Neural differentiation of P19 carcinoma cells and primary neurospheres: cell morphology, proliferation, viability, and functionality

High Concentrations of Cannabidiol Induce Neurotoxicity in Neurosphere Culture System

Recent studies have demonstrated that cannabinoids are potentially effective in the treatment of various neurological conditions, and cannabidiol (CBD), one of the most studied compounds, has been proposed as a non-toxic option. However, the adverse effects of CBD on neurodevelopmental processes have rarely been studied in cell culture systems. To better understand CBD's influence on neurodevelopment, we exposed neural progenitor cells (NPCs) to different concentrations of CBD (1 µM, 5 µM, and 10 µM). We assessed the morphology, migration, differentiation, cell death, and gene expression in 2D and 3D bioprinted models to stimulate physiological conditions more effectively. Our results showed that CBD was more toxic at higher concentrations (5 µM and 10 µM) and affected the viability of NPCs than at lower concentrations (1 µM), in both 2D and 3D models. Moreover, our study revealed that higher concentrations of CBD drastically reduced the size of neurospheres and the number of NPCs within neurospheres, impaired the morphology and mobility of neurons and astrocytes after differentiation, and reduced neurite sprouting. Interestingly, we also found that CBD alters cellular metabolism by influencing the expression of glycolytic and β-oxidative enzymes in the early and late stages of metabolic pathways. Therefore, our study demonstrated that higher concentrations of CBD promote important changes in cellular functions that are crucial during CNS development.

Neural induction drives body axis formation during embryogenesis, but a neural induction-like process drives tumorigenesis in postnatal animals

Characterization of cancer cells and neural stem cells indicates that tumorigenicity and pluripotency are coupled cell properties determined by neural stemness, and tumorigenesis represents a process of progressive loss of original cell identity and gain of neural stemness. This reminds of a most fundamental process required for the development of the nervous system and body axis during embryogenesis, i.e., embryonic neural induction. Neural induction is that, in response to extracellular signals that are secreted by the Spemann-Mangold organizer in amphibians or the node in mammals and inhibit epidermal fate in ectoderm, the ectodermal cells lose their epidermal fate and assume the neural default fate and consequently, turn into neuroectodermal cells. They further differentiate into the nervous system and also some non-neural cells via interaction with adjacent tissues. Failure in neural induction leads to failure of embryogenesis, and ectopic neural induction due to ectopic organizer or node activity or activation of embryonic neural genes causes a formation of secondary body axis or a conjoined twin. During tumorigenesis, cells progressively lose their original cell identity and gain of neural stemness, and consequently, gain of tumorigenicity and pluripotency, due to various intra-/extracellular insults in cells of a postnatal animal. Tumorigenic cells can be induced to differentiation into normal cells and integrate into normal embryonic development within an embryo. However, they form tumors and cannot integrate into animal tissues/organs in a postnatal animal because of lack of embryonic inducing signals. Combination of studies of developmental and cancer biology indicates that neural induction drives embryogenesis in gastrulating embryos but a similar process drives tumorigenesis in a postnatal animal. Tumorigenicity is by nature the manifestation of aberrant occurrence of pluripotent state in a postnatal animal. Pluripotency and tumorigenicity are both but different manifestations of neural stemness in pre- and postnatal stages of animal life, respectively. Based on these findings, I discuss about some confusion in cancer research, propose to distinguish the causality and associations and discriminate causal and supporting factors involved in tumorigenesis, and suggest revisiting the focus of cancer research.

Exosomes induce neurogenesis of pluripotent P19 cells

Exosomes play a role in tissue/organ development and differentiation. Retinoic acid induces differentiation of P19 cells (UD-P19) to P19 neurons (P19N) that behave like cortical neurons and express characteristic neuronal genes such as NMDA receptor subunits. Here we report P19N exosome-mediated differentiation of UD-P19 to P19N. Both UD-P19 and P19N released exosomes with characteristic exosome morphology, size, and common protein markers. P19N internalized significantly higher number of Dil-P19N exosomes as compared to UD-P19 with accumulation in the perinuclear region. Continuous exposure of UD-P19 to P19N exosomes for six days induced formation of small-sized embryoid bodies that differentiated into MAP2-/GluN2B-positive neurons recapitulating RA-induction of neurogenesis. Incubation with UD-P19 exosomes for six days did not affect UD-P19. Small RNA-seq identified enrichment of P19N exosomes with pro-neurogenic non-coding RNAs (ncRNAs) such as miR-9, let-7, MALAT1 and depleted with ncRNAs involved in maintenance of stem cell characteristics. UD-P19 exosomes were rich with ncRNAs required for maintenance of stemness. P19N exosomes provide an alternative method to genetic modifications for cellular differentiation of neurons. Our novel findings on exosomes-mediated differentiation of UD-P19 to P19 neurons provide tools to study pathways directing neuron development/differentiation and develop novel therapeutic strategies in neuroscience.

A review on 3D printing functional brain model

Modern neuroscience increasingly relies on 3D models to study neural circuitry, nerve regeneration, and neural disease. Several different biofabrication approaches have been explored to create 3D neural tissue model structures. Among them, 3D bioprinting has shown to have great potential to emerge as a high-throughput/high precision biofabrication strategy that can address the growing need for 3D neural models. Here, we have reviewed the design principles for neural tissue engineering. The main challenge to adapt printing technologies for biofabrication of neural tissue models is the development of neural bioink, i.e., a biomaterial with printability and gelation properties and also suitable for neural tissue culture. This review shines light on a vast range of biomaterials as well as the fundamentals of 3D neural tissue printing. Also, advances in 3D bioprinting technologies are reviewed especially for bioprinted neural models. Finally, the techniques used to evaluate the fabricated 2D and 3D neural models are discussed and compared in terms of feasibility and functionality.

Mechanical stretch promotes antioxidant responses and cardiomyogenic differentiation in P19 cells

Accumulating evidence has suggested that mechanical stimuli play a crucial role in regulating the lineage-specific differentiation of stem cells through fine-tuning redox balance. We aimed to investigate the effects of cyclic tensile strain (CTS) on the expression of antioxidant enzymes and cardiac-specific genes in P19 cells, a widely characterized tool for cardiac differentiation research. A stretching device was applied to generate different magnitude and duration of cyclic strains on P19 cells. The messenger RNA and protein levels of targeted genes were determined by real-time polymerase chain reaction and Western blot assays, respectively. Proper magnitude and duration of cognitive stimulation therapy (CST) stimulation substantially enhanced the expression of both antioxidant enzymes and cardiac-specific genes in P19 cells. Sirtuin 1 (SIRT1) played an essential role in the CTS-induced cardiomyogenic differentiation of P19, as evidenced by changes in the expression of antioxidant enzymes and cardiac-specific genes. Mechanical loading promoted the cardiomyogenic differentiation of P19 cells. SIRT1 was involved in CST-mediated P19 differentiation, implying that SIRT1 might serve as an important target for developing methods to promote cardiomyogenic differentiation of stem cells.

Aluminum affects neural phenotype determination of embryonic neural progenitor cells

Aluminum (Al) is a neurotoxin and is associated with the etiology of neurodegenerative diseases, such as Alzheimer's disease (AD). The Al-free ion (Al³⁺) is the biologically reactive and toxic form. However, the underlying mechanisms of Al toxicity in the brain remain unclear. Here, we evaluated the effects of Al³⁺ (in the chloride form-AlCl₃) at different concentrations (0.1-100 µM) on the morphology, proliferation, apoptosis, migration and differentiation of neural progenitor cells (NPCs) isolated from embryonic telencephalons, cultured as neurospheres. Our results reveal that Al³⁺ at 100 µM reduced the number and diameter of neurospheres. Cell cycle analysis showed that Al³⁺ had a decisive function in proliferation inhibition of NPCs during neural differentiation and induced apoptosis on neurospheres. In addition, 1 µM Al³⁺ resulted in deleterious effects on neural phenotype determination. Flow cytometry and immunocytochemistry analysis showed that Al³⁺ promoted a decrease in immature neuronal marker β3-tubulin expression and an increase in co-expression of the NPC marker nestin and glial fibrillary acidic protein. Thus, our findings indicate that Al³⁺ caused cellular damage and reduced proliferation and migration, resulting in global inhibition of NPC differentiation and neurogenesis.

Lead exposure reduces survival, neuronal determination, and differentiation of P19 stem cells

Lead (Pb) is a teratogen that poses health risks after acute and chronic exposure. Lead is deposited in the bones of adults and is continuously leached into the blood for decades. While this chronic lead exposure can have detrimental effects on adults such as high blood pressure and kidney damage, developing fetuses and young children are particularly vulnerable. During pregnancy, bone-deposited lead is released into the blood at increased rates and can cross the placental barrier, exposing the embryo to the toxin. Embryos exposed to lead display serious developmental and cognitive defects throughout life. Although studies have investigated lead's effect on late-stage embryos, few studies have examined how lead affects stem cell determination and differentiation. For example, it is unknown whether lead is more detrimental to neuronal determination or differentiation of stem cells. We sought to determine the effect of lead on the determination and differentiation of pluripotent embryonic testicular carcinoma (P19) cells into neurons. Our data indicate that lead exposure significantly inhibits the determination of P19 cells to the neuronal lineage by alteration of N-cadherin and Sox2 expression. We also observed that lead significantly alters subsequent neuronal and glial differentiation. Consequently, this research emphasizes the need to reduce public exposure to lead.

Resveratrol as a Therapy to Restore Neurogliogenesis of Neural Progenitor Cells Infected by Toxoplasma gondii

The intracellular protozoan Toxoplasma gondii may cause congenital toxoplasmosis and serious brain damage in fetus. However, the underlying mechanism of neuropathogenesis in brain toxoplasmosis remains unclear. For this study, neural progenitor cells (NPCs) were obtained from embryo telencephalons (embryonic day 13) and induced to proliferation in the presence of growth factors (GFs). For gathering insights into the biological effects of resveratrol (RSV) on neurogenesis, this study aimed to investigate effects of RSV concentrations (0.1 to 100 μM) on proliferation, migration and differentiation of NPCs infected by T. gondii. T. gondii infection increased the presence of cells in Sub G1 phase, reducing the global frequency of undifferentiated cells in S and G2/M phases of cell cycle and reduced cell viability/mithochondrial activity of infected NPCs. Moreover T. gondii stimulated neural migration and gliogenesis during neutral differentation. However, the treatment with RSV stimulated cell proliferation, restored cellular viability of infected NPCs and exerted an inhibitory effect on gliogenesis of infected NPCs favorecing neuronal maturation during toxoplasmosis infection. Thus, we have successfully to demonstrated that RSV is promising as therapeutic for congenital toxoplasmosis.

Human mutations in integrator complex subunits link transcriptome integrity to brain development

Integrator is an RNA polymerase II (RNAPII)-associated complex that was recently identified to have a broad role in both RNA processing and transcription regulation. Importantly, its role in human development and disease is so far largely unexplored. Here, we provide evidence that biallelic Integrator Complex Subunit 1 (INTS1) and Subunit 8 (INTS8) gene mutations are associated with rare recessive human neurodevelopmental syndromes. Three unrelated individuals of Dutch ancestry showed the same homozygous truncating INTS1 mutation. Three siblings harboured compound heterozygous INTS8 mutations. Shared features by these six individuals are severe neurodevelopmental delay and a distinctive appearance. The INTS8 family in addition presented with neuronal migration defects (periventricular nodular heterotopia). We show that the first INTS8 mutation, a nine base-pair deletion, leads to a protein that disrupts INT complex stability, while the second missense mutation introduces an alternative splice site leading to an unstable messenger. Cells from patients with INTS8 mutations show increased levels of unprocessed UsnRNA, compatible with the INT function in the 3’-end maturation of UsnRNA, and display significant disruptions in gene expression and RNA processing. Finally, the introduction of the INTS8 deletion mutation in P19 cells using genome editing alters gene expression throughout the course of retinoic acid-induced neural differentiation. Altogether, our results confirm the essential role of Integrator to transcriptome integrity and point to the requirement of the Integrator complex in human brain development.

Neurodevelopmental disorders often have a genetic cause, however the genes and the underlying mechanisms that are involved are increasingly diverse, pointing to the complexity of brain development. For normal cell function and in general for normal development, mechanisms that regulate gene transcription into mRNA are of outermost importance as proper spatial and temporal expression of key developmentally regulated transcripts is essential. The Integrator complex was recently identified to have a broad role in both RNA processing and transcription regulation. This complex is assembled from at least 14 different subunits and several animal studies have pointed to an important role in development. Nevertheless, studies directly demonstrating the relevance of this complex in human health and development have been lacking until now. We show here that mutations in the Integrator Complex Subunit 1 gene (INTS1) and Subunit 8 gene (INTS8) cause a severe neurodevelopmental syndrome, characterized by profound intellectual disability, epilepsy, spasticity, facial and limb dysmorphism and subtle structural brain abnormalities. While the role of the Integrator complex in neuronal migration has recently been established, we provide evidence that INTS8 mutations lead in vitro to instability of the complex and impaired function. In patients cultured fibroblasts we found evidence for abnormalities in mRNA transcription and processing. In addition, introduction of INTS8 mutations in an in vitro model of retinoic acid-induced neuronal differentiation results also in transcription alterations. Altogether our results suggest an evolutionary conserved requirement of INTS1 and INTS8 in brain development.

Apigenin-induced lysosomal degradation of β-catenin in Wnt/β-catenin signaling

The bioflavonoid apigenin has been shown to possess cancer-preventive and anti-cancer activities. In a drug screening, we found that apigenin can inhibit Wnt/β-catenin signaling, a pathway that participates in pivotal biological functions, which dis-regulation results in various human diseases including cancers. However, the underlying mechanism of apigenin in this pathway and its link to anti-cancer activities remain largely unknown. Here we showed that apigenin reduced the amount of total, cytoplasmic, and nuclear β-catenin, leading to the suppression in the β-catenin/TCF-mediated transcriptional activity, the expression of Wnt target genes, and cell proliferation of Wnt-stimulated P19 cells and Wnt-driven colorectal cancer cells. Western blotting and immunofluorescent staining analyses further revealed that apigenin could induce autophagy-mediated down-regulation of β-catenin in treated cells. Treatment with autophagy inhibitors wortmannin and chloroquine compromised this effect, substantiating the involvement of autophagy-lysosomal system on the degradation of β-catenin during Wnt signaling through inhibition of the AKT/mTOR signaling pathway. Our data not only pointed out a route for the inhibition of canonical Wnt signaling through the induction of autophagy-lysosomal degradation of key player β-catenin, but also suggested that apigenin or other treatments which can initiate this degradation event are potentially used for the therapy of Wnt-related diseases including cancers.

Paraoxon and Pyridostigmine Interfere with Neural Stem Cell Differentiation

Acetylcholinesterase (AChE) inhibition has been described as the main mechanism of organophosphate (OP)-evoked toxicity. OPs represent a human health threat, because chronic exposure to low doses can damage the developing brain, and acute exposure can produce long-lasting damage to adult brains, despite post-exposure medical countermeasures. Although the main mechanism of OP toxicity is AChE inhibition, several lines of evidence suggest that OPs also act by other mechanisms. We hypothesized that rat neural progenitor cells extracted on embryonic day 14.5 would be affected by constant inhibition of AChE from chronic exposure to OP or pyridostigmine (a reversible AChE blocker) during differentiation. In this work, the OP paraoxon decreased cell viability in concentrations >50 μM, as measured with the MTT assay; however, this effect was not dose-dependent. Reduced viability could not be attributed to blockade of AChE activity, since treatment with 200 µM pyridostigmine did not affect cell viability, even after 6 days. Although changes in protein expression patterns were noted in both treatments, the distribution of differentiated phenotypes, such as the percentages of neurons and glial cells, was not altered, as determined by flow cytometry. Since paraoxon and pyridostigmine each decreased neurite outgrowth (but did not prevent differentiation), we infer that developmental patterns may have been affected.

3D in vitro modeling of the central nervous system

There are currently more than 600 diseases characterized as affecting the central nervous system (CNS) which inflict neural damage. Unfortunately, few of these conditions have effective treatments available. Although significant efforts have been put into developing new therapeutics, drugs which were promising in the developmental phase have high attrition rates in late stage clinical trials. These failures could be circumvented if current 2D in vitro and in vivo models were improved. 3D, tissue-engineered in vitro systems can address this need and enhance clinical translation through two approaches: (1) bottom-up, and (2) top-down (developmental/regenerative) strategies to reproduce the structure and function of human tissues. Critical challenges remain including biomaterials capable of matching the mechanical properties and extracellular matrix (ECM) composition of neural tissues, compartmentalized scaffolds that support heterogeneous tissue architectures reflective of brain organization and structure, and robust functional assays for in vitro tissue validation. The unique design parameters defined by the complex physiology of the CNS for construction and validation of 3D in vitro neural systems are reviewed here.

KSRP silencing favors neural differentiation of P19 teratocarcinoma cells

Understanding the molecular mechanisms that control the balance between multipotency and differentiation is of great importance to elucidate the genesis of both developmental disorders and cell transformation events. To investigate the role of the RNA binding protein KSRP in controlling neural differentiation, we used the P19 embryonal carcinoma cell line that is able to differentiate into neuron-like cells under appropriate culture conditions. We have recently reported that KSRP controls the differentiative fate of multipotent mesenchymal cells owing to its ability to promote decay of unstable transcripts and to favor maturation of selected micro-RNAs (miRNAs) from precursors. Here we report that KSRP silencing in P19 cells favors neural differentiation increasing the expression of neuronal markers. Further, the expression of two master transcriptional regulators of neurogenesis, ASCL1 and JMJD3, was enhanced while the maturation of miR-200 family members from precursors was impaired in KSRP knockdown cells. These molecular changes can contribute to the reshaping of P19 cells transcriptome that follows KSRP silencing. Our data suggests that KSRP function is required to maintain P19 cells in a multipotent undifferentiated state and that its inactivation can orient cells towards neural differentiation.

Kinin-B2 receptor activity determines the differentiation fate of neural stem cells

Bradykinin is not only important for inflammation and blood pressure regulation, but also involved in neuromodulation and neuroprotection. Here we describe novel functions for bradykinin and the kinin-B2 receptor (B2BkR) in differentiation of neural stem cells. In the presence of the B2BkR antagonist HOE-140 during rat neurosphere differentiation, neuron-specific β3-tubulin and enolase expression was reduced together with an increase in glial protein expression, indicating that bradykinin-induced receptor activity contributes to neurogenesis. In agreement, HOE-140 affected in the same way expression levels of neural markers during neural differentiation of murine P19 and human iPS cells. Kinin-B1 receptor agonists and antagonists did not affect expression levels of neural markers, suggesting that bradykinin-mediated effects are exclusively mediated via B2BkR. Neurogenesis was augmented by bradykinin in the middle and late stages of the differentiation process. Chronic treatment with HOE-140 diminished eNOS and nNOS as well as M1-M4 muscarinic receptor expression and also affected purinergic receptor expression and activity. Neurogenesis, gliogenesis, and neural migration were altered during differentiation of neurospheres isolated from B2BkR knock-out mice. Whole mount in situ hybridization revealed the presence of B2BkR mRNA throughout the nervous system in mouse embryos, and less β3-tubulin and more glial proteins were expressed in developing and adult B2BkR knock-out mice brains. As a underlying transcriptional mechanism for neural fate determination, HOE-140 induced up-regulation of Notch1 and Stat3 gene expression. Because pharmacological treatments did not affect cell viability and proliferation, we conclude that bradykinin-induced signaling provides a switch for neural fate determination and specification of neurotransmitter receptor expression.