Wnt5a-treated midbrain neural stem cells improve dopamine cell replacement therapy in parkinsonian mice

Research progress of neural stem cells as a source of dopaminergic neurons for cell therapy in Parkinson's disease

Parkinson's disease (PD) is a neurodegenerative disease, the most characteristic pathological feature is the progressive loss of dopaminergic (DA) neurons in the substantia nigra pars compactus (SNpc) of the mesencephalon, along with reduced dopamine content in the striatum. Researchers have been searching for drugs and therapies to treat PD in decades. However, no approach could stop the progression of the disease, and even some of them caused adverse clinical side effects. PD has a well-defined lesion. Therefore, it is considered to be one of the most curable central nervous system diseases by cell replacement treatment. Fetal ventral mesencephalic tissue transplantation has been used to treat patients with PD and obtained positive treatment results. However, ethical issues, such as limited donor tissue, and side effects including graft-induced dyskinesias, limit its clinical applications. Neural stem cell (NSC) transplantation is a viable therapy choice because it possesses multipotency, self-renewal ability, and differentiation into DA neurons, which may substitute for lost DA neurons and slow down the neurodegenerative process in PD. Studies that investigated the delivery of NSCs by using animal models of PD revealed survival, migration, and even amelioration of behavioral deficits. Here, the research progress of NSCs or NSC-derived DA neurons in treating PD was reviewed, and the practicability of present manufacturing processes for clinical testing was considered. This review is expected to offer ideas for practical strategies to solve the present technical and biological problems related to the clinical application of NSCs in PD.

Differentiation of astrocytes with characteristics of ventral midbrain from human embryonic stem cells

Molecular and functional diversity among region-specific astrocytes is of great interest in basic neuroscience and the study of neurological diseases. In this study, we present the generation and characterization of astrocytes from human embryonic stem cells with the characteristics of the ventral midbrain (VM). Fine modulation of WNT and SHH signaling during neural differentiation induced neural precursor cells (NPCs) with high expression of EN1 and NKX6.1, but less expression of FOXA2. Overexpression of nuclear factor IB in NPCs induced astrocytes, thereby maintaining the expression of region-specific genes acquired in the NPC stage. When cocultured with dopaminergic (DA) precursors or DA neurons, astrocytes with VM characteristics (VM-iASTs) promoted the differentiation and survival of DA neurons better than those that were not regionally specified. Transcriptomic analysis showed that VM-iASTs were more closely related to human primary midbrain astrocytes than to cortical astrocytes, and revealed the upregulation of WNT1 and WNT5A, which supports their VM identity and explains their superior activity in DA neurons. Taken together, we hope that VM-iASTs can serve to improve ongoing DA precursor transplantation for Parkinson's disease, and that their transcriptomic data provide a valuable resource for investigating regional diversity in human astrocyte populations.

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.

TGFβ3, dibutyryl cAMP and a notch inhibitor modulate phenotype late in stem cell-derived dopaminergic neuron maturation

The generation of midbrain dopaminergic neurons (mDAs) from pluripotent stem cells (hPSC) holds much promise for both disease modelling studies and as a cell therapy for Parkinson's disease (PD). Generally, dopaminergic neuron differentiation paradigms rely on inhibition of smad signalling for neural induction followed by hedgehog signalling and an elevation of β-catenin to drive dopaminergic differentiation. Post-patterning, differentiating dopaminergic neuron cultures are permitted time for maturation after which the success of these differentiation paradigms is usually defined by expression of tyrosine hydroxylase (TH), the rate limiting enzyme in the synthesis of dopamine. However, during maturation, culture media is often supplemented with additives to promote neuron survival and or promote cell differentiation. These additives include dibutyryl cyclic adenosine monophosphate (dbcAMP), transforming growth factor β3 (TGFβ3) and or the γ-secretase inhibitor (DAPT). While these factors are routinely added to cultures, their impact upon pluripotent stem cell-derived mDA phenotype is largely unclear. In this study, we differentiate pluripotent stem cells toward a dopaminergic phenotype and investigate how the omission of dbcAMP, TGFβ3 or DAPT, late in maturation, affects the regulation of multiple dopaminergic neuron phenotype markers. We now show that the removal of dbcAMP or TGFβ3 significantly and distinctly impacts multiple markers of the mDA phenotype (FOXA2, EN1, EN2, FOXA2, SOX6), while commonly increasing both MSX2 and NEUROD1 and reducing expression of both tyrosine hydroxylase and WNT5A. Removing DAPT significantly impacted MSX2, OTX2, EN1, and KCNJ6. In the absence of any stressful stimuli, we suggest that these culture additives should be viewed as mDA phenotype-modifying, rather than neuroprotective. We also suggest that their addition to cultures is likely to confound the interpretation of both transplantation and disease modelling studies.

Single-cell transcriptomics reveals correct developmental dynamics and high-quality midbrain cell types by improved hESC differentiation

Stem cell technologies provide new opportunities for modeling cells in health and disease and for regenerative medicine. In both cases, developmental knowledge and defining the molecular properties and quality of the cell types is essential. In this study, we identify developmental factors important for the differentiation of human embryonic stem cells (hESCs) into functional midbrain dopaminergic (mDA) neurons. We found that laminin-511, and dual canonical and non-canonical WNT activation followed by GSK3β inhibition plus FGF8b, improved midbrain patterning. In addition, neurogenesis and differentiation were enhanced by activation of liver X receptors and inhibition of fibroblast growth factor signaling. Moreover, single-cell RNA-sequencing analysis revealed a developmental dynamics similar to that of the endogenous human ventral midbrain and the emergence of high-quality molecularly defined midbrain cell types, including mDA neurons. Our study identifies novel factors important for human midbrain development and opens the door for a future application of molecularly defined hESC-derived cell types in Parkinson disease.

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.

A combined cell and gene therapy approach for homotopic reconstruction of midbrain dopamine pathways using human pluripotent stem cells

Midbrain dopamine (mDA) neurons can be replaced in patients with Parkinson's disease (PD) in order to provide long-term improvement in motor functions. The limited capacity for long-distance axonal growth in the adult brain means that cells are transplanted ectopically, into the striatal target. As a consequence, several mDA pathways are not re-instated, which may underlie the incomplete restoration of motor function in patients. Here, we show that viral delivery of GDNF to the striatum, in conjunction with homotopic transplantation of human pluripotent stem-cell-derived mDA neurons, recapitulates brain-wide mDA target innervation. The grafts provided re-instatement of striatal dopamine levels and correction of motor function and also connectivity with additional mDA target nuclei not well innervated by ectopic grafts. These results demonstrate the remarkable capacity for achieving functional and anatomically precise reconstruction of long-distance circuitry in the adult brain by matching appropriate growth-factor signaling to grafting of specific cell types.

Potential role of cannabidiol in Parkinson's disease by targeting the WNT/β-catenin pathway, oxidative stress and inflammation

Parkinson's disease (PD) is a major neurodegenerative disease (ND), presenting a progressive degeneration of the nervous system characterized by a loss of dopamine in the substantia nigra pars compacta. Recent findings have shown that oxidative stress and inflammation play key roles in the development of PD. However, therapies remain uncertain and research for new treatment is of the utmost importance. This review focuses on the potential effects of using cannabidiol (CBD) as a potential therapeutic strategy for the treatment of PD and on some of the presumed mechanisms by which CBD provides its beneficial properties. CBD medication downregulates GSK-3β, the main inhibitor of the WNT/β-catenin pathway. Activation of the WNT/β-catenin could be associated with the control of oxidative stress and inflammation. Future prospective clinical trials should focus on CBD and its multiple interactions in the treatment of PD.

The association of enteric neuropathy with gut phenotypes in acute and progressive models of Parkinson's disease

Parkinson's disease (PD) is associated with neuronal damage in the brain and gut. This work compares changes in the enteric nervous system (ENS) of commonly used mouse models of PD that exhibit central neuropathy and a gut phenotype. Enteric neuropathy was assessed in five mouse models: peripheral injection of MPTP; intracerebral injection of 6-OHDA; oral rotenone; and mice transgenic for A53T variant human α-synuclein with and without rotenone. Changes in the ENS of the colon were quantified using pan-neuronal marker, Hu, and neuronal nitric oxide synthase (nNOS) and were correlated with GI function. MPTP had no effect on the number of Hu+ neurons but was associated with an increase in Hu+ nuclear translocation (P < 0.04). 6-OHDA lesioned mice had significantly fewer Hu+ neurons/ganglion (P < 0.02) and a reduced proportion of nNOS+ neurons in colon (P < 0.001). A53T mice had significantly fewer Hu+ neurons/area (P < 0.001) and exhibited larger soma size (P < 0.03). Treatment with rotenone reduced the number of Hu+ cells/mm2 in WT mice (P < 0.006) and increased the proportion of Hu+ translocated cells in both WT (P < 0.02) and A53T mice (P < 0.04). All PD models exhibited a degree of enteric neuropathy, the extent and type of damage to the ENS, however, was dependent on the model.

Parkinson's Disease: Potential Actions of Lithium by Targeting the WNT/β-Catenin Pathway, Oxidative Stress, Inflammation and Glutamatergic Pathway

Parkinson's disease (PD) is one of the major neurodegenerative diseases (ND) which presents a progressive neurodegeneration characterized by loss of dopamine in the substantia nigra pars compacta. It is well known that oxidative stress, inflammation and glutamatergic pathway play key roles in the development of PD. However, therapies remain uncertain and research for new treatment is mandatory. This review focuses on the potential effects of lithium, as a potential therapeutic strategy, on PD and some of the presumed mechanisms by which lithium provides its benefit properties. Lithium medication downregulates GSK-3beta, the main inhibitor of the WNT/β-catenin pathway. The stimulation of the WNT/β-catenin could be associated with the control of oxidative stress, inflammation, and glutamatergic pathway. Future prospective clinical trials could focus on lithium and its different and multiple interactions in PD.

Development and Differentiation of Midbrain Dopaminergic Neuron: From Bench to Bedside

Parkinson’s Disease (PD) is a neurodegenerative disorder affecting the motor system. It is primarily due to substantial loss of midbrain dopamine (mDA) neurons in the substantia nigra pars compacta and to decreased innervation to the striatum. Although existing drug therapy available can relieve the symptoms in early-stage PD patients, it cannot reverse the pathogenic progression of PD. Thus, regenerating functional mDA neurons in PD patients may be a cure to the disease. The proof-of-principle clinical trials showed that human fetal graft-derived mDA neurons could restore the release of dopamine neurotransmitters, could reinnervate the striatum, and could alleviate clinical symptoms in PD patients. The invention of human-induced pluripotent stem cells (hiPSCs), autologous source of neural progenitors with less ethical consideration, and risk of graft rejection can now be generated in vitro. This advancement also prompts extensive research to decipher important developmental signaling in differentiation, which is key to successful in vitro production of functional mDA neurons and the enabler of mass manufacturing of the cells required for clinical applications. In this review, we summarize the biology and signaling involved in the development of mDA neurons and the current progress and methodology in driving efficient mDA neuron differentiation from pluripotent stem cells.

LncRNA H19 diminishes dopaminergic neuron loss by mediating microRNA-301b-3p in Parkinson's disease via the HPRT1-mediated Wnt/β-catenin signaling pathway

Long non-coding RNAs (lncRNA) and microRNAs (miRNAs) are a subject of active investigation in neurodegenerative disorders including Parkinson's disease (PD). We hypothesized a regulatory role of lncRNA H19 with involvement of hypoxanthine phosphoribosyltransferase 1 (HPRT1) in dopaminergic neuron loss in PD model mice obtained by 6-hydroxydopamine (6-OHDA) lesions. We predicted the differentially expressed genes and related mechanisms by microarray analysis. We measured the expression of tyrosine hydroxylase (TH) and proneural genes in the substantia nigra of lesioned mice before and after treatment with lentiviral oe-HPRT1, agomir-miR-301b-3p and inhibition of the Wnt/β-catenin pathway. We also evaluated the relationship among lncRNA H19, HPRT1 and miR-301b-3p as well as the Wnt/β-catenin signaling pathway in these mice. The obtained results predicted and further confirmed a low level of HPRT1 in lesioned mice. We found low expression of lncRNA H19 and showed that its forced overexpression regulated HPRT1 by binding to miR-301b-3p. The overexpression of HPRT1 increased TH expression and inhibited dopaminergic neuron loss via activating the Wnt/β-catenin pathway, as reflected by increased expressions of Nurr-1, Pitx-3, Ngn-2 and NeuroD1. Thus, overexpressed lncRNA H19 protects against dopaminergic neuron loss in this PD model through activating the Wnt/β-catenin pathway via impairing miR-301b-3p-targeted inhibition of HPRT1 expression.

Wnt/β-Catenin Signaling in Neural Stem Cell Homeostasis and Neurological Diseases

Neural stem/progenitor cells (NSCs) maintain the ability of self-renewal and differentiation and compose the complex nervous system. Wnt signaling is thought to control the balance of NSC proliferation and differentiation via the transcriptional coactivator β-catenin during brain development and adult tissue homeostasis. Disruption of Wnt signaling may result in developmental defects and neurological diseases. Here, we summarize recent findings of the roles of Wnt/β-catenin signaling components in NSC homeostasis for the regulation of functional brain circuits. We also suggest that the potential role of Wnt/β-catenin signaling might lead to new therapeutic strategies for neurological diseases, including, but not limited to, spinal cord injury, Alzheimer's disease, Parkinson's disease, and depression.

Parkinson's disease, aging and adult neurogenesis: Wnt/β-catenin signalling as the key to unlock the mystery of endogenous brain repair

A common hallmark of age-dependent neurodegenerative diseases is an impairment of adult neurogenesis. Wingless-type mouse mammary tumor virus integration site (Wnt)/β-catenin (WβC) signalling is a vital pathway for dopaminergic (DAergic) neurogenesis and an essential signalling system during embryonic development and aging, the most critical risk factor for Parkinson's disease (PD). To date, there is no known cause or cure for PD. Here we focus on the potential to reawaken the impaired neurogenic niches to rejuvenate and repair the aged PD brain. Specifically, we highlight WβC-signalling in the plasticity of the subventricular zone (SVZ), the largest germinal region in the mature brain innervated by nigrostriatal DAergic terminals, and the mesencephalic aqueduct-periventricular region (Aq-PVR) Wnt-sensitive niche, which is in proximity to the SNpc and harbors neural stem progenitor cells (NSCs) with DAergic potential. The hallmark of the WβC pathway is the cytosolic accumulation of β-catenin, which enters the nucleus and associates with T cell factor/lymphoid enhancer binding factor (TCF/LEF) transcription factors, leading to the transcription of Wnt target genes. Here, we underscore the dynamic interplay between DAergic innervation and astroglial-derived factors regulating WβC-dependent transcription of key genes orchestrating NSC proliferation, survival, migration and differentiation. Aging, inflammation and oxidative stress synergize with neurotoxin exposure in "turning off" the WβC neurogenic switch via down-regulation of the nuclear factor erythroid-2-related factor 2/Wnt-regulated signalosome, a key player in the maintenance of antioxidant self-defense mechanisms and NSC homeostasis. Harnessing WβC-signalling in the aged PD brain can thus restore neurogenesis, rejuvenate the microenvironment, and promote neurorescue and regeneration.

Viral Delivery of GDNF Promotes Functional Integration of Human Stem Cell Grafts in Parkinson's Disease

Dopaminergic neurons (DAns), generated from human pluripotent stem cells (hPSCs), are capable of functionally integrating following transplantation and have recently advanced to clinical trials for Parkinson's disease (PD). However, pre-clinical studies have highlighted the low proportion of DAns within hPSC-derived grafts and their inferior plasticity compared to fetal tissue. Here, we examined whether delivery of a developmentally critical protein, glial cell line-derived neurotrophic factor (GDNF), could improve graft outcomes. We tracked the response of DAns implanted into either a GDNF-rich environment or after a delay in exposure. Early GDNF promoted survival and plasticity of non-DAns, leading to enhanced motor recovery in PD rats. Delayed exposure to GDNF promoted functional recovery through increases in DAn specification, DAn plasticity, and DA metabolism. Transcriptional profiling revealed a role for mitogen-activated protein kinase (MAPK)-signaling downstream of GDNF. Collectively, these results demonstrate the potential of neurotrophic gene therapy strategies to improve hPSC graft outcomes.

Peptide-Based Scaffolds for the Culture and Transplantation of Human Dopaminergic Neurons

Cell replacement therapy is a promising treatment strategy for Parkinson's disease (PD); however, the poor survival rate of transplanted neurons is a critical barrier to functional recovery. In this study, we used self-assembling peptide nanofiber scaffolds (SAPNS) based on the peptide RADA16-I to support the in vitro maturation and in vivo post-transplantation survival of encapsulated human dopaminergic (DA) neurons derived from induced pluripotent stem cells. Neurons encapsulated within the SAPNS expressed mature neuronal and midbrain DA markers and demonstrated in vitro functional activity similar to neurons cultured in two dimensions. A microfluidic droplet generation method was used to encapsulate cells within monodisperse SAPNS microspheres, which were subsequently used to transplant adherent, functional networks of DA neurons into the striatum of a 6-hydroxydopamine-lesioned PD mouse model. SAPNS microspheres significantly increased the in vivo survival of encapsulated neurons compared with neurons transplanted in suspension, and they enabled significant recovery in motor function compared with control lesioned mice using approximately an order of magnitude fewer neurons than have been previously needed to demonstrate behavioral recovery. These results indicate that such biomaterial scaffolds can be used as neuronal transplantation vehicles to successfully improve the outcome of cell replacement therapies for PD. Impact Statement Transplantation of dopaminergic (DA) neurons holds potential as a treatment for Parkinson's disease (PD), but low survival rates of transplanted neurons is a barrier to successfully improving motor function. In this study, we used hydrogel scaffolds to transplant DA neurons into PD model mice. The hydrogel scaffolds enhanced survival of the transplanted neurons compared with neurons that were transplanted in a conventional manner, and they also improved recovery of motor function by using significantly fewer neurons than have typically been transplanted to see functional benefits. This cell transplantation technology has the capability to improve the outcome of neuron transplantation therapies.

New insights into Wnt signaling alterations in amyotrophic lateral sclerosis: a potential therapeutic target?

Amyotrophic lateral sclerosis is a fatal neurodegenerative disorder characterized by upper and lower motor neuron degeneration, which leads to progressive paralysis of skeletal muscles and, ultimately, respiratory failure between 2–5 years after symptom onset. Unfortunately, currently accepted treatments for amyotrophic lateral sclerosis are extremely scarce and only provide modest benefit. As a consequence, a great effort is being done by the scientific community in order to achieve a better understanding of the different molecular and cellular processes that influence the progression and/or outcome of this neuropathological condition and, therefore, unravel new potential targets for therapeutic intervention. Interestingly, a growing number of experimental evidences have recently shown that, besides its well-known physiological roles in the developing and adult central nervous system, the Wnt family of proteins is involved in different neuropathological conditions, including amyotrophic lateral sclerosis. These proteins are able to modulate, at least, three different signaling pathways, usually known as canonical (β-catenin dependent) and non-canonical (β-catenin independent) signaling pathways. In the present review, we aim to provide a general overview of the current knowledge that supports the relationship between the Wnt family of proteins and its associated signaling pathways and amyotrophic lateral sclerosis pathology, as well as their possible mechanisms of action. Altogether, the currently available knowledge suggests that Wnt signaling modulation might be a promising therapeutic approach to ameliorate the histopathological and functional deficits associated to amyotrophic lateral sclerosis, and thus improve the progression and outcome of this neuropathology.

Wnt1 silencing enhances neurotoxicity induced by paraquat and maneb in SH-SY5Y cells

Wingless (Wnt) signaling regulates the proliferation and differentiation of midbrain dopamine (DA) neurons. Paraquat (PQ) and maneb (MB) are environmental pollutants that can be used to model Parkinson's disease (PD) in rodents. A previous study demonstrated that developmental exposure to PQ and MB affects the expression of Wnt1, Wnt5a, nuclear receptor-related factor 1 (NURR1) and tyrosine hydroxylase (TH). However, how Wnt signaling regulates these developmental factors in vitro is yet to be determined. To explore this, SH-SY5Y cells were exposed to PQ and MB. The results of the current study indicated that exposure to PQ and MB decreased Wnt1, β-catenin, NURR1 and TH levels and increased Wnt5a levels. Furthermore, Wnt1 silencing has the same effect as exposure to PQ and MB. Additionally, the neurotoxicity induced by PQ and MB is more severe in siWnt1-SH-SY5Y cells compared with normal SH-SY5Y cells. Therefore, Wnt1 may serve an important role in regulating developmental DA factors, and may be a candidate gene for PD diagnosis or gene therapy.

Wnt Signaling Alterations in the Human Spinal Cord of Amyotrophic Lateral Sclerosis Cases: Spotlight on Fz2 and Wnt5a

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disorder with no cure, and elucidation of the mechanisms mediating neuronal death in this neuropathology is crucial to develop effective treatments. It has recently been demonstrated in animal models that the Wnt family of proteins is involved in this neuropathology, although its potential involvement in case of humans is almost unknown. We analyzed the expression of Wnt signaling components in healthy and ALS human spinal cords by quantitative RT-PCR, and we found that most Wnt ligands, modulators, receptors, and co-receptors were expressed in healthy controls. Moreover, we observed clear alterations in the mRNA expression of different components of this family of proteins in human spinal cord tissue from ALS cases. Specifically, we detected a significant increase in the mRNA levels of Wnt3, Wnt4, Fz2, and Fz8, together with several non-significant increases in the mRNA expression of other genes such as Wnt2b, Wnt5a, Fz3, Lrp5, and sFRP3. Based on these observations and on previous reports of studies performed in animal models, we evaluated with immunohistochemistry the protein expression patterns of Fz2 and Fz5 receptors and their main ligand Wnt5a in control samples and ALS cases. No substantial changes were observed in Fz5 protein expression pattern in ALS samples. However, we detected an increase in the amount of Fz2+ astrocytes in the borderline between gray and white matter at the ventral horn in ALS samples. Finally, Wnt5a expression was observed in neurons and astrocytes in both control and ALS samples, although Wnt5a immunolabeling in astroglial cells was significantly increased in ALS spinal cords in the same region where changes in Fz2 were observed. Altogether, these observations strongly suggest that the Wnt family of proteins, and more specifically Fz2 and Wnt5a, might be involved in human ALS pathology.

Wnt5a induces and maintains prostate cancer cells dormancy in bone

Wnt5a from osteoblastic niche induces and maintains the dormancy of prostate cancer cells in bone and inhibits bone metastasis in a preventive manner, uncovering a potential therapeutic utility of Wnt5a in the treatment of bone metastatic prostate cancer.

In a substantial fraction of prostate cancer (PCa) patients, bone metastasis appears after years or even decades of latency. Canonical Wnt/β-catenin signaling has been proposed to be implicated in dormancy of cancer cells. However, how these tumor cells are kept dormant and recur under control of Wnt/β-catenin signaling derived from bone microenvironment remains unknown. Here, we report that Wnt5a from osteoblastic niche induces dormancy of PCa cells in a reversible manner in vitro and in vivo via inducing Siah E3 Ubiquitin Protein Ligase 2 (SIAH2) expression, which represses Wnt/β-catenin signaling. Furthermore, this effect of Wnt5a-induced dormancy of PCa cells depends on receptor tyrosine kinase-like orphan receptor 2 (ROR2), and a negative correlation of ROR2 expression with bone metastasis–free survival is observed in PCa patients. Therefore, these results demonstrate that Wnt5a/ROR2/SIAH2 signaling axis plays a crucial role in inducing and maintaining PCa cells dormancy in bone, suggesting a potential therapeutic utility of Wnt5a via inducing dormancy of PCa cells in bone.

Oxidative Stress Induces an Interactive Decline in Wnt and Nrf2 Signaling in Degenerating Retinal Pigment Epithelium

AIMS

Cells have evolved a highly sophisticated web of cytoprotective systems to neutralize unwanted oxidative stress, but are challenged by unique modern day stresses such as cigarette smoking and ingestion of a high-fat diet (HFD). Age-related disease, such as age-related macular degeneration (AMD), the most common cause of blindness among the elderly in Western societies, develops in part, when oxidative stress overwhelms cytoprotective systems to injure tissue. Since most studies focus on the protection by a single protective system, the aim of this study was to investigate the impact of more than one cytoprotective system against oxidative stress.

RESULTS

Wingless (Wnt) and nuclear factor-erythroid 2-related factor 2 (Nrf2), two fundamental signaling systems that are vital to cell survival, decline after mice are exposed to chronic cigarette smoke and HFD, two established AMD risk factors, in a bidirectional feedback loop through phosphorylated glycogen synthase kinase 3 beta. Decreased Wnt and Nrf2 signaling leads to retinal pigment epithelial dysfunction and apoptosis, and a phenotype that is strikingly similar to geographic atrophy (GA), an advanced form of AMD with no effective treatment.

INNOVATION

This study is the first to show that chronic oxidative stress from common modern day environmental exposures reduces two fundamental and vital cytoprotective networks in a bidirectional feedback loop, and their decline leads to advanced disease phenotype.

CONCLUSION

Our data offer new insights into how combined modern oxidative stresses of cigarette smoking and HFD contribute to GA through an interactive decline in Wnt and Nrf2 signaling. Antioxid. Redox Signal. 29, 389-407.

Primary tissue for cellular brain repair in Parkinson's disease: Promise, problems and the potential of biomaterials

The dopamine precursor, levodopa, remains the "gold standard" treatment for Parkinson's disease, and, although it provides superlative efficacy in the early stages of the disease, its long-term use is limited by the development of severe motor side effects and a significant abating of therapeutic efficacy. Therefore, there remains a major unmet clinical need for the development of effective neuroprotective, neurorestorative or neuroreparatory therapies for this condition. The relatively selective loss of dopaminergic neurons from the nigrostriatal pathway makes Parkinson's disease an ideal candidate for reparative cell therapies, wherein the dopaminergic neurons that are lost in the condition are replaced through direct cell transplantation into the brain. To date, this approach has been developed, validated and clinically assessed using dopamine neuron-rich foetal ventral mesencephalon grafts which have been shown to survive and reinnervate the denervated brain after transplantation, and to restore motor function. However, despite long-term symptomatic relief in some patients, significant limitations, including poor graft survival and the impact this has on the number of foetal donors required, have prevented this therapy being more widely adopted as a restorative approach for Parkinson's disease. Injectable biomaterial scaffolds have the potential to improve the delivery, engraftment and survival of these grafts in the brain through provision of a supportive microenvironment for cell adhesion, growth and immune shielding. This article will briefly review the development of primary cell therapies for brain repair in Parkinson's disease and will consider the emerging literature which highlights the potential of using injectable biomaterial hydrogels in this context.

Ryk receptors on unmyelinated nerve fibers mediate excitatory synaptic transmission and CCL2 release during neuropathic pain induced by peripheral nerve injury

Background

Neuropathic pain is a major pathology of the central nervous system associated with neuroinflammation. Ryk (receptor-like tyrosine kinase) receptors act as repulsive axon-guidance molecules during development of central nervous system and neural injury. Increasing evidence suggests the potential involvement of Wnt/Ryk (wingless and Int) signaling in the pathogenesis of neuropathic pain. However, its underlying mechanism remains unknown.

Results

The expression and location of Ryk receptor as well as its ligand Wnt1 were detected by qPCR, Western blot, and immunohistochemistry. We found that Ryk, a specific Wnt receptor, was expressed in IB4⁺ (Isolectin B4) and CGRP⁺ (calcitonin gene-related peptide) dorsal root ganglia neurons and their ascending unmyelinated fibers in the dorsal horn of the spinal cord. Ryk was upregulated after spinal nerve ligation surgery. Wnt1 was also increased in activated astrocytes in the dorsal horn after spinal nerve ligation. The presynaptic mechanism of Ryk in regulation of neuropathic pain was determined by electrophysiology in spinal slice. Spinal nerve ligation model was established, and the therapeutic potential of inhibiting Ryk receptor was determined. Spine-specific blocking of the Wnt/Ryk receptor signaling attenuated the spinal nerve ligation-induced mechanical allodynia but not thermal hyperalgesia. Further, it also blocked Ca²⁺-dependent signals including CaMKII and PKCγ, subsequent release of CCL2 (CCR-like protein) in the dorsal horn. An in vitro study showed that inactivating Ryk receptors with anti-Ryk antibodies or lentiviral Ryk shRNA led to the inactivation of Wnt1 for excitatory synaptic transmission in spinal slices and subsequent decrease in CCL2 expression in the dorsal root ganglia neurons.

Conclusion

These studies demonstrate the existence of critical crosstalk between astrocytes and unmyelinated fibers, which indicate the presynaptic mechanism of Ryk in cytokine transmission of neuropathic pain and the therapeutic potential for Wnt/Ryk signaling pathway in the treatment of neuropathic pain.

Thermodynamics in Neurodegenerative Diseases: Interplay Between Canonical WNT/Beta-Catenin Pathway-PPAR Gamma, Energy Metabolism and Circadian Rhythms

Entropy production rate is increased by several metabolic and thermodynamics abnormalities in neurodegenerative diseases (NDs). Irreversible processes are quantified by changes in the entropy production rate. This review is focused on the opposing interactions observed in NDs between the canonical WNT/beta-catenin pathway and PPAR gamma and their metabolic and thermodynamic implications. In amyotrophic lateral sclerosis and Huntington's disease, WNT/beta-catenin pathway is upregulated, whereas PPAR gamma is downregulated. In Alzheimer's disease and Parkinson's disease, WNT/beta-catenin pathway is downregulated while PPAR gamma is upregulated. The dysregulation of the canonical WNT/beta-catenin pathway is responsible for the modification of thermodynamics behaviors of metabolic enzymes. Upregulation of WNT/beta-catenin pathway leads to aerobic glycolysis, named Warburg effect, through activated enzymes, such as glucose transporter (Glut), pyruvate kinase M2 (PKM2), pyruvate dehydrogenase kinase 1(PDK1), monocarboxylate lactate transporter 1 (MCT-1), lactic dehydrogenase kinase-A (LDH-A) and inactivation of pyruvate dehydrogenase complex (PDH). Downregulation of WNT/beta-catenin pathway leads to oxidative stress and cell death through inactivation of Glut, PKM2, PDK1, MCT-1, LDH-A but activation of PDH. In addition, in NDs, PPAR gamma is dysregulated, whereas it contributes to the regulation of several key circadian genes. NDs show many dysregulation in the mediation of circadian clock genes and so of circadian rhythms. Thermodynamics rhythms operate far-from-equilibrium and partly regulate interactions between WNT/beta-catenin pathway and PPAR gamma. In NDs, metabolism, thermodynamics and circadian rhythms are tightly interrelated.

Retrograde interferon-gamma signaling induces major histocompatibility class I expression in human-induced pluripotent stem cell-derived neurons

Objective

Injury-associated axon-intrinsic signals are thought to underlie pathogenesis and progression in many neuroinflammatory and neurodegenerative diseases, including multiple sclerosis (MS). Retrograde interferon gamma (IFN γ) signals are known to induce expression of major histocompatibility class I (MHC I) genes in murine axons, thereby increasing the susceptibility of these axons to attack by antigen-specific CD8⁺ T cells. We sought to determine whether the same is true in human neurons.

Methods

A novel microisolation chamber design was used to physically isolate and manipulate axons from human skin fibroblast-derived induced pluripotent stem cell (iPSC)-derived neuron-enriched neural aggregates. Fluorescent retrobeads were used to assess the fraction of neurons with projections to the distal chamber. Axons were treated with IFN γ for 72 h and expression of MHC class I and antigen presentation genes were evaluated by RT-PCR and immunofluorescence.

Results

Human iPSC-derived neural stem cells maintained as 3D aggregate cultures in the cell body chamber of polymer microisolation chambers extended dense axonal projections into the fluidically isolated distal chamber. Treatment of these axons with IFN γ resulted in upregulation of MHC class I and antigen processing genes in the neuron cell bodies. IFN γ-induced MHC class I molecules were also anterogradely transported into the distal axon.

Interpretation

These results provide conclusive evidence that human axons are competent to express MHC class I molecules, suggesting that inflammatory factors enriched in demyelinated lesions may render axons vulnerable to attack by autoreactive CD8⁺ T cells in patients with MS. Future work will be aimed at identifying pathogenic anti-axonal T cells in these patients.

Neuronal replacement therapy: previous achievements and challenges ahead

Lifelong neurogenesis and incorporation of newborn neurons into mature neuronal circuits operates in specialized niches of the mammalian brain and serves as role model for neuronal replacement strategies. However, to which extent can the remaining brain parenchyma, which never incorporates new neurons during the adulthood, be as plastic and readily accommodate neurons in networks that suffered neuronal loss due to injury or neurological disease? Which microenvironment is permissive for neuronal replacement and synaptic integration and which cells perform best? Can lost function be restored and how adequate is the participation in the pre-existing circuitry? Could aberrant connections cause malfunction especially in networks dominated by excitatory neurons, such as the cerebral cortex? These questions show how important connectivity and circuitry aspects are for regenerative medicine, which is the focus of this review. We will discuss the impressive advances in neuronal replacement strategies and success from exogenous as well as endogenous cell sources. Both have seen key novel technologies, like the groundbreaking discovery of induced pluripotent stem cells and direct neuronal reprogramming, offering alternatives to the transplantation of fetal neurons, and both herald great expectations. For these to become reality, neuronal circuitry analysis is key now. As our understanding of neuronal circuits increases, neuronal replacement therapy should fulfill those prerequisites in network structure and function, in brain-wide input and output. Now is the time to incorporate neural circuitry research into regenerative medicine if we ever want to truly repair brain injury.

Stem Cell Technology for (Epi)genetic Brain Disorders

Despite the enormous efforts of the scientific community over the years, effective therapeutics for many (epi)genetic brain disorders remain unidentified. The common and persistent failures to translate preclinical findings into clinical success are partially attributed to the limited efficiency of current disease models. Although animal and cellular models have substantially improved our knowledge of the pathological processes involved in these disorders, human brain research has generally been hampered by a lack of satisfactory humanized model systems. This, together with our incomplete knowledge of the multifactorial causes in the majority of these disorders, as well as a thorough understanding of associated (epi)genetic alterations, has been impeding progress in gaining more mechanistic insights from translational studies. Over the last years, however, stem cell technology has been offering an alternative approach to study and treat human brain disorders. Owing to this technology, we are now able to obtain a theoretically inexhaustible source of human neural cells and precursors in vitro that offer a platform for disease modeling and the establishment of therapeutic interventions. In addition to the potential to increase our general understanding of how (epi)genetic alterations contribute to the pathology of brain disorders, stem cells and derivatives allow for high-throughput drugs and toxicity testing, and provide a cell source for transplant therapies in regenerative medicine. In the current chapter, we will demonstrate the validity of human stem cell-based models and address the utility of other stem cell-based applications for several human brain disorders with multifactorial and (epi)genetic bases, including Parkinson's disease (PD), Alzheimer's disease (AD), fragile X syndrome (FXS), Angelman syndrome (AS), Prader-Willi syndrome (PWS), and Rett syndrome (RTT).

The potential role of neuroinflammation and transcription factors in Parkinson disease

Parkinson disease (PD) is a neurodegenerative disorder characterized by dopaminergic neurons affected by inflammatory processes. Post-mortem analyses of brain and cerebrospinal fluid from PD patients show the accumulation of proinflammatory cytokines, confirming an ongoing neuroinflammation in the affected brain regions. These inflammatory mediators may activate transcription factors—notably nuclear factor κB, Ying-Yang 1 (YY1), fibroblast growth factor 20 (FGF20), and mammalian target of rapamycin (mTOR)—which then regulate downstream signaling pathways that in turn promote death of dopaminergic neurons through death domain-containing receptors. Dopaminergic neurons are vulnerable to oxidative stress and inflammatory attack. An increased level of inducible nitric oxide synthase observed in the substantia nigra and striatum of PD patients suggests that both cytokine—and chemokine-induced toxicity and inflammation lead to oxidative stress that contributes to degeneration of dopaminergic neurons and to disease progression. Lipopolysaccharide activation of microglia in the proximity of dopaminergic neurons in the substantia nigra causes their degeneration, and this appears to be a selective vulnerability of dopaminergic neurons to inflammation. In this review, we will look at the role of various transcription factors and signaling pathways in the development of PD.

Homophilic binding of the neural cell adhesion molecule CHL1 regulates development of ventral midbrain dopaminergic pathways

Abnormal development of ventral midbrain (VM) dopaminergic (DA) pathways, essential for motor and cognitive function, may underpin a number of neurological disorders and thereby highlight the importance of understanding the birth and connectivity of the associated neurons. While a number of regulators of VM DA neurogenesis are known, processes involved in later developmental events, including terminal differentiation and axon morphogenesis, are less well understood. Recent transcriptional analysis studies of the developing VM identified genes expressed during these stages, including the cell adhesion molecule with homology to L1 (Chl1). Here, we map the temporal and spatial expression of CHL1 and assess functional roles of substrate-bound and soluble-forms of the protein during VM DA development. Results showed early CHL1 in the VM, corresponding with roles in DA progenitor migration and differentiation. Subsequently, we demonstrated roles for CHL1 in both axonal extension and repulsion, selectively of DA neurons, suggestive of a role in guidance towards forebrain targets and away from hindbrain nuclei. In part, CHL1 mediates these roles through homophilic CHL1-CHL1 interactions. Collectively, these findings enhance our knowledge of VM DA pathways development, and may provide new insights into understanding DA developmental conditions such as autism spectrum disorders.

Critical role of TRPC1 in thyroid hormone-dependent dopaminergic neuron development

Thyroid hormones play a crucial role in midbrain dopaminergic (DA) neuron development. However, the underlying molecular mechanisms remain largely unknown. In this study, we revealed that thyroid hormone treatment evokes significant calcium entry through canonical transient receptor potential (TRPC) channels in ventral midbrain neural stem cells and this calcium signaling is essential for thyroid hormone-dependent DA neuronal differentiation. We also found that TRPC1 is the dominant TRPC channel expressed in ventral midbrain neural stem cells which responds to thyroid hormone. In addition, thyroid hormone increases TRPC1 expression through its receptor alpha 1 during DA neuron differentiation, and, importantly, produces calcium signals by activating TRPC1 channels. In vivo and in vitro gene silencing experiments indicate that TRPC1-mediated calcium signaling is required for thyroid hormone-dependent DA neuronal differentiation. Finally, we confirmed that the activation of OTX2, a determinant of DA neuron development and the expression of which is induced by thyroid hormone, is dependent on TRPC1-mediated calcium signaling. These data revealed the molecular mechanisms of how thyroid hormone regulates DA neuron development from ventral midbrain neural stem cells, particularly endowing a novel physiological relevance to TRPC1 channels.

Old and new challenges in Parkinson's disease therapeutics

Parkinson's disease (PD) is a neurodegenerative disorder characterized by the degeneration of dopaminergic neurons and/or loss od neuronal projections, in several dopaminergic networks. Current treatments for idiopathic PD rely mainly on the use of pharmacologic agents to improve motor symptomatology of PD patients. Nevertheless, so far PD remains an incurable disease. Therefore, it is of utmost importance to establish new therapeutic strategies for PD treatment. Over the last 20 years, several molecular, gene and cell/stem-cell therapeutic approaches have been developed with the aim of counteracting or retarding PD progression. The scope of this review is to provide an overview of PD related therapies and major breakthroughs achieved within this field. In order to do so, this review will start by focusing on PD characterization and current treatment options covering thereafter molecular, gene and cell/stem cell-based therapies that are currently being studied in animal models of PD or have recently been tested in clinical trials. Among stem cell-based therapies, those using MSCs as possible disease modifying agents for PD therapy and, specifically, the MSCs secretome contribution to meet the clinical challenge of counteracting or retarding PD progression, will be more deeply explored.

Dissociation between dopaminergic response and motor behavior following intrastriatal, but not intravenous, transplant of bone marrow mononuclear stem cells in a mouse model of Parkinson's disease

Parkinson's disease is characterized by the progressive loss of dopaminergic neurons from the substantia nigra, a process that leads to a dopamine deficiency in the striatum. This deficiency is responsible for the development of motor symptoms, including resting tremor, bradykinesia, rigidity and postural instability. Based on the observation of substantial neuronal death, alternatives to Parkinson's disease treatment have been studied, including cell-based therapies. The present study aimed to assess the therapeutic potential of intravenous and intrastriatal transplant of bone marrow mononuclear cells in a mouse model of Parkinson's disease. Animals underwent stereotaxic surgery and received an injection of 6-hydroxydopamine into their medial forebrain bundle. Three weeks later, mice were injected with bone marrow mononuclear cells or saline through the caudal vein or directly into their right striatum. Motor function was assessed using the rotarod and apomorphine-induced rotation tests. Our results showed that intrastriatal bone marrow mononuclear cells, but not intravenous, have a short-term therapeutic effect on dopaminergic response in this mice model of parkinsonism assessed by the apomorphine-induced rotation test. This phenomenon was not identified on the rotarod test, showing dissociation between dopaminergic response and motor behavior. Further experiments are needed to elucidate the precise mechanisms involved in these effects.

Developing drugs that target the Wnt pathway: recent approaches in cancer and neurodegenerative diseases

INTRODUCTION

Wnt/β-catenin signaling is an evolutionarily conserved pathway that has a crucial role in embryonic and adult life. Dysregulation of Wnt/β-catenin pathway has been associated with various diseases, including cancer and neurodegenerative disorders, including Parkinson's disease (PD). Several molecular components of the signaling have been proposed as innovative targets for cancer therapy, and very recently, some of them have been also evaluated as potential therapeutic targets for PD. Areas covered: This review focuses on the role of Wnt/β-catenin pathway in the pathogenensis of cancer and PD, examining some recent therapeutic approaches that are ongoing in preclinical and clinical studies. The possibilities that this signaling offers for diagnosis and prognosis of neoplastic diseases, and the concerns of targeting this pathway are also discussed. Expert opinion: Despite the stimulating results obtained in preclinical studies on cancer and other disease models, the clinical experience with Wnt modulators is still in its infancy, and is mainly restricted to anticancer therapy. Even with concerns of the safety of drugs targeting Wnt signaling, the attention of researchers worldwide is increasing to this issue in terms of their therapeutic potential for diseases such as PD, for which no cure exists.

Wnt5a Drives an Invasive Phenotype in Human Glioblastoma Stem-like Cells

Brain invasion by glioblastoma determines prognosis, recurrence, and lethality in patients, but no master factor coordinating the invasive properties of glioblastoma has been identified. Here we report evidence favoring such a role for the noncanonical WNT family member Wnt5a. We found the most invasive gliomas to be characterized by Wnt5a overexpression, which correlated with poor prognosis and also discriminated infiltrating mesenchymal glioblastoma from poorly motile proneural and classical glioblastoma. Indeed, Wnt5a overexpression associated with tumor-promoting stem-like characteristics (TPC) in defining the character of highly infiltrating mesenchymal glioblastoma cells (Wnt5a^High). Inhibiting Wnt5a in mesenchymal glioblastoma TPC suppressed their infiltrating capability. Conversely, enforcing high levels of Wnt5a activated an infiltrative, mesenchymal-like program in classical glioblastoma TPC and Wnt5a^Low mesenchymal TPC. In intracranial mouse xenograft models of glioblastoma, inhibiting Wnt5a activity blocked brain invasion and increased host survival. Overall, our results highlight Wnt5a as a master regulator of brain invasion, specifically TPC, and they provide a therapeutic rationale to target it in patients with glioblastoma. Cancer Res; 77(4); 996-1007. ©2016 AACR.

Efficiently Specified Ventral Midbrain Dopamine Neurons from Human Pluripotent Stem Cells Under Xeno-Free Conditions Restore Motor Deficits in Parkinsonian Rodents

Recent studies have shown evidence for the functional integration of human pluripotent stem cell (hPSC)‐derived ventral midbrain dopamine (vmDA) neurons in animal models of Parkinson’s disease. Although these cells present a sustainable alternative to fetal mesencephalic grafts, a number of hurdles require attention prior to clinical translation. These include the persistent use of xenogeneic reagents and challenges associated with scalability and storage of differentiated cells. In this study, we describe the first fully defined feeder‐ and xenogeneic‐free protocol for the generation of vmDA neurons from hPSCs and utilize two novel reporter knock‐in lines (LMX1A‐eGFP and PITX3‐eGFP) for in‐depth in vitro and in vivo tracking. Across multiple embryonic and induced hPSC lines, this “next generation” protocol consistently increases both the yield and proportion of vmDA neural progenitors (OTX2/FOXA2/LMX1A) and neurons (FOXA2/TH/PITX3) that display classical vmDA metabolic and electrophysiological properties. We identify the mechanism underlying these improvements and demonstrate clinical applicability with the first report of scalability and cryopreservation of bona fide vmDA progenitors at a time amenable to transplantation. Finally, transplantation of xeno‐free vmDA progenitors from LMX1A‐ and PITX3‐eGFP reporter lines into Parkinsonian rodents demonstrates improved engraftment outcomes and restoration of motor deficits. These findings provide important and necessary advancements for the translation of hPSC‐derived neurons into the clinic. Stem Cells Translational Medicine2017;6:937–948

Wnts Are Expressed in the Ependymal Region of the Adult Spinal Cord

The Wnt family of proteins plays key roles during central nervous system development and in several physiological processes during adulthood. Recently, experimental evidence has linked Wnt-related genes to regulation and maintenance of stem cells in the adult neurogenic niches. In the spinal cord, the ependymal cells surrounding the central canal form one of those niches, but little is known about their Wnt expression patterns. Using microdissection followed by TaqMan® low-density arrays, we show here that the ependymal regions of young, mature rats and adult humans express several Wnt-related genes, including ligands, conventional and non-conventional receptors, co-receptors, and soluble inhibitors. We found 13 genes shared between rats and humans, 4 exclusively expressed in rats and 9 expressed only in humans. Also, we observed a reduction with age on spontaneous proliferation of ependymal cells in rats paralleled by a decrease in the expression of Fzd1, Fzd8, and Fzd9. Our results suggest a role for Wnts in the regulation of the adult spinal cord neurogenic niche and provide new data on the specific differences in this region between humans and rodents.

Manipulating Wnt signaling at different subcellular levels affects the fate of neonatal neural stem/progenitor cells

The canonical Wnt signaling pathway plays an important role in embryogenesis, and the establishment of neurogenic niches. It is involved in proliferation and differentiation of neural progenitors, since elevated Wnt/β-catenin signaling promotes differentiation of neural stem/progenitor cells (NS/PCs¹) towards neuroblasts. Nevertheless, it remains elusive how the differentiation program of neural progenitors is influenced by the Wnt signaling output. Using transgenic mouse models, we found that in vitro activation of Wnt signaling resulted in higher expression of β-catenin protein and Wnt/β-catenin target genes, while Wnt signaling inhibition resulted in the reverse effect. Within differentiated cells, we identified three electrophysiologically and immunocytochemically distinct cell types, whose incidence was markedly affected by the Wnt signaling output. Activation of the pathway suppressed gliogenesis, and promoted differentiation of NS/PCs towards a neuronal phenotype, while its inhibition led to suppressed neurogenesis and increased counts of cells of glial phenotype. Moreover, Wnt signaling hyperactivation resulted in an increased incidence of cells expressing outwardly rectifying K⁺ currents, together with inwardly rectifying Na⁺ currents, a typical current pattern of immature neurons, while blocking the pathway led to the opposite effect. Taken together, our data indicate that the Wnt signaling pathway orchestrates neonatal NS/PCs differentiation towards cells with neuronal characteristics, which might be important for nervous tissue regeneration during central nervous system disorders. Furthermore, the transgenic mouse strains used in this study may serve as a convenient tool to manipulate β-catenin-dependent signaling in neural progenitors in the neonatal brain.

Microcarrier-Expanded Neural Progenitor Cells Can Survive, Differentiate, and Innervate Host Neurons Better When Transplanted as Aggregates

Neuronal progenitor cells (NPCs) derived from human embryonic stem cells (hESCs) are an excellent cell source for transplantation therapy due to their availability and ethical acceptability. However, the traditional method of expansion and differentiation of hESCs into NPCs in monolayer cultures requires a long time, and the cell yield is low. A microcarrier (MC) platform can improve the expansion of hESCs and increase the yield of NPCs. In this study, for the first time, we transplanted microcarrier-expanded hESC-derived NPCs into the striatum of adult NOD-SCID IL2Rgc null mice, either as single cells or as cell aggregates. The recipient mice were perfused, and the in vivo survival, differentiation, and targeted innervation of the transplanted cells were assessed by immunostaining. We found that both the transplanted single NPCs and aggregate NPCs were able to survive 1 month posttransplantation, as revealed by human-specific neural cell adhesion molecule (NCAM) and human nuclear antigen staining. Compared to the single cells, the transplanted cell aggregates showed better survival over a 3-month period. In addition, both the transplanted single NPCs and the aggregate NPCs were able to differentiate into DCX-positive immature neurons and Tuj1-positive neurons in vivo by 1 month posttransplantation. However, only the transplantation of aggregate NPCs was shown to result in mature neurons at 3 months posttransplantation. Furthermore, we found that the cell aggregates were able to send long axons to innervate their targets. Our study provides preclinical evidence that the use of MCs to expand and differentiate hESC-derived NPCs and transplantation of these cells as aggregates produce longer survival in vivo.

Stem cell transplantation therapy in Parkinson's disease

Ineffective therapeutic treatments and inadequate repair ability in the central nervous system are disturbing problems for several neurological diseases. Fortunately, the development of clinically applicable populations of stem cells has provided an avenue to overcome the failure of endogenous repair systems and substitute new cells into the damaged brain. However, there are still several existing obstacles to translating into clinical application. Here we review the stem-cell based therapies for Parkinson’s disease and discuss the potential advantages and drawbacks. We hope this review may provide suggestions for viable strategies to overcome the current technical and biological issues associated with the application of stem cells in Parkinson’s disease.

14-3-3ζ deficient mice in the BALB/c background display behavioural and anatomical defects associated with neurodevelopmental disorders

Sequencing and expression analyses implicate 14-3-3ζ as a genetic risk factor for neurodevelopmental disorders such as schizophrenia and autism. In support of this notion, we recently found that 14-3-3ζ^−/− mice in the Sv/129 background display schizophrenia-like defects. As epistatic interactions play a significant role in disease pathogenesis we generated a new congenic strain in the BALB/c background to determine the impact of genetic interactions on the 14-3-3ζ^−/− phenotype. In addition to replicating defects such as aberrant mossy fibre connectivity and impaired spatial memory, our analysis of 14-3-3ζ^−/− BALB/c mice identified enlarged lateral ventricles, reduced synaptic density and ectopically positioned pyramidal neurons in all subfields of the hippocampus. In contrast to our previous analyses, 14-3-3ζ^−/− BALB/c mice lacked locomotor hyperactivity that was underscored by normal levels of the dopamine transporter (DAT) and dopamine signalling. Taken together, our results demonstrate that dysfunction of 14-3-3ζ gives rise to many of the pathological hallmarks associated with the human condition. 14-3-3ζ-deficient BALB/c mice therefore provide a novel model to address the underlying biology of structural defects affecting the hippocampus and ventricle, and cognitive defects such as hippocampal-dependent learning and memory.

Thyroid Hormone-Otx2 Signaling Is Required for Embryonic Ventral Midbrain Neural Stem Cells Differentiated into Dopamine Neurons

Midbrain dopamine (DA) neurons are essential for maintaining multiple brain functions. These neurons have also been implicated in relation with diverse neurological disorders. However, how these neurons are developed from neuronal stem cells (NSCs) remains largely unknown. In this study, we provide both in vivo and in vitro evidence that the thyroid hormone, an important physiological factor for brain development, promotes DA neuron differentiation from embryonic ventral midbrain (VM) NSCs. We find that thyroid hormone deficiency during development reduces the midbrain DA neuron number, downregulates the expression of tyrosine hydroxylase (TH) and the dopamine transporter (DAT), and impairs the DA neuron-dependent motor behavior. In addition, thyroid hormone treatment during VM NSC differentiation in vitro increases the production of DA neurons and upregulates the expression of TH and DAT. We also found that the thyroid hormone enhances the expression of Otx2, an important determinant of DA neurogenesis, during DA neuron differentiation. Our in vitro gene silencing experiments indicate that Otx2 is required for thyroid hormone-dependent DA neuron differentiation from embryonic VM NSCs. Finally, we revealed both in vivo and in vitro that the thyroid hormone receptor alpha 1 is expressed in embryonic VM NSCs. Furthermore, it participates in the effects of thyroid hormone-induced Otx2 upregulation and DA neuron differentiation. These data demonstrate the role and molecular mechanisms of how the thyroid hormone regulates DA neuron differentiation from embryonic VM NSCs, particularly providing new mechanisms and a potential strategy for generating dopamine neurons from NSCs.

How to make a midbrain dopaminergic neuron

Midbrain dopaminergic (mDA) neuron development has been an intense area of research during recent years. This is due in part to a growing interest in regenerative medicine and the hope that treatment for diseases affecting mDA neurons, such as Parkinson's disease (PD), might be facilitated by a better understanding of how these neurons are specified, differentiated and maintained in vivo. This knowledge might help to instruct efforts to generate mDA neurons in vitro, which holds promise not only for cell replacement therapy, but also for disease modeling and drug discovery. In this Primer, we will focus on recent developments in understanding the molecular mechanisms that regulate the development of mDA neurons in vivo, and how they have been used to generate human mDA neurons in vitro from pluripotent stem cells or from somatic cells via direct reprogramming. Current challenges and future avenues in the development of a regenerative medicine for PD will be identified and discussed.

Direct in vivo assessment of human stem cell graft-host neural circuits

Despite the potential of stem cell-derived neural transplants for treating intractable neurological diseases, the global effects of a transplant's electrical activity on host circuitry have never been measured directly, preventing the systematic optimization of such therapies. Here, we overcome this problem by combining optogenetics, stem cell biology, and neuroimaging to directly map stem cell-driven neural circuit formation in vivo. We engineered human induced pluripotent stem cells (iPSCs) to express channelrhodopsin-2 and transplanted resulting neurons to striatum of rats. To non-invasively visualize the function of newly formed circuits, we performed high-field functional magnetic resonance imaging (fMRI) during selective stimulation of transplanted cells. fMRI successfully detected local and remote neural activity, enabling the global graft-host neural circuit function to be assessed. These results demonstrate the potential of a novel neuroimaging-based platform that can be used to identify how a graft's electrical activity influences the brain network in vivo.

The potential of alternate sources of cells for neural grafting in Parkinson's and Huntington's disease

Cell-based therapies for Parkinson's and Huntington's disease have provided mixed clinical outcomes and one of the reasons underlying this is the use of primary fetal tissue as the source of grafted cells. An alternate source of cells, such as stem cells, could overcome many of the issues associated with primary fetal tissue and would help bring forward cell replacement therapy as a reliable and effective treatment for these two neurodegenerative disorders. This review will discuss which stem cells are likely to go to clinic in the next generation of cells, based on trials for Parkinson's and Huntington's disease.

Transcriptome analysis reveals transmembrane targets on transplantable midbrain dopamine progenitors

An important challenge for the continued development of cell therapy for Parkinson's disease (PD) is the establishment of procedures that better standardize cell preparations for use in transplantation. Although cell sorting has been an anticipated strategy, its application has been limited by lack of knowledge regarding transmembrane proteins that can be used to target and isolate progenitors for midbrain dopamine (mDA) neurons. We used a "FACS-array" approach to identify 18 genes for transmembrane proteins with high expression in mDA progenitors and describe the utility of four of these targets (Alcam, Chl1, Gfra1, and Igsf8) for isolating mDA progenitors from rat primary ventral mesencephalon through flow cytometry. Alcam and Chl1 facilitated a significant enrichment of mDA neurons following transplantation, while targeting of Gfra1 allowed for robust separation of dopamine and serotonin neurons. Importantly, we also show that mDA progenitors isolated on the basis of transmembrane proteins are capable of extensive, functional innervation of the host striatum and correction of motor impairment in a unilateral model of PD. These results are highly relevant for current efforts to establish safe and effective stem cell-based procedures for PD, where clinical translation will almost certainly require safety and standardization measures in order to deliver well-characterized cell preparations.

Meningeal cells influence midbrain development and the engraftment of dopamine progenitors in Parkinsonian mice

Dopaminergic neuroblasts, isolated from ventral midbrain fetal tissue, have been shown to structurally and functionally integrate, and alleviate Parkinsonian symptoms following transplantation. The use of donor tissue isolated at an age younger than conventionally employed can result in larger grafts - a consequence of improved cell survival and neuroblast proliferation at the time of implantation. However studies have paid little attention to removal of the meninges from younger tissue, due to its age-dependent tight attachment to the underlying brain. Beyond the protection of the central nervous system, the meninges act as a signaling center, secreting a variety of trophins to influence neural development and additionally impact on neural repair. However it remains to be elucidated what influence these cells have on ventral midbrain development and grafted dopaminergic neuroblasts. Here we examined the temporal role of meningeal cells in graft integration in Parkinsonian mice and, using in vitro approaches, identified the mechanisms underlying the roles of meningeal cells in midbrain development. We demonstrate that young (embryonic day 10), but not older (E12), meningeal cells promote dopaminergic differentiation as well as neurite growth and guidance within grafts and during development. Furthermore we identify stromal derived factor 1 (SDF1), secreted by the meninges and acting on the CXCR4 receptor present on dopaminergic progenitors, as a contributory mediator in these effects. These findings identify new and important roles for the meningeal cells, and SDF1/CXCR4 signaling, in ventral midbrain development as well as neural repair following cell transplantation into the Parkinsonian brain.

Adult human neural stem cell therapeutics: Current developmental status and prospect

Over the past two decades, regenerative therapies using stem cell technologies have been developed for various neurological diseases. Although stem cell therapy is an attractive option to reverse neural tissue damage and to recover neurological deficits, it is still under development so as not to show significant treatment effects in clinical settings. In this review, we discuss the scientific and clinical basics of adult neural stem cells (aNSCs), and their current developmental status as cell therapeutics for neurological disease. Compared with other types of stem cells, aNSCs have clinical advantages, such as limited proliferation, inborn differentiation potential into functional neural cells, and no ethical issues. In spite of the merits of aNSCs, difficulties in the isolation from the normal brain, and in the in vitro expansion, have blocked preclinical and clinical study using aNSCs. However, several groups have recently developed novel techniques to isolate and expand aNSCs from normal adult brains, and showed successful applications of aNSCs to neurological diseases. With new technologies for aNSCs and their clinical strengths, previous hurdles in stem cell therapies for neurological diseases could be overcome, to realize clinically efficacious regenerative stem cell therapeutics.