Vitronectin promotes the progress of the initial differentiation stage in cerebellar granule cells

Nano-/micro-scaled hydroxyapatite ceramic construction and the regulation of immune-associated osteogenic differentiation

Hydroxyapatite (HA) bioceramic is a promising substitute for bone defects, and the surface properties are major factors that influence bioactivity and osteoinductivity. In this study, two kinds of HA bioceramics with nanoscale (n-HA) and microscale (m-HA) surface topography were designed to mimic the natural bone, thus enhancing the stimulation of osteogenic differentiation and revealing the potential mechanism. Compared to m-HA, n-HA owned a larger surface roughness, a stronger wettability, and reduced hardness and indentation modulus. Based on these properties, n-HA could maintain the conformation of vitronectin better than m-HA, which may contribute to higher cellular activities and a stronger promotion of osteogenic differentiation of mesenchymal stem cells (MSCs). Further RNA sequencing analysis compared the molecular expression between n-HA and m-HA. Six hundred twenty-seven differentially expressed genes were identified in MSCs, and 17 upregulated genes and 610 downregulated genes were included when n-HA compared to m-HA. The GO cluster analysis and enriched Kyoto encyclopedia of genes and genome signaling pathways revealed a close correlation with the immune process in both upregulated (chemokine signaling pathway and cytokine-cytokine receptor interaction) and downregulated pathways (osteoclasts differentiation). It suggested that the nanoscale surface topography of HA enhanced the osteoinductivity of MSCs and could not be separated from its regulation of immune function and the retention of adsorbed protein conformation.

Syndecan-3 regulates the time of transition from cell cycle exit to initial differentiation stage in mouse cerebellar granule cell precursors

To analyze the role of syndecan-3 (SDC3), a heparan sulfate proteoglycan, in cerebellum development, we examined the effect of SDC3 on the transition from cell cycle exit to the initial differentiation stage of cerebellar granule cell precursors (CGCPs). First, we examined SDC3 localization in the developing cerebellum. SDC3 was mainly localized to the inner external granule layer where the transition from the cell cycle exit to the initial differentiation of CGCPs occurs. To examine how SDC3 regulates the cell cycle exit of CGCPs, we performed SDC3-knockdown (SDC3-KD) and -overexpression (Myc-SDC3) assays using primary CGCPs. SDC3-KD significantly increased the ratio of p27^Kip1+ cells to total cells at day 3 in vitro (DIV3) and 4, but Myc-SDC3 reduced that at DIV3. Regarding the cell cycle exit efficiency using 24 h-labelled bromodeoxyuridine (BrdU) and a marker of cell cycling, Ki67, SDC3-KD significantly increased cell cycle exit efficiency (Ki67^-; BrdU⁺ cells/BrdU⁺ cells) in primary CGCP at DIV4 and 5, but Myc-SDC3 reduced that at DIV4 and 5. However, SDC3-KD and Myc-SDC3 did not affect the efficiency of the final differentiation from CGCPs to granule cells at DIV3-5. Furthermore, the ratio of CGCPs in the cell cycle exiting stage to total cells, identified by initial differentiation markers TAG1 and Ki67 (TAG1⁺; Ki67⁺ cells), was considerably decreased by SDC3-KD at DIV4, but increased by Myc-SDC3 at DIV4 and 5. Altogether, these results indicate that SDC3 regulates the timing of the transition from the cell cycle exit stage to the initial differentiation stage of CGCP.

Cooperation between primary cilia signaling and integrin receptor extracellular matrix engagement regulates progenitor proliferation and neuronal differentiation in the developing cerebellum

Neural progenitors and their neuronal progeny are bathed in extrinsic signals that impact critical decisions like the mode of cell division, how long they should reside in specific neuronal laminae, when to differentiate, and the timing of migratory decisions. Chief among these signals are secreted morphogens and extracellular matrix (ECM) molecules. Among the many cellular organelles and cell surface receptors that sense morphogen and ECM signals, the primary cilia and integrin receptors are some of the most important mediators of extracellular signals. Despite years of dissecting the function of cell-extrinsic sensory pathways in isolation, recent research has begun to show that key pathways work together to help neurons and progenitors interpret diverse inputs in their germinal niches. This mini-review utilizes the developing cerebellar granule neuron lineage as a model that highlights evolving concepts on the crosstalk between primary cilia and integrins in the development of the most abundant neuronal type in the brains of mammals.

Role of Vitronectin and Its Receptors in Neuronal Function and Neurodegenerative Diseases

Vitronectin (VTN), a multifunctional glycoprotein with various physiological functions, exists in plasma and the extracellular matrix. It is known to be involved in the cell attachment, spreading and migration through binding to the integrin receptor, mainly via the RGD sequence. VTN is also widely used in the maintenance and expansion of pluripotent stem cells, but its effects go beyond that. Recent evidence shows more functions of VTN in the nervous system as it participates in neural differentiation, neuronutrition and neurogenesis, as well as in regulating axon size, supporting and guiding neurite extension. Furthermore, VTN was proved to play a key role in protecting the brain as it can reduce the permeability of the blood-brain barrier by interacting with integrin receptors in vascular endothelial cells. Moreover, evidence suggests that VTN is associated with neurodegenerative diseases, such as Alzheimer's disease, but its function has not been fully understood. This review summarizes the functions of VTN and its receptors in neurons and describes the role of VTN in the blood-brain barrier and neurodegenerative diseases.

Vascular-derived SPARC and SerpinE1 regulate interneuron tangential migration and accelerate functional maturation of human stem cell-derived interneurons

Cortical interneurons establish inhibitory microcircuits throughout the neocortex and their dysfunction has been implicated in epilepsy and neuropsychiatric diseases. Developmentally, interneurons migrate from a distal progenitor domain in order to populate the neocortex - a process that occurs at a slower rate in humans than in mice. In this study, we sought to identify factors that regulate the rate of interneuron maturation across the two species. Using embryonic mouse development as a model system, we found that the process of initiating interneuron migration is regulated by blood vessels of the medial ganglionic eminence (MGE), an interneuron progenitor domain. We identified two endothelial cell-derived paracrine factors, SPARC and SerpinE1, that enhance interneuron migration in mouse MGE explants and organotypic cultures. Moreover, pre-treatment of human stem cell-derived interneurons (hSC-interneurons) with SPARC and SerpinE1 prior to transplantation into neonatal mouse cortex enhanced their migration and morphological elaboration in the host cortex. Further, SPARC and SerpinE1-treated hSC-interneurons also exhibited more mature electrophysiological characteristics compared to controls. Overall, our studies suggest a critical role for CNS vasculature in regulating interneuron developmental maturation in both mice and humans.

Vitronectin regulates the axon specification of mouse cerebellar granule cell precursors via αvβ5 integrin in the differentiation stage

Vitronectin, an extracellular matrix protein, controls the differentiation of cerebellar granule cell precursors (CGCPs) via αvβ5 integrin, particularly in the initial stage of differentiation to granule cells. In this study, we determined whether vitronectin regulates axon specification in this initial differentiation stage of CGCPs. First, we analyzed whether vitronectin deficiency, β5 integrin knockdown (KD), and β5 integrin overexpression affect axon specification of primary cultured CGCPs. Vitronectin deficiency and β5 integrin KD inhibited axon formation, while vitronectin administrated- and β5 integrin overexpressed-neurons formed multiple axons. Moreover, KD of β5 integrin suppressed vitronectin-induced multiple axon formation. These findings indicate that vitronectin contributes to regulating axon specification via αvβ5 integrin in CGCPs. Next, we determined the signaling pathway involved in regulating vitronectin-induced axon specification. Wortmannin, an inhibitor of phosphatidylinositol 3-kinase (PI3K), inhibited vitronectin-induced multiple axon specification, and lithium chloride, an inhibitor of glyocogen synthase kinase 3 beta (GSK3β), attenuated the inhibitory effect of vitronectin-KO and β5 integrin KD on the specification of CGCPs. In addition, vitronectin induced the phosphorylation of protein kinase B (Akt) and GSK3β in neuroblastoma Neuro2a cells. Taken together, our results indicate that vitronectin plays an important factor in axon formation process in CGCPs via a β5 integrin/PI3K/GSK3β pathway.

Siah2 integrates mitogenic and extracellular matrix signals linking neuronal progenitor ciliogenesis with germinal zone occupancy

Evidence is lacking as to how developing neurons integrate mitogenic signals with microenvironment cues to control proliferation and differentiation. We determine that the Siah2 E3 ubiquitin ligase functions in a coincidence detection circuit linking responses to the Shh mitogen and the extracellular matrix to control cerebellar granule neurons (CGN) GZ occupancy. We show that Shh signaling maintains Siah2 expression in CGN progenitors (GNPs) in a Ras/Mapk-dependent manner. Siah2 supports ciliogenesis in a feed-forward fashion by restraining cilium disassembly. Efforts to identify sources of the Ras/Mapk signaling led us to discover that GNPs respond to laminin, but not vitronectin, in the GZ microenvironment via integrin β1 receptors, which engages the Ras/Mapk cascade with Shh, and that this niche interaction is essential for promoting GNP ciliogenesis. As GNPs leave the GZ, differentiation is driven by changing extracellular cues that diminish Siah2-activity leading to primary cilia shortening and attenuation of the mitogenic response.

In neural development, progenitors transition from a proliferative to a differentiated state. Here, the authors show that cerebellar granule neurons retract primary cilia as they exit their proliferative niche upon decreased ECM engagement, enabling radial migration due to loss of Shh sensitivity.

The Role of Astrocytes in the Development of the Cerebellum

Astrocytes, initially described as merely support cells, are now known as a heterogeneous population of cells actively involved in a variety of biological functions such as: neuronal migration and differentiation; regulation of cerebral blood flow; metabolic control of extracellular potassium concentration; and modulation of synapse formation and elimination; among others. Cerebellar glial cells have been shown to play a significant role in proliferation, differentiation, migration, and synaptogenesis. However, less evidence is available about the role of neuron-astrocyte interactions during cerebellar development and their impact on diseases of the cerebellum. In this review, we will focus on the mechanisms underlying cellular interactions, specifically neuron-astrocyte interactions, during cerebellar development, function, and disease. We will discuss how cerebellar glia, astrocytes, and Bergmann glia play a fundamental role in several steps of cerebellar development, such as granule cell migration, axonal growth, neuronal differentiation, and synapse formation, and in diseases associated with the cerebellum. We will focus on how astrocytes and thyroid hormones impact cerebellar development. Furthermore, we will provide evidence of how growth factors secreted by glial cells, such as epidermal growth factor and transforming growth factors, control cerebellar organogenesis. Finally, we will argue that glia are a key mediator of cerebellar development and that identification of molecules and pathways involved in neuron-glia interactions may contribute to a better understanding of cerebellar development and associated disorders.

Vitronectin is Involved in the Morphological Transition of Neurites in Retinoic Acid-Induced Neurogenesis of Neuroblastoma Cell Line Neuro2a

Vitronectin (Vtn), one of the extracellular matrix proteins, has been reported to result in cell cycle exit, neurite formation, and polarization of neural progenitor cells during neurogenesis. The underlying mechanism, however, has not been fully understood. In this study, we investigated the roles of Vtn and its integrin receptors, during the transition of neurites from multipolar to bipolar morphology, accompanying the cell cycle exit in neural progenitor cells. We used mouse neuroblastoma cell line Neuro2a as a model of neural progenitor cells which can induce cell cycle exit and the morphological transition of neurites by retinoic acid (RA)-stimulation. Treatment with an antibody for Vtn suppressed the RA-induced cell cycle exit and multipolar-to-bipolar transition. Furthermore, immunostaining results showed that in the cells displaying multipolar morphology Vtn was partially localized at the tips of neurites and in cells displaying bipolar morphology at both tips. This Vtn localization and multipolar-to-bipolar transition was perturbed by the transfection of a dominant negative mutant of cell polarity regulator Par6. In addition, a knockdown of β5 integrin, which is a receptor candidate for Vtn, affected the multipolar-to-bipolar transition. Taken together, these results suggest that Vtn regulates the multipolar-to-bipolar morphological transition via αvβ5 integrin.

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.

Promotion of differentiation in developing mouse cerebellar granule cells by a cell adhesion molecule BT-IgSF

Brain- and testis-specific immunoglobulin superfamily (BT-IgSF) (also known as IgSF11), one of the immunoglobulin superfamily proteins, is a cell adhesion molecule, expressed in the developing cerebellum. We hypothesized that BT-IgSF might have some function in the development of cerebellum, although the physiological roles of BT-IgSF in the cerebellum remain unclear. To investigate the role of BT-IgSF in the development of mouse cerebellum, we first determined the presence of BT-IgSF in the newborn mouse cerebellum; its expression level was found to be much higher than that in the adults. BT-IgSF was abundantly expressed in the molecular layer, where cerebellar granule cell precursors (CGCPs) are in the differentiation stage during migration. We subsequently analyzed the effects of BT-IgSF-knockdown and -overexpression on the proliferation and differentiation of primary cultured CGCPs. BT-IgSF suppressed the proliferation of CGCPs, and promoted their differentiation into cerebellar granule cells. Taken together, our results suggested that BT-IgSF is one of the important cell adhesion molecules that regulate the developmentof mouse cerebellum.

Neurite Growth and Polarization on Vitronectin Substrate after in Vitro Trauma is not Enhanced after IGF Treatment

Following traumatic brain injuries (TBI), insulin-like growth factor (IGF) is cortically widely upregulated. This upregulation has a potential role in the recovery of neuronal tissue, plasticity, and neurotrophic activity, though the molecular mechanisms involved in IGF regulation and the exact role of IGF after TBI remain unclear. Vitronectin (VN), an extracellular matrix (ECM) molecule, has recently been shown to be of importance for IGF-mediated cellular growth and migration. Since VN is downregulated after TBI, we hypothesized that insufficient VN levels after TBI impairs the potential beneficial activity of IGF. To test if vitronectin and IGF-1/IGFBP-2 could contribute to neurite growth, we cultured hippocampal neurons on ± vitronectin-coated coverslips and them treated with ± IGF-1/IGF binding protein 2 (IGFBP-2). Under same conditions, cell cultures were also subjected to in vitro trauma to investigate differences in the posttraumatic regenerative capacity with ± vitronectin-coated coverslips and with ± IGF-1/IGFBP-2 treatment. In both the control and trauma situations, hippocampal neurons showed a stronger growth pattern on vitronectin than on the control substrate. Surprisingly, the addition of IGF-1/IGFBP-2 showed a decrease in neurite growth. Since neurite growth was measured as the number of neurites per area, we hypothesized that IGF-1/IGFBP-2 contributes to the polarization of neurons and thus induced a less dense neurite network after IGF-1/IGFBP-2 treatment. This hypothesis could not be confirmed and we therefore conclude that vitronectin has a positive effect on neurite growth in vitro both under normal conditions and after trauma, but that addition of IGF-1/IGFBP-2 does not have a positive additive effect.

αvβ5 integrin mediates the effect of vitronectin on the initial stage of differentiation in mouse cerebellar granule cell precursors

Vitronectin (VN), one of the extracellular matrix proteins, controls the maturation of cerebellar granule cells (CGCs) through the promotion of the initial differentiation stage progress. However, the receptors of VN in the initial differentiation stage of CGC precursors (CGCPs) have not been clarified. In this study, we characterized the receptor candidates for VN in CGCPs. First, we confirmed that αvβ3 and αvβ5 integrins, which are receptor candidates for VN, were co-localized with VN in the developing cerebellum and primary cultured CGCPs. Next, the knockdown (KD) of αv, β3, and β5 integrins with small interference RNA (siRNA) for each integrin reduced the ratio of Tuj1, a final differentiation marker, -positive CGCPs. We further studied whether αvβ3 and αvβ5 integrins control the initial differentiation stage. The KD of αv and β5, but not β3, integrins significantly increased the ratio of transient axonal glycoprotein 1 (TAG1), an initial differentiation marker, -positive CGCPs, whereas the KD of αv and β3 integrins, not β5 integrin, stimulated the proliferation of CGCPs. Overexpression of β5 integrin stimulated the progress of the initial differentiation stage as well. To confirm the interaction between αvβ5 integrin and VN, VN was added to β5 integrin-KD CGCPs. The promotion of the progress of initial differentiation by VN was abrogated by β5 integrin KD using small hairpin RNA (shRNA). Taken together, our results indicated that αvβ5 integrin, as the very receptor of VN, is responsible for the progress of the initial differentiation stage in mouse CGCPs.