Resident adult neural stem cells in Parkinson's disease--the brain's own repair system?

The therapeutic use of clonal neural stem cells in experimental Parkinson´s disease

BACKGROUND

Parkinson´s disease (PD), the second most common neurodegenerative disease in the world, is characterized by the death or impairment of dopaminergic neurons (DAn) in the substantia nigra pars compacta and dopamine depletion in the striatum. Currently, there is no cure for PD, and treatments only help to reduce the symptoms of the disease, and do not repair or replace the DAn damaged or lost in PD. Cell replacement therapy (CRT) seeks to relieve both pathological and symptomatic PD manifestations and has been shown to have beneficial effects in experimental PD models as well as in PD patients, but an apt cell line to be used in the treatment of PD has yet to be established. The purpose of this study was to examine the effects of the transplantation of hVM1 clone 32 cells, a bankable line of human neural stem cells (hNSCs), in a PD mouse model at four months post-transplant.

METHODS

Adult (five month-old) C57BL/6JRccHsd male mice were injected with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine and subsequently transplanted with hVM1 clone 32 cells, or buffer, in the left striatum. Four months post-transplant, behavioral effects were explored using the open field and paw print tests, and histological analyses were performed.

RESULTS

Transplantation of hVM1 clone 32 cells rescued dopaminergic nigrostriatal populations in adult Parkinsonian mice. Motor and neurological deterioration were observed in buffer-treated mice, the latter of which had a tendency to improve in hNSC-transplanted mice. Detection of mast cell migration to the superficial cervical lymph nodes in cell-transplanted mice denoted a peripheral effect. Transplantation of hNSCs also rescued neuroblast neurogenesis in the subgranular zone, which was correlated with dopaminergic recovery and is indicative of local recovery mechanisms.

CONCLUSIONS

In this proof-of-concept study, the transplantation of hVM1 clone 32 cells provided neuroprotection in adult Parkinsonian mice by restoring the dopaminergic nigrostriatal pathway and hippocampal neurogenesis, demonstrating the efficacy of cell replacement therapy as a treatment for PD.

Migratory Response of Cells in Neurogenic Niches to Neuronal Death: The Onset of Harmonic Repair?

Harmonic mechanisms orchestrate neurogenesis in the healthy brain within specific neurogenic niches, which generate neurons from neural stem cells as a homeostatic mechanism. These newly generated neurons integrate into existing neuronal circuits to participate in different brain tasks. Despite the mechanisms that protect the mammalian brain, this organ is susceptible to many different types of damage that result in the loss of neuronal tissue and therefore in alterations in the functionality of the affected regions. Nevertheless, the mammalian brain has developed mechanisms to respond to these injuries, potentiating its capacity to generate new neurons from neural stem cells and altering the homeostatic processes that occur in neurogenic niches. These alterations may lead to the generation of new neurons within the damaged brain regions. Notwithstanding, the activation of these repair mechanisms, regeneration of neuronal tissue within brain injuries does not naturally occur. In this review, we discuss how the different neurogenic niches respond to different types of brain injuries, focusing on the capacity of the progenitors generated in these niches to migrate to the injured regions and activate repair mechanisms. We conclude that the search for pharmacological drugs that stimulate the migration of newly generated neurons to brain injuries may result in the development of therapies to repair the damaged brain tissue.

The roles, mechanism, and mobilization strategy of endogenous neural stem cells in brain injury

Brain injury poses a heavy disease burden in the world, resulting in chronic deficits. Therapies for brain injuries have been focused on pharmacologic, small molecule, endocrine and cell-based therapies. Endogenous neural stem cells (eNSCs) are a group of stem cells which can be activated in vivo by damage, neurotrophic factors, physical factor stimulation, and physical exercise. The activated eNSCs can proliferate, migrate and differentiate into neuron, oligodendrocyte and astrocyte, and play an important role in brain injury repair and neural plasticity. The roles of eNSCs in the repair of brain injury include but are not limited to ameliorating cognitive function, improving learning and memory function, and promoting functional gait behaviors. The activation and mobilization of eNSCs is important to the repair of injured brain. In this review we describe the current knowledge of the common character of brain injury, the roles and mechanism of eNSCs in brain injury. And then we discuss the current mobilization strategy of eNSCs following brain injury. We hope that a comprehensive awareness of the roles and mobilization strategy of eNSCs in the repair of cerebral ischemia may help to find some new therapeutic targets and strategy for treatment of stroke.

Potentials of autophagy enhancing natural products in the treatment of Parkinson disease

Parkinson disease (PD) is a progressive neurodegenerative movement disorder characterized by motor and non-motor symptoms due to loss of striatal dopaminergic neurons and disruption of degradation signaling leading to the formation of Lewy bodies (aggregation of α-synuclein). Presently, there are no disease modifying therapy for PD despite improvement in the understanding of the disease pathogenesis. However, the drugs currently used in PD management provide symptomatic relieve for motor symptoms without significant improvement in non-motor complications, thus, a public health burden on caregivers and healthcare systems. There is therefore the need to discover disease modifying therapy with strong potential to halt the disease progression. Recent trend has shown that the dysfunction of lysosomal-autophagy pathway is highly implicated in PD pathology, hence, making autophagy a key player owing to its involvement in degradation and clearance of misfolded α-synuclein (a major hallmark in PD pathology). In this review, we described the current drugs/strategy in the management of PD including targeting the autophagy pathway as a novel approach that could serve as potential intervention for PD management. The discovery of small molecules or natural products capable of enhancing autophagy mechanism could be a promising strategy for PD treatment.

Potentials of autophagy enhancing natural products in the treatment of Parkinson disease

Parkinson disease (PD) is a progressive neurodegenerative movement disorder characterized by motor and non-motor symptoms due to loss of striatal dopaminergic neurons and disruption of degradation signaling leading to the formation of Lewy bodies (aggregation of α-synuclein). Presently, there are no disease modifying therapy for PD despite improvement in the understanding of the disease pathogenesis. However, the drugs currently used in PD management provide symptomatic relieve for motor symptoms without significant improvement in non-motor complications, thus, a public health burden on caregivers and healthcare systems. There is therefore the need to discover disease modifying therapy with strong potential to halt the disease progression. Recent trend has shown that the dysfunction of lysosomal-autophagy pathway is highly implicated in PD pathology, hence, making autophagy a key player owing to its involvement in degradation and clearance of misfolded α-synuclein (a major hallmark in PD pathology). In this review, we described the current drugs/strategy in the management of PD including targeting the autophagy pathway as a novel approach that could serve as potential intervention for PD management. The discovery of small molecules or natural products capable of enhancing autophagy mechanism could be a promising strategy for PD treatment.

Restoring lost nigrostriatal fibers in Parkinson's disease based on clinically-inspired design criteria

Parkinson's disease is a neurodegenerative disease affecting around 10 million people worldwide. The death of dopaminergic neurons in the substantia nigra and the axonal fibers that constitute the nigrostriatal pathway leads to a loss of dopamine in the striatum that causes the motor symptoms of this disease. Traditional treatments have focused on reducing symptoms, while therapies with human fetal or stem cell-derived neurons have centered on implanting these cells in the striatum to restore its innervation. An alternative approach is pathway reconstruction, which aims to rebuild the entire structure of neurons and axonal fibers of the nigrostriatal pathway in a way that matches its anatomy and physiology. This type of repair could be more capable of reestablishing the signaling mechanisms that ensure proper dopamine release in the striatum and regulation of other motor circuit regions in the brain. In this manuscript, we conduct a review of the literature related to pathway reconstruction as a treatment for Parkinson's disease, delve into the limitations of these studies, and propose the requisite design criteria to achieve this goal at a human scale. We then present our tissue engineering-based platform to fabricate hydrogel-encased dopaminergic axon tracts in vitro for later implantation into the brain to replace and reconstruct the pathway. These tissue-engineered nigrostriatal pathways (TE-NSPs) can be characterized and optimized for cell number and phenotype, axon growth lengths and rates, and the capacity for synaptic connectivity and dopamine release. We then show original data of advances in creating these constructs matching clinical design criteria using human iPSC-derived dopaminergic neurons and a hyaluronic acid hydrogel. We conclude with a discussion of future steps that are needed to further optimize human-scale TE-NSPs and translate them into clinical products.

Chronic-Progressive Dopaminergic Deficiency Does Not Induce Midbrain Neurogenesis

BACKGROUND

Consecutive adult neurogenesis is a well-known phenomenon in the ventricular-subventricular zone of the lateral wall of the lateral ventricles (V-SVZ) and has been controversially discussed in so-called "non-neurogenic" brain areas such as the periventricular regions (PVRs) of the aqueduct and the fourth ventricle. Dopamine is a known modulator of adult neural stem cell (aNSC) proliferation and dopaminergic neurogenesis in the olfactory bulb, though a possible interplay between local dopaminergic neurodegeneration and induction of aNSC proliferation in mid/hindbrain PVRs is currently enigmatic.

OBJECTIVE/HYPOTHESIS

To analyze the influence of chronic-progressive dopaminergic neurodegeneration on both consecutive adult neurogenesis in the PVRs of the V-SVZ and mid/hindbrain aNSCs in two mechanistically different transgenic animal models of Parkinson´s disease (PD).

METHODS

We used Thy1-m[A30P]h α synuclein mice and Leu9'Ser hypersensitive α4* nAChR mice to assess the influence of midbrain dopaminergic neuronal loss on neurogenic activity in the PVRs of the V-SVZ, the aqueduct and the fourth ventricle.

RESULTS

In both animal models, overall proliferative activity in the V-SVZ was not altered, though the proportion of B2/activated B1 cells on all proliferating cells was reduced in the V-SVZ in Leu9'Ser hypersensitive α4* nAChR mice. Putative aNSCs in the mid/hindbrain PVRs are known to be quiescent in vivo in healthy controls, and dopaminergic deficiency did not induce proliferative activity in these regions in both disease models.

CONCLUSIONS

Our data do not support an activation of endogenous aNSCs in mid/hindbrain PVRs after local dopaminergic neurodegeneration. Spontaneous endogenous regeneration of dopaminergic cell loss through resident aNSCs is therefore unlikely.

(+)4-Cholesten-3-one promotes differentiation of neural stem cells into dopaminergic neurons through TET1 and FoxA2

In this paper, we report the results of treating cells with an effective small molecule, (+)4-cholesten-3-one (PubChem CID: 91477), which can promote neural stem cell(NSC) differentiation into dopaminergic neurons. This study used rat neural stem cells stimulated with two different concentrations (7.8 μM and 78 μM) of (+)4-cholesten-3-one. Cell phenotypic analysis showed that (+)4-cholesten-3-one induced NSC differentiation into dopaminergic neurons, and the level of tyrosine hydroxylase(TH), which is specific for dopaminergic cells, was significantly increased compared with that of the drug-free control group. Furthermore, in this study, we found that this effect may be related to the transcription factor fork-head box a2 (FoxA2) and ten-eleven translocation 1 (TET1). The expression of TET1 and FoxA2 was upregulated after treatment with (+)4-cholesten-3-one. To verify the relationship between (+)4-cholesten-3-one and these genes, we found that the binding rate of TET1 and FoxA2 increased after the application of (+)4-cholesten-3-one, as confirmed by a coimmunoprecipitation (Co-IP) assay. With a small interfering RNA (siRNA) experiment, we found that only when Tet1 and Foxa2 were not silenced was the mRNA level of Th increased after (+)4-cholesten-3-one treatment. Taken together, these data show that (+)4-cholesten-3-one can promote the differentiation of NSCs into dopaminergic neurons by upregulating the expression of TET1 and FoxA2 and by increasing their binding. Thus, (+)4-cholesten-3-one may help address the application of neural stem cell replacement therapy in neurodegenerative diseases.

Comparative study between bone marrow mesenchymal stem cell and their conditioned medium in the treatment of rat model of Parkinsonism

Parkinsonism is one of the most common aging neurodegenerative disorders. This study aims to compare the therapeutic effect of stem cell versus its conditioned medium in the Parkinsonism model. Parkinsonism was induced by daily subcutaneous injection of 0.5 mg/kg of rotenone dissolved in dimethyl sulfoxide for 28 days. Fifty rats were divided randomly into five groups: control, dimethyl sulfoxide, Parkinsonism, stem cell-treated, and conditioned medium-treated groups. Midbrain specimens were obtained for histological, immunohistochemical, and biochemical studies. Lewy bodies were observed in the Parkinsonism group in the dopaminergic neuron and neuropil as well. Almost all of the pathological changes were clearly ameliorated in both stem cell- and conditioned medium-treated groups as confirmed by biochemical, histological, and immunohistochemical (anti-nestin, anti-glial fibrillary acidic protein, and anti-α synuclein) studies. However, the conditioned medium showed more superior therapeutic effect establishing nearly the normal histological architecture of substantia nigra. These results may pave the future for using stem cell-conditioned medium as a more convenient and effective adjuvant therapy in Parkinsonism and other neurodegenerative disorders.

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.

Mitochondria as central regulators of neural stem cell fate and cognitive function

Emerging evidence now indicates that mitochondria are central regulators of neural stem cell (NSC) fate decisions and are crucial for both neurodevelopment and adult neurogenesis, which in turn contribute to cognitive processes in the mature brain. Inherited mutations and accumulated damage to mitochondria over the course of ageing serve as key factors underlying cognitive defects in neurodevelopmental disorders and neurodegenerative diseases, respectively. In this Review, we explore the recent findings that implicate mitochondria as crucial regulators of NSC function and cognition. In this respect, mitochondria may serve as targets for stem-cell-based therapies and interventions for cognitive defects.

The A30P α-synuclein mutation decreases subventricular zone proliferation

Parkinson's disease (PD) is associated with olfactory defects in addition to dopaminergic degeneration. Dopaminergic signalling is necessary for subventricular zone (SVZ) proliferation and olfactory bulb (OB) neurogenesis. Alpha-synuclein (α-syn or Snca) modulates dopaminergic neurotransmission, and SNCA mutations cause familial PD, but how α-syn and its mutations affect adult neurogenesis is unclear. To address this, we studied a bacterial artificial chromosome transgenic mouse expressing the A30P SNCA familial PD point mutation on an Snca-/- background. We confirmed that the SNCA-A30P transgene recapitulates endogenous α-syn expression patterns and levels by immunohistochemical detection of endogenous α-syn in a wild-type mouse and transgenic SNCA-A30P α-syn protein in the forebrain. The number of SVZ stem cells (BrdU+GFAP+) was decreased in SNCA-A30P mice, whereas proliferating (phospho-histone 3+) cells were decreased in Snca-/- and even more so in SNCA-A30P mice. Similarly, SNCA-A30P mice had fewer Mash1+ transit-amplifying SVZ progenitor cells but Snca-/- mice did not. These data suggest the A30P mutation aggravates the effect of Snca loss in the SVZ. Interestingly, calbindin+ and calretinin (CalR)+ periglomerular neurons were decreased in both Snca-/-, and SNCA-A30P mice but tyrosine hydroxylase+ periglomerular OB neurons were only decreased in Snca-/- mice. Cell death decreased in the OB granule layer of Snca-/- and SNCA-A30P mice. In the same region, CalR+ numbers increased in Snca-/- and SNCA-A30P mice. Thus, α-syn loss and human A30P SNCA decrease SVZ proliferation, cell death in the OB and differentially alter interneuron numbers. Similar disruptions in human neurogenesis may contribute to the olfactory deficits, which are observed in PD.

Transcriptome and proteome profiling of neural stem cells from the human subventricular zone in Parkinson's disease

It is currently accepted that the human brain has a limited neurogenic capacity and an impaired regenerative potential. We have previously shown the existence of CD271-expressing neural stem cells (NSCs) in the subventricular zone (SVZ) of Parkinson's disease (PD) patients, which proliferate and differentiate towards neurons and glial cells in vitro. To study the molecular profile of these NSCs in detail, we performed RNA sequencing and mass spectrometry on CD271⁺ NSCs isolated from human post-mortem SVZ and on homogenates of the SVZ. CD271⁺ cells were isolated through magnetic cell separation (MACS). We first compared the molecular profile of CD271⁺ NSCs to the SVZ homogenate from control donors and then compared CD271⁺ cells to CD11b⁺ microglia. These results confirmed their neural stem cell identity. Finally we compared controls and PD patients to establish a specific molecular profile of NSCs and the SVZ in PD. While our transcriptome analysis did not identify any differentially expressed genes in the SVZ between control and PD patients, our proteome analysis revealed several proteins that were differentially expressed in PD. Some of these proteins are involved in cytoskeletal organization and mitochondrial function. Transcriptome and proteome analyses of NSCs from PD revealed changes in the expression of genes and proteins involved in metabolism, transcriptional activity and cytoskeletal organization. Our data suggest that NSCs may transit into a primed-quiescent state, that is in an "alert" non-proliferative phase in PD. Our results not only confirm pathological hallmarks of PD (e.g. impaired mitochondrial function), but also show that the NSCs from SVZ undergo significant changes at both transcriptome and proteome level following PD.

The Role of SVZ Stem Cells in Glioblastoma

As most common primary brain cancer, glioblastoma is also the most aggressive and malignant form of cancer in the adult central nervous system. Glioblastomas are genetic and transcriptional heterogeneous tumors, which in spite of intensive research are poorly understood. Over the years conventional therapies failed to affect a cure, resulting in low survival rates of affected patients. To improve the clinical outcome, an important approach is to identify the cells of origin. One potential source for these are neural stem cells (NSCs) located in the subventricular zone, which is one of two niches in the adult nervous system where NSCs with the capacity of self-renewal and proliferation reside. These cells normally give rise to neuronal as well as glial progenitor cells. This review summarizes current findings about links between NSCs and cancer stem cells in glioblastoma and discusses current therapeutic approaches, which arise as a result of identifying the cell of origin in glioblastoma.

Novel Targets for Parkinson's Disease: Addressing Different Therapeutic Paradigms and Conundrums

Parkinson's disease (PD) is a neurodegenerative disease that is pathologically characterized by degeneration of dopamine neurons in the substantia nigra pars compacta (SNpc). PD leads to clinical motor features that include rigidity, tremor, and bradykinesia. Despite multiple available therapies for PD, the clinical features continue to progress, and patients suffer progressive disability. Many advances have been made in PD therapy which directly target the cause of the disease rather than providing symptomatic relief. A neuroprotective or disease modifying strategy that can slow or cease clinical progression and worsening disability remains as a major unmet medical need for PD management. The present review discusses potential novel therapies for PD that include recent interventions in the form of immunomodulatory techniques and stem cell therapy. Further, an introspective approach to identify numerous other novel targets that can alleviate PD pathogenesis and enable physicians to practice multitargeted therapy and that may provide a ray of hope to PD patients in the future are discussed.

Kir6.2 Deficiency Promotes Mesencephalic Neural Precursor Cell Differentiation via Regulating miR-133b/GDNF in a Parkinson's Disease Mouse Model

The loss of dopaminergic (DA) neurons in the substantia nigra (SN) is a major feature in the pathology of Parkinson's disease (PD). Using neural stem or progenitor cells (NSC/NPCs), the prospect of replacing the missing or damaged DA neurons is very attractive for PD therapy. However, little is known about the endogenous mechanisms and molecular pathways regulating the NSC/NPC proliferation and differentiation in the development of PD. Herein, using Kir6.2 knockout (Kir6.2-/-) mice, we observed that genetic deficiency of Kir6.2 exacerbated the loss of SN DA neurons relatively early in a chronic MPTP/probenecid (MPTP/p) injection course, but rescued the damage of neurons 7 days after the last MPTP/p injection. Meanwhile, we found that Kir6.2 knockout predominantly increased the differentiation of nuclear receptor-related 1 (Nurr1+) precursors to DA neurons, indicating that Kir6.2 deficiency could activate an endogenous self-repair process. Furthermore, we demonstrated in vivo and in vitro that lack of Kir6.2 promoted neuronal differentiation via inhibiting the downregulation of glia cell line-derived neurotrophic factor (GDNF), which negatively related to the level of microRNA-133b. Notably, we revealed that Gdnf is a target gene of miR-133b and transfection of miR-133b could attenuate the enhancement of neural precursor differentiation induced by Kir6.2 deficiency. Collectively, we clarify for the first time that Kir6.2/K-ATP channel functions as a novel endogenous negative regulator of NPC differentiation, and provide a promising neuroprotective target for PD therapeutics.

Sex Steroids and Adult Neurogenesis in the Ventricular-Subventricular Zone

The forebrain ventricular-subventricular zone (V-SVZ) continuously generates new neurons throughout life. Neural stem cells (type B1 cells) along the lateral ventricle become activated, self-renew, and give rise to proliferating precursors which progress along the neurogenic lineage from intermediate progenitors (type C cells) to neuroblasts (type A cells). Neuroblasts proliferate and migrate into the olfactory bulb and differentiate into different interneuronal types. Multiple factors regulate each step of this process. Newly generated olfactory bulb interneurons are an important relay station in the olfactory circuits, controlling social recognition, reproductive behavior, and parental care. Those behaviors are strongly sexually dimorphic and changes throughout life from puberty through aging and in the reproductive age during estrous cycle and gestation. Despite the key role of sex hormones in regulating those behaviors, their contribution in modulating adult neurogenesis in V-SVZ is underestimated. Here, we compare the literature highlighting the sexual dimorphism and the differences across the physiological phases of the animal for the different cell types and steps through the neurogenic lineage.

Brilliant Blue G, But Not Fenofibrate, Treatment Reverts Hemiparkinsonian Behavior and Restores Dopamine Levels in an Animal Model of Parkinson's Disease

Parkinson's disease (PD) is a neurodegenerative disorder, characterized by the loss of dopaminergic neurons in the substantia nigra and their projections to the striatum. Several processes have been described as potential inducers of the dopaminergic neuron death, such as inflammation, oxidative stress, and mitochondrial dysfunction. However, the death of dopaminergic neurons seems to be multifactorial, and its cause remains unclear. ATP-activating purinergic receptors influence various physiological functions in the CNS, including neurotransmission. Purinergic signaling is also involved in pathological scenarios, where ATP is extensively released and promotes sustained purinergic P2X7 receptor (P2X7R) activation and consequent induction of cell death. This effect occurs, among other factors, by oxidative stress and during the inflammatory response. On the other hand, peroxisome proliferator-activated receptor-γ coactivator 1α (PGC-1α) is involved in energy metabolism and mitochondrial biogenesis. Expression and activity upregulation of this protein has been related with reduction of oxidative stress and neuroprotection. Therefore, P2X7R and PGC-1α are potential targets in the treatment of PD. Here hemiparkinsonism was induced by unilateral stereotactic injection of 6-OHDA in a rat model. After 7 days, the establishment of PD was confirmed and followed by treatment with the P2X7R antagonist Brilliant Blue G (BBG) or PGC-1α agonist fenofibrate. BBG, but not fenofibrate, reverted hemiparkinsonian behavior accompanied by an increase in tyrosine hydroxylase immunoreactivity in the substantia nigra. Our results suggest that the P2X7R may be a therapeutic target in Parkinson's disease.

FBXL5 Inactivation in Mouse Brain Induces Aberrant Proliferation of Neural Stem Progenitor Cells

FBXL5 is the substrate recognition subunit of an SCF-type ubiquitin ligase that serves as a master regulator of iron metabolism in mammalian cells. We previously showed that mice with systemic deficiency of FBXL5 fail to sense intracellular iron levels and die in utero at embryonic day 8.5 (E8.5) as a result of iron overload and subsequent oxidative stress. This early embryonic mortality has thus impeded study of the role of FBXL5 in brain development. We have now generated mice lacking FBXL5 specifically in nestin-expressing neural stem progenitor cells (NSPCs) in the brain. Unexpectedly, the mutant embryos manifested a progressive increase in the number of NSPCs and astroglia in the cerebral cortex. Stabilization of iron regulatory protein 2 (IRP2) as a result of FBXL5 deficiency led to accumulation of ferrous and ferric iron as well as to generation of reactive oxygen species. Pharmacological manipulation suggested that the phenotypes of FBXL5 deficiency are attributable to aberrant activation of mammalian target of rapamycin (mTOR) signaling. Our results thus show that FBXL5 contributes to regulation of NSPC proliferation during mammalian brain development.

Quantitative proteomic analysis of age-related subventricular zone proteins associated with neurodegenerative disease

Aging is characterized by a progressive decline in the function of adult tissues which can lead to neurodegenerative disorders. However, little is known about the correlation between protein changes in the subventricular zone (SVZ) and neurodegenerative diseases with age. In the present study, neural stem cells (NSCs) were derived from the SVZ on postnatal 7 d, 1 m, and 12 m-old mice. With age, NSCs exhibited increased SA-β-gal activity and decreased proliferation and pool size in the SVZ zone, and were associated with elevated inflammatory chemokines and cytokines. Furthermore, quantitative proteomics and ingenuity pathway analysis were used to evaluate the significant age-related alterations in proteins and their functions. Some downregulated proteins such as DPYSL2, TPI1, ALDH, and UCHL1 were found to play critical roles in the neurological disease and PSMA1, PSMA3, PSMC2, PSMD11, and UCHL1 in protein homeostasis. Taken together, we have provided valuable insight into the cellular and molecular processes that underlie aging-associated declines in SVZ neurogenesis for the early detection of differences in gene expression and the potential risk of neurological disease, which is beneficial in the prevention of the diseases.

Traceable microRNA-124 loaded nanoparticles as a new promising therapeutic tool for Parkinson's disease

Parkinson's disease (PD), a neurodegenerative disorder characterized by the selective degeneration of the nigrostriatal dopaminergic pathway, is a major socio-economic burden in modern society. While there is presently no cure for PD, enhancing the number of neural stem cells (NSCs) and/or stimulating their differentiation into new neurons are promising therapeutic strategies. Many proneurogenic factors have been implicated in controlling NSCs activity, including the microRNA (miR)-124. However, current strategies described for the intracellular delivery of miR involve mostly unspecific or inefficient platforms. In Saraiva et al. we developed miR-124 loaded nanoparticles (NPs) able to efficiently deliver miR-124 into neural stem/progenitor cells and boost neuronal differentiation and maturation in vitro. In vivo, the intracerebroventricular injection of miR-124 NPs increased the number of new neurons in the olfactory bulb of healthy and 6-hydroxidopamine (6-OHDA) lesioned mice, a model for PD. Importantly, miR-124 NPs enhanced the migration of new neurons into the 6-OHDA lesioned striatum, culminating in motor function improvement. Given the recent advent of clinical trials for miR-based therapies and the theranostic applications of our NPs, we expect to support the clinical translation of our delivery platform in the context of PD and other neurodegenerative diseases which may benefit from enhancing miR levels.

MicroRNA-124 loaded nanoparticles enhance brain repair in Parkinson's disease

Modulation of the subventricular zone (SVZ) neurogenic niche can enhance brain repair in several disorders including Parkinson's disease (PD). Herein, we used biocompatible and traceable polymeric nanoparticles (NPs) containing perfluoro-1,5-crown ether (PFCE) and coated with protamine sulfate to complex microRNA-124 (miR-124), a neuronal fate determinant. The ability of NPs to efficiently deliver miR-124 and prompt SVZ neurogenesis and brain repair in PD was evaluated. In vitro, miR-124 NPs were efficiently internalized by neural stem/progenitors cells and neuroblasts and promoted their neuronal commitment and maturation. The expression of Sox9 and Jagged1, two miR-124 targets and stemness-related genes, were also decreased upon miR-124 NP treatment. In vivo, the intracerebral administration of miR-124 NPs increased the number of migrating neuroblasts that reached the granule cell layer of the olfactory bulb, both in healthy and in a 6-hydroxydopamine (6-OHDA) mouse model for PD. MiR-124 NPs were also able to induce migration of neurons into the lesioned striatum of 6-OHDA-treated mice. Most importantly, miR-124 NPs proved to ameliorate motor symptoms of 6-OHDA mice, monitored by the apomorphine-induced rotation test. Altogether, we provide clear evidences to support the use of miR-124 NPs as a new therapeutic approach to boost endogenous brain repair mechanisms in a setting of neurodegeneration.

Neural stem cell transplantation for the treatment of primary torsion dystonia: A case report

Primary torsion dystonia (PTD) occurs due to a genetic mutation and often advances gradually. Currently, there is no therapy available that is able to inhibit progression. Neural stem cells (NSCs) are being investigated as potential therapies for neurodegenerative diseases, such as stroke and trauma. The present study evaluated the clinical effectiveness of NSC transplantation in an 18-year-old male patient with PTD, to assess the ability of this therapy to inhibit PTD progression. Genetic testing of the patient revealed a mutation in the torsion dystonia-1 (DYT1) gene (907–909 delGAG). NSCs were bilaterally implanted in the globus pallidus of the patient through stereotactic surgery. Prior to surgery, the patient's Burke-Fahn-Marsden dystonia movement score (BFMDMS) was 21, which progressively decreased after surgery to 18, 17, 15 and 13 at 1, 2, 3 and 4 postoperative years, respectively. BFMDMS was improved by 38.1% over the 4 postoperative years. Although computed tomography and magnetic resonance imaging examinations showed no significant changes prior to and following surgery, postoperative brain positron emission tomography scans revealed increased glucose metabolism in the transplanted region. The clinical efficacy of NSC transplantation in this patient suggests its potential for the treatment of DYT1-positive patients with PTD.

Implications of irradiating the subventricular zone stem cell niche

Radiation therapy is a standard treatment for brain tumor patients. However, it comes with side effects, such as neurological deficits. While likely multi-factorial, the effect may in part be associated with the impact of radiation on the neurogenic niches. In the adult mammalian brain, the neurogenic niches are localized in the subventricular zone (SVZ) of the lateral ventricles and the dentate gyrus of the hippocampus, where the neural stem cells (NSCs) reside. Several reports showed that radiation produces a drastic decrease in the proliferative capacity of these regions, which is related to functional decline. In particular, radiation to the SVZ led to a reduced long-term olfactory memory and a reduced capacity to respond to brain damage in animal models, as well as compromised tumor outcomes in patients. By contrast, other studies in humans suggested that increased radiation dose to the SVZ may be associated with longer progression-free survival in patients with high-grade glioma. In this review, we summarize the cellular and functional effects of irradiating the SVZ niche. In particular, we review the pros and cons of using radiation during brain tumor treatment, discussing the complex relationship between radiation dose to the SVZ and both tumor control and toxicity.

Immunomodulation in stem cell differentiation into neurons and brain repair

Immunomodulators regulate stem cell activity at all stages of development as well as during adulthood. Embryonic stem cell (ESC) proliferation as well as neurogenic processes during embryonic development are controlled by factors of the immune system. We review here immunophenotypic expression patterns of  different stem cell types, including ESC, neural (NSC) and tissue-specific mesenchymal stem cells (MSC), and focus on immunodulatory properties of these cells. Immune and inflammatory responses, involving actions of cytokines as well as toll-like receptor (TLR) signaling are known to affect the differentiation capacity of NSC and MSC. Secretion of pro- and anti-inflammatory messengers by MSC have been observed as the consequence of TLR and cytokine activation and promotion of differentiation into specified phenotypes. As result of augmented differentiation capacity, stem cells secrete angiogenic factors including vascular endothelial growth factor, resulting in multifactorial actions in tissue repair. Immunoregulatory properties of tissue specific adult stem cells are put into the context of possible clinical applications.

A well-refined in vitro model derived from human embryonic stem cell for screening phytochemicals with midbrain dopaminergic differentiation-boosting potential for improving Parkinson's disease

Stimulation of endogenous neurogenesis is a potential approach to compensate for loss of dopaminergic neurons of substantia nigra compacta nigra (SNpc) in patients with Parkinson's disease (PD). This objective was to establish an in vitro model by differentiating pluripotent human embryonic stem cells (hESCs) into midbrain dopaminergic (mDA) neurons for screening phytochemicals with mDA neurogenesis-boosting potentials. Consequently, a five-stage differentiation process was developed. The derived cells expressed many mDA markers including tyrosine hydroxylase (TH), β-III tubulin, and dopamine transporter (DAT). The voltage-gated ion channels and dopamine release were also examined for verifying neuron function, and the dopamine receptor agonists bromocriptine and 7-hydroxy-2-(dipropylamino)tetralin (7-OH-DPAT) were used to validate our model. Then, several potential phytochemicals including green tea catechins and ginsenosides were tested using the model. Finally, ginsenoside Rb1 was identified as the most potent phytochemical which is capable of upregulating neurotrophin expression and inducing mDA differentiation.

Collagen nanofibers facilitated presynaptic maturation in differentiated neurons from spinal-cord-derived neural stem cells through MAPK/ERK1/2-Synapsin I signaling pathway

Neural stem cells (NSCs) are deemed to be a potential cell therapy for brain and spinal cord reconstruction and regeneration following injury. In this study, we investigated the role of nanofibrous scaffolds on NSCs-derived neurons in the formation of neural networks. Miniature excitatory postsynaptic currents (mEPSCs) were recorded using the whole-cell patch clamp recording method after the spinal cord-derived NSCs were differentiated into neurons and cultured in vitro for 10-14 days. It was observed that the frequency of mEPSCs in the differentiated neurons cultured on both randomly oriented and aligned collagen nanofibrous scaffolds was higher than that on the collagen-coated control and can be inhibited by an ERK inhibitor (PD98059), indicating that the collagen nanofibers affected the maturation of the synapses from presynaptic sites via the MAPK/ERK1/2 pathway. In addition, both of the collagen nanofibers increased the phosphorylation of Synapsin I and facilitated the interaction of p-ERK1/2 and p-Synapsin I. All these results suggested that the collagen nanofibrous scaffolds contributed to the presynaptic maturation via the ERK1/2-Synapsin I signaling pathway.

Unconventional Neurogenic Niches and Neurogenesis Modulation by Vitamins

Although the generation of new neurons occurs in adult mammals, it has been classically described in two defined regions of the brain denominated neurogenic niches: the subventricular zone of the lateral ventricles and the subgranular zone of the dentate gyrus. In these regions, neural stem cells give rise to new neurons and glia, which functionally integrate into the existing circuits under physiological conditions. However, accumulating evidence indicates the presence of neurogenic potential in other brain regions, from which multipotent precursors can be isolated and differentiated in vitro. In some of these regions, neuron generation occurs at low levels; however, the addition of growth factors, hormones or other signaling molecules increases the proliferation and differentiation of precursor cells. In addition, vitamins, which are micronutrients necessary for normal brain development, and whose deficiency produces neurological impairments, have a regulatory effect on neural stem cells in vitro and in vivo. In the present review, we will describe the progress that has been achieved in determining the neurogenic potential in other regions, known as unconventional niches, as well as the characteristics of the neural stem cells described for each region. Finally, we will revisit the roles of commonly known vitamins as modulators of precursor cell proliferation and differentiation, and their role in the complex and tight molecular signaling that impacts these neurogenic niches.