Can flies help humans treat neurodegenerative diseases?

Neuroprotective Potential of Eugenol in Polyglutamine-Mediated Neurodegenerative Disease Using Transgenic Drosophila Model

Polyglutamine (PolyQ) diseases including Huntington's disease are devastating neurodegenerative disorders characterized by progressive neuronal loss and motor dysfunction. PolyQ pathology involves multiple cellular events and phytochemicals with multi-target mechanisms hold promise to treat these diseases with least side effects. One such promising phytochemical is Eugenol, which possesses antioxidant and anti-inflammatory properties, potentially targeting disrupted cellular pathways in PolyQ diseases. The present study investigated the effects of Eugenol on neurodegeneration and motor dysfunction in transgenic Drosophila models of PolyQ diseases. In this study, the robust pseudopupil assay was performed to analyze adult photoreceptor neuron degeneration, a marker of widespread degenerative events. Furthermore, the well-established crawling and climbing assays were conducted to evaluate progressive motor dysfunction in the PolyQ larvae and flies. This study found that Eugenol administration at disease onset or after progression reduced PolyQ disease phenotypes, particularly, neurodegeneration and motor dysfunction in a dose-dependent manner and with no side effects. Thus, this study suggests that Eugenol could be a viable candidate for developing treatments for PolyQ diseases, offering a multi-target approach with the potential for minimal or no side effects compared to conventional therapies.

Curcumin, inflammation, and neurological disorders: How are they linked?

Background

Despite the extensive research in recent years, the current treatment modalities for neurological disorders are suboptimal. Curcumin, a polyphenol found in Curcuma genus, has been shown to mitigate the pathophysiology and clinical sequalae involved in neuroinflammation and neurodegenerative diseases.

Methods

We searched PubMed database for relevant publications on curcumin and its uses in treating neurological diseases. We also reviewed relevant clinical trials which appeared on searching PubMed database using 'Curcumin and clinical trials'.

Results

This review details the pleiotropic immunomodulatory functions and neuroprotective properties of curcumin, its derivatives and formulations in various preclinical and clinical investigations. The effects of curcumin on neurodegenerative diseases such as Alzheimer's disease (AD), amyotrophic lateral sclerosis (ALS), brain tumors, epilepsy, Huntington's disorder (HD), ischemia, Parkinson's disease (PD), multiple sclerosis (MS), and traumatic brain injury (TBI) with a major focus on associated signalling pathways have been thoroughly discussed.

Conclusion

This review demonstrates curcumin can suppress spinal neuroinflammation by modulating diverse astroglia mediated cascades, ensuring the treatment of neurological disorders.

Amendment of Altered Immune Response by Curcumin in Drosophila Model of Huntington's Disease

BACKGROUND

Though primarily classified as a brain disorder, surplus studies direct Huntington's disease (HD) to be a multi-system disorder affecting various tissues and organs, thus affecting overall physiology of host. Recently, we have reported that neuronal expression of mutant huntingtin induces immune dysregulation in Drosophila and may pose chronic threat to challenged individuals. Therefore, we tested the polyphenolic compound curcumin to circumvent the impact of immune dysregulation in Drosophila model of HD.

OBJECTIVE

The present study examined the molecular basis underlying immune derangements and immunomodulatory potential of curcumin in HD.

METHODS

UAS-GAL4 system was used to imitate the HD symptoms in Drosophila, and the desired female progenies (elav > Httex1pQ25; control and elav > Httex1pQ93; diseased) were cultured on food mixed without and with 10 μM concentration of curcumin since early development. Effect of curcumin supplementation was investigated by monitoring the hemocytes' count and their functional abilities in diseased condition. Reactive oxygen species (ROS) level in cells was assessed by DHE staining and mitochondrial dysfunction was assessed by CMXros red dye. In addition, transcript levels of pro-inflammatory cytokines and anti-microbial peptides were monitored by qRT-PCR.

RESULTS

We found that curcumin supplementation commendably reduced higher crystal cell count and phenoloxidase activity in diseased flies. Interestingly, curcumin significantly managed altered plasmatocytes count, improved their phagocytic activity by upregulating the expression of key phagocytic receptors in HD condition. Moreover, substantial alleviation of ROS levels and mitochondria dysfunction was observed in plasmatocytes of diseased flies upon curcumin supplementation. Furthermore, curcumin administration effectively attenuated transcriptional expression of pro-inflammatory cytokines and AMPs in diseased flies.

CONCLUSIONS

Our results indicate that curcumin efficiently attenuates immune derangements in HD flies and may prove beneficial in alleviating complexities associated with HD.

Metabolism in Huntington's disease: a major contributor to pathology

Huntington's disease (HD) is a progressively debilitating neurodegenerative disease exhibiting autosomal-dominant inheritance. It is caused by an unstable expansion in the CAG repeat tract of HD gene, which transforms the disease-specific Huntingtin protein (HTT) to a mutant form (mHTT). The profound neuronal death in cortico-striatal circuits led to its identification and characterisation as a neurodegenerative disease. However, equally disturbing are the concomitant whole-body manifestations affecting nearly every organ of the diseased individuals, at varying extents. Altered central and peripheral metabolism of energy, proteins, nucleic acids, lipids and carbohydrates encompass the gross pathology of the disease. Intense fluctuation of body weight, glucose homeostasis and organ-specific subcellular abnormalities are being increasingly recognised in HD. Many of these metabolic abnormalities exist years before the neuropathological manifestations such as chorea, cognitive decline and behavioural abnormalities develop, and prove to be reliable predictors of the disease progression. In this review, we provide a consolidated overview of the central and peripheral metabolic abnormalities associated with HD, as evidenced from clinical and experimental studies. Additionally, we have discussed the potential of metabolic biomolecules to translate into efficient biomarkers for the disease onset as well as progression. Finally, we provide a brief outlook on the efficacy of existing therapies targeting metabolic remediation. While it is clear that components of altered metabolic pathways can mark many aspects of the disease, it is only conceivable that combinatorial therapies aiming for neuronal protection in consort with metabolic upliftment will prove to be more efficient than the existing symptomatic treatment options.

Management of altered metabolic activity in Drosophila model of Huntington's disease by curcumin

Huntington's disease (HD) is a devastating polyglutamine disorder characterized by extensive neurodegeneration and metabolic abnormalities at systemic, cellular and intracellular levels. Metabolic alterations in HD manifest as abnormal body weight, dysregulated biomolecule levels, impaired adipocyte functions, and defective energy state which exacerbate disease progression and pose acute threat to the health of challenged individuals in form of insulin resistance, cardiovascular disease, and energy crisis. To colossally mitigate disease symptoms, we tested the efficacy of curcumin in Drosophila model of HD. Curcumin is the bioactive component of turmeric (Curcuma longa Linn), well-known for its ability to modulate metabolic activities. We found that curcumin effectively managed abnormal body weight, dysregulated lipid content, and carbohydrate level in HD flies. In addition, curcumin administration lowered elevated reactive-oxygen-species levels in adult adipose tissue of diseased flies, and improved survival and locomotor function in HD flies at advanced disease stage. Altogether, these findings clearly suggest that curcumin efficiently attenuates metabolic derangements in HD flies and can prove beneficial in alleviating the complexities associated with HD.

Ameliorative Role of Nutraceuticals on Neurodegenerative Diseases Using the Drosophila melanogaster as a Discovery Model to Define Bioefficacy

Neurodegeneration is the destruction of neurons, and once the neurons degenerate they can't revive. This is one of the most concerned health conditions among aged population, more than ∼70% of the elderly people are suffering from neurodegeneration. Among all of the neurodegenerative diseases, Alzheimer's disease (AD), Parkinson's disease (PD) and Poly-glutamine disease (Poly-Q) are the major one and affecting most of the people around the world and posing excessive burden on the society. In order to understand this disease in non-human animal models it is pertinent to examine in model organism and various animal model are being used for such diseases like rat, mice and non-vertebrate model like Drosophila. Drosophila melanogaster is one of the best animal proven by several eminent scientist and had received several Nobel prizes for uncovering mechanism of human related genes and highly efficient model for studying neurodegenerative diseases due to its great affinity with human disease-related genes. Another factor is also employed to act as therapeutic or preventive method that is nutraceuticals. Nutraceuticals are functional natural compounds with antioxidant properties and had extensively showed the neuroprotective effect in different organisms. These nutraceuticals having antioxidant properties act through scavenging free radicals or by increasing endogenous cellular antioxidant defense molecules. For the best benefit, we are trying to utilize these nutraceuticals, which will have no or negligible side effects. In this review, we are dealing with various types of such nutraceuticals which have potent value in the prevention and curing of the diseases related to neurodegeneration.HighlightsNeurodegeneration is the silently progressing disease which shows its symptoms when it is well rooted.Many chemical drugs (almost all) have only symptomatic relief with side effects.Potent mechanism of neurodegeneration and improvement effect by nutraceuticals is proposed.Based on the Indian Cuisine scientists are trying to find the medicine from the food or food components having antioxidant properties.The best model to study the neurodegenerative diseases is Drosophila melanogaster.Many nutraceuticals having antioxidant properties have been studied and attenuated various diseases are discussed.

Dissolving the Complex Role Aggregation Plays in Neurodegenerative Disease

Prominent neuropathological hallmarks of many adult-onset neurodegenerative diseases include the deposition and accumulation of misfolded proteins or conformers; however, their role in pathogenesis has remained unclear. This is in part due to the deceptive simplicity of the question and our limited understanding of how protein homeostasis is maintained in the compartmentalized cells of the central nervous system, especially in the context of the adult brain. Building on studies from simple cell-based systems and invertebrate animals, we recently identified a protein central to the specific and selective turnover of aggregated proteins in the adult brain, the autophagy-linked FYVE protein (Alfy)/Wdfy3. Depletion of Alfy levels in a mouse model of Huntington's disease showed that it accelerated the accumulation of the aggregated mutant huntingtin protein, as well as the onset of behavioral deficits. Although the motor dysfunction was accelerated in the model, this was in the absence of increasing overt cell loss, implicating protein aggregates as a modifier of circuit dysfunction rather than driving degeneration per se. We discuss these findings in the context of what is known about protein accumulation and how we can use proteins such as Alfy to determine if protein accumulation is a shared pathogenic event across different adult-onset diseases. © 2021 International Parkinson and Movement Disorder Society.

Deciphering the key mechanisms leading to alteration of lipid metabolism in Drosophila model of Huntington's disease

Huntington's disease (HD) is an inherited, progressively debilitating disorder marked by prominent degeneration in striatal and cortical brain regions. HD is caused by (CAG)_n repeat expansion in huntingtin (HTT) gene that translates into a mutant form of the ubiquitously present Huntingtin (HTT) protein. Extensive metabolic dysfunction coexisting with overt neuropathies has been evidenced in clinical and experimental settings of HD. Body weight loss despite normal to high caloric intake remains a critical determinant of the disease progression and a challenge for therapeutic interventions. In the present study, we intended to monitor the cellular and molecular perturbations in Drosophila, caused by pan-neuronal expression of mHTT (mutant Huntingtin) protein. We found aberrant transcription profile of key lipolytic and lipogenic genes in whole-body of the fly with disease progression. Interestingly, fatbody undergoes extensive alteration of vital cellular processes and eventually surrenders to increased apoptotic cell death in terminal stage of the disease. Extensive mitochondrial dysfunction from early disease stage along with calcium derangement at terminal stage were observed in fatbody, which contribute to its deteriorating integrity. All the mechanisms were monitored progressively, at different disease stages, and many alterations were documented in the early stage itself. Our study hence provides insight into the mechanisms through which neuronal expression of mHTT might be inflicting the profound systemic effects, specifically on lipid metabolism, and may open new therapeutic avenues for alleviation of the multidimensional disease.

Human Tau isoform-specific presynaptic deficits in a Drosophila Central Nervous System circuit

Accumulation of normal or mutant human Tau isoforms in Central Nervous System (CNS) neurons of vertebrate and invertebrate models underlies pathologies ranging from behavioral deficits to neurodegeneration that broadly recapitulate human Tauopathies. Although some functional differences have begun to emerge, it is still largely unclear whether normal and mutant Tau isoforms induce differential effects on the synaptic physiology of CNS neurons. We use the oligosynaptic Giant Fiber System in the adult Drosophila CNS to address this question and reveal that 3R and 4R isoforms affect distinct synaptic parameters. Whereas 0N3R increased failure rate upon high frequency stimulation, 0N4R compromised stimulus conduction and response speed at a specific cholinergic synapse in an age-dependent manner. In contrast, accumulation of the R406W mutant of 0N4R induced mild, age-dependent conduction velocity defects. Because 0N4R and its mutant isoform are expressed equivalently, this demonstrates that the defects are not merely consequent of exogenous human Tau accumulation and suggests distinct functional properties of 3R and 4R isoforms in cholinergic presynapses.

The Tiny Drosophila Melanogaster for the Biggest Answers in Huntington's Disease

The average life expectancy for humans has increased over the last years. However, the quality of the later stages of life is low and is considered a public health issue of global importance. Late adulthood and the transition into the later stage of life occasionally leads to neurodegenerative diseases that selectively affect different types of neurons and brain regions, producing motor dysfunctions, cognitive impairment, and psychiatric disorders that are progressive, irreversible, without remission periods, and incurable. Huntington's disease (HD) is a common neurodegenerative disorder. In the 25 years since the mutation of the huntingtin (HTT) gene was identified as the molecule responsible for this neural disorder, a variety of animal models, including the fruit fly, have been used to study the disease. Here, we review recent research that used Drosophila as an experimental tool for improving knowledge about the molecular and cellular mechanisms underpinning HD.

Systematic genetic interaction studies identify histone demethylase Utx as potential target for ameliorating Huntington's disease

Huntington's disease (HD) is a dominantly inherited neurodegenerative disease caused by alterations in the huntingtin gene (htt). Transcriptional dysregulation is an early event in HD progression. Protein acetylation and methylation particularly on histones regulates chromatin structure thereby preventing or facilitating transcription. Although protein acetylation has been found to affect HD symptoms, little is known about the potential role of protein methylation in HD pathology. In recent years, a series of proteins have been described that are responsible for methylating and demethylating histones as well as other proteins. We carried out systematic genetic interaction studies testing lysine and arginine methylases and demethylases in a Drosophila melanogaster HD model. We found that modulating methylation enzymes that typically affect histone positions H3K4, H3K36 or H3K79 had varying effects on HD pathology while modulating ones that typically affect constitutive heterochromatin marks at H3K9 and H4K20 generally had limited impact on HD pathology. In contrast, modulating enzymes acting on the facultative heterochromatin mark at H3K27 had specific effects on HD pathology, with reduction of the demethylase Utx rescuing HTT-induced pathology while reducing Polycomb Repressive Complex2 core methylase components led to more aggressive pathology. Further exploration of the mechanism underlying the methylation-specific interactions suggest that these lysine and arginine methylases and demethylases are likely exerting their influence through non-histone targets. These results highlight a novel therapeutic approach for HD in the form of Utx inhibition.

Nonmammalian Models of Huntington's Disease

Flies, worms, yeast and more recently zebra fish have all been engineered to express expanded polyglutamine repeat versions of Huntingtin with various resulting pathologies including early death, neurodegeneration, and loss of motor function. Each of these models present particular features that make it useful in studying the mechanisms of polyglutamine pathology. However, one particular unbiased readout of mHTT pathology is functional loss of motor control. Loss of motor control is prominent in patients, but it remains unresolved whether pathogenic symptoms in patients result from overt degeneration and loss of neurons or from malfunctioning of surviving neurons as the pathogenic insult builds up. This is why a functional assay such as motor control can be uniquely powerful in revealing early as well as late neurological deficits and does not rely on assumptions such as that the level of inclusions or the degree of neuronal loss can be equated with the level of pathology. Drosophila is well suited for such assays because it contains a functioning nervous system with many parallels to the human condition. In addition, the ability to readily express mHTT transgenes in different tissues and subsets of neurons allows one the possibility of isolating a particular effect to a subset of neurons where one can correlate subcellular events in response to mHTT challenge with pathology at both the cellular and organismal levels. Here we describe methods to monitor the degree of motor function disruption in Drosophila models of HD and we include a brief summary of other nonmammalian models of HD and discussion of their unique strengths.

Altered lipid metabolism in Drosophila model of Huntington's disease

Huntington’s disease (HD) is late-onset, progressive neurodegenerative disorder caused by expansion of polyglutamine (polyQ) repeat within Huntingtin (Htt) protein. In HD patients, energy-related manifestations such as modulation of weight during entire course of disease with energy deficit at terminal stage have been reported, however, underlying reason remains elusive till date. Lipids, carbohydrate and protein constitute a predominant fraction of body’s energy reservoir and perturbation in their homeostasis may influence weight. To discern role of these energy molecules in weight alteration, we quantified them in an in vivo transgenic Drosophila model of HD. We document that diseased flies exhibit change in weight due to an altered lipid metabolism, as evident from considerably high lipid levels at the time of disease onset followed by a pathologic decline at end-stage. An alteration in intracellular lipid droplet size suggested altered cellular lipid turnover. Furthermore, diseased flies displayed substantial changes in carbohydrate and protein content. Interestingly, alteration in weight and lipid levels are independent of the feeding pattern in diseased condition and exhibit weak correlation with insulin-like peptide or adipokinetic hormone producing cells. We propose that therapeutic intervention aimed at restoring lipid levels and associated metabolic pathways may improve longevity and quality of patient’s life.

Curcumin modulates cell death and is protective in Huntington's disease model

Huntington’s disease (HD) is a progressive, dominantly inherited neurological disorder caused by an abnormal expansion of polyglutamine (polyQ) repeat within the Huntingtin (Htt) protein with no disease modifying treatments. In a Drosophila model of HD, expression of mutant Huntingtin (Htt) protein with expanded polyQ leads to formation of inclusion bodies (IBs), increase in cellular toxicity, progression of motor disabilities and reduced viability. Multiple cellular events such as oxidative stress, mitochondrial dysfunction, inflammation and transcriptional dysregulation are reported to contribute to pathology, however, till date there are no disease-modifying treatments with least side effects. Therefore, we investigated effect of the phytochemical curcumin on HD pathogenesis. Curcumin, a phytochemical and commonly used ingredient in Asian food has a wide spectrum of anti-oxidant, anti-inflammatory and anti-fibrilogenic properties. In this study, we provide evidence that curcumin significantly ameliorates disease symptoms in a Drosophila model of HD by suppressing cell death and can be a key to halting the progression of Huntington’s disease with least side effects.

Enhanced neuronal glucose transporter expression reveals metabolic choice in a HD Drosophila model

Huntington’s disease is a neurodegenerative disorder caused by toxic insertions of polyglutamine residues in the Huntingtin protein and characterized by progressive deterioration of cognitive and motor functions. Altered brain glucose metabolism has long been suggested and a possible link has been proposed in HD. However, the precise function of glucose transporters was not yet determined. Here, we report the effects of the specifically-neuronal human glucose transporter expression in neurons of a Drosophila model carrying the exon 1 of the human huntingtin gene with 93 glutamine repeats (HQ93). We demonstrated that overexpression of the human glucose transporter in neurons ameliorated significantly the status of HD flies by increasing their lifespan, reducing their locomotor deficits and rescuing eye neurodegeneration. Then, we investigated whether increasing the major pathways of glucose catabolism, glycolysis and pentose-phosphate pathway (PPP) impacts HD. To mimic increased glycolytic flux, we overexpressed phosphofructokinase (PFK) which catalyzes an irreversible step in glycolysis. Overexpression of PFK did not affect HQ93 fly survival, but protected from photoreceptor loss. Overexpression of glucose-6-phosphate dehydrogenase (G6PD), the key enzyme of the PPP, extended significantly the lifespan of HD flies and rescued eye neurodegeneration. Since G6PD is able to synthesize NADPH involved in cell survival by maintenance of the redox state, we showed that tolerance to experimental oxidative stress was enhanced in flies co-expressing HQ93 and G6PD. Additionally overexpressions of hGluT3, G6PD or PFK were able to circumvent mitochondrial deficits induced by specific silencing of genes necessary for mitochondrial homeostasis. Our study confirms the involvement of bioenergetic deficits in HD course; they can be rescued by specific expression of a glucose transporter in neurons. Finally, the PPP and, to a lesser extent, the glycolysis seem to mediate the hGluT3 protective effects, whereas, in addition, the PPP provides increased protection to oxidative stress.

Comparative study of naturally occurring huntingtin fragments in Drosophila points to exon 1 as the most pathogenic species in Huntington's disease

Although Huntington's disease is caused by the expansion of a CAG triplet repeat within the context of the 3144-amino acid huntingtin protein (HTT), studies reveal that N-terminal fragments of HTT containing the expanded PolyQ region can be produced by proteolytic processing and/or aberrant splicing. N-terminal HTT fragments are also prevalent in postmortem tissue, and expression of some of these fragments in model organisms can cause pathology. This has led to the hypothesis that N-terminal peptides may be critical modulators of disease pathology, raising the possibility that targeting aberrant splicing or proteolytic processing may present attractive therapeutic targets. However, many factors can contribute to pathology, including genetic background and differential expression of transgenes, in addition to intrinsic differences between fragments and their cellular effects. We have used Drosophila as a model system to determine the relative toxicities of different naturally occurring huntingtin fragments in a system in which genetic background, transgene expression levels and post-translational proteolytic processing can be controlled. These studies reveal that among the naturally occurring N-terminal HTT peptides, the exon 1 peptide is exceptionally pathogenic and exhibits unique structural and biophysical behaviors that do not appear to be incremental changes compared with other fragments. If this proves correct, efforts to specifically reduce the levels of exon 1 peptides or to target toxicity-influencing post-translational modifications that occur with the exon 1 context are likely to have the greatest impact on pathology.

Morphometric analysis of Huntington's disease neurodegeneration in Drosophila

Huntington's disease (HD) is an autosomal dominant neurodegenerative disorder. The HD gene encodes the huntingtin protein (HTT) that contains polyglutamine tracts of variable length. Expansions of the CAG repeat near the amino terminus to encode 40 or more glutamines (polyQ) lead to disease. At least eight other expanded polyQ diseases have been described. HD can be faithfully modeled in Drosophila with the key features of the disease such as late onset, slowly progressing degeneration, formation of abnormal protein aggregates and the dependence on polyQ length being evident. Such invertebrate model organisms provide powerful platforms to explore neurodegenerative mechanisms and to productively speed the identification of targets and agents that are likely to be effective at treating diseases in humans. Here we describe an optical pseudopupil method that can be readily quantified to provide a fast and sensitive assay for assessing the degree of HD neurodegeneration in vivo. We discuss detailed crossing schemes as well as factors including different drivers, various constructs, the number of UAS sites, genetic background, and temperature that can influence the result of pseudopupil measurements.

Cysteine-string protein's neuroprotective role

Cysteine-string protein (CSP), a member of the DnaJ/Hsp40 family of cochaperones, is critical for maintaining neurotransmitter release and preventing neurodegeneration. CSP likely forms a chaperone complex on synaptic vesicles together with the 70-kDa heat shock cognate (Hsc70) and the small glutamine-rich tetratricopeptide repeat (TPR)-containing protein (SGT) that may control or protect the assembly and activity of SNARE proteins and various other protein substrates. Here, the author summarizes studies that elucidated CSP's neuroprotective role.

Antiprion drugs 6-aminophenanthridine and guanabenz reduce PABPN1 toxicity and aggregation in oculopharyngeal muscular dystrophy

Oculopharyngeal muscular dystrophy (OPMD) is an adult-onset syndrome characterized by progressive degeneration of specific muscles. OPMD is caused by extension of a polyalanine tract in poly(A) binding protein nuclear 1 (PABPN1). Insoluble nuclear inclusions form in diseased muscles. We have generated a Drosophila model of OPMD that recapitulates the features of the disorder. Here, we show that the antiprion drugs 6-aminophenanthridine (6AP) and guanabenz acetate (GA), which prevent formation of amyloid fibers by prion proteins in cell models, alleviate OPMD phenotypes in Drosophila, including muscle degeneration and nuclear inclusion formation. The large ribosomal RNA and its activity in protein folding were recently identified as a specific cellular target of 6AP and GA. We show that deletions of the ribosomal DNA locus reduce OPMD phenotypes and act synergistically with sub-effective doses of 6AP. In a complementary approach, we demonstrate that ribosomal RNA accelerates in vitro fibril formation of PABPN1 N-terminal domain. These results reveal the conserved role of ribosomal RNA in different protein aggregation disorders and identify 6AP and GA as general anti-aggregation molecules.

ERK activation by the polyphenols fisetin and resveratrol provides neuroprotection in multiple models of Huntington's disease

Huntington's disease (HD) is an inherited, progressive and ultimately fatal neurodegenerative disorder that is characterized by psychiatric, cognitive and motor symptoms. Among the pathways implicated in HD are those involving mitogen-activated protein kinase signaling and particularly the Ras-extracellular signal-regulated kinase (ERK) cascade. Studies in both cells and animal models suggest that ERK activation might provide a novel therapeutic target for the treatment of HD but compounds that specifically activate ERK are few. To test the hypothesis that pharmaceutical activation of ERK might be protective for HD, a polyphenol, fisetin, which was previously shown to activate the Ras-ERK cascade, was tested in three different models of HD: PC12 cells expressing mutant Httex1 under the control of an inducible promoter, Drosophila expressing mutant Httex1 and the R6/2 mouse model of HD. The results indicate that fisetin can reduce the impact of mutant huntingtin in each of these disease models. Prompted by this observation, we determined that the related polyphenol, resveratrol, also activates ERK and is protective in HD models. Notably, although more than a dozen small molecule inhibitors of ERK activation are in clinical trials, very few small molecule activators of ERK signaling are reported. Thus, fisetin, resveratrol and related compounds might be useful for the treatment of HD by virtue of their unique ability to activate ERK.

Drosophila melanogaster in the study of human neurodegeneration

Human neurodegenerative diseases are devastating illnesses that predominantly affect elderly people. The majority of the diseases are associated with pathogenic oligomers from misfolded proteins, eventually causing the formation of aggregates and the progressive loss of neurons in the brain and nervous system. Several of these proteinopathies are sporadic and the cause of pathogenesis remains elusive. Heritable forms are associated with genetic defects, suggesting that the affected protein is causally related to disease formation and/or progression. The limitations of human genetics, however, make it necessary to use model systems to analyse affected genes and pathways in more detail. During the last two decades, research using the genetically amenable fruitfly has established Drosophila melanogaster as a valuable model system in the study of human neurodegeneration. These studies offer reliable models for Alzheimer's, Parkinson's, and motor neuron diseases, as well as models for trinucleotide repeat expansion diseases, including ataxias and Huntington's disease. As a result of these studies, several signalling pathways including phosphatidylinositol 3-kinase (PI3K)/Akt and target of rapamycin (TOR), c-Jun N-terminal kinase (JNK) and bone morphogenetic protein (BMP) signalling, have been shown to be deregulated in models of proteinopathies, suggesting that two or more initiating events may trigger disease formation in an age-related manner. Moreover, these studies also demonstrate that the fruitfly can be used to screen chemical compounds for their potential to prevent or ameliorate the disease, which in turn can directly guide clinical research and the development of novel therapeutic strategies for the treatment of human neurodegenerative diseases.

Transgenic Drosophila models of Alzheimer's disease and tauopathies

Alzheimer's disease (AD) is the most common form of senile dementia. Aggregation of the amyloid-beta42 peptide (Abeta42) and tau proteins are pathological hallmarks in AD brains. Accumulating evidence suggests that Abeta42 plays a central role in the pathogenesis of AD, and tau acts downstream of Abeta42 as a modulator of the disease progression. Tau pathology is also observed in frontotemporal dementia with Parkinsonism linked to chromosome 17 (FTDP-17) and other related diseases, so called tauopathies. Although most cases are sporadic, genes associated with familial AD and FTDP-17 have been identified, which led to the development of transgenic animal models. Drosophila has been a powerful genetic model system used in many fields of biology, and recently emerges as a model for human neurodegenerative diseases. In this review, we will summarize key features of transgenic Drosophila models of AD and tauopathies and a number of insights into disease mechanisms as well as therapeutic implications gained from these models.

Chemical measurements in Drosophila

The fruit fly, Drosophila melanogaster, has been extensively used as a model organism in genetics research and has significantly contributed to understanding molecular, cellular and evolutionary aspects of human behavior. Recently, research has focused on developing analytical methods to obtain highly sensitive chemical quantification along with spatiotemporal information from Drosophila melanogaster. We review a number of these advances in capillary electrophoresis, high-performance liquid chromatography, mass spectrometry and technologies involving intact organisms, including in vivo electrochemistry.

RNAi screening in Drosophila cells identifies new modifiers of mutant huntingtin aggregation

The fruitfly Drosophila melanogaster is well established as a model system in the study of human neurodegenerative diseases. Utilizing RNAi, we have carried out a high-throughput screen for modifiers of aggregate formation in Drosophila larval CNS-derived cells expressing mutant human Huntingtin exon 1 fused to EGFP with an expanded polyglutamine repeat (62Q). 7200 genes, encompassing around 50% of the Drosophila genome, were screened, resulting in the identification of 404 candidates that either suppress or enhance aggregation. These candidates were subjected to secondary screening in normal length (18Q)-expressing cells and pruned to remove dsRNAs with greater than 10 off-target effects (OTEs). De novo RNAi probes were designed and synthesized for the remaining 68 candidates. Following a tertiary round of screening, 21 high confidence candidates were analyzed in vivo for their ability to modify mutant Huntingtin-induced eye degeneration and brain aggregation. We have established useful models for the study of human HD using the fly, and through our RNAi screen, we have identified new modifiers of mutant human Huntingtin aggregation and aggregate formation in the brain. Newly identified modifiers including genes related to nuclear transport, nucleotide processes, and signaling, may be involved in polyglutamine aggregate formation and Huntington disease cascades.

Inhibition of specific HDACs and sirtuins suppresses pathogenesis in a Drosophila model of Huntington's disease

Huntington's disease (HD) is associated with transcriptional dysregulation, and multiple studies with histone deacetylase (HDAC) inhibitors suggest that global approaches for restoring transcriptional balance and appropriate protein acetylation are therapeutically promising. To determine whether more targeted approaches might be effective, we have tested the impact of all the HDACs in Drosophila on Huntingtin (Htt)-induced pathology. Among the zinc-dependent or 'classic' HDACs, we find that neurodegeneration is most sensitive to levels of Rpd3. We also find that among the NAD(+)-dependent class III deacetylases, genetic or pharmacological reduction of either Sir2 or Sirt2 provides neuroprotection to Htt-challenged animals and that even greater neuroprotection is achieved when Rpd3 and Sir2 are simultaneously reduced. Our experiments suggest that longevity promoting strategies may be distinct from those that protect against neurodegeneration in Drosophila challenged with mutant human Htt. These results highlight a novel therapeutic approach for HD in the form of Sir2 inhibition and possible combinatorial inhibition of Sir2 and Rpd3.

Specific N-terminal mutations in the human androgen receptor induce cytotoxicity

Polyglutamine (polyQ) stretch amplification in different proteins causes neurodegenerative disease. These proteins form intracellular aggregates thought to be cytotoxic but differ in pathology and tissue specificity. Here, we demonstrate that specific sequences outside the polyQ stretch of the human androgen receptor contribute to polyQ pathology. An exchange of two N-terminal serine phosphorylation residues to alanine in the wild type androgen receptor (ARQ22dm) resulted in cytoplasmic accumulation and increased early hormone-dependent aggregation of the receptor. In a Drosophila model, the ARQ22dm was cytotoxic, and developing larvae expressing this receptor showed behavioral abnormalities and severely impaired locomotion. In contrast, the same double mutation in an androgen receptor with an extended polyQ stretch was less toxic. The response of the receptors to inhibitors of polyglutamine toxicity is altered by the amino acid exchanges suggesting that careful consideration is needed in the choice of potential therapies of disorders involving toxic polyQ species.

Suppression of neurodegeneration and increased neurotransmission caused by expanded full-length huntingtin accumulating in the cytoplasm

Huntington's disease (HD) is a dominantly inherited neurodegenerative disorder caused by expansion of a translated CAG repeat in the N terminus of the huntingtin (htt) protein. Here we describe the generation and characterization of a full-length HD Drosophila model to reveal a previously unknown disease mechanism that occurs early in the course of pathogenesis, before expanded htt is imported into the nucleus in detectable amounts. We find that expanded full-length htt (128Qhtt(FL)) leads to behavioral, neurodegenerative, and electrophysiological phenotypes. These phenotypes are caused by a Ca2+-dependent increase in neurotransmitter release efficiency in 128Qhtt(FL) animals. Partial loss of function in synaptic transmission (syntaxin, Snap, Rop) and voltage-gated Ca2+ channel genes suppresses both the electrophysiological and the neurodegenerative phenotypes. Thus, our data indicate that increased neurotransmission is at the root of neuronal degeneration caused by expanded full-length htt during early stages of pathogenesis.

The stress of misfolded proteins: C. elegans models for neurodegenerative disease and aging

A growing number of human neurodegenerative diseases are associated with the expression of misfolded proteins that oligomerize and form aggregate structures. Over time, accumulation of misfolded proteins leads to the disruption of cellular protein folding homeostasis and eventually to cellular dysfunction and death. To investigate the relationship between misfolded proteins, neuropathology and aging, we have developed models utilizing the nematode C. elegans. In addition to being genetically tractable, C. elegans have rapid growth rates and short life-cycles, providing unique advantages for modeling neurodegenerative diseases of aging caused by the stress of misfolded proteins. The C. elegans models described here express polyglutamine expansion-containing proteins, as occur in Huntington's disease. Through the use of tissue-specific expression of different lengths of fluorescently tagged polyglutamine repeats, we have examined the dynamics of aggregate formation both within individual cells and over time throughout the lifetime of individual animals, identifying aging and other genetic modifiers as an important physiologic determinant of aggregation and toxicity.

A screen for neurotransmitter transporters expressed in the visual system of Drosophila melanogaster identifies three novel genes

The fly eye provides an attractive substrate for genetic studies, and critical transport activities for synaptic transmission and pigment biogenesis in the insect visual system remain unknown. We therefore screened for transporters in Drosophila melanogaster that are down-regulated by genetically ablating the eye. Using a large panel of transporter specific probes on Northern blots, we identified three transcripts that are down-regulated in flies lacking eye tissue. Two of these, CG13794 and CG13795, are part of a previously unknown subfamily of putative solute carriers within the neurotransmitter transporter family. The third, CG4476, is a member of a related subfamily that includes characterized nutrient transporters expressed in the insect gut. Using imprecise excision of a nearby transposable P element, we have generated a series of deletions in the CG4476 gene. In fast phototaxis assays, CG4476 mutants show a decreased behavioral response to light, and the most severe mutant behaves as if it were blind. These data suggest an unforeseen role for the "nutrient amino acid transporter" subfamily in the nervous system, and suggest new models to study transport function using the fly eye.

Drug-target identification in Drosophila cells: combining high-throughout RNAi and small-molecule screens

RNA interference (RNAi) and small-molecule approaches are synergistic on multiple levels, from technology and high-throughput screen development to target identification and functional studies. Here, we describe the RNAi screening platform that we have established and made available to the community through the Drosophila RNAi Screening Center at Harvard Medical School. We then illustrate how the combination of RNAi and small-molecule HTS can lead to effective identification of targets in drug discovery.

Drosophila in the Study of Neurodegenerative Disease

As populations benefit from increasing lifespans, neurodegenerative diseases have emerged as a critical health concern. How can the fruit fly, Drosophila melanogaster, contribute to curing human diseases of the nervous system? A growing number of neurodegenerative diseases, as well as other human diseases, are being modeled in Drosophila and used as a platform to identify and validate cellular pathways that contribute to neurodegeneration and to identify promising therapeutic targets by using a variety of approaches from screens to target validation. The unique properties and tools available in the Drosophila system, coupled with the fact that testing in vivo has proven highly productive, have accelerated the progress of testing therapeutic strategies in mice and, ultimately, humans. This review highlights selected recent applications to illustrate the use of Drosophila in studying neurodegenerative diseases.

A Drosophila ortholog of the human MRJ modulates polyglutamine toxicity and aggregation

In the Drosophila eye, proteins with an expanded polyglutamine (polyQ) tract form nuclear and cytoplasmic inclusions and produce cytotoxicity, demonstrated as loss of eye pigmentation and structural integrity. An EP P-element that suppressed the loss of eye pigmentation was inserted 9.7 kb upstream of dmrj, a gene that encodes an ortholog of a brain-enriched cochaperone, the human MRJ (mammalian relative of DnaJ). Despite the large distance between them, quantitative polymerase chain reaction indicated that the EP could overexpress dmrj. In the retina and other neurons, transgenic dMRJ suppressed polyQ toxicity and colocalized with its inclusions. In the photoreceptors, expression of another suppressor with a J domain, dHDJ1, but not dMRJ, prior to expression of expanded polyQs dramatically promoted cytoplasmic aggregation. However, both proteins increased the level of detergent-soluble, monomeric polyQ-expanded proteins. These findings exemplify the functional similarities and differences between J domain proteins in suppressing polyQ toxicity.

Cell type-specific processing of human Tau proteins in Drosophila

Accumulation of hyperphosphorylated Tau is associated with a number of neurodegenerative diseases collectively known as tauopathies. Differences in clinical and cognitive profiles among them suggest differential sensitivity of neuronal populations to Tau levels, phosphorylation and mutations. We used tissue specific expression of wild type and mutant human tau transgenes to demonstrate differential phosphorylation and stability in a cell type-specific manner, which includes different neuronal types and does not correlate with the level of accumulated protein. Rather, they likely reflect the spatial distribution or regulation of Tau-targeting kinases and phosphatases.

Palmitoyl-protein thioesterase 1 deficiency in Drosophila melanogaster causes accumulation of abnormal storage material and reduced life span

Human neuronal ceroid lipofuscinoses (NCLs) are a group of genetic neurodegenerative diseases characterized by progressive death of neurons in the central nervous system (CNS) and accumulation of abnormal lysosomal storage material. Infantile NCL (INCL), the most severe form of NCL, is caused by mutations in the Ppt1 gene, which encodes the lysosomal enzyme palmitoyl-protein thioesterase 1 (Ppt1). We generated mutations in the Ppt1 ortholog of Drosophila melanogaster to characterize phenotypes caused by Ppt1 deficiency in flies. Ppt1-deficient flies accumulate abnormal autofluorescent storage material predominantly in the adult CNS and have a life span 30% shorter than wild type, phenotypes that generally recapitulate disease-associated phenotypes common to all forms of NCL. In contrast, some phenotypes of Ppt1-deficient flies differed from those observed in human INCL. Storage material in flies appeared as highly laminar spherical deposits in cells of the brain and as curvilinear profiles in cells of the thoracic ganglion. This contrasts with the granular deposits characteristic of human INCL. In addition, the reduced life span of Ppt1-deficient flies is not caused by progressive death of CNS neurons. No changes in brain morphology or increases in apoptotic cell death of CNS neurons were detected in Ppt1-deficient flies, even at advanced ages. Thus, Ppt1-deficient flies accumulate abnormal storage material and have a shortened life span without evidence of concomitant neurodegeneration.

An arginine/lysine-rich motif is crucial for VCP/p97-mediated modulation of ataxin-3 fibrillogenesis

Arginine/lysine-rich motifs typically function as targeting signals for the translocation of proteins to the nucleus. Here, we demonstrate that such a motif consisting of four basic amino acids in the polyglutamine protein ataxin-3 (Atx-3) serves as a recognition site for the interaction with the molecular chaperone VCP. Through this interaction, VCP modulates the fibrillogenesis of pathogenic forms of Atx-3 in a concentration-dependent manner, with low concentrations of VCP stimulating fibrillogenesis and excess concentrations suppressing it. No such effect was observed with a mutant Atx-3 variant, which does not contain a functional VCP interaction motif. Strikingly, a stretch of four basic amino acids in the ubiquitin chain assembly factor E4B was also discovered to be critical for VCP binding, indicating that arginine/lysine-rich motifs might be generally utilized by VCP for the targeting of proteins. In vivo studies with Drosophila models confirmed that VCP selectively modulates aggregation and neurotoxicity induced by pathogenic Atx-3. Together, these results define the VCP-Atx-3 association as a potential target for therapeutic intervention and suggest that it might influence the progression of spinocerebellar ataxia type 3.

All neuropathies great and small

Autosomal-dominant pure hereditary spastic paraplegia (AD-HSP) is characterized by the degeneration of long axons in corticospinal tracts and dorsal columns, resulting in spasticity and difficulty walking. Mutations in the SPG4 gene product spastin are the predominant genetic lesions associated with this inherited disease. In this issue, Orso et al. examine and reconcile existing Drosophila mutants of spastin and generate a new model for HSP by overexpression of a fly spastin transgene that carries a mutation prevalent in human AD-HSP (see the related article beginning on page 3026). Expression of this mutant spastin protein produces pathology in flies reminiscent of the human disease, including adult locomotion defects, in addition to causing aberrant synaptic morphology and altered microtubule stability. Both movement and synaptic defects in fly mutants were ameliorated by treatment with the microtubule-modifying agent vinblastine. The results are consistent with disease-causing mutations in human spastin producing dominant-negative proteins and confirm the usefulness of Drosophila genetic techniques to understand HSP and other neurodegenerative diseases.

Rapamycin alleviates toxicity of different aggregate-prone proteins

Many neurodegenerative diseases are caused by intracellular, aggregate-prone proteins, including polyglutamine-expanded huntingtin in Huntington's disease (HD) and mutant tau in fronto-temporal dementia/tauopathy. Previously, we showed that rapamycin, an autophagy inducer, enhances mutant huntingtin fragment clearance and attenuated toxicity. Here we show much wider applications for this approach. Rapamycin enhances the autophagic clearance of different proteins with long polyglutamines and a polyalanine-expanded protein, and reduces their toxicity. Rapamycin also reduces toxicity in Drosophila expressing wild-type or mutant forms of tau and these effects can be accounted for by reductions in insoluble tau. Thus, our studies suggest that the scope for rapamycin as a potential therapeutic in aggregate diseases may be much broader than HD or even polyglutamine diseases.

Effects of amyloid peptides on A-type K+ currents ofDrosophila larval cholinergic neurons

Accumulation of amyloid (Abeta) peptides has been suggested to be the primary event in Alzheimer's disease. In neurons, K+ channels regulate a number of processes, including setting the resting potential, keeping action potentials short, timing interspike intervals, synaptic plasticity, and cell death. In particular, A-type K+ channels have been implicated in the onset of LTP in mammalian neurons, which is thought to underlie learning and memory. A number of studies have shown that Abeta peptides alter the properties of K+ currents in mammalian neurons. We set out to determine the effects of Abeta peptides on the neuronal A-type K+ channels of Drosophila. Treatment of cells for 18 h with 1 microM Abeta1-42 altered the kinetics of the A-type K+ current, shifting steady-state inactivation to more depolarized potentials and increasing the rate of recovery from inactivation. It also caused a decrease in neuronal viability. Thus it seems that alteration in the properties of the A-type K+ current is a prelude to the amyloid-induced death of neurons. This alteration in the properties of the A-type K+ current may provide a basis for the early memory impairment that was observed prior to neurodegeneration in a recent study of a transgenic Drosophila melanogaster line over-expressing the human Abeta1-42 peptide.

Screening for genetic modifiers of amyloid toxicity in yeast

In recent years the facile, yet powerful, genetics of the baker's yeast Saccharomyces cerevisiae has been appropriated for the study of amyloid toxicity. Several models of amyloid toxicity using this simple eukaryotic organism have been developed that faithfully recapitulate many disease-relevant phenotypes. Furthermore, these models have been exploited in genetic screens that have provided insight into conserved mechanisms of amyloid toxicity and identified potential therapeutic targets for disease. In this chapter, we discuss the strengths and weaknesses of yeast models of amyloid toxicity and how experiments with these models may be relevant to amyloid disorders. We suggest approaches for development of new yeast models of amyloid toxicity and provide an overview of screening protocols for genetic modifiers of amyloid toxicity by both random and systematic approaches.

Disease-related phenotypes in a Drosophila model of hereditary spastic paraplegia are ameliorated by treatment with vinblastine

Hereditary spastic paraplegias (HSPs) are a group of neurodegenerative diseases characterized by progressive weakness and spasticity of the lower limbs. Dominant mutations in the human SPG4 gene, encoding spastin, are responsible for the most frequent form of HSP. Spastin is an ATPase that binds microtubules and localizes to the spindle pole and distal axon in mammalian cell lines. Furthermore, its Drosophila homolog, Drosophila spastin (Dspastin), has been recently shown to regulate microtubule stability and synaptic function at the Drosophila larval neuromuscular junction. Here we report the generation of a spastin-linked HSP animal model and show that in Drosophila, neural knockdown of Dspastin and, conversely, neural overexpression of Dspastin containing a conserved pathogenic mutation both recapitulate some phenotypic aspects of the human disease, including adult onset, locomotor impairment, and neurodegeneration. At the subcellular level, neuronal expression of both Dspastin RNA interference and mutant Dspastin cause an excessive stabilization of microtubules in the neuromuscular junction synapse. In addition, we provide evidence that administration of the microtubule targeting drug vinblastine significantly attenuates these phenotypes in vivo. Our findings demonstrate that loss of spastin function elicits HSP-like phenotypes in Drosophila, provide novel insights into the molecular mechanism of spastin mutations, and raise the possibility that therapy with Vinca alkaloids may be efficacious in spastin-associated HSP and other disorders related to microtubule dysfunction.

Lithium rescues toxicity of aggregate-prone proteins in Drosophila by perturbing Wnt pathway

We have previously shown that lithium can protect against the polyglutamine toxicity of the Huntington's disease mutation in cell models. Here, we demonstrate for the first time in vivo that lithium can protect against the toxicity caused by aggregate-prone proteins with either polyglutamine or polyalanine expansions in Drosophila. We also show that these protective effects can be partly accounted for by lithium acting through the Wnt/Wg pathway, as a GSK3beta-specific inhibitor and overexpression of dTCF also mediate protective effects. Our data suggest that lithium deserves serious consideration for further studies as a therapeutic for polyglutamine diseases, particularly as it is an established drug that has been used for several decades for chronic treatment of affective disorders.

Suppression of Huntington's disease pathology in Drosophila by human single-chain Fv antibodies

Misfolded neuronal proteins have been identified in a number of neurodegenerative disorders and have been implicated in the pathogenesis of diseases that include Alzheimer's disease, Parkinson's disease, prion-based dementia, Huntington's disease (HD), and other polyglutamine diseases. Although underlying mechanisms remain the subject of ongoing research, it is clear that aberrant processing, protein degradation, and aggregate formation or spurious protein association of the abnormal neuronal proteins may be critical factors in disease progression. Recent work in these diseases has demonstrated in vitro that specific engineered antibody species, peptides, or other general agents may suppress the formation of aggregates. We have modified an approach with intracellularly expressed single-chain Fv (sFv) antibodies (intrabodies) that bind with unique HD protein epitopes. In cell and tissue culture models of HD, anti-N-terminal huntingtin intrabodies (C4 sFv) reduce aggregation and cellular toxicity. Here, we present the crucial experiment of intrabody-mediated in vivo suppression of neuropathology, using a Drosophila model of HD. In the presence of the C4 sFv intrabody, the proportion of HD flies surviving to adulthood increases from 23% to 100%, and the mean and maximum lifespan of adult HD flies is significantly prolonged. Neurodegeneration and formation of visible huntingtin aggregates are slowed. We conclude from this investigation that engineered intrabodies are a potential new class of therapeutic agents for the treatment of neurodegenerative diseases. They may also serve as tools for drug discovery and validation of sites on mutant neuronal proteins that could be exploited for rational drug design.

The end of "naive reductionism": rise of systems biology or renaissance of physiology?

Systems biology is an emerging discipline focused on tackling the enormous intellectual and technical challenges associated with translating genome sequence into a comprehensive understanding of how organisms are built and run. Physiology and systems biology share the goal of understanding the integrated function of complex, multicomponent biological systems ranging from interacting proteins that carry out specific tasks to whole organisms. Despite this common ground, physiology as an academic discipline runs the real risk of fading into the background and being superseded organizationally and administratively by systems biology. My goal in this article is to discuss briefly the cornerstones of modern systems biology, specifically functional genomics, nonmammalian model organisms and computational biology, and to emphasize the need to embrace them as essential components of 21st-century physiology departments and research and teaching programs.

Increased glutathione S-transferase activity rescues dopaminergic neuron loss in a Drosophila model of Parkinson's disease

Loss-of-function mutations of the parkin gene are a major cause of early-onset parkinsonism. To explore the mechanism by which loss of parkin function results in neurodegeneration, we are using a genetic approach in Drosophila. Here, we show that Drosophila parkin mutants display degeneration of a subset of dopaminergic (DA) neurons in the brain. The neurodegenerative phenotype of parkin mutants is enhanced by loss-of-function mutations of the glutathione S-transferase S1 (GstS1) gene, which were identified in an unbiased genetic screen for genes that modify parkin phenotypes. Furthermore, overexpression of GstS1 in DA neurons suppresses neurodegeneration in parkin mutants. Given the previous evidence for altered glutathione metabolism and oxidative stress in sporadic Parkinson's disease (PD), these data suggest that the mechanism of DA neuron loss in Drosophila parkin mutants is similar to the mechanisms underlying sporadic PD. Moreover, these findings identify a potential therapeutic approach in treating PD.

Identification of combinatorial drug regimens for treatment of Huntington's disease using Drosophila

We explore the hypothesis that pathology of Huntington's disease involves multiple cellular mechanisms whose contributions to disease are incrementally additive or synergistic. We provide evidence that the photoreceptor neuron degeneration seen in flies expressing mutant human huntingtin correlates with widespread degenerative events in the Drosophila CNS. We use a Drosophila Huntington's disease model to establish dose regimens and protocols to assess the effectiveness of drug combinations used at low threshold concentrations. These proof of principle studies identify at least two potential combinatorial treatment options and illustrate a rapid and cost-effective paradigm for testing and optimizing combinatorial drug therapies while reducing side effects for patients with neurodegenerative disease. The potential for using prescreening in Drosophila to inform combinatorial therapies that are most likely to be effective for testing in mammals is discussed.