Expression of the human ␤-amyloid peptide (A␤) in a transgenic Caenorhabditis elegans Alzheimer disease model leads to the induction of HSP-16 proteins, a family of small heat shockinducible proteins homologous to vertebrate ␣B crystallin. These proteins also co-localize and co-immunoprecipitate with A␤ in this model (Fonte, V., Kapulkin, V., Taft Accumulation of the ␤-amyloid (A␤)2 peptide in the brain has been proposed to be causally linked to Alzheimer disease (the "Amyloid Cascade" hypothesis (1)), even though the specific mechanisms by which the A␤ peptide induces AD pathology have not been resolved. Intracellular A␤ accumulation has also been proposed to underlie the muscle pathology observed in inclusion body myositis (2). To investigate A␤ toxicity in a genetically tractable model, we have engineered Caenorhabditis elegans nematodes to express the human A␤-(1-42) peptide in either body wall muscle (3) or neurons (4).In C. elegans transgenic models with muscle expression of A␤, the peptide accumulates in intracellular cytoplasmic deposits (5) despite the inclusion of a signal peptide in the transgene construct. The appropriate removal of the signal peptide and the association of Abeta with hsp-3, an ER chaperone homologous to mammalian GRP78/BiP (6), have led us to propose that Abeta is routed to the secretory pathway in this model but is retrotranslocated out of the ER because it is recognized as an abnormal protein (4). We have also demonstrated a role for autophagosomes and lysosomes in the clearance of Abeta in this model, suggesting that Abeta may also exist in these subcellular compartments (8). Intracellular Abeta is observed in the muscles of IBM patients or in transgenic mouse models of IBM (9, 10), although the subcellular distribution of Abeta has not been determined. Intracellular A␤ has also been observed in human brain neurons (11), and the relevance of intracellular A␤ in Alzheimer disease has been supported by studies with the LaFerla 3ϫ transgenic AD mouse model, where accumulation of intracellular A␤ precedes neurofibrillary tangle formation (12). A number of neurodegenerative diseases (Parkinson, Huntington, amyotrophic lateral sclerosis, etc.) are characterized by intracellular cytoplasmic accumulation of proteins causally associated with theses diseases, and thus the C. elegans transgenic model described in this study may be generally relevant to the proteotoxicity underlying neurodegenerative diseases. In this context, a transgenic C. elegans strain expressing human A␤ has been used recently to investigate the roles of insulin-like signaling and heat shock factor in proteotoxicity (13).A robust finding in these transgenic C. elegans models is the induction of the HSP-16 family of small chaperone proteins by A␤ expression (14, 15). HSP-16 proteins readily co-immunoprecipitate with A␤ in transgenic C. elegans worms and closely associate with intracellular A␤ deposits as observed by immunohistochemistry (16). The HSP-16 family proteins are homologous to ␣B crystallin and have been show...

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We find that expression of the GFP::degron in Caenorhabditis elegans muscle or neurons results in the formation of stable perinuclear deposits. Similar perinuclear deposition of GFP::degron was also observed upon transfection of primary rat hippocampal neurons or mouse Neuro2A cells. The generality of this observation was supported by transfection of HEK 293 cells with both GFP::degron and DsRed(monomer)::degron constructs. GFP::degron expressed in C. elegans is less soluble than unmodified GFP and induces the small chaperone protein HSP-16, which co-localizes and co-immunoprecipitates with GFP::degron deposits. Induction of GFP::degron in C. elegans muscle leads to rapid paralysis, demonstrating the in vivo toxicity of this aggregating variant. This paralysis is suppressed by co-expression of HSP-16, which dramatically alters the subcellular distribution of GFP::degron. Our results suggest that in C. elegans, and perhaps in mammalian cells, the degron peptide is not a specific proteasome-targeting signal but acts instead by altering GFP secondary or tertiary structure, resulting in an aggregation-prone form recognized by the chaperone system. This altered form of GFP can form toxic aggregates if its expression level exceeds the capacity of chaperone-based degradation pathways. GFP::degron may serve as an instructive "generic" aggregating control protein for studies of disease-associated aggregating proteins, such as huntingtin, ␣-synuclein, and the ␤-amyloid peptide.Aggregating proteins or peptides have been associated with numerous neurodegenerative diseases (1), although the molecular mechanisms remain unclear. The apparent toxicity of these protein aggregates has been demonstrated in cell culture and in many transgenic mouse and invertebrate models (reviewed in Refs. 2-4). We have shown previously that transgenic expression of the human ␤-amyloid peptide (A␤) 2 in Caenorhabditis elegans leads to the formation of intracellular aggregates and associated toxicity (5). Similar observations have been made for transgenic C. elegans animals expressing polyglutamine repeat proteins (6 -8), ␣-synuclein (9), or tau (10). One unanswered question for the C. elegans (as well as Drosophila and mammalian) disease models is the specificity of the observed toxicity, i.e. would any aggregating protein have the same effect? In theory, this question could be addressed by control experiments in which transgenic animals are constructed in parallel that express a nondisease-associated, "generic" aggregating protein. We show here that GFP can be converted into such a control aggregating protein and that expression of this aggregating GFP variant results in in vivo toxicity grossly similar to that observed for diseaseassociated aggregating proteins.In a search for random peptides that would confer instability on proteins expressed in yeast, Gilon et al. (11) identified a non-natural 16-residue peptide (CL1) that conferred apparent ubiquitin-dependent degradation on the Ura3 protein. This short C-terminal "degron" peptide was subseq...

Dietary restriction (DR) retards aging and mortality across a variety of taxa. In homeotherms, one of the hallmarks of DR is lower mean body temperature (T(b)), which might be directly responsible for some aspects of DR-mediated life extension. We conducted a quantitative trait locus (QTL) analysis of the response of T(b) to DR in mice using a panel of 22 LSXSS recombinant inbred strains, tested in two cohorts. T(b) in response to DR had a significant genetic component, explaining approximately 35% of the phenotypic variation. We mapped a statistically significant QTL to chromosome 9 and a provisional QTL to chromosome 17, which together accounted for about two thirds of the genetic variation. Such QTLs could be used to critically test whether the response of T(b) to DR also affects the response of life extension. In addition, this study demonstrates the feasibility of trying to map QTLs that affect other physiological responses to DR, including the life extension response. Importantly, the genes underlying such QTLs would be causal factors affecting these responses and could be identified by positional cloning.

Multiple gene expression alterations have been linked to Alzheimer’s disease (AD), implicating multiple metabolic pathways in its pathogenesis. However, a clear distinction between AD-specific gene expression changes and those resulting from non-specific responses to toxic aggregating proteins has not been made. We investigated alterations in gene expression induced by human β-amyloid peptide (Aβ) in a Caenorhabditis elegans Alzheimer’s disease model. Aβ-induced gene expression alterations were compared to those caused by a synthetic aggregating protein to identify Aβ-specific effects. Both Aβ-specific and non-specific alterations were observed. Among Aβ-specific genes were those involved in aging, proteasome function, and mitochondrial function. An intriguing observation was the significant overlap between gene expression changes induced by Aβ and those induced by Cry5B, a bacterial pore-forming toxin. This led us to hypothesize that Aβ exerts its toxic effect, at least in part, by causing damage to biological membranes. We provide in vivo evidence consistent with this hypothesis. This study distinguishes between Aβ-specific and non-specific mechanisms and provides potential targets for therapeutics discovery.

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