The ongoing pursuit of neuroprotective therapies in Parkinson disease

Insulin resistance and Parkinson's disease: A new target for disease modification?

There is growing evidence that patients with Type 2 diabetes have an increased risk of developing Parkinson's disease and share similar dysregulated pathways suggesting common underlying pathological mechanisms. Historically insulin was thought solely to be a peripherally acting hormone responsible for glucose homeostasis and energy metabolism. However accumulating evidence indicates insulin can cross the blood-brain-barrier and influence a multitude of processes in the brain including regulating neuronal survival and growth, dopaminergic transmission, maintenance of synapses and pathways involved in cognition. In conjunction, there is growing evidence that a process analogous to peripheral insulin resistance occurs in the brains of Parkinson's disease patients, even in those without diabetes. This raises the possibility that defective insulin signalling pathways may contribute to the development of the pathological features of Parkinson's disease, and thereby suggests that the insulin signalling pathway may potentially be a novel target for disease modification. Given these growing links between PD and Type 2 diabetes it is perhaps not unsurprising that drugs used the treatment of T2DM are amongst the most promising treatments currently being prioritised for repositioning as possible novel treatments for PD and several clinical trials are under way. In this review, we will examine the underlying cellular links between insulin resistance and the pathogenesis of PD and then we will assess current and future pharmacological strategies being developed to restore neuronal insulin signalling as a potential strategy for slowing neurodegeneration in Parkinson's disease.

A Novel Parkinson's Disease Drug Candidate with Potent Anti-neuroinflammatory Effects through the Src Signaling Pathway

Numerous drug treatments are available for Parkinson's disease (PD), an age-related neurodegenerative disease, but most cause serious side effects. Therefore, novel therapeutic strategies that halt disease progression and allow for long-term administration are urgently needed. Neuroinflammation critically contributes to the pathogenesis of PD. Here, we report the discovery and optimization of phloroglucinol derivatives, a novel class of anti-neuroinflammatory compounds. Structural modifications of the hit compound 3-methyl-1-(2,4,6-trihydroxyphenyl)butan-1-one produced 43 derivatives, including a preclinical candidate (compound 21), that exhibited potent in vitro anti-neuroinflammatory effects, good blood-brain barrier penetration, and desirable safety margins in mice at a median lethal dose (LD₅₀) >5000 mg/kg. Its in vivo efficacy was demonstrated in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)- and MPTP/probenecid (prob)-induced subacute and chronic PD models, respectively, and α-synuclein transgenic mice. Mechanistic studies revealed neuroinflammation inhibition by targeting Src/phosphatase and tensin homologue deleted on chromosome 10 (PTEN)/Akt signaling might be promising. We highlighted the potential usefulness of phloroglucinol derivatives in PD treatment.

Neuroprotective effects of fingolimod in mouse models of Parkinson's disease

Parkinson's disease (PD) is characterized by a progressive loss of dopaminergic neurons with limited treatment options. Emerging evidence shows that FTY720 protects against neural injury via modulation of the sphingosine-1-phosphate 1 receptor (S1PR1). However, it remains unclear whether FTY720 could influence neurodegeneration in PD. Therefore, the present study was designed to determine the impact of fingolimod (FTY720), a sphingosine-1-phosphate receptor (S1PR) agonist, on 2 mouse models of PD. We found that FTY720 significantly reduced the deficit of motor function, diminished the loss of tyrosine hydroxylase-positive neurons in the substantia nigra, and attenuated the decrease of striatal dopamine and metabolite levels in mice receiving 6-hydroxydopamine (6-OHDA) or rotenone to simulate PD. An S1PR1-selective antagonist, W146, blocked the neuroprotective effects of FTY720. Of note, FTY720 retained the phosphorylation of ERK, together with a decreased expression of cleaved caspase-3 in mice treated with 6-OHDA or rotenone. In vitro studies revealed that FTY720 also attenuated 6-OHDA- or rotenone-induced toxicity in SH-SY5Y cells. These findings suggest the potential of S1PR modulation as a treatment for PD.-Zhao, P., Yang, X., Yang, L., Li, M., Wood, K., Liu, Q., Zhu, X. Neuroprotective effects of fingolimod in mouse models of Parkinson's disease.

Neuroprotective Effects of Salidroside in the MPTP Mouse Model of Parkinson's Disease: Involvement of the PI3K/Akt/GSK3β Pathway

The degenerative loss through apoptosis of dopaminergic neurons in the substantia nigra pars compacta plays a primary role in the progression of Parkinson's disease (PD). Our in vitro experiments suggested that salidroside (Sal) could protect against 1-methyl-4-phenylpyridine-induced cell apoptosis in part by regulating the PI3K/Akt/GSK3β pathway. The current study aims to increase our understanding of the protective mechanisms of Sal in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropypridine- (MPTP-) induced PD mouse model. We found that pretreatment with Sal could protect against MPTP-induced increase of the time of turning downwards and climbing down to the floor. Sal also prevented MPTP-induced decrease of locomotion frequency and the increase of the immobile time. Sal provided a protection of in MPTP-induced loss of tyrosine hydroxylase-positive neurons in SNpc and the level of DA, DOPAC, and HVA in the striatum. Furthermore, Sal could increase the phosphorylation level of Akt and GSK3β, upregulate the ratio of Bcl-2/Bax, and inhibit the activation of caspase-3, caspase-6, and caspase-9. These results show that Sal prevents the loss of dopaminergic neurons and the PI3K/Akt/GSK3β pathway signaling pathway may have mediated the protection of Sal against MPTP, suggesting that Sal may be a potential candidate in neuroprotective treatment for PD.

Characterizations of a synthetic pituitary adenylate cyclase-activating polypeptide analog displaying potent neuroprotective activity and reduced in vivo cardiovascular side effects in a Parkinson's disease model

Parkinson's disease (PD) is characterized by a steady loss of dopamine neurons through apoptotic, inflammatory and oxidative stress processes. In that line of view, the pituitary adenylate cyclase-activating polypeptide (PACAP), with its ability to cross the blood-brain barrier and its anti-apoptotic, anti-inflammatory and anti-oxidative properties, has proven to offer potent neuroprotection in various PD models. Nonetheless, its peripheral actions, paired with low metabolic stability, hampered its clinical use. We have developed Ac-[Phe(pI)(6), Nle(17)]PACAP(1-27) as an improved PACAP-derived neuroprotective compound. In vitro, this analog stimulated cAMP production, maintained mitochondrial potential and protected SH-SY5Y neuroblastoma cells from 1-methyl-4-phenylpyridinium (MPP(+)) toxicity, as potently as PACAP. Furthermore, contrasting with PACAP, it is stable in human plasma and against dipeptidyl peptidase IV activity. When injected intravenously to 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated mice, PACAP and Ac-[Phe(pI)(6), Nle(17)]PACAP(1-27) restored tyrosine hydoxylase expression into the substantia nigra and modulated the inflammatory response. Albeit falls of mean arterial pressure (MAP) were observed with both PACAP- and Ac-[Phe(pI)(6), Nle(17)]PACAP(1-27)-treated mice, the intensity of the decrease as well as its duration were significantly less marked after iv injections of the analog than after those of the native polypeptide. Moreover, no significant changes in heart rate were measured with the animals for both compounds. Thus, Ac-[Phe(pI)(6), Nle(17)]PACAP(1-27) appears as a promising lead molecule for the development of PACAP-derived drugs potentially useful for the treatment of PD or other neurodegenerative diseases.

Outlining a Population "at Risk" of Parkinson's Disease: Evidence from a Case-Control Study

The multifactorial pathogenesis of Parkinson's Disease (PD) requires a careful identification of populations “at risk” of developing the disease. In this case-control study we analyzed a large Italian population, in an attempt to outline general criteria to define a population “at risk” of PD. We enrolled 300 PD patients and 300 controls, gender and age matched, from the same urban geographical area. All subjects were interviewed on demographics, family history of PD, occupational and environmental toxicants exposure, smoking status, and alcohol consumption. A sample of 65 patients and 65 controls also underwent serum dosing of iron, copper, mercury, and manganese by means of Inductively Coupled-Plasma-Mass-Spectrometry (ICP-MS). Positive family history, toxicants exposure, non-current-smoker, and alcohol nonconsumer status occurred as significant risk factors in our population. The number of concurring risk factors overlapping in the same subject impressively increased the overall risk. No significant differences were measured in the metal serum levels. Our findings indicate that combination of three to four concurrent PD-risk factors defines a condition “at risk” of PD. A simple stratification, based on these questionnaires, might be of help in identifying subjects suitable for neuroprotective strategies.

New concepts in the pathogenesis and presentation of Parkinson's disease

Parkinson's disease (PD) was first described by James Parkinson in 1817. He noted the complex nature of this condition and that non-motor symptoms (NMS) underpinned the classic motor symptoms of PD. The concept of what PD is has therefore undergone substantial changes and it is now recognised that PD is a combined motor and non-motor syndrome and NMS are present during the prodromal phase of PD, starting up to 20 years before the first clinical motor signs emerge. PD may originate from pathology in the gut, olfactory bulb and lower brainstem rather than in the substantia nigra. Complex phenotypes of PD may exist where clinical NMS overshadow motor features. Therapy needs to be adjusted based on motor and non-motor loads, ideally using validated tools. Recently, a multimodal biomarker battery in PD has emerged and might play an important role in the future.

Multifunction of Chrysin in Parkinson's Model: Anti-Neuronal Apoptosis, Neuroprotection via Activation of MEF2D, and Inhibition of Monoamine Oxidase-B

Chrysin, a flavonoid compound existing in several plants, is applied as a dietary supplement because of its beneficial effects on general human health and alleviation of neurological disorders. However, mechanisms underlying neuroprotection of chrysin has not been fully elucidated, and the effects of chrysin on the Parkinson's disease (PD) model in vivo have not been investigated. It is here shown that chrysin protects primary granular neurons against 1-methyl-4-phenylpyridinium ion insult via antiapoptosis by reversing the dysregulated expression of Bcl-2, Bax, and caspase 3. The mechanisms also involved activating transcriptional factor myocyte enhancer factor 2D (MEF2D) via regulation of AKT-GSK3β signaling. In this in vivo model of PD, chrysin rescued the dopaminergic neurons loss and alleviated the decrease in dopamine level induced by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine in mice. Moreover, chrysin markedly inhibited monoamine oxidase-B activity in vitro and in vivo. In conclusion, chrysin exerts beneficial effects to PD, possibly through multitarget mechanisms including antineuronal apoptosis, activation of the AKT-GSK3β/MEF2D pathway, and inhibition of the MAO-B activity.

Loss of collapsin response mediator protein 4 suppresses dopaminergic neuron death in an 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-induced mouse model of Parkinson's disease

Parkinson's disease (PD) is a progressive neurodegenerative disorder that is characterized by the selective loss of dopaminergic neurons in the substantia nigra pars compacta (SNc). Several lines of evidence suggest that neurodegeneration in PD is accelerated by a vicious cycle in which apoptosis in dopaminergic neurons triggers the activation of microglia and harmful inflammatory processes that further amplify neuronal death. Recently, we demonstrated that the deletion of collapsin response mediator protein 4 (CRMP4) suppresses inflammatory responses and cell death in a mouse model of spinal cord injury, leading to improved functional recovery. We thus hypothesized that Crmp4-/- mice may have limited inflammatory responses and a decrease in the loss of SNc dopaminergic neurons in an 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced PD mouse model. We observed CRMP4 expression in neurons, astrocytes, and microglia/macrophages following the injection of 25 mg/kg MPTP. We compared the number of dopaminergic neurons and the inflammatory response in SNc between Crmp4+/+ and Crmp4-/- mice after MPTP injection. Limited loss of SNc dopaminergic neurons and decreased activations of microglia and astrocytes were observed in Crmp4-/- mice. These results suggest that CRMP4 is a novel therapeutic target in the treatment of PD patients. We demonstrated that genetic CRMP4 deletion delays a vicious cycle of inflammation and neurodegeneration in a Parkinson's disease mouse model. MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) injection to wild-type mice induces collapsin response mediator protein 4 (CRMP4) up-regulation in neurons, astrocytes, and microglia. CRMP4-deficient mice show reduced inflammation and suppressed dopaminergic neuronal death after MPTP injection. These findings suggest that CRMP4 deletion may be a new therapeutic strategy against Parkinson's diseases.

Mitoapocynin Treatment Protects Against Neuroinflammation and Dopaminergic Neurodegeneration in a Preclinical Animal Model of Parkinson's Disease

Mitochondrial dysfunction, oxidative stress and neuroinflammation have been implicated as key mediators contributing to the progressive degeneration of dopaminergic neurons in Parkinson's disease (PD). Currently, we lack a pharmacological agent that can intervene in all key pathological mechanisms, which would offer better neuroprotective efficacy than a compound that targets a single degenerative mechanism. Herein, we investigated whether mito-apocynin (Mito-Apo), a newly-synthesized and orally available derivative of apocynin that targets mitochondria, protects against oxidative damage, glial-mediated inflammation and nigrostriatal neurodegeneration in cellular and animal models of PD. Mito-Apo treatment in primary mesencephalic cultures significantly attenuated the 1-methyl-4-phenylpyridinium (MPP(+))-induced loss of tyrosine hydroxylase (TH)-positive neuronal cells and neurites. Mito-Apo also diminished MPP(+)-induced increases in glial cell activation and inducible nitric oxide synthase (iNOS) expression. Additionally, Mito-Apo decreased nitrotyrosine (3-NT) and 4-hydroxynonenol (4-HNE) levels in primary mesencephalic cultures. Importantly, we assessed the neuroprotective property of Mito-Apo in the MPTP mouse model of PD, wherein it restored the behavioral performance of MPTP-treated mice. Immunohistological analysis of nigral dopaminergic neurons and monoamine measurement further confirmed the neuroprotective effect of Mito-Apo against MPTP-induced nigrostriatal dopaminergic neuronal loss. Mito-Apo showed excellent brain bioavailability and also markedly attenuated MPTP-induced oxidative markers in the substantia nigra (SN). Furthermore, oral administration of Mito-Apo significantly suppressed MPTP-induced glial cell activation, upregulation of proinflammatory cytokines, iNOS and gp91phox in IBA1-positive cells of SN. Collectively, these results demonstrate that the novel mitochondria-targeted compound Mito-Apo exhibits profound neuroprotective effects in cellular and pre-clinical animal models of PD by attenuating oxidative damage and neuroinflammatory processes.

How can rAAV-α-synuclein and the fibril α-synuclein models advance our understanding of Parkinson's disease?

Animal models of Parkinson's disease (PD) are important for understanding the mechanisms of the disease and can contribute to developing and validating novel therapeutics. Ideally, these models should replicate the cardinal features of PD, such as progressive neurodegeneration of catecholaminergic neurons and motor defects. Many current PD models emphasize pathological forms of α-synuclein, based on findings that autosomal dominant mutations in α-synuclein and duplications/triplications of the SNCA gene cause PD. In addition, Lewy bodies and Lewy neurites, primarily composed of α-synuclein, represent the predominant pathological characteristics of PD. These inclusions have defined features, such as insolubility in non-ionic detergent, hyperphosphorylation, proteinase K sensitivity, a filamentous appearance by electron microscopy, and β-sheet structure. Furthermore, it has become clear that Lewy bodies and Lewy neurites are found throughout the peripheral and central nervous system, and could account not only for motor symptoms, but also for non-motor symptoms of the disease. The goal of this review is to describe two new α-synuclein-based models: the recombinant adeno-associated viral vector-α-synuclein model and the α-synuclein fibril model. An advantage of both models is that they do not require extensive crossbreeding of rodents transgenic for α-synuclein with other rodents transgenic for genes of interest to study the impact of such genes on PD-related pathology and phenotypes. In addition, abnormal α-synuclein can be expressed in brain regions relevant for disease. Here, we discuss the features of each model, how each model has contributed thus far to our understanding of PD, and the advantages and potential caveats of each model. This review describes two α-synuclein-based rodent models of Parkinson's disease: the rAAV-α-synuclein model and the α-synuclein fibril model. The key features of these models are described, and the extent to which they recapitulate features of PD, such as α-synuclein inclusion formation, loss of dopaminergic synapses in the striatum, motor defects, inflammation, and dopamine neuron death. This article is part of a special issue on Parkinson disease.

Genetic manipulation for inherited neurodegenerative diseases: myth or reality?

Rare genetic diseases affect about 7% of the general population and over 7000 distinct clinical syndromes have been described with the majority being due to single gene defects. This review will provide a critical overview of genetic strategies that are being pioneered to halt or reverse disease progression in inherited neurodegenerative diseases. This field of research covers a vast area and only the most promising treatment paradigms will be discussed with a particular focus on inherited eye diseases, which have paved the way for innovative gene therapy paradigms, and mitochondrial diseases, which are currently generating a lot of debate centred on the bioethics of germline manipulation.

Cognition in individuals at risk for Parkinson's: Parkinson associated risk syndrome (PARS) study findings

OBJECTIVES

The Parkinson Associated Risk Syndrome Study identified a cohort of healthy adults with hyposmia and dopamine transporter binding reduction to characterize individuals at risk for Parkinson's disease (PD). We describe the cognitive profile of this cohort.

METHODS

Individuals older than 50 y without PD were recruited. Two hundred twenty-five completed cognitive testing and were included in the final analysis. A neuropsychological test battery was administered and normative scores created for global cognition, memory, executive function/working memory, processing speed/attention, visuospatial abilities, and language domains. Other non-motor symptoms (constipation, depression, anxiety, and rapid eye movement sleep behavior disorder) were assessed through questionnaires.

RESULTS

Individuals with both hyposmia and reduced dopamine transporter binding (n = 38) had lower mean scores for global cognition, executive function/working memory, and memory compared with all other participants (n = 187). In separate multivariate logistic regression models, lower global cognition (odds ratio, 1.97, P = 0.004), and specifically executive function/working memory (odds ratio, 1.84, P = 0.004) scores were associated with membership in the hyposmia with dopamine transporter reduction group. Combining hyposmia with relative impairment on specific cognitive domains increased the odds of dopamine transporter binding reduction compared with hyposmia alone, with the greatest increase in odds for hyposmia plus executive function/working memory relative impairment (68% increase in odds from 4.14 to 6.96).

CONCLUSION

Changes in global cognitive abilities, and specifically executive function/working memory, are present in individuals at risk for PD. Combining non-motor features, including cognition, improves prediction of dopamine transporter binding reduction.

Cognitive and Psychiatric Effects of STN versus GPi Deep Brain Stimulation in Parkinson's Disease: A Meta-Analysis of Randomized Controlled Trials

BACKGROUND

Deep brain stimulation (DBS) of either the subthalamic nucleus (STN) or the globus pallidus interna (GPi) can reduce motor symptoms in patients with Parkinson's disease (PD) and improve their quality of life. However, the effects of STN DBS and GPi DBS on cognitive functions and their psychiatric effects remain controversial. The present meta-analysis was therefore performed to clarify these issues.

METHODS

We searched the PUBMED, EMBASE, and the Cochrane Central Register of Controlled Trials databases. Other sources, including internet-based clinical trial registries and grey literature sources, were also searched. After searching the literature, two investigators independently performed literature screens to assess the quality of the included trials and to extract the data. The outcomes included the effects of STN DBS and GPi DBS on multiple cognitive domains, depression, anxiety, and quality of life.

RESULTS

Seven articles related to four randomized controlled trials that included 521 participants were incorporated into the present meta-analysis. Compared with GPi DBS, STN DBS was associated with declines in selected cognitive domains after surgery, including attention, working memory and processing speed, phonemic fluency, learning and memory, and global cognition. However, there were no significant differences in terms of quality of life or psychiatric effects, such as depression and anxiety, between the two groups.

CONCLUSIONS

A selective decline in frontal-subcortical cognitive functions is observed after STN DBS in comparison with GPi DBS, which should not be ignored in the target selection for DBS treatment in PD patients. In addition, compared to GPi DBS, STN DBS does not affect depression, anxiety, and quality of life.

Endocannabinoids and Neurodegenerative Disorders: Parkinson's Disease, Huntington's Chorea, Alzheimer's Disease, and Others

This review focuses on the role of the endocannabinoid signaling system in controlling neuronal survival, an extremely important issue to be considered when developing new therapies for neurodegenerative disorders. First, we will describe the cellular and molecular mechanisms, and the signaling pathways, underlying these neuroprotective properties, including the control of glutamate homeostasis, calcium influx, the toxicity of reactive oxygen species, glial activation and other inflammatory events; and the induction of autophagy. We will then concentrate on the preclinical studies and the few clinical trials that have been carried out targeting endocannabinoid signaling in three important chronic progressive neurodegenerative disorders (Parkinson's disease, Huntington's chorea, and Alzheimer's disease), as well as in other less well-studied disorders. We will end by offering some ideas and proposals for future research that should be carried out to optimize endocannabinoid-based treatments for these disorders. Such studies will strengthen the possibility that these therapies will be investigated in the clinical scenario and licensed for their use in specific disorders.

Cannabinoids in Neurodegenerative Disorders and Stroke/Brain Trauma: From Preclinical Models to Clinical Applications

Cannabinoids form a singular family of plant-derived compounds (phytocannabinoids), endogenous signaling lipids (endocannabinoids), and synthetic derivatives with multiple biological effects and therapeutic applications in the central and peripheral nervous systems. One of these properties is the regulation of neuronal homeostasis and survival, which is the result of the combination of a myriad of effects addressed to preserve, rescue, repair, and/or replace neurons, and also glial cells against multiple insults that may potentially damage these cells. These effects are facilitated by the location of specific targets for the action of these compounds (e.g., cannabinoid type 1 and 2 receptors, endocannabinoid inactivating enzymes, and nonendocannabinoid targets) in key cellular substrates (e.g., neurons, glial cells, and neural progenitor cells). This potential is promising for acute and chronic neurodegenerative pathological conditions. In this review, we will collect all experimental evidence, mainly obtained at the preclinical level, supporting that different cannabinoid compounds may be neuroprotective in adult and neonatal ischemia, brain trauma, Alzheimer's disease, Parkinson's disease, Huntington's chorea, and amyotrophic lateral sclerosis. This increasing experimental evidence demands a prompt clinical validation of cannabinoid-based medicines for the treatment of all these disorders, which, at present, lack efficacious treatments for delaying/arresting disease progression, despite the fact that the few clinical trials conducted so far with these medicines have failed to demonstrate beneficial effects.

Assessment of the Protection of Dopaminergic Neurons by an α7 Nicotinic Receptor Agonist, PHA 543613 Using [(18)F]LBT-999 in a Parkinson's Disease Rat Model

The inverse association between nicotine intake and Parkinson's disease (PD) is well established and suggests that this molecule could be neuroprotective through anti-inflammatory action mediated by nicotinic receptors, including the α7-subtype (α7R). The objective of this study was to evaluate the effects of an agonist of α7R, PHA 543613, on striatal dopaminergic neurodegeneration and neuroinflammation in a rat model of PD induced by 6-hydroxydopamine (6-OHDA) lesion. Adult male Wistar rats were lesioned in the right striatum and assigned to either the PHA group (n = 7) or the Sham group (n = 5). PHA 543613 hydrochloride at the concentration of 6 mg/kg (PHA group) or vehicle (Sham group) was intra-peritoneally injected 2 h before 6-OHDA lesioning and then at days 2, 4, and 6 post-lesion. Positron emission tomography (PET) imaging was performed at 7 days post-lesion using [(18)F]LBT-999 to quantify the striatal dopamine transporter (DAT). After PET imaging, neuroinflammation was evaluated in same animals in vitro through the measurement of the microglial activation marker 18 kDa translocator protein (TSPO) by quantitative autoradiography with [(3)H]PK-11195. The DAT density reflecting the integrity of dopaminergic neurons was significantly decreased while the intensity of neuroinflammation measured by TSPO density was significantly increased in the lesioned compared to intact striatum in both groups. However, these both modifications were partially reversed in the PHA group compared to Sham. In addition, a significant positive correlation between the degree of lesion and the intensity of neuroinflammation was evidenced. These findings indicate that PHA 543613 exerts neuroprotective effects on the striatal dopaminergic neurons associated with a reduction in microglial activation in this model of PD. This reinforces the hypothesis that an α7R agonist could provide beneficial effects for the treatment of PD.

Flies with Parkinson's disease

Parkinson's disease is an incurable neurodegenerative disease. Most cases of the disease are of sporadic origin, but about 10% of the cases are familial. The genes thus far identified in Parkinson's disease are well conserved. Drosophila is ideally suited to study the molecular neuronal cell biology of these genes and the pathogenic mutations in Parkinson's disease. Flies reproduce quickly, and their elaborate genetic tools in combination with their small size allow researchers to analyze identified cells and neurons in large numbers of animals. Furthermore, fruit flies recapitulate many of the cellular and molecular defects also seen in patients, and these defects often result in clear locomotor and behavioral phenotypes, facilitating genetic modifier screens. Hence, Drosophila has played a prominent role in Parkinson's disease research and has provided invaluable insight into the molecular mechanisms of this disease.

Can Parkinson's disease be cured by stimulating neurogenesis?

There have been many attempts at slowing down or even reversing the neurodegenerative process of Parkinson's disease (PD). To date, there are no treatments of proven value in this regard. One underexplored route to slow the neurodegenerative process is the use of agents that may stimulate neurogenesis in the subventricular zone. In animal models of PD, PDGF-BB has been shown to restore/protect against dopaminergic deficits caused by neurotoxins via increased neurogenesis in the subventricular zone. Previous work suggests that these new cells are not themselves dopaminergic but have trophic effects on residual dopaminergic cells in the substantia nigra. In this issue of the JCI, Paul et al. evaluate this agent in individuals with PD and show that i.c.v. administration of PDGF-BB is safe and well tolerated. This study lays the foundation for formal dose-finding studies and clinical trials to assess the efficacy of this agent as a potential neuroprotective treatment for PD.