Progress in direct reprogramming of dopaminergic cell replacement therapy.

Parkinson's disease (PD) is a gradual neurodegenerative disease. While drug therapy and surgical treatments have been the primary means of addressing PD, they do not offer a cure, and the risks associated with surgical treatment are high. Recent advances in cell reprogramming have given rise to new prospects for the treatment of Parkinson's disease (PD), with induced pluripotent stem cells (iPSCs), induced dopamine neurons (iDNs), and induced neural stem cells (iNSCs) being created. These cells can potentially be used in the treatment of Parkinson's disease. On the other hand, this article emphasizes the limits of iPSCs and iNSCs in the context of Parkinson's disease treatment, as well as approaches for direct reprogramming of somatic cells into iDNs. The paper will examine the benefits and drawbacks of directly converting somatic cells into iDNs.

Induced neural stem cells-derived spinal cord progenitor cells as stable stage for rapid and efficient generation of human oligodendrocytes and motor neurons.

Purpose: Previous studies have shown that oligodendrocytes and motor neurons have the same progenitors in the ventral spinal cord called spinal cord progenitor cells marked by oligodendrocyte lineage transcription factor 2 (Olig2). However, it is difficult to identify the spinal cord progenitor cell in vitro as they are present transiently and further transform into other neuronal (interneuron) and glial (oligodendrocyte) lineages during development. In the present study, we try to generated Olig2+ spinal cord progenitor cells from human induced neural stem cells (iNSCs) and identify those spinal cord progenitor cells in vitro Materials and Methods: Human peripheral blood mononuclear cells (PBMCs) were converted into induced neural stem cells (iNSCs), after they were identified by immunostaining using neural stem cell markers such as Nestin, Sox1, Sox2, iNSCs were transformed into Olig2+ spinal cord progenitor cells in 3 weeks by using small molecules. Results: Olig2+ spinal cord progenitor cells could expand for at least five passages and remained in a dividing state over a considerable period of time; in addition, the Olig2+ progenitor cells could mature into O4 and MBP positive oligodendrocytes and HB9 positive motor neurons in a short period. Conclusion: Our research provides a useful protocol for rapid generation of human oligodendrocytes and motor neurons from human iNSCs and demonstrates a progenitor cell model for exploring the origin of motor neurons and oligodendrocyte in vitro, which will contribute to research on the development of spinal cord and regenerative medicine.

ProNGF Is a Cell-Type-Specific Mitogen for Adult Hippocampal and for Induced Neural Stem Cells.

The role of proNGF, the precursor of nerve growth factor (NGF), in the biology of adult neural stem cells (aNSCs) is still unclear. Here, we analyzed adult hippocampal neurogenesis in AD11 transgenic mice, in which the constitutive expression of anti-NGF antibody leads to an imbalance of proNGF over mature NGF. We found increased proliferation of progenitors but a reduced neurogenesis in the AD11 dentate gyrus (DG)-hippocampus (HP). Also in vitro, AD11 hippocampal neural stem cells (NSCs) proliferated more, but were unable to differentiate into morphologically mature neurons. By treating wild-type hippocampal progenitors with the uncleavable form of proNGF (proNGF-KR), we demonstrated that proNGF acts as mitogen on aNSCs at low concentration. The mitogenic effect of proNGF was specifically addressed to the radial glia-like (RGL) stem cells through the induction of cyclin D1 expression. These cells express high levels of p75NTR , as demonstrated by immunofluorescence analyses performed ex vivo on RGL cells isolated from freshly dissociated HP-DG or selected in vitro from NSCs by leukemia inhibitory factor. Clonogenic assay performed in the absence of mitogens showed that RGLs respond to proNGF-KR by reactivating their proliferation and thus leading to neurospheres formation. The mitogenic effect of proNGF was further exploited in the expansion of mouse-induced neural stem cells (iNSCs). Chronic exposure of iNSCs to proNGF-KR increased their proliferation. Altogether, we demonstrated that proNGF acts as mitogen on hippocampal and iNSCs. Stem Cells 2019;37:1223-1237.

Visualizing the Synaptic and Cellular Ultrastructure in Neurons Differentiated from Human Induced Neural Stem Cells-An Optimized Protocol.

The size of the synaptic subcomponents falls below the limits of visible light microscopy. Despite new developments in advanced microscopy techniques, the resolution of transmission electron microscopy (TEM) remains unsurpassed. The requirements of tissue preservation are very high, and human post mortem material often does not offer adequate quality. However, new reprogramming techniques that generate human neurons in vitro provide samples that can easily fulfill these requirements. The objective of this study was to identify the culture technique with the best ultrastructural preservation in combination with the best embedding and contrasting technique for visualizing neuronal elements. Two induced neural stem cell lines derived from healthy control subjects underwent differentiation either adherent on glass coverslips, embedded in a droplet of highly concentrated Matrigel, or as a compact neurosphere. Afterward, they were fixed using a combination of glutaraldehyde (GA) and paraformaldehyde (PFA) followed by three approaches (standard stain, Ruthenium red stain, high contrast en-bloc stain) using different combinations of membrane enhancing and contrasting steps before ultrathin sectioning and imaging by TEM. The compact free-floating neurospheres exhibited the best ultrastructural preservation. High-contrast en-bloc stain offered particularly sharp staining of membrane structures and the highest quality visualization of neuronal structures. In conclusion, compact neurospheres growing under free-floating conditions in combination with a high contrast en-bloc staining protocol, offer the optimal preservation and contrast with a particular focus on visualizing membrane structures as required for analyzing synaptic structures.

Stem cell transplantation for Huntington's diseases.

Therapeutic approaches based on stem cells have received considerable attention as potential treatments for Huntington's disease (HD), which is a fatal, inherited neurodegenerative disorder, caused by progressive loss of GABAergic medium spiny neurons (MSNs) in the striatum of the forebrain. Transplantation of stem cells or their derivatives in animal models of HD, efficiently improved functions by replacing the damaged or lost neurons. In particular, neural stem cells (NSCs) for HD treatments have been developed from various sources, such as the brain itself, the pluripotent stem cells (PSCs), and the somatic cells of the HD patients. However, the brain-derived NSCs are difficult to obtain, and the PSCs have to be differentiated into a population of the desired neuronal cells that may cause a risk of tumor formation after transplantation. In contrast, induced NSCs, derived from somatic cells as a new stem cell source for transplantation, are less likely to form tumors. Given that the stem cell transplantation strategy for treatment of HD, as a genetic disease, is to replace the dysfunctional or lost neurons, the correction of mutant genes containing the expanded CAG repeats is essential. In this review, we will describe the methods for obtaining the optimal NSCs for transplantation-based HD treatment and the differentiation conditions for the functional GABAergic MSNs as therapeutic cells. Also, we will discuss the valuable gene correction of the disease stem cells by the CRISPR/Cas9 system for HD treatment.

Engineered extracellular vesicles for delivery of siRNA promoting targeted repair of traumatic spinal cord injury.

Spinal cord injury (SCI) is a severe disease of the nervous system that causes irreparable damage and loss of function, for which no effective treatments are available to date. Engineered extracellular vesicles (EVs) carrying therapeutic molecules hold promise as an alternative SCI therapy depending on the specific functionalized EVs and the appropriate engineering strategy. In this study, we demonstrated the design of a drug delivery system of peptide CAQK-modified, siRNA-loaded EVs (C-EVs-siRNA) for SCI-targeted therapy. The peptide CAQK was anchored through a chemical modification to the membranes of EVs isolated from induced neural stem cells (iNSCs). CCL2-siRNA was then loaded into the EVs through electroporation. The modified EVs still maintained the basic properties of EVs and showed favorable targeting and therapeutic effects in vitro and in vivo. C-EVs-siRNA specifically delivered siRNA to the SCI region and was taken up by target cells. C-EVs-siRNA used the inherent anti-inflammatory and neuroreparative functions of iNSCs-derived EVs in synergy with the loaded siRNA, thus enhancing the therapeutic effect against SCI. The combination of targeted modified EVs and siRNA effectively regulated the microenvironmental disturbance after SCI, promoted the transformation of microglia/macrophages from M1 to M2 and limited the negative effects of the inflammatory response and neuronal injury on functional recovery in mice after SCI. Thus, engineered EVs are a potentially feasible and efficacious treatment for SCI, and may also be used to develop targeted treatments for other diseases.

Therapeutic effects against high-grade glioblastoma mediated by engineered induced neural stem cells combined with GD2-specific CAR-NK.

PURPOSE: High-grade glioblastoma is extremely challenging to treat because of its aggressiveness and resistance to conventional chemo- and radio-therapies. On the contrary, genetic and cellular immunotherapeutic strategies based on the stem and immune cells are emerging as promising treatments against glioblastoma (GBM). We aimed to developed a novel combined immunotherapeutic strategy to improve the treatment efficacy using genetically engineered PBMC-derived induced neural stem cells (iNSCs) expressing HSV-TK and second-generation CAR-NK cells against GBM. METHODS: iNSCs cells expressing HSV-TK (iNSCsTK) and GD2-specific CAR-NK92 (GD2NK92) were generated from PBMC-derived iNSCs and NK92 cell lines, respectively. The anti-tumor effect of iNSCsTK and the combinational therapeutics of iNSCsTK and GD2NK92 were evaluated by GBM cell line using in vitro and in vivo experiments. RESULTS: PBMC-derived iNSCsTK possessed tumor-tropism migration ability in vitro and in vivo, which exhibited considerable anti-tumor activity via bystander effect in the presence of ganciclovir (GCV). iNSCsTK/GCV could slow GBM progression and prolong median survival in tumor-bearing mice. However, the anti-tumor effect was limited to single therapy. Therefore, the combinational therapeutic effect of iNSCsTK/GCV and GD2NK92 against GBM was investigated. This approach displayed a more significant anti-tumor effect in vitro and in xenograft tumor mice. CONCLUSIONS: PBMC-derived iNSCsTK showed a significant tumor-tropic migration and an effective anti-tumor activity with GCV in vitro and in vivo. In addition, combined with GD2NK92, iNSCsTK therapeutic efficacy improved dramatically to prolong the tumor-bearing animal model's median survival.

Induced neural stem cells from Macaca fascicularis show potential of dopaminergic neuron specification and efficacy in a mouse Parkinson's disease model.

Induced neural stem cells (iNSCs) can be reprogrammed from somatic cells and have shown potentials in treatment of various neurological diseases/disorders. Obtaining iNSCs of nonhuman primates serves as an important bridge for clinical translation using iNSCs. In the current study, cynomolgus (Macaca fascicularis) bone marrow mesenchymal stromal cells (MSCs) were reprogrammed into iNSCs by transduction of non-integrative Sendai virus encoding transgenes OCT4, SOX2, KLF4 and C-MYC. The obtained iNSCs showed characteristics of normal neural stem cells (NSCs) and could differentiate into neurons, astrocytes and oligodendrocytes. Furthermore, iNSCs could give rise to dopaminergic neural cells in vitro, which showed safety and efficacy after transplantation into the striatum of an immunodeficient mouse Parkinson's disease (PD) model.

Next-generation Tumor-homing Induced Neural Stem Cells as an Adjuvant to Radiation for the Treatment of Metastatic Lung Cancer.

The spread of non-small cell lung cancer (NSCLC) to the leptomeninges is devastating with a median survival of only a few months. Radiation offers symptomatic relief, but new adjuvant therapies are desperately needed. Spheroidal, human induced neural stem cells (hiNeuroS) secreting the cytotoxic protein, TRAIL, have innate tumoritropic properties. Herein, we provide evidence that hiNeuroS-TRAIL cells can migrate to and suppress growth of NSCLC metastases in combination with radiation. In vitro cell tracking and post-mortem tissue analysis showed that hiNeuroS-TRAIL cells migrate to NSCLC tumors. Importantly, isobolographic analysis suggests that TRAIL with radiation has a synergistic cytotoxic effect on NSCLC tumors. In vivo, mice treated with radiation and hiNeuroS-TRAIL showed significant (36.6%) improvements in median survival compared to controls. Finally, bulk mRNA sequencing analysis showed both NSCLC and hiNeuroS-TRAIL cells showed changes in genes involved in migration following radiation. Overall, hiNeuroS-TRAIL cells +/- radiation have the capacity to treat NSCLC metastases.

Impact of hydrogel stiffness on the induced neural stem cells modulation.

BACKGROUND: The induced neural stem cells (iNSCs) held great promises for cell replacement therapy, but iNSCs modulation need improvement. Matrix stiffness could control stem cell fates and might be effective to iNSCs modulations. Here the stiffness of hydrogel matrix on the adhesion, proliferation and differentiation of iNSCs were studied. METHODS: Hyaluronic acid (HA) hydrogels with gradient stiffness were prepared. The structure and stiffness of hydrogels were detected by scanning electron microscopy (SEM) and rheological test. iNSCs were generated from human blood mononuclear cells and cultured in the hydrogels. The cell adhesion, proliferation and differentiation on gradient stiffness hydrogels were examined by CCK-8 test and immunofluorescence staining. RESULTS: All hydrogels showed typical soft tissue, with the elastic modulus increasing with concentration (0.6-1.8%), ranging from 17 to 250 Pa. The iNSCs maintained growth and differentiation on all gels, but showed different behaviors to different stiffness. On the softer hydrogels, cells grew slowly at first but continuously and fast for long term, tending to differentiate into neurons; while on the harder hydrogels, cells adhered and grew faster at the early stage, tending to differentiate into glia cells after long term culture. CONCLUSIONS: The results suggested that hydrogels stiffness could regulate the key cellular processes of iNSCs. It was important for iNSCs modulation and application in the future.

Generation of Porcine Induced Neural Stem Cells Using the Sendai Virus.

The reprogramming of cells into induced neural stem cells (iNSCs), which are faster and safer to generate than induced pluripotent stem cells, holds tremendous promise for fundamental and frontier research, as well as personalized cell-based therapies for neurological diseases. However, reprogramming cells with viral vectors increases the risk of tumor development due to vector and transgene integration in the host cell genome. To circumvent this issue, the Sendai virus (SeV) provides an alternative integration-free reprogramming method that removes the danger of genetic alterations and enhances the prospects of iNSCs from bench to bedside. Since pigs are among the most successful large animal models in biomedical research, porcine iNSCs (piNSCs) may serve as a disease model for both veterinary and human medicine. Here, we report the successful generation of piNSC lines from pig fibroblasts by employing the SeV. These piNSCs can be expanded for up to 40 passages in a monolayer culture and produce neurospheres in a suspension culture. These piNSCs express high levels of NSC markers (PAX6, SOX2, NESTIN, and VIMENTIN) and proliferation markers (KI67) using quantitative immunostaining and western blot analysis. Furthermore, piNSCs are multipotent, as they are capable of producing neurons and glia, as demonstrated by their expressions of TUJ1, MAP2, TH, MBP, and GFAP proteins. During the reprogramming of piNSCs with the SeV, no induced pluripotent stem cells developed, and the established piNSCs did not express OCT4, NANOG, and SSEA1. Hence, the use of the SeV can reprogram porcine somatic cells without first going through an intermediate pluripotent state. Our research produced piNSCs using SeV methods in novel, easily accessible large animal cell culture models for evaluating the efficacy of iNSC-based clinical translation in human medicine. Additionally, our piNSCs are potentially applicable in disease modeling in pigs and regenerative therapies in veterinary medicine.

Urine-derived induced pluripotent/neural stem cells for modeling neurological diseases.

Neurological diseases are mainly modeled using rodents through gene editing, surgery or injury approaches. However, differences between humans and rodents in terms of genetics, neural development, and physiology pose limitations on studying disease pathogenesis in rodent models for neuroscience research. In the past decade, the generation of induced pluripotent stem cells (iPSCs) and induced neural stem cells (iNSCs) by reprogramming somatic cells offers a powerful alternative for modeling neurological diseases and for testing regenerative medicines. Among the different somatic cell types, urine-derived stem cells (USCs) are an ideal cell source for iPSC and iNSC reprogramming, as USCs are highly proliferative, multipotent, epithelial in nature, and easier to reprogram than skin fibroblasts. In addition, the use of USCs represents a simple, low-cost and non-invasive procedure for generating iPSCs/iNSCs. This review describes the cellular and molecular properties of USCs, their differentiation potency, different reprogramming methods for the generation of iPSCs/iNSCs, and their potential applications in modeling neurological diseases.

Robust and Reproducible Generation of Induced Neural Stem Cells from Human Somatic Cells by Defined Factors.

BACKGROUND AND OBJECTIVES: Recent studies have described direct reprogramming of mouse and human somatic cells into induced neural stem cells (iNSCs) using various combinations of transcription factors. Although iNSC technology holds a great potential for clinical applications, the low conversion efficiency and limited reproducibility of iNSC generation hinder its further translation into the clinic, strongly suggesting the necessity of highly reproducible method for human iNSCs (hiNSCs). Thus, in orderto develop a highly efficient and reproducible protocol for hiNSC generation, we revisited the reprogramming potentials of previously reported hiNSC reprogramming cocktails by comparing the reprogramming efficiency of distinct factor combinations including ours. METHODS: We introduced distinct factor combinations, OSKM (OCT4+SOX2+KLF4+C-MYC), OCT4 alone, SOX2 alone, SOX2+HMGA2, BRN4+SKM+SV40LT (BSKMLT), SKLT, SMLT, and SKMLT and performed comparative analysis of reprogramming potentials of distinct factor combinations in hiNSC generation. RESULTS: Here we show that ectopic expression of five reprogramming factors, BSKMLT leads the robust hiNSC generation (>80 folds enhanced efficiency) from human somatic cells compared with previously described factor combinations. With our combination, we were able to observe hiNSC conversion within 7 days of transduction. Throughout further optimization steps, we found that both BRN4 and KLF4 are not essential for hiNSC conversion. CONCLUSIONS: Our factor combination could robustly and reproducibly generate hiNSCs from human somatic cells with distinct origins. Therefore, our novel reprogramming strategy might serve as a useful tool for hiNSC-based clinical application.

Combined Method of Neuronal Cell-Inducible Vector and Valproic Acid for Enhanced Gene Expression under Hypoxic Conditions.

BACKGROUND: Gene therapy shows the ability to restore neuronal dysfunction via therapeutic gene expression. The efficiency of gene expression and delivery to hypoxic injury sites is important for successful gene therapy. Therefore, we established a gene/stem cell therapy system using neuron-specific enolase promoter and induced neural stem cells in combination with valproic acid to increase therapeutic gene expression in hypoxic spinal cord injury. METHODS: To examine the effect of combined method on enhancing gene expression, we compared neuronal cell-inducible luciferase levels under normoxia or hypoxia conditions in induced neural stem cells with valproic acid. Therapeutic gene, vascular endothelial growth factor, expression with combined method was investigated in hypoxic spinal cord injury model. We verified gene expression levels and the effect of different methods of valproic acid administration in vivo. RESULTS: The results showed that neuron-specific enolase promoter enhanced gene expression levels in induced neural stem cells compared to Simian Virus 40 promoter under hypoxic conditions. Valproic acid treatment showed higher gene expression of neuron-specific enolase promoter than without treatment. In addition, gene expression levels and cell viability were different depending on the various concentration of valproic acid. The gene expression levels were increased significantly when valproic acid was directly injected with induced neural stem cells in vivo. CONCLUSION: In this study, we demonstrated that the combination of neuron-specific enolase promoter and valproic acid induced gene overexpression in induced neural stem cells under hypoxic conditions and also in spinal cord injury depending on valproic acid administration in vivo. Combination of valproic acid and neuron-specific enolase promoter in induced neural stem cells could be an effective gene therapy system for hypoxic spinal cord injury.

SPON1 Can Reduce Amyloid Beta and Reverse Cognitive Impairment and Memory Dysfunction in Alzheimer's Disease Mouse Model.

Alzheimer's disease (AD) is a complex, age-related neurodegenerative disease that is the most common form of dementia. However, the cure for AD has not yet been founded. The accumulation of amyloid beta (Aß) is considered to be a hallmark of AD. Beta-site amyloid precursor protein cleaving enzyme 1 (BACE1), also known as beta secretase is the initiating enzyme in the amyloidogenic pathway. Blocking BACE1 could reduce the amount of Aß, but this would also prohibit the other functions of BACE1 in brain physiological activity. SPONDIN1 (SPON1) is known to bind to the BACE1 binding site of the amyloid precursor protein (APP) and blocks the initiating amyloidogenesis. Here, we show the effect of SPON1 in Aß reduction in vitro in neural cells and in an in vivo AD mouse model. We engineered mouse induced neural stem cells (iNSCs) to express Spon1. iNSCs harboring mouse Spon1 secreted SPON1 protein and reduced the quantity of Aß when co-cultured with Aß-secreting Neuro 2a cells. The human SPON1 gene itself also reduced Aß in HEK 293T cells expressing the human APP transgene with AD-linked mutations through lentiviral-mediated delivery. We also demonstrated that injecting SPON1 reduced the amount of Aß and ameliorated cognitive dysfunction and memory impairment in 5xFAD mice expressing human APP and PSEN1 transgenes with five AD-linked mutations.

Bioengineered in vitro enteric nervous system.

Bidirectional interactions between the human central nervous system and the gastrointestinal tract, via the enteric nervous system, are unmapped and central to many human conditions. There is a critical need to develop 3D human in vitro intestinal tissue models to emulate the intricate cell interactions of the human enteric nervous system within the gastrointestinal tract in order to better understand these complex interactions that cannot be studied utilizing in vivo animal models. In vitro systems, if sufficiently replicative of some in vivo conditions, may assist with the study of individual cell interactions. Here, we describe a 3D-innervated tissue model of the human intestine consisting of human-induced neural stem cells differentiated into relevant enteric nervous system neural cell types. Enterocyte-like (Caco-2) and goblet-like (HT29-MTX) cells are used to form the intestinal epithelial layer, and intestinal myofibroblasts are utilized to simulate the stromal layer. In vitro enteric nervous system cultures supported survival and function of the various cell types, with mucosal and neural transcription factors evident over 5 weeks. The human-induced neural stem cells migrated from the seeding location on the peripheral layer of the hollow scaffolds toward the luminal epithelial cells, prompted by the addition of neural growth factor. nNOS-expressing neurons and the substance P precursor gene TAC1 were expressed within the in vitro enteric nervous system to support the utility of the tissue model to recapitulate enteric nervous system phenotypes. This innervated tissue system offers a new tool to use to help in understanding neural circuits controlling the human intestine and associated communication networks.

mRNA-Driven Generation of Transgene-Free Neural Stem Cells from Human Urine-Derived Cells.

Human neural stem cells (NSCs) hold enormous promise for neurological disorders, typically requiring their expandable and differentiable properties for regeneration of damaged neural tissues. Despite the therapeutic potential of induced NSCs (iNSCs), a major challenge for clinical feasibility is the presence of integrated transgenes in the host genome, contributing to the risk for undesired genotoxicity and tumorigenesis. Here, we describe the advanced transgene-free generation of iNSCs from human urine-derived cells (HUCs) by combining a cocktail of defined small molecules with self-replicable mRNA delivery. The established iNSCs were completely transgene-free in their cytosol and genome and further resembled human embryonic stem cell-derived NSCs in the morphology, biological characteristics, global gene expression, and potential to differentiate into functional neurons, astrocytes, and oligodendrocytes. Moreover, iNSC colonies were observed within eight days under optimized conditions, and no teratomas formed in vivo, implying the absence of pluripotent cells. This study proposes an approach to generate transplantable iNSCs that can be broadly applied for neurological disorders in a safe, efficient, and patient-specific manner.

Fusion of Reprogramming Factors Alters the Trajectory of Somatic Lineage Conversion.

Simultaneous expression of Oct4, Klf4, Sox2, and cMyc induces pluripotency in somatic cells (iPSCs). Replacing Oct4 with the neuro-specific factor Brn4 leads to transdifferentiation of fibroblasts into induced neural stem cells (iNSCs). However, Brn4 was recently found to induce transient acquisition of pluripotency before establishing the neural fate. We employed genetic lineage tracing and found that induction of iNSCs with individual vectors leads to direct lineage conversion. In contrast, polycistronic expression produces a Brn4-Klf4 fusion protein that enables induction of pluripotency. Our study demonstrates that a combination of pluripotency and tissue-specific factors allows direct somatic cell transdifferentiation, bypassing the acquisition of a pluripotent state. This result has major implications for lineage conversion technologies, which hold potential for providing a safer alternative to iPSCs for clinical application both in vitro and in vivo.

Take the shortcut - direct conversion of somatic cells into induced neural stem cells and their biomedical applications.

Second-generation reprogramming of somatic cells directly into the cell type of interest avoids induction of pluripotency and subsequent cumbersome differentiation procedures. Several recent studies have reported direct conversion of human somatic cells into stably proliferating induced neural stem cells (iNSCs). Importantly, iNSCs are easier, faster, and more cost-efficient to generate than induced pluripotent stem cells (iPSCs), and also have a higher level of clinical safety. Stably, self-renewing iNSCs can be derived from different cellular sources, such as skin fibroblasts and peripheral blood mononuclear cells, and readily differentiate into neuronal and glial lineages that are indistinguishable from their iPSC-derived counterparts or from NSCs isolated from primary tissues. This review focuses on the derivation and characterization of iNSCs and their biomedical applications. We first outline different approaches to generate iNSCs and then discuss the underlying molecular mechanisms. Finally, we summarize the preclinical validation of iNSCs to highlight that these cells are promising targets for disease modeling, autologous cell therapy, and precision medicine.

Small Molecules for Neural Stem Cell Induction.

Generation of induced pluripotent stem cells (iPSCs) from other somatic cells has provided great hopes for transplantation therapies. However, these cells still cannot be used for clinical application due to the low reprogramming and differentiation efficiency beside the risk of mutagenesis and tumor formation. Compared to iPSCs, induced neural stem cells (iNSCs) are easier to terminally differentiate into neural cells and safe; thus, iNSCs hold more opportunities than iPSCs to treat neural diseases. On the other hand, recent studies have showed that small molecules (SMs) can dramatically improve the efficiency of reprogramming and SMs alone can even convert one kind of somatic cells into another, which is much safer and more effective than transcription factor-based methods. In this study, we provide a review of SMs that are generally used in recent neural stem cell induction studies, and discuss the main mechanisms and pathways of each SM.