Small molecule enhancers of autophagy for neurodegenerative diseases.

Neurodegenerative disorders such as Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis, prion diseases and polyglutamine disorders, including Huntington's disease and various spinocerebellar ataxias, are associated with the formation of protein aggregates. These aggregates and/or their precursors are thought to be toxic disease-causing species. Autophagy is a major degradation pathway for intracytosolic aggregate-prone proteins, including those associated with neurodegeneration.

Loss of PINK1 function affects development and results in neurodegeneration in zebrafish.

Parkinson's disease (PD) is the second most prevalent neurodegenerative disorder in the Western world. PTEN (phosphatase/tensin homolog on chromosome 10)-induced putative kinase 1 (PINK1), a putative kinase that is mutated in autosomal recessive forms of PD, is also implicated in sporadic cases of the disease. Although the mutations appear to result in a loss of function, the roles of this protein and the pathways involved in PINK1 PD are poorly understood.

Functional genomics approaches to neurodegenerative diseases.

Many of the neurodegenerative diseases that afflict humans are characterised by the protein aggregation in neurons. These include complex diseases like Alzheimer's disease and Parkinson's disease, and Mendelian diseases caused by polyglutamine expansion mutations [like Huntington's disease (HD) and various spinocerebellar ataxias (SCAs), like SCA3]. A range of functional genomic strategies have been used to try to elucidate pathways involved in these diseases.

Autophagy in neurodegeneration and development.

Efficient protein turnover is essential for the maintenance of cellular health. Here we review how autophagy has fundamental functions in cellular homeostasis and possible uses as a therapeutic strategy for neurodegenerative diseases associated with intracytosolic aggregate formation, like Huntington's disease (HD). Drugs like rapamycin, that induce autophagy, increase the clearance of mutant huntingtin fragments and ameliorate the pathology in cell and animal models of HD and related conditions.

Huntington's disease: degradation of mutant huntingtin by autophagy.

Autophagy is a nonspecific bulk degradation pathway for long-lived cytoplasmic proteins, protein complexes, or damaged organelles. This process is also a major degradation pathway for many aggregate-prone, disease-causing proteins associated with neurodegenerative disorders, such as mutant huntingtin in Huntington's disease. In this review, we discuss factors regulating the degradation of mutant huntingtin by autophagy.

Rapamycin and mTOR-independent autophagy inducers ameliorate toxicity of polyglutamine-expanded huntingtin and related proteinopathies.

The formation of intra-neuronal mutant protein aggregates is a characteristic of several human neurodegenerative disorders, like Alzheimer's disease, Parkinson's disease (PD) and polyglutamine disorders, including Huntington's disease (HD). Autophagy is a major clearance pathway for the removal of mutant huntingtin associated with HD, and many other disease-causing, cytoplasmic, aggregate-prone proteins. Autophagy is negatively regulated by the mammalian target of rapamycin (mTOR) and can be induced in all mammalian cell types by the mTOR inhibitor rapamycin.

Huntington's disease: from pathology and genetics to potential therapies.

Huntington's disease (HD) is a devastating autosomal dominant neurodegenerative disease caused by a CAG trinucleotide repeat expansion encoding an abnormally long polyglutamine tract in the huntingtin protein. Much has been learnt since the mutation was identified in 1993. We review the functions of wild-type huntingtin.

Association analysis of dynamin-binding protein (DNMBP) on chromosome 10q with late onset Alzheimer's disease in a large caucasian UK sample.

A recent scan of single nucleotide polymorphisms (SNPs) in the region 40-107 Mb on chromosome 10q in a large Japanese case-control cohort identified six SNPs in or near the dynamin-binding protein gene (DNMBP) that were associated with late onset Alzheimer's disease (LOAD) in individuals lacking the APOE epsilon4 allele [Kuwano et al. (2006); Hum Mol Genet 15:2170-2182]. We genotyped these six SNPs in 1,212 unrelated Caucasian patients of UK origin with LOAD and 1,389 ethnically, gender and age matched control subjects.

Rab5 modulates aggregation and toxicity of mutant huntingtin through macroautophagy in cell and fly models of Huntington disease.

Huntington disease (HD) is caused by a polyglutamine-expansion mutation in huntingtin (HTT) that makes the protein toxic and aggregate-prone. The subcellular localisation of huntingtin and many of its interactors suggest a role in endocytosis, and recently it has been shown that huntingtin interacts indirectly with the early endosomal protein Rab5 through HAP40. Here we show that Rab5 inhibition enhanced polyglutamine toxicity, whereas Rab5 overexpression attenuated toxicity in our cell and fly models of HD.

Clearance of mutant aggregate-prone proteins by autophagy.

The accumulation of mutant aggregate-prone proteins is a feature of several human disorders, collectively referred to as protein conformation disorders or proteinopathies. We have shown that autophagy, a cytosolic, non-specific bulk degradation system, is an important clearance route for many cytosolic toxic, aggregate-prone proteins, like mutant huntingtin and mutant alpha-synucleins. Induction of autophagy enhances the clearance of both soluble and aggregated forms of the mutant protein, and protects against toxicity caused by these mutations in cell, fly, and mouse models.

Spinocerebellar ataxias caused by polyglutamine expansions: a review of therapeutic strategies.

Six of the spinocerebellar ataxias (SCAs) are caused by expanded CAG trinucleotide repeats encoding polyglutamine tracts in different genes. Together with three other neurodegenerative diseases they represent the polyglutamine repeat disorders. These disorders share many pathological features beyond a common genetic mechanism.

Novel targets for Huntington's disease in an mTOR-independent autophagy pathway.

Autophagy is a major clearance route for intracellular aggregate-prone proteins causing diseases such as Huntington's disease. Autophagy induction with the mTOR inhibitor rapamycin accelerates clearance of these toxic substrates. As rapamycin has nontrivial side effects, we screened FDA-approved drugs to identify new autophagy-inducing pathways.

Guidelines for the use and interpretation of assays for monitoring autophagy in higher eukaryotes.

Research in autophagy continues to accelerate,(1) and as a result many new scientists are entering the field. Accordingly, it is important to establish a standard set of criteria for monitoring macroautophagy in different organisms. Recent reviews have described the range of assays that have been used for this purpose.

The itinerary of autophagosomes: from peripheral formation to kiss-and-run fusion with lysosomes.

Macroautophagy, a constitutive process in higher eukaryotic cells, mediates degradation of many long-lived proteins and organelles. The actual events occurring during the process in the dynamic system of a living cell have never been thoroughly investigated. We aimed to develop a live-cell assay in which to follow the complete itinerary of an autophagosome.

Wild-type PABPN1 is anti-apoptotic and reduces toxicity of the oculopharyngeal muscular dystrophy mutation.

Oculopharyngeal muscular dystrophy (OPMD) is a late-onset, progressive disease caused by the abnormal expansion of a polyalanine tract-encoding (GCG)(n) trinucleotide repeat in the poly-(A) binding protein nuclear 1 (PABPN1) gene. OPMD is generally inherited as an autosomal dominant disorder and the polyalanine expansion mutation is thought to confer a toxic gain-of-function on mutant PABPN1 which forms aggregates within skeletal myocyte nuclei. Here we describe a novel beneficial function of wild-type PABPN1.

Association analysis of 528 intra-genic SNPs in a region of chromosome 10 linked to late onset Alzheimer's disease.

Late-onset Alzheimer's disease (LOAD) is a genetically complex neurodegenerative disorder. Currently, only the epsilon4 allele of the Apolipoprotein E gene has been identified unequivocally as a genetic susceptibility factor for LOAD. Others remain to be found.

p21-activated kinase 1 promotes soluble mutant huntingtin self-interaction and enhances toxicity.

Huntington's disease (HD) is caused by a polyglutamine (polyQ) expansion in the huntingtin (htt) protein. While aggregation is a pathological hallmark of HD and related polyQ expansion diseases, the role of aggregates has been disputed. Here we report that p21-activated kinase 1 (Pak1) binds to htt in vivo and in vitro.

Evidence that common variation in NEDD9 is associated with susceptibility to late-onset Alzheimer's and Parkinson's disease.

Late-onset Alzheimer's disease (LOAD) and Parkinson's disease (PD) are the most common neurodegenerative disorders and in both diseases susceptibility is known to be influenced by genes. We set out to identify novel susceptibility genes for LOAD by performing a large scale, multi-tiered association study testing 4692 single nucleotide polymorphism (SNPs). We identified a SNP within a putative transcription factor binding site in the NEDD9 gene (neural precursor cell expressed, developmentally down-regulated), that shows good evidence of association with disease risk in four out of five LOAD samples [N = 3521, P = 5.

The ubiquitin proteasome system in Huntington's disease and the spinocerebellar ataxias.

Huntington's disease and several of the spinocerebellar ataxias are caused by the abnormal expansion of a CAG repeat within the coding region of the disease gene. This results in the production of a mutant protein with an abnormally expanded polyglutamine tract. Although these disorders have a clear monogenic cause, each polyglutamine expansion mutation is likely to cause the dysfunction of many pathways and processes within the cell.

Lysosomal storage diseases as disorders of autophagy.

The cellular turnover of proteins and organelles requires cooperation between the autophagic and the lysosomal degradation pathways. A crucial step in this process is the fusion of the autophagosome with the lysosome. In our study we demonstrate that in Lysosomal Storage Disorders (LSDs) accumulation of undegraded substrates in lysosomes, due to deficiency of specific lysosomal enzymes, impairs the fusion between autophagosomes and lysosomes.

Hydrophilic protein associated with desiccation tolerance exhibits broad protein stabilization function.

The ability of certain plants, invertebrates, and microorganisms to survive almost complete loss of water has long been recognized, but the molecular mechanisms of this phenomenon remain to be defined. One phylogenetically widespread adaptation is the presence of abundant, highly hydrophilic proteins in desiccation-tolerant organisms. The best characterized of these polypeptides are the late embryogenesis abundant (LEA) proteins, first described in plant seeds >20 years ago but recently identified in invertebrates and bacteria.

A rational mechanism for combination treatment of Huntington's disease using lithium and rapamycin.

Huntington's disease (HD) is caused by a polyglutamine expansion mutation in the huntingtin protein that confers a toxic gain-of-function and causes the protein to become aggregate-prone. Aggregate-prone proteins are cleared by macroautophagy, and upregulating this process by rapamycin, which inhibits the mammalian target of rapamycin (mTOR), attenuates their toxicity in various HD models. Recently, we demonstrated that lithium induces mTOR-independent autophagy by inhibiting inositol monophosphatase (IMPase) and reducing inositol and IP3 levels.

A block of autophagy in lysosomal storage disorders.

Most lysosomal storage disorders (LSDs) are caused by deficiencies of lysosomal hydrolases. While LSDs were among the first inherited diseases for which the underlying biochemical defects were identified, the mechanisms from enzyme deficiency to cell death are poorly understood. Here we show that lysosomal storage impairs autophagic delivery of bulk cytosolic contents to lysosomes.

Small molecule enhancers of rapamycin-induced TOR inhibition promote autophagy, reduce toxicity in Huntington's disease models and enhance killing of mycobacteria by macrophages.

Upregulation of autophagy may have therapeutic benefit in a range of diseases that includes neurodegenerative conditions caused by intracytosolic aggregate-prone proteins, such as Huntington's disease, and certain infectious diseases, such as tuberculosis. The best-characterized drug that enhances autophagy is rapamycin, an inhibitor of the TOR (target of rapamycin) proteins, which are widely conserved from yeast to man. Unfortunately, the side effects of rapamycin, especially immunosuppression, preclude its use in treating certain diseases including tuberculosis, which accounts for approximately 2 million deaths worldwide each year, spurring interest in finding novel drugs that selectively enhance autophagy.

Autophagy induction rescues toxicity mediated by proteasome inhibition.

The ubiquitin-proteasome and macroautophagy-lysosome pathways are major routes for intracytosolic protein degradation. In many systems, proteasome inhibition is toxic. A Nature article by Pandey et al.