The dopaminergic system in the aging brain of Drosophila

Loss of function in Drosophila transcription factor Dif delays brain development in larvae resulting in aging adult brain

Drosophila NF-κB transcription factor Dif has been well known for its function in innate immunity, and recent study also reveals its role in neuronal cells. However, the underlying mechanisms of Dif in the brain remain elusive. In this study, we aim to investigate the function of Dif in Drosophila brain development and how Dif regulates structure and plasticity of the brain to affect aging and behaviors. Based on the analysis of differentially expressed genes, we identified key genes associated with cell division, development and aging in the brain of Dif1 loss of function mutant. In Dif1 larvae, we found that the metamorphosis and brain development were delayed, and cell division was decreased. In Dif1 adults, the number of neuron cells was reduced in the brain, the lifespan and locomotor activity were decreased, protein markers associated with aging-related neurodegenerative diseases in the brain were altered in abundance or activity. Our results indicated that Dif plays a crucial role in brain plasticity and neurogenesis, dysfunction of Dif delays larval brain development and impacts proliferation of neuronal cells, resulting in aging adult brain by regulating expression of key genes in multiple signaling pathways involved in cell division, neurogenesis and aging.

Future avenues in Drosophila mushroom body research

How does the brain translate sensory information into complex behaviors? With relatively small neuronal numbers, readable behavioral outputs, and an unparalleled genetic toolkit, the Drosophila mushroom body (MB) offers an excellent model to address this question in the context of associative learning and memory. Recent technological breakthroughs, such as the freshly completed full-brain connectome, multiomics approaches, CRISPR-mediated gene editing, and machine learning techniques, led to major advancements in our understanding of the MB circuit at the molecular, structural, physiological, and functional levels. Despite significant progress in individual MB areas, the field still faces the fundamental challenge of resolving how these different levels combine and interact to ultimately control the behavior of an individual fly. In this review, we discuss various aspects of MB research, with a focus on the current knowledge gaps, and an outlook on the future methodological developments required to reach an overall view of the neurobiological basis of learning and memory.

Neuronal ageing is promoted by the decay of the microtubule cytoskeleton

Natural ageing is accompanied by a decline in motor, sensory, and cognitive functions, all impacting quality of life. Ageing is also the predominant risk factor for many neurodegenerative diseases, including Parkinson's disease and Alzheimer's disease. We need to therefore gain a better understanding of the cellular and physiological processes underlying age-related neuronal decay. However, gaining this understanding is a slow process due to the large amount of time required to age mammalian or vertebrate animal models. Here, we introduce a new cellular model within the Drosophila brain, in which we report classical ageing hallmarks previously observed in the primate brain. These hallmarks include axonal swellings, cytoskeletal decay, a reduction in axonal calibre, and morphological changes arising at synaptic terminals. In the fly brain, these changes begin to occur within a few weeks, ideal to study the underlying mechanisms of ageing. We discovered that the decay of the neuronal microtubule (MT) cytoskeleton precedes the onset of other ageing hallmarks. We showed that the MT-binding factors Tau, EB1, and Shot/MACF1, are necessary for MT maintenance in axons and synapses, and that their functional loss during ageing triggers MT bundle decay, followed by a decline in axons and synaptic terminals. Furthermore, genetic manipulations that improve MT networks slowed down the onset of neuronal ageing hallmarks and confer aged specimens the ability to outperform age-matched controls. Our work suggests that MT networks are a key lesion site in ageing neurons and therefore the MT cytoskeleton offers a promising target to improve neuronal decay in advanced age.

Experimental arena settings might lead to misinterpretation of movement properties

Movement is an important animal behavior contributing to reproduction and survival. Animal movement is often examined in arenas or enclosures under laboratory conditions. We used the red flour beetle (Tribolium castaneum) to examine here the effect of the arena size, shape, number of barriers, access to the arena's center, and illumination on six movement properties. We demonstrate great differences among arenas. For example, the beetles moved over longer distances in clear arenas than in obstructed ones. Movement along the arena's perimeter was greater in smaller arenas than in larger ones. Movement was more directional in round arenas than in rectangular ones. In general, the beetles stopped moving closer to the perimeter and closer to corners (in the square and rectangular arenas) than expected by chance. In some cases, the arena properties interacted with the beetle sex to affect several movement properties. All these suggest that arena properties might also interact with experimental manipulations to affect the outcome of studies and lead to results specific to the arena used. In other words, instead of examining animal movement, we in fact examine the animal interaction with the arena structure. Caution is therefore advised in interpreting the results of studies on movement in arenas under laboratory conditions and we recommend paying attention also to barriers or obstacles in field experiments. For instance, movement along the arena's perimeter is often interpreted as centrophobism or thigmotaxis but the results here show that such movement is arena dependent.

Endocrine Regulation of Aging in the Fruit Fly Drosophila melanogaster

The past few decades have witnessed increasing research clarifying the role of endocrine signaling in the regulation of aging in both vertebrates and invertebrates. Studies using the model organism fruit fly Drosophila melanogaster have largely advanced our understanding of evolutionarily conserved mechanisms in the endocrinology of aging and anti-aging. Mutations in single genes involved in endocrine signaling modify lifespan, as do alterations of endocrine signaling in a tissue- or cell-specific manner, highlighting a central role of endocrine signaling in coordinating the crosstalk between tissues and cells to determine the pace of aging. Here, we review the current landscape of research in D. melanogaster that offers valuable insights into the endocrine-governed mechanisms which influence lifespan and age-related physiology.

Analysis of α-syn and parkin interaction in mediating neuronal death in Drosophila model of Parkinson's disease

One of the hallmarks of Parkinson's Disease (PD) is aggregation of incorrectly folded α-synuclein (SNCA) protein resulting in selective death of dopaminergic neurons. Another form of PD is characterized by the loss-of-function of an E3-ubiquitin ligase, parkin. Mutations in SNCA and parkin result in impaired mitochondrial morphology, causing loss of dopaminergic neurons. Despite extensive research on the individual effects of SNCA and parkin, their interactions in dopaminergic neurons remain understudied. Here we employ Drosophila model to study the effect of collective overexpression of SNCA along with the downregulation of parkin in the dopaminergic neurons of the posterior brain. We found that overexpression of SNCA along with downregulation of parkin causes a reduction in the number of dopaminergic neuronal clusters in the posterior region of the adult brain, which is manifested as progressive locomotor dysfunction. Overexpression of SNCA and downregulation of parkin collectively results in altered mitochondrial morphology in a cluster-specific manner, only in a subset of dopaminergic neurons of the brain. Further, we found that SNCA overexpression causes transcriptional downregulation of parkin. However, this downregulation is not further enhanced upon collective SNCA overexpression and parkin downregulation. This suggests that the interactions of SNCA and parkin may not be additive. Our study thus provides insights into a potential link between α-synuclein and parkin interactions. These interactions result in altered mitochondrial morphology in a cluster-specific manner for dopaminergic neurons over a time, thus unraveling the molecular interactions involved in the etiology of Parkinson's Disease.

Spenito-dependent metabolic sexual dimorphism intrinsic to fat storage cells

Metabolism in males and females is distinct. Differences are usually linked to sexual reproduction, with circulating signals (e.g. hormones) playing major roles. In contrast, sex differences prior to sexual maturity and intrinsic to individual metabolic tissues are less understood. We analyzed Drosophila melanogaster larvae and find that males store more fat than females, the opposite of the sexual dimorphism in adults. We show that metabolic differences are intrinsic to the major fat storage tissue, including many differences in the expression of metabolic genes. Our previous work identified fat storage roles for Spenito (Nito), a conserved RNA-binding protein and regulator of sex determination. Nito knockdown specifically in the fat storage tissue abolished fat differences between males and females. We further show that Nito is required for sex-specific expression of the master regulator of sex determination, Sex-lethal (Sxl). "Feminization" of fat storage cells via tissue-specific overexpression of a Sxl target gene made larvae lean, reduced the fat differences between males and females, and induced female-like metabolic gene expression. Altogether, this study supports a model in which Nito autonomously controls sexual dimorphisms and differential expression of metabolic genes in fat cells in part through its regulation of the sex determination pathway.

Genetic modulation of CWD prion propagation in cervid PrP Drosophila

Chronic wasting disease is a fatal prion condition of cervids such as deer, elk, moose and reindeer. Secretion and excretion of prion infectivity from North American cervids with this condition causes environmental contamination and subsequent efficient lateral transmission in free-ranging and farmed cervids. Variants of cervid PrP exist that affect host susceptibility to chronic wasting disease. Cervid breeding programmes aimed at increasing the frequency of PrP variants associated with resistance to chronic wasting disease may reduce the burden of this condition in animals and lower the risk of zoonotic disease. This strategy requires a relatively rapid and economically viable model system to characterise and support selection of prion disease-modifying cervid PrP variants. Here, we generated cervid PrP transgenic Drosophila to fulfil this purpose. We have generated Drosophila transgenic for S138 wild type cervid PrP, or the N138 variant associated with resistance to chronic wasting disease. We show that cervid PrP Drosophila accumulate bona fide prion infectivity after exposure to cervid prions. Furthermore, S138 and N138 PrP fly lines are susceptible to cervid prion isolates from either North America or Europe when assessed phenotypically by accelerated loss of locomotor ability or survival, or biochemically by accumulation of prion seeding activity. However, after exposure to European reindeer prions, N138 PrP Drosophila accumulated prion seeding activity with slower kinetics than the S138 fly line. These novel data show that prion susceptibility characteristics of cervid PrP variants are maintained when expressed in Drosophila, which highlights this novel invertebrate host in modelling chronic wasting disease.

DVT: a high-throughput analysis pipeline for locomotion and social behavior in adult Drosophila melanogaster

BACKGROUND

Drosophila melanogaster is excellent animal model for understanding the molecular basis of human neurological and motor disorders. The experimental conditions and chamber design varied between studies. Moreover, most previously established paradigms focus on fly trace detection algorithm development. A comprehensive understanding on how fly behaves in the chamber is still lacking.

RESULTS

In this report, we established 74 unique behavior metrics quantifying spatiotemporal characteristics of adult fly locomotion and social behaviors, of which 49 were newly proposed. By the aiding of the developed analysis pipeline, Drosophila video tracking (DVT), we identified siginificantly different patterns of fly behavior confronted with different chamber height, fly density, illumination and experimental time. Meanwhile, three fly strains which are widely used as control lines, Canton-S(CS), w1118 and Oregon-R (OR), were found to exhibit distinct motion explosiveness and exercise endurance.

CONCLUSIONS

We believe the proposed behavior metrics set and pipeline should help identify subtle spatial and temporal differences of drosophila behavior confronted with different environmental factors or gene variants.

Fluorescence microscopy-based sensitive method to quantify dopaminergic neurodegeneration in a Drosophila model of Parkinson's disease

Death of dopaminergic (DAergic) neurons in the substantia nigra pars compacta of the human brain is the characteristic pathological feature of Parkinson's disease (PD). On exposure to neurotoxicants, Drosophila too exhibits mobility defects and diminished levels of brain dopamine. In the fly model of sporadic PD, our laboratory has demonstrated that there is no loss of DAergic neuronal number, however, a significant reduction in fluorescence intensity (FI) of secondary antibodies that target the primary antibody-anti-tyrosine hydroxylase (TH). Here, we present a sensitive, economical, and repeatable assay to characterize neurodegeneration based on the quantification of FI of the secondary antibody. As the intensity of fluorescence correlates with the amount of TH synthesis, its reduction under PD conditions denotes the depletion in the TH synthesis, suggesting DAergic neuronal dysfunction. Reduction in TH protein synthesis is further confirmed through Bio-Rad Stain-Free Western Blotting. Quantification of brain DA and its metabolites (DOPAC and HVA) using HPLC-ECD further demonstrated the depleted DA level and altered DA metabolism as evident from enhanced DA turnover rate. Together all these PD marker studies suggest that FI quantification is a refined and sensitive method to understand the early stages of DAergic neurodegeneration. FI quantification is performed using ZEN 2012 SP2, a licensed software from Carl Zeiss, Germany. This method will be of good use to biologists, as it with few modifications, can also be implemented to characterize the extent of degeneration of different cell types. Unlike the expensive and cumbersome confocal microscopy, the present method using fluorescence microscopy will be a feasible option for fund-constrained neurobiology laboratories in developing countries.

Spenito-dependent metabolic sexual dimorphism intrinsic to fat storage cells

Metabolism in males and females is distinct. Differences are usually linked to sexual reproduction, with circulating signals (e.g. hormones) playing major roles. By contrast, sex differences prior to sexual maturity and intrinsic to individual metabolic tissues are less understood. We analyzed Drosophila melanogaster larvae and find that males store more fat than females, the opposite of the sexual dimorphism in adults. We show that metabolic differences are intrinsic to the major fat storage tissue, including many differences in the expression of metabolic genes. Our previous work identified fat storage roles for Spenito (Nito), a conserved RNA-binding protein and regulator of sex determination. Nito knockdown specifically in the fat storage tissue abolished fat differences between males and females. We further show that Nito is required for sex-specific expression of the master regulator of sex determination, Sex-lethal (Sxl). "Feminization" of fat storage cells via tissue-specific overexpression of a Sxl target gene made larvae lean, reduced the fat differences between males and females, and induced female-like metabolic gene expression. Altogether, this study supports a model in which Nito autonomously controls sexual dimorphisms and differential expression of metabolic genes in fat cells in part through its regulation of the sex determination pathway.

The dual role of heme oxygenase in regulating apoptosis in the nervous system of Drosophila melanogaster

Accumulating evidence from mammalian studies suggests the dual-faced character of heme oxygenase (HO) in oxidative stress-dependent neurodegeneration. The present study aimed to investigate both neuroprotective and neurotoxic effects of heme oxygenase after the ho gene chronic overexpression or silencing in neurons of Drosophila melanogaster. Our results showed early deaths and behavioral defects after pan-neuronal ho overexpression, while survival and climbing in a strain with pan-neuronal ho silencing were similar over time with its parental controls. We also found that HO can be pro-apoptotic or anti-apoptotic under different conditions. In young (7-day-old) flies, both the cell death activator gene (hid) expression and the initiator caspase Dronc activity increased in heads of flies when ho expression was changed. In addition, various expression levels of ho produced cell-specific degeneration. Dopaminergic (DA) neurons and retina photoreceptors are particularly vulnerable to changes in ho expression. In older (30-day-old) flies, we did not detect any further increase in hid expression or enhanced degeneration, however, we still observed high activity of the initiator caspase. In addition, we used curcumin to further show the involvement of neuronal HO in the regulation of apoptosis. Under normal conditions, curcumin induced both the expression of ho and hid, which was reversed after exposure to high-temperature stress and when supplemented in flies with ho silencing. These results indicate that neuronal HO regulates apoptosis and this process depends on ho expression level, age of flies, and cell type.

Studies of neurodegenerative diseases using Drosophila and the development of novel approaches for their analysis

The use of Drosophila in neurodegenerative disease research has contributed to the identification of modifier genes for the pathology. The basis for neurodegenerative disease occurrence in Drosophila is the conservation of genes across species and the ability to perform rapid genetic analysis using a compact brain. Genetic findings previously discovered in Drosophila can reveal molecular pathologies involved in human neurological diseases in later years. Disease models using Drosophila began to be generated during the development of genetic engineering. In recent years, results of reverse translational research using Drosophila have been reported. In this review, we discuss research on neurodegenerative diseases; moreover, we introduce various methods for quantifying neurodegeneration in Drosophila.

Artificial gravity partially protects space-induced neurological deficits in Drosophila melanogaster

Spaceflight poses risks to the central nervous system (CNS), and understanding neurological responses is important for future missions. We report CNS changes in Drosophila aboard the International Space Station in response to spaceflight microgravity (SFμg) and artificially simulated Earth gravity (SF1g) via inflight centrifugation as a countermeasure. While inflight behavioral analyses of SFμg exhibit increased activity, postflight analysis displays significant climbing defects, highlighting the sensitivity of behavior to altered gravity. Multi-omics analysis shows alterations in metabolic, oxidative stress and synaptic transmission pathways in both SFμg and SF1g; however, neurological changes immediately postflight, including neuronal loss, glial cell count alterations, oxidative damage, and apoptosis, are seen only in SFμg. Additionally, progressive neuronal loss and a glial phenotype in SF1g and SFμg brains, with pronounced phenotypes in SFμg, are seen upon acclimation to Earth conditions. Overall, our results indicate that artificial gravity partially protects the CNS from the adverse effects of spaceflight.

Mitigation of age-dependent accumulation of defective mitochondrial genomes

Unknown processes promote the accumulation of mitochondrial DNA (mtDNA) mutations during aging. Accumulation of defective mitochondrial genomes is thought to promote the progression of heteroplasmic mitochondrial diseases and degenerative changes with natural aging. We used a heteroplasmic Drosophila model to test 1) whether purifying selection acts to limit the abundance of deleterious mutations during development and aging, 2) whether quality control pathways contribute to purifying selection, 3) whether activation of quality control can mitigate accumulation of deleterious mutations, and 4) whether improved quality control improves health span. We show that purifying selection operates during development and growth but is ineffective during aging. Genetic manipulations suggest that a quality control process known to enforce purifying selection during oogenesis also suppresses accumulation of a deleterious mutation during growth and development. Flies with nuclear genotypes that enhance purifying selection sustained higher genome quality, retained more vigorous climbing activity, and lost fewer dopaminergic neurons. A pharmacological agent thought to enhance quality control produced similar benefits. Importantly, similar pharmacological treatment of aged mice reversed age-associated accumulation of a deleterious mtDNA mutation. Our findings reveal dynamic maintenance of mitochondrial genome fitness and reduction in the effectiveness of purifying selection during life. Importantly, we describe interventions that mitigate and even reverse age-associated genome degeneration in flies and in mice. Furthermore, mitigation of genome degeneration improved well-being in a Drosophila model of heteroplasmic mitochondrial disease.

Advances in Evaluation of Antioxidant and Toxicological Properties of Stryphnodendron rotundifolium Mart. in Drosophila melanogaster Model

This study investigated the flavonoid content, antioxidant activity, and toxicological properties of the acetone–water fraction of stem bark of Stryphnodendron rotundifolium Mart. (TFSR). The total flavonoid content and antioxidant activity were determined, as typified by DPPH^● and ABTS^●+ radical scavenging abilities, Fe³⁺ reducing antioxidant power (FRAP), relative antioxidant capacity (RAC), and the inhibition of thiobarbituric acid reactive species (TBARs) in Drosophila melanogaster tissue. Toxicity and locomotor functions were evaluated in adult D. melanogaster flies through aging and survival assays, startle-induced negative geotaxis, and centrophobic responses with video-assisted open field motion tracking. The flavonoid content of dry TFSR (DF) was 3.36 mg quercetin/g. Furthermore, the significant antioxidant activity of TFSR was revealed through scavenging 95.3% of the ABTS^●+ radical and 82.4% of the DPPH^● radical, as well reducing 74.7% of Fe³⁺ in the FRAP assay and 80% Mo⁶⁺ in the RAC assay. TFSR conferred 70.25% protection against lipid peroxidation in Drosophila tissue. Survival rates ranged from 84.65 to 103.98% in comparison to the non-supplemented control and no evident deterioration of locomotor functions and centrophobia responses was observed. These results revealed that TFSR has potent antioxidant activity and low toxicity in vivo, profiling TFSR as a promising natural product in the treatment/management of iron overload and associated conditions.

Measuring metabolic rate in single flies during sleep and waking states via indirect calorimetry

BACKGROUND

Drosophila melanogaster is a leading genetic model for studying the neural regulation of sleep. Sleep is associated with changes in behavior and physiological state that are largely conserved across species. The investigation of sleep in flies has predominantly focused on behavioral readouts of sleep because physiological measurements, including changes in brain activity and metabolic rate, are less accessible. We have previously used stop-flow indirect calorimetry to measure whole body metabolic rate in single flies and have shown that in flies, like mammals, metabolic rate is reduced during sleep.

NEW METHOD

Here, we describe a modified version of this system that allows for efficient and highly sensitive acquisition of CO2 output from single flies.

RESULTS

In this modified system, we show that sleep-dependent changes in metabolic rate are diminished in aging flies, supporting the notion that sleep quality is reduced as flies age. We also describe a modification that allows for simultaneous acquisition of CO2 and O2 levels, providing a respiratory quotient that quantifies how metabolic stores are utilized. We find that the respiratory quotient identified in flies on an all-sugar diet is suggestive of lipogenesis, where the dietary sugar provided to the flies is being converted to fat.

COMPARISON WITH EXISTING METHODS AND CONCLUSIONS

Taken together, the measurement of metabolic rate via indirect calorimetry not only provides a physiological readout of sleep depth, but also provides insight the metabolic regulation of nutrient utilization, with broad applications to genetic studies in flies.

Clearance of variant Creutzfeldt-Jakob disease prions in vivo by the Hsp70 disaggregase system

The metazoan Hsp70 disaggregase protects neurons from proteotoxicity that arises from the accumulation of misfolded protein aggregates. Hsp70 and its co-chaperones disassemble and extract polypeptides from protein aggregates for refolding or degradation. The effectiveness of the chaperone system decreases with age and leads to accumulation rather than removal of neurotoxic protein aggregates. Therapeutic enhancement of the Hsp70 protein disassembly machinery is proposed to counter late-onset protein misfolding neurodegenerative disease that may arise. In the context of prion disease, it is not known whether stimulation of protein aggregate disassembly paradoxically leads to enhanced formation of seeding competent species of disease-specific proteins and acceleration of neurodegenerative disease. Here we have tested the hypothesis that modulation of Hsp70 disaggregase activity perturbs mammalian prion-induced neurotoxicity and prion seeding activity. To do so we used prion protein (PrP) transgenic Drosophila that authentically replicate mammalian prions. RNASeq identified that Hsp70, DnaJ-1 and Hsp110 gene expression was downregulated in prion-exposed PrP Drosophila. We demonstrated that RNAi knockdown of Hsp110 or DnaJ-1 gene expression in variant Creutzfeldt–Jakob disease prion-exposed human PrP Drosophila enhanced neurotoxicity, whereas overexpression mitigated toxicity. Strikingly, prion seeding activity in variant Creutzfeldt–Jakob disease prion-exposed human PrP Drosophila was ablated or reduced by Hsp110 or DnaJ-1 overexpression, respectively. Similar effects were seen in scrapie prion-exposed ovine PrP Drosophila with modified Hsp110 or DnaJ-1 gene expression. These unique observations show that the metazoan Hsp70 disaggregase facilitates the clearance of mammalian prions and that its enhanced activity is a potential therapeutic strategy for human prion disease.

Macroautophagy and normal aging of the nervous system: Lessons from animal models

Aging represents a cumulative form of cellular stress, which is thought to challenge many aspects of proteostasis. The non-dividing, long-lived neurons are particularly vulnerable to stress, and, not surprisingly, even normal aging is highly associated with a decline in brain function in humans, as well as in other animals. Macroautophagy is a fundamental arm of the proteostasis network, safeguarding proper protein turnover during different cellular states and against diverse cellular stressors. An intricate interplay between macroautophagy and aging is beginning to unravel, with the emergence of new tools, including those for monitoring autophagy in cultured neurons and in the nervous system of different organisms in vivo. Here, we review recent findings on the impact of aging on neuronal integrity and on neuronal macroautophagy, as they emerge from studies in invertebrate and mammalian models.

Plasma membrane calcium ATPase downregulation in dopaminergic neurons alters cellular physiology and motor behaviour in Drosophila melanogaster

The accumulation of Ca²⁺ and its subsequent increase in oxidative stress is proposed to be involved in selective dysfunctionality of dopaminergic neurons, the main cell type affected in Parkinson's disease. To test the in vivo impact of Ca²⁺ increment in dopaminergic neurons physiology, we downregulated the plasma membrane Ca²⁺ ATPase (PMCA), a pump that extrudes cytosolic Ca²⁺ , by expressing PMCA^RNAi in Drosophila melanogaster dopaminergic neurons. In these animals, we observed major locomotor alterations paralleled to higher cytosolic Ca²⁺ and increased levels of oxidative stress in mitochondria. Interestingly, although no overt degeneration of dopaminergic neurons was observed, evidences of neuronal dysfunctionality were detected such as increases in presynaptic vesicles in dopaminergic neurons and in the levels of dopamine in the brain, as well as presence of toxic effects when PMCA was downregulated in the eye. Moreover, reduced PMCA levels were found in a Drosophila model of Parkinson's disease, Parkin knock-out, expanding the functional relevance of PMCA reduction to other Parkinson's disease-related models. In all, we have generated a new model to study motor abnormalities caused by increments in Ca²⁺ that lead to augmented oxidative stress in a dopaminergic environment, added to a rise in synaptic vesicles and dopamine levels.

The Biology and Pathobiology of Glutamatergic, Cholinergic, and Dopaminergic Signaling in the Aging Brain

The elderly population is growing worldwide, with important health and socioeconomic implications. Clinical and experimental studies on aging have uncovered numerous changes in the brain, such as decreased neurogenesis, increased synaptic defects, greater metabolic stress, and enhanced inflammation. These changes are associated with cognitive decline and neurobehavioral deficits. Although aging is not a disease, it is a significant risk factor for functional worsening, affective impairment, disease exaggeration, dementia, and general disease susceptibility. Conversely, life events related to mental stress and trauma can also lead to accelerated age-associated disorders and dementia. Here, we review human studies and studies on mice and rats, such as those modeling human neurodegenerative diseases, that have helped elucidate (1) the dynamics and mechanisms underlying the biological and pathological aging of the main projecting systems in the brain (glutamatergic, cholinergic, and dopaminergic) and (2) the effect of defective glutamatergic, cholinergic, and dopaminergic projection on disabilities associated with aging and neurodegenerative disorders, such as Alzheimer's and Parkinson's diseases. Detailed knowledge of the mechanisms of age-related diseases can be an important element in the development of effective ways of treatment. In this context, we briefly analyze which adverse changes associated with neurodegenerative diseases in the cholinergic, glutaminergic and dopaminergic systems could be targeted by therapeutic strategies developed as a result of our better understanding of these damaging mechanisms.

A new model for sensitive detection of zoonotic prions by PrP transgenic Drosophila

Prions are transmissible protein pathogens most reliably detected by a bioassay in a suitable host, typically mice. However, the mouse bioassay is slow and cumbersome, and relatively insensitive to low titers of prion infectivity. Prions can be detected biochemically in vitro by the protein misfolding cyclic amplification (PMCA) technique, which amplifies disease-associated prion protein but does not detect bona fide prion infectivity. Here, we demonstrate that Drosophila transgenic for bovine prion protein (PrP) expression can serve as a model system for the detection of bovine prions significantly more efficiently than either the mouse prion bioassay or PMCA. Strikingly, bovine PrP transgenic Drosophila could detect bovine prion infectivity in the region of a 10^-12 dilution of classical bovine spongiform encephalopathy (BSE) inoculum, which is 10⁶-fold more sensitive than that achieved by the bovine PrP mouse bioassay. A similar level of sensitivity was observed in the detection of H-type and L-type atypical BSE and sheep-passaged BSE by bovine PrP transgenic Drosophila. Bioassays of bovine prions in Drosophila were performed within 7 weeks, whereas the mouse prion bioassay required at least a year to assess the same inoculum. In addition, bovine PrP transgenic Drosophila could detect classical BSE at a level 10⁵-fold lower than that achieved by PMCA. These data show that PrP transgenic Drosophila represent a new tractable prion bioassay for the efficient and sensitive detection of mammalian prions, including those of known zoonotic potential.

Drosophila tubulin polymerization promoting protein mutants reveal pathological correlates relevant to human Parkinson's disease

Parkinson's disease (PD) is a progressive neurodegenerative disorder with no known cure. PD is characterized by locomotion deficits, nigrostriatal dopaminergic neuronal loss, mitochondrial dysfunctions and formation of α-Synuclein aggregates. A well-conserved and less understood family of Tubulin Polymerization Promoting Proteins (TPPP) is also implicated in PD and related disorders, where TPPP exists in pathological aggregates in neurons in patient brains. However, there are no in vivo studies on mammalian TPPP to understand the genetics and neuropathology linking TPPP aggregation or neurotoxicity to PD. Recently, we discovered the only Drosophila homolog of human TPPP named Ringmaker (Ringer). Here, we report that adult ringer mutants display progressive locomotor disabilities, reduced lifespan and neurodegeneration. Importantly, our findings reveal that Ringer is associated with mitochondria and ringer mutants have mitochondrial structural damage and dysfunctions. Adult ringer mutants also display progressive loss of dopaminergic neurons. Together, these phenotypes of ringer mutants recapitulate some of the salient features of human PD patients, thus allowing us to utilize ringer mutants as a fly model relevant to PD, and further explore its genetic and molecular underpinnings to gain insights into the role of human TPPP in PD.

Impact of high-fat diet on lifespan, metabolism, fecundity and behavioral senescence in Drosophila

Excess consumption of high-fat diet (HFD) is likely to result in obesity and increases the predisposition to associated health disorders. Drosophila melanogaster has emerged as an important model to study the effects of HFD on metabolism, gut function, behavior, and ageing. In this study, we investigated the effects of HFD on physiology and behavior of female flies at different time-points over several weeks. We found that HFD decreases lifespan, and also with age leads to accelerated decline of climbing ability in both virgins and mated flies. In virgins HFD also increased sleep fragmentation with age. Furthermore, long-term exposure to HFD results in elevated adipokinetic hormone (AKH) transcript levels and an enlarged crop with increased lipid stores. We detected no long-term effects of HFD on body mass, or levels of triacylglycerides (TAG), glycogen or glucose, although fecundity was diminished. However, one week of HFD resulted in decreased body mass and elevated TAG levels in mated flies. Finally, we investigated the role of AKH in regulating effects of HFD during aging. Both with normal diet (ND) and HFD, Akh mutant flies displayed increased longevity compared to control flies. However, both mutants and controls showed shortened lifespan on HFD compared to ND. In flies exposed to ND, fecundity is decreased in Akh mutants compared to controls after one week, but increased after three weeks. However, HFD leads to a similar decrease in fecundity in both genotypes after both exposure times. Thus, long-term exposure to HFD increases AKH signaling, impairs lifespan and fecundity and augments age-related behavioral senescence.

Vesicular glutamate transporter modulates sex differences in dopamine neuron vulnerability to age-related neurodegeneration

Age is the greatest risk factor for Parkinson's disease (PD) which causes progressive loss of dopamine (DA) neurons, with males at greater risk than females. Intriguingly, some DA neurons are more resilient to degeneration than others. Increasing evidence suggests that vesicular glutamate transporter (VGLUT) expression in DA neurons plays a role in this selective vulnerability. We investigated the role of DA neuron VGLUT in sex- and age-related differences in DA neuron vulnerability using the genetically tractable Drosophila model. We found sex differences in age-related DA neurodegeneration and its associated locomotor behavior, where males exhibit significantly greater decreases in both DA neuron number and locomotion during aging compared with females. We discovered that dynamic changes in DA neuron VGLUT expression mediate these age- and sex-related differences, as a potential compensatory mechanism for diminished DA neurotransmission during aging. Importantly, female Drosophila possess higher levels of VGLUT expression in DA neurons compared with males, and this finding is conserved across flies, rodents, and humans. Moreover, we showed that diminishing VGLUT expression in DA neurons eliminates females' greater resilience to DA neuron loss across aging. This offers a new mechanism for sex differences in selective DA neuron vulnerability to age-related DA neurodegeneration. Finally, in mice, we showed that the ability of DA neurons to achieve optimal control over VGLUT expression is essential for DA neuron survival. These findings lay the groundwork for the manipulation of DA neuron VGLUT expression as a novel therapeutic strategy to boost DA neuron resilience to age- and PD-related neurodegeneration.

A conserved role for sleep in supporting Spatial Learning in Drosophila

Sleep loss and aging impair hippocampus-dependent Spatial Learning in mammalian systems. Here we use the fly Drosophila melanogaster to investigate the relationship between sleep and Spatial Learning in healthy and impaired flies. The Spatial Learning assay is modeled after the Morris Water Maze. The assay uses a "thermal maze" consisting of a 5 × 5 grid of Peltier plates maintained at 36-37°C and a visual panorama. The first trial begins when a single tile that is associated with a specific visual cue is cooled to 25°C. For subsequent trials, the cold tile is heated, the visual panorama is rotated and the flies must find the new cold tile by remembering its association with the visual cue. Significant learning was observed with two different wild-type strains-Cs and 2U, validating our design. Sleep deprivation prior to training impaired Spatial Learning. Learning was also impaired in the classic learning mutant rutabaga (rut); enhancing sleep restored learning to rut mutants. Further, we found that flies exhibited a dramatic age-dependent cognitive decline in Spatial Learning starting at 20-24 days of age. These impairments could be reversed by enhancing sleep. Finally, we find that Spatial Learning requires dopaminergic signaling and that enhancing dopaminergic signaling in aged flies restored learning. Our results are consistent with the impairments seen in rodents and humans. These results thus demonstrate a critical conserved role for sleep in supporting Spatial Learning, and suggest potential avenues for therapeutic intervention during aging.

Presynaptic accumulation of α-synuclein causes synaptopathy and progressive neurodegeneration in Drosophila

Alpha-synuclein (α-syn) mislocalization and accumulation in intracellular inclusions is the major pathological hallmark of degenerative synucleinopathies, including Parkinson's disease, Parkinson's disease with dementia and dementia with Lewy bodies. Typical symptoms are behavioural abnormalities including motor deficits that mark disease progression, while non-motor symptoms and synaptic deficits are already apparent during the early stages of disease. Synucleinopathies have therefore been considered synaptopathies that exhibit synaptic dysfunction prior to neurodegeneration. However, the mechanisms and events underlying synaptopathy are largely unknown. Here we investigated the cascade of pathological events underlying α-syn accumulation and toxicity in a Drosophila model of synucleinopathy by employing a combination of histological, biochemical, behavioural and electrophysiological assays. Our findings demonstrate that targeted expression of human α-syn leads to its accumulation in presynaptic terminals that caused downregulation of synaptic proteins, cysteine string protein, synapsin, and syntaxin 1A, and a reduction in the number of Bruchpilot puncta, the core component of the presynaptic active zone essential for its structural integrity and function. These α-syn-mediated presynaptic alterations resulted in impaired neuronal function, which triggered behavioural deficits in ageing Drosophila that occurred prior to progressive degeneration of dopaminergic neurons. Comparable alterations in presynaptic active zone protein were found in patient brain samples of dementia with Lewy bodies. Together, these findings demonstrate that presynaptic accumulation of α-syn impairs the active zone and neuronal function, which together cause synaptopathy that results in behavioural deficits and the progressive loss of dopaminergic neurons. This sequence of events resembles the cytological and behavioural phenotypes that characterise the onset and progression of synucleinopathies, suggesting that α-syn-mediated synaptopathy is an initiating cause of age-related neurodegeneration.

Structural aspects of the aging invertebrate brain

Aging is characterized by a decline in neuronal function in all animal species investigated so far. Functional changes are accompanied by and may be in part caused by, structurally visible degenerative changes in neurons. In the mammalian brain, normal aging shows abnormalities in dendrites and axons, as well as ultrastructural changes in synapses, rather than global neuron loss. The analysis of the structural features of aging neurons, as well as their causal link to molecular mechanisms on the one hand, and the functional decline on the other hand is crucial in order to understand the aging process in the brain. Invertebrate model organisms like Drosophila and C. elegans offer the opportunity to apply a forward genetic approach to the analysis of aging. In the present review, we aim to summarize findings concerning abnormalities in morphology and ultrastructure in invertebrate brains during normal aging and compare them to what is known for the mammalian brain. It becomes clear that despite of their considerably shorter life span, invertebrates display several age-related changes very similar to the mammalian condition, including the retraction of dendritic and axonal branches at specific locations, changes in synaptic density and increased accumulation of presynaptic protein complexes. We anticipate that continued research efforts in invertebrate systems will significantly contribute to reveal (and possibly manipulate) the molecular/cellular pathways leading to neuronal aging in the mammalian brain.

Increasing neuronal glucose uptake attenuates brain aging and promotes life span under dietary restriction in Drosophila

Brain neurons play a central role in organismal aging, but there is conflicting evidence about the role of neuronal glucose availability because glucose uptake and metabolism are associated with both aging and extended life span. Here, we analyzed metabolic changes in the brain neurons of Drosophila during aging. Using a genetically encoded fluorescent adenosine triphosphate (ATP) biosensor, we found decreased ATP concentration in the neuronal somata of aged flies, correlated with decreased glucose content, expression of glucose transporter and glycolytic enzymes and mitochondrial quality. The age-associated reduction in ATP concentration did not occur in brain neurons with suppressed glycolysis or enhanced glucose uptake, suggesting these pathways contribute to ATP reductions. Despite age-associated mitochondrial damage, increasing glucose uptake maintained ATP levels, suppressed locomotor deficits, and extended the life span. Increasing neuronal glucose uptake during dietary restriction resulted in the longest life spans, suggesting an additive effect of enhancing glucose availability during a bioenergetic challenge on aging.

•

Imaging of Drosophila brain reveals aged neurons suffer from energy deficits

•

Increased neuronal glucose uptake attenuates age-dependent declines in ATP

•

Increased glucose uptake is beneficial despite age-dependent mitochondrial damage

•

Increased neuronal glucose uptake and dietary restriction further extend life span

Analysis of Dopaminergic Functions in Drosophila

Dopaminergic (DA) neurons regulate various physiological functions, including motor function, emotion, learning, sleep, and arousal. Degeneration of DA neurons in the substantia nigra of the midbrain causes motor disturbance in Parkinson's disease (PD). Studies on familial PD have revealed that a subset of PD genes encode proteins that regulate mitochondrial function and synaptic dynamics. Drosophila is a powerful model of PD, whereby genetic interactions of PD genes with well-conserved cellular signaling can be evaluated. Morphological changes in mitochondria, along with dysfunction and degeneration of DA neurons, have been reported in many studies using Drosophila PD models. In this chapter, we will describe imaging methods to visualize mitochondria in DA neurons and to evaluate spontaneous neural activity of DA neurons in the Drosophila brain.

Aging mechanisms-A perspective mostly from Drosophila

A mechanistic understanding of the natural aging process, which is distinct from aging-related disease mechanisms, is essential for developing interventions to extend lifespan or healthspan. Here, we discuss current trends in aging research and address conceptual and experimental challenges in the field. We examine various molecular markers implicated in aging with an emphasis on the role of heterochromatin and epigenetic changes. Studies in model organisms have been advantageous in elucidating conserved genetic and epigenetic mechanisms and assessing interventions that affect aging. We highlight the use of Drosophila, which allows controlled studies for evaluating genetic and environmental contributors to aging conveniently. Finally, we propose the use of novel methodologies and future strategies using Drosophila in aging research.

Rodent and fly models in behavioral neuroscience: An evaluation of methodological advances, comparative research, and future perspectives

The assessment of behavioral outcomes is a central component of neuroscientific research, which has required continuous technological innovations to produce more detailed and reliable findings. In this article, we provide an in-depth review on the progress and future implications for three model organisms (mouse, rat, and Drosophila) essential to our current understanding of behavior. By compiling a comprehensive catalog of popular assays, we are able to compare the diversity of tasks and usage of these animal models in behavioral research. This compilation also allows for the evaluation of existing state-of-the-art methods and experimental applications, including optogenetics, machine learning, and high-throughput behavioral assays. We go on to discuss novel apparatuses and inter-species analyses for centrophobism, feeding behavior, aggression and mating paradigms, with the goal of providing a unique view on comparative behavioral research. The challenges and recent advances are evaluated in terms of their translational value, ethical procedures, and trustworthiness for behavioral research.

A connectome and analysis of the adult Drosophila central brain

The neural circuits responsible for animal behavior remain largely unknown. We summarize new methods and present the circuitry of a large fraction of the brain of the fruit fly Drosophila melanogaster. Improved methods include new procedures to prepare, image, align, segment, find synapses in, and proofread such large data sets. We define cell types, refine computational compartments, and provide an exhaustive atlas of cell examples and types, many of them novel. We provide detailed circuits consisting of neurons and their chemical synapses for most of the central brain. We make the data public and simplify access, reducing the effort needed to answer circuit questions, and provide procedures linking the neurons defined by our analysis with genetic reagents. Biologically, we examine distributions of connection strengths, neural motifs on different scales, electrical consequences of compartmentalization, and evidence that maximizing packing density is an important criterion in the evolution of the fly's brain.

Effects on Dopaminergic Neurons Are Secondary in COX-Deficient Locomotor Dysfunction in Drosophila

Dopaminergic (DA) neurons have been implicated as key targets in neurological disorders, notably those involving locomotor impairment, and are considered to be highly vulnerable to mitochondrial dysfunction, a common feature of such diseases. Here we investigated a Drosophila model of locomotor disorders in which functional impairment is brought about by pan-neuronal RNAi knockdown of subunit COX7A of cytochrome oxidase (COX). Despite minimal neuronal loss by apoptosis, the expression and activity of tyrosine hydroxylase was decreased by half. Surprisingly, COX7A knockdown specifically targeted to DA neurons did not produce locomotor defect. Instead, using various drivers, we found that COX7A knockdown in specific groups of cholinergic and glutamatergic neurons underlay the phenotype. Based on our main finding, the vulnerability of DA neurons to mitochondrial dysfunction as a cause of impaired locomotion in other organisms, including mammals, warrants detailed investigation.

Drosophila Skp1 Homologue SkpA Plays a Neuroprotective Role in Adult Brain

Skp1, a component of the ubiquitin E3 ligases, was found to be decreased in the brains of sporadic Parkinson's disease (PD) patients, and its overexpression prevented death of murine neurons in culture. Here we expose the neuroprotective role of the Drosophila skp1 homolog, skpA, in the adult brain. Neuronal knockdown of skpA leads to accumulation of ubiquitinated protein aggregates and loss of dopaminergic neurons accompanied by motor dysfunction and reduced lifespan. Conversely, neuronal overexpression of skpA reduces aggregate load, improves age-related motor decline, and prolongs lifespan. Moreover, SkpA rescues neurodegeneration in a Drosophila model of PD. We also show that a Drosophila homolog of FBXO7, the F Box protein, Nutcracker (Ntc), works in the same pathway with SkpA. However, skpA overexpression rescues ntc knockdown phenotype, suggesting that SkpA interacts with additional F box proteins in the adult brain neurons. Collectively, our study discloses Skp1/SkpA as a potential therapeutic target in neurodegenerative diseases.

•

SkpA-mediated protein degradation is required for normal function of the adult brain

•

SkpA overexpression rescues neurodegeneration in α-synuclein-induced fly PD model

•

SkpA and Ntc work in the same pathway of protein degradation in adult brain neurons

Transcriptional signature of prion-induced neurotoxicity in a Drosophila model of transmissible mammalian prion disease

Prion diseases are fatal transmissible neurodegenerative conditions of humans and animals that arise through neurotoxicity induced by PrP misfolding. The cellular and molecular mechanisms of prion-induced neurotoxicity remain undefined. Understanding these processes will underpin therapeutic and control strategies for human and animal prion diseases, respectively. Prion diseases are difficult to study in their natural hosts and require the use of tractable animal models. Here we used RNA-Seq-based transcriptome analysis of prion-exposed Drosophila to probe the mechanism of prion-induced neurotoxicity. Adult Drosophila transgenic for pan neuronal expression of ovine PrP targeted to the plasma membrane exhibit a neurotoxic phenotype evidenced by decreased locomotor activity after exposure to ovine prions at the larval stage. Pathway analysis and quantitative PCR of genes differentially expressed in prion-infected Drosophila revealed up-regulation of cell cycle activity and DNA damage response, followed by down-regulation of eIF2 and mTOR signalling. Mitochondrial dysfunction was identified as the principal toxicity pathway in prion-exposed PrP transgenic Drosophila. The transcriptomic changes we observed were specific to PrP targeted to the plasma membrane since these prion-induced gene expression changes were not evident in similarly treated Drosophila transgenic for cytosolic pan neuronal PrP expression, or in non-transgenic control flies. Collectively, our data indicate that aberrant cell cycle activity, repression of protein synthesis and altered mitochondrial function are key events involved in prion-induced neurotoxicity, and correlate with those identified in mammalian hosts undergoing prion disease. These studies highlight the use of PrP transgenic Drosophila as a genetically well-defined tractable host to study mammalian prion biology.

Ancestral regulatory mechanisms specify conserved midbrain circuitry in arthropods and vertebrates

Comparative developmental genetics indicate insect and mammalian forebrains form and function in comparable ways. However, these data are open to opposing interpretations that advocate either a single origin of the brain and its adaptive modification during animal evolution; or multiple, independent origins of the many different brains present in extant Bilateria. Here, we describe conserved regulatory elements that mediate the spatiotemporal expression of developmental control genes directing the formation and function of midbrain circuits in flies, mice, and humans. These circuits develop from corresponding midbrain-hindbrain boundary regions and regulate comparable behaviors for balance and motor control. Our findings suggest that conserved regulatory mechanisms specify cephalic circuits for sensory integration and coordinated behavior common to all animals that possess a brain.

Corresponding attributes of neural development and function suggest arthropod and vertebrate brains may have an evolutionarily conserved organization. However, the underlying mechanisms have remained elusive. Here, we identify a gene regulatory and character identity network defining the deutocerebral–tritocerebral boundary (DTB) in Drosophila. This network comprises genes homologous to those directing midbrain-hindbrain boundary (MHB) formation in vertebrates and their closest chordate relatives. Genetic tracing reveals that the embryonic DTB gives rise to adult midbrain circuits that in flies control auditory and vestibular information processing and motor coordination, as do MHB-derived circuits in vertebrates. DTB-specific gene expression and function are directed by cis-regulatory elements of developmental control genes that include homologs of mammalian Zinc finger of the cerebellum and Purkinje cell protein 4. Drosophila DTB-specific cis-regulatory elements correspond to regulatory sequences of human ENGRAILED-2, PAX-2, and DACHSHUND-1 that direct MHB-specific expression in the embryonic mouse brain. We show that cis-regulatory elements and the gene networks they regulate direct the formation and function of midbrain circuits for balance and motor coordination in insects and mammals. Regulatory mechanisms mediating the genetic specification of cephalic neural circuits in arthropods correspond to those in chordates, thereby implying their origin before the divergence of deuterostomes and ecdysozoans.

Rpt2 proteasome subunit reduction causes Parkinson's disease like symptoms in Drosophila

The dysfunction of the proteasome-ubiquitin system is commonly reported in several neurodegenerative diseases. Post mortem samples of brains of patients with Parkinson´s disease present cytoplasmic inclusions that are rich in proteins such as ubiquitin, Tau, and α-synuclein. In Parkinson´s disease, a specific reduction of some of the proteasome subunits has also been reported. However, the specific role of the different proteasome subunits in dopaminergic neuron degeneration has not been thoroughly explored. In this work, we used the Gal4/UAS system to test fourteen Drosophila melanogaster RNAi lines from the Bloomington Drosophila Stock Center. Each of these lines targets a different proteasome subunit. To identify the strains that were able to induce neurodegeneration, we drove the expression of these lines to the eye and cataloged them as a function of the extent of neurodegeneration that they induced. The targeted proteasomal subunits are conserved in mammals and therefore may be relevant to study proteasome related diseases. The RNAi line among the regulatory subunits with the most penetrant phenotype targeted the proteasomal subunit Rpt2 and we decided to further characterize its phenotypes. Rpt2 knockdown in the Drosophila central nervous system reduced the activity of the proteasome, augmented the amount of insoluble ubiquitinated protein, and elicited motor and non-motor phenotypes that were similar to the ones found in Drosophila and other models for Parkinson's disease. When Rpt2 is silenced pan-neurally, third instar larvae have locomotion dysfunctions and die during pupation. Larval lethality was avoided using the Gal80-Gal4 system to induce the expression of the Rpt2 RNAi to dopaminergic neurons only after pupation. The reduction of Rpt2 in adult dopaminergic neurons causes reduced survival, hyperactivity, neurodegeneration, and sleep loss; probably recapitulating some of the sleep disorders that Parkinson's disease patients have before the appearance of locomotion disorders.

Inhibiting thrombin improves motor function and decreases oxidative stress in the LRRK2 transgenic Drosophila melanogaster model of Parkinson's disease

Parkinson's disease (PD) is a complex neurodegenerative disease characterized by the presence of tremors, loss of dopaminergic neurons and accumulation of α-synuclein. While there is no single direct cause of PD, genetic mutations, exposure to pesticides, diet and traumatic brain injury have been identified as risk factors. Increasing evidence suggests that oxidative stress and neuroinflammation contribute to the pathogenesis of neuronal injury in neurodegenerative diseases such as PD and Alzheimer's disease (AD). We have previously documented that the multifunctional inflammatory mediator thrombin contributes to oxidative stress and neuroinflammation in AD. Here, for the first time, we explore the role of thrombin in a transgenic PD model, the LRRK2 mutant Drosophila melanogaster. Transgenic flies were treated with the direct thrombin inhibitor dabigatran for 7 days and locomotor activity and indices of oxidative stress evaluated. Our data show that dabigatran treatment significantly (p < 0.05) improved climbing activity, a measurement of locomotor ability, in male but had no effect on locomotor performance in female flies. Dabigatran treatment had no effect on tyrosine hydroxylase levels. Analysis of oxidative stress in male flies showed that dabigatran was able to significantly (p < 0.01) lower reactive oxygen species levels. Furthermore, Western blot analysis showed that the pro-oxidant proteins iNOS and NOX4 are elevated in LRRK2 male flies compared to wildtype and that treatment with dabigatran reduced expression of these proteins. Our results indicate that dabigatran treatment could improve motor function in PD by reducing oxidative stress. These data suggest that targeting thrombin may improve oxidative stress related pathologies in PD.

The function of bacterial HtrA is evolutionally conserved in mammalian HtrA2/Omi

Although the malfunction of HtrA2/Omi leads to Parkinson's disease (PD), the underlying mechanism has remained unknown. Here, we showed that HtrA2/Omi specifically removed oligomeric α-Syn but not monomeric α-Syn to protect oligomeric α-Syn-induced neurodegeneration. Experiments using mnd2 mice indicated that HtrA2/Omi degraded oligomeric α-Syn specifically without affecting monomers. Transgenic Drosophila melanogaster experiments of the co-expression α-Syn and HtrA2/Omi and expression of genes individually also confirmed that pan-neuronal expression of HtrA2/Omi completely rescued Parkinsonism in the α-Syn-induced PD Drosophila model by specifically removing oligomeric α-Syn. HtrA2/Omi maintained the health and integrity of the brain and extended the life span of transgenic flies. Because HtrA2/Omi specifically degraded oligomeric α-Syn, co-expression of HtrA2/Omi and α-Syn in Drosophila eye maintained a healthy retina, while the expression of α-Syn induced retinal degeneration. This work showed that the bacterial function of HtrA to degrade toxic misfolded proteins is evolutionarily conserved in mammalian brains as HtrA2/Omi.

Neuroprotection by the Immunomodulatory Drug Pomalidomide in the Drosophila LRRK2WD40 Genetic Model of Parkinson's Disease

The search for new disease-modifying drugs for Parkinson's disease (PD) is a slow and highly expensive process, and the repurposing of drugs already approved for different medical indications is becoming a compelling alternative option for researchers. Genetic variables represent a predisposing factor to the disease and mutations in leucine-rich repeat kinase 2 (LRRK2) locus have been correlated to late-onset autosomal-dominant PD. The common fruit fly Drosophila melanogaster carrying the mutation LRRK2 loss-of-function in the WD40 domain (LRRK2^WD40), is a simple in vivo model of PD and is a valid tool to first evaluate novel therapeutic approaches to the disease. Recent studies have suggested a neuroprotective activity of immunomodulatory agents in PD models. Here the immunomodulatory drug Pomalidomide (POM), a Thalidomide derivative, was examined in the Drosophila LRRK2^WD40 genetic model of PD. Mutant and wild type flies received increasing POM doses (1, 0.5, 0.25 mM) through their diet from day 1 post eclosion, until postnatal day (PN) 7 or 14, when POM's actions were evaluated by quantifying changes in climbing behavior as a measure of motor performance, the number of brain dopaminergic neurons and T-bars, mitochondria integrity. LRRK2^WD40 flies displayed a spontaneous age-related impairment of climbing activity, and POM significantly and dose-dependently improved climbing performance both at PN 7 and PN 14. LRRK2^WD40 fly motor disability was underpinned by a progressive loss of dopaminergic neurons in posterior clusters of the protocerebrum, which are involved in the control of locomotion, by a low number of T-bars density in the presynaptic bouton active zones. POM treatment fully rescued the cell loss in all posterior clusters at PN 7 and PN 14 and significantly increased the T-bars density. Moreover, several damaged mitochondria with dilated cristae were observed in LRRK2^WD40 flies treated with vehicle but not following POM. This study demonstrates the neuroprotective activity of the immunomodulatory agent POM in a genetic model of PD. POM is an FDA-approved clinically available and well-tolerated drug used for the treatment of multiple myeloma. If further validated in mammalian models of PD, POM could rapidly be clinically tested in humans.

MicroRNAs Regulate Multiple Aspects of Locomotor Behavior in Drosophila

Locomotion is an ancient and fundamental output of the nervous system required for animals to perform many other complex behaviors. Although the formation of motor circuits is known to be under developmental control of transcriptional mechanisms that define the fates and connectivity of the many neurons, glia and muscle constituents of these circuits, relatively little is known about the role of post-transcriptional regulation of locomotor behavior. MicroRNAs have emerged as a potentially rich source of modulators for neural development and function. In order to define the microRNAs required for normal locomotion in Drosophila melanogaster, we utilized a set of transgenic Gal4-dependent competitive inhibitors (microRNA sponges, or miR-SPs) to functionally assess ca. 140 high-confidence Drosophila microRNAs using automated quantitative movement tracking systems followed by multiparametric analysis. Using ubiquitous expression of miR-SP constructs, we identified a large number of microRNAs that modulate aspects of normal baseline adult locomotion. Addition of temperature-dependent Gal80 to identify microRNAs that act during adulthood revealed that the majority of these microRNAs play developmental roles. Comparison of ubiquitous and neural-specific miR-SP expression suggests that most of these microRNAs function within the nervous system. Parallel analyses of spontaneous locomotion in adults and in larvae also reveal that very few of the microRNAs required in the adult overlap with those that control the behavior of larval motor circuits. These screens suggest that a rich regulatory landscape underlies the formation and function of motor circuits and that many of these mechanisms are stage and/or parameter-specific.

High-Salt Diet Causes Sleep Fragmentation in Young Drosophila Through Circadian Rhythm and Dopaminergic Systems

Salt (sodium chloride) is an essential dietary requirement, but excessive consumption has long-term adverse consequences. A high-salt diet (HSD) increases the risk of chronic diseases such as cardiovascular conditions and diabetes and is also associated with poor sleep quality. Little is known, however, about the neural circuit mechanisms that mediate HSD-induced sleep changes. In this study, we sought to identify the effects of HSD on the sleep and related neural circuit mechanisms of Drosophila. Strikingly, we found that HSD causes young Drosophila to exhibit a fragmented sleep phenotype similar to that of normal aging individuals. Importantly, we further showed that HSD slightly impairs circadian rhythms and that the HSD-induced sleep changes are dependent on the circadian rhythm system. In addition, we demonstrated that HSD-induced sleep changes are dopaminergic-system dependent. Together, these results provide insight into how elevated salt in the diet can affect sleep quality.

Neuronal Mechanisms that Drive Organismal Aging Through the Lens of Perception

Sensory neurons provide organisms with data about the world in which they live, for the purpose of successfully exploiting their environment. The consequences of sensory perception are not simply limited to decision-making behaviors; evidence suggests that sensory perception directly influences physiology and aging, a phenomenon that has been observed in animals across taxa. Therefore, understanding the neural mechanisms by which sensory input influences aging may uncover novel therapeutic targets for aging-related physiologies. In this review, we examine different perceptive experiences that have been most clearly linked to aging or age-related disease: food perception, social perception, time perception, and threat perception. For each, the sensory cues, receptors, and/or pathways that influence aging as well as the individual or groups of neurons involved, if known, are discussed. We conclude with general thoughts about the potential impact of this line of research on human health and aging.

A Genetic Toolkit for Dissecting Dopamine Circuit Function in Drosophila

The neuromodulator dopamine (DA) plays a key role in motor control, motivated behaviors, and higher-order cognitive processes. Dissecting how these DA neural networks tune the activity of local neural circuits to regulate behavior requires tools for manipulating small groups of DA neurons. To address this need, we assembled a genetic toolkit that allows for an exquisite level of control over the DA neural network in Drosophila. To further refine targeting of specific DA neurons, we also created reagents that allow for the conversion of any existing GAL4 line into Split GAL4 or GAL80 lines. We demonstrated how this toolkit can be used with recently developed computational methods to rapidly generate additional reagents for manipulating small subsets or individual DA neurons. Finally, we used the toolkit to reveal a dynamic interaction between a small subset of DA neurons and rearing conditions in a social space behavioral assay.

Behavioral and molecular markers of death in Drosophila melanogaster

Fly movement was tracked through 3-dimensional (3D) space as the fly died, using either reflected visible light, reflected infrared (IR) light, or fly GFP fluorescence. Behaviors measured included centrophobism, negative geotaxis, velocity, and total activity. In addition, frequency of directional heading changes (FDHC) was calculated as a measure of erratic movement. Nine middle-aged flies were tracked as they died during normal aging, and fifteen young flies were tracked as they died from dehydration/starvation stress. Episodes of increased FDHC were observed 0-8 h prior to death for the majority of the flies. FDHC was also increased with age in flies with neuronal expression of a human Abeta42 protein fragment associated with Alzheimer's disease. Finally, green autofluorescence appeared in the eye and body immediately prior to and coincident with death, and fluorescence of GFP targeted to the retina increased immediately prior to and coincident with death. The results suggest the potential utility of FDHC, green autofluorescence, and retinal GFP as markers of neuronal malfunction and imminent death.

Effect of the Resveratrol Rice DJ526 on Longevity

Resveratrol is the best-known chemical for extending the lifespan of various organisms. Extensive recent research has shown that resveratrol can extend the lifespan of single-celled organisms, but its effects on the extension of animal lifespans are marginal. Despite the limited efficacy of pure resveratrol, resveratrol with the endogenous property of the DJ rice in the resveratrol rice DJ526 previously showed profound health benefits. Here, we report that the resveratrol rice DJ526 markedly extended the lifespan of the fruit fly Drosophila melanogaster by as much as 41.4% compared to that of the control. The resveratrol rice DJ526 also improved age-related symptoms such as locomotive deterioration, body weight gain, eye degeneration and neurodegeneration in D. melanogaster upon aging. This result shows the most significantly improved lifespan in animal experiments to date, meaning that the resveratrol rice DJ526 will assist in the development of a therapeutic agent for longevity or addressing age-related degeneration.

Social behavior and aging: A fly model

The field of behavioral genetics has recently begun to explore the effect of age on social behaviors. Such studies are particularly important, as certain neuropsychiatric disorders with abnormal social interactions, like autism and schizophrenia, have been linked to older parents. Appropriate social interaction can also have a positive impact on longevity, and is associated with successful aging in humans. Currently, there are few genetic models for understanding the effect of aging on social behavior and its potential transgenerational inheritance. The fly is emerging as a powerful model for identifying the basic molecular mechanisms underlying neurological and neuropsychiatric disorders. In this review, we discuss these recent advancements, with a focus on how studies in Drosophila melanogaster have provided insight into the effect of aging on aspects of social behavior, including across generations.

A feedback loop between dipeptide-repeat protein, TDP-43 and karyopherin-α mediates C9orf72-related neurodegeneration

Accumulation and aggregation of TDP-43 is a major pathological hallmark of amyotrophic lateral sclerosis and frontotemporal dementia. TDP-43 inclusions also characterize patients with GGGGCC (G4C2) hexanucleotide repeat expansion in C9orf72 that causes the most common genetic form of amyotrophic lateral sclerosis and frontotemporal dementia (C9ALS/FTD). Functional studies in cell and animal models have identified pathogenic mechanisms including repeat-induced RNA toxicity and accumulation of G4C2-derived dipeptide-repeat proteins. The role of TDP-43 dysfunction in C9ALS/FTD, however, remains elusive. We found G4C2-derived dipeptide-repeat protein but not G4C2-RNA accumulation caused TDP-43 proteinopathy that triggered onset and progression of disease in Drosophila models of C9ALS/FTD. Timing and extent of TDP-43 dysfunction was dependent on levels and identity of dipeptide-repeat proteins produced, with poly-GR causing early and poly-GA/poly-GP causing late onset of disease. Accumulating cytosolic, but not insoluble aggregated TDP-43 caused karyopherin-α2/4 (KPNA2/4) pathology, increased levels of dipeptide-repeat proteins and enhanced G4C2-related toxicity. Comparable KPNA4 pathology was observed in both sporadic frontotemporal dementia and C9ALS/FTD patient brains characterized by its nuclear depletion and cytosolic accumulation, irrespective of TDP-43 or dipeptide-repeat protein aggregates. These findings identify a vicious feedback cycle for dipeptide-repeat protein-mediated TDP-43 and subsequent KPNA pathology, which becomes self-sufficient of the initiating trigger and causes C9-related neurodegeneration.