Drosophila PINK1 and parkin loss-of-function mutants display a range of non-motor Parkinson's disease phenotypes

Understanding role of pesticides in development of Parkinson's disease: Insights from Drosophila and rodent models

Parkinson's disease is a neurodegenerative illness linked to ageing, marked by the gradual decline of dopaminergic neurons in the midbrain. The exact aetiology of Parkinson's disease (PD) remains uncertain, with genetic predisposition and environmental variables playing significant roles in the disease's frequency. Epidemiological data indicates a possible connection between pesticide exposure and brain degeneration. Specific pesticides have been associated with important characteristics of Parkinson's disease, such as mitochondrial dysfunction, oxidative stress, and α-synuclein aggregation, which are crucial for the advancement of the disease. Recently, many animal models have been developed for Parkinson's disease study. Although these models do not perfectly replicate the disease's pathology, they provide valuable insights that improve our understanding of the condition and the limitations of current treatment methods. Drosophila, in particular, has been useful in studying Parkinson's disease induced by toxins or genetic factors. The review thoroughly analyses many animal models utilised in Parkinson's research, with an emphasis on issues including pesticides, genetic and epigenetic changes, proteasome failure, oxidative damage, α-synuclein inoculation, and mitochondrial dysfunction. The text highlights the important impact of pesticides on the onset of Parkinson's disease (PD) and stresses the need for more research on genetic and mechanistic alterations linked to the condition.

A circadian clock regulates the blood-brain barrier across phylogeny

As the central regulatory system of an organism, the brain is responsible for overseeing a wide variety of physiological processes essential for an organism's survival. To maintain the environment necessary for neurons to function, the brain requires highly selective uptake and elimination of specific molecules through the blood-brain barrier (BBB). As an organism's activities vary throughout the day, how does the BBB adapt to meet the changing needs of the brain? A mechanism is through temporal regulation of BBB permeability via its circadian clock, which will be the focal point of this chapter. To comprehend the circadian clock's role within the BBB, we will first examine the anatomy of the BBB and the transport mechanisms enabling it to fulfill its role as a restrictive barrier. Next, we will define the circadian clock, and the discussion will encompass an introduction to circadian rhythms, the Transcription-Translation Feedback Loop (TTFL) as the mechanistic basis of circadian timekeeping, and the organization of tissue clocks found in organisms. Then, we will cover the role of the circadian rhythms in regulating the cellular mechanisms and functions of the BBB. We discuss the implications of this regulation in influencing sleep behavior, the progression of neurodegenerative diseases, and finally drug delivery for treatment of neurological diseases.

Toxicity evaluation of novel imidacloprid nanoribbons, using somatic mutation and fitness indexes in Drosophila melanogaster

Nanoribbons of imidacloprid, a systemic and chloronicotinyl insecticide, were successfully synthesized by laser-induced fragmentation/exfoliation of imidacloprid powders suspended in water, with widths ranging from 160 to 470 nm, lengths in the micron scale, and thickness of a few atoms layers. The aim of the present study was to examine the effects of acute and chronic exposure to imidacloprid (IMC) bulk and compare its effects with synthesized imidacloprid nanoribbons (IMCNR) on larval and adult viability, developmental time, olfactory capacity, longevity, productivity, and genotoxicity in Drosophila melanogaster. Larvae or adults were exposed at 0.01, 0.02, or 0.03 ppm to IMC or IMCNR. Results demonstrated that IMCNR produced a significant reduction in viability and olfactory ability. IMC did not significantly alter viability and olfactory ability. Similarly, marked differences on longevity were detected between treatment with IMC and IMCNR where the lifespan of males treated with IMC was significantly higher than control while IMCNR produced a reduction. As for productivity, developmental time, and genotoxicity, no marked differences were found between both forms of IMC.

A neuron-glia lipid metabolic cycle couples daily sleep to mitochondrial homeostasis

Sleep is thought to be restorative to brain energy homeostasis, but it is not clear how this is achieved. We show here that Drosophila glia exhibit a daily cycle of glial mitochondrial oxidation and lipid accumulation that is dependent on prior wake and requires the Drosophila APOE orthologs NLaz and GLaz, which mediate neuron-glia lipid transfer. In turn, a full night of sleep is required for glial lipid clearance, mitochondrial oxidative recovery and maximal neuronal mitophagy. Knockdown of neuronal NLaz causes oxidative stress to accumulate in neurons, and the neuronal mitochondrial integrity protein, Drp1, is required for daily glial lipid accumulation. These data suggest that neurons avoid accumulation of oxidative mitochondrial damage during wake by using mitophagy and passing damage to glia in the form of lipids. We propose that a mitochondrial lipid metabolic cycle between neurons and glia reflects a fundamental function of sleep relevant for brain energy homeostasis.

Pathogenesis of DJ-1/PARK7-Mediated Parkinson's Disease

Parkinson's disease (PD) is a common movement disorder associated with the degeneration of dopaminergic neurons in the substantia nigra pars compacta. Mutations in the PD-associated gene PARK7 alter the structure and function of the encoded protein DJ-1, and the resulting autosomal recessively inherited disease increases the risk of developing PD. DJ-1 was first discovered in 1997 as an oncogene and was associated with early-onset PD in 2003. Mutations in DJ-1 account for approximately 1% of all recessively inherited early-onset PD occurrences, and the functions of the protein have been studied extensively. In healthy subjects, DJ-1 acts as an antioxidant and oxidative stress sensor in several neuroprotective mechanisms. It is also involved in mitochondrial homeostasis, regulation of apoptosis, chaperone-mediated autophagy (CMA), and dopamine homeostasis by regulating various signaling pathways, transcription factors, and molecular chaperone functions. While DJ-1 protects neurons against damaging reactive oxygen species, neurotoxins, and mutant α-synuclein, mutations in the protein may lead to inefficient neuroprotection and the progression of PD. As current therapies treat only the symptoms of PD, the development of therapies that directly inhibit oxidative stress-induced neuronal cell death is critical. DJ-1 has been proposed as a potential therapeutic target, while oxidized DJ-1 could operate as a biomarker for PD. In this paper, we review the role of DJ-1 in the pathogenesis of PD by highlighting some of its key neuroprotective functions and the consequences of its dysfunction.

Brain-Derived Neurotrophic Factor - The Protective Agent Against Neurological Disorders

The burden of neurological illnesses on global health is significant. Our perception of the molecular and biological mechanisms underlying intellectual processing and behavior has significantly advanced over the last few decades, laying the groundwork for potential therapies for various neurodegenerative diseases. A growing body of literature reveals that most neurodegenerative diseases could be due to the gradual failure of neurons in the brain's neocortex, hippocampus, and various subcortical areas. Research on various experimental models has uncovered several gene components to understand the pathogenesis of neurodegenerative disorders. One among them is the brain-derived neurotrophic factor (BDNF), which performs several vital functions, enhancing synaptic plasticity and assisting in the emergence of long-term thoughts. The pathophysiology of some neurodegenerative diseases, including Alzheimer's, Parkinson's, Schizophrenia, and Huntington's, has been linked to BDNF. According to numerous research, high levels of BDNF are connected to a lower risk of developing a neurodegenerative disease. As a result, we want to concentrate on BDNF in this article and outline its protective role against neurological disorders.

Protective Role of AMPK against PINK1B9 Flies' Neurodegeneration with Improved Mitochondrial Function

Adenosine 5'-monophosphate-activated protein kinase (AMPK)'s effect in PTEN-induced kinase 1 (PINK1) mutant Parkinson's disease (PD) transgenic flies and the related mechanism is seldom studied. The classic MHC-Gal4/UAS PD transgenic flies was utilized to generate the disease characteristics specifically expressed in flies' muscles, and Western blot (WB) was used to measure the expression of the activated form of AMPK to investigate whether activated AMPK alters in PINK1B9 PD flies. MHC-Gal4 was used to drive AMPK overexpression in PINK1B9 flies to demonstrate the crucial role of AMPK in PD pathogenesis. The abnormal wing posture and climbing ability of PINK1B9 PD transgenic flies were recorded. Mitochondrial morphology via transmission electron microscopy (TEM) and ATP and NADH: ubiquinone oxidoreductase core subunit S3 (NDUFS3) protein levels were tested to evaluate the alteration of the mitochondrial function in PINK1B9 PD flies. Phosphorylated AMPKα dropped significantly in PINK1B9 flies compared to controls, and AMPK overexpression rescued PINKB9 flies' abnormal wing posture rate. The elevated dopaminergic neuron number in PPL1 via immunofluorescent staining was observed. Mitochondrial dysfunction in PINK1B9 flies has been ameliorated with increased ATP level, restored mitochondrial morphology in muscle, and increased NDUFS3 protein expression. Conclusively, AMPK overexpression could partially rescue the PD flies via improving PINK1B9 flies' mitochondrial function.

Kanamycin treatment in the pre-symptomatic stage of a Drosophila PD model prevents the onset of non-motor alterations

Parkinson's disease (PD) is a neurodegenerative disorder characterized by motor alterations, which is preceded by a prodromal stage where non-motor symptoms are observed. Over recent years, it has become evident that this disorder involves other organs that communicate with the brain like the gut. Importantly, the microbial community that lives in the gut plays a key role in this communication, the so-called microbiota-gut-brain axis. Alterations in this axis have been associated to several disorders including PD. Here we proposed that the gut microbiota is different in the presymptomatic stage of a Drosophila model for PD, the Pink1^B9 mutant fly, as compared to that observed in control animals. Our results show this is the case: there is basal dysbiosis in mutant animals evidenced by substantial difference in the composition of midgut microbiota in 8-9 days old Pink1^B9 mutant flies as compared with control animals. Further, we fed young adult control and mutant flies kanamycin and analyzed motor and non-motor behavioral parameters in these animals. Data show that kanamycin treatment induces the recovery of some of the non-motor parameters altered in the pre-motor stage of the PD fly model, while there is no substantial change in locomotor parameters recorded at this stage. On the other hand, our results show that feeding young animals the antibiotic, results in a long-lasting improvement of locomotion in control flies. Our data support that manipulations of gut microbiota in young animals could have beneficial effects on PD progression and age-dependent motor impairments.

Melatonin Mitigates Rotenone-Induced Oxidative Stress and Mitochondrial Dysfunction in the Drosophila melanogaster Model of Parkinson's Disease-like Symptoms

Parkinson's disease (PD) is the second most common neurodegenerative disorder; however, its etiology remains elusive. Antioxidants are considered to be a promising approach for decelerating neurodegenerative disease progression owing to extensive examination of the relationship between oxidative stress and neurodegenerative diseases. In this study, we investigated the therapeutic effect of melatonin against rotenone-induced toxicity in the Drosophila model of PD. The 3-5 day old flies were divided into four groups: control, melatonin alone, melatonin and rotenone, and rotenone alone groups. According to their respective groups, flies were exposed to a diet containing rotenone and melatonin for 7 days. We found that melatonin significantly reduced the mortality and climbing ability of Drosophila because of its antioxidative potency. It alleviated the expression of Bcl 2, tyrosine hydroxylase (TH), NADH dehydrogenase, mitochondrial membrane potential, and mitochondrial bioenergetics and decreased caspase 3 expression in the Drosophila model of rotenone-induced PD-like symptoms. These results indicate the neuromodulatory effect of melatonin, and that it is likely modulated against rotenone-induced neurotoxicity by suppressing oxidative stress and mitochondrial dysfunctions.

Circadian disruption and sleep disorders in neurodegeneration

Disruptions of circadian rhythms and sleep cycles are common among neurodegenerative diseases and can occur at multiple levels. Accumulating evidence reveals a bidirectional relationship between disruptions of circadian rhythms and sleep cycles and neurodegenerative diseases. Circadian disruption and sleep disorders aggravate neurodegeneration and neurodegenerative diseases can in turn disrupt circadian rhythms and sleep. Importantly, circadian disruption and various sleep disorders can increase the risk of neurodegenerative diseases. Thus, harnessing the circadian biology findings from preclinical and translational research in neurodegenerative diseases is of importance for reducing risk of neurodegeneration and improving symptoms and quality of life of individuals with neurodegenerative disorders via approaches that normalize circadian in the context of precision medicine. In this review, we discuss the implications of circadian disruption and sleep disorders in neurodegenerative diseases by summarizing evidence from both human and animal studies, focusing on the bidirectional links of sleep and circadian rhythms with prevalent forms of neurodegeneration. These findings provide valuable insights into the pathogenesis of neurodegenerative diseases and suggest a promising role of circadian-based interventions.

Functionally Validating Evolutionary Conserved Risk Genes for Parkinson's Disease in Drosophila melanogaster

Parkinson's disease (PD) is a heterogeneous and complex neurodegenerative disorder and large-scale genetic studies have identified >130 genes associated with PD. Although genomic studies have been decisive for our understanding of the genetic contributions underlying PD, these associations remain as statistical associations. Lack of functional validation limits the biological interpretation; however, it is labour extensive, expensive, and time consuming. Therefore, the ideal biological system for functionally validating genetic findings must be simple. The study aim was to assess systematically evolutionary conserved PD-associated genes using Drosophila melanogaster. From a literature review, a total of 136 genes have found to be associated with PD in GWAS studies, of which 11 are strongly evolutionary conserved between Homo sapiens and D. melanogaster. By ubiquitous gene expression knockdown of the PD-genes in D. melanogaster, the flies' escape response was investigated by assessing their negative geotaxis response, a phenotype that has previously been used to investigate PD in D. melanogaster. Gene expression knockdown was successful in 9/11 lines, and phenotypic consequences were observed in 8/9 lines. The results provide evidence that genetically modifying expression levels of PD genes in D. melanogaster caused reduced climbing ability of the flies, potentially supporting their role in dysfunctional locomotion, a hallmark of PD.

Huntingtin Plays a Role in the Physiological Response to Ethanol in Drosophila

BACKGROUND

Huntingtin (htt) protein is an essential regulator of nervous system function through its various neuroprotective and pro-survival functions, and loss of wild-type htt function is implicated in the etiology of Huntington's disease. While its pathological role is typically understood as a toxic gain-of-function, some neuronal phenotypes also result from htt loss. Therefore, it is important to understand possible roles for htt in other physiological circumstances.

OBJECTIVE

To elucidate the role of htt in the context of ethanol exposure, we investigated how loss of htt impacts behavioral and physiological responses to ethanol in Drosophila.

METHODS

We tested flies lacking htt for ethanol sensitivity and tolerance, preference for ethanol using capillary feeder assays, and recovery of mobility after intoxication. Levels of dopamine neurotransmitter and numbers of dopaminergic cells in brains lacking dhtt were also measured.

RESULTS

We found that dhtt-null flies are both less sensitive and more tolerant to ethanol exposure in adulthood. Moreover, flies lacking dhtt are more averse to alcohol than controls, and they recover mobility faster following acute ethanol intoxication. We showed that dhtt mediates these effects at least in part through the dopaminergic system, as dhtt is required to maintain normal levels of dopamine in the brain and normal numbers of dopaminergic cells in the adult protocerebrum.

CONCLUSIONS

Our results demonstrate that htt regulates the physiological response to ethanol and indicate a novel neuroprotective role for htt in the dopaminergic system, raising the possibility that it may be involved more generally in the response to toxic stimuli.

A new model for fatty acid hydroxylase-associated neurodegeneration reveals mitochondrial and autophagy abnormalities

Fatty acid hydroxylase-associated neurodegeneration (FAHN) is a rare disease that exhibits brain modifications and motor dysfunctions in early childhood. The condition is caused by a homozygous or compound heterozygous mutation in fatty acid 2 hydroxylase (FA2H), whose encoded protein synthesizes 2-hydroxysphingolipids and 2-hydroxyglycosphingolipids and is therefore involved in sphingolipid metabolism. A few FAHN model organisms have already been established and give the first insight into symptomatic effects. However, they fail to establish the underlying cellular mechanism of FAHN so far. Drosophila is an excellent model for many neurodegenerative disorders; hence, here, we have characterized and validated the first FAHN Drosophila model. The investigation of loss of dfa2h lines revealed behavioral abnormalities, including motor impairment and flying disability, in addition to a shortened lifespan. Furthermore, alterations in mitochondrial dynamics, and autophagy were identified. Analyses of patient-derived fibroblasts, and rescue experiments with human FA2H, indicated that these defects are evolutionarily conserved. We thus present a FAHN Drosophila model organism that provides new insights into the cellular mechanism of FAHN.

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.

Vexed mutations promote degeneration of dopaminergic neurons through excessive activation of the innate immune response

The hallmark of Parkinson's disease (PD) is the loss of dopaminergic (DA) neurons in the brain. However, little is known about why DA neurons are selectively vulnerable to PD. We previously completed a screen identifying genes associated with the progressive degeneration of DA neurons. Here we describe the role of a previously uncharacterized gene, CG42339, in the loss of DA neurons using Drosophila Melanogaster. CG42339 mutants display a progressive loss of DA neurons and locomotor dysfunction, along with an accumulation of advanced glycation end products (AGEs) in the brain. Based on this phenotype, we refer to CG42339 as vexed. We demonstrate that vexed is specifically required within cortex glia to maintain neuronal viability. Loss of vexed function results in excessive activation of the innate immune response in the brain, leading to loss of DA neurons. We show that activation of the innate immune response leads to increased nitric oxide signaling and accumulation of AGEs, which ultimately result in neurodegeneration. These results provide further insight into the relationship between the role of the immune response in the central nervous system and how this impacts neuronal viability.

Gut microbiome and Parkinson's disease: Perspective on pathogenesis and treatment

BACKGROUND

Parkinson's disease (PD) is a disease of ⍺-synuclein aggregation-mediated dopaminergic neuronal loss in the substantia nigra pars compacta, which leads to motor and non-motor symptoms. Through the last two decades of research, there has been growing consensus that inflammation-mediated oxidative stress, mitochondrial dysfunction, and cytokine-induced toxicity are mainly involved in neuronal damage and loss associated with PD. However, it remains unclear how these mechanisms relate to sporadic PD, a more common form of PD. Both enteric and central nervous systems have been implicated in the pathogenesis of sporadic PD, thus highlighting the crosstalk between the gut and brain.

AIM

of Review: In this review, we summarize how alterations in the gut microbiome can affect PD pathogenesis. We highlight various mechanisms increasing/decreasing the risk of PD development. Based on the previous supporting evidence, we suggest how early interventions could protect against PD development and how controlling specific factors, including our diet, could modify our perspective on disease mechanisms and therapeutics. We explain the strong relationship between the gut microbiota and the brain in PD subjects, by delineating the multiple mechanisms involved inneuroinflammation and oxidative stress. We conclude that the neurodetrimental effects of western diet (WD) and the neuroprotective effects of Mediterranean diets should be further exploredin humans through clinical trials. Key Scientific Concepts of Review: Alterations in the gut microbiome and associated metabolites may contribute to pathogenesis in PD. In some studies, probiotics have been shown to exert anti-oxidative effects in PD via improved mitochondrial dynamics and homeostasis, thus reducing PD-related consequences. However, there is a significant unmet need for randomized clinical trials to investigate the effectiveness of microbial products, probiotic-based supplementation, and dietary intervention in reversing gut microbial dysbiosis in PD.

Tollip negatively regulates mitophagy by promoting the mitochondrial processing and cytoplasmic release of PINK1

PTEN-induced putative kinase 1 (PINK1) is a serine/threonine kinase that phosphorylates several substrates and exerts neuroprotective effects against stress-induced apoptotic cell death. Mutations in PINK1 have been linked to autosomal recessive forms of Parkinson’s disease (PD). Mitophagy is a type of autophagy that selectively promotes mitochondrial turnover and prevents the accumulation of dysfunctional mitochondria to maintain cellular homeostasis. Toll-interacting protein (Tollip) was initially identified as a negative regulator of IL-1β receptor signaling, suppressing inflammatory TLR signaling cascades. Recently, Tollip has been reported to play a role in autophagy and is implicated in neurodegeneration. In this study, we determined whether Tollip was functionally linked to PINK1-mediated mitophagy. Our results demonstrated that Tollip promoted the mitochondrial processing of PINK1 and altered the localization of PINK1, predominantly to the cytosol. This action was attributed to increased binding of PINK1 to mitochondrial processing peptidase β (MPPβ) and the subsequent increase in MPPβ-mediated mitochondrial PINK1 cleavage. Furthermore, Tollip suppressed mitophagy following carbonyl cyanide m-chlorophenylhydrazone-induced mitochondrial dysfunction. These findings suggest that Tollip inhibits mitophagy via the PINK1/parkin pathway upon mitochondrial damage, leading to the blockade of PINK1-mediated neuroprotection.

Mitochondrial autophagy in the sleeping brain

A significant percentage of the mitochondrial mass is replaced on a daily basis via mechanisms of mitochondrial quality control. Through mitophagy (a selective type of autophagy that promotes mitochondrial proteostasis) cells keep a healthy pool of mitochondria, and prevent oxidative stress and inflammation. Furthermore, mitophagy helps adapting to the metabolic demand of the cells, which changes on a daily basis.

Core components of the mitophagy process are PINK1 and Parkin, which mutations are linked to Parkinson’s Disease. The crucial role of PINK1/Parkin pathway during stress-induced mitophagy has been extensively studied in vitro in different cell types. However, recent advances in the field allowed discovering that mitophagy seems to be only slightly affected in PINK1 KO mice and flies, putting into question the physiological relevance of this pathway in vivo in the whole organism. Indeed, several cell-specific PINK1/Parkin-independent mitophagy pathways have been recently discovered, which appear to be activated under physiological conditions such as those that promote mitochondrial proteome remodeling during differentiation or in response to specific physiological stimuli.

In this Mini Review we want to summarize the recent advances in the field, and add another level of complexity by focusing attention on a potentially important aspect of mitophagy regulation: the implication of the circadian clock. Recent works showed that the circadian clock controls many aspects of mitochondrial physiology, including mitochondrial morphology and dynamic, respiratory activity, and ATP synthesis. Furthermore, one of the essential functions of sleep, which is controlled by the clock, is the clearance of toxic metabolic compounds from the brain, including ROS, via mechanisms of proteostasis. Very little is known about a potential role of the clock in the quality control mechanisms that maintain the mitochondrial repertoire healthy during sleep/wake cycles. More importantly, it remains completely unexplored whether (dys)function of mitochondrial proteostasis feedbacks to the circadian clockwork.

Mitochondrial electron transport chain defects modify Parkinson's disease phenotypes in a Drosophila model

INTRODUCTION

Mitochondrial defects have been implicated in Parkinson's disease (PD) since complex I poisons were found to cause accelerated parkinsonism in young people in the early 1980s. More evidence of mitochondrial involvement arose when many of the genes whose mutations caused inherited PD were discovered to be subcellularly localized to mitochondria or have mitochondrial functions. However, the details of how mitochondrial dysfunction might impact or cause PD remain unclear. The aim of our study was to better understand mitochondrial dysfunction in PD by evaluating mitochondrial respiratory complex mutations in a Drosophila melanogaster (fruit fly) model of PD.

METHODS

We have conducted a targeted heterozygous enhancer/suppressor screen using Drosophila mutations within mitochondrial electron transport chain (ETC) genes against a null PD mutation in parkin. The interactions were assessed by climbing assays at 2-5 days as an indicator of motor function. A strong enhancer mutation in COX5A was examined further for L-dopa rescue, oxygen consumption, mitochondrial content, and reactive oxygen species. A later timepoint of 16-20 days was also investigated for both COX5A and a suppressor mutation in cyclope. Generalized Linear Models and similar statistical tests were used to verify significance of the findings.

RESULTS

We have discovered that mutations in individual genes for subunits within the mitochondrial respiratory complexes have interactions with parkin, while others do not, irrespective of complex. One intriguing mutation in a complex IV subunit (cyclope) shows a suppressor rescue effect at early time points, improving the gross motor defects caused by the PD mutation, providing a strong candidate for drug discovery. Most mutations, however, show varying degrees of enhancement or slight suppression of the PD phenotypes. Thus, individual mitochondrial mutations within different oxidative phosphorylation complexes have different interactions with PD with regard to degree and direction. Upon further investigation of the strongest enhancer (COX5A), the mechanism by which these interactions occur initially does not appear to be based on defects in ATP production, but rather may be related to increased levels of reactive oxygen species.

CONCLUSIONS

Our work highlights some key subunits potentially involved in mechanisms underlying PD pathogenesis, implicating ETC complexes other than complex I in PD.

Suppression of intestinal dysfunction in a Drosophila model of Parkinson's disease is neuroprotective

The innate immune response mounts a defense against foreign invaders and declines with age. An inappropriate induction of this response can cause diseases. Previous studies showed that mitochondria can be repurposed to promote inflammatory signaling. Damaged mitochondria can also trigger inflammation and promote diseases. Mutations in pink1, a gene required for mitochondrial health, cause Parkinson's disease, and Drosophila melanogaster pink1 mutants accumulate damaged mitochondria. Here, we show that defective mitochondria in pink1 mutants activate Relish targets and demonstrate that inflammatory signaling causes age-dependent intestinal dysfunction in pink1-mutant flies. These effects result in the death of intestinal cells, metabolic reprogramming and neurotoxicity. We found that Relish signaling is activated downstream of a pathway stimulated by cytosolic DNA. Suppression of Relish in the intestinal midgut of pink1-mutant flies restores mitochondrial function and is neuroprotective. We thus conclude that gut-brain communication modulates neurotoxicity in a fly model of Parkinson's disease through a mechanism involving mitochondrial dysfunction.

Gut mitochondrial defects drive neurodegeneration

Neurodegenerative diseases, including Parkinson’s disease, are linked to the accumulation of defective mitochondria in the brain and to microbial dysbiosis in the gut. However, the interplay between these factors is incompletely understood. Fedele et al. reveal how gut mitochondrial dysfunction activates intestinal inflammation to drive neurodegeneration in a Parkinson’s disease model.

Sleep and circadian rhythms in Parkinson's disease and preclinical models

The use of animals as models of human physiology is, and has been for many years, an indispensable tool for understanding the mechanisms of human disease. In Parkinson's disease, various mouse models form the cornerstone of these investigations. Early models were developed to reflect the traditional histological features and motor symptoms of Parkinson's disease. However, it is important that models accurately encompass important facets of the disease to allow for comprehensive mechanistic understanding and translational significance. Circadian rhythm and sleep issues are tightly correlated to Parkinson's disease, and often arise prior to the presentation of typical motor deficits. It is essential that models used to understand Parkinson's disease reflect these dysfunctions in circadian rhythms and sleep, both to facilitate investigations into mechanistic interplay between sleep and disease, and to assist in the development of circadian rhythm-facing therapeutic treatments. This review describes the extent to which various genetically- and neurotoxically-induced murine models of Parkinson's reflect the sleep and circadian abnormalities of Parkinson's disease observed in the clinic.

Deconstructing the molecular genetics behind the PINK1/Parkin axis in Parkinson’s disease using Drosophila melanogaster as a model organism

Background

Parkinson’s disease (PD) is a multifactorial neurodegenerative disorder marked by the death of nigrostriatal dopaminergic neurons in response to the compounding effects of oxidative stress, mitochondrial dysfunction and protein aggregation. Transgenic Drosophila models have been used extensively to decipher the underlying genetic interactions that exacerbate neural health in PD. Autosomal recessive forms of the disease have been linked to mutations in the serine/threonine kinase PINK1(PTEN-Induced Putative Kinase 1) and E3 ligase Parkin, which function in an axis that is conserved in flies. This review aims to probe the current understanding of PD pathogenesis via the PINK1/Parkin axis while underscoring the importance of several molecular and pharmacologic rescues brought to light through studies in Drosophila.

Main body

Mutations in PINK1 and Parkin have been shown to affect the axonal transport of mitochondria within dopaminergic neurons and perturb the balance between mitochondrial fusion/fission resulting in abnormal mitochondrial morphology. As per studies in flies, ectopic expression of Fwd kinase and Atg-1 to promote fission and mitophagy while suppressing fusion via MUL1 E3 ligase may aid to halt mitochondrial aggregation and prolong the survival of dopaminergic neurons. Furthermore, upregulation of Hsp70/Hsp90 chaperone systems (Trap1, CHIP) to target misfolded mitochondrial respiratory complexes may help to preserve their bioenergetic capacity. Accumulation of reactive oxygen species as a consequence of respiratory complex dysfunction or antioxidant enzyme deficiency further escalates neural death by inducing apoptosis, lipid peroxidation and DNA damage. Fly studies have reported the induction of canonical Wnt signalling to enhance the activity of transcriptional co-activators (PGC1α, FOXO) which induce the expression of antioxidant enzymes. Enhancing the clearance of free radicals via uncoupling proteins (UCP4) has also been reported to ameliorate oxidative stress-induced cell death in PINK1/Parkin mutants.

Conclusion

While these novel mechanisms require validation through mammalian studies, they offer several explanations for the factors propagating dopaminergic death as well as promising insights into the therapeutic importance of transgenic fly models in PD.

Gene Therapeutic Approaches for the Treatment of Mitochondrial Dysfunction in Parkinson's Disease

Background: Mitochondrial dysfunction has been identified as a pathophysiological hallmark of disease onset and progression in patients with Parkinsonian disorders. Besides the overall emergence of gene therapies in treating these patients, this highly relevant molecular concept has not yet been defined as a target for gene therapeutic approaches. Methods: This narrative review will discuss the experimental evidence suggesting mitochondrial dysfunction as a viable treatment target in patients with monogenic and idiopathic Parkinson’s disease. In addition, we will focus on general treatment strategies and crucial challenges which need to be overcome. Results: Our current understanding of mitochondrial biology in parkinsonian disorders opens up the avenue for viable treatment strategies in Parkinsonian disorders. Insights can be obtained from primary mitochondrial diseases. However, substantial knowledge gaps and unique challenges of mitochondria-targeted gene therapies need to be addressed to provide innovative treatments in the future. Conclusions: Mitochondria-targeted gene therapies are a potential strategy to improve an important primary disease mechanism in Parkinsonian disorders. However, further studies are needed to address the unique design challenges for mitochondria-targeted gene therapies.

Circadian rhythms in neurodegenerative disorders

Endogenous biological clocks, orchestrated by the suprachiasmatic nucleus, time the circadian rhythms that synchronize physiological and behavioural functions in humans. The circadian system influences most physiological processes, including sleep, alertness and cognitive performance. Disruption of circadian homeostasis has deleterious effects on human health. Neurodegenerative disorders involve a wide range of symptoms, many of which exhibit diurnal variations in frequency and intensity. These disorders also disrupt circadian homeostasis, which in turn has negative effects on symptoms and quality of life. Emerging evidence points to a bidirectional relationship between circadian homeostasis and neurodegeneration, suggesting that circadian function might have an important role in the progression of neurodegenerative disorders. Therefore, the circadian system has become an attractive target for research and clinical care innovations. Studying circadian disruption in neurodegenerative disorders could expand our understanding of the pathophysiology of neurodegeneration and facilitate the development of novel, circadian-based interventions for these disabling disorders. In this Review, we discuss the alterations to the circadian system that occur in movement (Parkinson disease and Huntington disease) and cognitive (Alzheimer disease and frontotemporal dementia) neurodegenerative disorders and provide directions for future investigations in this field.

Disruption of Mitochondrial Homeostasis: The Role of PINK1 in Parkinson's Disease

The progressive reduction of the dopaminergic neurons of the substantia nigra is the fundamental process underlying Parkinson’s disease (PD), while the mechanism of susceptibility of this specific neuronal population is largely unclear. Disturbances in mitochondrial function have been recognized as one of the main pathways in sporadic PD since the finding of respiratory chain impairment in animal models of PD. Studies on genetic forms of PD have provided new insight on the role of mitochondrial bioenergetics, homeostasis, and autophagy. PINK1 (PTEN-induced putative kinase 1) gene mutations, although rare, are the second most common cause of recessively inherited early-onset PD, after Parkin gene mutations. Our knowledge of PINK1 and Parkin function has increased dramatically in the last years, with the discovery that a process called mitophagy, which plays a key role in the maintenance of mitochondrial health, is mediated by the PINK1/Parkin pathway. In vitro and in vivo models have been developed, supporting the role of PINK1 in synaptic transmission, particularly affecting dopaminergic neurons. It is of paramount importance to further define the role of PINK1 in mitophagy and mitochondrial homeostasis in PD pathogenesis in order to delineate novel therapeutic targets.

Parkinson's disease and microRNAs - Lessons from model organisms and human studies

Parkinson's disease (PD) is a progressive, age-associated neurodegenerative disorder that affects an estimated 10 million people worldwide. PD is characterized by proteinaceous, cytoplasmic inclusions containing α-synuclein, called Lewy Bodies, which form in dopaminergic neurons in an age-dependent manner, and are associated with the emergence of characteristic PD symptoms such as resting tremor, rigidity, slow movements and postural instability. Although considerable progress has been made in recent years in identifying genetic and environmental factors that are associated with PD, early diagnosis and therapeutic options remain severely lacking. Recently, microRNAs (miRNAs) have emerged as novel therapeutic targets in various diseases, such as cancer and neurodegenerative diseases. MiRNAs have been shown to play roles in various aging and neurodegenerative disease models across phyla. More recently, studies have identified specific roles for miRNAs and their targets in the pathogenesis and progression of PD in several model organisms. Here, we discuss the evolving field of miRNAs, their association with PD, and the outlook for the future.

Precision Medicine on the Fly: Using Drosophila to Decipher Gene-Environment Interactions in Parkinson's Disease

Big data approaches have profoundly influenced state-of-the-art in many fields of research, with toxicology being no exception. Here, we use Parkinson's disease as a window through which to explore the challenges of a dual explosion of metabolomic data addressing the myriad environmental exposures individuals experience and genetic analyses implicating many different loci as risk factors for disease. We argue that new experimental approaches are needed to convert the growing body of omics data into molecular mechanisms of disease that can be therapeutically targeted in specific patients. We outline one attractive strategy, which capitalizes on the rapid generation time and advanced molecular tools available in the fruit fly, Drosophila, to provide a platform for mechanistic dissection and drug discovery.

Mitochondrial Ca2+ oscillation induces mitophagy initiation through the PINK1-Parkin pathway

Dysregulation of the PINK1/Parkin-mediated mitophagy is essential to Parkinson’s disease. Although important progress has been made in previous researches, the biochemical reagents that induce global and significant mitochondrial damage may still hinder deeper insights into the mechanisms of mitophagy. The origin of PINK1/Parkin pathway activation in mitophagy remains elusive. In this study, we develop an optical method, ultra-precise laser stimulation (UPLaS) that delivers a precise and noninvasive stimulation onto a submicron region in a single mitochondrial tubular structure. UPLaS excites localized mitochondrial Ca²⁺ (mitoCa²⁺) oscillations with tiny perturbation to mitochondrial membrane potential (MMP) or mitochondrial reactive oxygen species. The UPLaS-induced mitoCa²⁺ oscillations can directly induce PINK1 accumulation and Parkin recruitment on mitochondria. The Parkin recruitment by UPLaS requires PINK1. Our results provide a precise and noninvasive technology for research on mitophagy, which stimulates target mitochondria with little damage, and reveal mitoCa²⁺ oscillation directly initiates the PINK1-Parkin pathway for mitophagy without MMP depolarization.

Using radio frequency identification and locomotor activity monitoring to assess sleep, locomotor, and foraging rhythmicity in bumblebees

Bumblebees are a key pollinator. Understanding the factors that influence the timing of sleep and foraging trips is important for efficient foraging and pollination. Here, we illustrate how individual locomotor activity monitoring and colony-wide radio frequency identification tracking can be combined to analyze the effects of agrochemicals like neonicotinoids on locomotor and foraging rhythmicity and sleep quantity/quality in bumblebees. We also highlight aspects of the design that can be adapted for other invertebrates or agrochemicals, allowing broader application of these techniques.

For complete details on the use and execution of this protocol, please refer to Tasman et al. (2020).

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Easy and reliable way of testing circadian rhythmicity and sleep in invertebrates

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Covers colony care, equipment adaptation, and setup and experimental protocol

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This protocol can be used to study the effects of any water soluble/liquid insecticide

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The multiple ways to adapt the protocol for other organisms are highlighted

Loss of p21-activated kinase Mbt/PAK4 causes Parkinson-like phenotypes in Drosophila

Parkinson's disease (PD) provokes bradykinesia, resting tremor, rigidity and postural instability, and also non-motor symptoms such as depression, anxiety, sleep and cognitive impairments. Similar phenotypes can be induced in Drosophila melanogaster through modification of PD-relevant genes or the administration of PD-inducing toxins. Recent studies correlated deregulation of human p21-activated kinase 4 (PAK4) with PD, leaving open the question of a causative relationship of mutations in this gene for manifestation of PD symptoms. To determine whether flies lacking the PAK4 homolog Mushroom bodies tiny (Mbt) show PD-like phenotypes, we tested for a variety of PD criteria. Here, we demonstrate that mbt mutant flies show PD-like phenotypes including age-dependent movement deficits, reduced life expectancy and fragmented sleep. They also react to a stressful situation with higher immobility, indicating an influence of Mbt on emotional behavior. Loss of Mbt function has a negative effect on the number of dopaminergic protocerebral anterior medial (PAM) neurons, most likely caused by a proliferation defect of neural progenitors. The age-dependent movement deficits are not accompanied by a corresponding further loss of PAM neurons. Previous studies highlighted the importance of a small PAM subgroup for age-dependent PD motor impairments. We show that impaired motor skills are caused by a lack of Mbt in this PAM subgroup. In addition, a broader re-expression of Mbt in PAM neurons improves life expectancy. Conversely, selective Mbt knockout in the same cells shortens lifespan. We conclude that mutations in Mbt/PAK4 can play a causative role in the development of PD phenotypes.

The dysregulated Pink1- Drosophila mitochondrial proteome is partially corrected with exercise

One of the genes which has been linked to the onset of juvenile/early onset Parkinson’s disease (PD) is PINK1. There is evidence that supports the therapeutic potential of exercise in the alleviation of PD symptoms. It is possible that exercise may enhance synaptic plasticity, protect against neuro-inflammation and modulate L-Dopa regulated signalling pathways. We explored the effects of exercise on Pink1 deficient Drosophila melanogaster which undergo neurodegeneration and muscle degeneration. We used a ‘power-tower’ type exercise platform to deliver exercise activity to Pink1^- and age matched wild-type Drosophila. Mitochondrial proteomic profiles responding to exercise were obtained. Of the 516 proteins identified, 105 proteins had different levels between Pink1^- and wild-type non-exercised Drosophila. Gene ontology enrichment analysis and STRING network analysis highlighted proteins and pathways with altered expression within the mitochondrial proteome. Comparison of the Pink1^- exercised proteome to wild-type proteomes showed that exercising the Pink1^- Drosophila caused their proteomic profile to return towards wild-type levels.

The Importance of Drosophila melanogaster Research to UnCover Cellular Pathways Underlying Parkinson's Disease

Parkinson's disease (PD) is a complex neurodegenerative disorder that is currently incurable. As a consequence of an incomplete understanding of the etiology of the disease, therapeutic strategies mainly focus on symptomatic treatment. Even though the majority of PD cases remain idiopathic (~90%), several genes have been identified to be causative for PD, facilitating the generation of animal models that are a good alternative to study disease pathways and to increase our understanding of the underlying mechanisms of PD. Drosophila melanogaster has proven to be an excellent model in these studies. In this review, we will discuss the different PD models in flies and key findings identified in flies in different affected pathways in PD. Several molecular changes have been identified, of which mitochondrial dysfunction and a defective endo-lysosomal pathway emerge to be the most relevant for PD pathogenesis. Studies in flies have significantly contributed to our knowledge of how disease genes affect and interact in these pathways enabling a better understanding of the disease etiology and providing possible therapeutic targets for the treatment of PD, some of which have already resulted in clinical trials.

Multiple Pathways of LRRK2-G2019S/Rab10 Interaction in Dopaminergic Neurons

BACKGROUND

Inherited mutations in the LRRK2 protein are common causes of Parkinson's disease, but the mechanisms by which increased kinase activity of mutant LRRK2 leads to pathological events remain to be determined. In vitro assays (heterologous cell culture, phospho-protein mass spectrometry) suggest that several Rab proteins might be directly phosphorylated by LRRK2-G2019S. An in vivo screen of Rab expression in dopaminergic neurons in young adult Drosophila demonstrated a strong genetic interaction between LRRK2-G2019S and Rab10.

OBJECTIVE

To determine if Rab10 is necessary for LRRK2-induced pathophysiological responses in the neurons that control movement, vision, circadian activity, and memory. These four systems were chosen because they are modulated by dopaminergic neurons in both humans and flies.

METHODS

LRRK2-G2019S was expressed in Drosophila dopaminergic neurons and the effects of Rab10 depletion on Proboscis Extension, retinal neurophysiology, circadian activity pattern ('sleep'), and courtship memory determined in aged flies.

RESULTS

Rab10 loss-of-function rescued LRRK2-G2019S induced bradykinesia and retinal signaling deficits. Rab10 knock-down, however, did not rescue the marked sleep phenotype which results from dopaminergic LRRK2-G2019S. Courtship memory is not affected by LRRK2, but is markedly improved by Rab10 depletion. Anatomically, both LRRK2-G2019S and Rab10 are seen in the cytoplasm and at the synaptic endings of dopaminergic neurons.

CONCLUSION

We conclude that, in Drosophila dopaminergic neurons, Rab10 is involved in some, but not all, LRRK2-induced behavioral deficits. Therefore, variations in Rab expression may contribute to susceptibility of different dopaminergic nuclei to neurodegeneration seen in people with Parkinson's disease.

Human Dopaminergic Neurons Lacking PINK1 Exhibit Disrupted Dopamine Metabolism Related to Vitamin B6 Co-Factors

PINK1 loss-of-function mutations cause early onset Parkinson disease. PINK1-Parkin mediated mitophagy has been well studied, but the relevance of the endogenous process in the brain is debated.

Here, the absence of PINK1 in human dopaminergic neurons inhibits ionophore-induced mitophagy and reduces mitochondrial membrane potential. Compensatory, mitochondrial renewal maintains mitochondrial morphology and protects the respiratory chain. This is paralleled by metabolic changes, including inhibition of the TCA cycle enzyme mAconitase, accumulation of NAD⁺, and metabolite depletion. Loss of PINK1 disrupts dopamine metabolism by critically affecting its synthesis and uptake. The mechanism involves steering of key amino acids toward energy production rather than neurotransmitter metabolism and involves cofactors related to the vitamin B6 salvage pathway identified using unbiased multi-omics approaches.

We propose that reduction of mitochondrial membrane potential that cannot be controlled by PINK1 signaling initiates metabolic compensation that has neurometabolic consequences relevant to Parkinson disease.

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PINK1 KO hDANs do not undergo ionophore-induced mitophagy yet CI remains active

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PINK1 KO impacts the TCA cycle via mAconitase leading to depletion of key amino acids

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PINK1 KO silences PNPO, which provides essential biological co-factors

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Dopamine pools and neurotransmitter uptake are reduced by PINK1 loss of function

PINK1/PARKIN signalling in neurodegeneration and neuroinflammation

Mutations in the PTEN-induced kinase 1 (PINK1) and Parkin RBR E3 ubiquitin-protein ligase (PARKIN) genes are associated with familial forms of Parkinson’s disease (PD). PINK1, a protein kinase, and PARKIN, an E3 ubiquitin ligase, control the specific elimination of dysfunctional or superfluous mitochondria, thus fine-tuning mitochondrial network and preserving energy metabolism. PINK1 regulates PARKIN translocation in impaired mitochondria and drives their removal via selective autophagy, a process known as mitophagy. As knowledge obtained using different PINK1 and PARKIN transgenic animal models is being gathered, growing evidence supports the contribution of mitophagy impairment to several human pathologies, including PD and Alzheimer’s diseases (AD). Therefore, therapeutic interventions aiming to modulate PINK1/PARKIN signalling might have the potential to treat these diseases. In this review, we will start by discussing how the interplay of PINK1 and PARKIN signalling helps mediate mitochondrial physiology. We will continue by debating the role of mitochondrial dysfunction in disorders such as amyotrophic lateral sclerosis, Alzheimer’s, Huntington’s and Parkinson’s diseases, as well as eye diseases such as age-related macular degeneration and glaucoma, and the causative factors leading to PINK1/PARKIN-mediated neurodegeneration and neuroinflammation. Finally, we will discuss PINK1/PARKIN gene augmentation possibilities with a particular focus on AD, PD and glaucoma.

Knockout of PINK1 altered the neural connectivity of Drosophila dopamine PPM3 neurons at input and output sites

Impairment of the dopamine system is the main cause of Parkinson disease (PD). PTEN-induced kinase 1 (PINK1) is possibly involved in pathogenesis of PD. However, its role in dopaminergic neurons has not been fully established yet. In the present investigation, we have used the PINK1 knockout Drosophila model to explore the role of PINK1 in dopaminergic neurons. Electrophysiological and behavioral tests indicated that PINK1 elimination enhances the neural transmission from the presynaptic part of dopaminergic neurons in the protocerebral posterior medial region 3 (PPM3) to PPM3 neurons (which are homologous to those in the substantia nigra in humans). Firing properties of the action potential in PPM3 neurons were also altered in the PINK1 knockout genotypes. Abnormal motor ability was also observed in these PINK1 knockout animals. Our results indicate that knockout of PINK1 could alter both the input and output properties of PPM3 neurons.

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.

PRPS-Associated Disorders and the Drosophila Model of Arts Syndrome

While a plethora of genetic techniques have been developed over the past century, modifying specific sequences of the fruit fly genome has been a difficult, if not impossible task. clustered regularly interspaced short palindromic repeat (CRISPR)/Cas9 truly redefined molecular genetics and provided new tools to model human diseases in Drosophila melanogaster. This is particularly true for genes whose protein sequences are highly conserved. Phosphoribosyl pyrophosphate synthetase (PRPS) is a rate-limiting enzyme in nucleotide metabolism whose missense mutations are found in several neurological disorders, including Arts syndrome. In addition, PRPS is deregulated in cancer, particularly those that become resistant to cancer therapy. Notably, DrosophilaPRPS shares about 90% protein sequence identity with its human orthologs, making it an ideal gene to study via CRISPR/Cas9. In this review, we will summarize recent findings on PRPS mutations in human diseases including cancer and on the molecular mechanisms by which PRPS activity is regulated. We will also discuss potential applications of Drosophila CRISPR/Cas9 to model PRPS-dependent disorders and other metabolic diseases that are associated with nucleotide metabolism.

EGCG ameliorates neuronal and behavioral defects by remodeling gut microbiota and TotM expression in Drosophila models of Parkinson's disease

Parkinson's disease (PD) is the second most common neurodegenerative disease. Eigallocatechin-3-gallate (EGCG), the major polyphenol in green tea, is known to exert a beneficial effect on PD patients. Although some mechanisms were suggested to underlie this intervention, it remains unknown if the EGCG-mediated protection was achieved by remodeling gut microbiota. In the present study, 0.1 mM or 0.5 mM EGCG was administered to the Drosophila melanogaster with PINK1 (PTEN induced putative kinase 1) mutations, a prototype PD model, and their behavioral performances, as well as neuronal/mitochondrial morphology (only for 0.5 mM EGCG treatment) were determined. According to the results, the mutant PINK1^B9 flies exhibited dopaminergic, survival, and behavioral deficits, which were rescued by EGCG supplementation. Meanwhile, EGCG resulted in profound changes in gut microbial compositions in PINK1^B9 flies, restoring the abundance of a set of bacteria. Notably, EGCG protection was blunted when gut microbiota was disrupted by antibiotics. We further isolated four bacterial strains from fly guts and the supplementation of individual Lactobacillus plantarum or Acetobacter pomorum strain exacerbated the neuronal and behavioral dysfunction of PD flies, which could not be rescued by EGCG. Transcriptomic analysis identified TotM as the central gene responding to EGCG or microbial manipulations. Genetic ablation of TotM blocked the recovery activity of EGCG, suggesting that EGCG-mediated protection warrants TotM. Apart from familial form, EGCG was also potent in improving sporadic PD symptoms induced by rotenone treatment, wherein gut microbiota shared regulatory roles. Together, our results suggest the relevance of the gut microbiota-TotM pathway in EGCG-mediated neuroprotection, providing insight into indirect mechanisms underlying nutritional intervention of Parkinson's disease.

The Drosophila melanogaster as Genetic Model System to Dissect the Mechanisms of Disease that Lead to Neurodegeneration in Adrenoleukodystrophy

Drosophila melanogaster is the most successful genetic model organism to study different human disease with a recent increased popularity to study neurological disorders. Drosophila melanogaster has a complex yet well-defined brain with defined anatomical regions with specific functions. The neuronal network in the adult brain has a structural organization highly similar to human neurons, but in a brain that is much more amenable for complex analyses. The availability of sophisticated genetic tools to study neurons permits to examine neuronal functions at the single cell level in the whole brain by confocal imaging, which does not require sections. Thus, Drosophila has been used to successfully study many neurological disorders such as Parkinson's disease and has been recently adopted to understand the complex networks leading to neurological disorders with metabolic origins such as Leigh disease and X-linked adrenoleukodystrophy (X-ALD).In this review, we will describe the genetic tools available to study neuronal structures and functions and also illustrate some limitations of the system. Finally, we will report the experimental efforts that in the past 10 years have established Drosophila melanogaster as an excellent model organism to study neurodegenerative disorders focusing on X-ALD.

Human Periapical Cyst-Derived Stem Cells Can Be A Smart "Lab-on-A-Cell" to Investigate Neurodegenerative Diseases and the Related Alteration of the Exosomes' Content

Promising researches have demonstrated that the alteration of biological rhythms may be consistently linked to neurodegenerative pathologies. Parkinson's disease (PD) has a multifactorial pathogenesis, involving both genetic and environmental and/or molecular co-factors. Generally, heterogeneous alterations in circadian rhythm (CR) are a typical finding in degenerative processes, such as cell aging and death. Although numerous genetic phenotypes have been discovered in the most common forms of PD, it seems that severe deficiencies in synaptic transmission and high vesicular recycling are frequently found in PD patients. Neuron-to-neuron interactions are often ensured by exosomes, a specific type of extracellular vesicle (EV). Neuron-derived exosomes may carry several active compounds, including miRNAs: Several studies have found that circulating miRNAs are closely associated with an atypical oscillation of circadian rhythm genes, and they are also involved in the regulation of clock genes, in animal models. In this context, a careful analysis of neural-differentiated Mesenchymal Stem Cells (MSCs) and the molecular and genetic characterization of their exosome content, both in healthy cells and in PD-induced cells, could be a strategic field of investigation for early diagnosis and better treatment of PD and similar neurodegenerative pathologies. A novel MSC population, called human periapical cyst-mesenchymal stem cells (hPCy-MSCs), has demonstrated that it naively expresswa the main neuronal markers, and may differentiate towards functional neurons. Therefore, hPCy-MSCs can be considered of particular interest for testing of in vitro strategies to treat neurological diseases. On the other hand, the limitations of using stem cells is an issue that leads researchers to perform experimental studies on the exosomes released by MCSs. Human periapical cyst-derived mesenkymal stem cells can be a smart "lab-on-a-cell" to investigate neurodegenerative diseases and the related exosomes' content alteration.

Shaw and Shal voltage-gated potassium channels mediate circadian changes in Drosophila clock neuron excitability

As in mammals, Drosophila circadian clock neurons display rhythms of activity with higher action potential firing rates and more positive resting membrane potentials during the day. This rhythmic excitability has been widely observed but, critically, its regulation remains unresolved. We have characterized and modelled the changes underlying these electrical activity rhythms in the lateral ventral clock neurons (LNvs). We show that currents mediated by the voltage-gated potassium channels Shaw (Kv3) and Shal (Kv4) oscillate in a circadian manner. Disruption of these channels, by expression of dominant negative (DN) subunits, leads to changes in circadian locomotor activity and shortens lifespan. LNv whole-cell recordings then show that changes in Shaw and Shal currents drive changes in action potential firing rate and that these rhythms are abolished when the circadian molecular clock is stopped. A whole-cell biophysical model using Hodgkin-Huxley equations can recapitulate these changes in electrical activity. Based on this model and by using dynamic clamp to manipulate clock neurons directly, we can rescue the pharmacological block of Shaw and Shal, restore the firing rhythm, and thus demonstrate the critical importance of Shaw and Shal. Together, these findings point to a key role for Shaw and Shal in controlling circadian firing of clock neurons and show that changes in clock neuron currents can account for this. Moreover, with dynamic clamp we can switch the LNvs between morning-like and evening-like states of electrical activity. We conclude that changes in Shaw and Shal underlie the daily oscillation in LNv firing rate.

Alzheimer's disease-associated tau alters Drosophila circadian activity, sleep and clock neuron electrophysiology

Alzheimer's disease (AD) is the most common cause of dementia, which is associated with an enormous personal, social and economic burden worldwide. However, there are few current treatments with none of them targeting the underlying causes of the disease. Sleep and circadian rhythm defects are not only distressing symptoms of AD and other tauopathies and are a leading cause of care home admission but are also thought to accelerate AD pathology. Despite this, little is understood about the underlying causes of these behavioural changes. Expression of the 0N4R isoform of tau has been associated with AD pathology and we show that expressing it in the Drosophila clock network gives rise to circadian and sleep phenotypes which closely match the behavioural changes seen in human AD patients. Tauopathic flies exhibited greater locomotor activity throughout the day and night and displayed a loss of sleep, particularly at night. Under constant darkness, the locomotor behaviour of tau-expressing flies was less rhythmic than controls indicating a defect in their intrinsic circadian rhythm. Current clamp recordings from wake-promoting, pigment dispersing factor (PDF)-positive large lateral ventral clock neurons (l-LNvs) revealed elevated spontaneous firing throughout the day and night which likely underlies the observed hyperactive circadian phenotype. Interestingly, expression of tau in only the PDF-positive pacemaker neurons, which are thought to be the most important for behaviour under constant conditions, was not sufficient or even necessary to affect circadian rhythmicity. This work establishes Drosophila as a model to investigate interactions between human pathological versions of tau and the machinery that controls neuronal excitability, allowing the identification of underlying mechanisms of disease that may reveal new therapeutic targets.

Effects of MUL1 and PARKIN on the circadian clock, brain and behaviour in Drosophila Parkinson's disease models

Background

Mutants which carry mutations in genes encoding mitochondrial ligases MUL1 and PARKIN are convenient Drosophila models of Parkinson’s disease (PD). In several studies it has been shown that in Parkinson’s disease sleep disturbance occurs, which may be the result of a disturbed circadian clock.

Results

We found that the ROS level was higher, while the anti-oxidant enzyme SOD1 level was lower in mul1^A6 and park¹ mutants than in the white mutant used as a control. Moreover, mutations of both ligases affected circadian rhythms and the clock. The expression of clock genes per, tim and clock and the level of PER protein were changed in the mutants. Moreover, expression of ATG5, an autophagy protein also involved in circadian rhythm regulation, was decreased in the brain and in PDF-immunoreactive large ventral lateral clock neurons. The observed changes in the molecular clock resulted in a longer period of locomotor activity rhythm, increased total activity and shorter sleep at night. Finally, the lack of both ligases led to decreased longevity and climbing ability of the flies.

Conclusions

All of the changes observed in the brains of these Drosophila models of PD, in which mitochondrial ligases MUL1 and PARKIN do not function, may explain the mechanisms of some neurological and behavioural symptoms of PD.

Electronic supplementary material

The online version of this article (10.1186/s12868-019-0506-8) contains supplementary material, which is available to authorized users.

Cross-species models of attention-deficit/hyperactivity disorder and autism spectrum disorder: lessons from CNTNAP2, ADGRL3, and PARK2

Animal and cellular models are essential tools for all areas of biological research including neuroscience. Model systems can also be used to investigate the pathophysiology of psychiatric disorders such as attention-deficit/hyperactivity disorder (ADHD) and autism spectrum disorder (ASD). In this review, we provide a summary of animal and cellular models for three genes linked to ADHD and ASD in human patients - CNTNAP2, ADGRL3, and PARK2. We also highlight the strengths and weaknesses of each model system. By bringing together behavioral and neurobiological data, we demonstrate how a cross-species approach can provide integrated insights into gene function and the pathogenesis of ADHD and ASD. The knowledge gained from transgenic models will be essential to discover and validate new treatment targets for these disorders.