Recent developments in the understanding and treatment of neurodegenerative disorders involving protein conformational misfolding and amyloid formation

Conformational disease represents an intriguing but devastating class of neurodegenerative disorders that includes prion disease, Alzheimer’s disease, Parkinson’s disease and Huntington’s disease. Although symptoms, on-set times and prognosis among the diseases can vary markedly, the deposition of neurotoxic protein aggregates is a significant commonality, and as such is an attractive therapeutic target. Understanding the mechanisms of protein misfolding and deposition in these conditions is critical to developing effective diagnostic and therapeutic agents. This review serves as an update for the sister publication “Protein Conformational Misfolding and Amyloid Formation: Characteristics of a New Class of Disorders that Include Alzheimer’s and Prion Diseases” in Curr. Med. Chem. 2002, 9, 1751-62, and focuses primarily on recent developments in understanding prion disease and Alzheimer’s disease in context with other conformational disease. New research in amyloid-related therapeutic strategies is also discussed. INTRODUCTION Protein misfolding and amyloid formation occurs in a number of neurodegenerative disorders including but not limited to Alzheimer’s disease (AD), Parkinson’s disease (PD), Huntington’s disease (HD) and prion diseases. Although the identity and nature of the aggregating protein and the mechanisms of aggregation and toxicity vary widely between the diseases, protein conformational change and subsequent aggregation are central to their pathology. This shared characteristic has led to the categorization of these diseases under the umbrella terms ‘conformational disease’ and ‘cerebral proteopathies’ [1]. These diseases have been more comprehensively reviewed previously [2]. This review serves as an update on recent advances in the field which have focused predominantly on Prion diseases and AD. Recent advances in amyloid-related therapeutic strategies are also presented, which can target specific diseases but may also have the potential for broader application in treating conformational diseases in general. RECENT ADVANCES IN UNDERSTANDING PRION DISEASES Numerous advances in the understanding of prion diseases have occurred over the last few years. Further understanding of the mechanism of conversion of PrP to PrP and the means of neurotoxicity and infectivity of PrP, has led to the development of first generation diagnostic tests for prions and new therapeutic strategies. Improved mechanistic models and therapeutic strategies for other amyloidgenic disorders such as Alzheimer’s disease have also increased the rate of progress in prion disease research. Most proteins and peptides can be made to form amyloid under appropriate environmental conditions. Proteins that form amyloid in the brain and cause neuronal damage include the amyloid-β (Aβ) peptide in AD, α-synuclein in Parkinson’s disease, the Huntingtin protein in Huntington’s disease, and PrP in prion diseases such as Creutzfeldt-Jakob’s disease (CJD) [2]. In these diseases a conformationally misfolded protein induces the same protein in its normal form to also misfold and/or deposit. In prion diseases not only does the misfolding protein contribute to disease progression, it is also infective. However, the ability of any amyloid to catalyze the aggregation of other amyloidogenic proteins is highly sequence specific [3]. In prions this specificity provides a barrier to interspecies transmission. Understanding the mechanism of prion conversion and the role of mutations and species variations in neurodegeneration and prion transmission is important for the development of treatments and diagnostics. Recently, yeast prion mutations have been generated that provide new transmission barriers, while not preventing amyloid formation [3]. In this study point mutations altered the range of infectious conformations and changed amyloid seeding specificity. Using mutations to specifically disfavor subsets of prion strains led to the generation of a new transmission