Transplantation of motoneurons derived from MASH1-transfected mouse ES cells reconstitutes neural networks and improves motor function in hemiplegic mice

Neuronal Cell Sheets of Cortical Motor Neuron Phenotype Derived from Human iPSCs

Transplantation of stem cells that differentiate into more mature neural cells brings about functional improvement in preclinical studies of stroke. Previous transplant approaches in the diseased brain utilized injection of the cells in a cell suspension. In addition, neural stem cells were preferentially used for grafting. However, these cells had no specific relationship to the damaged tissue of stroke and brain injury patients. The injection of cells in a suspension destroyed the cell–cell interactions that are suggested to be important for promoting functional integrity of cortical motor neurons. In order to obtain suitable cell types for grafting in patients with stroke and brain damage, a protocol was modified for differentiating human induced pluripotent stem cells from cells phenotypically related to cortical motor neurons. Moreover, cell sheet technology was applied to neural cell transplantation, as maintaining the cell–cell communications is regarded important for the repair of host brain architecture. Accordingly, neuronal cell sheets that were positive Forebrain Embryonic Zinc Finger (Fez) family zinc finger 2 (FEZF2), COUP-TF-interacting protein 2, insulin-like growth factor–binding protein 4 (IGFBP4), cysteine-rich motor neuron 1 protein precursor (CRIM1), and forkhead box p2 (FOXP2) were developed. These markers are associated with cortical motoneurons that are appropriate for the transplant location in the lesions. The sheets allowed preservation of cell–cell interactions shown by synapsin1 staining after transplantation to damaged mouse brains. The sheet transplantation brought about partial structural restoration and the improvement of motor functions in hemiplegic mice. Collectively, the novel neuronal cell sheets were transplanted into damaged motor cortices; the cell sheets maintained cell–cell interactions and improved the motor functions in the hemiplegic model mice. The motoneuron cell sheets are possibly applicable for stroke patients and patients with brain damage by using patient-specific induced pluripotent stem cells.

Derivation of motor neuron-like cells from neonatal mouse testis in a simple culture condition

Embryonic stem cell (ESC) therapy is an exciting way to treat neurodegenerative disease and central nervous system injury. However, many ethical and immunological problems surround the use of embryonic stem cells. Finding an alternative source of stem cells is therefore pertinent. In this study, spermatogonia stem cells (SSCs) were used to generate mature motor neurons. SSCs were extracted from neonatal testes and cultured in DMED/F12 medium for 3 weeks. Characterisation of SSC-derived ESC-like cells was confirmed by RT-qPCR, immunostaining, alkaline phosphatase activity and their ability to form embryoid bodies (EBs). The EBs were induced by retinoic acid and Sonic hedgehog and trypsinised to obtain single induced cells. The single cells were cultured in neural medium for 18 days. Characterisation of neural precursors and motor neuron-like cells was confirmed by RT-qPCR and immunocytochemical analysis at the 7th day (early stage) and 18th day (late stage), respectively, of culturing. The neural precursors were found to be positive for nestin and Sox2, and a small fraction of cells expressed β-tubulin III. Upon further differentiation, multipolar neurons were detected that expressed β-tubulin III and MAP2 markers. Moreover, the expression levels of Olig2 and PAX6 were significantly lower, while HB9, Isl1 and Isl2 expression levels were higher at the late stage when compared to the early stage. These results show that SSCs have the potential to differentiate to motor neuron-like cells and express markers specific for mature motor neurons. However, the functional ability of these cells remains to be evaluated in future studies.

Mash1 efficiently reprograms rat astrocytes into neurons

To date, it remains poorly understood whether astrocytes can be easily reprogrammed into neurons. Mash1 and Brn2 have been previously shown to cooperate to reprogram fibroblasts into neurons. In this study, we examined astrocytes from 2-month-old Sprague-Dawley rats, and found that Brn2 was expressed, but Mash1 was not detectable. Thus, we hypothesized that Mash1 alone could be used to reprogram astrocytes into neurons. We transfected a recombinant MSCV-MASH1 plasmid into astrocytes for 72 hours, and saw that all cells expressed Mash1. One week later, we observed the changes in morphology of astrocytes, which showed typical neuronal characteristics. Moreover, β-tubulin expression levels were significantly higher in astrocytes expressing Mash1 than in control cells. These results indicate that Mash1 alone can reprogram astrocytes into neurons.

Bone morphogenetic protein 2 inhibits neurite outgrowth of motor neuron-like NSC-34 cells and up-regulates its type II receptor

Bone morphogenetic proteins (BMPs) regulate several aspects of neuronal behavior. For instance, BMP-2 has the ability to modulate, either positively or negatively, the outgrowth of neuronal processes in diverse cell types. In Drosophila motor neurons, the BMP type II receptor (BMPRII) homolog wishful thinking plays crucial roles on neuromuscular synaptogenesis signaling through Smad-dependent and Smad-independent pathways. However, a role for BMP signaling at the vertebrate neuromuscular junction has not been addressed. Herein, we have analyzed the expression of BMPRII and the effect of BMP-2 during the morphological differentiation of motor neuron-like NSC-34 cells. Our data indicate that BMPRII is up-regulated and becomes accumulated in somas and growth cones upon motor neuronal differentiation. BMP-2 inhibits the differentiation of NSC-34 cells, an effect that correlates with activation of a Smad-dependent pathway, induction of the inhibitory Id1 transcription factor, and down-regulation of the neurogenic factor Mash1. BMP-2 also activates effectors of Smad-independent pathways. Remarkably, BMP-2 treatment significantly increases the expression of BMPRII. Our findings provide the first evidence to suggest a role for BMP pathways on the differentiation of motor neurons leading to successful assembly and/or regeneration of the vertebrate neuromuscular synapse.

Role of SDF1/CXCR4 interaction in experimental hemiplegic models with neural cell transplantation

Much attention has been focused on neural cell transplantation because of its promising clinical applications. We have reported that embryonic stem (ES) cell derived neural stem/progenitor cell transplantation significantly improved motor functions in a hemiplegic mouse model. It is important to understand the molecular mechanisms governing neural regeneration of the damaged motor cortex after the transplantation. Recent investigations disclosed that chemokines participated in the regulation of migration and maturation of neural cell grafts. In this review, we summarize the involvement of inflammatory chemokines including stromal cell derived factor 1 (SDF1) in neural regeneration after ES cell derived neural stem/progenitor cell transplantation in mouse stroke models.

Directed expression of Gata2, Mash1, and Foxa2 synergize to induce the serotonergic neuron phenotype during in vitro differentiation of embryonic stem cells

Investigation of serotonergic neuronal activity and its relationship to disease has been limited by a lack of physiologically relevant in vitro cell models. Serotonergic neurons derived from embryonic stem cells (ESCs) could provide a platform for such studies and provide models for use in drug discovery. Here, we report enhancement of serotonergic differentiation using a genetic approach. Expression of Gata2 increased the yield of serotonergic neurons. Enhancement was only achieved when Gata2 was expressed under the control of the tissue-specific promoter of the transcription factor Nkx6.1. High levels of Gata2 expression in ESCs compromised pluripotency and induced non-neuronal differentiation. Combined directed expression of Gata2, proneural gene Mash1, and forkhead transcription factor Foxa2 further enhanced serotonergic neural differentiation, resulting in a 10-fold increase in serotonin content. These neurons were also capable of depolarization (KCl, 30 mM)-induced elevations of intracellular Ca(2+) . The presence of sonic hedgehog during differentiation produced a further modest increase in numbers (1.5-fold). Transgene expression did not influence the number of tyrosine hydroxylase positive neurons in the cultures after 20 days, implying that Gata2, Mash1, and Foxa2 modulate in vitro differentiation at a time beyond the decision-point for dopaminergic or nondopaminergic commitment. This study demonstrates that the directed expression of specific transcription factors enhances serotonergic neuron differentiation in vitro and highlights the importance of transgene expression at the right stage of ESC differentiation to effect the generation of a desired neural subtype.

Effects of constraint-induced movement therapy on neurogenesis and functional recovery after early hypoxic-ischemic injury in mice

AIM

Constraint-induced movement therapy (CIMT) has emerged as a promising therapeutic strategy for improving affected upper limb function in children with hemiplegic cerebral palsy (CP). However, little is known about the changes in the brain that are induced by CIMT. This study was designed to investigate these changes and behavioural performance after CIMT intervention in mice with neonatal hypoxic-ischemic brain injury.

METHOD

We utilized the neonatal hypoxic-ischemic brain injury model established in mice pups. Three weeks after the injury, the mice were randomly assigned to the following three groups: the control group (n = 15), the enriched-environment group (n = 17), and the CIMT with an enriched-environment group (CIMT-EE, n = 15). 5-bromo-2-deoxyuridine (BrdU) was injected daily to label proliferating cells during the 2 weeks of intervention.

RESULTS

The CIMT-EE group showed better fall rate in the horizontal ladder rung walking test (mean 5.4%, SD 3.6%) than either the control (mean 14.3%, SD 7.3%; p = 0.001) or enriched-environment (mean 12.4%, SD 7.7%; p = 0.010) groups 2 weeks after the end of intervention. The CIMT-EE group also showed more neurogenesis (mean 7069 cells/mm³, SD 4017 cells/mm³) than either the control group (mean 1555 cells/mm³, SD 1422 cells/mm³; p < 0.001) or enriched-environment group (mean 2994 cells/mm³, SD 3498 cells/mm³; p = 0.001) in the subventricular zone. In the striatum, neurogenesis in the CIMT-EE group (mean 534 cells/mm³, SD 441 cells/mm³) was greater than in the control group (mean 95 cells/mm³, SD 133 cells/mm³; p = 0.001).

INTERPRETATION

There was CIMT-EE enhanced neurogenesis in the brain along with functional benefits in mice after early hypoxic-ischemic brain injury. This is the first study to demonstrate the effects of CIMT on neurogenesis and functional recovery after experimental injury to an immature brain.

Kinetic analysis of neurotrophin-3-mediated differentiation of embryonic stem cells into neurons

The goal of this study was to develop a kinetic analysis that could predict the behavior of embryonic stem cell-derived neural progenitor cells (ESNPCs) in response to treatment with neurotrophin-3 (NT-3). Previous studies have shown that NT-3 activates the mitogen-activated protein (MAP) kinase cascade in embryonic stem cells and promotes differentiation of ESNPCs into neurons. MAP kinase activation after NT-3 stimulation was confirmed experimentally, and a kinetic analysis was developed using rate constants obtained from the literature. Concentrations of select signaling components were estimated for ESNPCs using real-time reverse transcription polymerase chain reaction by comparing mRNA levels to those of cell types with known protein concentrations. This assumption was validated using Western blots, and incorporated into the analysis. This analysis was used to predict the minimum NT-3 concentration necessary to promote neuronal differentiation of ESNPCs based on the activation of MAP kinase. These predictions were then tested experimentally to confirm the validity of the analysis. Finally, expression of the transcription factor mammalian achate schute homolog 1 and beta-tubulin III (an early neuronal marker) was examined in response to the different NT-3 doses to confirm the link between MAP kinase activation and neuronal differentiation. Overall, this study provides insight into the kinetics of the intracellular processes that promote ESNPC differentiation to neurons.

Combined extrinsic and intrinsic manipulations exert complementary neuronal enrichment in embryonic rat neural precursor cultures: an in vitro and in vivo analysis

Numerous central nervous system (CNS) disorders share a common pathology in dysregulation of gamma-aminobutyric acid (GABA) inhibitory signaling. Transplantation of GABA-releasing cells at the site of disinhibition holds promise for alleviating disease symptoms with fewer side effects than traditional drug therapies. We manipulated fibroblast growth factor (FGF)-2 deprivation and mammalian achaete-scute homolog (MASH)1 transcription factor levels in an attempt to amplify the default GABAergic neuronal fate in cultured rat embryonic neural precursor cells (NPCs) for use in transplantation studies. Naïve and MASH1 lentivirus-transduced NPCs were maintained in FGF-2 or deprived of FGF-2 for varying lengths of time. Immunostaining and quantitative analysis showed that GABA- and beta-III-tubulin-immunoreactive cells generally decreased through successive passages, suggesting a loss of neurogenic potential in rat neurospheres expanded in vitro. However, FGF-2 deprivation resulted in a small, but significantly increased population of GABAergic cells derived from passaged neurospheres. In contrast to naïve and GFP lentivirus-transduced clones, MASH1 transduction resulted in increased bromodeoxyuridine (BrdU) incorporation and clonal colony size. Western blotting showed that MASH1 overexpression and FGF-2 deprivation additively increased beta-III-tubulin and decreased cyclic nucleotide phosphodiesterase (CNPase) expression, whereas FGF-2 deprivation alone attenuated glial fibrillary acidic protein (GFAP) expression. These results suggest that low FGF-2 signaling and MASH1 activity can operate in concert to enrich NPC cultures for a GABA neuronal phenotype. When transplanted into the adult rat spinal cord, this combination also yielded GABAergic neurons. These findings indicate that, even for successful utilization of the default GABAergic neuronal precursor fate, a combination of both extrinsic and intrinsic manipulations will likely be necessary to realize the full potential of NSC grafts in restoring function.

Derive and conquer: sourcing and differentiating stem cells for therapeutic applications

Although great progress has been made in the isolation and culture of stem cells, the future of stem-cell-based therapies and their productive use in drug discovery and regenerative medicine depends on two key factors: finding reliable sources of multipotent and pluripotent cells and the ability to control their differentiation to generate desired derivatives. It is essential for clinical applications to establish reliable sources of pathogen-free human embryonic stem cells (ESCs) and develop suitable differentiation techniques. Here, we address some of the problems associated with the sourcing of human ESCs and discuss the current status of stem-cell differentiation technology.

Embryonic stem cells and prospects for their use in regenerative medicine approaches to motor neurone disease

Human embryonic stem cells are pluripotent cells with the potential to differentiate into any cell type in the presence of appropriate stimulatory factors and environmental cues. Their broad developmental potential has led to valuable insights into the principles of developmental and cell biology and to the proposed use of human embryonic stem cells or their differentiated progeny in regenerative medicine. This review focuses on the prospects for the use of embryonic stem cells in cell-based therapy for motor neurone disease or amyotrophic lateral sclerosis, a progressive neurodegenerative disease that specifically affects upper and lower motor neurones and leads ultimately to death from respiratory failure. Stem cell-derived motor neurones could conceivably be used to replace the degenerated cells, to provide authentic substrates for drug development and screening and for furthering our understanding of disease mechanisms. However, to reliably and accurately culture motor neurones, the complex pathways by which differentiation occurs in vivo must be understood and reiterated in vitro by embryonic stem cells. Here we discuss the need for new therapeutic strategies in the treatment of motor neurone disease, the developmental processes that result in motor neurone formation in vivo, a number of experimental approaches to motor neurone production in vitro and recent progress in the application of stem cells to the treatment and understanding of motor neurone disease.

Transplantation of Myocyte Precursors Derived from Embryonic Stem Cells Transfected with IGFII Gene in a Mouse Model of Muscle Injury

BACKGROUND

Reconstruction of skeletal muscle tissue is hampered by the lack of availability of functional substitution of the tissue.

METHODS

Embryonic stem (ES) cells were transfected with the insulin-like growth factor (IGF) II gene and were selected with G418. The resultant cell clones were analyzed regarding their myogenic differentiation in vitro and in vivo.

RESULTS

The cells expressed early and late myogenic differentiation markers, including myoD, myogenin, and dystrophin in vitro. They had phosphorylated Akt within the cells, suggesting their activation by the secreted IGFII. Transplantation of the cells to injured anterior tibial muscle of mice significantly improved their motor functions compared to injured mice transplanted with undifferentiated ES cells and injured mice given vehicle alone. The transfected cells adapted to the injured muscle, formed myofibers positive for dystrophin and negative for MyoD and myogenin. Trichrome staining and toluidine blue staining support myofiber formation in vivo. The enzymatic activity of acetylcholine esterase suggested the functional activity of the regenerated motor units. The evoked electromyogram of anterior tibial muscle transplanted with the transfected cells showed significantly higher potentials compared to that transplanted with undifferentiated ES cells and that injected with phosphate-buffered saline (control injury). Electron microscopic examination confirmed the myofiber formation in the cells in vivo.

CONCLUSIONS

Transfection of IGFII gene into ES cells may be applicable for transplantation therapy of muscle damage due to injury and myopathies.

Introduction of the MASH1 gene into mouse embryonic stem cells leads to differentiation of motoneuron precursors lacking Nogo receptor expression that can be applicable for transplantation to spinal cord injury

ES cells transfected with the MASH1 gene yielded purified spinal motoneuron precursors expressing HB9 and Islet1. The cells lacked the expression of Nogo receptor that was of great advantage for axon growth after transplantation to an injured spinal cord. After transplantation, mice with the complete transection of spinal cord exhibited excellent improvement of the motor functions. Electrophysiological assessment confirmed the quantitative recovery of motor-evoked potential in the transplanted spinal cord. In the grafted spinal cord, gliosis was inhibited and Nogo receptor expression was scarcely detected. The transplanted cells labeled with GFP showed extensive outgrowth of axons positive for neurofilament middle chain, connected to each other and expressed Synaptophysin, Lim1/2 and Islet1. Thus, the in vivo differentiation into mature spinal motoneurons and the reconstitution of neuronal pathways were suggested. The grafted cell population was purified for neurons and was free from teratoma development. These therapeutic strategies may contribute to a potent treatment for spinal cord injury in future.

Gene Therapy Progress and Prospects: In tissue engineering

Tissue engineering (TE) has existed for several years as an area spanning many disciplines, including medicine and engineering. The use of stem cells as a biological basis for TE coupled with advances in materials science has opened up an entirely new chapter in medicine and holds the promise of major contributions to the repair, replacement and regeneration of damaged tissues and organs. In this article, we review the spectrum of stem cells and scaffolds being investigated for their potential applications in medicine.