BMP and WNT signalling cooperate through LEF1 in the neuronal specification of adult hippocampal neural stem and progenitor cells

Multi-omics in MECP2 duplication syndrome patients and carriers

MECP2 duplication syndrome (MDS) is an X-linked neurodevelopmental disorder caused by the gain of dose of at least the genes MECP2 and IRAK1 and is characterised by intellectual disability (ID), developmental delay, hypotonia, epilepsy and recurrent infections. It mainly affects males, and females can be affected or asymptomatic carriers. Rett syndrome (RTT) is mainly triggered by loss of function mutations in MECP2 and is a well described syndrome that presents ID, epilepsy, lack of purposeful hand use and impaired speech, among others. As a result of implementing omics technology, altered biological pathways in human RTT samples have been reported, but such molecular characterisation has not been performed in patients with MDS. We gathered human skin fibroblasts from 17 patients with MDS, 10 MECP2 duplication carrier mothers and 21 patients with RTT, and performed multi-omics (RNAseq and proteomics) analysis. Here, we provide a thorough description and compare the shared and specific dysregulated biological processes between the cohorts. We also highlight the genes TMOD2, SRGAP1, COPS2, CNPY2, IGF2BP1, MOB2, VASP, FZD7, ECSIT and KIF3B as biomarker and therapeutic target candidates due to their implication in neuronal functions. Defining the RNA and protein profiles has shown that our four cohorts are less alike than expected by their shared phenotypes.

Characteristics of quiescent adult neural stem cells induced by the bFGF/BMP4 combination or BMP4 alone in vitro

Bone morphogenetic protein-4 (BMP4) is involved in regulation of neural stem cells (NSCs) proliferation, differentiation, migration and survival. It was previously thought that the treatment of NSCs with BMP4 alone induces astrocytes, whereas the treatment of NSCs with the bFGF/BMP4 combination induces quiescent neural stem cells (qNSCs). In this study, we performed bulk RNA sequencing (RNA-Seq) to compare the transcriptome profiles of BMP4-treated NSCs and bFGF/BMP4-treated NSCs, and found that both NSCs treated by these two methods were Sox2 positive qNSCs which were able to generate neurospheres. However, NSCs treated by those two methods exhibited different characteristics in state and the potential for neuronal differentiation based on transcriptome analysis and experimental results. We found that BMP4-treated NSCs tended to be in a deeper quiescent state than bFGF/BMP4-treated NSCs as the percentage of ki67-positive cells were lower in BMP4-treated NSCs. And after exposure to differentiated environment, bFGF/BMP4-treated NSCs generated more DCX-positive immature neurons and MAP2-positive neurons than BMP4-treated NSCs. Our study characterized qNSCs treated with BMP4 alone and bFGF/BMP4 combination, providing a reference for the scientific use of BMP4 and bFGF/BMP4-induced qNSCs models.

Aucubin Promotes Osteogenic Differentiation and Facilitates Bone Formation through the lncRNA-H19 Driven Wnt/β-Catenin Signaling Regulatory Axis

Objectives

Traditional Chinese medicine Cortex Eucommiae has been used to treat bone fracture for hundreds of years, which exerts a significant improvement in fracture healing. Aucubin, a derivative isolated from Cortex Eucommiae, has been demonstrated to possess anti-inflammatory, immunoregulatory, and antioxidative potential. In the present study, our aim was to explore its function in bone regeneration and elucidate the underlying mechanism.

Materials and Methods

The effects of Aucubin on osteoblast and osteoclast were examined in mouse bone marrow-derived mesenchymal stem cells (BM-MSCs) and RAW 264.7 cells, respectively. Moreover, the lncRNA H19 and Wnt/β-catenin signaling were detected by qPCR examination, western blotting, and luciferase activity assays. Using the femur fracture mice model, the in vivo effect of Aucubin on bone formation was monitored by X-ray, micro-CT, histomorphometry, and immunohistochemistry staining.

Results

In the present study, Aucubin was found to significantly promote osteogenic differentiation in vitro and stimulated bone formation in vivo. Regarding to the underlying mechanism, H19 was found to be obviously upregulated by Aucubin in MSCs and thus induced the activation of Wnt/β-catenin signaling. Moreover, H19 knockdown partially reversed the Aucubin-induced osteogenic differentiation and successfully suppressed the activation of Wnt/β-catenin signaling. We therefore suggested that Aucubin induced the activation of Wnt/β-catenin signaling through promoting H19 expression.

Conclusion

Our results demonstrated that Aucubin promoted osteogenesis in vitro and facilitated fracture healing in vivo through the H19-Wnt/β-catenin regulatory axis.

Mitochondrial metabolism in neural stem cells and implications for neurodevelopmental and neurodegenerative diseases

Mitochondria are cytoplasmic organelles having a fundamental role in the regulation of neural stem cell (NSC) fate during neural development and maintenance.During embryonic and adult neurogenesis, NSCs undergo a metabolic switch from glycolytic to oxidative phosphorylation with a rise in mitochondrial DNA (mtDNA) content, changes in mitochondria shape and size, and a physiological augmentation of mitochondrial reactive oxygen species which together drive NSCs to proliferate and differentiate. Genetic and epigenetic modifications of proteins involved in cellular differentiation (Mechanistic Target of Rapamycin), proliferation (Wingless-type), and hypoxia (Mitogen-activated protein kinase)-and all connected by the common key regulatory factor Hypoxia Inducible Factor-1A-are deemed to be responsible for the metabolic shift and, consequently, NSC fate in physiological and pathological conditions.Both primary mitochondrial dysfunction due to mutations in nuclear DNA or mtDNA or secondary mitochondrial dysfunction in oxidative phosphorylation (OXPHOS) metabolism, mitochondrial dynamics, and organelle interplay pathways can contribute to the development of neurodevelopmental or progressive neurodegenerative disorders.This review analyses the physiology and pathology of neural development starting from the available in vitro and in vivo models and highlights the current knowledge concerning key mitochondrial pathways involved in this process.

mRNA Abundance of Neurogenic Factors Correlates with Hearing Capacity in Auditory Brainstem Nuclei of the Rat

Neural stem cells (NSCs) have previously been described up to the adult stage in the rat cochlear nucleus (CN). A decreasing neurogenic potential was observed with critical changes around hearing onset. A better understanding of molecular factors affecting NSCs and neurogenesis is of interest as they represent potential targets to treat the cause of neurologically based hearing disorders. The role of genes affecting NSC development and neurogenesis in CN over time on hearing capacity has remained unclear. This study investigated the mRNA abundance of genes influencing NSCs and neurogenesis in rats' CN over time. The CN of rats on postnatal days 6, 12, and 24 were examined. Real-time quantitative polymerase chain reaction arrays were used to compare mRNA levels of 84 genes relevant to NSCs and neurogenesis. Age- and hearing-specific patterns of changes in mRNA abundance of neurogenically relevant genes were detected in the rat CN. Additionally, crucial neurogenic factors with significant and relevant influence on neurogenesis were identified. The results of this work should contribute to a better understanding of the molecular mechanisms underlying the neurogenesis of the auditory pathway.

Wif1 Mediates Coordination of Bone Morphogenetic Protein and Wnt Signaling in Neural and Glioma Stem Cells

Wnts, bone morphogenetic protein (BMP), and fibroblast growth factor (FGF) are paracrine signaling pathways implicated in the niche control of stem cell fate decisions. BMP-on and Wnt-off are the dominant quiescent niche signaling pathways in many cell types, including neural stem cells (NSCs). However, among the multiple inhibitory family members of the Wnt pathway, those with direct action after BMP4 stimulation in NSCs remain unclear. We examined 11 Wnt inhibitors in NSCs after BMP4 treatment. Wnt inhibitory factor 1 (Wif1) has been identified as the main factor reacting to BMP4 stimuli. RNA sequencing confirmed that Wif1 was markedly upregulated after BMP4 treatment in different gene expression analyses. Similar to the functional role of BMP4, Wif1 significantly decreased the cell cycle of NSCs and significantly inhibited cell proliferation (P < 0.05). Combined treatment with BMP4 and Wif1 significantly enhanced the inhibition of cell growth compared with the single treatment (P < 0.05). Wif1 expression was clearly lower in glioblastoma and low-grade glioma samples than in normal samples (P < 0.05). A functional analysis revealed that both BMP4 and Wif1 could decrease glioma cell growth. These effects were abrogated by the BMP inhibitor Noggin. The collective findings demonstrate that Wif1 plays a key role in quiescent NSC homeostasis and glioma cell growth downstream of BMP-on signaling. The functional roles of Wif1/BMP4 in glioma cells may provide a technical basis for regenerative medicine, drug discovery, and personal molecular therapy in future clinical treatments.

ZEB2 haploinsufficient Mowat-Wilson syndrome induced pluripotent stem cells show disrupted GABAergic transcriptional regulation and function

Mowat-Wilson syndrome (MWS) is a severe neurodevelopmental disorder caused by heterozygous variants in the gene encoding transcription factor ZEB2. Affected individuals present with structural brain abnormalities, speech delay and epilepsy. In mice, conditional loss of Zeb2 causes hippocampal degeneration, altered migration and differentiation of GABAergic interneurons, a heterogeneous population of mainly inhibitory neurons of importance for maintaining normal excitability. To get insights into GABAergic development and function in MWS we investigated ZEB2 haploinsufficient induced pluripotent stem cells (iPSC) of MWS subjects together with iPSC of healthy donors. Analysis of RNA-sequencing data at two time points of GABAergic development revealed an attenuated interneuronal identity in MWS subject derived iPSC with enrichment of differentially expressed genes required for transcriptional regulation, cell fate transition and forebrain patterning. The ZEB2 haploinsufficient neural stem cells (NSCs) showed downregulation of genes required for ventral telencephalon specification, such as FOXG1, accompanied by an impaired migratory capacity. Further differentiation into GABAergic interneuronal cells uncovered upregulation of transcription factors promoting pallial and excitatory neurons whereas cortical markers were downregulated. The differentially expressed genes formed a neural protein-protein network with extensive connections to well-established epilepsy genes. Analysis of electrophysiological properties in ZEB2 haploinsufficient GABAergic cells revealed overt perturbations manifested as impaired firing of repeated action potentials. Our iPSC model of ZEB2 haploinsufficient GABAergic development thus uncovers a dysregulated gene network leading to immature interneurons with mixed identity and altered electrophysiological properties, suggesting mechanisms contributing to the neuropathogenesis and seizures in MWS.

The transcription factor LEF1 interacts with NFIX and switches isoforms during adult hippocampal neural stem cell quiescence

Stem cells in adult mammalian tissues are held in a reversible resting state, known as quiescence, for prolonged periods of time. Recent studies have greatly increased our understanding of the epigenetic and transcriptional landscapes that underlie stem cell quiescence. However, the transcription factor code that actively maintains the quiescence program remains poorly defined. Similarly, alternative splicing events affecting transcription factors in stem cell quiescence have been overlooked. Here we show that the transcription factor T-cell factor/lymphoid enhancer factor LEF1, a central player in canonical β-catenin-dependent Wnt signalling, undergoes alternative splicing and switches isoforms in quiescent neural stem cells. We found that active β-catenin and its partner LEF1 accumulated in quiescent hippocampal neural stem and progenitor cell (Q-NSPC) cultures. Accordingly, Q-NSPCs showed enhanced TCF/LEF1-driven transcription and a basal Wnt activity that conferred a functional advantage to the cultured cells in a Wnt-dependent assay. At a mechanistic level, we found a fine regulation of Lef1 gene expression. The coordinate upregulation of Lef1 transcription and retention of alternative spliced exon 6 (E6) led to the accumulation of a full-length protein isoform (LEF1-FL) that displayed increased stability in the quiescent state. Prospectively isolated GLAST + cells from the postnatal hippocampus also underwent E6 retention at the time quiescence is established in vivo. Interestingly, LEF1 motif was enriched in quiescence-associated enhancers of genes upregulated in Q-NSPCs and quiescence-related NFIX transcription factor motifs flanked the LEF1 binding sites. We further show that LEF1 interacts with NFIX and identify putative LEF1/NFIX targets. Together, our results uncover an unexpected role for LEF1 in gene regulation in quiescent NSPCs, and highlight alternative splicing as a post-transcriptional regulatory mechanism in the transition from stem cell activation to quiescence.

The effects of Bone Morphogenetic Protein 4 on adult neural stem cell proliferation, differentiation and survival in an in vitro model of ischemic stroke

The subventricular zone (SVZ) of the lateral ventricles represents a main region where neural stem cells (NSCs) of the mature central nervous system (CNS) reside. Bone Morphogenetic Proteins (BMPs) are the largest subclass of the transforming growth factor-β (TGF-β) superfamily of ligands. BMP4 is one such member and plays important roles in adult NSC differentiation. However, the exact effects of BMP4 on SVZ adult NSCs in CNS ischemia are still unknown. Using oxygen and glucose deprivation (OGD) as an in vitro model of ischemia, we examined the behavior of adult NSCs. We observed that anoxia resulted in reduced viability of adult NSCs, and that BMP4 treatment clearly rescued apoptotic cell death following anoxia. Furthermore, BMP4 treatment exhibited a strong inhibitory effect on cellular proliferation of the adult NSCs in normoxic conditions. Moreover, such inhibitory effects of BMP4 treatment were also found in OGD conditions, despite the enhanced cellular proliferation of the adult NSCs that was observed under such ischemic conditions. Increased neuronal and astroglial commitment of adult NSCs were found in the OGD conditions, whereas a reduction in differentiated neurons and an increase in differentiated astrocytes were observed following BMP4 treatment. The present data indicate that BMP4 modulates proliferation and differentiation of SVZ-derived adult NSCs and promotes cell survival in the in vitro model of ischemic stroke.

BMP4 Exerts Anti-Neurogenic Effect via Inducing Id3 during Aging

Bone morphogenetic protein (BMP) signaling has been shown to be intimately associated with adult neurogenesis in the subventricular zone (SVZ) and subgranular zone (SGZ). Adult neurogenesis declines in aging rodents and primates. However, the role of BMP signaling in the age-related neurogenesis decline remains elusive and the effect of BMP4 on adult SVZ neurogenesis remains controversial. Here, the expression of BMP4 and its canonical effector phosphorylated-Smad1/5/8 (p-Smad1/5/8) in the murine SVZ and SGZ were found to be increased markedly with age. We identified Id3 as a major target of BMP4 in neuronal stem cells (NSCs) of both neurogenic regions, which exhibited a similar increase during aging. Intracerebroventricular infusion of BMP4 activated Smad1/5/8 phosphorylation and upregulated Id3 expression, which further restrained NeuroD1, leading to attenuated neurogenesis in both neurogenic regions and defective differentiation in the SGZ. Conversely, noggin, a potent inhibitor of BMP4, demonstrated opposing effects. In support of this, BMP4 treatment or lentiviral overexpression of Id3 resulted in decreased NeuroD1 protein levels in NSCs of both neurogenic regions and significantly inhibited neurogenesis. Thus, our findings revealed that the increased BMP4 signaling with age inhibited adult neurogenesis in both SVZ and SGZ, which may be attributed at least in part, to the changes in the Id3-NeuroD1 axis.

Impaired LEF1 Activation Accelerates iPSC-Derived Keratinocytes Differentiation in Hutchinson-Gilford Progeria Syndrome

Hutchinson–Gilford progeria syndrome (HGPS) is a detrimental premature aging disease caused by a point mutation in the human LMNA gene. This mutation results in the abnormal accumulation of a truncated pre-lamin A protein called progerin. Among the drastically accelerated signs of aging in HGPS patients, severe skin phenotypes such as alopecia and sclerotic skins always develop with the disease progression. Here, we studied the HGPS molecular mechanisms focusing on early skin development by differentiating patient-derived induced pluripotent stem cells (iPSCs) to a keratinocyte lineage. Interestingly, HGPS iPSCs showed an accelerated commitment to the keratinocyte lineage than the normal control. To study potential signaling pathways that accelerated skin development in HGPS, we investigated the WNT pathway components during HGPS iPSCs-keratinocytes induction. Surprisingly, despite the unaffected β-catenin activity, the expression of a critical WNT transcription factor LEF1 was diminished from an early stage in HGPS iPSCs-keratinocytes differentiation. A chromatin immunoprecipitation (ChIP) experiment further revealed strong bindings of LEF1 to the early-stage epithelial developmental markers K8 and K18 and that the LEF1 silencing by siRNA down-regulates the K8/K18 transcription. During the iPSCs-keratinocytes differentiation, correction of HGPS mutation by Adenine base editing (ABE), while in a partial level, rescued the phenotypes for accelerated keratinocyte lineage-commitment. ABE also reduced the cell death in HGPS iPSCs-derived keratinocytes. These findings brought new insight into the molecular basis and therapeutic application for the skin abnormalities in HGPS.

Wnt signaling in the adult hippocampal neurogenic niche

The subgranular zone (SGZ) of the hippocampal dentate gyrus (DG) is a neurogenic niche of the adult brain that contains neural stem cells (NSCs) able to generate excitatory glutamatergic granule neurons, which integrate into the DG circuit and contribute to hippocampal plasticity, learning, and memory. Thus, endogenous NSCs could be harnessed for therapeutic purposes. In this context, it is critical to characterize the molecular mechanisms controlling the generation and functional integration of adult-born neurons. Adult hippocampal neurogenesis is tightly controlled by both cell-autonomous mechanisms and the interaction with the complex niche microenvironment, which harbors the NSCs and provides the signals to support their maintenance, activation, and differentiation. Among niche-derived factors, Wnt ligands play diverse roles. Wnts are secreted glycoproteins that bind to Frizzled receptors and co-receptors to trigger the Wnt signaling pathway. Here, we summarize the current knowledge about the roles of Wnts in the regulation of adult hippocampal neurogenesis. We discuss the possible contribution of the different niche cells to the regulation of local Wnt signaling activity, and how Wnts derived from different cell types could induce differential effects. Finally, we discuss how the effects of Wnt signaling on hippocampal network activity might contribute to neurogenesis regulation. Although the evidence supports relevant roles for Wnt signaling in adult hippocampal neurogenesis, defining the cellular source and the mechanisms controlling secretion and diffusion of Wnts will be crucial to further understand Wnt signaling regulation of adult NSCs, and eventually, to propose this pathway as a therapeutic target to promote neurogenesis.

Molecular Insights to the Wnt Signaling During Alzheimer's Disorder: a Potential Target for Therapeutic Interventions

In the adult brain, Wnt signaling is crucial for neurogenesis, and it also regulates neuronal development, neuronal maturation, neuronal differential, and proliferation. Impaired Wnt signaling pathways are associated with enhanced levels of amyloid-β, reduced β-catenin levels, and increased expression of GSK-3β enzyme, suggesting its direct association with the pathogenesis of Alzheimer's disorder (AD). These findings are consolidated by reports where activation of Wnt signaling by genetic factors and pharmacological intervention has improved the cognitive functions in animals and restored neurogenesis in the adult brain. Various natural and synthetic molecules have been identified that modulate Wnt signaling in the adult brain and promote neurogenesis and alleviate behavioral dysfunction. These molecules include lithium, valproic acid, ethosuximide, selenomethionine, curcumin, andrographolide, xanthoceraside, huperzine A, pyridostigmine, ginkgolide-B, ricinine, cannabidiol, and resveratrol. These molecules are associated with the DKK1 and GSK-3β inhibition and β-catenin stabilization along with their effects on neurogenesis, neuronal proliferation, and differentiation in the hippocampus through modulation of Wnt signaling and thereby could prove beneficial in the management of AD pathogenesis. Although modulation of the Wnt signaling seems to suggest to be promising in the management of AD, unfortunately, most of the literature available for the association of Wnt signaling and AD pathogenesis is either from preclinical studies or post-mortem brain. Therefore, it will be interesting to understand the role of Wnt signaling in AD patients, and a rigorous investigation could provide us with a better understanding of AD pathogenesis and the identification of novel targets for therapeutic interventions.

Adult Neurogenesis: A Story Ranging from Controversial New Neurogenic Areas and Human Adult Neurogenesis to Molecular Regulation

The generation of new neurons in the adult brain is a currently accepted phenomenon. Over the past few decades, the subventricular zone and the hippocampal dentate gyrus have been described as the two main neurogenic niches. Neurogenic niches generate new neurons through an asymmetric division process involving several developmental steps. This process occurs throughout life in several species, including humans. These new neurons possess unique properties that contribute to the local circuitry. Despite several efforts, no other neurogenic zones have been observed in many years; the lack of observation is probably due to technical issues. However, in recent years, more brain niches have been described, once again breaking the current paradigms. Currently, a debate in the scientific community about new neurogenic areas of the brain, namely, human adult neurogenesis, is ongoing. Thus, several open questions regarding new neurogenic niches, as well as this phenomenon in adult humans, their functional relevance, and their mechanisms, remain to be answered. In this review, we discuss the literature and provide a compressive overview of the known neurogenic zones, traditional zones, and newly described zones. Additionally, we will review the regulatory roles of some molecular mechanisms, such as miRNAs, neurotrophic factors, and neurotrophins. We also join the debate on human adult neurogenesis, and we will identify similarities and differences in the literature and summarize the knowledge regarding these interesting topics.

Bone morphogenetic proteins (BMPs) in the central regulation of energy balance and adult neural plasticity

The current worldwide obesity pandemic highlights a need to better understand the regulation of energy balance and metabolism, including the role of the nervous system in controlling energy intake and energy expenditure. Neural plasticity in the hypothalamus of the adult brain has been implicated in full-body metabolic health, however, the mechanisms surrounding hypothalamic plasticity are incompletely understood. Bone morphogenetic proteins (BMPs) control metabolic health through actions in the brain as well as in peripheral tissues such as adipose, together regulating both energy intake and energy expenditure. BMP ligands, receptors, and inhibitors are found throughout plastic adult brain regions and have been demonstrated to modulate neurogenesis and gliogenesis, as well as synaptic and dendritic plasticity. This role for BMPs in adult neural plasticity is distinct from their roles in brain development. Existing evidence suggests that BMPs induce weight loss through hypothalamic pathways, and part of the mechanism of action may be through inducing neural plasticity. In this review, we summarize the data regarding how BMPs affect neural plasticity in the adult mammalian brain, as well as the relationship between central BMP signaling and metabolic health.

Deficient LEF1 expression is associated with lithium resistance and hyperexcitability in neurons derived from bipolar disorder patients

Bipolar disorder (BD) is a psychiatric condition characterized by depressive and manic episodes that affect 2% of the world population. The first-line long-term treatment for mood stabilization is lithium (Li). Induced pluripotent stem cell modeling of BD using hippocampal dentate gyrus-like neurons derived from Li-responsive (LR) and Li-non-responsive (NR) patients previously showed neuronal hyperexcitability. Li treatment reversed hyperexcitability only on the LR neurons. In this study we searched for specific targets of Li resistance in NR neurons and found that the activity of Wnt/β-catenin signaling pathway was severely affected, with a significant decrease in expression of LEF1. Li targets the Wnt/β-catenin signaling pathway by inhibiting GSK-3β and releasing β-catenin that forms a nuclear complex with TCF/LEF1, activating the Wnt/β-catenin transcription program. Therefore, we propose that downregulation of LEF1 may account for Li resistance in NR neurons. Our results show that valproic acid (VPA), a drug used to treat NR patients that also acts downstream of GSK-3β, upregulated LEF1 and Wnt/β-catenin gene targets, increased transcriptional activity of complex β-catenin/TCF/LEF1, and reduced excitability in NR neurons. In addition, decreasing LEF1 expression in control neurons using shLEF1 caused hyperexcitability, confirming that the impact of VPA on excitability in NR neurons was connected to changes in LEF1 and in the Wnt/β-catenin pathway. Our results suggest that LEF1 may be a useful target for the discovery of new drugs for BD treatment.

Bone-to-Brain: A Round Trip in the Adaptation to Mechanical Stimuli

Besides the classical ones (support/protection, hematopoiesis, storage for calcium, and phosphate) multiple roles emerged for bone tissue, definitively making it an organ. Particularly, the endocrine function, and in more general terms, the capability to sense and integrate different stimuli and to send signals to other tissues, has highlighted the importance of bone in homeostasis. Bone is highly innervated and hosts all nervous system branches; bone cells are sensitive to most of neurotransmitters, neuropeptides, and neurohormones that directly affect their metabolic activity and sensitivity to mechanical stimuli. Indeed, bone is the principal mechanosensitive organ. Thanks to the mechanosensing resident cells, and particularly osteocytes, mechanical stimulation induces metabolic responses in bone forming (osteoblasts) and bone resorbing (osteoclasts) cells that allow the adaptation of the affected bony segment to the changing environment. Once stimulated, bone cells express and secrete, or liberate from the entrapping matrix, several mediators (osteokines) that induce responses on distant targets. Brain is a target of some of these mediator [e.g., osteocalcin, lipocalin2, sclerostin, Dickkopf-related protein 1 (Dkk1), and fibroblast growth factor 23], as most of them can cross the blood-brain barrier. For others, a role in brain has been hypothesized, but not yet demonstrated. As exercise effectively modifies the release and the circulating levels of these osteokines, it has been hypothesized that some of the beneficial effects of exercise on brain functions may be associated to such a bone-to-brain communication. This hypothesis hides an interesting clinical clue: may well-addressed physical activities support the treatment of neurodegenerative diseases, such as Alzheimer’s and Parkinson’s diseases?

Adult neurogenesis and the molecular signalling pathways in brain: the role of stem cells in adult hippocampal neurogenesis

Molecular signalling pathways are an evolutionarily conserved multifaceted pathway that can control diverse cellular processes. The role of signalling pathways in regulating development and tissue homeostasis as well as hippocampal neurogenesis is needed to study in detail. In the adult brain, the Notch signalling pathway, in collaboration with the Wnt/β-catenin, bone morphogenetic proteins (BMPs), and sonic hedgehog (Shh) molecular signalling pathways, are involved in stem cell regulation in the hippocampal formation, and they also control the plasticity of the neural stem cells (NSCs) or neural progenitor cells (NPCs) which involved in neurogenesis processes. Here we discuss the distinctive roles of molecular signalling pathways involved in the generation of new neurons from a pool of NSCs in the adult brain. Our approach will facilitate the understanding of the molecular signalling mechanism of hippocampal neurogenesis during NSCs development in the adult brain using molecular aspects coupled with cell biological and physiological analysis.

Single-cell transcriptomics identifies limbal stem cell population and cell types mapping its differentiation trajectory in limbal basal epithelium of human cornea

PURPOSE

This study aimed to uncover novel cell types in heterogenous basal limbus of human cornea for identifying LSC at single cell resolution.

METHODS

Single cells of human limbal basal epithelium were isolated from young donor corneas. Single-cell RNA-Sequencing was performed using 10x Genomics platform, followed by clustering cell types through the graph-based visualization method UMAP and unbiased computational informatic analysis. Tissue RNA in situ hybridization with RNAscope, immunofluorescent staining and multiple functional assays were performed using human corneas and limbal epithelial culture models.

RESULTS

Single-cell transcriptomics of 16,360 limbal basal cells revealed 12 cell clusters belonging to three lineages. A smallest cluster (0.4% of total cells) was identified as LSCs based on their quiescent and undifferentiated states with enriched marker genes for putative epithelial stem cells. TSPAN7 and SOX17 are discovered and validated as new LSC markers based on their exclusive expression pattern and spatial localization in limbal basal epithelium by RNAscope and immunostaining, and functional role in cell growth and tissue regeneration models with RNA interference in cultures. Interestingly, five cell types/states mapping a developmental trajectory of LSC from quiescence to proliferation and differentiation are uncovered by Monocle3 and CytoTRACE pseudotime analysis. The transcription factor networks linking novel signaling pathways are revealed to maintain LSC stemness.

CONCLUSIONS

This human corneal scRNA-Seq identifies the LSC population and uncovers novel cell types mapping the differentiation trajectory in heterogenous limbal basal epithelium. The findings provide insight into LSC concept and lay the foundation for understanding the corneal homeostasis and diseases.

ROS Dynamics Delineate Functional States of Hippocampal Neural Stem Cells and Link to Their Activity-Dependent Exit from Quiescence

Cellular redox states regulate the balance between stem cell maintenance and activation. Increased levels of intracellular reactive oxygen species (ROS) are linked to proliferation and lineage specification. In contrast to this general principle, we here show that in the hippocampus of adult mice, quiescent neural precursor cells (NPCs) maintain the highest ROS levels (hiROS). Classifying NPCs on the basis of cellular ROS content identified distinct functional states. Shifts in ROS content primed cells for a subsequent state transition, with lower ROS content marking proliferative activity and differentiation. Physical activity, a physiological activator of adult hippocampal neurogenesis, recruited hiROS NPCs into proliferation via a transient Nox2-dependent ROS surge. In the absence of Nox2, baseline neurogenesis was unaffected, but the activity-induced increase in proliferation disappeared. These results provide a metabolic classification of NPC functional states and describe a mechanism linking the modulation of cellular ROS by behavioral cues to the activation of adult NPCs.

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A ROS gradient delineates cell types in the course of adult hippocampal neurogenesis

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Quiescent hippocampal stem cells have unusually high intracellular ROS

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Physical activity recruits quiescent stem cells in a ROS-dependent manner

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NOX2 dependency distinguishes this recruitment from baseline proliferation

The differentiation effect of bone morphogenetic protein (BMP) on human amniotic epithelial stem cells to express ectodermal lineage markers

Stem cells are a promising tool for treatment of a variety of degenerative diseases. Human amniotic epithelial stem cells (hAECs) have desirable and unique characteristics that make them a proper candidate for cell therapy. In this study, we have investigated the effects of BMP-4 (bone morphogenetic protein-4) and its inhibition on differentiation of AECs into ectodermal lineages. Analysis of AEC-derived ectodermal lineages (neurons and keratinocytes) was performed by using flow cytometry technique for Map2 and β-tubulin (as neuron markers), Olig2 and MBP (as oligodendrocyte markers), and K14 and K10 (as keratinocyte markers). The results of this study illustrated that noggin (as BMP antagonist), BMP4, and both BMP4 and heparin (together or separately) increased neural and keratinocyte marker expression, respectively. The expression of markers MAP2, olig2, and K14 in hAECs has been significantly decreased 21 days after exposure to differentiation medium (without growth factors) compared with isolation day, which supports the hypothesis that AECs can be dedifferentiated into pluripotent cells. Moreover, activation and inhibition of BMP signaling have no effects on viability of hAECs. The results of this study showed that BMP signaling and its inhibition are the key factors for ectodermal lineage differentiation of amnion-derived stem cells.

Nanomaterial integration into the scaffolding materials for nerve tissue engineering: a review

The nervous system, which consists of a complex network of millions of neurons, is one of the most highly intricate systems in the body. This complex network is responsible for the physiological and cognitive functions of the human body. Following injuries or degenerative diseases, damage to the nervous system is overwhelming because of its complexity and its limited regeneration capacity. However, neural tissue engineering currently has some capacities for repairing nerve deficits and promoting neural regeneration, with more developments in the future. Nevertheless, controlling the guidance of stem cell proliferation and differentiation is a challenging step towards this goal. Nanomaterials have the potential for the guidance of the stem cells towards the neural lineage which can overcome the pitfalls of the classical methods since they provide a unique microenvironment that facilitates cell-matrix and cell-cell interaction, and they can manipulate the cell signaling mechanisms to control stem cells' fate. In this article, the suitable cell sources and microenvironment cues for neuronal tissue engineering were examined. Afterward, the nanomaterials that impact stem cell proliferation and differentiation towards neuronal lineage were reviewed.

Glia and Neural Stem and Progenitor Cells of the Healthy and Ischemic Brain: The Workplace for the Wnt Signaling Pathway

Wnt signaling plays an important role in the self-renewal, fate-commitment and survival of the neural stem/progenitor cells (NS/PCs) of the adult central nervous system (CNS). Ischemic stroke impairs the proper functioning of the CNS and, therefore, active Wnt signaling may prevent, ameliorate, or even reverse the negative effects of ischemic brain injury. In this review, we provide the current knowledge of Wnt signaling in the adult CNS, its status in diverse cell types, and the Wnt pathway’s impact on the properties of NS/PCs and glial cells in the context of ischemic injury. Finally, we summarize promising strategies that might be considered for stroke therapy, and we outline possible future directions of the field.

Mesenchymal Bmp7 Controls Onset of Tooth Mineralization: A Novel Way to Regulate Molar Cusp Shape

Investigating the molecular basis for tooth shape variation provides an important glimpse into the evolution of tooth function. We recently showed that loss of mesenchymal BMP7 is sufficient to alter morphology and function of the toothrow. Here we report on the underlying mechanism. Expression of mesenchymal Bmp7 is observed at sites where mineralization is initiated, in tooth cusps of developing molars. Neural crest-specific deletion of Bmp7 (Bmp7^ncko) resulted in a complete lack of dentin/enamel formation at birth, the time when mineralization is normally initiated in the upper molars, similar to what was observed in Bmp2^ncko mice. Unlike loss of Bmp2, loss of Bmp7 did not affect odontoblast polarization and did not significantly alter the levels of pSmad1/5/8, but almost completely abolished canonical Wnt signaling in (pre)-ameloblasts. Tooth mineralization resumed with a 48-h delay allowing for additional mesenchymal proliferation. Enamel volume was still reduced at P4 and P8, but was comparable in erupted teeth, which were broader and had altered cusp shapes. Tooth eruption was also delayed. Overall, enamel appeared inconspicuous, although some structural changes along with reduced mineral density could be observed. Loss of Bmp7 led to an increase in mesenchymal Bmp6 suggesting an interplay between Bmp6 and Bmp7 in the regulation of mineralization initiation. Our findings show that regulation of the onset of tooth mineralization is a hitherto unsuspected mechanism controlling tooth shape variation. Initiation of tooth mineralization is regulated by a complex epithelial-mesenchymal Bmp/Wnt-signaling network to which Bmp7 contributes. This network is separate and independent of the Bmp2-signaling network regulating odontoblast cell polarization. From an evolutionary perspective, addition of Bmp7 as initiator of tooth mineralization might be akin to an upgrade of an existing computer operating system. While not essential, it provides obviously sufficient advantage warranting its evolutionary incorporation.

Cytokines Induce Monkey Neural Stem Cell Differentiation through Notch Signaling

The mammalian central nervous system (CNS) has a limited ability to renew the damaged cells after a brain or spinal cord injury whether it is nonhuman primates like monkeys or humans. Transplantation of neural stem cells (NSCs) is a potential therapy for CNS injuries due to their pluripotency and differentiation abilities. Cytokines play an important role in CNS development and repair of CNS injuries. However, the detailed cytokine signaling response in monkey neural stem cells is rarely studied. In our previous research, we isolated NSCs from the adult monkey brain and found the effects of cytokines on monkey NSCs. Now, we further analyzed the regulation mechanisms of cytokines to the proliferation of monkey NSCs such as bone morphogenic protein 4 (BMP4), BMP4/leukaemia inhibitory factor (LIF), or retinoic acid (RA)/Forskolin. The data showed that BMP4 inhibited cell proliferation to arrest, but it did not affect the stemness of NSCs. BMP4/LIF promoted the astrocyte-like differentiation of monkey NSCs, and RA/forskolin induced the neuronal differentiation of monkey NSCs. BMP4/LIF and RA/forskolin induced monkey NSC differentiation by regulating Notch signaling. These results provide some theoretical evidence for NSC therapy to brain or spinal cord injury in regenerative medicine.

miR-29a Promotes the Neurite Outgrowth of Rat Neural Stem Cells by Targeting Extracellular Matrix to Repair Brain Injury

Neural stem cells (NSCs) can generate new neurons to repair brain injury and central nervous system disease by promoting neural regeneration. MicroRNAs (miRNAs) involve in neural development, brain damage, and neurological diseases repair. Recent reports show that several miRNAs express in NSCs and are important to neurogenesis. Neurites play a key role in NSC-related neurogenesis. However, the mechanism of NSC neurite generation is rarely studied. We surprisingly noticed that the neurites increased after bone morphogenetic protein (BMP) treatment in rat NSCs. This process was accompanied by the dynamic change of miRNA-29. Then we discovered that miR-29a regulated neural neurites in rat hippocampus NSCs. Overexpression of miR-29a reduced the cell soma area and promoted the neurite outgrowth of NSCs. Cell soma area became small, whereas the number of neurite increased. Moreover, neurite complexity increased dramatically, with more primary and secondary branches after miR-29a overexpression. In addition, miR-29a overexpression still maintained the stemness of NSCs. Besides, we identified that miR-29a can promote the neurite outgrowth by targeting extracellular matrix-related genes like Fibrillin 1 (Fbn1), Follistatin-like 1 (Fstl1), and laminin subunit gamma 2 (Lamc2). These findings may provide a novel role of miR-29a to regulate neurite outgrowth and development of NSCs. We also offered a possible theoretical basis to the migration mechanism of NSCs in brain development and damage repair.

Transplantation of hMSCs Genome Edited with LEF1 Improves Cardio-Protective Effects in Myocardial Infarction

Stem cell-based therapy is one of the most attractive approaches to ischemic heart diseases, such as myocardial infarction (MI). We evaluated the cardio-protective effects of the human umbilical cord blood-derived mesenchymal stem cells (hUCB-MSCs) stably expressing lymphoid enhancer-binding factor 1 (LEF1; LEF1/hUCB-MSCs) in a rat model of MI. LEF1 overexpression in hUCB-MSCs promoted cell-proliferation and anti-apoptotic effects in hypoxic conditions. For the application of its therapeutic effects in vivo, the LEF1 gene was introduced into an adeno-associated virus integration site 1 (AAVS1) locus, known as a safe harbor site on chromosome 19 by CRISPR/Cas9-mediated gene integration in hUCB-MSCs. Transplantation of LEF1/hUCB-MSCs onto the infarction region in the rat model significantly improved overall survival. The cardio-protective effect of LEF1/hUCB-MSCs was proven by echocardiogram parameters, including greatly improved left-ventricle ejection fraction (EF) and fractional shortening (FS). Moreover, histology and immunohistochemistry successfully presented reduced MI region and fibrosis by LEF1/hUCB-MSCs. We found that these overall positive effects of LEF1/hUCB-MSCs are attributed by increased proliferation and survival of stem cells in oxidative stress conditions and by the secretion of various growth factors by LEF1. In conclusion, this study suggests that the stem cell-based therapy, conjugated with genome editing of transcription factor LEF1, which promotes cell survival, could be an effective therapeutic strategy for cardiovascular disease.

Dexmedetomidine Promotes Hippocampal Neurogenesis and Improves Spatial Learning and Memory in Neonatal Rats

Background

Dexmedetomidine (Dex) is a highly selective α2-adrenoceptor agonist used as an off-label medication for pediatric sedation and analgesia. Recently, Dex was reported to exhibit neuroprotective efficacy in several brain injury models. Here we investigate whether neonatal Dex administration promotes hippocampal neurogenesis and enhances hippocampus-dependent spatial learning and memory under physiological conditions.

Methods

Postnatal day 7 (P7) pups were administered saline (vehicle control) or Dex (10, 20, or 40 µg/kg) by intraperitoneal injection. Neurogenesis and astrogenesis were examined in brain slices by BrdU immunostaining on P8 and changes in the expression levels of GDNF, NCAM, CREB, PSD95, and GAP43 were assessed by Western blotting on P35, respectively. Open field and Morris water maze (MWM) tests were conducted from P28 to P36 in order to assess effects on general motor activity and spatial learning, respectively.

Results

Dexmedetomidine at 20 µg/kg significantly enhanced neurogenesis and astrogenesis in hippocampus and upregulated GDNF, NCAM, CREB, PSD95, and GAP43 compared to vehicle and other Dex doses. Moreover, 20 µg/kg Dex-injected rats showed no changes in motor or anxiety-like behavior but performed better in the MWM test compared to all other groups.

Conclusion

Neonatal injection of Dex (20 µg/kg) enhances spatial learning and memory in rat pups, potentially by promoting hippocampal neurogenesis and synaptic plasticity via activation of GDNF/NCAM/CREB signaling.

Dual Inhibition of BMP and WNT Signals Promotes Pancreatic Differentiation from Human Pluripotent Stem Cells

Pathological or functional loss of pancreatic beta cells is the cause of diabetes. Understanding how signaling pathways regulate pancreatic lineage and searching for combinations of signal modulators to promote pancreatic differentiation will definitely facilitate the robust generation of functional beta cells for curing hyperglycemia. In this study, we first tested the effect of several potent BMP inhibitors on pancreatic differentiation using human embryonic stem cells. Next, we examined the endodermal lineage bias upon potent BMP inhibitor treatment and further checked the crosstalk between signal pathways governing endodermal lineage determination. Furthermore, we improved current pancreatic differentiation system based on the signaling pathway study. Finally, we used human-induced pluripotent stem cells to validate our finding. We found BMP inhibitors indeed not only blocked hepatic lineage but also impeded intestinal lineage from human definitive endoderm unexpectedly. Signaling pathway analysis indicated potent BMP inhibitor resulted in the decrease of WNT signal activity and inhibition of WNT could contribute to the improved pancreatic differentiation. Herein, we combined the dual inhibition of BMP and WNT signaling and greatly enhanced human pancreatic progenitor differentiation as well as beta cell generation from both embryonic stem cells and induced pluripotent stem cells. Conclusively, our present work identified the crosstalk between the BMP and WNT signal pathways during human endoderm patterning and pancreas specification, and provided an improved in vitro pancreatic directed differentiation protocol from human pluripotent stem cells.

Herpes Simplex Virus Type-1 Infection Impairs Adult Hippocampal Neurogenesis via Amyloid-β Protein Accumulation

We previously reported that Herpes simplex virus type-1 (HSV-1) infection of cultured neurons triggered intracellular accumulation of amyloid-β protein (Aβ) markedly impinging on neuronal functions. Here, we demonstrated that HSV-1 affects in vitro and in vivo adult hippocampal neurogenesis by reducing neural stem/progenitor cell (NSC) proliferation and their neuronal differentiation via intracellular Aβ accumulation. Specifically, cultured NSCs were more permissive for HSV-1 replication than mature neurons and, once infected, they exhibited reduced proliferation (assessed by 5'-bromo-deoxyuridine incorporation, Ki67 immunoreactivity, and Sox2 mRNA expression) and impaired neuronal differentiation in favor of glial phenotype (evaluated by immunoreactivity for the neuronal marker MAP2, the glial marker glial fibrillary astrocyte protein, and the expression of the proneuronal genes Mash1 and NeuroD1). Similarly, impaired adult neurogenesis was observed in the subgranular zone of hippocampal dentate gyrus of an in vivo model of recurrent HSV-1 infections, that we recently set up and characterized, with respect to mock-infected mice. The effects of HSV-1 on neurogenesis did not depend on cell death and were due to Aβ accumulation in infected NSCs. Indeed, they were: (a) reverted, in vitro, by the presence of either β/γ-secretase inhibitors preventing Aβ production or the specific 4G8 antibody counteracting the action of intracellular Aβ; (b) not detectable, in vivo, in HSV-1-infected amyloid precursor protein knockout mice, unable to produce and accumulate Aβ. Given the critical role played by adult neurogenesis in hippocampal-dependent memory and learning, our results suggest that multiple virus reactivations in the brain may contribute to Alzheimer's disease phenotype by also targeting NSCs. Stem Cells 2019;37:1467-1480.

Rutaecarpine may improve neuronal injury, inhibits apoptosis, inflammation and oxidative stress by regulating the expression of ERK1/2 and Nrf2/HO-1 pathway in rats with cerebral ischemia-reperfusion injury

BACKGROUND

Cerebral ischemia-reperfusion (CI/R) injury is a more serious brain injury caused by the recovery of blood supply after cerebral ischemia for a certain period of time. Rutaecarpine (Rut) is an alkaloid isolated from Evodia officinalis with various biological activities. Previous studies have shown that Rut has a certain protective effect on ischemic brain injury, but the specific molecular mechanism is still unknown.

METHODS

In this study, a rat model of CI/R was established to explore the effects and potential molecular mechanisms of Rut on CI/R injury in rats.

RESULTS

The results showed that Rut alleviated neuronal injury induced by CI/R in a dose-dependent manner. Besides, Rut inhibited neuronal apoptosis by inhibiting the activation of caspase 3 and the expression of Bax. In addition, Rut alleviated the inflammatory response and oxidative stress caused by CI/R through inhibiting the production of pro-inflammatory factors (IL-6 and IL-1β), lactate dehydrogenase (LDH), malondialdehyde (MDA) and ROS, and increased the levels of anti-inflammatory factors (IL-4 and IL-10) and superoxide dismutase (SOD). Biochemically, Western blot analyses showed that Rut inhibited the phosphorylation of ERK1/2 and promoted the expression of nuclear factor-erythroid 2 related factor 2 (Nrf2) pathway-related proteins (Nrf2, heme oxygenase 1 (HO-1) and NAD (P) H-quinone oxidoreductase 1) in a dose-dependent manner. These results show that Rut may alleviate brain injury induced by CI/R by regulating the expression of ERK1/2 and the activation of Nrf2/HO-1 pathway.

CONCLUSION

In conclusion, these results suggest that Rut may be used as an effective therapeutic agent for damage caused by CI/R.

Divide or Commit - Revisiting the Role of Cell Cycle Regulators in Adult Hippocampal Neurogenesis

The adult dentate gyrus continuously generates new neurons that endow the brain with increased plasticity, helping to cope with changing environmental and cognitive demands. The process leading to the birth of new neurons spans several precursor stages and is the result of a coordinated series of fate decisions, which are tightly controlled by extrinsic signals. Many of these signals act through modulation of cell cycle (CC) components, not only to drive proliferation, but also for linage commitment and differentiation. In this review, we provide a comprehensive overview on key CC components and regulators, with emphasis on G₁ phase, and analyze their specific functions in precursor cells of the adult hippocampus. We explore their role for balancing quiescence versus self-renewal, which is essential to maintain a lifelong pool of neural stem cells while producing new neurons “on demand.” Finally, we discuss available evidence and controversies on the impact of CC/G₁ length on proliferation versus differentiation decisions.

Cell-Biological Requirements for the Generation of Dentate Gyrus Granule Neurons

The dentate gyrus (DG) receives highly processed information from the associative cortices functionally integrated in the trisynaptic hippocampal circuit, which contributes to the formation of new episodic memories and the spontaneous exploration of novel environments. Remarkably, the DG is the only brain region currently known to have high rates of neurogenesis in adults (Andersen et al., 1966, 1971). The DG is involved in several neurodegenerative disorders, including clinical dementia, schizophrenia, depression, bipolar disorder and temporal lobe epilepsy. The principal neurons of the DG are the granule cells. DG granule cells generated in culture would be an ideal model to investigate their normal development and the causes of the pathologies in which they are involved and as well as possible therapies. Essential to establish such in vitro models is the precise definition of the most important cell-biological requirements for the differentiation of DG granule cells. This requires a deeper understanding of the precise molecular and functional attributes of the DG granule cells in vivo as well as the DG cells derived in vitro. In this review we outline the neuroanatomical, molecular and cell-biological components of the granule cell differentiation pathway, including some growth- and transcription factors essential for their development. We summarize the functional characteristics of DG granule neurons, including the electrophysiological features of immature and mature granule cells and the axonal pathfinding characteristics of DG neurons. Additionally, we discuss landmark studies on the generation of dorsal telencephalic precursors from pluripotent stem cells (PSCs) as well as DG neuron differentiation in culture. Finally, we provide an outlook and comment critical aspects.