Cell replacement therapy for Parkinson's disease: how close are we to the clinic?

Development of a Smart Wireless Multisensor Platform for an Optogenetic Brain Implant

Implantable cell replacement therapies promise to completely restore the function of neural structures, possibly changing how we currently perceive the onset of neurodegenerative diseases. One of the major clinical hurdles for the routine implementation of stem cell therapies is poor cell retention and survival, demanding the need to better understand these mechanisms while providing precise and scalable approaches to monitor these cell-based therapies in both pre-clinical and clinical scenarios. This poses significant multidisciplinary challenges regarding planning, defining the methodology and requirements, prototyping and different stages of testing. Aiming toward an optogenetic neural stem cell implant controlled by a smart wireless electronic frontend, we show how an iterative development methodology coupled with a modular design philosophy can mitigate some of these challenges. In this study, we present a miniaturized, wireless-controlled, modular multisensor platform with fully interfaced electronics featuring three different modules: an impedance analyzer, a potentiostat and an optical stimulator. We show the application of the platform for electrical impedance spectroscopy-based cell monitoring, optical stimulation to induce dopamine release from optogenetically modified neurons and a potentiostat for cyclic voltammetry and amperometric detection of dopamine release. The multisensor platform is designed to be used as an opto-electric headstage for future in vivo animal experiments.

Current Developments in Cell Replacement Therapy for Parkinson's Disease

Parkinson's disease (PD) is characterized by tremor, rigidity, and bradykinesia. PD is caused mainly by depletion of the nigrostriatal pathway. Conventional medications such as levodopa are highly effective in the early stage of PD; however, these medications fail to prevent the underlying neurodegeneration. Cell replacement therapy (CRT) is a strategy to achieve long-term motor improvements by preventing or slowing disease progression. Replacement therapy can also increase the number of surviving dopaminergic neurons, an outcome confirmed by positron emission tomography and immunostaining. Several promising cell sources offer authentic and functional dopaminergic replacement neurons. These cell sources include fetal ventral mesencephalic tissue, embryonic stem cells (ESCs), neural stem cells (NSCs), mesenchymal stem cells (MSCs) from various tissues, induced pluripotent stem cells (iPSCs), and induced neural cells. To fully develop the potential of CRT, we need to recognize the advantages and limitations of these cell sources. For example, although fetal ventral midbrain is efficacious in some patients, its ethical issues and the existence of graft-induced dyskinesias (GID) have prevented its use in large-scale clinical applications. ESCs have reliable isolation protocols and the potential to differentiate into dopaminergic progenitors. iPSCs and induced neural cells are suitable for autologous grafting. Here we review milestone improvements and emerging sources for cell-based PD therapy to serve as a framework for clinicians and a key reference to develop replacement therapy for other neurological disorders.

Challenges and translational considerations of mesenchymal stem/stromal cell therapy for Parkinson's disease

Parkinson's disease (PD) is the second most common neurodegenerative disease characterized by the progressive loss of dopaminergic neurons in the substantia nigra pars compacta and the presence of Lewy bodies, which gives rise to motor and non-motor symptoms. Unfortunately, current therapeutic strategies for PD merely treat the symptoms of the disease, only temporarily improve the patients' quality of life, and are not sufficient for completely alleviating the symptoms. Therefore, cell-based therapies have emerged as a novel promising therapeutic approach in PD treatment. Mesenchymal stem/stromal cells (MSCs) have arisen as a leading contender for cell sources due to their regenerative and immunomodulatory capabilities, limited ethical concerns, and low risk of tumor formation. Although several studies have shown that MSCs have the potential to mitigate the neurodegenerative pathology of PD, variabilities in preclinical and clinical trials have resulted in inconsistent therapeutic outcomes. In this review, we strive to highlight the sources of variability in studies using MSCs in PD therapy, including MSC sources, the use of autologous or allogenic MSCs, dose, delivery methods, patient factors, and measures of clinical outcome. Available evidence indicates that while the use of MSCs in PD has largely been promising, conditions need to be standardized so that studies can be effectively compared with one another and experimental designs can be improved upon, such that this body of science can continue to move forward.

Neuroprotective and neurogenic effects of novel tetramethylpyrazine derivative T-006 in Parkinson's disease models through activating the MEF2-PGC1α and BDNF/CREB pathways

T-006, a new derivative of tetramethylpyrazine, has been recently found to protect against 6-hydroxydopamine (6-OHDA)-induced neuronal damage and clear α-synuclein (α-syn) by enhancing proteasome activity in an α-syn transgenic Parkinson’s disease (PD) model. The effect of T-006 on the 1-methyl-4-phenyl-1, 2, 3, 6-tetrahydropyridine (MPTP)-induced PD model, however, has not been tested and T-006’s neuroprotective mechanisms have not been fully elucidated. In this study, we further investigated the neuroprotective and neurogenic effects of T-006 and explored its underlying mechanism of action in both cellular and animal PD models. T-006 was able to improve locomotor behavior, increase survival of nigra dopaminergic neurons and boost striatal dopamine levels in both MPTP- and 6-OHDA-induced animals. T-006 treatment restored the altered expressions of myocyte enhancer factor 2D (MEF2D), peroxisome proliferator-activated receptor γ (PPARγ) co-activator 1α (PGC1α) and NF-E2-related factor 1/2 (Nrf1/2) via modulation of Akt/GSK3β signaling. T-006 stimulated MEF2, PGC1α and Nrf2 transcriptional activities, inducing Nrf2 nuclear localization. Interestingly, T-006 promoted endogenous adult neurogenesis toward a dopaminergic phenotype by activating brain-derived neurotrophic factor (BDNF) and cAMP responsive element-binding protein (CREB) in 6-OHDA rats. Our work demonstrated that T-006 is a potent neuroprotective and neuroregenerative agent that may have therapeutic potential in the treatment of PD.

Complementation of dopaminergic signaling by Pitx3-GDNF synergy induces dopamine secretion by multipotent Ntera2 cells

Human teratocarcinoma cell line Ntera2 (NT2) expresses dopamine signals and has shown its safe profile for clinical applications. Attempts to restore complete dopaminergic (DAergic) phenotype enabling these cells to secrete dopamine have not been fully successful so far. We applied a blend of gene transfer techniques and a defined medium to convert NT2 cells to fully DAergic. The cells were primarily engineered to overexpress the Pitx3 gene product and then cultured in a growth medium supplemented with knockout serum and retinoic acid to form embroid bodies (EBs). Trypsinization of EB colonies produced single cells ready for differentiation. Neuronal/DAergic induction was promoted by applying conditioned medium taken from engineered human astrocytomas over-secreting glial cell-derived neurotrophic factor (GDNF). Immunocytochemistry, reverse-transcription and real-time polymerase chain reaction analyses confirmed significantly induced expression of molecules involved in dopamine signaling and metabolism including tyrosine hydroxylase, Nurr1, dopamine transporter, and aromatic acid decarboxylase. High-performance liquid chromatography analysis indicated release of dopamine only from a class of fully differentiated cells expressing Pitx3 and exposed to GDNF. In addition, Pitx3 and GDNF additively promoted in vitro neuroprotection against Parkinsonian toxin. One month after transplantation to the striatum of 6-OHDA-leasioned rats, differentiated NT2 cells survived and induced significant increase in striatal volume. Besides, cell implantation improved motor coordination in Parkinson's disease (PD) rat models. Our findings highlight the importance of Pitx3-GDNF interplay in dopamine signaling and indicate that our strategy might be useful for the restoration of DAergic fate of NT2 cells to make them clinically applicable toward cell replacement therapy of PD.

Trabecular meshwork mesenchymal stem cell transplantation improve motor symptoms of parkinsonian rat model

Stem cell transplantation is a new therapeutic strategy in the treatment of neurodegenerative disorders such as Parkinson's disease (PD). Therefore, in this study, the therapeutic effects of Trabecular Meshwork Mesenchymal Stem Cells (TM-MSCs) transplantation, as a new source of mesenchymal stem cells, were evaluated in the animal model of PD. After the development and confirmation of hemi-parkinsonian rats by administration of 6-hydroxy dopamine (6-OHDA) and apomorphine-induced rotation test, green fluorescent protein (GFP) labeled TM-MSCs (normal and induced cells) were transplanted in the striatum of rats. Next, the rotation test, rotarod test, open field, passive avoidance memory tests and immunohistochemistry for tyrosine hydroxylase (TH) were done. The results showed that the number of turns significantly decreased and the improvement of motor performance was achieved after cell transplantation. However, there was no significant difference in passive avoidance memory of animals documented by shuttle box test. The number of GFP- labeled cells expressing TH significantly is increased compared to the vehicle group. Collectively, it seems that TM-MSCs and induced TM-MSCs cell transplantation have positive effects on some aspects of the animal model of PD. Other studies may reveal the potentially positive aspects of these cells in the laboratory and clinical studies.

Liver X receptors agonist promotes differentiation of rat bone marrow derived mesenchymal stem cells into dopaminergic neuron-like cells

Dopaminergic (DA) neurons derived from bone marrow derived mesenchymal stem cells (BMSCs) maybe a valuable source for cell replacement therapy in Parkinson disease. Recent studies showed that new functions of LXR and their ligands have been proposed to prevent PD in the adult nervous system. The present study was designed to observe the effect of liver X receptors (LXR) agonist on differentiation of rat BMSCs into DA neurons. Expressions of the neuronal markers (Tuj1 and Nestin), the specific marker of DA neurons (tyrosine hydroxylase, TH), LXR α and LXR β were measured by immunocytochemical assay and TH/Tuj1 positive cells were determined by quantitative cell count analyses. mRNA expressions of LXR α, LXR β, TH, DAT, Nurr1, Pitx3, En1 and Lmx1b were measured by qPCR. Compared with growth factors (GF) treated group, combined use of LXR and GF induced rat BMSCs to TH-expressing cells with 87.42% of efficiency in 6 days of period of induction. LXR agonist alone did not induce the differentiation. Compared with GF alone, combined use of LXR and GF increased expressions of LXR α and LXR β protein and mRNA and TH, DAT, Nurr1, and Pitx3 mRNA, decreased expressions of En1 and Lmx1b mRNA. Our experimental results indicated that LXR activation leads to improve induction efficiency and shorten induction period of rat BMSCs into DA neuron-like cells through regulating DA development-related genes expressions and that LXR can be considered as a candidate target for drug development to improve differentiation of BMSCs into DA neurons.

Mesenchymal Stem Cells of Dental Origin-Their Potential for Antiinflammatory and Regenerative Actions in Brain and Gut Damage

Alzheimer’s disease, Parkinson’s disease, traumatic brain and spinal cord injury and neuroinflammatory multiple sclerosis are diverse disorders of the central nervous system. However, they are all characterized by various levels of inappropriate inflammatory/immune response along with tissue destruction. In the gastrointestinal system, inflammatory bowel disease (IBD) is also a consequence of tissue destruction resulting from an uncontrolled inflammation. Interestingly, there are many similarities in the immunopathomechanisms of these CNS disorders and the various forms of IBD. Since it is very hard or impossible to cure them by conventional manner, novel therapeutic approaches such as the use of mesenchymal stem cells, are needed. Mesenchymal stem cells have already been isolated from various tissues including the dental pulp and periodontal ligament. Such cells possess transdifferentiating capabilities for different tissue specific cells to serve as new building blocks for regeneration. But more importantly, they are also potent immunomodulators inhibiting proinflammatory processes and stimulating anti-inflammatory mechanisms.

The present review was prepared to compare the immunopathomechanisms of the above mentioned neurodegenerative, neurotraumatic and neuroinflammatory diseases with IBD. Additionally, we considered the potential use of mesenchymal stem cells, especially those from dental origin to treat such disorders. We conceive that such efforts will yield considerable advance in treatment options for central and peripheral disorders related to inflammatory degeneration.

Iron Deposition Leads to Neuronal α-Synuclein Pathology by Inducing Autophagy Dysfunction

Growing evidence has indicated that iron deposition in the substantia nigra plays an important role in Parkinson’s disease (PD). However, the underlying mechanism is still elusive. Using primary dopaminergic neurons and SH-SY5Y cells cultured in vitro, we observed that iron loading increased α-synuclein and reactive oxygen species (ROS) levels in these cells but did not affect the intracellular α-synuclein mRNA levels. Furthermore, iron loading significantly downregulated Beclin-1 levels and decreased the ratio of microtubule-associated protein 1 light chain 3 isoforms (LC3 II/LC3 I). However, a significant change in the levels of autophagy-related gene 5 (Atg5) was not observed in either neurons or SH-SY5Y cells after iron treatment. After treatment with rapamycin, the iron loading-induced increase in the α-synuclein level was significantly reversed and ROS generation was alleviated in both cultured neurons and SH-SY5Y cells. These results indicate that the inhibition of autophagy is critical for the pathological alterations in α-synuclein induced by iron loading. Moreover, treatment with vitamin E did not affect the increase in the α-synuclein levels but significantly eliminated the iron-induced ROS production. Together, our study shows that autophagy dysfunction contributes to iron-induced α-synuclein pathology.

Genetic modification of H2AX renders mesenchymal stromal cell-derived dopamine neurons more resistant to DNA damage and subsequent apoptosis

BACKGROUND AIMS

Aberrant production of reactive oxygen species (ROS) and its impact on the integrity of genomic DNA have been considered one of the major risk factors for the loss of dopaminergic neurons in Parkinson's disease (PD). Stem cell transplantation as a strategy to replenish new functional neurons has great potential for PD treatment. However, limited survival of stem cells post-transplantation has always been an obstacle ascribed to the existence of neurotoxic environment in PD patients.

METHODS

To improve the survival of transplanted stem cells for PD treatment, we explored a new strategy based on the function of the H2AX gene (H2A histone family, member X) in determination of DNA repair and cell apoptosis. We introduced a mutant form Y142F of H2AX into dopamine (DA) neuron-like cells differentiated from bone marrow-derived mesenchymal stromal cells (BMSCs).

RESULTS

Expression of H2AX(Y142F) renders DA neuron-like cells more resistant to DNA damage and subsequent cell death induced by ultraviolet irradiation and 1-methyl-4-phenylpyridinium (MPP+) treatment.

DISCUSSION

This is a meaningful attempt to improve the sustainability of BMSC-derived dopamine neurons under a brain neurotoxic environment. Further studies are needed to evaluate the implications of our findings in stem cell therapy for PD and related diseases.

Cortex Fraxini (Qingpi) Protects Rat Pheochromocytoma Cells against 6-Hydroxydopamine-Induced Apoptosis

Parkinson's disease (PD) is a chronic neurodegenerative disorder having close relationship with oxidative stress induced by reactive oxygen species (ROS). Cortex Fraxini (QP) is a kind of traditional Chinese medicinal herb with antioxidant properties. It may be a potential candidate for preventing the development of chronic neurodegenerative diseases. Thus, the key objective of the current study was to investigate the neuroprotective effect of QP water extract on 6-hydroxydopamine (6-OHDA) induced apoptosis in rat pheochromocytoma (PC12) cells. It was found that QP water extract possesses strong antioxidant property with SC₅₀ = 0.15 mg/mL. Total phenolic content of QP water extract was found to be 200.78 ± 2.65 mg GAE/g. QP water extract's free radical scavenging capacity was demonstrated by reversing the increased level of intracellular ROS induced by 6-OHDA, using 2′,7′-dichlorodihydrofluorescein diacetate. Moreover, QP water extract (0.5 mg/mL) could remarkably increase the viability of PC12 cells treated with 6-OHDA. The protective effect of QP water extract was found to be via inhibiting MEK/ERK pathway and reversing PI3-K/Akt/GSK3β pathway. The current results suggest that QP might be a potential candidate for preventing the development of neurodegenerative diseases, such as PD.

Dopaminergic-like neurons derived from oral mucosa stem cells by developmental cues improve symptoms in the hemi-parkinsonian rat model

Achieving safe and readily accessible sources for cell replacement therapy in Parkinson’s disease (PD) is still a challenging unresolved issue. Recently, a primitive neural crest stem cell population (hOMSC) was isolated from the adult human oral mucosa and characterized in vitro and in vivo. In this study we assessed hOMSC ability to differentiate into dopamine-secreting cells with a neuronal-dopaminergic phenotype in vitro in response to dopaminergic developmental cues and tested their therapeutic potential in the hemi-Parkinsonian rat model. We found that hOMSC express constitutively a repertoire of neuronal and dopaminergic markers and pivotal transcription factors. Soluble developmental factors induced a reproducible neuronal-like morphology in the majority of hOMSC, downregulated stem cells markers, upregulated the expression of the neuronal and dopaminergic markers that resulted in dopamine release capabilities. Transplantation of these dopaminergic-induced hOMSC into the striatum of hemi-Parkinsonian rats improved their behavioral deficits as determined by amphetamine-induced rotational behavior, motor asymmetry and motor coordination tests. Human TH expressing cells and increased levels of dopamine in the transplanted hemispheres were observed 10 weeks after transplantation. These results demonstrate for the first time that soluble factors involved in the development of DA neurons, induced a DA phenotype in hOMSC in vitro that significantly improved the motor function of hemiparkinsonian rats. Based on their neural-related origin, their niche accessibility by minimal-invasive procedures and their propensity for DA differentiation, hOMSC emerge as an attractive tool for autologous cell replacement therapy in PD.

In vivo cell reprogramming to pluripotency: exploring a novel tool for cell replenishment and tissue regeneration

The potential of cell-replacement strategies for the treatment of disorders in which a particular cell type is damaged or degenerated has prompted the search for the perfect cell source. iPSCs (induced pluripotent stem cells) stand out as very advantageous candidates thanks to their self-renewal capacity and differentiation potential, together with the possibility of generating them from autologous somatic cells with minimally invasive techniques. However, their differentiation into the required cell type, precise delivery and successful engraftment and survival in the host are still challenging. We have proposed the transient reprogramming of somatic cells towards a pluripotent state in their in vivo microenvironment as a means to facilitate the regeneration of the tissue. The initial reports of in vivo reprogramming to pluripotency in the literature are reviewed and the potential clinical applications of this strategy are discussed.

Astrocyte-like cells derived from human oral mucosa stem cells provide neuroprotection in vitro and in vivo

Human oral mucosa stem cells (hOMSC) are a recently described neural crest-derived stem cell population. Therapeutic quantities of potent hOMSC can be generated from small biopsies obtained by minimally invasive procedures. Our objective was to evaluate the potential of hOMSC to differentiate into astrocyte-like cells and provide peripheral neuroprotection. We induced hOMSC differentiation into cells showing an astrocyte-like morphology that expressed characteristic astrocyte markers as glial fibrillary acidic protein, S100β, and the excitatory amino acid transporter 1 and secreted neurotrophic factors (NTF) such as brain-derived neurotrophic factor, vascular endothelial growth factor, glial cell line-derived neurotrophic factor, and insulin-like growth factor 1. Conditioned medium of the induced cells rescued motor neurons from hypoxia or oxidative stress in vitro, suggesting a neuroprotective effect mediated by soluble factors. Given the neuronal support (NS) ability of the cells, the differentiated cells were termed hOMSC-NS. Rats subjected to sciatic nerve injury and transplanted with hOMSC-NS showed improved motor function after transplantation. At the graft site we found the transplanted cells, increased levels of NTF, and a significant preservation of functional neuromuscular junctions, as evidenced by colocalization of α-bungarotoxin and synaptophysin. Our findings show for the first time that hOMSC-NS generated from oral mucosa exhibit neuroprotective effects in vitro and in vivo and point to their future therapeutic use in neural disorders.

Sox-2 Positive Neural Progenitors in the Primate Striatum Undergo Dynamic Changes after Dopamine Denervation

The existence of endogenous neural progenitors in the nigrostriatal system could represent a powerful tool for restorative therapies in Parkinson's disease. Sox-2 is a transcription factor expressed in pluripotent and adult stem cells, including neural progenitors. In the adult brain Sox-2 is expressed in the neurogenic niches. There is also widespread expression of Sox-2 in other brain regions, although the neurogenic potential outside the niches is uncertain. Here, we analyzed the presence of Sox-2⁺ cells in the adult primate (Macaca fascicularis) brain in naïve animals (N = 3) and in animals exposed to systemic administration of 1-methyl-4-phenyl-1,2,3,6 tetrahydropyridine to render them parkinsonian (N = 8). Animals received bromodeoxyuridine (100 mg/kg once a day during five consecutive days) to label proliferating cells and their progeny. Using confocal and electron microscopy we analyzed the Sox-2⁺ cell population in the nigrostriatal system and investigated changes in the number, proliferation and neurogenic potential of Sox-2⁺ cells, in control conditions and at two time points after MPTP administration. We found Sox-2⁺ cells with self-renewal capacity in both the striatum and the substantia nigra. Importantly, only in the striatum Sox-2⁺ was expressed in some calretinin⁺ neurons. MPTP administration led to an increase in the proliferation of striatal Sox-2⁺ cells and to an acute, concomitant decrease in the percentage of Sox-2⁺/calretinin⁺ neurons, which recovered by 18 months. Given their potential capacity to differentiate into neurons and their responsiveness to dopamine neurotoxic insults, striatal Sox-2⁺ cells represent good candidates to harness endogenous repair mechanisms for regenerative approaches in Parkinson's disease.