Maturation of neural stem cells and integration into hippocampal circuits - a functional study in an in situ model of cerebral ischemia

mNSCs overexpressing Rimkla transplantation facilitates cognitive recovery in a mouse model of traumatic brain injury

N-acetyl aspartyl-glutamate (NAAG) is easily inactivated for the hydrolysis of NAAG peptidase on the surface of glial cells, thereby losing its endogenous neuroprotective effect after traumatic brain injury. In this study, lentiviral vectors were used to over express/knock out NAAG synthetase II (Rimkla) in mouse embryonic neural stem cells (mNSCs) in vitro and these mNSCs were transplanted at the lesion site in a mouse model of controlled cortical impact (CCI). In vivo experiments showed that transplantation of mNSCs overexpressing Rimkla regulated glutamate-glutamine cycling between adjacent astrocytes and neurons in the subacute phase of CCI, thereby enhancing support for neuronal metabolism and promoting neuronal synaptic repair in the hippocampal CA3 region. Taken together, these findings demonstrate that transplantation of neural stem cells overexpressing Rimkla can effectively increase the NAAG concentration in local brain regions, which opens up new ideas for the maintenance of NAAG neuroprotective effects after TBI.

Multi-target action of β-alanine protects cerebellar tissue from ischemic damage

Brain ischemic stroke is among the leading causes of death and long-term disability. New treatments that alleviate brain cell damage until blood supply is restored are urgently required. The emerging focus of anti-stroke strategies has been on blood-brain-barrier permeable drugs that exhibit multiple sites of action. Here, we combine single-cell electrophysiology with live-cell imaging to find that β-Alanine (β-Ala) protects key physiological functions of brain cells that are exposed to acute stroke-mimicking conditions in ex vivo brain preparations. β-Ala exerts its neuroprotective action through several distinct pharmacological mechanisms, none of which alone could reproduce the neuroprotective effect. Since β-Ala crosses the blood-brain barrier and is part of a normal human diet, we suggest that it has a strong potential for acute stroke treatment and facilitation of recovery.

Increased excitability of human iPSC-derived neurons in HTR2A variant-related sleep bruxism

Sleep bruxism (SB) is a sleep-related movement disorder characterized by grinding and clenching of the teeth during sleep. We previously found a significant association between SB and a single nucleotide polymorphism (SNP), rs6313, in the neuronal serotonin 2A receptor gene (HTR2A), and established human induced pluripotent stem cell (iPSC)-derived neurons from SB patients with a genetic variant. To elucidate the electrophysiological characteristics of SB iPSC-derived neural cells bearing an SB-related genetic variant, we generated ventral hindbrain neurons from SB patients and unaffected controls, and explored the intrinsic membrane properties of these neurons using the patch-clamp technique. We found that the electrophysiological properties of iPSC-derived neurons mature in a time-dependent manner in long-term control cultures. SB neurons exhibited higher action potential firing frequency, higher gain, and shorter action potential half duration. This is the first in vitro modeling of SB using patient-specific iPSCs. The revealed electrophysiological characteristics may serve as a benchmark for further investigation of pathogenic mechanisms underlying SB. Moreover, our results on long-term cultures provide a strategy to define the functional maturity of human neurons in vitro, which can be implemented for stem cell research of neurogenesis, and neurodevelopmental disorders.

Mitochondrial ROS control neuronal excitability and cell fate in frontotemporal dementia

INTRODUCTION

The second most common form of early-onset dementia-frontotemporal dementia (FTD)-is often characterized by the aggregation of the microtubule-associated protein tau. Here we studied the mechanism of tau-induced neuronal dysfunction in neurons with the FTD-related 10+16 MAPT mutation.

METHODS

Live imaging, electrophysiology, and redox proteomics were used in 10+16 induced pluripotent stem cell-derived neurons and a model of tau spreading in primary cultures.

RESULTS

Overproduction of mitochondrial reactive oxygen species (ROS) in 10+16 neurons alters the trafficking of specific glutamate receptor subunits via redox regulation. Increased surface expression of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) and N-methyl-D-aspartate (NMDA) receptors containing GluA1 and NR2B subunits leads to impaired glutamatergic signaling, calcium overload, and excitotoxicity. Mitochondrial antioxidants restore the altered response and prevent neuronal death. Importantly, extracellular 4R tau induces the same pathological response in healthy neurons, thus proposing a mechanism for disease propagation.

DISCUSSION

These results demonstrate mitochondrial ROS modulate glutamatergic signaling in FTD, and suggest a new therapeutic strategy.

Genetically engineered MAPT 10+16 mutation causes pathophysiological excitability of human iPSC-derived neurons related to 4R tau-induced dementia

Human iPSC lines represent a powerful translational model of tauopathies. We have recently described a pathophysiological phenotype of neuronal excitability of human cells derived from the patients with familial frontotemporal dementia and parkinsonism (FTDP-17) caused by the MAPT 10+16 splice-site mutation. This mutation leads to the increased splicing of 4R tau isoforms. However, the role of different isoforms of tau protein in initiating neuronal dementia-related dysfunction, and the causality between the MAPT 10+16 mutation and altered neuronal activity have remained unclear. Here, we employed genetically engineered cells, in which the IVS10+16 mutation was introduced into healthy donor iPSCs to increase the expression of 4R tau isoform in exon 10, aiming to explore key physiological traits of iPSC-derived MAPT IVS10+16 neurons using patch-clamp electrophysiology and multiphoton fluorescent imaging techniques. We found that during late in vitro neurogenesis (from ~180 to 230 days) iPSC-derived cortical neurons of the control group (parental wild-type tau) exhibited membrane properties compatible with "mature" neurons. In contrast, MAPT IVS10+16 neurons displayed impaired excitability, as reflected by a depolarized resting membrane potential, an increased input resistance, and reduced voltage-gated Na+- and K+-channel-mediated currents. The mutation changed the channel properties of fast-inactivating Nav and decreased the Nav1.6 protein level. MAPT IVS10+16 neurons exhibited reduced firing accompanied by a changed action potential waveform and severely disturbed intracellular Ca2+ dynamics, both in the soma and dendrites, upon neuronal depolarization. These results unveil a causal link between the MAPT 10+16 mutation, hence overproduction of 4R tau, and a dysfunction of human cells, identifying a biophysical basis of changed neuronal activity in 4R tau-triggered dementia. Our study lends further support to using iPSC lines as a suitable platform for modelling tau-induced human neuropathology in vitro.

Maturation and phenotype of pathophysiological neuronal excitability of human cells in tau-related dementia

Frontotemporal dementia and parkinsonism (FTDP-17) caused by the 10+16 splice-site mutation in the gene encoding microtubule-associated protein tau (MAPT) provides an established platform to model tau-related dementia in vitro Neurons derived from human induced pluripotent stem cells (iPSCs) have been shown to recapitulate the neurodevelopmental profile of tau pathology during in vitro corticogenesis, as in the adult human brain. However, the neurophysiological phenotype of these cells has remained unknown, leaving unanswered questions regarding the functional relevance and the gnostic power of this disease model. In this study, we used electrophysiology to explore the membrane properties and intrinsic excitability of the generated neurons and found that human cells mature by ∼150 days of neurogenesis to become compatible with matured cortical neurons. In earlier FTDP-17, however, neurons exhibited a depolarized resting membrane potential associated with increased resistance and reduced voltage-gated Na+- and K+-channel-mediated conductance. Expression of the Nav1.6 protein was reduced in FTDP-17. These effects led to reduced cell capability of induced firing and changed the action potential waveform in FTDP-17. The revealed neuropathology might thus contribute to the clinicopathological profile of the disease. This sheds new light on the significance of human in vitro models of dementia.

Impact of a Histone Deacetylase Inhibitor-Trichostatin A on Neurogenesis after Hypoxia-Ischemia in Immature Rats

Hypoxia-ischemia (HI) in the neonatal brain frequently results in neurologic impairments, including cognitive disability. Unfortunately, there are currently no known treatment options to minimize ischemia-induced neural damage. We previously showed the neuroprotective/neurogenic potential of a histone deacetylase inhibitor (HDACi), sodium butyrate (SB), in a neonatal HI rat pup model. The aim of the present study was to examine the capacity of another HDACi—Trichostatin A (TSA)—to stimulate neurogenesis in the subgranular zone of the hippocampus. We also assessed some of the cellular/molecular processes that could be involved in the action of TSA, including the expression of neurotrophic factors (glial cell line-derived neurotrophic factor (GDNF), nerve growth factor (NGF), and brain-derived neurotrophic factor (BDNF)) as well as the TrkB receptor and its downstream signalling substrate— cAMP response element-binding protein (CREB). Seven-day-old rat pups were subjected to unilateral carotid artery ligation followed by hypoxia for 1 h. TSA was administered directly after the insult (0.2 mg/kg body weight). The study demonstrated that treatment with TSA restored the reduced by hypoxia-ischemia number of immature neurons (neuroblasts, BrdU/DCX-positive) as well as the number of oligodendrocyte progenitors (BrdU/NG2+) in the dentate gyrus of the ipsilateral damaged hemisphere. However, new generated cells did not develop the more mature phenotypes. Moreover, the administration of TSA stimulated the expression of BDNF and increased the activation of the TrkB receptor. These results suggest that BDNF-TrkB signalling pathways may contribute to the effects of TSA after neonatal hypoxic-ischemic injury.

A Multi-Channel System for Temperature Sensing of Neural Stem Cells in Adherent Culture

Neural stem cells (NSCs) can gradually proliferate or differentiate during adherent culture. It is found that stem cells have different temperature characteristics in different physiological states. In order to detect the temperature of NSCs during adherent culture, in this study, we have designed a temperature monitoring system, in which a thin-film platinum resistor was used as the sensor. The NSCs were seeded on the sensor, and the data acquisition device was connected to the host computer via Bluetooth. Results indicate that there are about 5000 cells attached on the surface of each sensor, and the cell viability is maintained at about 90% after 24 h culture. An electrostatic force microscope (EFM) result proves that there is no electric field on the sensor surface to influence the activity of NSCs. This system can work continuously for more than 24 h with 0.05 °C detection sensitivity. Furthermore, the significant temperature change of NSCs is observed when stimulated by different concentrations of thyroid hormone, which demonstrates that the temperature change related to cell activity. Therefore, by detecting the temperature of the cell population, the fabricated system can provide reference information for studying the metabolic state of NSCs, as well as physiological responses of cells under various conditions in biomedical applications.

Microfluidic Brain-on-a-Chip: Perspectives for Mimicking Neural System Disorders

Neurodegenerative diseases (NDDs) include more than 600 types of nervous system disorders in humans that impact tens of millions of people worldwide. Estimates by the World Health Organization (WHO) suggest NDDs will increase by nearly 50% by 2030. Hence, development of advanced models for research on NDDs is needed to explore new therapeutic strategies and explore the pathogenesis of these disorders. Different approaches have been deployed in order to investigate nervous system disorders, including two-and three-dimensional (2D and 3D) cell cultures and animal models. However, these models have limitations, such as lacking cellular tension, fluid shear stress, and compression analysis; thus, studying the biochemical effects of therapeutic molecules on the biophysiological interactions of cells, tissues, and organs is problematic. The microfluidic "organ-on-a-chip" is an inexpensive and rapid analytical technology to create an effective tool for manipulation, monitoring, and assessment of cells, and investigating drug discovery, which enables the culture of various cells in a small amount of fluid (10-9 to 10-18 L). Thus, these chips have the ability to overcome the mentioned restrictions of 2D and 3D cell cultures, as well as animal models. Stem cells (SCs), particularly neural stem cells (NSCs), induced pluripotent stem cells (iPSCs), and embryonic stem cells (ESCs) have the capability to give rise to various neural system cells. Hence, microfluidic organ-on-a-chip and SCs can be used as potential research tools to study the treatment of central nervous system (CNS) and peripheral nervous system (PNS) disorders. Accordingly, in the present review, we discuss the latest progress in microfluidic brain-on-a-chip as a powerful and advanced technology that can be used in basic studies to investigate normal and abnormal functions of the nervous system.

Monitoring maturation of neural stem cell grafts within a host microenvironment

Neural stem cells (NSC) act as a versatile tool for neuronal cell replacement strategies to treat neurodegenerative disorders in which functional neurorestorative mechanisms are limited. While the beneficial effects of such cell-based therapy have already been documented in terms of neurodegeneration of various origins, a neurophysiological basis for improvement in the recovery of neurological function is still not completely understood. This overview briefly describes the cumulative evidence from electrophysiological studies of NSC-derived neurons, aimed at establishing the maturation of differentiated neurons within a host microenvironment, and their integration into the host circuits, with a particular focus on the neurogenesis of NSC grafts within the post-ischemic milieu. Overwhelming evidence demonstrates that the host microenvironment largely regulates the lineage of NSC grafts. This regulatory role, as yet underestimated, raises possibilities for the favoured maturation of a subset of neural phenotypes in order to gain timely remodelling of the impaired brain tissue and amplify the therapeutic effects of NSC-based therapy for recovery of neurological function.

Isolation of Neural Stem Cells from the embryonic mouse hippocampus for in vitro growth or engraftment into a host tissue

For both stem cell research and treatment of the central nervous system disorders, neural stem/progenitor cells (NSPCs) represent an important breakthrough tool. In the expanded stem cell-based therapy use, NSPCs not only provide a powerful cell source for neural cell replacement but a useful model for developmental biology research. Despite numerous approaches were described for isolation of NSPCs from either fetal or adult brain, the main issue remains in extending cell survival following isolation. Here we provide a simple and affordable protocol for making viable NSPCs from the fetal mouse hippocampi, which are capable of maintaining the high viability in a 2D monolayer cell culture or generating 3D neuro-spheroids of cell aggregates. Further, we describe the detailed method for engraftment of embryonic NSPCs onto a host hippocampal tissue for promoting multilinear cell differentiation and maturation within endogenous environment. Our experimental data demonstrate that embryonic NSPCs isolated using this approach show the high viability (above 88%). Within a host tissue, these cells were capable of differentiating to the main neural subpopulations (principal neurons, oligodendrocytes, astroglia). Finally, NSPC-derived neurons demonstrated matured functional properties (electrophysiological activity), becoming functionally integrated into the host hippocampal circuits within a couple of weeks after engraftment.