Early Stages for Parkinson’s Development: α-Synuclein Misfolding and Aggregation

Misfolding and aggregation of proteins are common threads linking a number of important human health problems, including various neurodegenerative disorders such as Parkinson’s disease in particular. The first and perhaps most important elements in most neurodegenerative processes are misfolding and aggregation of specific proteins. Despite the crucial importance of protein misfolding and abnormal interactions, very little is currently known about the molecular mechanism underlying these processes. Factors that lead to protein misfolding and aggregation in vitro are poorly understood, in addition to the complexities involved in the formation of protein nanoparticles with different morphologies (e.g. nanopores and other species) in vivo. A clear understanding of the molecular mechanisms of misfolding and aggregation will facilitate rational approaches to prevent protein misfolding mediated pathologies. To accomplish this goal and to elucidate the mechanism of protein misfolding, we developed a novel nanotechnology tool capable of detecting protein misfolding. We applied single molecule probing technique to characterize misfolding and self-assembly of α-synuclein dimers, which is the very first step of the aggregation process. Using AFM force spectroscopy approach, we were able to detect protein misfolding via enhanced interprotein interaction. Moreover, such an important characteristic as the lifetime of dimers formed by misfolded α-synuclein was measured. These data suggest that compared to highly dynamic monomeric forms, α-synuclein dimers are practically static and thus can play a role of aggregation nuclei for the formation of aggregates. Importantly, two different dissociation channels were detected suggesting that aggregation process can follow different pathways. The application of these findings for understanding of the aggregation phenomenon and the development of the disease is discussed.     

Pharmacoperones: a new therapeutic approach for diseases caused by misfolded G protein-coupled receptors

G Protein-coupled receptors (GPCRs) are cell membrane proteins that recognize specific chemical signals such as drugs and hormones and transduce these signals into cellular responses by activating G-proteins. As is the case for all newly synthesized proteins, GPCRs are subjected to conformational scrutiny at the endoplasmic reticulum prior to processing and trafficking to the cell surface membrane. Because of this stringent quality control screening mechanism, mutations that result in protein misfolding frequently lead to retention in the endoplasmic reticulum, aggregation or other misrouting and, eventually, to disease. This article reviews some patents and new therapeutic opportunities based on the misfolding and retention of otherwise functional GPCRs that represent promising approaches to correct conformational abnormalities leading to distinct disease states.     

Drosophila models of proteinopathies: the little fly that could

Alzheimer's, Parkinson's, and Huntington's disease are complex neurodegenerative conditions with high prevalence characterized by protein misfolding and deposition in the brain. Considerable progress has been made in the last two decades in identifying the genes and proteins responsible for several human 'proteinopathies'. A wide variety of wild type and mutant proteins associated with neurodegenerative conditions are structurally unstable, misfolded, and acquire conformations rich in ?-sheets (?-state). These conformers form highly toxic self-assemblies that kill the neurons in stereotypical patterns. Unfortunately, the detailed understanding of the molecular and cellular perturbations caused by these proteins has not produced a single disease-modifying therapy. More than a decade ago, several groups demonstrated that human proteinopathies reproduce critical features of the disease in transgenic flies, including protein mis-folding, aggregation, and neurotoxicity. These initial reports led to an explosion of research that has contributed to a better understanding of the molecular mechanisms regulating conformational dynamics and neurotoxic cascades. To remain relevant in this competitive environment, Drosophila models will need to expand their flexible, innovative, and multidisciplinary approaches to find new discoveries and translational applications.     

The role of chaperones in Parkinson's disease and prion diseases

The etiologies of neurodegenerative diseases, such as Alzheimer's disease, Parkinson's disease, polyglutamine diseases, or prion diseases may be diverse; however, aberrations in protein folding, processing, and/or degradation are common features of these entities, implying a role of quality control systems, such as molecular chaperones and the ubiquitin-proteasome pathway. There is substantial evidence for a causal role of protein misfolding in the pathogenic process coming from neuropathology, genetics, animal modeling, and biophysics. The presence of protein aggregates in all neurodegenerative diseases gave rise to the hypothesis that protein aggregates, be it intracellular or extracellular deposits, may perturb the cellular homeostasis and disintegrate neuronal function (Table 1). More recently, however, an increasing number of studies have indicated that protein aggregates are not toxic per se and might even serve a protective role by sequestering misfolded proteins. Specifically, experimental models of polyglutamine diseases, Alzheimer's disease, and Parkinson's disease revealed that the appearance of aggregates can be dissociated from neuronal toxicity, while misfolded monomers or oligomeric intermediates seem to be the toxic species. The unique features of molecular chaperones to assist in the folding of nascent proteins and to prevent stress-induced misfolding was the rationale to exploit their effects in different models of neurodegenerative diseases. This chapter concentrates on two neurodegenerative diseases, Parkinson's disease and prion diseases, with a special focus on protein misfolding and a possible role of molecular chaperones.     

Protein conformational misfolding and amyloid formation: characteristics of a new class of disorders that include Alzheimer's and Prion diseases

The accumulation of proteinaceous deposits has been recognised to occur in several neurodegenerative conditions including Prion diseases, Alzheimer's disease, Parkinson's disease, and Huntington's disease. Over the last two decades interest in these conditions has increased markedly, fueled partially by an increasing prevalence of these diseases in the Western world. Evidence indicates that anomalous protein misfolding and aggregation, with an accompanying "toxic gain of function" is central to the neuropathogenesis of these diseases. An increased understanding of the similarities and differences in the production, aggregation and accumulation of the respective proteins involved in these diseases, and the associated mechanisms of neurodegeneration, should aid in the development of new therapeutic agents to treat this group of related disorders.     

Modulation of protein-protein interactions as a therapeutic strategy for the treatment of neurodegenerative tauopathies

The recognition that malfunction of the microtubule (MT) associated protein tau is likely to play a defining role in the onset and/or progression of a number of neurodegenerative diseases, including Alzheimer's disease, has resulted in the initiation of drug discovery programs that target this protein. Tau is an endogenous MT-stabilizing agent that is highly expressed in the axons of neurons. The MT-stabilizing function of tau is essential for the axonal transport of proteins, neurotransmitters and other cellular constituents. Under pathological conditions, tau misfolding and aggregation results in axonal transport deficits that appear to have deleterious consequences for the affected neurons, leading to synapse dysfunction and, ultimately, neuronal loss. This review focuses on both progress and unresolved issues surrounding the development of novel therapeutics for the treatment of neurodegenerative tauopathies, which are based on (A) MT-stabilizing agents to compensate for the loss of normal tau function, and (B) small molecule inhibitors of tau aggregation.     

Generalization of the prion hypothesis to other neurodegenerative diseases: an imperfect fit

Protein misfolding diseases have been classically understood as diffuse errors in protein folding, with misfolded protein arising autonomously throughout a tissue due to a pathologic stressor. The field of prion science has provided an alternative mechanism whereby a seed of pathologically misfolded protein, arising exogenously or through a rare endogenous structural fluctuation, yields a template to catalyze misfolding of the native protein. The misfolded protein may then spread intercellularly to communicate the misfold to adjacent areas and ultimately infect a whole tissue. Mounting evidence implicates a prion-like process in the propagation of several neurodegenerative diseases, including Alzheimer's, Parkinson's, Huntington's, amyotrophic lateral sclerosis, and the tauopathies. However, the parallels between the events observed in these conditions and those in prion disease are often incomplete. The aim of this review was to examine the current state of knowledge concerning the mechanisms of protein misfolding and aggregation for neurodegeneration-associated proteins. In addition, possible methods of intercellular spread are described that focus on the hypothesis that released microvesicles function as misfolded protein delivery vehicles, and the therapeutic options enabled by viewing these diseases from the prion perspective.     

海藻糖治疗帕金森病的作用机制研究进展

帕金森病是一种常见的神经变性疾病,特征性病理改变主要是黑质多巴胺能神经元丢失和路易小体的形成。路易小体中主要成分是纤维化的α-突触核蛋白,研究表明多巴胺能神经元中异常的蛋白质沉积可能与溶酶体自噬途径的失调有关。自噬调节剂的治疗潜力已在帕金森病动物模型中得到证实。海藻糖是一种天然双糖,被认为是治疗神经退行性疾病的新候选药物。它具有类似伴侣活性,防止蛋白质错误折叠或聚集,并有助于通过促进自噬去除积聚的蛋白质。总结异常自噬在帕金森病疾病发展过程中的潜在机制,讨论使用海藻糖对抗帕金森病的促进自噬、蛋白质稳定和抗神经炎症作用。     

Neurodegenerative diseases caused by protein aggregation: a phenomenon at the borderline between molecular evolution and ageing.

A process of protein aggregation that causes intracellular or extracellular accumulation of insoluble protein deposits causes many important neurodegenerative diseases associated with the ageing. The recognition that protein aggregation plays a prominent role in pathogenesis of important pathologies such as Alzheimer's and Parkinson's diseases prompted the scientific community to focus on the molecular mechanism of protein aggregation. Many proteins with sophisticated functions can self-aggregate because their folding is complicate and abnormal intermolecular contacts can predominate over the normal intramolecular interactions. The review of biochemical functional and pathogenic implications attributed to alpha synuclein, A beta peptide, presenilin and apoE highlights for these proteins a common conformational plasticity and the capacity to adapt their secondary structure to surrounding solvent as well as to the contacted ligands. Their functions are not fully elucidated but there is an elevated number of metabolic pathways in which apparently they are involved as well as they generate functional contact with a remarkable number of other proteins. The mechanism by which alpha synuclein and A beta protein make fibrils is an example of conformational plasticity because both these polypeptides can visit a coil or helical structure, but otherwise they convert into a pathogenic beta sheet structure highly suitable for polymerisation and fibril formation. The emerging question in the puzzling pathogenic basis of these diseases is if protein aggregation associated with ageing has a role in molecular evolution of the species or if it just represents a calculated drawback.     

Protein conformational diseases: from mechanisms to drug designs

Amyloidosis comprises a group of diseases characterized by the deposition of insoluble protein fibrils in specific organs and includes several serious medical disorders, such as Alzheimer's disease, prion-associated transmissible spongiform encephalitis, and type II diabetes. Despite the structural dissimilarity between the soluble proteins and peptides, these fibrils exhibit similar morphologies under electron microscopy with a characteristic "cross beta-sheet" pattern examined by x-ray fiber diffraction experiments. Many studies have revealed that each of these diseases is associated to a specific protein that is partially unfolded, misfolded, and aggregated. However, the detailed structures of the causative agents and the toxicity mechanisms are less known. This review summarizes recent studies in the conformational disorders leading to aggregation; including which proteins potentially cause conformational diseases, the aggregation mechanisms of these proteins, and recent researches on the conformational changes using advanced experiments or molecular dynamics simulations. Finally, current drug designs towards these protein conformational diseases are also discussed. It is believed that the advances in basic understanding of the mechanisms of conformational changes as well as biological functions of these proteins will shed light on the development and design of potential interfering compounds against amyloid formation associated with protein conformational diseases.     

Rapamycin inhibits polyglutamine aggregation independently of autophagy by reducing protein synthesis

Accumulation of misfolded proteins and protein assemblies is associated with neuronal dysfunction and death in several neurodegenerative diseases such as Alzheimer's, Parkinson's, and Huntington's disease (HD). It is therefore critical to understand the molecular mechanisms of drugs that act on pathways that modulate misfolding and/or aggregation. It is noteworthy that the mammalian target of rapamycin inhibitor rapamycin or its analogs have been proposed as promising therapeutic compounds clearing toxic protein assemblies in these diseases via activation of autophagy. However, using a cellular model of HD, we found that rapamycin significantly decreased aggregation-prone polyglutamine (polyQ) and expanded huntingtin and its inclusion bodies (IB) in both autophagy-proficient and autophagy-deficient cells (by genetic knockout of the atg5 gene in mouse embryonic fibroblasts). This result suggests that rapamycin modulates the levels of misfolded polyQ proteins via pathways other than autophagy. We show that rapamycin reduces the amount of soluble polyQ protein via a modest inhibition of protein synthesis that in turn significantly reduces the formation of insoluble polyQ protein and IB formation. Hence, a modest reduction in huntingtin synthesis by rapamycin may lead to a substantial decrease in the probability of reaching the critical concentration required for a nucleation event and subsequent toxic polyQ aggregation. Thus, in addition to its beneficial effect proposed previously of reducing polyQ aggregation/toxicity via autophagic pathways, rapamycin may alleviate polyQ disease pathology via its effect on global protein synthesis. This finding may have important therapeutic implications.     

C-terminus of Hsp70 Interacting Protein (CHIP) and Neurodegeneration: Lessons from the Bench and Bedside

Neurodegenerative diseases are characterized by the increasing dysfunction and death of neurons, resulting in progressive impairment of a person’s mobility and/or cognition. Protein misfolding and aggregation are commonly hypothesized to cause neurotoxicity and, eventually, neuronal degeneration that are associated with these diseases. Emerging experimental evidence, as well as recent findings from human studies, reveal that the C-terminus of Hsp70 Interacting Protein (CHIP), or STIP1 Homology and U-box containing Protein 1 (STUB1), is a quality control protein involved in neurodegeneration. Here, we review evidence that CHIP interacts with and plays a role in regulating proteins implicated in the pathogenesis of Parkinson’s disease, Alzheimer’s disease, amyotrophic lateral sclerosis, and polyglutamine diseases, including Huntington’s disease and spinocerebellar ataxias. We also review clinical findings identifying mutations in STUB1 as a cause of both autosomal recessive and autosomal dominant forms of cerebellar ataxia. We propose that CHIP modulation may have therapeutic potential for the treatment of multiple neurodegenerative diseases.     

Protein misfolding in conformational disorders: rescue of folding defects and chemical chaperoning

Protein folding in the cell is a tightly regulated process, involving a series of proteins, from molecular chaperones to proteases that assist the folding process and monitor the quality of the final product. Despite this control, genetic or sporadic factors may compromise protein folding and the folded state resulting in the formation of non-native misfolded, destabilised, aggregated or fibrillar species. These are hallmarks of the so-called protein conformational disorders, in which the altered protein conformations result in cell toxicity, functional deficiency or lead to dominant negative effects. Examples of such pathologies include neurodegenerative and metabolic disorders. In recent years, it has become clear that several different small chemical compounds such as osmolytes, protein inhibitors, ligands and cofactors exert a chemical chaperoning effect and are able to rescue folding and trafficking defects, minimising or partly overcoming the pathological consequences of protein misfolding. Here we review the different types of chemical chaperones and provide a structural and energetic rationale for their action. Examples of chemical chaperoning are overviewed and discussed on the basis of the reported effects exerted by chemical compounds at different stages of the protein folding process and protein conformational states.     

Inhibition of protein misfolding and aggregation by small rationally-designed peptides

Several human diseases are associated with the presence of toxic fibrillar protein deposits. These diseases called protein misfolding disorders, are characterized by the accumulation of misfolded protein aggregates in diverse tissues. Strong evidence indicates that the conversion of a normal soluble protein into a beta-sheet-rich oligomeric structure and further fibrillar aggregation are the key events in the disease pathogenesis. Therefore, a promising therapeutic target consists of the prevention and dissolution of misfolded protein aggregates. Peptides designed to specifically bind to the pathogenic protein and block and/or reverse its abnormal conformational change constitute a new class of drugs. This article reviews this approach, describing diverse compounds reported to have this activity.     

锰神经毒性机制研究进展

过量锰暴露可能会损害中枢神经系统,产生不可逆转的神经毒性,导致严重的神经退行性疾病.锰的神经毒性机制可能与转运稳态失调、氧化应激与线粒体损伤、自噬、蛋白质折叠错误、细胞凋亡、神经炎症有关,其中蛋白质错误折叠、线粒体损伤和神经炎症等又称锰神经毒性的3种主要损伤机制.本文对上述研究进展予以综述,以期为锰中毒防治提供科学依据...     

Tissue transglutaminase: a novel pharmacological target in preventing toxic protein aggregation in neurodegenerative diseases

Alzheimer's disease, Parkinson's disease and Huntington's disease are neurodegenerative diseases, characterized by the accumulation and deposition of neurotoxic protein aggregates. The capacity of specific proteins to self-interact and form neurotoxic aggregates seems to be a common underlying mechanism leading to pathology in these neurodegenerative diseases. This process might be initiated and/or accelerated by proteins that interact with these aggregating proteins. The transglutaminase (TG) family of proteins are calcium-dependent enzymes that catalyze the formation of covalent ε-(γ-glutamyl)lysine isopeptide bonds, which can result in both intra- and intermolecular cross-links. Intramolecular cross-links might modify self-interacting proteins, and make them more prone to aggregate. In addition, intermolecular cross-links could link self-aggregating proteins and thereby initiate and/or stimulate the aggregation process. So far, increased levels and activity of tissue transglutaminase (tTG), the best characterized member of the TG family, have been observed in many neurodegenerative diseases, and the self-interacting proteins, characteristic of Alzheimer's disease, Parkinson's disease and Huntington's disease, are known substrates of tTG. Here, we focus on the role of tTG in the initiation of the aggregation process of self-interacting proteins in these diseases, and promote the notion that tTG might be an attractive novel target for treatment of neurodegenerative diseases.     

Therapeutic strategies against protein misfolding in neurodegenerative diseases

Background: Neurodegenerative diseases are a group of chronic and progressive disorders of the nervous system. A hallmark event in these diseases is the misfolding and accumulation in the brain of protein aggregates. Objective: In this article, we describe the knowledge of the mechanism of protein misfolding and aggregation, its role in neurodegeneration and the diverse therapeutic targets for intervention. We also critically review various strategies under development to discover drugs attacking this process. Conclusion: In spite of the substantial progress on understanding the critical role of protein misfolding and aggregation, drugs effective against this process are still years away from approval.     

Conformational toxicity and sporadic conformational diseases

Spontaneous, so-called 'conformational' diseases, specially of the neurodegenerative type like Alzheimer's, are linked to certain protein types which have the normal amino-acid sequence but are misfolded and accumulate due to resistance to proteolysis. In the case of prion diseases, the 'protein only' hypothesis assumes that the misconformation of a native protein could be initiated upon interaction with a sister-protein already in the misfolded state. There is an alternative to this sister protein contamination scheme, which assumes that the misconformation is acquired upon protein synthesis, that is de novo. Misfoldling and resistance to proteolysis could result from defects responsible for shortage or inactivity of the cellular factors in charge of protein folding and degradation. The defects could have a genetic origin (the gene of the faulty factor involved could have been mutated, or control and regulation of its expression could have been altered, etc.). Alternatively, the cell's actual biosynthetic and/or proteolytic resources could have become overloaded and unavailable, due to unscheduled mass-production of proteins resulting from unscheduled cell growth or proliferation, cell stress, etc. Xenobiotics, active for instance as endocrine proliferators, stressors, or inducing copious, unscheduled gene expression, etc. could give rise to shortage of cellular factors necessary for the production of native proteins and for proteolysis. Alternatively, xenobiotics could alter expression or activity of some of these factors. In both cases, the xenobiotic could be a 'conformational toxicant' by inducing misfolding of selected proteins. The xenobiotic could trigger some conformational disease if it targets a specific protein and tissue.