred in control AD lysates.

CONCLUSIONS

In reference to their human brain counterparts, neuritic plaques seen in transgenic AD model mouse brains represent an incomplete form of this AD pathological hallmark. The species difference in neuritic plaque constituents also indicates more complex secondary proteopathies in the human brain relative to rodents and nonhuman primates during aging and in AD.

Locus coeruleus complex of the family Delphinidae

The locus coeruleus (LC) is the largest catecholaminergic nucleus and extensively projects to widespread areas of the brain and spinal cord. The LC is the largest source of noradrenaline in the brain. To date, the only examined Delphinidae species for the LC has been a bottlenose dolphin (Tursiops truncatus). In our experimental series including different Delphinidae species, the LC was composed of five subdivisions: A6d, A6v, A7, A5, and A4. The examined animals had the A4 subdivision, which had not been previously described in the only Delphinidae in which this nucleus was investigated. Moreover, the neurons had a large amount of neuromelanin in the interior of their perikarya, making this nucleus highly similar to that of humans and non-human primates. This report also presents the first description of neuromelanin in the cetaceans’ LC complex, as well as in the cetaceans’ brain.

Outstanding Phenotypic Differences in the Profile of Amyloid-β between Tg2576 and APPswe/PS1dE9 Transgenic Mouse Models of Alzheimer's Disease

APPswe/PS1dE9 and Tg2576 are very common transgenic mouse models of Alzheimer’s disease (AD), used in many laboratories as tools to research the mechanistic process leading to the disease. In order to augment our knowledge about the amyloid-β (Aβ) isoforms present in both transgenic mouse models, we have developed two chromatographic methods, one acidic and the other basic, for the characterization of the Aβ species produced in the brains of the two transgenic mouse models. After immunoprecipitation and micro-liquid chromatography-electrospray ionization mass spectrometry/mass spectrometry, 10 species of Aβ, surprisingly all of human origin, were detected in the brain of Tg2576 mouse, whereas 39 species, of both murine and human origin, were detected in the brain of the APP/PS1 mouse. To the best of our knowledge, this is the first study showing the identification of such a high number of Aβ species in the brain of the APP/PS1 transgenic mouse, whereas, in contrast, a much lower number of Aβ species were identified in the Tg2576 mouse. Therefore, this study brings to light a relevant phenotypic difference between these two popular mice models of AD.

Differential transgene expression patterns in Alzheimer mouse models revealed by novel human amyloid precursor protein-specific antibodies

Alzheimer's disease (AD) is histopathologically characterized by neurodegeneration, the formation of intracellular neurofibrillary tangles and extracellular Aβ deposits that derive from proteolytic processing of the amyloid precursor protein (APP). As rodents do not normally develop Aβ pathology, various transgenic animal models of AD were designed to overexpress human APP with mutations favouring its amyloidogenic processing. However, these mouse models display tremendous differences in the spatial and temporal appearance of Aβ deposits, synaptic dysfunction, neurodegeneration and the manifestation of learning deficits which may be caused by age-related and brain region-specific differences in APP transgene levels. Consequentially, a comparative temporal and regional analysis of the pathological effects of Aβ in mouse brains is difficult complicating the validation of therapeutic AD treatment strategies in different mouse models. To date, no antibodies are available that properly discriminate endogenous rodent and transgenic human APP in brains of APP-transgenic animals. Here, we developed and characterized rat monoclonal antibodies by immunohistochemistry and Western blot that detect human but not murine APP in brains of three APP-transgenic mouse and one APP-transgenic rat model. We observed remarkable differences in expression levels and brain region-specific expression of human APP among the investigated transgenic mouse lines. This may explain the differences between APP-transgenic models mentioned above. Furthermore, we provide compelling evidence that our new antibodies specifically detect endogenous human APP in immunocytochemistry, FACS and immunoprecipitation. Hence, we propose these antibodies as standard tool for monitoring expression of endogenous or transfected APP in human cells and APP expression in transgenic animals.

A Review of Cognitive Abilities in Dogs, 1911 Through 2016

In this review, we pose and respond to three questions concerning canine cognition: How has the history of this field influenced what we currently know about dog cognition? How confident should we be about what we know? Finally, what should we find out next? We begin by presenting two perspectives on canine cognition. We then survey the existing literature by conducting a quantitative summary of over 100 years of empirical work, focusing on power and replicability. Last, we lament the dearth of individual-differences studies in dog cognition (only three since 1911). We claim that a test of dog IQ with good psychometric properties will benefit basic science on dog and human health (including aging and dementia research). As a complement to an existing rich program of ethological investigation, we argue that individual-differences work on dogs should be a research priority.

Opportunities and challenges in developing relevant animal models for Alzheimer's disease

A major impediment to the development of safe and effective therapeutics in Alzheimer's disease (AD) lies in difficulties in translating research findings across species: therapies that work in rodents often do not translate to humans. A route to bridge the gap between promising rodent research and the human clinical condition consists in using non-human primates (NHPs), which are phylogenetically much closer to humans. In this article, we discuss the importance of investigating disease mechanisms from cell culture, through different animal models of disease. We highlight that developing a viable, validated NHP AD model will likely be a key step toward understanding AD-relevant pathogenic mechanisms and for developing therapies that will effectively translate to the human disease condition.

Overview of Alzheimer's Disease and Some Therapeutic Approaches Targeting Aβ by Using Several Synthetic and Herbal Compounds

Alzheimer's disease (AD) is a complex age-related neurodegenerative disease. In this review, we carefully detail amyloid-β metabolism and its role in AD. We also consider the various genetic animal models used to evaluate therapeutics. Finally, we consider the role of synthetic and plant-based compounds in therapeutics.

Detection and Quantification of β-Amyloid, Pyroglutamyl Aβ, and Tau in Aged Canines

Canine cognitive dysfunction syndrome is an age-associated disorder that resembles many aspects of human Alzheimer disease. The characterization of canine cognitive dysfunction syndrome has been restricted to selected laboratory dogs and mongrels, thereby limiting our knowledge of potential breed-related and age-related differences. We examined the brains of 24 dogs from various breeds. The frontal cortex, hippocampus, and entorhinal cortex were investigated. Deposits of β-amyloid (Aβ) and tau were analyzed phenotypically and quantified stereologically. In all dogs aged 10 years or older, plaques containing pyroglutamyl Aβ and Aβ8-17 were detected. Within the ventral hippocampus, significantly more pyroglutamyl Aβ plaques were deposited in small and medium dogs than in large dogs. Hyperphosphorylated tau with formation of neurofibrillary tangles was observed in 3 animals aged 13 to 15 years. This study provides the first investigation of pyroglutamyl Aβ in comparison with total Aβ (as shown by Aβ8-17 immunoreactivity) in dogs of different breeds, sizes, and ages. Our results indicate that canine cognitive dysfunction syndrome is relatively common among aged canines, thereby emphasizing the relevance of such populations to translational Alzheimer disease research.

Computational Prediction of Alzheimer's and Parkinson's Disease MicroRNAs in Domestic Animals

As the most common neurodegenerative diseases, Alzheimer’s disease (AD) and Parkinson’s disease (PD) are two of the main health concerns for the elderly population. Recently, microRNAs (miRNAs) have been used as biomarkers of infectious, genetic, and metabolic diseases in humans but they have not been well studied in domestic animals. Here we describe a computational biology study in which human AD- and PD-associated miRNAs (ADM and PDM) were utilized to predict orthologous miRNAs in the following domestic animal species: dog, cow, pig, horse, and chicken. In this study, a total of 121 and 70 published human ADM and PDM were identified, respectively. Thirty-seven miRNAs were co-regulated in AD and PD. We identified a total of 105 unrepeated human ADM and PDM that had at least one 100% identical animal homolog, among which 81 and 54 showed 100% sequence identity with 241 and 161 domestic animal miRNAs, respectively. Over 20% of the total mature horse miRNAs (92) showed perfect matches to AD/PD-associated miRNAs. Pigs, dogs, and cows have similar numbers of AD/PD-associated miRNAs (63, 62, and 59). Chickens had the least number of perfect matches (34). Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analyses suggested that humans and dogs are relatively similar in the functional pathways of the five selected highly conserved miRNAs. Taken together, our study provides the first evidence for better understanding the miRNA-AD/PD associations in domestic animals, and provides guidance to generate domestic animal models of AD/PD to replace the current rodent models.

Anti-amyloid Aggregation Activity of Natural Compounds: Implications for Alzheimer's Drug Discovery

Several plant-derived natural compounds are known to exhibit anti-amyloid aggregation activity which makes them attractive as potential therapies to treat Alzheimer's disease. The mechanisms of their anti-amyloid activity are not well known. In this regard, many natural compounds are known to exhibit direct binding to various amyloid species including oligomers and fibrils, which in turn can lead to conformational change in the beta-sheet assembly to form nontoxic aggregates. This review discusses the mechanism of anti-amyloid activity of 16 natural compounds and gives structural details on their direct binding interactions with amyloid aggregates. Our computational investigations show that the physicochemical properties of natural products do fit Lipinski's criteria and that catechol and catechol-type moieties present in natural compounds act as lysine site-specific inhibitors of amyloid aggregation. Based on these observations, we propose a structural template to design novel small molecules containing site-specific ring scaffolds, planar aromatic and nonaromatic linkers with suitably substituted hydrogen bond acceptors and donors. These studies will have significant implications in the design and development of novel amyloid aggregation inhibitors with superior metabolic stability and blood-brain barrier penetration as potential agents to treat Alzheimer's disease.

Accelerating Alzheimer's research through 'natural' animal models

PURPOSE OF REVIEW

Alzheimer's disease is a complex multifactorial age-related neurodegenerative disorder. Current transgenic animal models do not fully recapitulate human Alzheimer's disease at the molecular, cellular and behavioural levels. This review aims to address the clinical relevance of using 'physiologically' aged rats, dogs and Octodon degus, as more representative 'natural' ecologically valid models to elucidate mechanistic aspects of Alzheimer's disease, and for the development of therapeutic agents to attenuate age-related cognitive decline.

RECENT FINDINGS

Aged rats, dogs and O. degus decline cognitively and ultimately develop Alzheimer's disease-like symptoms in response to the natural ageing process. Aged rats provide a tractable and popular model to examine the neurobiological basis underlying cognitive decline with age, but they do not develop Alzheimer's disease pathology. Progressive accumulation of abnormal amyloid-beta in extracellular plaques and surrounding cerebral vasculature is a common feature in human Alzheimer's disease, aged canine model and most nonhuman primates. Interestingly, the O. degus develops amyloid-beta deposits, neurofibrillary tangles containing hyperphosphorylated tau protein, altered cholinergic transmission and cognitive deficits analogous to those observed in Alzheimer's disease. Natural animal models better represent the full pathophysiology of Alzheimer's disease and are not only a viable alternative to transgenic models, but also are arguably the preferable model.

SUMMARY

'Natural' models are useful to elucidate the neurobiological basis of Alzheimer's disease and develop effective therapeutic strategies that can be translated into human clinical trials.

Quantitative expression analysis of APP pathway and tau phosphorylation-related genes in the ICV STZ-induced non-human primate model of sporadic Alzheimer's disease

The accumulation and aggregation of misfolded proteins in the brain, such as amyloid-β (Aβ) and hyperphosphorylated tau, is a neuropathological hallmark of Alzheimer's disease (AD). Previously, we developed and validated a novel non-human primate model for sporadic AD (sAD) research using intracerebroventricular administration of streptozotocin (icv STZ). To date, no characterization of AD-related genes in different brain regions has been performed. Therefore, in the current study, the expression of seven amyloid precursor protein (APP) pathway-related and five tau phosphorylation-related genes was investigated by quantitative real-time PCR experiments, using two matched-pair brain samples from control and icv STZ-treated cynomolgus monkeys. The genes showed similar expression patterns within the control and icv STZ-treated groups; however, marked differences in gene expression patterns were observed between the control and icv STZ-treated groups. Remarkably, other than β-secretase (BACE1) and cyclin-dependent kinase 5 (CDK5), all the genes tested showed similar expression patterns in AD models compared to controls, with increased levels in the precuneus and occipital cortex. However, significant changes in gene expression patterns were not detected in the frontal cortex, hippocampus, or posterior cingulate. Based on these results, we conclude that APP may be cleaved via the general metabolic mechanisms of increased α- and γ-secretase levels, and that hyperphosphorylation of tau could be mediated by elevated levels of tau protein kinase, specifically in the precuneus and occipital cortex.

Lost after translation: missorting of Tau protein and consequences for Alzheimer disease

Tau is a microtubule-associated-protein that is sorted into neuronal axons in physiological conditions. In Alzheimer disease (AD) and other tauopathies, Tau sorting mechanisms fail and Tau becomes missorted into the somatodendritic compartment. In AD, aberrant amyloid-β (Aβ) production might trigger Tau missorting. The physiological axonal sorting of Tau depends on the developmental stage of the neuron, the phosphorylation state of Tau and the microtubule cytoskeleton. Disease-associated missorting of Tau is connected to increased phosphorylation and aggregation of Tau, and impaired microtubule interactions. Disease-causing mechanisms involve impaired transport, aberrant kinase activation, non-physiological interactions of Tau, and prion-like spreading. In this review we focus on the physiological and pathological (mis)sorting of Tau, the underlying mechanisms, and effects in disease.

Comparison of arylalkylamine N-acetyltransferase and melatonin receptor type 1B immunoreactivity between young adult and aged canine spinal cord

Melatonin affects diverse physiological functions through its receptor and plays an important role in the central nervous system. In the present study, we compared immunoreactivity patterns of arylalkylamine N-acetyltransferase (AANAT), an enzyme essential for melatonin synthesis, and melatonin receptor type 1B (MT2) in the spinal cord of young adult (2~3 years) and aged (10~12 years) beagle dogs using immunohistochemistry and Western blotting. AANAT-specific immunoreactivity was observed in the nuclei of spinal neurons, and was significantly increased in aged dog spinal neurons compared to young adult spinal neurons. MT2-specific immunoreactivity was found in the cytoplasm of spinal neurons, and was predominantly increased in the margin of the neuron cytoplasm in aged spinal cord compared to that in the young adult dogs. These increased levels of AANAT and MT2 immunoreactivity in aged spinal cord might be a feature of normal aging and associated with a feedback mechanism that compensates for decreased production of melatonin during aging.

A canine model of Alzheimer's disease generated by overexpressing a mutated human amyloid precursor protein

Canines are considered the most authentic model for studying multifactorial human diseases, as these animals typically share a common environment with man. Somatic cell nuclear transfer (SCNT) technology along with genetic engineering of nuclear donor cells provides a unique opportunity for examining human diseases using transgenic canines. In the present study, we generated transgenic canines that overexpressed the human amyloid precursor protein (APP) gene containing well-characterized familial Alzheimer's disease (AD) mutations. We successfully obtained five out of six live puppies by SCNT. This was confirmed by observing the expression of green fluorescence protein in the body as a visual transgenic marker and the overexpression of the mutated APP gene in the brain. The transgenic canines developed AD-like symptoms, such as enlarged ventricles, an atrophied hippocampus, and β-amyloid plaques in the brain. Thus, the transgenic canines we created can serve as a novel animal model for studying human AD.

Neprilysin is poorly expressed in the prefrontal cortex of aged dogs with cognitive dysfunction syndrome

Neprilysin (NEP) is the principal amyloid β (A β ) degrading peptidase; this activity may protect against Alzheimer's disease (AD), the most important age-related neurodegenerative process. The aim of this work was to analyze NEP mRNA expression in the frontal cortex of dogs with and without canine cognitive dysfunction syndrome (CDS), which is considered a natural model for AD. Expression of canine cerebral NEP mRNA was assessed by RT-PCR followed by qPCR in young, aged-cognitively unimpaired (CU), and aged-cognitively impaired (CI) dogs. On average, aged-CI dogs showed 80% (P < 0.01) lower expression levels of NEP mRNA than their aged-CU counterparts. Furthermore, the standard deviation of the qPCR measurements was more than 6 times higher in the cognitively healthy animals (young and aged-CU) than in the aged-CI group. Another interesting find is the determination of a positive correlation between NEP expression and the number of cholinergic neurons in basal telencephalon, indicating a probable connection between both events in these types of neurodegeneration processes. These results suggest that high expression levels of NEP might be a protective factor for canine CDS and, most likely, for other A β -associated neurodegenerative diseases, such as AD.

Selection of internal reference genes for normalization of quantitative reverse transcription polymerase chain reaction (qRT-PCR) analysis in the canine brain and other organs

Quantitative reverse transcription polymerase chain reaction (qRT-PCR) is a specific and sensitive technique for quantifying gene expression. To analyze qRT-PCR data accurately, suitable reference genes that show consistent expression patterns across different tissues and experimental conditions should be selected. The objective of this study was to obtain the most stable reference genes in dogs, using samples from 13 different brain tissues and 10 other organs. 16 well-known candidate reference genes were analyzed by the geNorm, NormFinder, and BestKeeper programs. Brain tissues were derived from several different anatomical regions, including the forebrain, cerebrum, diencephalon, hindbrain, and metencephalon, and grouped accordingly. Combination of the three different analyses clearly indicated that the ideal reference genes are ribosomal protien S5 (RPS5) in whole brain, RPL8 and RPS5 in whole body tissues, RPS5 and RPS19 in the forebrain and cerebrum, RPL32 and RPS19 in the diencephalon, GAPDH and RPS19 in the hindbrain, and MRPS7 and RPL13A in the metencephalon. These genes were identified as ideal for the normalization of qRT-PCR results in the respective tissues. These findings indicate more suitable and stable reference genes for future studies of canine gene expression.