Altered behavioral responses to gamma‐aminobutyric acid pharmacological agents in a mouse model of Huntington's disease

Background : Disruptions in gamma‐aminobutyric (GABA) acid signaling are believed to be involved in Huntington's disease pathogenesis, but the regulation of GABAergic signaling remains elusive. Here we evaluated GABAergic signaling by examining the function of GABAergic drugs in Huntington's disease and the expression of GABAergic molecules using mouse models and human brain tissues from Huntington's disease. Methods : We treated wild‐type and R6/2 mice (a transgenic Huntington's disease mouse model) acutely with vehicle, diazepam, or gaboxadol (drugs that selectively target synaptic or extrasynaptic GABA_A receptors) and monitored their locomotor activity. The expression levels of GABA_A receptors and a major neuron‐specific chloride extruder (potassium‐chloride cotransporter‐2) were analyzed by real‐time quantitative polymerase chain reaction, Western blot, and immunocytochemistry. Results : The R6/2 mice were less sensitive to the sedative effects of both drugs, suggesting reduced function of GABA_A receptors. Consistently, the expression levels of α1/α2 and δ subunits were lower in the cortex and striatum of R6/2 mice. Similar results were also found in 2 other mouse models of Huntington's disease and in Huntington's disease patients. Moreover, the interaction and expression levels of potassium‐chloride cotransporter‐2 and its activator (brain‐type creatine kinase) were decreased in Huntington's disease neurons. These findings collectively suggest impaired chloride homeostasis, which further dampens GABA_A receptor‐mediated inhibitory signaling in Huntington's disease brains. Conclusions : The dysregulated GABAergic responses and altered expression levels of GABA_A receptors and potassium‐chloride cotransporter‐2 in Huntington's disease mice appear to be authentic and may contribute to the clinical manifestations of Huntington's disease patients. © 2017 International Parkinson and Movement Disorder Society     

Sunlight exposure is important for preventing hip fractures in patients with Alzheimer's disease, Parkinson's disease, or stroke

Iwamoto J, Takeda T, Matsumoto H. Sunlight exposure is important for preventing hip fractures in patients with Alzheimer’s disease, Parkinson’s disease, or stroke.
Acta Neurol Scand: 2012: 125: 279–284.
© 2011 John Wiley & Sons A/S. Objectives – Hypovitaminosis D as a result of malnutrition or sunlight deprivation, increased bone resorption, low bone mineral density (BMD), or an increased risk of falls may contribute to an increased risk of hip fractures in patients with neurological diseases, including Alzheimer’s disease, Parkinson’s disease, and stroke. The purpose of this study was to clarify the efficacy of sunlight exposure for reducing the risk of hip fractures in patients with such neurological diseases. Methods – The English literature was searched using PubMed, and randomized controlled trials evaluating the efficacy of sunlight exposure for reducing the risk of hip fractures in patients with Alzheimer’s disease, Parkinson’s disease, and stroke were identified. The relative risk and the 95% confidence interval were calculated for individual randomized controlled trials, and a pooled data analysis (meta‐analysis) was performed. Results – Three randomized controlled trials were identified. Sunlight exposure improved hypovitaminosis D and increased the BMD. The relative risk (95% confidence interval) of hip fractures was 0.22 (0.05, 1.01) for Alzheimer’s disease, 0.27 (0.08, 0.96) for Parkinson’s disease, and 0.17 (0.02, 1.36) for stroke. The relative risk (95% confidence interval) calculated for the pooled data analysis was 0.23 (0.10, 0.56) (P = 0.0012), suggesting a significant risk reduction rate of 77%. Conclusion – The present meta‐analysis added additional evidence indicating the efficacy of sunlight exposure for reducing the risk of hip fractures in patients with Alzheimer’s disease, Parkinson’s disease, and stroke.     

Muscarinic Acetylcholine Receptor Subtypes as Potential Drug Targets for the Treatment of Schizophrenia, Drug Abuse and Parkinson's Disease

The neurotransmitter dopamine plays important roles in modulating cognitive, affective, and motor functions. Dysregulation of dopaminergic neurotransmission is thought to be involved in the pathophysiology of several psychiatric and neurological disorders, including schizophrenia, Parkinson's disease and drug abuse. Dopaminergic systems are regulated by cholinergic, especially muscarinic, input. Not surprisingly, increasing evidence implicates muscarinic acetylcholine receptor-mediated pathways as potential targets for the treatment of these disorders classically viewed as "dopamine based". There are five known muscarinic receptor subtypes (M(1) to M(5)). Due to their overlapping expression patterns and the lack of receptor subtype-specific ligands, the roles of the individual muscarinic receptors have long remained elusive. During the past decade, studies with knock-out mice lacking specific muscarinic receptor subtypes have greatly advanced our knowledge of the physiological roles of the M(1)-M(5) receptors. Recently, new ligands have been developed that can interact with allosteric sites on different muscarinic receptor subtypes, rather than the conventional (orthosteric) acetylcholine binding site. Such agents may lead to the development of novel classes of drugs useful for the treatment of psychosis, drug abuse and Parkinson's disease. The present review highlights recent studies carried out using muscarinic receptor knock-out mice and new subtype-selective allosteric ligands to assess the roles of M(1), M(4), and M(5) receptors in various central processes that are under strong dopaminergic control. The outcome of these studies opens new perspectives for the use of novel muscarinic drugs for several severe disorders of the CNS.     

Klotho基因在神经变性病中的研究进展

Klotho(Kl)是一种衰老抑制基因,其对CNS有保护作用,与神经变性疾病如Alzheimer's病、帕金森病等具有明显的相关性.在Alzheimer's病中,Kl对抗β淀粉样物质对海马神经元造成的损害,细胞层面上能显著改善长时程记忆基础中的N-甲基-D-天冬氨酸受体结构功能和网络反应敏感性,分子层面上能调节硫氧还蛋...     

Structural plasticity in G-protein coupled receptors as demonstrated by the allosteric actions of homocysteine and computer-assisted analysis of disordered domains

Structural plasticity of G-protein coupled receptors (GPCRs) is of basic importance for their interactions with ligands, in particular with other proteins such as receptors or receptor-modifying proteins that can lead to different functions for the same GPCR. In the present paper, structural plasticity of GPCRs has been investigated discussing allosteric modulatory actions of Homocysteine (Hcy) on D2 receptors together with data obtained by computer-assisted analysis of the presence of disordered domains in GPCRs. Previous evidence for a modulatory action of Hcy on D2 receptors has been further extended by means of experiments on the effects of Hcy local intrastriatal injection on rotational behaviour. Altogether the present data allow considering under a new angle the well known proposal of A2A antagonists as new therapeutic agents in Parkinson's disease (PD). Furthermore, they point out to not only the importance of drugs capable of reducing Hcy brain levels, but also to the potential therapeutic impact of drugs capable of regionally blocking (for PD) or enhancing (for some schizophrenic syndromes) Hcy allosteric action on D2 receptors. As far as the investigations on GPCR plastic domains, extracellular, intracellular and transmembrane domains of 14 GPCRs have been considered and propensity of each of these domains for a structured or unstructured conformation has been evaluated by means of ad hoc computer programs. It has been shown that the N- and C-terminals as well as intracellular loop 3 have a high propensity towards an unstructured conformation, hence they are potentially very plastic domains, which can undergo easily to interactions with other ligands, particularly with other protein domains. This aspect is obviously of the greatest importance not only for the function of single GPCRs, but also for their interactions either with other receptors (receptor-receptor interactions) or, more generally, for formation of clusters of membrane associated proteins, hence of "protein mosaics", where the GPCRs could represent the input unit of the supra-molecular device.     

Death‐associated protein kinase 1 variation and Parkinson’s disease

Background and purpose: Mutations of the LRRK2 gene are now recognized as major risk factors for Parkinson’s disease. The Lrrk2 protein is a member of the ROCO family, which also includes Lrrk1 and Dapk1. Functional genetic variants of the DAPK1 gene (rs4877365 and rs4878104) have been previously associated with Alzheimer’s disease. Methods: Herein, we assessed the role of DAPK1 variants (rs4877365 and rs4878104) in risk of Parkinson’s disease with Sequenom iPLEX genotyping, employing one Taiwanese series (391 patients with Parkinson’s disease, 344 controls) and five separate Caucasian series’ (combined sample size 1962 Parkinson’s disease patients, 1900 controls). Results: We observed no evidence of association for rs4877365 and rs4878104 and risk of Parkinson’s disease in any of the individual series or in the combined Caucasian series under either an additive or recessive model. Conclusion: These specific DAPK1 intronic variants do not increase the risk of Parkinson’s disease. However, further functional studies are required to elucidate the potential therapeutic implications with the dimerization of the Dapk1 and Lrrk2 proteins.     

Memantine hydrochloride in the treatment of dementia subtypes

Memantine hydrochloride is a first-line therapeutic drug approved by the US Food and Drug Administration for the management of moderate to severe Alzheimer’s disease (AD). We conducted a review of the literature to determine the changes to the central glutamatergic neurotransmitter system in dementia subtypes and the available clinical evidence regarding the use of memantine in the treatment of different dementia subtypes. We conclude from our review that memantine may be an effective therapeutic option in managing AD, frontotemporal dementia, dementia with Lewy bodies, Parkinson’s disease dementia and vascular dementia. When a diagnosis of the dementia subtype cannot be clearly identified or when there is no clear therapeutic option, memantine may be simple and safe.     

Neuroprotective role of fibronectin in neuron-glial extrasynaptic transmission

Most hypotheses concerning the mechanisms underlying Parkinson’s disease are based on altered synaptic transmission of the nigrostriatal system.However,extrasynaptic transmission was recently found to affect dopamine neurotransmitter delivery by anisotropic diffusion in the extracellular matrix,which is modulated by various extracellular matrix components such as fibronectin.The present study reviewed the neuroprotective effect of fibronectin in extrasynaptic transmission.Fibronectin can regulate neuroactive substance diffusion and receptor activation,and exert antineuroinflammatory,adhesive and neuroprotective roles.Fibronectin can bind to integrin and growth factor receptors to transactivate intracellular signaling events such as the phosphatidylinositol 3-kinase/protein kinase B pathway to regulate or amplify growth factor-like neuroprotective actions.Fibronectin is assembled into a fibrillar network around cells to facilitate cell migration,molecule and ion diffusion,and even drug delivery and treatment.In addition,the present study analyzed the neuroprotective mechanism of fibronectin in the pathogenesis of Parkinson’s disease,involving integrin and growth factor receptor interactions,and discussed the possible therapeutic and diagnostic significance of fibronectin in Parkinson’s disease.     

Glycogen Synthase Kinase-3 Inhibitors as Potent Therapeutic Agents for the Treatment of Parkinson Disease.

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Harnessing Cerebrospinal Fluid Biomarkers in Clinical Trials for Treating Alzheimer's and Parkinson's Diseases: Potential and Challenges

No disease-modifying therapies (DMT) for neurodegenerative diseases (NDs) have been established, particularly for Alzheimer''s disease (AD) and Parkinson''s disease (PD). It is unclear why candidate drugs that successfully demonstrate therapeutic effects in animal models fail to show disease-modifying effects in clinical trials. To overcome this hurdle, patients with homogeneous pathologies should be detected as early as possible. The early detection of AD patients using sufficiently tested biomarkers could demonstrate the potential usefulness of combining biomarkers with clinical measures as a diagnostic tool. Cerebrospinal fluid (CSF) biomarkers for NDs are being incorporated in clinical trials designed with the aim of detecting patients earlier, evaluating target engagement, collecting homogeneous patients, facilitating prevention trials, and testing the potential of surrogate markers relative to clinical measures. In this review we summarize the latest information on CSF biomarkers in NDs, particularly AD and PD, and their use in clinical trials. The large number of issues related to CSF biomarker measurements and applications has resulted in relatively few clinical trials on CSF biomarkers being conducted. However, the available CSF biomarker data obtained in clinical trials support the advantages of incorporating CSF biomarkers in clinical trials, even though the data have mostly been obtained in AD trials. We describe the current issues with and ongoing efforts for the use of CSF biomarkers in clinical trials and the plans to harness CSF biomarkers for the development of DMT and clinical routines. This effort requires nationwide, global, and multidisciplinary efforts in academia, industry, and regulatory agencies to facilitate a new era.     

Rationale for the use of multifunctional drugs as neuroprotective agents for glaucoma

Glaucoma, the leading cause globally of irreversible blindness, is a neurodegenerative disease characterized by progressive retinal ganglion cell death. To date, no drug has been shown to prevent the retinal ganglion cell loss associated with glaucoma. Multiple mechanisms lead to ganglion cell death in glaucoma, suggesting that a neuroprotectant that has a single mode of action, like memantine, would have a limited positive effect at slowing down ganglion cell death. Conversely, simultaneously targeting several factors may be the best therapeutic approach to improve outcomes. Multifunctional drugs are fast gaining acceptance as a strategy for the treatment of complex disor-ders of the central nervous system, such as Parkinson’s disease, Alzheimer’s disease and other progressive neurodegenerative diseases. In this paper, we review the current literature on multi-functional drugs and propose a rationale for the use of multifunctional drugs in glaucomatous optic neuropathy.     

Mechanisms of platelet activation by thrombin: a short history

Platelet activation by thrombin is relevant to arterial thrombosis, therefore it is an attractive target for the development of new antithrombotic drugs. In the 1970s the platelet membrane complex glycoprotein (GP) Ib-V-IX was shown to have a high affinity binding site for thrombin on GPIbα and a substrate cleaved by thrombin, GPV. For several years it was considered to be involved in platelet activation by thrombin. The discovery of the protease activated receptors (PARs) in 1991 was a major breakthrough in the field. The first member of this family of receptors to be discovered was PAR1, a seven transmembrane G-protein coupled receptor which, upon cleavage by thrombin, unmasks a new amino-terminus able to bind intramolecularly to PAR1 itself thus inducing signaling. On human platelets PAR1 and, later PAR4, were demonstrated to mediate most of the platelet responses to thrombin. However, after the discovery of PARs, different groups demonstrated that GPIbα is required to stimulate a full platelet activation by thrombin. A model where thrombin binds to the GPIb receptor prior to proteolysis of the PAR receptors was supported by several lines of evidence. A role for GPV as inhibitor of GPIbα signaling has been shown by using GPV knock-out mice. Crystallographic data suggested that thrombin bound to GPIbα might be able to interact with other GPIbα molecules on the same or other platelets, shedding light on a new role for thrombin binding to GPIbα. Finally, anti-PAR1 molecules were developed which are now in phase II and III clinical studies as antithrombotic drugs.     

Deregulation of brain insulin signaling in Alzheimer’s disease

Contrary to the previous belief that insulin does not act in the brain, studies in the last three decades have demonstrated important roles of insulin and insulin signal transduction in various functions of the central nervous system. Deregulated brain insulin signaling and its role in molecular pathogenesis have recently been reported in Alzheimer’s disease (AD). In this article, we review the roles of brain insulin signaling in memory and cognition, the metabolism of amyloid β precursor protein, and tau phosphorylation. We further discuss deficiencies of brain insulin signaling and glucose metabolism, their roles in the development of AD, and recent studies that target the brain insulin signaling pathway for the treatment of AD. It is clear now that deregulation of brain insulin signaling plays an important role in the development of sporadic AD. The brain insulin signaling pathway also offers a promising therapeutic target for treating AD and probably other neurodegenerative disorders.     

Antihypertensives for combating dementia? A perspective on candidate molecular mechanisms and population-based prevention

Age-related increases in prevalent dementia over the next 30–40 years risk collapsing medical resources or radically altering the way we treat patients. Better prevention of dementia therefore needs to be one of our highest medical priorities. We propose a perspective on the pathological basis of dementia based on a cerebrovascular-Alzheimer disease spectrum that provides a more powerful explanatory framework when considering the impact of possible public health interventions. With this in mind, a synthesis of evidence from basic, clinical and epidemiological studies indeed suggests that the enhanced treatment of hypertension could be effective for the primary prevention of dementia of either Alzheimer or vascular etiology. In particular, we focus on candidate preventative mechanisms, including reduced cerebrovascular disease, disruption of hypoxia-dependent amyloidogenesis and the potential neuroprotective properties of calcium channel blockers. Following the successful translation of large, long-term and resource-intense trials in cardiology into improved vascular health outcomes in many countries, new multinational prevention trials with dementia-related primary outcomes are now urgently required.     

Immunotherapeutic Approaches Targeting Amyloid-β, α-Synuclein,and Tau for the Treatment of Neurodegenerative Disorders

Disease-modifying alternatives are sorely needed for the treatment of neurodegenerative disorders, a group of diseases that afflict approximately 50 million Americans annually. Immunotherapy is one of the most developed approaches in this direction. Vaccination against amyloid-β, α-synuclein, or tau has been extensively explored, specially as the discovery that these proteins may propagate cell-to-cell and be accessible to antibodies when embedded into the plasma membrane or in the extracellular space. Likewise, the use of passive immunization approaches with specific antibodies against abnormal conformations of these proteins has also yielded promising results. The clinical development of immunotherapies for Alzheimer’s disease, Parkinson’s disease, frontotemporal dementia, dementia with Lewy bodies, and other neurodegenerative disorders is a field in constant evolution. Results to date suggest that immunotherapy is a promising therapeutic approach for neurodegenerative diseases that progress with the accumulation and prion-like propagation of toxic protein aggregates. Here we provide an overview of the most novel and relevant immunotherapeutic advances targeting amyloid-β in Alzheimer’s disease, α-synuclein in Alzheimer’s disease and Parkinson’s disease, and tau in Alzheimer’s disease and frontotemporal dementia.     

Function of Nogo‐A/Nogo‐A Receptor in Alzheimer's Disease

Nogo‐A is a protein inhibiting axonal regeneration, which is considered a major obstacle to nerve regeneration after injury in mammals. Rapid progress has been achieved in new physiopathological function of Nogo‐A in Alzheimer's disease in the past decade. Recent research shows that through binding to Nogo‐A receptor, Nogo‐A plays an important role in Alzheimer's disease (AD) pathogenesis. Particularly, Nogo‐A/Nogo‐A receptors modulate the generation of amyloid β‐protein (Aβ), which is thought to be a major cause of AD. This review describes the recent development of Nogo‐A, Nogo‐A receptor, and downstream signaling involved in AD and pharmacological basis of therapeutic drugs. We concluded the Nogo‐A/Nogo‐A receptor provide new insight into potential mechanisms and promising therapy strategies in AD.     

基于Aβ与tau蛋白过度磷酸化损伤机制的阿尔茨海默病治疗靶点

阿尔茨海默病(Alzheimer's disease,AD)的发病机制主要包括Aβ蛋白表达增高在脑内聚集形成老年斑和tau蛋白过度磷酸化在胞内形成神经原纤维缠结.尽管Aβ与tau蛋白的损伤机制一直是AD研究的重点,但目前仍未找到能有效治疗AD的药物.本文主要概述了Aβ蛋白聚集与tau蛋白过度磷酸化对大脑损伤作用的分子机...     

Is activation of GDNF/RET signaling the answer for successful treatment of Parkinson's disease?A discussion of data from the culture dish to the clinic

The neurotrophic signaling of glial cell line-derived neurotrophic factor(GDNF)with its canonical receptor,the receptor tyrosine kinase RET,coupled together with the GDNF family receptor alpha 1 is important for dopaminergic neuron survival and physiology in cell culture experiments and animal models.This prompted the idea to try GDNF/RET signaling as a therapeutic approach to treat Parkinson’s disease with the hallmark of dopaminergic cell death in the substantia nigra of the midbrain.Despite several clinical trials with GDNF in Parkinson’s disease patients,which mainly focused on optimizing the GDNF delivery technique,benefits were only seen in a few patients.In general,the endpoints did not show significant improvements.This suggests that it will be helpful to learn more about the basic biology of this fascinating but complicated GDNF/RET signaling system in the dopaminergic midbrain and about recent developments in the field to facilitate its use in the clinic.Here we will refer to the latest publications and point out important open questions in the field.     

Parkinsonism Associated with Glucocerebrosidase Mutation

Background

Gaucher''s disease is an autosomal recessive, lysosomal storage disease caused by mutations of the β-glucocerebrosidase gene (GBA). There is increasing evidence that GBA mutations are a genetic risk factor for the development of Parkinson''s disease (PD). We report herein a family of Koreans exhibiting parkinsonism-associated GBA mutations.

Case Report

A 44-year-old woman suffering from slowness and paresthesia of the left arm for the previous 1.5years, visited our hospital to manage known invasive ductal carcinoma. During a preoperative evaluation, she was diagnosed with Gaucher''s disease and double mutations of S271G and R359X in GBA. Parkinsonian features including low amplitude postural tremors, rigidity, bradykinesia and shuffling gait were observed. Genetic analysis also revealed that her older sister, who had also been diagnosed with PD and had been taking dopaminergic drugs for 8-years, also possessed a heterozygote R359X mutation in GBA. ¹⁸F-fluoropropylcarbomethoxyiodophenylnortropane positron-emission tomography in these patients revealed decreased uptake of dopamine transporter in the posterior portion of the bilateral putamen.

Conclusions

This case study demonstrates Korean familial cases of PD with heterozygote mutation of GBA, further supporting the association between PD and GBA mutation.     

Invited Review – A 5-year update on epigenome-wide association studies of DNA modifications in Alzheimer’s disease: progress,practicalities and promise

In late 2014, the first epigenome-wide association studies of DNA modifications in Alzheimer’s disease brain samples were published. Over the last 5 years, further studies have been reported in the field and have highlighted consistent and robust alterations in DNA modifications in AD cortex. However, there are some caveats associated with the majority of studies undertaken to date; for example, they are predominantly restricted to profiling a limited number of loci, are principally focused on DNA methylation, are performed on bulk tissue at the end stage of disease and are restricted to nominating associations rather than demonstrating causal relationships. Consequently, the downstream interpretation of these studies is limited. Owing to recent advances in state-of-the-art cell profiling techniques, long-read genomic technologies and genetic engineering methodologies, identifying cell-type-specific causal epigenetic changes is becoming feasible. This review seeks to provide an overview of the last 5 years of epigenomic studies of DNA modifications in Alzheimer’s disease brain samples and propose new avenues for future research.