Classic and novel stem cell niches in brain homeostasis and repair

Harnessing the Stem Cell Niche in Regenerative Medicine: Innovative Avenue to Combat Neurodegenerative Diseases

Regenerative medicine harnesses the body's innate capacity for self-repair to restore malfunctioning tissues and organs. Stem cell therapies represent a key regenerative strategy, but to effectively harness their potential necessitates a nuanced understanding of the stem cell niche. This specialized microenvironment regulates critical stem cell behaviors including quiescence, activation, differentiation, and homing. Emerging research reveals that dysfunction within endogenous neural stem cell niches contributes to neurodegenerative pathologies and impedes regeneration. Strategies such as modifying signaling pathways, or epigenetic interventions to restore niche homeostasis and signaling, hold promise for revitalizing neurogenesis and neural repair in diseases like Alzheimer's and Parkinson's. Comparative studies of highly regenerative species provide evolutionary clues into niche-mediated renewal mechanisms. Leveraging endogenous bioelectric cues and crosstalk between gut, brain, and vascular niches further illuminates promising therapeutic opportunities. Emerging techniques like single-cell transcriptomics, organoids, microfluidics, artificial intelligence, in silico modeling, and transdifferentiation will continue to unravel niche complexity. By providing a comprehensive synthesis integrating diverse views on niche components, developmental transitions, and dynamics, this review unveils new layers of complexity integral to niche behavior and function, which unveil novel prospects to modulate niche function and provide revolutionary treatments for neurodegenerative diseases.

Critical Growth of Cerebral Tissue in Organoids: Theory and Experiments

We develop a Fokker-Planck theory of tissue growth with three types of cells (symmetrically dividing, asymmetrically dividing, and nondividing) as main agents to study the growth dynamics of human cerebral organoids. Fitting the theory to lineage tracing data obtained in next generation sequencing experiments, we show that the growth of cerebral organoids is a critical process. We derive analytical expressions describing the time evolution of clonal lineage sizes and show how power-law distributions arise in the limit of long times due to the vanishing of a characteristic growth scale. We discuss that the independence of critical growth on initial conditions could be biologically advantageous.

Crosstalk between autophagy and CSCs: molecular mechanisms and translational implications

Cancer stem cells(CSCs) play a key role in regulating tumorigenesis, progression, as well as recurrence, and possess typical metabolic characteristics. Autophagy is a catabolic process that can aid cells to survive under stressful conditions such as nutrient deficiency and hypoxia. Although the role of autophagy in cancer cells has been extensively studied, CSCs possess unique stemness, and their potential relationship with autophagy has not been fully analyzed. This study summarizes the possible role of autophagy in the renewal, proliferation, differentiation, survival, metastasis, invasion, and treatment resistance of CSCs. It has been found that autophagy can contribute to the maintenance of CSC stemness, facilitate the tumor cells adapt to changes in the microenvironment, and promote tumor survival, whereas in some other cases autophagy acts as an important process involved in the deprivation of CSC stemness thus leading to tumor death. Mitophagy, which has emerged as another popular research area in recent years, has a great scope when explored together with stem cells. In this study, we have aimed to elaborate on the mechanism of action of autophagy in regulating the functions of CSCs to provide deeper insights for future cancer treatment.

Directional induction of neural stem cells, a new therapy for neurodegenerative diseases and ischemic stroke

Due to the limited capacity of the adult mammalian brain to self-repair and regenerate, neurological diseases, especially neurodegenerative disorders and stroke, characterized by irreversible cellular damage are often considered as refractory diseases. Neural stem cells (NSCs) play a unique role in the treatment of neurological diseases for their abilities to self-renew and form different neural lineage cells, such as neurons and glial cells. With the increasing understanding of neurodevelopment and advances in stem cell technology, NSCs can be obtained from different sources and directed to differentiate into a specific neural lineage cell phenotype purposefully, making it possible to replace specific cells lost in some neurological diseases, which provides new approaches to treat neurodegenerative diseases as well as stroke. In this review, we outline the advances in generating several neuronal lineage subtypes from different sources of NSCs. We further summarize the therapeutic effects and possible therapeutic mechanisms of these fated specific NSCs in neurological disease models, with special emphasis on Parkinson's disease and ischemic stroke. Finally, from the perspective of clinical translation, we compare the strengths and weaknesses of different sources of NSCs and different methods of directed differentiation, and propose future research directions for directed differentiation of NSCs in regenerative medicine.

The vasculature of neurogenic niches: Properties and function

In the adult rodent brain, neural stem cells (NSCs) reside in the subventricular zone (SVZ) of the lateral ventricles and the subgranular zone (SGZ) of the hippocampus. In these areas, NSCs and their progeny integrate intrinsic signals and extrinsic cues provided by their microenvironment that control their behavior. The vasculature in the SVZ and SGZ, and the choroid plexus (ChP) in the SVZ, have emerged as critical compartments of the neurogenic niches as they provide a rich repertoire of cues to regulate NSC quiescence, proliferation, self-renewal and differentiation. Physical contact between NSCs and blood vessels is also a feature within the niches and supports different processes such as quiescence, migration and vesicle transport. In this review, we provide a description of the brain and choroid plexus vasculature in both stem cell niches, highlighting the main properties and role of the vasculature in each niche. We also summarize the current understanding of how blood vessel- and ChP-derived signals influence the behavior of NSCs in physiological adulthood, as well as upon aging.

High-efficiency pharmacogenetic ablation of oligodendrocyte progenitor cells in the adult mouse CNS

Approaches to investigate adult oligodendrocyte progenitor cells (OPCs) by targeted cell ablation in the rodent CNS have limitations in the extent and duration of OPC depletion. We have developed a pharmacogenetic approach for conditional OPC ablation, eliminating >98% of OPCs throughout the brain. By combining recombinase-based transgenic and viral strategies for targeting OPCs and ventricular-subventricular zone (V-SVZ)-derived neural precursor cells (NPCs), we found that new PDGFRA-expressing cells born in the V-SVZ repopulated the OPC-deficient brain starting 12 days after OPC ablation. Our data reveal that OPC depletion induces V-SVZ-derived NPCs to generate vast numbers of PDGFRA+NG2+ cells with the capacity to proliferate and migrate extensively throughout the dorsal anterior forebrain. Further application of this approach to ablate OPCs will advance knowledge of the function of both OPCs and oligodendrogenic NPCs in health and disease.

Insights into nervous system repair from the fruit fly

Millions of people experience injury to the central nervous system (CNS) each year, many of whom are left permanently disabled, providing a challenging hurdle for the field of regenerative medicine. Repair of damage in the CNS occurs through a concerted effort of phagocytosis of debris, cell proliferation and differentiation to produce new neurons and glia, distal axon/dendrite degeneration, proximal axon/dendrite regeneration and axon re-enwrapment. In humans, regeneration is observed within the peripheral nervous system, while in the CNS injured axons exhibit limited ability to regenerate. This has also been described for the fruit fly Drosophila. Powerful genetic tools available in Drosophila have allowed the response to CNS insults to be probed and novel regulators with mammalian orthologs identified. The conservation of many regenerative pathways, despite considerable evolutionary separation, stresses that these signals are principal regulators and may serve as potential therapeutic targets. Here, we highlight the role of Drosophila CNS injury models in providing key insight into regenerative processes by exploring the underlying pathways that control glial and neuronal activation in response to insult, and their contribution to damage repair in the CNS.

Recent advancements in chromone as a privileged scaffold towards the development of small molecules for neurodegenerative therapeutics

Neurodegenerative disorders, i.e., Alzheimer's or Parkinson's disease, involve progressive degeneration of the central nervous system, resulting in memory loss and cognitive impairment. The intensification of neurodegenerative research in recent years put some molecules into clinical trials, but still there is an urgent need to develop effective therapeutic molecules to combat these diseases. Chromone is a well-identified privileged structure for the design of well-diversified therapeutic molecules of potential pharmacological interest, particularly in the field of neurodegeneration. In this short review, we focused on the recent advancements and developments of chromones for neurodegenerative therapeutics. Different small molecules were reviewed as multi-target-directed ligands (MTDLs) with potential inhibition of AChE, BuChE, MAO-A, MAO-B, Aβ plaque formation and aggregation. Recently developed MTDLs emphasized that the chromone scaffold has the potential to develop new molecules for the treatment of neurodegenerative diseases.

The Mitochondrial Antioxidant Sirtuin3 Cooperates with Lipid Metabolism to Safeguard Neurogenesis in Aging and Depression

Neural stem cells (NSCs), crucial for memory in the adult brain, are also pivotal to buffer depressive behavior. However, the mechanisms underlying the boost in NSC activity throughout life are still largely undiscovered. Here, we aimed to explore the role of deacetylase Sirtuin 3 (SIRT3), a central player in mitochondrial metabolism and oxidative protection, in the fate of NSC under aging and depression-like contexts. We showed that chronic treatment with tert-butyl hydroperoxide induces NSC aging, markedly reducing SIRT3 protein. SIRT3 overexpression, in turn, restored mitochondrial oxidative stress and the differentiation potential of aged NSCs. Notably, SIRT3 was also shown to physically interact with the long chain acyl-CoA dehydrogenase (LCAD) in NSCs and to require its activation to prevent age-impaired neurogenesis. Finally, the SIRT3 regulatory network was investigated in vivo using the unpredictable chronic mild stress (uCMS) paradigm to mimic depressive-like behavior in mice. Interestingly, uCMS mice presented lower levels of neurogenesis and LCAD expression in the same neurogenic niches, being significantly rescued by physical exercise, a well-known upregulator of SIRT3 and lipid metabolism. Our results suggest that targeting NSC metabolism, namely through SIRT3, might be a suitable promising strategy to delay NSC aging and confer stress resilience.

Microglia and Macrophages in Neuroprotection, Neurogenesis, and Emerging Therapies for Stroke

Stroke remains the number one cause of morbidity in the United States. Within weeks to months after an ischemic event, there is a resolution of inflammation and evidence of neurogenesis; however, years following a stroke, there is evidence of chronic inflammation in the central nervous system, possibly by the persistence of an autoimmune response to brain antigens as a result of ischemia. The mechanisms underlying the involvement of macrophage and microglial activation after stroke are widely acknowledged as having a role in ischemic stroke pathology; thus, modulating inflammation and neurological recovery is a hopeful strategy for treating the long-term outcomes after ischemic injury. Current treatments fail to provide neuroprotective or neurorestorative benefits after stroke; therefore, to ameliorate brain injury-induced deficits, therapies must alter both the initial response to injury and the subsequent inflammatory process. This review will address differences in macrophage and microglia nomenclature and summarize recent work in elucidating the mechanisms of macrophage and microglial participation in antigen presentation, neuroprotection, angiogenesis, neurogenesis, synaptic remodeling, and immune modulating strategies for treating the long-term outcomes after ischemic injury.

Adult brain cytogenesis in the context of mood disorders: From neurogenesis to the emergent role of gliogenesis

Psychiatric disorders severely impact patients' lives. Motivational, cognitive and emotional deficits are the most common symptoms observed in these patients and no effective treatment is still available, either due to the adverse side effects or the low rate of efficacy of currently available drugs. Neurogenesis recovery has been one important focus in the treatment of psychiatric disorders, which undeniably contributes to the therapeutic action of antidepressants. However, glial plasticity is emerging as a new strategy to explore the deficits observed in mood disorders and the efficacy of therapeutic interventions. Thus, it is crucial to understand the mechanisms behind glio- and neurogenesis to better define treatments and preventive therapies, once adult cytogenesis is of pivotal importance to cognitive and emotional components of behavior, both in healthy and pathological contexts, including in psychiatric disorders. Here, we review the concepts and history of neuro- and gliogenesis, providing as well a reflection on the functional importance of cytogenesis in the context of disease.

Adult Neural Stem Cells as Promising Targets in Psychiatric Disorders

The development of new therapies for psychiatric disorders is of utmost importance, given the enormous toll these disorders pose to society nowadays. This should be based on the identification of neural substrates and mechanisms that underlie disease etiopathophysiology. Adult neural stem cells (NSCs) have been emerging as a promising platform to counteract brain damage. In this perspective article, we put forth a detailed view of how NSCs operate in the adult brain and influence brain homeostasis, having profound implications at both behavioral and functional levels. We appraise evidence suggesting that adult NSCs play important roles in regulating several forms of brain plasticity, particularly emotional and cognitive flexibility, and that NSC dynamics are altered upon brain pathology. Furthermore, we discuss the potential therapeutic value of utilizing adult endogenous NSCs as vessels for regeneration, highlighting their importance as targets for the treatment of multiple mental illnesses, such as affective disorders, schizophrenia, and addiction. Finally, we speculate on strategies to surpass current challenges in neuropsychiatric disease modeling and brain repair.

Neural Stem Cells for Early Ischemic Stroke

Clinical treatments for ischemic stroke are limited. Neural stem cell (NSC) transplantation can be a promising therapy. Clinically, ischemia and subsequent reperfusion lead to extensive neurovascular injury that involves inflammation, disruption of the blood-brain barrier, and brain cell death. NSCs exhibit multiple potentially therapeutic actions against neurovascular injury. Currently, tissue plasminogen activator (tPA) is the only FDA-approved clot-dissolving agent. While tPA’s thrombolytic role within the vasculature is beneficial, tPA’s non-thrombolytic deleterious effects aggravates neurovascular injury, restricting the treatment time window (time-sensitive) and tPA eligibility. Thus, new strategies are needed to mitigate tPA’s detrimental effects and quickly mediate vascular repair after stroke. Up to date, clinical trials focus on the impact of stem cell therapy on neuro-restoration by delivering cells during the chronic stroke stage. Also, NSCs secrete factors that stimulate endogenous repair mechanisms for early-stage ischemic stroke. This review will present an integrated view of the preclinical perspectives of NSC transplantation as a promising treatment for neurovascular injury, with an emphasis on early-stage ischemic stroke. Further, this will highlight the impact of early sub-acute NSC delivery on improving short-term and long-term stroke outcomes.

Two Faces of Autophagy in the Struggle against Cancer

Autophagy can play a double role in cancerogenesis: it can either inhibit further development of the disease or protect cells, causing stimulation of tumour growth. This phenomenon is called "autophagy paradox", and is characterised by the features that the autophagy process provides the necessary substrates for biosynthesis to meet the cell's energy needs, and that the over-programmed activity of this process can lead to cell death through apoptosis. The fight against cancer is a difficult process due to high levels of resistance to chemotherapy and radiotherapy. More and more research is indicating that autophagy may play a very important role in the development of resistance by protecting cancer cells, which is why autophagy in cancer therapy can act as a "double-edged sword". This paper attempts to analyse the influence of autophagy and cancer stem cells on tumour development, and to compare new therapeutic strategies based on the modulation of these processes.

Cryogel biomaterials for neuroscience applications

Biomaterials in the form of 3D polymeric scaffolds have been used to create structurally and functionally biomimetic constructs of nervous system tissue. Such constructs can be used to model defects and disease or can be used to supplement neuronal tissue regeneration and repair. One such group of biomaterial scaffolds are hydrogels, which have been widely investigated for cell/tissue culture and as cell or molecule delivery systems in the field of neurosciences. However, a subset of hydrogels called cryogels, have shown to possess several distinct structural advantages over conventional hydrogel networks. Their macroporous structure, created via the time and resource efficient fabrication process (cryogelation) not only allows mass fluid transport throughout the structure, but also creates a high surface area to volume ratio for cell growth or drug loading. In addition, the macroporous structure of cryogels is ideal for applications in the central nervous system as they are very soft and spongey, yet also robust, which makes them a user-friendly and reproducible tool to address neuroscience challenges. In this review, we aim to provide the neuroscience community, who may not be familiar with the fundamental concepts of cryogels, an accessible summary of the basic information that pertain to their use in the brain and nervous tissue. We hope that this review shall initiate creative ways that cryogels could be further adapted and employed to tackle unsolved neuroscience challenges.

The Impact of Estrogen and Estrogen-Like Molecules in Neurogenesis and Neurodegeneration: Beneficial or Harmful?

Estrogens and estrogen-like molecules can modify the biology of several cell types. Estrogen receptors alpha (ERα) and beta (ERβ) belong to the so-called classical family of estrogen receptors, while the G protein-coupled estrogen receptor 1 (GPER-1) represents a non-classical estrogen receptor mainly located in the plasma membrane. As estrogen receptors are ubiquitously distributed, they can modulate cell proliferation, differentiation, and survival in several tissues and organs, including the central nervous system (CNS). Estrogens can exert neuroprotective roles by acting as anti-oxidants, promoting DNA repair, inducing the expression of growth factors, and modulating cerebral blood flow. Additionally, estrogen-dependent signaling pathways are involved in regulating the balance between proliferation and differentiation of neural stem/progenitor cells (NSPCs), thus influencing neurogenic processes. Since several estrogen-based therapies are used nowadays and estrogen-like molecules, including phytoestrogens and xenoestrogens, are omnipresent in our environment, estrogen-dependent changes in cell biology and tissue homeostasis have gained attention in human health and disease. This article provides a comprehensive literature review on the current knowledge of estrogen and estrogen-like molecules and their impact on cell survival and neurodegeneration, as well as their role in NSPCs proliferation/differentiation balance and neurogenesis.

L-lactate induces neurogenesis in the mouse ventricular-subventricular zone via the lactate receptor HCA1

AIM

Adult neurogenesis occurs in two major niches in the brain: the subgranular zone of the hippocampal formation and the ventricular-subventricular zone. Neurogenesis in both niches is reduced in ageing and neurological disease involving dementia. Exercise can rescue memory by enhancing hippocampal neurogenesis, but whether exercise affects adult neurogenesis in the ventricular-subventricular zone remains unresolved. Previously, we reported that exercise induces angiogenesis through activation of the lactate receptor HCA1. The aim of the present study is to investigate HCA₁ -dependent effects on neurogenesis in the two main neurogenic niches.

METHODS

Wild-type and HCA₁ knock-out mice received high intensity interval exercise, subcutaneous injections of L-lactate, or saline injections, five days per week for seven weeks. Well-established markers for proliferating cells (Ki-67) and immature neurons (doublecortin), were used to investigate neurogenesis in the subgranular zone and the ventricular-subventricular zone.

RESULTS

We demonstrated that neurogenesis in the ventricular-subventricular zone is enhanced by HCA₁ activation: Treatment with exercise or lactate resulted in increased neurogenesis in wild-type, but not in HCA₁ knock-out mice. In the subgranular zone, neurogenesis was induced by exercise in both genotypes, but unaffected by lactate treatment.

CONCLUSION

Our study demonstrates that neurogenesis in the two main neurogenic niches in the brain is regulated differently: Neurogenesis in both niches was induced by exercise, but only in the ventricular-subventricular zone was neurogenesis induced by lactate through HCA₁ activation. This opens for a role of HCA₁ in the physiological control of neurogenesis, and potentially in counteracting age-related cognitive decline.

The Role of Acupuncture Improving Cognitive Deficits due to Alzheimer's Disease or Vascular Diseases through Regulating Neuroplasticity

Dementia affects millions of elderly worldwide causing remarkable costs to society, but effective treatment is still lacking. Acupuncture is one of the complementary therapies that has been applied to cognitive deficits such as Alzheimer's disease (AD) and vascular cognitive impairment (VCI), while the underlying mechanisms of its therapeutic efficiency remain elusive. Neuroplasticity is defined as the ability of the nervous system to adapt to internal and external environmental changes, which may support some data to clarify mechanisms how acupuncture improves cognitive impairments. This review summarizes the up-to-date and comprehensive information on the effectiveness of acupuncture treatment on neurogenesis and gliogenesis, synaptic plasticity, related regulatory factors, and signaling pathways, as well as brain network connectivity, to lay ground for fully elucidating the potential mechanism of acupuncture on the regulation of neuroplasticity and promoting its clinical application as a complementary therapy for AD and VCI.

Long term intravital single cell tracking under multiphoton microscopy

Visualizing and tracking cells over time in a living organism has been a much-coveted dream before the invention of intravital microscopy. The opaque nature of tissue was a major hurdle that was remedied by the multiphoton microscopy. With the advancement of optical imaging and fluorescent labeling tools, intravital high resolution imaging has become increasingly accessible over the past few years. Long-term intravital tracking of single cells (LIST) under multiphoton microscopy provides a unique opportunity to gain insight into the longitudinal changes in the morphology, migration, or function of cells or subcellular structures. It is particularly suitable for studying slow-evolving cellular and molecular events during normal development or disease progression, without losing the opportunity of catching fast events such as calcium signals. Here, we review the application of LIST under 2-photon microscopy in various fields of neurobiology and discuss challenges and new directions in labeling and imaging methods for LIST. Overall, this review provides an overview of current applications of LIST in mammals, which is an emerging field that will contribute to a better understanding of essential molecular and cellular events in health and disease.

Leptin enhances adult neurogenesis and reduces pathological features in a transgenic mouse model of Alzheimer's disease

Alzheimer's disease (AD) is the most common dementia worldwide and is characterized by the presence of senile plaques by amyloid-beta (Aβ) and neurofibrillary tangles of hyperphosphorylated Tau protein. These changes lead to progressive neuronal degeneration and dysfunction, resulting in severe brain atrophy and cognitive deficits. With the discovery that neurogenesis persists in the adult mammalian brain, including brain regions affected by AD, studies of the use of neural stem cells (NSCs) for the treatment of neurodegenerative diseases to repair or prevent neuronal cell loss have increased. Here we demonstrate that leptin administration increases the neurogenic process in the dentate gyrus of the hippocampus as well as in the subventricular zone of lateral ventricles of adult and aged mice. Chronic treatment with leptin increased NSCs proliferation with significant effects on proliferation and differentiation of newborn cells. The expression of the long form of the leptin receptor, LepRb, was detected in the neurogenic niches by reverse qPCR and immunohistochemistry. Moreover, leptin modulated astrogliosis, microglial cell number and the formation of senile plaques. Additionally, leptin led to attenuation of Aβ-induced neurodegeneration and superoxide anion production as revealed by Fluoro-Jade B and dihydroethidium staining. Our study contributes to the understanding of the effects of leptin in the brain that may lead to the development of new therapies to treat Alzheimer's disease.

The Median Eminence, A New Oligodendrogenic Niche in the Adult Mouse Brain

The subventricular zone (SVZ) of the lateral ventricles and the subgranular zone (SGZ) of the dentate gyrus in the hippocampus are known as neurogenic niches. We show that the median eminence (ME) of the hypothalamus comprises BrdU+ newly proliferating cells co-expressing NG2 (oligodendrocyte progenitors) and RIP (pre-myelinating oligodendrocytes), suggesting their differentiation toward mature oligodendrocytes (OLs). ME cells can generate neurospheres (NS) in vitro, which differentiate mostly to OLs compared with SVZ-NS that typically generate neurons. Interestingly, this population of oligodendrocyte progenitors is increased in the ME from experimental autoimmune encephalomyelitis (EAE)-affected mice. Notably, the thrombospondin 1 (TSP1) expressed by astrocytes, acts as negative regulator of oligodendrogenesis in vitro and is downregulated in the ME of EAE mice. Importantly, transplanted ME-NS preferentially differentiate to MBP+ OLs compared with SVZ-NS in Shiverer mice. Hence, discovering the ME as a new site for myelin-producing cells has a great importance for advising future therapy for demyelinating diseases and spinal cord injury.

Neurogenesis: A process ontogenically linked to brain cavities and their content, CSF

Neurogenesis is the process underlying the development of the highly evolved central nervous system (CNS) in vertebrates. Neurogenesis takes place by differentiation of specific Neural Precursor Cells in the neurogenic niche. The main objective of this review is to highlight the specific relationship between the brain cavities, and neurogenesis from neural precursors. Brain cavities and their content, Cerebrospinal Fluid (CSF), establish a key relation with the neurogenic "niche" because of the presence in this fluid of neurogenic signals able to control neural precursor cell behaviour, inducing precursor proliferation and neuronal differentiation. This influence seems to be ontogenically preserved, despite the temporal and spatial variations that occur throughout life. In order to better understand this concept, we consider three main life periods in the CSF-Neurogenesis interaction: The "Embryonic" period, which take place at the Neural Tube stage and extends from the isolation of the neural tube at the end of "neurulation" to the beginning of Choroid Plexus activity; the "Fetal" period, which includes the remaining developmental and the early postnatal stages; and the "Adult" period, which continues for the rest of adult life. Each period has specific characteristics in respect of CSF synthesis and composition, and the location, extension and neurogenic activity of the neurogenic niche. However, CSF interaction with the neurogenic niche is a common factor, which should be taken into account to better understand the ontogeny of neuron formation and replacement, as well as its potential role in the success or failure of therapies for the ageing, injured or diseased brain.

Origin and development of circumventricular organs in living vertebrate

The circumventricular organs (CVOs) function by mediating chemical communication between blood and brain across the blood-brain barrier. Their origin and developmental mechanisms involved are not understood in enough detail due to a lack of molecular markers common for CVOs. These rather small and inconspicuous organs are found in close vicinity to the third and fourth brain ventricles suggestive of ancient evolutionary origin. Recently, an integrated approach based on analysis of CVOs development in the enhancer-trap transgenic zebrafish led to an idea that almost all of CVOs could be highlighted by GFP expression in this transgenic line. This in turn suggested that an enhancer along with a set of genes it regulates may illustrate the first common element of developmental regulation of CVOs. It seems to be related to a mechanism of suppression of the canonical Wnt/ β-catenin signaling that functions in development of fenestrated capillaries typical for CVOs. Based on that observation the common molecular elements of the putative developmental mechanism of CVOs will be discussed in this review.

Multiple functions of DYRK2 in cancer and tissue development

Dual-specificity tyrosine-regulated kinases (DYRKs) are evolutionarily conserved from yeast to mammals. Accumulating studies have revealed that DYRKs have important roles in regulation of the cell cycle and survival. DYRK2, a member of the class II DYRK family protein, is a key regulator of p53, and phosphorylates it at Ser46 to induce apoptosis in response to DNA damage. Moreover, recent studies have uncovered that DYRK2 regulates G1/S transition, epithelial-mesenchymal-transition, and stemness in human cancer cells. DYRK2 also appears to have roles in tissue development in lower eukaryotes. Thus, the elucidation of mechanisms for DYRK2 during mammalian tissue development will promote the understanding of cell differentiation, tissue homeostasis, and congenital diseases as well as cancer. In this review, we discuss the roles of DYRK2 in tumor cells. Moreover, we focus on DYRK2-dependent developmental mechanisms in several species including fly (Drosophila), worm (Caenorhabditis elegans), zebrafish (Danio rerio), and mammals.

High dose vs low dose irradiation of the subventricular zone in patients with glioblastoma-a systematic review and meta-analysis

PURPOSE

The published data indicate that the irradiation of the subventricular zone (SVZ) might play a role in the treatment of patients with glioblastoma (GBM). We aimed to determine whether radiation treatment doses (high vs low) applied to the SVZ can lead to an increase in progression free survival (PFS) and overall survival (OS).

PATIENTS AND METHODS

We undertook a systematic review and meta-analysis according to the PICOS research criteria of patients with glioblastoma which received high doses compared to low doses in order to determine if they have a better survival in observational and experimental studies.

RESULTS

Our survey of the literature yielded 2573 unique records. After screening, 17 were assessed for eligibility, and in the end 8 were included in the qualitative and 4 in the quantitative analysis. Subjects who received higher doses of ipsilateral SVZ (iSVZ) irradiation had a statistically significant better PFS than those receiving lower doses (HR 0.58 [95% CI 0.42-0.82], p=0.002). Subjects receiving higher doses of contralateral SVZ (cSVZ) irradiation did not have a statistically significant better PFS than those receiving lower doses (HR =0.89 [95% CI 0.35-2.26], p=0.81). Also for OS the subjects receiving higher doses to the iSVZ did not have a statistically significant better survival than those receiving lower doses (HR =0.75 [95% CI 0.51-1.11], p=0.15).

CONCLUSION

The data indicate a possible involvement of the SVZ in the onset and progression of the GBM, as well as a possible role of the SVZ in radiation therapy.

Neural Stem Cell Regulation by Adhesion Molecules Within the Subependymal Niche

In the mammalian adult brain, neural stem cells persist in neurogenic niches. The subependymal zone is the most prolific neurogenic niche in adult rodents, where residing stem cells generate large numbers of immature neurons that migrate into the olfactory bulb, where they differentiate into different types of interneurons. Subependymal neural stem cells derive from embryonic radial glia and retain some of their features like apico-basal polarity, with apical processes piercing the ependymal layer, and a basal process contacting blood vessels, constituting an epithelial niche. Conservation of the cytoarchitecture of the niche is of crucial importance for the maintenance of stem cells and for their neurogenic potential. In this minireview we will focus on extracellular matrix and adhesion molecules in the adult subependymal zone, showing their involvement not only as structural elements sustaining the niche architecture and topology, but also in the maintenance of stemness and regulation of the quiescence-proliferation balance.

Blood Vessels as Regulators of Neural Stem Cell Properties

In the central nervous system (CNS), a precise communication between the vascular and neural compartments is essential for proper development and function. Recent studies demonstrate that certain neuronal populations secrete various molecular cues to regulate blood vessel growth and patterning in the spinal cord and brain during development. Interestingly, the vasculature is now emerging as a critical component that regulates stem cell niches during neocortical development, as well as during adulthood. In this review article, we will first provide an overview of blood vessel development and maintenance in embryonic and adult neurogenic niches. We will also summarize the current understanding of how blood vessel-derived signals influence the behavior of neural stem cells (NSCs) during early development as well as in adulthood, with a focus on their metabolism.

Autophagy and cancer stem cells: molecular mechanisms and therapeutic applications

Autophagy and mitophagy act in cancer as bimodal processes, whose differential functions strictly depend on cancer ontogenesis, progression, and type. For instance, they can act to promote cancer progression by helping cancer cells survive stress or, instead, when mutated or abnormal, to induce carcinogenesis by influencing cell signaling or promoting intracellular toxicity. For this reason, the study of autophagy in cancer is the main focus of many researchers and several clinical trials are already ongoing to manipulate autophagy and by this way determine the outcome of disease therapy. Since the establishment of the cancer stem cell (CSC) theory and the discovery of CSCs in individual cancer types, autophagy and mitophagy have been proposed as key mechanisms in their homeostasis, dismissal or spread, even though we still miss a comprehensive view of how and by which regulatory molecules these two processes drive cell fate. In this review, we will dive into the deep water of autophagy, mitophagy, and CSCs and offer novel viewpoints on possible therapeutic strategies, based on the modulation of these degradative systems.

Neural stem cell niche heterogeneity

In mammals, new neurons can be generated from neural stem cells in specific regions of the adult brain. Neural stem cells are characterized by their abilities to differentiate into all neural lineages and to self-renew. The specific microenvironments regulating neural stem cells, commonly referred to as neurogenic niches, comprise multiple cell populations whose precise contributions are under active current exploration. Understanding the cross-talk between neural stem cells and their niche components is essential for the development of therapies against neurological disorders in which neural stem cells function is altered. In this review, we describe and discuss recent studies that identified novel components in the neural stem cell niche. These discoveries bring new concepts to the field. Here, we evaluate these recent advances that change our understanding of the neural stem cell niche heterogeneity and its influence on neural stem cell function.

miR-195 Has a Potential to Treat Ischemic and Hemorrhagic Stroke through Neurovascular Protection and Neurogenesis

Tissue plasminogen activator is the only U.S. FDA-approved therapy for ischemic stroke, while there is no specific medication for hemorrhagic stroke. Therefore, the treatment of acute stroke continues to be a major unmet clinical need. We explored the effects of miR-195 on neurovascular protection and its potential in treating acute stroke. Using both cellular and animal studies, we showed that miR-195’s beneficial effects are mediated by four mechanisms: (1) anti-apoptosis for injured neural cells by directly suppressing Sema3A/Cdc42/JNK signaling, (2) neural regeneration by promoting neural stem cell proliferation and migration, (3) anti-inflammation by directly blocking the NF-kB pathway, and (4) improvement of endothelial functions. We intravenously injected miR-195 carried by nanoparticles into rats with either ischemic or hemorrhagic stroke in the acute stage. The results showed that miR-195 reduced the size of brain damage and improved functional recovery in both types of stroke rats. The reduction of injured brain volume could be up to 45% in ischemic stroke and approximately 30% in hemorrhagic stroke. The therapeutic window between stroke onset and miR-195 treatment could be up to 6 h. Our data demonstrated that miR-195 possesses the potential to become a new drug to treat acute ischemic and hemorrhagic stroke.

Stem Cells in Psychiatry

The development of regenerative medicine has provided new perspectives in many scientific fields, including psychiatry. Stem cell research is getting us closer to discovering the biological foundation of mental disorders. In this chapter, we consider the information relating to stem cells and factors involved in their trafficking in peripheral blood in some psychiatric disorders (major depressive disorder, bipolar disorder, schizophrenia, anxiety disorder, and alcohol dependence). The authors also include the implementation of current research regarding neurogenesis in adult brain and induced pluripotent stem cells in investigating concerns in etiopathogenesis of mental disorders as well as the implication of research for treatment of these disorders.

Systemic Factors Trigger Vasculature Cells to Drive Notch Signaling and Neurogenesis in Neural Stem Cells in the Adult Brain

It is well documented that adult neural stem cells (NSCs) residing in the subventricular zone (SVZ) and the subgranular zone (SGZ) are induced to proliferate and differentiate into new neurons after injury such as stroke and hypoxia. However, the role of injury‐related cues in driving this process and the means by which they communicate with NSCs remains largely unknown. Recently, the coupling of neurogenesis and angiogenesis and the extensive close contact between vascular cells and other niche cells, known as the neurovascular unit (NVU), has attracted interest. Further facilitating communication between blood and NSCs is a permeable blood‐brain‐barrier (BBB) present in most niches, making vascular cells a potential conduit between systemic signals, such as vascular endothelial growth factor (VEGF), and NSCs in the niche, which could play an important role in regulating neurogenesis. We show that the leaky BBB in stem cell niches of the intact and stroke brain can respond to circulating VEGF₁₆₅ to drive induction of the Notch ligand DLL4 (one of the most important cues in angiogenesis) in endothelial cells (ECs), pericytes, and further induce significant proliferation and neurogenesis of stem cells. Stem Cells2019;37:395–406

Adaptive neurogenesis in the cerebral cortex and contralateral subventricular zone induced by unilateral cortical devascularization: Possible modulation by dopamine neurotransmission

Understanding endogenous neurogenesis and neuronal replacement to mature circuits is a topic of discussion as a therapeutic alternative under acute and chronic neurodegenerative disorders. Adaptive neurogenic response may result as a result of ischemia which could support long-term recovery of behavioral functions. Endogenous sources of neural progenitors may be stimulated by changes in blood flow or neuromodulation. Using a mouse model of unilateral cortical devascularization, we have observed reactive neurogenesis in the perilesional cortex and subventricular zone neurogenic niche. C57BL/6L 4 weeks old male mice were craneotomized at 1 mm caudal from frontal suture and 1 mm lateral from midline to generate a window of 3 mm side. Brain injury was produced by removal of the meninges and superficial vasculature of dorsal parietal cortex. BrdU agent (50 mg/kg, ip) was injected to lesioned and sham animals, during days 0 and 1 after surgery. Sagittal sections were analyzed at 1, 4, 7, and 10 days post-injury. A time-dependent increase in BrdU⁺ cells in the perilesional parietal cortex was accompanied by augmented BrdU⁺ cells in the sub ventricular and rostral migratory stream of ipsilateral and contralateral hemispheres. Neural progenitors and neuroblasts proliferated in the lesioned and non-lesioned subventricular zone and rostral migratory stream on day 4 after injury. Augmented contralateral neurogenesis was associated with an increase in vesicular monoamine transporter 2 protein in the striosomal sub ventricular neurogenic niche of non-lesioned hemisphere.

Biohybrids of scaffolding hyaluronic acid biomaterials plus adipose stem cells home local neural stem and endothelial cells: Implications for reconstruction of brain lesions after stroke

Endogenous neurogenesis in stroke is insufficient to replace the lost brain tissue, largely due to the lack of a proper biological structure to let new cells dwell in the damaged area. We hypothesized that scaffolds made of hyaluronic acid (HA) biomaterials (BM) could provide a suitable environment to home not only new neurons, but also vessels, glia and neurofilaments. Further, the addition of exogenous cells, such as adipose stem cells (ASC) could increase this effect. Athymic mice were randomly assigned to a one of four group: stroke alone, stroke and implantation of BM, stroke and implantation of BM with ASC, and sham operated animals. Stroke model consisted of middle cerebral artery thrombosis with FeCl₃ . After 30 days, animals underwent magnetic resonance imaging (MRI) and were sacrificed. Proliferation and neurogenesis increased at the subventricular zone ipsilateral to the ventricle and neuroblasts, glial, and endothelial cells forming capillaries were seen inside the BM. Those effects increased when ASC were added, while there was less inflammatory reaction. Three-dimensional scaffolds made of HA are able to home newly formed neurons, glia, and endothelial cells permitting the growth neurofilaments inside them. The addition of ASC increase these effects and decrease the inflammatory reaction to the implant. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 107B: 1598-1606, 2019.

Neuroglobin promotes neurogenesis through Wnt signaling pathway

Neuroglobin (Ngb) has been demonstrated by our lab and others to be neuroprotective against neurological disorders including stroke. However, the roles of Ngb in neurogenesis remain elusive. Neurogenesis can occur in adulthood and can be induced by pathological conditions in the brain such as stroke, and significantly contributes to functional recovery, thus enhancing endogenous neurogenesis may be a promising therapeutic strategy for neurodegenerative diseases. In this study we aimed to investigate the roles of Ngb in neurogenesis using Lentivirus overexpressing Ngb (Lv-Ngb). We show that Ngb overexpression promoted the proliferation of neural progenitor cells (NPC) marked by increased neurosphere number and size. Ngb overexpression also enhanced neuronal differentiation of cultured NPC under differentiation conditions. Moreover, subventricular injection of Lv-Ngb in mice after middle cerebral artery occlusion (MCAO) increased PSA-NCAM positive neuroblasts and Tuj1 positive immature neurons, suggesting that Ngb overexpression promotes neurogenesis in mice brain after stroke. We further show that the pro-neurogenesis effect of Ngb overexpression might be mediated through Dvl1 up-regulation, and subsequent activation of Wnt signaling, indicated by increased nuclear localization of beta-catenin. These results suggest that Ngb may play an important role in promoting neurogenesis in neurodegenerative diseases such as stroke, which may eventually benefit the development of stroke therapeutics targeting neurogenesis through Ngb upregulation.

Resident brain neural precursor cells develop age-dependent loss of therapeutic functions in Alzheimer's mice

There is vast knowledge on pathogenic mechanisms in Alzheimer's disease but very little on means by which the brain protects itself from disease. A major candidate in providing neuroprotection is the resident brain neural precursor/stem cell (NPC) pool. Transplanted NPCs possess powerful immune-modulatory and trophic properties in vivo and in vitro, underscoring the question whether resident brain NPCs have any role in regulating disease pathology in Alzheimer's disease, and particularly whether they fail to protect the brain from degeneration. To evaluate brain NPC function in relation to disease pathology, we first characterized the pathological properties of 5xFAD transgenic mouse model of Alzheimer's disease at different ages. We found that age 7 months is a critical time point of heavy amyloid deposition and gliosis but before neurodegeneration and a normal basal rate of NPC turnover in the subventricular zone (SVZ) of 5xFAD mice as compared to wild-type mice. Analysis of NPC functional properties showed that despite preserved rate of turnover, there was substantial SVZ NPC dysfunction as indicated by both ex vivo and in vivo assays. Freshly isolated NPCs from 7-month-old 5xFAD mice exhibited reduced expansion rate and diminished immune-modulatory and trophic properties. Moreover, there was slowed recovery of SVZ NPCs after cytosine-arabinoside insult and markedly reduced migratory response following a lysolecithin-induced lesion in the corpus callosum in vivo. Importantly, these functions were fully preserved in 2-month-old 5xFAD mice, a time point before Alzheimer's disease-specific pathological changes. There was reduced expression of key genes involved in NPC proliferative and migratory response in NPCs derived from 7-month-old 5xFAD mice. The dysfunctional properties and downregulation of gene expression were reversible in NPCs derived from 7-month-old 5xFAD mice following in vitro expansion and were reproduced in wild-type NPC by addition of amyloid beta peptide. Thus, there is age-dependent acquired NPC dysfunction, with loss of immune-modulatory and neurotrophic properties, which is induced by the pathological Alzheimer's brain environment at a critical time point before neurodegeneration. We suggest that failure of resident NPC to provide tissue support may be involved in promoting neurodegeneration.

Neural stem cell heterogeneity in the mammalian forebrain

The brain was long considered an organ that underwent very little change after development. It is now well established that the mammalian central nervous system contains neural stem cells that generate progeny that are capable of making new neurons, astrocytes, and oligodendrocytes throughout life. The field has advanced rapidly as it strives to understand the basic biology of these precursor cells, and explore their potential to promote brain repair. The purpose of this review is to present current knowledge about the diversity of neural stem cells in vitro and in vivo, and highlight distinctions between neural stem cell populations, throughout development, and within the niche. A comprehensive understanding of neural stem cell heterogeneity will provide insights into the cellular and molecular regulation of neural development and lifelong neurogenesis, and will guide the development of novel strategies to promote regeneration and neural repair.

Differential Response in Novel Stem Cell Niches of the Brain after Cervical Spinal Cord Injury and Traumatic Brain Injury

Populations of neural stem cells (NSCs) reside in a number of defined niches in the adult central nervous system (CNS) where they continually give rise to mature cell types throughout life, including newly born neurons. In addition to the prototypical niches of the subventricular zone (SVZ) and subgranular zone (SGZ) of the hippocampal dentate gyrus, novel stem cell niches that are also neurogenic have recently been identified in multiple midline structures, including circumventricular organs (CVOs) of the brain. These resident NSCs serve as a homeostatic source of new neurons and glial cells under intact physiological conditions. Importantly, they may also have the potential for reparative processes in pathological states such as traumatic spinal cord injury (SCI) and traumatic brain injury (TBI). As the response in these novel CVO stem cell niches has been characterized after stroke but not following SCI or TBI, we quantitatively assessed cell proliferation and the neuronal and glial lineage fate of resident NSCs in three CVO nuclei-area postrema (AP), median eminence (ME), and subfornical organ (SFO) -in rat models of cervical contusion-type SCI and controlled cortical impact (CCI)-induced TBI. Using bromodeoxyuridine (BrdU) labeling of proliferating cells, we find that TBI significantly enhanced proliferation in AP, ME, and SFO, whereas cervical SCI had no effects at early or chronic time-points post-injury. In addition, SCI did not alter NSC differentiation profile into doublecortin-positive neuroblasts, GFAP-expressing astrocytes, or Olig2-labeled cells of the oligodendrocyte lineage within AP, ME, or SFO at both time-points. In contrast, CCI induced a pronounced increase in Sox2- and doublecortin-labeled cells in the AP and Iba1-labeled microglia in the SFO. Lastly, plasma derived from CCI animals significantly increased NSC expansion in an in vitro neurosphere assay, whereas plasma from SCI animals did not exert such an effect, suggesting that signaling factors present in blood may be relevant to stimulating CVO niches after CNS injury and may explain the differential in vivo effects of SCI and TBI on the novel stem cell niches.

Stepwise impairment of neural stem cell proliferation and neurogenesis concomitant with disruption of blood-brain barrier in recurrent ischemic stroke

Stroke patients are at increased risk for recurrent stroke and development of post-stroke dementia. In this study, we investigated the effects of recurrent stroke on adult brain neurogenesis using a novel rat model of recurrent middle cerebral artery occlusion (MCAO) developed in our laboratory. Using BrdU incorporation, activation and depletion of stem cells in the subgranular zone (SGZ) and subventricular zone (SVZ) were assessed in control rats and rats after one or two strokes. In vitro neurosphere assay was used to assess the effects of plasma from normal and stroke rats. Also, EM and permeability studies were used to evaluate changes in the blood-brain-barrier (BBB) of the SGZ after recurrent stroke. We found that proliferation and neurogenesis was activated 14 days after MCAO. This was correlated with increased permeability in the BBB to factors which increase proliferation in a neurosphere assay. However, with each stroke, there was a stepwise decrease of proliferating stem cells and impaired neurogenesis on the ipsilateral side. On the contralateral side, this process stabilized after a first stroke. These studies indicate that stem cells are activated after MCAO, possibly after increased access to systemic stroke-related factors through a leaky BBB. However, the recruitment of stem cells for neurogenesis after stroke results in a stepwise ipsilateral decline with each ischemic event, which could contribute to post-stroke dementia.

Adult stem cells in psychiatric disorders - New discoveries in peripheral blood

The new area of research in psychiatric disorders is concerned with abnormal regeneration processes. The role of brain neurogenesis has been studied for decades. New discoveries, concerned with the pluripotency of VSEL cells and the role of factors involved in stem cell trafficking in peripheral blood create hope that it will be possible to develop a better understanding of the processes of neuroregeneration/neurodegeneration. There is an ongoing research investigating concentrations of: sphingosine -1-phosphate, SDF-1, elements of complement cascade, and stem cells in peripheral blood, including their possible connection to psychiatric disorders. Collected data, suggesting an abnormal course of regeneration processes in psychiatric disorders, raises hope of finding new potential markers of psychosis and anxiety disorders.

Inhibition of Drp1-mediated mitochondrial fission improves mitochondrial dynamics and bioenergetics stimulating neurogenesis in hippocampal progenitor cells from a Down syndrome mouse model

Functional and structural damages to mitochondria have been critically associated with the pathogenesis of Down syndrome (DS), a human multifactorial disease caused by trisomy of chromosome 21 and associated with neurodevelopmental delay, intellectual disability and early neurodegeneration. Recently, we demonstrated in neural progenitor cells (NPCs) isolated from the hippocampus of Ts65Dn mice -a widely used model of DS - a severe impairment of mitochondrial bioenergetics and biogenesis and reduced NPC proliferation. Here we further investigated the origin of mitochondrial dysfunction in DS and explored a possible mechanistic link among alteration of mitochondrial dynamics, mitochondrial dysfunctions and defective neurogenesis in DS. We first analyzed mitochondrial network and structure by both confocal and transmission electron microscopy as well as by evaluating the levels of key proteins involved in the fission and fusion machinery. We found a fragmentation of mitochondria due to an increase in mitochondrial fission associated with an up-regulation of dynamin-related protein 1 (Drp1), and a decrease in mitochondrial fusion associated with a down-regulation of mitofusin 2 (Mnf2) and increased proteolysis of optic atrophy 1 (Opa1). Next, using the well-known neuroprotective agent mitochondrial division inhibitor 1 (Mdivi-1), we assessed whether the inhibition of mitochondrial fission might reverse alteration of mitochondrial dynamics and mitochondrial dysfunctions in DS neural progenitors cells. We demonstrate here for the first time, that Mdivi-1 restores mitochondrial network organization, mitochondrial energy production and ultimately improves proliferation and neuronal differentiation of NPCs. This research paves the way for the discovery of new therapeutic tools in managing some DS-associated clinical manifestations.

Electromagnetic Fields for the Regulation of Neural Stem Cells

Localized magnetic fields (MFs) could easily penetrate the scalp, skull, and meninges, thus inducing an electrical current in both the central and peripheral nervous systems, which is primarily used in transcranial magnetic stimulation (TMS) for inducing specific effects on different regions or cells that play roles in various brain activities. Studies of repetitive transcranial magnetic stimulation (rTMS) have led to novel attractive therapeutic approaches. Neural stem cells (NSCs) in adult human brain are able to self-renew and possess multidifferential ability to maintain homeostasis and repair damage after acute central nervous system. In the present review, we summarized the electrical activity of NSCs and the fundamental mechanism of electromagnetic fields and their effects on regulating NSC proliferation, differentiation, migration, and maturation. Although it was authorized for the rTMS use in resistant depression patients by US FDA, there are still unveiling mechanism and limitations for rTMS in clinical applications of acute central nervous system injury, especially on NSC regulation as a rehabilitation strategy. More in-depth studies should be performed to provide detailed parameters and mechanisms of rTMS in further studies, making it a powerful tool to treat people who are surviving with acute central nervous system injuries.

Elements of the niche for adult stem cell expansion

Adult stem cells are crucial for tissue homeostasis. These cells reside within exclusive locations in tissues, termed niches, which protect adult stem cell fidelity and regulate their many functions through biophysical-, biochemical- and cellular-mediated mechanisms. There is a growing understanding of how these mechanisms and their components contribute towards maintaining stem cell quiescence, self-renewal, expansion and differentiation patterns. In vitro expansion of adult stem cells is a powerful tool for understanding stem cell biology, and for tissue engineering and regenerative medicine applications. However, it is technically challenging, since adult stem cell removal from their native microenvironment has negative repercussions on their sustainability. In this review, we overview specific elements of the biomimetic niche and how recreating such elements can help in vitro propagation of adult stem cells.

Prolonged human neural stem cell maturation supports recovery in injured rodent CNS

Neural stem cells (NSCs) differentiate into both neurons and glia, and strategies using human NSCs have the potential to restore function following spinal cord injury (SCI). However, the time period of maturation for human NSCs in adult injured CNS is not well defined, posing fundamental questions about the design and implementation of NSC-based therapies. This work assessed human H9 NSCs that were implanted into sites of SCI in immunodeficient rats over a period of 1.5 years. Notably, grafts showed evidence of continued maturation over the entire assessment period. Markers of neuronal maturity were first expressed 3 months after grafting. However, neurogenesis, neuronal pruning, and neuronal enlargement continued over the next year, while total graft size remained stable over time. Axons emerged early from grafts in very high numbers, and half of these projections persisted by 1.5 years. Mature astrocyte markers first appeared after 6 months, while more mature oligodendrocyte markers were not present until 1 year after grafting. Astrocytes slowly migrated from grafts. Notably, functional recovery began more than 1 year after grafting. Thus, human NSCs retain an intrinsic human rate of maturation, despite implantation into the injured rodent spinal cord, yet they support delayed functional recovery, a finding of great importance in planning human clinical trials.

The Adaptability of Somatic Stem Cells: A Review

Cell and tissue specific somatic stem cells develop as dynamic populations of precursor cells to discrete tissue and organ differentiation during embryonic and fetal stages and their potential evolves with development. Some of their progeny are sequestered into separate cell niches of tissues as adult somatic stem cells at various times during organ development and differentiation These are diverse cell populations of stem and progenitor cells that respond to homeostatic needs for cell and tissue maintenance and the cycling of differentiated cells for physiological/ endocrinological changes. Nominally, multipotent stem cells in one or more niches follow specific lineages of differentiation that can be followed by diverse markers of differentiation. The activation of precursors appears to be stochastic and results in a population of heterogeneous progenitor cells. When variations in the functional need of the tissue or organ occurs, the progenitor cells exhibit flexibility in their differentiation capacity. Regulation of the progenitors is the result of signals from the stem cell niche that can cause adaptive changes in the behavior or function of the stem -progenitor cell lineage. A possible mechanism may be alteration in the differentiation capacity of the resident or introduced cells. Certain quiescent stem cells also serve as a potential cell reservoir for trauma induced cell regeneration through adaptive changes in differentiation of stem cells, progenitor cells and differentiated cells. If the stem-progenitor cell population is normally depleted or destroyed by trauma, differentiated cells from the niche microenvironment can restore the specific stem potency which suggests the process of dedifferentiation.

Nutrients, neurogenesis and brain ageing: From disease mechanisms to therapeutic opportunities

Appreciation of the physiological relevance of mammalian adult neurogenesis has in recent years rapidly expanded from a phenomenon of homeostatic cell replacement and brain repair to the current view of a complex process involved in high order cognitive functions. In parallel, an array of endogenous or exogenous triggers of neurogenesis has also been identified, among which metabolic and nutritional cues have drawn significant attention. Converging evidence from animal and in vitro studies points to nutrient sensing and energy metabolism as major physiological determinants of neural stem cell fate, and modulators of the whole neurogenic process. While the cellular and molecular circuitries underlying metabolic regulation of neurogenesis are still incompletely understood, the key role of mitochondrial activity and dynamics, and the importance of autophagy have begun to be fully appreciated; moreover, nutrient-sensitive pathways and transducers such as the insulin-IGF cascade, the AMPK/mTOR axis and the transcription regulators CREB and Sirt-1 have been included, beside more established "developmental" signals like Notch and Wnt, in the molecular networks that dictate neural-stem-cell self-renewal, migration and differentiation in response to local and systemic inputs. Many of these nutrient-related cascades are deregulated in the contest of metabolic diseases and in ageing, and may contribute to impaired neurogenesis and thus to cognition defects observed in these conditions. Importantly, accumulating knowledge on the metabolic control of neurogenesis provides a theoretical framework for the trial of new or repurposed drugs capable of interfering with nutrient sensing as enhancers of neurogenesis in the context of neurodegeneration and brain senescence.

TC003132 is essential for the follicle stem cell lineage in telotrophic Tribolium oogenesis

Background

Stem cells are undifferentiated cells with a potential for self-renewal, which are essential to support normal development and homeostasis. To gain insight into the molecular mechanisms underlying adult stem cell biology and organ evolution, we use the telotrophic ovary of the beetle Tribolium. To this end, we participated in a large-scale RNAi screen in the red flour beetle Tribolium, which identified functions in embryonic and postembryonic development for more than half of the Tribolium genes.

Results

We identified TC003132 as candidate gene for the follicle stem cell linage in telotrophic Tribolium oogenesis. TC003132 belongs to the Casein Kinase 2 substrate family (CK2S), which in humans is associated with the proliferative activity of different cancers. Upon TC003132 RNAi, central pre-follicular cells are lost, which results in termination of oogenesis. Given that also Notch-signalling is required to promote the mitotic activity of central pre-follicular cells, we performed epistasis experiments with Notch and cut. In addition, we identified a putative follicle stem cell population by monitoring the mitotic pattern of wild type and TC003132 depleted follicle cells by EdU incorporations. In TC003132 RNAi these putative FSCs cease the expression of differentiation makers and are eventually lost.

Conclusions

TC003132 depleted pre-follicular cells neither react to mitosis or endocycle stimulating signals, suggesting that TC003132 provides competence for differentiation cues. This may resemble the situation in C. elegans were CK2 is required to maintain the balance between proliferation and differentiation in the germ line. Since the earliest effect of TC003132 RNAi is characterized by the loss of putative FSCs, we posit that TC003132 crucially contributes to the proliferation or maintenance of follicle stem cells in the telotrophic Tribolium ovary.

Electronic supplementary material

The online version of this article (doi:10.1186/s12983-017-0212-2) contains supplementary material, which is available to authorized users.