Proteome response to the panneural expression of human wild-type alpha-synuclein: a Drosophila model of Parkinson's disease

The Drosophila melanogaster Levodopa-Induced Depression Model Exhibits Negative Geotaxis Deficits and Differential Gene Expression in Males and Females

More than 320 million people live with depression in the world, a disorder that severely limits psychosocial functioning and diminishes quality of life. The prevalence of major depression is almost two times higher in women than in men. However, the molecular mechanisms of its sex-specific pathophysiology are still poorly understood. Drosophila melanogaster is an established model for neurobiological research of depression-like states, as well as for the study of molecular and genetic sex differences in the brain. Here, we investigated sex-specific effects on forced-climbing locomotion (negative geotaxis) and gene expression of a fly model of depression-like phenotypes induced by levodopa administration, which was previously shown to impair normal food intake, mating frequency, and serotonin concentration. We observed that both males and females show deficits in the forced-climbing paradigm; however, modulated by distinct gene expression patterns after levodopa administration. Our results suggest that Drosophila models can be a valuable tool for identifying the molecular mechanisms underlying the difference of depressive disorder prevalence between men and women.

Impact of Autophagy and Aging on Iron Load and Ferritin in Drosophila Brain

Biometals such as iron, copper, potassium, and zinc are essential regulatory elements of several biological processes. The homeostasis of biometals is often affected in age-related pathologies. Notably, impaired iron metabolism has been linked to several neurodegenerative disorders. Autophagy, an intracellular degradative process dependent on the lysosomes, is involved in the regulation of ferritin and iron levels. Impaired autophagy has been associated with normal pathological aging, and neurodegeneration. Non-mammalian model organisms such as Drosophila have proven to be appropriate for the investigation of age-related pathologies. Here, we show that ferritin is expressed in adult Drosophila brain and that iron and holoferritin accumulate with aging. At whole-brain level we found no direct relationship between the accumulation of holoferritin and a deficit in autophagy in aged Drosophila brain. However, synchrotron X-ray spectromicroscopy revealed an additional spectral feature in the iron-richest region of autophagy-deficient fly brains, consistent with iron-sulfur. This potentially arises from iron-sulfur clusters associated with altered mitochondrial iron homeostasis.

Drug induces depression-like phenotypes and alters gene expression profiles in Drosophila

BACKGROUND

Major depressive disorder (MDD) is a severe mental illness that affects more than 350 million people worldwide. However, the molecular mechanisms of depression are currently unclear. Studies suggest that Drosophila and humans have similar depression-like symptoms under pressure. In this research, we choose Drosophila melanogaster as the animal model to explore the molecular mechanisms that trigger depression.

RESULTS

We found that feeding D. melanogaster with the medium containing Levodopa or Chlorpromazine could induce depression-like phenotypes in both behavioral and biochemical biomarkers, including significantly decreased food intake, mating frequency, serotonin (5-HT) concentration, and increased malondialdehyde (MDA) concentration as well as reduced activity of superoxide dismutase (SOD). Moreover, the progeny of Chlorpromazine-treated flies also showed these depression-like features. By RNA-seq technology, we identified 467 genes that were differentially expressed between Chlorpromazine treated (CPZ) and control male flies [fold-change of ≥2 (q-value<5%)]. When comparing CPZ with control flies, 312 genes were upregulated and 155 genes downregulated. Differential expression of genes related to metabolic pathway, Parkinson's disease, Huntington's disease, Alzheimer's disease and lysozyme pathways were observed. Quantitative reverse transcriptase PCR (qRT-PCR) confirmed that 19 genes are differentially expressed in CPZ and control male flies.

CONCLUSIONS

Levodopa, or Chlorpromazine can induce depression-like phenotypes in D. melanogaster regarding changes of appetite and sexual activity, and some key biochemical markers. A total of 467 genes were identified by RNA-seq analysis to have at least a 2-fold-change in expression between CPZ and control flies, including genes involved in metabolism, neurological diseases and lysozyme pathways. Our data provide additional insight into molecular mechanisms underlying depressive disorders in humans and may also contribute to clinical treatment.

Glia in Drosophila behavior

Glial cells constitute about 10 % of the Drosophila nervous system. The development of genetic and molecular tools has helped greatly in defining different types of glia. Furthermore, considerable progress has been made in unraveling the mechanisms that control the development and differentiation of Drosophila glia. By contrast, the role of glia in adult Drosophila behavior is not well understood. We here summarize recent work describing the role of glia in normal behavior and in Drosophila models for neurological and behavioral disorders.

The dietary supplementation of nordihydroguaiaretic acid (NDGA) delayed the loss of climbing ability in Drosophila model of Parkinson's disease

Parkinson's disease (PD) is characterized by the progressive loss of dopaminergic neurons and the aggression of alpha Synuclein (αS) in the brain. Drosophila mutants and transgenes have provided a platform to understand the mechanistic insight associated with the degenerative diseases. A number of polyphenols have been reported to inhibit the αS aggregation resulting in the possible prevention of PD. The involvement of free radicals in mediating the neuronal death in PD has also been implicated. In the present study, the effect of Nordihydroguaiaretic acid (NDGA) was studied on the climbing ability of the PD model Drosophila expressing normal human alpha synuclein (h-αS) in the neurons. These flies exhibit locomotor dysfunction as the age progresses. NDGA at final concentration of 0.01, 0.1, 0.5, and 1μl/ml was supplemented with the diet and the flies were allowed to feed for the 24 days. NDGA at 0.01 μl/ml did not showed any significant delay in the loss of climbing ability of PD model flies. However, NDGA doses at 0.1, 0.5, and 1.0 μl/ml showed a dose dependent significant (p < .05) delay in the loss of climbing ability of PD model flies as compared to the untreated PD flies. The results suggest that the NDGA is potent in delaying the climbing disability of PD model flies and also supports the utility of this model in studying PD symptoms.

Ferritin overexpression in Drosophila glia leads to iron deposition in the optic lobes and late-onset behavioral defects

Cellular and organismal iron storage depends on the function of the ferritin protein complex in insects and mammals alike. In the central nervous system of insects, the distribution and relevance of ferritin remain unclear, though ferritin has been implicated in Drosophila models of Alzheimers' and Parkinsons' disease and in Aluminum-induced neurodegeneration. Here we show that transgene-derived expression of ferritin subunits in glial cells of Drosophila melanogaster causes a late-onset behavioral decline, characterized by loss of circadian rhythms in constant darkness and impairment of elicited locomotor responses. Anatomical analysis of the affected brains revealed crystalline inclusions of iron-loaded ferritin in a subpopulation of glial cells but not significant neurodegeneration. Although transgene-induced glial ferritin expression was well tolerated throughout development and in young flies, it turned disadvantageous at older age. The flies we characterize in this report contribute to the study of ferritin in the Drosophila brain and can be used to assess the contribution of glial iron metabolism in neurodegenerative models of disease.

Drosophila models of Parkinson's disease: discovering relevant pathways and novel therapeutic strategies

Parkinson's disease (PD) is the second most common neurodegenerative disorder and is mainly characterized by the selective and progressive loss of dopaminergic neurons, accompanied by locomotor defects. Although most PD cases are sporadic, several genes are associated with rare familial forms of the disease. Analyses of their function have provided important insights into the disease process, demonstrating that three types of cellular defects are mainly involved in the formation and/or progression of PD: abnormal protein aggregation, oxidative damage, and mitochondrial dysfunction. These studies have been mainly performed in PD models created in mice, fruit flies, and worms. Among them, Drosophila has emerged as a very valuable model organism in the study of either toxin-induced or genetically linked PD. Indeed, many of the existing fly PD models exhibit key features of the disease and have been instrumental to discover pathways relevant for PD pathogenesis, which could facilitate the development of therapeutic strategies.

Understanding the molecular basis of Parkinson's disease, identification of biomarkers and routes to therapy

These are really exciting times in the field of Parkinson's disease research. Although the etiology of sporadic disease still remains a mystery, many of the proteins associated with hereditary disease (5-10% of all disease) have now been identified. Only time will tell whether proteins associated with hereditary disease are involved in the development of sporadic disease. The most valuable proteomic studies performed to date are, and continue to be, those aimed at identifying endogenous binding partners, substrates, post-translational modifications and cellular pathways affected by these proteins. Similar to global proteomic approaches, even these approaches have surprisingly often been characterized by the production of very long lists of proteins. Consequently, the parallel development of more refined protein-protein interactions maps has aided the chance of identifying those protein complexes and/or cellular pathways, which, when disrupted, lead to the development of disease. The knowledge gained from these studies is essential, as targeting the activities of these proteins, or the pathways they operate in, currently offers the best opportunity to develop new therapeutic strategies to treat the disease. They may include agents to modulators of kinase activities (e.g., PINK1 and LRRK2), modulators of the activity of the ubiquitin-protein ligase, Parkin, proteostasis agents to block alpha-synuclein filament assembly and toxicity, or promote the refolding of mutant proteins, modulators of alpha-synuclein transfer between cells, reagents to regulate cargo dynamics along axonal microtubule networks, stimulators of autophagy and/or modulators of cellular stress pathways. The second major challenge will be to identify biomarkers to enable population screening to identify those with asymptomatic early-stage disease. Whether the analysis of blood or urine samples will yield such a marker, remains to be determined. Success or failure will be highly dependent on adopting strict standard operating procedures for the collection, processing and storage of samples, combined with the need for the identification of the most robust methods of prefractionation of samples to remove the most abundant proteins prior to proteomic screening.

Experimental selection for Drosophila survival in extremely high O2 environments

Although oxidative stress is deleterious to mammals, the mechanisms underlying oxidant susceptibility or tolerance remain to be elucidated. In this study, through a long-term laboratory selection over many generations, we generated a Drosophila melanogaster strain that can live and reproduce in very high O₂ environments (90% O₂), a lethal condition to naïve flies. We demonstrated that tolerance to hyperoxia was heritable in these flies and that these hyperoxia-selected flies exhibited phenotypic differences from naïve flies, such as a larger body size and increased weight by 20%. Gene expression profiling revealed that 227 genes were significantly altered in expression and two third of these genes were down-regulated. Using a mutant screen strategy, we studied the role of some altered genes (up- or down-regulated in the microarrays) by testing the survival of available corresponding P-element or UAS construct lines under hyperoxic conditions. We report that down-regulation of several candidate genes including Tropomyosin 1, Glycerol 3 phosphate dehydrogenase, CG33129, and UGP as well as up-regulation of Diptericin and Attacin conferred tolerance to severe hyperoxia. In conclusion, we identified several genes that were not only altered in hyperoxia-selected flies but we also prove that these play an important role in hyperoxia survival. Thus our study provides a molecular basis for understanding the mechanisms of hyperoxia tolerance.

When peptides fly: advances in Drosophila proteomics

In the past decade, improvements in genome annotation, protein fractionation methods and mass spectrometry instrumentation resulted in rapid growth of Drosophila proteomics. This review presents the current status of proteomics research in the fly. Areas that have seen major advances in recent years include efforts to map and catalog the Drosophila proteome and high-throughput as well as targeted studies to analyze protein-protein interactions and post-translational modifications. Stable isotope labeling of flies and other applications of quantitative proteomics have opened up new possibilities for functional analyses. It is clear that proteomics is becoming an indispensable tool in Drosophila systems biology research that adds a unique dimension to studying gene function.

Grape extract protects mitochondria from oxidative damage and improves locomotor dysfunction and extends lifespan in a Drosophila Parkinson's disease model

A botanical extract (Regrapex-R) prepared from whole grape (Vitis vinifera) and Polygonum cuspidatum, which contains polyphenols, including flavans, anthocyanins, emodin, and resveratrol, exhibited dose-dependent scavenging effects on reactive oxygen species (ROS). The extract inhibited increases of ROS and protein carbonyl in isolated rat liver mitochondria following exposure to 2,2'-azobis (2-amidino propane) dihydrocholoride (AAPH), a potent lipid oxidant generator. The antioxidant effects of this extract were further demonstrated by protecting enzyme activities of the mitochondrial respiratory electron transport chain (complexes I and II) and pyruvate dehydrogenase in isolated liver mitochondria with AAPH insult. In human neuroblastoma cells (SKN-MC), pretreatment of extract protected cells against AAPH induced oxidation in maintaining cell viability and inhibiting excessive ROS generation. Extract was fed to transgenic Drosophila expressing human alpha-synuclein. This model for Parkinson disease recapitulates essential features of the disorder, including loss of dopaminergic neurons in the substantia nigra and a locomotor dysfunction that is displayed by a progressive loss of climbing ability measured using a geotaxis assay. Male transgenic flies fed the extract (0.16-0.64 mg/100 g of culture medium) showed a significant improvement in climbing ability compared to controls. Female transgenic flies showed a significant extension in average lifespan. These results suggest that Regrapex-R is a potent free radical scavenger, a mitochondrial protector, and a candidate for further studies to assess its ability to protect against neurodegenerative disease and potentially extend lifespan.

Stable isotope labeling and label-free proteomics of Drosophila parkin null mutants

Parkinson's disease (PD) is characterized by loss of dopaminergic neurons in the substantia nigra and formation of intracytoplasmic Lewy bodies (LBs). Loss-of-function mutations in parkin which encodes an E3 ubiquitin protein ligase contribute to a predominant cause of a familial form of PD termed autosomal recessive juvenile Parkinsonism (AR-JP). Drosophila parkin null mutants display muscle degeneration and mitochondrial dysfunction, providing an animal model to study Parkin-associated molecular pathways in PD. To define protein alterations involved in Parkin pathogenesis, we performed quantitative proteomic analyses of Drosophila parkin null mutants and age-matched controls utilizing both global internal standard technology (GIST) and extracted ion chromatogram peak area (XICPA) label-free approaches. A total of 375 proteins were quantified with a minimum of two peptide identifications from the combination of the XICPA and GIST measurements applied to two independent biological replicates. Sixteen proteins exhibited significant alteration. Seven of the dysregulated proteins are involved in energy metabolism, of which six were down-regulated. All five proteins involved in transporter activity exhibited higher levels, of which larval serum protein 1alpha, larval serum protein 1beta, larval serum protein 1gamma, and fat body protein 1 showed >10-fold up-regulation and substantially higher level of fat body protein 1 was confirmed by Western blot analysis. These findings suggest that abnormalities in energy metabolism and protein transporter activity pathways may be associated with the pathogenesis of Parkin-associated AR-JP.

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.

Effects of lithium chloride on the gene expression profiles in Drosophila heads

To gain insight into the basic neurobiological processes regulated by lithium--an effective drug for bipolar disorder--we used Affymetrix Genome Arrays to examine lithium-induced changes in genome-wide gene expression profiles of head mRNA from the genetic model organism Drosophila melanogaster. First, to identify the individual genes whose transcript levels are most significantly altered by lithium, we analyzed the microarray data with stringent criteria (fold change>2; p<0.001) and evaluated the results by RT-PCR. This analysis identified 12 genes that encode proteins with various biological functions, including an enzyme responsible for amino acid metabolism and a putative amino acid transporter. Second, to uncover the biological pathways involved in lithium's action in the nervous system, we used less stringent criteria (fold change>1.2; FDR<0.05) and assigned the identified 66 lithium-responsive genes to biological pathways using DAVID (Database for Annotation, Visualization and Integrated Discovery). The gene ontology categories most significantly affected by lithium were amino acid metabolic processes. Taken together, these data suggest that amino acid metabolism is important for lithium's actions in the nervous system, and lay a foundation for future functional studies of lithium-responsive neurobiological processes using the versatile molecular and genetic tools that are available in Drosophila.