Neurogenesis and neuronal migration in the postnatal ventricular-subventricular zone: Similarities and dissimilarities between rodents and primates

Research Advances in Neuroblast Migration in Traumatic Brain Injury

Neuroblasts were first derived from the adult mammalian brains in the 1990s by Reynolds et al. Since then, persistent neurogenesis in the subgranular zone (SGZ) of the hippocampus and subventricular zone (SVZ) has gradually been recognized. To date, reviews on neuroblast migration have largely investigated glial cells and molecular signaling mechanisms, while the relationship between vasculature and cell migration remains a mystery. Thus, this paper underlines the partial biological features of neuroblast migration and unravels the significance and mechanisms of the vasculature in the process to further clarify theoretically the neural repair mechanism after brain injury. Neuroblast migration presents three modes according to the characteristics of cells that act as scaffolds during the migration process: gliophilic migration, neurophilic migration, and vasophilic migration. Many signaling molecules, including brain-derived neurotrophic factor (BDNF), stromal cell-derived factor 1 (SDF-1), vascular endothelial growth factor (VEGF), and angiopoietin-1 (Ang-1), affect vasophilic migration, synergistically regulating the migration of neuroblasts to target areas along blood vessels. However, the precise role of blood vessels in the migration of neuroblasts needs to be further explored. The in-depth study of neuroblast migration will most probably provide theoretical basis and breakthrough for the clinical treatment of brain injury diseases.

Identification of the growth cone as a probe and driver of neuronal migration in the injured brain

Axonal growth cones mediate axonal guidance and growth regulation. We show that migrating neurons in mice possess a growth cone at the tip of their leading process, similar to that of axons, in terms of the cytoskeletal dynamics and functional responsivity through protein tyrosine phosphatase receptor type sigma (PTPσ). Migrating-neuron growth cones respond to chondroitin sulfate (CS) through PTPσ and collapse, which leads to inhibition of neuronal migration. In the presence of CS, the growth cones can revert to their extended morphology when their leading filopodia interact with heparan sulfate (HS), thus re-enabling neuronal migration. Implantation of an HS-containing biomaterial in the CS-rich injured cortex promotes the extension of the growth cone and improve the migration and regeneration of neurons, thereby enabling functional recovery. Thus, the growth cone of migrating neurons is responsive to extracellular environments and acts as a primary regulator of neuronal migration.

Ganglioside GD3 regulates neural stem cell quiescence and controls postnatal neurogenesis

The postnatal neural stem cell (NSC) pool hosts quiescent and activated radial glia-like NSCs contributing to neurogenesis throughout adulthood. However, the underlying regulatory mechanism during the transition from quiescent NSCs to activated NSCs in the postnatal NSC niche is not fully understood. Lipid metabolism and lipid composition play important roles in regulating NSC fate determination. Biological lipid membranes define the individual cellular shape and help maintain cellular organization and are highly heterogeneous in structure and there exist diverse microdomains (also known as lipid rafts), which are enriched with sugar molecules, such as glycosphingolipids. An often overlooked but key aspect is that the functional activities of proteins and genes are highly dependent on their molecular environments. We previously reported that ganglioside GD3 is the predominant species in NSCs and that the reduced postnatal NSC pools are observed in global GD3-synthase knockout (GD3S-KO) mouse brains. The specific roles of GD3 in determining the stage and cell-lineage determination of NSCs remain unclear, since global GD3S-KO mice cannot distinguish if GD3 regulates postnatal neurogenesis or developmental impacts. Here, we show that inducible GD3 deletion in postnatal radial glia-like NSCs promotes NSC activation, resulting in the loss of the long-term maintenance of the adult NSC pools. The reduced neurogenesis in the subventricular zone (SVZ) and the dentate gyrus (DG) of GD3S-conditional-knockout mice led to the impaired olfactory and memory functions. Thus, our results provide convincing evidence that postnatal GD3 maintains the quiescent state of radial glia-like NSCs in the adult NSC niche.

A PrP EGFR signaling axis controls neural stem cell senescence through modulating cellular energy pathways

Mis-folding of the prion protein (PrP) is known to cause neurodegenerative disease; however, the native function of this protein remains poorly defined. PrP has been linked with many cellular functions, including cellular proliferation and senescence. It is also known to influence epidermal growth factor receptor (EGFR) signaling, a pathway that is itself linked with both cell growth and senescence. Adult neural stem cells (NSCs) persist at low levels in the brain throughout life and retain the ability to proliferate and differentiate into new neural lineage cells. KO of PrP has previously been shown to reduce NSC proliferative capacity. We used PrP KO and WT NSCs from adult mouse brain to examine the influence of PrP on cellular senescence, EGFR signaling, and the downstream cellular processes. PrP KO NSCs showed decreased cell proliferation and increased senescence in in vitro cultures. Expression of EGFR was decreased in PrP KO NSCs compared with WT NSCs and additional supplementation of EGF was sufficient to reduce senescence. RNA-seq analysis confirmed that significant changes were occurring at the mRNA level within the EGFR signaling pathway and these were associated with reduced expression of mitochondrial components and correspondingly reduced mitochondrial function. Metabolomic analysis of cellular energy pathways showed that blockages were occurring at critical sites for production of energy and biomass, including catabolism of pyruvate. We conclude that, in the absence of PrP, NSC growth pathways are downregulated as a consequence of insufficient energy and growth intermediates.

Structural plasticity in the entorhinal and perirhinal cortices following hippocampal lesions in rhesus monkeys

Immature neurons expressing the Bcl2 protein are present in various regions of the mammalian brain, including the amygdala and the entorhinal and perirhinal cortices. Their functional role is unknown but we have previously shown that neonatal and adult hippocampal lesions increase their differentiation in the monkey amygdala. Here, we assessed whether hippocampal lesions similarly affect immature neurons in the entorhinal and perirhinal cortices. Since Bcl2-positive cells were found mainly in areas Eo, Er, and Elr of the entorhinal cortex and in layer II of the perirhinal cortex, we also used Nissl-stained sections to determine the number and soma size of immature and mature neurons in layer III of area Er and layer II of area 36 of the perirhinal cortex. We found different structural changes in these regions following hippocampal lesions, which were influenced by the time of the lesion. In neonate-lesioned monkeys, the number of immature neurons in the entorhinal and perirhinal cortices was generally higher than in controls. The number of mature neurons was also higher in layer III of area Er of neonate-lesioned monkeys but no differences were found in layer II of area 36. In adult-lesioned monkeys, the number of immature neurons in the entorhinal cortex was lower than in controls but did not differ from controls in the perirhinal cortex. The number of mature neurons in layer III of area Er did not differ from controls, but the number of small, mature neurons in layer II of area 36 was lower than in controls. In sum, hippocampal lesions impacted populations of mature and immature neurons in discrete regions and layers of the entorhinal and perirhinal cortices, which are interconnected with the amygdala and provide major cortical inputs to the hippocampus. These structural changes may contribute to some functional recovery following hippocampal injury in an age-dependent manner.

Methamphetamine exposure drives cell cycle exit and aberrant differentiation in rat hippocampal-derived neurospheres

Introduction: Methamphetamine (METH) abuse by pregnant drug addicts causes toxic effects on fetal neurodevelopment; however, the mechanism underlying such effect of METH is poorly understood. Methods: In the present study, we applied three-dimensional (3D) neurospheres derived from the embryonic rat hippocampal tissue to investigate the effect of METH on neurodevelopment. Through the combination of whole genome transcriptional analyses, the involved cell signalings were identified and investigated. Results: We found that METH treatment for 24 h significantly and concentration-dependently reduced the size of neurospheres. Analyses of genome-wide transcriptomic profiles found that those down-regulated differentially expressed genes (DEGs) upon METH exposure were remarkably enriched in the cell cycle progression. By measuring the cell cycle and the expression of cell cycle-related checkpoint proteins, we found that METH exposure significantly elevated the percentage of G0/G1 phase and decreased the levels of the proteins involved in the G1/S transition, indicating G0/G1 cell cycle arrest. Furthermore, during the early neurodevelopment stage of neurospheres, METH caused aberrant cell differentiation both in the neurons and astrocytes, and attenuated migration ability of neurospheres accompanied by increased oxidative stress and apoptosis. Conclusion: Our findings reveal that METH induces an aberrant cell cycle arrest and neuronal differentiation, impairing the coordination of migration and differentiation of neurospheres.

Sevoflurane Induces a Cyclophilin D-Dependent Decrease of Neural Progenitor Cells Migration

Clinical studies have suggested that repeated exposure to anesthesia and surgery at a young age may increase the risk of cognitive impairment. Our previous research has shown that sevoflurane can affect neurogenesis and cognitive function in young animals by altering cyclophilin D (CypD) levels and mitochondrial function. Neural progenitor cells (NPCs) migration is associated with cognitive function in developing brains. However, it is unclear whether sevoflurane can regulate NPCs migration via changes in CypD. To address this question, we treated NPCs harvested from wild-type (WT) and CypD knockout (KO) mice and young WT and CypD KO mice with sevoflurane. We used immunofluorescence staining, wound healing assay, transwell assay, mass spectrometry, and Western blot to assess the effects of sevoflurane on CypD, reactive oxygen species (ROS), doublecortin levels, and NPCs migration. We showed that sevoflurane increased levels of CypD and ROS, decreased levels of doublecortin, and reduced migration of NPCs harvested from WT mice in vitro and in WT young mice. KO of CypD attenuated these effects, suggesting that a sevoflurane-induced decrease in NPCs migration is dependent on CypD. Our findings have established a system for future studies aimed at exploring the impacts of sevoflurane anesthesia on the impairment of NPCs migration.

Restoration of Adult Neurogenesis by Intranasal Administration of Gangliosides GD3 and GM1 in The Olfactory Bulb of A53T Alpha-Synuclein-Expressing Parkinson's-Disease Model Mice

Parkinson's disease (PD) is the second most common neurodegenerative disorder affecting the body and mind of millions of people in the world. As PD progresses, bradykinesia, rigidity, and tremor worsen. These motor symptoms are associated with the neurodegeneration of dopaminergic neurons in the substantia nigra. PD is also associated with non-motor symptoms, including loss of smell (hyposmia), sleep disturbances, depression, anxiety, and cognitive impairment. This broad spectrum of non-motor symptoms is in part due to olfactory and hippocampal dysfunctions. These non-motor functions are suggested to be linked with adult neurogenesis. We have reported that ganglioside GD3 is required to maintain the neural stem cell (NSC) pool in the subventricular zone (SVZ) of the lateral ventricles and the subgranular layer of the dentate gyrus (DG) in the hippocampus. In this study, we used nasal infusion of GD3 to restore impaired neurogenesis in A53T alpha-synuclein-expressing mice (A53T mice). Intriguingly, intranasal GD3 administration rescued the number of bromodeoxyuridine + (BrdU +)/Sox2 + NSCs in the SVZ. Furthermore, the administration of gangliosides GD3 and GM1 increases doublecortin (DCX)-expressing immature neurons in the olfactory bulb, and nasal ganglioside administration recovered the neuronal populations in the periglomerular layer of A53T mice. Given the relevance of decreased ganglioside on olfactory impairment, we discovered that GD3 has an essential role in olfactory functions. Our results demonstrated that intranasal GD3 infusion restored the self-renewal ability of the NSCs, and intranasal GM1 infusion promoted neurogenesis in the adult brain. Using a combination of GD3 and GM1 has the potential to slow down disease progression and rescue dysfunctional neurons in neurodegenerative brains.

Repeated administration of acrylamide for 28 days suppresses adult neurogenesis of the olfactory bulb in young-adult rats

Acrylamide (AA) is a neurotoxicant that inhibits synaptic function in distal axons. We previously found that AA decreased neural cell lineages during late-stage differentiation of adult hippocampal neurogenesis and downregulated genes related to neurotrophic factor, neuronal migration, neurite outgrowth, and synapse formation in the hippocampal dentate gyrus in rats. To investigate whether olfactory bulb (OB)-subventricular zone (SVZ) neurogenesis is similarly affected by AA exposure, AA was administered to 7-week-old male rats via oral gavage at doses of 0, 5, 10, and 20 mg/kg for 28 days. Immunohistochemical analysis revealed that AA decreased the numbers of doublecortin-positive ⁽⁺⁾ cells and polysialic acid-neural cell adhesion molecule⁺ cells in the OB. On the other hand, the numbers of doublecortin⁺ cells and polysialic acid-neural cell adhesion molecule⁺ cells in the SVZ did not change with AA exposure, suggesting that AA impaired neuroblasts migrating in the rostral migratory stream and OB. Gene expression analysis in the OB revealed that AA downregulated Bdnf and Ncam2, which are related to neuronal differentiation and migration. These results suggest that AA decreased neuroblasts in the OB by suppressing neuronal migration. Thus, AA decreased neuronal cell lineages during late-stage differentiation of adult neurogenesis in the OB-SVZ, similar to the effect on adult hippocampal neurogenesis.

Chitinase-like protein 3: A novel niche factor for mouse neural stem cells

The concept of a perivascular niche has been proposed for neural stem cells (NSCs). This study examined endothelial colony-forming cell (ECFC)-secreted proteins as potential niche factors for NSCs. Intraventricle infusion with ECFC-secreted proteins increased the number of NSCs. ECFC-secreted proteins were more effective in promoting NSC self-renewal than marrow stromal cell (MSC)-secreted proteins. Differential proteomics analysis of MSC-secreted and ECFC-secreted proteins was performed, which revealed chitinase-like protein 3 (CHIL3; also called ECF-L or Ym1) as a candidate niche factor for NSCs. Experiments with recombinant CHIL3, small interfering RNA, and neutralizing antibodies demonstrated that CHIL3 stimulated NSC self-renewal with neurogenic propensity. CHIL3 was endogenously expressed in the neurogenic niche of the brain and retina as well as in the injured brain and retina. Transcriptome and phosphoproteome analyses revealed that CHIL3 activated various genes and proteins associated with NSC maintenance or neurogenesis. Thus, CHIL3 is a novel niche factor for NSCs.

Water-Soluble, Alanine-Modified Fullerene C60 Promotes the Proliferation and Neuronal Differentiation of Neural Stem Cells

As carbon-based nanomaterials, water-soluble C₆₀ derivatives have potential applications in various fields of biomedicine. In this study, a water-soluble fullerene C₆₀ derivative bearing alanine residues (Ala-C₆₀) was synthesized. The effects of Ala-C₆₀ on neural stem cells (NSCs) as seed cells were explored. Ala-C₆₀ can promote the proliferation of NSCs, induce NSCs to differentiate into neurons, and inhibit the migration of NSCs. Most importantly, the Ala-C₆₀ can significantly increase the cell viability of NSCs treated with hydrogen peroxide (H₂O₂). The glutathioneperoxidase (GSH-Px) and superoxide dismutase (SOD) activities and glutathione (GSH) content increased significantly in NSCs treated even by 20 μM Ala-C₆₀. These findings strongly indicate that Ala-C₆₀ has high potential to be applied as a scaffold with NSCs for regeneration in nerve tissue engineering for diseases related to the nervous system.

Location, Location, Location: The Expression of D3 Dopamine Receptors in the Nervous System

When the rat D3 dopamine receptor (D3R) was cloned and the distribution of its mRNA examined in 1990-1991, it attracted attention due to its peculiar distribution in the brain quite different from that of its closest relative, the D2 receptor. In the rat brain, the D3R mRNA is enriched in the limbic striatum as opposed to the D2 receptor, which is highly expressed in the motor striatal areas. Later studies in the primate and human brain confirmed relative enrichment of the D3R in the limbic striatum but also demonstrated higher abundance of the D3R in the primate as compared to the rodent brain. Additionally, in the rodent brain, the D3R in the dorsal striatum appears to be co-expressed with the D1 dopamine receptor-bearing striatal neurons giving rise to the direct output striatal pathway, although the picture is less clear with respect to the nucleus accumbens. In contrast, in the primate striatum, the D3R co-localizes with the D2 receptor throughout the basal ganglia as well as in extrastriatal brain areas. The relative abundance of the D3R in the limbic striatum, its output structures, secondary targets, and some of the other connected limbic territories may underpin its role in reward, drug dependence, and impulse control. Selective expression of D3R in the brain proliferative areas may point to its important role in the neural development as well as in neurodevelopmental abnormalities associated with schizophrenia and other developmental brain disorders.

Decreased Brain Ventricular Volume in Psychiatric Inpatients with Serotonin Reuptake Inhibitor Treatment

Background

Brain ventricles have been reported to be enlarged in several neuropsychiatric disorders and in aging. Whether human cerebral ventricular volume can decrease over time with psychiatric treatment is not well-studied. The aim of this study was to examine whether inpatients taking serotonin reuptake inhibitors (SRI) exhibited reductions in cerebral ventricular volume.

Methods

Psychiatric inpatients, diagnosed mainly with depression, substance use, anxiety, and personality disorders, underwent two imaging sessions (Time 1 and Time 2, approximately 4 weeks apart). FreeSurfer was used to quantify volumetric features of the brain, and ANOVA was used to analyze ventricular volume differences between Time 1 and Time 2. Inpatients' brain ventricle volumes were normalized by dividing by estimated total intracranial volume (eTIV). Clinical features such as depression and anxiety levels were collected at Time 1, Time 1.5 (approximately 2 weeks apart), and Time 2.

Results

Inpatients consistently taking SRIs (SRI + , n = 44) showed statistically significant reductions of brain ventricular volumes particularly for their left and right lateral ventricular volumes. Reductions in their third ventricular volume were close to significance (p = .068). The inpatients that did not take SRIs (SRI-, n = 25) showed no statistically significant changes in brain ventricular volumes. The SRI + group also exhibited similar brain structural features to the healthy control group based on the 90% confidence interval comparsions on brain ventricular volume parameters, whereas the SRI- group still exhibited relatively enlarged brain ventricular volumes after treatment.

Conclusions

SRI treatment was associated with decreased brain ventricle volume over treatment.

Neuron-Glia Crosstalk Plays a Major Role in the Neurotoxic Effects of Ketamine via Extracellular Vesicles

Background: There is a compelling evidence from animal models that early exposure to clinically relevant general anesthetics (GAs) interferes with brain development, resulting in long-lasting cognitive impairments. Human studies have been inconclusive and are challenging due to numerous confounding factors. Here, we employed primary human neural cells to analyze ketamine neurotoxic effects focusing on the role of glial cells and their activation state. We also explored the roles of astrocyte-derived extracellular vesicles (EVs) and different components of the brain-derived neurotrophic factor (BDNF) pathway.

Methods: Ketamine effects on cell death were analyzed using live/dead assay, caspase 3 activity and PARP-1 cleavage. Astrocytic and microglial cell differentiation was determined using RT-PCR, ELISA and phagocytosis assay. The impact of the neuron-glial cell interactions in the neurotoxic effects of ketamine was analyzed using transwell cultures. In addition, the role of isolated and secreted EVs in this cross-talk were studied. The expression and function of different components of the BDNF pathway were analyzed using ELISA, RT-PCR and gene silencing.

Results: Ketamine induced neuronal and oligodendrocytic cell apoptosis and promoted pro-inflammatory astrocyte (A1) and microglia (M1) phenotypes. Astrocytes and microglia enhanced the neurotoxic effects of ketamine on neuronal cells, whereas neurons increased oligodendrocyte cell death. Ketamine modulated different components in the BDNF pathway: decreasing BDNF secretion in neurons and astrocytes while increasing the expression of p75 in neurons and that of BDNF-AS and pro-BDNF secretion in both neurons and astrocytes. We demonstrated an important role of EVs secreted by ketamine-treated astrocytes in neuronal cell death and a role for EV-associated BDNF-AS in this effect.

Conclusions: Ketamine exerted a neurotoxic effect on neural cells by impacting both neuronal and non-neuronal cells. The BDNF pathway and astrocyte-derived EVs represent important mediators of ketamine effects. These results contribute to a better understanding of ketamine neurotoxic effects in humans and to the development of potential approaches to decrease its neurodevelopmental impact.

β2 and α2 adrenergic receptors mediate the proneurogenic in vitro effects of norquetiapine

Positive modulation of adult hippocampal neurogenesis may contribute to the therapeutic effects of clinically relevant antidepressant drugs, including atypical antipsychotics. Quetiapine, an antipsychotic which represents a therapeutic option in patients who are resistant to classical antidepressants, promotes adult hippocampal neurogenesis in preclinical studies. Norquetiapine, the key active metabolite of quetiapine in humans, has a distinctive receptor profile than the parent compound. The drug is indeed a high affinity norepinephrine transporter inhibitor and such activity has been proposed to contribute to its antidepressant effect. At present, no information is available on the effects of norquetiapine on adult neurogenesis. We extensively investigated the activity of quetiapine and norquetiapine on adult murine neural stem/progenitor cells and their progeny. Additionally, selective antagonists for β₂/α₂ adrenergic receptors allowed us to evaluate if these receptors could mediate quetiapine and norquetiapine effects. We demonstrated that both drugs elicit in vitro proneurogenic effects but also that norquetiapine had distinctive properties which may depend on its ability to inhibit norepinephrine transporter and involve β₂/α₂ adrenergic receptors. Animal care and experimental procedures were approved by the Institutional Animal Care and Use Committees (IACUC) at University of Piemonte Orientale, Italy (approval No. 1033/2015PR) on September 29, 2015.