Vascular-derived TGF-β increases in the stem cell niche and perturbs neurogenesis during aging and following irradiation in the adult mouse brain

Epothilone B impairs functional recovery after spinal cord injury by increasing secretion of macrophage colony-stimulating factor

The microtubule-stabilizing drug epothilone B (epoB) has shown potential value in the treatment of spinal cord injury (SCI) through diverse mechanisms. However, it remains elusive why a limited overall effect was observed. We aim to investigate the limiting factors underlying functional recovery promoted by epoB. The same SCI model treated by epoB was established as discussed previously. We used a cerebrospinal fluid (CSF) sample to assess the changes in cytokines in milieu of the SCI lesion site after epoB treatment. We then analyzed the source of cytokines, the state of microglia/macrophages/monocytes (M/Ms), and the recruitment of neutrophil in the lesion site by using the results of antibody array. Following these findings, we further evaluated the motor functional recovery caused by the reshaped microenvironment. Systemic administration of epoB significantly increased levels of several cytokines in the CSF of the rat SCI model; macrophage colony-stimulating factor (M-CSF) secreted by intact central nervous system (CNS) cells was one of the cytokines with increased levels. Along with epoB and other cytokines, M-CSF reshapes the SCI milieu by activating the microglias, killing bone marrow-derived macrophages, polarizing the M/M to M1 phenotype, and activating downstream cytokines to exacerbate the SCI injury, but it also increases the expression of neurotrophic factors. Anti-inflammatory therapy using a neutralizing antibody mix shows encouraging results. Using in vivo experiments, our findings indicate that epoB inhibits the SCI functional recovery in many ways by reshaping the milieu, which counteracts the therapeutic efficacy that led to the limited overall effectiveness.

Effect of captopril on radiation-induced TGF-β1 secretion in EA.Hy926 human umbilical vein endothelial cells

The pathophysiological mechanism involved in the sustained endothelial secretion of cytokines that leads to fibrosis 6–16 months after radiotherapy remains unclear. Angiotensin II (Ang II) is produced by the endothelium in response to stressing stimuli, like radiation, and may induce the synthesis of TGF-β, a profibrotic cytokine. In this study we tested the hypothesis that captopril, an angiotensin-converting enzyme (ACE) inhibitor, inhibits or attenuates radiation-induced endothelial TGF-β1 secretion. The human endothelial hybrid cell line EA.HY926 was irradiated with split doses of x-rays (28 Gy delivered in 14 fractions of 2 Gy). TGF-β1 mRNA, TNF-α mRNA and TGF-β1 protein levels were evaluated by RT-PCR and western blotting each month until the fifth month post radiation. Ang II was detected using radioimmunoassays, NF-κB activity was examined using EMSA, and western blotting was used to detect the expression of Iκ-Bα. To explore the role of Ang II on radiation-induced TGF-β1 release and Iκ-Bα expression, captopril was added to cultured cells before, during, or after irradiation. Sustained strong expression of TGF-β1 was observed after conventional fractionated irradiation. TNF-α, Ang II, and NF-κB activity were also increased in EA.Hy926 cells after radiation. Captopril decreased Ang II expression, inhibited the NF-κB pathway and reduced TGF-β1 expression. These data suggest that captopril might protect the endothelium from radiation-induced injury.

Inhibition of the transforming growth factor-β/SMAD cascade mitigates the anti-neurogenic effects of the carbamate pesticide carbofuran

The widely used carbamate pesticide carbofuran causes neurophysiological and neurobehavioral deficits in rodents and humans and therefore poses serious health hazards around the world. Previously, we reported that gestational carbofuran exposure has detrimental effects on hippocampal neurogenesis, the generation of new neurons from neural stem cells (NSC), in offspring. However, the underlying cellular and molecular mechanisms for carbofuran-impaired neurogenesis remain unknown. Herein, we observed that chronic carbofuran exposure from gestational day 7 to postnatal day 21 altered expression of genes and transcription factors and levels of proteins involved in neurogenesis and the TGF-β pathway (i.e. TGF-β; SMAD-2, -3, and -7; and SMURF-2) in the rat hippocampus. We found that carbofuran increases TGF-β signaling (i.e. increased phosphorylated SMAD-2/3 and reduced SMAD-7 expression) in the hippocampus, which reduced NSC proliferation because of increased p21 levels and reduced cyclin D1 levels. Moreover, the carbofuran-altered TGF-β signaling impaired neuronal differentiation (BrdU/DCX⁺ and BrdU/NeuN⁺ cells) and increased apoptosis and neurodegeneration in the hippocampus. Blockade of the TGF-β pathway with the specific inhibitor SB431542 and via SMAD-3 siRNA prevented carbofuran-mediated inhibition of neurogenesis in both hippocampal NSC cultures and the hippocampus, suggesting the specific involvement of this pathway. Of note, both in vitro and in vivo studies indicated that TGF-β pathway attenuation reverses carbofuran's inhibitory effects on neurogenesis and associated learning and memory deficits. These results suggest that carbofuran inhibits NSC proliferation and neuronal differentiation by altering TGF-β signaling. Therefore, we conclude that TGF-β may represent a potential therapeutic target against carbofuran-mediated neurotoxicity and neurogenesis disruption.

The blood brain barrier: Insights from development and ageing

The blood brain barrier is a necessity for cerebral homeostasis and response to environmental insult, thus loss in functionality with age creates opportunities for disease to arise in the aged brain. Understanding how the barrier is developed and maintained throughout the earlier years of adult life can identify key processes that may have beneficial applications in the restoration of the aged brain. With an unprecedented increasing global aged population, the prevention and treatment of age-associated disorders has become a rising healthcare priority demanding novel approaches for the development of therapeutic strategies. The aging cardiovascular system has long been recognised to be a major factor in age-associated diseases such as stroke, atherosclerosis and cardiac arrest. Changes in the highly specialised cerebral vasculature may similarly drive neurodegenerative and neuropsychiatric disease.

Stem Cells and Other Emerging Agents as Innovative "Drugs" in Neurodegenerative Diseases: Benefits and Limitations

The brain has a limited process of repair/regeneration linked to the restricted and localized activity of neuronal stem cells. Consequently, it shows a reduced capacity to counteract the age-related loss of neural and glial cells and to repair the consequent injuries/lesions of nervous system. This progressively determines nervous dysfunction and onset/progression of neurodegenerative diseases, which represent a serious social (and economic) problem of our populations. Thus, the research of efficient treatments is encouraged. Stem cell therapy might represent a solution. Today, it, indeed, represents the object of intensive research with the hope of using it, in a near future, as effective therapy for these diseases and preventive treatment in susceptible individuals. Here, we report and discuss the data of the recent studies on this field, underling the obstacles and benefits. We also illustrate alternative measures of intervention, which represent another parallel aim for the care of neurodegenerative pathology-affected individuals. Thus, the road for delaying or retarding these diseases appears hard and long, but the advances might be different.

Rejuvenating Strategies for Stem Cell-Based Therapies in Aging

Recent advances in our understanding of tissue regeneration and the development of efficient approaches to induce and differentiate pluripotent stem cells for cell replacement therapies promise exciting avenues for treating degenerative age-related diseases. However, clinical studies and insights from model organisms have identified major roadblocks that normal aging processes impose on tissue regeneration. These new insights suggest that specific targeting of environmental niche components, including growth factors, ECM, and immune cells, and intrinsic stem cell properties that are affected by aging will be critical for the development of new strategies to improve stem cell function and optimize tissue repair processes.

Cancer Cell Death-Inducing Radiotherapy: Impact on Local Tumour Control, Tumour Cell Proliferation and Induction of Systemic Anti-tumour Immunity

Radiotherapy (RT) predominantly is aimed to induce DNA damage in tumour cells that results in reduction of their clonogenicity and finally in tumour cell death. Adaptation of RT with higher single doses has become necessary and led to a more detailed view on what kind of tumour cell death is induced and which immunological consequences result from it. RT is capable of rendering tumour cells immunogenic by modifying the tumour cell phenotype and the microenvironment. Danger signals are released as well as the senescence-associated secretory phenotype. This results in maturation of dendritic cells and priming of cytotoxic T cells as well as in activation of natural killer cells. However, RT on the other hand can also result in immune suppressive events including apoptosis induction and foster tumour cell proliferation. That's why RT is nowadays increasingly combined with selected immunotherapies.

Factors Released from Endothelial Cells Exposed to Flow Impact Adhesion, Proliferation, and Fate Choice in the Adult Neural Stem Cell Lineage

The microvasculature within the neural stem cell (NSC) niche promotes self-renewal and regulates lineage progression. Previous work identified endothelial-produced soluble factors as key regulators of neural progenitor cell (NPC) fate and proliferation; however, endothelial cells (ECs) are sensitive to local hemodynamics, and the effect of this key physiological process has not been defined. In this study, we evaluated adult mouse NPC response to soluble factors isolated from static or dynamic (flow) EC cultures. Endothelial factors generated under dynamic conditions significantly increased neuronal differentiation, while those released under static conditions stimulated oligodendrocyte differentiation. Flow increases EC release of neurogenic factors and of heparin sulfate glycosaminoglycans that increase their bioactivity, likely underlying the enhanced neuronal differentiation. Additionally, endothelial factors, especially from static conditions, promoted adherent growth. Together, our data suggest that blood flow may impact proliferation, adhesion, and the neuron-glial fate choice of adult NPCs, with implications for diseases and aging that reduce flow.

Pharmacogenomic identification of small molecules for lineage specific manipulation of subventricular zone germinal activity

Strategies for promoting neural regeneration are hindered by the difficulty of manipulating desired neural fates in the brain without complex genetic methods. The subventricular zone (SVZ) is the largest germinal zone of the forebrain and is responsible for the lifelong generation of interneuron subtypes and oligodendrocytes. Here, we have performed a bioinformatics analysis of the transcriptome of dorsal and lateral SVZ in early postnatal mice, including neural stem cells (NSCs) and their immediate progenies, which generate distinct neural lineages. We identified multiple signaling pathways that trigger distinct downstream transcriptional networks to regulate the diversity of neural cells originating from the SVZ. Next, we used a novel in silico genomic analysis, searchable platform-independent expression database/connectivity map (SPIED/CMAP), to generate a catalogue of small molecules that can be used to manipulate SVZ microdomain-specific lineages. Finally, we demonstrate that compounds identified in this analysis promote the generation of specific cell lineages from NSCs in vivo, during postnatal life and adulthood, as well as in regenerative contexts. This study unravels new strategies for using small bioactive molecules to direct germinal activity in the SVZ, which has therapeutic potential in neurodegenerative diseases.

The subventricular zone (SVZ) is the largest germinal zone of the postnatal and adult brain. It contains neural stem cells (NSCs) that give rise to neurons and oligodendrocytes (OLs) in a region-specific manner. Here, we use a bioinformatics approach to identify multiple signaling pathways that regulate the diversity of cell lineages that originate from different subregions of the SVZ. We further use a computational-based drug-discovery strategy to identify a catalogue of small molecules that can be used to manipulate the regionalization of the SVZ. We provide proof that, by administration of small molecules in vivo, it is possible to promote the specific generation of neurons and OLs from NSCs in both the postnatal and adult brain, as well as in regenerative contexts after lesion. This study unravels novel strategies for using small bioactive molecules to direct germinal activity in the SVZ, which has therapeutic potential in neurodegenerative diseases.

Efficient generation of functional Schwann cells from adipose-derived stem cells in defined conditions

Schwann cells (SCs) are hitherto regarded as the most promising candidates for viable cell-based therapy to peripheral nervous system (PNS) injuries or degenerative diseases. However, the extreme drawbacks of transplanting autologous SCs for clinical applications still represent a significant bottleneck in neural regenerative medicine, mainly owing to the need of sacrificing a functional nerve to generate autologous SCs and the nature of slow expansion of the SCs. Thus, it is of great importance to establish an alternative cell system for the generation of sufficient SCs. Here, we demonstrated that adipose-derived stem cells (ADSCs) of rat robustly give rise to morphological, phenotypic and functional SCs using an optimized protocol. After undergoing a 3-week in vitro differentiation, almost all of treated ADSCs exhibited spindle shaped morphology similar to genuine SCs and expressed SC markers GFAP and S100. Most importantly, apart from acquisition of SC antigenic and biochemical features, the ADSC-derived SCs were functionally identical to native SCs as they possess a potential ability to form myelin, and secret nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF) and glia-derived neurotrophic factor (GDNF). The current study may provide an ideal strategy for harvesting sufficient SCs for cell-based treatment of various peripheral nerve injuries or disorders.

The vasculature as a neural stem cell niche

Neural stem cells (NSCs) are multipotent, self-renewing progenitors that generate progeny that differentiate into neurons and glia. NSCs in the adult mammalian brain are generally quiescent. Environmental stimuli such as learning or exercise can activate quiescent NSCs, inducing them to proliferate and produce new neurons and glia. How are these behaviours coordinated? The neurovasculature, the circulatory system of the brain, is a key component of the NSC microenvironment, or 'niche'. Instructive signals from the neurovasculature direct NSC quiescence, proliferation, self-renewal and differentiation. During ageing, a breakdown in the niche accompanies NSC dysfunction and cognitive decline. There is much interest in reversing these changes and enhancing NSC activity by targeting the neurovasculature therapeutically. Here we discuss principles of neurovasculature-NSC crosstalk, and the implications for the design of NSC-based therapies. We also consider the emerging contributions to this field of the model organism Drosophila melanogaster.

The Feather Model for Chemo- and Radiation Therapy-Induced Tissue Damage

Chemo- and radiation therapy are the main modalities for cancer treatment. A major limiting factor is their toxicity to normal tissue, thus reducing the dose and duration of the therapy. The hair follicle, gastrointestinal tract, and hematopoietic system are among the target organs that often show side effects in cancer therapy . Although these organs are highly mitotic in common, the molecular mechanism of the damage remains unclear. The feather follicle is a fast-growing mini-organ, which allows observation and manipulation on each follicle individually. As a model system, the feather follicle is advantageous because of the following reasons: (1) its complex structure is regulated by a set of evolutionarily conserved molecular pathways, thus facilitating the effort to dissect the specific signaling events involved; (2) its morphology allows the continuity of normal-perturbed-normal structure in a single feather, thus "recording" the damaging effect of chemo- and radiation therapy; (3) further histological and molecular analysis of the damage response can be performed on each plucked feather; thus, it is not necessary to sacrifice the experimental animal. Here, we describe methods of applying the feather model to study the molecular mechanism of chemo- and radiation therapy-induced tissue damage.

Regulation of Asymmetric Cell Division in Mammalian Neural Stem and Cancer Precursor Cells

Stem and progenitor cells are characterized by their abilities to self-renew and produce differentiated progeny. The balance between self-renewal and differentiation is achieved through control of cell division mode, which can be either asymmetric or symmetric. Failure to properly control cell division mode may result in premature depletion of the stem/progenitor cell pool or abnormal growth and impaired differentiation. In many tissues, including the brain, stem cells and progenitor cells undergo asymmetric cell division through the establishment of cell polarity. Cell polarity proteins are therefore potentially critical regulators of asymmetric cell division. Decrease or loss of asymmetric cell division can be associated with reduced differentiation common during aging or impaired remyelination as seen in demyelinating diseases. Progenitor-like glioma precursor cells show decreased asymmetric cell division rates and increased symmetric divisions, which suggests that asymmetric cell division suppresses brain tumor formation. Cancer stem cells, on the other hand, still undergo low rates of asymmetric cell division, which may provide them with a survival advantage during therapy. These findings led to the hypotheses that asymmetric cell divisions are not always tumor suppressive but can also be utilized to maintain a cancer stem cell population. Proper control of cell division mode is therefore not only deemed necessary to generate cellular diversity during development and to maintain adult tissue homeostasis but may also prevent disease and determine disease progression. Since brain cancer is most common in the adult and aging population, we review here the current knowledge on molecular mechanisms that regulate asymmetric cell divisions in the neural and oligodendroglial lineage during development and in the adult brain.

Adult NSC diversity and plasticity: the role of the niche

Adult somatic stem cells are generally defined as cells with the ability to differentiate into multiple different lineages and to self-renew during long periods of time. These features were long presumed to be represented in one single tissue-specific stem cell. Recent development of single-cell technologies reveals the existence of diversity in fate and activation state of somatic stem cells within the blood, skin and intestinal compartments [1] but also in the adult brain. Here we review how recent advances have expanded our view of neural stem cells (NSCs) as a diverse pool of cells and how the specialized microenvironment in which they reside acts to maintain this diversity. In addition, we discuss the plasticity of the system in the injured brain.

A mosaic world: puzzles revealed by adult neural stem cell heterogeneity

Neural stem cells (NSCs) reside in specialized niches in the adult mammalian brain. The ventricular-subventricular zone (V-SVZ), adjacent to the lateral ventricles, gives rise to olfactory bulb (OB) neurons, and some astrocytes and oligodendrocytes throughout life. In vitro assays have been widely used to retrospectively identify NSCs. However, cells that behave as stem cells in vitro do not reflect the identity, diversity, and behavior of NSCs in vivo. Novel tools including fluorescence activated cell sorting, lineage-tracing, and clonal analysis have uncovered multiple layers of adult V-SVZ NSC heterogeneity, including proliferation state and regional identity. In light of these findings, we reexamine the concept of adult NSCs, considering heterogeneity as a key parameter for analyzing their dynamics in vivo. V-SVZ NSCs form a mosaic of quiescent (qNSCs) and activated cells (aNSCs) that reside in regionally distinct microdomains, reflecting their regional embryonic origins, and give rise to specific subtypes of OB interneurons. Prospective purification and transcriptome analysis of qNSCs and aNSCs has illuminated their molecular and functional properties. qNSCs are slowly dividing, have slow kinetics of neurogenesis in vivo, can be recruited to regenerate the V-SVZ, and only rarely give rise to in vitro colonies. aNSCs are highly proliferative, undergo rapid clonal expansion of the neurogenic lineage in vivo, and readily form in vitro colonies. Key open questions remain about stem cell dynamics in vivo and the lineage relationship between qNSCs and aNSCs under homeostasis and regeneration, as well as context-dependent plasticity of regionally distinct adult NSCs under different external stimuli. WIREs Dev Biol 2016, 5:640-658. doi: 10.1002/wdev.248 For further resources related to this article, please visit the WIREs website.

P53 regulates disruption of neuronal development in the adult hippocampus after irradiation

Inhibition of hippocampal neurogenesis is implicated in neurocognitive dysfunction after cranial irradiation for brain tumors. How irradiation results in impaired neuronal development remains poorly understood. The Trp53 (p53) gene is known to regulate cellular DNA damage response after irradiation. Whether it has a role in disruption of late neuronal development remains unknown. Here we characterized the effects of p53 on neuronal development in adult mouse hippocampus after irradiation. Different bromodeoxyuridine incorporation paradigms and a transplantation study were used for cell fate mapping. Compared with wild-type mice, we observed profound inhibition of hippocampal neurogenesis after irradiation in mice deficient in p53 despite the absence of acute apoptosis of neuroblasts. The putative neural stem cells were apoptosis resistant after irradiation regardless of p53 genotype. Cell fate mapping using different bromodeoxyuridine incorporation paradigms revealed enhanced activation of neural stem cells and their consequential exhaustion in the absence of p53 after irradiation. Both p53-knockout and wild-type mice demonstrated similar extent of microglial activation in the hippocampus after irradiation. Impairment of neuronal differentiation of neural progenitors transplanted in irradiated hippocampus was not altered by p53 genotype of the recipient mice. We conclude that by inhibiting neural progenitor activation, p53 serves to mitigate disruption of neuronal development after irradiation independent of apoptosis and perturbation of the neural stem cell niche. These findings suggest for the first time that p53 may have a key role in late effects in brain after irradiation.

Hedgehog Controls Quiescence and Activation of Neural Stem Cells in the Adult Ventricular-Subventricular Zone

Identifying the mechanisms controlling quiescence and activation of neural stem cells (NSCs) is crucial for understanding brain repair. Here, we demonstrate that Hedgehog (Hh) signaling actively regulates different pools of quiescent and proliferative NSCs in the adult ventricular-subventricular zone (V-SVZ), one of the main brain neurogenic niches. Specific deletion of the Hh receptor Patched in NSCs during adulthood upregulated Hh signaling in quiescent NSCs, progressively leading to a large accumulation of these cells in the V-SVZ. The pool of non-neurogenic astrocytes was not modified, whereas the activated NSC pool increased after a short period, before progressively becoming exhausted. We also showed that Sonic Hedgehog regulates proliferation of activated NSCs in vivo and shortens both their G₁ and S-G₂/M phases in culture. These data demonstrate that Hh orchestrates the balance between quiescent and activated NSCs, with important implications for understanding adult neurogenesis under normal homeostatic conditions or during injury.

Systemic Problems: A perspective on stem cell aging and rejuvenation

This review provides balanced analysis of the advances in systemic regulation of young and old tissue stem cells and suggests strategies for accelerating development of therapies to broadly combat age-related tissue degenerative pathologies. Many highlighted recent reports on systemic tissue rejuvenation combine parabiosis with a “silver bullet” putatively responsible for the positive effects. Attempts to unify these papers reflect the excitement about this experimental approach and add value in reproducing previous work. At the same time, defined molecular approaches, which are “beyond parabiosis” for the rejuvenation of multiple old organs represent progress toward attenuating or even reversing human tissue aging.

When stem cells grow old: phenotypes and mechanisms of stem cell aging

All multicellular organisms undergo a decline in tissue and organ function as they age. An attractive theory is that a loss in stem cell number and/or activity over time causes this decline. In accordance with this theory, aging phenotypes have been described for stem cells of multiple tissues, including those of the hematopoietic system, intestine, muscle, brain, skin and germline. Here, we discuss recent advances in our understanding of why adult stem cells age and how this aging impacts diseases and lifespan. With this increased understanding, it is feasible to design and test interventions that delay stem cell aging and improve both health and lifespan.

Age-Associated Increase in BMP Signaling Inhibits Hippocampal Neurogenesis

Hippocampal neurogenesis, the product of resident neural stem cell proliferation and differentiation, persists into adulthood but decreases with organismal aging, which may contribute to the age-related decline in cognitive function. The mechanisms that underlie this decrease in neurogenesis are not well understood, although evidence in general indicates that extrinsic changes in an aged stem cell niche can contribute to functional decline in old stem cells. Bone morphogenetic protein (BMP) family members are intercellular signaling proteins that regulate stem and progenitor cell quiescence, proliferation, and differentiation in various tissues and are likewise critical regulators of neurogenesis in young adults. Here, we establish that BMP signaling increases significantly in old murine hippocampi and inhibits neural progenitor cell proliferation. Furthermore, direct in vivo attenuation of BMP signaling via genetic and transgenic perturbations in aged mice led to elevated neural stem cell proliferation, and subsequent neurogenesis, in old hippocampi. Such advances in our understanding of mechanisms underlying decreased hippocampal neurogenesis with age may offer targets for the treatment of age-related cognitive decline.

Unmasking the responses of the stem cells and progenitors in the subventricular zone after neonatal and pediatric brain injuries

There is great interest in the regenerative potential of the neural stem cells and progenitors that populate the subventricular zone (SVZ). However, a comprehensive understanding of SVZ cell responses to brain injuries has been hindered by the lack of sensitive approaches to study the cellular composition of this niche. Here we review progress being made in deciphering the cells of the SVZ gleaned from the use of a recently designed flow cytometry panel that allows SVZ cells to be parsed into multiple subsets of progenitors as well as putative stem cells. We review how this approach has begun to unmask both the heterogeneity of SVZ cells as well as the dynamic shifts in cell populations with neonatal and pediatric brain injuries. We also discuss how flow cytometric analyses also have begun to reveal how specific cytokines, such as Leukemia inhibitory factor are coordinating SVZ responses to injury.

Age-related neurogenesis decline in the subventricular zone is associated with specific cell cycle regulation changes in activated neural stem cells

Although neural stem cells (NSCs) sustain continuous neurogenesis throughout the adult lifespan of mammals, they progressively exhibit proliferation defects that contribute to a sharp reduction in subventricular neurogenesis during aging. However, little is known regarding the early age-related events in neurogenic niches. Using a fluorescence-activated cell sorting technique that allows for the prospective purification of the main neurogenic populations from the subventricular zone (SVZ), we demonstrated an early decline in adult neurogenesis with a dramatic loss of progenitor cells in 4 month-old young adult mice. Whereas the activated and quiescent NSC pools remained stable up to 12 months, the proliferative status of activated NSCs was already altered by 6 months, with an overall extension of the cell cycle resulting from a specific lengthening of G₁. Whole genome analysis of activated NSCs from 2- and 6-month-old mice further revealed distinct transcriptomic and molecular signatures, as well as a modulation of the TGFβ signalling pathway. Our microarray study constitutes a cogent identification of new molecular players and signalling pathways regulating adult neurogenesis and its early modifications.

Role of TGFβ signaling in the pathogenesis of Alzheimer's disease

Aging is the main risk factor for Alzheimer’s disease (AD); being associated with conspicuous changes on microglia activation. Aged microglia exhibit an increased expression of cytokines, exacerbated reactivity to various stimuli, oxidative stress, and reduced phagocytosis of β-amyloid (Aβ). Whereas normal inflammation is protective, it becomes dysregulated in the presence of a persistent stimulus, or in the context of an inflammatory environment, as observed in aging. Thus, neuroinflammation can be a self-perpetuating deleterious response, becoming a source of additional injury to host cells in neurodegenerative diseases. In aged individuals, although transforming growth factor β (TGFβ) is upregulated, its canonical Smad3 signaling is greatly reduced and neuroinflammation persists. This age-related Smad3 impairment reduces protective activation while facilitating cytotoxic activation of microglia through several cellular mechanisms, potentiating microglia-mediated neurodegeneration. Here, we critically discuss the role of TGFβ-Smad signaling on the cytotoxic activation of microglia and its relevance in the pathogenesis of AD. Other protective functions, such as phagocytosis, although observed in aged animals, are not further induced by inflammatory stimuli and TGFβ1. Analysis in silico revealed that increased expression of receptor scavenger receptor (SR)-A, involved in Aβ uptake and cell activation, by microglia exposed to TGFβ, through a Smad3-dependent mechanism could be mediated by transcriptional co-factors Smad2/3 over the MSR1 gene. We discuss that changes of TGFβ-mediated regulation could at least partially mediate age-associated microglia changes, and, together with other changes on inflammatory response, could result in the reduction of protective activation and the potentiation of cytotoxicity of microglia, resulting in the promotion of neurodegenerative diseases.

Impaired TGF-β induced growth inhibition contributes to the increased proliferation rate of neural stem cells harboring mutant p53

Gliomas have been classified according to their histological properties. However, their respective cells of origin are still unknown. Neural progenitor cells (NPC) from the subventricular zone (SVZ) can initiate tumors in murine models of glioma and are likely cells of origin in the human disease. In both, p53 signaling is often functionally impaired which may contribute to tumor formation. Also, TGF-beta, which under physiological conditions exerts a strong control on the proliferation of NPCs in the SVZ, is a potent mitogen on glioma cells. Here, we approach on the crosstalk between p53 and TGF-beta by loss of function experiments using NPCs derived from p53 mutant mice, as well as pharmacological inhibition of TGF-beta signaling using TGF-beta receptor inhibitors. NPC derived from p53 mutant mice showed increased clonogenicity and more rapid proliferation than their wildtype counterparts. Further, NPC derived from p53(mut/mut) mice were insensitive to TGF-beta induced growth arrest. Still, the canonical TGF-beta signaling pathway remained functional in the absence of p53 signaling and expression of key proteins as well as phosphorylation and nuclear translocation of SMAD2 were unaltered. TGF-beta-induced p21 expression could, in contrast, only be detected in p53(wt/wt) but not in p53(mut/mut) NPC. Conversely, inhibition of TGF-beta signaling using SB431542 increased proliferation of p53(wt/wt) but not of p53(mut/mut) NPC. In conclusion, our data suggest that the TGF-beta induced growth arrest in NPC depends on functional p53. Mutational inactivation of p53 hence contributes to increased proliferation of NPC and likely to the formation of hyperplasia of the SVZ observed in p53 deficient mice in vivo.

Runx1 promotes proliferation and neuronal differentiation in adult mouse neurosphere cultures

Traumatic brain injury alters the signaling environment of the adult neurogenic niche and may activate unique proliferative cell populations that contribute to the post-injury neurogenic response. Runx1 is not normally expressed by adult neural stem or progenitor cells (NSPCs) but is induced in a subpopulation of putative NSPCs after brain injury in adult mice. In order to investigate the role of Runx1 in NSPCs, we established neurosphere cultures of adult mouse subventricular zone NSPCs. We show that Runx1 is basally expressed in neurosphere culture. Removal of the mitogen bFGF or addition of 1% FBS decreased Runx1 expression. Inhibition of endogenous Runx1 activity with either Ro5-3335 or shRNA-mediated Runx1 knockdown inhibited NSPC proliferation without affecting differentiation. Lentiviral mediated over-expression of Runx1 in neurospheres caused a significant change in cell morphology without reducing proliferation. Runx1-overexpressing neurospheres changed from floating spheres to adherent colonies or individual unipolar or bipolar cells. Flow cytometry analysis indicated that Runx1 over-expression produced a significant increase in expression of the neuronal marker TuJ1 and a minor increase in the astrocytic marker S100β. Thus, Runx1 expression drove adult NSPC differentiation, predominantly toward a neuronal lineage. These data suggest that Runx1 could be manipulated after injury to promote neuronal differentiation to facilitate repair of the CNS.

The aged brain: genesis and fate of residual progenitor cells in the subventricular zone

Neural stem cells (NSCs) persist in the adult mammalian brain through life. The subventricular zone (SVZ) is the largest source of stem cells in the nervous system, and continuously generates new neuronal and glial cells involved in brain regeneration. During aging, the germinal potential of the SVZ suffers a widespread decline, but the causes of this turn down are not fully understood. This review provides a compilation of the current knowledge about the age-related changes in the NSC population, as well as the fate of the newly generated cells in the aged brain. It is known that the neurogenic capacity is clearly disrupted during aging, while the production of oligodendroglial cells is not compromised. Interestingly, the human brain seems to primarily preserve the ability to produce new oligodendrocytes instead of neurons, which could be related to the development of neurological disorders. Further studies in this matter are required to improve our understanding and the current strategies for fighting neurological diseases associated with senescence.

Activated regulatory T cell regulates neural stem cell proliferation in the subventricular zone of normal and ischemic mouse brain through interleukin 10

Recent studies have demonstrated that the depletion of Regulatory T cells (Tregs) inhibits neural progenitor cell migration after brain ischemia. However, whether Tregs affect neural stem/progenitor cell proliferation is unclear. We explored the effect of Tregs on neurogenesis in the subventricular zone (SVZ) after ischemia. Tregs were isolated and activated in vitro. Adult male C57BL/6 mice underwent 60 min transient middle cerebral artery occlusion (tMCAO). Then Tregs (1 × 10⁵) were injected into the left lateral ventricle (LV) of normal and ischemic mouse brain. Neurogenesis was determined by immunostaining. The mechanism was examined by inhibiting interleukin 10 (IL-10) and transforming growth factor (TGF-β) signaling. We found that the number of BrdU⁺ cells in the SVZ was significantly increased in the activated Tregs-treated mice. Double immunostaining showed that these BrdU⁺ cells expressed Mash1. Blocking IL-10 reduced the number of Mash1⁺/BrdU⁺ cells, but increased the amount of GFAP⁺/BrdU⁺ cells. Here, we conclude that activated Tregs enhanced neural stem cell (NSC) proliferation in the SVZ of normal and ischemic mice; blockage of IL-10 abolished Tregs-mediated NSC proliferation in vivo and in vitro. Our results suggest that activated Tregs promoted NSC proliferation via IL-10, which provides a new therapeutic approach for ischemic stroke.

Cell Sorting of Neural Stem and Progenitor Cells from the Adult Mouse Subventricular Zone and Live-imaging of their Cell Cycle Dynamics

Neural stem cells (NSCs) in the subventricular zone of the lateral ventricles (SVZ) sustain olfactory neurogenesis throughout life in the mammalian brain. They successively generate transit amplifying cells (TACs) and neuroblasts that differentiate into neurons once they integrate the olfactory bulbs. Emerging fluorescent activated cell sorting (FACS) techniques have allowed the isolation of NSCs as well as their progeny and have started to shed light on gene regulatory networks in adult neurogenic niches. We report here a cell sorting technique that allows to follow and distinguish the cell cycle dynamics of the above-mentioned cell populations from the adult SVZ with a LeX/EGFR/CD24 triple staining. Isolated cells are then plated as adherent cells to explore in details their cell cycle progression by time-lapse video microscopy. To this end, we use transgenic Fluorescence Ubiquitination Cell Cycle Indicator (FUCCI) mice in which cells are red-fluorescent during G₁ phase due to a G₁ specific red-Cdt1 reporter. This method has recently revealed that proliferating NSCs progressively lengthen their G₁ phase during aging, leading to neurogenesis impairment. This method is easily transposable to other systems and could be of great interest for the study of the cell cycle dynamics of brain cells in the context of brain pathologies.

Dystrophin induced cognitive impairment: mechanisms, models and therapeutic strategies

Existence of conserved domains in dystrophin and its associated complexes provide an opportunity to understand the role of dystrophin associated signalling and its association with neuronal metabolism in a variety of model organisms. We critically reviewed the studies till 2013 through established search engines and databases. Thus, we review the role of dystrophin and its isoforms in different animal models at developmental stages in the neuronal metabolism to enhance the therapeutic strategies. Dystrophin interacts with other proteins in such a way that, when affected, it results in co-morbidities including autism and other neuropsychiatric disorders. It is speculated that various signalling molecules may converge to disrupt neuronal metabolism not adequately studied. TGF-β, RhoGAP and CAM mediated signalling molecules are the chief cause of mortalities due to respiratory and cardiac involvement but remain underevaluated targets for cognitive impairment in DMD/BMD. Manipulation of these signalling pathways could be potent intervention in dystrophin induced cognitive impairment while complementary therapeutic approaches may also be helpful in the treatment of cognitive impairment associated with DMD/BMD.

The prion protein is critical for DNA repair and cell survival after genotoxic stress

The prion protein (PrP) is highly conserved and ubiquitously expressed, suggesting that it plays an important physiological function. However, despite decades of investigation, this role remains elusive. Here, by using animal and cellular models, we unveil a key role of PrP in the DNA damage response. Exposure of neurons to a genotoxic stress activates PRNP transcription leading to an increased amount of PrP in the nucleus where it interacts with APE1, the major mammalian endonuclease essential for base excision repair, and stimulates its activity. Preventing the induction of PRNP results in accumulation of abasic sites in DNA and impairs cell survival after genotoxic treatment. Brains from Prnp^−/− mice display a reduced APE1 activity and a defect in the repair of induced DNA damage in vivo. Thus, PrP is required to maintain genomic stability in response to genotoxic stresses.

Spontaneous white matter damage, cognitive decline and neuroinflammation in middle-aged hypertensive rats: an animal model of early-stage cerebral small vessel disease

Introduction

Cerebral small vessel disease (cSVD) is one of the most prevalent neurological disorders. The progressive remodeling of brain microvessels due to arterial hypertension or other vascular risk factors causes subtle, but constant cognitive decline through to manifest dementia and substantially increases the risk for stroke. Preliminary evidence suggests the contribution of the immune system to disease initiation and progression, but a more detailed understanding is impaired by the unavailability of appropriate animal models. Here, we introduce the spontaneously hypertensive rat (SHR) as a model for early onset cSVD and unveiled substantial immune changes in conjunction with brain abnormalities that resemble clinical findings.

Results

In contrast to age-matched normotensive Wistar Kyoto (WKY) rats, male SHR exhibited non-spatial memory deficits. Magnetic resonance imaging showed brain atrophy and a reduction of white matter volumes in SHR. Histological analyses confirmed white matter demyelination and unveiled a circumscribed blood brain barrier dysfunction in conjunction with micro- and macrogliosis in deep cortical regions. Flow cytometry and histological analyses further revealed substantial disparities in cerebral CD45high leukocyte counts and distribution patterns between SHR and WKY. SHR showed lower counts of T cells in the choroid plexus and meningeal spaces as well as decreased interleukin-10 levels in the cerebrospinal fluid. On the other hand, both T and NK cells were significantly augmented in the SHR brain microvasculature.

Conclusions

Our results indicate that SHR share behavioral and neuropathological characteristics with human cSVD patients and further undergird the relevance of immune responses for the initiation and progression of cSVD.

Electronic supplementary material

The online version of this article (doi:10.1186/s40478-014-0169-8) contains supplementary material, which is available to authorized users.

Regulation of tissue morphogenesis by endothelial cell-derived signals

Endothelial cells (ECs) form an extensive network of blood vessels that has numerous essential functions in the vertebrate body. In addition to their well-established role as a versatile transport network, blood vessels can induce organ formation or direct growth and differentiation processes by providing signals in a paracrine (angiocrine) fashion. Tissue repair also requires the local restoration of vasculature. ECs are emerging as important signaling centers that coordinate regeneration and help to prevent deregulated, disease-promoting processes. Vascular cells are also part of stem cell niches and have key roles in hematopoiesis, bone formation, and neurogenesis. Here, we review these newly identified roles of ECs in the regulation of organ morphogenesis, maintenance, and regeneration.

Lung cancer cells induce senescence and apoptosis of pleural mesothelial cells via transforming growth factor-beta1

Pleural dissemination is commonly associated with metastatic advanced lung cancer. The injury of pleural mesothelial cells (PMCs) by soluble factors, such as transforming growth factor-beta1 (TGF-β1), is a major driver of lung cancer pleural dissemination (LCPD). In this study, we examine the effects of TGF-β1 on PMC injury and the ability of TGF-β1 inhibition to alleviate this effect both in vitro and in vivo. PMCs were co-cultured with the high TGF-β1-expressing lung cancer cell line A549 and with various TGF-β1 signaling inhibitors. Expression of cleaved-caspase 3, cleaved-caspase 9, p21, and p16 were evaluated by Western blot and immunofluorescent confocal imaging. Apoptosis was measured by 3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltrazoliumbromide assay and AnnexinV-propidium iodide (PI) staining. PMC senescence was assessed by staining for senescence-associated β-galactosidase (SA-β-Gal). The ability of lung cancer cells (LCCs) to adhere to injured PMCs was investigated using an LCC-PMC adhesion assay. In our mouse model, PMC injury status was monitored by hematoxylin-eosin (H&E) and Masson's trichrome staining. LCCs expressing high levels of TGF-β1 induce apoptosis and senescence of PMCs in a co-culture system. Injured PMCs adhere to LCCs, which may further promote LCPD. Importantly, PMC monolayer injury could be reversed with TGF-β1 inhibitors. This was consistent with our in vivo data showing that the TGF-β1 inhibitor SB-431542 attenuated PMC barrier injury induced by A549 culture medium in our mouse model. Our study highlights the importance of TGF-β1 signaling in LCPD and establishes this signaling pathway as a potential therapeutic target in the disease.

Neurogenesis in the embryonic and adult brain: same regulators, different roles

Neurogenesis persists in adult mammals in specific brain areas, known as neurogenic niches. Adult neurogenesis is highly dynamic and is modulated by multiple physiological stimuli and pathological states. There is a strong interest in understanding how this process is regulated, particularly since active neuronal production has been demonstrated in both the hippocampus and the subventricular zone (SVZ) of adult humans. The molecular mechanisms that control neurogenesis have been extensively studied during embryonic development. Therefore, we have a broad knowledge of the intrinsic factors and extracellular signaling pathways driving proliferation and differentiation of embryonic neural precursors. Many of these factors also play important roles during adult neurogenesis, but essential differences exist in the biological responses of neural precursors in the embryonic and adult contexts. Because adult neural stem cells (NSCs) are normally found in a quiescent state, regulatory pathways can affect adult neurogenesis in ways that have no clear counterpart during embryogenesis. BMP signaling, for instance, regulates NSC behavior both during embryonic and adult neurogenesis. However, this pathway maintains stem cell proliferation in the embryo, while it promotes quiescence to prevent stem cell exhaustion in the adult brain. In this review, we will compare and contrast the functions of transcription factors (TFs) and other regulatory molecules in the embryonic brain and in adult neurogenic regions of the adult brain in the mouse, with a special focus on the hippocampal niche and on the regulation of the balance between quiescence and activation of adult NSCs in this region.

Aging and regeneration in vertebrates

Aging is marked by changes that affect organs and resident stem cell function. Shorting of telomeres, DNA damage, oxidative stress, deregulation of genes and proteins, impaired cell-cell communication, and an altered systemic environment cause the eventual demise of cells. At the same time, reparative activities also decline. It is intriguing to correlate aging with the decline of regenerative abilities. Animal models with strong regenerative capabilities imply that aging processes might not be affecting regeneration. In this review, we selectively present age-dependent changes in stem/progenitor cells that are vital for tissue homeostasis and repair. In addition, the aging effect on regeneration following injury in organs such as lung, skeletal muscle, heart, nervous system, cochlear hair, lens, and liver are discussed. These tissues are also known for diseases such as heart attack, stroke, cognitive impairment, cataract, and hearing loss that occur mostly during aging in humans. Conclusively, vertebrate regeneration declines with age with the loss of stem/progenitor cell function. Future studies on improving the function of stem cells, along with studies in fish and amphibians where regeneration does not decline with age, will undoubtedly provide insights into both processes.

Aging of the hematopoietic stem cells niche

Homeostasis of the hematopoietic system has its roots in the maintenance of hematopoietic stem cells (HSCs) in the bone marrow (BM). HSCs change both phenotypically and functionally with physiological age. The alterations noted in aged HSCs are thought to be a consequence of both cell-intrinsic and extrinsic changes. We review here the age-related changes that the BM microenvironment exerts on HSCs.

The decay of stem cell nourishment at the niche

One of the main features of human aging is the loss of adult stem cell homeostasis. Organs that are very dependent on adult stem cells show increased susceptibility to aging, particularly organs that present a vascular stem cell niche. Reduced regenerative capacity in tissues correlates with reduced stem cell function, which parallels a loss of microvascular density (rarefraction) and plasticity. Moreover, the age-related loss of microvascular plasticity and rarefaction has significance beyond metabolic support for tissues because stem cell niches are regulated co-ordinately with the vascular cells. In addition, microvascular rarefaction is related to increased inflammatory signals that may negatively regulate the stem cell population. Thus, the processes of microvascular rarefaction, adult stem cell dysfunction, and inflammation underlie the cycle of physiological decline that we call aging. Observations from new mouse models and humans are discussed here to support the vascular aging theory. We develop a novel theory to explain the complexity of aging in mammals and perhaps in other organisms. The connection between vascular endothelial tissue and organismal aging provides a potential evolutionary conserved mechanism that is an ideal target for the development of therapies to prevent or delay age-related processes in humans.

Cytokines: shifting the balance between glioma cells and tumor microenvironment after irradiation

Malignant gliomas invariably recur after irradiation, showing radioresistance. Meanwhile, cranial irradiation can bring some risk for developing cognitive dysfunction. There is increasing evidence that cytokines play their peculiar roles in these processes. On the one hand, cytokines directly influence the progression of malignant glioma, promoting or suppressing tumor progression. On the other hand, cytokines indirectly contribute to the immunologic response against gliomas, exhibiting pro-inflammatory or immunosuppressive activities. We propose that cytokines are not simply unregulated products from tumor cells or immune cells, but mediators finely adjust the balance between glioma cells and tumor microenvironment after irradiation. The paper, therefore, focuses on the changes of cytokines after irradiation, analyzing how these mediate the response of tumor cells and normal cells to irradiation. In addition, cytokine-based immunotherapeutic strategies, accompanied with irradiation, for the treatment of gliomas are also discussed.

Selective TGF-β1/ALK inhibitor improves neuronal differentiation of mouse embryonic stem cells

The transforming growth factor-β1 (TGF-β1), a polypeptide member of the TGF-β superfamily, has myriad cellular functions, including cell fate differentiation. We hypothesized that suppression of TGF-β1 signaling would improve the efficacy of neuronal differentiation during embryoid body (EB) development. In this study, mouse embryonic stem cells (ESCs) were allowed to differentiate into their neuronal lineage, both with, and without the TGF-β1 inhibitor (A83-01). After 8 days of EB suspension culture, the samples were examined by morphological analysis, immunocytochemistry and immunohistochemistry with pluripotent (Oct4, Sox2) and neuronal specific markers (Pax6, NeuN). The alteration of gene expressions during EB development was determined by quantitative RT-PCR. Our results revealed that the TGF-β1/ALK inhibitor potentially suppressed pluripotent gene (Oct4) during a rapidly up-regulation of neuronal associated genes including Sox1 and MAP2. Strikingly, during EB development, the expression of GFAP, the astrocyte specific gene, remarkably decreased compared to the non-treated control. This strategy demonstrated the beneficial function of TGF-β1/ALK inhibitor that rapidly and uniformly drives cell fate alteration from pluripotent state toward neuronal lineages.

Age-dependent and differential effects of Smad7ΔEx1 on neural progenitor cell proliferation and on neurogenesis

We recently reported that young (3 to 4 months old) mice lacking Exon 1 of the Smad7 gene (S7ΔEx1 mice) show enhanced proliferation of neural stem and progenitor cells (NPCs) in the hippocampal dentate gyrus (DG) and in the subventricular zone (SVZ) of the lateral ventricles. It remained unclear, however, whether this phenotype would persist along aging, the latter typically being associated with a profound decrease in neurogenesis. Analysis of NPCs' proliferation based on the cell cycle marker PCNA in 12 month-old S7ΔEx1 mice revealed a reversal of the phenotype. Hence, in contrast to their younger counterparts, 12 month-old S7ΔEx1 mice had a reduced number of proliferating cells, compared to wildtype (WT) mice. At the same time, the survival of newly generated cells was enhanced in the aged transgenic animals. 12 month-old S7ΔEx1 mice further displayed a reduced level of neurogenesis based on the numbers of cells expressing doublecortin (DCX), a marker for newborn neurons. The reduced neurogenesis in aged S7ΔEx1 mice was not due to a stem cell depletion, which might have occurred as a consequence of hyperproliferation in the young mice, since the number of Nestin and Sox2 positive cells was similar in WT and S7ΔEx1 mice. Instead, Nestin positive cells in the DG as well as primary neurosphere cultures derived from 12 month-old S7ΔEx1 mice had a reduced capability to proliferate. However, after passaging, when released from their age- and niche-associated proliferative block, neurospheres from aged S7ΔEx1 mice regained the hyperproliferative property. Further, pSmad2 antibody staining intensity was elevated in the DG and SVZ of 12-month old transgenic compared to WT mice, indicating increased intracellular TGF-beta signaling in the aged S7ΔEx1 mice. In summary, this points toward differential effects of S7ΔEx1 on neurogenesis: (i) a hyperproliferation in young animals caused by a cell autonomous mechanism, and (ii) a TGF-beta dependent modulation of neurogenesis in aged S7ΔEx1 animals that abrogates the cell-intrinsic hyperproliferative properties and results in reduced proliferation, increased stem cell quiescence, and enhanced survival of newly generated cells.

TGF-beta signalling in the adult neurogenic niche promotes stem cell quiescence as well as generation of new neurons

Members of the transforming growth factor (TGF)-β family govern a wide range of mechanisms in brain development and in the adult, in particular neuronal/glial differentiation and survival, but also cell cycle regulation and neural stem cell maintenance. This clearly created some discrepancies in the field with some studies favouring neuronal differentiation/survival of progenitors and others favouring cell cycle exit and neural stem cell quiescence/maintenance. Here, we provide a unifying hypothesis claiming that through its regulation of neural progenitor cell (NPC) proliferation, TGF-β signalling might be responsible for (i) maintaining stem cells in a quiescent stage, and (ii) promoting survival of newly generated neurons and their functional differentiation. Therefore, we performed a detailed histological analysis of TGF-β1 signalling in the hippocampal neural stem cell niche of a transgenic mouse that was previously generated to express TGF-β1 under a tetracycline regulatable Ca-Calmodulin kinase promoter. We also analysed NPC proliferation, quiescence, neuronal survival and differentiation in relation to elevated levels of TGF-β1 in vitro and in vivo conditions. Finally, we performed a gene expression profiling to identify the targets of TGF-β1 signalling in adult NPCs. The results demonstrate that TGF-β1 promotes stem cell quiescence on one side, but also neuronal survival on the other side. Thus, considering the elevated levels of TGF-β1 in ageing and neurodegenerative diseases, TGF-β1 signalling presents a molecular target for future interventions in such conditions.

Vascular regulation of adult neurogenesis under physiological and pathological conditions

Neural stem cells in the mammalian adult brain continuously produce new neurons throughout life. Accumulating evidence in rodents suggests that various aspects of adult neurogenesis, including the genesis, migration, and maturation of new neurons, are regulated by factors derived from blood vessels and their microenvironment. Brain injury enhances both neurogenesis and angiogenesis, thereby promoting the cooperative regeneration of neurons and blood vessels. In this paper, we briefly review the mechanisms for the vascular regulation of adult neurogenesis in the ventricular-subventricular zone under physiological and pathological conditions, and discuss their clinical potential for brain regeneration strategies.

Dissecting the molecular mechanism of ionizing radiation-induced tissue damage in the feather follicle

Ionizing radiation (IR) is a common therapeutic agent in cancer therapy. It damages normal tissue and causes side effects including dermatitis and mucositis. Here we use the feather follicle as a model to investigate the mechanism of IR-induced tissue damage, because any perturbation of feather growth will be clearly recorded in its regular yet complex morphology. We find that IR induces defects in feather formation in a dose-dependent manner. No abnormality was observed at 5 Gy. A transient, reversible perturbation of feather growth was induced at 10 Gy, leading to defects in the feather structure. This perturbation became irreversible at 20 Gy. Molecular and cellular analysis revealed P53 activation, DNA damage and repair, cell cycle arrest and apoptosis in the pathobiology. IR also induces patterning defects in feather formation, with disrupted branching morphogenesis. This perturbation is mediated by cytokine production and Stat1 activation, as manipulation of cytokine levels or ectopic Stat1 over-expression also led to irregular feather branching. Furthermore, AG-490, a chemical inhibitor of Stat1 signaling, can partially rescue IR-induced tissue damage. Our results suggest that the feather follicle could serve as a useful model to address the in vivo impact of the many mechanisms of IR-induced tissue damage.

Cellular mechanisms of somatic stem cell aging

Tissue homeostasis and regenerative capacity rely on rare populations of somatic stem cells endowed with the potential to self-renew and differentiate. During aging, many tissues show a decline in regenerative potential coupled with a loss of stem cell function. Cells including somatic stem cells have evolved a series of checks and balances to sense and repair cellular damage to maximize tissue function. However, during aging the mechanisms that protect normal cell function begin to fail. In this review, we will discuss how common cellular mechanisms that maintain tissue fidelity and organismal lifespan impact somatic stem cell function. We will highlight context-dependent changes and commonalities that define aging, by focusing on three age-sensitive stem cell compartments: blood, neural, and muscle. Understanding the interaction between extrinsic regulators and intrinsic effectors that operate within different stem cell compartments is likely to have important implications for identifying strategies to improve health span and treat age-related degenerative diseases.

The subventricular zone is able to respond to a demyelinating lesion after localized radiation

Radiation is a common tool in the treatment of brain tumors that induces neurological deficits as a side effect. Some of these deficits appear to be related to the impact of radiation on the neurogenic niches, producing a drastic decrease in the proliferative capacity of these regions. In the adult mammalian brain, the subventricular zone (SVZ) of the lateral ventricles is the main neurogenic niche. Neural stem/precursor cells (NSCs) within the SVZ play an important role in brain repair following injuries. However, the irradiated NSCs' ability to respond to damage has not been previously elucidated. In this study, we evaluated the effects of localized radiation on the SVZ ability to respond to a lysolecithin-induced demyelination of the striatum. We demonstrated that the proliferation rate of the irradiated SVZ was increased after brain damage and that residual NSCs were reactivated. The irradiated SVZ had an expansion of doublecortin positive cells that appeared to migrate from the lateral ventricles toward the demyelinated striatum, where newly generated oligodendrocytes were found. In addition, in the absence of demyelinating damage, remaining cells in the irradiated SVZ appeared to repopulate the neurogenic niche a year post-radiation. These findings support the hypothesis that NSCs are radioresistant and can respond to a brain injury, recovering the neurogenic niche. A more complete understanding of the effects that localized radiation has on the SVZ may lead to improvement of the current protocols used in the radiotherapy of cancer.

Tissue resident stem cells: till death do us part

Aging is accompanied by reduced regenerative capacity of all tissues and organs and dysfunction of adult stem cells. Notably, these age-related alterations contribute to distinct pathophysiological characteristics depending on the tissue of origin and function and thus require special attention in a type by type manner. In this paper, we review the current understanding of the mechanisms leading to tissue-specific adult stem cell dysfunction and reduced regenerative capacity with age. A comprehensive investigation of the hematopoietic, the neural, the mesenchymal, and the skeletal stem cells in age-related research highlights that distinct mechanisms are associated with the different types of tissue stem cells. The link between age-related stem cell dysfunction and human pathologies is discussed along with the challenges and the future perspectives in stem cell-based therapies in age-related diseases.