Development and characterisation of a novel rat model of Parkinson's disease induced by sequential intranigral administration of AAV-α-synuclein and the pesticide, rotenone

Sequential or Simultaneous Injection of Preformed Fibrils and AAV Overexpression of Alpha-Synuclein Are Equipotent in Producing Relevant Pathology and Behavioral Deficits

BACKGROUND

Preclinical rodent models for Parkinson's disease (PD) based on viral human alpha-synuclein (h-αSyn) overexpression recapitulate some of the pathological hallmarks as it presents in humans, such as progressive cell loss and additional synucleinopathy in cortical and subcortical structures. Recent studies have combined viral vector-based overexpression of human wild-type αSyn with the sequential or simultaneous inoculation of preformed fibrils (PFFs) derived from human αSyn.

OBJECTIVE

The goal of the study was to investigate whether sequential or combined delivery of the AAV vector and the PFFs are equipotent in inducing stable neurodegeneration and behavioral deficits.

METHODS

Here we compare between four experimental paradigms (PFFs only, AAV-h-αSyn only, AAV-h-αSyn with simultaneous PFFs, and AAV-h-αSyn with sequential PFFs) and their respective GFP control groups.

RESULTS

We observed reduction of TH expression and loss of neurons in the midbrain in all AAV (h-αSyn or GFP) injected groups, with or without additional PFFs inoculation. The overexpression of either h-αSyn or GFP alone induced motor deficits and dysfunctional dopamine release/reuptake in electrochemical recordings in the ipsilateral striatum. However, we observed a substantial formation of insoluble h-αSyn aggregates and inflammatory response only when h-αSyn and PFFs were combined. Moreover, the presence of h-αSyn induced higher axonal pathology compared to control groups.

CONCLUSION

Simultaneous AAV and PFFs injections are equipotent in the presented experimental setup in inducing histopathological and behavioral changes. This model provides new and interesting possibilities for characterizing PD pathology in preclinical models and means to assess future therapeutic interventions.

The Small Molecule Alpha-Synuclein Aggregator, FN075, Enhances Alpha-Synuclein Pathology in Subclinical AAV Rat Models

Animal models of Parkinson's disease, in which the human α-synuclein transgene is overexpressed in the nigrostriatal pathway using viral vectors, are widely considered to be the most relevant models of the human condition. However, although highly valid, these models have major limitations related to reliability and variability, with many animals exhibiting pronounced α-synuclein expression failing to demonstrate nigrostriatal neurodegeneration or motor dysfunction. Therefore, the aim of this study was to determine if sequential intra-nigral administration of AAV-α-synuclein followed by the small α-synuclein aggregating molecule, FN075, would enhance or precipitate the associated α-synucleinopathy, nigrostriatal pathology and motor dysfunction in subclinical models. Rats were given unilateral intra-nigral injections of AAV-α-synuclein (either wild-type or A53T mutant) followed four weeks later by a unilateral intra-nigral injection of FN075, after which they underwent behavioral testing for lateralized motor functionality until they were sacrificed for immunohistological assessment at 20 weeks after AAV administration. In line with expectations, both of the AAV vectors induced widespread overexpression of human α-synuclein in the substantia nigra and striatum. Sequential administration of FN075 significantly enhanced the α-synuclein pathology with increased density and accumulation of the pathological form of the protein phosphorylated at serine 129 (pS129-α-synuclein). However, despite this enhanced α-synuclein pathology, FN075 did not precipitate nigrostriatal degeneration or motor dysfunction in these subclinical AAV models. In conclusion, FN075 holds significant promise as an approach to enhancing the α-synuclein pathology in viral overexpression models, but further studies are required to determine if alternative administration regimes for this molecule could improve the reliability and variability in these models.

Psychological Stress Phenocopies Brain Mitochondrial Dysfunction and Motor Deficits as Observed in a Parkinsonian Rat Model

Psychological distress is a public health issue as it contributes to the development of human diseases including neuropathologies. Parkinson's disease (PD), a chronic, progressive neurodegenerative disorder, is caused by multiple factors including aging, mitochondrial dysfunction, and/or stressors. In PD, a substantial loss of substantia nigra (SN) neurons leads to rigid tremors, bradykinesia, and chronic fatigue. Several studies have reported that the hypothalamic-pituitary-adrenal (HPA) axis is altered in PD patients, leading to an increase level of cortisol which contributes to neurodegeneration and oxidative stress. We hypothesized that chronic psychological distress induces PD-like symptoms and promotes neurodegeneration in wild-type (WT) rats and exacerbates PD pathology in PINK1 knockout (KO) rats, a well-validated animal model of PD. We measured the bioenergetics profile (oxidative phosphorylation and glycolysis) in the brain by employing an XF24e Seahorse Extracellular Flux Analyzer in young rats subjected to predator-induced psychological distress. In addition, we analyzed anxiety-like behavior, motor function, expression of antioxidant enzymes, mitochondrial content, and neurotrophic factors brain-derived neurotrophic factor (BDNF) in the brain. Overall, we observed that psychological distress diminished up to 50% of mitochondrial respiration and glycolysis in the prefrontal cortex (PFC) derived from both WT and PINK1-KO rats. Mechanistically, the level of antioxidant proteins, mitochondrial content, and BDNF was significantly altered. Finally, psychological distress robustly induced anxiety and Parkinsonian symptoms in WT rats and accelerated certain symptoms of PD in PINK1-KO rats. For the first time, our collective data suggest that psychological distress can phenocopy several aspects of PD neuropathology, disrupt brain energy production, as well as induce ataxia-like behavior.

The functional microscopic neuroanatomy of the human subthalamic nucleus

The subthalamic nucleus (STN) is successfully used as a surgical target for deep brain stimulation in the treatment of movement disorders. Interestingly, the internal structure of the STN is still incompletely understood. The objective of the present study was to investigate three-dimensional (3D) immunoreactivity patterns for 12 individual protein markers for GABA-ergic, serotonergic, dopaminergic as well as glutamatergic signaling. We analyzed the immunoreactivity using optical densities and created a 3D reconstruction of seven postmortem human STNs. Quantitative modeling of the reconstructed 3D immunoreactivity patterns revealed that the applied protein markers show a gradient distribution in the STN. These gradients were predominantly organized along the ventromedial to dorsolateral axis of the STN. The results are of particular interest in view of the theoretical underpinning for surgical targeting, which is based on a tripartite distribution of cognitive, limbic and motor function in the STN.

Time course and magnitude of alpha-synuclein inclusion formation and nigrostriatal degeneration in the rat model of synucleinopathy triggered by intrastriatal α-synuclein preformed fibrils

Animal models that accurately recapitulate the accumulation of alpha-synuclein (α-syn) inclusions, progressive neurodegeneration of the nigrostriatal system and motor deficits can be useful tools for Parkinson's disease (PD) research. The preformed fibril (PFF) synucleinopathy model in rodents generally displays these PD-relevant features, however, the magnitude and predictability of these events is far from established. We therefore sought to optimize the magnitude of α-syn accumulation and nigrostriatal degeneration, and to understand the time course of both. Rats were injected unilaterally with different quantities of α-syn PFFs (8 or 16 μg of total protein) into striatal sites selected to concentrate α-syn inclusion formation in the substantia nigra pars compacta (SNpc). Rats displayed an α-syn PFF quantity-dependent increase in the magnitude of ipsilateral SNpc inclusion formation at 2 months and bilateral loss of nigral dopamine neurons at 6 months. Unilateral 16 μg PFF injection also resulted in modest sensorimotor deficits in forelimb adjusting steps associated with degeneration at 6 months. Bilateral injection of 16 μg α-syn PFFs resulted in symmetric bilateral degeneration equivalent to the ipsilateral nigral degeneration observed following unilateral 16 μg PFF injection (~50% loss). Bilateral PFF injections additionally resulted in alterations in several gait analysis parameters. These α-syn PFF parameters can be applied to generate a reproducible synucleinopathy model in rats with which to study pathogenic mechanisms and vet potential disease-modifying therapies.

Quality Over Quantity: Advantages of Using Alpha-Synuclein Preformed Fibril Triggered Synucleinopathy to Model Idiopathic Parkinson's Disease

Animal models have significantly advanced our understanding of Parkinson's disease (PD). Alpha-synuclein (α-syn) has taken center stage due to its genetic connection to familial PD and localization to Lewy bodies, one pathological hallmark of PD. Animal models developed on the premise of elevated alpha-synuclein via germline manipulation or viral vector-mediated overexpression are used to investigate PD pathophysiology and vet novel therapeutics. While these models represented a step forward compared to their neurotoxicant model predecessors, they rely on overexpression of supraphysiological levels of α-syn to trigger toxicity. However, whereas SNCA-linked familial PD is associated with elevated α-syn, elevated α-syn is not associated with idiopathic PD. Therefore, the defining feature of the α-syn overexpression models may fail to appropriately model idiopathic PD. In the last several years a new model has been developed in which α-syn preformed fibrils are injected intrastriatally and trigger normal endogenous levels of α-syn to misfold and accumulate into Lewy body-like inclusions. Following a defined period of inclusion accumulation, distinct phases of neuroinflammation and progressive degeneration can be detected in the nigrostriatal system. In this perspective, we highlight the fact that levels of α-syn achieved in overexpression models generally exceed those observed in idiopathic and even SNCA multiplication-linked PD. This raises the possibility that supraphysiological α-syn expression may drive pathophysiological mechanisms not relevant to idiopathic PD. We argue in this perspective that synucleinopathy triggered to form within the context of normal α-syn expression represents a more faithful animal model of idiopathic PD when examining the role of neuroinflammation or the relationship between a-syn aggregation and toxicity.

Intermittent Fasting Applied in Combination with Rotenone Treatment Exacerbates Dopamine Neurons Degeneration in Mice

Intermittent fasting (IF) was suggested to be a powerful nutritional strategy to prevent the onset of age-related neurodegenerative diseases associated with compromised brain bioenergetics. Whether the application of IF in combination with a mitochondrial insult could buffer the neurodegenerative process has never been explored yet. Herein, we defined the effects of IF in C57BL/6J mice treated once per 24 h with rotenone (Rot) for 28 days. Rot is a neurotoxin that inhibits the mitochondrial complex I and causes dopamine neurons degeneration, thus reproducing the neurodegenerative process observed in Parkinson's disease (PD). IF (24 h alternate-day fasting) was applied alone or in concomitance with Rot treatment (Rot/IF). IF and Rot/IF groups showed the same degree of weight loss when compared to control and Rot groups. An accelerating rotarod test revealed that only Rot/IF mice have a decreased ability to sustain the test at the higher speeds. Rot/IF group showed a more marked decrease of dopaminergic neurons and increase in alpha-synuclein (α-syn) accumulation with respect to Rot group in the substantia nigra (SN). Through lipidomics and metabolomics analyses, we found that in the SN of Rot/IF mice a significant elevation of excitatory amino acids, inflammatory lysophospholipids and sphingolipids occurred. Collectively, our data suggest that, when applied in combination with neurotoxin exposure, IF does not exert neuroprotective effects but rather exacerbate neuronal death by increasing the levels of excitatory amino acids and inflammatory lipids in association with altered brain membrane composition.

Subthalamic Nucleus Deep Brain Stimulation Does Not Modify the Functional Deficits or Axonopathy Induced by Nigrostriatal α-Synuclein Overexpression

Subthalamic nucleus deep brain stimulation (STN DBS) protects dopaminergic neurons of the substantia nigra pars compacta (SNpc) against 6-OHDA and MPTP. We evaluated STN DBS in a parkinsonian model that displays α-synuclein pathology using unilateral, intranigral injections of recombinant adeno-associated virus pseudotype 2/5 to overexpress wildtype human α-synuclein (rAAV2/5 α-syn). A low titer of rAAV2/5 α-syn results in progressive forelimb asymmetry, loss of striatal dopaminergic terminal density and modest loss of SNpc dopamine neurons after eight weeks, corresponding to robust human-Snca expression and no effect on rat-Snca, Th, Bdnf or Trk2. α-syn overexpression increased phosphorylation of ribosomal protein S6 (p-rpS6) in SNpc neurons, a readout of trkB activation. Rats received intranigral injections of rAAV2/5 α-syn and three weeks later received four weeks of STN DBS or electrode implantation that remained inactive. STN DBS did not protect against α-syn-mediated deficits in forelimb akinesia, striatal denervation or loss of SNpc neuron, nor did STN DBS elevate p-rpS6 levels further. ON stimulation, forelimb asymmetry was exacerbated, indicating α-syn overexpression-mediated neurotransmission deficits. These results demonstrate that STN DBS does not protect the nigrostriatal system against α-syn overexpression-mediated toxicity. Whether STN DBS can be protective in other models of synucleinopathy is unknown.

Pituitary adenylate cyclase-activating polypeptide (PACAP) has a neuroprotective function in dopamine-based neurodegeneration in rat and snail parkinsonian models

Pituitary adenylate cyclase-activating polypeptide (PACAP) rescues dopaminergic neurons from neurodegeneration and improves motor changes induced by 6-hydroxy-dopamine (6-OHDA) in rat parkinsonian models. Recently, we investigated the molecular background of the neuroprotective effect of PACAP in dopamine (DA)-based neurodegeneration using rotenone-induced snail and 6-OHDA-induced rat models of Parkinson's disease. Behavioural activity, monoamine (DA and serotonin), metabolic enzyme (S-COMT, MB-COMT and MAO-B) and PARK7 protein concentrations were measured before and after PACAP treatment in both models. Locomotion and feeding activity were decreased in rotenone-treated snails, which corresponded well to findings obtained in 6-OHDA-induced rat experiments. PACAP was able to prevent the behavioural malfunctions caused by the toxins. Monoamine levels decreased in both models and the decreased DA level induced by toxins was attenuated by ∼50% in the PACAP-treated animals. In contrast, PACAP had no effect on the decreased serotonin (5HT) levels. S-COMT metabolic enzyme was also reduced but a protective effect of PACAP was not observed in either of the models. Following toxin treatment, a significant increase in MB-COMT was observed in both models and was restored to normal levels by PACAP. A decrease in PARK7 was also observed in both toxin-induced models; however, PACAP had a beneficial effect only on 6-OHDA-treated animals. The neuroprotective effect of PACAP in different animal models of Parkinson's disease is thus well correlated with neurotransmitter, enzyme and protein levels. The models successfully mimic several, but not all etiological properties of the disease, allowing us to study the mechanisms of neurodegeneration as well as testing new drugs. The rotenone and 6-OHDA rat and snail in vivo parkinsonian models offer an alternative method for investigation of the molecular mechanisms of neuroprotective agents, including PACAP.

Summary: PACAP has a neuroprotective effect in different toxin-induced rat and snail parkinsonian models, acting partially through the same mechanisms.

Viral Vector-Based Modeling of Neurodegenerative Disorders: Parkinson's Disease

Gene therapy methods are increasingly used to model Parkinson's disease (PD) in animals in an effort to test experimental therapeutics within a more relevant context to disease pathophysiology and neuropathology. We have detailed several criteria that are critical or advantageous to accurately modeling PD in a murine model or in a nonhuman primate. Using these criteria, we then evaluate approaches made to model PD using viral vectors to date, including both adeno-associated viruses and lentiviruses. Lastly, we comment on the consideration of aging as a critical factor for modeling PD.

Interaction between subclinical doses of the Parkinson's disease associated gene, α-synuclein, and the pesticide, rotenone, precipitates motor dysfunction and nigrostriatal neurodegeneration in rats

In most patients, Parkinson's disease is thought to emerge after a lifetime of exposure to, and interaction between, various genetic and environmental risk factors. One of the key genetic factors linked to this condition is α-synuclein, and the α-synuclein protein is pathologically associated with idiopathic cases. However, α-synuclein pathology is also present in presymptomatic, clinically "normal" individuals suggesting that environmental factors, such as Parkinson's disease-linked agricultural pesticides, may be required to precipitate Parkinson's disease in these individuals. In this context, the aim of this study was to assess the behavioural and neuropathological impact of exposing rats with a subclinical load of α-synuclein to subclinical doses of the organic pesticide, rotenone. Rats were randomly assigned to two groups for intra-nigral infusion of AAV_2/5-GFP or AAV_2/5-α-synuclein. Post viral motor function was assessed at 8, 10 and 12 weeks in the Corridor, Stepping and Whisker tests of lateralised motor function. At week 12, animals were performance-matched to receive a subsequent intra-striatal challenge of the organic pesticide rotenone (or its vehicle) to yield four final groups (Control, Rotenone, AAV_2/5-α-synuclein and Combined). Behavioural testing resumed one week after rotenone surgery and continued for 5 weeks. We found that, when administered alone, neither intra-nigral AAV-α-synuclein nor intra-striatal rotenone caused sufficient nigrostriatal neurodegeneration to induce a significant motor impairment in their own right. However, when these were administered sequentially to the same rats, the interaction between the two Parkinsonian challenges significantly exacerbated nigrostriatal neurodegeneration which precipitated a pronounced impairment in motor function. These results indicate that exposing rats with a subclinical α-synuclein-induced pathology to the pesticide, rotenone, profoundly exacerbates their Parkinsonian neuropathology and dysfunction, and highlights the potential importance of this interaction in the etiology of, and in driving the pathogenesis of Parkinson's disease.

Differential pattern of motor impairments in neurotoxic, environmental and inflammation-driven rat models of Parkinson's disease

One of the reasons proposed for the paucity of drug discovery for Parkinson's disease is the lack of relevant animal models of the condition. Parkinson's disease has been modelled extensively using the selective neurotoxin, 6-hydroxydopamine (6-OHDA). However, as this model bears little etiological resemblance to the human condition, there has been a drive to develop models with improved etiological validity. Two such models are those induced by the pesticide, rotenone, and the inflammagen, lipopolysaccharide (LPS). However, to date, these models have been poorly characterised in terms of their motor profiles and have never been directly compared to the more established models. Thus, the aim of this study was to characterise the behavioural profile of the rotenone and LPS models, and to compare them with the 6-OHDA model. Animals underwent baseline testing on the Stepping, Whisker, Corridor and Cylinder Tests of motor function. They were then grouped for unilateral intra-striatal infusion of 6-OHDA, rotenone or LPS. Motor testing continued for ten weeks after which the rats were processed for immunohistochemical analysis of nigrostriatal integrity. We found that, although all neurotoxins induced a similar level of nigrostriatal neurodegeneration, neither the rotenone nor LPS models were associated with amphetamine-induced rotation, and they were associated with significantly less pronounced and stable impairments in the spontaneous tasks than the 6-OHDA model. In conclusion, this study demonstrates key differences in the pattern of motor dysfunction induced by Parkinsonian neurotoxins which should be taken into consideration when selecting the most appropriate model for Parkinson's disease preclinical studies.

Neurotoxin mechanisms and processes relevant to Parkinson's disease: an update

The molecular mechanism responsible for degenerative process in the nigrostriatal dopaminergic system in Parkinson's disease (PD) remains unknown. One major advance in this field has been the discovery of several genes associated to familial PD, including alpha synuclein, parkin, LRRK2, etc., thereby providing important insight toward basic research approaches. There is an consensus in neurodegenerative research that mitochon dria dysfunction, protein degradation dysfunction, aggregation of alpha synuclein to neurotoxic oligomers, oxidative and endoplasmic reticulum stress, and neuroinflammation are involved in degeneration of the neuromelanin-containing dopaminergic neurons that are lost in the disease. An update of the mechanisms relating to neurotoxins that are used to produce preclinical models of Parkinson´s disease is presented. 6-Hydroxydopamine, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine, and rotenone have been the most wisely used neurotoxins to delve into mechanisms involved in the loss of dopaminergic neurons containing neuromelanin. Neurotoxins generated from dopamine oxidation during neuromelanin formation are likewise reviewed, as this pathway replicates neurotoxin-induced cellular oxidative stress, inactivation of key proteins related to mitochondria and protein degradation dysfunction, and formation of neurotoxic aggregates of alpha synuclein. This survey of neurotoxin modeling-highlighting newer technologies and implicating a variety of processes and pathways related to mechanisms attending PD-is focused on research studies from 2012 to 2014.

An update on the rotenone models of Parkinson's disease: their ability to reproduce the features of clinical disease and model gene-environment interactions

Parkinson's disease (PD) is the second most common neurodegenerative disorder that is characterized by two major neuropathological hallmarks: the degeneration of dopaminergic neurons in the substantia nigra (SN) and the presence of Lewy bodies in the surviving SN neurons, as well as other regions of the central and peripheral nervous system. Animal models have been invaluable tools for investigating the underlying mechanisms of the pathogenesis of PD and testing new potential symptomatic, neuroprotective and neurorestorative therapies. However, the usefulness of these models is dependent on how precisely they replicate the features of clinical PD with some studies now employing combined gene-environment models to replicate more of the affected pathways. The rotenone model of PD has become of great interest following the seminal paper by the Greenamyre group in 2000 (Betarbet et al., 2000). This paper reported for the first time that systemic rotenone was able to reproduce the two pathological hallmarks of PD as well as certain parkinsonian motor deficits. Since 2000, many research groups have actively used the rotenone model worldwide. This paper will review rotenone models, focusing upon their ability to reproduce the two pathological hallmarks of PD, motor deficits, extranigral pathology and non-motor symptoms. We will also summarize the recent advances in neuroprotective therapies, focusing on those that investigated non-motor symptoms and review rotenone models used in combination with PD genetic models to investigate gene-environment interactions.

Overexpression of alpha-synuclein at non-toxic levels increases dopaminergic cell death induced by copper exposure via modulation of protein degradation pathways

Gene multiplications or point mutations in alpha (α)-synuclein are associated with familial and sporadic Parkinson's disease (PD). An increase in copper (Cu) levels has been reported in the cerebrospinal fluid and blood of PD patients, while occupational exposure to Cu has been suggested to augment the risk to develop PD. We aimed to elucidate the mechanisms by which α-synuclein and Cu regulate dopaminergic cell death. Short-term overexpression of wild type (WT) or mutant A53T α-synuclein had no toxic effect in human dopaminergic cells and primary midbrain cultures, but it exerted a synergistic effect on Cu-induced cell death. Cell death induced by Cu was potentiated by overexpression of the Cu transporter protein 1 (Ctr1) and depletion of intracellular glutathione (GSH) indicating that the toxic effects of Cu are linked to alterations in its intracellular homeostasis. Using the redox sensor roGFP, we demonstrated that Cu-induced oxidative stress was primarily localized in the cytosol and not in the mitochondria. However, α-synuclein overexpression had no effect on Cu-induced oxidative stress. WT or A53T α-synuclein overexpression exacerbated Cu toxicity in dopaminergic and yeast cells in the absence of α-synuclein aggregation. Cu increased autophagic flux and protein ubiquitination. Impairment of autophagy by overexpression of a dominant negative Atg5 form or inhibition of the ubiquitin/proteasome system (UPS) with MG132 enhanced Cu-induced cell death. However, only inhibition of the UPS stimulated the synergistic toxic effects of Cu and α-synuclein overexpression. Our results demonstrate that α-synuclein stimulates Cu toxicity in dopaminergic cells independent from its aggregation via modulation of protein degradation pathways.

Genetic variants and animal models in SNCA and Parkinson disease

Parkinson disease (PD; MIM 168600) is the second most common progressive neurodegenerative disorder characterized by a variety of motor and non-motor features. To date, at least 20 loci and 15 disease-causing genes for parkinsonism have been identified. Among them, the α-synuclein (SNCA) gene was associated with PARK1/PARK4. Point mutations, duplications and triplications in the SNCA gene cause a rare dominant form of PD in familial and sporadic PD cases. The α-synuclein protein, a member of the synuclein family, is abundantly expressed in the brain. The protein is the major component of Lewy bodies and Lewy neurites in dopaminergic neurons in PD. Further understanding of its role in the pathogenesis of PD through various genetic techniques and animal models will likely provide new insights into our understanding, therapy and prevention of PD.

Morphological and behavioral impact of AAV2/5-mediated overexpression of human wildtype alpha-synuclein in the rat nigrostriatal system

The discovery of the involvement of alpha-synuclein (α-syn) in Parkinson’s disease (PD) pathogenesis has resulted in the development and use of viral vector-mediated α-syn overexpression rodent models. The goal of these series of experiments was to characterize the neurodegeneration and functional deficits resulting from injection of recombinant adeno-associated virus (rAAV) serotype 2/5-expressing human wildtype α-syn in the rat substantia nigra (SN). Rats were unilaterally injected into two sites in the SN with either rAAV2/5-expressing green fluorescent protein (GFP, 1.2 x 10¹³) or varying titers (2.2 x 10¹², 1.0 x 10¹³, 5.9 x 10¹³, or 1.0 x 10¹⁴) of rAAV2/5-α-syn. Cohorts of rats were euthanized 4, 8, or 12 weeks following vector injection. The severity of tyrosine hydroxylase immunoreactive (THir) neuron death in the SN pars compacta (SNpc) was dependent on vector titer. An identical magnitude of nigrostriatal degeneration (60-70% SNpc THir neuron degeneration and 40-50% loss of striatal TH expression) was observed four weeks following 1.0 x 10¹⁴ titer rAAV2/5-α-syn injection and 8 weeks following 1.0 x 10¹³ titer rAAV2/5-α-syn injection. THir neuron degeneration was relatively uniform throughout the rostral-caudal axis of the SNpc. Despite equivalent nigrostriatal degeneration between the 1.0 x 10¹³ and 1.0 x 10¹⁴ rAAV2/5-α-syn groups, functional impairment in the cylinder test and the adjusting steps task was only observed in rats with the longer 8 week duration of α-syn expression. Motor impairment in the cylinder task was highly correlated to striatal TH loss. Further, 8 weeks following 5.9 x 10¹³ rAAV2/5-α-syn injection deficits in ultrasonic vocalizations were observed. In conclusion, our rAAV2/5-α-syn overexpression model demonstrates robust nigrostriatal α-syn overexpression, induces significant nigrostriatal degeneration that is both vector and duration dependent and under specific parameters can result in motor impairment that directly relates to the level of striatal TH denervation.

Heat shock protein 70 reduces α-synuclein-induced predegenerative neuronal dystrophy in the α-synuclein viral gene transfer rat model of Parkinson's disease

AIMS

It has become increasingly evident that the nigrostriatal degeneration associated with Parkinson's disease initiates at the level of the axonal terminals in the putamen, and this nigrostriatal terminal dystrophy is either caused or exacerbated by the presence of α-synuclein immunopositive neuronal inclusions. Therefore, strategies aimed at reducing α-synuclein-induced early neuronal dystrophy may slow or halt the progression to overt nigrostriatal neurodegeneration. Thus, this study sought to determine if adeno-associated virus (AAV) mediated overexpression of two molecular chaperone heat shock proteins, namely Hsp27 or Hsp70, in the AAV-α-synuclein viral gene transfer rat model of Parkinson's disease could prevent α-synuclein-induced early neuronal pathology.

METHODS

Male Sprague-Dawley rats were intranigrally coinjected with pathogenic (AAV-α-synuclein) and putative therapeutic (AAV-Hsp27 or AAV-Hsp70) viral vectors and were sacrificed 18 weeks postviral injection.

RESULTS

Intranigral injection of AAV-α-synuclein resulted in significant α-synuclein accumulation in the substantia nigra and striatal terminals which led to significant dystrophy of nigrostriatal dopaminergic neurons without overt nigrostriatal neurodegeneration. Coinjection of AAV-Hsp70, but not AAV-Hsp27, significantly reduced AAV-α-synuclein-induced neuronal dystrophy.

CONCLUSIONS

These data confirm that overexpression of Hsp70 holds significant potential as a disease-modulating therapeutic approach for Parkinson's disease, with protective effects against early-onset α-synuclein-induced pathology demonstrated in the AAV-α-synuclein model.

RING finger protein 11 (RNF11) modulates susceptibility to 6-OHDA-induced nigral degeneration and behavioral deficits through NF-κB signaling in dopaminergic cells

Chronic activation of the NF-κB pathway is associated with progressive neurodegeneration in Parkinson's disease (PD). Given the role of neuronal RING finger protein 11 (RNF11) as a negative regulator of the NF-κB pathway, in this report we investigated the function of RNF11 in dopaminergic cells in PD-associated neurodegeneration. We found that RNF11 knockdown in an in vitro model of PD mediated protection against 6-OHDA-induced toxicity. In converse, over-expression of RNF11 enhanced 6-OHDA-induced dopaminergic cell death. Furthermore, by directly manipulating NF-κB signaling, we showed that the observed RNF11-enhanced 6-OHDA toxicity is mediated through inhibition of NF-κB-dependent transcription of TNF-α, antioxidants GSS and SOD1, and anti-apoptotic factor BCL2. Experiments in an in vivo 6-OHDA rat model of PD recapitulated the in vitro results. In vivo targeted RNF11 over-expression in nigral neurons enhanced 6-OHDA toxicity, as evident by increased amphetamine-induced rotations and loss of nigral dopaminergic neurons as compared to controls. This enhanced toxicity was coupled with the downregulation of NF-κB transcribed GSS, SOD1, BCL2, and neurotrophic factor BDNF mRNA levels, in addition to decreased TNF-α mRNA levels in ventral mesenchephalon samples. In converse, knockdown of RNF11 was associated with protective phenotypes and increased expression of above-mentioned NF-κB transcribed genes. Collectively, our in vitro and in vivo data suggest that RNF11-mediated inhibition of NF-κB in dopaminergic cells exaggerates 6-OHDA toxicity by inhibiting neuroprotective responses while loss of RNF11 inhibition on NF-κB activity promotes neuronal survival. The decreased expression of RNF11 in surviving cortical and nigral tissue detected in PD patients, thus implies a compensatory response in the diseased brain to PD-associated insults. In summary, our findings demonstrate that RNF11 in neurons can modulate susceptibility to 6-OHDA toxicity through NF-κB mediated responses. This neuron-specific role of RNF11 in the brain has important implications for targeted therapeutics aimed at preventing neurodegeneration.

Further characterisation of the LPS model of Parkinson's disease: a comparison of intra-nigral and intra-striatal lipopolysaccharide administration on motor function, microgliosis and nigrostriatal neurodegeneration in the rat

Chronic neuroinflammation has been established as one of the many processes involved in the pathogenesis of Parkinson's disease (PD). Because of this, researchers have attempted to replicate this pathogenic feature in animal models using the potent inflammagen, lipopolysaccharide (LPS), in order to gain better understanding of immune-mediated events in PD. However, although the effect of intra-cerebral LPS on neuroinflammation and neurodegeneration has been relatively well characterised, its impact on motor function has been less well studied. Therefore, the aim of this study was to further characterise the neuropathological and behavioural impact of intra-nigral and intra-striatal administration of LPS. To do, LPS (10 μg) or vehicle (sterile saline) were stereotaxically injected into the adult rat substantia nigra or striatum on one side only. The effect of LPS administration on lateralised motor function was assessed using the Corridor, Stepping and Whisker tests for two weeks post-injection, after which, amphetamine-induced rotational asymmetry was completed. Post-mortem, the impact of LPS on nigrostriatal degeneration and microgliosis was assessed using quantitative tyrosine hydroxylase and OX-42 immunohistochemistry respectively. We found that intra-nigral administration of LPS led to localised microgliosis in the substantia nigra and this was accompanied by nigrostriatal neurodegeneration and stable spontaneous motor deficits. In contrast, intra-striatal administration of LPS led to localised microgliosis in the striatum but this did not lead to any nigrostriatal neurodegeneration and only induced transient motor dysfunction. In conclusion, this study reveals the impact of intra-cerebral LPS administration on PD-related neuropathology and motor function, and it indicates that the intra-nigral model may be a highly relevant model as it is associated with stable motor decline underpinned by nigral microgliosis and nigrostriatal neurodegeneration.

The neurotoxicity of gene vectors and its amelioration by packaging with collagen hollow spheres

Over the last twenty years there have been several reports on the use of nonviral vectors to facilitate gene transfer in the mammalian brain. Whilst a large emphasis has been placed on vector transfection efficiency, the study of the adverse effects upon the brain, caused by the vectors themselves, remains completely overshadowed. To this end, a study was undertaken to study the tissue response to three commercially available transfection agents in the brain of adult Sprague Dawley rats. The response to these transfection agents was compared to adeno-associated viral vector (AAV), PBS and naked DNA. Furthermore, the use of a collagen hollow sphere (CHS) sustained delivery system was analysed for its ability to reduce striatal toxicity of the most predominantly studied polymer vector, polyethyleneimine (PEI). The size of the gross tissue loss at the injection site was analysed after immunohistochemical staining and was used as an indication of acute toxicity. Polymeric vectors showed similar levels of acute brain toxicity as seen with AAV, and CHS were able to significantly reduce the toxicity of the PEI vector. In addition; the host response to the vectors was measured in terms of reactive astrocytes and microglial cell recruitment. To understand whether this gross tissue loss was caused by the direct toxicity of the vectors themselves an in vitro study on primary astrocytes was conducted. All vectors reduced the viability of the cells which is brought about by direct necrosis and apoptosis. The CHS delivery system reduced cell necrosis in the early stages of post administration. In conclusion, whilst polymeric gene vectors cause acute necrosis, administration in the brain causes adverse effects no worse than that of an AAV vector. Furthermore, packaging the PEI vector with CHS reduces surface charge and direct toxicity without elevating the host response.

Deguelin, a novel anti-tumorigenic agent targeting apoptosis, cell cycle arrest and anti-angiogenesis for cancer chemoprevention

Deguelin is a natural compound of the flavonoid family products isolated from Derris trifoliata Lour. or Mundulea sericea (Leguminosae). It exhibited significant anti-tumorigenesis and anti-proliferative activity in various types of cancer both in vitro and in vivo. Deguelin induced cell apoptosis by blocking anti-apoptotic pathways, such as PI3K-Akt, IKK-IκBα-NF-κB and AMPK-mTOR-survivin, while inhibiting tumor cell propagation and malignant transformation through p27-cyclinE-pRb-E2F1 cell cycle control and HIF-1α-VEGF anti-angiogenic pathways. In pre-clinical trials, deguelin markedly decreased the tumor incidence. These biological findings identified deguelin as a novel anti-tumorigenic agent targeting apoptosis, cell cycle arrest and anti-angiogenesis for cancer chemoprevention and chemotherapy.

Animal models of Parkinson's disease: limits and relevance to neuroprotection studies

Over the last two decades, significant strides has been made toward acquiring a better knowledge of both the etiology and pathogenesis of Parkinson's disease (PD). Experimental models are of paramount importance to obtain greater insights into the pathogenesis of the disease. Thus far, neurotoxin-based animal models have been the most popular tools employed to produce selective neuronal death in both in vitro and in vivo systems. These models have been commonly referred to as the pathogenic models. The current trend in modeling PD revolves around what can be called the disease gene-based models or etiologic models. The value of utilizing multiple models with a different mechanism of insult rests on the premise that dopamine-producing neurons die by stereotyped cascades that can be activated by a range of insults, from neurotoxins to downregulation and overexpression of disease-related genes. In this position article, we present the relevance of both pathogenic and etiologic models as well as the concept of clinically relevant designs that, we argue, should be utilized in the preclinical development phase of new neuroprotective therapies before embarking into clinical trials.