Chemical Control of Grafted Human PSC-Derived Neurons in a Mouse Model of Parkinson's Disease

Past, present, and future of cell replacement therapy for parkinson's disease: a novel emphasis on host immune responses

Parkinson's disease (PD) stands as the second most common neurodegenerative disorder after Alzheimer's disease, and its prevalence continues to rise with the aging global population. Central to the pathophysiology of PD is the specific degeneration of midbrain dopamine neurons (mDANs) in the substantia nigra. Consequently, cell replacement therapy (CRT) has emerged as a promising treatment approach, initially supported by various open-label clinical studies employing fetal ventral mesencephalic (fVM) cells. Despite the initial favorable results, fVM cell therapy has intrinsic and logistical limitations that hinder its transition to a standard treatment for PD. Recent efforts in the field of cell therapy have shifted its focus towards the utilization of human pluripotent stem cells, including human embryonic stem cells and induced pluripotent stem cells, to surmount existing challenges. However, regardless of the transplantable cell sources (e.g., xenogeneic, allogeneic, or autologous), the poor and variable survival of implanted dopamine cells remains a major obstacle. Emerging evidence highlights the pivotal role of host immune responses following transplantation in influencing the survival of implanted mDANs, underscoring an important area for further research. In this comprehensive review, building upon insights derived from previous fVM transplantation studies, we delve into the functional ramifications of host immune responses on the survival and efficacy of grafted dopamine cells. Furthermore, we explore potential strategic approaches to modulate the host immune response, ultimately aiming for optimal outcomes in future clinical applications of CRT for PD.

iPS cell therapy 2.0: Preparing for next-generation regenerative medicine

This year marks the tenth anniversary of the world's first transplantation of tissue generated from induced pluripotent stem cells (iPSCs). There is now a growing number of clinical trials worldwide examining the efficacy and safety of autologous and allogeneic iPSC-derived products for treating various pathologic conditions. As we patiently wait for the results from these and future clinical trials, it is imperative to strategize for the next generation of iPSC-based therapies. This review examines the lessons learned from the development of another advanced cell therapy, chimeric antigen receptor (CAR) T cells, and the possibility of incorporating various new bioengineering technologies in development, from RNA engineering to tissue fabrication, to apply iPSCs not only as a means to achieve personalized medicine but also as designer medical applications.

Mild hypothermia promotes neuronal differentiation of human neural stem cells via RBM3-SOX11 signaling pathway

Both therapeutic hypothermia and neural stem cells (NSCs) transplantation have shown promise in neuroprotection and neural repair after brain injury. However, the effects of therapeutic hypothermia on neuronal differentiation of NSCs are not elucidated. In this study, we aimed to investigate whether mild hypothermia promoted neuronal differentiation in cultured and transplanted human NSCs (hNSCs). A significant increase in neuronal differentiation rate of hNSCs was found when exposed to 35°C, from 33% to 45% in vitro and from 7% to 15% in vivo. Additionally, single-cell RNA sequencing identified upregulation of RNA-binding motif protein 3 (RBM3) in neuroblast at 35°C, which stabilized the SRY-box transcription factor 11 (SOX11) mRNA and increased its protein expression, leading to an increase in neuronal differentiation of hNSCs. In conclusion, our study highlights that mild hypothermia at 35°C enhances hNSCs-induced neurogenesis through the novel RBM3-SOX11 signaling pathway, and provides a potential treatment strategy in brain disorders.

Clinical translation of pluripotent stem cell-based therapies: successes and challenges

The translational stem cell research field has progressed immensely in the past decade. Development and refinement of differentiation protocols now allows the generation of a range of cell types, such as pancreatic β-cells and dopaminergic neurons, from human pluripotent stem cells (hPSCs) in an efficient and good manufacturing practice-compliant fashion. This has led to the initiation of several clinical trials using hPSC-derived cells to replace lost or dysfunctional cells, demonstrating evidence of both safety and efficacy. Here, we highlight successes from some of the hPSC-based trials reporting early signs of efficacy and discuss common challenges in clinical translation of cell therapies.

Recent approaches in regenerative medicine in the fight against neurodegenerative disease

Neurodegenerative diseases arise due to slow and gradual loss of structure and/or function of neurons and glial cells and cause different degrees of loss of cognition abilities and sensation. The little success in developing effective treatments imposes a high and regressive economic impact on society, patients and their families. In recent years, regenerative medicine has provided a great opportunity to research new innovative strategies with strong potential to treatleva these diseases. These effects are due to the ability of suitable cells and biomaterials to regenerate damaged nerves with differentiated cells, creating an appropriate environment for recovering or preserving existing healthy neurons and glial cells from destruction and damage. Ultimately, a better understanding and thus a further investigation of stem cell technology, tissue engineering, gene therapy, and exosomes allows progress towards practical and effective treatments for neurodegenerative diseases. Therefore, in this review, advances currently being developed in regenerative medicine using animal models and human clinical trials in neurological disorders are summarized.

One-step cell biomanufacturing platform: porous gelatin microcarrier beads promote human embryonic stem cell-derived midbrain dopaminergic progenitor cell differentiation in vitro and survival after transplantation in vivo

Numerous studies have shown that cell replacement therapy can replenish lost cells and rebuild neural circuitry in animal models of Parkinson's disease. Transplantation of midbrain dopaminergic progenitor cells is a promising treatment for Parkinson's disease. However, transplanted cells can be injured by mechanical damage during handling and by changes in the transplantation niche. Here, we developed a one-step biomanufacturing platform that uses small-aperture gelatin microcarriers to produce beads carrying midbrain dopaminergic progenitor cells. These beads allow midbrain dopaminergic progenitor cell differentiation and cryopreservation without digestion, effectively maintaining axonal integrity in vitro. Importantly, midbrain dopaminergic progenitor cell bead grafts showed increased survival and only mild immunoreactivity in vivo compared with suspended midbrain dopaminergic progenitor cell grafts. Overall, our findings show that these midbrain dopaminergic progenitor cell beads enhance the effectiveness of neuronal cell transplantation.

Dopaminergic Cell Replacement for Parkinson's Disease: Addressing the Intracranial Delivery Hurdle

Parkinson's disease (PD) is an increasingly prevalent neurological disorder, affecting more than 8.5 million individuals worldwide. α-Synucleinopathy in PD is considered to cause dopaminergic neuronal loss in the substantia nigra, resulting in characteristic motor dysfunction that is the target for current medical and surgical therapies. Standard treatment for PD has remained unchanged for several decades and does not alter disease progression. Furthermore, symptomatic therapies for PD are limited by issues surrounding long-term efficacy and side effects. Cell replacement therapy (CRT) presents an alternative approach that has the potential to restore striatal dopaminergic input and ameliorate debilitating motor symptoms in PD. Despite promising pre-clinical data, CRT has demonstrated mixed success clinically. Recent advances in graft biology have renewed interest in the field, resulting in several worldwide ongoing clinical trials. However, factors surrounding the effective neurosurgical delivery of cell grafts have remained under-studied, despite their significant potential to influence therapeutic outcomes. Here, we focus on the key neurosurgical factors to consider for the clinical translation of CRT. We review the instruments that have been used for cell graft delivery, highlighting current features and limitations, while discussing how future devices could address these challenges. Finally, we review other novel developments that may enhance graft accessibility, delivery, and efficacy. Challenges surrounding neurosurgical delivery may critically contribute to the success of CRT, so it is crucial that we address these issues to ensure that CRT does not falter at the final hurdle.

Enhanced production of mesencephalic dopaminergic neurons from lineage-restricted human undifferentiated stem cells

Current differentiation protocols for generating mesencephalic dopaminergic (mesDA) neurons from human pluripotent stem cells result in grafts containing only a small proportion of mesDA neurons when transplanted in vivo. In this study, we develop lineage-restricted undifferentiated stem cells (LR-USCs) from pluripotent stem cells, which enhances their potential for differentiating into caudal midbrain floor plate progenitors and mesDA neurons. Using a ventral midbrain protocol, 69% of LR-USCs become bona fide caudal midbrain floor plate progenitors, compared to only 25% of human embryonic stem cells (hESCs). Importantly, LR-USCs generate significantly more mesDA neurons under midbrain and hindbrain conditions in vitro and in vivo. We demonstrate that midbrain-patterned LR-USC progenitors transplanted into 6-hydroxydopamine-lesioned rats restore function in a clinically relevant non-pharmacological behavioral test, whereas midbrain-patterned hESC-derived progenitors do not. This strategy demonstrates how lineage restriction can prevent the development of undesirable lineages and enhance the conditions necessary for mesDA neuron generation.

Modeling of intramembranous ossification using human pluripotent stem cell-derived paraxial mesoderm derivatives

Vertebrates form their skeletal tissues from three distinct origins (the neural crest, paraxial mesoderm, and lateral plate mesoderm) through two distinct modes of ossification (intramembranous and endochondral ossification). Since the paraxial mesoderm generates both intramembranous and endochondral bones, it is thought to give rise to both osteoprogenitors and osteo-chondroprogenitors. However, it remains unclear what directs the paraxial mesoderm-derived cells toward these different fates in distinct skeletal elements during human skeletal development. To answer this question, we need experimental systems that recapitulate paraxial mesoderm-mediated intramembranous and endochondral ossification processes. In this study, we aimed to develop a human pluripotent stem cell (hPSC)-based system that models the human intramembranous ossification process. We found that spheroid culture of the hPSC-derived paraxial mesoderm derivatives generates osteoprogenitors or osteo-chondroprogenitors depending on stimuli. The former induced intramembranous ossification, and the latter endochondral ossification, in mouse renal capsules. Transcriptional profiling supported the notion that bone signatures were enriched in the intramembranous bone-like tissues. Thus, we developed a system that recapitulates intramembranous ossification, and that enables the induction of two distinct modes of ossification by controlling the cell fate of the hPSC-derived paraxial mesoderm derivatives.

Human Embryonic Stem Cell-Derived Immature Midbrain Dopaminergic Neurons Transplanted in Parkinsonian Monkeys

Human embryonic stem cells (hESCs) differentiate into specialized cells, including midbrain dopaminergic neurons (DANs), and Non-human primates (NHPs) injected with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine develop some alterations observed in Parkinson's disease (PD) patients. Here, we obtained well-characterized DANs from hESCs and transplanted them into two parkinsonian monkeys to assess their behavioral and imaging changes. DANs from hESCs expressed dopaminergic markers, generated action potentials, and released dopamine (DA) in vitro. These neurons were transplanted bilaterally into the putamen of parkinsonian NHPs, and using magnetic resonance imaging techniques, we calculated the fractional anisotropy (FA) and mean diffusivity (MD), both employed for the first time for these purposes, to detect in vivo axonal and cellular density changes in the brain. Likewise, positron-emission tomography scans were performed to evaluate grafted DANs. Histological analyses identified grafted DANs, which were quantified stereologically. After grafting, animals showed signs of partially improved motor behavior in some of the HALLWAY motor tasks. Improvement in motor evaluations was inversely correlated with increases in bilateral FA. MD did not correlate with behavior but presented a negative correlation with FA. We also found higher 11C-DTBZ binding in positron-emission tomography scans associated with grafts. Higher DA levels measured by microdialysis after stimulation with a high-potassium solution or amphetamine were present in grafted animals after ten months, which has not been previously reported. Postmortem analysis of NHP brains showed that transplanted DANs survived in the putamen long-term, without developing tumors, in immunosuppressed animals. Although these results need to be confirmed with larger groups of NHPs, our molecular, behavioral, biochemical, and imaging findings support the integration and survival of human DANs in this pre-clinical PD model.

Midbrain organoids-development and applications in Parkinson's disease

Human brain development is spatially and temporally complex. Insufficient access to human brain tissue and inadequacy of animal models has limited the study of brain development and neurodegenerative diseases. Recent advancements of brain organoid technology have created novel opportunities to model human-specific neurodevelopment and brain diseases. In this review, we discuss the use of brain organoids to model the midbrain and Parkinson's disease. We critically evaluate the extent of recapitulation of PD pathology by organoids and discuss areas of future development that may lead to the model to become a next-generation, personalized therapeutic strategy for PD and beyond.

Directional induction of neural stem cells, a new therapy for neurodegenerative diseases and ischemic stroke

Due to the limited capacity of the adult mammalian brain to self-repair and regenerate, neurological diseases, especially neurodegenerative disorders and stroke, characterized by irreversible cellular damage are often considered as refractory diseases. Neural stem cells (NSCs) play a unique role in the treatment of neurological diseases for their abilities to self-renew and form different neural lineage cells, such as neurons and glial cells. With the increasing understanding of neurodevelopment and advances in stem cell technology, NSCs can be obtained from different sources and directed to differentiate into a specific neural lineage cell phenotype purposefully, making it possible to replace specific cells lost in some neurological diseases, which provides new approaches to treat neurodegenerative diseases as well as stroke. In this review, we outline the advances in generating several neuronal lineage subtypes from different sources of NSCs. We further summarize the therapeutic effects and possible therapeutic mechanisms of these fated specific NSCs in neurological disease models, with special emphasis on Parkinson's disease and ischemic stroke. Finally, from the perspective of clinical translation, we compare the strengths and weaknesses of different sources of NSCs and different methods of directed differentiation, and propose future research directions for directed differentiation of NSCs in regenerative medicine.

Immortal orexin cell transplants restore motor-arousal synchrony during cataplexy

Waking behaviors such as sitting or standing require suitable levels of muscle tone. But it is unclear how arousal and motor circuits communicate with one another so that appropriate motor tone occurs during wakefulness. Cataplexy is a peculiar condition in which muscle tone is involuntarily lost during normal periods of wakefulness. Cataplexy therefore provides a unique opportunity for identifying the signaling mechanisms that synchronize motor and arousal behaviors. Cataplexy occurs when hypothalamic orexin neurons are lost in narcolepsy; however, it is unclear if motor-arousal decoupling in cataplexy is directly or indirectly caused by orexin cell loss. Here, we used genomic, proteomic, chemogenetic, electrophysiological, and behavioral assays to determine if grafting orexin cells into the brain of cataplectic (i.e., orexin^-/-) mice restores normal motor-arousal behaviors by preventing cataplexy. First, we engineered immortalized orexin cells and found that they not only produce and release orexin but also exhibit a gene profile that mimics native orexin neurons. Second, we show that engineered orexin cells thrive and integrate into host tissue when transplanted into the brain of mice. Next, we found that grafting only 200-300 orexin cells into the dorsal raphe nucleus-a region densely innervated by native orexin neurons-reduces cataplexy. Last, we show that real-time chemogenetic activation of orexin cells restores motor-arousal synchrony by preventing cataplexy. We suggest that orexin signaling is critical for arousal-motor synchrony during wakefulness and that the dorsal raphe plays a pivotal role in coupling arousal and motor behaviors.

Mapping of clonal lineages across developmental stages in human neural differentiation

The cell lineages across developmental stages remain to be elucidated. Here, we developed single-cell split barcoding (SISBAR) that allows clonal tracking of single-cell transcriptomes across stages in an in vitro model of human ventral midbrain-hindbrain differentiation. We developed "potential-spective" and "origin-spective" analyses to investigate the cross-stage lineage relationships and mapped a multi-level clonal lineage landscape depicting the whole differentiation process. We uncovered many previously uncharacterized converging and diverging trajectories. Furthermore, we demonstrate that a transcriptome-defined cell type can arise from distinct lineages that leave molecular imprints on their progenies, and the multilineage fates of a progenitor cell-type represent the collective results of distinct rather than similar clonal fates of individual progenitors, each with distinct molecular signatures. Specifically, we uncovered a ventral midbrain progenitor cluster as the common clonal origin of midbrain dopaminergic (mDA) neurons, midbrain glutamatergic neurons, and vascular and leptomeningeal cells and identified a surface marker that can improve graft outcomes.

A Comprehensive Review on Barium Titanate Nanoparticles as a Persuasive Piezoelectric Material for Biomedical Applications: Prospects and Challenges

Stimulation of cells with electrical cues is an imperative approach to interact with biological systems and has been exploited in clinical practices over a wide range of pathological ailments. This bioelectric interface has been extensively explored with the help of piezoelectric materials, leading to remarkable advancement in the past two decades. Among other members of this fraternity, colloidal perovskite barium titanate (BaTiO₃ ) has gained substantial interest due to its noteworthy properties which includes high dielectric constant and excellent ferroelectric properties along with acceptable biocompatibility. Significant progression is witnessed for BaTiO₃ nanoparticles (BaTiO₃ NPs) as potent candidates for biomedical applications and in wearable bioelectronics, making them a promising personal healthcare platform. The current review highlights the nanostructured piezoelectric bio interface of BaTiO₃ NPs in applications comprising drug delivery, tissue engineering, bioimaging, bioelectronics, and wearable devices. Particular attention has been dedicated toward the fabrication routes of BaTiO₃ NPs along with different approaches for its surface modifications. This review offers a comprehensive discussion on the utility of BaTiO₃ NPs as active devices rather than passive structural unit behaving as carriers for biomolecules. The employment of BaTiO₃ NPs presents new scenarios and opportunity in the vast field of nanomedicines for biomedical applications.

Structural and functional integration of human forebrain organoids with the injured adult rat visual system

Brain organoids created from human pluripotent stem cells represent a promising approach for brain repair. They acquire many structural features of the brain and raise the possibility of patient-matched repair. Whether these entities can integrate with host brain networks in the context of the injured adult mammalian brain is not well established. Here, we provide structural and functional evidence that human brain organoids successfully integrate with the adult rat visual system after transplantation into large injury cavities in the visual cortex. Virus-based trans-synaptic tracing reveals a polysynaptic pathway between organoid neurons and the host retina and reciprocal connectivity between the graft and other regions of the visual system. Visual stimulation of host animals elicits responses in organoid neurons, including orientation selectivity. These results demonstrate the ability of human brain organoids to adopt sophisticated function after insertion into large injury cavities, suggesting a translational strategy to restore function after cortical damage.

Clinical considerations in Parkinson's disease cell therapy

Cell replacement therapy is an area of increasing interest for treating Parkinson's disease (PD). However, to become a clinically practical option for PD patients, it must first overcome significant barriers, including establishment of safe and standardized surgical procedures, determination of appropriate perioperative medication regimens, demonstration of long-term graft survival and incorporation, and standardized, clinically meaningful follow-up measures. In this review, we will describe the current status of cell therapy for PD with special attention to these critical requirements, to define guideposts on the road to bring the benefit of this therapy to the Parkinson's clinic.

iPSCs-Derived Neurons and Brain Organoids from Patients

Induced pluripotent stem cells (iPSCs) can be differentiated into specific neurons and brain organoids by adding induction factors and small molecules in vitro, which carry human genetic information and recapitulate the development process of human brain as well as physiological, pathological, and pharmacological characteristics. Hence, iPSC-derived neurons and organoids hold great promise for studying human brain development and related nervous system diseases in vitro, and provide a platform for drug screening. In this chapter, we summarize the development of the differentiation techniques for neurons and brain organoids from iPSCs, and their applications in studying brain disease, drug screening, and transplantation.

Advanced molecular therapies for neurological diseases: focus on stroke, alzheimer's disease, and parkinson's disease

Neurological diseases (NDs) are one of the leading causes of disability and the second leading cause of death globally. Among these stroke, Alzheimer's disease (AD), and Parkinson's disease (PD) are the most common NDs. A rise in the absolute number of individuals affected with these diseases indicates that the current treatment strategies in management and prevention of these debilitating diseases are not effective sufficiently. Therefore, novel treatment strategies are being explored to cure these diseases by addressing the causative mechanisms at the molecular level. Advanced therapies like gene therapy (gene editing and gene silencing) and stem cell therapies aim to cure diseases by gene editing, gene silencing and tissue regeneration, respectively. Gene editing results in the deletion of the aberrant gene or insertion of the corrected gene which can be executed using the CRISPR/Cas gene editing tool a promising treatment strategy being explored for many other prevalent diseases. Gene silencing using siRNA silences the gene by inhibiting protein translation, thereby silencing its expression. Stem cell therapy aims to regenerate damaged cells or tissues because of their ability to divide into any type of cell in the human body. Among these approaches, gene editing and gene silencing have currently been applied in vitro and to animal models, while stem cell therapy has reached the clinical trial stage for the treatment of NDs. The current status of these strategies suggests a promising outcome in their clinical translation.

Current Status and Future Perspectives on Stem Cell-Based Therapies for Parkinson's Disease

Parkinson's disease (PD) is the second most common neurodegenerative disorder after Alzheimer's disease, affecting 1%-2% of the population over the age of 65. As the population ages, it is anticipated that the burden on society will significantly escalate. Although symptom reduction by currently available pharmacological and/or surgical treatments improves the quality of life of many PD patients, there are no treatments that can slow down, halt, or reverse disease progression. Because the loss of a specific cell type, midbrain dopamine neurons in the substantia nigra, is the main cause of motor dysfunction in PD, it is considered a promising target for cell replacement therapy. Indeed, numerous preclinical and clinical studies using fetal cell transplantation have provided proof of concept that cell replacement therapy may be a viable therapeutic approach for PD. However, the use of human fetal cells remains fraught with controversy due to fundamental ethical, practical, and clinical limitations. Groundbreaking work on human pluripotent stem cells (hPSCs), including human embryonic stem cells and human induced pluripotent stem cells, coupled with extensive basic research in the stem cell field offers promising potential for hPSC-based cell replacement to become a realistic treatment regimen for PD once several major issues can be successfully addressed. In this review, we will discuss the prospects and challenges of hPSC-based cell therapy for PD.

Functional reconstruction of the basal ganglia neural circuit by human striatal neurons in hypoxic-ischaemic injured brain

Perinatal hypoxic-ischaemic encephalopathy is the leading cause of neonatal death and permanent neurological deficits, while the basal ganglia is one of the major nuclei that is selectively and greatly affected in the brains of hypoxic-ischaemic encephalopathy patients, especially in severe cases. Human embryonic stem cell-derived neurons have shown great potential in different types of brain disorders in adults. However, it remains unknown whether and how grafted human embryonic stem cell-derived neurons can repair immature brains with hypoxic-ischaemic encephalopathy. Here, by administrating genetically labelled human embryonic stem cell-derived striatal neural progenitors into the ipsilateral striatum of hypoxic-ischaemic encephalopathy-injured mice, we found that the grafted cells gradually matured into GABA spiny projection neurons morphologically and electrophysiologically, and significantly rescued the area loss of hypoxic-ischaemic encephalopathy-injured brains. Intriguingly, using immunohistochemical staining combined with enhanced ascorbate peroxidase-based immunoelectron microscopy and rabies virus-mediated trans-synaptic tracing, we show that the grafts start to extend axonal projections to the endogenous target areas (globus pallidus externa, globus pallidus internus, substantia nigra), form synapses with host striatal, globus pallidus and nigra neurons, and receive extensive and stable synaptic inputs as early as 2 months post-transplantation. Importantly, we further demonstrated functional neural circuits re-established between the grafted neurons and host cortical, striatal and substantial nigra neurons at 3-6 months post-transplantation in the hypoxic-ischaemic encephalopathy-injured brain by optogenetics combined with electrophysiological recording. Finally, the transplanted striatal spiny projection neurons but not spinal GABA neurons restored the motor defects of hypoxic-ischaemic encephalopathy, which were reversed by clozapine-N-oxide-based inhibition of graft function. These findings demonstrate anatomical and functional reconstruction of the basal ganglia neural circuit including multiple loops by striatal spiny projection neurons in hypoxic-ischaemic encephalopathy-injured immature brains, which raises the possibility of such a cell replacement therapeutic strategy for hypoxic-ischaemic encephalopathy in neonates.

Assessment of the anti-nociceptive effects of fetal ventral mesencephalic tissue allografts in a rat model of hemi-Parkinson's disease using fMRI

Extensive studies showed increased subjective pain sensitivity in Parkinson's disease (PD), which appeared to be partially reversed by dopaminergic (DA) treatment. Although cell replacement represents an attractive therapeutic strategy, its potential for PD-related hyperalgesia remains unclear. We investigated re-establishment of DA function via allografting exogenic DA cells on pain hypersensitivity in a rat model of PD. We evaluated the anti-nociceptive effects of fetal ventral mesencephalic (rVM) tissue allografts in PD rats after unilateral 6-OHDA-induced toxicity in the medial forebrain bundle. The drug -induced rotation test was used to validate the severity of the nigrostriatal lesion; von Frey and thermal pain tests were employed to evaluate nociceptive function. Nociception-induced cerebral blood volume (CBV) response was measured using a 4.7-T MR system. Finally, the immunohistochemical (IHC) studies were performed and the results were compared with the imaging findings from functional magnetic resonance imaging (fMRI). The grafts significantly improved drug-induced rotation behavior and increased mechanical and thermal nociceptive thresholds in PD rats. The elevation of CBV signals significantly recovered on the grafted striatum, whereas this effect was inhibited by the D2R antagonist eticlopride in each striatum. Quantitative IHC analysis revealed the transplantation markedly increased the numbers of tyrosine hydroxylase immunoreactive cells. Therefore, we concluded transplantation of rVM tissue results in anti-nociceptive effects and improves motor function. Moreover, in vivo CBV response confirmed the key role of D2R-mediated pain modulation. Therefore, we demonstrate fMRI as a reliable imaging index in evaluating the anti-nociceptive therapeutic effects of fetal rVM transplantation in the rat model of PD.

Challenges in progressing cell therapies to the clinic for Huntington's disease: A review of the progress made with pluripotent stem cell derived medium spiny neurons

Huntington's disease (HD) is a hereditary, neurodegenerative disorder characterized by a triad of symptoms: motor, cognitive and psychiatric. HD is caused by a genetic mutation, expansion of the CAG repeat in the huntingtin gene, which results in loss of medium spiny neurons (MSNs) of the striatum. Cell replacement therapy (CRT) has emerged as a possible therapy for HD, aiming to replace those cells lost to the disease process and alleviate its symptoms. Initial pre-clinical studies used primary fetal striatal cells to provide proof-of-principal that CRT can bring about functional recovery on some behavioral tasks following transplantation into HD models. Alternative donor cell sources are required if CRT is to become a viable therapeutic option and human pluripotent stem cell (hPSC) sources, which have undergone differentiation toward the MSNs lost to the disease process, have proved to be strong candidates. The focus of this chapter is to review work conducted on the functional assessment of animals following transplantation of hPSC-derived MSNs. We discuss different ways that graft function has been assessed, and the results that have been achieved to date. In addition, this chapter presents and discusses challenges that remain in this field.

Sequestration of Inflammation in Parkinson's Disease via Stem Cell Therapy

Parkinson’s disease is the second most common neurodegenerative disease. Insidious and progressive, this disorder is secondary to the gradual loss of dopaminergic signaling and worsening neuroinflammation, affecting patients’ motor capabilities. Gold standard treatment includes exogenous dopamine therapy in the form of levodopa–carbidopa, or surgical intervention with a deep brain stimulator to the subcortical basal ganglia. Unfortunately, these therapies may ironically exacerbate the already pro-inflammatory environment. An alternative approach may involve cell-based therapies. Cell-based therapies, whether endogenous or exogenous, often have anti-inflammatory properties. Alternative strategies, such as exercise and diet modifications, also appear to play a significant role in facilitating endogenous and exogenous stem cells to induce an anti-inflammatory response, and thus are of unique interest to neuroinflammatory conditions including Parkinson’s disease. Treating patients with current gold standard therapeutics and adding adjuvant stem cell therapy, alongside the aforementioned lifestyle modifications, may ideally sequester inflammation and thus halt neurodegeneration.

Grafted hPSC-derived GABA-ergic interneurons regulate seizures and specific cognitive function in temporal lobe epilepsy

Interneuron loss/dysfunction contributes to spontaneous recurrent seizures (SRS) in chronic temporal lobe epilepsy (TLE), and interneuron grafting into the epileptic hippocampus reduces SRS and improves cognitive function. This study investigated whether graft-derived gamma-aminobutyric acid positive (GABA-ergic) interneurons directly regulate SRS and cognitive function in a rat model of chronic TLE. Human pluripotent stem cell-derived medial ganglionic eminence-like GABA-ergic progenitors, engineered to express hM4D(Gi), a designer receptor exclusively activated by designer drugs (DREADDs) through CRISPR/Cas9 technology, were grafted into hippocampi of chronically epileptic rats to facilitate the subsequent silencing of graft-derived interneurons. Such grafting substantially reduced SRS and improved hippocampus-dependent cognitive function. Remarkably, silencing of graft-derived interneurons with a designer drug increased SRS and induced location memory impairment but did not affect pattern separation function. Deactivation of DREADDs restored both SRS control and object location memory function. Thus, transplanted GABA-ergic interneurons could directly regulate SRS and specific cognitive functions in TLE.

Human midbrain dopaminergic neuronal differentiation markers predict cell therapy outcome in a Parkinson's disease model

Human pluripotent stem cell (hPSC)-based replacement therapy holds great promise in treating Parkinson's disease (PD). However, the heterogeneity of hPSC-derived donor cells and the low yield of midbrain dopaminergic (mDA) neurons after transplantation hinder its broad clinical application. Here, we depicted the single-cell molecular landscape during mDA neuron differentiation. We found that this process recapitulated the development of multiple but adjacent fetal brain regions including ventral midbrain, isthmus, and ventral hindbrain, resulting in heterogenous donor cell population. We reconstructed the differentiation trajectory of mDA lineage and identified CLSTN2 and PTPRO as specific surface markers of mDA progenitors, which were predictive of mDA neuron differentiation and could facilitate highly enriched mDA neurons (up to 80%) following progenitor sorting and transplantation. Marker sorted progenitors exhibited higher therapeutic potency in correcting motor deficits of PD mice. Different marker sorted grafts had a strikingly consistent cellular composition, in which mDA neurons were enriched, while off-target neuron types were mostly depleted, suggesting stable graft outcomes. Our study provides a better understanding of cellular heterogeneity during mDA neuron differentiation, and establishes a strategy to generate highly purified donor cells to achieve stable and predictable therapeutic outcomes, raising the prospect of hPSC-based PD cell replacement therapies.

Dysfunction of vesicular storage in young-onset Parkinson's patient-derived dopaminergic neurons and organoids revealed by single cell electrochemical cytometry

Electrochemical cytometry based on nano-tip microelectrodes was used to quantify the vesicular storage at the single-cell level in human neurons and midbrain organoids which acted as disease models of young-onset Parkinson's disease (YOPD). Human dopaminergic (DA) neurons and midbrain organoids were derived from an induced pluripotent stem cell line from one YOPD patient. We show a significant deficiency in vesicular catecholamine storage and a slower pore forming process on the surface of the microelectrode in the DA neurons derived from the YOPD patient. The upregulation of α-synuclein in both neurons and organoids derived from the YOPD patient is associated with vesicular storage dysfunction, revealing a correlation between the pathogenesis of YOPD and vesicular chemical storage deficiency, a novel chemical insight into the potential pathology of YOPD. Notably, efficacy evaluation and drug testing were performed with our platform to demonstrate that both amantadine, a clinical drug for Parkinson's disease (PD), and phorbol 12-myristate 13-acetate, an attractive candidate, ameliorate the dysfunction of vesicular storage in DA neurons derived from the YOPD patient. Our platform offers promising avenues for new drug discovery for PD and other neurodegenerative disorders.

Chemogenetics as a neuromodulatory approach to treating neuropsychiatric diseases and disorders

Chemogenetics enables precise, non-invasive, and reversible modulation of neural activity via the activation of engineered receptors that are pharmacologically selective to endogenous or exogenous ligands. With recent advances in therapeutic gene delivery, chemogenetics is poised to support novel interventions against neuropsychiatric diseases and disorders. To evaluate its translational potential, we performed a scoping review of applications of chemogenetics that led to the reversal of molecular and behavioral deficits in studies relevant to neuropsychiatric diseases and disorders. In this review, we present these findings and discuss the potential and challenges for using chemogenetics as a precision medicine-based neuromodulation strategy.

Spotting-based differentiation of functional dopaminergic progenitors from human pluripotent stem cells

To fully realize the potential of human pluripotent stem cells (hPSCs) for both therapeutic and research purposes, it is critical to follow an efficient and reliable in vitro differentiation method that is based on optimal physical, chemical and developmental cues. This highly reproducible protocol describes how to grow hPSCs such as human induced pluripotent and embryonic stem cells in a physically confined area ('spot') and efficiently differentiate them into a highly enriched population of healthy and functional midbrain dopamine progenitors (mDAPs) and midbrain dopamine neurons (mDANs). The protocol takes 28 d, during which cells first grow and differentiate in spots for 14 d and then are replated and further differentiated for a further 14 d as a monolayer culture. We describe how to produce mDAPs, control the quality of cells and cryopreserve mDAPs without loss of viability. Previously we showed that mDANs generated by this 'spotting'-based method exhibit gene expression and (electro)physiological properties typical of A9 mDANs lost in Parkinson's disease brains and can rescue motor defects when transplanted into the striatum of 6-hydroxydopamine-lesioned rats. This protocol is scalable for production of mDAPs under good manufacturing practice conditions and was also previously successfully used to generate cells for the first autologous cell replacement therapy of a patient with Parkinson's disease without the need for immune suppression. We anticipate this protocol could also be readily adapted to use spotting-based culture to further optimize the differentiation of hPSC to alternative differentiated cell types.

Assessing Gq-GPCR-induced human astrocyte reactivity using bioengineered neural organoids

Astrocyte reactivity can directly modulate nervous system function and immune responses during disease and injury. However, the consequence of human astrocyte reactivity in response to specific contexts and within neural networks is obscure. Here, we devised a straightforward bioengineered neural organoid culture approach entailing transcription factor-driven direct differentiation of neurons and astrocytes from human pluripotent stem cells combined with genetically encoded tools for dual cell-selective activation. This strategy revealed that Gq-GPCR activation via chemogenetics in astrocytes promotes a rise in intracellular calcium followed by induction of immediate early genes and thrombospondin 1. However, astrocytes also undergo NF-κB nuclear translocation and secretion of inflammatory proteins, correlating with a decreased evoked firing rate of cocultured optogenetic neurons in suboptimal conditions, without overt neurotoxicity. Altogether, this study clarifies the intrinsic reactivity of human astrocytes in response to targeting GPCRs and delivers a bioengineered approach for organoid-based disease modeling and preclinical drug testing.

Modulation by DREADD reveals the therapeutic effect of human iPSC-derived neuronal activity on functional recovery after spinal cord injury

Transplantation of neural stem/progenitor cells (NS/PCs) derived from human induced pluripotent stem cells (hiPSCs) is considered to be a promising therapy for spinal cord injury (SCI) and will soon be translated to the clinical phase. However, how grafted neuronal activity influences functional recovery has not been fully elucidated. Here, we show the locomotor functional changes caused by inhibiting the neuronal activity of grafted cells using a designer receptor exclusively activated by designer drugs (DREADD). In vitro analyses of inhibitory DREADD (hM4Di)-expressing cells demonstrated the precise inhibition of neuronal activity via administration of clozapine N-oxide. This inhibition led to a significant decrease in locomotor function in SCI mice with cell transplantation, which was exclusively observed following the maturation of grafted neurons. Furthermore, trans-synaptic tracing revealed the integration of graft neurons into the host motor circuitry. These results highlight the significance of engrafting functionally competent neurons by hiPSC-NS/PC transplantation for sufficient recovery from SCI.

•

The neuronal activity of hM4Di-NS/PCs was controlled by CNO administration

•

Inhibiting the neuronal activity of grafted NS/PCs led to functional decline

•

Grafted neurons derived from hiPSC-NS/PCs integrated into host motor circuits

Emerging Methods in Modeling Brain Development and Disease with Human Pluripotent Stem Cells

The Nobel Prize-winning discovery that human somatic cells can be readily reprogrammed into pluripotent cells has revolutionized our potential to understand the human brain. The rapid technological progression of this field has made it possible to easily obtain human neural cells and even intact tissues, offering invaluable resources to model human brain development. In this chapter, we present a brief history of hPSC-based approaches to study brain development and then, provide new insights into neurological diseases, focusing on those driven by aberrant cell death. Furthermore, we will shed light on the latest technologies and highlight the methods that researchers can use to employ established hPSC approaches in their research. Our intention is to demonstrate that hPSC-based modeling is a technical approach accessible to all researchers who seek a deeper understanding of the human brain.

A novel two-factor monosynaptic TRIO tracing method for assessment of circuit integration of hESC-derived dopamine transplants

Transplantation in Parkinson's disease using human embryonic stem cell (hESC)-derived dopaminergic (DA) neurons is a promising future treatment option. However, many of the mechanisms that govern their differentiation, maturation, and integration into the host circuitry remain elusive. Here, we engrafted hESCs differentiated toward a ventral midbrain DA phenotype into the midbrain of a preclinical rodent model of Parkinson's disease. We then injected a novel DA-neurotropic retrograde MNM008 adeno-associated virus vector capsid, into specific DA target regions to generate starter cells based on their axonal projections. Using monosynaptic rabies-based tracing, we demonstrated for the first time that grafted hESC-derived DA neurons receive distinctly different afferent inputs depending on their projections. The similarities to the host DA system suggest a previously unknown directed circuit integration. By evaluating the differential host-to-graft connectivity based on projection patterns, this novel approach offers a tool to answer outstanding questions regarding the integration of grafted hESC-derived DA neurons.

•

A novel retrograde AAV-capsid (MNM008) allows highly accurate monosynaptic tracing

•

Nigral human dopamine (DA) grafts reconstitute the nigrostriatal pathway

•

The host rat brain makes circuit-specific connections with hESC-derived DA grafts

•

The herein developed tool allows for detailed mapping of CNS circuits and repair

CRISPR-Cas9-Mediated Gene Therapy in Neurological Disorders

Neurological disorders are primarily diseases with sophisticated etiology that are always refractory and recrudescent. The major obstruction to effective therapies for neurological disorders is the poor understanding of their pathogenic mechanisms. CRISPR-Cas9 technology, which allows precise and effective gene editing in almost any cell type and organism, is accelerating the pace of basic biological research. An increasing number of groups are focusing on uncovering the molecular mechanisms of neurological disorders and developing novel therapies using the CRISPR-Cas9 system. This review highlights the application of CRISPR-Cas9 technology in the treatment of neurological disorders, including Alzheimer's disease, amyotrophic lateral sclerosis and/or frontotemporal dementia, Duchenne muscular dystrophy, Dravet syndrome, epilepsy, Huntington's disease, and Parkinson's disease. Hopefully, it will improve our understanding of neurological disorders and give insights into future treatments for neurological disorders.

Biomaterial Strategies for Restorative Therapies in Parkinson's Disease

Parkinson's disease (PD) is a progressive neurological disorder, in which dopaminergic midbrain neurons degenerate, leading to dopamine depletion that is associated with neuronal death. In this Review, we initially describe the pathogenesis of PD and established therapies that unfortunately only delay progression of the disease. With a rapidly escalating incidence in PD, there is an urgent need to develop new therapies that not only halt progression but even reverse degeneration. Biomaterials are playing critical roles in these new therapies which include controlled and site-specific delivery of neurotrophins, increased engraftment of implanted neural stem cells, and redirection of endogenous stem cell populations away from their niche to encourage reparative mechanisms. This Review will therefore cover important design features of biomaterials used in regenerative medicine and tissue engineering strategies targeted at PD.

Differentiation of Human Pluripotent Stem Cells Into Specific Neural Lineages

Human pluripotent stem cells (hPSCs) are sources of several somatic cell types for human developmental studies, in vitro disease modeling, and cell transplantation therapy. Improving strategies of derivation of high-purity specific neural and glial lineages from hPSCs is critical for application to the study and therapy of the nervous system. Here, we will focus on the principles behind establishment of neuron and glia differentiation methods according to developmental studies. We will also highlight the limitations and challenges associated with the differentiation of several “difficult” neural lineages and delay in neuronal maturation and functional integration. To overcome these challenges, we will introduce strategies and novel technologies aimed at improving the differentiation of various neural lineages to expand the application potential of hPSCs to the study of the nervous system.

Generation of hiPSC-Derived Functional Dopaminergic Neurons in Alginate-Based 3D Culture

Human induced pluripotent stem cells (hiPSCs) represent an unlimited cell source for the generation of patient-specific dopaminergic (DA) neurons, overcoming the hurdle of restricted accessibility to disease-affected tissue for mechanistic studies on Parkinson's disease (PD). However, the complexity of the human brain is not fully recapitulated by existing monolayer culture methods. Neurons differentiated in a three dimensional (3D) in vitro culture system might better mimic the in vivo cellular environment for basic mechanistic studies and represent better predictors of drug responses in vivo. In this work we established a new in vitro cell culture system based on the microencapsulation of hiPSCs in small alginate/fibronectin beads and their differentiation to DA neurons. Optimization of hydrogel matrix concentrations and composition allowed a high viability of embedded hiPSCs. Neural differentiation competence and efficiency of DA neuronal generation were increased in the 3D cultures compared to a conventional 2D culture methodology. Additionally, electrophysiological parameters and metabolic switching profile confirmed increased functionality and an anticipated metabolic resetting of neurons grown in alginate scaffolds with respect to their 2D counterpart neurons. We also report long-term maintenance of neuronal cultures and preservation of the mature functional properties. Furthermore, our findings indicate that our 3D model system can recapitulate mitochondrial superoxide production as an important mitochondrial phenotype observed in neurons derived from PD patients, and that this phenotype might be detectable earlier during neuronal differentiation. Taken together, these results indicate that our alginate-based 3D culture system offers an advantageous strategy for the reliable and rapid derivation of mature and functional DA neurons from hiPSCs.

Reprogramming Glial Cells into Functional Neurons for Neuro-regeneration: Challenges and Promise

The capacity for neurogenesis in the adult mammalian brain is extremely limited and highly restricted to a few regions, which greatly hampers neuronal regeneration and functional restoration after neuronal loss caused by injury or disease. Meanwhile, transplantation of exogenous neuronal stem cells into the brain encounters several serious issues including immune rejection and the risk of tumorigenesis. Recent discoveries of direct reprogramming of endogenous glial cells into functional neurons have provided new opportunities for adult neuro-regeneration. Here, we extensively review the experimental findings of the direct conversion of glial cells to neurons in vitro and in vivo and discuss the remaining issues and challenges related to the glial subtypes and the specificity and efficiency of direct cell-reprograming, as well as the influence of the microenvironment. Although in situ glial cell reprogramming offers great potential for neuronal repair in the injured or diseased brain, it still needs a large amount of research to pave the way to therapeutic application.

Trophoblast glycoprotein is a marker for efficient sorting of ventral mesencephalic dopaminergic precursors derived from human pluripotent stem cells

Successful cell therapy for Parkinson’s disease (PD) requires large numbers of homogeneous ventral mesencephalic dopaminergic (vmDA) precursors. Enrichment of vmDA precursors via cell sorting is required to ensure high safety and efficacy of the cell therapy. Here, using LMX1A-eGFP knock-in reporter human embryonic stem cells, we discovered a novel surface antigen, trophoblast glycoprotein (TPBG), which was preferentially expressed in vmDA precursors. TPBG-targeted cell sorting enriched FOXA2⁺LMX1A⁺ vmDA precursors and helped attain efficient behavioral recovery of rodent PD models with increased numbers of TH⁺, NURR1⁺, and PITX3⁺ vmDA neurons in the grafts. Additionally, fewer proliferating cells were detected in TPBG⁺ cell-derived grafts than in TPBG⁻ cell-derived grafts. Our approach is an efficient way to obtain enriched bona fide vmDA precursors, which could open a new avenue for effective PD treatment.

Bringing Advanced Therapies for Parkinson's Disease to the Clinic: The Scientist's Perspective

After many years of preclinical development, cell and gene therapies have advanced from research tools in the lab to clinical-grade products for patients, and today they constitute more than a quarter of all new Phase I clinical trials for Parkinson’s disease. Whereas efficacy has been convincingly proven for many of these products in preclinical models, the field is now entering a new phase where the functionality and safety of these products will need to stand the test in clinical trials. If successful, these new products can have the potential to provide patients with a one-time administered treatment which may alleviate them from daily symptomatic dopaminergic medication.

Dopamine Cell Therapy: From Cell Replacement to Circuitry Repair

Cell therapy for Parkinson's disease (PD) is aimed to replace the degenerated midbrain dopamine (mDA) neurons and restore DA neurotransmission in the denervated forebrain targets. A limitation of the intrastriatal grafting approach, which is currently used in clinical trials, is that the mDA neurons are implanted into the target area, in most cases the putamen, and not in the ventral midbrain where they normally reside. This ectopic location of the cells may limit their functionality due to the lack of appropriate afferent regulation from the host. Homotopic transplantation, into the substantia nigra, is now being pursued in rodent PD models as a way to achieve more complete circuitry repair. Intranigral grafts of mDA neurons, derived from human embryonic stem cells, have the capacity to re-establish the nigrostriatal and mesolimbic pathways in their entirety and restore dense functional innervations in striatal, limbic and cortical areas. Tracing of host afferent inputs using the rabies tracing technique shows that the afferent connectivity of grafts implanted in the nigra matches closely that of the intrinsic mDA system, suggesting a degree of circuitry reconstruction that exceeds what has been achieved before. This approach holds great promise, but to match the larger size of the human brain, and the 10 times greater distance between substantia nigra and its forebrain targets, it may be necessary to find ways to improve the growth capacity of the grafted mDA neurons, pointing to a combined approach where growth promoting factors are used to enhance the performance of mDA neuron grafts.

Human spinal GABA neurons alleviate spasticity and improve locomotion in rats with spinal cord injury

Spinal cord injury (SCI) often results in spasticity. There is currently no effective therapy for spasticity. Here, we describe a method to efficiently differentiate human pluripotent stem cells from spinal GABA neurons. After transplantation into the injured rat spinal cord, the DREADD (designer receptors exclusively activated by designer drug)-expressing spinal progenitors differentiate into GABA neurons, mitigating spasticity-like response of the rat hindlimbs and locomotion deficits in 3 months. Administering clozapine-N-oxide, which activates the grafted GABA neurons, further alleviates spasticity-like response, suggesting an integration of grafted GABA neurons into the local neural circuit. These results highlight the therapeutic potential of the spinal GABA neurons for SCI.

Quantitative Rodent Brain Receptor Imaging

Positron emission tomography (PET) is a non-invasive imaging technology employed to describe metabolic, physiological, and biochemical processes in vivo. These include receptor availability, metabolic changes, neurotransmitter release, and alterations of gene expression in the brain. Since the introduction of dedicated small-animal PET systems along with the development of many novel PET imaging probes, the number of PET studies using rats and mice in basic biomedical research tremendously increased over the last decade. This article reviews challenges and advances of quantitative rodent brain imaging to make the readers aware of its physical limitations, as well as to inspire them for its potential applications in preclinical research. In the first section, we briefly discuss the limitations of small-animal PET systems in terms of spatial resolution and sensitivity and point to possible improvements in detector development. In addition, different acquisition and post-processing methods used in rodent PET studies are summarized. We further discuss factors influencing the test-retest variability in small-animal PET studies, e.g., different receptor quantification methodologies which have been mainly translated from human to rodent receptor studies to determine the binding potential and changes of receptor availability and radioligand affinity. We further review different kinetic modeling approaches to obtain quantitative binding data in rodents and PET studies focusing on the quantification of endogenous neurotransmitter release using pharmacological interventions. While several studies have focused on the dopamine system due to the availability of several PET tracers which are sensitive to dopamine release, other neurotransmitter systems have become more and more into focus and are described in this review, as well. We further provide an overview of latest genome engineering technologies, including the CRISPR/Cas9 and DREADD systems that may advance our understanding of brain disorders and function and how imaging has been successfully applied to animal models of human brain disorders. Finally, we review the strengths and opportunities of simultaneous PET/magnetic resonance imaging systems to study drug-receptor interactions and challenges for the translation of PET results from bench to bedside.

Dose-related biphasic effect of the Parkinson's disease neurotoxin MPTP, on the spread, accumulation, and toxicity of α-synuclein

BACKGROUND

Parkinson's disease (PD), the second most common progressive neurodegenerative disorder, is characterized by the abnormal accumulation of intraneuronal inclusions enriched in aggregated α-synuclein (α-syn), known as Lewy bodies (LBs) and Lewy neurites (LNs), and significant loss of dopaminergic (DA) neurons in the substantia nigra pars compacta (SNpc) of the brain. Recent evidence suggests that the intrastriatal inoculation of α-syn preformed fibrils (PFF) in mice brain triggers endogenous α-syn in interconnected brain regions. 1-methyl, 4-phenyl, 1,2,3,6 tetrahydropyridine (MPTP), a mitochondrial neurotoxin, has been used previously to generate a PD mouse model. However, the common methods of MPTP exposure do not induce LB or α-syn aggregation in mice. In the present study, we evaluated the effect of different doses of MPTP (10 mg/kg.b.wt and/or 25 mg/kg.b.wt) on the spread, accumulation, and toxicity of endogenous α-syn in mice administered an intrastriatal injection of human α-syn PFF.

METHODS

We inoculated human WT α-syn PFF in mouse striatum. At 6 weeks post PFF injection, we challenged the animal with two different doses of MPTP (10 mg/kg.b.wt and 25 mg/kg.b.wt) once daily for five consecutive days. At 2 weeks from the start of the MPTP regimen, we collected the mice brain and performed immunohistochemical analysis, and Rotarod test to assess motor coordination and muscle strength before and after MPTP injection.

RESULTS

A single injection of human WT α-syn PFF in the mice striatum induced the propagation of α-syn, occurring as phosphorylated α-synuclein (pS129), towards the SNpc, within a very short time. Injection of a low dose of MPTP (10 mg/kg.b.wt) at 6 weeks post α-syn PFF inoculation further enhanced the spread, whereas a high dose of MPTP (25 mg/kg.b.wt.) reduced the spread. Majority of the accumulated α-syn were proteinase K resistant, as recognized using a conformation-specific α-syn antibody. Injection of α-syn PFF alone caused 12 % reduction in the number of tyrosine hydroxylase positive neurons while α-syn PFF + a low dose of MPTP caused 33 % reduction (loss), compared to the control mice injected with saline. This combination also reduced the motor coordination. Interestingly, a low dose of MPTP alone did not cause any significant reduction in the number of tyrosine hydroxylase positive neurons compared to saline treatment. Animals that received α-syn PFF and a high dose of MPTP showed massive activation of glial cells and decreased spread of α-syn, majority of which were detected in the nucleus.

CONCLUSION

Our results suggest that a combination of human WT α-syn PFF and a low dose of MPTP increases the pathological conversion and propagation of endogenous α-syn, and neurodegeneration, within a very short time. Our model can be used to study the mechanisms of α-syn propagation and screen for potential drugs against PD.

Narrative review of stem cell therapy for ischemic brain injury

Ischemic brain injury is a common cause of long-term neurological deficits in children as well as adults, and no efficient treatments could reverse the sequelae in clinic till now. Stem cells have the capacity of self-renewal and multilineage differentiation. The therapeutic efficacy of stem cell transplantation for ischemic brain injury have been tested for many years. The grafts could survive and mature in the ischemic brain environment. Stem cell transplantation could improve functional recovery of ischemic brain injury models in pre-clinical trials. The potential mechanisms included cell replacement, release of neurotrophic and anti-inflammatory factors, immunoregulation as well as activation of endogenous neurogenesis. Besides, many clinical trials were conducted and some of trials already had preliminary results. From the current published data, cell transplantation for clinical application is safe and feasible. No severe adverse events and tumorigenesis were reported. While the therapeutic efficacy of stem cell therapy in clinic still needs more evidences. In this review, we overviewed the studies about stem cell therapy for ischemic brain injury. Different types of stem cells used for transplantation as well as the therapeutic mechanisms were discussed in detail. The related pre-clinical and clinical trials were summarized into two separate tables. In addition, we also discussed the unsolved problems and concerns about stem cell therapy for ischemic brain injury that need to be overcome before clinic transformation.

Characterization of Brevibacillus laterosporus Cas9 (BlatCas9) for Mammalian Genome Editing

Compact CRISPR/Cas9 systems that can be delivered by AAV for in vivo genome editing hold great promise for clinical applications. Brevibacillus laterosporus Cas9 (BlatCas9) is a compact Cas9 nuclease that has been identified for plant genome editing. Here, we characterize BlatCas9 as an alternative tool for mammalian genome editing. We demonstrate that BlatCas9 prefers a N4CNAA protospacer adjacent motif (PAM), but N4C PAM is also editable in mammalian cells. We next demonstrate that BlatCas9 enables genome editing in a variety of cell types. Furthermore, BlatCas9 can be packaged into AAV for genome editing. Finally, we characterize the specificity of BlatCas9. In summary, BlatCas9 offers an alternative tool for both basic research and clinical applications.

Stem Cell-Based Therapies for Parkinson Disease

Parkinson disease (PD) is a neurological movement disorder resulting primarily from damage to and degeneration of the nigrostriatal dopaminergic pathway. The pathway consists of neural populations in the substantia nigra that project to the striatum of the brain where they release dopamine. Diagnosis of PD is based on the presence of impaired motor features such as asymmetric or unilateral resting tremor, bradykinesia, and rigidity. Nonmotor features including cognitive impairment, sleep disorders, and autonomic dysfunction are also present. No cure for PD has been discovered, and treatment strategies focus on symptomatic management through restoration of dopaminergic activity. However, proposed cell replacement therapies are promising because midbrain dopaminergic neurons have been shown to restore dopaminergic neurotransmission and functionally rescue the dopamine-depleted striatum. In this review, we summarize our current understanding of the molecular pathogenesis of neurodegeneration in PD and discuss the development of new therapeutic strategies that have led to the initiation of exploratory clinical trials. We focus on the applications of stem cells for the treatment of PD and discuss how stem cell research has contributed to an understanding of PD, predicted the efficacy of novel neuroprotective therapeutics, and highlighted what we believe to be the critical areas for future research.

hESC-Derived Dopaminergic Transplants Integrate into Basal Ganglia Circuitry in a Preclinical Model of Parkinson's Disease

Cell replacement is currently being explored as a therapeutic approach for neurodegenerative disease. Using stem cells as a source, transplantable progenitors can now be generated under conditions compliant with clinical application in patients. In this study, we elucidate factors controlling target-appropriate innervation and circuitry integration of human embryonic stem cell (hESC)-derived grafts after transplantation to the adult brain. We show that cell-intrinsic factors determine graft-derived axonal innervation, whereas synaptic inputs from host neurons primarily reflect the graft location. Furthermore, we provide evidence that hESC-derived dopaminergic grafts transplanted in a long-term preclinical rat model of Parkinson’s disease (PD) receive synaptic input from subtypes of host cortical, striatal, and pallidal neurons that are known to regulate the function of endogenous nigral dopamine neurons. This refined understanding of how graft neurons integrate with host circuitry will be important for the design of clinical stem-cell-based replacement therapies for PD, as well as for other neurodegenerative diseases.

•

Pattern of graft-derived innervation is determined by phenotype of grafted cells

•

Synaptic inputs from host-to-graft depend on location of graft

•

Intrastriatal dopaminergic grafts receive correct excitatory and inhibitory host inputs

•

Individual host neurons provide inputs to both dopaminergic grafts and the host nigra

Human Stem Cell-Derived Neurons Repair Circuits and Restore Neural Function

Although cell transplantation can rescue motor defects in Parkinson's disease (PD) models, whether and how grafts functionally repair damaged neural circuitry in the adult brain is not known. We transplanted hESC-derived midbrain dopamine (mDA) or cortical glutamate neurons into the substantia nigra or striatum of a mouse PD model and found extensive graft integration with host circuitry. Axonal pathfinding toward the dorsal striatum was determined by the identity of the grafted neurons, and anatomical presynaptic inputs were largely dependent on graft location, whereas inhibitory versus excitatory input was dictated by the identity of grafted neurons. hESC-derived mDA neurons display A9 characteristics and restore functionality of the reconstructed nigrostriatal circuit to mediate improvements in motor function. These results indicate similarity in cell-type-specific pre- and post-synaptic integration between transplant-reconstructed circuit and endogenous neural networks, highlighting the capacity of hPSC-derived neuron subtypes for specific circuit repair and functional restoration in the adult brain.