Targeted transgene expression in neuronal precursors: watching young neurons in the old brain

Single-cell RNA sequencing of aging neural progenitors reveals loss of excitatory neuron potential and a population with transcriptional immune response

In the adult murine brain, neural stem cells (NSCs) can be found in two main niches: the dentate gyrus (DG) and the subventricular zone (SVZ). In the DG, NSCs produce intermediate progenitors (IPs) that differentiate into excitatory neurons, while progenitors in the SVZ migrate to the olfactory bulb (OB), where they mainly differentiate into inhibitory interneurons. Neurogenesis, the process of generating new neurons, persists throughout life but decreases dramatically with aging, concomitantly with increased inflammation. Although many cell types, including microglia, undergo significant transcriptional changes, few such changes have been detected in neural progenitors. Furthermore, transcriptional profiles in progenitors from different neurogenic regions have not been compared on a single-cell level, and little is known about how they are affected by aging-related inflammation. We have generated a single cell RNA sequencing dataset enriched for IPs, which revealed that most aged neural progenitors only acquire minor transcriptional changes. However, progenitors set to become excitatory neurons decrease faster than others. In addition, a population in the aged SVZ, not detected in the OB, acquired major transcriptional activation related to immune responses. This suggests that differences in age related neurogenic decline between regions is not due to tissue differences but rather cell type specific intrinsic transcriptional programs, and that subset of neuroblasts in the SVZ react strongly to age related inflammatory cues.

The awakening of dormant neuronal precursors in the adult and aged brain

Beyond the canonical neurogenic niches, there are dormant neuronal precursors in several regions of the adult mammalian brain. Dormant precursors maintain persisting post-mitotic immaturity from birth to adulthood, followed by staggered awakening, in a process that is still largely unresolved. Strikingly, due to the slow rate of awakening, some precursors remain immature until old age, which led us to question whether their awakening and maturation are affected by aging. To this end, we studied the maturation of dormant precursors in transgenic mice (DCX-CreERT2 /flox-EGFP) in which immature precursors were labelled permanently in vivo at different ages. We found that dormant precursors are capable of awakening at young age, becoming adult-matured neurons (AM), as well as of awakening at old age, becoming late AM. Thus, protracted immaturity does not prevent late awakening and maturation. However, late AM diverged morphologically and functionally from AM. Moreover, AM were functionally most similar to neonatal-matured neurons (NM). Conversely, late AM were endowed with high intrinsic excitability and high input resistance, and received a smaller amount of spontaneous synaptic input, implying their relative immaturity. Thus, late AM awakening still occurs at advanced age, but the maturation process is slow.

Influence of Chronic Electroconvulsive Seizures on Plasticity-Associated Gene Expression and Perineuronal Nets Within the Hippocampi of Young Adult and Middle-Aged Sprague-Dawley Rats

BACKGROUND

Electroconvulsive seizure therapy is often used in both treatment-resistant and geriatric depression. However, preclinical studies identifying targets of chronic electroconvulsive seizure (ECS) are predominantly focused on animal models in young adulthood. Given that putative transcriptional, neurogenic, and neuroplastic mechanisms implicated in the behavioral effects of chronic ECS themselves exhibit age-dependent modulation, it remains unknown whether the molecular and cellular targets of chronic ECS vary with age.

METHODS

We subjected young adult (2-3 months) and middle-aged (12-13 months), male Sprague Dawley rats to sham or chronic ECS and assessed for despair-like behavior, hippocampal gene expression, hippocampal neurogenesis, and neuroplastic changes in the extracellular matrix, reelin, and perineuronal net numbers.

RESULTS

Chronic ECS reduced despair-like behavior at both ages, accompanied by overlapping and unique changes in activity-dependent and trophic factor gene expression. Although chronic ECS had a similar impact on quiescent neural progenitor numbers at both ages, the eventual increase in hippocampal progenitor proliferation was substantially higher in young adulthood. We noted a decline in reelin⁺ cell numbers following chronic ECS only in young adulthood. In contrast, an age-invariant, robust dissolution of perineuronal net numbers that encapsulate parvalbumin⁺ neurons in the hippocampus were observed following chronic ECS.

CONCLUSION

Our findings indicate that age is a key variable in determining the nature of chronic ECS-evoked molecular and cellular changes in the hippocampus. This raises the intriguing possibility that chronic ECS may recruit distinct, as well as overlapping, mechanisms to drive antidepressant-like behavioral changes in an age-dependent manner.

Direct FACS Isolation of Neural Stem/Progenitor Lineages from the Adult Brain

Adult neural stem and progenitor cells reside in the neurogenic niche of the adult brain and have tremendous potential in regenerative medicine. Compelling evidence suggests that adult neurogenesis plays an important role in hippocampal memory formation, plasticity, and mood regulation. Understanding the mechanisms that regulate the function of neural stem/progenitor cells within the brain is a critical step for the development of regenerative strategies to maintain or enhance neurological function. A major challenge in studying these cells is the limited cell number of adult neural stem cells, and the significant changes in their properties induced by in vitro culture and expansion. To best understand the regulation of these cells, they must be studied within their niche context. In this chapter, we provide a simplified protocol for the harvest and isolation of neural stem cell lineages directly from the murine brain, to provide input material for single-cell RNA-seq. This approach will elucidate the true transcriptional signatures and activated pathways in neural stem cell lineages, within the context of their niche environment.

Sparsification of AP firing in adult-born hippocampal granule cells via voltage-dependent α5-GABAA receptors

GABA can depolarize immature neurons close to the action potential (AP) threshold in development and adult neurogenesis. Nevertheless, GABAergic synapses effectively inhibit AP firing in newborn granule cells of the adult hippocampus as early as two weeks post-mitosis. The underlying mechanisms are largely unclear. Here, we analyze GABAergic inputs in newborn hippocampal granule cells mediated by soma-targeting parvalbumin and dendrite-targeting somatostatin interneurons. Surprisingly, both interneuron subtypes activate α5-subunit-containing GABA_A receptors (α5-GABA_ARs) in young neurons, showing a nonlinear voltage dependence with increasing conductance around the AP threshold. By contrast, in mature cells, parvalbumin interneurons mediate linear GABAergic synaptic currents lacking α5-subunits, while somatostatin interneurons continue to target nonlinear α5-GABA_ARs. Computational modeling shows that the voltage-dependent amplification of α5-GABA_AR opening in young neurons is crucial for inhibition of AP firing to generate balanced and sparse firing activity, even with depolarized GABA reversal potential.

A critical period of neuronal activity results in aberrant neurogenesis rewiring hippocampal circuitry in a mouse model of epilepsy

In the mammalian hippocampus, adult-born granule cells (abGCs) contribute to the function of the dentate gyrus (DG). Disruption of the DG circuitry causes spontaneous recurrent seizures (SRS), which can lead to epilepsy. Although abGCs contribute to local inhibitory feedback circuitry, whether they are involved in epileptogenesis remains elusive. Here, we identify a critical window of activity associated with the aberrant maturation of abGCs characterized by abnormal dendrite morphology, ectopic migration, and SRS. Importantly, in a mouse model of temporal lobe epilepsy, silencing aberrant abGCs during this critical period reduces abnormal dendrite morphology, cell migration, and SRS. Using mono-synaptic tracers, we show silencing aberrant abGCs decreases recurrent CA3 back-projections and restores proper cortical connections to the hippocampus. Furthermore, we show that GABA-mediated amplification of intracellular calcium regulates the early critical period of activity. Our results demonstrate that aberrant neurogenesis rewires hippocampal circuitry aggravating epilepsy in mice.

Characterization of Hippocampal Adult-borne Granule Cells in a Transient Cerebral Ischemia Model

Long-term consequences of stroke significantly impair the quality of life in a growing population of stroke survivors. Hippocampal adult neurogenesis has been hypothesized to play a role in the pathophysiology of cognitive and neuropsychiatric long-term sequelae of stroke. Reliable animal models of stroke are paramount to understanding their biomechanisms and to advancing therapeutic strategies. We present a detailed protocol of a transient cerebral ischemia model which does not cause direct ischemic damage in the hippocampus, allowing investigations into the pathophysiology of long-term neurocognitive deficits of stroke. Furthermore, we describe a protocol for obtaining acute hippocampal slices for the purpose of electrophysiological and morphological characterization of adult-borne granule cells. Particularities relating to performing electrophysiological recordings from small cells, such as immature adult-borne granule cells, are also discussed. The present protocol may be complemented by multi-modal investigations (behavioral, morpho-structural, biochemical), to hopefully facilitate research and advances into the long-term sequelae of stroke and the discovery of new therapeutic opportunities.

DCX+ neuronal progenitors contribute to new oligodendrocytes during remyelination in the hippocampus

A pool of different types of neural progenitor cells resides in the adult hippocampus. Apart from doublecortin-expressing (DCX⁺) neuronal progenitor cells (NPCs), the hippocampal parenchyma also contains oligodendrocyte precursor cells (OPCs), which can differentiate into myelinating oligodendrocytes. It is not clear yet to what extent the functions of these different progenitor cell types overlap and how plastic these cells are in response to pathological processes. The aim of this study was to investigate whether hippocampal DCX⁺ NPCs can generate new oligodendrocytes under conditions in which myelin repair is required. For this, the cell fate of DCX-expressing NPCs was analyzed during cuprizone-induced demyelination and subsequent remyelination in two regions of the hippocampal dentate gyrus of DCX-CreER^T2/Flox-EGFP transgenic mice. In this DCX reporter model, the number of GFP⁺ NPCs co-expressing Olig2 and CC1, a combination of markers typically found in mature oligodendrocytes, was significantly increased in the hippocampal DG during remyelination. In contrast, the numbers of GFP⁺PDGFRα⁺ cells, as well as their proliferation, were unaffected by de- or remyelination. During remyelination, a higher portion of newly generated BrdU-labeled cells were GFP⁺ NPCs and there was an increase in new oligodendrocytes derived from these proliferating cells (GFP⁺Olig2⁺BrdU⁺). These results suggest that DCX-expressing NPCs were able to contribute to the generation of mature oligodendrocytes during remyelination in the adult hippocampus.

The X-linked intellectual disability gene product and E3 ubiquitin ligase KLHL15 degrades doublecortin proteins to constrain neuronal dendritogenesis

Proper brain development and function requires finely controlled mechanisms for protein turnover, and disruption of genes involved in proteostasis is a common cause of neurodevelopmental disorders. Kelch-like 15 (KLHL15) is a substrate adaptor for cullin3-containing E3 ubiquitin ligases, and KLHL15 gene mutations were recently described as a cause of severe X-linked intellectual disability. Here, we used a bioinformatics approach to identify a family of neuronal microtubule-associated proteins as KLHL15 substrates, which are themselves critical for early brain development. We biochemically validated doublecortin (DCX), also an X-linked disease protein, and doublecortin-like kinase 1 and 2 as bona fide KLHL15 interactors and mapped KLHL15 interaction regions to their tandem DCX domains. Shared with two previously identified KLHL15 substrates, a FRY tripeptide at the C-terminal edge of the second DCX domain is necessary for KLHL15-mediated ubiquitination of DCX and doublecortin-like kinase 1 and 2 and subsequent proteasomal degradation. Conversely, silencing endogenous KLHL15 markedly stabilizes these DCX domain-containing proteins and prolongs their half-life. Functionally, overexpression of KLHL15 in the presence of WT DCX reduces dendritic complexity of cultured hippocampal neurons, whereas neurons expressing FRY-mutant DCX are resistant to KLHL15. Collectively, our findings highlight the critical importance of the E3 ubiquitin ligase adaptor KLHL15 in proteostasis of neuronal microtubule-associated proteins and identify a regulatory network important for development of the mammalian nervous system.

Proliferation, Adult Neuronal Stem Cells and Cells Migration in Pallium during Constitutive Neurogenesis and after Traumatic Injury of Telencephalon of Juvenile Masu Salmon, Oncorhynchus masou

A study of the lateral pallium in zebrafish and the visual tectum of the medaka revealed a population of adult neuroepithelial (NE) cells supported from the early stage of development to various postembryonic stages of ontogenesis. These data emphasize the importance of non-radial glial stem cells in the neurogenesis of adult animals, in particular fish. However, the distribution, cell cycle features, and molecular markers of NE cells and glial progenitors in fish are still poorly understood at the postembryonic stages of ontogenesis. Fetalization predominates in the ontogenetic development of salmon fish, which is associated with a delay in development and preservation of the features of the embryonic structure of the brain during the first year of life. In the present work, we studied the features of proliferation and the migration of neuronal precursors in the pallial proliferative zone of juvenile Oncorhynchus masou. The aim of the study is a comparative analysis of the distribution of glial-type aNSCs markers, such as vimentin and glial fibrillar acid protein GFAP, as well as the proliferation marker BrdU and migratory neuronal precursor doublecortin, in the pallial zone of the intact telencephalon in juvenile O. masou normal and after mechanical injury. The immunohistochemical IHC labeling with antibodies to vimentin, GFAP and doublecortin in the pallium of intact fish revealed single, small, round and oval immunopositive cells, that correspond to a persistent pool of neuronal and/or glial progenitors. After the injury, heterogeneous cell clusters, radial glia processes, single and small intensely labeled GFAP+ cells in the parenchyma of Dd and lateral part of pallium (Dl) appeared, corresponding to reactive neurogenic niches containing glial aNSCs. A multifold increase in the pool of Vim+ neuronal precursor cells (NPCs) resulting from the injury was observed. Vim+ cells of the neuroepithelial type in Dd and Dm and cells of the glial type were identified in Dl after the injury. Doublecortine (Dc) immunolabeling after the injury revealed the radial migration of neuroblasts into Dm from the neurogenic zone of the pallium. The appearance of intensely labeled Dc+ cells in the brain parenchyma might indicate the activation of resident aNSCs as a consequence of the traumatic process.

Functional Integration of Neuronal Precursors in the Adult Murine Piriform Cortex

The extent of functional maturation and integration of nonproliferative neuronal precursors, becoming neurons in the adult murine piriform cortex, is largely unexplored. We thus questioned whether precursors eventually become equivalent to neighboring principal neurons or whether they represent a novel functional network element. Adult brain neuronal precursors and immature neurons (complex cells) were labeled in transgenic mice (DCX-DsRed and DCX-CreERT2 /flox-EGFP), and their cell fate was characterized with patch clamp experiments and morphometric analysis of axon initial segments. Young (DCX+) complex cells in the piriform cortex of 2- to 4-month-old mice received sparse synaptic input and fired action potentials at low maximal frequency, resembling neonatal principal neurons. Following maturation, the synaptic input detected on older (DCX-) complex cells was larger, but predominantly GABAergic, despite evidence of glutamatergic synaptic contacts. Furthermore, the rheobase current of old complex cells was larger and the maximal firing frequency was lower than those measured in neighboring age-matched principal neurons. The striking differences between principal neurons and complex cells suggest that the latter are a novel type of neuron and new coding element in the adult brain rather than simple addition or replacement for preexisting network components.

Surface-Directed Structural Transition of Amyloidogenic Aggregates and the Resulting Neurotoxicity

The transition of amyloidogenic species into ordered structures (i.e., prefibrillar oligomers, protofibrils, mature fibrils, and amyloidogenic aggregates) is closely associated with many neurodegenerative disease pathologies. It is increasingly appreciated that the liquid-solid interface contributes to peptide aggregation under physiological conditions. However, much remains to be explored on the molecular mechanism of surface-directed amyloid formation. We herein demonstrate that physical environmental conditions (i.e., negatively charged surface) affect amyloid formation. Nontoxic amyloid aggregates quickly develop into intertwisting fibrils on a negatively charged mica surface. These fibrillar structures show significant cytotoxicity on both neuroblastoma cell-lines (SH-SY5Y) and primary neural stem cells. Our results suggest an alternative amyloid development pathway, following which Aβ peptides form large amyloidogenic aggregates upon stimulation, and later transit into neurotoxic fibrillar structures while being trapped and aligned by a negatively charged surface. Conceivably, the interplay between chemical and physical environmental conditions plays important roles in the development of neurodegenerative diseases.

Cellular Plasticity in the Adult Murine Piriform Cortex: Continuous Maturation of Dormant Precursors Into Excitatory Neurons

Neurogenesis in the healthy adult murine brain is based on proliferation and integration of stem/progenitor cells and is thought to be restricted to 2 neurogenic niches: the subventricular zone and the dentate gyrus. Intriguingly, cells expressing the immature neuronal marker doublecortin (DCX) and the polysialylated-neural cell adhesion molecule reside in layer II of the piriform cortex. Apparently, these cells progressively disappear along the course of ageing, while their fate and function remain unclear. Using DCX-CreER^T2/Flox-EGFP transgenic mice, we demonstrate that these immature neurons located in the murine piriform cortex do not vanish in the course of aging, but progressively resume their maturation into glutamatergic (TBR1⁺, CaMKII⁺) neurons. We provide evidence for a putative functional integration of these newly differentiated neurons as indicated by the increase in perisomatic puncta expressing synaptic markers, the development of complex apical dendrites decorated with numerous spines and the appearance of an axonal initial segment. Since immature neurons found in layer II of the piriform cortex are generated prenatally and devoid of proliferative capacity in the postnatal cortex, the gradual maturation and integration of these cells outside of the canonical neurogenic niches implies that they represent a valuable, but nonrenewable reservoir for cortical plasticity.

Ultra-multiplexed analysis of single-cell dynamics reveals logic rules in differentiation

Dynamical control of cellular microenvironments is highly desirable to study complex processes such as stem cell differentiation and immune signaling. We present an ultra-multiplexed microfluidic system for high-throughput single-cell analysis in precisely defined dynamic signaling environments. Our system delivers combinatorial and time-varying signals to 1500 independently programmable culture chambers in week-long live-cell experiments by performing nearly 106 pipetting steps, where single cells, two-dimensional (2D) populations, or 3D neurospheres are chemically stimulated and tracked. Using our system and statistical analysis, we investigated the signaling landscape of neural stem cell differentiation and discovered "cellular logic rules" that revealed the critical role of signal timing and sequence in cell fate decisions. We find synergistic and antagonistic signal interactions and show that differentiation pathways are highly redundant. Our system allows dissection of hidden aspects of cellular dynamics and enables accelerated biological discovery.

Morozova-Roche L, Zhang C. HEWL interacts with dissipated oleic acid micelles, and decreases oleic acid cytotoxicity

Senile plaques are well-known hallmarks of Alzheimer's Diseases (AD). However, drugs targeting tangles of the protein tau and plaques of β-amyloid have no significant effect on disease progression, and the studies on the underlying mechanism of AD remain in high demand. Growing evidence supports the protective role of senile plaques in local inflammation driven by S100A9. We herein demonstrate that oleic acid (OA) micelles interact with hen egg white lysozyme (HEWL) and promote its amyloid formation. Consequently, SH-SY5Y cell line and mouse neural stem cells are rescued from OA toxicity by co-aggregation of OA and HEWL. Using atomic force microscopy in combination with fluorescence microscopy, we revealed that HEWL forms round-shaped aggregates in the presence of OA micelles instead of protofibrils of HEWL alone. These HEWL amyloids act as a sink for toxic OA micelles and their co-aggregate form large clumps, suggesting a protective function in amyloid and OA cytotoxicity.

Stroke Accelerates and Uncouples Intrinsic and Synaptic Excitability Maturation of Mouse Hippocampal DCX+ Adult-Born Granule Cells

Stroke robustly stimulates adult neurogenesis in the hippocampal dentate gyrus. It is currently unknown whether this process induces beneficial or maladaptive effects, but morphological and behavioral studies have reported aberrant neurogenesis and impaired hippocampal-dependent memory following stroke. However, the intrinsic function and network incorporation of adult-born granule cells (ABGCs) after ischemia is unclear. Using patch-clamp electrophysiology, we evaluated doublecortin-positive (DCX⁺) ABGCs as well as DCX^- dentate gyrus granule cells 2 weeks after a stroke or sham operation in DCX/DsRed transgenic mice of either sex. The developmental status, intrinsic excitability, and synaptic excitability of ABGCs were accelerated following stroke, while dendritic morphology was not aberrant. Regression analysis revealed uncoupled development of intrinsic and network excitability, resulting in young, intrinsically hyperexcitable ABGCs receiving disproportionately large glutamatergic inputs. This aberrant functional maturation in the subgroup of ABGCs in the hippocampus may contribute to defective hippocampal function and increased seizure susceptibility following stroke.SIGNIFICANCE STATEMENT Stroke increases hippocampal neurogenesis but the functional consequences of the postlesional response is mostly unclear. Our findings provide novel evidence of aberrant functional maturation of newly generated neurons following stroke. We demonstrate that stroke not only causes an accelerated maturation of the intrinsic and synaptic parameters of doublecortin-positive, new granule cells in the hippocampus, but that this accelerated development does not follow physiological dynamics due to uncoupled intrinsic and synaptic maturation. Hyperexcitable immature neurons may contribute to disrupted network integration following stroke.

Integrity of Cajal-Retzius cells in the reeler-mouse hippocampus

Cajal-Retzius (CR) cells are early-born glutamatergic neurons that are primarily known as the early main source of the signal protein Reelin. In the reeler mutant, the absence of Reelin causes severe defects in the radial migration of neurons, resulting in abnormal cortical layering. To date, the exact morphological properties of CR-cells independent of Reelin are unknown. With this in view, we studied the ontogenesis, density, and distribution of CR-cells in reeler mice that were cross-bred with a CXCR4-EGFP reporter mouse line, thus enabling us to clearly identify CR-cells positions in the disorganized hippocampus of the reeler mouse. As evidenced by morphological analysis, differences were found regarding CR-cell distribution and density: generally, we found fewer CR-cells in the developing and adult reeler hippocampus as compared to the hippocampus of wild-type animals (WT); however, in reeler mice, CR-cells were much more closely associated to the hippocampal fissure (HF), resulting in relatively higher local CR-cell densities. This higher local cell density was accompanied by stronger immunoreactivity of the CXCR4 ligand, stroma-derived factor-1 (SDF-1) that is known to regulate CR-cell positioning. Importantly, confocal microscopy indicates an integration of CR-cells into the developing and adult hippocampal network in reeler mice, raising evidence that network integration of CR-cells might be independent of Reelin.

Excitable Adult-Generated GABAergic Neurons Acquire Functional Innervation in the Cortex after Stroke

Ischemic stroke enhances the proliferation of adult-generated precursor cells that ectopically migrate toward the infarct. Studies have correlated precursor cell proliferation and subsequent adult neurogenesis with enhanced stroke recovery, yet it remains unclear whether stroke can generate new neurons capable of functional integration into the injured cortex. Here, using single and bitransgenic reporter mice, we identify spatial and temporal features of a multilineage cellular response to focal ischemia. We reveal that a small population of stroke-induced immature neurons accumulate within the peri-infarct region of the adult sensorimotor cortex, exhibit voltage-dependent conductances, fire action potentials, express GABAergic markers, and receive sparse GABAergic synaptic inputs. Collectively, these findings reveal that GABAergic neurons arising from the lateral ventricle have the capacity to integrate into the stroke-injured cortex, although their limited number and exiguous synaptic integration may limit their ability to participate in stroke recovery.

Early postnatal behavioral, cellular, and molecular changes in models of Huntington disease are reversible by HDAC inhibition

In Huntington disease (HD) gene carriers the disease-causing mutant Huntingtin (mHTT) is already present during early developmental stages, but, surprisingly, HD patients develop clinical symptoms only many years later. While a developmental role of Huntingtin has been described, so far new therapeutic approaches targeting those early neurodevelopmental processes are lacking. Here, we show that behavioral, cellular, and molecular changes associated with mHTT in the postnatal period of genetic animal models of HD can be reverted using low-dose treatment with a histone deacetylation inhibitor. Our findings support a neurodevelopmental basis for HD and provide proof of concept that pre-HD symptoms, including aberrant neuronal differentiation, are reversible by early therapeutic intervention in vivo.

Huntington disease (HD) is an autosomal dominant neurodegenerative disorder caused by expanded CAG repeats in the huntingtin gene (HTT). Although mutant HTT is expressed during embryonic development and throughout life, clinical HD usually manifests later in adulthood. A number of studies document neurodevelopmental changes associated with mutant HTT, but whether these are reversible under therapy remains unclear. Here, we identify very early behavioral, molecular, and cellular changes in preweaning transgenic HD rats and mice. Reduced ultrasonic vocalization, loss of prepulse inhibition, and increased risk taking are accompanied by disturbances of dopaminergic regulation in vivo, reduced neuronal differentiation capacity in subventricular zone stem/progenitor cells, and impaired neuronal and oligodendrocyte differentiation of mouse embryo-derived neural stem cells in vitro. Interventional treatment of this early phenotype with the histone deacetylase inhibitor (HDACi) LBH589 led to significant improvement in behavioral changes and markers of dopaminergic neurotransmission and complete reversal of aberrant neuronal differentiation in vitro and in vivo. Our data support the notion that neurodevelopmental changes contribute to the prodromal phase of HD and that early, presymptomatic intervention using HDACi may represent a promising novel treatment approach for HD.

Running reorganizes the circuitry of one-week-old adult-born hippocampal neurons

Adult hippocampal neurogenesis is an important form of structural and functional plasticity in the mature mammalian brain. The existing consensus is that GABA regulates the initial integration of adult-born neurons, similar to neuronal development during embryogenesis. Surprisingly, virus-based anatomical tracing revealed that very young, one-week-old, new granule cells in male C57Bl/6 mice receive input not only from GABAergic interneurons, but also from multiple glutamatergic cell types, including mature dentate granule cells, area CA1-3 pyramidal cells and mossy cells. Consistently, patch-clamp recordings from retrovirally labeled new granule cells at 7-8 days post retroviral injection (dpi) show that these cells respond to NMDA application with tonic currents, and that both electrical and optogenetic stimulation can evoke NMDA-mediated synaptic responses. Furthermore, new dentate granule cell number, morphology and excitatory synaptic inputs at 7 dpi are modified by voluntary wheel running. Overall, glutamatergic and GABAergic innervation of newly born neurons in the adult hippocampus develops concurrently, and excitatory input is reorganized by exercise.

Silent synapses generate sparse and orthogonal action potential firing in adult-born hippocampal granule cells

In adult neurogenesis young neurons connect to the existing network via formation of thousands of new synapses. At early developmental stages, glutamatergic synapses are sparse, immature and functionally 'silent', expressing mainly NMDA receptors. Here we show in 2- to 3-week-old young neurons of adult mice, that brief-burst activity in glutamatergic fibers is sufficient to induce postsynaptic AP firing in the absence of AMPA receptors. The enhanced excitability of the young neurons lead to efficient temporal summation of small NMDA currents, dynamic unblocking of silent synapses and NMDA-receptor-dependent AP firing. Therefore, early synaptic inputs are powerfully converted into reliable spiking output. Furthermore, due to high synaptic gain, small dendritic trees and sparse connectivity, neighboring young neurons are activated by different distinct subsets of afferent fibers with minimal overlap. Taken together, synaptic recruitment of young neurons generates sparse and orthogonal AP firing, which may support sparse coding during hippocampal information processing.

Distinct Features of Doublecortin as a Marker of Neuronal Migration and Its Implications in Cancer Cell Mobility

Neuronal migration is a critical process in the development of the nervous system. Defects in the migration of the neurons are associated with diseases like lissencephaly, subcortical band heterotopia (SBH), and pachygyria. Doublecortin (DCX) is an essential factor in neurogenesis and mutations in this protein impairs neuronal migration leading to several pathological conditions. Although, DCX is capable of modulating and stabilizing microtubules (MTs) to ensure effective migration, the mechanisms involved in executing these functions remain poorly understood. Meanwhile, there are existing gaps regarding the processes that underlie tumor initiation and progression into cancer as well as the ability to migrate and invade normal cells. Several studies suggest that DCX is involved in cancer metastasis. Unstable interactions between DCX and MTs destabilizes cytoskeletal organization leading to disorganized movements of cells, a process which may be implicated in the uncontrolled migration of cancer cells. However, the underlying mechanism is complex and require further clarification. Therefore, exploring the importance and features known up to date about this molecule will broaden our understanding and shed light on potential therapeutic approaches for the associated neurological diseases. This review summarizes current knowledge about DCX, its features, functions, and relationships with other proteins. We also present an overview of its role in cancer cells and highlight the importance of studying its gene mutations.

Hydrogel-delivered brain-derived neurotrophic factor promotes tissue repair and recovery after stroke

Stroke is the leading cause of adult disability. Systemic delivery of candidate neural repair therapies is limited by the blood-brain barrier and off-target effects. We tested a bioengineering approach for local depot release of BDNF from the infarct cavity for neural repair in chronic periods after stroke. The brain release levels of a hyaluronic acid hydrogel + BDNF were tested in several stroke models in mouse (strains C57Bl/6, DBA) and non-human primate ( Macaca fascicularis) and tracked with MRI. The behavioral recovery effects of hydrogel + BDNF and the effects on tissue repair outcomes were determined. Hydrogel-delivered BDNF diffuses from the stroke cavity into peri-infarct tissue over 3 weeks in two mouse stroke models, compared with 1 week for direct BDNF injection. Hydrogel delivery of BDNF promotes recovery of motor function. Mapping of motor system connections indicates that hydrogel-BDNF induces axonal sprouting within existing cortical and cortico-striatal systems. Pharmacogenetic studies show that hydrogel-BDNF induces the initial migration of immature neurons into the peri-infarct cortex and their long-term survival. In chronic stroke in the non-human primate, hydrogel-released BDNF can be detected up to 2 cm from the infarct, a distance relevant to human functional recovery in stroke. The hydrogel can be tracked by MRI in mouse and primate.

High-Throughput Toxicity and Phenotypic Screening of 3D Human Neural Progenitor Cell Cultures on a Microarray Chip Platform

A 3D cell culture chip was used for high-throughput screening of a human neural progenitor cell line. The differential toxicity of 24 compounds was determined on undifferentiated and differentiating NPCs. Five compounds led to significant differences in IC₅₀ values between undifferentiated and differentiating cultures. This platform has potential use in phenotypic screening to elucidate molecular toxicology on human stem cells.

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Demonstrated chip platform for HTS of protein expression and toxicity of 3D cultures

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Dose-response viability and proliferation of a 24-compound library on human NPC lines

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Assessed differential toxicity between progenitors and differentiating progeny

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Identified five compounds more toxic to undifferentiated progenitors

Early Changes in Hippocampal Neurogenesis in Transgenic Mouse Models for Alzheimer's Disease

Alzheimer's disease (AD) is the most prevalent neurodegenerative disease in the Western world and is characterized by a progressive loss of cognitive functions leading to dementia. One major histopathological hallmark of AD is the formation of amyloid-beta plaques, which is reproduced in numerous transgenic animal models overexpressing pathogenic forms of amyloid precursor protein (APP). In human AD and in transgenic amyloid plaque mouse models, several studies report altered rates of adult neurogenesis, i.e. the formation of new neurons from neural stem and progenitor cells, and impaired neurogenesis has also been attributed to contribute to the cognitive decline in AD. So far, changes in neurogenesis have largely been considered to be a consequence of the plaque pathology. Therefore, possible alterations in neurogenesis before plaque formation or in prodromal AD have been largely ignored. Here, we analysed adult hippocampal neurogenesis in amyloidogenic mouse models of AD at different points before and during plaque progression. We found prominent alterations of hippocampal neurogenesis before plaque formation. Survival of newly generated cells and the production of new neurons were already compromised at this stage. Moreover and surprisingly, proliferation of doublecortin (DCX) expressing neuroblasts was significantly and specifically elevated during the pre-plaque stage in the APP-PS1 model, while the Nestin-expressing stem cell population was unaffected. In summary, changes in neurogenesis are evident already before plaque deposition and might contribute to well-known early hippocampal dysfunctions in prodromal AD such as hippocampal overactivity.

Transgenic mouse models for studying adult neurogenesis

The mammalian hippocampus shows a remarkable capacity for continued neurogenesis throughout life. Newborn neurons, generated by the radial neural stem cells (NSCs), are important for learning and memory as well as mood control. During aging, the number and responses of NSCs to neurogenic stimuli diminish, leading to decreased neurogenesis and age-associated cognitive decline and psychiatric disorders. Thus, adult hippocampal neurogenesis has garnered significant interest because targeting it could be a novel potential therapeutic strategy for these disorders. However, if we are to use neurogenesis to halt or reverse hippocampal-related pathology, we need to understand better the core molecular machinery that governs NSC and their progeny. In this review, we summarize a wide variety of mouse models used in adult neurogenesis field, present their advantages and disadvantages based on specificity and efficiency of labeling of different cell types, and review their contribution to our understanding of the biology and the heterogeneity of different cell types found in adult neurogenic niches.

Lysophosphatidic Acid Receptor Is a Functional Marker of Adult Hippocampal Precursor Cells

Here, we show that the lysophosphatidic acid receptor 1 (LPA₁) is expressed by a defined population of type 1 stem cells and type 2a precursor cells in the adult mouse dentate gyrus. LPA₁, in contrast to Nestin, also marks the quiescent stem cell population. Combining LPA₁-GFP with EGFR and prominin-1 expression, we have enabled the prospective separation of both proliferative and non-proliferative precursor cell populations. Transcriptional profiling of the isolated proliferative precursor cells suggested immune mechanisms and cytokine signaling as molecular regulators of adult hippocampal precursor cell proliferation. In addition to LPA₁ being a marker of this important stem cell population, we also show that the corresponding ligand LPA is directly involved in the regulation of adult hippocampal precursor cell proliferation and neurogenesis, an effect that can be attributed to LPA signaling via the AKT and MAPK pathways.

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LPA₁-GFP⁺ allows the prospective isolation of hippocampal precursor cells

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Method for separation of proliferative from non-proliferative precursor cells

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Proliferative precursor cells have a unique immune-cell-like transcriptional profile

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LPA increases in vivo hippocampal neurogenesis via the LPA₁-AKT and MAPK pathways

Bidirectional GABAergic control of action potential firing in newborn hippocampal granule cells

Newly generated young neurons in the adult hippocampus receive GABAergic synaptic inputs, which are crucial for activity-dependent survival and functional maturation between 1-3 weeks after mitosis. We found synaptically driven action potential (AP) firing in these newborn young cells in adult mice. Although glutamatergic synaptic inputs remained subthreshold, activation of GABAergic synaptic inputs depolarized young neurons and reliably evoked APs. Furthermore, pairing of subthreshold excitatory postsynaptic potentials or somatic current injection with brief bursts of GABAergic inputs revealed efficient GABAergic excitation at conductances of ∼ 1.5 nS, corresponding to the activity of only three or four interneurons. Stronger GABAergic inputs (>4 nS) effectively blocked AP firing via shunting inhibition, which might be important to dynamically control spiking output in both directions. Taken together, GABAergic interneurons differentially recruit newborn young granule cells by supporting either AP generation or shunting inhibition dependent on hippocampal network activity.

Maturation and Functional Integration of New Granule Cells into the Adult Hippocampus

The adult hippocampus generates functional dentate granule cells (GCs) that release glutamate onto target cells in the hilus and cornus ammonis (CA)3 region, and receive glutamatergic and γ-aminobutyric acid (GABA)ergic inputs that tightly control their spiking activity. The slow and sequential development of their excitatory and inhibitory inputs makes them particularly relevant for information processing. Although they are still immature, new neurons are recruited by afferent activity and display increased excitability, enhanced activity-dependent plasticity of their input and output connections, and a high rate of synaptogenesis. Once fully mature, new GCs show all the hallmarks of neurons generated during development. In this review, we focus on how developing neurons remodel the adult dentate gyrus and discuss key aspects that illustrate the potential of neurogenesis as a mechanism for circuit plasticity and function.

Conditional Reduction of Adult Born Doublecortin-Positive Neurons Reversibly Impairs Selective Behaviors

Adult neurogenesis occurs in the adult mammalian subventricular zone (SVZ) along the walls of the lateral ventricles and the subgranular zone (SGZ) of the hippocampal dentate gyrus. While a burgeoning body of research implicates adult neurogenesis in olfactory bulb (OB)- and hippocampal-related behaviors, the precise function continues to elude. To further assess the behavioral importance of adult neurogenesis, we herein generated a novel inducible transgenic mouse model of adult neurogenesis reduction where mice with CreER^T2 under doublecortin (DCX) promoter control were crossed with mice where diphtheria toxin A (DTA) was driven by the Rosa26 promoter. Activation of DTA, through the administration of tamoxifen (TAM), results in a specific reduction of DCX+ immature neurons in both the hippocampal dentate gyrus and OB. We show that the decrease of DCX+ cells causes impaired social discrimination ability in both young adult (from 3 months) and middle aged (from 10 months) mice. Furthermore, these animals showed an age-independent altered coping behavior in the Forced Swim Test without clear changes in anxiety-related behavior. Notably, these behavior changes were reversible on repopulating the neurogenic zones with DCX+ cells on cessation of the TAM treatment, demonstrating the specificity of this effect. Overall, these results support the notion that adult neurogenesis plays a role in social memory and in stress coping but not necessarily in anxiety-related behavior.

RNA interference machinery-mediated gene regulation in mouse adult neural stem cells

Background

Neurogenesis in the brain of adult mammals occurs throughout life in two locations: the subventricular zone of the lateral ventricle and the subgranular zone of the dentate gyrus in the hippocampus. RNA interference mechanisms have emerged as critical regulators of neuronal differentiation. However, to date, little is known about its function in adult neurogenesis.

Results

Here we show that the RNA interference machinery regulates Doublecortin levels and is associated with chromatin in differentiating adult neural progenitors. Deletion of Dicer causes abnormal higher levels of Doublecortin. The microRNA pathway plays an important role in Doublecortin regulation. In particular miRNA-128 overexpression can reduce Doublecortin levels in differentiating adult neural progenitors.

Conclusions

We conclude that the RNA interference components play an important role, even through chromatin association, in regulating neuron-specific gene expression programs.

Electronic supplementary material

The online version of this article (doi:10.1186/s12868-015-0198-7) contains supplementary material, which is available to authorized users.

Molecular Biomarkers for Embryonic and Adult Neural Stem Cell and Neurogenesis

The procedure of neurogenesis has made numerous achievements in the past decades, during which various molecular biomarkers have been emerging and have been broadly utilized for the investigation of embryonic and adult neural stem cell (NSC). Nevertheless, there is not a consistent and systematic illustration to depict the functional characteristics of the specific markers expressed in distinct cell types during the different stages of neurogenesis. Here we gathered and generalized a series of NSC biomarkers emerging during the procedures of embryonic and adult neural stem cell, which may be used to identify the subpopulation cells with distinguishing characters in different timeframes of neurogenesis. The identifications of cell patterns will provide applications to the detailed investigations of diverse developmental cell stages and the extents of cell differentiation, which will facilitate the tracing of cell time-course and fate determination of specific cell types and promote the further and literal discoveries of embryonic and adult neurogenesis. Meanwhile, via the utilization of comprehensive applications under the aiding of the systematic knowledge framework, researchers may broaden their insights into the derivation and establishment of novel technologies to analyze the more detailed process of embryogenesis and adult neurogenesis.

Neurogenesis in the Adult Hippocampus

Of the neurogenic zones in the adult brain, adult hippocampal neurogenesis attracts the most attention, because it is involved in higher cognitive function, most notably memory processes, and certain affective behaviors. Adult hippocampal neurogenesis is also found in humans at a considerable level and appears to contribute significantly to hippocampal plasticity across the life span, because it is regulated by activity. Adult hippocampal neurogenesis generates new excitatory granule cells in the dentate gyrus, whose axons form the mossy fiber tract that links the dentate gyrus to CA3. It originates from a population of radial glia-like precursor cells (type 1 cells) that have astrocytic properties, express markers of neural stem cells and divide rarely. They give rise to intermediate progenitor cells with first glial (type 2a) and then neuronal (type 2b) phenotype. Through a migratory neuroblast-like stage (type 3), the newborn, lineage-committed cells exit the cell cycle and enter a maturation stage, during which they extend their dendrites into a the molecular layer and their axon to CA3. They go through a period of several weeks, during which they show increased synaptic plasticity, before finally becoming indistinguishable from the older granule cells.

Viral and transgenic reporters and genetic analysis of adult neurogenesis

Stem and progenitor cells of the developing and adult brain can be effectively identified and manipulated using reporter genes, introduced into transgenic reporter mouse lines or recombinant viruses. Such reporters rely on an ever-increasing variety of fluorescent proteins and a continuously expanding list of regulatory elements and of mouse lines engineered for cell- or time-specific recombination. An important extension of stem-cell-based genetic strategies is an opportunity to explore the properties of newly generated neurons and their contribution to synaptic plasticity. Here, we review available strategies for marking and quantifying various classes of stem and progenitor cells in the adult brain, genetically tracing their progeny, and studying the properties of stem cells and new neurons. We compare various experimental approaches to labeling and investigating stem cells and their progeny and discuss caveats and limitations inherent to each approach.

Emerging evidence of insulin-like growth factor 2 as a memory enhancer: a unique animal model of cognitive dysfunction with impaired adult neurogenesis

In the current aging society, cognitive dysfunction is one of the most serious issues that should be urgently resolved. It also affects a wide range of age groups harboring neurological and psychiatric disorders, such as Alzheimer's disease and schizophrenia. Although the molecular mechanism of memory impairment still remains to be determined, neuronal loss and dysfunction has been revealed to mainly attribute to its pathology. The discovery of neural stem cells in the adult brain that are proliferating and able to generate functional neurons has given rise to the idea that neuronal loss could be rescued by manipulating endogenous neural progenitor and stem cells. To this end, we must characterize them in detail and their developmental programming must be better understood. A growing body of evidence has indicated that insulin-like peptides are involved in learning and memory and maintenance of neural progenitor and stem cells, and clinical trials of insulin as a memory enhancer have begun. In contrast to the expectation of insulin and IGF1, the roles of IGF2 in cognitive ability have been poorly understood. However, recent evidence demonstrated in rodents suggests that IGF2 may play a pivotal role in adult neurogenesis and cognitive function. Here, we would like to review the rapidly growing world of IGF2 in cognitive neuroscience and introduce the evidence that its deficit is indeed involved in the impairment of the hippocampal neurogenesis and cognitive dysfunction in the model mouse of 22q11.2 deletion syndrome, which deletes Dgcr8, a critical gene for microRNA processing.

Two distinct populations of doublecortin-positive cells in the perilesional zone of cortical infarcts

Background

Recovery following stroke depends on cellular plasticity in the perilesional zone (PZ). Doublecortin (DCX), a protein mainly labeling immature neurons in neurogenic niches is also highly expressed in the vicinity of focal cortical infarcts. Notably, the number of DCX+ cells positively correlates with the recovery of functional deficits after stroke though the nature and origin of these cells remains unclear.

Results

In the present study, we aimed to characterize the population of DCX+ cells in the vicinity of ischemic infarcts in a mouse model in detail. Employing a photothrombosis model, distinct immunohistochemical techniques, stereology and confocal microscopy, we show that: i) DCX+ cells in the perilesional zone do not constitute a homogenous population and two cell types, stellate and polar cells can be distinguished according to their morphology. ii) Stellate cells are mainly located in the lateral and medial vicinity of the insult and express astrocytic markers. iii) Polar cells are found almost exclusively in the corpus callosum region including in the preserved deep cortical layers close to the subventricular zone (SVZ). Further, they do not show any colocalisation of glial markers. Polar morphology and distribution suggest a migration towards the lesion.

Conclusions

In summary, our findings provide evidence that in mice DCX+ cells in the perilesional zone of cortical infarcts comprise a distinct cell population and the majority of cells are of glial nature.

Electronic supplementary material

The online version of this article (doi:10.1186/s12868-015-0160-8) contains supplementary material, which is available to authorized users.

Neurogenesis within the adult hippocampus under physiological conditions and in depression

Adult neurogenesis can only be observed in some specific brain regions. One of these areas is the dentate gyrus of the hippocampal formation. The progenitor cells located in the subgranular layer of the dentate gyrus proliferate, differentiate, and give rise to young neurons that can become integrated into existing neuronal circuits. Under physiological conditions, hippocampal neurogenesis is linked to hippocampal-dependent learning, whereas deficits in adult hippocampal neurogenesis have been shown to correlate with disturbances in spatial learning and memory. This review summarizes the phenomenon of adult hippocampal neurogenesis and the use of suitable markers for the investigation of adult hippocampal neurogenesis. In addition, we focused on the disturbances in neurogenesis that can be seen in depression. Interestingly, several antidepressants have been found to be capable of increasing the rate of hippocampal neurogenesis. Based on that, it can be speculated that factors, which directly or indirectly increase the rate of hippocampal neurogenesis, may be helpful in the treatment of depression.

Role of adult hippocampal neurogenesis in cognition in physiology and disease: pharmacological targets and biomarkers

Adult hippocampal neurogenesis is a remarkable form of brain structural plasticity by which new functional neurons are generated from adult neural stem cells/precursors. Although the precise role of this process remains elusive, adult hippocampal neurogenesis is important for learning and memory and it is affected in disease conditions associated with cognitive impairment, depression, and anxiety. Immature neurons in the adult brain exhibit an enhanced structural and synaptic plasticity during their maturation representing a unique population of neurons to mediate specific hippocampal function. Compelling preclinical evidence suggests that hippocampal neurogenesis is modulated by a broad range of physiological stimuli which are relevant in cognitive and emotional states. Moreover, multiple pharmacological interventions targeting cognition modulate adult hippocampal neurogenesis. In addition, recent genetic approaches have shown that promoting neurogenesis can positively modulate cognition associated with both physiology and disease. Thus the discovery of signaling pathways that enhance adult neurogenesis may lead to therapeutic strategies for improving memory loss due to aging or disease. This chapter endeavors to review the literature in the field, with particular focus on (1) the role of hippocampal neurogenesis in cognition in physiology and disease; (2) extrinsic and intrinsic signals that modulate hippocampal neurogenesis with a focus on pharmacological targets; and (3) efforts toward novel strategies pharmacologically targeting neurogenesis and identification of biomarkers of human neurogenesis.

Characterization of dsRed2-positive cells in the doublecortin-dsRed2 transgenic adult rat retina

Doublecortin (DCX) is predominantly expressed in neuronal precursor cells and young immature neurons of the developing and adult brain, where it is involved in neuronal differentiation, migration and plasticity. Moreover, its expression pattern reflects neurogenesis, and transgenic DCX promoter-driven reporter models have been previously used to investigate adult neurogenesis. In this study, we characterize dsRed2 reporter protein-expressing cells in the adult retina of the transgenic DCX promoter-dsRed2 rat model, with the aim to identify cells with putative neurogenic activity. Additionally, we confirmed the expression of the dsRed2 protein in DCX-expressing cells in the adult hippocampal dentate gyrus. Adult DCX-dsRed2 rat retinas were analyzed by immunohistochemistry for expression of DCX, NF200, Brn3a, Sox2, NeuN, calbindin, calretinin, PKC-a, Otx2, ChAT, PSA-NCAM and the glial markers GFAP and CRALBP, followed by confocal laser-scanning microscopy. In addition, brain sections of transgenic rats were analyzed for dsRed2 expression and co-localization with DCX, NeuN, GFAP and Sox2 in the cortex and dentate gyrus. Endogenous DCX expression in the adult retina was confined to horizontal cells, and these cells co-expressed the DCX promoter-driven dsRed2 reporter protein. In addition, we encountered dsRed2 expression in various other cell types in the retina: retinal ganglion cells (RGCs), a subpopulation of amacrine cells, a minority of bipolar cells and in perivascular cells. Since also RGCs expressed dsRed2, the DCX-dsRed2 rat model might offer a useful tool to study RGCs in vivo under various conditions. Müller glial cells, which have previously been identified as cells with stem cell features and with neurogenic potential, did express neither endogenous DCX nor the dsRed2 reporter. However, and surprisingly, we identified a perivascular glial cell type expressing the dsRed2 reporter, enmeshed with the glia/stem cell marker GFAP and colocalizing with the neural stem cell marker Sox2. These findings suggest the so far undiscovered existence of perivascular associated cell with neural stem cell-like properties in the adult retina.

Hippocampal neurogenesis and antidepressive therapy: shocking relations

Speculations on the involvement of hippocampal neurogenesis, a form of neuronal plasticity, in the aetiology of depression and the mode of action of antidepressive therapies, started to arise more than a decade ago. But still, conclusive evidence that adult neurogenesis contributes to antidepressive effects of pharmacological and physical therapies has not been generated yet. This review revisits recent findings on the close relation between the mode(s) of action of electroconvulsive therapy (ECT), a powerful intervention used as second-line treatment of major depression disorders, and the neurogenic response to ECT. Following application of electroconvulsive shocks, intricate interactions between neurogenesis, angiogenesis, and microglia activation, the hypothalamic-pituitary-adrenal axis and the secretion of neurotrophic factors have been documented. Furthermore, considering the fact that neurogenesis strongly diminishes along aging, we investigated the response to electroconvulsive shocks in young as well as in aged cohorts of mice.

IGF2 ameliorates amyloidosis, increases cholinergic marker expression and raises BMP9 and neurotrophin levels in the hippocampus of the APPswePS1dE9 Alzheimer's disease model mice

The development of an effective therapy for Alzheimer's disease (AD) is a major challenge to biomedical sciences. Because much of early AD pathophysiology includes hippocampal abnormalities, a viable treatment strategy might be to use trophic factors that support hippocampal integrity and function. IGF2 is an attractive candidate as it acts in the hippocampus to enhance memory consolidation, stimulate adult neurogenesis and upregulate cholinergic marker expression and acetylcholine (ACh) release. We performed a seven-day intracerebroventricular infusion of IGF2 in transgenic APPswe.PS1dE9 AD model mice that express green fluorescent protein in cholinergic neurons (APP.PS1/CHGFP) and in wild type WT/CHGFP littermates at 6 months of age representing early AD-like disease. IGF2 reduced the number of hippocampal Aβ40- and Aβ42-positive amyloid plaques in APP.PS1/CHGFP mice. Moreover, IGF2 increased hippocampal protein levels of the ACh-synthesizing enzyme, choline acetyltransferase in both WT/CHGFP and APP.PS1/CHGFP mice. The latter effect was likely mediated by increased protein expression of the cholinergic differentiating factor, BMP9, observed in IGF2-treated mice as compared to controls. IGF2 also increased the protein levels of hippocampal NGF, BDNF, NT3 and IGF1 and of doublecortin, a marker of neurogenesis. These data show that IGF2 administration is effective in reversing and preventing several pathophysiologic processes associated with AD and suggest that IGF2 may constitute a therapeutic target for AD.

Targeted CNS Delivery Using Human MiniPromoters and Demonstrated Compatibility with Adeno-Associated Viral Vectors

Critical for human gene therapy is the availability of small promoter tools to drive gene expression in a highly specific and reproducible manner. We tackled this challenge by developing human DNA MiniPromoters using computational biology and phylogenetic conservation. MiniPromoters were tested in mouse as single-copy knock-ins at the Hprt locus on the X Chromosome, and evaluated for lacZ reporter expression in CNS and non-CNS tissue. Eighteen novel MiniPromoters driving expression in mouse brain were identified, two MiniPromoters for driving pan-neuronal expression, and 17 MiniPromoters for the mouse eye. Key areas of therapeutic interest were represented in this set: the cerebral cortex, embryonic hypothalamus, spinal cord, bipolar and ganglion cells of the retina, and skeletal muscle. We also demonstrated that three retinal ganglion cell MiniPromoters exhibit similar cell-type specificity when delivered via adeno-associated virus (AAV) vectors intravitreally. We conclude that our methodology and characterization has resulted in desirable expression characteristics that are intrinsic to the MiniPromoter, not dictated by copy number effects or genomic location, and results in constructs predisposed to success in AAV. These MiniPromoters are immediately applicable for pre-clinical studies towards gene therapy in humans, and are publicly available to facilitate basic and clinical research, and human gene therapy.

Functional properties of extrasynaptic AMPA and NMDA receptors during postnatal hippocampal neurogenesis

In the mammalian hippocampus, new granule cells are continuously generated throughout life. Although it is well known that they rapidly form several thousand new glutamatergic synapses, the underlying mechanisms are not well understood. As extrasynaptic NMDA receptors are believed to support the generation of new spines, we have studied the functional properties of extrasynaptic ionotropic glutamate receptors in newborn granule cells in juvenile rats during and after synaptic integration. Using the fast application of glutamate to outside-out membrane patches, we show that all immature granule cells express functional AMPA and NMDA receptors. The density of AMPA receptors was small in cells starting to receive excitatory synaptic input (∼30 pS μm(-2)) but substantially increased during synaptic integration to finally reach ∼120 pS μm(-2) in fully mature cells. Interestingly, AMPA receptors showed a biphasic change in desensitization time constant which was slowest during synaptic integration and substantially faster before and afterwards. This was paralleled by a change in the non-desensitizing current component which was maximal during synaptic integration and about 50% smaller afterwards. Surprisingly, the NMDA receptor kinetics and density in young cells was already comparable to mature cells (∼10 pS μm(-2)), leading to an enhanced NMDA/AMPA receptor density ratio. Similar to somatic outside-out patches, iontophoretic application of glutamate onto dendrites also revealed an enhanced dendritic NMDA/AMPA ratio in young cells. These data indicate that prolonged AMPA receptor currents in newly generated young granule cells might support the effective activation of extrasynaptic NMDA receptors and therefore constitute a competitive advantage over mature cells for new synapse formation.

Ageing stem and progenitor cells: implications for rejuvenation of the central nervous system

The growing burden of the rapidly ageing global population has reinvigorated interest in the science of ageing and rejuvenation. Among organ systems, rejuvenation of the central nervous system (CNS) is arguably the most complex and challenging of tasks owing, among other things, to its startling structural and functional complexity and its restricted capacity for repair. Thus, the prospect of meaningful rejuvenation of the CNS has seemed an impossible goal; however, advances in stem cell science are beginning to challenge this assumption. This Review outlines these advances with a focus on ageing and rejuvenation of key endogenous stem and progenitor cell compartments in the CNS. Insights gleaned from studies of model organisms, chiefly rodents, will be considered in parallel with human studies.

Analysis of adult neurogenesis: evidence for a prominent "non-neurogenic" DCX-protein pool in rodent brain

Here, we have developed a highly sensitive immunoassay for Dcx to characterize expression in brain and cerebrospinal fluid (CSF) of rodents. We demonstrate that Dcx is widely expressed during development in various brain regions and as well can be detected in cerebrospinal fluid of rats (up to 30 days postnatal). While Dcx protein level decline in adulthood and were detectable in neurogenic regions of the adult rodent brain, similar levels were also detectable in brain regions expected to bear no neurogenesis including the cerebral cortex and CA1/CA3 enriched hippocampus. We monitored DCX protein levels after paradigms to increase or severely decrease adult hippocampal neurogenesis, namely physical activity and cranial radiation, respectively. In both paradigms, Dcx protein- and mRNA-levels clearly reflected changes in neurogenesis in the hippocampus. However, basal Dcx-levels are unaffected in non-neurogenic regions (e.g. CA1/CA3 enriched hippocampus, cortex). These data suggest that there is a substantial "non-neurogenic" pool of Dcx- protein, whose regulation can be uncoupled from adult neurogenesis suggesting caution for the interpretation of such studies.