Fractone-heparan sulfates mediate BMP-7 inhibition of cell proliferation in the adult subventricular zone

Optimal Extracellular Matrix Niches for Neurogenesis: Identifying Glycosaminoglycan Chain Composition in the Subventricular Neurogenic Zone

In the adult mammalian brain, new neurons are generated in a restricted region called the neurogenic niche, which refers to the specific regulatory microenvironment of neural stem cells (NSCs). Among the constituents of neurogenic niches, the extracellular matrix (ECM) has emerged as a key player in NSC maintenance, proliferation, and differentiation. In particular, heparan sulfate (HS) proteoglycans are capable of regulating various growth factor signaling pathways that influence neurogenesis. In this review, we summarize our current understanding of the ECM niche in the adult subventricular zone (SVZ), with a special focus on basement membrane (BM)-like structures called fractones, and discuss how fractones, particularly their composition of glycosaminoglycans (GAGs), may influence neurogenesis.

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

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

Criss-crossing autism spectrum disorder and adult neurogenesis

Autism spectrum disorder (ASD) comprises a group of multifactorial neurodevelopmental disorders primarily characterized by deficits in social interaction and repetitive behavior. Although the onset is typically in early childhood, ASD poses a lifelong challenge for both patients and caretakers. Adult neurogenesis (AN) is the process by which new functional neurons are created from neural stem cells existing in the post-natal brain. The entire event is based on a sequence of cellular processes, such as proliferation, specification of cell fate, maturation, and ultimately, synaptic integration into the existing neural circuits. Hence, AN is implicated in structural and functional brain plasticity throughout life. Accumulating evidence shows that impaired AN may underlie some of the abnormal behavioral phenotypes seen in ASD. In this review, we approach the interconnections between the molecular pathways related to AN and ASD. We also discuss existing therapeutic approaches targeting such pathways both in preclinical and clinical studies. A deeper understanding of how ASD and AN reciprocally affect one another could reveal important converging pathways leading to the emergence of psychiatric disorders.

Bioengineering the neurovascular niche to study the interaction of neural stem cells and endothelial cells

The ability of mammalian neural stem cells (NSCs) to self-renew and differentiate throughout adulthood has made them ideal to study neurogenesis and attractive candidates for neurodegenerative disease therapies. In the adult mammalian brain, NSCs are maintained in the neurovascular niche (NVN) where they are found near the specialized blood vessels, suggesting that brain endothelial cells (BECs) are prominent orchestrators of NSC fate. However, most of the current knowledge of the mammalian NVN has been deduced from nonhuman studies. To circumvent the challenges of in vivo studies, in vitro models have been developed to better understand the reciprocal cellular mechanisms of human NSCs and BECs. This review will cover the current understanding of mammalian NVN biology, the effects of endothelial cell-derived signals on NSC fate, and the in vitro models developed to study the interactions between NSCs and BECs.

Endogenous neural precursor cells in health and disease

Neurogenesis persists in the adult brain of mammals in the subventricular zone (SVZ) of the lateral ventricles and in the subgranular zone (SGZ) of the dentate gyrus (DG). The complex interactions between intrinsic and extrinsic signals provided by cells in the niche but also from distant sources regulate the fate of neural stem/progenitor cells (NPCs) in these sites. This fine regulation is perturbed in aging and in pathological conditions leading to a different NPC behavior, tailored to the specific physio-pathological features. Indeed, NPCs exert in physiological and pathological conditions important neurogenic and non-neurogenic regulatory functions and participate in maintaining and protecting brain tissue homeostasis. In this review, we discuss intrinsic and extrinsic signals that regulate NPC activation and NPC functional role in various homeostatic and non-homeostatic conditions.

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.

Neural stem cells: origin, heterogeneity and regulation in the adult mammalian brain

In the adult rodent brain, neural stem cells (NSCs) persist in the ventricular-subventricular zone (V-SVZ) and the subgranular zone (SGZ), which are specialized niches in which young neurons for the olfactory bulb (OB) and hippocampus, respectively, are generated. Recent studies have significantly modified earlier views on the mechanisms of NSC self-renewal and neurogenesis in the adult brain. Here, we discuss the molecular control, heterogeneity, regional specification and cell division modes of V-SVZ NSCs, and draw comparisons with NSCs in the SGZ. We highlight how V-SVZ NSCs are regulated by local signals from their immediate neighbors, as well as by neurotransmitters and factors that are secreted by distant neurons, the choroid plexus and vasculature. We also review recent advances in single cell RNA analyses that reveal the complexity of adult neurogenesis. These findings set the stage for a better understanding of adult neurogenesis, a process that one day may inspire new approaches to brain repair.

Heterogeneity of Neural Stem Cells in the Ventricular-Subventricular Zone

In this chapter, heterogeneity is explored in the context of the ventricular-subventricular zone, the largest stem cell niche in the mammalian brain. This niche generates up to 10,000 new neurons daily in adult mice and extends over a large spatial area with dorso-ventral and medio-lateral subdivisions. The stem cells of the ventricular-subventricular zone can be subdivided by their anatomical position and transcriptional profile, and the stem cell lineage can also be further subdivided into stages of pre- and post-natal quiescence and activation. Beyond the stem cells proper, additional differences exist in their interactions with other cellular constituents of the niche, including neurons, vasculature, and cerebrospinal fluid. These variations in stem cell potential and local interactions are discussed, as well as unanswered questions within this system.

Vitronectin from brain pericytes promotes adult forebrain neurogenesis by stimulating CNTF

Vitronectin (VTN) is a glycoprotein in the blood and affects hemostasis. VTN is also present in the extracellular matrix of various organs but little is known about its function in healthy adult tissues. We show, in adult mice, that VTN is uniquely expressed by approximately half of the pericytes of subventricular zone (SVZ) where neurogenesis continues throughout life. Intracerebral VTN antibody injection or VTN knockout reduced neurogenesis as well as expression of pro-neurogenic CNTF, and anti-neurogenic LIF and IL-6. Conversely, injections of VTN, or plasma from VTN+/+, but not VTN-/- mice, increased these cytokines. VTN promoted SVZ neurogenesis when LIF and IL-6 were suppressed by co-administration of a gp130 inhibitor. Unexpectedly, VTN inhibited FAK signaling and VTN-/- mice had increased FAK signaling in the SVZ. Further, an FAK inhibitor or VTN increased CNTF expression, but not in conditional astrocytic FAK knockout mice, suggesting that VTN increases CNTF through FAK inhibition in astrocytes. These results identify a novel role of pericyte-derived VTN in the brain, where it regulates SVZ neurogenesis through co-expression of CNTF, LIF and IL-6. VTN-integrin-FAK and gp130 signaling may provide novel targets to induce neurogenesis for cell replacement therapies.

Ventricular-subventricular zone fractones are speckled basement membranes that function as a neural stem cell niche

Neural stem cells (NSCs) are retained in the adult ventricular–subventricular zone (V-SVZ), a specialized neurogenic niche with a unique cellular architecture. It currently remains unclear whether or how NSCs utilize basement membranes (BMs) in this niche. Here, we examine the molecular compositions and functions of BMs in the adult mouse V-SVZ. Whole-mount V-SVZ immunostaining revealed that fractones, which are fingerlike processes of extravascular BMs, are speckled BMs unconnected to the vasculature, and differ in their molecular composition from vascular BMs. Glial fibrillary acidic protein (GFAP)-positive astrocytes and NSCs produce and adhere to speckled BMs. Furthermore, Gfap-Cre-mediated Lamc1^flox(E1605Q) knockin mice, in which integrin-binding activities of laminins are specifically nullified in GFAP-positive cells, exhibit a decreased number and size of speckled BMs and reduced in vitro neurosphere-forming activity. Our results reveal niche activities of fractones/speckled BMs for NSCs and provide molecular insights into how laminin–integrin interactions regulate NSCs in vivo.

Fractone Bulbs Derive from Ependymal Cells and Their Laminin Composition Influence the Stem Cell Niche in the Subventricular Zone

Fractones are extracellular matrix structures in the neural stem cell niche of the subventricular zone (SVZ), where they appear as round deposits named bulbs or thin branching lines called stems. Their cellular origin and what determines their localization at this site is poorly studied, and it remains unclear whether they influence neural stem and progenitor cell formation, proliferation, and/or maintenance. To address these questions, we analyzed whole-mount preparations of the lateral ventricle of male and female mice by confocal microscopy using different extracellular matrix and cell markers. We found that bulbs are rarely connected to stems and that they contain laminin α5 and α2 chains, respectively. Fractone bulbs were profusely distributed throughout the SVZ and appeared associated with the center of pinwheels, a critical site for adult neurogenesis. We demonstrate that bulbs appear at the apical membrane of ependymal cells at the end of the first week after birth. The use of transgenic mice lacking laminin α5 gene expression (Lama5) in endothelium and in FoxJ1-expressing ependymal cells revealed ependymal cells as the source of laminin α5-containing fractone bulbs. Deletion of laminin α5 from ependymal cells correlated with a 60% increase in cell proliferation, as determined by phospho-histone H3 staining, and with a selective reduction in the number of slow-dividing cells. These results indicate that fractones are a key component of the SVZ and suggest that laminin α5 modulates the physiology of the neural stem cell niche.SIGNIFICANCE STATEMENT Our work unveils key aspects of fractones, extracellular matrix structures that are present in the SVZ that still lack a comprehensive characterization. We show that fractones extensively interact with neural stem cells, whereas some of them are located precisely at pinwheel centers, which are hotspots for adult neurogenesis. Our results also demonstrate that fractones increase in size during aging and that their interactions with neural stem and progenitor cells become more complex in old mice. Last, we show that fractone bulbs are produced by ependymal cells and that their laminin content regulates neural stem cells.

BMP7 regulates lung fibroblast proliferation in newborn rats with bronchopulmonary dysplasia

The present study investigated the expression of bone morphogenetic protein (BMP) 7 in a newborn rat model of bronchopulmonary dysplasia (BPD) and the biological effects of BMP7 on newborn rat lung fibroblast (LF) cells. For this purpose, a total of 196 newborn rats were randomly and equally assigned to a model group and a control group. Lung tissue was collected at days 3, 7, 14 and 21 for histological analysis. The location and expression of BMP7 was examined by immunohistochemical staining and reverse transcription‑quantitative polymerase chain reaction (RT‑qPCR) analysis. A total of 38 full‑term newborn rats on the day of birth were sacrificed and LF cells were isolated and treated with BMP7. The biological effects of BMP7 on LF cells were assessed by cell proliferation and cell cycle analysis. The findings demonstrated that abnormal alveolar development due to BPD was gradually intensified in the model group over time. Immunohistochemical staining revealed that the location of BMP7 in lung tissue was altered. Immunohistochemistry and RT‑qPCR assays demonstrated a gradual decrease in BMP7 expression in the model group induced by hyperoxia. MTT assays demonstrated that BMP7 inhibited LF cells and the inhibitory effect was dose‑dependent and time‑dependent. Flow cytometry revealed that the inhibitory effect of BMP7 in LF cells was causing cell cycle arrest at the G1 phase. The present study demonstrated that BMP7 may serve an important role in alveolar development in a BPD model. BMP7 may be involved in abnormal alveolar development through the regulation of LF proliferation.

Heparin, Heparan Sulphate and the TGF-β Cytokine Superfamily

Of the circa 40 cytokines of the TGF-β superfamily, around a third are currently known to bind to heparin and heparan sulphate. This includes TGF-β1, TGF-β2, certain bone morphogenetic proteins (BMPs) and growth and differentiation factors (GDFs), as well as GDNF and two of its close homologues. Experimental studies of their heparin/HS binding sites reveal a diversity of locations around the shared cystine-knot protein fold. The activities of the TGF-β cytokines in controlling proliferation, differentiation and survival in a range of cell types are in part regulated by a number of specific, secreted BMP antagonist proteins. These vary in structure but seven belong to the CAN or DAN family, which shares the TGF-β type cystine-knot domain. Other antagonists are more distant members of the TGF-β superfamily. It is emerging that the majority, but not all, of the antagonists are also heparin binding proteins. Any future exploitation of the TGF-β cytokines in the therapy of chronic diseases will need to fully consider their interactions with glycosaminoglycans and the implications of this in terms of their bioavailability and biological activity.

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.

Fractones: extracellular matrix niche controlling stem cell fate and growth factor activity in the brain in health and disease

The stem cell niche refers to a specific microenvironment where stem cells proliferate and differentiate to produce new specialized cells throughout an organism's adulthood. Growth factors are crucial signaling molecules that diffuse through the extracellular space, reach the stem cell niche, and ultimately promote stem cell proliferation and differentiation. However, it is not well known how multiple growth factors, often with antagonistic activities, work together in the stem cell niche to select target stem cell populations and determine stem cell fate. There is accumulating evidence suggesting that extracellular matrix (ECM) molecules play an important role in promoting growth factor access and activity in the stem cell niche. In the adult brain neurogenic zone, where neural stem cells (NSCs) reside, there exist specialized ECM structures, which we have named fractones. The processes of NSC allow them to come into contact with fractones and interact with its individual components, which include heparan sulfate proteoglycans (HSPGs) and laminins. We have demonstrated that fractone-associated HSPGs bind growth factors and regulate NSC proliferation in the neurogenic zone. Moreover, emerging results show that fractones are structurally altered in animal models with autism and adult hydrocephalus, as demonstrated by changes in fractone size, quantity, or HSPG content. Interestingly, ECM structures similar to fractones have been found throughout β-amyloid plaques in the brain of patients with Alzheimer's disease. Pathological fractones may cause imbalances in growth factor activity and impair neurogenesis, leading to inflammation and disorder. Generally speaking, these stem cell niche structures play a potentially vital role in controlling growth factor activity during both health and disease.

Dystroglycan Suppresses Notch to Regulate Stem Cell Niche Structure and Function in the Developing Postnatal Subventricular Zone

While the extracellular matrix (ECM) is known to regulate neural stem cell quiescence in the adult subventricular zone (SVZ), the function of ECM in the developing SVZ remains unknown. Here, we report that the ECM receptor dystroglycan regulates a unique developmental restructuring of ECM in the early postnatal SVZ. Dystroglycan is furthermore required for ependymal cell differentiation and assembly of niche pinwheel structures, at least in part by suppressing Notch activation in radial glial cells, which leads to the increased expression of MCI, Myb, and FoxJ1, transcriptional regulators necessary for acquisition of the multiciliated phenotype. Dystroglycan also regulates perinatal radial glial cell proliferation and transition into intermediate gliogenic progenitors, such that either acute or constitutive loss of function in dystroglycan results in increased oligodendrogenesis. These findings reveal a role for dystroglycan in orchestrating both the assembly and function of the SVZ neural stem cell niche.

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.

Fractone aging in the subventricular zone of the lateral ventricle

In adulthood, the subventricular zone (SVZ) is one of the restricted places where neurogenesis persists. In this neurogenic niche, specialized extracellular matrix (ECM) structures termed fractones contact neural stem cells and their immediate progeny. Fractones are composed of ubiquitous ECM components including heparan sulfate proteoglycans such as perlecan and agrin. We have previously shown that fractones can capture growth factors and promote growth factor activity through a heparin binding mechanism in order to regulate neurogenesis. With aging, neurogenesis is known to decrease. However, the effect of aging on fractones structure and composition remains unknown. Here, we report that, while fractone number decreased, fractone size dramatically increased with aging. Despite the changes in fractones morphology, niche cells expressing glial fibrillary acidic protein kept direct contact with fractones. Furthermore, we have observed that heparan sulfate chains contained in fractones were modified with aging. However, FGF-2 was still captured by fractones via heparan sulfates. Together, our results suggest that the changes observed in fractones structure and composition are critically related to aging of the SVZ neurogenic niche.

It takes a village: constructing the neurogenic niche

Although many features of neurogenesis during development and in the adult are intrinsic to the neurogenic cells themselves, the role of the microenvironment is irrefutable. The neurogenic niche is a melting pot of cells and factors that influence CNS development. How do the diverse elements assemble and when? How does the niche change structurally and functionally during embryogenesis and in adulthood? In this review, we focus on the impact of non-neural cells that participate in the neurogenic niche, highlighting how cells of different embryonic origins influence this critical germinal space.

Long-term hydrocephalus alters the cytoarchitecture of the adult subventricular zone

Hydrocephalus can develop secondarily to a disturbance in production, flow and/or absorption of cerebrospinal fluid. Experimental models of hydrocephalus, especially subacute and chronic hydrocephalus, are few and limited, and the effects of hydrocephalus on the subventricular zone are unclear. The aim of this study was to analyze the effects of long-term obstructive hydrocephalus on the subventricular zone, which is the neurogenic niche lining the lateral ventricles. We developed a new method to induce hydrocephalus by obstructing the aqueduct of Sylvius in the mouse brain, thus simulating aqueductal stenosis in humans. In 120-day-old rodents (n=18 per group), the degree of ventricular dilatation and cellular composition of the subventricular zone were studied by immunofluorescence and transmission electron microscopy. In adult patients (age>18years), the sizes of the subventricular zone, corpus callosum, and internal capsule were analyzed by magnetic resonance images obtained from patients with and without aqueductal stenosis (n=25 per group). Mice with 60-day hydrocephalus had a reduced number of Ki67+ and doublecortin+cells on immunofluorescence, as well as decreased number of neural progenitors and neuroblasts in the subventricular zone on electron microscopy analysis as compared to non-hydrocephalic mice. Remarkably, a number of extracellular matrix structures (fractones) contacting the ventricular lumen and blood vessels were also observed around the subventricular zone in mice with hydrocephalus. In humans, the widths of the subventricular zone, corpus callosum, and internal capsule in patients with aqueductal stenosis were significantly smaller than age and gender-matched patients without aqueductal stenosis. In summary, supratentorial hydrocephalus reduces the proliferation rate of neural progenitors and modifies the cytoarchitecture and extracellular matrix compounds of the subventricular zone. In humans, this similar process reduces the subventricular niche as well as the width of corpus callosum and internal capsule.

Bone morphogenetic protein-4 inhibits adult neurogenesis and is regulated by fractone-associated heparan sulfates in the subventricular zone

Fractones are extracellular matrix structures that display a fractal ultrastructure and that are visualized as puncta after immunolabeling for laminin or heparan sulfate proteoglycans. In the adult brain, fractones are found throughout the subventricular zone (SVZ). The role of fractones is just emerging. We have recently shown that fractones sequester fibroblast growth factor-2 and bone morphogenetic protein-7 from the brain ventricles to regulate cell proliferation in the SVZ of the lateral ventricle, the primary neural stem cell niche and neurogenic zone in adulthood. Here, we have examined in vivo the effect of bone morphogenetic protein-4 (BMP-4) on cell proliferation in the SVZ and we have determined whether BMP-4 interacts with fractones to promote this effect. To examine BMP-4 effect on cell proliferation, BMP-4 was intracerebroventricularly injected, and bromodeoxyuridine immunolabeling was performed on frozen sections of the adult mouse brain. To identify the location of BMP-4 binding, biotinylated-BMP-4 was injected, and its binding localized post-mortem with streptavidin, Texas red conjugate. Injection of heparitinase-1 was used to desulfate fractones and determine whether the binding and the effect of BMP-4 on cell proliferation are heparan sulfate-dependent. BMP-4 inhibited cell proliferation in the SVZ neurogenic zone. Biotinylated-BMP-4 bound to fractones and some adjacent blood vessels. Co-injection of heparitinase-1 and biotinylated-BMP-4 resulted in the absence of signal for biotinylated-BMP-4, indicating that the binding was heparan sulfate dependent. Moreover, preventing the binding of BMP-4 to fractones by heparitinase-1 reinforced the inhibitory effect of BMP-4 on cell proliferation in the SVZ. These results show that BMP-4 inhibits cell proliferation in the SVZ neurogenic zone and that the binding of BMP-4 to fractone-associated heparan sulfates moderates this inhibitory effect. Together with our previous results, these data support the view that fractones capture growth factors and modulate their activity in the neural tissues lining the ventricles.

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.

Perlecan is required for FGF-2 signaling in the neural stem cell niche

In the adult subventricular zone (neurogenic niche), neural stem cells double-positive for two markers of subsets of neural stem cells in the adult central nervous system, glial fibrillary acidic protein and CD133, lie in proximity to fractones and to blood vessel basement membranes, which contain the heparan sulfate proteoglycan perlecan. Here, we demonstrate that perlecan deficiency reduces the number of both GFAP/CD133-positive neural stem cells in the subventricular zone and new neurons integrating into the olfactory bulb. We also show that FGF-2 treatment induces the expression of cyclin D2 through the activation of the Akt and Erk1/2 pathways and promotes neurosphere formation in vitro. However, in the absence of perlecan, FGF-2 fails to promote neurosphere formation. These results suggest that perlecan is a component of the neurogenic niche that regulates FGF-2 signaling and acts by promoting neural stem cell self-renewal and neurogenesis.

Adult neural stem cells and their niche: a dynamic duo during homeostasis, regeneration, and aging

Stem cells persist in specialized niches in the adult mammalian brain. Emerging findings highlight the complexity and heterogeneity of different compartments in the niche, as well as the presence of local signaling microdomains. Stem cell quiescence and activation are regulated not only by anchorage to the niche and diffusible signals, but also by biophysical properties, including fluid dynamics. Importantly, the adult neural stem cell niche integrates both local and systemic changes, reflecting the physiological state of the organism. Moreover niche signaling is bidirectional, with stem cells and their progeny and niche cells dynamically interacting with each other during homeostasis, regeneration and aging.

Fractone-heparan sulphates mediate FGF-2 stimulation of cell proliferation in the adult subventricular zone

OBJECTIVES

Fractones are extracellular matrix structures that form a niche for neural stem cells and their immediate progeny in the subventricular zone of the lateral ventricle (SVZa), the primary neurogenic zone in the adult brain. We have previously shown that heparan sulphates (HS) associated with fractones bind fibroblast growth factor-2 (FGF-2), a powerful mitotic growth factor in the SVZa. Here, our objective was to determine whether the binding of FGF-2 to fractone-HS is implicated in the mechanism leading to cell proliferation in the SVZa.

MATERIALS AND METHODS

Heparitinase-1 was intracerebroventricularly injected with FGF-2 to N-desulfate HS proteoglycans and determine whether the loss of HS and of FGF-2 binding to fractones modifies FGF-2 effect on cell proliferation. We also examined in vivo the binding of Alexa-Fluor-FGF-2 in relationship with the location of HS immunoreactivity in the SVZa.

RESULTS

Heparatinase-1 drastically reduced the stimulatory effect of FGF-2 on cell proliferation in the SVZa. Alexa-Fluor-FGF-2 binding was strictly co-localized with HS immunoreactivity in fractones and adjacent vascular basement membranes in the SVZa.

CONCLUSIONS

Our results demonstrate that FGF-2 requires HS to stimulate cell proliferation in the SVZa and suggest that HS associated with fractones and vascular basement membranes are responsible for activating FGF-2. Therefore, fractones and vascular basement membranes may function as a HS niche to drive cell proliferation in the adult neurogenic zone.