Application of optogenetic Amyloid-ß distinguishes between metabolic and physical damages in neurodegeneration.

The brains of Alzheimer's disease patients show a decrease in brain mass and a preponderance of extracellular Amyloid-ß plaques. These plaques are formed by aggregation of polypeptides that are derived from the Amyloid Precursor Protein (APP). Amyloid-ß plaques are thought to play either a direct or an indirect role in disease progression, however the exact role of aggregation and plaque formation in the aetiology of Alzheimer's disease (AD) is subject to debate as the biological effects of soluble and aggregated Amyloid-ß peptides are difficult to separate in vivo. To investigate the consequences of formation of Amyloid-ß oligomers in living tissues, we developed a fluorescently tagged, optogenetic Amyloid-ß peptide that oligomerizes rapidly in the presence of blue light. We applied this system to the crucial question of how intracellular Amyloid-ß oligomers underlie the pathologies of A. We use Drosophila, C. elegans and D. rerio to show that, although both expression and induced oligomerization of Amyloid-ß were detrimental to lifespan and healthspan, we were able to separate the metabolic and physical damage caused by light-induced Amyloid-ß oligomerization from Amyloid-ß expression alone. The physical damage caused by Amyloid-ß oligomers also recapitulated the catastrophic tissue loss that is a hallmark of late AD. We show that the lifespan deficit induced by Amyloid-ß oligomers was reduced with Li+ treatment. Our results present the first model to separate different aspects of disease progression.

Alzheimer's disease is a progressive condition that damages the brain over time. The cause is not clear, but a toxic molecule called Amyloid-ß peptide seems to play a part. It builds up in the brains of people with Alzheimer's disease, forming hard clumps called plaques. Yet, though the plaques are a hallmark of the disease, experimental treatments designed to break them down do not seem to help. This raises the question ­ do Amyloid-ß plaques actually cause Alzheimer's disease? Answering this question is not easy. One way to study the effect of amyloid plaques is to inject clumps of Amyloid-ß peptides into model organisms. This triggers Alzheimer's-like brain damage, but it is not clear why. It remains difficult to tell the difference between the damage caused by the injected Amyloid-ß peptides and the damage caused by the solid plaques that they form. For this, researchers need a way to trigger plaque formation directly inside animal brains. This would make it possible to test the effects of plaque-targeting treatments, like the drug lithium. Optogenetics is a technique that uses light to control molecules in living animals. Hsien, Kaur et al. have now used this approach to trigger plaque formation by fusing light-sensitive proteins to Amyloid-ß peptides in worms, fruit flies and zebrafish. This meant that the peptides clumped together to form plaques whenever the animals were exposed to blue light. This revealed that, while both the Amyloid-ß peptides and the plaques caused damage, the plaques were much more toxic. They damaged cell metabolism and caused tissue loss that resembled late Alzheimer's disease in humans. To find out whether it was possible to test Alzheimer's treatments in these animals, Hsien, Kaur et al. treated them with the drug, lithium. This increased their lifespan, reversing some of the damage caused by the plaques. Alzheimer's disease affects more than 46.8 million people worldwide and is the sixth leading cause of death in the USA. But, despite over 50 years of research, there is no cure. This new plaque-formation technique allows researchers to study the effects of amyloid plaques in living animals, providing a new way to test Alzheimer's treatments. This could be of particular help in studies of experimental drugs that aim to reduce plaque formation.

Drug synergy as a strategy for compression of morbidity in a Caenorhabditis elegans model of Alzheimer's disease.

Alzheimer's disease (AD) is the most common cause of dementia worldwide. AD is a multifactorial disease with simultaneous occurrence of several connected pathological processes including mitochondrial dysfunction and impaired proteostasis. Most of these are also implicated in organismal aging per se. The presence of separable pathological conditions poses the opportunity to try combination treatments that target these different processes separately. This approach may provide an effective strategy to target AD; therefore, we investigated whether a combination of metformin (targeting mitochondria and energy metabolism) and lithium (targeting proteostasis) could result in synergistic benefits. In this perspective paper, we looked for benefits in lifespan and healthspan using a transgenic nematode strain, GRU102, which expresses pan-neuronal human amyloid-beta (Aß). Individually, metformin and lithium extended the lifespan of both non-transgenic GRU101 controls and GRU102. Combination treatment using metformin and lithium did not result in any synergistic increase in GRU102 lifespan, but this treatment did result in a significant compression of morbidity when compared with each individual drug, resulting in relative and absolute extension of healthspan. Despite over-expressing pathogenic human Aß in their neurons, GRU102 worms treated with the combination treatment enjoyed longer lifespans and significantly compressed morbidity, even compared with untreated non-transgenic animals. These findings suggest combination treatment as a strategy to compress morbidity, and highlight the distinction between healthspan and lifespan.

Use of Optogenetic Amyloid-ß to Monitor Protein Aggregation in Drosophila melanogaster, Danio rerio and Caenorhabditis elegans.

Alzheimer's Disease (AD) has long been associated with accumulation of extracellular amyloid plaques (Aß) originating from the Amyloid Precursor Protein. Plaques have, however, been discovered in healthy individuals and not all AD brains show plaques, suggesting that extracellular Aß aggregates may play a smaller role than anticipated. One limitation to studying Aß peptide in vivo during disease progression is the inability to induce aggregation in a controlled manner. We developed an optogenetic method to induce Aß aggregation and tested its biological influence in three model organisms-D. melanogaster, C. elegans and D. rerio. We generated a fluorescently labeled, optogenetic Aß peptide that oligomerizes rapidly in vivo in the presence of blue light in all organisms. Here, we detail the procedures for expressing this fusion protein in animal models, investigating the effects on the nervous system using time lapse light-sheet microscopy, and performing metabolic assays to measure changes due to intracellular Aß aggregation. This method, employing optogenetics to study the pathology of AD, allows spatial and temporal control in vivo that cannot be achieved by any other method at present.

Metabolic stress is a primary pathogenic event in transgenic Caenorhabditis elegans expressing pan-neuronal human amyloid beta.

Alzheimer's disease (AD) is the most common neurodegenerative disease affecting the elderly worldwide. Mitochondrial dysfunction has been proposed as a key event in the etiology of AD. We have previously modeled amyloid-beta (Aß)-induced mitochondrial dysfunction in a transgenic Caenorhabditis elegans strain by expressing human Aß peptide specifically in neurons (GRU102). Here, we focus on the deeper metabolic changes associated with this Aß-induced mitochondrial dysfunction. Integrating metabolomics, transcriptomics and computational modeling, we identify alterations in Tricarboxylic Acid (TCA) cycle metabolism following even low-level Aß expression. In particular, GRU102 showed reduced activity of a rate-limiting TCA cycle enzyme, alpha-ketoglutarate dehydrogenase. These defects were associated with elevation of protein carbonyl content specifically in mitochondria. Importantly, metabolic failure occurred before any significant increase in global protein aggregate was detectable. Treatment with an anti-diabetes drug, Metformin, reversed Aß-induced metabolic defects, reduced protein aggregation and normalized lifespan of GRU102. Our results point to metabolic dysfunction as an early and causative event in Aß-induced pathology and a promising target for intervention.

A novel vibration-induced exercise paradigm improves fitness and lipid metabolism of Caenorhabditis elegans.

Exercise has been known to reduce the risk of obesity and metabolic syndrome, but the mechanisms underlying many exercise benefits remain unclear. This is, in part, due to a lack of exercise paradigms in invertebrate model organisms that would allow rapid mechanistic studies to be conducted. Here we report a novel exercise paradigm in Caenorhabditis elegans (C. elegans) that can be implemented under standard laboratory conditions. Mechanical stimulus in the form of vibration was transduced to C. elegans grown on solid agar media using an acoustic actuator. One day post-exercise, the exercised animals showed greater physical fitness compared to the un-exercised controls. Despite having higher mitochondrial reactive oxygen species levels, no mitohormetic adaptations and lifespan extension were observed in the exercised animals. Nonetheless, exercised animals showed lower triacylglycerides (TAG) accumulation than the controls. Among the individual TAG species, the most significant changes were found in mono- and polyunsaturated fatty acid residues. Such alteration resulted in an overall lower double bond index and peroxidation index which measure susceptibility towards lipid peroxidation. These observations are consistent with findings from mammalian exercise literature, suggesting that exercise benefits are largely conserved across different animal models.

Energy crisis precedes global metabolic failure in a novel Caenorhabditis elegans Alzheimer Disease model.

Alzheimer Disease (AD) is a progressive neurological disorder characterized by the deposition of amyloid beta (Aß), predominantly the Aß1-42 form, in the brain. Mitochondrial dysfunction and impaired energy metabolism are important components of AD pathogenesis. However, the causal and temporal relationships between them and AD pathology remain unclear. Using a novel C. elegans AD strain with constitutive neuronal Aß1-42 expression that displays neuromuscular defects and age-dependent behavioural dysfunction reminiscent of AD, we have shown that mitochondrial bioenergetic deficit is an early event in AD pathogenesis, preceding dysfunction of mitochondrial electron transfer chain (ETC) complexes and the onset of global metabolic failure. These results are consistent with an emerging view that AD may be a metabolic neurodegenerative disease, and also confirm that Aß-driven metabolic and mitochondrial effects can be reproduced in organisms separated by large evolutionary distances.

Caenorhabditis elegans: What We Can and Cannot Learn from Aging Worms.

SIGNIFICANCE: The nematode Caenorhabditis elegans is a widely used model organism for research into aging. However, nematodes diverged from other animals between 600 and 1300 million years ago. Beyond the intuitive impression that some aspects of aging appear to be universal, is there evidence that insights into the aging process of nematodes may be applicable to humans? RECENT ADVANCES: There have been a number of results in nematodes that appear to contradict long-held beliefs about mechanisms and causes of aging. For example, ablation of several key antioxidant systems has often failed to result in lifespan shortening in C. elegans. CRITICAL ISSUES: While it is clear that some central signaling pathways controlling lifespan are broadly conserved across large evolutionary distances, it is less clear to what extent downstream molecular mechanisms of aging are conserved. In this review we discuss the biology of C. elegans and mammals in the context of aging and age-dependent diseases. We consider evidence from studies that attempt to investigate basic, possibly conserved mechanisms of aging especially in the context of the free radical theory of aging. Practical points, such as the need for blinding of lifespan studies and for appropriate biomarkers, are also considered. FUTURE DIRECTIONS: As data on the aging process(es) in different organisms increase, it is becoming increasingly clear that there are both conserved (public) and private aspects to aging. It is important to explore the dividing lines between these two aspects and to be aware of the large gray areas in-between.