The Role of Clusterin in Alzheimer’s Disease: Pathways,Pathogenesis, and Therapy

Genetic variation in clusterin gene, also known as apolipoprotein J, has been associated with Alzheimer’s disease (AD) through replicated genome-wide studies, and plasma clusterin levels are associated with brain atrophy, baseline prevalence and severity, and rapid clinical progression in patients with AD, highlighting the importance of clusterin in AD pathogenesis. Emerging data suggest that clusterin contributes to AD through various pathways, including amyloid-β aggregation and clearance, lipid metabolism, neuroinflammation, and neuronal cell cycle control and apoptosis. Moreover, epigenetic regulation of the clusterin expression also seems to play an important role in the pathogenesis of AD. Emerging knowledge of the contribution of clusterin to the pathogenesis of AD presents new opportunities for AD therapy.     

Neurovascular and Cognitive failure in Alzheimer’s Disease: Benefits of Cardiovascular Therapy

Alzheimer’s disease (AD) is a multifactorial and multifaceted disease for which we currently have very little to offer since there is no curative therapy, with only limited disease-modifying drugs. Recent studies in AD mouse models that recapitulate the amyloid-β (Aβ) pathology converge to demonstrate that it is possible to salvage cerebrovascular function with a variety of drugs and, particularly, therapies used to treat cardiovascular diseases such as hypercholesterolemia and hypertension. These drugs can reestablish dilatory function mediated by various endothelial and smooth muscle ion channels as well as nitric oxide availability, benefits that result in normalized brain perfusion. These cerebrovascular benefits would favor brain perfusion, which may help maintain neuronal function and, possibly, delay cognitive failure. However, restoring cerebrovascular function in AD mouse models was not necessarily accompanied by rescue of cognitive deficits related to spatial learning and memory. The results with cardiovascular therapies rather suggest that drugs originally designed to treat cardiovascular diseases that concurrently restore cerebrovascular and cognitive function do so through their pleiotropic effects. Specifically, recent findings suggest that these drugs act directly on brain cells and neuronal pathways involved in memory formation, hence, working simultaneously albeit independently on neuronal and vascular targets. These findings may help select medications for patients with cardiovascular diseases at risk of developing AD with increasing age. Further, they may identify molecular targets for recovering memory pathways that bear potential for new therapeutic avenues.     

Anti-amyloid Therapy of Alzheimer’s Disease: Current State and Prospects

Drug development for the treatment of Alzheimer’s disease (AD) has been for a long time focused on agents that were expected to support endogenous β-amyloid (Aβ) in a monomeric state and destroy soluble Aβ oligomers and insoluble Aβ aggregates. However, this strategy has failed over the last 20 years and was eventually abandoned. In this review, we propose a new approach to the anti-amyloid AD therapy based on the latest achievements in understanding molecular causes of cerebral amyloidosis in AD animal models.     

Molecular Basis of Etiological Implications in Alzheimer’s Disease: Focus on Neuroinflammation

Significant bodies of evidences have shown different mechanisms known to be the etiological cause of Alzheimer’s disease (AD) involving amyloid-beta protein accumulation, chronic inflammatory reactions, oxidative stress, proteasome inhibition, and high-cholesterol level, but the presize etiology of AD still remains enigmatic. Recent studies indicate that these mechanisms seem to be interlinked, and neuroinflammation emerges as a major regulatory and commen factor in all these mechanisms. In amyloid-beta protein, induced neurodegenerative hypothesis of AD inflammatory cytokines IFN-γ, TNF-α, interleukin (IL)-1α plays an important role in the progression of the disease. In cholesterol induced hypothesis liver X receptor mediated IL-4 also plays a major role in the progression of neuroinflammation. Notably, Omi and HtrA2 proteases play very important functions in neuronal dysfunction, which may lead to neurodegeneration. Further at genetic level, alterations in the genes occur especially in APP, PSEN1, PSEN2, APO E(ε4), ADAM12, and SH3MD1 which mediate neurodegeneration. Additionaly, The role of SP-1, NF-κB, and BCAE-1 is critical in the regulation of neuroinflammation-associated disease pathogenesis. All together, in this review, we discus the importance of neuroinflammatory mediators and their mechanistic role in the process of AD neurodegeneration.     

Targeting Synaptic Dysfunction in Alzheimer’s Disease Therapy

In the past years, major efforts have been made to understand the genetics and molecular pathogenesis of Alzheimer??s disease (AD), which has been translated into extensive experimental approaches aimed at slowing down or halting disease progression. Advances in transgenic (Tg) technologies allowed the engineering of different mouse models of AD recapitulating a range of AD-like features. These Tg models provided excellent opportunities to analyze the bases for the temporal evolution of the disease. Several lines of evidence point to synaptic dysfunction as a cause of AD and that synapse loss is a pathological correlate associated with cognitive decline. Therefore, the phenotypic characterization of these animals has included electrophysiological studies to analyze hippocampal synaptic transmission and long-term potentiation, a widely recognized cellular model for learning and memory. Transgenic mice, along with non-Tg models derived mainly from exogenous application of A??, have also been useful experimental tools to test the various therapeutic approaches. As a result, numerous pharmacological interventions have been reported to attenuate synaptic dysfunction and improve behavior in the different AD models. To date, however, very few of these findings have resulted in target validation or successful translation into disease-modifying compounds in humans. Here, we will briefly review the synaptic alterations across the different animal models and we will recapitulate the pharmacological strategies aimed at rescuing hippocampal plasticity phenotypes. Finally, we will highlight intrinsic limitations in the use of experimental systems and related challenges in translating preclinical studies into human clinical trials.     

The Study of Golgi Apparatus in Alzheimer’s Disease

Alzheimer’s disease is an irreversible, progressive neurodegenerative disorder leading invariably to death, usually within 7–10 years after diagnosis and is the leading cause of dementia in the elderly. Not only is Alzheimer’s disease a tragic disease in which people suffer from neurodegeneration in the years to come, it also becomes an incredible burden on the public health system. However, there is currently no effective treatment to halt the progression or prevent the onset of Alzheimer’s disease. This is partly due to the fact that the complex pathophysiology of Alzheimer’s disease is not yet completely understood. Recently, Golgi apparatus is found to play an important role in Alzheimer’s disease. In this review, we discuss the changes of Golgi apparatus during clinical progression and pathological development of Alzheimer’s disease. First, changes of Golgi apparatus size in Alzheimer’s disease are summarized. We then address the role of Golgi apparatus in the neuropathology of Alzheimer’s disease. Finally, the role of Golgi apparatus in the pathogenesis of Alzheimer’s disease is discussed. Understanding the contribution of Golgi apparatus dysfunction to Alzheimer’s disease and its pathophysiological basis will significantly impact our ability to develop more effective therapies for Alzheimer’s disease.     

Protein Prenylation and Synaptic Plasticity: Implications for Alzheimer’s Disease

Protein prenylation is an important lipid posttranslational modification of proteins. It includes protein farnesylation and geranylgeranylation, in which the 15-carbon farnesyl pyrophosphate or 20-carbon geranylgeranyl pyrophosphate is attached to the C-terminus of target proteins, catalyzed by farnesyl transferase or geranylgeranyl transferases, respectively. Protein prenylation facilitates the anchoring of proteins into the cell membrane and mediates protein–protein interactions. Among numerous proteins that undergo prenylation, small GTPases represent the largest group of prenylated proteins. Small GTPases are involved in regulating a plethora of cellular functions including synaptic plasticity. The prenylation status of small GTPases determines the subcellular locations and functions of the proteins. Dysregulation or dysfunction of small GTPases leads to the development of different types of disorders. Emerging evidence indicates that prenylated proteins, in particular small GTPases, may play important roles in the pathogenesis of Alzheimer’s disease. This review focuses on the prenylation of Ras and Rho subfamilies of small GTPases and its relation to synaptic plasticity and Alzheimer’s disease.     

Alzheimer’s Disease and Cholesterol: The Fat Connection

Since the discovery of the significance of the cholesterol-carrying apolipoprotein E and cholesterolaemia as major risk factors for Alzheimer's Disease (AD) there has been a mounting interest in the role of this lipid as a possible pathogenic agent. In this review we analyse the current evidence linking cholesterol metabolism and regulation in the CNS with the known mechanisms underlying the development of Alzheimer's Disease. Cholesterol is known to affect amyloid-beta generation and toxicity, although it must be considered that the results studies using the statin class of drugs to lower plasma cholesterol may be affected by other effects associated with these drugs. Finally, we report some of our results pointing at the interplay between neurons and astrocytes and NADPH oxidase activation as a new candidate mechanism linking cholesterol and AD pathology.     

The Endocannabinoid System and Alzheimer’s Disease

The importance of the role of the endocannabinoid system (ECS) in neurodegenerative diseases has grown during the past few years. Mostly because of the high density and wide distribution of cannabinoid receptors of the CB₁ type in the central nervous system (CNS), much research focused on the function(s) that these receptors might play in pathophysiological conditions. Our current understanding, however, points to much diverse roles for this system. In particular, other elements of the ECS, such as the fatty acid amide hydrolase (FAAH) or the CB₂ cannabinoid receptor are now considered as promising pharmacological targets for some diseases and new cannabinoids have been incorporated as therapeutic tools. Although still preliminary, recent reports suggest that the modulation of the ECS may constitute a novel approach for the treatment of Alzheimer’s disease (AD). Data obtained in vitro, as well as in animal models for this disease and in human samples seem to corroborate the notion that the activation of the ECS, through the use of agonists or by enhancing the endogenous cannabinoid tone, may induce beneficial effects on the evolution of this disease.     

Advances in developing novel therapeutic strategies for Alzheimer’s disease

Alzheimer’s Disease (AD), the most prevalent neurodegenerative disease of aging, affects one in eight older Americans. Nearly all drug treatments tested for AD today have failed to show any efficacy. There is a great need for therapies to prevent and/or slow the progression of AD. The major challenge in AD drug development is lack of clarity about the mechanisms underlying AD pathogenesis and pathophysiology. Several studies support the notion that AD is a multifactorial disease. While there is abundant evidence that amyloid plays a role in AD pathogenesis, other mechanisms have been implicated in AD such as tangle formation and spread, dysregulated protein degradation pathways, neuroinflammation, and loss of support by neurotrophic factors. Therefore, current paradigms of AD drug design have been shifted from single target approach (primarily amyloid-centric) to developing drugs targeted at multiple disease aspects, and from treating AD at later stages of disease progression to focusing on preventive strategies at early stages of disease development. Here, we summarize current strategies and new trends of AD drug development, including pre-clinical and clinical trials that target different aspects of disease (mechanism-based versus non-mechanism based, e.g. symptomatic treatments, lifestyle modifications and risk factor management).     

Expression of Novel Alzheimer’s Disease Risk Genes in Control and Alzheimer’s Disease Brains

Late onset Alzheimer’s disease (LOAD) etiology is influenced by complex interactions between genetic and environmental risk factors. Large-scale genome wide association studies (GWAS) for LOAD have identified 10 novel risk genes: ABCA7, BIN1, CD2AP, CD33, CLU, CR1, EPHA1, MS4A6A, MS4A6E, and PICALM. We sought to measure the influence of GWAS single nucleotide polymorphisms (SNPs) and gene expression levels on clinical and pathological measures of AD in brain tissue from the parietal lobe of AD cases and age-matched, cognitively normal controls. We found that ABCA7, CD33, and CR1 expression levels were associated with clinical dementia rating (CDR), with higher expression being associated with more advanced cognitive decline. BIN1 expression levels were associated with disease progression, where higher expression was associated with a delayed age at onset. CD33, CLU, and CR1 expression levels were associated with disease status, where elevated expression levels were associated with AD. Additionally, MS4A6A expression levels were associated with Braak tangle and Braak plaque scores, with elevated expression levels being associated with more advanced brain pathology. We failed to detect an association between GWAS SNPs and gene expression levels in our brain series. The minor allele of rs3764650 in ABCA7 is associated with age at onset and disease duration, and the minor allele of rs670139 in MS4A6E was associated with Braak tangle and Braak plaque score. These findings suggest that expression of some GWAS genes, namely ABCA7, BIN1, CD33, CLU, CR1 and the MS4A family, are altered in AD brains.     

The Emerging Therapeutic Role of NGF in Alzheimer’s Disease

Alzheimer’s disease (AD) is the most common type of neurodegenerative dementia that affects the elderly population. Nerve growth factor (NGF) contributes to the survival, regeneration and death of neurons during aging and in neurodegenerative diseases. Recently, research has shown that NGF is related to the pathology, mechanisms and symptoms of AD. Therefore, there is a need to summarize the new advancements in NGF research and its potential therapeutic implications in AD. In this review, we will focus on NGF distribution, production, and function; the interaction of Aβ and NGF; and the effect of different therapy methods on AD. In summary, we hope to describe the experimental and clinical data demonstrating the important roles of NGF for AD treatment.