Isolation and culture of ventral mesencephalic precursor cells and dopaminergic neurons from rodent brains

The antipsychotic medications aripiprazole, brexpiprazole and cariprazine are off-target respiratory chain complex I inhibitors

Antipsychotic drugs are the mainstay of treatment for schizophrenia and provide adjunct therapies for other prevalent psychiatric conditions, including bipolar disorder and major depressive disorder. However, they also induce debilitating extrapyramidal syndromes (EPS), such as Parkinsonism, in a significant minority of patients. The majority of antipsychotic drugs function as dopamine receptor antagonists in the brain while the most recent 'third'-generation, such as aripiprazole, act as partial agonists. Despite showing good clinical efficacy, these newer agents are still associated with EPS in ~ 5 to 15% of patients. However, it is not fully understood how these movement disorders develop. Here, we combine clinically-relevant drug concentrations with mutliscale model systems to show that aripiprazole and its primary active metabolite induce mitochondrial toxicity inducing robust declines in cellular ATP and viability. Aripiprazole, brexpiprazole and cariprazine were shown to directly inhibit respiratory complex I through its ubiquinone-binding channel. Importantly, all three drugs induced mitochondrial toxicity in primary embryonic mouse neurons, with greater bioenergetic inhibition in ventral midbrain neurons than forebrain neurons. Finally, chronic feeding with aripiprazole resulted in structural damage to mitochondria in the brain and thoracic muscle of adult Drosophila melanogaster consistent with locomotor dysfunction. Taken together, we show that antipsychotic drugs acting as partial dopamine receptor agonists exhibit off-target mitochondrial liabilities targeting complex I.

Axonal Tract Reconstruction Using a Tissue-Engineered Nigrostriatal Pathway in a Rat Model of Parkinson's Disease

Parkinson's disease (PD) affects 1-2% of people over 65, causing significant morbidity across a progressive disease course. The classic PD motor deficits are caused by the degeneration of dopaminergic neurons in the substantia nigra pars compacta (SNpc), resulting in the loss of their long-distance axonal projections that modulate striatal output. While contemporary treatments temporarily alleviate symptoms of this disconnection, there is no approach able to replace the nigrostriatal pathway. We applied microtissue engineering techniques to create a living, implantable tissue-engineered nigrostriatal pathway (TE-NSP) that mimics the architecture and function of the native pathway. TE-NSPs comprise a discrete population of dopaminergic neurons extending long, bundled axonal tracts within the lumen of hydrogel micro-columns. Neurons were isolated from the ventral mesencephalon of transgenic rats selectively expressing the green fluorescent protein in dopaminergic neurons with subsequent fluorescent-activated cell sorting to enrich a population to 60% purity. The lumen extracellular matrix and growth factors were varied to optimize cytoarchitecture and neurite length, while immunocytochemistry and fast-scan cyclic voltammetry (FSCV) revealed that TE-NSP axons released dopamine and integrated with striatal neurons in vitro. Finally, TE-NSPs were implanted to span the nigrostriatal pathway in a rat PD model with a unilateral 6-hydroxydopamine SNpc lesion. Immunohistochemistry and FSCV established that transplanted TE-NSPs survived, maintained their axonal tract projections, extended dopaminergic neurites into host tissue, and released dopamine in the striatum. This work showed proof of concept that TE-NSPs can reconstruct the nigrostriatal pathway, providing motivation for future studies evaluating potential functional benefits and long-term durability of this strategy. This pathway reconstruction strategy may ultimately replace lost neuroarchitecture and alleviate the cause of motor symptoms for PD patients.

Dopaminergic Neurons Differentiated from LRRK2 I1371V-Induced Pluripotent Stem Cells Display a Lower Yield, α-Synuclein Pathology, and Functional Impairment

Being a large multidomain protein, LRRK2 has several confirmed pathological mutant variants for PD, and the incidence of these variants shows ethnicity biases. I1371V, a mutation in the GTPase domain, has been reported in East-Asian populations, but there are no studies reported on dopaminergic (DA) neurons differentiated from this variant. The aim here was to assess the yield, function, and α-synuclein pathology of DA neurons differentiated from LRRK2 I1371V iPSCs. FACS analysis of neural progenitors (NPs) showed a comparable immunopositive population of cells for neural and glial progenitor markers nestin and S100β; however, NPs from I1371V iPSCs showed lower clonogenic and proliferative capacities than healthy control NPs as determined by the neurosphere assay and Ki67 expression. Floor plate cells obtained from I1371V NPs primed with FGF8 showed distinctly lower immunopositivity for FOXA2 and CLIC5 than healthy control FPCs and similar DOC2B expression. On SHH addition, a similar mature neuronal population was obtained from both groups; however, the yield of TH-immunopositive cells was significantly lower in I1371V, with lower expression of mature DA neuronal markers En1, Nurr1, and DAT. Vesicular dopamine release and intracellular Ca²⁺ response with KCl stimulation were lower in I1371V DA neurons, along with a significantly reduced expression of resting vesicle marker VMAT2. A concurrently lower expression of PSD95/Syn-I immunopositive puncta was observed in I1371V differentiated cells. Further, higher phosphorylation of α-synuclein and aggregation of oligomeric α-synuclein in I1371V DA neurons were observed. Our data demonstrated conclusively for the first time that mutations in the I1371V allele of LRRK2 showed developmental deficit from the FPC stage and generated a lower yield/number of TH-immunopositive neurons with impairment in their function and synapse density along with increased α-synuclein pathology.

β2-subunit alternative splicing stabilizes Cav2.3 Ca2+ channel activity during continuous midbrain dopamine neuron-like activity

In dopaminergic (DA) Substantia nigra (SN) neurons Cav2.3 R-type Ca2+-currents contribute to somatodendritic Ca2+-oscillations. This activity may contribute to the selective degeneration of these neurons in Parkinson's disease (PD) since Cav2.3-knockout is neuroprotective in a PD mouse model. Here, we show that in tsA-201-cells the membrane-anchored β2-splice variants β2a and β2e are required to stabilize Cav2.3 gating properties allowing sustained Cav2.3 availability during simulated pacemaking and enhanced Ca2+-currents during bursts. We confirmed the expression of β2a- and β2e-subunit transcripts in the mouse SN and in identified SN DA neurons. Patch-clamp recordings of mouse DA midbrain neurons in culture and SN DA neurons in brain slices revealed SNX-482-sensitive R-type Ca2+-currents with voltage-dependent gating properties that suggest modulation by β2a- and/or β2e-subunits. Thus, β-subunit alternative splicing may prevent a fraction of Cav2.3 channels from inactivation in continuously active, highly vulnerable SN DA neurons, thereby also supporting Ca2+ signals contributing to the (patho)physiological role of Cav2.3 channels in PD.

A New Method for the Visualization of Living Dopaminergic Neurons and Prospects for Using It to Develop Targeted Drug Delivery to These Cells

This is the first study aiming to develop a method for the long-term visualization of living nigrostriatal dopaminergic neurons using 1-(2-(bis(4-fluorophenyl)methoxy)ethyl)-4-(3-phenylpropyl)piperazine-BODIPY (GBR-BP), the original fluorescent substance, which is a derivative of GBR-12909, a dopamine uptake inhibitor. This method is based on the authors’ hypothesis about the possibility of specifically internalizing into dopaminergic neurons substances with a high affinity for the dopamine transporter (DAT). Using a culture of mouse embryonic mesencephalic and LUHMES cells (human embryonic mesencephalic cells), as well as slices of the substantia nigra of adult mice, we have obtained evidence that GBR-BP is internalized specifically into dopaminergic neurons in association with DAT via a clathrin-dependent mechanism. Moreover, GBR-BP has been proven to be nontoxic. As we have shown in a primary culture of mouse metencephalon, GBR-BP is also specifically internalized into some noradrenergic and serotonergic neurons, but is not delivered to nonmonoaminergic neurons. Our data hold great promise for visualization of dopaminergic neurons in a mixed cell population to study their functioning, and can also be considered a new approach for the development of targeted drug delivery to dopaminergic neurons in pathology, including Parkinson’s disease.

Extracellular Vesicles as Drug Delivery System for Treatment of Neurodegenerative Disorders: Optimization of the Cell Source

Extracellular vesicles (EVs) represent a next generation drug delivery system that combines nanoparticle size with extraordinary ability to cross biological barriers, reduced immunogenicity, and low offsite toxicity profiles. A successful application of this natural way of delivering biological compounds requires deep understanding EVs intrinsic properties inherited from their parent cells. Herein, we evaluated EVs released by cells of different origin, with respect to drug delivery to the brain for treatment of neurodegenerative disorders. The morphology, size, and zeta potential of EVs secreted by primary macrophages (mEVs), neurons (nEVs), and astrocytes (aEVs) were examined by nanoparticle NTA, DLS, cryoTEM, and AFM. Spherical nanoparticles with average size 110-130 nm and zeta potential around -20 mV were identified for all EVs types. mEVs showed the highest levels of tetraspanins and integrins compared to nEVs and aEVs, suggesting superior adhesion and targeting to the inflamed tissues by mEVs. Strikingly, aEVs were preferentially taken up by neuronal cells in vitro, followed by mEVs and nEVs. Nevertheless, the brain accumulation levels of mEVs in a transgenic mouse model of Parkinson's disease were significantly higher than those of nEVs or aEVs. Therefore, mEVs were suggested as the most promising nanocarrier system for drug delivery to the brain.

Dose-Dependent and Subset-Specific Regulation of Midbrain Dopaminergic Neuron Differentiation by LEF1-Mediated WNT1/b-Catenin Signaling

The mesodiencephalic dopaminergic (mdDA) neurons, including the nigrostriatal subset that preferentially degenerates in Parkinson’s Disease (PD), strongly depend on an accurately balanced Wingless-type MMTV integration site family member 1 (WNT1)/beta-catenin signaling pathway during their development. Loss of this pathway abolishes the generation of these neurons, whereas excessive WNT1/b-catenin signaling prevents their correct differentiation. The identity of the cells responding to this pathway in the developing mammalian ventral midbrain (VM) as well as the precise progression of WNT/b-catenin action in these cells are still unknown. We show that strong WNT/b-catenin signaling inhibits the differentiation of WNT/b-catenin-responding mdDA progenitors into PITX3⁺ and TH⁺ mdDA neurons by repressing the Pitx3 gene in mice. This effect is mediated by RSPO2, a WNT/b-catenin agonist, and lymphoid enhancer binding factor 1 (LEF1), an essential nuclear effector of the WNT/b-catenin pathway, via conserved LEF1/T-cell factor binding sites in the Pitx3 promoter. LEF1 expression is restricted to a caudolateral mdDA progenitor subset that preferentially responds to WNT/b-catenin signaling and gives rise to a fraction of all mdDA neurons. Our data indicate that an attenuation of WNT/b-catenin signaling in mdDA progenitors is essential for their correct differentiation into specific mdDA neuron subsets. This is an important consideration for stem cell-based regenerative therapies and in vitro models of neuropsychiatric diseases.

Glial cells in intracerebral transplantation for Parkinson's disease

In the last few decades, intracerebral transplantation has grown from a dubious neuroscientific topic to a plausible modality for treatment of neurological disorders. The possibility for cell replacement opens a new field of perspectives in the therapy of neurodegenerative disorders, ischemia, and neurotrauma, with the most lessons learned from intracerebral transplantation in Parkinson's disease. Multiple animal studies and a few small-scale clinical trials have proven the concept of intracerebral grafting, but still have to provide a uniform and highly efficient approach to the procedure, suitable for clinical application. The success of intracerebral transplantation is highly dependent on the integration of the grafted cells with the host brain. In this process, glial cells are clearly more than passive bystanders. They provide transplanted cells with mechanical support, trophics, mediate synapse formation, and participate in graft vascularization. At the same time, glial cells mediate scarring, graft rejection, and neuroinflammation, which can be detrimental. We can use this information to try to understand the mechanisms behind the glial reaction to intracerebral transplantation. Recognizing and utilizing glial reactivity can move translational research forward and provide an insight not only to post-transplantation events but also to mechanisms of neuronal death and degeneration. Knowledge about glial reactivity to transplanted cells could also be a key for optimization of transplantation protocols, which ultimately should contribute to greater patient benefit.

Extracellular Vesicles as Drug Carriers for Enzyme Replacement Therapy to Treat CLN2 Batten Disease: Optimization of Drug Administration Routes

CLN2 Batten disease (BD) is one of a broad class of lysosomal storage disorders that is characterized by the deficiency of lysosomal enzyme, TPP1, resulting in a build-up of toxic intracellular storage material in all organs and subsequent damage. A major challenge for BD therapeutics is delivery of enzymatically active TPP1 to the brain to attenuate progressive loss of neurological functions. To accomplish this daunting task, we propose the harnessing of naturally occurring nanoparticles, extracellular vesicles (EVs). Herein, we incorporated TPP1 into EVs released by immune cells, macrophages, and examined biodistribution and therapeutic efficacy of EV-TPP1 in BD mouse model, using various routes of administration. Administration through intrathecal and intranasal routes resulted in high TPP1 accumulation in the brain, decreased neurodegeneration and neuroinflammation, and reduced aggregation of lysosomal storage material in BD mouse model, CLN2 knock-out mice. Parenteral intravenous and intraperitoneal administrations led to TPP1 delivery to peripheral organs: liver, kidney, spleen, and lungs. A combination of intrathecal and intraperitoneal EV-TPP1 injections significantly prolonged lifespan in BD mice. Overall, the optimization of treatment strategies is crucial for successful applications of EVs-based therapeutics for BD.

Targeting Cannabinoid Receptor Activation and BACE-1 Activity Counteracts TgAPP Mice Memory Impairment and Alzheimer's Disease Lymphoblast Alterations

Alzheimer's disease (AD), the leading cause of dementia in the elderly, is a neurodegenerative disorder marked by progressive impairment of cognitive ability. Patients with AD display neuropathological lesions including senile plaques, neurofibrillary tangles, and neuronal loss. There are no disease-modifying drugs currently available. With the number of affected individuals increasing dramatically throughout the world, there is obvious urgent need for effective treatment strategy for AD. The multifactorial nature of AD encouraged the development of multifunctional compounds, able to interact with several putative targets. Here, we have evaluated the effects of two in-house designed cannabinoid receptors (CB) agonists showing inhibitory actions on β-secretase-1 (BACE-1) (NP137) and BACE-1/butyrylcholinesterase (BuChE) (NP148), on cellular models of AD, including immortalized lymphocytes from late-onset AD patients. Furthermore, the performance of TgAPP mice in a spatial navigation task was investigated following chronic administration of NP137 and NP148. We report here that NP137 and NP148 showed neuroprotective effects in amyloid-β-treated primary cortical neurons, and NP137 in particular rescued the cognitive deficit of TgAPP mice. The latter compound was able to blunt the abnormal cell response to serum addition or withdrawal of lymphoblasts derived from AD patients. It is suggested that NP137 could be a good drug candidate for future treatment of AD.

Quantal Release of Dopamine and Action Potential Firing Detected in Midbrain Neurons by Multifunctional Diamond-Based Microarrays

Micro-Graphitic Single Crystal Diamond Multi Electrode Arrays (μG-SCD-MEAs) have so far been used as amperometric sensors to detect catecholamines from chromaffin cells and adrenal gland slices. Besides having time resolution and sensitivity that are comparable with carbon fiber electrodes, that represent the gold standard for amperometry, μG-SCD-MEAs also have the advantages of simultaneous multisite detection, high biocompatibility and implementation of amperometric/potentiometric protocols, aimed at monitoring exocytotic events and neuronal excitability. In order to adapt diamond technology to record neuronal activity, the μG-SCD-MEAs in this work have been interfaced with cultured midbrain neurons to detect electrical activity as well as quantal release of dopamine (DA). μG-SCD-MEAs are based on graphitic sensing electrodes that are embedded into the diamond matrix and are fabricated using MeV ion beam lithography. Two geometries have been adopted, with 4 × 4 and 8 × 8 microelectrodes (20 μm × 3.5 μm exposed area, 200 μm spacing). In the amperometric configuration, the 4 × 4 μG-SCD-MEAs resolved quantal exocytosis from midbrain dopaminergic neurons. KCl-stimulated DA release occurred as amperometric spikes of 15 pA amplitude and 0.5 ms half-width, at a mean frequency of 0.4 Hz. When used as potentiometric multiarrays, the 8 × 8 μG-SCD-MEAs detected the spontaneous firing activity of midbrain neurons. Extracellularly recorded action potentials (APs) had mean amplitude of ∼-50 μV and occurred at a mean firing frequency of 0.7 Hz in 67% of neurons, while the remaining fired at 6.8 Hz. Comparable findings were observed using conventional MEAs (0.9 and 6.4 Hz, respectively). To test the reliability of potentiometric recordings with μG-SCD-MEAs, the D₂-autoreceptor modulation of firing was investigated by applying levodopa (L-DOPA, 20 μM), and comparing μG-SCD-MEAs, conventional MEAs and current-clamp recordings. In all cases, L-DOPA reduced the spontaneous spiking activity in most neurons by 70%, while the D₂-antagonist sulpiride reversed this effect. Cell firing inhibition was generally associated with increased APs amplitude. A minority of neurons was either insensitive to, or potentiated by L-DOPA, suggesting that AP recordings originate from different midbrain neuronal subpopulations and reveal different modulatory pathways. Our data demonstrate, for the first time, that μG-SCD-MEAs are multi-functional biosensors suitable to resolve real-time DA release and AP firing in in vitro neuronal networks.

Tissue engineered nigrostriatal pathway for treatment of Parkinson's disease

The classic motor deficits of Parkinson's disease are caused by degeneration of dopaminergic neurons in the substantia nigra pars compacta, resulting in the loss of their long-distance axonal projections that modulate the striatum. Current treatments only minimize the symptoms of this disconnection as there is no approach capable of replacing the nigrostriatal pathway. We are applying microtissue engineering techniques to create living, implantable constructs that mimic the architecture and function of the nigrostriatal pathway. These constructs consist of dopaminergic neurons with long axonal tracts encased within hydrogel microcolumns. Microcolumns were seeded with dopaminergic neuronal aggregates, while lumen extracellular matrix, growth factors, and end targets were varied to optimize cytoarchitecture. We found a 10-fold increase in axonal outgrowth from aggregates versus dissociated neurons, resulting in remarkable axonal lengths of over 6 mm by 14 days and 9 mm by 28 days in vitro. Axonal extension was also dependent upon lumen extracellular matrix, but did not depend on growth factor enrichment or neuronal end target presence. Evoked dopamine release was measured via fast scan cyclic voltammetry and synapse formation with striatal neurons was observed in vitro. Constructs were microinjected to span the nigrostriatal pathway in rats, revealing survival of implanted neurons while maintaining their axonal projections within the microcolumn. Lastly, these constructs were generated with dopaminergic neurons differentiated from human embryonic stem cells. This strategy may improve Parkinson's disease treatment by simultaneously replacing lost dopaminergic neurons in the substantia nigra and reconstructing their long-projecting axonal tracts to the striatum.

Activation of the Cannabinoid Type 2 Receptor by a Novel Indazole Derivative Normalizes the Survival Pattern of Lymphoblasts from Patients with Late-Onset Alzheimer's Disease

BACKGROUND

Alzheimer's disease is a multifactorial disorder for which there is no disease-modifying treatment yet. CB2 receptors have emerged as a promising therapeutic target for Alzheimer's disease because they are expressed in neuronal and glial cells and their activation has no psychoactive effects.

OBJECTIVE

The aim of this study was to investigate whether activation of the CB2 receptor would restore the aberrant enhanced proliferative activity characteristic of immortalized lymphocytes from patients with late-onset Alzheimer's disease. It is assumed that cell-cycle dysfunction occurs in both peripheral cells and neurons in patients with Alzheimer's disease, contributing to the instigation of the disease.

METHODS

Lymphoblastoid cell lines from patients with Alzheimer's disease and age-matched control individuals were treated with a new, in-house-designed dual drug PGN33, which behaves as a CB2 agonist and butyrylcholinesterase inhibitor. We analyzed the effects of this compound on the rate of cell proliferation and levels of key regulatory proteins. In addition, we investigated the potential neuroprotective action of PGN33 in β-amyloid-treated neuronal cells.

RESULTS

We report here that PGN33 normalized the increased proliferative activity of Alzheimer's disease lymphoblasts. The compound blunted the calmodulin-dependent overactivation of the PI3K/Akt pathway, by restoring the cyclin-dependent kinase inhibitor p27 levels, which in turn reduced the activity of the cyclin-dependent kinase/pRb cascade. Moreover, this CB2 agonist prevented β-amyloid-induced cell death in neuronal cells.

CONCLUSION

Our results suggest that the activation of CB2 receptors could be considered a useful therapeutic approach for Alzheimer's disease.

Asiatic acid attenuates methamphetamine-induced neuroinflammation and neurotoxicity through blocking of NF-kB/STAT3/ERK and mitochondria-mediated apoptosis pathway

Background

Methamphetamine (METH) is a commonly abused drug that may result in neurotoxic effects. Recent studies have suggested that involvement of neuroinflammatory processes in brain dysfunction is induced by misuse of this drug. However, the mechanism underlying METH-induced inflammation and neurotoxicity in neurons is still unclear. In this study, we investigated whether asiatic acid (AA) effected METH-mediated neuroinflammation and neurotoxicity in dopaminergic neuronal cells. And we further determined whether the effect involved in the nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) and signal transducer and activator of transcription (STAT)3 and extracellular signal-regulated kinase (ERK) pathway.

Methods

We used the human dopaminergic neuroblastoma SH-SY5Y cell line, murine microglial BV2 cell line, and primary culture of rat embryo mesencephalic neurons. Pro-inflammatory cytokine production was monitored by ELISA and RT/real-time PCR. The cell cycle distribution and mitochondrial membrane integrity was analyzed by flow cytometry. We used immunoblotting, DNA-binding activity, and immunofluorescence staining to analyze the effect of AA on activation of the NF-κB, STAT3, MAPK-ERK, and apoptosis signaling pathways.

Results

METH induced TNF receptor (TNFR) expression and led to morphological changes of cells. Additionally, this drug increased pro-inflammatory cytokine (TNFα and IL-6) expression. AA significantly suppressed METH-induced TNFR expression in concentration dependent. Increased secretion of TNFα and IL-6 was inhibited in METH-stimulated neuronal cells by AA administration. AA showed significant protection against METH-induced translocation of NF-κB/STAT3 and ERK phosphorylation. AA inhibited METH-induced proteolytic fragmentation of caspase-3 and PARP. The pro-apoptotic protein Bax was significantly decreased, while the anti-apoptotic protein Bcl-xL was increased by AA treatment in METH-stimulated cells. A similar protective effect of AA on mitochondrial membrane integrity was also confirmed by flow cytometry and immunofluorescence staining.

Conclusions

Based on the literatures and our findings, AA is a promising candidate for an anti-neurotoxic agent, and it can potentially be used for the prevention and treatment of various neurological disorders.

Electronic supplementary material

The online version of this article (10.1186/s12974-017-1009-0) contains supplementary material, which is available to authorized users.

Astrogliosis has Different Dynamics after Cell Transplantation and Mechanical Impact in the Rodent Model of Parkinson's Disease

Background:

Transplantation of fetal mesencephalic tissue is a well-established concept for functional reinnervation of the dopamine-depleted rat striatum. However, there is no extensive description of the glial response of the host brain following this procedure.

Aims:

The present study aimed to quantitatively and qualitatively analyse astrogliosis surrounding intrastriatal grafts and compare it to the reaction to mechanical injury with the transplantation instrument only.

Study Design:

Animal experimentation.

Methods:

The standard 6-hydroxydopamine-induced unilateral model of Parkinson’s disease was used. The experimental animals received transplantation of a single-cell suspension of E14 ventral mesencephalic tissue. Control animals (sham-transplanted) were subjected to injury by the transplantation cannula, without injection of a cell suspension. Histological analyses were carried out 7 and 28 days following the procedure by immunohistochemistry assays for tyrosine hydroxylase and glial fibrillary acidic protein. To evaluate astrogliosis, the cell density and immunopositive area were measured in distinct zones within and surrounding the grafts or the cannula tract.

Results:

Statistical analysis revealed that astrogliosis in the grafted striatum increased from day 7 to day 28, as shown by a significant change in both cell density and the immunopositive area. The cell density increased from 816.7±370.6 to 1403±272.1 cells/mm² (p<0.0001) аnd from 523±245.9 to 1164±304.8 cells/mm² (p<0.0001) in the two zones in the graft core, and from 1151±218.6 to 1485±210.6 cells/mm² (p<0.05) for the zone in the striatum immediately adjacent to the graft. The glial fibrillary acidic protein-expressing area increased from 0.3109±0.1843 to 0.7949±0.1910 (p<0.0001) and from 0.1449±0.1240 to 0.702±0.2558 (p<0.0001) for the same zones in the graft core, and from 0.5277±0.1502 to 0.6969±0.1223 (p<0.0001) for the same area adjacent to the graft zone. However, astrogliosis caused by mechanical impact only (control) did not display such dynamics. This finding suggests an influence of the grafted cells on the host’s glia, possibly through cross-talk between astrocytes and transplanted neurons.

Conclusion:

This bidirectional relationship is affected by multiple factors beyond the mechanical trauma. Elucidation of these factors might help achieve better functional outcomes after intracerebral transplantation.

Pharmacologically increasing microtubule acetylation corrects stress-exacerbated effects of organophosphates on neurons

Many veterans of the 1990-1991 Gulf War contracted Gulf War Illness (GWI), a multisymptom disease that primarily affects the nervous system. Here, we treated cultures of human or rat neurons with diisopropyl fluorophosphate (DFP), an analog of sarin, one of the organophosphate (OP) toxicants to which the military veterans were exposed. All observed cellular defects produced by DFP were exacerbated by pretreatment with corticosterone or cortisol, which, in rat and human neurons, respectively, serves in our experiments to mimic the physical stress endured by soldiers during the war. To best mimic the disease, DFP was used below the level needed to inhibit acetylcholinesterase. We observed a diminution in the ratio of acetylated to total tubulin that was correctable by treatment with tubacin, a drug that inhibits HDAC6, the tubulin deacetylase. The reduction in microtubule acetylation was coupled with deficits in microtubule dynamics, which were correctable by HDAC6 inhibition. Deficits in mitochondrial transport and dopamine release were also improved by tubacin. Thus, various negative effects of the toxicant/stress exposures were at least partially correctable by restoring microtubule acetylation to a more normal status. Such an approach may have therapeutic benefit for individuals suffering from GWI or other neurological disorders linked to OP exposure.

Smoking-Relevant Nicotine Concentration Attenuates the Unfolded Protein Response in Dopaminergic Neurons

Retrospective epidemiological studies show an inverse correlation between susceptibility to Parkinson's disease and a person's history of tobacco use. Animal model studies suggest nicotine as a neuroprotective agent and nicotinic acetylcholine (ACh) receptors (nAChRs) as targets for neuroprotection, but the underlying neuroprotective mechanism(s) are unknown. We cultured mouse ventral midbrain neurons for 3 weeks. Ten to 20% of neurons were dopaminergic (DA), revealed by tyrosine hydroxylase (TH) immunoreactivity. We evoked mild endoplasmic reticulum (ER) stress with tunicamycin (Tu), producing modest increases in the level of nuclear ATF6, phosphorylated eukaryotic initiation factor 2α, nuclear XBP1, and the downstream proapoptotic effector nuclear C/EBP homologous protein. We incubated cultures for 2 weeks with 200 nm nicotine, the approximate steady-state concentration between cigarette smoking or vaping, or during nicotine patch use. Nicotine incubation suppressed Tu-induced ER stress and the unfolded protein response (UPR). Study of mice with fluorescent nAChR subunits showed that the cultured TH+ neurons displayed α4, α6, and β3 nAChR subunit expression and ACh-evoked currents. Gene expression profile in cultures from TH-eGFP mice showed that the TH+ neurons also express several other genes associated with DA release. Nicotine also upregulated ACh-induced currents in DA neurons by ∼2.5-fold. Thus, nicotine, at a concentration too low to activate an appreciable fraction of plasma membrane nAChRs, induces two sequelae of pharmacological chaperoning in the ER: UPR suppression and nAChR upregulation. Therefore, one mechanism of neuroprotection by nicotine is pharmacological chaperoning, leading to UPR suppression. Measuring this pathway may help in assessing neuroprotection.

SIGNIFICANCE STATEMENT

Parkinson's disease (PD) cannot yet be cured or prevented. However, many retrospective epidemiological studies reveal that PD is diagnosed less frequently in tobacco users. Existing programs attempting to develop nicotinic drugs that might exert this apparent neuroprotective effect are asking whether agonists, antagonists, partial agonists, or channel blockers show the most promise. The underlying logic resembles the previous development of varenicline for smoking cessation. We studied whether, and how, nicotine produces neuroprotective effects in cultured dopaminergic neurons, an experimentally tractable, mechanistically revealing neuronal system. We show that nicotine, operating via nicotinic receptors, does protect these neurons against endoplasmic reticulum stress. However, the mechanism is probably "inside-out": pharmacological chaperoning in the endoplasmic reticulum. This cellular-level insight could help to guide neuroprotective strategies.

Dickkopf 3 Promotes the Differentiation of a Rostrolateral Midbrain Dopaminergic Neuronal Subset In Vivo and from Pluripotent Stem Cells In Vitro in the Mouse

Wingless-related MMTV integration site 1 (WNT1)/β-catenin signaling plays a crucial role in the generation of mesodiencephalic dopaminergic (mdDA) neurons, including the substantia nigra pars compacta (SNc) subpopulation that preferentially degenerates in Parkinson's disease (PD). However, the precise functions of WNT1/β-catenin signaling in this context remain unknown. Stem cell-based regenerative (transplantation) therapies for PD have not been implemented widely in the clinical context, among other reasons because of the heterogeneity and incomplete differentiation of the transplanted cells. This might result in tumor formation and poor integration of the transplanted cells into the dopaminergic circuitry of the brain. Dickkopf 3 (DKK3) is a secreted glycoprotein implicated in the modulation of WNT/β-catenin signaling. Using mutant mice, primary ventral midbrain cells, and pluripotent stem cells, we show that DKK3 is necessary and sufficient for the correct differentiation of a rostrolateral mdDA neuron subset. Dkk3 transcription in the murine ventral midbrain coincides with the onset of mdDA neurogenesis and is required for the activation and/or maintenance of LMX1A (LIM homeobox transcription factor 1α) and PITX3 (paired-like homeodomain transcription factor 3) expression in the corresponding mdDA precursor subset, without affecting the proliferation or specification of their progenitors. Notably, the treatment of differentiating pluripotent stem cells with recombinant DKK3 and WNT1 proteins also increases the proportion of mdDA neurons with molecular SNc DA cell characteristics in these cultures. The specific effects of DKK3 on the differentiation of rostrolateral mdDA neurons in the murine ventral midbrain, together with its known prosurvival and anti-tumorigenic properties, make it a good candidate for the improvement of regenerative and neuroprotective strategies in the treatment of PD. Significance statement: We show here that Dickkopf 3 (DKK3), a secreted modulator of WNT (Wingless-related MMTV integration site)/β-catenin signaling, is both necessary and sufficient for the proper differentiation and survival of a rostrolateral (parabrachial pigmented nucleus and dorsomedial substantia nigra pars compacta) mesodiencephalic dopaminergic neuron subset, using Dkk3 mutant mice and murine primary ventral midbrain and pluripotent stem cells. The progressive loss of these dopamine-producing mesodiencephalic neurons is a hallmark of human Parkinson's disease, which can up to now not be halted by clinical treatments of this disease. Thus, the soluble DKK3 protein might be a promising new agent for the improvement of current protocols for the directed differentiation of pluripotent and multipotent stem cells into mesodiencephalic dopaminergic neurons and for the promotion of their survival in situ.

A High-content screen identifies compounds promoting the neuronal differentiation and the midbrain dopamine neuron specification of human neural progenitor cells

Small molecule compounds promoting the neuronal differentiation of stem/progenitor cells are of pivotal importance to regenerative medicine. We carried out a high-content screen to systematically characterize known bioactive compounds, on their effects on the neuronal differentiation and the midbrain dopamine (mDA) neuron specification of neural progenitor cells (NPCs) derived from the ventral mesencephalon of human fetal brain. Among the promoting compounds three major pharmacological classes were identified including the statins, TGF-βRI inhibitors, and GSK-3 inhibitors. The function of each class was also shown to be distinct, either to promote both the neuronal differentiation and mDA neuron specification, or selectively the latter, or promote the former but suppress the latter. We then carried out initial investigation on the possible mechanisms underlying, and demonstrated their applications on NPCs derived from human pluripotent stem cells (PSCs). Our study revealed the potential of several small molecule compounds for use in the directed differentiation of human NPCs. The screening result also provided insight into the signaling network regulating the differentiation of human NPCs.

Efficient Expression of Igf-1 from Lentiviral Vectors Protects In Vitro but Does Not Mediate Behavioral Recovery of a Parkinsonian Lesion in Rats

Gene therapy approaches delivering neurotrophic factors have offered promising results in both preclinical and clinical trials of Parkinson's disease (PD). However, failure of glial cell line-derived neurotrophic factor in phase 2 clinical trials has sparked a search for other trophic factors that may retain efficacy in the clinic. Direct protein injections of one such factor, insulin-like growth factor (IGF)-1, in a rodent model of PD has demonstrated impressive protection of dopaminergic neurons against 6-hydroxydopamine (6-OHDA) toxicity. However, protein infusion is associated with surgical risks, pump failure, and significant costs. We therefore used lentiviral vectors to deliver Igf-1, with a particular focus on the novel integration-deficient lentiviral vectors (IDLVs). A neuron-specific promoter, from the human synapsin 1 gene, excellent for gene expression from IDLVs, was additionally used to enhance Igf-1 expression. An investigation of neurotrophic effects on primary rat neuronal cultures demonstrated that neurons transduced with IDLV-Igf-1 vectors had complete protection on withdrawal of exogenous trophic support. Striatal transduction of such vectors into 6-OHDA-lesioned rats, however, provided neither protection of dopaminergic substantia nigra neurons nor improvement of animal behavior.

Dopaminergic control of autophagic-lysosomal function implicates Lmx1b in Parkinson's disease

The role of developmental transcription factors in maintenance of neuronal properties and in disease remains poorly understood. Lmx1a and Lmx1b are key transcription factors required for the early specification of ventral midbrain dopamine (mDA) neurons. Here we show that conditional ablation of Lmx1a and Lmx1b after mDA neuron specification resulted in abnormalities that show striking resemblance to early cellular abnormalities seen in Parkinson's disease. We found that Lmx1b was required for the normal execution of the autophagic-lysosomal pathway and for the integrity of dopaminergic nerve terminals and long-term mDA neuronal survival. Notably, human LMX1B expression was decreased in mDA neurons in brain tissue affected by Parkinson's disease. Thus, these results reveal a sustained and essential requirement of Lmx1b for the function of midbrain mDA neurons and suggest that its dysfunction is associated with Parkinson's disease pathogenesis.

Crucial role of nicotinic α5 subunit variants for Ca2+ fluxes in ventral midbrain neurons

Neuronal nicotinic acetylcholine receptors (nAChRs) containing the α5 subunit modulate nicotine consumption, and the human CHRNA5 rs16969968 polymorphism, causing the replacement of the aspartic acid residue at position 398 with an asparagine (α5DN), has recently been associated with increased use of tobacco and higher incidence of lung cancer. We show that in ventral midbrain neurons, the α5 subunit is essential for heteromeric nAChR-induced intracellular-free Ca(2+) concentration elevations and that in α5(-/-) mice, a class of large-amplitude nicotine-evoked currents is lost. Furthermore, the expression of the α5DN subunit is not able to restore nicotinic responses, indicating a loss of function by this subunit in native neurons. To understand how α5DN impairs heteromeric nAChR functions, we coexpressed α4, α5, or α5DN subunits with a dimeric concatemer (β2α4) in a heterologous system, to obtain nAChRs with fixed stoichiometry. Both α5(β2α4)2 and α5DN(β2α4)2 nAChRs yielded similar levels of functional expression and Ca(2+) permeability, measured as fractional Ca(2+) currents (8.2 ± 0.7% and 8.0 ± 1.9%, respectively), 2-fold higher than α4(β2α4)2. Our results indicate that the loss of function of nicotinic responses observed in α5DN-expressing ventral midbrain neurons is neither due to an intrinsic inability of this subunit to form functional nAChRs nor to an altered Ca(2+) permeability but likely to intracellular modulation.

Continuous High-Frequency Stimulation of the Subthalamic Nucleus Improves Cell Survival and Functional Recovery Following Dopaminergic Cell Transplantation in Rodents

Subthalamic nucleus (STN) high-frequency stimulation (HFS) is a routine treatment in Parkinson's disease (PD), with confirmed long-term benefits. An alternative, but still experimental, treatment is cell replacement and restorative therapy based on transplanted dopaminergic neurons. The current experiment evaluated the potential synergy between neuromodulation and grafting by studying the effect of continuous STN-HFS on the survival, integration, and functional efficacy of ventral mesencephalic dopaminergic precursors transplanted into a unilateral 6-hydroxydopamine medial forebrain bundle lesioned rodent PD model. One group received continuous HFS of the ipsilateral STN starting a week prior to intrastriatal dopaminergic neuron transplantation, whereas the sham-stimulated group did not receive STN-HFS but only dopaminergic grafts. A control group was neither lesioned nor transplanted. Over the following 7 weeks, the animals were probed on a series of behavioral tasks to evaluate possible graft and/or stimulation-induced functional effects. Behavioral and histological data suggest that STN-HFS significantly increased graft cell survival, graft-host integration, and functional recovery. These findings might open an unexplored road toward combining neuromodulative and neuroregenerative strategies to treat severe neurologic conditions.

Exosomes as drug delivery vehicles for Parkinson's disease therapy

Exosomes are naturally occurring nanosized vesicles that have attracted considerable attention as drug delivery vehicles in the past few years. Exosomes are comprised of natural lipid bilayers with the abundance of adhesive proteins that readily interact with cellular membranes. We posit that exosomes secreted by monocytes and macrophages can provide an unprecedented opportunity to avoid entrapment in mononuclear phagocytes (as a part of the host immune system), and at the same time enhance delivery of incorporated drugs to target cells ultimately increasing drug therapeutic efficacy. In light of this, we developed a new exosomal-based delivery system for a potent antioxidant, catalase, to treat Parkinson's disease (PD). Catalase was loaded into exosomes ex vivo using different methods: the incubation at room temperature, permeabilization with saponin, freeze-thaw cycles, sonication, or extrusion. The size of the obtained catalase-loaded exosomes (exoCAT) was in the range of 100-200nm. A reformation of exosomes upon sonication and extrusion, or permeabilization with saponin resulted in high loading efficiency, sustained release, and catalase preservation against proteases degradation. Exosomes were readily taken up by neuronal cells in vitro. A considerable amount of exosomes was detected in PD mouse brain following intranasal administration. ExoCAT provided significant neuroprotective effects in in vitro and in vivo models of PD. Overall, exosome-based catalase formulations have a potential to be a versatile strategy to treat inflammatory and neurodegenerative disorders.

Targeting cyclin D3/CDK6 activity for treatment of Parkinson's disease

At present, treatment for Parkinson's disease (PD) is only symptomatic; therefore, it is important to identify new targets tackling the molecular causes of the disease. We previously found that lymphoblasts from sporadic PD patients display increased activity of the cyclin D3/CDK6/pRb pathway and higher proliferation than control cells. These features were considered systemic manifestations of the disease, as aberrant activation of the cell cycle is involved in neuronal apoptosis. The main goal of this work was to elucidate whether the inhibition of cyclin D3/CDK6-associated kinase activity could be useful in PD treatment. For this purpose, we investigated the effects of two histone deacetylase (HDAC) inhibitors, suberoylanilide hydroxamic (SAHA) acid and sodium butyrate (NaB), and the m-TOR inhibitor rapamycin on cell viability and cyclin D3/CDK6 activity. Moreover, the potential neuroprotective action of these drugs was evaluated in 6-hydroxy-dopamine (6-OHDA) treated dopaminergic SH-SY5Y cells and primary rat mesencephalic cultures. Here, we report that both compounds normalized the proliferative activity of PD lymphoblasts and reduced the 6-OHDA-induced cell death in neuronal cells by preventing the over-activation of the cyclin D3/CDK6/pRb cascade. Considering that these drugs are already used in clinic for treatment of other diseases with good tolerance, it is plausible that they may serve as novel therapeutic drugs for PD. We report here that peripheral cells from Parkinson's disease (PD) patients show an enhanced proliferative activity due to the activation of cyclin D3/CDK6-mediated phosphorylation of retinoblastoma protein (pRb). Treatment of PD lymphoblasts with inhibitors of histone deacetylases like suberoylanilide hydroxamic acid (SAHA) and sodium butyrate (NaB), or with rapamycin, inhibitor of mechanistic target of rapamycin (mTOR) normalized the proliferation of PD lymphoblasts by preventing the over-activation of the cyclin D3/CDK6/pRb cascade. These drugs were shown to have neuroprotective effects in both human neuroblastoma SH-SY5Y cells and primary rat mid-brain dopaminergic neuronal cultures toxicity induced by 6-hidroxydopamine. Considering that these drugs are already used in clinic for treatment of other diseases with good tolerance, it seems reasonable to believe that the repositioning of these drugs toward PD holds promise as a novel therapeutic strategy.

Flow cytometry protocols for surface and intracellular antigen analyses of neural cell types

Flow cytometry has been extensively used to define cell populations in immunology, hematology and oncology. Here, we provide a detailed description of protocols for flow cytometric analysis of the cluster of differentiation (CD) surface antigens and intracellular antigens in neural cell types. Our step-by-step description of the methodological procedures include: the harvesting of neural in vitro cultures, an optional carboxyfluorescein succinimidyl ester (CFSE)-labeling step, followed by surface antigen staining with conjugated CD antibodies (e.g., CD24, CD54), and subsequent intracellar antigen detection via primary/secondary antibodies or fluorescently labeled Fab fragments (Zenon labeling). The video demonstrates the most critical steps. Moreover, principles of experimental planning, the inclusion of critical controls, and fundamentals of flow cytometric analysis (identification of target population and exclusion of debris; gating strategy; compensation for spectral overlap) are briefly explained in order to enable neurobiologists with limited prior knowledge or specific training in flow cytometry to assess its utility and to better exploit this powerful methodology.

Electric signals regulate directional migration of ventral midbrain derived dopaminergic neural progenitor cells via Wnt/GSK3β signaling

Neural progenitor cell (NPC) replacement therapy is a promising treatment for neurodegenerative disorders including Parkinson's disease (PD). It requires a controlled directional migration and integration of NPCs, for example dopaminergic (DA) progenitor cells, into the damaged host brain tissue. There is, however, only limited understanding of how to regulate the directed migration of NPCs to the diseased or damaged brain tissues for repair and regeneration. The aims of this study are to explore the possibility of using a physiological level of electrical stimulation to regulate the directed migration of ventral midbrain NPCs (NPCs(vm)), and to investigate their potential regulation via GSK3β and associated downstream effectors. We tested the effects of direct-current (DC) electric fields (EFs) on the migration behavior of the NPCs(vm). A DC EF induced directional cell migration toward the cathode, namely electrotaxis. Reversal of the EF polarity triggered a sharp reversal of the NPC(vm) electrotaxis. The electrotactic response was both time and EF voltage dependent. Pharmacologically inhibiting the canonical Wnt/GSK3β pathway significantly reduced the electrotactic response of NPCs(vm), which is associated with the down-regulation of GSK3β phosphorylation, β-catenin activation and CLASP2 expression. This was further proved by RNA interference of GSK3β, which also showed a significantly reduced electrotactic response in association with reduced β-catenin activation and CLASP2 expression. In comparison, RNA interference of β-catenin slightly reduced electrotactic response and CLASP2 expression. Both pharmacological inhibition of Wnt/GSK3β and RNA interference of GSK3β/β-catenin clearly reduced the asymmetric redistribution of CLASP2 and its co-localization with α-tubulin. These results suggest that Wnt/GSK3β signaling contributes to the electrotactic response of NPCs(vm) through the coordination of GSK3β phosphorylation, β-catenin activation, CLASP2 expression and asymmetric redistribution to the leading edge of the migrating cells.

Modelling of a targeted nanotherapeutic 'stroma' to deliver the cytokine LIF, or XAV939, a potent inhibitor of Wnt-β-catenin signalling, for use in human fetal dopaminergic grafts in Parkinson's disease

The endogenous reparative capacity of the adult human brain is low, and chronic neurodegenerative disorders of the central nervous system represent one of the greatest areas of unmet clinical need in the developing world. Novel therapeutic strategies to treat them include: (i) growth factor delivery to boost endogenous repair and (ii) replacement cell therapy, including replacing dopaminergic neurons to treat Parkinson’s disease (PD). However, these approaches are restricted not only by rapid degradation of growth factors, but also by the limited availability of cells for transplant and the poor survival of implanted cells that lack the necessary stromal support. We therefore hypothesised that provision of a transient artificial stroma for paracrine delivery of pro-survival factors could overcome both of these issues. Using leukaemia inhibitory factor (LIF) – a proneural, reparative cytokine – formulated as target-specific poly(lactic-co-glycolic acid) (PLGA) nano-particles (LIF-nano-stroma), we discovered that attachment of LIF-nano-stroma to freshly isolated fetal dopaminergic cells improved their survival fourfold: furthermore, in vivo, the number of surviving human fetal dopaminergic cells tended to be higher at 3 months after grafting into the striatum of nude rats, compared with controls treated with empty nanoparticles. In addition, we also analysed the effect of a novel nano-stroma incorporating XAV939 (XAV), a potent inhibitor of the developmentally important Wnt–β-catenin signalling pathway, to investigate whether it could also promote the survival and differentiation of human fetal dopaminergic precursors; we found that the numbers of both tyrosine-hydroxylase-positive neurons (a marker of dopaminergic neurons) and total neurons were increased. This is the first demonstration that LIF-nano-stroma and XAV-nano-stroma each have pro-survival effects on human dopaminergic neurons, with potential value for target-specific modulation of neurogenic fate in cell-based therapies for PD.

Intracellular Nogo-A facilitates initiation of neurite formation in mouse midbrain neurons in vitro

Nogo-A is a transmembrane protein originally discovered in myelin, produced by postnatal CNS oligodendrocytes. Nogo-A induces growth cone collapse and inhibition of axonal growth in the injured adult CNS. In the intact CNS, Nogo-A functions as a negative regulator of growth and plasticity. Nogo-A is also expressed by certain neurons. Neuronal Nogo-A depresses long-term potentiation in the hippocampus and modulates neurite adhesion and fasciculation during development in mice. Here we show that Nogo-A is present in neurons derived from human midbrain (Lund human mesencephalic (LUHMES) cell line), as well as in embryonic and postnatal mouse midbrain (dopaminergic) neurons. In LUHMES cells, Nogo-A was upregulated threefold upon differentiation and neurite extension. Nogo-A was localized intracellularly in differentiated LUHMES cells. Cultured midbrain (dopaminergic) neurons from Nogo-A knock-out mice exhibited decreased numbers of neurites and branches when compared with neurons from wild-type (WT) mice. However, this phenotype was not observed when the cultures from WT mice were treated with an antibody neutralizing plasma membrane Nogo-A. In vivo, neither the regeneration of nigrostriatal tyrosine hydroxylase fibers, nor the survival of nigral dopaminergic neurons after partial 6-hydroxydopamine lesions was affected by Nogo-A deletion. These results indicate that during maturation of cultured midbrain (dopaminergic) neurons, intracellular Nogo-A supports neurite growth initiation and branch formation.

Long distance directional growth of dopaminergic axons along pathways of netrin-1 and GDNF

Different experimental and clinical strategies have been used to promote survival of transplanted embryonic ventral mesencephalic (VM) neurons. However, few studies have focused on the long-distance growth of dopaminergic axons from VM transplants. The aim of this study is to identify some of the growth and guidance factors that support directed long-distance growth of dopaminergic axons from VM transplants. Lentivirus encoding either glial cell line-derived neurotrophic factor (GDNF) or netrin-1, or a combination of lenti-GDNF with either lenti-GDNF family receptor α1 (GFRα-1) or lenti-netrin-1 was injected to form a gradient along the corpus callosum. Two weeks later, a piece of embryonic day 14 VM tissue was transplanted into the corpus callosum adjacent to the low end of the gradient. Results showed that tyrosine hydroxylase (TH(+)) axons grew a very short distance from the VM transplants in control groups, with few axons reaching the midline. In GDNF or netrin-1 expressing groups, more TH(+) axons grew out of transplants and reached the midline. Pathways co-expressing GDNF with either GFRα-1 or netrin-1 showed significantly increased axonal outgrowth. Interestingly, only the GDNF/netrin-1 combination resulted in the majority of axons reaching the distal target (80%), whereas along the GDNF/GFRα-1 pathway only 20% of the axons leaving the transplant reached the distal target. This technique of long-distance axon guidance may prove to be a useful strategy in reconstructing damaged neuronal circuits, such as the nigrostriatal pathway in Parkinson's disease.

Human midbrain precursors activate the expected developmental genetic program and differentiate long-term to functional A9 dopamine neurons in vitro. Enhancement by Bcl-X(L)

Understanding the molecular programs of the generation of human dopaminergic neurons (DAn) from their ventral mesencephalic (VM) precursors is of key importance for basic studies, progress in cell therapy, drug screening and pharmacology in the context of Parkinson's disease. The nature of human DAn precursors in vitro is poorly understood, their properties unstable, and their availability highly limited. Here we present positive evidence that human VM precursors retaining their genuine properties and long-term capacity to generate A9 type Substantia nigra human DAn (hVM1 model cell line) can be propagated in culture. During a one month differentiation, these cells activate all key genes needed to progress from pro-neural and pro-dopaminergic precursors to mature and functional DAn. For the first time, we demonstrate that gene cascades are correctly activated during differentiation, resulting in the generation of mature DAn. These DAn have morphological and functional properties undistinguishable from those generated by VM primary neuronal cultures. In addition, we have found that the forced expression of Bcl-X(L) induces an increase in the expression of key developmental genes (MSX1, NGN2), maintenance of PITX3 expression temporal profile, and also enhances genes involved in DAn long-term function, maintenance and survival (EN1, LMX1B, NURR1 and PITX3). As a result, Bcl-X(L) anticipates and enhances DAn generation.

The Lewis GFP transgenic rat strain is a useful cell donor for neural transplantation

Stem cell transplantation is a promising therapeutic approach in neurodegenerative diseases. Studying graft survival and development has important implications for the further development of experimental and clinical transplantation protocols. Cellular elements in neural transplants are sometimes difficult to identify. The existing labeling methods cannot reliably provide stably labeled cells that can be detected in long-term experiments. Transgenic (tg) Lewis rats ubiquitously expressing green fluorescent protein (GFP) provide an ideal donor source. The aim of this project was to investigate the potential of GFP-tg Lewis rats to serve as donor tissue for neural stem cell transplantation. Ventral mesencephalon (VM) GFP-tg E14.5-derived cells were compared to wild-type (wt) in vitro and in vivo. Firstly, cells from GFP and non-GFP VM tissue were compared with regard to their proliferation and response towards 6-OHDA-toxicity in culture. Secondly, 6-OHDA-lesioned hemiparkinsonian Sprague-Dawley/Crl:CD(SD) rats received intrastriatal grafts derived from VM of E14.5 GFP-tg rats. Due to the fact that donor and recipient belong to two different rat strains, we focused on graft survival in correlation with immunosuppression and graft GFP and tyrosine hydroxylase (TH) expression. In summary, in vitro tg cells exhibited 98% GFP expression and did not differ from wt cells in any of the measured parameters. In vivo, all experimental groups showed a significant compensation in rotation behavior after transplantation. Furthermore, there was no difference on rotation behavior or graft morphology and survival pattern as well as GFP expression between immunosuppressed and nonimmunosuppressed animals. The GFP-positive population of the graft was composed of 13.3% GFAP-positive, 56.1% NeuN-positive, and 1.9% TH-positive cells. Analysis of graft subpopulations manifested that 70.6% of GFAP-positive, 86.9% of NeuN-positive, and 80.1% of TH-positive cells coexpressed GFP. In conclusion, our data show that the Lewis GFP-tg rats serve as an excellent cell source for studying primary neural precursor cells in the transplantation paradigm.

Sustained expression of PGC-1α in the rat nigrostriatal system selectively impairs dopaminergic function

Mitochondrial dysfunction and oxidative stress have been implicated in the etiology of Parkinson's disease. Therefore, pathways controlling mitochondrial activity rapidly emerge as potential therapeutic targets. Here, we explore the neuronal response to prolonged overexpression of peroxisome proliferator-activated receptor gamma coactivator-1 alpha (PGC-1α), a transcriptional regulator of mitochondrial function, both in vitro and in vivo. In neuronal primary cultures from the ventral midbrain, PGC-1α induces mitochondrial biogenesis and increases basal respiration. Over time, we observe an increasing proportion of the oxygen consumed by neurons which are dedicated to adenosine triphosphate production. In parallel to enhanced oxidative phosphorylation, PGC-1α progressively leads to a decrease in mitochondrial polarization. In the adult rat nigrostriatal system, adeno-associated virus (AAV)-mediated overexpression of PGC-1α induces the selective loss of dopaminergic markers and increases dopamine (DA) catabolism, leading to a reduction in striatal DA content. In addition, PGC-1α prevents the labeling of nigral neurons following striatal injection of the fluorogold retrograde tracer. When PGC-1α is expressed at higher levels following intranigral AAV injection, it leads to overt degeneration of dopaminergic neurons. Finally, PGC-1α overexpression does not prevent nigrostriatal degeneration in pathologic conditions induced by α-synuclein overexpression. Overall, we find that lasting overexpression of PGC-1α leads to major alterations in the metabolic activity of neuronal cells which dramatically impair dopaminergic function in vivo. These results highlight the central role of PGC-1α in the function and survival of dopaminergic neurons and the critical need for maintaining physiological levels of PGC-1α activity.

Direct generation of functional dopaminergic neurons from mouse and human fibroblasts

Transplantation of dopaminergic neurons can potentially improve the clinical outcome of Parkinson's disease, a neurological disorder resulting from degeneration of mesencephalic dopaminergic neurons. In particular, transplantation of embryonic-stem-cell-derived dopaminergic neurons has been shown to be efficient in restoring motor symptoms in conditions of dopamine deficiency. However, the use of pluripotent-derived cells might lead to the development of tumours if not properly controlled. Here we identified a minimal set of three transcription factors--Mash1 (also known as Ascl1), Nurr1 (also known as Nr4a2) and Lmx1a--that are able to generate directly functional dopaminergic neurons from mouse and human fibroblasts without reverting to a progenitor cell stage. Induced dopaminergic (iDA) cells release dopamine and show spontaneous electrical activity organized in regular spikes consistent with the pacemaker activity featured by brain dopaminergic neurons. The three factors were able to elicit dopaminergic neuronal conversion in prenatal and adult fibroblasts from healthy donors and Parkinson's disease patients. Direct generation of iDA cells from somatic cells might have significant implications for understanding critical processes for neuronal development, in vitro disease modelling and cell replacement therapies.

CD15, CD24, and CD29 define a surface biomarker code for neural lineage differentiation of stem cells

Identification and use of cell surface cluster of differentiation (CD) biomarkers have enabled much scientific and clinical progress. We identify a CD surface antigen code for the neural lineage based on combinatorial flow cytometric analysis of three distinct populations derived from human embryonic stem cells: (1) CD15(+)/CD29(HI)/CD24(LO) surface antigen expression defined neural stem cells; (2) CD15(-)/CD29(HI)/CD24(LO) revealed neural crest-like and mesenchymal phenotypes; and (3) CD15(-)/CD29(LO)/CD24(HI) selected neuroblasts and neurons. Fluorescence-activated cell sorting (FACS) for the CD15(-)/CD29(LO)/CD24(HI) profile reduced proliferative cell types in human embryonic stem cell differentiation. This eliminated tumor formation in vivo, resulting in pure neuronal grafts. In conclusion, combinatorial CD15/CD24/CD29 marker profiles define neural lineage development of neural stem cell, neural crest, and neuronal populations from human stem cells. We believe this set of biomarkers enables analysis and selection of neural cell types for developmental studies and pharmacological and therapeutic applications.