Effect of 6-hydroxydopamine (6-OHDA) on proliferation of glial cells in the rat cortex and striatum: evidence for de-differentiation of resident astrocytes

GPR40 agonist ameliorates neurodegeneration and motor impairment by regulating NLRP3 inflammasome in Parkinson's disease animal models

Parkinson's disease (PD) is characterized by the progressive degeneration of dopaminergic neurons in the substantia nigra (SN) and accumulation of intracellular α-synuclein (ɑ-syn) aggregates known as Lewy bodies and Lewy neurites. Levels of polyunsaturated fatty acids (PUFAs) have previously been shown to be reduced in the SN of PD patients. G protein-coupled receptor 40 (GPR40) serves as a receptor for PUFAs, playing a role in neurodevelopment and neurogenesis. Additionally, GPR40 has been implicated in several neuropathological conditions, such as apoptosis and inflammation, suggesting its potential as a therapeutic target in PD. In this study, we investigated the neuroprotective effects of the GPR40 agonist, TUG469 in PD models. Our results demonstrated that TUG469 reduces the neurotoxicity induced by 6-OHDA in SH-SY5Y cells. In 6-OHDA-induced PD model mice, TUG469 treatment improved motor impairment, preserved dopaminergic fibers and cell bodies in the striatum (ST) or SN, and attenuated 6-OHDA-induced microgliosis and astrogliosis in the brain. Furthermore, in a PD model involving the injection of mouse ɑ-syn fibrils into the brain (mPFFs-PD model), TUG469 treatment reduced the levels of pSer129 ɑ-syn, and decreased microgliosis and astrogliosis. Our investigation also revealed that TUG469 modulates inflammasome activation, apoptosis, and autophagy in the 6-OHDA-PD model, as evidenced by the results of RNA-seq and western blotting analyses. In summary, our findings highlight the neuroprotective effects of GPR40 agonists on dopaminergic neurons and their potential as therapeutic agents for PD. These results underscore the importance of targeting GPR40 in PD treatment, particularly in mitigating neuroinflammation and preserving neuronal integrity.

Increased expression of Nav1.6 of reactive astrocytes in the globus pallidus is closely associated with motor deficits in a model of Parkinson's disease

Parkinson's disease (PD) is a common neurodegenerative disease in elderly people, which is characterized by motor disabilities in PD patients. Nav1.6 is the most abundant subtype of voltage-gated sodium channels (VGSCs) in the brain of adult mammals and rodents. Here we investigated the role of Nav1.6 in the external globus pallidus (GP) involved in the pathogenesis of motor deficits in unilateral 6-OHDA(6-hydroxydopamine)lesioned rats. The results show that Nav1.6 is dramatically increased in reactive astrocytes of the ipsilateral GP in the middle stage, but not different from the control rats in the later stage of the pathological process in 6-OHDA lesioned rats. Furthermore, the down-regulation of Nav1.6 expression in the ipsilateral GP can significantly improve motor deficits in 6-OHDA lesioned rats in the middle stage of the pathological process. The electrophysiological experiments show that the down-regulation of Nav1.6 expression in the ipsilateral GP significantly decreases the abnormal high synchronization between the ipsilateral M1 (the primary motor cortex) and GP in 6-OHDA lesioned rats. Ca2+ imaging reveals that the down-regulation of Nav1.6 expression reduces the intracellular concentration of Ca2+ ([Ca2+ ]i) in primary cultured astrocytes. These findings suggest that the increased Nav1.6 expression of reactive astrocytes in the GP play an important role in the pathogenesis of motor dysfunction in the middle stage in 6-OHDA lesioned rats, which may participate in astrocyte-neuron communication by regulating [Ca2+ ]i of astrocytes, thereby contributing to the formation of abnormal electrical signals of the basal ganglia (BG) in 6-OHDA lesioned rats.

Pathological α-synuclein accumulation, CSF metabolites changes and brain microstructures in cynomolgus monkeys treated with 6-hydroxydopamine

The lack of evidence indicating the accumulation of phosphorylated α-synuclein (P-α-syn), a neuropathological hallmark of Parkinson disease (PD), limits the application of 6-OHDA animal models. In cynomolgus monkeys received unilateral 6-hydroxydopamine (6-OHDA) injection, we identified nigrostriatal dysfunction related behavioral defects, such as the increase of PD score, decrease of locomotor activities, and exhibition of typical rotations. We found the dopaminergic neurons were significantly reduced and had fragmented morphology in substantia nigra (SN). Furthermore, insoluble P-α-syn aggregates were observed. The P-α-syn aggregates were extracellular distributed and had typical morphology of inclusion. Immunofluorescence staining showed that the P-α-syn colocalized with ubiquitin (Ub) and p62. We also found there were more actived astrocytes and microglial in SN and striatum, reflecting neuroinflammations increase in nigrostriatal pathway. At last, to determine the long-term consequence of dopamine (DA) neuron loss induced by 6-OHDA injection, the changes of cerebrospinal fluid (CSF) neurotransmitters over time as well as the brain microstructure alternations were examined. The dopamine-related metabolites were decreased after 6-OHDA injection reflecting dopaminergic neuron loss. The levels of γ-aminobutyric acid (GABA) and acetylcholine (Ach) showed an increasing trend but not significant. By diffusion tensor Magnetic Resonance Imaging (MRI) image scans, the fractional anisotropy (FA) value in the ipsilateral SN and caudate was found to reduce, which indicated neural fiber injury. Therefore, these results suggested that α-syn pathology might participate in process of 6-OHDA injuring DA neurons, and may expand the application of 6-OHDA monkeys on investigations into the pathogenesis of PD.

Re-routing Metabolism by the Mitochondrial Pyruvate Carrier Inhibitor MSDC-0160 Attenuates Neurodegeneration in a Rat Model of Parkinson's Disease

A growing body of evidence supports the idea that mitochondrial dysfunction might represent a key feature of Parkinson's disease (PD). Central regulators of energy production, mitochondria, are also involved in several other essential functions such as cell death pathways and neuroinflammation which make them a potential therapeutic target for PD management. Interestingly, recent studies related to PD have reported a neuroprotective effect of targeting mitochondrial pyruvate carrier (MPC) by the insulin sensitizer MSDC-0160. As the sole point of entry of pyruvate into the mitochondrial matrix, MPC plays a crucial role in energetic metabolism which is impacted in PD. This study therefore aimed at providing insights into the mechanisms underlying the neuroprotective effect of MSDC-0160. We investigated behavioral, cellular, and metabolic impact of chronic MSDC-0160 treatment in unilateral 6-OHDA PD rats. We evaluated mitochondrially related processes through the expression of pivotal mitochondrial enzymes in dorsal striatal biopsies and the level of metabolites in serum samples using nuclear magnetic resonance spectroscopy (NMR)-based metabolomics. MSDC-0160 treatment in unilateral 6-OHDA rats improved motor behavior, decreased dopaminergic denervation, and reduced mTOR activity and neuroinflammation. Concomitantly, MSDC-0160 administration strongly modified energy metabolism as revealed by increased ketogenesis, beta oxidation, and glutamate oxidation to satisfy energy needs and maintain energy homeostasis. MSDC-0160 exerts its neuroprotective effect through reorganization of multiple pathways connected to energy metabolism.

Re-routing Metabolism by the Mitochondrial Pyruvate Carrier Inhibitor MSDC-0160 Attenuates Neurodegeneration in a Rat Model of Parkinson's Disease

A growing body of evidence supports the idea that mitochondrial dysfunction might represent a key feature of Parkinson's disease (PD). Central regulators of energy production, mitochondria, are also involved in several other essential functions such as cell death pathways and neuroinflammation which make them a potential therapeutic target for PD management. Interestingly, recent studies related to PD have reported a neuroprotective effect of targeting mitochondrial pyruvate carrier (MPC) by the insulin sensitizer MSDC-0160. As the sole point of entry of pyruvate into the mitochondrial matrix, MPC plays a crucial role in energetic metabolism which is impacted in PD. This study therefore aimed at providing insights into the mechanisms underlying the neuroprotective effect of MSDC-0160. We investigated behavioral, cellular, and metabolic impact of chronic MSDC-0160 treatment in unilateral 6-OHDA PD rats. We evaluated mitochondrially related processes through the expression of pivotal mitochondrial enzymes in dorsal striatal biopsies and the level of metabolites in serum samples using nuclear magnetic resonance spectroscopy (NMR)-based metabolomics. MSDC-0160 treatment in unilateral 6-OHDA rats improved motor behavior, decreased dopaminergic denervation, and reduced mTOR activity and neuroinflammation. Concomitantly, MSDC-0160 administration strongly modified energy metabolism as revealed by increased ketogenesis, beta oxidation, and glutamate oxidation to satisfy energy needs and maintain energy homeostasis. MSDC-0160 exerts its neuroprotective effect through reorganization of multiple pathways connected to energy metabolism.

Insights Into the Role of Platelet-Derived Growth Factors: Implications for Parkinson’s Disease Pathogenesis and Treatment

Parkinson’s disease (PD), the second most common neurodegenerative disease after Alzheimer’s disease, commonly occurs in the elderly population, causing a significant medical and economic burden to the aging society worldwide. At present, there are few effective methods that achieve satisfactory clinical results in the treatment of PD. Platelet-derived growth factors (PDGFs) and platelet-derived growth factor receptors (PDGFRs) are important neurotrophic factors that are expressed in various cell types. Their unique structures allow for specific binding that can effectively regulate vital functions in the nervous system. In this review, we summarized the possible mechanisms by which PDGFs/PDGFRs regulate the occurrence and development of PD by affecting oxidative stress, mitochondrial function, protein folding and aggregation, Ca2+ homeostasis, and cell neuroinflammation. These modes of action mainly depend on the type and distribution of PDGFs in different nerve cells. We also summarized the possible clinical applications and prospects for PDGF in the treatment of PD, especially in genetic treatment. Recent advances have shown that PDGFs have contradictory roles within the central nervous system (CNS). Although they exert neuroprotective effects through multiple pathways, they are also associated with the disruption of the blood–brain barrier (BBB). Our recommendations based on our findings include further investigation of the contradictory neurotrophic and neurotoxic effects of the PDGFs acting on the CNS.

Physical exercise influences astrocytes in the striatum of a Parkinson's disease male mouse model

Physical exercise is considered an adjuvant treatment to Parkinson's disease (PD) patients, possibly reducing inflammatory responses in the brain. Studies have stated that physical exercise protects dopaminergic neurons in PD models produced by neurotoxins. However, few studies focused on immunohistochemically reacted astrocytes and morphometric analyses of these cells in a PD mouse model submitted to physical exercise. We investigated the effects of treadmill training on striatal astrocytes of a PD mouse model combining immunohistochemistry and western-blotting for glial fibrillary acidic protein (GFAP) with morphometric analyses. Male Swiss mice were divided into 4 groups: sedentary control (SEDCONT), exercise control (EXERCONT), sedentary Parkinson (SEDPD), and exercise Parkinson (EXERPD). Stereotaxic bilateral injections of 6-hydroxydopamine into the striatum were adopted for PD groups. Striatal astrocytes showed increased GFAP in EXERPD, and we observed a higher level of GFAP in EXERPD than SEDPD. The number of primary and secondary processes was similar in striatal astrocytes of control groups and EXERPD. The astrocyte primary processes of SEDPD were larger than those of EXERPD, EXERCONT and SEDCONT. Cell body diameters and areas showed no difference between groups. We concluded that physical exercise influences striatal astrocytes in exercised parkinsonian mice.

Regulation of Actg1 and Gsta2 is possible mechanism by which capsaicin alleviates apoptosis in cell model of 6-OHDA-induced Parkinson's disease

The present study aimed to identify the gene expression changes conferred by capsaicin in the cell model of 6-OHDA-induced Parkinson's disease, to disclose the molecular mechanism of action of capsaicin. We used capsaicin-treated and paraffin-embedded wax blocks containing substantia nigra tissue from 6-OHDA-induced Parkinson's disease rats to analyze transcriptional changes using Affymetrix GeneChip Whole Transcript Expression Arrays. A total of 108 genes were differentially expressed in response to capsaicin treatment, and seven of these genes were selected for further analysis: Olr724, COX1, Gsta2, Rab5a, Potef, Actg1, and Acadsb, of which Actg1 (actin gamma 1) was down-regulated and Gsta2 (Glutathione S-transferase alpha 2) was up-regulated. We successfully overexpressed Actg1 and Gsta2 in vitro. CCK-8 detection and flow cytometry demonstrated that overexpression of Actg1 and Gsta2 increased apoptosis in the 6-OHDA-induced Parkinson's disease cell model. The imbalance between Actg1 and Gsta2 may be one of the mechanisms of cell damage in Parkinson's disease (PD). Capsaicin can protect the cells and reduce the apoptosis rate by regulating Actg1 and Gsta2.

Activation of Nrf2 signaling by Icariin protects against 6-OHDA-induced neurotoxicity

Nerve damage is the main pathogenesis of neurodegenerative diseases. Recently, in search for a promising therapeutic target that could stop neurodegenerative diseases progression, the antioxidant signaling pathway regulated by transcription factor nuclear factor erythroid 2-related factor 2 (Nrf2) has attracted new hopes. Icariin (ICA) exhibited a battery of pharmacological properties, including antioxidation, anti-aging, and anti-inflammation activities. Recent studies indicate ICA conferred neuroprotection against brain ischemic injury and neurodegenerative diseases. However, the mechanisms underlying ICA-mediated neuroprotection remain unelucidated. This study aimed at analyzing whether ICA evoked neuroprotection against 6-hydroxydopamine (6-OHDA)-induced neurotoxicity in PC12 cells and the mechanisms of action. ICA protected against 6-OHDA-induced neuronal damage, accompanied by the inhibition of cell apoptosis through the marked decreases in the Bax/Bcl-2 ratio, cytochrome c release, and caspase-3 cleavage. In addition, the activation of Nrf2 signaling pathway was responsible for ICA-mediated neuroprotection. First, ICA relieved reactive oxygen species accumulation and increased superoxide dismutase generation via the activation of Nrf2 signaling. Second, Nrf2 knockdown by siRNA reversed ICA-mediated neuroprotection. Together, these results suggested ICA-mediated neuroprotection might be attributable to the activation of Nrf2 pathway via antioxidative signaling pathways.

Time dependent degeneration of the nigrostriatal tract in mice with 6-OHDA lesioned medial forebrain bundle and the effect of activin A on L-Dopa induced dyskinesia

Background

Accurately assessing promising therapeutic interventions for human diseases depends, in part, on the reproducibility of preclinical disease models. With the development of transgenic mice, the rapid adaptation of a 6-OHDA mouse model of Parkinson’s disease that was originally described for the use in rats has come with a lack of a comprehensive characterization of lesion progression. In this study we therefore first characterised the time course of neurodegeneration in the substantia nigra pars compacta and striatum over a 4 week period following 6-OHDA injection into the medial forebrain bundle of mice. We then utilised the model to assess the anti-dyskinetic efficacy of recombinant activin A, a putative neuroprotectant and anti-inflammatory that is endogenously upregulated during the course of Parkinson’s disease.

Results

We found that degeneration of fibers in the striatum was fully established within 1 week following 6-OHDA administration, but that the loss of neurons continued to progress over time, becoming fully established 3 weeks after the 6-OHDA injection. In assessing the anti-dyskinetic efficacy of activin A using this model we found that treatment with activin A did not significantly reduce the severity, or delay the time-of-onset, of dyskinesia.

Conclusion

First, the current study concludes that a 3 week duration is required to establish a complete lesion of the nigrostriatal tract following 6-OHDA injection into the medial forebrain bundle of mice. Second, we found that activin A was not anti-dyskinetic in this model.

Electronic supplementary material

The online version of this article (10.1186/s12868-019-0487-7) contains supplementary material, which is available to authorized users.

Antioxidant and Anti-Apoptotic Activity of Octadecaneuropeptide Against 6-OHDA Toxicity in Cultured Rat Astrocytes

Oxidative stress, associated with various neurodegenerative diseases, promotes ROS generation, impairs cellular antioxidant defenses, and finally, triggers both neurons and astroglial cell death by apoptosis. Astrocytes specifically synthesize and release endozepines, a family of regulatory peptides, including the octadecaneuropeptide (ODN). We have previously reported that ODN acts as a potent neuroprotective agent that prevents 6-OHDA-induced apoptotic neuronal death. The purpose of the present study was to investigate the potential glioprotective effect of ODN on 6-OHDA-induced oxidative stress and cell death in cultured rat astrocytes. Incubation of astrocytes with graded concentrations of ODN (10^-14 to 10^-8 M) inhibited 6-OHDA-evoked cell death in a concentration- and time-dependent manner. In addition, ODN prevented the decrease of mitochondrial activity and caspase-3 activation induced by 6-OHDA. 6-OHDA-treated cells also exhibited enhanced levels of ROS associated with a generation of H₂O₂ and O₂^°-, and a reduction of both superoxide dismutase (SOD) and catalase (CAT) activities. Co-treatment of astrocytes with low concentrations of ODN dose-dependently blocked 6-OHDA-evoked production of ROS and inhibition of antioxidant enzyme activities. Concomitantly, ODN stimulated Mn-SOD, CAT, glutathione peroxidase-1, and sulfiredoxin-1 gene transcription and rescued 6-OHDA-associated reduced expression of endogenous antioxidant enzymes. Taken together, these data indicate that, in rat astrocytes, ODN exerts anti-apoptotic and anti-oxidative activities, and hence prevents 6-OHDA-induced oxidative assault and cell death. ODN is thus a potential candidate to delay neuronal damages in various pathological conditions involving oxidative neurodegeneration.

Astrocyte-Like Cells Differentiated from Dental Pulp Stem Cells Protect Dopaminergic Neurons Against 6-Hydroxydopamine Toxicity

Dental pulp stem cells (DPSCs) are promising for use in neurodegenerative-diseases because of their neural crest origin. While neuronal differentiation of DPSCs has been shown, their plasticity towards astrocyte-like cells remains to be studied. We aimed to examine differentiation potential of DPSCs to astrocytes and their consequent neuroprotective role towards dopaminergic (DA) neurons under 6-hydroxydopamine (6-OHDA) toxicity. Induction of DPSCs to astrocytes with differentiation factors showed definitive increase in astrocyte-specific markers glial fibrillary acidic protein (GFAP), and excitatory amino acid transporter 2 along with glial calcium-binding protein S100β through FACS and immunofluorescence assays. RT-PCR and ELISA showed significant increase in BDNF and GDNF expression and secretion in astrocyte-differentiated DPSCs over naïve DPSCs. Neuroprotective role of these cells on DA neurons under 6-OHDA stress was evaluated by both contact and non-contact methods. FACS analysis of PKH26-stained SH-SY5Y homogenous cells in contact method and of TH immunopositive cells in primary midbrain culture in non-contact method both indicated higher survival of DA neurons in astrocyte-differentiated DPSCs over naïve DPSCs. Recovery of β-tubulin III and TH immunopositive cells was reduced in the presence of TrkB inhibitor, suggesting a key neuroprotective role of BDNF secretion by DPSCs. When nitric oxide (NO) release was inhibited by L-NAME in primary midbrain culture, BDNF release in co-culture under 6-OHDA stress reduced further in naïve DPSCs than in astrocyte-differentiated DPSCs, suggesting that BDNF release in naïve DPSCs is primarily regulated by paracrine signaling while for differentiated DPSCs, it is equally through autocrine and paracrine signaling with NO being the mediator. In conclusion, we suggest that DPSCs exposed to glial commitment cues exhibit substantial differentiation towards astrocyte-like cells with better neuroprotective activity against 6-OHDA toxicity than naïve DPSCs.

Growth Factors and Neuroglobin in Astrocyte Protection Against Neurodegeneration and Oxidative Stress

Neurodegenerative diseases, such as Parkinson and Alzheimer, are among the main public health issues in the world due to their effects on life quality and high mortality rates. Although neuronal death is the main cause of disruption in the central nervous system (CNS) elicited by these pathologies, other cells such as astrocytes are also affected. There is no treatment for preventing the cellular death during neurodegenerative processes, and current drug therapy is focused on decreasing the associated motor symptoms. For these reasons, it has been necessary to seek new therapeutical procedures, including the use of growth factors to reduce α-synuclein toxicity and misfolding in order to recover neuronal cells and astrocytes. Additionally, it has been shown that some growth factors are able to reduce the overproduction of reactive oxygen species (ROS), which are associated with neuronal death through activation of antioxidative enzymes such as catalase, superoxide dismutase, glutathione peroxidase, and neuroglobin. In the present review, we discuss the use of growth factors such as PDGF-BB, VEGF, BDNF, and the antioxidative enzyme neuroglobin in the protection of astrocytes and neurons during the development of neurodegenerative diseases.

Capsaicin Protects Against Oxidative Insults and Alleviates Behavioral Deficits in Rats with 6-OHDA-Induced Parkinson's Disease via Activation of TRPV1

Increasing evidence suggests that capsaicin may play a role in modulating neuronal function and controlling motor behavior. However, the underlying mechanism is still unclear and the activation of transient receptor potential vanilloid 1 (TRPV1) might be involved in. This study investigated the potential neuroprotective role of capsaicin in a rat model of 6-hydroxydopamine (6-OHDA)-induced Parkinson's disease (PD). Capsaicin was treated intraperitoneally for the 6-OHDA induced PD rats and the locomotor activity and abnormal involuntary movements were found alleviated. Besides, brain oxidative stress (lipid peroxidation, superoxide dismutase and catalase) was also assessed, and oxidative insults were investigated relieved. Both the expression of tyrosine hydroxylase and TRPV1 were increased in the striatal and substantia nigra areas of 6-OHDA induced rats after the treatment of capsaicin by the semi-quantitative analysis of Western Blot. And the immunostaining of substantia nigra further suggested that capsaicin might protect against dopaminergic neuronal loss. Our results showed that TRPV1 might be a novel therapeutic target for PD.

An investigation of gene expression in single cells derived from Nestin-expressing cells in the adult mouse midbrain in vivo

Generation of new dopamine (DA) neurons in the adult midbrain is a controversial issue in development of better treatments for Parkinson's disease (PD). Previous research suggests Nestin-expressing neural precursor cells (NPCs) have a propensity to differentiate into neurons here, including DA neurons. In the present study we sought confirmation of this by studying gene expression in single Nestin-expressing cells and their progeny/ontogeny within the adult mouse midbrain. Cells were identified by administering a pulse of Tamoxifen to adult Nestin-CreER^T2×R26eYFP transgenic mice. Samples of cytoplasm were harvested 4 days to 8 months later from individual eYFP+ cells in acutely prepared midbrain slices and analysed by RT-qPCR for gene expression. Remarkably, most eYFP+ cells co-expressed genes associated with mature (including DA) neurons (i.e. NeuN, Gad1, Gad2, vGlut2, TH and/or D2R) and neurogenesis (i.e. Ki67, Dcx, Ncam, Pax6, Ngn2 and/or Msx1), and this was true at all time-points following Tamoxifen. Indeed, cell proliferation genes (Nestin, Ki67) were exclusively expressed by eYFP+ cells with mature neuronal morphology and gene expression, and only at early time-points after Tamoxifen. Expression of proneuronal genes (Pax6, Msx1, Ngn2) was, however, higher in eYFP+ cells with immature morphology compared with mature morphology. Gene expression bore no relationship to cell location indicating that, in contrast to development, Nestin-expressing cells arise throughout the midbrain parenchyma and do not migrate long distances. On the other hand, gene expression did change with time after Tamoxifen, although not in a way consistent with neurogenesis. Overall, our results suggest that Nestin expression in the adult midbrain occurs in mature neurons, casting doubt on the premise of neurogenesis from Nestin+ NPCs here.

Activin A Inhibits MPTP and LPS-Induced Increases in Inflammatory Cell Populations and Loss of Dopamine Neurons in the Mouse Midbrain In Vivo

Parkinson’s disease is a chronic neurodegenerative disease characterized by a significant loss of dopaminergic neurons within the substantia nigra pars compacta region and a subsequent loss of dopamine within the striatum. A promising avenue of research has been the administration of growth factors to promote the survival of remaining midbrain neurons, although the mechanism by which they provide neuroprotection is not understood. Activin A, a member of the transforming growth factor β superfamily, has been shown to be a potent anti-inflammatory following acute brain injury and has been demonstrated to play a role in the neuroprotection of midbrain neurons against MPP⁺-induced degeneration in vitro. We hypothesized that activin A may offer similar anti-inflammatory and neuroprotective effects in in vivo mouse models of Parkinson’s disease. We found that activin A significantly attenuated the inflammatory response induced by both MPTP and intranigral administration of lipopolysaccharide in C57BL/6 mice. We found that administration of activin A promoted survival of dopaminergic and total neuron populations in the pars compacta region both 8 days and 8 weeks after MPTP-induced degeneration. Surprisingly, no corresponding protection of striatal dopamine levels was found. Furthermore, activin A failed to protect against loss of striatal dopamine transporter expression in the striatum, suggesting the neuroprotective action of activin A may be localized to the substantia nigra. Together, these results provide the first evidence that activin A exerts potent neuroprotection and anti-inflammatory effects in the MPTP and lipopolysaccharide mouse models of Parkinson’s disease.

6-hydroxydopamine-induced Parkinson's disease-like degeneration generates acute microgliosis and astrogliosis in the nigrostriatal system but no bioluminescence imaging-detectable alteration in adult neurogenesis

Parkinson's disease is a slowly progressing neurodegenerative disorder caused by loss of dopaminergic neurons in the substantia nigra (SN), leading to severe impairment in motor and non-motor functions. Endogenous subventricular zone (SVZ) neural stem cells constantly give birth to new cells that might serve as a possible source for regeneration in the adult brain. However, neurodegeneration is accompanied by neuroinflammation and dopamine depletion, potentially compromising regeneration. We therefore employed in vivo imaging methods to study striatal deafferentation (N-ω-fluoropropyl-2β-carbomethoxy-3β-(4-[(123) I]iodophenyl)nortropane single photon emission computed tomography, DaTscan(™) ) and neuroinflammation in the SN and striatum (N,N-diethyl-2-(2-(4-(2-[(18) F]fluoroethoxy)phenyl)-5,7-dimethylpyrazolo[1,5-a]pyrimidin-3-yl)acetamide positron emission tomography, [(18) F]DPA-714 PET) in the intranigral 6-hydroxydopamine Parkinson's disease mouse model. Additionally, we transduced cells in the SVZ with a lentivirus encoding firefly luciferase and followed migration of progenitor cells in the SVZ-olfactory bulb axis via bioluminescence imaging under disease and control conditions. We found that activation of microglia in the SN is an acute process accompanying the degeneration of dopaminergic cell bodies in the SN. Dopaminergic deafferentation of the striatum does not influence the generation of doublecortin-positive neuroblasts in the SVZ, but generates chronic astrogliosis in the nigrostriatal system.

Involvement of BDNF/ERK signaling in spontaneous recovery from trimethyltin-induced hippocampal neurotoxicity in mice

Trimethyltin (TMT) toxicity causes histopathological damage in the hippocampus and induces seizure behaviors in mice. The lesions and symptoms recover spontaneously over time; however, little is known about the precise mechanisms underlying this recovery from TMT toxicity. We investigated changes in the brain-derived neurotrophic factor/extracellular signal-regulated kinases (BDNF/ERK) signaling pathways in the mouse hippocampus following TMT toxicity. Mice (7 weeks old, C57BL/6) administered TMT (2.6 mg/kg intraperitoneally) showed acute and severe neurodegeneration with increased TUNEL-positive cells in the dentate gyrus (DG) of the hippocampus. The mRNA and protein levels of BDNF in the hippocampus were elevated by TMT treatment. Immunohistochemical analysis showed that TMT treatment markedly increased phosphorylated ERK1/2 expression in the mouse hippocampus 1-4 days after TMT treatment, although the intensity of ERK immunoreactivity in mossy fiber decreased at 1-8 days post-treatment. In addition, ERK-immunopositive cells were localized predominantly in doublecortin-positive immature progenitor neurons in the DG. In primary cultured immature hippocampal neurons (4 days in vitro), BDNF treatment alleviated TMT-induced neurotoxicity, via activation of the ERK signaling pathway. Thus, we suggest that BDNF/ERK signaling pathways may be associated with cell differentiation and survival of immature progenitor neurons, and will eventually lead to spontaneous recovery in TMT-induced hippocampal neurodegeneration.

Transplantation of Human Neural Stem Cells in a Parkinsonian Model Exerts Neuroprotection via Regulation of the Host Microenvironment

Parkinson’s disease (PD) is characterized by a progressive loss of dopaminergic neurons and consequent dopamine (DA) deficit, and current treatment still remains a challenge. Although neural stem cells (NSCs) have been evaluated as appealing graft sources, mechanisms underlying the beneficial phenomena are not well understood. Here, we investigate whether human NSCs (hNSCs) transplantation could provide neuroprotection against DA depletion by recruiting endogenous cells to establish a favorable niche. Adult mice subjected to 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) were transplanted with hNSCs or vehicle into the striatum. Behavioral and histological analyses demonstrated significant neurorescue response observed in hNSCs-treated animals compared with the control mice. In transplanted animals, grafted cells survived, proliferated, and migrated within the astrocytic scaffold. Notably, more local astrocytes underwent de-differentiation, acquiring the properties of NSCs or neural precursor cells (NPCs) in mice given hNSCs. Additionally, we also detected significantly higher expression of host-derived growth factors in hNSCs-transplanted mice compared with the control animals, together with inhibition of local microglia and proinflammatory cytokines. Overall, our results indicate that hNSCs transplantation exerts neuroprotection in MPTP-insulted mice via regulating the host niche. Harnessing synergistic interaction between the grafts and host cells may help optimize cell-based therapies for PD.

The degeneration of dopaminergic synapses in Parkinson's disease: A selective animal model

Available evidence increasingly suggests that the degeneration of dopamine neurons in Parkinson's disease starts in the striatal axons and synaptic terminals. A selective procedure is described here to study the mechanisms involved in the striatal denervation of dopaminergic terminals. This procedure can also be used to analyze mechanisms involved in the dopaminergic re-innervation of the striatum, and the role of astrocytes and microglia in both processes. Adult Sprague-Dawley rats were injected in the lateral ventricles with increasing doses of 6-hydroxydopamine (12-50 μg), which generated a dose-dependent loss of dopaminergic synapses and axons in the striatum, followed by an axonal sprouting (weeks later) and by a progressive recovery of striatal dopaminergic synapses (months later). Both the degeneration and regeneration of the dopaminergic terminals were accompanied by astrogliosis. Because the experimental manipulations did not induce unspecific damage in the striatal tissue, this method could be particularly suitable to study the basic mechanisms involved in the distal degeneration and regeneration of dopaminergic nigrostriatal neurons, and the possible role of astrocytes and microglia in the dynamics of both processes.

Neuroinflammation in Parkinson's disease animal models: a cell stress response or a step in neurodegeneration?

The motor symptoms of Parkinson's disease are due to the progressive degeneration of dopaminergic neurons in the substantia nigra. Multiple neuroinflammatory processes are exacerbated in Parkinson's disease, including glial-mediated reactions, increased expression of proinflammatory substances, and lymphocytic infiltration, particularly in the substantia nigra. Neuroinflammation is also implicated in the neurodegeneration and consequent behavioral symptoms of many Parkinson's disease animal models, although it is not clear whether these features emulate pathogenic steps in the genuine disorder or if some inflammatory features provide protective stress responses. Here, we compare and summarize findings on neuroinflammatory responses and effects on behavior in a wide range of toxin-based, inflammatory and genetic Parkinson's disease animal models.

Decreased anti-regenerative effects after spinal cord injury in spry4-/- mice

Previously, we have demonstrated a role for fibroblast growth factor (Fgf) in spinal cord regeneration in both zebrafish and mouse. We have shown that exogenous Fgf2 treatment attenuates astrocytic gliosis and induces glia cells to become progenitors that undergo neurogenesis as well as differentiating into bipolar astrocytes that support axonal regeneration (Goldshmit et al., 2012, 2014). One of the downstream signaling target genes of Fgf is spry4, which acts as a feedback inhibitor for Fgf signaling. In this study we examined the effects of increased endogenous Fgf signaling, in spry4-/- mice, on the early events that occur after spinal cord injury (SCI). We demonstrate that in spry4-/- mice inflammatory responses, such as tumor necrosis factor α (TNFα) secretion and macrophage/neutrophil invasion into the lesion site are reduced. In addition, astrocytic gliosis is attenuated and neuronal survival is increased. These results further support a pro-regenerative role of Fgf after SCI, and suggest that increased endogenous Fgf signaling after SCI may contribute to functional recovery and therefore presents this pathway as a target for new therapy development.

Intrastriatal transplantation of adult human neural crest-derived stem cells improves functional outcome in parkinsonian rats

Parkinson's disease (PD) is considered the second most frequent and one of the most severe neurodegenerative diseases, with dysfunctions of the motor system and with nonmotor symptoms such as depression and dementia. Compensation for the progressive loss of dopaminergic (DA) neurons during PD using current pharmacological treatment strategies is limited and remains challenging. Pluripotent stem cell-based regenerative medicine may offer a promising therapeutic alternative, although the medical application of human embryonic tissue and pluripotent stem cells is still a matter of ethical and practical debate. Addressing these challenges, the present study investigated the potential of adult human neural crest-derived stem cells derived from the inferior turbinate (ITSCs) transplanted into a parkinsonian rat model. Emphasizing their capability to give rise to nervous tissue, ITSCs isolated from the adult human nose efficiently differentiated into functional mature neurons in vitro. Additional successful dopaminergic differentiation of ITSCs was subsequently followed by their transplantation into a unilaterally lesioned 6-hydroxydopamine rat PD model. Transplantation of predifferentiated or undifferentiated ITSCs led to robust restoration of rotational behavior, accompanied by significant recovery of DA neurons within the substantia nigra. ITSCs were further shown to migrate extensively in loose streams primarily toward the posterior direction as far as to the midbrain region, at which point they were able to differentiate into DA neurons within the locus ceruleus. We demonstrate, for the first time, that adult human ITSCs are capable of functionally recovering a PD rat model.

Nestin expression and glial response in the hippocampus of mice after trimethyltin treatment

Nestin is a protein of embryonic intermediate filaments expressed by multipotent neural stem cells. In the present study, the nestin expression pattern in the mouse hippocampus 1, 2, 3, 4, and 8 days after treatment with trimethyltin (TMT) was examined to explore the possible role played by nestin in chemically induced hippocampal injury. TMT treatment (2.5mg/kg, intraperitoneally) selectively injured the dentate gyrus (DG) of the mouse hippocampus. The level of hippocampal mRNA encoding nestin increased significantly 2 and 3 days post-treatment and thereafter decreased (at 4 and 8 days post-treatment). The level of nestin protein significantly increased 2 - 4 days post-treatment, particularly in the injured region of the DG, and predominantly in glial fibrillary acidic protein-positive astrocytes in the hippocampal DG. Ki67-positive proliferating cells were increased following TMT treatment and co-localized with nestin-positive reactive astrocytes. Thus, we suggest that nestin contributes to remodeling of the chemically injured DG via glial scar formation and the alteration of neurogenesis.

Intraventricular injection of 6-hydroxydopamine results in an increased number of tyrosine hydroxylase immune-positive cells in the rat cortex

Previously we have demonstrated that intraventricular injection of 6-hydroxydopamine (6-OHDA) results in increased proliferation and de-differentiation of rat cortical astrocytes into progenitor-like cells 4 days after lesion (Wachter et al., 2010). To find out if these cells express tyrosine hydroxylase (TH), the rate-limiting enzyme in the catecholamine synthesis pathway, we performed immunohistochemistry in the rat cortex following intraventricular injection of 6-OHDA. Four days after injection we demonstrated a strong emergence of TH-positive (TH(+)) somata in the cortices of 6-OHDA-lesioned animals. The number of TH(+) cells in the cortex of 6-OHDA-lesioned animals was 15 times higher than in sham-operated animals, where virtually no TH(+) somata occurred. Combining TH immunohistochemistry with classical Nissl stain yielded complete congruency, and ∼45% of the TH(+) cells co-expressed calretinin, which indicates an interneuron affiliation. There was no co-staining of TH with other interneuron markers or with glial markers such as glial fibrillary acidic protein (GFAP) or the neural stem/progenitor marker Nestin, nor could we find co-localization with the proliferation marker Ki67. However, we found a co-localization of TH with glial progenitor cell markers (Sox2 and S100β) and with polysialylated-neural cell adhesion molecule (PSA-NCAM), which has been shown to be expressed in immature, but not recently generated cortical neurons. Taken together, this study seems to confirm our previous findings with respect to a 6-OHDA-induced expression of neuronal precursor markers in cells of the rat cortex, although the TH(+) cells found in this study are not identical with the potentially de-differentiated astrocytes described recently (Wachter et al., 2010). The detection of cortical cells expressing the catecholaminergic key enzyme TH might indicate a possible compensatory role of these cells in a dopamine-(DA)-depleted system. Future studies are needed to determine whether the TH(+) cells are capable of DA synthesis to confirm this hypothesis.

Transgenic rat model of Huntington's disease: a histopathological study and correlations with neurodegenerative process in the brain of HD patients

Rats transgenic for Huntington's disease (tgHD51 CAG rats), surviving up to two years, represent an animal model of HD similar to the late-onset form of human disease. This enables us to follow histopathological changes in course of neurodegenerative process (NDP) within the striatum and compare them with postmortem samples of human HD brains. A basic difference between HD pathology in human and tgHD51 rats is in the rate of NDP progression that originates primarily from slow neuronal degeneration consequently resulting in lesser extent of concomitant reactive gliosis in the brain of tgHD51 rats. Although larger amount of striatal neurons displays only gradual decrease in their size, their number is significantly reduced in the oldest tgHD51 rats. Our quantitative analysis proved that the end of the first year represents the turn in the development of morphological changes related to the progression of NDP in tgHD51 rats. Our data also support the view that all types of CNS glial cells play an important, irreplaceable role in NDP. To the best of our knowledge, our findings are the first to document that tgHD51 CAG rats can be used as a valid animal model for detailed histopathological studies related to HD in human.

NDRG2 as a marker protein for brain astrocytes

The protein NDRG2 (N-myc downregulated gene 2) is expressed in astrocytes. We show here that NDRG2 is located in the cytosol of protoplasmic and fibrous astrocytes throughout the mammalian brain, including Bergmann glia as observed in mouse, rat, tree shrew, marmoset and human. NDRG2 immunoreactivity is detectable in the astrocytic cell bodies and excrescencies including fine distal processes. Glutamatergic and GABAergic nerve terminals are associated with NDRG2 immunopositive astrocytic processes. Müller glia in the retina displays no NDRG2 immunoreactivity. NDRG2 positive astrocytes are more abundant and more evenly distributed in the brain than GFAP (glial fibrillary acidic protein) immunoreactive cells. Some regions with very little GFAP such as the caudate nucleus show pronounced NDRG2 immunoreactivity. In white matter areas, NDRG2 is less strong than GFAP labeling. Most NDRG2 positive somata are immunoreactive for S100ß but not all S100ß cells express NDRG2. NDRG2 positive astrocytes do not express nestin and NG2 (chondroitin sulfate proteoglycan 4). The localization of NDRG2 overlaps only partially with that of aquaporin 4, the membrane-bound water channel that is concentrated in the astrocytic endfeet. Reactive astrocytes at a cortical lesion display very little NDRG2, which indicates that expression of the protein is reduced in reactive astrocytes. In conclusion, our data show that NDRG2 is a specific marker for a large population of mature, non-reactive brain astrocytes. Visualization of NDRG2 immunoreactive structures may serve as a reliable tool for quantitative studies on numbers of astrocytes in distinct brain regions and for high-resolution microscopy studies on distal astrocytic processes.

Advances in non-dopaminergic treatments for Parkinson's disease

Since the 1960's treatments for Parkinson's disease (PD) have traditionally been directed to restore or replace dopamine, with L-Dopa being the gold standard. However, chronic L-Dopa use is associated with debilitating dyskinesias, limiting its effectiveness. This has resulted in extensive efforts to develop new therapies that work in ways other than restoring or replacing dopamine. Here we describe newly emerging non-dopaminergic therapeutic strategies for PD, including drugs targeting adenosine, glutamate, adrenergic, and serotonin receptors, as well as GLP-1 agonists, calcium channel blockers, iron chelators, anti-inflammatories, neurotrophic factors, and gene therapies. We provide a detailed account of their success in animal models and their translation to human clinical trials. We then consider how advances in understanding the mechanisms of PD, genetics, the possibility that PD may consist of multiple disease states, understanding of the etiology of PD in non-dopaminergic regions as well as advances in clinical trial design will be essential for ongoing advances. We conclude that despite the challenges ahead, patients have much cause for optimism that novel therapeutics that offer better disease management and/or which slow disease progression are inevitable.

A spatiotemporal study of gliosis in relation to depth electrode tracks in drug-resistant epilepsy

Key questions remain regarding the processes governing gliogenesis following central nervous system injury that are critical to understanding both beneficial brain repair mechanisms and any long-term detrimental effects, including increased risk of seizures. We have used cortical injury produced by intracranial electrodes (ICEs) to study the time-course and localization of gliosis and gliogenesis in surgically resected human brain tissue. Seventeen cases with ICE injuries of 4–301 days age were selected. Double-labelled immunolabelling using a proliferative cell marker (MCM2), markers of fate-specific transcriptional factors (PAX6, SOX2), a microglial marker (IBA1) and glial markers (nestin, GFAP) was quantified in three regions: zone 1 (immediate vicinity: 0–350 μm), zone 2 (350–700 μm) and zone 3 (remote ≥2000 μm) in relation to the ICE injury site. Microglial/macrophage cell densities peaked at 28–30 days post-injury (dpi) with a significant decline in proliferating microglia with dpi in all zones. Nestin-expressing cells (NECs) were concentrated in zones 1 and 2, showed the highest regenerative capacity (MCM2 and PAX6 co-expression) and were intimately associated with capillaries within the organizing injury cavity. There was a significant decline in nestin/MCM2 co-expressing cells with dpi in zones 1 and 2. Nestin-positive fibres remained in the chronic scar, and NECs with neuronal morphology were noted in older injuries. GFAP-expressing glia were more evenly distributed between zones, with no significant decline in density or proliferative capacity with dpi. Colocalization between nestin and GFAP in zone 1 glial cells decreased with increasing dpi. In conclusion, NECs at acute injury sites are a proliferative, transient cell population with capacity for maturation into astrocytes with possible neuronal differentiation observed in older injuries.

The expression and release of Hsp60 in 6-OHDA induced in vivo and in vitro models of Parkinson's disease

In Parkinson's disease, dopaminergic neuron damage/death causes the release of soluble substances that are selectively toxic to neighboring/additional dopaminergic neurons through the activation of microglia. Hsp60 can be released from injured cells of central nervous system to activate microglia. However, its expression and role in Parkinson's disease has not been well understood. Here, we performed a 6-OHDA treated Parkinson's disease model in adult rats. Western blot analysis showed a time-course expression of Hsp60, which decreased gradually and then rose back. Immunofluorescence staining showed that Hsp60 was decreased in dopaminergic neuron, and most Hsp60 located on the surface of activated microglia. Furthermore, in cellular Parkinson's disease model, Hsp60 was obviously detected in the culture supernatants after 6-OHDA treatment, and a concomitant decrease in cell extracts. Taken together, our results suggested that Hsp60 could be released extracellularly to activate microglia in Parkinson's disease model.

Increased CD133(+) cell infiltration in the rat brain following fluid percussion injury

The prominin-1/CD133 epitope is expressed in undifferentiated cells. Studies have reported that craniocerebral trauma in animal models of fluid percussion injury induces production of a specific stem cell subgroup. It has been hypothesized that fluid percussion injury induces CD133(+) cell infiltration in the brain tissue. The present study established a traumatic brain injury model through fluid percussion injury. Immunohistochemical staining showed significantly increased CD133 antigen expression in the rat brain following injury. CD133(+) cells were mainly distributed in hippocampal CA1-3 regions, as well as the dentate gyrus and hilus, of the lesioned hemisphere. Occasional cells were also detected in the cortex. In addition, reverse transcription-PCR revealed that no change in CD133 mRNA expression in injured brain tissue. These results suggested that fluid percussion injury induced CD133 antigen expression in the brain tissues as a result of conformational epitope changes, but not transcriptional expression.

Inflammation in Parkinson's disease

Parkinson's disease (PD) is a common neurodegenerative disease that is characterized by the degeneration of dopaminergic neurons in the substantia nigra pars compacta. Inflammatory responses manifested by glial reactions, T cell infiltration, and increased expression of inflammatory cytokines, as well as other toxic mediators derived from activated glial cells, are currently recognized as prominent features of PD. The consistent findings obtained by various animal models of PD suggest that neuroinflammation is an important contributor to the pathogenesis of the disease and may further propel the progressive loss of nigral dopaminergic neurons. Furthermore, although it may not be the primary cause of PD, additional epidemiological, genetic, pharmacological, and imaging evidence support the proposal that inflammatory processes in this specific brain region are crucial for disease progression. Recent in vitro studies, however, have suggested that activation of microglia and subsequently astrocytes via mediators released by injured dopaminergic neurons is involved. However, additional in vivo experiments are needed for a deeper understanding of the mechanisms involved in PD pathogenesis. Further insight on the mechanisms of inflammation in PD will help to further develop alternative therapeutic strategies that will specifically and temporally target inflammatory processes without abrogating the potential benefits derived by neuroinflammation, such as tissue restoration.